1. Technical Field
The present invention relates to a spindle motor.
2. Description of the Related Art
Generally, in spindle motors, sleeves which are provided around rotating shafts rotatably support the rotating shafts, thus ensuring a high level of operating characteristics. Because of these characteristics, spindle motors are widely used as drive units of recording media, such as hard disk drives, optical disk drives, etc., which need high speed rotation.
Such a spindle motor uses a fluid dynamic bearing which is operated in such a way that a predetermined amount of fluid is injected between a rotating shaft and a sleeve, which coaxially supports the rotating shaft, so as to form dynamic pressure when the rotating shaft rotates, thus making the rotating shaft rotate more smoothly.
Specially, after 2000's shafting systems of spindle motors have largely gone away from using ball bearings to the use of dynamic bearings. Compared to existing ball bearings, the dynamic bearings reduce noise, enhance the impact resistance, and have an extended lifetime. For example, in a fluid dynamic shafting system, there is a dynamic pressure gap between a rotating shaft and a sleeve. A dynamic pressure depression is formed in the sleeve or the rotating shaft. When the rotating shaft rotates with respect to the sleeve, fluid is moved by this relative rotation. Pressure generated by the movement of the fluid serves as a bearing. However, there are problems of friction with the fluid and contact between the rotating shaft and the sleeve.
In an effort to overcome these problems, a spindle motor in which a spacing depression is formed in a rotating shaft or sleeve to reduce friction attributable to fluid was proposed. However, for example, in the case where the spacing depression is formed in the rotating shaft, edges formed on the rotating shaft by the spacing depression may come into contact with the surface of the sleeve and thus damage the sleeve.
Therefore, studies into a spindle motor which can be manufactured by inexpensive processes, such as an ECM process, unlike the conventional technique which includes a pressing process using a plastic deformation principle, and which aims to solve the problem of contact between the rotating shaft and the sleeve which is induced by the edges of the spacing depression formed in the rotating shaft have been conducted.