| 摘要 |
Embodiments of the present invention effectively control, by a simple structure, floating of a rotor of a fluid dynamic bearing motor mounted in a hard disk drive. In one embodiment, a base is formed of a magnetic material. The attractive force caused by the magnetic force acts between a bottom of the base and a magnet unit that is constituted of a rotor magnet and a back yoke. This makes it possible to attract a rotor to the base against the buoyant force produced by a thrust bearing, and thereby to effectively control the rotation of the rotor. On the bottom of the base, at a position facing the magnet unit, a convex part protruding from the inner surface of the base is formed in a ring-shape. Adjusting the height, or the width, of the convex part makes it possible to control the magnetic back pressure applied to the rotor.
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