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Hence, the X-axis and the Y-axis of the torch co-ordinates frame will be contained in the referred planes. For approach orientations contained in planes between planes 3 and 4, the torch co-ordinates frame will be rotated about its X-axis by an angle between 0 deg and 90 deg, proportionally to the angle of rotation of the plane which contains the approach direction, from 120 deg to 225 deg. Figure 3.19 and Figure 3.20 show the resulting robot positions for approach orientations contained in planes between planes 3 and 4. For approach orientations contained in planes between planes 1 and 2, the torch co-ordinates frame will be rotated about its own X-axis by an angle between 0 deg and -90 deg, proportionally to the angle of rotation of the plane which contains the approach direction, from 60 deg to -45 deg. Figure 3.21 shows the resulting robot positions for approach orientations contained in planes between planes 1 and 2. Approach orientations contained in planes between planes 2 and 4 cannot be defined. These rules were devised in order to take advantage of the mounting position of the welding torch relative to the robot's end joint. Another important aspect of off-line programming is the definition of the robot path for approaching and withdrawing from the weld joint. In order to generate the points necessary to define such a path, it was assumed that all the welds were located on the external surface of the workpiece. The path which the torch must follow to achieve a weld start point is defined by the weld approach points and the path the torch must follow to withdraw from a weld end point is defined by the weld withdrawal points. Up to four weld approach points and up to four weld withdrawal points are defined automatically by the program for each weld, depending on the orientation of the approach vectors at the weld start and end points and on the size of the workpiece. The aim of these approach and withdrawal points is to prevent collisions between the welding torch and the workpiece. This is achieved by defining a workpiece extension box, which is an imaginary box whose dimensions are such that the workpiece is fully contained inside it (see Figure 3.22). This extension box is given in terms of two points16, situated at two diagonally opposite corners of the imaginary box: a) a point with the minimum co-ordinates of the box and b) a point with the maximum co-ordinates of the box. With the minimum and maximum co-ordinates of the box, the other corners are also obtained. These points are then transformed to the robot world co-ordinates frame by using equation (3.16) and a second imaginary box is defined, the workpiece clearance box (see Figure 3.22), whose corners are obtained by subtracting a clearance value (e. g. 50 mm) from the minimum transformed co- ordinates and adding the same clearance value to the maximum transformed co- ordinates. The workpiece clearance box will define the limits outside which the welding torch can be moved without colliding with the workpiece. Figure 3.23 shows an example of how the weld approach points are obtained. In the example of this figure, to achieve a weld start point, the robot must follow the weld approach points from ap3 to apl. The robot is always restricted to linear movements between points, thus ensuring a predictable path. Note that the torch orientation in ap3 is such that the X-axis of the torch co-ordinates frame points downwards (-Z world co-ordinate direction) and the Z-axis of the torch co-ordinates 16 Relative to the CAD world co-ordinates frame 83
frame points to the front of the robot (+X world co-ordinate direction). The welding torch in moved from ap3 to ap2 in a linear path while the torch orientation is changed to assume the orientation required for the weld start point. Keeping this orientation, the torch is moved to apl and then to the weld start point (wl). If the point apt falls under the workpiece clearance box (i. e. the ap2z17 = zmin - clearance), a further point is necessary such that the robot moves the torch in a path around the workpiece clearance box. Figure 3.24 illustrates this case, in which the first approach point to be achieved by the welding torch is ap4. These points are generated such that the first weld approach point to be achieved by the welding torch is always located at the top surface of the workpiece clearance box The same rules are used for generating both weld approach points and weld withdrawal points (wdr). After obtaining the welding parameters, the weld start and end points, and the approach and withdrawal points for each weld on the workpiece, the off-line programming module generates three files: a) one containing the welding parameters, which are input to the control system; b) a second file containing the robot teach- points, which describe positions in space, in terms of robot world co-ordinates, and orientations, in terms of quartenions18, and c) a third file containing the robot program with comments explaining each command and the input and output signals necessary for communicating with the control system. Appendix C shows the user interface for the off-line programming module and some of its outputs. 3.3 2.3 Robot simulation Having generated the robot teach points and the robot program, a simulation can be performed in order to verify if all the teach points are achievable and if any collisions are detected between the robot and the welding torch structure and also between the robot and the other components of the welding cell. If any problem is detected it can be solved by either changing the position of the workpiece (e. g. by making it further or closer to the robot and/or changing its height) or by adding more teach points in order to change the previously defined robot path. If any modifications are necessary in the workpiece positioning, the same modification must be carried out in the real cell and a new program must be generated by using the off-line programming module with a different. CAD-to-Robot transformation matrix. After correcting the detected errors, the corrected robot program can be compiled and downloaded to the robot controller for execution. Once the system is correctly calibrated, the only possible sources of error will stem from the component error group and from process disturbances. As mentioned before, these errors should be dealt with by an on-line adaptive control system. "Z co-ordinate of point ap2 1$ A quartenion (Q) is a mathematical way of representing a rotation by a certain angle about an axis by means of a scalar (s) and a vector (v): Q-[s+v] (see refs. 192,193). 84
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CRANFIELD UNIVERSITY GC CARVALHO AN
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ABSTRACT The aim of this work was t
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I dedicate this work to the memory
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FIGURES TABLES APPENDICES NOTATION
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3.3.2.1 Welding parameters generato
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References Further reading Appendic
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Figure 3.12 Offsets for weld start
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Figure 6.31 Voltage step input test
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Figure J. 2 Plot of stand-off varia
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Table A. 1 Welding extended entity
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NOTATION A, Electrode sectional are
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Pr(ign) Possibility measure of proc
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1. Introduction Welding is the thir
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Chapter 4 describes the on-line pos
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In pulse transfer, the welding curr
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Pd = Pv - pzh-s (2.1) where Pd is t
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the bridge. Another factor that ind
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establish the stable conditions for
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Philpott [ref. 21] developed an on-
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current peak at the moment the tip
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obot on the line must be individual
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collision detection capabilities wh
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cause dynamic variation in the seam
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Another type of robot static calibr
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spatter the gas nozzle is particula
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Table 2.1: Joint positioning tolera
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In order to minimise the undesirabl
Page 57 and 58: c) Ultrasonic sensors; d) Through-t
Page 59 and 60: where K,, K2, K3 and K4 are constan
Page 61 and 62: Philpott [refs. 21,131], based on t
Page 63 and 64: centre. This is attributed to the m
Page 65 and 66: technique must be employed to preve
Page 67 and 68: " digital hardware, which is basica
Page 69 and 70: " Maximum value, W.: Wmý = max(W )
Page 71 and 72: process studied over a small range.
Page 73 and 74: In-process welding control is a muc
Page 75 and 76: volume caused by the presence of a
Page 77 and 78: SHIELDING GAS IN CONSUMABLE ELECTRO
Page 79 and 80: Arc voltage Anode Arc length I Anod
Page 81 and 82: computed ideal procedure optimisnti
Page 83 and 84: CONSTANT CURRENT POWER SOURCE `j' O
Page 85 and 86: Original Surface New Surface Electr
Page 87 and 88: otating welding wire direction weld
Page 89 and 90: 3.1.1.1 Robot errors A robot arm is
Page 91 and 92: 3.2.2 Programming error correction
Page 93 and 94: 3.3.2 Off-line programming module I
Page 95 and 96: Pen is the weld penetration (side p
Page 97 and 98: a. 2) Geometrical constraints from
Page 99 and 100: Step 11 Step 12 Step 13 Step 14 Ste
Page 101 and 102: Step 21 Step 22 If the wire feed sp
Page 103 and 104: the Y'-axis results in a positive "
Page 105 and 106: _ p1e0a - pORoba m31 Ilp! - poll (3
Page 107: of a robot in its zero position12 w
Page 111 and 112: CAD Off-line (AutoCAD) programming
Page 113 and 114: Z Surface 4 A Y 7 M2 Open Edge Join
Page 115 and 116: WCF World Co-ordinates Frame 2a = J
Page 117 and 118: x Torch Co-ordinates Frame o Indica
Page 119 and 120: vo Ö 't7 Y7 't O m O 'S O O S O S
Page 121 and 122: ýý aý 0 oA aW ö A O Zt A OO 't
Page 123 and 124: Ti 9ý-! i4 *Tx t ap31 jx ý- ymin
Page 125 and 126: errors', (i. e. joint positioning,
Page 127 and 128: was considered to be outside the sc
Page 129 and 130: Table 4.3 - Linguistic representati
Page 131 and 132: The introduction of such a reduced
Page 133 and 134: Table 4.8 - Final welding process c
Page 135 and 136: the collection of welding data corr
Page 137 and 138: Step 4- Calculate the confidence of
Page 139 and 140: Z Table Co-ordinates Frame Y X Robo
Page 141 and 142: 5.3 Monitoring system The monitorin
Page 143 and 144: the torch end. Only one degree of f
Page 145 and 146: Current: 500 Position: 234.5 5.7.3
Page 147 and 148: I" va JI ºr ö C 3 r" r" rl f_ £-
Page 149 and 150: IgurC a. H -I UI qur vCiSUJ JpCCU C
Page 151 and 152: 126
Page 153 and 154: Table 6.1 - Welding trials carried
Page 155 and 156: Table 6.3 - Coefficients of Ogunbiy
Page 157 and 158: Note that the calibration model sho
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Table 6.6 - Welding parameters used
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constant set-up welding parameters
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stickout lengths and the temperatur
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of the dip mode of metal transfer.
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which would become active by settin
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In section 4.2.5 it has been mentio
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300 280 260 240 rd 35- 3D 25 20 15
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Figure 6.5 - Measured "versus" Pred
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i S 0 -0.1 -0.2 -0.3 -0.7- 68 10 12
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32.0 E 31.5 y 31.0 30.5 30.0 j 29.5
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35 - 30 p 15 10 0.00 2.60 5.42 8.23
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40 35 30 25 20 15 10 A+iIII+F0.17 2
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30 28 26 24 22 SO_act [mm] DipR [mo
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22 20 18 SO_act [mm] DipR [ohm/100]
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!: 30 25 20t 10 5-- 0 Dip Transfer
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0.430- - 0.380- - :r 0.330 fPR L- 0
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7.2 Tests with varying stand-off an
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Table 7.3 - Bead geometry along the
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ö a2 ., u" u,.., g .,. aucyuaac VI
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0 24-- 22-- 18 210 1 90 0 v 170 mm
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Q 34 32 3o mIm Viewing direction Fl
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ýa 34 mm JO a .. ý nn ýr "u 00 M
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22 20 18 Viewing direction Flange W
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36 33 31 o 29 t 350 310 o 290 U due
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I C, x -i 23 21 j 19 Q 240c WFS =10
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en 34 32 - vsec 30- 26- 24 + .. ++
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186
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" to design and build the hardware
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Although only linear joints were im
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for predicting possibility of bad a
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8.4 Process monitoring and control
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satisfy the required quality criter
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198
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types of joints and multi-pass weld
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[14] NEMCHINSKY, V. A. The effect o
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[38] D1LTHEY, U. , REICHELL, T. , S
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[64] KING, F-J. and HIRSCH, P. Seam
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[86] CARGNELLI, M. and ROGOWSKI, A.
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[109] KURKIN, N. S. and DRIKKER, V.
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[130] USHIO, M. , LIU, W. , MAO, W.
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[151] DAVIS, A. R. Orr-line gap det
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[177] COOK, G. E. Feedback and adap
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[201] WON, Y. J. and CHO, H. S. A f
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220
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222
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wnum: local variable which defines
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Table A. 1 - continuation List item
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Imean = a2 + b2*WFS + c2*SO + d2*SO
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TCP2 number are also defined. The o
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f ROBSET. DAT: This file is created
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Figure C. 3 - Main dialogue box of
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Choose the set of welding parameter
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Water Cooling optic fibre bundle 0
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Figure E. 1 - Main graphical screen
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242
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Table G. 2 - Interface box external
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Robot ii Controller +24W CO . +24Vd
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248
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Table 1.1 - continuation Run Vpk M
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10- y =0.001ac 0 r. dSO [mm] $0 '10
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5.00- 0.00 y=0.0019x 1000 1500 2000
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Table J. 7 - Welding data collected
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Table J. 10 - Welding data collecte
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20.00- 15. M y=0.0047x - 1.7922 10.
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266
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Table K. 1- continuation Set-up par
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Table K. 1 - continuation Set-up pa
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Table K. 2 - continuation Set up pa
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Table K. 2 - Continuation Set-up pa
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Table K. 3 - Continuation Set-up pa
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Table K. 3 - Continuation Setup par
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