Disturbance Rejection Control Scheme for Optical Disk Drive Systems

A disturbance rejection control scheme is developed for optical disk drive (ODD) systems. Disturbances acting on these servo systems inherently contain significant periodic components that cause tracking errors of a periodic nature. Such disturbances can be effectively rejected by employing a modified repetitive compensator. The proposed control scheme overcomes the drawback of typical internal-model-based repetitive control schemes, which cancel repeatable disturbances but amplify disturbances at other frequencies. A sufficient stability criterion is developed when the proposed control scheme is used in a closed-loop system. Some practical guidelines are also given for tuning the control scheme. A comparison of the control scheme with and without the modified repetitive compensator shows significant improvement of the tracking performance of the proposed scheme.