Fine Seek Control of Extended Applicable Range for Optical Disk Drives

Optical disk drive has excellent advantage of random accessibility of which performance is measured by access time. However, due to the increased rotational velocity of the disk and constraints of mechanical structure, two-stage seek algorithm which executes coarse and fine seeks sequentially has been adopted in most commercial optical disk drives. Although the laser spot is moved to a target track by a single seek operation, the limited operation range of the fine actuator restricts the application of the fine seek algorithm below a few hundreds of tracks. Especially, excessive movement of the objective lens causes a failure in generation of track-cross pulse and results in an unstable seek operation. In this paper, a new control algorithm for extending the fine seek range is proposed with an appropriate control structure. The coarse actuator is utilized to reduce the misalignment between the objective lens and the laser beam axis, and the fine actuator is controlled to follow the reference velocity trajectory. The proposed algorithm is applied to a CD-ROM drive to show its feasibility and some experimental results are presented.