| 摘要 |
PROBLEM TO BE SOLVED: To stably stop an objective lens in a neutral point so as to perform good control by specifying the dimension of a magnetic piece in a polarizing direction such that a center point and a gravity center are roughly coincident with each other in a magnetic circuit composed of a polarized and magnetized driving magnet and a restoring force is generated in a focusing or tracking direction by magnetic attraction. SOLUTION: By arranging a magnetic piece 8 in a magnetic circuit composed of a tracking driving magnet 7 and a yoke 9, a magnetic attracting force is applied. By a restoring force produced in a focusing or tracking direction based on this, an objective lens 1 is restored to a neutral point. If the dimension and thickness of the tracking driving magnet 7 in a polarizing direction are respectively 2A and B and the maximum operation distance of the objective lens 1 is C, the magnetic piece 8 is regulated such that its polarizing direction W satisfies W<[A+(B/π)-C]. The magnetic piece 8 is also formed to be parallelepiped and thus machining is facilitated and yield is improved.
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