| 摘要 |
PURPOSE:To drive rationally and selectively, access structure and to stabilize access operation by calculation the difference in the number of tracks between the neutral point of a close access structure and a target track, and selecting the close or rough access structure on the basis of the calculation result. CONSTITUTION:The difference alpha in the number of tracks between the current track position corresponding to the displacement of the lens of an optical head 5 and the neutral point of the close access structure is counted and the difference beta in the number of tracks between the neutral point and the target track position is calculated. This difference beta is compared by a comparator 24 with the value DELTA a half as large as the movable range 2DELTA of the close access structure. Then, the close or rough access structures is selected rationally to stabilize access operation.
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