GB1357529A - Actuators - Google Patents

Abstract

1357529 Fluid-operated actuator control systems ROTORK Ltd 27 Aug 1971 [4 Sept 1970 19 April 1971] 42352/70 and 9758/71 Heading F1P [Also in Divisions F2 and G1] An actuator comprises a linearly movable shaft 20 attached to the piston 22 of an hydraulic singleacting unit 11, solenoid valves 42, 49 for controlling fluid-flow to and from the working chamber 23 of unit 11, control means, Fig. 6, for controlling the solenoids 43, 50 of valves 42, 49, and selector means Figs.3, 4 and 5, (not shown, see division F2) for either causing the piston to be returned by spring means 35, 36 when the control circuit fails or is de-energized, or for holding the piston 22 in the position within the cylinder at which such failing or de-energization occurs. The low pressure side of piston 22 is open to the pressure of reservoir 24 in which a pump 14 operated by motor 13 is located. The fluid is pumped from reservoir 24 to the working chamber 23 and eventually, when required, returns to the reservoir. Expansion and contraction of the reservoir fluid is compensated for by a gas-filled bladder 25. The pump 40 pumps fluid from reservoir 24 to a line 41 and back to reservoir 24 via the normally open valve 42. If valve 42 is closed then the fluid is fed past the checkvalve 47 and thence to chamber 23 to move piston 22, the valve 49 being normally closed. If the valve 49 is opened, fluid can flow from chamber 23 back to reservoir 24, the piston be urged by the spring means. Clearly, if actuation of the solenoid 50 normally closes valve 49 then deenergization of the circuit stops solenoid operation to open valve 49 and permit the piston to be returned. An alternative fail-safe result can be obtained by arranging for valve 49 to be open during solenoid actuation so that de-energization closes the valve and thus holds the fluid in chamber 23 to keep the piston 22 in the position it attained at that time. Operation of the valves, by control of solenoids 43, is effected by the circuit of Fig. 6 in which the signals of a zero-set potentiometer 62 and a "required travel" potentiometer 60 are fed to a differential amplifier 64 for comparison with a feedback potentiometer 66. Amplifier feeds the required signal to control unit 55 which controls the solenoid-operated valves 42, 49 to produce the required length of piston stroke. The mechanism by which the position of the piston 22 is fed to the potentiometer is also described (See division G1).