Patent GB-1243726-A (GB)
Title: Position control system
IPC: G05B19/18
Filed: 1969-05-01
Abstract: 1,243,726. Controlling machine tools. INDUCTOSYN Ltd. 1 May, 1969 [14 May, 1968; 9 April, 1969], No. 22161/69. Heading G4H. [Also in Division G3] A positioning system has a temporary store, for holding a command position, a counter for the present position, a comparator comparing the present and command positions and stepping the counter into agreement with the store, and a reversible counter which is counted up in step with the output of the comparator to indicate the distance to be moved to bring a positioned member to the command position. As shown, a signal CK, Fig. 1a, from a timing and clock generator 1 is fed to a reference counter 2, comprising decade counter stages 230-232 and a JK flip-flop 233 for the thousand stage, the count signal from each stage of which is compared in a comparator 3 with corresponding signals from an internal counter 4. The count signal RCT for counter 4 is generated by an internal logic 5 from an error signal e and holds a count representing the position of a movable machine member 12 in a cycle of a transformer type measuring device 11. The comparator 3, by NAND logic, sends + and - ve coincidence signals to a function generator 10, which derives sine and cosine function pulsewidth signals for the movable member positioned input windings 12 of device 11, machine motion being reversed by a switch 14. The positional error signal from the fixed winding 13 of the device 11 is fed through an amplifier 16 and a low-pass filter 17 to provide a sinusoidal signal to a phase detector 19, generating the D.C. error signal e, and to a rectifier 18 generating a signal E s  representative of the magnitude of the positional error. The internal logic 5 generates the count signals RCT as a function of e, through a relay 229, and E s  the magnitude of which determines the frequency of the RCT pulses. An external control logic 9, including a biquinary counter, controls the sequence of operations in the set-up and read-out modes, set by a mode switch 26, and provides an up-down signal U/D Y  for controlling the counting direction of an external counter 201, Fig. 1b the contents of which is slaved to a display 21. The counter 20 and the display 21 are set to zero by a push-button 25. The part starting number is set up in a store 22 and offset in a store 23. The stores comprise BCD thumb-wheel switches. The external counter 20, Fig. 1b comprises reversible decade counter 239-244, the outputs of which are connected to display 21 and to stores 22, 23 providing count coincidence signals on lines PS, OS, Fig. 1a, to the external control logic during the set-up mode. Data in a temporary store 34, representing a present commanded position, is compared in a comparator 35 with data in the counter 20, representing the previous commanded position, generating, at equality, a signal EQ, or more/less signals M/L. The signals EQ, M/L are fed to a data distributer 33 which directs counting ARCT, RCT pulses into the external counter 20 and a delta counter 36. The count direction of the delta counter 36 is controlled by logic 32 which generates a signal U/D in response to RCT pulses, CLn signals from the logic 9, Fig. 1a, M/L and U/Dn signals from the logic 5, Fig. 1a. The delta counter is loaded from distributer 33, with the computed difference between the data in store 34 and counter 20 and is counted down towards zero as the movable member 12 is positioned from one point to another. The least significant digits in the delta counter 36, representative of position error, are displayed on a two-stage counter 31 and are used to adjust the stopping procedure while the count in counter 20 is incremented to the next commanded position, to avoid positioning errors. The setup, positioning or read-out mode is selected by a switch 51 coupled to the switch 24, Fig. 1a, and co-operates with the data distributer 33, which controls the distribution of data, from dial switches 29, a tape reader 20 or a computer, not shown, selected by device 191, to the temporary store 34 and a machine control device 27, the transfer being synchronized by a strobe signal from reference counter 2. The perforated tape, not shown, is read mechanically or optically and is wordaddressed to one of a plurality axes. The control device 27 provides control signals to a control device 26 for a motor 195 having velocityfeedback from a tachometer 194. The control device 27 also provides auxiliary commands and receives feedback signals indicating the response of the machine. TAc/relay 229 switches the error signal e from logic 5 to the device 27 for control of the motor 196 in servo mode and, under control of a relay logic 227 when the frequency control signal Es is less than the detected servo count, by slow-down and stop signals SP.