Reduction of seek time of tracking actuator with pulsed excitation in optical disk

Abstract

Time consumption during the track seek is an important factor which indicates the ability of an optical disk system. In a two-stage tracking actuator, latency time exists before the laser beam follows the destination track because of the vibration of the fine actuator. Modified velocity profiles and control techniques for the actuator have been proposed to reduce the latency time. When a fine actuator is locked to the coarse actuator, another latency time caused by the disk eccentricity cannot be reduced. It becomes possible to forecast the eccentricity as the rotation type of the optical disk changes to constant angular velocity (CAV). Thus the latency time can be reduced by excitation of the fine actuator with the same velocity of the track when the coarse actuator stops. Pulsed excitation is used for the excitation. This method is applied to a compact disk read-only memory (CD-ROM).