Patent GB-912657-A (GB)
Title: Improvements in or relating to automatic machine tool control
IPC: G05B19/37
Filed: 1959-02-24
Abstract: 912,657. Numerically-controlled milling-machines. THOMPSON RAMO WOOLDRIDGE Inc. Feb. 24, 1959 [March 31, 1958], No. 6374/59. Classes 38 (6) and 40 (1). Numerical control of four axes of a milling-machine is effected by recording for each axis in binarydecimal code, successive increments of movement together with selected times for effecting each increment, converting this into a train of incremental pulses occurring during the selected period of time, using this pulse train to phase modulate a higher frequency pulse train, comparing this phase-modulated train with signals from a resolver driven by the controlled member and operating an electro-hydraulic servomotor to eliminate the error. The four axes controlled are, Fig. 2 (not shown), X, Y, Z, and a rotation of the work-holder. Information is recorded in blocks, Fig. 3 (not shown), each block containing one increment of movement for each of the axes and a code letter indicating which one of ten available machining times shall be used. The direction of each movement is also coded and recorded. The record is prepared manually. Since each axis is controlled in substantially the same manner, only one will be described. Each of the five decimal digits of the distance increment are defined by four possible holes across the width of the punched tape input, representing 5, 2, 1 and 1 (and combinations thereof) thus providing twenty bits. The tape is read at 21, the information being routed by a counter-circuit 36 to the appropriate number of bi-stable circuits forming an intermediate store 38, from whence it is transferred in parallel to a similar final store 43, where the time, distance, and direction codes are segregated. Timing pulses from a master oscillator 66 are frequency divided by a decade counter 46, Fig. 7 (not shown); the output from each stage is gated and the required timing train is selected by the time code. Five decades of multivibrators 48 then count off 10<SP>5</SP> of these timing pulses, before emitting a pulse which resets the stores in turn and initiating the next tape read-out. Each of the five decades in the counter 48 consists of four multi-vibrators and these are so arranged, Fig. 6 (not shown), that during each count the ten thousands decade supplies four output lines with 5, 2, 1 and 1 pulses respectively, the thousands decade supplies four more output lines with 50, 20, 10 and 10 pulses respectively and so forth. These 20 output lines control 20 AND gates 64, Fig. 8 (not shown), to which are also applied the 20 bits of the distance signal so that during the selected time interval a train of pulses corresponding in number to the distance signal is passed to the sign gates 62. Distances of one inch or greater cannot be decoded if one of the three shortest time intervals has been selected. The sign gates 62 are controlled from the store 43 and determine whether the incremental pulse train is added to, or subtracted from a train of timing pulses in a phase modulator 125, Fig. 9 (not shown). The resulting composite train is passed to a frequency dividing counter which provides output one pulse for every 500 input pulses. This output pulse therefore appears earlier for every incremental pulse that has been interleaved into the timing train and later for pulses omitted, thus giving a phase modulated output. A reference signal is also obtained by similarly dividing, at 134, an unmodulated train of timing pulses. The phase modulated command signal is compared, Fig. 14 (not shown), with the output of a resolver which is rotated through a rack-and-pinion by movement of the milling- machine part to provide a D.C. error signal of variable magnitude and reversible polarity. This signal controls an electro-hydraulic servo, Fig. 11 (not shown). The resolver signal can also be further phase-shifted manually. In a modification, Figs. 12 and 13 (not shown), the programmed machining time can be altered manually by supplying the timing pulses to the counter 46 from a variable frequency oscillator instead of the master oscillator 66. This also necessitates an additional synchronizing circuit for the phase modulator 125.