Design and experiment of add-on track following controller for optical disc drives based on robust output regulation

An add-on type output regulator is proposed in this paper. By an add-on controller, we mean an additional controller which operates harmonically with a pre-designed feedback controller. The role of the add-on controller is to reject a sinusoidal disturbance of unknown magnitude and phase but with a known frequency. The proposed output regulator can be designed independent of the feedback controller (that has been possibly pre-designed independently), thus we need only a knowledge of the plant under control. Advantages of the proposed controller are as follows. (1) It can be used only when the performance of disturbance rejection needs to be enhanced. (2) It is turned on and off without unwanted transient. Thus, controller scheduling is possible. (3) It is designed for perfect disturbance rejection not just for disturbance reduction. (4) Ability for perfect rejection is preserved even with uncertain plant model. Experimental results for an optical disc drive system confirm the effectiveness of the proposed method.