GB1412284A - Control systems - Google Patents

Abstract

1412284 Automatic position control MOOG Inc 24 Oct 1972 [26 Oct 1971] 48911/72 Heading G3N In a servo-control system, a load (screwdown of rollers 23, 24) is positioned at a controlled velocity proportional to the magnitude of a command signal on lead 67, and, in response to the attainment of the value zero for the command signal, a position holding control loop is activated to maintain the load's position, the rotor phase of resolver 75 being maintained at substantially zero, any deviation therefrom providing a command signal to the servo-control. As shown, the command signal is provided either manually 65, 66, or pre-, and post-rolling thickness sensors 51, 52 of material being rolled provide signals to auto gauge control 55 receiving also a pre-set signal and providing to amplifier 58 itself providing the command signal, downstream, and anticipation trim signals. The command signal is combined with a signal from tachometer 69 representing the actual velocity of screwdown actuator members 36, 38, the resultant, via integrating amplifier 48, controlling torque motor winding 46, the motor controlling electrohydraulic servovalve 41, the flow in leads 44, 45 being proportional to the signal on line 50. Position control. Should the command signal be zero for at least a predetermined interval, null detector 85, together with a zero of resolver phase detected by unit 86 enables flip-flop 88 to change state, frequency dividing command counter 84 in combination with one shot 90 providing short-lived sampling control pulses at a frequency corresponding to the resolver supply frequency from frequency dividing reference counter 83. The sampling control pulses, representing a reference phase, control sampling demodulator 91, capacitor 133 ensuring that there is provided on lead 130 coupled to amplifier 48 a D.C. signal representing in magnitude and sign the deviation of the resolver rotor phase from zero, any such deviation resulting in a restoring force being exerted by actuator 34. The system may be used to control a grinding element, a drill, a short cylinder in a die casting machine, or injectant piston of a plastics parison forming injection moulding machine, or load positioning, the movable part having a manually selected feed rate to a held position.