Software engineering used in simulation of Flexible Manufacturing Systems FOTA ADRIANA, BARABAS SORIN Faculty of Technological Engineering and Industrial Management Transilvania University of Brasov 29, Bd. Eroilor St, Brasov ROMANIA fota.a@unitbv.ro http://www.unitbv.ro Abstract: - With increasing sophistication of computer hardware and software, one area which has grown rapidly is computer simulation of manufacturing processes and systems. Process simulation takes two basic forms. The first is a model of a specific operation intended to determine the viability of process or to optimize or improve its performance. The second one models multiple processes and their interactions, and helps process planners and plant designers in the layout of machinery and facilities. The researches performed within the scientific paper proposed will be directed to the study of flexible manufacturing systems (FMS), in order to know their behaviour and their performances very well, and if it is possible, before their physical manufacturing, and in order to establish on scientific bases dimensioning models, representation and simulation of FMS. Key-Words: - modeling, simulation, software engineering, flexible manufacturing systems 1 Introduction Simulation of an entire manufacturing system involving multiple processes and equipment helps plant engineers in the organization machinery and identification of critical machinery elements. In addition, such models can assist manufacturing engineers with scheduling and routing. Commercially available software packages are often used for such simulations, but dedicated software programs written for a particular company are not unusual, [4]. Individual processes have been modelled using various mathematical schemes. Finite element analysis has been increasingly applied as software packages that are commercially available and inexpensive. Typical problems addressed are process viability (such a formability of sheet metal in a certain die), as well as process optimization (such as material flow in forging in a given die to identify potential defects, or mould design in casting to eliminate hot spots, promote uniform cooling, and minimize defects). Simulation is a powerful tool to analyse manufacturing systems for purposes of design and on-going operation. In recent years, simulation modelling and analysis have been enhanced significantly by increasingly powerful computational platforms. This has enabled development of high-fidelity models of manufacturing systems, at least from a computational perspective. Such high fidelity modelling has important benefits in prototyping system performance; however, it must be supported by an underlying modelling discipline, or structured approach to modelling factory operations, [2, 7]. Using simulation models on the field of big systems is presently very widespread. With the view to the projection flexible manufacturing systems (FMS) is used a modern procedure of modelling and simulation. In present, the simulation of the flexible manufacturing systems is the more dynamical and controversy area to the research to the domain. The absence to the mathematical models recognized is the projection of flexible manufacturing systems (FMS) makes difficult the realization of these systems, having consequences to their performances. In following paper [1] were anterior published, elaborated mathematical models used in the dimensioning and the configuration of FMS. Trough original approaches were realized the algorithm and simulation program using the Delphi software product. The inner structure of flexible manufacturing systems in round shafts processing was detailed, so that operating systems of all its component subsystems, may be calculated and computerized step by step, respecting precision and taking into account ISBN: 978-1-61804-126-5 304
interactions with the external medium. The program accomplished as per such a computer simulation method of the system s operating process represents the simulation program. As dynamic systems, input function of the state of flexible systems for processing round shafts, may be described as algorithms or complex proceedings, which, on their turn, describe as well as possible, the real function. By means of the Delphi 7 software product, on grounds of sizing and shaping models presented within the paper [3], a simulation program of flexible manufacturing systems in round shafts processing was set up. Excepting the codified transcription of the simulation model, this simulation language allows to achieve also graphical animation, by visualization on display screens the simulating behaviour. The programming language used hereby allows dynamic simulation of discrete technical systems, were also flexible manufacturing systems in round shafts processing are enclosed. There are used terms as: entity part of system setting up a sub-system; attributes features of entities; activities dynamic processes conducing to attribute value changes; event produces value change of an attribute. Programming language s structure used in simulation is a dynamic one it refers to introducing methods of simulated time in the model function. 2 Computer simulations of manufacturing processes and systems 2.1 Simulation software program Simulation allows definition of some aspects of manufacturing management, definition of algorithms for transporting ways and detection of tight points delaying manufacturing flow, study of breakdown influence over the process, [4]. By evaluating the flow of pieces on processing machines and stations and examining conflicts with regard to requirement of some limited resources, the system layout, selecting manner of equipment, as well as operating proceedings can be evaluated. The program drawn up allows planning / programming and managing in real time the whole processing system. Simulation was realized in dynamic working conditions. The state evolution in the time of the flexible manufacturing system for processing round shafts, as a dynamic system is described by algorithms or complex proceedings, expressing as well as possible, the operation in real medium and time. 2.2.1 Layout of simulation system A simulation of simultaneous processing of the above three items is made fact met usually in real mediums. Within the system, the three processed pieces have each of them an own technological route, with phases of different duration. In Figure 1, a computer display image catch during the simulation of processing the three items R1, R2 and R3 is shown. Specifying different interactions between processes makes the description of the whole system s function. For flexible manufacturing systems, pieces are generally interacting with the other processes, what explains their moving within the system. Simulation is made describing the movement of pieces, passing through different processes, according to the tool-machines, transporting and handling means, i.e. The Delphi programming medium is able to automatically supply entities in the system, according to a predefined delivery sequence [3]. This is made by drawing up lists of stations of destination and an optional assignment of some attributes or variables for each former presented station. Also processing times for each working station were assigned to. Constraints as below were imposed to the simulation program: choosing a minimal critical path-type itinerary; selecting free machines of the station; using the most expensive machines of the station and providing high loading degrees; using avoidance industrial logistic subsystems of unusable stations; using in full all handling stations; achieving a minimal path algorithm for robots displacement within the system. Fig. 1 Computer display images of layout of simulation systems ISBN: 978-1-61804-126-5 305
2.1.2 Used data structures Some specialists consider Delphi as a version of RAD (Rapid Application Development) of Borland Pascal programming medium. One of the first things to be understand when working in a RAD medium refers to the fact that a RAD medium is a drawing up technology of solutions for several informatical questions based on a series of concepts, components and protocols concerning their use. Initial data needed in achieving a simulation model of FMS are: number and types of the system s working stations and of machine tools; number and types of conveyors and conveying speed; type of the used logistic sub-system industrial robots and their number; number of the systems stockers and their accumulating capacity; type of pieces, their technological route; duration of the processing cycle for each piece-type of each flexible manufacturing system model; number of items being simultaneously processed; volume of series of manufactured products, [1]. Subsequently the main used data structures shall be presented in view of achieving simulation, Figure 2. model categories by counting key model types of each category and, second, specifies the way of achieving programmed objects, starting from the real ones. The object oriented functional networks methodology was developed in view of incorporating all aspects concerning a system: structure, functionality and behaviour. 2.2 The simulation program for manufacturing task in FMS There will be created a data base for the synthesis of the geometric representation from the manufacturing task references, and by the applicative research there will be performed the simulation on the computer for real manufacturing items. The simulating program realized has as objective the application of flexible manufacturing systems for processing round shafts. The computer program has been realised in the Visual C ++ programming language. A database DB has been conceived, containing the sizes and features of all the elements belonging to the previously fixed round shafts families. The main stages of the program usage are as follows. Through the decision block, called <option> the user may automatically select, at any time, from the database, from the six generalized items, the generalized shafts family he or she wants to use. The two windows are visualised on the screen (Figure 3). Fig. 2 Sequence from Delphi simulation software program for FMS Essential in simulation modelling, the logic element is set up by data structures convenient for the event s processing. The object oriented modelling outlook [6] first introduces fundamental Fig.3 Application window - Initialization of the client shaft ISBN: 978-1-61804-126-5 306
The logic chart of the program is presented in Figure 4. Fig.4 The logical chart of simulation ISBN: 978-1-61804-126-5 307
3 Model of real-time management systems Real-time management systems primarily involves the distribution to driving equipment of programs necessary for accomplishment of activities assigned by ordering, the execution of these programs, realtime diagnostic equipment (locally) and monitoring processes. The programs are usually automatically generated for parts designing and they are stored in specialized libraries. For FMS is used hierarchical structure. At the lowest level is done real-time management of equipment and transport system, as the hierarchical level rise, the timeframe allocated rise too, and frequency of control action decreases. At the lower level is found not only computers, but equipment CNC, PLC, e.a., for which must be provided adequate equipment of communication and data storage. Graph theory is used successfully in flexible manufacturing systems optimization. It is useful in determining optimal trajectories of moving parts in the system and reliability FMS calculations. In developing mathematical models were used concepts such as meshing, Petri Networks and theory of Grafcet and innovative concept of realtime modification of the production process [1, 8]. In developing mathematical models were used concepts such as meshing, Petri networks and theory of Grafcet and innovative concept of real-time modification of the production process. It was designed and calibrated a data acquisition system trought computer and sensors to make the driving process and feedback to optimize the design of flexible manufacturing system. It were designed corresponding Graf-cet module, for example Fgure 5. Sequencing component states and their configuration was made trought the discretization method. Logical associations made in a standard GUI environment, based on action and conditioning, was determinated the system status. Each step was assigned a binary variable with values true and false logic based on active or inactive state of that step. Applications development was based on OMRON software package whichwas used to build the program CCSF-v1 - Technological flow control and configuration. Transferring's Grafcet from theoretical environment of graphical representation to the program module was carried out using the compiler Ladder, [5] a modern programming language used in the study of FMS whose instructions are superior mathematical Boolean instructions (auto-tuning, loops) and better respond to problems arising in production planning processes. Compiler and interpreter Ladder is included in CX-Programmer application belonging OMRON software, used in making the source code from grafcets to CCSF-v1 program, used for the whole system that ensures the flow of manufacturing simulation (Figure 6) for cylindrical parts by PLC (Programmable Logic Controller). Fig. 5 Grafcet for real-time processing Fig. 6 CCSF-v1 program interface ISBN: 978-1-61804-126-5 308
The command of the designed industrial system is maded by this computer (PLC) whose construction is based on a RISC (Reduced Instruction Set Computer) arhitecture. Microprocessor takes Ladder Logic instructions them submit to the entire system which is subordinated. Physical process and feedback control is performed using sensors and relays. By evaluating the flow of pieces on processing machines and stations and examining conflicts with regard to requirement of some limited resources, the system layout, selecting manner of equipment, as well as operating proceedings can be evaluated. The program drawn up allows planning / programming and managing in real time the whole processing system. 4 Conclusion The use of modelling and simulation techniques for optimising system structure and behaviour is determined by the present conditions regarding the management systems, international affairs systems, which have the tendency of becoming more and more complex, under the influence of a growing number of internal and external factors. Models are used that are abstract representations of reality or of the system behaviour, with the use of adequate languages. The simulation of flexible manufacturing systems in processing round shafts is dynamic being made in real medium and time. The simulation program contains a data basis concerning entities and states of the flexible manufacturing systems for processing round shafts, organized as standard allowing facile adding or eliminating entities accomplishing the applications. The program allows definition of initial conditions: states of the system s component parts on the starting moment of simulation, positions of the system s component parts, i.e. By means of the warning manager representing the interface, the program achieved allows the control at any time of the simulation concerning the state of the flexible manufacturing system s component parts. The simulation program also allows achieving the animation function of movements made within the flexible manufacturing system for processing round shafts. Its validation is made by computer simulation for real physical applications consisting in complete processing of three round shafts item-types. As a result of the simulation model validity, their use in designing and managing processes within real mediums and times is set up. After simulating the functioning of the flexible fabrication system, the validity of the models will be confirmed, as well as their utility in the design and the management of the processes in real time and environment. The first essential aspect in using computer simulation of real manufacturing items refers to confronting the flexible manufacturing system designer with a huge volume of information, sometimes unpredictable, uncertain, depending on time, incomplete, which under uncertainty conditions may be appreciated as irrelevant and, consequently, eliminated from the configuring process. Simulation allows definition of some aspects of manufacturing management, definition of algorithms for transporting ways and detection of tight points delaying manufacturing flow, study of breakdown influence over the process. Acknowledgement: This work was supported by CNCSIS UEFISCDI, project number PN II IDEI code PCE_756 / 2008, no. 641 / 2009. References: [1] Boncoi Gh., Calefariu G et all., Product Systems, Publishing House Transilvania University of Brasov, 2001. [2] Douglas A. B., Leon F. McGinnis, A Structured Approach to Simulation Modeling of Manufacturing Systems, Proceedings of the 2002 Industrial Engineering Research Conference, Orlando, FL, May 19-22, 6 p. [3] Fota A., Machine systems design. Modelling and simulation, Transilvania University Publishing House, 2004. [4] Joseph, O. A., Sridharan, R., Simulation modelling and analysis of routing flexibility of a flexible manufacturing system, International Journal of Industrial and Systems Engineering 2011 - Vol. 8, No.1 pp. 61-82. [5] Lewis R. W., editor, Programming industrial systems using IEC1131-3, standard documents, 2002. [6] Mahdavi I., Mahadevan B., An algorithm for cellular manufacturing system and layout design using sequence data, Journal Robotics and Computer-Integrated Manufacturing, Vol. 24 Issue 3, June, 2008, Pergamone Press, Inc. Tarrytown, NY, USA, pg. 488-497. [7] Mohora C., Simulation of Flexible Production Systems, Romanian Academy Publising House, Bucharest, 2001. [8] Shivanand, M. K., Benal, M. M. & Koti, V., Flexible Manufacturing Systems, Editor: New Age International, 2006. ISBN: 978-1-61804-126-5 309