An Introduction to the Time-Modulated Acceleration Switching Electrohydraulic Servomechanism

A discussion of a new concept in electrohydraulic control is presented in this paper. The usual hydraulic servomechanism design uses a d-c amplifier and a flow-control servo valve to obtain hydraulic flow proportional to the position or velocity error of the load. In the acceleration switching servo these components are replaced by an electronic multivibrator and an especially designed electrohydraulic-servo valve called an acceleration switching valve. System control is obtained through modulation of the multivibrator square-wave dwell time by which the driven-load acceleration is regulated. The servo valve behaves as a pure integrator throughout most of its operating frequency range. Use of this technique has resulted in increased reliability, excellent servo valve resolution, negligible center-shift due to temperature extremes, and near infinite pressure-gain characteristics.