Importance

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Abstract

A hydraulic jack for the controlled displacement of a load, such as a platform used in the training of aircraft pilots, has a servo valve normally settable by an error signal Ve from an actuator including a subtractor followed by an amplifier, the subtractor emitting the error signal as the difference between an externally generated position-control signal Vc and a position-feedback signal Vx sent out by the jack. A monitoring device includes an error detector which generates a safety signal AL disconnecting the servo valve from its actuator whenever the position-feedback signal Vx deviates excessively from a reference signal V'x derived from the position-control signal Vc by means of a simulation circuit whose transfer constant equals, in first approximation, that of the servo system encompassing the jack and the actuator. In addition to several cascaded operational amplifiers, the last of which is an integrator representing an electronic model of the jack, the simulation circuit may include a component responsive to a force-proportional output signal Vp from sensors attached to the jack for limiting the dynamic range of an intermediate signal V's supplied to the integrating operational amplifier, the output signal Vp being also degeneratively fed to the subtractor of the actuator to stabilize the operation of the system.

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First Claim