Focusing servo system and focus servo acquisition enable method

摘要

A focusing servo system executes a focus search procedure in which the position on which a light beam projected on a disk-shaped recording medium is varied by driving an objective lens for movement on the basis of a predetermined driving signal to detect a focus aquisition enable range (FOK), and then closes a focusing servo loop to carry out a focusing servo operation. The driving signal is produced in two steps by a control means. In the first step (F302), a first focus search signal generating means generates a first focus search signal for driving the objective lens for movement at comparatively high velocity. At a point in time determined by the focus aquisition enable range detection signal (F303), the second step (F312) is effected, in which a second focus search signal generating means generates a second focus search signal for driving the objective lens for movement at a comparatively low velocity. The focusing servo operation (F315) is then started on the basis of the focus aquisition enable range detection signal and/or the in-focus detection signal (F313).