A Study on the Effects of Servovalve Lap on the Performance of a Closed - Loop Electrohydraulic Position Control System

Abstract

This paper deals with a closed-loop position control of a double acting and double-rod actuator using an electrohydraulic servovalve (EHSV). This system is studied by using symmetric critical center spool valve (zerolapped) and open center spool valve (underlapped). The nonlinear dynamic behavior of each case is undertaken and simulated. The system is modeled by using five state variables (piston position, piston velocity, actuator pressures, and servovalve spool displacement) and is tested under different step inputs. The EHSV is modeled with a first order differential equation. The closed-loop system stability is investigated by introducing equilibrium state into Jacobian matrix and determining the eignvalues. Viscous friction and compressibility of oil are included in the modeling of the system. Because the electrohydraulic position servo system is not very sensitive to coulomb friction and piston leakage they are neglected. The work showed that when the underlapped servovalve operates in the underlap region, the hydraulic position control system has more stable operation and better transient responses.