A Mechatronic Marvel: The Barcode Scanner

Transcription

1 A Mechatronic Marvel: The Barcode Scanner Dr. Kevin Craig & Dr. Mark Nagurka Professors of Mechanical Engineering Marquette University Bar Code Scanner K. Craig & M. Nagurka 1

2 Design News Web Cast Web Cast Introduction Mechatronics and the Barcode Scanner Part 1: Barcodes and Barcode Scanners Types of Barcodes Types of Barcode Scanners Part 2: Barcode Scanner Uncovered Key Elements Mechatronic System Design Part 3: What s Next? Bar Code Scanner K. Craig & M. Nagurka 2

3 Web Cast Introduction Mechatronics and the Barcode Scanner Bar Code Scanner K. Craig & M. Nagurka 3

4 Plant Design Plant Dynamics & Control Structure Bar Code Scanner K. Craig & M. Nagurka 4

5 Mechatronics is the synergistic integration of physical systems, electronics, controls, and computers through the design process, from the very start of the design process, thus enabling complex decision making. Integration is the key element in mechatronic design as complexity has been transferred from the mechanical domain to the electronic and computer software domains. Mechatronics is an evolutionary design development that demands horizontal integration among the various engineering disciplines as well as vertical integration between design and manufacturing. Mechatronics is the best practice for synthesis by engineers driven by the needs of human beings and industry. Plant dynamics and control structure must be included in the plant design from the very start of the design process. Bar Code Scanner K. Craig & M. Nagurka 5

6 A Mechatronic Marvel Today Yesterday Bar Code Scanner K. Craig & M. Nagurka 6

7 As a young boy growing up in the late 1950s, I remember well trips to the grocery store on a Saturday morning with my dad and going to the check-out line where a person would quickly read the price of the item, punch the keys on the cash register, and be able to add and subtract with lightening speed if a correction needed to be made. Then there was the familiar kaching sound when the cash drawer was opened. Most youngsters received a toy cash register as a birthday present in those days. How the world has changed! Barcode scanners are everywhere most of us hardly notice them anymore. Everything seems to have a barcode and the world would come to a standstill if barcode scanners stopped working. Bar Code Scanner K. Craig & M. Nagurka 7

8 Barcode technology began revolutionizing the retail market in 1974, when a checker at a supermarket in Troy, OH, slid a pack of gum imprinted with a simple linear barcode over a fixed scanner to ring up the price. Thirty four years later barcodes are scanned about five billion times a day, and are used as much for tracking packages as they are for ringing up purchases. Barcodes can be found on airline and concert tickets, driver licenses, library books, hospital wristbands the list of products bearing these black-and-white symbols is nearly endless, and still growing. But barcodes are not just consumer-based, point-of-service tools; they actually have their roots in manufacturing and distribution for ensuring the accuracy of inventory and that the correct item is delivered to the correct location in a timely manner. Bar Code Scanner K. Craig & M. Nagurka 8

9 Barcodes are now being used in many industries outside retail and manufacturing, particularly for quality control and security applications. Hospitals are investing in barcode scanners to lower the risk of medication errors. The U.S. Food and Drug Administration now requires drug makers and blood suppliers to include barcodes on most of their products. Educational institutions are implementing barcodes on student and faculty identification cards to improve campus security and communication. Most airlines now offer ticketless tickets printed with barcodes that streamline the check-in process and allow security personnel to quickly verify the identity of passengers and their baggage. Bar Code Scanner K. Craig & M. Nagurka 9

10 In a recent Design News article and web cast, we explored the world of the digital camera. A barcode scanner can be considered a very specialized digital camera and, since barcodes convey digital information through a combination of narrow and wide bars and spaces, they can be viewed as the optical version of the Morse code. The barcode scanner is truly a mechatronic device as it encompasses so many engineering areas: mechanical, electrical, materials, manufacturing, optics, controls, signal processing, electronics, microcontrollers, actuators, and sensors. It is a very complex integrated system in which all the components work together, and improvements in performance come from a systems approach and not just by upgrading individual components. So what is this mechatronic marvel that looks like a Star Trek phaser and what is next in the world of automatic identification? Bar Code Scanner K. Craig & M. Nagurka 10

11 Web Cast Part 1 Barcodes and Barcode Scanners Bar Code Scanner K. Craig & M. Nagurka 11

12 What is a Barcode? Anatomy of a Barcode Bar Code Scanner K. Craig & M. Nagurka 12

13 Many industries utilize an identification system in which the products are marked with a barcode symbol consisting of a series of lines and spaces of varying widths, or other types of symbols consisting of series of contrasting markings. A number of different barcode readers and laser scanning systems have been developed to decode the symbol pattern to a multiple digit representation for inventory, production tracking, and for check out or sales purposes. Barcode symbols are formed from bars or elements that are typically rectangular in shape with a variety of possible widths. The specific arrangement of elements defines the character represented according to a set of rules and definitions specified by the symbology used. The relative width of the bars and spaces is determined by the type of symbology used, and the actual size of the bars and spaces is usually determined by the application. Bar Code Scanner K. Craig & M. Nagurka 13

14 The number of characters per inch represented by the barcode symbol is referred to as the density of the symbol. A barcode normally includes several barcode characters. A barcode character is a group of lines (bars) and spacings that represent a single number or letter. A barcode symbol consists of a series of light and dark regions, typically in the form of rectangles. The widths of the dark regions, the bars, and/or the widths of the light spaces between the bars indicate the encoded information. A barcode symbol is a collection of several barcode characters which represent an identification of a particular object. Bar Code Scanner K. Craig & M. Nagurka 14

15 Typically, the barcode symbol includes a quiet zone, start code or pattern data characters, stop code, and trailing quiet zone. Different bar codes have different information densities and contain a different number of elements in a given area representing different amounts of encoded data. The denser the code is, the smaller the elements and spacings. A typical one dimensional (1D) barcode includes a series of parallel lines and spaces of varying widths which in accordance with known conventions may be used to represent desired information relating to the item. A two dimensional (2D) barcode provides more complex lines and spaces in two orthogonal axes for representing even more information regarding an item than is available in 1D barcodes. Bar Code Scanner K. Craig & M. Nagurka 15

16 Although simple and cost-effective to implement, 1-D barcodes are limited in the amount of data they can contain by the size of the product they are printed on and the linearity of the code itself. With the growing pressure for factories, shipping companies, retail outlets, government agencies, and hospitals to better track and trace their inventory and monitor and protect their customers, increasingly sophisticated barcode symbologies and scanners are now needed. Thus, Symbol, Intermec, and others have invested in linear and 2D symbols and scanners that offer greater functionality than traditional 1D scanners. Bar Code Scanner K. Craig & M. Nagurka 16

17 In a 2D barcode, the information is stacked or arranged in an array of dark and light square pixels that can hold more than a kilobyte of machine-readable data and are scanned both horizontally and vertically. Standard 2D barcodes are smaller and more flexible than their 1D counterparts, making them more amenable to applications such as hospital wristbands while also boosting their anticounterfeiting capabilities. In addition, the scanners required to read them typically offer more advanced imaging capabilities such as optical character recognition, signature capture, and image capture via embedded CCD or CMOS cameras. Bar Code Scanner K. Craig & M. Nagurka 17

18 Bar Code Scanner K. Craig & M. Nagurka 18

19 Bar Code Scanner K. Craig & M. Nagurka 19

20 Bar Code Scanner K. Craig & M. Nagurka 20

21 UPS MaxiCode Maxicode is developed by the biggest delivery company in the world, UPS. It is used for sorting or tracking deliveries. The Maxicode has a triple circle of the discriminative finder pattern on its center. With this triple circle, a reader instantaneously recognizes the position of a 2D code. It is suitable for high-speed reading and is used for sorting in conveyor lines, especially in the United States. Bar Code Scanner K. Craig & M. Nagurka 21

22 Barcode Scanners Barcode scanners generally fall into two categories: handheld and stationary. Handheld scanners include laser scanners, linear imagers (with LEDs as the primary light source), 2D imagers, and pen scanners. Stationary systems range from industrial lasers and imagers to point-of-service scanners and barcode verifiers. Bar Code Scanner K. Craig & M. Nagurka 22

23 There are four main types of barcode scanners / readers: Pen-type Readers Pen type readers scan or read a barcode by emitting visible red or infrared light such as from an LED which strikes the barcode while the scanner is moved across the barcode in a linear direction with the tip of the scanner touching the bar code label. Pen type barcode readers have a light source and a photo diode placed next to each other in the tip of a pen or wand. Bar Code Scanner K. Craig & M. Nagurka 23

24 To read a barcode, the tip of the pen moves across the bars in a steady motion. The photodiode measures the intensity of the light reflected back from the light source and generates a waveform that is used to measure the widths of the bars and spaces in the barcode. Dark bars in the barcode absorb light and white spaces reflect light so that the voltage waveform generated by the photo diode is a representation of the bar and space pattern in the barcode. The barcode reader sends the waveform to the decoder, which decodes this waveform in a manner similar to the way Morse code dots and dashes are decoded. The decoded information is sent to the computer in a traditional data format. Bar Code Scanner K. Craig & M. Nagurka 24

25 Laser Scanner Bar Code Scanner K. Craig & M. Nagurka 25

26 Laser scanners work the same way as pen-type readers except that they use a laser beam as the light source and typically employ either a reciprocating mirror or a rotating mirror to scan the laser beam back and forth across the bar code (1). As with the pen type reader, a photodiode is used to measure the intensity of the light of diffuse reflection from the bar code (2). In both pen readers and laser scanners, the light emitted by the reader is tuned to a specific frequency and the photodiode is designed to detect only this modulated light of the same frequency. This diffuse reflection looks like an analog wave form (3) which the barcode reader coverts to a digital wave form (4). The narrow/wide bars and spaces are identified (5) and then the signal combination of the bars and spaces is converted into data according to the barcode rules (6). Bar Code Scanner K. Craig & M. Nagurka 26

27 Oscillating mirrors are used in hand-held scanners and rotating mirrors are used in fixed-mounted scanners. Why? The answer gives considerable insight into the design and operation of this mechatronic marvel. Oscillating mirrors use less power and survive shocks and drops better, making them suitable for hand held scanners. An oscillating mirror also fits in a smaller space, which is an important consideration for a hand held scanner. More importantly, however, since the moving mass of an oscillating mirror is so much less then a rotating polygon, it can be accelerated to full speed much more rapidly, with a minimum surge current (important since many scanners are battery operated). In hand-held scanners, the scan motor is turned off after each barcode is decoded, and started up again the next time the trigger is pulled, so the motor has to start up very fast if a 50 ms decode time is to be achieved, which feels almost instantaneous to a user. Bar Code Scanner K. Craig & M. Nagurka 27

28 Another interesting fact about these oscillating motors is that, unlike other mechanical devices, they have no inherent failure mechanism. People expect that any mechanical device will ultimately fail, even if it isn't abused. This perception is based on the fact that most mechanisms use bearings which will ultimately fail due to friction. Since oscillating motors have no bearings, they have no friction. You might expect that the flexing part of the motor will ultimately fatigue and fail just as most things will eventually break if you bend them back and forth enough. In fact, if the mechanical stresses in a flexing member are kept below a threshold, failure from fatigue can be totally avoided. Oscillating motors are therefore designed to operate well below this threshold. This extreme reliability is central to the ability to sell an inexpensive scanner with a long warrantee. If the failure rate wasn't close to zero, the cost of servicing them would consume profits. Bar Code Scanner K. Craig & M. Nagurka 28

29 Rotating polygon mirrors are generally used in fixed-mounted scanners even though they cannot achieve the essentially infinite operational life of the oscillating mirrors. The main reason is that a rotating polygon can scan the laser beam over a much larger angle then an oscillating mirror can, and can also produce many more scan lines per second. For example, with a four-sided rotating polygon mirror, the laser beam is scanned four times for every 360 degree rotation of the scan motor (one scan as each of the four mirror surfaces intercepts the incoming laser beam). A four-sided polygon will scan the beam over an angle of 180 degrees before it rotates so far that the next mirror moves into the laser beam and the next scan begins. This wide scan angle is very useful when creating an omnidirectional laser scanner (a scanner that can read a barcode in any orientation). Bar Code Scanner K. Craig & M. Nagurka 29

30 These scanners need to project an array of scan lines in different orientations so as to read a barcode in whatever orientation it is presented to the scanner. These multiple scan lines are created by scanning the laser (using the rotating polygon) over an array of stationary mirrors, which divide up the 180 degree scan line from the polygon into smaller angular segments and project them out of the scanner in different orientations. The wide scan angle of the rotating polygon is necessary here or it wouldn't be possible to scan across the entire array of stationary mirrors. The high speed of the rotating polygon is also useful in these scanners. Omni-directional scanners, such as the scanners used in supermarkets, must be able to read barcodes that might be in any orientation, while the barcode is moving rapidly through the field of view of the scanner. The scanner must therefore produce scan lines in every orientation in a very short period of time to be sure that the barcode is decoded, regardless of its orientation. Bar Code Scanner K. Craig & M. Nagurka 30

31 In one omni-directional scanner, for example, the four sided polygon is spinning at 4500 RPM (75 revolutions/second). Each of the four scans that result from each revolution is scanned over a stationary array of five mirrors, creating five scan lines from each line produced by the polygon. This arrangement therefore produces a total of 1500 scan lines/second (75 revolutions/second times 4 scans per revolution times 5 stationary mirrors). Bar Code Scanner K. Craig & M. Nagurka 31

32 Specular Reflection vs. Diffuse Reflection Bar Code Scanner K. Craig & M. Nagurka 32

33 If you mount the barcode reader so that its laser is applied perpendicular to the barcode label (specular reflection mounting) as shown, the barcode reader receives excessively strong reflection (specular reflection or direct reflection) from the bar code label. In this type of mounting, some level of the analog waveform is extremely high, causing improper conversion into a digital waveform. As a result, bar codes cannot be read with specular reflection mounting. If you mount the bar code reader at a skew angle (i.e., tilt the barcode reader at an angle of degrees), the whole light beam results in diffuse reflection, allowing for proper conversion from an analog waveform into the digital waveform as shown. Bar Code Scanner K. Craig & M. Nagurka 33

34 CCD Barcode Reader Bar Code Scanner K. Craig & M. Nagurka 34

35 CCD readers (also referred to LED scanners) use an array of hundreds of tiny light sensors lined up in a row in the head of the reader. Each sensor can be thought of as a single photodiode that measures the intensity of the light immediately in front of it. Each individual light sensor in the CCD reader is extremely small and because there are hundreds of sensors lined up in a row, a voltage pattern identical to the pattern in a barcode is generated in the reader by sequentially measuring the voltages across each sensor in the row. The important difference between a CCD reader and a pen or laser scanner is that the CCD reader is measuring emitted ambient light from the barcode whereas pen or laser scanners are measuring reflected light of a specific frequency originating from the scanner itself. Bar Code Scanner K. Craig & M. Nagurka 35

36 1. The LED for the light source radiates light onto a barcode. At this time, the LED flashes in pulses which is advantageous when reading a moving object. 2. The CCD image sensor receives the light of diffuse reflection from the barcode as an image. Although the LED radiates light onto a wide range, the reflection received as the image is only the one reflected from the light-receiving axis (line). The barcode reader cannot read a barcode if it is not on the light-receiving axis. 3. The barcode reader scans the image data of the barcode on the CCD image sensor from edge to edge to obtain the analog waveform. The obtained waveforms represent the scan rate of the CCD barcode reader. A high scan rate ensures stable readings. 4. The barcode reader converts the analog waveforms to digital waveforms (A/D conversion). 5. The barcode reader converts the obtained digital waveforms into data according to the barcode rules (decoding). Bar Code Scanner K. Craig & M. Nagurka 36

37 Camera-Based Reader 2D imaging scanners are the newest type of barcode reader and are becoming more popular due to increased data carrying ability. They use a small video camera to capture an image of a barcode. The reader then uses digital image processing techniques to decode the barcode. Video cameras use the same CCD technology as in a CCD barcode reader except that instead of having a single row of sensors, a video camera has hundreds of rows of sensors arranged in a two-dimensional array so that they can generate an image. Bar Code Scanner K. Craig & M. Nagurka 37

38 Comparison: Laser vs. CCD The laser-type scanner, while larger and more expensive, has significant advantages over the CCD-type scanner including long-distance reading, a wide readable range, the ability to scan moving objects, and the possibility of raster (multiple) scanning. Bar Code Scanner K. Craig & M. Nagurka 38

39 What are the Benefits of Barcode Systems, i.e., barcode, scanner, software, and computer? Improved Operational Efficiency Since barcodes permit faster and more accurate recording of information, work in process can move quickly and be tracked precisely. Quite a bit of time can be spent tracking down the location or status of projects, folders, instruments, materials, or anything else that moves within an organization. Barcodes help one keep better track so one can save time and respond more quickly to inquiries and changes. Save Time Depending on the application, time savings can be significant. Often the most dramatic examples involve the chore of taking inventory, but even in routine day-to-day operations the time savings of barcodes add up and improve productivity. Bar Code Scanner K. Craig & M. Nagurka 39

40 Reduce Errors Clerical and data-entry errors can be a significant source of costs and related problems and in some situations clerical errors can have a much more dramatic impact consider the importance of accuracy in pharmaceutical or blood bank applications. The typical error rate for human data entry is 1 error per 300 characters. Barcode scanners are much more accurate; the error rate can be as good as 1 error in 36 trillion characters depending on the type of barcode used. Cut Costs Barcodes are effective tools that can be used to address specific, localized problems or integrated into organization-wide information systems. When applied with thought and planning they can save time and reduce errors, resulting in a reduction of costs. Customer or Regulatory Requirements Regulatory agencies or customers may impose labeling requirements that can easily be met with barcodes. Bar Code Scanner K. Craig & M. Nagurka 40

41 Web Cast Part 2 Barcode Scanner Uncovered Bar Code Scanner K. Craig & M. Nagurka 41

42 Handheld Barcode Scanner 2D bar code 1D bar code Bar Code Scanner K. Craig & M. Nagurka 42

43 Barcode Scanner Bar Code Scanner K. Craig & M. Nagurka 43

44 Overhead View: Cover Removed Image Sensor Front Window Back Laser Mirror Bar Code Scanner K. Craig & M. Nagurka 44

45 Overhead View: Path of Laser Light OUT (photo lightened) To Barcode Laser Mirror Bar Code Scanner K. Craig & M. Nagurka 45

46 Overhead View: Path of Light from Barcode IN (photo lightened) Image Sensor From Barcode Mirror Bar Code Scanner K. Craig & M. Nagurka 46

47 Front Image Sensor Overhead View: Closer Back Laser Mirror Solenoid Bar Code Scanner K. Craig & M. Nagurka 47

48 Mirror Mirror Bar Code Scanner K. Craig & M. Nagurka 48

49 View of mirror with central laser-reflecting mirror Mirror reflecting laser light out Mirror collecting light reflected from barcode Bar Code Scanner K. Craig & M. Nagurka 49

50 Another view of central laser-reflecting mirror (removed from board) Mirror collecting light reflected from barcode Mirror reflecting laser light out Image sensor Barcode Laser Bar Code Scanner K. Craig & M. Nagurka 50

51 Laser Image Sensor Back of Mirror Back of Mirror Solenoid to oscillate mirror Bar Code Scanner K. Craig & M. Nagurka 51

52 Flexural stiffness Flexural stiffness Two coils: (1) electromagnet to oscillate mirror & (2) coil to sense frequency Magnetic plunger Bar Code Scanner K. Craig & M. Nagurka 52

53 Laser Image Sensor Adjustment for aiming laser Bar Code Scanner K. Craig & M. Nagurka 53

54 Laser & Image Sensor Cover Laser photodiode nm laser with 1.0 mw output Class 2 Laser Image Sensor Cover Bar Code Scanner K. Craig & M. Nagurka 54

55 Image Sensor Uncovered Lens in front of Image Sensor Reflected off mirror from barcode Bar Code Scanner K. Craig & M. Nagurka 55

56 Image Sensor Uncovered Image Sensor (with lens removed) Bar Code Scanner K. Craig & M. Nagurka 56

57 Mechatronic System Design What is Mechatronic about barcode scanners? The scanner is an example of a mechatronic system: image sensor, actuator, optics, electronics, computer control all integrated from the very beginning of the design! A barcode scanner is part of a higher level mechatronic system comprised of the barcode itself, the scanner, and the computer software and hardware that processes the information. Clearly this is an integrated multidisciplinary engineering system that could only have been designed with a mechatronic approach by a team led by a mechatronics engineer. Bar Code Scanner K. Craig & M. Nagurka 57

58 Web Cast Part 3 What s Next? Future of Barcode Scanners Bar Code Scanner K. Craig & M. Nagurka 58

59 Future of Barcode Scanners Barcodes and barcode scanners have been around for over three decades and will be around for many more. However, there are concerns that barcodes are vulnerable to security breaches and counterfeiting. Increasing pressure to ensure the country of origin for products and the authenticity of those products is pushing businesses to adopt moresophisticated tracking technologies. RFID (radio-frequency identification) is designed to further increase the amount and complexity of data that can be encoded, the security of that data, and the authenticity of the item the code or chip is attached to. Bar Code Scanner K. Craig & M. Nagurka 59

60 It costs about $0.005 to implement a barcode compared to a passive radio frequency identification device which costs about $0.07 to $0.30 per tag. So barcodes are basically free, but RF tags are not and probably never will be. Also RFID doesn t work well on some types of packages, e.g., metal cans, and barcode scanners are selective while RFID devices might capture data not intended for capture. So while there has been much speculation that RFID might eventually replace conventional barcodes, the general consensus is that the two methods will remain complementary for many years to come. Bar Code Scanner K. Craig & M. Nagurka 60

61 The success of the modern barcode scanner is based on a combination of small size, high scanning performance, and superior reliability. Over the past 2-3 years, a number of new developments have become available which have the potential to significantly increase the performance of the scan engine. Liquid Polymer (LP) Scan Element This patented technology eliminates friction and wear and is so reliable that Symbol Technologies (now owned by Motorola) offers a lifetime warranty! This scanning technology has been configured for use in small scan engines. Bar Code Scanner K. Craig & M. Nagurka 61

62 In a scan element, liquid polymer is used to create a single-piece structure that includes rigid and flexible portions. The rigid portions are used to mount the scan element. A mirror and magnet are mounted on the flexible portion, which can be moved magnetically to scan a laser. The liquid-polymer element can be fabricated in high volume, at low cost, and with consistent quality with a process that is similar to conventional injection molding. Liquid Polymer Scan Element Bar Code Scanner K. Craig & M. Nagurka 62

63 One of the primary factors affecting the effectiveness of laser scanner engines is the speed of the laser beam movement. Too slow, and the scanner may seem unresponsive to the experienced user. As scan speed increases, however, the signals that the scanner must process also increase in frequency, making it more difficult to distinguish these signals from non-barcode related noise. As a result, the working range of the scanner may be restricted. Earlier miniature laser engines operated at speeds of around 50 scans per second. The LP scan element is designed to operate at 100 scans per second - fast enough to make the scanner feel extremely responsive, but not so fast as to compromise the signal quality and limit the working range. Bar Code Scanner K. Craig & M. Nagurka 63

64 Moving vs. Stationary Collection Optics The primary function of a laser scanning device is to move the laser beam back and forth. A few high performance scanners also use the scan element to move the optics that collect and concentrate the laser light reflected off the barcode. Moving the collection optics in coordination with the laser beam allows the scanner to reject unwanted light, such as sunlight, which can mask the laser signal. Moving collection optics require the use of a large scan mirror, because the larger the mirror, the more light can be collected and the greater the working range of the scanner. Bar Code Scanner K. Craig & M. Nagurka 64

65 Multi-Focus Laser Optics Lasers are famous for their ability to project a beam of light over a long distance without the beam diverging (spreading out), as light from other light sources does. Although laser light can be focused to diverge much less than other light sources, divergence cannot be totally eliminated. It is this unavoidable divergence that is one of the things that limits the working range of laser scanners, especially when scanning barcodes with narrow bars or spaces. When the laser beam diverges too much at a distance from the scanner, the scanner can no longer resolve small bars and spaces, so a bar code with small bars and spaces cannot be decoded beyond that distance. Bar Code Scanner K. Craig & M. Nagurka 65

66 Special laser focusing optics have been developed that have the ability to counteract divergence of the laser beyond that which can be accomplished with conventional optics. The shape of the laser beam is also controlled so as to project an elliptical laser spot on the barcode, as opposed to a conventional circular spot. The elliptical spot helps the scanner ignore defects in the printed bar code, improving performance on damaged and poorly printed barcodes. Bar Code Scanner K. Craig & M. Nagurka 66

67 Parallel Signal Processing with Variable Resolution One potential advantage of high scan speed is that it can give a scanner more attempts to read a damaged barcode, increasing the chances that it will read quickly. Unfortunately, increasing the scan speed also degrades signal quality, which can actually make it more difficult to read some bar codes of marginal quality. This loss of signal quality partially cancels any advantage that might be expected from the higher scan speed. New approaches to consistently obtain a rapid decode without degrading signal quality are being developed. Bar Code Scanner K. Craig & M. Nagurka 67

68 For example, a scan engine can use two individual signal processing circuits, each optimized to read different kinds of barcodes. One is designed to read damaged or poorly printed barcodes, while the other excels at reading high density bar codes. Both circuits can also easily process the signals from good quality barcodes. The outputs from both of these processing circuits are available to the decoder on every scan, so even though the scanner is running at 100 scans per second, the decoder gets 200 chances to decode the bar code every second. Bar Code Scanner K. Craig & M. Nagurka 68

69 The two signal processors are designed to complement each other, so one, the other, or both will succeed in decoding the vast majority of barcodes. In the event that a barcode is extremely disfigured, however, the scanner can automatically adjust both circuits to further improve the probability of obtaining a rapid decode. For example, if the barcode is badly scratched, the resolution of the signal processing circuits can be reduced, enabling the scanner to ignore the defects. When scanning bar codes with very narrow bars or spaces down to around 4 mils (0.004 in.), resolution is increased to assure accurate detection of every bar and space in the barcode. Bar Code Scanner K. Craig & M. Nagurka 69

70 Adaptive Electronics When a scanner is positioned close to a bar code, there is a lot of reflected laser light for the scanner to detect, producing a strong signal for the signal processing circuitry to work with. As distance between the scanner and bar code increases, however, the amount of reflected laser light and resulting signal is smaller and weaker. As it becomes weaker, it is more susceptible to being masked by various types of electrical noise. Sources of electrical noise that may degrade a scanner s performance come from other electronic devices that may be positioned close to the scanner or even by the same power supply as the scanner. The circuitry within the scanner itself also produces some unavoidable noise, which can ultimately limit the working range of a scanner. Bar Code Scanner K. Craig & M. Nagurka 70

71 New scanners include circuitry that automatically adjusts to compensate for signal variations that result from scanning from different distances, and from scanning barcodes with different print contrasts, in order to maintain the signal applied to the signal processing circuits at an optimum level. The scan engine also includes automatically varying filters to remove noise that might otherwise degrade scanning performance. Bar Code Scanner K. Craig & M. Nagurka 71

72 MEMS-Based Barcode Scanner A MEMS-based barcode scanner is being developed. It is claimed that MEMS technology produces a laser scan engine with faster scan rates, miniaturization, improved durability, and frictionless mechanical parts. The MEMS design also allows high-speed scanning in two dimensions, omni-directional reading of 1D and stacked barcodes, and 2D raster scanning for matrix codes. The advantages claimed for MEMS devices are that it is solid state, which means it has less chance of failing and lends itself to mass production. The mirror is made to oscillate 250 times/sec and starts at 400 scans/sec, but can go up to 5000 scans/sec, while conventional electro mechanical mirrors operate at 30 to 40 scans/s. Bar Code Scanner K. Craig & M. Nagurka 72

73 The question is which technology offers better signal quality and working range, lower cost, and greater reliability. A MEMS system needs a separate optical system to collect the light, in addition to the optical system that projects the light. One view is that this is one way to go, but maybe not the best way to make a scanner because it doesn t allow you to optimize the receiving signal. A larger scanning mirror than is possible to create using MEMS allows one to collect the light off the same mirror and then concentrate the photodetector wherever the laser beam happens to be pointing at the moment. In the MEMS design there is a second mirror that does not move so it has to have a very large field of view, which means it collects not only the reflected laser light but also a lot of ambient light. And that is noise as far as the scanner is concerned. Bar Code Scanner K. Craig & M. Nagurka 73

74 References Ed Barkan, Motorola Fellow and holder of over 216 barcode scanner patents. Co-inventor of the hand-held laser scanner patented in Telephone conversation. Kathy Kincade, July 2006, Barcode Scanners Aren t Just for Groceries Anymore, Laser Focus World Magazine. Motorola White Paper: New Technologies Drive Superior Scan Performance Bar Code Scanner K. Craig & M. Nagurka 74

75 Survey Questions The Barcode Scanner is a mechatronic system that impacts our lives as much any technology ever developed. What other mechatronic systems have impacted our lives? How is the integration required for a mechatronic system such as this implemented in your company? How is the control system design done? In an integrated way or as after-thought add-on? What skills do you feel you are lacking that you would urge young engineers to focus on? Bar Code Scanner K. Craig & M. Nagurka 75

76 THANK YOU! Bar Code Scanner K. Craig & M. Nagurka 76