Patent GB-1344386-A (GB)
Title: Phase signal responsive system
IPC: G05B19/33
Filed: 1971-04-19
Abstract: 1344386 Numerically controlled machine tools GENERAL ELECTRIC CO 19 April 1971[12 March 1970] 23814/71 Heading G3N [Also in Division G4] In a numerically controlled machine tool, e. g. a lathe 38 Fig. 2 having a chuck with drive motor 818 and holding a workpiece 40 to be screw threaded for instance, there is provided a control system including a resolver 816 coupled to the drive motor and which produces a sinusoidal output signal the phase of which (called the input phase) is a function of the angular position of the resolver rotor and of the workpiece, and after shaping to square waveform in 820 and conversion to a pulse of short duration by a phase pulse generator 812, synchronized with a clock 21 and timing signal generator 809, is compared in a phase sensor 822 with a reference phase provided by a buffer phase counter 830. Any phase difference causes the input phase sensing circuit 822 in co-operation with an input phase detection circuit 824 to produce a pulse having a sense which is dependent upon whether the input phase lags or leads the reference phase. A phase difference shift register 826 stores the pulse count (or rather a digital complement thereof), which is dependent upon the amount of the phase difference. The comparison is effected at regular intervals during periods (called the interphase period) determined by the buffer counter 830 and which may comprise ten C-2 clock periods (derived from 2À5 MHz clock pulse generator 21 Fig.1) before and after zero count of counter 830 i. e. from 999 to 009. An output pulse generator 828 produces a plurality of pulses numerically proportional to the stored quantity and at a pulse rate determined by a timing signal generator 809 and the clock generator 21. When cutting screw threads, a cutting index 834 receives signals from a counter in the timing signal generator circuit 809 and when a predetermined count is reached indicative of a desired angular position of the workpiece, it emits a signal to enable the pulse generator 828 and a control 9, which in turn actuates a switch 8 to connect pulses from the pulse generator 828 to a velocity command unit 24. Each output pulse from 828 on line 828A, signifies 1/1000 of a revolution of the workpiece drive motor 818 and resolver 816, and these pulses are used as timing pulses at the velocity command unit 24 to control the X and Y axis movements of the cutting tool 42, so that they are fully co-ordinated with the rotational speed of the workpiece 40. At the end of each comparison cycle the reference phase at the buffer counter, may be changed to that of the previous input phase, so that any phase difference is that which has occurred since the last comparison. A speed range control circuit 836 is connected to the input phase sensing circuit 822 to detect low speed of the lathe drive motor. If low speed is detected over three successive comparison cycles, the circuit 836 actuates a pulse multi-  plier 838 to cause the pulse generator 828 to emit ten pulses for every unit of phase difference count stored in register 826. Also an output is sent to a function generator 25 Fig. 1 to cause the X, Y axes positioning control to recognize that only one tenth as much tool position change should be commanded for each pulse from generator 828 and received by the velocity command. If the speed is high (i.e. five or more units of phase difference) then pulse generator 828 is caused to emit only one pulse for every ten units of phase difference. The system also includes a speed forcing circuit 832 which receives programmed signals from numerical input data unit 20 and over-rides the automatic speed range control 832 to cause the system to operate at the programmed speed range only.