Force sensorless robust tracking servo system suppressing periodic disturbance and sudden disturbance for optical disk system

In optical recording system, the tracking servo system must follow the track of optical disk against the influence of the track eccentricity and the force disturbance. In tracking servo system, the influence of the track eccentricity becomes periodic disturbance. The influence of force disturbance caused by shaking is treated as sudden disturbance. The several control methods suppressing the periodic disturbance have been proposed. On the other hand, it is difficult to detect the sudden disturbance without force sensor. In the conventional tracking servo system, the influence of sudden disturbance has been suppressed by the feedback controller. This paper proposes a new force sensorless robust tracking servo system, which detects and suppresses the both periodic disturbance and the sudden disturbance without force sensor. The proposed system estimates the both periodic disturbance and sudden disturbance based on a new sudden disturbance observer and memory of tracking error. Moreover, in order to suppress the periodic disturbance quickly, this paper designs the ZPET feedforward servo system with prediction of tracking error. The experimental results point out that the proposed tracking servo system has a precise tracking response against both periodic disturbance and sudden disturbance.