Patent GB-1019896-A (GB)
Title: Automatic control apparatus
IPC: G05B19/416
Filed: 1962-09-05
Abstract: 1,019,896. Electronic counters. GENERAL ELECTRIC CO. Sept. 5, 1962 [Sept. 5, 1961 (2)], No. 34089/62. Heading G4A. [Also in Division G3] In a programmed control arrangement for machine tools, incorporating a pulse rate control system, a pulse clock 23 provides a signal, having a pulse rate of 250 kc/s. with a pulse width of 2 microsecs., to a 3-stage decade divider 28 having an output at 60 cycles per second which is applied to a filter 62, modifying the square-wave to a sinusoidal wave. Two outputs are derived from the filter 62, one of which is phase-shifted by 90 degrees in unit 65, and applied as a two-phase excitation to the stators of a Y-axis position feedback resolver 16 and an X-axis resolver 16<SP>1</SP>. The X and Y axis systems being similar the description is limited to that for the Y-axis, wherein the rotor signal, representative of movement of a tool or work table within one revolution of the rotor is fed through a pulse-shaper 69, producing square pulses, to a phase-discriminator 18. The phase discriminator 18 compares a command reference signal from a command phase counter 31 with the squared rotor signal, the difference in phase between these signals constituting the error signal applied to the servo loop. The error signal, by a digital to analogue converter 73, is modified to a direct analogue potential which is applied through an operational amplifier 74 to a Y-axis servomotor 75. The feedback loop is completed through a feed motor, not shown, driving shaft 76. For error signals in excess of 360 degrees a reversible counter 78 is excited by the converter 73 so that the input to the operational amplifier 74 is a direct potential proportional to the fraction of a cycle phase difference and to each addition full cycle of phase difference. Numerical data input equipment.-A programmed punched tape is read by a reader 21 converting the binary-coded-decimal representation into corresponding electrical impulses which are fed to a velocity command 29. Velocity command.-The output from the pulse clock 23 is fed to a divide-by-five counter 30 to produce a 50 kc. signal which is fed to a manual feed-rate over-ride 52 which comprises a plurality of decade divider circuits arranged to provide an output pulse variation, set by manual switches, of from zero to 150% of 33À3 kc/s. which corresponds to the normal cutting tool feed-rate. The manually adjusted pulse-rate is fed to the velocity command 29 which furnishes a pulse-rate to a function generator 37 corresponding to the programmed feed-rate as modified by the manual over-ride 52. The velocity command comprises a pulse rate multiplier 54, formed by a counter 55, command storage 57 interconnected by multiplication gates 56, to which numerical data signals are fed from the reader 21 via a buffer storage 59 and a binary-coded-decimal comparator 58 which simultaneously senses the working and buffer storages 57, 59 to ascertain which holds the larger number to control the application of a 250 p.p.s. pulse train from a line 84 to the working command storage 57 to equalize the number stored in it with the number stored in the buffer storage 59. Since the command rate to the function generator can only change at 250 p.p.s., acceleration or deceleration of the tool feed is automatically limited. Function generator.-The X and Y programmed departures are applied to the function generator 37 which comprises two pulse rate multipliers 86, 87 related to X and Y coordinates respectively. For linear interpolation the X output of multiplier 86 is the input pulse rate multiplied by the sine of the slope angle to be cut and conversely the Y-output of multiplier 87 is dependent on the cosine of the angle. The Y output is fed to a Y-axis distance counter 42 and the X output to an X-axis distance counter 42<SP>1</SP>. The circuit arrangements being similar, the Y-axis circuit only is described. Circular tool centre paths are generated by cross-coupling pulse-rate-multipliers 86, 87 by a connection 91 set-up by slope-circle switch. Axis distance counter.-The commanded number of pulses from the function generator 37 are fed to distance and a count-down counter 92 of the distance counter 42 and the Y departure for each block of data is applied from the reader 21 to a buffer store 91 which sets the count-down counter to read the Y departure. The pulse train from the function generator counts down towards zero from the Y departure set in the counter 92 which at zero provides a pulse to the first decade of a Y axis command phase counter 31, to block it and provide a zero command signal to the phase discriminator 18. When both the Y-axis and X-axis distance counters generate a zero-state output and both command phase counters are therefore disabled, the condition is set for the next block of data to be acted upon and the instructions in the buffer storages throughout the system are transferred to the working storage registers. Command phase counter.-The command phase counter 31 generates a command signal to the phase discriminator 18 and comprises three decades of binary-coded-decimal countup counters 95-97. Counter 95 is arranged to add feed rate pulses to clock pulses from a line 26 when a command from the reader 21 indicates that the Y component of velocity is in the positive direction and for a negative component, to subtract feed rate pulses from the clock pulses. The command of a positive or negative direction determines whether the phase of the signal from the counter 31 to the discriminator 18 is advancing or retarding with respect to the output from the divider 28.