Patent GB-829824-A (GB)
Title: Automatic programme control for machine tools
IPC: G05B19/18
Filed: 1956-07-30
Abstract: 829,824. Milling-machines. BENDIXAVIATION CORPORATION. July 30, 1956 [Aug. 1, 1955], No. 23493/56. Class 83 (3). An automatically-controlled machine-tool comprises tool and work-carriers 158, 130, a motor 116 to which electric command-pulses are applied in accordance with a storedprogramme to produce a relative displacement of the carriers in a first-direction by successive amounts specified by the programme, means for generating electric pulses corresponding to elementary relative displacements of the two carriers in a second direction, and an interpolator jointly controlled by the programme and by said displacement pulses for transmitting and applying to the motor a number of command-pulses specified by the programme, for each fixed number of said displacement pulses corresponding to a predetermined displacement interval in said second direction. In a cam-milling machine, a tape-reader 100 is connected through storage registers 102, 104 to a four-stage binary counter or interpolator 108, which has an output connected back to these members and a further output to an error register 110. A spindle control 106 is connected through a servo-amplifier 112, to the spindle drive 116, which consists of a torquemotor, a valve and an hydraulic motor. In response to the voltage output of the amplifier 112, the. torque-motor controls the opening of the valve according to the magnitude and polarity of the voltage, to determine the direction and speed of rotation of the hydraulic motor. The drive 116 rotates gears 128, 136 to rotate the cam-blank 132, and to move a slide 140 axially of the cam through a screw 138. The spindle drive also rotates a gear 144, causing a reading-head 148 to transmit pulses to the interpolator 108 at the rate of 576 per cam revolution. The output of an amplifier 114 connected to the error register 110 passes to a cross-feed drive 150, which rotates a screw 152 to move a slide 154 carrying a milling- cutter 160 rotated at 3600 r.p.m. by a motor 162. For each revolution of the cam the screw 138 moves the slide 140, 0.005 inch. The pitch of the screw 152 is 0.02 inch. The crossfeed drive 150 also rotates a gear 166 to cause a reading-head 172 to transmit feedback pulses to the error register 110. The components of the registers 102, 104 and of the interpolator 108 are shown in Fig. 2, where a symbol such as 202 represents a bistable multivibrator initially having a left-output and left and rightinputs which are low, and a high right-output; 210 represents an " and "-gate which has a high output only when all of the inputs are high; 234 represents a one-input bistable multivibrator initially having a high rightoutput and a low left-output, and 250 represents an " or " gate which has a high output whenever any of its inputs are high. The tape 264 contains the programme in binary code, and each multivibrator 202, 204, 206, 208 is caused to have a high left-input from the tape reader as soon as a hole is located in the corresponding column a, b, c or d. Initially, switches are momentarily closed manually to gates 252, 254, 256 to clear the store 104, to transfer information in the store 102 to the store 104, and to advance the tape. This procedure is then repeated so that the information in row 266 is in the register 104, and that in row 268 is in the register 102. The machine is then ready for automatic operation. Hydraulic power is supplied to the drives 116, 150 and the spindlecontrol 106 is set to introduce a voltage to the servo-amplifier 112 for rotating the drive 116 at a particular velocity. Each stage in the interpolator halves the number of spindle pulses introduced to the stage, which are initially introduced from the head 148 to the gate 226, the multivibrator 234 and the gate 236. The information in row 266 of the tape results in an output of 13 pulses, Fig. 3 (F), from the gate 250, and an "overflow" pulse from the gate 248 which is introduced to the gate 252 to clear the store 104, and to the gate 256 to advance the tape so that the reader 100 will read the information in row 270. It is also introduced through the gate 254 to the multivibrator 262 to transfer the information between the stores 102, 104, there being a slight delay to permit the store 104 to be cleared. Rows 268, 270 of the information of the tape produce respectively outputs of 11 and 7 pulses from the interpolator for the next 20 degrees of spindle rotation. Considering the first output from the information 266, the drive 150 is rotated by thirteen pulse increments and moves the tool 160 a distance of 0.0002 inch for each pulse. Thirteen pulses are thereby produced by the head 172 and are fed back, to zero the error-register 110. The interpolator feeds the pulses in the manner shown in Fig. 3 (F), so that the tool cuts in a path, as shown in Fig. 5, and is not suddenly fed by thirteen pulse increments at the commencement of a 10-degree rotational interval of the spindle, as represented by the line 406, Fig. 4. A modified machine comprises a reader 500, Fig. 7, a temporary store 502, an active store 507, an interpolator 521, a spindle speed-control 523, and a spindle directioncontrol 520. The store 507 includes a decoder 836, Fig. 11, having four outputs connected to the spindle speed-control, and also to gates in the interpolator. According to the condition of two multivibrators 809, 811 in the store 507, a particular output of the decoder is high and serves to cause a flow of current through a tube in the spindle speed-control and, through a servo-amplifier 524, to drive the spindle servo 525 at a particular speed. Rotation of the spindle drive 525 produces a rotation of a spindle reading-head 526 which has a carrierwave introduced to it from a demodulator 534 and which produces a modulated voltage at each output, for introduction to the demodulator. The modulated voltages have envelopes which are displaced from each other, and are functions of spindle position. The voltages are demodulated by the demodulator 534, and two voltages which are proportional to the envelopes of the modulated voltages are introduced to a spindle pulse-synchronizer 539, which synchronizes the clock pulses to the multivibrators with the spindle pulses. A cross-feed reading-head 538, the demodulator 534 and a cross-feed synchronizer 522 operate similarly to the spindle reading-head 526, the demodulator 534 and the spindle pulse-synchronizer 539. The number of passes is controlled by a pass counter control 552, a pass counter 548 and a number-of-passes-required control 585. The outputs of gates 516, 533, Figs. 7 and 17, are introduced to the grids of tubes 1400, 1406 respectively which are normally biased below cut-off. When current flows through the tubes, relay switches 1404, 1410 are actuated. The switch 1404 is connected in series with a power supply 1412 and a positive solenoid 1414 of a ganged stepping switch 1416, comprising units 1420, 1422, 1424, 1426. Thus, actuation of the solenoid 1414 will advance to each of the switch arms 1427-1430 from the position shown to the "one" terminal. The switch 1410 cooperates with a negative solenoid 1432 to move the stepping switches in the opposite direction. Terminals in the units 1426, 1424 are connected respectively to terminals in manual setting switches 1436, 1438. As shown, the switch arms 1440, 1442 are set to produce 4 passes of the tool. A closed coil of tape is carried on rollers 602, Fig. 8, freely mounted on a base 604. As the tape is fed to the reader 500 by a sprocket 620 advanced by a multi-vibrator, a pulley 614 is raised until it actuates a switch to start a motor which rotates rollers 608, 610 to draw further tape from the coil. The tape 600, Fig. 9, has sprocket holes 622 and double rows of information denoting the items shown against row 650. The presence or absence of a hole in the position " Spindle direction " determines the direction of rotation of the spindle 118, Fig. 1. The information "Angular interval " determines the speed of spindle rotation through the decoder 836 and the spindle speed control 523 and the interval through which the spindle will rotate while the information in the store 507 is used. When no. holes are present at these positions, 255 pulses are counted and the 256th pulse returns the counter to zero and resets the stores; since 256 pulses are produced in a 5-degree rotation of the spindle, each block of information is used during a 5-degree interval. When a hole is present at the lower position only, the speed control 523 is adjusted and each block is used during a 10-degree interval. The other alternatives produce 20. and 80-degree intervals. In operation, the tool 160 is first set in a datum-position 1800, Fig. 24, relatively to the blank 132. The control 585 is set at position 4 (i.e. the number of passes required), a ganged-switch 865, Fig. 11, is set to introduce high outputs to gates 868,878, 879, 870 and a ganged-switch 866 is set to introduce high outputs to gates 882, 883, 871. These settings provide information that three coarse-cuts 1802, 1804, 1806 of 0.06 inch depth, and one fine-cut 1808 of 0.01 inch depth, are to be taken. Tape advance switches 547, 568 are then closed to feed the information in the row 660 to the store 507, and that in the row 662 to store 502. The operator next turns on the hydraulic power for the spindle drive 525, and for the cross-feed drive 536, and presses an automatic-start button. A hole in position 6 of the row 2 of the information 660 causes the spindles 118, 130 to rotate at particular speeds. The absence of a hole in position 7 results in positive rotation of the spindle 130. The spindle pulses produced pass through a buffer-register 519, which ensures that the number of spindle pulses transmitted to the interpolator 521 is truely proportional to the net-motion of the spindle. For instance, due to excessive cutting forces on the tool, the spindle 130 may