| 摘要 |
A closed magnetic circuit is formed in a rotary drum by first and second yokes of a soft magnetic material and a permanent magnet. In addition, a drive coil is provided in a gap provided between the first and second yokes so as to cross a magnetic flux running in the closed magnetic circuit. The first yoke is supported by a parallel leaf spring so as to be movable along the axis of the rotary drum. An electromagnetic force is applied to the first yoke in the direction of the axis of the rotary drum by applying a control current to the drive coil. The first yoke can be shifted in this manner to a position where the electromagnetic force balances the reaction force of the parallel leaf spring. In this manner, the closed magnetic circuit generates a sufficient drive force and eliminate a leak magnetic flux that affects a head or a transformer. Moreover, the movable portion is light-weighted, and the following frequency of a dynamic tracking operation is improved, compared to a case where all the closed circuit section is disposed with a movable portion of the parallel leaf spring.
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