| 摘要 |
PROBLEM TO BE SOLVED: To provide a control device for focus of an optical disk in which focus-pull-in is performed surely for all layers of optical disks having multi-layer structure. SOLUTION: An object lens is moved in the direction of approaching an optical disk by sampling a focus error FE signal with fixed time intervals t0, t1, t2,... by a reference voltage generating means and comparing successively the present data in sampling and data directly before sampling of one data before. In this case, since a state of variation of each S type curve, that is, each layer is surely recognized, reference voltage is appropriately generated and set using peak values d30, d34 of S type curves of which the amplitude is the minimum out of plural peak values d4, d12,... d30, d34, focus-pull-in of all layers of an optical disk having multi-layer structure can be surely performed.
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