| 摘要 |
PURPOSE:To stably lead in focus by letting an objective lens move in the direc tion inverse to moving direction from a prescribed position by means of reverse moving signal in a prescribed level, and driving said lens by means of the sum of the reverse moving signal and a value proportionate to a focus error signal corresponding to the period of the reverse moving signal. CONSTITUTION:The sum signal R as the result of summing the reverse moving signal R1 in prescribed level V1 and the waveform kR2 proportionate to the focus error signal R2 corresponding to the period of the signal R1, is impressed to an objective lens drive coil 5a. The level V1 is preliminarily set at value smaller than an reverse moving signal level +V. This signal R2 has a waveform symmetrical on time base whose center is a prescribed point of time, however, since the prescribed level V1 of the corresponding drive waveform is set low, the peak value V2 also comes low, hence the inclinations on both sides from the peak in the center is made mild. Accordingly, the sum signal R, also, comes in a triangular shape whose inclination value is small. As a result, the objective lens that converges to the just-focus point can perform a gradual and stable leading-in of the focus.
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