Digital tracking controller design for CD player using disturbance observer

Disturbance rejection is becoming more and more important as optical disk players are being utilized in more applications. The paper considers the design of a tracking servo controller for a CD player using the disturbance observer (DOB) theory. By adding a DOB to the conventional PID controller, the tracking performance is dramatically improved in the presence of sinusoidal vibrations or a shock disturbance. The effectiveness of the DOB is verified by experimentation using an actual CD player as well as by computer simulations.