All Digital Electrohydrostatic Servoactuator

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. The paper describes a redundancy application and shows how the operation principles of the digital servo can apply to a direct drive digital valve. A list of design concerns and a start-up development plan are also presented.