Focusing servo device

Abstract

Abstract PURPOSE:To improve focusing control, by controlling the relative position of a focusing lens with a prediction signal based on a focus error signal before the fall of the level of a light quantity detection signal below a prescribed value, and moving the lens to a prescribed position when the level is lowered below the prescribed value. CONSTITUTION:The output of an equalizer 15 is outputted from a changeover switch 21 when the level of the light quantity detection signal is higher than a reference voltage Vr, and also a prescribed time does not elapse, and the output of a previous value holding circuit 22 is outputted from the change-over switch 21 when the level of the light quantity detection signal is lower than the reference voltage Vr, and also the prescribed time does not elapse. Also, the output of a driving signal generation circuit 18 is outputted from the changeover switch 21 when the level of the light quantity detection signal is lower than the reference voltage Vr, and also the prescribed time elapses. Therefore, when an incident light quantity to a four-division detector 9 is lowered by a scanning operation, or drop-out, etc., and no focus error signal corresponding exactly to the displacement of the convergent point of a laser beam is obtained, the focus control can be performed by holding the focus error signal just prior to the lowering of the incident light quantity to the four-division detector 9.

Inventors

• 👤 Satoshi Kusano
• 👤 草野　諭

Bibliographic Details