Abstract: The starting of electro-hydraulic position servo system might cause system pressure drop, actuator velocity fluctuation and hydraulic impact. When more than one actuator work in the system, the sudden pressure drop can cause other actuators to misact or even lead to safety accidents. Aiming at the said the problems, two solutions are proposed. One is to divide the position control procedure into a position control procedure and a velocity control procedure in which the maximum velocity of the actuator is restricted within the supply flow rate and the liquid compressibility. The other is to adjust the flow rate at the servovalve by means of pressure difference of the chambers. The principles of the two methods are described theoretically and verified by digital simulation and experiments of an electro-hydraulic position servo system. It is finally proven that the sudden drop of the supply pressure and hydraulic impact during the starting of electro-hydraulic position servo system can be removed with the two new methods without influence upon the system response properties.

Key words: Electro-hydraulic servo system, Flow rate modifying, Hydraulic impact, Liquid compressibility