| 摘要 |
An automatic focusing device of an optical disk apparatus with a capability of automatically focusing a light beam at an optimal position relative to the surface of a track of an optical disk by a selection of an optimal value of an offset voltage is disclosed. A focusing servo of the device keeps a focal point of the light beam at a relative position to the surface of the track, which is adapted to shift the relative position by applying an offset voltage. A tracking error detector generates a tracking error signal with peaks same in number as the number of tracks having been traversed by the focal point. A comparator generates a comparison pulse each time when the peak is higher than a predetermined threshold level. A counter counts the number of the pulses in the tracking error signal. After repeating the generation, the comparison and the counting for a plurality of times, each time with the application of a different value of the offset volatge, a judging circuit adopts the value of the offset voltage corresponding to the maximum number among the counted numbers as the optimal value of the offset voltage to be applied in a seek mode of the optical disk apparatus to directly transfer the focal point to a desired track.
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