An Application of the Self-Excited Oscillation Method to a Hydraulic Motor Angular Velocity System

It has been known that a hydraulic servo system can be generally dealt with a second order delay element for designing an adequate controller. In the previous work, our research group developed a simple method utilizing the self-excited oscillation of a hydraulic servo system to directly estimate the dynamic parameters such as the damping ratio and undamped natural frequency. The advantage of this method is the “on-line” ability that is able to identify these parameters instantaneously with changing the operating conditions. Although this method was found to be very useful, it is available only when the spool valve is close to the neutral position. This paper proposes an online parameter estimation method for the hydraulic motor angular velocity system. In this method, the self-excited oscillation around the displaced position from the neutral spool position is utilized. In order to demonstrate the effectiveness, the experimental work is conducted by giving the various input voltages, system pressures and angular velocities. The resulting frequency characteristics of these identified transfer functions are then compared with those of the measured data by the frequency characteristics method in order to confirm coincidence.