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A two part description of two digital-hydrostatic servoactuators is presented. The first servoactuator described is based on a digital valve that can be hydraulically or pneumatically powered. The actuator is incremented by discrete volumes of fluid discharged by the valve at a frequency and polarity dependent on the servo error magnitude and sign. The basic principle of operation of the fluid-powered servoactuator applies to an electrically-powered one. In this version, however, the discrete flow is derived from a digitally controlled pump driven by a constant speed motor. This part of the paper includes a preliminary layout of a dual power-hinge servoactuator which shows that a compact, fully integrated module is feasible.

This paper describes a completely digital, electrically powered servo wherein the servo is minutely incremented at a frequency proportional to the magnitude of an error binary number. The power unit of the servo is electrohydrostatic and as such is entirely electrically controlled and powered. Hydraulic fluid is confined to the power unit where it serves as a link between two solenoid driven pumps, a common mode volume adjuster, and an actuator. The direction the actuator is incremented is dependent on which of the two solenoid driven pumps the error polarity directs pulsed electrical power. Design equations are presented that allow the control engineer to set component parameters such that the servo may meet a particular set of operation requirements. Several energy saving schemes are discussed which can further enhance the inherent energy efficiency of the servo.