GB1136821A - Improvements in or relating to numerical control systems - Google Patents

Abstract

1,136,821. Programmed control of position. TELEHOIST Ltd. May 5, 1966 [Feb.13, 1965], No. 6305/65. Heading G3N. A numerical control system for positioning an element relatively to an earlier or datum position comprises a digital control section which is operative during most of the measured movement and an analogue control section which is operative during final positioning. As shown, a lead-screw is driven by an hydraulic motor 2, the speed of which is determined by a controller 3 supplied with hydraulic fluid through a solenoid valve 5 from a pump 4. The valve 5 cuts out the controller 3 and brings in a slow-speed restrictor 6. Driven from the other end of the lead-screw is an induction transducer 8 and a photo-electric pulse producing device 9 which, through a pulse shaping circuit 20, drives a stepping motor 10 coupled to the rotor of the transducer. The pulses from the circuit 20 are also fed to counter 45 having a bank of manual switches 46, set up for cutter offset, which, when empty, transfers the pulses by an electronic switch 21 to count down a displacement counter 23 set up by manual switches 24. At a first predetermined count during emptying the counter 23 provides a signal which actuates the solenoid valve 5 to bring into operation the slow-speed restrictor 6, and at a second predetermined count an electronic relay 19 disconnects the pulsing device 9 from the circuit 20 and connects it to a circuit 46 which provides a pulse train which rapidly empties the counter 23 and positions the stepping motor in advance of the lead-screw. At zero count, a digital to analogue change-over switch 42 renders operative relay contacts 40 and isolates the stepping motor 10. The hydraulic motor is then actuated through the contacts 40 by a relay 38 responsive to the positional signal from the transducer 8 through a demodulator 37. A manually set potentiometer 43 provides fine adjustment of the final position. In a modification, a high-speed resetting counter 50 is connected between a gate 52 and a two-way switch 51 which feed the pulses from the device 9 to cycle the counter 50 and countdown the displacement counter 23 until the table is within a short distance from the final position when the pulses are routed to the stepping motor 10 instead of the counter 50. The count in counter 23 is set through binaryto-decimal decode devices 26 and stores 28 by uni-selectors 27 responsive to a tape-reader 25. The tape-reader additionally sets the count in the off-set counter 45 and the speed of the hydraulic motor 2 by adjustment of the controller 3.