Patent GB-909509-A (GB)
Title: Apparatus for reproducing a contour of a pattern on a workpiece
IPC: B23Q35/128
Filed: 1960-07-27
Abstract: 909,509. Curve-following. GENERAL MOTORS CORPORATION. July 27, 1960 [Sept. 2, 1959; Sept. 3, 1959], No. 26108/60. Class 40 (3). For reproducing the contour of a pattern on a workpiece, motor-driven tool and workpiece supports are arranged to move in mutually transverse paths under the control of a first photo-sensitive device sensing parallel misalignments thereof from the pattern contour and a second device sensing off-line deviations. The workpiece 28, Fig. 1, on which a contour is to be engraved corresponding to the contour 136 on a plate 132 is supported relative to a cutting tool 26 driven by a motor 20 and mounted on a support 18 which can be moved vertically on a frame 14 on a table 12 which itself can be moved horizontally on a table 10. The horizontal and vertical movements are effected by threaded shafts 58, 64 and gear trains 50, 52 driven by motors 54, 60 controlled by fluid pressure control units 66, 68 actuated respectively for X-axis and Y-axis control from servo amplifiers 114, 118 fed by scanning circuits 112, 116 to which pulses are applied from potentiometers 250, 252 driven from a tracer arrangement 162 comprising a bracket 168 movable with the support 18 and rotatable relative thereto. The tracer arrangement 162 comprises a photoelectric scanning head 172 formed by two pairs 180, 182 of steering photo-cells connected to an amplifer 188, Fig. 9, a pair of " on line " photo-cells 176 connected to an amplifier 184 and a pair of " off line " photo-cells 178 connected to an amplifier 186. A magnified image of the line 136 on the plate 132 is projected through an optical system, Fig. 3, (not shown), on to the screen 152 of a vertical tower member 140 which is arranged to move with the tool support 18. A second image passed through opening 154 in the base of the tower is correlated with a reticule 156 simulating the tool 26 and is passed from a television transmitter 158 over a closed circuit to a television receiver 164 in an adjoining room so that an operator can view the disposition of the cutting tool 26 relative to the desired contour 136. The diagonally opposite cells of the four cells 180, 182 are connected so that an output is produced to rotate the scanning head 172 if the course pursued is not parallel to the contour line. The " on line " photo-cells 176 normally straddle the contour line 136, but if the head 172 is off course, a potential of magnitude and polarity corresponding to the deviation will be produced and applied to preamplifier 184. Normally one of the off-line photo-cells 178 produces a pulse, but the absence of a signal which occurs when the head 172 is off course is utilized to effect stoppage of the apparatus. The outputs from the amplifiers 184, 186, 188 are fed to a brush and slip-ring arrangement 190. The steering error signals are applied through the commutator arrangement 190 to a D.C. amplifier 218 through a manual-automatic switching circuit 200, Fig. 9a, and to a magnetic amplifier 234, Fig. 6, to control rotation on one or the other direction of a two-phase motor 238 having a tachometer generator 240 providing a feed-back voltage to suppress minor variations, and also to prevent overshooting. The rotation of the motor 238 rotates a steering sine-cosine potentiometer to provide corresponding X and Y voltages to scanning circuits 112, 116, Fig. 7, controlling the servo motors 54, 60 to provide horizontal and vertical movements of the tool carriage 18. The errorsignal from the " on course " cells 176 is passed from the commutator 190 via an amplifier 254 with two equal and opposite outputs to an " on line " sine-cosine potentiometer 252 which provides corresponding voltages to the scanning circuits 112, 116 and servo amplifiers 114, 118 controlling the servomotors 54, 60. In the case of manual steering the switch 422, Fig. 8, is actuated to open the circuits of relays 222, 226, 274 and 302, the potentiometers 250, 252 are disconnected and a steering sine-cosine potentiometer 340 similar to the member 250, is controlled by a steering handle 332 at the operator's position. The rate of movement effected by the steering system is controlled by varying the voltage applied to the potentiometers 250, 340 by means of two adjustable potentiometers 318, 320 controlled by a rotatable knob 312 at the operator's position. For manual operation the control knob 332, Fig. 9a, rotates a shaft 334, a cam limit switch 336, a synchro 338, steering control potentiometer 340 and through slip clutch 342, a speed reducer 344 and a servomotor 346. The motors 346, 238 are kept in synchronism by synchros 248, 338 having rotors 400, 406 and associated stators so that the change from manual to automatic operation and vice versa can be effected immediately. If the curve to be followed has intersecting positions, the operation can be changed temporarily to a quasimanual control by the actuation of a " freeze " button 430, Fig. 8, so that the desired path at the intersection can be followed, with a return to automatic operation by the release of the button. The apparatus includes limit switches operated when the tool carriage reaches predetermined horizontal and vertical positions to cut-off the supply of fluid to the servo valves. Arrangements for an adjustable support member for the workpiece and the positioning of the workpiece on the member are described in detail in connection with Figs. 11 to 17 (not shown). The system also includes a device, Fig. 10 (not shown), for withdrawing from the cutting area chips and debris produced by the tool 26.