Patent GB-876550-A (GB)
Title: Improvements relating to movement control systems
Inventor: WALKER DONALD FERGUSON
IPC: G05B19/408
Filed: 1958-03-06
Abstract: 876,550. Electric copying machines. FERRANTI Ltd. May 14, 1959 [March 6, 1958], No. 7177/58. Class 38 (6). In a system in which the movements of a machine tool are controlled by incremental pulses recorded on a magnetic tape, auxiliary control pulse signals are carried at intervals on the same track and a circuit is provided to discriminate between the two types of pulse. It is assumed that the magnetic tape carries four tracks, one each for 3 movement axes and one for monitoring the control tracks. At intervals along the tape are short spaces common to all four tracks, and the presence or absence of an auxiliary signal in each of the four spaces forms a binary coded signal for an unspecified purpose. The main pulses may be negative or positive according to the direction of movement required, and are of necessity widely spaced because of the inertia of the members to be positionally controlled. The auxiliary signals are therefore in the form of closely spaced positive and negative pairs which do not affect the positional control system, and on each track eight of such pairs are used to indicate the presence of an auxiliary signal. Three alternative circuits are disclosed for detecting the presence of the auxiliary pulse pairs. Considering one track, Figs. 1 and 2, auxiliary signals A produce a differentiated output B from a tape reader 12. These signals amplified at 13 are applied in opposite senses to limiting amplifiers 17, 19 which pass only their positive signals, C and D respectively. These pulses trigger oscillators 18, 20 which are also cross-connected to inhibit the other oscillator. Hence oscillator 18 will be triggered by pulses 41 to produce waveform E, and oscillator 20 will be inhibited by pulses 41 and so not respond to pulses 42, but will respond to pulses 43 to produce waveform F. Similarly, oscillator 18 will not respond to pulses 44. Pulse trains E and F are shaped and amplified to G and H at 23, 24 and passed to integrators 25, 26 which each produce an output pulse I, J if at least 5 of the possible 8 auxiliary pulses are received during the time allocated to these signals. Pulse I and J are fed to an AND gate 27 so that if both are present, an overlap pulse K is passed via a delay-line 28 and differentiator 29 to one input of a bi-stable device 30 to trigger it to an ON state. The overlap pulse K is also fed, undelayed, via OR gate 31 and differentiator 32 to the other input of device 30 to ensure that it is in the OFF state before the delayed pulse from 29 arrives. The resetting pulses from all four tracks are fed by the OR gate 31 to the differentiator 32 and thence to all four of the devices 30 so that all are re-set to OFF by whichever track supplies its output first. In a modification, Fig. 3 (not shown), the simultaneous presence of the integrated pulses I and J causes a pulse to be stored by recirculation in a regenerative amplifier until interrupted by a resetting pulse. In a further modification, Fig. 4 (not shown), the two integrators 25, 26 are replaced by a single integrator responsive only to successive pulse pairs of opposite polarity.