Patent GB-966379-A (GB)
IPC: H03K7/00
Abstract: 966,379. Electric selective signalling systems. GEORGE RICHARDS & CO. Ltd. July 29,1960 [Aug. 7, 1959], No. 27147/59. Heading G4H. A train of pulses is phase modulated in accordance with information supplied in the form of command pulses by means of apparatus comprising a source of regularly spaced pulses, a counter of the pulses giving an output pulse train with a normal interval between pulses equal to the time taken to count a certain number of the regularly spaced pulses, and means for adding a pulse to, or subtracting a pulse from the regularly spaced pulses in response to a command pulse. Phase modulator. Multivibrator 31 and monostable circuits 43, 44 provide two trains of regularly spaced pulses differing in phase by 180 degrees. A command pulse at terminal 51 sets flip-flop 61 to give a 1 output so that an output is obtained from AND gate 62 when the next pulse from circuit 43 arrives. Flip-flop 63 is set to give a 1 output so that an output is obtained from AND gate 64 when the next pulse from circuit 44 arrives, the output of gate 64 being fed through OR gate 45 between two pulses supplied directly from circuit 43. Similarly, a command pulse at terminal 52 produces an output from the corresponding gate 64 in synchronism with a pulse from circuit 43, this output being inverted and supplied to AND gate 46 so that a pulse from circuit 43 is blocked. In this manner the number of pulses supplied in a given time to counter 47, 48 is varied and the times at which flip-flop 48 changes over vary accordingly to produce the phase modulated command signal 22. Machine-tool control system. The command signal is compared in phase with a signal 21 whose phase represents the position of the machine tool in a bi-stable circuit 49, giving an output 23 whose D.C. component is detected and supplied to a servomotor to drive the machine to the desired position. Circuit 49 only utilizes the leading edges of the waveforms supplied to it, so that an additional variable may be controlled by providing a similar phase modulating circuit with corresponding command pulse terminals 51, 52 the circuit producing a command signal 22 whose trailing edges represent for example a desired spindle speed or tool change, the signals 22 being supplied to control the leading and trailing edges of the output of bi-stable circuit 49. Alternatively, a further control circuit, Fig. 3 (not shown) may be arranged to alter the markspace ratio of the pulse train supplied to bi-stable circuit 49 in accordance with the additional variable. Position signal generator. The position of the machine-tool slide is indicated by the relative position of diffraction gratings 11, 13 which produce a light pattern having a sinusoidal intensity distribution 20 detected by phototransistors 16 spaced apart by one quarter wavelength of the pattern 20. Phototransistors 16 are scanned in sequence by means of switching circuit 34 and individual switching transistors 35 to provide an output on common load 19 which is then integrated and applied to Schmidt trigger 41 whose output is a square waveform phase modulated in accordance with the relative position of gratings 11, 13. Specification 966,380 is referred to. Reference has been directed by the Comptroller to Specifications 869, 013 and 869, 015.