Home

View/Open - UWSpace - University of Waterloo

1. where A a j De m we El sina Up Ye gt VUP yn 28 am ve al cosa p e 3 17 VI EE P Parameters zl and y are distances between the axis Z of joystick coordinate system and the axis Z of indexing head coordinate system Ideally they should both be zero The mounting base was designed so as to minimize them However it is necessary to indicate them in the calibration process although their values are both less than one half millimeter The value of zp 22 is the distance d tan 0 in which d 22 5mm 0 0 25 and corresponds to the distance between the pivot on the centering shaft and the pivot axes of the joystick which is not acceptable This distance can be varied between 48 25mm and 53 24mm Consequently B and D in Equation and 3 17 will be very small lt 0 01 and can be safely ignored in the computations Equation 3 18 and 3 19 6 arctan Asin a well 3 18 0 arctan A cos a p 3 19 mMm _ aym 2 m m 2 where A VOP ye B v2 3 20 e c sina SE 3 21 VUE ye x8 az cosa Tp te 3 22 VE ym a am 65 Output Voltage Values for Result Estimating of Calibration Experimental Re sult Equation to is derived from Equation 3 1Lo d Vote VE ker AVor Kar 3 23 0 Vite Ve Kia AVi2 Kan 3 24 Oy Voc VP AV ga 3 25 Oy VES Mg AVja ky2
2. index x error y error z error index x error y error z error 1 0 003 0 384 1 431 11 0 046 1 505 0 591 0 033 0 046 2 065 13 0 263 0 356 1 389 0 225 0 161 2 602 14 0 511 0 363 1 947 0 651 0 202 2 588 15 0 638 0 198 2 344 1 121 0 025 2 268 16 0 564 0 006 2 494 0 510 0 380 2 267 18 0 350 0 249 1 406 0 581 0 835 1 487 19 0 176 0 239 0 331 10 0 367 1 244 0 214 20 0 014 0 045 0 860 ce oco cc AJo The differences between the position of the tooling ball in computation and the position of the ball in actual space are the error of detection Errors computed are given in Tablq3 11 and plotted in Figurd3 20 As the accuracy of detection required in 1 1 4 position errors on each axis of milling machine coordinate system should locate within the range of 1mm Two black lines in the Figurd3 20 are the boundaries of accuracy requirement Result points plotted in the figure should locate between two black lines If not the detection is not as accurate as is required 3 4 Evaluation and Analysis The accuracy of position computation is not satisfied according to Figurq3 20 All of position errors on the three axis of the milling machine coordinate system do not fully locate within the range of 1mm especially the value of z error on axis Zm In order to determine what is causing the low detec
3. 1 Connection between the detector and the sixth axis of the robot arm The detector is mounted on the sixth axis of the robot arm and the mechanism for the connection needs to be designed There are two requirements in the design process e The torch for welding task should not be removed when detecting the tooling ball because of the complicated assembly work of the torch In the other hand the detecting process should not be affected by the torch e The detector should be able to be connected with the robot arm quickly and conveniently in order to increase work efficiency Tooling ball detection is just a small part of the entire welding task so it is not necessary to spend a lot of time on this 2 Cables among components for signal transmission and power supply Both joystick and electrical components require a 5V DC power supply This is provided by the USB port of the robot controller and cables are required to be assigned The joystick moves with the robot arm so the cable that provides power should be securely attached to the robot arm for the convenience of the detecting operation Lots of signals are to be transmitted among components The selection of cables for signal transmission and connecting method between cables and ports are important for securing the transmission quality and operation durability 3 Software integration The softwares engineer at Tool Tec Welding Inc developed an application for auto matic TIG
4. 5 99 5 80 9 10 52 10 99 10 75 9 70 9 94 9 82 10 6 94 7 45 7 20 12 81 12 90 12 85 11 2 50 2 98 2 74 14 44 14 50 14 47 12 1 35 1 16 1 26 14 81 14 75 14 78 13 5 94 5 89 5 91 13 76 13 65 13 70 14 9 98 9 98 9 98 11 34 11 24 11 29 15 1297 13 03 13 00 7 80 7 67 7 73 16 14 58 14 72 14 65 3 32 3 41 3 37 17 14 88 15 01 14 95 1 08 0 65 0 87 18 13 85 13 95 13 90 5 69 5 17 5 43 19 11 45 11 48 11 46 9 67 9 16 9 42 20 7 80 7 78 7 79 12 72 12 09 12 41 85 Table 3 8 Results of Detector Calibration Experiment index 60 L mm Az mm index 00 L mm Az mm 1 13 105 100 32 69 125 11 10 529 98 341 67 103 2 14 784 100 33 69 145 12 13 212 97 651 66 473 3 14 113 101 00 69 758 13 12 969 97 519 66 305 4 13 350 101 57 70 295 14 12 545 97 059 65 746 5 12 421 101 43 70 281 15 12 454 96 648 65 349 6 11 413 101 15 69 961 16 12 691 96 584 65 200 T 13 142 100 95 69 765 17 14 800 96 687 65 390 8 12 527 101 17 69 960 18 14 969 97 581 66 288 9 11 651 100 44 69 180 19 14 667 98 611 67 361 10 11 015 99 19 67 907 20 13 877 99 731 68 553 Table 3 9 Average Values of 60 L and Az at Calibration Positions 60 L mm
5. Data are processed following the steps described in Firstly all voltage signals are converted into deflection angles according to Equations and 3 41 as given in Tabld3 7 There are six voltage values obtained in each detecting position Four values 0 1 0 5 0 and 0 5 are computed from output voltage values measured from the joystick according to the result of joystick calibration experiment 3 2 2 d and 0 5 represent deflection angle of the joystick shaft about axis Xj 0 1 and 0 2 represent deflection angle of the joystick shaft about axis Y Therefore the smaller the value difference between 0 and 0 5 and the value difference between 6 and 6 2 the better the results for joystick calibration Figurq3 16 illustrates the consistency of angle computation The maximal difference of 0 is 0 51 and the maximal difference of 6 is 0 76 Secondly following Step 2 to Step 6 described in 3 3 4 we have 00 L and Az computed 84 Table 3 7 Results of Deflection Angle Computation index 621 amp s 02 2 f ei Our 1 3 41 3 28 3 34 14 44 13 68 14 06 2 0 07 0 43 0 25 14 59 13 91 14 25 3 5 22 5 67 5 44 13 62 13 06 13 34 4 9 18 9 62 9 40 11 11 10 71 10 91 5 12 15 12 59 12 37 7 54 7 17 7 35 6 13 82 14 25 14 03 3 03 2 75 2 89 7 14 06 14 52 14 29 1 01 1 47 1 24 8 12 95 1340 1317 5 62
6. Min 3 46 Zp cL z op Az 1 1 Step 4 Solve 00 as Equation B 47 00 atan2 xTop YTcp o 3 47 where atan2 is a function in Matlab 16 82 Step 5 Solve L as Equation 3 48 L tTop va 0 sin 00 a 3 48 Step 6 Solve Az as Equation 3 49 Az r cL Sen 3 49 Equations 3 47 and are derived from Equation Any detecting position with op 0 cannot be selected for calibration because when rib 0 00 and L will be zero in Equations and 3 3 5 Detector Testing Detector testing is aimed at testing the performance of the detector including the operating condition of the mechanical components and the accuracy of detection Firstly the position of the tooling ball to be detected should be known Secondly the coefficients for position computing should be obtained from the detector calibration process Finally the position of the tooling ball obtained from the computation process should be compared with the position value that is known The procedure for detector calibration and detector testing are the same so the data obtained in the detector calibration process can be used for detector testing There are twenty groups of data obtained Four groups of the data are used for detector calibration and the other 16 groups are used for detector testing 83 ar amp x M ad l d N l a Index Figure 3 16 Consistency of Angle Computation 3 3 6 Results of Data Processing
7. values of two groups Deflection angle computation 1 y2 and V5 After obtaining voltage outputs for joystick V1 Viz V 0 and 0 can be computed using Equation and 3 41 Values of kz ba kyi ky2 and val ys VV V2 are listed in Tabld3 1 the deflection angles 71 Ox 05 Ball 3 40 where Bau Vi V2 ke1 O22 ER Vi Kaa 0 Oyi 0y2 2 3 41 where Oy ia VID ky 0 2 Vir Mx V Kye 3 3 Detector Calibration and Testing 3 3 1 Objectives of Detector Calibration Experiment The objectives of the detector calibration experiment are to determine unknown coefficients for position computation As mentioned in Chapter 2 there are ten coefficients in Equation for tooling ball position computation These coefficients are described below 1 Deflection angles 0 and 6 Two coefficients depend on deflection angles of the joystick They can be computed according to the output voltage values center voltage outputs and slopes obtained from the joystick calibration experiment Therefore they are known values in Equa tion after the joystick calibration experiment 2 Distance from the deflection center of the joystick to the spherical center of the tooling ball L Once the parts of the detector have been machined measured and assembled this parameter only depends on the diameter of the tooling ball to be detected Before 72 locating the tooling ball on the mould the d
8. e Considering the accuracy requirement of tooling ball detection optical sensing or vision based methods are too accurate which is not necessary As a result the mechanical touching method is chosen to be developed because of the following advantages e The method for position computation is deterministic e Mechanical components are cheaper and more robust than optical sensors and vision devices e Applying standard parts the mechanical touching style detector can be easily re paired when some components are broken In conclusion in light of the shortcomings of current methods that have been developed and applied it is valuable to develop a new mechanical touching style tooling ball detector for mould calibration of the automatic TIG welding process 18 1 3 Chapter Summary 1 3 1 Brief conclusion of Chapter 1 In conclusion this research will develop a mechanical contact style tooling ball detector for an ABB welding robot in the mould calibration process of automatic TIG welding The detector should be able to sustain a high temperature working environment within the time of operation and the position of the tooling ball s spherical center detected by the detector should be sufficiently accurate according to the requirements of the mould calibration process The operation and cell system design of the detector should be suitable to be integrated by the whole TIG welding system And finally under the condition of ach
9. fit data with curves by Levenberg Marquardt fitting method which is a kind of least square fitting method and output result 15 The result of fitting contains amplitudes A A and phases Qi Ay for each data set According to Equation 3 20 A represents the value of tan fr Since 0 does not change during the rotation of indexing head ideally speaking values of A that are computed from four signals in each group should be the same and the eight values of should also be 70 Table 3 2 Amplitudes and Phases Offsets of Data in Group 1 Ari Ayi e Qyi Goodness of Fitting RM SE As 0 2387 0 13 4253 a4 58 47 0 01580 Au 0 2408 0 13 5391 agg 58 03 0 01535 Ay 0 2381 0 13 3928 ay 58 34 0 01409 Aya 0 2440 0 13 7122 ayo 58 35 0 01983 Table 3 3 Amplitudes and Phases Offsets of Data in Group 2 35525 eg Qyi Goodness of Fitting RMSE As 0 1934 6 10 9459 agi 58 43 0 01727 AA 0 1950 0 11 0342 a2 57 94 0 01876 Ay 0 1918 6 10 8575 a1 58 39 0 01268 Aya 0 1969 6 11 1390 amp y2 58 39 0 01049 the same in the two groups of data Therefore considering the data in Tabld3 2 and the values of A and o are reasonable The average value of H is 13 5175 in group 1 and 10 9942 in group 2 The average value of a is 58 29 which is computed from eight
10. shape reflection image of the tooling ball within the two images is the tm object in J and the tn object in In The center position of the target object s fitting circle is utilized for finding dark points 106 Substep 3 7 Look for eight dark points within the dark region of the tooling ball for two photos Substep 3 8 Find the fitting circle of eight dark points for two photos Substep 3 9 Define the fitting circle s center position of eight dark points as the approximate center position of tooling ball within the photo frame 4 4 3 Transformation from Photo Coordinate System to World Coordinate System The position transforming procedure cannot be implemented in this project because of the limitation of equipment The light source and camera used for the experiment are not set exactly the same as is required Also the devices are not able to be mounted on the ABB robot Therefore the method for position transformation is described in general without being tested Firstly after analyzing the two photos the position of the tooling ball s spherical center within the photo frame of the two photos is known as P pay pyi and Pproto pxo pya Also the positions of camera for taking the two photos in theworld coordinate system are recorded as C qu yS z8 1 and C qu Be uL The focal length of the camera s lens is also known as f Secondly suppose there is a transformation matrix T representin
11. 3 26 Considering Equations 3 18 and 3 19 and Equations 3 23 to 3 26 the voltage values of the output signals can be written as Equations 3 27 to 3 30 3 30 K arctan A sin ogi q He VA 3 27 ve arctan Agosin ae2 v eo VA 3 28 Ve farctan Ay1 cos ay1 pi ky V 3 29 3 30 Vi arctan A cos ay2 q yo V out Method for Data Processing Parameters H d and the corresponding parameter Or in Figurd3 9 are related as relation ship where subscript i refers to group number This can be used for processing data from the calibration experiments in order to obtain values for Kan k Eu and ky Two groups of 66 outputs are measured at two different heights of the working table following the calibration procedure previously described For the i group of data 0 Osi when 0 0 and 0 0r when 0 0 This means that the maximum and the minimum output voltage values of signals represent the same deflection angle 0 As a result we have Equation 3 32 to 3 35 for computing 0 from the two groups of data bja maz Vz1 min Vz4 2 VE ka arcsin d H 3 32 6 maz V22 min Vz2 2 VZ kaz arcsin d H 3 33 65 Test d min VZ 2 TK arcsin d H 3 34 65 Test d min V2 2 BLK arcsin d H 3 85 Because the z values of the milling machine at each measuring position
12. 5 5 mm maximum thread depth from rear side 5 5 mm profondeur de vissage maximale partir de la partie inf rieure Analog analogue jeweils X und Y Achse each X and Y axis Zur Erkennung der Mittel In order to obtain a centre Stellung m ssen die Ana position signal the analogue logignale der X und outputs from both the x and Y Achse ausgewertet yaxes must be evaluated werden typ Wert 25 V analogique axes X et Y point milieu r el 2 5 V Point milieu pour l axe X Point milieu pour l axe Y Der Winkelmessbereich betr gt 15 Das Messprinzip ist kontaktlos beim analogen Messprinzip dreht sich ein Magnetfeld um einen Hallsensor Bei analoger Ausf hrung ist das System kurzschlusssicher bei unbegrenzter Kurzschlussdauer gegen Spannungsversorgung J1 ist mit 6 8 10 oder 12 PIN Molex 5557 Stecker ausger stet Alternativen auf Anfrage Technische Anderungen vorbehalten We reserve the right to change specifications without notice Sous r serve de modifications techniques The angular operating range is 15 The operating principle is non contacting analogue rotating magnetic field over hall sensor Short circuit proof with analogue version short circuit duration unlimited toward power supply J1 has a 6 8 10 or 12 PIN Molex 5557 connector alternatives on request Kabels tze siehe S 366 L2 D001A Cable sets see p 366 L2 D001A Cables associ s voir p
13. Az mm Average Value 13 9845 98 9045 67 6933 for each group of data using values of 0 and 6 in Tablq3 7 Results of computation are shown in Tablq3 8 and plotted in Figurq3 17 and respectively Thirdly select the 2 4 7 12 and 17 detecting positions as positions for calibration The other positions are used for testing the detector Compute average values of 00 L and Az at calibration positions are the final result of calibration and they are given in Tabld3 9 Finally use results in Tablq3 9 and the other 16 groups of deflection angles in Tabld3 8 to compute positions of the tooling ball according to Equation We also have positions of tooling ball computations shown in Tabld3 10 86 Figure 3 17 60 Figure 3 18 L 87 Figure 3 19 Az Table 3 10 Results of Detector Calibration Experiment index TC P TCP TCP index TCP TCP TCP 1 0 003 0 384 9 356 11 0 046 1 505 7 334 3 0 033 0 046 9 990 13 0 263 0 356 6 536 4 0 225 0 161 10 527 14 0 511 0 363 5 978 5 0 651 0 202 10 513 15 0 638 0 198 5 581 6 1 121 0 025 10 193 16 0 564 0 006 5 431 8 0 510 0 380 10 192 18 0 350 0 249 6 519 9 0 581 0 835 9 412 19 0 176 0 239 7 593 10 0 367 1 244 8 139 20 0 014 0 045 8 785 88 Table 3 11 Errors of Tooling Ball Position Detection mm
14. Bo ete oe ee eee ee RAE RS MR BUS 91 T ZI Relationship Between Lam Correspondent Positions NS E EE 93 Sd ek Bk rrr 96 4 2 Position Relationship among the Camera Light Source and the Tooling Ball 97 A Ce ey ID UR E IRE HOP ace oe Er S 99 Tr 100 Seg ce ee ay Gr alae eG ne Gs es ee Ge ee EE 104 ee ae EEN 105 4 7 8 Dark Donal wo hw oe PH ae he wae wo Bre ee eS 105 oa RR E a as 108 4 9 A Sample Image for Describing Center Deviation 110 ay ek SEE Se Sa ae SU A EE E EE E 110 xii A 1 JIRGAAADOO Copied from Elobau Sensor Technology 118 A 2 J6R6AA A00 Copied from Elobau Sensor Technology 119 A 3 B3F5000 Tactile Switch Copied from Omron Electronic Components LLC 120 xiii Chapter 1 Introduction In the ABB welding system for automatic TIG welding the spherical centers of tooling balls can be considered as reference points in robot working space Place tooling balls on the mould detect positions of spherical center of tooling balls in robot working space then position information can be applied by robot for calibrating the position and orientation of the mould in robot working space Applying a fast tooling ball detecting method in mould calibration procedure can increase the efficiency A fast one time mechanical touching tooling ball detecting method is developed and the method will be introduced in this thesis This chapter introduces the background and direction of the research The
15. Evaluation and Analysis auos ler ee ee wa eS xc xe Xs 89 95 EI Hardware CG arica E enio or a ea ad A 96 4 2 Optical Characteristics of Tooling Ball 2 4 2 ee eae NEEN e 98 p cC 98 CHER 100 4 4 1 Predescribed Concepts o 100 106 ba chy Bee Oe ee bea eee ates 107 4 5 Experiment and Result Seas eee BAe ee Ree ER CEE OR S 108 46 Chapter Span ie ee ee ee Rim ee ROS E EE KS 109 vil 5 1 Thesis Summary E ee EE e Re e REOR A RU 5 2 _ F t re WOTK os ebe ta er Aerer e Ge ee RN EE tek un APPENDICES A Technical Specifications of Joysticks and Tactile Switch B 1 Program in Microprocessor B 2 RAPID Code for Computational Component Bibliography viii 112 112 115 116 117 121 121 130 137 List of Tables 3 1 Results of Joystick Calibration Experiment 68 3 2 Amplitudes and Phases Offsets of Data in Group 1 71 3 3 Amplitudes and Phases Offsets of Data in Group 2 71 3 4 Ideal Detecting positions of TCP mm 78 3 5 Actual Detecting positions of TCP mm screens 81 Sh ee ee ROME ee ee a eee NS 81 ee rane ae eae RR NOR we BUS 85 3 8 Results of Detector Calibration Experiment 86 I ur 86 3 10 Results of Detector Calibration Experiment 88 3 11 Errors of Tooling Ball Position Detection mm e a aaa 89 ix List of Figures Ll Robot Cell Setting
16. L cos 0 sin 0y l L cos 0 sin 0 Pi di _ y Ty Pr gb L cos 0 cos 6 1 1 cosy sing 0 d ED cosy y sin p r5 B sing cosy 0 y y cospi 17 sin qi UP 3 11 0 0 1 g zp 0 0 0 1 1 and so we have Equatioxf3 12 ai zB 27 cos pi yp ym sin pe l yP y cos pi a 2 sin pi N TREZ sin ps 3 12 E Es 1 Then we can equate the two equations for PI as shown in Equation 3 13 63 L cos 6 sin 0 al 2 xa cos p yg y sin p L cos 0 sin 6 J y y cos qi 2 27 sin icc sin 6 _ ye YP ye cos gpi xp sin pe 3 13 L cos 0 cos by SE 1 1 Solve Equation and the deflection angles of the joystick can then be obtained by Equations and 3 15 respectively j j m ym TTT sin 0 arctan 2 arctan EE a 2 mm T p c where sgn 0 sgn yp sgn yi yP ye cosp vp a7 sime 3 14 j j m m m Mia 0 arctan 2 arctan T xp Te cos Pt yp Ye sin E z zm zm P p c where sgn 0 Suna sgn zi p xg cosy y ye sin el 3 15 Equations and can also be simplified into Equations and 0 arctan A sin a p B here 4 YEAST E GR amy EE B WV Zp T Em sina E vg v9 sg any cosa al 3 16 V yR ym 2B am 64 0 arctan Acos a ps D VE CP T epum
17. Welding Process Simulation Welding simulation is necessary for analyzing programs of robot control to avoid conflicts in the actual welding process If conflicts arise in the simulation process the actual welding task can not be carry out and the welding tool path should be rebuilt until the simulation pass Mould Calibration The mould calibration process aims to obtain the transformation matrix from the CAD coordinate system in the CAD space to the world coordinate system in robot space Within the project the SVD algorithm based on least square method devel oped by Arun et al 5 is applied in solving the calibration problem popaceNamey means a point set in space SpaceName The first step of the mould calibration procedure is to select several reference points on the surface of the mould in CAD space obtaining the point set PAP Next the operator operates the robot arm carrying the detecting tool to detect reference points in robot space and obtaining the point set UR under the condition of existing detecting error Viper The algorithm supposes that there is a fixed linear relationship between positions of points in robot space and in CAD space represented by Equation Risa rotation matrix and T is a translation matrix P 4 is the point set in CAD space and Pre is the point set in robot space corresponding to P 4 Since the existence of the detecting error the point sets PGP and P787 can be fitted 10 Moul
18. Xm and Ym of the milling machine until values of xp and y gp become almost the same as the data in Tabld3 4within the range of 0 1mm Coordinate values of TCP of the milling machine are displayed on the LCD screen with three significant digits which can be read directly and be recorded manually 2 Twenty groups of voltage outputs of the joystick at which the digital signal is acti vated see Tablq3 6 After recording the position of TCP at each detecting position multimeter is used for measuring output voltage values of the joystick The voltage values are measured by the multi meter with three significant digits 80 Table 3 5 Actual Detecting positions of TCP mm index t YTOP rop index Top VTCP ZTOP 1 24 990 0 005 20 100 11 24 965 0 010 20 085 2 23 770 6 715 20 170 12 23 770 7 705 20 000 3 20 230 14 695 20 145 13 20 200 14 670 20 010 4 14 690 20 225 20 175 14 14 690 20 160 20 070 5 7 745 23 770 20 060 15 7 730 23 770 20 040 6 0 005 24 990 20 120 16 0 005 24 990 20 160 T 7 730 23 775 20 115 17 7 735 23 745 20 090 8 14 700 20 230 20 115 18 14 685 20 235 20 085 9 20 210 14 685 20 125 19 20 195 14 700 20 055 10 23 8050 7 710 20 110 20 23 775 7 730 20 025 Table 3 6 Volta
19. a circle through direct least squares circle fitting algorithm by V Pratt 18 This circle is called the fitting circle of this object The fitting circle is described by three parameters position of circle center and its radius In the process of implementing the circle fitting algorithm the direct circle fitting function is programmed by Nikolai Chernov in Matlab according to V Pratt s paper Position of Object The position of the object s fitting circle center is the position of the object Geometry Properties G Property of an Object An object within a photo has six geometric properties similarity area compactness contour number fullness and the radius of fitting circle G property 1 Similarity TL Similarity M D R nR 4 1 i l where Dj CP Equation describes the degree of the fitting condition between the object and its fitting circle Parameter D is the distance between object pixels P and 101 the center C of the object s fitting circle and parameter R is the radius of the fitting circle There are n pixels in total belonging to the object G property 2 Area Area is the size of the object measured by its number of pixels G property 3 Compactness Compactness Areaoyjea ATEA FilledCircle 4 2 Compactness of an object is not able to be affected by the object s scale Thus it is useful for distinguishing an object with specific shape As shown in Equa tion parameter Area
20. detecting detecting finish locating well locate Detectecting Process Figure 2 2 Illustration of Tooling Ball Detecting Process 25 Deflection surface about Y Figure 2 3 Joystick the minimal output value when the shaft is deflected to angle a V is the output voltage when the shaft is not deflected According to the voltage outputs that represent deflection angles of the shaft about X and Y it is easy to compute the position of a point that locates on the center axis of the shaft As shown in Figurq2 4 0 and 6 are defection angles of about X and Y that are obtained from output voltage signals P is a point located on the center axis of the shaft and the distance from O to P is L L is positive when P located on X7 vice versa The position of P in joystick coordinate system can be computed by Equation 26 a Th L cos 0 sin 0 m y B L cos 6 sin 0 2 3 e L cos 0 cos 0y 1 1 If we let the spherical center of a tooling ball be located on the center axis of the shaft which is the same condition as the point in Figurq2 4 according to Equation 2 3 the position of the tooling ball s spherical center within the joystick coordinate system can be computed Also the transformation from the joystick coordinate system to the detector coordinate system is decided when the whole detector is manufactured and assembled and the position of the tooling ball in the detector coordinate system can be
21. of the working table are recorded as Z4 and Za at Step 6 and Step 7 the difference between H and H can be computed as AH AH AH Z2 Z4 Thus we have Equation to 2 V k arcsin d Hi 2 V Mk arcsin d H AH 3 36 2 VZY k arcsin d Hi 2 V k arcsin d H AH 3 37 2 V jk arcsin d Hi 2 V k arcsin d H AHT 3 38 2 VP ko arcsin d Hi a Phe a m hen na Ss Ld e 8 no no ro e ro noO no lt ar SS n wa A 3 PES wo S Go ros PATOS Lom yo e m E n wn mn 2 V ky arcsin d H AH 3 39 67 Table 3 1 Results of Joystick Calibration Experiment vet y22 yy yy 2 55V 2 56V 2 55V 2 53V ka kso ky ky2 0 0836 0 0828 0 0828 0 0812 There are only two unknown values k 1 kz2 ky1 ky2 and H in each group with only two equations Thus kz1 ke2 ky1 ky and Hy can be solved 3 2 2 Result of Joystick Calibration Experiment The recorded data for the two heights are plotted in Figurd3 10 The horizontal axis is the values of y ranging from o to 364 and the vertical axis is the output voltage values of joystick V According to Equation 3 27 to it is known that phases and periods of output voltage values VI and VO are the same with opposite values to the center output T T voltage values Output voltage values V1 and V 3 have the s
22. output relationship of the joystick would not need to be re calibrated Furthermore the data from Elobau Sensor Technology regarding the joystick can even be used to evaluate the performance of the design of the joystick calibration e More research about error analyzing is required Errors exist in the mechanical machining and assembling process the AD conversion and signal communication process and the position data of the ABB robot obtaining process How these errors affects the final result of position computation needs to be analyzed e Integrate the tooling ball detecting system with the whole ABB robot system and test the performance Though the mechanical component has been tested on the NC milling machine the settings of the joystick coordinate system the detecting operation the calibration of the detector and the working environment all need to be changed if the detecting processes are tested in the robot system e Test the detecting method on tooling balls with different dimensions The detecting method is tested based on only one tooling ball with a diameter of 15 85mm It is necessary to test it on a differently dimensioned series of balls to obtain the detecting range and the range of tooling ball sizes that can be detected by the detecting method Finally a vision based tooling ball detecting method is also taken into consideration to compensate for the performance of a mechanical style touching style detect
23. shaft extension in order to avoid generating scores on the shaft extension caused by the bearing balls e Using multi meter with a higher accuracy to obtain better voltage measuring results Electrical components and computational components have been programmed and tested on a personal laptop without being tested in an actual robot system Further experiments and improvements are still required e Improving the AD conversion process and serial communication process For AD conversion and serial communication purposes an ARM7 microprocessor is not the best choice However it is the most convenient choice for testing the feasibility It is better at selecting better chips for achieving these two processes The converting accuracy of an AD converter in a microprocessor is just 10 bits and the maximum convertible voltage input is only 2 48V If we can specialize the AD conversion process by a chip with higher accuracy and convertible voltage value MAX187 with 12 bits accuracy of conversion for instance the electrical component can be designed to be more integrated and more durable e Stabilizing the operating voltage supplied to the joystick at 5V by DC stabilizer A cell phone charger was used to provide DC power to the joystick The output voltage is 5 11V which locates within the range of allowance However if the voltage was stabilized to 5V as was recommended in the technical specifications of the 113 joystick the input
24. than 128 will always exist within the image and these pixels will appear as a shape C shape similar to the shape of the light source The position of reflection image within the photo can be considered an approximate position of tooling ball R Property 2 The gray values of the pixels which are close to the high gray value pixels appear dark the gray value is always lower than 128 because the reflected ray at these regions cannot be captured by the camera R Property 3 The gray values of pixels which are surrounding dark regions of the tooling ball are much higher than the dark regions A sample of the reflection image of the light source is shown in Figurd4 3 99 r photo Photo x Gi Let L R photo Figure 4 4 Pixel in Photo Coordinate System 4 4 Vision Based Tooling Ball Detecting Method De sign 4 4 1 Pre described Concepts e Photo Coordinate System Figurd4 4 defines the photo coordinate system of a photo The position of a pixel within the photo can be defined by a pair of coordinate values e Object Pixel and Background Pixel 100 All the values of elements in the binary image are binary numbers 1 and 0 Binary number 0 represents a background pixel of the color black and the binary number 1 represents an object pixel of the color white Objects If a group of object pixels are called one object they are 8 connected 16 Fitting Circle Fit pixels of an object into
25. the outside Vectors and Y positive axis of the photo form angles from 0 to 135 with a step increase of 45 Eight dark points are the dark points along these eight directions Figurd4 7 illustrates one of the examples of these eight dark points 105 4 4 2 Procedures for Acquiring Position of Tooling Ball in Pho tos A simplified and specialized vision based tooling ball detecting method is designed as following steps Step 1 Set the camera and the light source Step 2 Take two photos for the tooling ball from two different positions Two photos J and are acquired and then record two photos taking places in the world coordinate system as Ci qu a z8 1 and C i qu qu ZM cq respectively Step 3 Process and analyze two photos J and Io Substep 3 1 Apply average filter to get two filtered images 1 and Ja Substep 3 2 Threshold and La using threshold value of 128 into two binary images Ju and Substep 3 3 Segment Jo and I into several binary images with only one object inside Delete objects whose areas are less than 1 1000 of the whole image size The remaining objects are called the main objects of the two images Substep 3 4 Compute the G properties of the main objects Substep 3 5 Compute the difference matrix Muer using the G properties of the main objects Substep 3 6 Find out the index itm itn of the element in Majrr with the minimal value We say the target object C
26. the tool coordinate system Secondly there is a translation from the tooling coordinate system to the joystick coordinate system followed by a rotation about the axis Z Then according to Equation the position of the tooling ball in the milling machine coordinate system can be computed by Equation The milling machine coordinate system is simply the world coordinate system discussed in Chapter 2 The position of the TCP in the world coordinate T system is then represented by TCP instead of TCP m m m Trop UTCP trop 1 T 10 Ww w En YTCP TCP 1 78 Contour of the cone surface Figure 3 15 Positions of TCP for Tooling Ball Detection E L cos 00 cos 6 sin 0y sin 00 cos 0 sin 0 len Ax ja L sin 00 cos 0 sin 0 cos 00 cos 0 sin 0 Yap Ay 3 43 e L cos 6 cos 6 27 Gp Az 1 Equation is simplified into Equation 3 44 79 r5 Ly a b sin 60 a zpop Ax m L a b cos 00 a yap A pm UP _ Yop y 3 44 zb cL zpop Az 1 1 where a cos 0 sin0 b cos6 sin 0 c Co cos sina a va b cosa b Va P 3 3 4 Method for Data Processing After the detector calibration procedure we have the following data and equations 1 Positions of TCP at 20 detecting positions at which the digital signal is activated see Tabld3 5 Twenty detecting positions are predetermined in according to positions in Tabld3 4 Operate the position of table on axes
27. the work pieces surface is smaller than 1 3 in most cases Geometrical characteristics of image formation are totally different between the two types of reflection surfaces A light source with special shape will form different reflection images on two different types of surfaces 17 O Difference 2 Since the spherical surface of a tooling ball is fine polished the surface smoothness of a tooling ball is always higher than the surface of a work piece As well the surface of a tooling ball is always closer to the light source than the work piece As a result the gray level of the pixels in the image which is formed by reflecting light from the tooling ball is one of the highest areas of pixels within the image Moreover dark regions with high contrast to the region where the reflection image is formed will also be formed on the tooling ball s spherical surface around the brightened region 4 3 The Reflection Phenomenon According to the mirror reflection principle of light 17 if the stainless steel tooling ball is located within the lighting environment which is described below a C shape reflection 98 reflection image bright region dark region reflected ray not being captured Figure 4 3 Reflection Image image of the light source will be formed on the tooling ball s spherical surface with the following three properties R Property R Property 1 A group of high gray value pixels always higher
28. welding tasks It is installed in the FlexPendant for the operator to carry AT out All of procedures of the automatic TIG welding task can be achieved by run ning the application Tooling ball detection is one of the steps in the task of mould calibration The program programmed for a computational component should be integrated by the application and this is the software integration of cell detecting system 2 8 Chapter Summary Other than for the integration process the new tooling ball detecting method is designed and implemented and it is theoretically described in this chapter As mentioned in four slopes of joystick output signals are to be obtained by the joystick calibration process and five coefficients need to be calibrated by the detector calibration process Experiments for joystick calibration and detector calibration are designed and will be described in the next chapter In addition the next chapter also describes the simulation of the tooling ball detecting process and evaluates the detecting method designed 48 Chapter 3 Calibration and Detecting Test The joystick needs to be calibrated in order to obtain the slopes of the input output curves for deflection angle computation The detector also needs to be calibrated to obtain un known coefficients Calibration experiments are designed to achieve these targets They are described in this chapter and include the calibration mechanism experimental procedure math
29. 1 VICVectAddr 0x00 void __irq IRQ_Eint3 void extern ADCmark ADCmark 0 while EXTINT amp 0x08 0 EXTINT 0x08 VICVectAddr 0x00 uint32 ADC_Data 4 uint32 SendData 14 uint8 ReceiveData 14 UARTO buffer for receiving data uint8 ADCmark uint8 SendMark int main void const uint32 baud 19200 uint32 mid mid number for computing baud rate uint8 s loop counter of UARTO data sending uint8 r loop counter of UARTO data receiving PINSELO PINSELO 0x00000005 126 UARTO and GPIO PINSEL1 PINSEL1 0x15400301 ADO O ADO 3 EINTO KEY1 and EINT3 KEY5 PINSEL2 PINSEL2 0x00000000 LEDO LED8 GPIO IOODIR 0x01 lt lt 7 DelayNS 200 BEEP IOOPIN IOOPIN 0x01 lt lt 7 stop beeping IO1DIR OxFF lt lt 18 LED IO1PIN OxOO lt lt 18 Turn on all LEDs initialization of UARTO setting of baud UOLCR 0x80 mid Fpclk 16 baud UODLM mid gt gt 8 UODLL mid amp OxFF UART initialization UOLCR 3 lt lt 0 3 gt 8Char 0 2 0 1 stop 1 2 stops 1 lt lt 3 0 diable i enable odd even 1 lt lt 4 odd even selection 0 lt lt 6 0 disable 1 enable interval sending 0 lt lt 7 divider lock FIFO setting UOFCR 0x81 UOIER Ox01 IRQ Setting 127 EXTMODE 0x00 set EINTO and EINT3 activated by level EXTPOLAR 0x00 IRQEnable E
30. 366 L2 D001A 118 Le d battement angulaire est 15 Le principe de mesure est sans contact analogique champ magn tique tour nant sur d tecteur a effet Hall Prot g contre les courts circuits avec version analogique dur e de court circuit illimit e en sens alimentation J1 est quip avec 6 8 10 ou 12 broches Molex 5557 alternative sur demande 285 Figure A 1 JIR6AAA00 Copied from Elobau Sensor Technology Joysticks www elobau com Joysticks Joysticks Joystick kompakte Bauform Joystick compact design Joystick version compacte x Achse x axis axe x St 82 83 nl y Analog analogue 0 95 nle 25 100 gt jeweils X und Y Achse each X and Y axis lt WH UWA zer Erkennung der Mittel In order to obtain a centre BN oV stellung m ssen die Ana position signal the analogue Lol Mol een outputs from both the x and Y Achse ausgewertet y axes must be evaluated werden typ Wert 2 5 V H I analogique axes X et Y point milieu r el 2 5 TII point milieu pour l axe T E Point milieu pour l axe Y NE a N BN Digital digital rS Si aK leweilsX undY Achse each X and Y axis H S i BK LB BU Su Erkennung der Mittel In order to obtain a centre E 282 WH stellung m ssen be
31. Basic Rule for Tooling Ball Detecting Method Design 3 2 2 Cell System Design 2 3 Mechanical Component Design 2 3 1 Analog Biaxial Joystick sas Dans 49 3 5 OX eed RE n 2 3 2 Detecting Part cojea rear Ree Ba eed op RR 2 4 Implementation of Mechanical Component e 2 4 1 Version 1 2 42 Version 2 2 5 Electrical Component Design seas mca AE ee aw e 2 6 Computational Component Design e 2 6 1 Compute Deflection angles of joystick P EE Aa Fa ee peed eee PA wp a 2 8 Chapter Summary Calibration and Detecting Test 3 1 NC Milling Machine with Indexing Head amp Tooling Ball 3 1 1 NC Milling Machine with Indexing Head 3 1 2 Tooling Ball vi 20 20 22 23 24 at 27 30 33 36 38 41 43 43 46 46 48 49 3 2 Joystick Calibration oa EE EE AAA A 52 3 2 1 Method for Joystick Calibration 048 54 3 2 2 Result of Joystick Calibration Experiment 68 3 3 Detector Calibration and Testing e 72 3 9 1 Objectives of Detector Calibration Experiment 72 3 3 2 Detector Calibration Procedure ls sn 75 3 3 3 Transformation PROCESS 30e oce Gee ww eG C UR EOE TR 3 3 4 Method tor Data Processing as S AN Bae ad RR n 80 3 3 9 Detector esting s raras x e E AA ro X eas 83 3 3 6 Results of Data Processing ess ANN peras aoe ew wed 84 3 4
32. ByteCL 14 VAR string OutStrSA 14 VAR num OutByteSA 14 VAR string OutStrOK 14 VAR num OutByteOK 14 VAR iodev channel PRES bool flag VAR pos TCPpos VAR num TCPx VAR num TCPy 130 VAR num TCPz VAR bool RecChec PERS string rec VAR string recl VAR string rec2 VAR string aVstr1 VAR num aVnum VAR string bVstr1 VAR byte bVbit VAR string bVstr2 VAR num bVnum VAR bool TempChec VAR num Vnum 4 VAR num k 4 VAR num Vcx VAR num Vcy VAR num Amax VAR num Ax VAR num Ay VAR num L VAR num dx VAR num dy VAR num dz 131 VAR num dt PERS num X PERS num Y PERS num Z PROC main BallNum 0 FOR i FROM 1 TO 14 STEP 1 DO OutStrCL i StrPart CL000000000000 i 1 OutByteCL i StrToByte OutStrCL i Char ENDFOR FOR i FROM 1 TO 14 STEP 1 DO OutStrSA i StrPart SA000000000000 i 1 OutByteSA i StrToByte OutStrSA i Char ENDFOR FOR i FROM 1 TO 14 STEP 1 DO OutStrOK i StrPart 0K000000000000 i 1 OutByteOK i StrToByte OutStrOK i Char ENDFOR Open comi channel Bin ClearIOBuff channel Clear input buffer for comi flag TRUE WHILE flag TRUE Do Voltage string receiving RecChec FALSE WHILE RecChec FALSE ClearIOBuff channel Clear input buffer for comi 132 reci ReadStrBin channel 14 1600 Wait for input from comi rec2 ReadStrBin channel 14 600 Wait for input from comi IF reci lt gt rec2
33. Change the position of the TCP and detect the tooling ball to obtain voltage signal outputs Record voltage values at each detecting position and position the TCP when the digital signal is activated Use the multi meter to measure the resistor of the tactile switch once the resistor changes from infinite to a very small value the digital signal is considered as being activated The position of the measured locations should follow the x and y values of the TCP as shown in Tabld3 4 and as 76 Fixed by the tool holder of milling machine Fixed by the fixture of indexing head Figure 3 14 Coordinate Systems in Detector Calibration Process TT Table 3 4 Ideal Detecting positions of TCP mm index or Vrop index trop YTOP 1 25 0 11 25 0 2 23 776 7 725 12 23 776 7 725 3 20 225 14 605 13 20 225 14 695 4 14 695 20 225 14 14 695 20 225 5 7 725 23 776 15 7 725 23 776 6 0 25 16 0 25 7 7 725 23 776 17 7 725 23 776 8 14 695 20 225 18 14 695 20 225 9 20 225 14 605 19 20 225 14 695 10 23 776 7 725 20 23 776 7 725 illustrated in Figurq3 15 The positions do not need to be exactly the same as the data in Tabld3 4 3 3 3 Transformation Process The transformation process is similar to the process in the ABB robot system Firstly there is a translation from the milling machine coordinate system to
34. Ng p 1 L L 4 Sang CL i Salle L 0 4 D e 10 12 14 16 18 2 Figure 3 21 Relationship between 0 1 8 2 and 0 1 0 5 and Correspondent Positions of TCP 10 ep 125 Figure 3 22 Relationship Between 90 and Correspondent Positions of TCP on Xm 91 102 101 Figure 3 23 Relationship Between L and Correspondent Positions of TCP on Ym 4 Sc K d to xs d DNO d i Je CDEN TENET ZE jette perti Be ifs L ROS i Figure 3 24 Relationship Between Az and Correspondent Positions of TCP on Ym 92 Figure 3 25 Relationship between Errors of Position Detection and Correspondent Posi tions of TCP the design of the joystick calibration process three deficiencies were found 1 Loose fit caused by using the screw connecting the centering shaft and bearing fixer The centering shaft and bearing housing are connected by an M3 40 socket head cap screw with nut The screw is also utilized as the shaft for the bearing housing to rotate about The distance between the center axis of this shaft and the center axis of the linear motion bearing d is one of the most important distances for slope computation The screw and the hole are loose fit so that distance d cannot be satisfied as the one designed in 3D modeling software 2 Scoring of shaft extension caused by the bearing balls The shaft extension is inserted into the linear motion bearing In the process of ro t
35. THEN WriteBin channel OutByteSA 14 ELSE rec reci WriteBin channel OutByteOK 14 RecChec TRUE ENDIF ENDWHILE TCPpos CPos Tool tool0 WObj wobj0 TCPx TCPpos x TCPx TCPpos y TCPx TCPpos z IVoltage translation FOR i FROM 1 TO 4 STEP 1 DO aVstri StrPart rec i 3 2 1 TempChec StrToVal aVstri aVnum bVstri StrPart rec i 3 1 2 bVbit StrToByte bVstri Hex bVstr2 ByteToStr bVbit TempChec StrToVal bVstr2 bVnum Vnum i aVnum 256 bVnum ENDFOR Iparameter value assignment k 1 k 2 0 5 0 5 133 k 3 0 5 k 4 0 5 Vcx 2500 Vcy 2500 Amax 15 FOR i FROM 1 TO 4 STEP 1 DO Vnum i Vnum i k i ENDFOR lAngle translation Ax Vnum 3 Vcx Amax Vcx Vcx Vnum 4 Amax Vcx 2 Ay L Vnum 2 Vcy Amax Vcy Vcy Vnum 1 Amax Vcy 2 IPosition computation a Cos Ax Sin Ay b Cos Ay Sin Ax c Cos Ax Cos Ay X a L TCPx dx Cos dt b L TCPy dy Sin dt Y a L TCPx dx Sin dt b L TCPy dy Cos dt Z c L TCPz dz BallNum BallNum 1 ENDWHILE Close channel ENDPROC ENDMODULE 134 Bibliography H 2 E Tool Tec Welding Inc Full Proposal Document 2007 William H Minnick Gas Tungsten Arc Welding handbook Goodheart Willcox Pub 1996 3 ABB Automation Technologies AB Robotics Operating manual IRC5 with FlexPen dant 2004 6 William W Melek ME547 Robot Mani
36. Tooling Ball Detecting Method Design for ABB Welding Robot in Automatic TIG Welding Process by Zhenhao Li A thesis presented to the University of Waterloo in fulfillment of the thesis requirement for the degree of Master of Applied Science in Mechanical Engineering Waterloo Ontario Canada 2010 Zhenhao Li 2010 I hereby declare that I am the sole author of this thesis This is a true copy of the thesis including any required final revisions as accepted by my examiners I understand that my thesis may be made electronically available to the public i Abstract This thesis provides the design process for a new tooling ball detection method to cal ibrate moulds in automatic TIG welding A mechanical component is designed to locate the tooling ball and convert the position information into analog signals An electrical component is designed to process signals from the mechanical component and achieve the signal communication process Finally the computational component is designed and programmed to receive bits from the electrical component and convert information into position values for the tooling ball The homogeneous transformation process is mathe matically modeled for position computation in a robot system The method is significantly different from current methods that have been developed and applied Firstly it uses a mechanical touch style operation to locate the tooling ball with only a one time detection
37. Xw Yw Zw the tool coordinate system X Y Z and the joy stick coordinate system X Y Z P is the spherical center of a tooling ball The transformation process from a world coordinate system to a joystick coordinate system is described by the following two transformations From X Y Zw to X Y Z there is a translation which is described by transformation matrix in Equation 43 Figure 2 14 Transformation Process in Robot System 44 j t Rotation Tj VS 100 Tier 0 1 0 ym f YTCP 2 8 0 0 1 zpop 000 1 From X Y Z to X Y Zj there is a translation followed by a rotation about the axis Z which are described by transformation matrixes in Equation 2 9 100 Az cos 0 sin 0 0 0 e 0 10 Ay sind cos 0 0 0 Ty Tg Ti 2 9 001 Az 0 0 1 0 000 1 0 0 0 1 Describes the position of a tooling ball s spherical center in the world coordinate system by P quoq ee 1 iP Describes position of a tooling ball s spherical center in the joystick coordinate system by PJ ah yb 2h 1 y They can be converted to each other in accordance with the relationship set forth in Equation 2 10 P Tn 1 0 0 on 100 Az oos 00 sin 0 0 L cos 0 sin 0 E 0 1 0 Wen 010 Ay sind cos 0 0 L cos 0 sin 0 20100 1 zy 10 0 1 Az 0 o 1 0 Lcos 6 cos 0 0 0 1 000 1 0 0 0 1 1 2 10 After computing the right side of Equation 2 10 the positio
38. all the parts Without his hard work all my designs would just be on paper His experience in mechanical design was very important to my research As well I wish to thank the Department of Mechanical Engineering and Ontario Centers of Excellence for providing me with a world class study environment And to my friends in Canada especially Jiheng and Zhiyue Vladimir and Murtasim I extend a big thank you for the advice on my research and assistance in my day to day life They have made my time here full of happiness and pleasure Finally I owe my sincere appreciation to my parents No words could describe how much I love them and no words could describe they ve shown their love for me over the past twenty five years of my life I thank everyone for all their help I truly appreciate it Contents List of Tables List of Figures 1 Introduction 1 1 Automatic TIG Welding Project 1 1 4 Mould Modification and TIG welding 1 1 2 Project of Automatic TIG welding 11 3 Direction of the research 1 1 4 Requirements for the New Tooling Ball Detecting Method 1 2 Current Methods for Position Measurement 1 2 1 Methods Currently Applied in the Project EE L3 Chapter Summa 1 3 1 Brief conclusion of Chapter 1 1 3 2 General Description of Other Chapters in the Thesis 1x xiii 2 Tooling Ball Detecting Method Design 2 1
39. alues at the position of each increment Step 6 Record z value of milling machine as Zi Step 7 Change the position of the working table in Z direction of the milling machine Repeat Step 4 and Step 6 to obtain a second group of output voltage values and another value of milling machine as Za Step 8 Process two groups of data obtained and figure out ka kz2 ky and kyo Transformations in Calibration Process There are three coordinate systems in calibration process as illustrated in Figurq3 8 e Milling Machine Coordinate System F Axis Zm is vertical to the ground pointing down Axis Ym points toward the operator and axis X follows the right hand rule e Joystick Coordinate System F The setting of F is the same as that described in Figurq3 5 e Indexing Head Coordinate System E Axis Z is vertical to the ground pointing down Axis X maintains the same direction as X rotating around axis Z and axis Y follows the right hand rule Plane X O Y coincides with plane X Oj Y From Fn to Fe the transformation process is a translation followed by a rotation The corresponding transformation matrix T nc is given in Equation 3 5 Tic describes the pose of F in Fm 58 Translation Translation Figure 3 8 Three Coordinate Systems in Joystick Calibration Process 59 1 0 0 r cosy sinyg 0 0 0 1 0 sin cos 0 0 Tao Ye Yt Pt 3 5 00 1 2 0 0 0 0 000 1 0 0 0 1 p is the a
40. ame condition as NP and Vs with Z phase difference Therefore Figurd3 10 shows that data obtained from the calibration experiment are reasonable Tabld3 1 shows the center position voltage outputs and the slopes of each signal computed from the data obtained from the experiment as described in 3 2 1 Two groups of data obtained from the calibration experiment follow Equations 3 27 to Knowing the slopes of each signal output voltages and angle of rotation the other four parameters Azi Ay and o Ou can be obtained using the nonlinear fitting tool box in Matlab by the following steps The results are given in Tables3 2 and The fitting curves are illustrated in Figurd3 11 Step 1 Create data set for two groups of data in the form of V vs p 68 xl Vat x2 yl D Vos ps D 9 y D BW HR t D D D D eco rrn K Ze Se Figure 3 10 Output Voltage Values of Joystick at Two Heights in Joystick Calibration Process 69 Group Group 2 N Group 1 Group 2 A Group 2 Group 5d Group 2 Group Figure 3 11 Fit to the Data of Joystick Calibration Experiment Step 2 Type cftool in Matlab to open the curve fitting tool box Step 3 Smooth data sets created previously in Step 1 Step 4 Select Custom Equations as the fitting type and input Equation to for fitting Step 5 For each smoothed data set of output voltage value
41. and the techniques for the mould adjusting process have a great impact on production efficiency The mould adjusting process can be achieved by NC machines to remove excess ma terials and by welding techniques to add missing materials TIG Tungsten Inert Gas welding also known as GTAW Gas Tungsten Arc Welding is a commonly used welding technique In the TIG welding process metal is melted by the heat from a current passing between the non consumable tungsten electrode and the workpiece During the welding process inert gas e g argon is continually provided preventing materials from reacting with atmospheric contamination By applying this technique almost all types of materials can be welded by TIG welding and the weld is clean and of high quality Unlike MIG Metal Inert Gas welding there are no pinholes in the welds and no sparks during the welding process However tungsten electrodes cannot sustain a high current the weld ing speed is limited and becomes time consuming According to data from experienced welders the speed of MIG welding is about 6lb hour while the speed of TIG welding in manual operation mode is only 0 5lb hour Another reason that limits the efficiency of TIG welding is that it requires skilled welders as it is a labor intensive process As a result in order to increase the efficiency of production while still maintaining the high quality of the weld methods for automatic robotic TIG welding are now being
42. ating the indexing head the shaft extension keeps rotating in the bearing However the hardness of stainless steel balls is much higher than the hardness of the shaft ex tension which is made of 1045 without being heat treated After rounds of rotation 93 the shaft extension is broken by the balls of bearing and the coaxiality between the shaft extension and the linear motion bearing decreases The combined deflection angle 0 can not be maintained the same in the whole rotation process 3 Low accuracy of multi meter for measuring the output voltage signals Finally the accuracy of multi meter for measuring the output voltage signals is too low with two significant digits to secure the accuracy of the voltage value measure ment Future works is required to improve these three deficiencies in order to achieve better results from the joystick calibration experiment 94 Chapter 4 An Extension Optical Detecting Method Design The idea of developing a vision based detecting method comes from the project requirement of course SYDE 677 Computer Vision taught by Professor Tizhoosh According to the knowledge of image processing and concepts of computer vision obtained from the course a simplified and specialized vision based detecting method is designed The simplification and specialization are achieved by utilizing the geometry properties of reflection image which is formed by a C shape light source onto the sphe
43. ation Digital signal activate ADC Analog signal are read by microprocessor and waiting to be processed Figure 2 9 Signal Transmission Flow of Tooling Ball Detecting Process Analysis of the design The design of version 2 achieves the target functions without the deficiencies which occurred in version 1 The tooling ball is properly located and the satisfactory performance of the J6 joystick increased the effects of the ball locating operation The experiments and testing process of the J6 joystick and the detector of version 2 will be introduced in Chapter 3 2 5 Electrical Component Design Figurq2 9 illustrates the signal transmission flow of the tooling ball detecting process From the Figurd2 9 we can see that there are five output signals of the mechanical 36 JTAG Port 20 Pins USB Power Supply for Program burning RS232 Port for Serial Communication GPIO for Signals Input Microcontroller LPC2131 Figure 2 10 LPC2131 ARM7 Microcontroller with the Development Board EasyARM 2131 component one digital signal from the tactile switch and four analog voltage signals from the joystick The electrical component should let the robot controller know the value of the four voltage signals when the digital signal is generated Therefore two processes are required to achieve the target the AD conversion process and the communication process They are to be implemented by a Philips LPC2131 ARM7 microprocessor based o
44. automatic TIG welding process for mould modification is first described and then the mould registration and calibration processes are outlined in detail Several methods which have been previously applied or developed are considered and compared Next a tooling ball detection method designed for use with an ABB welding robot in the mould registration process is proposed Finally a brief conclusion of the chapter is provided together with an outline of the following chapters 1 1 Automatic TIG Welding Project 1 1 1 Mould Modification and TIG welding In the mould fabrication industry moulds are commonly machined from a large billet of expensive tool steel using NC machining programmed to remove material based on a CAD model of the desired mould cavity According to the requirements of practice mould machine always need adjustment This is because a mould may be not be made to specifications due to a machining error Materials that are over machined need to be added and excess materials should be removed Also when a previous mould design is not suitable and needs to be improved the mould machined has to be adjusted Moreover when an old unused mould is similar to a new mould designed doing a mould adjustment for the old mould is obviously an efficient choice for time and cost saving As a result mould adjusting including removing excess materials and adding missing materials is necessary and unavoidable in the mould fabrication industry
45. axis Y 0 outputs voltage signals VY and V2 The slopes of V and V2 are k and ky 3 y out out out out u u respectively The slopes of V and V are ky and ky respectively The output voltages at the center position with no deflection are V V7 V9 and V2 for the axes X and Yj respectively There are thus four input output relationships as represented by Equation 3 Ito 3 4 respectively 53 E Kd V 3 1 VE ef VE 3 2 Vout Kky0y VY 3 3 3 4 K be V 3 4 3 2 1 Method for Joystick Calibration First a mechanism for joystick calibration is designed Second operation instructions about applying the mechanism for calibration is described Third a mathematical model is introduced describing the operation process for position computation Finally the method for processing the data obtained is given Mechanism for Joystick Calibration The mechanism designed for calibrating the joystick is illustrated in Figurd3 6 Parts within Figurd3 6 are listed below Part 1 Joystick Mounting Base Part 2 Joystick Mounting Post Part 3 Joystick 3 1 body 3 2 shaft Part 4 Shaft Extension Part 5 Centering Shaft Part 6 Linear Motion Bearing 54 Rotation Axis Figure 3 6 Mechanism for Joystick Calibration 59 Part 7 Bearing Housing The joystick mounting base is fixed by the jaw of the indexing head The body of the joystick is secured to the mounting base by
46. ccuracy for tooling ball detection is required to be 1mm on three axes of the world coordinate system e De able to be applied in a different calibration application 15 As a product design the detector should not be limited to the project of TIG welding but should be appicable to other types of applications such as the CNC machine calibration process As a result the additional value of the detector itself can be increased 1 2 Current Methods for Position Measurement 1 2 1 Methods Currently Applied in the Project e Dall Surface Point Detecting by Tungsten Electrode Applying 4 point Method There is a sharp tip at the end of the tungsten electrode in TIG welding The position of the tip in the world coordinate system can be directly read by the robot controller so that it can be utilized as a point detector The position of the sphere can be computed by its surface points at least four points Therefore if four surface points of the tooling ball can be detected by the tip of the tungsten electrode spherical center of the tooling ball can be figured out 4 point method 6 This is the easiest tooling ball detecting method that can be applied for tooling ball detection in an ABB robot system A tungsten electrode is needed for TIG welding in the entire working process and there is no need to mount any other detecting tools The detecting operation is simple for operators especially when the operator is familiar with robot op
47. considered and developed 2 1 1 2 Project of Automatic TIG welding A project called Automatic TIG Welding based on ABB Welding Robot is being developed by Tool Tec Welding Inc The project is set up based on automotive mould adjusting task The automotive mould is made of P 20 tool steel with several projections to be added while the surface of the desired mould is required to be a Class A tool steel surface The actual mould and CAD data of both actual mould and desired mould in 3D CAD software solidworks for instance are provided by the customer There are three main steps in achieving the task First remove materials at the posi tions where the projections are added in order to obtain a new ground surface Second based on this new ground surface materials are welded to the desired position with the volume of materials being slightly more than the one desired Finally excess materials are removed and the desired surface is achieved The welding accuracy and efficiency of the second step are important in saving time and lowering costs An accurate welding operation makes the excess materials to be removed at the final step as little as possible so that machining time and the cost of welding materials can be maximally reduced In order to satisfy the requirements of surface quality the project applies TIG welding as the welding technique used in the second step A ABB welding robot is the product from ABB company Detail
48. d Position In Position of Reference Point Ree CAD Space wi In Robot Space SVD Algorithm Base on Least Square Transformation Matrix pee pup Position of Reference Point In Mould Position CAD Space In Robot Space Figure 1 4 General Description of the Mould Calibration Process into an improved Equation 1 2 in solving the optimal transformation matrixes R and T instead of R and T Finally All points in the point set P94P can be transformed into point set PY using Equation 1 3 and R and T are the target transformation matrices The mould calibration process is illustrated in Figure pm RDA iT 1 1 rw R ier T nat 1 2 proe Ree E T 1 3 e Automatic Welding After finishing all the five previous procedures the robot knows what is to be welded and how the welding works should be carried out Then robot starts doing the actual 11 welding process following the programs in the robot controller and finishes the TIG welding task automatically 1 1 3 Direction of the research There are two types of reference points that are usually selected in the mould calibration process They are spherical centers of tooling balls and vertices of the mould itself in tersection points of edges for instance Figure and figure illustrate vertices and tooling balls In figure A B C and D are four vertices of the mould The mould is symmetric and thus there are four vertices in another side of the mould ar
49. d Save the Texuit of AD Convention for sending result of AD conversion in buffer into Relevant Variable ADC Datui EINTO is used to activate the whole process of AD conversion and serial communication However once result of AD conversion can not be received by robot controller successfully it can be send again by activating EINT3 Change the status of LEDs and BEEP Adjusting Data in Variables ADC Datt ADC_Data3 into Suitable Format for Communication Purpose Initialization for the UARTO Serial Communication Global Variables UARTO Serial Communication Send the Data to Buffer uint32 ADC Darat Data is the result of AD Send the Data to Buller uint32 ADC Datal conversion Data is the result of AD uint32 ADC Data2 g uint32 ADC_Data3 Send the data to robot controller uint8 SendData 8 Send the data to robot controller First four variables above are utilized for saving results of AD conversion After transforming data into suitable format for communication data to be send to the buffer is stored in the array SendData OUTPUT conversion Figure 2 11 Program Flow Chart of ARM7 Microprocessor 39 Flow of RAPID Code Rapid Program Flow Variables declaration Votage values receiving Relevant Variables PERS string rec TCP position recording VAR num TCPx VAR num TCPy VAR num TCPz Voltage values translation num Vaum 4 Parameter values assignment Angle values translation VAR nu
50. del Color Long service life Flat Blue 4 3 x 12 5 mm General purpose 130 g B3F 5000 Weight Approx 0 85 g Contact form SPST NO Switching 1 to 50 mA 5 to 24 VDC resistive load capacity Contact 100 MQ max Initial Value Rated 1mA 5VDC resistance Insulation 100 MQ min at 250 VDC resistance Dielectric strength 500 VAC 50 60 Hz for 1 minute Bounce time 5 ms max Vibration Malfunction durability 10 to 55 Hz 1 5 mm double amplitude Shock Mechanical durability 1 000 m s2 approx 100 G Malfunction durability 100 m s2 approx 10 G temperature 25 to 70 C with no icing Humidity 35 to 85 RH Life Expectancy 10 000 000 operations min Pre travel PT 0 3 0 2 0 1 mm Construction Contact Form Cover Terminals Plunger dads aa OU ca COM Uu ae Dome contact Fixed contact Figure A 3 B3F5000 Tactile Switch Copied from Omron Electronic Components LLC 120 Appendix B Programs B 1 Program in Microprocessor include config h define EINTO 14 Interrupt NO of EINTO define EINT3 17 Interrupt NO of EINT3 define UARTO 6 Interrupt NO of UARTO 7 extern void DelayNS uint32 dly uint32 loop for dly gt 0 dly for loop 0 loop lt 5000 loopt uint32 ToASCII uint32 data0 121 T uint32 data if data0 9 data data0 48 else data data0 55 return da
51. e also required to be selected as reference points The tooling ball in figure is specified by figure in page Vertices are easier to detect because they can be found directly at the point using a detecting pin However it may confuse the operator in the reference point detecting process when the mould surface is complicated with large quantities of vertices in high intensity On another hand a tooling ball is easy for the operator to capture but it can only be detected in an indirect way as the reference point of a tooling ball is the spherical center which is a point located inside the solid Considering the terrible working environment of welding if a detecting tool for a detecting tooling ball with high efficiency can be applied for the mould calibration process for reference points detecting incorrect detecting operation could be avoided and the efficiency of the calibration process will be improved As a result this research aims to develop a tooling ball detecting method for the mould calibration process of automatic TIG welding system Applying this detecting method a robot controller should know the position of the tooling ball in the world coordinate system The efficiency of the tooling ball detecting process should increase with the new method and the detecting accuracy should locate within the range of requirement 12 Figure 1 5 Vertices of the mould 13 Figure 1 6 Mould with tooling balls 14 1 1 4 Requireme
52. e pose of the torch in robot space can be described by the pose of its tool coordinate system in the world coordinate system e User coordinate system Fuser Xu Y Zu The user coordinate system is located on the heating table and its pose in the world coordinate system represents the location of the heating table in the robot space Working Flow of Welding Task Figurd 1 2 describes the main flow of the working process for the robot s automatic TIG welding task There are six main sections Difference Computation Path Generation Welding Process Simulation Welding Parameters Adjusting Mould Calibration and Au tomatic Welding e Differences Computation Figure 1 3 describes the differences computation process briefly 2Word pose in the thesis represents position and orientation Data Input Desired Mould Actual Mould Differences Computation Welding Parameters Adjusting Path Generation Welding Process Simulation Mould Calibration Automatic Welding Figure 1 2 Working Flow of Robot Automatic Welding in General Obtaining Compare Differences Desired Mould with Projections to be added Actual Mould Projections to be added Figure 1 3 Differences Computation Compare actual mould data with ideal mould data and obtain the differences simply by subtracting with the 3D modeling software Solidworks There is a customized ap plication called robot designer developed for the pu
53. e s inner surface and the ball surface forms a tangent circle and the tooling ball is properly located In order to ensure the locating status the detector keeps being dropped down until the tactile switch is activated by a sliding mechanism and the detecting process is finished A compressing spring is applied to the sliding mechanism to ensure the cone s inner surface keeps contact with the ball s surface 2 3 1 Analog Biaxial Joystick An analog biaxial joystick is a type of sensor that converts mechanical values deflection angles of the shaft into analog voltage signals As the joystick coordinate system shown in Figurd2 3 the shaft deflects about X Y and the origin of the coordinate system O is the deflection center Z coincides with the center axis of the shaft when the shaft locates at the center position with no deflection Once the shaft is deflected the joystick emits voltage signals representing deflection angles of the two axes The shaft deflects about each axis in a range of a a and there is a linear input output relationship that is described by Equation Vout kin Sp Ve 2 2 k is the slope of the line and there is k Vmax Vmin 20 Vout is the output voltage Vinax is the maximal output voltage when the shaft is deflected to angle a and Vmin is 24 silding mechanism Joystick defiection center shaft detecting part tooling boll Tangent Contact tangent circle detecting range before
54. e temperature of the mould can be controlled The heating table is used to maintain the temperature of the mould instead of heating the mould to the required temperature The heating table is not able to heat the mould to 700F The reason is that the speed of heat missing from large areas of the mould surface is higher than the speed of absorbing heat from the heating table ke E e 5 g E O T E e D e D E Robot Working Environment Robot Cell Figure 1 1 Robot Cell Setting for TIG Welding As a result the mould is heated in an oven until 700F is reached after which the mould is moved to the heating table to be worked on e PC Robot and PC Office PCs are used for robot programming welding tool path planning and welding parameters controlling There are two PCs one is placed in the robot s working environment for direct robot programming and control and the other one is placed in the office for engineers for off line programming simulating and working status monitoring Spaces and Coordinate Systems in ABB Robot System There are two spaces in a robot system one is robot space representing the actual working space of the robot and the other is CAD space which is a virtual space in 3D CAD software Space can be numerically described by a coordinate system in the form of coordinate values x y z There are five coordinate systems defined in the ABB robot system the base coordinate syste
55. ematical modeling results and analysis The mechanical component is first tested on the NC milling machine The testing process is combined with the detector calibration experiment Base on the results of the experiment the mechanical component is also evaluated in this chapter 49 Table Indexing Head Figure 3 1 Milling Machine 3 1 NC Milling Machine with Indexing Head amp Tool ing Ball 3 1 1 NC Milling Machine with Indexing Head The NC milling used in the experiments is described The axes of the milling machine coordinate system are illustrated in Figurd3 1 The origin is defined by the operator which is not fixed To decide the position of the origin select any point on the center axis of the tool holder that is convenient for operation as the Tool Center Point TCP detect another selected position in space as the origin of the milling machine coordinate system and set the position of the TCP to zero The position of the TCP is displayed on the screen of the milling machine There is an indexing head mounted on the table of the milling machine and the center 50 Figure 3 2 Tooling Ball 5 d gt al 2 61 Figure 3 3 Dimension of the Tooling Ball axis of both the chuck of milling machine and the indexing head are parallel to the vertical axis of the milling machine The indexing head can be rotated by the operator 3 1 2 Tooling Ball The tooling ball used for detection simula
56. eration However this method is time consuming because of the four times detecting oper ation required and its detecting accuracy is difficult to control because it is hard to make touching judgements whether the tip of the electrode touches the surface or not and also because it is difficult to control the position of surface points that are detected According to the analysis in 6 the most accurate result of detection can 16 only be obtained when four detecting points form a regular polyhedron and this is im possible for operators to achieve by operating the ABB robot On the another hand the high temperature of the mould about 700F is dangerous for operators working around it for long periods of time especially for work requiring careful operation High accuracy probe As an improvement for the 4 point method using tungsten electrode as a point de tector a high accuracy probe is applied to take the place of the electrode The probe is able to generate touched not touched digital signal as feed back information to the robot controller Once the tip of the probe touches the surface of the tooling ball the feed back signal is generated immediately to let the robot arm stop moving Touching status is judged by the feedback signal rather than by the eyes of operator Though the reliability of touching status judgment is enhanced by using the high accuracy probe time for the detecting operation is not reduced The probe
57. es Patent 6721444 2004 Hua Zhang Ligong Zhou Introduction to ARM7 Beijing Unversity of Aeronautics and Astronautics 2005 K Levenberg A method for the solution of certain non linear problems in least squares Quarterly of Applied Mathematics 2 164 168 1944 Help Document of Matlab 7 Abdul Al Azzawi Light and optics principles and practices CRC Taylor and Francis 2006 Vaughan Pratt Direct Least Squares Fitting of Algebraic Surfaces Computer Graph ics 21 4 1987 Han Sun Mingwu Ren Jingyu Yang Tracing Boundary Contours in a Binary Image Image and Vision Computing 20 125C131 2002 136 20 Holbrook L Horton Henry H Ryffel Christopher J McCauley Ricardo Heald Erik Oberg Franklin D Jones Machinery s handbook Industrial Press 2008 137
58. f detector calibration Position of TCP in world coordinate system Trap yprop and Sen These are obviously known values in the ABB welding system and are also known in most of the systems of NC machines as the NC milling machine to be used for detector calibration for instance 73 Deflection Cente of Joystick Peak of the Cone Surface Spherical Center Figure 3 12 The relationship between L and d 74 5 The position of joystick deflection center in tool coordinate system Ax Ay and Az Determining the values of these three coefficients is the last target of detector cal ibration They designate the position of the joystick s deflection center in the tool coordinate system so that different settings of tool coordinate system cause different values of these three values In order to achieve the targets the calibration method is designed based on the process of solving Equation Suppose the position of the tooling ball is known and simulate the detecting process designed in Chapter 2 Equation 2 11 becomes an equation set with three equations and five unknown coefficients Once two of the unknown coefficients are fixed the other three can be determined The NC milling machine with indexing head is utilized for the detector calibration 3 3 2 Detector Calibration Procedure Step 1 Obtain x and y value of the tooling ball in the milling machine coordinate system In the later processes of tooling bal
59. figured out Locating the ball to the center axis of the shaft is the task of the detecting part as described in next paragraph 2 3 2 Detecting Part Figurq2 5 illustrates the tooling ball locating method of the detecting part Only when the tooling ball is properly located can the compressing spring start being compressed until the digital signal is activated After finishing the detecting process and lifting the detector the compressing spring is released and goes back to the original status 2 4 Implementation of Mechanical Component There are two design versions of design for implementing the mechanical component as discussed below 27 Figure 2 4 Shaft Deflection of the Joystick 28 Shaft of joystick with extension for sliding 4 Compressing spring Tactile switch Digital signal output Tangent circle Cone inner surface Figure 2 5 Tooling Ball Locating 29 2 4 1 Version 1 Figurq2 6 illustrates the mechanical component of version 1 Parts within Figure 2 6 are listed below Part 1 Joystick Mounting Base Part 2 Joystick Part 3 Connecting Cap Part 4 PCB Part 5 Tactile Switch Part 6 Distance Fixing Part Part 7 Locking Nut 1 Part 8 Locking Nut 2 Part 9 Linear Motion Bearing Part 10 Cone Part Part 11 Outer Compressing Spring Part 12 Outer Spring Position Fixer Part 13 M3 Nut Part 14 M3 Washer Part 15 M3 40 Socket Head Cap Screw Part 16 Inner Compres
60. for TIG Welding 2 2 2 04 28454 Senet es 5 1 2 Working Flow of Robot Automatic Welding in General 8 oa daa da ea a 9 e H 1 5 Vertices of the mould ouod Roy SOR o S RE pde eR oh ke OS 13 KC EE a M NERONE NR eel a 14 SEENEN 22 Puce ee ee eee 25 KT REENEN 26 2 4 Shaft Deflection of the Joystick e 28 2 5 Tooling Ball Lagcatmpl 4 2 4 Ce nibo ee Gk UR Oe EU reU 29 2 6 Mechanical Component of Version 1 0 00002 e ee 31 2 7 the Broken Shaft of Jost 33 2 8 Mechanical Component of Version 2 oa a a a oll 34 I 36 2 10 LPC2131 ARM7 Microcontroller with the Development Board EasyARM E I a ed oe SEPA Ee LAU dd Eee Reese 37 i ea eee a a 39 2 12 RAPID Program Flow Chart 6 dee Ee E EO yy xn 40 Ge Ee ved x E ENEE 42 La bene RANG IS 44 P gx Sax Y Sx Rm e A A dE d 50 3 2 Tooling Ball aye ehh ke x ah ee wie RS ae eee ee ee 51 3 3 Dimensi n of the Tooling Ball 2 oy ae wis ware ed Bee Ra bl 0 92 T LII 53 NOR P ee od ee ee CURE 55 fe here ae ee a Be ee 57 TE 59 I S 62 SE EE 69 3 11 Fit to the Data of Joystick Calibration Experiment 70 3 12 The relationship between Land d llle 74 3 13 Obtain z value of the tooling ball center by the chuck 2 76 I 77 oo RA 79 xi SALOU 444 8 4k eee SOL ow EOE A DSR EE OSES ED Em 87 BIS AA 87 ea e aid EE oe ee eee e 88 ee ee AA 90 3 21 Relationship between 0 1 0 3 and 0 1 0 3 and Correspondent Posi Sed Bae ee
61. g the transformation process from the world coordinate system to the photo coordinate system depending on CT C and f Then according to homogeneous transformation we can have two position re sults for a tooling ball from the two photos represented by Pj Sen Mun d d and Py Thall2 Hai bala 1 I Then finally the position of the ball s spherical center with respect to the world coor dinate system can be computed by Pe Pein Pens 2 107 Figure 4 8 9 Types of Same Photos 4 5 Experiment and Result e Sample Photos There are 50 sample photos taken by camera The position of the tooling ball within the photos can be separated into nine main types Center Up middle Up left Up Right Middle Middle left Middle right Down middle Down left and Down right Figurd4 8 The background of the photos is a stainless steel block with several holes and edges Also the surface of the block is mid level polished so that it appears to have a similar 108 optic property as the one of the mould to be calibrated Result Because there are 50 sample photos in total and any two of them can be selected for each time of detection there are 1225 combinations for sample photos to be tested Finally it was found that all of the 8 dark points within the photos were captured correctly However the position of the tooling ball s spherical center in the photo coordinate system is not correct if the center position of the eigh
62. ge Signal Outputs index V V V N Voue V Vaal V index VAN Voa V Vou V Vou V 1 3 694 1 364 2 268 2 796 11 1 338 3 756 2 757 2 288 2 3 713 1 352 2 556 2 495 12 1 817 3 786 2 438 2 624 3 3 642 1 432 2 982 2 070 13 1 409 3 699 2 058 3 008 4 3 445 1 600 3 310 1 749 14 1 610 3 499 1 724 3 340 5 3 149 1 936 3 556 1 508 15 1 909 3 206 1 476 3 588 6 2 780 2 309 3 694 1 373 16 2 265 2 885 1 343 3 725 7 2 427 2 644 3 714 1 351 17 2 604 2 470 1 318 3 749 8 2 049 3 025 3 622 1 442 18 2 982 2 089 1 403 3 663 9 1 719 3 363 3 421 1 638 19 3 316 1 759 1 602 3 462 10 1 472 3 621 3 125 1 925 20 3 561 1 507 1 904 3 162 8l 3 Position of the tooling ball center in the milling machine coordinate system Equation 3 45 This is obtained from the second step of the detector calibration procedure described in 3 3 2 a 0 0 m 0 0 pm 3 45 2 R 7 925 1 1 1 4 Equation for position computation The data are processed by the following steps Step 1 Compute the deflection angles according to the voltage outputs and results ob tained from the joystick calibration procedure for Equations and Step 2 Compute a b c and a according to Equation 3 44 Step 3 For Ax 0 and Ay 0 we have Equation 3 46 rS La b sin 60 a z Top n Ly a b cos 00 a y pm Up
63. h other through RS232 Cables and bits converted by the AD converter can be obtained by the robot controller The program that is burned in the microprocessor is provided in AppendixB and the program flow chart is shown in Figurd2 11 2 6 Computational Component Design The computational component designed contains two layers The first layer is designed for data processing which is implemented by programs programmed in the robot controller The second layer is the computing layer which is designed for position computing utilizing known parameters The second layer is inserted into the first layer The first layer s operating data that is required in the second layer The program flow chart is given in Figurd2 12 and details of the program are provided in AppendixB In order to compute the position of the tooling ball in the second layer bits representing output voltage values of the joystick received from the microprocessor are first read and translated into the deflection angles of the joystick Next according to Equation the 38 Flow of ARM Program Initialization tor the AD Conversion LED and BEEP Status Initialization IRQ Interrupt Request Initialization Loop amp Wait for External Interrupts Digital signals AD Conversion for Channel ADO i 1 Digital signal from EINTO AD conversion is activated and serial communcation process is activated after 2 Digital signal from EINT3 serial communication process is activate
64. he cell system with the automatic TIG welding system are discussed 2 1 Basic Rule for Tooling Ball Detecting Method De sign The target of research is to design a new tooling ball detecting method for an ABB weld ing robot in the mould calibration process of automatic TIG welding The position of the tooling ball s spherical center in the world coordinate system is to be computed and 20 transmitted to the robot controller Coordinate systems transform from one to another following the rule of homogeneous transformation which is also the basic rule for design ing the new detecting method Coordinate systems utilized in the tooling ball detecting process are mentioned again e World coordinate system Fworta Xw Yw Zw e Tool coordinate system Fico X Y Zi AII tools that are applied in the robot system are described by their own tool coordinate system Fi Xu Yu Zu and every time after mounting a tool the tool should be calibrated to let robot know the pose of the tool coordinate system in the world coordinate system The origin of the tool coordinate system is defined as the Tool Center Point TCP and both of the position of TCP and the orientation of the tool coordinate system can be read by the robot controller directly T Suppose the position of a point P in Fuworia is P am y8 z8 1 A tool is currently applied in robot system with tool coordinate system buet with position of T TCP i
65. iameter of the tooling ball is to be measured and recorded for computing L Tooling balls with different diameters to be detected cause different L As shown in Figurd3 12 the diameter of the tooling ball measured is d with corresponding distance L L is the distance from the deflection center of joystick to the peak of cone surface D is the angle between the center axis of the detecting part and the cone surface w is the width of the cone surface Thus we have the relationship L L d 2 sin B 3 42 For different sizes of tooling ball L does not change and L can be computed by LU and 0 However because of machining tolerance and the activation distance of the tactile switch L may not be exactly as designed As a result obtaining the value of L corresponding to the different values of the tooling ball diameter is the first target of the detector calibration experiment There is only one tooling ball to be detected so only L is computed in the detector calibration process without computing LU Rotation angle of rotation transformation process 00 The detector is mounted on the sixth axis of a robot arm or other type of machine Different mechanism designs for attaching the detector to the machine or robot are required After mounting the detector the x axis of the joystick coordinate system X usually does not coincide with the x axis of the tool coordinate system X This is the rotation angle 00 as the second compact o
66. ide position signal contact 52 a a Kontakte S2 der X und of both xand y axes must be Y Achse UND verkn pft closed 673 werden digital 72 axes X et Y point milieu r el point milieu pour l axe X point milieu pour l axe Y Ge Ausf hrung Elektronikgehduse CAN Construction with electronic case CAN lt Darstellung in Mittelstellung S2 bet tigt Construction avec boitier lectronique CAN shown with knob in centre postion S2 operated tat des contacts en position milieu 8 or Redundant Aufbauh he f r Ausf hrung Digital Redundant Jeweils X und Y Achse panel thickness for execution digital redundant redundant 58 Epaisseur pour ex cution tact X and Yaris E digital redondant 4x52 c redondant axes X et Y Standardgriff ohne Microtaste Standardgriff mit Microtaste 3 Tasten Griff max 3 Microtasten Standard knob without micro button Standard knob with micro button 3 button knob max 3 micro button Poign e standard sans micro touche Poign e standard avec micro touche Poign e 3 touches max 3 micro touches DN UU gu t S Ein CAN H L e om 294 Technische Anderungen vorbehalten We reserve the right to change specifications without notice Sous r serve de modifications techniques Figure A 2 JoR6AA A00 Copied from Elobau Sensor Technology 119 Technical Specification of B3F5000 Tactile Switch Type Plunger Type Switch height x pitch Operating force Mo
67. ieving the calibration task in the project of automatic TIG welding the adaptability of the design to other applications should be considered 1 3 2 General Description of Other Chapters in the Thesis Chapter 2 describes the whole designing process The design of mechanical component electrical component and computational component are introduced in detail Chapter 3 describes the calibration process of the joystick and the detector A simulation of the tool ing ball detecting process based on the design in Chapter 2 is also described and according to the results of the simulation the new tooling ball detecting method is evaluated As an extension and comparison between optical and mechanical detection methods a simple optical detecting method utilizing reflection image forming of light source is given and dis cussed in Chapter 4 Finally Chapter 5 concludes the research with an overall summary conclusions and thoughts towards future works 19 Chapter 2 Tooling Ball Detecting Method Design This chapter introduces the design of the new tooling ball detecting method for the mould calibration process of the automatic TIG welding task First the basic rule for designing the detecting method is given Next the cell system for tooling ball detection which is the structure of whole designing process is described Third three components in the cell system are described separately in detail Finally some points about integrating t
68. ing base stay in the indexing head jaws and close the 56 Figure 3 7 Center the tool holder on the steel rod jaws securely With the chuck fully opened raise the joystick with the mounting base and post to get close to the chuck by operating the table of the milling machine on its vertical axis until the joystick shaft is about 2cm into the chuck Close the chuck gently until it just makes contact with the joystick shaft the joystick shaft should still be able to rotate in the chuck Rotate the indexing head while monitoring the joystick output voltages If the joystick is properly centered below the chuck the output voltages will not change significantly as the indexing head is rotated If the output voltages do change adjust the position of the table along the axes X and Ym of the milling machine until this voltage change in minimized over one rotation of the indexing head This is then the properly centered position with center voltage outputs V V2 V9 and V2 Step 4 Mount all the parts in Figurq3 6 Open the chuck and lower the joystick with the mounting base and the post by operating the table of the milling machine on its vertical axis Attach the other parts 4 5 6 7 to the joystick and then raise the whole mechanism so that the centering shaft enters the chuck Close the chuck on the centering shaft 57 Step 5 Rotate the indexing head four degrees for each increment from 0 to 364 Record output voltage v
69. ing method in environments with high temperature The idea is only roughly proven here and further works is required 114 5 2 Future Work Further developments of the detecting method is described in general by following points Improve the mechanical design of the joystick calibration mechanism and the detec tor Stabilize the operating voltage of the joystick Increase the convertibility of AD conversion process and the stability of serial com munication process Integrate the detecting method with the ABB welding robot system Test the accuracy repeatability heat resistance and the durability of the detecting method Analyze the reasons that cause position errors in the tooling ball detecting process 115 APPENDICES 116 Appendix A Technical Specifications of Joysticks and Tactile Switch 117 Joysticks www elobau com Joysticks Joysticks Joystick kleine Bauform Joystick small version Joystick version compacte dieses E ae 100 38 15 SIGI 0 SIG1100 45 150 SIGI 0 i SIG2 0 SIG2 100 SIG2 0 E ae IS Redundant relent E X Achse Y Achse redundant redundant X axis Y axis zi redondant redondant S axes X axes Y Y Achse Y axis axe Y X Achse X axis axe X Darstellung ohne Litzen view without wires repr sentation sans cordon mm maximale Einschraubtiefe ab Unterseite
70. is ex pensive about 5000 and the feeding speed of the robot arm s movement has to be set at the slowest level 0 1mm increment to protect the probe from collision Also because the working temperature range of the probe is 257F which is much lower than the temperature of the mould the probe can be applied only when the mould is cold 1 2 2 Other Developed Methods Currently methods for tooling ball detecting can be divided into three types mechanical touching optical sensor detecting and vision based object recognition The mechanical touching method is seldom considered because of its low accuracy compared to the other Methods of optical sensor detecting 7 9 11 and vision based object recognition 12 13 have their own advantages 17 e There is no contact between the device and targets so collisions are avoided e The detecting accuracy is higher than in mechanical touching methods e Detecting targets are not limited by their physical characteristics For example not only spherical objects can be detected but also other types of objects cube sheet etc can be recognized However there are also disadvantages in the application environment of this project e High accuracy is always related to strict requirements about operation and work ing environment The working environment and requirements about ball detecting operation cannot satisfy requirements of applying optical sensors or vision devices
71. l Component Design The task of mechanical component design is to design a detector in order to obtain position information of a tooling ball with respect to the detector The detector is mounted on the sixth axis of the robot arm as one of the tools applied in the robot system It has its own tool coordinate system detector coordinate system Fy Xa Y Za All the position information with respect to the detector is described in Fy The detector is designed as an analog biaxial joystick with a detecting part mounted on the deflection shaft The detecting part has a tactile switch that can be activated by a sliding mechanism to generate a digital signal output showing the status of detection l The idea to use a biaxial joystick came from professor Jan Huissoon 23 The detecting process is illustrated in Figurd2 2Jand details of the joystick and detecting part are given in the following paragraphs Before detecting the ball the detector is set vertical to the plane X Ow Yw of the world coordinate system and moved to a position that allows the tooling ball to be located within the detecting range Next the detector is dropped down as a ball detecting process The tooling ball tangent contacts with the cone s inner surface of the detecting part and slides to the center position Finally once the spherical center of the tooling ball coincides with the center axis of the joystick s shaft the tangent points between the con
72. l detection the tooling ball is fixed in the jaws of the indexing head As a result the x and y values of the tooling ball center are positioned at the center axis of the indexing head in the milling machine coordinate system By repeating the first two steps of the joystick calibration experiment the x and y values of the tooling ball center can be obtained For convenience in computing set the x and y values displayed on the screen of the milling machine to zero Step 2 Obtain z value of tooling ball center in milling machine coordinate system Remove the steel rod and fix the tooling ball with the jaws of the indexing head Close the chuck and let the bottom surface of the chuck tangent contact the surface of the tooling ball as shown in Figurq3 13 Set the z value of the milling machine to 75 Figure 3 13 Obtain z value of the tooling ball center by the chuck zero The origin of the milling machine coordinate system is then set at the highest point of the tooling ball surface With the radius of the tooling ball R 7 925mm measured previously the position of the center of the tooling ball in milling machine coordinate system is T T T pr am up X 1 0 R 1 0 D 7 925 e p p Step 3 Set up the detector Mount the detector to the milling machine by the tool holder Figurq3 14 illustrates the coordinate systems in the detector calibration process Step 4 Detect the tooling ball from different positions
73. m the world coordinate system the tool coordinate system the workpiece coordinate system and the user coordinate system Definitions of each coordinate system can be found in the ABB robot user manual they are not mentioned here The relationship among different coordinate systems in robot space can be described by homogeneous transformation 4 e World coordinate system and base coordinate system Fog Xw Yw Zw Since there is only one ABB robot in the project the world coordinate system and the base coordinate system coincide with each other and both are to be called the world coordinate system The world coordinate system can be used to describe the position information of robot space e Workpiece coordinate system FworkpieceorFcan Xe Ye Ze The workpiece coordinate system located on the mould and the CAD data of work piece mould in 3D CAD software are described based on the workpiece coordinate system The workpiece coordinate system can be used to describe the position infor mation of CAD space e Tool coordinate system Froot X Y Zi The robot system is able to have several different tool coordinate systems at the same time representing information of different tools applied Take the welding task for example A torch for TIG welding is designed and mounted on the sixth axis of the robot so there is a tool coordinate system representing the torch The torch moves with the robot arm and th
74. m Ax VAR num Ay Position computation Position of Tooling ball PERS num X PERS num Y PERS num Z gt Program Flow Information Input EE 7 Information Output Figure 2 12 RAPID Program Flow Chart 40 position of the tooling ball in relation to the joystick is computed according to the values of deflection angles Third according to the transformation in the tooling ball detecting process the position of the tooling ball in the world coordinate system is computed as the final result The final result of computation is saved into memory for the mould calibration process of TIG automatic welding and the results display the result on the screen of FlexPendant to be checked by the operator 2 6 1 Compute Deflection angles of joystick Values of four output voltage signals of joystick are firstly read from the microprocessor Define joystick coordinate system as which is shown in Figurq2 13 There is a group of output voltage signals V1 V22 VI and V for a detecting process received from 2 microprocessor V is the voltage value of signal 1 for X and V2 is the voltage value of signal 2 for Xj V out is the voltage value of is the voltage value of signal 1 for Y and Vi signal 2 for Y Output voltage values are proportional to the deflection angle Slopes of each signal ky1 kz2 ky1 ky and output voltage values at center position V VT V2 V9 are obtained from joystick calibration experimen
75. means of the mounting post The shaft extension both extends the length of the joystick shaft and provides a smooth surface for the linear motion bearing to slide along The linear bearing is mounted in the bearing housing which also provides a pivot by which the linear bearing is attached to the centering shaft The indexing head on the milling machine table is centered under the chuck and the centering shaft is secured in the tool holder The rotation axis is vertical during the whole joystick calibration process The deflection angles around each axis of the joystick change as the indexing head is rotated However the combined deflection angle is not changed The combined deflection angle of the shaft as is indicated in ge is the angle between the center axis of the shaft and the axis of joystick coordinate system 0 is a combination of 0 and 6 Joystick Calibration Procedure Step 1 Preset and fasten the indexing head and milling machine Locate the indexing head on the table of the milling machine Step 2 Align the rotation axes Fix a steel rod in the jaws of the indexing head Adjust the position of the milling ma chine table until the chuck is centered on the steel rod Figurd3 7 Reset coordinate values x and y displayed on the LCD screen to zero Step 3 Obtain V1 V2 V and V2 of joystick at the center position Attach the joystick onto the mounting base with the mounting post by M5 counter sunk screws Locate the mount
76. n the development board Easy ARM 2131 which is developed by Zhouligong Microcontroller Development Co Ltd Figurq2 10 Voltage signals are input into the development board from GPIO General Purpose I O and converted into bits by the AD converter that is integrated into the microprocessor From the serial port of the development board bits are sent to the robot controller through the COMI port and read by programs within the robot system The values of four voltage signals range between 0 55V and 4 95V when the supply voltage is 5 5V the maximal input voltage of the joystick The convertible voltage value 3T of the AD converter is from UY to 2 48V because the reference voltage of the development board is 2 48V 14 As a result output voltage signals from the joystick should be decreased into half 0 275V to 2 475V before being input into the microprocessor from GPIO This is achieved by the pre processing unit The digital signal from the detecting part is considered as the External Interrupt to the microprocessor Once the interrupt is activated the detector stops detecting the ball and AD converter starts converting the voltage signals into bits UART Universal Asynchronous Receiver Transmitter that is integrated into the microprocessor can be utilized for serial communication There is also a COMI port in the robot controller for serial communication The microprocessor and the robot controller can communicate with eac
77. n fL as TOP rop tos zop 1 Position of P in Fo is Pt T rb yb z 1 The robot arm is operated such that the directions of all the axes of Foo coincide with the direction of the axes of Forja According to homogeneous trans formation we have Equation 2 1 j TP 100 Tier Lp w 0 1 0 w J pee Up T Pt YTCP di 2 1 ze 0 0 1 op zb 1 0 0 0 1 1 Matrix Ti is the transformation matrix from Fuorta to Froo with only a translating process without rotation The transformation matrix defines the pose of Froot in F4 21 Power supply Detector Signal Pre processing Unit I Robot Controller 2 Position Computing Programs Detecting operation Pre processed signal Tooling Ball FlexPendant Mechanical Component Electrical Component Computational Component ABB Welding Robot Figure 2 1 Cell System for Tooling Ball Detection Consider the position of tooling ball in Forja as point P in Equation Then if the position of the tooling ball in Fa is known the position of the tooling ball in baad can be computed This is the basic rule for the tooling ball detecting method design 2 2 Cell System Design The flow chart in Figurd2 1 describes the cell system designed for tooling ball detecting in the robot system There are three components in the cell system the mechanical component the electrical component and the computational component The mechanical component contains a detector that is mounted on the
78. n of the tooling ball in the world coordinate system can be figured out Equation is derived from Equation2 10 and applied in the program of computational component 45 TP L cos 00 cos 6 sin 0 sin 00 cos 6 sin 0s Top Ax i L sin 00 cos 0 sin H cos 0 cos 0 sin 0 yp A be PLA y WR Gr AV ig Zp L cos 0 cos Oy zpop Az 1 1 2 6 4 Coefficients for Computation There are ten coefficients in Equation for position computation 1 Deflection angles 0 and 6 2 Distance from the deflection center of the joystick to the spherical center of the tooling ball L 3 The rotation angle of rotation transformation process 66 4 The position of the TCP in the world coordinate system xTop yfop and Zpop 5 The position of the joystick deflection center in the tool coordinate system Az Ay and Az z and 0 can be computed from the output signals of the joystick using Equations 2 4 to IR p Yrcp and zpop can be directly obtained by a robot controller However L 00 Ax Ay and Az are not previously known and therefore need to be figured out through detector calibration which will be introduced in Chapter 3 2 7 Cell System Integration As a requirement mentioned in Chapter 1 the cell system designed should be able to be integrated by the automatic TIG welding system Though the integration work has not 46 been started some points will be introduced here Integration contains the following three tasks
79. nable the function of IRQ open EINTO EINT3 and UARTO VICIntSelect 0x00000000 set all the interrupt as the IRQ VICVectCntlO 0x20 EINTO set EINTO to IRQO VICVectAddrO uint32 IRQ EintO address assignment for EINTO VICVectCnt11 0x20 UARTO set UARTO to IRQ1 VICVectAddri uint32 IRQ UARTO address assignment for EINT3 VICVectCntl2 0x20 EINT3 set EINT3 to IRQ2 VICVectAddr2 uint32 IRQ_Eint3 address assignment for EINT3 EXTINT 0x09 clear the IRQ mark of EINTO and EINTS VICIntEnable 1 lt lt 14 1 lt lt 17 Enable EINTO and EINT3 ADCmark 0 SendMark 0 while 1 128 t IO1PIN 0x03 lt lt 18 LED Status Display3 Waiting for IRQ DelayNS 200 IO1PIN Ox0C lt lt 18 DelayNS 200 IO1PIN 0x30 lt lt 18 DelayNS 200 IO1PIN OxCO lt lt 18 DelayNS 200 if UOLSR amp 0x01 1 GetStr ReceiveData 14 if ReceiveData 0 0x53 amp amp ReceiveData 1 0x41 SA d for s 0 s lt 14 s UOTHR SendDatal s else if ReceiveData 0 0x4F amp amp ReceiveData 1 Ox4B OK for s 0 s lt 14 s UOTHR ReceiveData s else for s 0 s lt 14 s UOTHR 0x57 W ADCmark 0 129 T return 0 B 2 RAPID Code for Computational Component hhh VERSION 1 LANGUAGE ENGLISH hh MODULE MainModule PERS BallNum VAR num i VAR string OutStrCL 14 VAR num Out
80. ngle from Xm to Xe about Ze We have y qo qi Po is the original rotation angle of the indexing head and y is the rotation angle of the indexing head which is accumulated from the original situation It s 4 for each increment of rotating of the indexing head If the indexing head has been rotated for i increments we have Qt Qo Ax i From F to F the transformation process is a translation and there are transformation matrix T and its inverse matrix Te are shown in Equation 3 6 T describes the pose of F in F and Te describes the pose of F in F 100 2 10 0 2 010 y 0 1 0 yj Tie MEn N 3 6 001 0 001 0 000 1 000 1 As a result from Fm to Fj there is a transformation matrix Tm shown in Equation It can be simplified into Equation 3 8 Tmj describes the pose of F in Fm 1 0 0 x cosy sinys O U 100 P 010 y sin COS 0 0 010 y T uf SS E Ye am D 1 27 0 0 0 0 001 0 000 1 0 0 0 1 000 1 60 cosy sin yr T DL COS pp Y sin pr Ta 3 8 m C U U U U U sing cosy 0 y yi cosp TL sin qi 1 0 1 Also since Tim T ma describing the pose of Fm in F we have transformation matrix Tim for the transformation from F to Fm as is shown in Equation 3 9 N m m D cosy Sing qj T COS pp Y Sm uy Tim m Cc 0 0 0 0 0 siny cosy 0 yj y cospi 1 sin py 1 Z 0 1 Deflection Angles of Joystick in Calibration Process Fig
81. nt for ball position computation However the threaded connection between the shaft and the connecting cap is not able to control the tightness of the threading so that the distance is not fixed This will have negative effects on computing the position of the tooling ball As a result improvements should focus on these two defects The second version of the mechanical component design is given in the next section with improvements on the defects 2 4 2 Version 2 Figurd2 8 illustrates the mechanical component of version 2 33 LL Je Y lt a c Figure 2 8 Mechanical Component of Version 2 Parts within Figurd2 8 are listed below Part 1 Cone Part Part 2 PCB Part 3 M3 Counter Sunk Screw Part 4 Bottom Spring Fixer Part 5 Tactile Switch Part 6 Sliding Part Part 7 Inner Compressing Spring Part 8 Outer Compressing Spring 34 Part 9 Brass Pushing Part 10 Joystick Mounting Base Part 11 Joystick Mounting Post Part 12 Stopper 1 Part 13 Stopper 2 Part 14 Top Spring Fixing Part 15 Joystick Joystick that is applied in version 2 is J6 series joystick purchased from Elobau Sensor Technology The technical specifications of the joystick are provided in AppendixA Part 5 the tactile switch is the B3F 5000 one purchased from Omron Electronic Components LLC Its technical specifications are provided in AppendixA Feature description The joystick mounting base is made of 1045 steel and connec
82. nts for the New Tooling Ball Detecting Method The following requirements are considered in the research process e Work robustly in a heavy duty working environment of TIG welding High temperature dusty air strong illumination from surrounding welding works high possibility of causing impact by collision between robot arm and objects are five main factors that have negative effects on the tooling ball detection process The new tooling ball detecting method should avoid being effected by these factors e Be able to be integrated with the whole system of automatic TIG welding The new tooling ball detecting method is designed for the Automatic TIG Welding system and therefore the design should be able to be easily integrated into the whole system e Strike a balance among detecting accuracy detecting efficiency and the cost of the product The accuracy of robot motion is 1mm on three axes of the world coordinate system Base on the experimental results in the mould calibration process calibration results which are obtained from setting a vertex as the only type of reference point is ac ceptable This means that the accuracy of the new detecting method for tooling ball spherical center detection should be the same as for vertex detection by a detection needle which is still 1mm on each axis Currently the tip of a tungsten electrode is used to detect the vertex and the accuracy is the same as for robot motion Therefore the a
83. operation Secondly it introduces a new approach for utilizing the joystick Rather than as a manually operated direction controller for mobile control of devices the joystick is used as a passive detection angle sensor In order to properly use the joystick as an angle sensor the joystick calibration method is also designed and tested The designs of the three components are all implemented and tested separately The re sults of these tests prove the feasibility of the new detecting method however the accuracy of detection is not yet acceptable and further improvements need to be made In addition a vision based detecting method is also discussed at the end of the thesis Compared to mechanical touch style detection the vision based detecting method is de signed to obtain better performance in a high temperature environment and to automate the tooling ball detecting process iii Acknowledgements I gratefully acknowledge the assistance provided to me by many people during my research I especially would like to thank Professor Huissoon for affording me the opportunity to spend two years in Canada as an international student His invaluable support knowledge and experience helped guide me through the complexties of mechatronics and Canadian culture Without his valuable suggestions and insights I cannot imagine how my two years research and study would have gone I also wish to thank Robert for his excellent machining of
84. opject represents the pixel number of the object and parameter rea FilledCircle represents the area of a fulfilled circle which has the same perimeter as the object G property 4 Contour Number There is only one contour for the fulfilled object and the number is more than one when the object has holes G property 5 Fullness Fullness describes how many percentages that the contour of the object s fitting circle is covered by object pixels Project the object to another side of the fitting circle with respect to the circle center If the total object number becomes two then the fullness of the object is 2 or else the fullness of the object is 1 G property 6 Radius Radius of an object is the radius of the object s Fitting Circle e Difference Matrix Mary 102 Suppose we have two binary images and there are and 7 objects within the images respectively Compute all six G Properties and put the G Properties 1 2 3and 6 into two property matrices Equations 4 3 and 4 4 Mpi m La 4 m T Pho P Pa 4 3 where m 1 2 1 Mp n 1 4 Ph Iu Pu Pu 4 4 where n 1 2 3 Where row vector Pu Ji Pha d represents the G properties of the m object in the first image and row vector pe Pa Pa Pa represents the G properties of the n object in the second image Then we have a i x j difference matrix Maer through Equation 4 Marin n DEA 45 where s 123 6 Finally Mapp needs to be adjusted by G p
85. outside the bearing to enable it to return to a sliding position The bearing the connecting cap and the distance fixing part are connected by four pairs of M3 Socket Head Cap Screws and M3 nuts Analysis of the design Generally speaking the design of version 1 achieve the target function However two defects regarding assembly detecting durability and detecting accuracy are not able to be overlooked Firstly the shaft of the joystick is not strong enough to sustain repeated tooling ball detecting operation and assembly tasks The shaft was broken already when 32 Figure 2 7 the Broken Shaft of Joystick it was threaded with the connecting cap in the assembling process The broken position is at the shoulder of the shaft which can be seen in Figurd2 7 When the connecting cap is connected with the shaft the threaded connection generates axial tension force and tangential force on the shaft by the connecting cap When the connecting cap stops at the shoulder of the shaft the tension force will increase sharply if the tread keeps being tightened The shaft is made of engineering plastic and the increased force is much higher that the maximal force allowed of the shaft However the design is not able to control the tightness of threading to avoid the increased force The other defect is a weakness related to distance control The distance between the deflection center of joystick and the ball center is a very important coefficie
86. pulators Kinematics Dynamics and Control 2009 6 R B Fisher D W Eggert A Lorusso Estimating 3 D rigid body transformations a comparison of four major algorithms Machine Vision and Applications 9 272 290 1997 Zhang Defen Zhang Cuoxiong The Optimal Plan for Measuring Center and Radius of a Ball Part by 4 Point Method Acta Metrologica Sinica 14 4 247 250 1993 Timothy J Gill John A Hanlon Machine tool locator United States Patent 6301007 2001 D Scott Ackerson Robert E Bridges Lawrence B Brown Retroreflector for use with tooling ball United States Patent 5861956 1999 135 9 Tsing Wong Hsu Louis J Everett Method and apparatus for locating physical objects 10 11 13 14 15 16 17 18 19 no A CT oo Zi c Ze C A United States Patent 5111563 1993 Hideaki Hashimoto obot hand including optical approach sensing apparatus United States Patent 4766322 1988 Shinsuke Sakakibara Hajimu Inaba Gripping device United States Patent 4423998 1984 17 Hidekazu Araki all of Kadoma Japan Katsuhiro Sasada Tomoharu Nakahara Method of Utilizing a Two dimensional Image for Detecting the Position Posture and Shape of a Three dImensional Objective United States Patent 5692061 1997 Hidekazu Araki Hiroyuki Fujii Haisong Gu Tomoharu Nakahara 3 Dimensional ob ject recognition method and bin picking system using the method United Stat
87. rce which is shown in Figurd4 1 e Camera 96 photoing surface moving surface lens of camera of ring light 9 NE APTA COME incident ray optic AXis 3 Figure 4 2 Position Relationship among the Camera Light Source and the Tooling Ball SONY T100 Cyber shot digital camera is selected to take images of the tooling ball The resolution of the camera is 1536 by 2048 pixels e Position and Operation Configuration When the camera is taking images of tooling ball the optic axis of the camera s lens should always coincide with the center axis of the ring shaped light source As well the optic axis should always be perpendicular to the Xu Ow Y plane of the world coordinate system The position relationship amongst the camera the light source and the tooling ball is briefly displayed in Figur 4 2 97 4 2 Optical Characteristics of Tooling Ball The fine polished surface makes the tooling ball appears as a spherical mirror with unique optic characteristics regarding light reflection and reflection image formation if it is com pared with the surface of work pieces like moulds of autos for instance Two differences O Difference between optic characteristics of the tooling ball and the work piece are described as followings O Difference 1 The ratio between the diameter of the tooling ball s effective reflection surface and the radius of the ball is always two The ratio of
88. re possible to be compensated by doing research on figuring out the relationship between the reflection image and tooling ball s center so that a better fitting circle of compensated dark points can be created to give better results The mechanical touching detecting method described in Chapters 2 and 3 have not been tested in the ABB robot system for detecting the tooling ball when the mould is heated up to about 700F However high heat is a potential threat to the durability of the detector The experiment proves the feasibility of the vision based detecting method and as a result the vision based detecting method can be applied to compensate for the mechanical touching detecting method Divide the mould calibration process into two steps cold calibration and hot calibra tion The tooling ball can be firstly be detected by the mechanical touching method when the mould is cold obtaining position data in cold status Since the mould will be extended by the heat when it is heated the position of the tooling ball will be changed within a certain range According to the position data in cold status the camera with a partial ring shaped light source is carried by the robot arm to the positions tooling ball when the mould is cold After taking photos and applying the vision based detecting method designed the position data of the tooling ball in hot status can be obtained The whole process can be controlled fully automatically so that dangerou
89. rical surface of a stainless steel tooling ball Because the vision based detecting is a non touch detection method and the distance in taking photos can be controlled it may perform better than mechanical touching in a high temperature environment Therefore for tooling ball detecting purposes in a mould calibration process in a high temperature working environment at about 700F a vision based tooling ball detecting method can be applied as an extension for the mechanical touch detection described in Chapters 2 and 3 Due to lack of time and devices to achieve the entire detecting method based on an 95 Figure 4 1 Partial Ring Shaped Light Source ABB robot the target of the course project is simply to find out the C shape reflection image in photos and compute the position of the tooling ball in a photo coordinate system in order to test the feasibility of the vision based method Firstly the hardware setting for taking photos of the tooling ball is introduced Secondly relevant optical characteristics are mentioned Thirdly a vision based tooling ball detecting method is described with the results of the experiment provided Finally the chapter summary concludes the vision based detecting method design and the compensation relationship between the mechanical touch detection and vision based detecting methods are discussed 4 1 Hardware Setting e Light source The light source is a partial ring shaped light sou
90. roperties 4 and 5 of each Myr m n Once one of the G properties 4 of 5 of either the m object in the first image or the nt object in the second image is not equal to one Mais m n is reset to a very large number so that this pair of objects cannot be selected as the target result G properties 4 of 5 sharply reduce the number of irrelative objects e Dark Region According to the three R properties of the C shape reflection image the area of the tooling ball within the photo has two types of region a bright region and a dark 103 Figure 4 5 Dark Region region The dark region is divided into two parts by the bright region Therefore from the center position of the tooling ball to the outside in any directions the gray value of each pixel has useful characteristics which is shown in Figurd4 5 The vertical axis represents the gray value of the pixel and the horizontal axis represents the distance from the tooling ball center to the pixel in that direction The changing condition of gray values always has a peak first followed by a local minimum Define the first local minimum as the dark point Even if the gray values of the pixels in the direction of where the gap of shape C is the gray value of the dark point is still the first local minimum after a peak as is shown in Figurd4 6 e 8 Dark Points 104 Figure 4 7 8 Dark Points Create eight direction vectors from center of tooling ball to
91. rpose of achieving this computing process The data of differences are position information of materials to be welded The position data is located within CAD space Welding Parameters Adjusting Skilled welders achieve the TIG welding task manually using traditional manual op eration mode based on experience However in the automatic welding process the human experiences of welding techniques should be transferred into welding param eters for automated robot welding operation control According to actual welding practices and manual welding experience of welders parameters such as feed rate of filler metal voltage and current supplied for arc generation welding angle of the torch moving speed of robot arm and so on are decided after large numbers of weld ing experiments and a mathematical model is created for the welding task Using such a mathematical model of welding parameters a welding tooling path can be set up in the next step Path Generation After obtaining the differences data and setting welding parameters the welding paths for the robot in the welding process are generated The differences data are usually several pieces of 3D solid parts and the can be formed by welding layer by layer As a result the robot designer separates the 3D solid into several layers and then separates the layers into welding paths that are connected with each other The robot works following these paths and the solid piece can be formed
92. s of the robot can be found from http www abb ca product us 9AAC100735 aspx programmable ABB welding robot robot IRB4450s with robot controller IRC5 is also utilized to automate the welding operation to increase the working efficiency and accuracy Working Environment Setting of the Project Figurd1 1 describes the whole setting of the robot cell for TIG welding There are seven components within the robot cell ABB Welding Robot Robot Controller Mould Heating Table Temperature Controller PC Robot and PC Office e ABB Welding Robot amp Robot Controller ABB welding robot IRB4450s and robot controller IRC5 are applied for the welding task The robot controller contains a user interface called FlexPendant with which the operator can operate the robot and control the program flow of welding e Heating Table Temperature Controller amp Mould Tool steel TIG welding for the automotive mould requires the mould to be preheated to a temperature of about 700F This temperature should be maintained throughout the whole welding process Therefore the mould to be worked on is placed on a heating table designed by Tool Tec Inc The heating table generates a flame for heating the mould and the temperature of the mould is reflected to the temperature controller through a temperature sensor The temperature controller controls the power of the heating table and according to the temperature setting and mould temperature sensed th
93. s working environment can be avoided 111 Chapter 5 Conclusion 5 1 Thesis Summary The design of a mechanical touch style tooling ball detecting method for the mould cal ibration process in the project of automatic TIG welding is described in this thesis from Chapter 1 to Chapter 3 The design includes the mechanical design of the detector the mechanical component design the programming design in the microprocessor for signal processing the electrical component design and the design of the position computing programmed in the robot controller the computational component design The mechanical component has been implemented and tested base on the NC milling machine as mentioned in Chapter 3 While the feasibility of the detecting method is proven the accuracy of the position detection of the tooling ball does not satisfy the requirement especially on the Z of the milling machine under the present design The problem may occur during the process of calibrating the joystick where a good input output relationship is not obtained Three deficiencies are thus to be improved for obtaining a better joystick calibration result 112 e Changing the connecting method between the bearing housing and the centering shaft in order to obtain an accurate distance for computing the slopes of input output relationship curves e Changing the mechanism of deflecting and rotating the shaft of the joystick or ad justing the material of the
94. sing Spring 30 Na L he edad wow m ee al B d di raum L 14 d A LE EREK P d Moos P i k S Si y E E Figure 2 6 Mechanical Component of Version 1 31 Joystick that is applied in version 1 is J1 series joystick purchased from Elobau Sensor Technology The technical specifications of the joystick are provided in AppendixA Part 5 the tactile switch is the B3F 5000 one purchased from Omron Electronic Components LLC Its technical specifications are provided in AppendixA Feature description The joystick mounting base is made of brass and thread connected with the sixth axis of the robot arm The angular operating range of the joystick is 15 The joystick is fixed to the joystick mounting base through thread holes at the bottom of the base The shaft of the joystick is threaded and the connecting cap is thread connected with the shaft A linear motion bearing is applied to achieve a sliding movement The cone part is made of steel and inserted into the bearing to enable the sliding movement The space in the connecting cap for the cone part to slide is kept at a distance by a distance fixing part The inner compressing spring is applied to activate the tactile switch which is soldered onto the PCB Once the cone part slides in the spring is compressed until the elastic force of the spring reaches the activating force of the switch and the digital signal is generated Another compressing spring is applied
95. sixth axis of the robot arm for tooling ball detection The power to run the detector comes from robot controller USB port for 5 volts voltage output The operator operates the robot arm to detect the tooling ball and the detector generates output signals describing the position of the tooling ball with respect to the 22 detector Output signals are transmitted into the electrical component which contains a signal pre processing unit and a microprocessor with a piece of development board The target of the electrical component is to let the robot controller know the content of the output signals value of voltage signal outputs for instance Because the robot controller has a COMI port for serials communication output signals can be converted into bits and sent to the robot controller by serial channels The pre processing unit adjusts the original output signals into a suitable status for the microprocessor to receive The microprocessor achieves both the signal conversion task and the serial communication task The last component is the computational component which translates output signals into position information and computes the position of the tooling ball using programs programmed in the controller The results of position computation are displayed on the LCD screen of FlexPendant The design of each component is carried out according to the flow chart in Figurd2 1 described in detail in following sections 2 3 Mechanica
96. t dark points fitting circle is considered as the spherical center Deviation occurs when the tooling ball locates far away from the middle position of the photo The reason is that a small part of the dark region unexpected lightened area is lightened by the ray which is reflected by the stainless steel block so that the areas of dark region decrease Take one of the sample images as an example Figureg4 9 and 4 10 Eight small white points represent dark points detected The square white point is the center of the dark points fitting circle The round white point is the ideal circle center of the contour of the tooling ball The position of the tooling ball in the sample image locates at the up left of the whole image frame and the expected lightened area locates at the bottom right of the tooling ball Obviously there is a deviated distance between the actual center of the tooling ball and the circle center of the dark points fitting circle 4 6 Chapter Summary According to the results of the experiment the target of the course project is achieved in that the feature of the reflection image is distinguished correctly and the approximate center position of the tooling ball in the photo is detected Although the position of the tooling ball in the photo coordinate system is detected with some error the detected 109 Ideal contour of the ball Ideal center Figure 4 10 Center Deviation 110 eight dark points a
97. t which is described in Chapter 3 Then according to Equation we have du Vou VE ka AV ka 2 4 du Vaa Vi kag AV ka2 2 5 On Vou HIK AV ky 2 6 Oy VEZ VP ky AV ku 2 7 0 is the deflection angle about the axis X computed from signal 1 and 0 5 is the deflection angle about the axis X computed from signal 2 6 is the deflection angle A Figure 2 13 Joystick Coordinate system 42 about the axis Y computed from signal 1 and 6 9 is the deflection angle about the axis Y computed from signal 2 Then deflection angle about the axis X is 0 0 4 0 2 2 and deflection angle about the axis Y is 0 0 1 Oy2 2 2 6 2 Compute position of tooling ball in joystick coordinate sys tem According to the setting of the joystick coordinate system in Figurd2 13 once the tooling ball is appropriately located by the detector Equation 2 3 can still be applied to compute the position of the tooling ball in the joystick coordination system L is the distance form the deflection center of the joystick the origin of the joystick coordinate system to the spherical center of the tooling ball It is a negative value 2 6 3 Transformation process in tooling ball detecting process The transformation process in the robot system among coordinate systems is shown in Figurd2 14 There are three coordinate systems in the process of tooling ball detection the world coordinate system
98. ta uint32 GetByte void T uint32 RecByte RecByte UORBR return RecByte void GetStr uint8 s uint32 n for n gt 0 n xs GetByte if UOLSR 0x01 0 break void __irq IRQ EintO void 1 extern ADC Data 4 uint32 ADC DataM extern SendData 14 extern ADCmark uint8 s loop counter of UARTO data sending uint8 i normal used loop counter including ADC 122 if ADCmark 0 ADCmark 1 initialization of ADC process ADOCR 1 lt lt 0 Fpclk 1000000 1 lt lt 8 0 lt lt 16 0 lt lt 17 1 lt lt 21 0 lt lt 22 1 lt lt 24 0 lt lt 27 DelayNS 10 ADC_DataM ADODR for i 0 i lt 4 i ADOCR 1 lt lt i Fpclk 1000000 1 lt lt 8 0 lt lt 16 0 lt lt 17 1 lt lt 21 0 lt lt 22 1 lt lt 24 0 lt lt 27 DelayNS 10 ADC_DataM ADODR ADOCR 1 lt lt i 123 Fpclk 1000000 1 lt lt 8 0 lt lt 16 0 lt lt 17 1 lt lt 21 0 lt lt 22 1 lt lt 24 0 lt lt 27 DelayNS 10 while ADODR amp 0x80000000 0 ADC_DataM ADODR ADC_DataM ADC_DataM gt gt 6 ADC_DataM ADC DataM amp Ox000003FF ADC Data i ADC DataM IOOPIN IOOPIN amp OxFFFFFFTF DelayNS 100 IOOPIN IOOPIN 0x01 lt lt 7 DelayNS 100 IO1PIN 0x03 lt lt 18 i 2 LED S
99. tatus Display2 Finished DelayNS 100 ADC_DataM 0x00000000 d following program is for data processing so that the data can be converted into suitable format to be sent SendData 0 ADC_Data 0 amp Ox00000F00 gt gt 8 SendData 1 ADC_Data 0 amp 0x000000F0 gt gt 4 SendData 2 ADC_Data 0 amp Ox0000000F SendData 3 ADC Data 1 amp 0x00000F00 gt gt 8 124 SendData 4 ADC Data 1 amp Ox000000F0 gt gt 4 SendData 5 ADC Data 1 amp 0x0000000F SendData 6 ADC Data 2 amp 0x00000F00 gt gt 8 SendData 7 ADC_Data 2 amp 0Ox000000F0 gt gt 4 SendData 8 ADC Data 2 amp 0x0000000F SendData 9 ADC Data 3 amp 0x00000F00 gt gt 8 SendData 10 ADC Data 3 amp 0Ox000000F0 gt gt 4 SendData 11 ADC Data 3 amp 0x0000000F SendData 0 ToASCII SendData 0 SendData 1 ToASCII SendData 1 SendData 2 ToASCII SendData 2 SendData 3 ToASCII SendData 3 SendData 4 ToASCII SendData 4 SendData 5 ToASCII SendData 5 SendData 6 ToASCII SendData 6 SendData 7 ToASCII SendData T7 SendData 8 ToASCII SendData 8 SendData 9 ToASCII SendData 9 SendData 10 ToASCII SendData 10 SendData 11 ToASCII SendData 11 SendData 12 0x24 SendData 13 0x26 for s 0 s lt 14 s UOTHR SendData s while UOLSR amp 0x20 0 while EXTINT amp 0x01 0 125 T EXTINT 0x0
100. ted with the sixth axis of the robot arm through the cylinder The position of the joystick mounting base with the robot arm is fixed by those two threaded holds The angular operating range of the joystick is 25 and the joystick is fixed to the joystick mounting base and the joystick mounting post through four M5 counter sunk screws at the four corners of the joystick A pusher made of brass is fixed to the shaft of joystick by stopper 1 and 2 The sliding part slides on the pusher and its position is fixed by the outer compressing spring and two stoppers The cone part is connected to the sliding part by three M3 counter sunk screws and the PCB is fixed between the sliding part and the cone part with the tactile switch soldered on The method for generating the digital signal is the same as the method in version 1 35 gt Mechanical Mounting S gt Signal amp Information E Power Supply 4 7V gt Operation S Cables 2 P Components of Robot Cell es Microprocessor AD Conversion Pre processing Unit amp Signal Preprocess COM Port Communi Detect another ball amp Go back to step 1 Mechanical Connected Detector 1 l d e igna Well Locate Now n0 USB Extension Port o A Analo amp amp evel sear signa U pig RAPID Code Receiving Data from COMI amp Position Comput
101. ting accuracy a common phe nomenon within the distribution of errors and target values difference between 0 1 and 89 y error T 1 X CIror Figure 3 20 Errors of Tooling Ball Position Detection 6 2 difference between 0 1 and 0 2 00 L and Az are found The trends of errors and target values are similar to the trends of positions of TCP as shown in Figurq3 21 to Figurq3 21 shows the relationship between curves of 0 1 0 3 and 0 1 0 5 and correspondent positions of TCP on axis Xm and axis Ym Values of 0 1 0 5 and 8 4 0 5 are used to describe the difference between 0 1 and 0 9 and the difference between 0 1 and 6 2 respectively Figures3 22 to show the relationship between values of 00 L and Az and corre spondent positions of TCP on axis Xm and axis Ym Figurq3 25 shows the relationship between errors on axes Xm Ym and Zm and corre spondent positions of TCP on axes Xm and Ym This phenomenon shows that the problem of generating unsatisfied results may happen at the process of calibrating the joystick for computing deflection angle After rethinking 90 1 TI T T T T T T T EN P oar d 2 ES AME A 85 a D r 7 E Y L 1 1 k C ME S Q 8 9 2 7 A N E i 02 J eee V E di q a AAA N 4 y Ka S or a H E Ge E AA k ER E 7 m 195 4 A N nen Z A dij x E A m 25 N X 125 N 06 TCP ES 4 4 os 4
102. tion is made of stainless steel and has a diameter of 15 85mm Figurq3 2 The dimension of the tooling ball is provided in Figurd3 3 51 Signal 1 amp 2 for each axis DeflectionAngle TTT TTT TTT n Figure 3 4 The output voltage of joystick is proportional to the deflection angle 3 2 Joystick Calibration The joystick used in the mechanical design J6 series joystick is a redundant biaxial joystick from Elobau Sensor Technology The outputs are two pairs of analog voltage signals and each pair represents the deflection angle of one axis One deflection angle is represented by two output signals and this is why the joystick is called redundant In each pair there are two voltage signals of which the values are opposite to each other The most important property of the output signals is that the output voltage is proportional to the deflection angle as shown in Figurq3 4 In Figurd3 4 Vmin and Vmax are the minimum and maximum values of the output voltage signals for an operating voltage Vin Q maz is the max deflection angle and V is the value of the output voltage signal when the shaft of the joystick is spring returned to the center position 52 Figure 3 5 Configuration Example of Joystick Coordinate System The joystick coordinate system is set as shown in Figurd3 5 The deflection angle about the axis X 0 outputs voltage signals VZ and V 4 The deflection angle about the
103. urd3 9 illustrates the geometrical relationship of the mechanism for the deflection angle computing in the joystick calibration process The pivot point P the point at which the linear bearing housing is attached to the centering shaft is located on a virtual plane V to which the axis of the shaft extension is normal This means that the distance between the pivot point and the shaft extension axis is fixed and in the present design measures 22 5mm as shown in Figurq3 9 The angle that the joystick axis is deflected can therefore be set by adjusting the distance between the chuck of the milling machine and the indexing head This angle indicated as 0 in Figurd3 9 is what we refer to as the combined deflection angle in that it is a combination of 0 and 0 According to Equation 2 3 in Chapter 2 the position of point P in the joystick coordi nate system is known by Equation 3 10 61 L 8 E Virtual Plane V Center Axis of Shaft Extension DETAIL A SCALE 1 1 Rotation Axis Figure 3 9 Deflection Angles of Joystick in Calibration Process 62 a Th L cos 0 sin 0 Bis y B L cos 6 sin 0 3 10 e L cos 0 cos 6 1 1 The position of point P in milling machine coordinate system Fn is P oe qur e 1 and since the transformation matrix Tj defines coordinate system Fm in the coordinate system F the position of point P in the joystick coordinate system is computed by Equa tion 3 11 r

View/Open - UWSpace - University of Waterloo

Contents

Download Pdf Manuals

Related Search

Related Contents