Dual Observers for the Disturbance Rejection of a Motion Control System

The conventional motion control system simply consists of a PID position controller and a disturbance observer. The estimated speed from the observer has been used to control the speed as a feedback and the estimated disturbance force, which is a byproduct of the observer, has been used to reject the disturbance. However, in this case the disturbance rejection performance should be traded off with speed estimation performance. This paper explains this trade-off using Bode analysis and presents a dual observer system for the motion control application. The proposed method uses two observers, where one is dedicated to the speed estimation and the other to disturbance compensation. The disturbance rejection performance is enhanced by the custom tuned disturbance observer in the proposed method. The feasibility of the proposed method has been verified by the experimental results using a high precision linear motion control system as well as by the analysis based on Bode plot.