** * Sony Energy Devices Corporation

This paper deals with unsteady-state friction characteristics of a hydraulic actuator. Using a single rod hydraulic cylinder, friction characteristics are experimentally investigated under various conditions of velocity variation at different supply pressures. The friction force of the hydraulic cylinder is measured based on the equation of motion using measured values of the pressures in the cylinder chambers and the acceleration of the hydraulic piston. A method to identify dynamic parameters included in the modified LuGre model, which has been proposed by Yanada and Sekikawa, is proposed. Comparison between measured unsteady-state friction characteristics and those simulated by the modified LuGre model is conducted. It is shown that the unsteady-state friction characteristics simulated using the parameters identified agree with those obtained by experiments with a relatively good accuracy and that the proposed method to identify the dynamic parameters is appropriate. The effect of the supply pressure on the friction characteristics and the dynamic parameters are shown