Online System Identification of Hydraulic Servo Actuators by the Self-Excited Oscillation Method (Application to Angular Velocity Control System)

Abstract

It has been well known that hydraulic servo actuators can often be approximated with a standard second order transfer function when the controller is designed for these systems. Earlier research developed a simple method utilizing the self-excited oscillation caused from the hydraulic servo actuators to directly estimate the dynamic parameters such as the damping ratio and undamped natural frequency. The advantage of this method is an online identification ability that is able to identify these parameters while the operation conditions are continually changing. Although this method was confirmed to be very useful, it is available only when the spool valve is close to the neutral position, which corresponds to the operation of position control systems. In the practical situations, the spool valve sometimes operates at displaced position from the neutral center position such that a hydraulic motor speed is controlled. This paper proposes a revised self-excited oscillation method for this system. The experimental works are conducted by giving the various system pressures and angular velocities so as to validate the method. The resulting frequency characteristics of these identified transfer functions are then compared with those of the measured data by the frequency characteristics method. In addition, in order to demonstrate the effectiveness of the self-excited oscillation method, the dynamic parameters of two practical devices such as a motion seat and aircraft tail surface control simulator are identified and compared with the results from the frequency response method.