THE POSITION CONTROL OF ELECTROHYDRAULIC SERVOMECHANISM VIA A NOVEL VARIABLE-STRUCTURE CONTROL

There are many distinct advantages of a hydraulic control system, such as a higher speed of response with fast motions and possible speed re versals, a higher torque stiffness and a continuous operation. The hyd raulic control system is becoming the most common form of precise mani pulation system. However, some nonlinear phenomena, such as the relati onship between input current and output flow, the fluid compressibilit y and the deadband due to internal leakage and hysteresis, make the co ntrol of the hydraulic system difficult. A novel variable structure co ntrol (VSC) with a time-varying switching gain, a second-order relatio n between sliding surface and uncertainties, and a boundary layer for the sliding surface, is employed to deal with the position control of the electrohydraulic servomechanism which is subjected to parameter un certainties and external disturbances. Furthermore, the robust stabili ty of the system is verified by a Lyapunov stability criterion. Finall y, the simulations show that the proposed appraoch can achieve an accu rate and robust tracking performance.