Dynamic magnetic information storage or retrieval – Record transport with head stationary during transducing – Disk record
Reexamination Certificate
1998-09-29
2001-12-11
Miller, Brian E. (Department: 2652)
Dynamic magnetic information storage or retrieval
Record transport with head stationary during transducing
Disk record
C310S06700R
Reexamination Certificate
active
06330126
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spindle motor employed in a recording disk apparatus such as a hard disk drive unit (HDD), in particular, to a spindle motor comprising a stationary axis fixed to a housing of the recording disk apparatus, and a hub body supported around the stationary axis by a bearing for rotation so as to receive a recording disk.
2. Description of the Related Art
The hub of a spindle motor employed in an HDD is often made of aluminum. One reason is to meet the demand for a lighter weight. Another reason is to allow the linear expansivity of the hub to coincide with that of an aluminum recording disk. The uniform linear expansivity is considered to avoid displacement between the recording disk and the hub, which holds the recording disk, under a temperature change.
Aluminum has a relatively large thermal expansion coefficient, 23.5×10
−6
/° C., so that the hub suffers from thermal expansion when the HDD is operated and the temperature rises. The thermal expansion causes the hub to expand in the radial direction, so that the rotation center may be decentered in the recording disk and/or the hub may wobble with respect to an annular outer race of the ball bearing. In particular, in case the annular outer race is made of a material, such as steel, having a thermal expansion coefficient that is relatively smaller than that of aluminum, significant eccentricity and/or wobble are expected. The eccentricity and/or wobble may cause displacement of a magnetic head off a target recording cylinder on the recording disk. Therefore, the recording density for a magnetic disk can hardly be improved unless such eccentricity and wobble are suppressed.
SUMMARY OF THE INVENTION
It is accordingly an object of the present invention to provide a spindle motor and a recording disk apparatus capable of avoiding eccentricity and/or wobble of a hub due to a temperature change.
According to the present invention, there is provided a spindle motor comprising: a stationary axis; a hub body supported around the stationary axis by a bearing for rotation; and a member encircling at least a part of the hub body around the bearing, said member having a thermal expansion coefficient smaller than that of the hub body.
When temperature rises to cause thermal expansion of the hub body, the member serves to restrain the thermal expansion of the hub body, since the member has a thermal expansion coefficient smaller than that of the hub body. Accordingly, restraint of the thermal expansion may serve to prevent the hub body from being decentered and wobbled with respect to the bearing, such as a ball bearing.
If the spindle motor is employed in a recording disk apparatus, the stationary axis is fixed to a housing of the recording disk apparatus while the hub body is adapted to receive a recording disk. Since eccentricity and wobble of the hub body can be suppressed in the spindle motor, wobble of the rotating recording disk can be prevented so that it contributes to a further improvement of the recording density of the recording disk. A recording disk apparatus may include, in addition to a magnetic disk apparatus such as an HDD, an optical disk apparatus and a photomagnetic disk apparatus.
The member is preferably cast in the hub body. If the member is cast in the hub body for fixation, it is unnecessary to finish the member with a higher dimensional accuracy, as compared with a member fit in the hub body. Moreover, the member can be formed into any shape without restriction.
Production of a spindle hub comprising the member cast in the hub body can be realized, for example, by a method of preparing a member out of material having a thermal expansion coefficient smaller than that of material for a hub body, positioning the member in a mold for forming the hub body, and pouring a melt of the material for the hub body into the mold. Soft metal such as aluminum can be selected as the material for the hub body.
A slip preventing mechanism may be formed on the surface of the hub body. The slip preventing mechanism may serve to prevent slip between the member and the hub body so as to suppress thermal expansion of the hub body along its rotation axis. The slip preventing mechanism may comprise a flange extending toward the stationary axis, or a slot formed on the surface of the member.
The member preferably comprises a cylinder continuous in an axial direction of the stationary axis. The member continuous in the axial direction may suppress thermal expansion of the hub body constantly in the axial direction of the hub body. Therefore, the hub body can be prevented from deformation caused by a local thermal expansion.
REFERENCES:
patent: 4775906 (1988-10-01), Suzuki et al.
patent: 5160865 (1992-11-01), Gururangan
patent: 5373407 (1994-12-01), Stupak, Jr. et al.
patent: 5594606 (1997-01-01), Hans et al.
Ishizaki Hirokazu
Tsukada Shinji
Fujitsu Limited
Greer Burns & Crain Ltd.
Miller Brian E.
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