Bearings – Rotary bearing – Fluid bearing
Patent
1998-10-28
2000-07-04
Footland, Lenard A.
Bearings
Rotary bearing
Fluid bearing
384114, F16C 1702
Patent
active
060829001
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention generally relates to a hydrodynamic gas bearing structure, and more specifically, it relates to a hydrodynamic gas bearing structure supporting a rotator rotating at a high speed and a method of manufacturing the same.
BACKGROUND TECHNIQUE
In recent years, high rotational accuracy is being required to a rotation driving part, such as an optical deflection scanner, for example, of a magnetic recording apparatus or a laser beam printer along with a high rotational speed. In order to rotate a precision motor to which such high rotational speed and high rotational accuracy are required at a higher speed, employment of a gas bearing (hydrodynamic gas bearing) for the rotation driving part is proposed. In the rotation driving part employing this gas bearing, air is forcibly introduced into at least a clearance between a radial gas bearing body and a rotator when the rotator rotates. Thus, the air pressure in the clearance is increased, and the rotator rotates at a high speed through the gas bearing. Thus, maintenance of the rotational accuracy is expected also during high-speed rotation, by employing the gas bearing.
In the aforementioned radial gas bearing, a wedge clearance is formed by eccentricity of a shaft body in the bearing body, as shown in "Gas Bearing" by Shinichi Tohgo, Kyoritsu Shuppan (1984), for example. Pressure is generated when air passes through this wedge clearance since the air is compressed. Thus, it becomes possible to support the shaft body and the bearing body in a non-contact manner.
According to "About Whirl of Gas Bearing" by Atsunobu Mori, pp. 481 to 488, "Lubrication" Vol. 20, No. 7 (1975), however, an unstable phenomenon called "whirl" (H/W) is observed in a cylindrical journal bearing when set in an unloaded state such as the case of supporting a vertical shaft or the like. This phenomenon is such that the shaft is pressed against the bearing surface by centrifugal force to whirl in the interior of the bearing. In the cylindrical journal bearing, the bearing center and the rotation center deviate from each other by a static load to generate pressure in one portion and bring stable rotation. In case of employing the cylindrical journal bearing for a vertical structure, i.e., a structure supporting a vertical shaft or the like, however, the bearing is set in an unloaded state and hence a pressure-producing point changes by disturbance and rotation becomes unstable.
In case of applying the aforementioned hydrodynamic gas bearing to a rotation driving part of a magnetic recording apparatus such as a hard disk driver or a laser printer, the aforementioned unstable factor must be eliminated since the positional accuracy of the rotator is regarded as important.
Accordingly, there is proposed in Japanese Patent Publication No. 4-21844 (corresponds to Japanese Patent Laying-Open No. 58-224324) that generated pressure increases by forming shallow grooves mainly on a side of a shaft body, serving as a rotator, into which gas flows by rotation circumferentially in equal distribution, to improve whirling stability in high-speed rotation, i.e., to prevent a whirl phenomenon.
Further, there is proposed in Japanese Patent Laying-Open No. 8-312639 means of forming at least three grooves extending in the axial direction on a shaft body circumferentially in equal distribution and controlling the groove shape, thereby improving whirl stability in high-speed rotation and preventing a whirl phenomenon.
According to experiments by the inventors, however, it has been proved that there are the following problems in case of forming grooves on a shaft body in accordance with the aforementioned proposals, although a whirl phenomenon in high-speed rotation can be suppressed:
FIG. 11 is a cross-sectional view of a shaft body. As shown in FIG. 11, three portions of grooves 13 are formed on the outer peripheral surface of the shaft body 1. In this case, the shape of the grooves 13 has a laterally symmetrical shape in the circumferential direction of the shaft body 1. The
REFERENCES:
patent: 4512626 (1985-04-01), Kamiya et al.
patent: 5628567 (1997-05-01), Murabe et al.
Shinichi Tohgo, "Gas Bearing", published by Kyoritsu Shuppan (1984), pp. 4 to 7, with partial English Translation.
Atsunobu Mori, "About Whirling of Gas Bearing", in "Lubrication" vol. 20, No. 7 (1975) pp. 481-488, with partial English Translation.
Awazu Tomoyuki
Komura Osamu
Murabe Kaoru
Takeuchi Hisao
Fasse W. F.
Fasse W. G.
Footland Lenard A.
Sumitomo Electric Industries Ltd.
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