| 摘要 |
PROBLEM TO BE SOLVED: To early and reliably perform collision avoidance operation for avoiding the collision of an optical disk with an optical pickup caused by the servo-off of focus servo focusing or a flaw in an optical disk. SOLUTION: On the basis of a main focus signal M generated from a focus signal coming from the center of a recording track and a sub focus signal S generated from a focus signal coming from the place with a prescribed distance, when the signal S becomes LOW a first predetermined time period or more after the signal M, it is determined that focus servo has become servo-off, and collision avoidance operation is performed. When the signal S and the signal M become LOW almost simultaneously, it is determined that the flaw is being passed through. When a time period until returning to HIGH is longer than a second predetermined time period, it is determined that the flaw is long, and the collision avoidance operation is performed. When the time until returning to HIGH is shorter than the second predetermined time, it is determined that the flaw is short, and the collision avoidance operation is not performed. COPYRIGHT: (C)2011,JPO&INPIT
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