Human Factors Engineering and ergonomical aspects in the design of set-up friendly production equipment

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1 Human Factors Engineering and ergonomical aspects in the design of set-up friendly production equipment Hanne Deschildre Benedict Saelen Promotor: prof. dr. ir. Dirk Van Goubergen Supervisor: ir. Karel Bauters Master thesis handed in to obtain the academic degree of Master of engineering: Industrial engineering and operations research Department of Industrial Engineering Chairman: prof. dr. El-Houssaine Aghezzaf Faculty of engineering Academic year:

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3 Human Factors Engineering and ergonomical aspects in the design of set-up friendly production equipment Hanne Deschildre Benedict Saelen Promotor: prof. dr. ir. Dirk Van Goubergen Supervisor: ir. Karel Bauters Master thesis handed in to obtain the academic degree of Master of engineering: Industrial engineering and operations research Department of Industrial Engineering Chairman: prof. dr. El-Houssaine Aghezzaf Faculty of engineering Academic year:

4 Preface Ergonomics is very important in production and nowadays company leaders begin to see the value of such an environment for their employees. Results of ergonomic interventions include cost reduction and employee satisfaction which will both coincide with the company goals. This increasing importance was the incentive to introduce ergonomics in the design of machines for fast changeover. Acknowledgements We would like to thank Prof. Van Goubergen for proposing this interesting subject and his contacts within Philips Lighting. We would also like to thank Ir. Karel Bauters for the extra support as well as Prof. Lockhart for providing additional papers. Concerning the case, we would like to render thanks to Herman Van Dijck and Peter Van Thienen (Philips Lighting) for their cooperation. "De auteur(s) geeft(geven) de toelating deze masterproef voor consultatie beschikbaar te stellen en delen van de masterproef te kopiëren voor persoonlijk gebruik. Elk ander gebruik valt onder de beperkingen van het auteursrecht, in het bijzonder met betrekking tot de verplichting de bron uitdrukkelijk te vermelden bij het aanhalen van resultaten uit deze masterproef." "The author(s) gives (give) permission to make this master dissertation available for consultation and to copy parts of this master dissertation for personal use. In the case of any other use, the limitations of the copyright have to be respected, in particular with regard to the obligation to state expressly the source when quoting results from this master dissertation."

5 Human Factors Engineering and ergonomical aspects in the design of set-up friendly production equipment Hanne Deschildre & Benedict Saelen Master thesis handed in to obtain the academic degree of Master of engineering: Industrial engineering and operations research Academic year: Promotor: prof. dr. ir. Dirk Van Goubergen Supervisor: ir. Karel Bauters Faculty of engineering, University Ghent, Department of industrial engineering Chairman: prof. dr. El-Houssaine Aghezzaf Summary The goal of this master thesis is to build a quantitative assessment framework to evaluate the design of a machine that requires a fast changeover. The emphasis in this work is put on the incorporation of ergonomics into the model. In order to do so, the link between time and ergonomics is investigated as well. In essence the assessment framework contains a set of questions to evaluate the design. So the literature study starts with the development of a new set of ergonomic rules, which are quantified by means of a score and a weight system. These questions and values are based on a thorough literature study of the body of knowledge of ergonomics. Previous studies have already investigated the time aspect of this questionnaire; therefore a link between time and ergonomics is required and has been made in this script. This has resulted into an Excel file, which contains a questionnaire that has to be answered by the designer, preferably for a machine in the design phase. An existing machine can be evaluated as well, but for a machine in design phase the cost of implementing improvements will be smaller. Using the assessment framework, will lead to a total score for the design that combines two weighed components: a time score and an ergonomic score. These scores are used to set up graphs, which show the potential improvement. After evaluating, the designer can implement improvement proposals that are suggested in the file, so their potential is used and a higher score can be obtained. In addition to this evaluation, also a financial feature is provided. This allows the user to compare costs and benefits of an improvement. Finally the framework offers the possibility to compare (very) different designs through the use of a compare index. To conclude, the framework is tested on a real life case from Philips, a company that designs its own machines. The case validates the model and conclusions are drawn concerning future research. Key words: Ergonomics in machine changeover, machine in design phase, design for fast changeover, setup time reduction, assessment tool

6 Human Factors Engineering en ergonomische aspecten in het ontwerp van de set-upvriendelijke productie uitrusting Hanne Deschildre, Benedict Saelen Begeleiders: Dirk Van Goubergen, Karel Bauters Abstract Dit artikel bespreekt het ontwerp van een kwantitatief evaluatie model om het design van een machine te evalueren die een snelle omstelling vereist. De nadruk ligt op het incorporeren van ergonomische aspecten in de evaluatie. Hiervoor is ook onderzoek naar de link tussen tijd en ergonomie vereist. Sleutelwoorden Ergonomie tijdens machine omstelling, machine in design fase, design voor snelle omstelling, setup tijdsreductie, evaluatie model I. INLEIDING Ergonomie is erg belangrijk in een productieomgeving. Vandaag de dag, beginnen bedrijfsleiders ook het belang ervan in te zien voor hun werknemers. Zowel kostreductie als werknemertevredenheid zijn belangrijke gevolgen van ergonomische interventies, en beiden dragen bij tot de doelstellingen van het bedrijf. Dit toenemende belang was de aanzet om ergonomie te introduceren in het design van machines met een snelle omstelling. Tijdens een snelle omstelling zijn zowel tijd en ergonomische aspecten belangrijk, en dus moeten beide geëvalueerd worden. Deze aspecten worden bij voorkeur in overweging genomen in de design fase van de machine, aangezien de bijhorende kosten een stuk lager liggen in dit stadium. Het model wordt voorgesteld in de vorm van een vragenlijst, die door de designer ingevuld kan worden. Elk van zijn antwoorden kent een score toe aan het design en toont het verbeterpotentieel. Gesuggereerde verbeteringen kunnen na een eerste evaluatie geïmplementeerd worden. II. LITERATUUR Een eerste stap in de bouw van een model werd gezet door Van Goubergen en Van Landeghem (2002). Ze introduceerden een set van regels die een design in de richting van een snelle omstelling stuurt. De regels zijn ingedeeld in 9 categorieën. Verder onderzoek door De Nil (2009) stelt een eerste bruikbaar model voor dat toelaat een design te evalueren op de geschiktheid voor een snelle omstelling. Naast het tijdsaspect, toont onderzoek, van Van Goubergen en Lockhart (2005), aan dat bepaalde ergonomische aspecten ondervertegenwoordigd zijn in de set regels van Van Goubergen en Van Landeghem (2002). Daarom is er nood aan een nieuw model dat zowel tijd als ergonomie in overweging neemt. De body of knowledge van ergonomie wordt onder de loep genomen om een nieuwe set regels te bekomen. Deze regels, gecombineerd met de bestaande set, vormen de basis van een vragenlijst die ingevuld wordt door de designer. Het resultaat is een kwantitatieve evaluatie, met verwijzingen naar zowel tijd als ergonomie. Dus niet alleen ergonomie wordt in deze scriptie bestudeerd, maar ook de link met tijd. Bovendien worden scores en gewichten toegekend op basis van deze grondige literatuurstudie. III. HET EVALUATIE MODEL Figuur 1 geeft een overzicht van het model, dat ontwikkeld is in Excel. De designer beantwoordt vragen in het Machine Sheet en het Parts Sheet. Beide tabbladen resulteren in een ergonomische score en een tijdscore. Deze worden samengebracht in een gecombineerde score per blad door middel van een belangrijkheidfactor. De Machine en Parts scores leiden tot een totale score. i

7 Figuur 1: Algemene structuur van het model Een extra item dat gecoverd wordt door het model, is het financiële aspect. Het stelt de gebruiker in staat om de kosten en voordelen van een verbetering tegenover elkaar af te wegen. IV. PRAKTIJK CASES Figuur 2: Voorbeeld output model Deze scores worden verwerkt en gebruikt om een grotendeels grafische output te genereren. De grafieken bieden een overzicht van alle scores en het verbeterpotentieel. Een voorbeeld hiervan is te zien in figuur 2: de scores en verbeterpotentiëlen per categorie. Deze output laat de designer toe zijn beste concept te kiezen. Het model bevat eveneens een feature dat (erg) verschillende designs met elkaar kan vergelijken. Om het model te testen is een praktijkstudie uitgevoerd bij Philips Lighting, dat zijn eigen design afdeling heeft. Uit deze toepassing kan afgeleid worden dat het model praktisch is en inzicht biedt bij het ontwerpen van machines, die een snelle en ergonomische omstelling eisen. De gebruiker kan onmiddellijk met het bestand werken, zonder dat een uitgebreide voorafgaande uitleg nodig is. De tool werd overzichtelijk en toegankelijk bevonden en de suggesties, aangebracht door Philips Lighting, werden geïmplementeerd. V. CONCLUSIE De praktijkcase besluit dat de tool goed opgebouwd is en een duidelijke evaluatie van het machine design levert. Een toepassing op meerdere cases zou dit kunnen bevestigen en zou een reeks voorbeelden kunnen opleveren, wat handig is voor verder gebruik van het model. Sommige elementen dienen echter nog verder onderzoek te worden. Zo zijn tot dusver de categorieën communicatiehulpmiddelen en automatisering uit het onderzoek van Van ii

8 Goubergen en Lockhart (2005) niet genoeg in het model verwerkt. Ook moet bij sommige vragen het verband met tijd verder onderzocht worden. Tot slot kan nog een diepgaand onderzoek worden verricht naar de link tussen tijd en ergonomie: een wetenschappelijke onderbouwde factor die de verhouding ergonomie tijd bepaalt, kan een meerwaarde leveren aan het model. VI. REFERENTIES De Nil, N., Design for Fast Changeover, 2009 Van Goubergen, D., Lockhart, T. E., Human Factors Aspects in Set-Up Time Reduction, International Federation for Information Processing, volume 160, 2005, Van Goubergen, D., Van Landeghem, H., Rules for integrating fast changeover capabilities into new equipment design, Robotics and Computer- Integrated Manufacturing, volume 18, issues 3-4, 2002, iii

9 Human Factors Engineering and ergonomical aspects in the design of set-up friendly production equipment Hanne Deschildre, Benedict Saelen Supervisors: Dirk Van Goubergen, Karel Bauters Abstract This article explains the construction of a quantitative assessment framework to evaluate the design of a machine that requires a fast changeover. The emphasis in this work is put on the incorporation of ergonomics into the evaluation. In order to do so, the link between time and ergonomics is investigated as well. Keywords Ergonomics in machine changeover, machine in design phase, design for fast changeover, setup time reduction, assessment tool I.INTRODUCTION Ergonomics is very important in production. Company leaders also begin to see the value of an ergonomic environment for their employees nowadays. Results of ergonomic interventions include cost reduction and employee satisfaction, which will both coincide with the company goals. This increasing importance was the incentive to introduce ergonomics in the design of machines for fast changeover. During a fast changeover both time and ergonomic aspects are important and need to be evaluated. These aspects are preferably taken into account during the design phase, since the accompanying costs are significantly lower in design phase. The model is presented through a questionnaire, which has to be filled in by a designer. His answers will allocate a score to the design and show the improvement potential. Suggested improvements can be implemented after evaluation. II. LITERATURE A first step towards the model was created by Van Goubergen and Van Landeghem (2002), who introduced a set of rules that direct a design towards a fast changeover. The rules are divided into 9 categories. Further research conducted by De Nil (2009) proposes a first working model that could be used to evaluate a design for fast changeover. In addition to the time aspect, research of Van Goubergen and Lockhart (2005) indicates that certain ergonomic aspects are underrepresented in the set of rules developed by Van Goubergen and Van Landeghem (2002). Therefore a new model is required to take into account both time and ergonomics. A focus is put on the body of knowledge of ergonomics in order to obtain a new set of rules. These rules, combined with the existing set, form the basis of a questionnaire, that has to be filled in by the designer. The result is a quantitative evaluation with reference to time and ergonomics. So not only ergonomics is investigated but also its link with time. On top of that, scores and weights are allocated based upon this thorough literature study. III. THE ASSESSMENT MODEL Figure 1 gives an overview of the model, which is developed in Excel. The designer answers the questions in both the Machine Sheet and the Parts Sheet. Both sheets result into an ergonomic and a time score. These are united into a combined score per sheet through an importance factor. The Machine and Parts scores lead to a total score. These scores are processed and used to generate graphs. The graphs provide an overview of all scores and potential improvements. Figure 2 shows an example of this graphic representation: the scores and their improvement potential per question category. This output allows the designer to choose his best concept. An additional item that is covered by the model is the financial aspect. It allows the user to compare costs and benefits of an improvement. i

10 Figure 1: General structure of the model The user can immediately start working with the file, without any extensive preliminary explanation. The tool was considered to be well-organized and accessible and the suggestions, provided by Philips Lighting were implemented. Figure 2: Example output of the model IV. PRACTICAL CASES In order to test the model, a case study has been conducted at Philips Lighting, which has its own design department. The case proves that the model is practical and provides insight when designing machines that require fast and ergonomic changeovers. V. CONCLUSION The case proves that the tool is well- organized and provides a thorough evaluation of the machine design. Applying the tool to several cases could confirm this and might give a portfolio of examples, which are useful for further use of the model. Some elements, however, deserve further investigation. So far, the categories communication aids and automation from the research of Van Goubergen and Lockhart (2005) have not enough been incorporated in the model. Furthermore, for some questions, the link with time needs to be investigated more. And finally a more thorough study of the link between time and ergonomics could be done: a fixed, scientific based factor, that mirrors the proportion of time to ergonomics, can ameliorate the model. ii

11 VI. REFERENCES De Nil, N., Design for Fast Changeover, 2009 Van Goubergen, D., Lockhart, T. E., Human Factors Aspects in Set-Up Time Reduction, International Federation for Information Processing, volume 160, 2005, Van Goubergen, D., Van Landeghem, H., Rules for integrating fast changeover capabilities into new equipment design, Robotics and Computer- Integrated Manufacturing, volume 18, issues 3-4, 2002, iii

12 Human Factors Engineering en ergonomische aspecten in het ontwerp van de set-upvriendelijke productie uitrusting Hanne Deschildre & Benedict Saelen Masterproef ingediend tot het behalen van de academische graad van Master in de ingenieurswetenschappen: bedrijfskundige systeemtechnieken en operationeel onderzoek Academiejaar Promotor: prof. dr. ir. Dirk Van Goubergen Begeleider: ir. Karel Bauters Faculteit ingenieurswetenschappen, Universiteit Gent, Vakgroep technische bedrijfsvoering Voorzitter: prof. dr. El-Houssaine Aghezzaf Uitgebreide Nederlandstalige samenvatting 1. Situering Snelle omstellingen zijn al jaren een onderwerp van onderzoek. In de jaren 80 heeft Shingo (1985) het idee gelanceerd en vele anderen zijn hem daarin gevolgd (Mileham et al., 1999; Culley et al., 2000; McIntosh et al., 2001; Van Goubergen en Van Landeghem, 2002; Cakmakci en Karasu, 2007; Trovinger en Bohn, 2007). Samen verduidelijken ze een aantal belangrijke redenen voor een snelle omstelling maar een stapje verder zijn ze niet geraakt: ergonomie zit nog niet verweven in de studies. Toch levert hun onderzoek een waardevolle bijdrage aan het belang van tijd in het ontwerp voor machines met korte omsteltijden. Dit wordt verwezenlijkt door het bestuderen van tijd met betrekking tot flexibiliteit, bottleneckcapaciteit, kosten, doorlooptijden, productiekwaliteit en procestijd. Deze ideeën vormden de basis voor het werk van Van Goubergen en Van Landeghem (2002). In hun onderzoek staat een set van regels die een snelle omstelling bevorderen. De regels zijn bedoeld voor zowel machines in designfase als bestaande machines. De nadruk wordt op de eerste groep gelegd aangezien aanpassingen hier eenvoudiger en beduidend goedkoper zijn (Figuur 1). De regels die in het werk van Van Goubergen en Van Landeghem ontwikkeld werden, zijn ingedeeld in 9 categorieën: 1. Lager gewicht 6. Handling 2. Vereenvoudiging 7. Offline activiteiten 3. Standaardisatie 8. Machinelijnen 4. Bevestiging 9. Methode en organisatie 5. Plaats en bijstelling i

13 Figuur 1: Invloed van de timing van een investering (Van Goubergen, 2007) Het is met deze regels en indeling in gedachte dat De Nil (2009) een basis framework ontwikkelde in Excel. Dit model kan een machinedesign beoordelen op haar geschiktheid voor een snelle omstelling. Door een selectie van de regels van Van Goubergen en Van Landeghem in een vraagvorm te gieten, ontstond er een gebruiksvriendelijk instrument dat bruikbare output genereert voor de designer. Deze thesis is bedoeld om de volgende stap in het onderzoek te nemen. De aanleiding hiervoor is de problematiek, besproken door Van Goubergen en Lockhart (2005). Ze stellen vast dat te weinig rekening gehouden wordt met ergonomische aspecten bij het beoordelen van een design op snelheid van de omstelling. Dit ontbreekt dus ook in het model van De Nil. Concreet besluiten Van Goubergen en Lockhart (2005) dat 14 facetten nog te weinig vertegenwoordigd zijn in de lijst met regels (Van Goubergen en Van Landeghem, 2002), en in bestaande tools : 1. Communicatie hulpmiddelen 8. Motivatie 2. Taaktoewijzing 9. Auditieve perceptie 3. Geluid 10. Beslissingen nemen 4. Klimaat 11. Automatisering 5. Verlichting 12. Visuele displays 6. Trillingen 13. Auditieve displays 7. Gevaarlijke materialen 14. Veiligheid Om die redenen werd in dit werk een uitgebreider framework ontwikkeld dat machines beoordeelt op gebied van tijd en ergonomie. Kwalitatieve input resulteert in kwantitatieve output. Dit zorgt voor een gemakkelijke vergelijking tussen machines en machine ontwerpen. Door de voordelen die een beoordeling in design fase biedt, werd het model ontworpen voor machines in design fase. Toch is er, ter volledigheid, een uitbreiding voorzien voor bestaande machines. ii

14 2. Methode De gevolgde strategie wordt in deze tekst aan de hand van onderstaande figuur geïllustreerd. Figuur 2: Ideeën thesis Er wordt gestart met een literatuurstudie. Daarin wordt verder gewerkt op het bestaande onderzoek, vermeld in de vorige paragraaf. Uit deze studie resulteert een nieuwe set regels die zowel ergonomische- als tijdsaspecten omvat. Na opbouw van deze set wordt het praktijk model, in Excel, voorgesteld. Een concreet overzicht verduidelijkt het model, de onderdelen en de functionaliteiten. Tot slot wordt het model toegepast op een bestaand machineontwerp waarna een conclusie geformuleerd wordt, die een aanzet geeft tot verder onderzoek. 3. Onderzoeksfase In de verkennende fase was het belangrijk om de noden van de tool te vinden. Welke elementen moet de tool bevatten? Welke opbouw spreekt de designer aan?... De nadruk van het onderzoek ligt vooral op ergonomie. Het is een erg brede discipline, die vooral de laatste decennia heel wat aan populariteit gewonnen heeft. Deze evolutie heeft tot gevolg dat er een erg groot aanbod aan informatie beschikbaar is. Niet alles is echter van toepassing en er werd voornamelijk gezocht binnen de 14 domeinen, aangegeven door Van Goubergen en Lockhart (2005). De verzamelde data werd in regels en vragen gegoten (Paragraaf 2.2), analoog aan de regels van Van Goubergen en Van Landeghem (2002) en de vragenlijst van De Nil (2009). Bij iedere regel wordt een beknopte samenvatting gegeven van het wetenschappelijk onderzoek dat aan de basis ervan ligt. Elke regel is dus omgezet naar een vraag. De mogelijke antwoorden op een vraag worden beoordeeld aan de hand van een score, afgeleid uit de wetenschappelijke basis van die vraag. Een scoretabel omvat alle mogelijke antwoorden. Zowel deze scriptie als het praktisch Excel model is volgens die logica opgebouwd. Tot slot horen bij elke vraag (of groep van vragen) één of meerdere verbetervoorstellen. De score op een vraag kan opgedreven worden, indien de gebruiker aangeeft dat de verbetering geïmplementeerd is. iii

15 Tot dusver is een onderzoek naar ergonomie verricht, resulterend in vragen en ergonomiescores. Maar het element tijd is ook van groot belang, wat leidt tot een koppeling tussen tijd en ergonomie. De vragen in paragraaf hebben naast een ergonomiescore, een tijdsscore (paragraaf 2.2.2). Deze link leggen was niet evident aangezien bitter weinig onderzoek verricht is naar het tijdseffect van ergonomische implementaties. Af en toe worden beide gekoppeld maar vaak zijn de omstandigheden te specifiek of wordt de koppeling te vaag vermeld. Globaal gezien is gestart van een set wetenschappelijk onderbouwde ergonomievragen en hun bijhorende ergonomiescore. Voor deze ergonomische vragen is een tijdsscore opgesteld (op basis van wetenschappelijk onderzoek en intuïtie). Tot slot werden ook verbetervoorstellen gekoppeld aan een scoreverbetering. De scriptie verschilt van het werk van De Nil (2009). Daar ligt de focus op een intuïtieve aanpak, bij gebrek aan literatuur over tijd. In deze masterproef wordt de omstellingsproblematiek echter vanuit een ergonomische invalshoek bekeken; dit komt de wetenschappelijke onderbouwdheid ten goede en doet de werkwijze verschillen van die van De Nil. 4. Het model Hierboven werd toelichting gegeven over het tot stand komen van een set ergonomische vragen. Met het opstellen van deze vragenreeks kunnen we echter nog niet spreken van een volwaardig framework. De vragenreeks wordt daarom aangevuld met de vragen, ontwikkeld door De Nil (2009), die naast het ergonomische nog enkele facetten coveren die van belang zijn. Bij de toevoeging werd ook rekening gehouden met eerder onderzoek. Het werd duidelijk dat de lijst met regels van Van Goubergen en Van Landeghem (2002) toch nog een aantal extra regels bevat, die niet opgenomen zijn in het model van De Nil. Ook die regels horen bij een afgewerkt framework. Met deze twee toevoegingen is er sprake van een allesomvattende vragenlijst. De toevoeging van deze regels vereist extra onderzoek naar scores. Zowel aan de bijkomende regels van Van Goubergen en Van Landeghem als aan deze van De Nil zijn ergonomische scores toegekend. Voor de bijkomende regels van Van Goubergen en Van Landeghem zijn bovendien ook tijdscores bepaald. De volledige vragenlijst (zonder onderscheid in oorsprong van de vragen) is in het Excel model onderverdeeld in 9 categorieën, volgens Van Goubergen en Van Landeghem (2002). Verder is ook een onderscheid gemaakt tussen vragen die van toepassing zijn op een specifiek onderdeel dat tijdens de omstelling gemonteerd wordt ( Parts sheet in Excel), en vragen die een ruimere toepassing kennen ( Machine sheet in Excel). In beide sheets moet de designer de vragen beantwoorden of aanvinken wanneer ze niet van toepassing zijn. Hierna wordt een score gegenereerd en kan de gebruiker verbetervoorstellen implementeren. De volledige vragenlijst is te vinden in Appendix A. iv

16 Score genereren Figuur 2 omvat de grafische weergave van de manier waarop de scores gegenereerd worden. Elke vraag krijgt een score op basis van het antwoord. Elke vraag wordt gewogen ten opzichte van andere vragen binnen een categorie om de belangrijkheid ten opzichte van elkaar in rekening te brengen. Tussen de groepen is er ook een gewicht voorzien om deze van elkaar te onderscheiden. De uiteindelijke score van een vraag is dus het product van een categoriegewicht, een vraaggewicht en een specifieke antwoordscore. Sectie omvat een gedetailleerde bespreking van de gewichten. Dit systeem wordt 2 maal toegepast aangezien elke vraag op vlak van tijd en ergonomie beoordeeld wordt. Beide scores kunnen los van elkaar gezien worden maar in het Excel bestand worden ze uiteindelijk gecombineerd tot één totaalscore. Een aan te geven factor in het model bepaalt hoe belangrijk ergonomie ten opzichte van tijd is voor de designer. Hoe groter de factor gekozen wordt, hoe belangrijker de gebruiker de design/tijd component van de score vindt. Hoe kleiner de factor, hoe belangrijker de ergonomische component beschouwd wordt. Figuur 3: Structuur model v

17 Output Van de gebruiker wordt verwacht dat hij de vragenlijst overloopt in de tabbladen Machine Sheet en Parts Sheet. Per vraag wordt een antwoord geselecteerd of, als de vraag niet van toepassing is, dan wordt ze gemarkeerd. De output wordt volledig automatisch gegenereerd, hoofdzakelijk onder de vorm van grafieken. Deze output laat de gebruiker toe om te ontdekken in welke van de 9 categorieën nog verbetering mogelijk is. Figuur 4 geeft een voorbeeld van de output. Hierin worden scores tegenover een maximale score gezet om zo het verbeterpotentieel aan te duiden. De designer ziet duidelijk of het gros van de verbetermogelijkheden gekoppeld zijn aan één bepaald onderdeel. Hij kan de situatie voor de verbeteringen vergelijken met die erna en à la limite kan hij zelfs twee verschillende omstellingen met elkaar vergelijken. Figuur 4: Voorbeeld output model Financiële evaluatie Tot nu toe bleef 1 pijler van figuur 3 onbesproken. Dit omvat het financiële gedeelte van het model. De (ergonomische) verbetervoorstellen die verweven zijn in het model, gaan uiteraard gepaard met een bepaalde investering. Daarom wordt de financiële kant als een noodzakelijk onderdeel van het framework beschouwd. Het financiële aspect is ook vaak één van de elementen die de doorslag geven bij het management van de onderneming. Op basis van de opbrengsten en de kosten van de implementatie van de verbetering, wordt er een beslissing vi

18 genomen. Het probleem met ergonomische interventies is echter dat ze moeilijk te kwantificeren zijn. Een ergonomische verbetering beïnvloedt de productie op verschillende manieren (direct en indirect) en heeft dus dikwijls een invloed op meerdere kostenposten. Er is niet echt één boekhoudkundig model voor handen dat alle posten combineert. Meerdere auteurs doen een poging om met één totale, correcte kost naar voor te komen (Riel and Imbeau, 1996; Hendrick, 2003; Lahiri et al., 2005; Goggins et al., 2008), waarvan de één al beter geschikt is dan de ander. Uiteindelijk is gekozen voor een benadering, gelijkaardig aan deze van Hendrick (2003). Deze aanpak bespreekt alle kostenposten en opbrengsten die nodig zijn en het geheel blijft toch voldoende abstract. Deze abstracte aanpak is nodig om het model algemeen te houden zodat het toepasbaar is op een brede waaier van gevallen. Tabel 1 geeft een overzicht van de kosten en opbrengsten die in rekening moeten gebracht worden. Tabel 1: Categorieën kosten en uitgaven vii

19 Het financiële gedeelte kan gebruikt worden maar staat vrij los van de rest van het model. Hierdoor kan dit deel zonder probleem opengelaten worden in het bestand. Wanneer de designer het invult, wordt een grafische weergave gegenereerd in de Excel tool. Tot slot, bij deze bespreking van het model, moet benadrukt worden dat de thesistekst samen hoort met het ontwikkelde Excel model. Daarom moeten ze samen bekeken worden. Tekst en tool moeten als verlengstuk van elkaar gezien worden: het nut van de onderzoeksfase in de tekst wordt duidelijk na gebruik van de tool en de essentie van de tool wordt verklaard in de tekst. Voor het gebruik van de tool wordt verwezen naar Appendix B die een nauwkeurige handleiding van de EDAT-MC (Ergonomic and Design Assessment Tool for Machine Changeover) omvat. 5. Praktijkcases Om de werking van de tool na te gaan, werd het Excel model doorgestuurd naar Philips Lighting. Een praktijk case betekent een aanzienlijke meerwaarde voor de thesis en biedt de mogelijkheid om te ontdekken of het ontworpen model functioneert zoals verwacht. Via prof. Van Goubergen werden Herman Van Dijck en Peter Van Thienen (Philips Lighting Plant in Turnhout) aangesproken. Uit de case blijkt dat de tool overzichtelijk en toegankelijk is. Bovendien is er geen uitgebreide voorafgaande uitleg nodig om ermee aan de slag te gaan. Op basis van de praktijkcase werden nog een aantal gesuggereerde verbeteringen doorgevoerd. Eén van de belangrijkste opmerkingen die naar voor kwam, is dat een Nederlandstalige versie van de tool interessant zou zijn. Dit zou de tool nog gebruiksvriendelijker maken, en op die manier zouden ook operatoren de tool probleemloos kunnen gebruiken. Gedetailleerde resultaten van dit praktijkgeval is te vinden in sectie 3.2 van de thesis. 6. Conclusies en verder onderzoek Deze thesis heeft geleid tot een kwantitatief beoordelingsmodel voor een machine die een snelle omstelling vereist. De nadruk werd gelegd op de implementatie van ergonomie in het model en eerdere studies als Van Goubergen en Van Landeghem (2002), Van Goubergen en Lockhart (2005) en De Nil (2009) vormen de basis. In praktijk resulteerde het onderzoek in een Excel bestand met een vragenlijst. De designer vult de lijst best in vooraleer de machine gemaakt wordt, zodat de kosten van verbeteringen gelimiteerd blijven. De output van dit model is een score die de designer toelaat om verschillende ontwerpen te vergelijken. Zowel voor gelijkaardige als voor totaal verschillende designs is een vergelijking mogelijk. De output wordt grafisch voorgesteld om een snel overzicht te geven van de tekortkomingen en de gebieden waar een groot verbeterpotentieel zit. Het model werd toegepast op een testcase en hieruit bleek dat het een duidelijke interface naar de designer biedt. Een opleiding is niet vereist maar een basis achtergrond wordt aangeraden. Daarom is het aangewezen om de handleiding (Appendix B) te lezen. viii

20 De tool heeft zijn effectiviteit bewezen maar toch zijn er zowel vanuit wetenschappelijk standpunt als vanuit het gebruik van de tool enkele verbeteringen mogelijk. Wat betreft wetenschappelijk onderzoek kan de connectie tussen tijd en ergonomie nog verder uitgediept worden. Ergonomie werd in detail behandeld maar voor de link met tijd is niet veel literatuur voor handen. De Nil (2009) voorziet een goede basis maar wetenschappelijke onderbouwdheid ontbreekt. Ook ontbreken nog twee aspecten van de lijst opgegeven door Van Goubergen and Van Landeghem (2002). Wat betreft de Excel tool zijn ook nog enkele aanpassingen mogelijk. Er zou kunnen overgestapt worden naar een softwarepakket dat de tool nog gebruiksvriendelijker maakt. Methoden zoals NIOSH en RULA zijn online te vinden en worden ondersteund door software. Ze worden op een aantrekkelijke manier voorgesteld en maken potentiële gebruikers nieuwsgierig. Ook kan de tool in het Nederlands aangeboden worden. Deze terechte opmerking kwam vanuit Philips Lighting. Tot slot zou de factor, die de ergonomie- en tijdsscores linkt, wetenschappelijk onderzocht kunnen worden. ix

21 Table of content Chapter 1 Introduction... 1 Chapter 2 Literature study Previous studies and findings Time linked to changeover Cost linked to changeover Ergonomics linked to changeover Development of additional rules and scores Ergonomic score: explanation of the ergonomic rules Task allocation Motivation Noise, vibrations & auditory perception Climate Illumination Decision making Visual displays Auditory displays Safety and hazardous materials Design score: ergonomics linked to time Task allocation Motivation Noise, vibrations & auditory perception Climate Illumination Decision making Visual displays Auditory displays Safety and hazardous materials Chapter 3 Practical assessment framework Assessment framework Overview of the model Essential calculations i

22 Score calculation Combined compare index Visual Basic code in EDAT-MC Extra feature: Financial aspect Application of the assessment framework Philips Test Case Chapter 4 Conclusion and future research Appendix A Set of questions and improvements Appendix B Manual EDAT-MC Appendix C Visual Basic code Bibliography ii

23 List of figures Figure 1: Thesis ideas... 2 Figure 2: Influence of the timing of an investment... 5 Figure 3: Human factors systems design model... 6 Figure 4 Number of design rules related to the elements of the category Operator... 7 Figure 5: Relationship between sound pressure level and annoyance Figure 6: Relationship between sound pressure level and percentage of correct answers Figure 7: Relationship between sound pressure level and reaction time Figure 8: Relationship workload metabolic heat Figure 9: Lines of permissible exposure to work in hot conditions Figure 10: Upper limit for unimpaired mental performance Figure 11: Link between visual angle, distance to the object and height of the object Figure 12: The viewing angle Figure 13: Colors at opposite ends of the spectrum should not be combined Figure 14: Text and background colors 15 points from each boundary Figure 15: Guide for color selection Figure 16: The relative increase in task completion time: interrupted vs non-interrupted tasks Figure 17: Mean reaction times and standard error bars for four posture conditions Figure 18: Mean reaction times and standard error bars for four posture conditions Figure 19: Mean reaction times as a function of exposure for the four posture conditions Figure 20: Mean reaction time as a function of intensity of the imperative signal: CRT and SRT Figure 21: Mean reaction time as a function of intensity of the imperative signal: CRT and DRT Figure 22: Mean reaction time as a function of the auditory intensity or error proportions Figure 23: Mean reaction time to intensity gradient for the accessory Figure 24: Workload metabolic heat diagram Figure 25: Percentage change in performance vs. temperature Figure 26: Normalized performance vs. temperature Figure 27: Change in performance with increasing ventilation rate Figure 28: Change in performance per 10 liter/s-person increase in ventilation rate Figure 29: Relative performance in relation to the reference value at 6,5 L/s-person Figure 30: Fonts used in the study by Beard et al Figure 31: Response times in seconds between event start and releasing accelerator Figure 32: Brake response times in seconds Figure 33: Non-audio vs. audio display response times Figure 34: Accuracy and reaction time results for 4 primary mapping ensembles Figure 35: Audio display indicator response times Figure 36: General structure of the model Figure 37: Calculations of the ergonomic and design scores per category Figure 38: Calculations of the total machine and parts scores Figure 39: Philips Absolute design scores for Machine Figure 40: Philips Score versus potential of total for Machine Figure 41: Philips Absolute Total scores for Part A Figure 42: Philips Score versus potential Total Part A iii

24 Figure 43: Philips Compare indices Figure 44: Philips Question Classification sheet iv

25 List of tables Table 1: The costs of using ergonomics in design... 5 Table 2: Number of rules per category... 6 Table 3: Overview of the limits of long and short term memory Table 4: Exposure limit values & action values for hand transmitted & whole-body vibrations Table 5: Vibration magnitude that corresponds to the Directive of the EU Table 6: Matters to be considered if the exposure action value is exceeded Table 7: improvements for noise, vibrations and auditory perception Table 8: Relationship between heart rate and energy expenditure Table 9: Advised temperature ( C) for a workplace in combination with airspeed Table 10: Improvements concerning climate Table 11: Dimensions for visibility of near and far objects Table 12: Advantages and disadvantages of using color as to differentiate information Table 13: Systems to combine with color differentiation Table 14: Three functional attention fields Table 15: The links between auditory signals and basic quantities Table 16: NBN Table 17: Overview of general used shapes and colors for signs Table 18: Mean reaction times Table 19: Improvements for noise, vibrations & auditory perception regarding time & designs Table 20: Improvements concerning climate Table 21: Mean percentage of trials for which performance was better under bright light Table 22: Average observation scales in function of the number of monitors used for 8 images Table 23: Sets ( ensembles ) of data-to-display mappings Table 24: Explanation of the abbreviations used in Figure 40 and Table 25: Calculations needed for the compare index and max compare index Table 26: Calculations needed for the combined compare index Table 27: Explanations for the values in Table Table 28: Overview of the sheets that need VB-code to function Table 29: Costs and yield categories v

26 Chapter 1 Introduction A changeover is a critical element of the production process. It has taken some time until the industry realized this, but since Shingo (1985) has introduced the subject, and stressed its importance in his work, it has been recognized as a fundamental issue in production. Shingo has presented several initiatives to optimize a changeover. Making improvements does not stop with implementing them. Van Goubergen and Lockhart (2005) have spent attention to the moment of implementation of these improvements. Obviously, the sooner they can be realized the better, and preferably already in the design stage of the machine. De Nil developed an assessment framework to rate a design for fast changeover. In literature, very little that can be found in this domain. There were no similar tools available and this has been a motive for his work. His tool allows the user to rate a changeover already in the design phase and this results in showing where improvements are possible. The assessment model presented in this master thesis is based upon his work. In this script however, an attempt is presented to improve and expand the model developed by De Nil (2009). Ergonomics and human factors are added to the model. The framework of De Nil has no indications to this facet but neither have other investigations of changeovers. This aspect is nearly always left out of consideration. As far as ergonomics and human factors are concerned, a huge body of knowledge is available. Still it is not evident to find documents concerning time combined with the well-being of workers. Time is one of the most important aspects in a changeover and it is also closely related to costs, which will always be a very (or even the most) important aspect in production. The quicker it is done, the better. So combining time and ergonomics is a major issue in this thesis. The study results in a complete assessment tool for design for fast changeover. A system of questions, scores and weights is made and allows the user to compare changeovers or to estimate which elements of the changeover are susceptible for improvement. Improvement proposals are 1

27 CHAPTER 1. INTRODUCTION included, as well as an attempt to estimate their cost. A schematic overview of the ideas developed in this thesis can be found in Figure 1. Figure 1: Thesis ideas Finally, an application of the tool in a real life case from industry is discussed. This allows to verify how and if the tool works, and whether it corresponds with reality and expectations. It might indicate whether it truly has an added value compared to the less comprehensive tool of De Nil, which did not include any ergonomic aspects. 2

28 Chapter 2 Literature study 2.1 Previous studies and findings Two parts are covered in the literature study. On one hand the distillation of useful information from the body of knowledge of ergonomics is covered and on the other hand the connection between ergonomics and time is investigated Time linked to changeover The importance of time and a quick, fluent changeover is already known since the 80 s. Shingo (1985) was the first to introduce it and a lot of others (Cakmakci and Karasu, 2007; McIntosh et al., 2001; Trovinger and Bohn, 2007; Van Goubergen and Van Landeghem, 2002; Culley et al., 2000; Mileham et al., 1999) followed by confirming the same ideas. Their most important reasons for a short changeover time are: Increased flexibility: The demand of the customer is becoming more and more diverse and companies have to go with the flow if they do not want lose customers. This results into a similar demand quantity but more varieties have to be produced instead of one standard product. Production needs small lot sizes to obtain such a level of flexibility. Considering the higher number of changeovers, reducing the time needed to perform a changeover becomes important as well. Increased bottleneck capacity: The machine for which market demand transcends the capacity the most, is called the bottleneck. If a higher production has to be achieved there are two obvious measures: working overtime or buying a new machine. A third option which should also be taken into account is reducing the time needed for a changeover in order to increase the availability of the machine and thus the capacity. 3

29 CHAPTER 2. LITERATURE STUDY Cost reduction: Since a faster changeover means an increased availability and a larger number of products that can be produced, the same equipment is used more efficiently. If a review of the changeover procedure also includes a better instructed way of working, this can cause the required number of test runs to drop and reduce waste. This leads to a cost reduction. A shorter changeover also stands for a smaller amount of inventory that is needed to bridge the downtime. Shorter lead time: Lead time is a very important parameter in production. It is the time between start and finish of the process. If this can be reduced through a shorter changeover, it means that the customer can receive his product faster. On top of that, changeover time is non-value adding so these activities have to be limited as much as possible. Higher product quality: A review of the changeover process can result in a much better working method, easier adjustment of settings, etc. This is beneficial for product quality. Less variable process time: If a higher quality is achieved and the need for test runs is reduced, this is beneficial for the variability of the process. De Nil (2009) presents an example of a changeover assessment framework. The proposed tool is based upon a paper of Van Goubergen and Van Landeghem (2002) in which a list of rules is mentioned that need to be considered when performing a changeover. Some of these rules are left out of the model by De Nil. The rules that were implemented have been transformed into questions and divided into categories. For more detailed information about the tool of De Nil, we refer to his master thesis (De Nil, 2009). When ergonomic aspects are left out of consideration, the framework developed by De Nil seems appropriate. However, Van Goubergen and Lockhart (2005) address a blind spot in changeover theory: ergonomics and human factors. Ergonomics and human factors are an area of which the importance in many disciplines keeps growing but in changeover it remains largely unaddressed. It is a specialty that is fit to be applied in the design phase of a machine so it has great potential in the domain of fast changeover. It fits perfect into an assessment framework and that is exactly what this thesis is addressing. The assessment is intended to be used in the design phase of a machine since the earlier it is implemented, the less it will cost. 4

30 CHAPTER 2. LITERATURE STUDY Cost linked to changeover The assessment can be done when the machine is already made, but if possible it should be performed in design phase. Figure 2 shows that the earlier the investment is made, the bigger the influence of an amount of money will be. Similar findings were reported by Alexander (1999). Table 1 shows the results of his research. Figure 2: Influence of the timing of an investment (Van Goubergen, 2007) Table 1: The costs of using ergonomics in design (Alexander, 1999) Stage of development Portion of engineering budget (%) Early design Blueprint Construction Commissioning Normal operations Ergonomics linked to changeover Ergonomics are somewhat of a blind spot in machine changeovers. Some aspects of ergonomics are implemented by coincidence. Van Goubergen and Lockhart (2005) investigated the matter and state that there are areas which are more underrepresented than others. To discover this, they divided the rules for a fast changeover, developed by Van Goubergen and Van Landeghem (2002), into categories (Table 2). 5

31 CHAPTER 2. LITERATURE STUDY Table 2: Number of rules per category (Van Goubergen and Lockhart, 2005) Category Number of rules Less weight 2 Simplification 10 Standardization 3 Securing 5 Location and adjustment 15 Handling 8 Off-line activities 2 Machine lines 1 Method and organization 7 An attempt is made to map each of these categories onto a human factors system design-model (Figure 3). In other words, each of the categories above is linked to one of the factors in the human factors systems design model by Helander (1997). Some aspects though, are underrepresented (Figure 4). Figure 3: Human factors systems design model (Helander, 1997) 6

32 CHAPTER 2. LITERATURE STUDY Figure 4 Number of design rules related to the elements of the category Operator in the human factors system design model (Van Goubergen and Lockhart, 2005) In total, the following human factor issues are not adequately addressed in the set of rules set up by Van Goubergen and Van Landeghem (2002): 1. Communication aids 8. Motivation 2. Task allocation 9. Auditory perception 3. Noise 10. Decision making 4. Climate 11. Automation 5. Illumination 12. Visual displays 6. Vibration 13. Auditory displays 7. Hazardous materials 14. Safety This thesis is based upon these aspects. They are covered in the next section in order to come up with a more comprehensive assessment framework. Since there is a substantial body of knowledge concerning ergonomics and human factors, finding information is not the issue. The link to time, though, is. The time gain or loss, obtained by the implementation of an ergonomic rule is hard to quantify. Virtually no direct information is available on this topic and certainly not in the domain of changeovers. So for nearly every new rule a substantial amount of research was required. Often highly specialized data from other disciplines needed to be linked to the changeover in order to quantify the new rules. The use of the assessment model is similar to most of the assessment models, available today. It is a well structured questionnaire that leads to score allocation when completed. Score allocation to every answer is done intuitively but based upon scientific research and scores are relative. Even people who are not familiar with the model will easily be able to fill it in. Simplicity is a great asset since the framework should be accessible for everyone who sees the benefit of it. Other ways of organizing an assessment tool, next to the chosen method of a questionnaire, have been considered but found less fit for the purpose than the approach which is used now. A system based on a MTM-way of working is one of the alternatives but such a procedure does not cover enough of the ergonomic aspects. Mental and environmental facets are more difficult to implement using such a way of working. 7

33 CHAPTER 2. LITERATURE STUDY 2.2 Development of additional rules and scores The model that is presented is built around a set of questions, rules and improvement proposals. This was done in order to facilitate the use of the assessment framework, and to easily guide the user through the entire assessment. A subset of these rules was presented by De Nil (2009) and Van Goubergen and Van Landeghem (2002). Some of the rules in the model presented here, are adapted from those research papers. Other rules, questions and improvement proposals (those with an ergonomic background) are designed within the scope of this thesis. They are the result of an extensive literature research, focused on the areas which were not fully covered by the existing rules. Both new ergonomic and former design/time rules are put together in the new assessment tool. First the newly developed rules are explained; later on the complete set of rules will be presented. Along with the questions, some improvement proposals have been developed as well. Some proposals are specifically linked to one question; others are applicable to a set of questions. In a second phase or application of the tool, these improvements can refine the design and increase the score. To set up an appropriate assessment framework, there has to be a score on each of the rules to evaluate the machine (preferably in the design phase). The better the answer or the more improvements implemented, the higher the score of the machine will be. Obviously, not all the questions are equally important. In order to show this, the model works with two weight factors. First of all, questions are put together in groups, each group covers one area. Weights are assigned to each of these groups. A second weight factor is used to rank the questions in one area. These two weight factors are combined with the score provided by the answer, to result in a total score for the question. Further explanation of each rule will show how the rules were established, keeping in mind that there is focus missing on 14 areas, as has been discussed earlier. Appendix A gives an overview of the entire established set of rules Ergonomic score: explanation of the ergonomic rules Task allocation a. Multitasking capacities depend upon the operator, they cannot be required when defining the setup mode. Because the mental resources of each individual are limited, integrating multitasking in setups for machines should be handled with great care. Intelligence and working memory are both strongly related to multitasking, and especially the working memory of the operator is determining; intelligence is strongly correlated with it (Hambrick et al., 2009). 8

34 CHAPTER 2. LITERATURE STUDY Within the working memory, processing and storage capacity are important. Processing can be further divided into coordination and supervision (Hambrick et al., 2009): - Storage means that the operator has to remember input while performing another task and that he has to be able to reproduce the remembered input eventually. - Coordination makes sure that the relationship between various independent changing objects is being monitored and that the operator has to be capable of detecting certain critical relations. - Supervision means making the right choices within the allowable reaction time. An operator has to score well on all three domains to be able to perform multitasking in a setup. The multitask capacity can be increased by good training and in time via automatisms and experience. This enables certain handlings to become subroutines, so the operator can focus simultaneously on another task or he can switch between tasks. Studies (Hambrick et al. 2009) have experienced a higher multitask capacity for men than women. So the wider accepted, but not proven cliché perhaps is not so correct after all According to Hambrick et al. (2009), the explanation can be found in the experience of men with computer games, which makes multitasking a trainable feature. This rule is also applicable when evaluating the motivational score of the setup. When too much multitasking is required and the operator does not have the capabilities for it, it can lead to a strong decrease in motivation. Score allocation and improvement proposal: Ergonomic score Explanation When multitasking is When multitasking is required. not required. Note that this score should get a large weight since it is important not to demand multitasking from operators. Certain operators are not capable of performing several tasks at once. Multitasking can have a huge decrease in motivation; it should absolutely not be asked. Score improvement Explanation Help through Elimination another (extra) operator. (Improvement is only possible if score was 0) Question for the Excel model: Is multitasking required? 9

35 CHAPTER 2. LITERATURE STUDY Motivation a. The limits of long and short term memory have to be taken into account. Short term memory An operator can remember about 7 items on short term basis. This number (7) is not a constant (Miller et al. 1956). The number of parts that an operator can remember immediately after the representation depends upon the kind of element (e.g. for numbers, 7 is appropriate, for letters 6 and for words the number 5 is better). But there are other factors that can influence the items to remember: + In general, verbal content can strongly depend upon the time, necessary to pronounce the word out loud. + The knowledge of the operator, who has to remember, is of importance. When the operator already knows a word, it is easier to remember the word and the application of the word in his task. + Abstract words are more difficult to remember than concrete ones: e.g. balloon is easier to remember than the term philosophy. Age also has its role in this difficulty. Older people have more difficulty to remember than younger ones and this effect is more visible for concrete than abstract words (Peters, 2008). + Through well considered division (called chunking ), larger amounts of information can be stored. E.g. a telephone number: versus 0487/ The use of the short term memory can degrade rapidly when disturbances occur such as a conversation or verbal secondary tasks. E.g. picking up the phone while doing a calculation. Taking the positive and negative influences into account, the limit is rather 5 than 7 (which corresponds more to the conclusion of Cowan et al. (2001)). Table 3 shows an overview of short term memory characteristics. Table 3: Overview of the limits of long and short term memory (Bridger, 1995) Short term memory Long term memory Storing capacity 7 items ± 2 Large Storing duration 5-30 sec Many years Learning process Small/short Larger Long term memory When using the long term memory, a learning process and experience is required. When good learning methods are available, this part of the memory can be addressed. For a good long term storage process, the following rules can be taken into account (Bridger, 1995): - To store things on long term base, the element needs a meaning. A description is essential: the more detailed, the bigger the chance for remembering. The idea behind this concept can be seen as follows: the more characteristics of an item are coded in our memory, the bigger the chance that at least one of them will be recollected later on. 10

36 CHAPTER 2. LITERATURE STUDY - Visual images can help to learn something (Bridger, 1995). 1. Every item that needs to be remembered, is being visualized (obvious figures are required). 2. The images need to be connected to each other. 3. The sequences need to be generated by operators with knowledge of the process. 4. The semantic equalities between items should be kept to a minimum. - When new elements can be connected to existing ones, the chance of remembering increases. Besides figure representation, a network of links can stimulate the remembering. Practice experience and explanation of the terms strengthens the links. - The more elements need to be remembered, the more elements will actually be remembered. This sounds paradoxical but it is not. More information increases the number of links between items (in the network representation). This is important in remembering random elements, not when following procedures in which the sequence is important. These steps are important when learning new things. After repeated use, everything will happen automatically. Images can fade or even disappear; the steps/words will be remembered. This rule is relevant for motivation but also for task allocation. Score allocation and improvement proposal: Short term memory Ergonomic score for short term score Explanation Less than 5 items/values need to be remembered during the setup When more than 5 items need to be remembered, and no aids are available (simple pen and paper could suffice). Score improvement Explanation Making remembering aids available. Reducing the number of items to remember <5. Making the need for short term remembering unnecessary. Long term memory Ergonomic score for long term score Explanation When no training is provided and long term memory needs to be addressed. When training is provided. 11

37 CHAPTER 2. LITERATURE STUDY Score improvement +100 Explanation Provide training (Improvement is only possible if score is 0) Question for the Excel model: Have limits for short and long term memory been taken into account? Noise, vibrations & auditory perception A. Rules Noise is one of the factors that contribute to the workload. Noise, as well as other environmental factors, can make a job more difficult to execute. Noise sources can rarely be identified as the cause of a decrease in performance of an operator, but there is no doubt they have an impact on the psychological and physical load on an operator. Noise should be seen as one of many environmental factors that interact and have a combined influence on performance (Leather et al., 2003). It can cause an increase in psychological and physiological stress for operators. Also annoyance and fatigue can increase which result in a poor post-work quality of life (Melamed and Bruhis,1996). Vibrations can be considered in a similar way. Often it is hard to objectively and exclusively assign the increase in stress or decrease in performance to vibrations, even though it is experienced this way by the operator(ljungberg and Neely, 2007). If an operator is exposed to vibrations during a short period in time, this can have a positive influence on muscle activity. Exposure during a longer period, on the other hand, can cause muscle fatigue (Torvinen et al., 2002). Because vibrations stimulate muscle contractions, they can cause an operator to grasp objects more firmly. This can cause nerve and tendon disorders. The presence of vibrations can decrease sensitivity of hands and fingers, which causes operators to grasp objects more firmly (Armstrong et al., 1987). Noise usually influences performance negatively. It can decrease accuracy, as well as vigilance. It is often experienced as mentally stressing. In rare cases it can have a positive effect. It can counter annoyance or postpone mental fatigue (Bridger, 1995). Following rules should restrict the bad influences of both noise and vibrations. a. Try to avoid a very loud (>81 db(a)) environment. 81 db(a) can be considered a good indication for a noisy environment (Ljungberg et al., 2004). OSHA prescribes a limit of 90 db(a) for continuous noise during an 8h shift but in practice an 85 db(a) limit is often applied (Bridger,1995). An equal-energy-rule can also be used to specify what the maximum exposure duration is in case of louder noise. A dose of 90 db(a) during 8h is equivalent to a dose of 95 db(a) during 4h or to a dose of 100 db(a) during 2h. An upper limit for the noise level is 115 db(a) according to OSHA (Bridger,1995). Working at higher noise levels is not allowed. In the excel model, a limit of 81 db is used but if the designer wants to be more specific, the previous method can be used. 12

38 CHAPTER 2. LITERATURE STUDY Score allocation: Ergonomic score Explanation The noise level is The noise level is higher than the limit. below the limit. Question for the Excel model: Is the volume to high (>81 db(a))? b. Try to avoid powerful vibrations as much as possible. As already mentioned earlier, powerful vibrations can have a negative influence on human performance (Ljungberg et al., 2004). In Europe, guidelines are provided with regard to vibrations. Hand and Whole-body vibrations are discussed (Table 4), exposure durations and vibration magnitudes are provided (Table 5) as well as considerations that should be made if the exposure action value is exceeded (Table 6). In the Excel model, table 6 is used to find the vibration limit since it is the most complete one. Table 4: Exposure limit values and action values for hand transmitted and wholebody vibrations (Griffin, 2004) Hand-transmitted vibration The daily exposure limit value standardized to an 8h reference period shall be 5 ms -2 r.m.s. The daily exposure action value standardized to an 8h reference period shall be 2,5 ms -2 r.m.s. Whole-body vibration The daily exposure limit value standardized to an 8h reference period shall be 1,15 ms -2 r.m.s. or, at the choice of the Member State concerned, a vibration dose value of 21 ms -1,75 The daily exposure action value standardized to an 8h reference period shall be 0,5 ms-2 r.m.s. or, at the choice of the Member State concerned, a vibration dose value of 9,1 ms -1,75 Table 5: Vibration magnitude (in ms -2 r.m.s.) that corresponds to the hand-transmitted vibration and whole-body vibration exposure action values and exposure limit values in the 2002 Physical Agents (Vibration) Directive of the European Union (Griffin, 2004) 13

39 CHAPTER 2. LITERATURE STUDY Table 6: Matters to be considered if the exposure action value is exceeded; the measures listed are in addition to health surveillance (Griffin, 2004) Other working methods that require less exposure to mechanical vibration Choice of appropriate work equipment of appropriate ergonomic design and, taking account of the work to be done, producing the least possible vibration Provision of auxiliary equipment that reduces the risk of injuries caused by vibration, such as seats that effectively reduce whole-body vibration and handles which reduce the vibration transmitted to the hand-arm system Appropriate maintenance programs for work equipment, the workplace and workplace systems Design and layout of workplaces and workstations Adequate information and training to instruct workers to use work equipment correctly and safely in order to reduce their exposure to mechanical vibration to a minimum Limitation of the duration and intensity of the exposure Appropriate work schedules with adequate rest periods Provision of clothing to protect exposed workers form cold and damp Score allocation: Ergonomic score Explanation Vibrations are more powerful than the regulation prescribes. Vibrations are below the threshold prescribed. Question for the Excel model: Are the vibrations too powerful? c. Avoid the combination of vibrations and a noisy environment. The combination of vibrations and a noisy environment is experienced by operators as extremely annoying and difficult, even though it does not have a clearly identifiable influence on performance. This situation should be avoided at all times even if it is just to allow operators a quiet environment (Ljungberg et al., 2004). Score allocation: Ergonomic score Explanation A noisy environment is combined with vibrations. Vibrations or a noisy environment are present. They are both not present. Question for the Excel model: Are vibrations combined with a noisy environment? 14

40 CHAPTER 2. LITERATURE STUDY d. Take into account the nature of the noise. Apart from the volume, the nature of the sound has to be taken into consideration. Some sounds can bother operators more than others. Also knowing where the noise comes from and what the source is, can make a difference (Saeki, 2004). Knowing that your co-operator is playing with his drill behind the corner can put a higher load on you than when you hear a distant humming of another division. This is illustrated by the following graphs: Figure 5: Relationship between sound pressure level and annoyance (Saeki, 2004) Figure 6: Relationship between sound pressure level and percentage of correct answers (Saeki, 2004) 15

41 CHAPTER 2. LITERATURE STUDY Figure 7: Relationship between sound pressure level and reaction time (Saeki, 2004) Score allocation: Ergonomic score Explanation The noise is The noise is meaningless. meaningful. Question for the Excel model: Is the nature of the noise taken into account? e. Avoid noise at low frequencies. Noise at low frequencies (20 200Hz, e.g. ventilation) sooner causes a decrease in the social behavior of operators: helpfulness, teamwork, communication, become more difficult (Persson Waye, 1997). Score allocation: Ergonomic score Explanation Frequency of the noise is not within the mentioned range. Frequency of the noise falls within the mentioned range. Question for the Excel model: Does the noise have low frequencies? 16

42 CHAPTER 2. LITERATURE STUDY f. Avoid contact between vibrating objects and hands and arms. Hands and arms can be extra sensitive (Armstrong et al., 1987) and we often get in touch with objects via our hands and arms. Especially our hands are very fragile instruments (think about the high concentration of nerves in our fingers). Cramping of the hands because of vibrations can become an issue. Score allocation: Ergonomic score Explanation Hands and arms do not get in touch with a vibrating object. Hands and arms get in touch with a vibrating object. Question for the Excel model: Do arms and hands get in touch with a vibrating object? g. Avoid the combination of vibrations and uncomfortable body postures (as are possible during a changeover). The combination of vibrations and uncomfortable body postures can cause an increase in workload and is experienced as annoying by operators. Providing armrests can reduce these consequences (Newell and Mansfield, 2008). Score allocation: Ergonomic score Explanation There are no armrests Armrests are provided. provided. Question for the Excel model: Are armrests provided when vibrations are combined with uncomfortable body postures? h. Try to avoid that oral communication has a frequency similar to the one of the background noise. A hindered communication is more likely when the background noise shares frequencies which are very similar to those of the target signal. This is called masking, and masking is stronger when the signal and the background frequencies are similar. Several indices have been developed to predict whether noise will interfere with oral communication. A lot of information in spoken language is transferred rather by consonants than by vowels. One index for speech transfer is the percentage articulation loss of consonants (%AL). An %AL of <12 signifies an Excellent communication. An %AL > 30 means unintelligible. 17

43 CHAPTER 2. LITERATURE STUDY One should also keep in mind that the comprehensibility of oral communication depends upon the knowledge of the subject matter of the listener, on the nature of the subject and on the volume (Bridger,1995). Score allocation: Ergonomic score Explanation The communication has a similar frequency as the background noise. The communication does not share frequencies with the background noise. Question for the Excel model: Does the oral communication have a frequency similar to the one of the background noise? i. The intensity of the warning signal should be sufficiently high at the place where it has to be noticed. An effective auditory warning should have an intensity which is louder than the background noise, and differ in pitch, waveform, The human ear is most sensitive in the range of Hz, so warning signals are ideally situated in this range with higher intensities at lower frequencies because lower frequencies are not deflected by objects and reach further than higher frequencies. Auditory warnings should be at least 10 db(a) louder than the background noise. Others recommend a ratio signal to noise of 8 to 12 db(a) (Bridger,1995). The following considerations are essential in the determination of warning signals (Bridger,1995): - The intensity of background noise at the place where the warning has to be noticed - Frequency of the background noise - Weakening of the intensity of the signal, away from the source Score allocation: Ergonomic score Explanation The intensity of the warning signal is less than 10 db(a) higher than that of the background noise. The intensity of the warning signal is more than 10 db(a) higher than that of the background noise. Question for the Excel model: Is the intensity of the warning signal sufficiently high at the place where it needs to be noticed? 18

44 CHAPTER 2. LITERATURE STUDY B. Improvements concerning noise, vibrations & auditory perception The following general suggestions have been found in literature and can be used to improve the rating of the current situation (Bridger, 1995). Some of the improvements are easier to implement than others and some have a more proactive nature. Table 7: improvements for noise, vibrations and auditory perception Adjustment rating Provide ear plugs or other ear protection +5 Reposition noisy machines +20 Reduce the machine noise, even if it is not extremely high +20 Mark noise zones with signs +20 Rotate operators between noisy and quiet jobs +20 Make very noisy machines sound proof +40 Replace machines by less noisy models +40 Change the process (fix the problem at the source) +40 Provide acoustic refuges +40 Conduct audiometric tests +40 Provide elastic bumpers in the impact zone of impact tools +20 Apply an audiometric testing program +40 Use a larger fan, rotating at lower speeds +20 Use mechanic, hydraulic or electric equivalents instead of +20 pneumatic tools Reduce cavitations in pumps +20 Eliminate vibrations at the machine(fix the problem at the source) +40 Put heavy machinery on damping blocks Climate A. Rules It is obvious that some environmental factors such as temperature and humidity can influence the performance. Also less obvious factors like ventilation and air quality can be of importance. Vigilance, reaction time and accuracy can all suffer because of suboptimal environmental conditions (Enander, 1989; Enander and Hygge, 1990). Usually warmth and cold have a higher influence as complexity of the job increases. It is clear that operators function better in optimal conditions. The less the operator is disturbed with his activities, the better. a. At a certain energy expenditure, temperature must fall within the corresponding range. It has been a while since the link between the ability to perform in a hot environment and energy expenditure was found (Lind, 1963). The prescribed upper limit for temperature in a working environment changes with energy expenditure and a guidance is provided by the diagram below (NIOSH). A maximum rectal temperature of 38 C can serve as a good upper limit. Up to this temperature, the probability that the temperature of the operator reaches 39,2 C or 42 C is 10-4 respectively 10-7 (Malchaire et al., 2000). 19

45 CHAPTER 2. LITERATURE STUDY Figure 8: Relationship workload metabolic heat (Amsey, 1998) The diagram can be read as follows: for a certain workload, limits are set for the acceptable temperature of the environment at the workload under consideration. As long as the actual temperature stays below this limit, there is no problem. Other authors present similar findings. In the diagram below, graph (A) stands for 8h of continuous work, (B) stands for 75% work and 25% rest each hour, (C) stands for 50% work and 50% rest each hour, and (D) stands for 25% work and 75% rest each hour. 20

46 CHAPTER 2. LITERATURE STUDY Figure 9: Lines of permissible exposure to work in hot conditions (Bridger, 1995) Score allocation: Ergonomic score Explanation Temperature is more than 2 below the advised limit. Temperature falls between the limit and 2 below. Temperature lies in between the advised limit and the upper limit. Temperature has risen beyond the upper limit. Question for the Excel model: Does temperature fall within the range corresponding to a certain energy expenditure? b. Check whether the person carrying out the changeover is wearing heat/cold protective clothing. Wearing protective clothing can limit freedom of movement of some joints as well as speed. On top of that, it can cause an increase in heart rate because of the extra weight that has to be carried (Bridger, 1995). These are some reasons for investigating the use of protective clothing. 21

47 CHAPTER 2. LITERATURE STUDY Score allocation: Ergonomic score Explanation No Sometimes/insufficient Yes Question for the Excel model: Is the person, carrying out the changeover, wearing heat/cold protective clothing? c. Sweat rate should be limited. When sweating a lot, an operator is not working in optimal conditions. Sweating can bring along uncomfortable consequences such as slippery hands or absorption by clothing (and thus heavier clothing). A maximum sweat rate (in g/hr), as a function of the metabolic rate M (watt), is presented by Malchaire et al. (2000): Eq. 1 SW max = 2.62 x M 149 g/h for non acclimatized persons Eq. 2 SW max = 3.27 x M 186 g/h for acclimatized persons The metabolic rate (M) can be calculated as follows: First the heart rate of the operator is measured while he performs the changeover. From Table 8 the energy expenditure in kcal/min can be derived. A figure in kcal/min can easily be transformed into a figure in watt (1 W = 4,186 x 1000/60 x kcal/min). Table 8: Relationship between heart rate and energy expenditure Heart rate [bpm] Energy expenditure [kcal/min] <70 1,25-1, , , , ,5 >175 12,5-20 Score allocation: Ergonomic score Explanation Sweat rate is higher than the Sweat rate is below the advised value. advised value. Question for the Excel model: Is sweat rate higher or lower than the advised value? 22

48 CHAPTER 2. LITERATURE STUDY d. Fluid loss should be limited. The avoidance of dehydration is stressed in literature. Malchaire et al. (2000) state a maximum Dmax (in g) of 5% of the body weight is sufficient to protect 95% of the working population. Score allocation: Ergonomic score Explanation Fluid loss is above the Fluid loss is below the threshold value. threshold value. Question for the Excel model: Is fluid loss higher or lower than the advised limit? e. Try to avoid that environmental temperature has a negative influence on performance. Most literature concerning the influence of environmental temperatures on performance is written for jobs similar to office work. Performance improves up to a temperature of C (Seppänen and Fisk, 2006) and starts to decrease from temperatures higher than C. The highest productivity can be found around 22 C. Following equation is applicable: Eq. 3 P = T T T => P is productivity, relative to the maximum value (so P max = 1) => T is room temperature in C (Seppänen et al., 2006) For other types of activities, specific optimal temperature ranges can be set up as well. Surprisingly, jobs where vigilance is important or jobs which have to be performed simultaneously are done best at C. Observation jobs decrease in the same range. Jobs where creativity is important seem to go better around 27 C (Enander and Hygge, 1990). For seated work, temperatures from 19 to 23 C at relative humidity between 40 and 70% are advised. In industrial environments temperatures of C are better (Bridger, 1995). Another finding states that air is experienced as stale, starting from a relative humidity of 60% at 24 C and from 80% at 18 C (Bridger, 1995). Score allocation: Ergonomic score Explanation Temperature is outside the Temperature is inside the advised range. advised range. Question for the Excel model: Does environmental temperature have a negative influence on performance? 23

49 CHAPTER 2. LITERATURE STUDY f. Try to keep temperatures sufficiently high. In cold environments especially the temperature of fingers and hands is very important. It appears that the critical temperature for sensitivity in fingers lies around 8-10 C. For work that requires a higher degree of handiness, temperature should not drop below C (Enander, 1989). Cold causes peripheral vasoconstriction, shivering, poor neural conduction and decreased muscle control. These can have several effects, e.g. slower reaction time which can seem of a rather psychological nature. Other possible effects can be larger hesitation or reduction of errors. In general, one could state that work in cold environments is done slower but more careful (Bridger, 1995). As it is the case with heat, it seems that especially the reaction to the climatologic conditions and not the conditions themselves determine whether performance will decrease (Bridger, 1995). Well trained workers are better equipped to maintain their level of performance in cold environments, even though they have not been in touch with the stressor ever before (Bridger, 1995). Score allocation: Ergonomic score Explanation Temperature is below the Temperature is above the advised value. advised value. Question for the Excel model: Is temperature sufficiently high? g. Avoid working in the sun. Working in the sun should be avoided. It decreases sight and is an important source of warmth (Bridger,1995). This is a very straightforward rule but perhaps also one of the easiest to find a solution for. Score allocation: Ergonomic score Explanation Yes No Question for the Excel model: Does the operator have to work in the sun? 24

50 CHAPTER 2. LITERATURE STUDY h. Check whether there is an appropriate ventilation speed. The degree of ventilation can have an influence on performance (Seppänen and Fisk, 2006). It does not only provide a cooler feeling, it also removes air pollutants (Wyon, 2004). Airspeeds below 0,1 m/s cause a muggy feeling, even at relatively low temperatures. Airspeeds above 2 m/s are being experienced as draughty. In hot environments (corrected effective temperature > 24 C) airspeeds of 0,2 0,5 m/s help to cool the body, especially when relative humidity is high (Bridger, 1995). Advised threshold values for Wet Bulb Globe Temperature (WBGT) ( C) are provided in Table 9 (Bridger, 1995). The WBGT is a composite temperature used to estimate the effect of temperature, humidity, wind speed and solar radiation on humans. Its formula: Eq. 4 where WBGT = 0.7 T w T g T d T w = Natural wet-bulb temperature (humidity indicator) T g = Globe thermometer temperature (to measure solar radiation) T d = Dry-bulb temperature (normal air temperature) Table 9: Advised temperature ( C) for a workplace in combination with airspeed Work pace Airspeed = 1,5 m/s Lower limit Upper limit Light 30 C 32 C Moderate 27,8 C 30,5 C High 26 C 28,9 C Table 9 should be read as follows: at a moderate work pace for instance, an airspeed of 1,5 m/s is appropriate as long as temperature falls between 27,8 C and 30,5 C. If temperature is higher than 30,5 C, the appropriate airspeed should be higher than 1,5 m/s. The same work method is applied for temperatures lower than 27,8 C for a moderate work pace. Score allocation: Ergonomic score Explanation Taking into account temperature, airspeed does not match the advised values. Taking into account temperature, airspeed does match the advised values. Question for the Excel model: Is there sufficient ventilation? 25

51 CHAPTER 2. LITERATURE STUDY i. Air quality has to be acceptable. Air quality can influence performance (Seppänen and Fisk, 2006; Wyon, 2004). Think about an urban environment where the busy traffic can already cause hindrance for breathing. City workers have to work in this type of environment. A lot of industrial processes pollute the air as well. When combustion of organic substances takes place, carbon monoxide is released into the air. As soon as the carbon monoxide concentration is higher than 6,5 ppm, it starts to accumulate in the blood during sub maximal efforts. In the case of city traffic there are 37 to 54 ppm in the air, so the risk of a decrease in work capacity is real. Also wearing breathing equipment e.g. to filter the air or extra oxygen can influence performance. Firstly because it limits the movements of the operator and secondly because it can cause difficulty when breathing. The maximum oxygen intake can be reduced with 9% (Bridger,1995). Score allocation: Ergonomic score Explanation The amount of carbon monoxide is less than 6,5 ppm. The amount of carbon monoxide is higher than 6,5 ppm. Question for the Excel model: Is air quality acceptable? j. Exposure time to a hot environment should be limited. Not only the intensity (temperature level, workload) of exposure to a hot environment should be regulated. Also the duration of exposure is important. As the duration of exposure increases, the temperature which goes with an acceptable performance level, drops (Bridger,1995). Figure 10: Upper limit for unimpaired mental performance as a function of exposure time to different effective temperatures (Bridger,1995) 26

52 CHAPTER 2. LITERATURE STUDY Score allocation: Ergonomic score Explanation The duration of exposure is longer than the value given by the diagram for the current temperature of the environment. The duration of exposure is shorter than the value given by the diagram for the current temperature of the environment. Question for the Excel model: Is exposure time to a hot environment limited? k. In hot industrial environments, drinking fluids should be available at all times and operators should be encouraged to make up for lost fluids, in order to avoid both dehydration as overhydration. This rule is strongly emphasized by literature (Bridger,1995). Trying to limit the loss of fluids (as mentioned in the rules above) is one thing. But one also has to think about making up for the fluids lost. If the fluid loss is not replenished, even if there is only minor or moderate loss, this can have consequences for the human performance. The human body exists for over 60% out of water and even minor unbalances cause troubles. Score allocation: Ergonomic score Explanation Operators do not have the opportunity to regain fluids, and are not encouraged either to do so. Operators have the opportunity to regain fluids, but are not encouraged to do so. Operators have the opportunity to regain fluids, and are encouraged to do so. Question for the Excel model: Are drinking fluids available, and are operators encouraged to consume them frequently? l. Provide breaks for operators to recover. This is a rather intuitive rule. From experience, everyone knows that a break can be more than welcome while working. It allows our body to relax for a moment and can offer a possibility to cool down or warm ourselves again. When breaks are provided, the total time one can work, is higher compared to the situation when one would try to do the same type of job in one single, stretched effort. This of course in a specific environment and on a specified day. Score allocation: Ergonomic score Explanation No Yes 27

53 CHAPTER 2. LITERATURE STUDY Question for the Excel model: Can operators take breaks to recover? m. Hot working conditions are dangerous when they are coupled to an increase in body temperature. In literature (Bridger,1995) it can be found that the human body is very sensitive to changes in temperature. Even changes as small as a few degrees can be significant. Changes in both directions (up- or downwards) are important. Score allocation: Ergonomic score Explanation Yes No Question for the Excel model: Do the hot working conditions lead to an increase in body temperature? B. Improvements concerning climate The following general suggestions have been found in literature and can be used to improve the rating of the current situation (Bridger, 1995). Table 10: Improvements concerning climate Improvement Adjustment rating Humidity reduction +50 Improvement air currents +50 Removal heavy clothing/introduction loose-fitting overalls +50 Work pace reduction +50 Provide regular breaks +50 Job rotation +50 Outside work on cooler moments of the day +50 Acclimatization period +50 Provision of drinking water or other fluids +50 Provide shade +50 Building cool spots and refuges +50 Mechanize the job

54 CHAPTER 2. LITERATURE STUDY Illumination a. Provide a bright work environment. To measure whether the work place has enough light, a photometer can be used, but for this assessment model, it does not have to be this precise. The designer only has to make sure the light is sufficient for the task and does not result into visual stress. The model can use light intensity, provided by the manufacturer and the calculations below: We choose a brightness from 500 to 1000 candelas (cd) which corresponds to 500 or 1000 x 12,57 lumen (lm). This can be seen as performing visual tasks of medium contrast of small size, e.g.: reading medium pencil handwriting, bad printed or reproduced material, medium bench and machine work, difficult inspection, medium assemblage (Bridger, 1995). Notice that the height of the lighting source should be taken into account. (Lighting (lx) = cd/d² with D = distance of the light to the work environment) E.g.: Lamp on 5m height and 1000 lx is demanded => 1000 lx = X / 5² X = cd = lm Determine the number of lighting bulbs of e.g lm To know the wattage, often the conversion factor 683 is used. This number is based upon the international definition for a wavelength 555nm (website TU Delft). Another wave length needs an adjustment to the factor but in this system 683 will be used at all times for simplicity. 1 Watt corresponds to 683 lumen. Score allocation and improvement proposal: Ergonomic score Explanation < 500 cd 500 cd 1000 cd > 1000 cd Score improvement Explanation Renew the lighting bulbs (increase # candelas) Renew the light infrastructure into more natural light (2 possibilities) New light infrastructure: lamps that are more natural and resemble natural daylight Reconstruction of work environment: more daylight admission is possible (Improvement is only possible if score was not 100, if score was 66 only 1 improvement will be necessary at maximum) Question for the Excel model: Is every working position of the operator provided with enough light? 29

55 CHAPTER 2. LITERATURE STUDY Decision making a. Feedback is necessary in the decision making process. Feedback is essential when operators have to make choices in the setup. Especially when using electronic interaction systems, an approval by the system or a simple view of the setup values can avoid problems or reduce the psychological strain for the operator. Of course, when the first new products are completed, the machine provides feedback but it is better to be aware of problems in advance. The decision process contains 4 steps, the last one is reserved for feedback (Bridger, 1995): - Collecting information (to and from which product is the changeover needed?) - Evaluation of alternative actions concerning setups - Execution (after choosing an alternative, the setup can be performed) - Feedback Score allocation and improvement proposal: Ergonomic score Explanation No overview of the settings. Overview of the settings. Overview of the settings and evaluation of the value (e.g. by color: red or green). Overview of the settings, evaluation of the value and readjusting procedure. (Improvement is possible by adjusting and reaching a higher score in the table above) Question for the Excel model: Did the designer provide enough feedback after setting or adjusting values? Visual displays a. Use letters/characters/icons, on a display, that are big enough and readable for every operator. Ideal light, big contrast conditions and a person with a sight of 20/20 1 would be perfect to identify the target with a critical detail (visual acuity) of 1 minute. The ideal light and contrast can be created (if necessary with some adjustments) but demanding a sight of 20/20 for every operator who executes the setup is unfeasible, that is why a sight of 20/40 is taken into account when designing the visual aspects of the machine. 20/40 means that the person can see critical details at a distance of 20 feet 2 when a person with perfect sight would already see the details at 40 feet. 1 Sight of 20/20 (according to Snellen): denominator = distance between the eye and the chart, nominator = distance at which the target should be clear at a visual angle of 1 minute (when using meters instead of feet, one can use 6/6) 2 1 foot = m 30

56 CHAPTER 2. LITERATURE STUDY For far away objects 20/40 is used, for nearby elements 14/28 is used. This corresponds to a visual acuity of 2 minutes and a relative acuity of 0,5. (Bridger, 1995) Table 11: Dimensions for visibility of near and far objects (Bridger, 1995) VA(min) Snellen Far (feet) Snellen Near (inches) Relative Acuity /10 14/ /20 14/ /40 14/ /80 14/ When converting to meter/centimeter: - For nearby elements: 20/40 (in feet) 6/12 (in m) - For far away elements: 14/28 (in inches) 35/71 (in cm) Score allocation and improvement proposal: The score allocation can be done according to two types of measures. The visual angle can be calculated. In this case, the angle is directly related to the height of the object and its distance to the eye. The second way of working is by calculating the visual acuity. The latter will be used in the assessment model. Proposition 1: The visual angle could be the measure. The aim lies towards an angle of minimum 1. In the equation (Figure 11) height (H) and distance (D) are easy to measure, the angle can be used as comparable criterion. Figure 11: Link between visual angle, distance to the object and height of the object Ergonomic score Explanation Angle 1 Angle > 1 Proposition 2: As alternative measure, the visual acuity value can (and will) be used. VA = nominator / denominator = distance from the eye to the image / distance at which the target should be clear at a visual angle of 1 minute. The improvement of the score depends upon the recalculated VA or angle. 31

57 CHAPTER 2. LITERATURE STUDY Ergonomic score Explanation VA < VA 2 VA > 2 (Improvement is possible by adjusting and reaching a higher score in the table above) Improvement is necessary when the score is lower than 50: - Increase the height of the figure/text - Bring the figure/text closer to the operator Question for the Excel model: Are all letters/characters/icons, displayed, big enough and readable for every operator? b. Place the display at a good distance and under an appropriate angle. Convergence Objects that are located too close demand muscular contraction of the eye to allow focus on the object. Multiple focus causes fatigue. A minimal convergence is required (when the object is placed closer it should be put lower, when located further it has to be higher). A distance of 1 meter is appropriate when looking straight forward, when it is located at 80 cm, an angle of 45 is better. This rule of thumb accounts for mounting/controlling of parts, but also when placing a display (Bridger, 1995). A study of Shieh et al. (2007) shows the effects on the viewing distance and screen angle of text to be read in the form of electronic papers. The displays placed on setup machines will normally contain less text than a paper, but this study could be used as a reference for displays with text areas that contain more than 1 line of text. Viewing distance of E-papers is experienced to be similar to that of visual display terminals. The general distance for viewing the papers was 500 mm, which is higher than reading conventional paper sheets (360 mm) and lower than CRT. Shin & Hedge (2010) performed a much more detailed experiment on the preferred position of the display and keyboard during a data entry task in four display setups. The conclusions are in line with those of Shieh et al. (2007), but are more detailed. Since displays are not used during the whole setup, this kind of detail is unnecessary for our application. Further investigation shows that the higher the ambient illumination is, the higher the viewing distance and the smaller the screen angle. Also character size has an effect on viewing distance (the larger the character, the higher the possible viewing distance). Although these effects are proven significant, they are rather small in practice. The angle of the displays is about horizontally. This is approximately 30 lower than the horizontal eye level (Figure 12). 32

58 CHAPTER 2. LITERATURE STUDY Score allocation and improvement proposal: 2 criteria need to be satisfied: First ergonomic score: the viewing angle for all operators Explanation <0 or > or ± 5 Figure 12: The viewing angle Second ergonomic score: the viewing distance Explanation < 20cm or > 75 cm 20cm - 45cm or 55cm 75 cm 50 cm ± 5 cm Improvements: Improved score Explanation Relocate the display Provide a dynamic display support that is adjustable in height and angle. This gets maximum points, since it can provide the perfect display location for every operator. (These are new scores, not to be accumulated with the original ones) Question for the Excel model: Are displays placed at a good distance and can operators read the screens under an appropriate angle? c. Use the correct colors Chromatic colors Because of the wave length (and thus the color) of light, the eye will be focused slightly nearer or further. This is called chromatic aberration. It can cause the edges of objects to be purple or red (respectively the shortest and longest wave lengths) and this phenomenon is worsened by bad lighting. The refractive ability of the eye is approximately 3 diopters 3 higher for saturated 4 blue 3 Diopter = the unit for refractive ability of the eye 1 diopter = a lens that can focus parallel rays of light up to 1 meter away from its axis 2 diopter = a lens that can focus parallel rays of light up to 50 cm away from its axis 10 diopter = a lens that can focus parallel rays of light up to 10 cm away from its axis 4 Saturated color: contains only the wave lengths for this color. Unsaturated colors are mixed with white. 33

59 CHAPTER 2. LITERATURE STUDY than for saturated red. So blue objects are focused in front of red ones and both cannot be focused at the same time. Purple letters on a screen can look fuzzy because of this. On a screen it is better to use less saturated colors with a difference of no more than 1 diopter. And even this can still create visual effects like the illusion of depth (Bridger, 1995). This blur causes accommodation of the eye and such irresolvable fuzzy elements can create destabilization of the accommodation mechanism in the eye, which results in visual fatigue. Colors such as red, orange and green can be viewed without focusing, but cyan or blue can not be viewed together with red because they are situated at opposite ends of the sight spectrum (Figure 13). To avoid odd, unwanted visual effects, these opposite colors should be avoided. According to a study of the Heinrich University, the best combinations within a clear environment are dark text on a light background and light text on dark surroundings. For displays, the paper of Buchner et al. (2009) mentions that text with positive polarity is more appropriate. In addition to this, the colors that are located 15 RGB points away from the borders of the color spectrum are the best colors (Figure 14).. Red. Figure 13: Colors at opposite ends of the spectrum should not be combined Figure 14: Text and background colors 15 points from each boundary Afterimage Some color combinations are to be avoided because of the opponent process system. This means that the eye can create an afterimage in a color after focusing on another color. After focusing on the color blue, yellow will appear. Bearing this in mind, following color combinations ought to be avoided: - Red on green - Blue on yellow - Green on blue - Red on blue Color symbolism Certain colors are linked to operational modes. Ergonomically, these links may not be reset. Operational modes: - Green = safe, normal modus - Orange = be careful - Red = unsafe 34

60 CHAPTER 2. LITERATURE STUDY Temperature: - Red = (too) hot - Blue = (too) cold Color selection When choosing colors, the following guide for color selection should be taken into account (Bridger, 1995) : a. In general 1. Choose compatible combinations, avoid combinations that contain achromatic colors and result in afterimage effects. 2. Use large color contrasts for character versus background. 3. Do not use too many colors: 4 if possible (max. 7). 4. Use light blue only for backgrounds. 5. Use white for side information. 6. Use redundancy: do not only use color differences, also use different forms because 6 to 10% of the men is color blind. b. For visual display units 1. Brightness reduces in the following sequence: white, yellow, cyan, green, magenta, red, blue. 2. Use white, yellow, cyan or green opposite to a dark background. 3. Avoid highly saturated colors. Figure 15: Guide for color selection (R.S. Bridger, 1995) Score allocation and improvement proposal: The ratings depend upon 3 aspects: the contrast between text and background, the use of bad color combinations, and respecting color symbolism. The total score is the sum of all sub-scores. For improvements: follow the guide of selection until each of the 3 criteria has a score of Is the contrast between text and background big enough? Ergonomic score Explanation No Yes - Are any of the previously mentioned bad color combinations being used? Ergonomic score Explanation No Yes - Is color symbolism being respected? Ergonomic score Explanation No Yes 35

61 CHAPTER 2. LITERATURE STUDY Question for the Excel model: Does the display show information in appropriate colors? d. Do not only use color to differentiate information. Color offers a lot of advantages in the representation of information. Nevertheless it can not be used as the only differentiator to represent a specific kind of information. The advantages and disadvantages of using color as differentiator for information are listed in Table 12. Table 13 provides systems that could easily be used together with color, in order to get rid of the disadvantages of Table 12. Table 12: Advantages and disadvantages of using color as to differentiate information (Bridger, 1995). Advantages Puts the focus on data Faster absorption of information Differs items that are located closer Can increase reaction speed Adds a new dimension Seems more natural Disadvantages 8% 10% of all men is color blind, for women this percentage is lower Can cause confusion Can cause fatigue Can create unwanted classification Can cause an afterimage Table 13: Systems to combine with color differentiation (Bridger, 1995) Figure-background differentiation Grouping Icons With a large contour or a large view, the image can be distinguished from the background much easier. Colors can group items that belong together but grouping can also fulfill the task. Grouping the items physically is preferred opposed to giving them the same color. Icons can replace text. Instead of grouping or coloring the text, an icon can be used. Score allocation and improvement proposal: Ergonomic score Explanation Differentiation is needed but has not been done. Differentiation is needed and is performed by coloring. Differentiation is needed and is performed by figure-background differentiation, grouping or icons (this may or may not be in combination with coloring). No differentiation is needed in the text. 36

62 CHAPTER 2. LITERATURE STUDY Improved score Explanation Figure-background differentiation, grouping or icons are used with or Simplification eliminates the need of differentiation. without color differentiation. (These are new scores, not to be accumulated with the original score.) Question for the Excel model: Is there a need of differentiating specific information in the text? Is this done by coloring or is coloring used in combination with other methods? e. Keep the navigation through complex display structures simple and logical. Extensive structures which are too big to show on 1 screen, can be displayed through: - Truncating = cutting of information (gives good results when reproducing text) - Roaming = floating across the screen/image - Zooming = enlarging specific parts - Map window = an extra view of the extended structure Beard and Walker (1990) state that each of the techniques works faster in combination with a map window than without one, and that roaming and the combination of roaming and zooming works faster than a scrollbar. A fifth technique that should not be encouraged is shrinking. This method does not guarantee a fast and flawless result. Also note that a display structure should be kept as simple as possible and 3-dimensional views should also be avoided. Bearing all of this in mind, a logical view can be provided. Score allocation and improvement proposal: Ergonomic score Explanation Navigation is needed but has not been implemented by one of the four techniques Navigation has been done by one of the four techniques but is still experienced as illogical or difficult Navigation has been done by truncating, roaming, zooming or map windowing No navigation is needed Score improvement Explanation Simplify the navigation (Improvement is only possible if score was not 100) Question for the Excel model: Use 1 technique (more) of the 4 techniques Provide extra training when navigation is still difficult Do operators experience the navigation through complex display structures as simple and logical? Are techniques used such as truncating, roaming, zooming or map windowing? 37

63 CHAPTER 2. LITERATURE STUDY f. Choose a good representation on the display: digital or analog. When high accuracy is required, digital views are preferred. When monitoring change in values, the designer should implement an analog view or display. Often a combination of both is even better (Bridger, 1995). Score allocation and improvement proposal: Ergonomic score Explanation When using analog view to read a single value instead of digital view, or when using digital view to check whether a value is within a range instead of analog view. When adjustment is needed on a single value and analog is used. When - digital view is used to read a value - analog view is used to check whether a value is within a range - digital view is used to adjust a single value Improvement of a rating goes from 0 to 100 by replacing the view to a more appropriate one (digital to analog and vice versa). Question for the Excel model: Is the implemented digital or analog representation appropriate for the information that is shown? g. Keep the handling of panels for displays simple. Steering mechanisms (e.g. switches) are placed near the display to control/adjust them. Three functional attention fields can separate control switches that belong together (Table 14). When reducing the angle between switches or steering mechanisms that belong together or should be used shortly after one another, the probability of mistakes reduces and the reaction time increases (Clohessy et al., 2001). Table 14: Three functional attention fields according to Clohessy et al. (2001) <30 Stationary field Eye field >80 Head- and eye movement required Score allocation and improvement proposal: Ergonomic score Explanation If all mechanisms that belong together can not be placed in the stationary field. If all mechanisms that belong together are placed in the stationary field and the rest in the head- and eye movement field. If all mechanisms that belong together are placed in the stationary field and the rest in the eye field. 38

64 CHAPTER 2. LITERATURE STUDY Improved score Explanation When mechanisms that belong together are placed within the stationary field, but it is not possible to place the other ones in that field, they should be provided in the eye field. When the number of mechanisms can be reduced and all can be placed within the stationary field. Question for the Excel model: Are steering mechanisms, that belong together, placed in the stationary field? h. The most appropriate model needs to be implemented in interactive systems. In interactive systems such as electronic calculators or word processors the designer should make sure the system supports the operator. This provides psychological ease for the operator and it saves time. The appropriate model needs to be implemented, but the best solution would be to eliminate the need of calculations for the operator. For calculation interaction: Two fundamental operations are available: RPN (reverse polish notation) and ALG (algebra). The difference is situated in the control logic. ALG is the standard method, used in calculators and for simple calculations; this is the best method. When more difficult calculations are required, RPN is preferred. Both systems can be improved by showing the relevant previous inputs on a multiline display (Young, 1981 and Hoffman et al., 1994). Score allocation and improvement proposal: Ergonomic score Explanation Calculations are necessary and the way of working is inappropriate. Calculations are necessary and the appropriate way of working is applied (RPN /ALG). No calculations are necessary. Question for the Excel model: Is the most appropriate model implemented in interactive systems? Auditory displays A. Rules Although visual incentives from our environment are our most important source of information, one can not underestimate the importance of auditory information. In busy environments it can often be experienced as less burdensome to provide information through the auditory channel and in this way, relieve the visual channel. Auditory information should also be provided in an appropriate way, because it can make a job more difficult as well and can even work disturbing for the operator instead of making his or her job easier. 39

65 CHAPTER 2. LITERATURE STUDY a. Try to use alarm signals or feedback noises to point out mistakes to the operator, or to keep him up to date with the machine s or the process status. One of the possible advantages of auditory feedback is its attention demanding capacity. It breaks in on the attention of the operator. Visual stimuli however, do not necessarily have this captive audience. The operator has to be looking towards the display in order to perceive the stimulus (Rauterberg, 1998). This makes auditory displays or signals an adequate method to provide feedback. Score allocation: Ergonomic score Explanation Alarm signals or feedback noises are not being used. Question for the Excel model: Sometimes alarm signals or feedback noises are being used, but improvement is still possible. Alarm signals or feedback noises are being optimally used. Are alarm signals or feedback noises being used to point out mistakes to the operator, or to keep him up to date with the machine s or the process status? b. Try to combine visual information (displays) with auditory information, to discharge the visual channels and to reinforce the information. A lot of authors support this thought (Takao, 2002; Rauterberg, 1998; Lee and Chan, 2008; McBride and Ntuen, 1997). Often (perhaps unconsciously) people have the tendency to transfer information visually. But eventually this can result in such a huge amount of visual information, that the visual channel is overloaded and that information might be missed or skipped. Score allocation: Ergonomic score Explanation Auditory information is never combined with visual information. Auditory information is sometimes combined with visual information. Auditory information is always combined with visual information. Question for the Excel model: Is visual information (displays) combined with auditory information, to discharge the visual channels and to reinforce the information? 40

66 CHAPTER 2. LITERATURE STUDY c. If time plays a critical role, try to use sounds which are representative for the possible consequences. This can allow a faster reaction time. It is always a good idea to link the alarm sounds to their goal in the best way possible (Petocz et al., 1998; McKeown et al., 2010). Usually, when alarm sounds are used, the situation is rather urgent. Important (costly) time can be saved when the need to check first what the sound actually means, is avoided. Score allocation: Ergonomic score Explanation The signals chosen are not representative. The signals chosen are sometimes representative. The signals chosen are always representative. Question for the Excel model: Are the sounds which are used, representative for the possible consequences if time plays a critical role? d. Use auditory signals in control-consoles with both visual and auditory modalities and where reaction time is of the highest order of importance. The visual effect seems to be dominant and leads to faster reaction times (Lee and Chan, 2008). Score allocation: Ergonomic score Explanation Auditory signals are never used in control-consoles where reaction time is very important. Auditory signals are sometimes used in control-consoles where reaction time is very important. Auditory signals are always used in control-consoles where reaction time is very important. Question for the Excel model: Are auditory signals used in control-consoles with both visual and auditory modalities and where reaction time is of the highest order of importance? e. Incorporate a warning period (2 4 s), which precedes the signal. Introducing a warning period can reduce the reaction time (Lee and Chan, 2008). It is rather obvious that a human being can react faster if he or she is prepared for what is coming. Score allocation: Ergonomic score Explanation A warning period A warning period is A warning period is is never provided. sometimes provided. always provided. 41

67 CHAPTER 2. LITERATURE STUDY Question for the Excel model: Is there a warning period (2 4 s), which precedes the signal? f. Take into account the effectiveness of the links between auditory signals and basic quantities when deciding upon the characteristics of the warning signal. The way in which we relate a change in an auditory signal to a change in a basic quantity depends upon the quantity represented (Walker and Kramer, 2005). For instance, intuitively it is easier to associate an increase in size with an increase in pitch instead of an increase in pace. Score allocation: Table 15: The links between auditory signals and basic quantities Loudness Pitch Pace Preamble Temperature good ok ok bad Pressure ok ok bad bad Size ok ok bad good Pace ok good ok bad Ergonomic score Explanation bad ok good Question for the Excel model: Has the effectiveness of links between auditory signals and basic quantities been taken into account, when deciding upon the characteristics of the warning signal? g. Take polarity into account. A higher pitch is intuitively linked to a higher frequency for instance (Walker and Kramer, 2005). Again, this is a very simple finding which everyone will recognize. It would be counter intuitive and unproductive to link an increase in pitch to a decrease in rotations per minute, for instance. Score allocation: Ergonomic score Explanation Polarity is never taken into account. Question for the Excel model: Has polarity been taken into account? Polarity is sometimes taken into account. Polarity is always taken into account. 42

68 CHAPTER 2. LITERATURE STUDY h. Make sure the way in which the data is portrayed matches with the auditory signal. The combination of a flashing red light with an auditory signal for instance is much more efficient than the combination of a dial with an auditory signal (McBride and Ntuen, 1997). Score allocation: Ergonomic score Explanation There has never been paid attention to the matching of auditory and visual signals. Sometimes there has been paid attention to the matching of auditory and visual signals. There has always been paid attention to the matching of auditory and visual signals. Question for the Excel model: Has the designer paid attention to the match between the way the data is portrayed and the auditory signal? B. Improvements for auditory displays As far as auditory displays are concerned, specific improvements have not been provided. The reason for this is very simple: implementing an improvement requires nothing else but changing the answer on the question under consideration. In this way the improvements are implemented in the Excel file that can be used to do a practical assessment Safety and hazardous materials a. Use color and symbols as indication for danger and remain consequent. If possible, use indications with international and/or legal value. Marking dangerous situations has to be in accordance with the law concerning safety. For the Belgian regulation references are made to the KB of June 17 th of 1997 concerning safety and health issues at work. Color is not implemented in that legislation but provides good indications (Braun et al. 1995). Some rules of thumb can be taken into account: - Legislation does not specify colors of pipes. These colors can provide information on the product that fills the pipes, so a good choice of color is important. As a basis for choosing the color, codes of good practice can be used, such as NBN

69 CHAPTER 2. LITERATURE STUDY Table 16: NBN 69, found in the course: Veiligheid, kwaliteit- en milieumanagement by Ann Dermaux Green Silver grey Brown Yellow ochre Violet Light blue Black Red Water Steam Mineral, vegetable and animal oils and liquid fuels Gas of liquid gas Acids and bases Air Non-flammable liquids Fire-fighting equipment - The background color and shape of icons on and around the machine should fit the general known dimensions that are linked to a specific meaning. Table 17: Overview of general used shapes and colors for signs (course: Veiligheid, kwaliteit- en milieumanagement) Red Prohibition Fire-fighting equipment Yellow Caution: danger Blue Obligation Information or recommendations green Rescue and evacuation - Obligation signs have the same binding character as prohibition signs. This is often forgotten on the shop floor. Signs that show an obligation of e.g. safety goggles or safety gloves, for performing a subtask in a setup, should be experienced as binding for every operator. In training this can be highlighted. - Through training, colors can get an even stronger meaning for operators. Without training, the effect of red will be the most effective (Leonard et al., 1999). Score allocation and improvement proposal: Ergonomic score Explanation If there are no danger indications while they are needed If indications consist of words If indications consist of an image If indications consist of an image and colors Improved score Explanation Remodel the indications, create Remove the dangerous items images and color them 44

70 CHAPTER 2. LITERATURE STUDY Question for the Excel model: Are color and symbols being used to indicate danger? Is text eliminated from safety indications? b. Use as little text as possible for safety indications. Warnings should be presented by forms and colors if possible. Signaling through text can cause language problems and is less effective. Especially untrained operators can experience problems, so training is required when text is used (Lesch et al., 2008). The score allocation is being handled by the previous rule. c. Use risk assessment tools when designing the setup. By using risk assessment tools, risk factors associated with increased probability on injuries, can be recognized fast and efficiently (Bridger, 1995). Risk analysis is very important and through recordings of the evolution of assessments and interventions, safe setups are possible. Some good risk assessment tools: - Biomechanical analysis - NIOSH WPG (work practices guide for lifting) - Checklists/Tools o OSHA screening tool o NIOSH workplace evaluation o OWAS (Ovaka working posture analysis system) o REBA (rapid entire body assessment) o RULA (rapid upper limb assessment) o Strain index o Score allocation and improvement proposal: Ergonomic score Explanation No Yes For improvement: use at least one of those tools. The score will increase up to 100. Question for the Excel model: Are risk assessment tools being used? 45

71 CHAPTER 2. LITERATURE STUDY Design score: ergonomics linked to time The model now contains the necessary ergonomic questions and their score. It should however also contain time scores as based upon a previous study of De Nil (2009). So the new rules as mentioned in paragraph should also be linked to time. This section covers the link between ergonomics and time reduction or -increase. Some of the rules mentioned above could directly be linked to time. Since time is one of the levels on which the rules are rated. The rules for which specific time-linked information was available, are provided of additional this information. It provides an extra foundation for the time-scoring and weighting system behind these rules. The scoring of rules for which such information was not available is based on common sense, intuition and comparison Task allocation a. Multitask capacities depend upon the operator, they can not be required when defining the setup mode. Multitasking can be seen as switching from one task to another. A task will therefore be interrupted in order to start another one and this second task can subsequently be interrupted by the first one or even a third one and so on. When multitasking is required in the method of working, switching to another task can be seen as an interruption. 41% of interruptions result in the discontinuing of the interrupted task beyond the duration of the interruption itself (O Conaill and Frohlich, 1995). When multitasking on a display, the same reasoning can be applied. It s not convenient to interrupt a task that is performed on a display by another computer-initiated task. Interrupting a task can increase task completion time by 5% to 40% (Bailey et al., 2000). The percentage strongly depends upon the memory load. The more memory load the task requires, the more time the operator needs to reorientate after being interrupted. Tasks can qualitatively be categorized into 3 groups (Bailey et al., 2000): - Adding and counting tasks (highest memory load) - Image and reading comprehension tasks (intermediate memory load) - Selection and registration tasks (lowest memory load) The graph (Figure 16) shows large differences in percentages according to the kind of task that is performed. Reference values for the assessment model are based on these values. - Adding: 24% - Counting: 35% - Image viewing: 16% - Reading: 11% - Registering: 5% - Selecting: 18% Figure 16: The relative increase in task completion time (TOT) for interrupted versus non-interrupted tasks (Bailey et al., 2000) 46

72 CHAPTER 2. LITERATURE STUDY Bailey et al. (2000) also state that there is no reason to believe that the duration of the interruption has an additional effect on the total completion time of the primal (interrupted) task. Furthermore it is found that other experiments contradict certain findings by Bailey et al. (2000), but still this experiment approaches the setup situation the best since the test persons were asked to perform the task as quickly as possible while maintaining accuracy. Score allocation and improvement proposal: The ergonomic score improvements were based upon intermediate and low memory load tasks since high memory tasks are rarely required in setups. An improvement of about 18% means that when multitasking is required, the score should be about 82 as opposed to 100 when it is not required. Design score Explanation When multitasking is When multitasking is required. not required When eliminating the multitasking activities, the duration of the tasks will be reduced again, giving a score of 100. When another operator helps, the time will also reduced but from a design point of view this is not optimal, so a score of 90 is more appropriate. Improved design score Explanation Help through another Elimination (extra) operator Motivation a. The limits of long and short term memory have to be taken into account. No previous studies have been found in which time is linked to exceeding the limits of long and short term memory. For this rule however, common sense could indicate that ergonomics and time are closely related. When the number of elements that need to be remembered, exceeds the capabilities of the operator, he will lose motivation but also time. Further studies might indicate a connection between time and ergonomics and perhaps even determine a factor. At present a factor 1 will be used, so ergonomics and time influences in this rule will be considered to be the same. Score allocation and improvement proposal: Short term memory Design score for short term score Explanation Less than 5 items/values need to be remembered during the setup. When more than 5 items need to be remembered, and no aids are available (simple pen and paper could suffice). 47

73 CHAPTER 2. LITERATURE STUDY Long term memory Design score for long term score Explanation When no training is provided and long term memory needs to be addressed. When training is provided. Score improvement +100 Explanation Provide training (Improvement is only possible if score is 0) Noise, vibrations & auditory perception A. Rules a. Try to avoid a very loud (>81 db(a)) environment. Design score Explanation The sound volume is higher The sound volume is below the than the limit. limit. b. Try to avoid powerful vibrations as much as possible. Design score Explanation Vibrations are more powerful Vibrations are below the than the regulation prescribes. prescribed threshold. c. Avoid the combination of vibrations and a noisy environment. Design score Explanation A noisy environment is combined with vibrations. Vibrations or a noisy environment are present. Neither are present. d. Take into account the nature of the noise. Design score Explanation The noise is meaningless. The noise is meaningful. e. Avoid noise at low frequencies. Design score Explanation Frequency of the noise is not Frequency of the noise falls within the mentioned range. within the mentioned range. 48

74 CHAPTER 2. LITERATURE STUDY f. Avoid contact between vibrating objects and hands and arms. Design score Explanation Hands and arms do not get in touch with a vibrating object. Hands and arms do get in touch with a vibrating object. g. Avoid the combination of vibrations and uncomfortable body postures (as are possible during a changeover). The combination of vibrations and awkward postures can be very disadvantageous (Newell and Mansfield, 2008). In the diagrams below the difference in reaction time can be read for a number of different body postures. Changes in reaction time of more than 18 percent can be noticed. Figure 17: Mean reaction times and standard error bars for four posture conditions; black solid lines represent males and black dashed lines females (Newell and Mansfield, 2008) Figure 18: Mean reaction times and standard error bars for four posture conditions with and without vibration exposure and one posture condition with no vibration exposure (twisted posture control was maintained for 3 min. while seated under stationary condition (Newell and Mansfield, 2008) 49

75 CHAPTER 2. LITERATURE STUDY Figure 19: Mean reaction times as a function of exposure for the four posture conditions (presented as estimated marginal means) (Newell and Mansfield, 2008) Design score Explanation There are no armrests provided. Armrests are provided. h. Try to avoid that oral communication has a frequency similar to the one of the background noise. Design score Explanation The communication has a similar frequency as that of the background noise. The communication does not share frequencies with the background noise. i. The intensity of the warning signal should be sufficiently high at the place where it has to be noticed. Table 18: Mean reaction times for different signal positions, warning times, signal presentation sequences and sound intensity levels (Lee and Chan, 2008) 50

76 CHAPTER 2. LITERATURE STUDY From Table 18 (Lee and Chan, 2008), one can calculate that a sufficiently high intensity of the warning signal can result in a 3% time gain. Other authors (Van Der Molen and Keuss, 1979) even noted a time gain of 15% when signal intensity increased (Figure 20 and Figure 21). Squares stand for non lead, black circles for auditory lead, and white circles stand for visual lead. The proportion of errors for the intensity values of the imperative signals in the CRT task is displayed as well. Left shaded columns stand for no lead, open columns stand for an auditory lead, and right shaded columns stand for a visual lead. The proportion of premature responses summed over intensities of the imperative signal in the SRT task is shown as well: the left shaded column stands for no lead, the open column stands for auditory lead, and the right shaded column stands for visual lead. Proportion of errors for the intensity values of the imperative signal in the CRT task and the DRT task are shown as well in (Figure 20 and Figure 21). Keuss et al. (1990) found reaction time improvements of up to 10% when intensity was increased (Figure 22 and Figure 23). Figure 20: Mean reaction time as a function of intensity of the imperative signal in the CRT task (a) and the SRT task (b) (Van Der Molen and Keuss, 1979) Figure 21: Mean reaction time as a function of intensity of the imperative signal in the CRT task (a) and the DRT task (b) (Van Der Molen and Keuss, 1979) 51

77 CHAPTER 2. LITERATURE STUDY Figure 22: Mean reaction time as a function of the auditory intensity (accessory), error proportions and an example of the stimuli given Keuss et al. (1990) Figure 23: Mean reaction time to intensity gradient for the accessory, and an example of the stimuli Keuss et al. (1990) Design score Explanation The intensity of the warning signal is less than 10 db(a) higher than that of the background noise. The intensity of the warning signal is more than 10 db(a) higher than that of the background noise. B. Improvements concerning noise, vibrations & auditory perception: The following general suggestions have been found in literature, and have been mentioned earlier as ergonomic improvements. Here, a design/time score is assigned if determined necessary. 52

78 CHAPTER 2. LITERATURE STUDY Table 19: Improvements for noise, vibrations and auditory perception with regard to time and design Improvement Adjustment rating Provide ear plugs or other ear protection +0 Reposition noisy machines +0 Make noisy machines sound proof +0 Mark noise zones with signs +0 Rotate operators between noisy and quiet jobs +0 Make machines sound proof +0 Replace machines by less noisy models +0 Change the process +0 Provide acoustic refuges +0 Conduct audiometric tests +0 Apply rules and procedures to wear ear protection +0 Apply an audiometric testing program +0 Use a larger fan, rotating at lower speeds +0 Use mechanic, hydraulic or electric equivalents instead of +0 pneumatic tools Provide elastic bumpers in the impact zone of impact tools +0 Reduce cavitations in pumps +0 Put heavy machinery on damping blocks Climate A. Rules a. At a certain energy expenditure, temperature must fall within the corresponding range. Figure 24: Workload metabolic heat diagram (Amsey, 1999) 53

79 CHAPTER 2. LITERATURE STUDY Energy expenditure can be expressed in Watt, which is J/s. In other words, energy expenditure is an amount of work per unit of time. So if the allowable energy expenditure for work at a certain temperature should be divided by two, either the amount of work is divided by two, or the time needed to perform the work has to be doubled. So according to this interpretation, this would allow us to see energy expenditure at a certain temperature as a measure of performance or even of time required for the job at the temperature under consideration. The diagram shown in Figure 24 (Amsey, 1999) has already been discussed before, but is repeated here as illustration for the reasoning. Design score Explanation Temperature is more than 2 below the advised limit. Temperature falls between the advised limit and 2 below. Temperature lies in between the advised limit and the upper limit. Temperature has risen beyond the upper limit. b. Check whether the person carrying out the changeover is wearing heat/cold protective clothing. Design score Explanation No Sometimes/insufficient Yes c. Sweat rate should be limited. Design score Explanation Sweat rate is higher than the Sweat rate is below the advised value. advised value. d. Fluid loss should be limited. Design score Explanation Fluid loss is above the Fluid loss is below the threshold value. threshold value. e. Try to avoid that environmental temperature has a negative influence on performance. The effect of environmental temperature on performance is studied in detail (Seppänen et al., 2006). Research proves that temperatures around 22 C are the most beneficial (Figure 25). It shows a variation of 2% in the performance across a range of temperatures. Positive values indicate improved performance and negative values show deteriorated performance with an increase in temperature. 54

80 CHAPTER 2. LITERATURE STUDY Figure 25: Percentage change in performance vs. temperature (Seppänen et al., 2006) Figure 26: Normalized performance vs. temperature (Seppänen et al., 2006) Design score Explanation Temperature is outside the Temperature is inside the advised range. advised range. f. Try to keep temperatures sufficiently high. Design score Explanation Temperature is below the Temperature is above the advised value. advised value. 55

81 CHAPTER 2. LITERATURE STUDY g. Avoid working in the sun. Design score Explanation Yes No h. Check whether there is an appropriate ventilation speed. The presence of an appropriate ventilation can make a difference. In a study about call-center workers (Federspiel et al., 2002), a talk time increase of about 2% was noticed. In other words, the performance of the workers improved (Figure 27). The same findings are supported by other authors (Seppänen and Fisk, 2006). They have noted a change in performance that is very similar (Figure 28 and Figure 29). Figure 27: Change in performance with increasing ventilation rate (Federspiel et al., 2002) Figure 28: Change in performance per 10 liter/s-person increase in ventilation rate versus average ventilation rate in the experiment and regression models (Seppänen and Fisk, 2006) 56

82 CHAPTER 2. LITERATURE STUDY Figure 29: Relative performance in relation to the reference value at 6,5 L/s-person Design score Explanation Taking into account temperature, airspeed does not match the advised values. Taking into account temperature, airspeed does match the advised values. i. Air quality has to be acceptable. Design score Explanation The amount of carbon monoxide is less than 6,5 ppm. The amount of carbon monoxide is higher than 6,5 ppm. j. Exposure time to a hot environment should be limited. Design score Explanation The duration of exposure is longer than the value given by the diagram for the current temperature of the environment. The duration of exposure is shorter than the value given by the diagram for the current temperature of the environment. k. In hot industrial environments fluids should be available at all times and operators should be encouraged to make up for lost fluids, in order to avoid both dehydration as overhydration. Design score Explanation Operators do not have the opportunity to regain fluids, and are not encouraged either to do so. Operators have the opportunity to regain fluids, but are not encouraged to do so. Operators have the opportunity to regain fluids, and are encouraged to do so. 57

83 CHAPTER 2. LITERATURE STUDY l. Provide breaks for operators to recover. Design score Explanation No Yes m. Hot working conditions are dangerous when they are coupled to an increase in body temperature. Design score Explanation Yes No B. Improvements concerning climate The following general suggestions have been found in literature and have already been mentioned earlier as ergonomic improvements. Here a design/time score is assigned if necessary. Table 20: Improvements concerning climate Improvement Adjustment rating Humidity reduction +10 Improvement air currents +5 Removal heavy clothing/introduction loose-fitting overalls +5 Work pace reduction +0 Provide regular breaks +0 Job rotation +0 Outside work on cooler moments of the day +5 Acclimatization period +5 Provision of drinking water or other fluids +0 Provide shade +5 Building cool spots and refuges +5 Mechanize the job Illumination a. Provide a bright work environment. The performance when working in bright light is higher than in dim light. Wright et al. (1997) illustrates this statement with a case study. The bright light placebo data is compared to a dim light placebo situation (In this context placebo means that the test persons did not drink any caffeine liquids; the whole study considers light and caffeine effects on performance). Note that caffeine has a good influence on performance, but is not taken into account in the ergonomic design rules. The results for several tasks, in bright light placebo conditions, are summarized in Table 21. The numbers show the mean percentages of trials for which performance was better under bright light conditions than under dim light. 58

84 CHAPTER 2. LITERATURE STUDY Table 21: Mean percentage of trials for which performance was better under bright light (Wright et al., 1997) Bright light (%) All trials Trials after 2h Dual task throughput (T) Dual task control losses Modified psychomotor vigilance task reaction time Wilinson throughput Switching task mannequin throughput (T) Switching task math throughput Probed force memory recall weak associates (T) Probed force memory recall strong associates Digit recall - throughput Two-column addition throughput Continuous recognition throughput (T) Thurstone (words generated) Reaction time (time uncertainty block) - throughput Mean percentage 61,7% 69,2 % It shows that working under bright light increases the performance. Since performance and time (loss) are strongly related, we can use these percentages to determine the extra time that is needed when working under bad (dim light) conditions. Normally the bad illumination will remain during the full shift (often 8 hours), so we use the trial percentage after 2h. When both conditions were the same, they would both have a percentage of about 50%. We assume that when a setup performance is bad, the operator will have to recheck the settings because a bad setup can result into a big cost. So in bright light 30,8% rechecking is needed, in dim light this percentage is about 69,2%, an increase of 38,4%. When assigning a time percentage, it has been taken into account that rechecking leads to less time than the initial setting. So the time increase percentage when working under bad lighting conditions is 19,2% (½ x 38,4%). Note that the division by 2 is our own interpretation. The task does not have to be redone completely, so 38,4 % is too much. But still, rechecking takes some time so a factor ½ seems appropriate. A second remark needs to be made concerning the interpretation of the word better. A better performance does not necessarily mean that the previous, worse performance was intolerably bad, but here the assumption is made that it is. This assumption is justified because a good setup is needed that avoids initial errors, because they always lead to extra costs. Also immediate feedback has to be provided in order to know if the performance can be labeled as good or bad. Seen through the eyes of an ergonomist, this means implementing the rule a in paragraph Decision making. Score allocation and improvement proposal: Design score Explanation < 500 cd 500 cd 1000 cd > 1000 cd 59

85 CHAPTER 2. LITERATURE STUDY Decision making a. Feedback is necessary in the decision making process. Once again time and ergonomics seem closely related. Further research should acknowledge this. Score allocation and improvement proposal: Ergonomic score Explanation No overview of the settings. Overview of the settings. Overview of the settings and evaluation of the value (e.g. by color: red or green). Overview of the settings, evaluation of the value and readjusting procedure Visual displays a. Use letters/characters/icons on a display that are big enough and readable for every operator. When using letters on a display, one standard typeface is preferred and switching between different typefaces should be avoided. Bernard et al. (2003) show a preference for 12-point text as opposed to 10-point text. But 14 points is even better. On average the 14-point text is read 8% faster than the same passage written in 12-point text. This percentage was deducted from Bernard et al. (2001). No significant interactions except for the size were found. As mentioned, other parameters such as typeface do not have a significant influence on the reading time, but many readers do have a preference. Beard et al. (2001) compared 2 serif fonts to 2 sans serif fonts in 12 and 14 points (Figure 30). All 14-point sans serif fonts were significantly preferred to all serif and sans serif 12-points fonts. The 14-point serif fonts were only preferred to the 12-point serif fonts. Serif fonts Sans serif fonts Times New Roman (12) Arial (12) Georgia (12) Verdana (12) Times New Roman (14) Arial (14) Georgia (14) Verdana (14) Figure 30: Fonts used in the study by Beard et al. (2001) Furthermore Beard et al. (2001) did not experience more mistakes in the different type faces. People tend to read as correct as possible and adjust the reading speed when the typeface makes reading more difficult. 60

86 CHAPTER 2. LITERATURE STUDY When looking at this rule ergonomically, visual acuity is the measure. According to the size of the text (10, 12, 14, ) and the distance, visual acuity can be calculated as well. Next to the actual measure, above findings concerning the type fonts can be taken into account. But since these fonts have a personal preference, they are not included in the assessment model. A visual acuity that is too small, can be solved by an amount of steps towards the text. When VA is between 0.5 and 2, one or two steps are required; when VA is less than 0.5, more steps will be needed. Taken the MTM-1 measures into account, the design scores were assigned. Per pace 15 TMU is allocated (=half a second) which is small with regard to the entire changeover. This reflects in the design scores. Design score Explanation VA < VA 2 VA > 2 b. Place the display at a good distance and under an appropriate angle. Linking the location and position of a display to time is not evident. One way of associating could be to find out the preferred distance and position, and to link every extra step that is needed to achieve this optimal distance to time through MTM-1. Distance The distance problem can be solved by taking a few steps or a bigger display. A bigger display can be placed further away from the operator. If this is impossible, the operator needs to walk towards the display. The time needed for these steps is integrated in the model by MTM-1 measures. Display angle: In the experiment of Shin & Hedge (2010), no significant differences were found concerning the number of typed words in a period of time or the number of errors that were made during a setup. This leads us to conclude that, on short time basis, the display angle, tilt angle and height do not cause time change, only ergonomic discomfort. Therefore they do not represent time in the assessment model. Score allocation and improvement proposal: First design score: the viewing angle for all operators Explanation <0 or > or ± 5 Second design score: the viewing distance Explanation < 20cm or > 75 cm 20cm - 45cm or 55cm 75 cm 50 cm ± 5 cm 61

87 CHAPTER 2. LITERATURE STUDY Improvements: Improved score Explanation Relocate the display Provide a dynamic display support that is adjustable in height and angle. This gets maximum points, since it can provide the perfect display location for every operator. (These are new scores, not to be accumulated with the original score) c. Use the correct colors Color is of importance to the ergonomic point of view. Time will also be influenced by the use of colors, but the effect will be smaller. - Is the contrast between text and background big enough? Design score Explanation No Yes - Are any of the previously mentioned bad color combinations being used? Design score Explanation No Yes - Is color symbolism being respected? Design score Explanation No Yes d. Do not only use color to differentiate information. Similar to the ergonomic point of view, differentiation leads to improvement. The only difference is that in the design/time score, differentiation through color is not that bad. The disadvantages in Table 12 mostly concern ergonomic topics. On a long term base, time will be affected by ergonomics, but a setup should be kept as short as possible and monitoring of visual displays should not take long enough to evoke these time effects. Score allocation and improvement proposal: Design score Explanation Differentiation is needed, but has not been done. Differentiation is needed and is performed by coloring. Differentiation is needed and is performed by figurebackground differentiation, grouping or icons (this may or may not be in combination with coloring). No differentiation is needed in the text. 62

88 CHAPTER 2. LITERATURE STUDY Improved score Explanation Figure-background differentiation, grouping or icons are used with or without color differentiation. Simplification eliminates the need of differentiation. e. Keep the navigation through complex display structures simple and logical. A study of Beard et al. (1997) shows that displaying images on several displays instead of roaming or zooming, can decrease the observation time. Beard and Walker (1990) state that using a map window decreases time as well as roaming, and that a scroll bar is less efficient. Taking this into account, a design/time score is determined. When using the figures provided by Beard et al. (1997), monitoring 2 images (4000 x 5000 pixels) on one display (2000 x 2500 pixels) takes about 57 seconds. This was determined by multiplying the time for one operation (3 seconds) with the number of operations needed, which is 19 (Table 22). If extra zooming and roaming is required, 12 extra manipulations of one second are required. If then the structure still seems illogical, the operator will need even more extra manipulation time. Taken these considerations into account, the scores are composed. The maximum of a score is always 100, so when no navigation is needed the score is set to 100. If extra manipulation is required, the time increases with 21 % so a score reduction of the same percentage is taken into account. When the structure still seems illogical, the score again reduces with 21. So eventually a minimal score of 37 is reached. Table 22: Average observation scales in function of the number of monitors used for eight images Number of monitors Avg. Image display operations (3sec) Avg. zooming operations (1sec) Avg. roaming operations (1sec) Score allocation and improvement proposal: Design score Explanation Navigation is needed but hasn t been implemented by one of the four techniques Navigation has been done by one of the four techniques but is still experienced as illogical or difficult Navigation has been done by truncating, roaming, zooming or map windowing No navigation is needed Score improvement Explanation Simplify the navigation Use 1 technique (more) of the 4 techniques Provide extra training when navigation is still difficult (Improvement is only possible if score was not 100) 63

89 CHAPTER 2. LITERATURE STUDY f. Choose a good representation on the display: digital or analog. When using the wrong representation, extra effort is required from the operator. Ergonomics could therefore be improved, but the influence on time as well. Once again the two are related. Score allocation and improvement proposal: Design score Explanation When using analog view to read a single value instead of digital view or when using digital view to check whether a value is within a range instead of analog view. When adjustment is needed on a single value and analog is used. When - digital view is used to read a value - analog view is used to check whether a value is within a range - digital view is used to adjust a single value g. Keep the handling of panels for displays simple. As mentioned before, the visual world can be divided into a stationary field for which selection requires no large change, an eye field which only requires eye movements, and a head field which involves both head- and eye movements (Clohessy et al., 2001). Since the stationary field requires no extra attention or time, it gets the maximum score. Similar to the ergonomic scores, a score reduction is provided when steering mechanisms are in the eye field or the head and eyemovement field. The score allocation is similar, but the score reductions are a bit smaller since the time changes are in seconds or even milliseconds. Score allocation and improvement proposal: Design score Explanation If all mechanisms that belong together can not be placed in the stationary or eye field. If all mechanisms that belong together are placed in the stationary field and the rest in the head- and eye movement field. If all mechanisms that belong together are placed in the stationary field and the rest in the eye field. Improved score Explanation When mechanisms, that belong together, are placed within the stationary field, but it is not possible to place the other ones in that field, they should be foreseen in the eye field. When the number of mechanisms can be reduced and all can be placed within the stationary field. 64

90 CHAPTER 2. LITERATURE STUDY h. The most appropriate model needs to be implemented in interactive systems. Score allocation and improvement proposal: Ergonomic score Explanation Calculations are necessary and the way of working is inappropriate. Calculations are necessary and the appropriate way of working is applied (RPN or ALG). No calculations are necessary Auditory displays a. Try to use alarm signals or feedback noises to point out mistakes to the operator, or to keep him up to date with the machine s or the process status. Design score Explanation Alarm signals or feedback noises are not being used. Sometimes alarm signals or feedback noises are being used, but improvement is still possible. Alarm signals or feedback noises are being optimally used. b. Try to combine visual information (displays) with auditory information, to discharge the visual channels and to reinforce the information. Design score Explanation Auditory information is never combined with visual information. Auditory information is sometimes combined with visual information. Auditory information is always combined with visual information. c. If time plays a critical role, try to use sounds which are representative for the possible consequences. The two diagrams (Figure 31 and Figure 32) provide evidence that a warning signal, which represents a possible consequence, can be more effective. When an environmental sound (braking sound) is used to warn a driver for a possible collision, an improvement in reaction time of up to 13% is noticed. 65

91 CHAPTER 2. LITERATURE STUDY Figure 31: Response times in seconds between event start and releasing accelerator. Standard deviations are shown (McKeown et al., 2010) Figure 32: Brake response times in seconds. Standard deviations are shown (McKeown et al., 2010) Design score Explanation The signals chosen are not representative. The signals chosen are sometimes representative. The signals chosen are always representative. d. Use auditory signals in control-consoles with both visual and auditory modalities and where reaction time is of the highest order of importance. In the diagram (Figure 33) an improvement in reaction time of about 37% can be detected in a situation where auditory signals are used, compared to the situation without auditory signals. 66

92 CHAPTER 2. LITERATURE STUDY Figure 33: Non-audio vs. audio display response times (McBride & Ntuen, 1997) Design score Explanation Auditory signals are never used in control-consoles where reaction time is very important. Auditory signals are sometimes used in control-consoles where reaction time is very important. Auditory signals are always used in control-consoles where reaction time is very important. e. Incorporate a warning period (2 4 s), which precedes the signal. From Table 18, one can see that a warning period can result in a time gain of about 3%. Design score Explanation A warning period is never provided. A warning period is sometimes provided. A warning period is always provided. f. Take into account the effectiveness of the links between auditory signals and basic quantities when deciding upon the characteristics of the warning signal. In Table 23 and Figure 34 one can read that a good fit between the quantity displayed and the choice of the signal can make a difference (Walker and Kramer, 2005). Taking into account the percentage of correct answers and the mean reaction times for correct answers, some links between auditory signals and quantities can be 14% more effective than others. Table 23: Sets ( ensembles ) of data-to-display mappings (Walker and Kramer, 2005) 67

93 CHAPTER 2. LITERATURE STUDY Figure 34: Accuracy and reaction time results for 4 primary mapping ensembles (Walker and Kramer, 2005) Design score Explanation bad ok good g. Take polarity into account. Design score Explanation There is never taken into account. Sometimes polarity is taken into account. Polarity is always taken into account. h. Make sure the way in which the data is portrayed matches with the auditory signal. Figure 35 shows an improvement of up to 56%, only based on the type of display. Figure 35: Audio display indicator response times (McBride and Ntuen, 1997) Design score Explanation There has never been paid attention to the matching of auditory and visual signals. Sometimes there has been paid attention to the matching of auditory and visual signals. There has always been paid attention to the matching of auditory and visual signals. 68

94 CHAPTER 2. LITERATURE STUDY Safety and hazardous materials a. Use color and symbols as indication for danger and stay consequent. If possible, use indications with international and/or legal value. Reading takes a little more time than interpreting an image (if it is known). Safety indications will normally contain few words, so the difference between the reading and interpreting will be negligible. The time weight of this rule is low and so is the score difference. It is an ergonomic rule that does not affect time that much. Score allocation and improvement proposal: Design score Explanation If there are no danger indications while they are needed. If indications consist of words. If indications consist of an image. If indications consist of an image and colors. Improved score Explanation Remodel the indications, create Remove the dangerous items. images and color them. b. Use as little text as possible for safety indications. As in the ergonomic score part, this rule is implemented in the previous one. c. Use risk assessment tools when designing the setup. Since this rule does not affect the setup time directly (more indirectly), it was not taken into account for time reduction or -increase. Score allocation and improvement proposal: Design score Explanation No Yes 69

95 Chapter 3 Practical assessment framework 3.1 Assessment framework Overview of the model The core of the model is a set of questions. As mentioned in paragraph 2.2, some questions, rules and improvement proposals were already provided, before the start of the construction of the assessment model. The two sources were De Nil (2009) and Van Goubergen and Van Landeghem (2002). Not all of the rules mentioned in these works are included in the final model. Some rules are covered in both works, others are considered less important. Only the rules which are considered necessary, are added to the rules in this thesis and included in the final framework. The complete list of questions, rules and improvement proposals is presented in appendix A, and the reader is referred to this section of the work, if he would like to study the questions in more detail. The improvement proposals are always mentioned below the (set of) rule(s) or question(s) for which they are relevant. They are preceded by a + sign. The origin of each rule, question or improvement proposal is explained through the use of colors: black stands for the work of professors Van Goubergen and Van Landeghem, red stands for the work of De Nil, and green is the result of this thesis. As discussed above, this work is built around a set of questions. In this section more information is provided on how this list of questions has been implemented in a practical tool. On the next page a schematic overview of the model is shown. It might give a better understanding of the structure of the tool. 70

96 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Figure 36: General structure of the model The Excel file (EDAT-MC: Ergonomics & Design Assessment Tool Machine Changeover) that contains the model has several sheets: Machine Sheet: This is the first sheet the user will see as the file opens. This sheet contains a portion of the total set of questions. Questions that have a more general nature and that cover not just one piece involved in the changeover, have been placed under this heading. The questions are divided among the 9 categories proposed by Van Goubergen and Van Landeghem (2002). The user can select whether he wants to answer a question (if it is applicable, he usually will), and he can select his answer from a drop-down menu. Additionally, he can decide to implement one of the improvement proposals that are mentioned together with each (set of) question(s). Choosing an answer results in the calculation of two scores for each question: a design/time score, and an ergonomic score. The details of the score calculation will be discussed in section At the bottom of the sheet, the user has to fill out a factor (between 0 and 1). This factor indicates the importance of the design/time score vs. the ergonomic score in the calculation of a total score. 71

97 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Parts Sheet: This is the second sheet in the tool. It contains the questions that have a more specific nature and that are applicable to only one of the parts used, during changeover. It is developed in a similar way to the Machine Sheet. Financial Sheet: In this sheet, the user can fill out all the costs and expected yields that come with the implemented improvements. They are all split up in standard categories. Extra info: When completing the Machine Sheet, the user is sometimes referred to the Extra info sheet. It contains some background information that might be useful when answering a certain question. Question classification: This sheet contains buttons. They will generate the division of the Machine Sheet questions among different score intervals (0-10, 10-20, ). The first button performs this function for the time scores, the second one handles the ergonomic scores. Results Machine: The Results Machine sheet contains absolute design- and ergonomic scores. It also shows a relative score and improvement potential per category, both for design and ergonomic scores. On top of that, an absolute total score and total relative score is calculated. The presence of an absolute score allows the user to estimate the importance of each category. Results Parts: This sheet is constructed in a similar way as the previous one. This time, however, the absolute design and ergonomic scores, as well as a relative score and improvement potential (design and ergonomic) are calculated per part. Next, a total absolute and relative score is generated, again per part. And the final graphs show a total absolute and relative score for all parts together. Results Machine and Parts: This sheet combines Machine Sheet scores with Parts Sheet scores and compares them to the maximum score that is attainable for the questions. This feature allows the user to objectively compare changeovers on two different designs or machines. Results financial: This last result sheet allows the user to draw conclusions from the financial data that has been entered. 72

98 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Numeric results: This is a calculation sheet which is hidden for the user. It uses all the scores that are generated in the Machine Sheet and Parts Sheet, in order to generate the graphical output that is introduced in the result sheets. Sheet settings: A second, hidden sheet is called Sheet settings. It contains all possible answers for each question. Every possible answer has a design score and an ergonomic score. These answers are linked to the ones in Machine Sheet and Parts Sheet to complete the drop-down menu and to generate the score linked to the answer that is picked Essential calculations Score calculation Scores and weights: The score calculation is performed in Machine Sheet and Parts Sheet. The questions in these sheets are divided among the 9 categories of Van Goubergen and Van Landeghem (2002). So regardless the source of the questions (De Nil, (2009); Van Goubergen and Van Landeghem (2002); own rules), they have been placed under one of the 9 headings. Not all of the categories are equally important. Therefore a weight factor is developed. Each category has its weight, which mirrors the importance in relation to the other categories. This weighing system is used for the design/time scores as well as the ergonomic scores. A second weighing factor is used to express the importance of each question within a category. Once again this system is used for the design/time scores and the ergonomic scores per question. Note that the weights for time are based upon differences upon tasks that take minutes versus tasks that are performed within (milli)seconds. The weights for ergonomics are based upon physical or mental load. Next to the weights, each question has its score according to the answer. To obtain a total score per question, the weights and the score are multiplied. The same way of working has been used for the improvement proposals. They get a score and have the same weights as the corresponding question. The sum of the scores per question and per improvement lead to a total design/time score and a total ergonomic score (Figure 37, Eq. 5 and Eq. 6). It is important to know that the score allocation has been done so that the maximum score (answer score + improvement score) for each question equals 100. This approach makes it very easy to generate a maximum score for all the questions that have been answered. Design/time and ergonomic scores are treated separately for each question so far. The following text explains how the two scores are merged. 73

99 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Figure 37: Calculations of the ergonomic and design scores per category (abbriviations are explained in Table 24) Eq. 5 Score design /time = Answer Score design /time + Improvement Score design /time x weigt 1 design /time x weigt 2 design /time Eq. 6 Score ergonomic = Answer Score ergonomic + Improvement Score ergonomic x weigt 1 ergonomic x weigt 2 ergo nomic Total score: It is interesting to combine both scores into one total score that takes into account all aspects. Through multiplication factor (alpha) the importance of the design/time score is compared to that of the ergonomic score. In the calculations, the design score is multiplied with alpha and the ergonomic score with (1-alpha). The choice of this factor is up to user. This way he can choose the importance of ergonomics for his design. Calculation of the total score is shown in Figure 38 and Eq. 7. Eq. 7 Total score = α x total score design /time + 1 α x total score ergonomic 74

100 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Figure 38: Calculations of the total machine and parts scores (abbreviations are explained in Table 24) Table 24: Explanation of the abbreviations used in Figure 37 and Figure 38 Abbreviation Explanation Q2.1 Question score for question 2.1. One answer for both ergonomic and design part QDS / QES 2.1 Question design/ergonomic score for the answer on question 2.1 DQW / EQW Design/ ergonomic question weight within the category, to differentiate the importance of each question as opposed to the others in this category DGW / EGW Group design / ergonomic weight to differentiate the importance of each category as opposed to another DCS/ECS Design/ ergonomic category score TMS Total machine score TPSx Total parts score for part x Combined compare index Next to the individual assessment, a method of comparison between designs has been provided. Very different machines or designs can be compared, but the feature is mainly developed to compare designs that compete in the same area. One single value is linked to each design: the combined compare index. Three compare indices are provided: one for the machine, one for each replaceable part and a combined compare index. Table 25, Table 26 and Table 27 explain the idea behind each index. The maximum possible scores, indicated by Max, take the questions into account that are applicable for the design. This means that the maximum possible score of questions, that are not applicable, is not added to the total sum of maximum scores. 75

101 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Table 25: Calculations needed for the (Machine and Parts) compare index and max compare index Machine Part A Part B Part C Part D Part E Part F Design Score Score Score Score Score Score Score Max Max Max Max Max Max Max Ergonomics Score Score Score Score Score Score Score Max Max Max Max Max Max Max Total Score Score Score Score Score Score Score Max Max Max Max Max Max Max Compare index Max Compare index Total score Total max x 100 Total score Total max x 100 Total score Total max x 100 Total score Total max x 100 Total score Total max x 100 Total score Total max x 100 Total score Total max x 100 Score and Max are collected from Machine sheet & Parts sheet Design score x α + Ergonomic score x (1- α) Design max x α + Ergonomic max x (1- α) 76

102 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Table 26: Calculations needed for the combined compare index Machine & Parts Design Score <value1> Max <value2> Ergonomic Score <value3> Max <value4> Total Score <value5> Max <value6> Combined compare index <value7> Max combined compare index 100 Table 27: Explanations for the values in Table 26: Calculations needed for the combined compare index <value 1> <value 2> <value 3> <value 4> <value 5> <value 6> The design score for M&P The maximum design score for M&P The ergonomic score for M&P The maximum ergonomic score for M&P The total score The maximum total score <value 7> The value of the compare index (%) = Macine design score + = Max macine design score + = Macine ergonomic score + = Max macine ergonomic score + = Total macine score + = Max total macine score + = <value 5> <value 7> x The compare index is 100 at maximum = fixed value Note that the part design scores, as well as their maximum, are 0 when not used in the Excel. all Parts design scores number of parts to be replaced on te mac ine all Max parts design scores number of parts to be replaced on te mac ine all Parts ergonomic scores number of parts to be replaced on te mac ine all Max parts ergonomic scores number of parts to be replaced on te mac ine all Total parts scores number of parts to be replaced on te mac ine all Max total parts scores number of parts to be replaced on te mac ine 77

103 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Visual Basic code in EDAT-MC It will become clear when using the EDAT-MC Excel file, that programming has been done in Visual basic: message boxes appear when opening the file, error messages pop up when necessary, information buttons are provided, A brief overview is given by Table 28: and in appendix C. Table 28: Overview of the sheets that need VB-code to function Sheet Purpose of the code Code reference Machine sheet Information buttons Appendix C: Figure 1 Excel file: Module 3 Question Classification Design check button Excel file: Module 1 Ergonomic check button Excel file: Module 2 Question Classification Results Parts Results Machine Results Machine & Parts Results Financial Safety check that indicates the questions that have not been filled in and have no indication that they are not applicable for the evaluated machine. Appendix C: Figure 2 Excel file: <name of the sheet> Workbook The message boxes that appear Excel file: This Workbook when opening the file Note that most of the references refer to the Excel file. This code has not been added in the appendix since it is too extended Extra feature: Financial aspect Another aspect of the model is the financial part. Financial data is considered to be an elementary part of an (ergonomic) intervention. Often, it is this financial facet which is determining to management. Based upon the gains the costs, management decides to implement an (ergonomic) improvement. The problem with ergonomic interventions however, is that costs are hard to quantify. An ergonomic intervention influences production in different ways and has an impact on several expenses. A standard accounting model that collects all of these expenses does not really exist. In literature, several attempts have been made to set up an accounting model that incorporates all of these expenses and that comes up with one total, correct cost (Riel and Imbeau, 1996; Hendrick, 2003; Lahiri et al., 2005; Goggins et al., 2008). Some of these attempts cover the expenses and gains more in detail than others, but most of them go towards the same general classification. The approach that is followed in this model is very similar to the one taken by Hendrick (2003). This variant is chosen, because it covers all expenses, but remains at a level which is abstract enough. If the financial part would be more detailed, it would become hard result in a model that is very general and applicable to a wide variety of cases. Costs and yield are divided among the categories that can be found in Table 29. The majority of them can easily be obtained at the accounting department of any firm. The same structure can be found in the Financial Sheet of the Excel tool. 78

104 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK The following rules have to be taken into account when filling out the form: - numbers entered in the cost category are positive if they represent a cost - numbers entered in the cost category are negative if they represent yield - numbers entered in the yield category are positive if they represent yield - numbers entered in the yield category are negative if they represent a cost As mentioned before, the most important expenses are covered in this framework and can be obtained with minimal effort. However, some expenses and gains are more difficult to quantify. What happens with an increase in production due to employee motivation, for instance? It is a realistic idea that employee motivation would increase thanks to the implementation of ergonomic improvements. If employees feel that their well-being is important to management, they experience that they can work in a safer environment, which is beneficial to their attitude. If employees are in a better mood and their good mood results in an increase of production, this can not be seen as a direct result of the implementation of the improvement. It is a side effect, but nearly impossible to quantify. This is a problem we are unable to solve, but is worth noticing. Table 29: Costs and yield categories The financial part stands on its own. It can be applied separately, or the user can decide to fill out the Machine Sheet and Parts Sheet, while ignoring the Financial Sheet. The financial output can be found in the Results financial sheet of the Excel tool. 79

105 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK 3.2 Application of the assessment framework The model is successfully applied to a test case. The design department of Philips Lighting used the model on one of their machines. In order to do so, they read the manual (Appendix B). Appendix B briefly explains how to use EDAT-MC when assessing a machine Philips Test Case The machine that is evaluated fabricates miniature electrodes for gas discharge lamps (the CDM lamp for shops). To give an idea: the electrodes that are produced have a length of at least 2 mm, a bar diameter of at least 150 µm and an electrode head diameter of 350 µm. One machine is equipped with several servo axles to manipulate and to construct the electrodes. It also contains two lasers for thermal treatment, two measuring cameras for production control with display interface, One employee is responsible for the operation and changeover of 6 machines. The dimensions of the machines are: 1330 x 1000 x 2300 (l x b x h) mm. We asked the designer to fill in the Excel model and following results were obtained. Result Machine sheet This graph shows the score of each category in comparison with its maximum. It also shows the differences between categories. For this design, the categories: weight, securing and machine lines are not applicable. Standardization and method on the other hand are essential. And even though the offline activities category does not seem substantial, the improvement potential is high Absolute total scores for Machine Total actual score Total maximum score Figure 39: Philips Absolute design scores for Machine 80

106 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK The previous graph perfectly illustrates the share of each category compared to the others, but the risk exists of neglecting small groups. So a second graph is provided which demonstrates the percentage of potential in each area individually. Now the offline activities will not be overlooked. Quick and easy improvements will probably be possible in simplification, standardization, location and offline activities. So the questions in these areas need to be revised and when looking at the input sheets, it will be clear which improvement proposals can be implemented. In addition to this, the Question Classification sheet provides a quick overview of the questions with a low score (so with a high improvement potential). 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Sore vs. potential Total Total potential Total score Figure 40: Philips Score versus potential of total for Machine This was the evaluation of the total score; similar graphs are available for a time and ergonomic review separately. Result Parts sheet Similar graphs exist for every part that needs to be changed during the setup. For this machine, only one part needs to be changed, but if more parts are involved, extra graphs can be generated per part. In addition to this, combined graphs give an overview of all parts together. In this case the overview graphs are the same since only one part is involved in the changeover. As opposed to the Machine sheet, Figure 41 indicates that securing, location, methods and offline activities are important. These areas, as well as simplification are in need of improvement. These findings are confirmed by the graph in Figure

107 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Absolute total scores for Part A Total actual score Total maximum score Figure 41: Philips Absolute Total scores for Part A 100% 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% Sore vs. potential Total Part A Total potential Total score Figure 42: Philips Score versus potential Total Part A 82

108 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Result Machine & Parts sheet The compare indices for the machine and all the parts are represented in a graph together with their combined index. This facilitates the comparison of several designs in a quick, well-organized way. 100 Compare indices - Machine - Parts - Combined 80 Machine 68,51 Part A 66,53 Machine & Parts 68, Part B 0,00 Part C 0,00 Part D 0,00 Part E 0,00 Part F 0,00 Figure 43: Philips Compare indices Question Classification sheet Previous results show the categories which have a lot of improvement potential. This sheet offers a more detailed overview on the scores, linked to each question. Questions with low scores will definitely need revision. This sheets allows the user to track the questions that have not been answered or that have an incorrect input (incorrect, meaning that improvements are ticked off which can not be combined with the current situation). Figure 44: Philips Question Classification sheet 83

109 CHAPTER 3. PRACTICAL ASSESSMENT FRAMEWORK Results Financial sheet For this case, the financial sheet has not been filled in. An example of this sheet can be found in the manual (Appendix B). 84

110 Chapter 4 Conclusion and future research Conclusion In this work a quantitative assessment framework was built to evaluate the design of a machine that requires a fast changeover. The emphasis was put on the incorporation of ergonomics into the model. The research has resulted into an Excel file, which contains a questionnaire. This has to be answered by the designer, preferably in the design phase in order to keep the improvement cost low. The output of the model is a score, which allows the designer to compare several designs for the same machine and to pick the best one, or to compare completely different designs. An output using several graphs provides a quick and clear overview of the design. It shows the design s shortcomings and the areas that offer the biggest improvement potential. The model has proven to be successful in a test case. It has a clear interface towards the designer, but still a basic background is advised. Therefore it is mandatory that the user reads the manual carefully and when scientific explanations are required, this script should be read. Further research and developments The assessment tool has shown to be effective but still some improvements are possible. Both from the scientific point of view and on the use of the Excel file, a few suggestions are made. With regard to the research in literature, two shortages are noticed. Firstly the basis for time and the connection between ergonomics and time could be a topic for extra investigation. Ergonomics have thoroughly been investigated, but for the time aspect, not much literature is provided. De Nil (2009) provided a good basis but there is a lack of scientific proof. Secondly the model does not cover 2 aspects, although they have been discussed by Van Goubergen and Van Landeghem (2002): communication aids and automation. On these two aspects, no significant literature is found so this might also be a topic that encourages further research. 85

111 CHAPTER 4. CONCLUSION AND FUTURE RESEARCH Concerning the Excel tool, users have experienced the file as clear and user friendly. But still, three suggestions can be made to optimize the file. Firstly, another software package could be used to make the model even more fool proof and user friendly. Methods like NIOSH and RULA have been implemented online in an attractive way and this makes potential users curious to discover the tool. Secondly the tool could be provided in Dutch. This remark was made by one of the users in the test case. Finally a remark can be made concerning the ratio that combines ergonomic -and time scores. Now, an alpha of 0.5 has been chosen in order to make both scores equally important and it is up to the user to set his priorities. Further application of the tool could lead to a fixed (average) value for this parameter. 86

112 Appendix A Set of questions and improvements Machine sheet questions: 1. Weight 2. Simplification 2.1. Do operators experience the navigation through complex display structures as simple and logical? Are techniques used such as truncating, roaming, zooming or map windowing? + Simplify the navigation + Use 1 technique (more) of the 4 techniques + Provide extra training when navigation is still difficult 2.2. The most appropriate model needs to be implemented in interactive (calculation) systems + Adjust the way of delivering input to the system (RPN <-- --> ALG), provide training + Elimination of calculations that need to be performed by the operator 2.3. Are alarm signals or feedback noises being used to point out mistakes to the operator, or to keep him up to date with the machine s or the process status? 2.4. How many pipe connections can be eliminated or replaced by quick release couplings? 2.5. Can control procedures such as timing diagrams be simplified? 3. Standardization 3.1. Use the right colors on the displays: 1. Is the contrast between text and background big enough? + Follow the color guide of selection 2. Are any of the previous mentioned, bad color combinations being used? + Avoid combinations: Red & green / Blue & yellow / Green & blue / Red & blue 3. Is color symbolism being respected? + Respect: Green = safe, normal modus / Orange = be careful / Red = unsafe or hot / blue = cold 3.2. Is there a need of differentiating specific information in the text? Is this done by coloring or is coloring used in combination with other methods? + Figure-background differentiation, grouping or icons are used with our without color differentiation + Simplification eliminates the need of differentiation 87

113 APPENDIX A. SET OF QUESTIONS AND IMPROVEMENTS 3.3. Is the implemented digital or analog representation appropriate for the information that is shown? + Use digital for reading or adjusting exact values, analog for ranges 3.4. Use letters/characters/icons, on a display, that are big enough and readable for every operator + Increase the height of the figure/text + Bring the figure/text closer to the operator 3.5. Did the designer provide enough feedback after setting or adjusting values? 3.6. Are color and symbols being used to indicate danger? Is text eliminated from safety indications? + Remodel the indications, create images and color them + Remove the dangerous items 3.7. Is visual information (displays) combined with auditory information, to discharge the visual channels and to reinforce the information? 3.8. Are the sounds which are used, representative for the possible consequences if time plays a critical role? 3.9. Are auditory signals used in control-consoles with both visual and auditory modalities and where reaction time is of the highest order of importance? Is there a warning period (2 4 s), which precedes the signal? Has the effectivity of links between auditory signals and basic quantities been taken into account, when deciding upon the characteristics of the warning signal? Has polarity been taken into account? Is there is a relation between pitch and the represented quantity? Has the designer paid attention to the match between the way the data is portrayed and the auditory signal? Can the same size shut height for presses be used? Can the same size securing bolts be used? Can the same type of electrical motors be used? 4. Securing 5. Location and adjustment 5.1. How many parameters need to be set? + Try to provide only 1 parameter per setting + Try to separate parameters which are linked 5.2. Is there a logical and clear certainty where the problem is situated when the setting hasn t been done correctly? If yes: Is it clear how much adjustment is necessary? + Provide a process chart to discover which mistake is linked to which parameter, and how much it has to be adjusted 5.3. Can the use of spacers and shims be avoided? 88

114 APPENDIX A. SET OF QUESTIONS AND IMPROVEMENTS 6. Handling movements 6.1. Are steering mechanisms, that belong together, placed in the stationary field? + Mechanisms that belong together in stationary field and other ones at least in the eye field + Number of mechanisms can be reduced and all placed in stationary field 6.2. Can the need to handle awkward items be eliminated? 6.3. Can power aids be provided? 6.4. Can remote actuation be provided? 6.5. Can tools etc. easily be delivered to the machine? 6.6. Is good access provided? 7. Off-line activities 7.1. Is it necessary to load data for this setup? If yes: is this being done during setup? + Execute the data loading procedure off-line, before the setup has to be done 7.2. Did the designer consider if certain activities in the setup can be performed offline? If Yes: What percentage of these activities has already been made offline? + Try to change certain on-line activities into off-line activities + Standardize changeover procedures for a quicker on-line changeover 8. Machine lines 8.1. Can the drive of every station be decoupled to enable setup activities on a single station while the last/first products run through the other workstations? 9. Method and organization 9.1. What is the entire perimeter of the machine area (in m)? How far (in meters) does the operator have to walk for the entire setup? (the measure is: a=circumference/distance) (circumference = perimeter) + Use a routing diagram to discover waste + Place changeover elements closely together + Place the changeover elements at the same side of the machine + Try to incorporate a U-shape into the machine structure 9.2. Does every operator have his own work instructions for the setup? + Use person/machine activity diagrams to balance workloads among operators 9.3. Are finished parts being brought to the warehouse during setup? + Provide an area where the finished parts can be put during the changeover 9.4. Are the (spare) parts ready at the machine before setup? + Use a checklist + Use a checktable + Put the parts close to where they are needed + Turn pieces in the right direction + Hang pieces above the machine 9.5. Are changed spare parts being brought to the warehouse during setup? + Provide an area where the changed spare parts can be put during the changeover 89

115 APPENDIX A. SET OF QUESTIONS AND IMPROVEMENTS 9.6. When the parts need to be treated (warming up, cleaning, ), is this being done during setup? + Try to do these treatments off-line, before the setup 9.7. Is the setup possible in a bright environment with enough light? + Renew the lighting bulbs (increase # candelas) + New light infrastructure: lamps that are more natural and resemble natural daylight + Reconstruction of work environment: more daylight admission is possible 9.8. Are displays placed at a good distance and can operators read the screens under an appropriate angle? + Relocate the display + Provide a dynamic display support (adjustable in height and angle) => perfect display location for everyone 9.9. Have limits for short term memory been taken into account? + Making remembering aids available + Reducing the number of items to remember <5 + Making the need for short term remembering unnecessary Have limits for long term memory been taken into account? Is multitasking required? + Add an extra operator + Eliminate the need for multitasking Are risk assessment tools being used? Can the order in which the activities are performed be optimized, to minimize movements and walking distance? Noise, vibration & auditory perception + Provide ear plugs or other ear protection + Reposition noisy machines + Make noisy machines sound proof + Mark noise zones with signs + Rotate operators between noisy and quiet jobs + Make machines sound proof + Replace machines by less noisy models + Change the process + Provide acoustic refuges + Conduct audiometric tests + Apply rules and procedures to wear ear protection + Apply an audiometric testing program + Use a larger fan, rotating at lower speeds + Use mechanic, hydraulic or electric equivalents instead of pneumatic tools + Provide elastic bumpers in the impact zone of impact tools + Reduce cavitations in pumps+ Put heavy machinery on damping blocks Is the volume to high (>81 db(a))? Are the vibrations too powerful? 90

116 APPENDIX A. SET OF QUESTIONS AND IMPROVEMENTS Are vibrations combined with a noisy environment? Is the nature of the noise taken into account? Does the noise have low ( Hz) frequencies? Do arms and hands get in touch with a vibrating object? Are armrests provided when vibrations are combined with uncomfortable body postures? Does the oral communication have a frequency similar to the one of the background noise? Is the intensity of the warning signal sufficiently high (at least 10 db(a) higher) at the place where it needs to be noticed? Climate + Humidity reduction + Improvement air currents + Removal heavy clothing/introduction loose-fitting overalls + Work pace reduction + Provide regular breaks + Job rotation + Outside work on cooler moments of the day + Acclimatization period + Provision of drinking water or other fluids + Provide shade + Building cool spots and refuges + Mechanize the job Does temperature fall within the range corresponding to a certain energy expenditure? Is sweat rate higher or lower than the prescribed value? Is fluid loss higher or lower than the advised limit? Does environmental temperature have a negative influence on performance? Is temperature sufficiently high? Does the operator have to work in the sun? Is there sufficient ventilation, taking into account work pace and temperature? Is air quality acceptable? Is exposure time to a hot environment limited? Are fluids available, and are operators encouraged to consume them frequently? Can operators take breaks to recover (possibly after the setup)? Do the hot working conditions lead to an increase in body temperature? Is the person, carrying out the changeover, wearing heat/cold protective clothing? 91

117 APPENDIX A. SET OF QUESTIONS AND IMPROVEMENTS Parts sheet questions: 1. Weight 1.1. How much does the piece weigh (kg)? + Use less material + Use lighter material + Provide a lifting device 2. Simplification 2.1. How many pipe connections can be eliminated or replaced by quick release couplings? 2.2. Can the number of hand/powertools required, be reduced? 3. Standardization 3.1. Can the same size securing bolts be used? 4. Securing 4.1. How many fasteners are being used? + Use the minimum number which can resist the tension, and which can ensure a safe working environment 4.2. Is it a bolt nut connection? What is the expected time per fastener (in sec)? + Use quick fixtures 4.3. Is a tool required? If yes: Does the tool have a fixed location? + Reduce the number of tools required by standardizing e.g. nut- and boltsizes + Try to eliminate the use of tools by implementing quick fixtures + Provide a tool belt, so tools can be easily located 4.4. Does the fastener have a fixed location? + Provide a fixed location for each fastener which is removed from the machine/part + Leave the fastener on the part (as with a lot of quick fixtures) 4.5. For firm fixtures: can they be replaced by hydraulic, pneumatic or electromagnetic fixtures? 5. Location and adjustment 5.1. How many parameters need to be set? + Try to provide only 1 parameter per setting + Try to separate parameters which are linked 5.2. Is there a logical and clear certainty where the problem is situated when the setting hasn t been done correctly? If yes: Is it clear how much adjustment is necessary? + Provide a process chart to discover which mistake is linked to which parameter, and how much it has to be adjusted 5.3. Can the use of spacers and shims be avoided? 92

118 APPENDIX A. SET OF QUESTIONS AND IMPROVEMENTS 6. Handling movements 6.1. Can a piece become hot in normal usage? + Provide insulation around the piece, or provide insulated zones + Provide a fixed location for the operator s gloves 6.2. How far is the piece situated at the beginning of the setup? + Set the piece closer + Turn pieces in the right direction + Hang pieces above the machine 6.3. Is cleaning necessary before mounting the piece? + Provide a replica for the part, so it can be cleaned off-line + Provide good access to the area which has to be cleaned + Make sure that the surfaces are smooth and easy to clean 6.4. Can the need to handle awkward items be eliminated? 6.5. Can power aids be provided? 6.6. Can remote actuation be provided? 7. Off-line activities 7.1. Is it part of an (eventually offline composed) (sub)assembly? If No: Is it possible to combine the piece with other pieces to one assembly? If yes: Is the assembly being done during setup? + Combine several parts into 1 module + Try to prepare this module off-line 7.2. Is the setting being done during setup? What is the estimated time of the setting (in sec)? + Try to design larger assemblies, so the setting can be done off-line + Provide dead stop positioning + Provide positioning using centering pins and holes + Use discrete positioning of parts instead of continuous + Provide measuring devices, preferably using digital displays + Use stepping motors for accurate setting + Every knob/wheel needs to have a measuring scale 8. Machine lines 9. Method and organization 9.1. Is the piece, that is taken off the machine, actually being replaced or is it put back onto the machine? + Implement a new design + Make sure mounting the piece goes very smoothly 9.2. On how many different ways is positioning possible (wrong or right)? + Make sure the piece can only be mounted in 1 possible way (Poka Yoke) 9.3. How many different sizes/varieties are needed of this piece? If there are 2, is there a possibility to fix one of the two pieces permanently on the machine? + Build one of the two variations into the machine 93

119 Appendix B Manual EDAT-MC Manual for the Ergonomic Design Assessment Tool for Machine Changeover Hanne Deschildre Benedict Saelen Accompanies the master thesis: Ergonomic aspects in the design of machines with short changeovers Ghent University (Belgium) Faculty of Engineering Department of Industrial management Year:

120 APPENDIX B. MANUAL EDAT-MC Content Chapter 1: Purpose of the tool. 97 Chapter 2: The Excel file Chapter 3: Using EDAT-MC..100 STEP 1: Opening the file STEP 2: Filling in the sheets STEP 3: Results

121 APPENDIX B. MANUAL EDAT-MC List of Figures Figure 1: Idea behind the input, score allocation and output of EDAT-MC Figure 2: Hidden sheets in the tool Figure 3: Message box structure that pops up when opening the file Figure 4: Print screen of the Machine sheet Figure 5: Drop down menu Figure 6: Exclamation marks in the score cells Figure 7: Answer cell of sub question is colored red Figure 8: Question with hidden improvement proposals Figure 9: Question with visible improvement proposals Figure 10: Show or hide all the improvement proposals Figure 11: The warning box that is shown at each result sheet Figure 12: Action buttons in the Question classification sheet Figure 13: An overview of the graphs in the Results Machine sheet Figure 14: An overview of some of the graphs in the Results Parts sheet Figure 15: The graph in the Results Machine & Parts sheet Figure 16: An overview of the graphs in the Results financial sheets List of Tables Table 1: Overview of the sheets

122 APPENDIX B. MANUAL EDAT-MC Chapter 1: Purpose of the tool EDAT-MC stands for Ergonomic Design Assessment Tool for Machine Changeover and is developed to assess machines for fast changeover. The tool was initially made to assess machines in the design phase, but is extended in a way that permits the assessment of existing machines as well. The EDAT-MC allows a designer to get a complete assessment of the design while having to complete only a simple questionnaire; simple input resulting in a valuable evaluation. The results are based on an ergonomic score as well as a design/time score. To optimize the tool, a cost analysis is provided as well. Take into account that when costs are included, more specific input is required from the designer. Furthermore a designer should know that a scientific background concerning ergonomics and human factors is not required. The tool has a well thought and scientifically based structure, but gets its strength from the simplicity towards the user. The subdivision of questions and weights which are allocated to each question are interesting for designers with ergonomic and human factors background, but can easily be ignored by others since completing the assessment does not depend upon these tool properties. After assessing, the designer can compare the scores from several machines and choose the best design. The scores are composed in a way that allows fairly big differences between the comparing designs. The machine in itself can be different as well as the parts and number of parts that have to be replaced during the changeover. An overview of the idea behind the assessment model is given by Figure 1. 97

123 APPENDIX B. MANUAL EDAT-MC Figure 1: Idea behind the input, score allocation and output of EDAT-MC 98

124 APPENDIX B. MANUAL EDAT-MC Chapter 2: The Excel file The Excel file contains 11 sheets (Table 1) of which 2 are hidden. These sheets are not addressed by the designer when performing the assessment. Still, watching the sheets is possible by making the following selection: Format > Sheet > Unhide Select the sheet that needs to be visible (Figure 2). Table 1: Overview of the sheets Sheet name Machine sheet Parts sheet Financial sheet Extra info Question classification Results Machine Results Parts Results Machine and Parts Results Financial Numeric results Sheet settings Function Machine questions to be filled in and their specific score as well as the total machine (without parts) score Parts questions to be filled in and their specific score as well as the total Parts score per part Cost and profit sheet, specific costs and profits as well as total cost/profit Additional information linked to the machine sheet Verification sheet Graphic results of the machine, replaceable parts not included Graphic results of each replaced part on the machine Graphic results of the entire machine Graphic results of the costs versus the profit of the improvements Hidden sheet, needed for background calculations Hidden sheet, needed for background calculations Figure 2: Hidden sheets in the tool 99

125 APPENDIX B. MANUAL EDAT-MC Chapter 3: Using EDAT-MC The Excel file that is required to perform the assessment is named EDAT-MC.xlsx. This chapter contains a step-by-step approach towards a complete assessment. STEP 1: Opening the file When opening the file the user can choose to perform an assessment on an existing machine, on a machine still in design phase or just to cancel and continue with the file. The message box structure is shown in Figure 3. At any point, the user can abort his choice and continue with the file as it is. The safest answer is always preselected so when being careless and pressing enter, no harm is done. The machine is evaluated on the topics that are important for a machine in design phase. Irrelevant questions are eliminated. The machine is evaluated on the topics that are important for an existing machine. Nothing happens Figure 3: Message box structure that pops up when opening the file 100

126 APPENDIX B. MANUAL EDAT-MC STEP 2: Filling in the sheets Three sheets need to be filed in. Machine- and Parts sheet contain a questionnaire, Financial sheet requires the input of the cost per aspect. 1. Machine sheet Figure 4: Print screen of the Machine sheet Column A: Classification of the rules. Column B: Tick off the checkbox if the rule is not applicable in this design. If this is forgotten and the question has no answer, the rule will not be taken into account in the results, but an annoying message box will appear in every result sheet. This message box contains a warning and indicates where the problem is situated. Column C: When extra information is provided, a link towards it will be shown in this column. It refers to the extra info sheet and immediately shows the information that is related to this question in the upper left corner. Column D: The question number: x.y where x stands for the category number and y gives the question number within a category. Column E: The questions. Column F: The answers should be placed in the light grey cells. Most of the cells have a dropdown menu. Column I: The design/time score that results from the given answer. At the bottom the total design/time score is given, as well as a factor to point out the importance of the design score as opposed to the ergonomic score Column J: The ergonomic score that results from the given answer. At the bottom the total ergonomic score is given. Note that the ergonomic- and design scores can become 100 at maximum. Through weights, mentioned in hidden columns, the rules are weighed against each other. 101

127 APPENDIX B. MANUAL EDAT-MC Remarks: - The dropdown menu appears when the cell is selected (Figure 5). Figure 5: Drop down menu - When exclamation marks appear in the score cells, an extra answer is required in the neighboring light grey cell. Figure 6: Exclamation marks in the score cells - When answering cells are red, it means that the previous light grey cell needs an appropriate answer to allow the use of this part of the question. Figure 7: Answer cell of sub question is colored red - When the cell below the question contains Improve and adjust answer, no improvement proposals are provided. The only improvement possible is adjusting the situation so that another answer from the dropdown menu can be chosen. When this cell contains improvements ^, improvement proposals are provided (Figure 8). Figure 8: Question with hidden improvement proposals In order to see the proposals, select the plus sign in the margin. Figure 9: Question with visible improvement proposals This menu shows all the possible improvements. When implementing an improvement, the corresponding dark grey cell should contain Improvement implemented from the drop down menu. Note that some improvements do not have a corresponding dark grey cell and adjustments can be made in the original light grey answering cell when the improvement is implemented. 102

128 APPENDIX B. MANUAL EDAT-MC - If all the improvement proposals need to be shown, select the button with caption 2 in the upper right part of the margin. If they need to be hidden, press button 1 (Figure 10). Figure 10: Show or hide all the improvement proposals - When an improvement is implemented and therefore the following improvement becomes impossible or unnecessary, this last one will get a red background. The same happens when the answer to a question indicates that this topic is already optimal; the background of possible improvements will become red. - When one of the answers to a question in the dropdown menu is Improvement implemented, this needs to be chosen when an improvement is actually being implemented. If it is not selected, the dark grey improvement cells will have a red background. So in this case improvements are possible, but the designer needs to indicate this in his answer. This way of working differs from the method used in other questions, so be aware. 2. Parts sheet The Parts sheet has the same functionalities as the Machine sheet. But instead of one answer per question, this sheet requires an answer per question, per part. Up to 6 replaceable parts are possible. When less than 6 replaceable parts are present, no answers need to be filled in for the unused cells. 3. Financial sheet When costs and profits are important, this sheet comes in handy. The designer should have a rough estimate of the costs and profits that accompany the improvements. The yellow cells have to be filled in and eventually a cost (red cell), yield (green cell) and total net result is provided. 103

129 APPENDIX B. MANUAL EDAT-MC STEP 3: Results The evaluation of the model is presented through 5 sheets. When selecting one of them, an automatic check is done to see whether each question is taken into account. The check is done by looking if a question has an answer; if not, the checkbox corresponding to this question should be ticked off. If neither the checkbox is ticked nor the answer is filled in, the error will arise when looking at the results. The message box, indicating the error, also mentions in which question the problem is situated (Figure 11). Apart from this, the result sheets are rather specific and will be discussed separately. Figure 11: The warning box that is shown at each result sheet. This one indicates that there is a problem with Machine question 9.35 and Parts question Question classification The Question classification sheet gives an overview of the score distribution. It shows which questions perform well and which ones need improvement. An extra asset of this sheet is the quick overview it gives on wrong inputs. When a score, associated with a question, becomes higher than 100, something went wrong. The Machine and Parts sheets are fool proof since a cell turns red when it should not be addressed, but ignoring this could cause problems. Also the rules that are not applicable have their own column. This classification was made for all the design/time scores as well as the ergonomic scores in the Machine sheet. Two separate running buttons (Figure 12) are provided and Visual Basic code behind the tool takes care of it all. Figure 12: Action buttons in the Question classification sheet 104

130 APPENDIX B. MANUAL EDAT-MC 2. Results Machine This sheet is divided into 2 parts (Figure 13). The left side contains graphs for design/time- and ergonomic scores and the right side combines these scores into a total graphic representation. On the left side of the sheet four graphs present the results of the questions in the Machine sheet for the ergonomic- and design/time scores: - Absolute design score: the design/time scores per group are shown next to their possible maximum. Note that if the checkbox next to the rule is ticked, the rule is not taken into account when calculating the maximum possible score. A rule which is not applicable does not influence the score and its possible maximum. When the score does not approach the possible maximum, improvements can be implemented and should subsequently be indicated in the Machine sheet. - Absolute ergonomic score: The same graph is presented for the ergonomic scores. - Score versus potential (design): Each category is presented in percentages. This way the potential improvement is indicated as opposed to the total score (in percentage). The categories can be compared, but that is not a recommendation since not every category is equally important. - Score versus potential (ergonomic): Once again a similar presentation is made for the ergonomics part. On the right side of the sheet two graphs are provided to evaluate the combination of the two scores (ergonomic and design/time). Both scores are combined into a total score through a factor (mentioned in Machine sheet). Once again an absolute score-graph is presented as well as a graph that shows the score versus the potential. Figure 13: An overview of the graphs in the Results Machine sheet 105

131 APPENDIX B. MANUAL EDAT-MC 3. Results Parts The same four graphs are presented for each part that is replaceable on the machine on the left side of this sheet. In the middle, once again, both scores are combined and 2 graphs are presented. A third graph is provided to combine the results of all replaceable parts (Figure 14). Figure 14: An overview of some of the graphs in the Results Parts sheet 4. Results Machine & Parts All previous results are combined to obtain one single value linked to the design. This compare index can be used to compare several machines and select the most appropriate one. The graph shows the machine index, the several part indices and the combined compare index. Figure 15: The graph in the Results Machine & Parts sheet 106

132 APPENDIX B. MANUAL EDAT-MC 5. Results Financial Three graphs evaluate the financial situation of the changeover improvements. The costs are displayed and it becomes clear which subdivision has the largest cost. For the yield a similar graph is provided and in a third graph both values are compared. Figure 16: An overview of the graphs in the Results financial sheet 107