New fine seek control for optical disk drives

An optical disk drive has an excellent advantage of random accessibility. However, increased rotational velocity of a disk and limitations of mechanical structure have hindered implementation of direct seek control despite its effectiveness in reducing access time. A two-stage seek operation is instead adopted in conventional optical disk drives. In this case, fine seek control is restricted in its applicable range by the risk of misalignment between objective lens and laser beam axis, which causes the access time to increase enormously. In the paper, a control algorithm for extending the applicable range of fine seek is proposed with an appropriate control structure. The conventional fine seek technique utilized only a fine actuator without any maneuvering of a coarse actuator. With assistance of the coarse actuator, however, the misalignment of objective lens is compensated and the range of fine seek is extended in result. The proposed algorithm is applied to an optical disk drive to show its feasibility and some results are presented