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from three previously estimated values. This resulted in a stand-off control cycle of approximately 750 milliseconds with maximum correction of ±1mm per cycle. This limit in the table movement was imposed to prevent any undesirable arc instability due to an excessive sudden change in stand-off. This control strategy gave a good and robust performance. 4.2.5 Communications delay An important factor to be considered in the control loop is the delay resulting from the transfer of control instructions and their full implementation by the welding power source and the table controller. These delays were compensated for by introducing time delays between the control cycles. In a control loop, the control instructions are the result of applying the control rules to a measured process state. If during the measurement the process state is still changing as a result of a previous control instruction, an unreliable measurement will be obtained. If the controller uses this measurement to generate new control instructions to compensate for deviations, this may result in oscillations in the control loop and in process instability. Therefore, by introducing suitable time delays in the control loop, these unstable situations can be prevented. In the case of stand-off control, the use of a third order filter guaranteed that the table controller was given sufficient time to adjust the stand-off without incurring instability. However, since a correction signal could be issued every monitoring cycle, in the case of the welding process control a time delay should be introduced. In order to have a good estimate of this time delay, some-voltage step input tests were carried out using two different ways of communicating with the welding power sources: a) via direct serial communication with the power source controller and b) via analogue signals, using a special interface tailored for robots. The results of the tests can be found in section 6.3. The power source was found to have a response time of approximately 50 ms for direct serial communications and 200 ms for analogue input via the robot interface. Since the serial communications protocol for the power source used was still being developed, some limitations were found in terms of available power source commands. This led the author to opt for the robot interface, thus in effect having a time delay of 200 ms. This time delay was introduced in the control cycle in such a way that the control instructions to the power source would be issued every other monitoring cycle. Consequently a voltage control cycle of approximately 500 milliseconds was obtained, that is, two control cycles would occur every second. 5 Migatronic BDH550 113
Z Table Co-ordinates Frame Y X Robot World Co-orcinates Frame Moving structure Y X Direction of Movement 0 0 \ Stepper Motor ° Stationary " 0 structure Ball-nut screw Figure 4.1 - Sketch of the moving table implemented in the control system Pow er Ratio Dip Con sistency Index Trans fer Index Transfer Stability Index 1.0 1.0 1.0 6.0 0.97 _V - ideal spray J 0.95 v J+v 0.8 0.6 0 4 . maxPRdi minPRdip 0.2 _V -V ideal dip +V +V 0.05 ideal dip 0.4 0.45 +V ideal spray _V ideal dip 1.9 1.6 0.3 - -V 0 1 +V V ideal dip . ideal spray ideal spray ý 0 0 0 1.0 - ---- Figure 4.2 - Process control shown schematically 114 3 S
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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
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c) Ultrasonic sensors; d) Through-t
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where K,, K2, K3 and K4 are constan
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Philpott [refs. 21,131], based on t
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centre. This is attributed to the m
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technique must be employed to preve
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" digital hardware, which is basica
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" Maximum value, W.: Wmý = max(W )
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process studied over a small range.
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In-process welding control is a muc
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volume caused by the presence of a
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SHIELDING GAS IN CONSUMABLE ELECTRO
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Arc voltage Anode Arc length I Anod
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computed ideal procedure optimisnti
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CONSTANT CURRENT POWER SOURCE `j' O
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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 and 108: of a robot in its zero position12 w
Page 109 and 110: frame points to the front of the ro
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: Step 4- Calculate the confidence of
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
Page 159 and 160: Table 6.6 - Welding parameters used
Page 161 and 162: constant set-up welding parameters
Page 163 and 164: stickout lengths and the temperatur
Page 165 and 166: of the dip mode of metal transfer.
Page 167 and 168: which would become active by settin
Page 169 and 170: In section 4.2.5 it has been mentio
Page 171 and 172: 300 280 260 240 rd 35- 3D 25 20 15
Page 173 and 174: Figure 6.5 - Measured "versus" Pred
Page 175 and 176: i S 0 -0.1 -0.2 -0.3 -0.7- 68 10 12
Page 177 and 178: 32.0 E 31.5 y 31.0 30.5 30.0 j 29.5
Page 179 and 180: 35 - 30 p 15 10 0.00 2.60 5.42 8.23
Page 181 and 182: 40 35 30 25 20 15 10 A+iIII+F0.17 2
Page 183 and 184: 30 28 26 24 22 SO_act [mm] DipR [mo
Page 185 and 186: 22 20 18 SO_act [mm] DipR [ohm/100]
Page 187 and 188: !: 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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