Master Thesis - Fachbereich Informatik

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5.1. EXPERIMENTAL DESIGN 103 Ground Truth Length [mm] 52.5 52 51.5 51 50.5 50 49.5 49 48.5 Intra Human Variance 48 0 2 4 6 8 10 12 14 Tube (a) Ground Truth Length [mm] 52.5 52 51.5 51 50.5 50 49.5 49 48.5 Inter Human Variance 48 0 2 4 6 8 10 12 14 Tube Figure 5.2: Intra and inter human variance for the test set in Table 5.3 under ideal laboratory conditions. The error bars indicate the maximum and minimum length for each of the 12 tubes as well as the mean value of the measurements once for one person (a) and once for 10 persons (b). The average inter human variance is slightly larger compared to the intra human variance. Theerrorbarsindicatethemaximumandminimumlengthaswellasthemeanvalueof all measurements. The computed mean standard deviation is 0.078mm. In a second experiment, the inter human variance is determined. Therefore, 10 persons have been asked to measure the same test set again as precise as possible. The inter human variance is slightly larger than the intra human variance (see Figure 5.2(b)). In this case, the mean standard deviation was observed to be 0.083mm. Furthermore, it is important to state that the manual measurements for the ground truth data have been acquired very carefully with elevated concentration under laboratory conditions and with the aim to be as precise as possible using the digital measuring slide (see Figure 5.1). Less than 5 tubes can be measured within one minute at this precision. At production, the sample measurements are performed with a standard sliding caliper and at a much higher rate. There is a definitively tradeoff between accuracy and speed. The expected individual measuring error at production is much larger. Furthermore, factors like tiredness or distraction can significantly increase the inter and intra human measuring variance. The accuracy and precision of the visual inspection system, however, should be evaluated with respect to the maximum possible accuracy humans can reach with the given measuring slide under ideal conditions. Throughout this thesis, manual ground truth measurements always refer to the ideal, laboratory condition measurements. One has to keep in mind that there is still a certain unsureness in these measurements. The real absolute length of a tube can not be determined exactly. For the following experiments, all tubes have been measured three times to reduce the influence of the human variance. The mean of the three measurements is taken as ground truth reference. All measurements are stored in a database and each measured tube is labeled by hand with a four digit ID using a white touch-up pen. (b)
104 CHAPTER 5. RESULTS AND EVALUATION Figure 5.3: At velocities > 30m/min larger sequences of tubes with a small spacing have to be placed on the conveyor using a special supply tube. 5.1.4. Strategies Online vs Offline Inspection There are two main strategies for evaluation of the inspection system. The first strategy analyzes the tubes online, i.e. in real-time on the conveyor. This includes the tube localization, tracking, measuring as well as the good/bad classification. The results are stored in a file and can be further processed or visualized afterward. This is closely related to the application at production. The drawback of this approach is that if there is some interesting or strange behavior observed in the resulting data, it is difficult to localize the origin. Therefore, the second evaluation strategy is based on an offline inspection. This means a sequence of tubes is first captured into a file at the maximum frame rate that can be processed online. Then, the sequence can be analyzed repetitive with different sets of parameters or methods. This is a significant advantage if one wants to compare different techniques or parameter settings. In the following experiments, both strategies will be applied. Tube Placement The prototype setup in the laboratory has one significant drawback. The tubes to be inspected have to be added manually to the conveyor, since there is no second conveyor from which the tubes fall onto continuously like in production. The size of the conveyor allows for about 21 tubes of 50mm length with a spacing of 10mm in between. If all tubes are placed on the inactive conveyor it takes some time until the desired velocity is reached. Therefore, at faster velocities, the first tubes pass the measuring area with a slower velocity leading to unequal conditions between measurements. Hence, either less tubes have to be placed on the conveyor (starting further away from themeasuringarea)orthetubeshavetobeplacedontotheconveyorwhileitisrunning at the desired velocity. The later is hardly possible for a human without producing large spacings between two consecutive tubes. Instead a certain supply tube of about 1.30m length, with a diameter slightly larger than the current tube diameter, can be used as magazine for about 25 tubes of 50mm length (see Figure 5.3). The supply tube is placed at steep angle at the front of the conveyor (in moving direction). If the conveyor is not moving, the tubes are blocked and can not leave the supply tube. On the other hand if theconveyorismoving,thebottomtubeisgrippedbythebeltandcanleavethesupply tube through a bevel opening in moving direction. If the velocity of the conveyor is fast
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Fachbereich Informatik Department o
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Acknowledgments First of all, I wou
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Contents Acknowledgments iii Abstra
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Contents ix 5.3.7. TubeLength .....
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List of Tables 1.1. Rangeoftubetype
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List of Figures 2.1. AccuracyandPre
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1. Introduction Heat shrinkable tub
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1.2. PROBLEM STATEMENT 3 hazards, r
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1.4. RELATED WORK 5 Length [mm] Tol
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1.5. THESIS OUTLINE 7 The vision pa
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2. Technical Background 2.1. Visual
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2.1. VISUAL MEASUREMENTS 11 (a) Fig
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2.1. VISUAL MEASUREMENTS 13 Figure
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2.1. VISUAL MEASUREMENTS 15 � xd
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2.2. ILLUMINATION 17 tubes alternat
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2.2. ILLUMINATION 19 effect of comp
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2.3. EDGE DETECTION 21 i 2 i 1 0 (a
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2.3. EDGE DETECTION 23 N × 1 kerne
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2.3. EDGE DETECTION 25 These operat
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2.3. EDGE DETECTION 27 (a) 0 ◦ (b
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2.4. TEMPLATE MATCHING 29 accuracy
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3. Hardware Configuration This chap
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3.2. CAMERA SETUP 33 3.2. Camera se
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3.2. CAMERA SETUP 35 eachcolorchann
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3.2. CAMERA SETUP 37 Figure 3.4: Co
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3.2. CAMERA SETUP 39 adjusting scre
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3.2. CAMERA SETUP 41 further distan
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3.3. ILLUMINATION 43 f V 12mm 129mm
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3.3. ILLUMINATION 45 (a) (b) (c) Fi
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3.3. ILLUMINATION 47 (a) (b) Figure
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3.4. BLOW OUT MECHANISM 49 A light
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4. Length Measurement Approach Whil
Page 68 and 69: 4.2. MODEL KNOWLEDGE AND ASSUMPTION
Page 74 and 75: 4.3. CAMERA CALIBRATION 59 4.2.7. B
Page 76 and 77: 4.3. CAMERA CALIBRATION 61 Figure 4
Page 78 and 79: 4.3. CAMERA CALIBRATION 63 is compu
Page 80 and 81: 4.4. TUBE LOCALIZATION 65 (a) (b) F
Page 82 and 83: 4.4. TUBE LOCALIZATION 67 � 1 Psm
Page 84 and 85: 4.4. TUBE LOCALIZATION 69 Global Th
Page 86 and 87: 4.4. TUBE LOCALIZATION 71 but also
Page 88 and 89: 4.4. TUBE LOCALIZATION 73 Global Re
Page 90 and 91: 4.5. MEASURING POINT DETECTION 75 f
Page 92 and 93: 4.5. MEASURING POINT DETECTION 77 T
Page 94 and 95: 4.5. MEASURING POINT DETECTION 79 -
Page 96 and 97: 4.5. MEASURING POINT DETECTION 81 0
Page 98 and 99: 4.5. MEASURING POINT DETECTION 83 o
Page 100 and 101: 4.5. MEASURING POINT DETECTION 85 (
Page 102 and 103: 4.5. MEASURING POINT DETECTION 87 w
Page 104 and 105: 4.6. MEASURING 89 side of the tube,
Page 106 and 107: 4.6. MEASURING 91 fcor(x) =−(c1x
Page 108 and 109: 4.7. TEACH-IN 93 inthemeasuringplan
Page 110 and 111: 4.7. TEACH-IN 95 The pair of a pixe
Page 112 and 113: 5. Results and Evaluation 5.1. Expe
Page 114 and 115: 5.1. EXPERIMENTAL DESIGN 99 between
Page 116 and 117: 5.1. EXPERIMENTAL DESIGN 101 where
Page 120 and 121: 5.2. TEST SCENARIOS 105 enough, the
Page 122 and 123: 5.3. EXPERIMENTAL RESULTS 107 The t
Page 124 and 125: 5.3. EXPERIMENTAL RESULTS 109 Detec
Page 126 and 127: 5.3. EXPERIMENTAL RESULTS 111 Lengt
Page 128 and 129: 5.3. EXPERIMENTAL RESULTS 113 GTD [
Page 130 and 131: 5.3. EXPERIMENTAL RESULTS 115 gray
Page 134 and 135: 5.3. EXPERIMENTAL RESULTS 119 (a) (
Page 136 and 137: 5.3. EXPERIMENTAL RESULTS 121 (a) (
Page 140 and 141: 5.3. EXPERIMENTAL RESULTS 125 Total
Page 142 and 143: 5.3. EXPERIMENTAL RESULTS 127 Color
Page 144 and 145: 5.3. EXPERIMENTAL RESULTS 129 Task
Page 146 and 147: 5.4. DISCUSSION AND FUTURE WORK 131
Page 148 and 149: 6. Conclusion In this thesis a func
Page 150: Appendix 135
Page 153 and 154: 138 APPENDIX A. PROFILE ANALYSIS IM
Page 155 and 156: 140 APPENDIX A. PROFILE ANALYSIS IM
Page 157 and 158: 142 APPENDIX B. HARDWARE COMPONENTS
Page 159 and 160: 144 APPENDIX B. HARDWARE COMPONENTS
Page 161 and 162: 146 Bibliography [18] C. Demant, B.
Page 163 and 164: 148 Bibliography [51] K.K. Pingle.
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Master Thesis - Fachbereich Informatik

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