| 摘要 |
PURPOSE:To attain accurate position control of an objective lens by forming a projection to a yoke face opposite to the magnetic pole face of a permanent magnet. CONSTITUTION:The permanent magnet 5 is provided on a moving holder 1 holding an objective lens 3 and the yoke 2 has an opposed face with a magnetic pole face of the permanent magnet 5. A control coil 10 is provided to an opposed face of the yoke 2 and controls the position of the moving holder 1 by the interaction with the permanent magnet 5 through the excitation and projections 20a, 20b are formed to the opposed face of the yoke 2. That is, a force opposite to the displacement of the permanent magnet acts onto the permanent magnet at all times by the projection provided on the yoke face opposed to the magnetic pole face of the permanent magnet provided to the moving holder to attain the holding of the moving holder at the neutral point in the focus control direction. Thus, the effect of a restoring force F caused due to the change in the magnetic flux density on the surface of the permanent magnet is eliminated and the accurate positioning control of the objective lens is attained.
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