Optical disk drive focus servo control system with focus servo being turned off or having gain reduced after tracking servo has been off a predetermined time period

摘要

A focus servo control system for use in optical disk drive units prevents a large current from continuously flowing through a focus actuator coil FC when a focus error signal FES in the focus servo loop increases while a track servo loop is in an "off" state, thereby preventing deterioration of the coil FC. The focus servo control further includes a controller for detecting a length of time during which an "off" state of the track servo loop in a servo controller continues, and for turning off the focus servo loop or, alternatively, reducing the gain of the focus servo loop when the detected length of time exceeds a predetermined value.