| 摘要 |
PURPOSE:To detect the position in tracking direction of an objective lens by being equipped with a hall device and a permanent magnet for detecting an objective lens position respectively to an objective lens holding member and a main body frame. CONSTITUTION:A permanent magnet 12 for detecting an objective lens position accompanied by a hall device 11 for an objective lens holding member 4 and a yoke for a main body frame 1 is provided. Since the direction of the magnetic flux by the permanent magnet 12 for detecting the objective lens position is reverse in right and left directions while centering an origin and a magnetic flux density is changed as the flux is away from the origin, the moving quantity of an objective lens 3 can be known by the output of the hall device 11 to move in proportion to the moving quantity of an objective lens 3 in the magnetic flux. Thus, since the position of the tracking direction of the objective lens can be detected and the action of the tracking direction of the objective lens can be found, the objective lens cannot be moved to the allowance or above.
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