Digital Simulation of a Coulomb-Damped Hydraulic Servosystem

Abstract

A valve-controlled ram-type servosystem employing position feedback with an electrohydraulic servovalve and servoamplifier is modeled to simulate with a digital computer all of the possibly significant physical characteristics of such a system, including turbulent flow in certain connecting passages, distributed-parameter supply line dynamics, and Coulomb-type dryfriction in the ram and mass load. The simulated responses are compared with corresponding measured responses of the real system for the case of a single-period sawtooth wave input. It is shown how system stability can become marginal when small amplitude inputs are used, with the system barely moving at low speed, due to lack of damping from dry friction, and minimal valve damping at small flowrates.