Digital hydrostatic servoactuation

This paper pertains to a novel discrete flow valve and its use in an all-digital servoactuator. This flow valve is hydraulically or pneumatically powered, electrically controlled, and hydrostatically operated. The hydraulic actuator is minutely incremented by the valve at a frequency proportional to the magnitude of the error between the commanded actuator position and the indicated actuator position. Each increment of volume discharged by the valve is metered by the limited displacement of a floating piston that is end-to-end displaced by alternately switching the input (power) side between the supply and return pressures of a secondary power source following the switching of the output (control) side from one actuator control chamber to the other. The control flow polarity is determined by the order of switching between the input side switch and the output side switch, as selected by the servo error sign. The indication of actuator position can be provided by simply up counting or down counting the switching pulses, with the count direction dependent on the servo error sign