Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2002-04-17
2004-03-09
Bucci, David A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S292000, C384S100000
Reexamination Certificate
active
06702466
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a ceramic dynamic-pressure bearing, a motor having a bearing, a hard disk drive, a polygon scanner and method for manufacturing a ceramic dynamic-pressure bearing.
2. Description of the Related Art
Conventionally, a ball bearing has often been used as a bearing for the shaft of a motor serving as a drive unit of electric equipment. High-speed rotation of a motor has been rapidly implemented in precision equipment, such as peripheral equipment of a computer. In this connection, in order to obtain excellent bearing performance with low rotation-speed fluctuation and reduced noise and vibration, or in order to elongate bearing service life, a dynamic-pressure bearing, which uses fluid, such as air, as a medium, has been employed. The dynamic-pressure bearing operates in the following manner: when, for example, a spindle and a bearing member disposed to surround the spindle undergo relative rotation about an axis, the axis of rotation is supported by the action of fluid dynamic-pressure generated in the gap formed between the outer circumferential surface of the spindle and the inner circumferential surface of the bearing member. Also, a certain other bearing is configured such that the thrust face of a spindle or that of a bearing member is supported by action of dynamic pressure.
3. Problems to be Solved by the Invention
When a dynamic-pressure bearing as described above is in a high-speed rotation state, in which generated dynamic-pressure is sufficiently high, two members which face each other with a dynamic-pressure gap present therebetween do not come into contact with each other. However, at the time of starting or stopping, when rotational speed is low, sufficiently high dynamic pressure is not generated; thus, the two members come into contact with each other. Component members of such a dynamic-pressure bearing have generally been formed of a metal, such as stainless steel, and in some cases have been further coated with resin or like material. However, the two metallic members may cause a problem of wear or seize-up caused by mutual contact thereof at the time of starting or stopping.
In order to prevent the above-described seize-up of a dynamic-pressure bearing at the time of starting or stopping, either or both of the spindle and the bearing have been formed of a ceramic, such as alumina, which is not prone to seize-up and exhibits excellent wear resistance.
However, even when a dynamic-pressure component is formed of a ceramic, a problem may arise such that vibration occurs during rotation of a spindle, which hinders smooth rotation of the spindle. Further, when one of the spindle and the bearing is formed of a metal, seize-up may occur. In order to prevent this problem, a ceramic dynamic-pressure bearing has been proposed, configured such that the two members which face each other with a dynamic-pressure gap present therebetween are formed of ceramic. However, sufficiently smooth rotation has still not been realized.
Furthermore, in order to increase dynamic pressure to be generated, a dynamic-pressure bearing has employed dynamic-pressure grooves formed on a dynamic-pressure gap definition surface. In the case of a ceramic dynamic-pressure bearing, the dynamic-pressure grooves have been engraved by sandblasting.
However, a sandblasting process for engraving dynamic-pressure grooves involves masking with a wear-resistant material, which is troublesome. Since blasting of abrasive grains tends to be uneven, variations in groove depth tend to arise. Additionally, since the number of workpieces which can simultaneously undergo a groove formation process is limited, productivity is poor. Further, the inner surface, particularly a bottom surface, of a dynamic-pressure groove thus formed tends to become rough, and a meeting portion where a sidewall surface and a bottom surface meet tends to assume an irregular sharp shape, thereby preventing smooth generation of dynamic pressure and potentially causing center runout or vibration.
SUMMARY OF THE INVENTION
It is therefore a first object of the present invention to provide a ceramic dynamic-pressure bearing which can realize smooth rotation. A second object of the invention is to provide a ceramic dynamic-pressure bearing having dynamic-pressure grooves capable of smoothly generating dynamic pressure and allowing for excellent productivity, a method for manufacturing the dynamic-pressure bearing, and a motor having a bearing, a hard disk drive, and a polygon scanner which employ the dynamic-pressure bearing.
The above-described first object of the invention, has been achieved by providing:
(1) A ceramic dynamic-pressure bearing in which, when either a spindle or a bearing serving as a rotation body rotates relative to the other, the rotary surfaces (i.e., radial dynamic-pressure gap definition surfaces) of the spindle and the bearing come into a non-contacting state, at least the rotary surface of the spindle and/or the bearing is formed of a ceramic, and the surface porosity of the rotary surface is 10 to 60%.
When a ceramic material is used for a dynamic-pressure bearing, the surface state of the rotary surface of the ceramic component serving as a spindle or a bearing becomes important. That is, in general, fine pores are present on the surface of a ceramic component that has been subjected to polishing, due to dropping off of particles during the course of polishing; and the number, size, and distribution of such pores are considered to greatly effect the state of rotation of the dynamic-pressure bearing.
Specifically, when pores of large diameter are present on a rotary surface of the ceramic component, turbulence is generated in the fluid layer present between the spindle and the bearing upon rotation of, for example, the spindle, so that vibration of the spindle occurs. By contrast, when the number of pores present on a rotary surface of the ceramic component is excessively small, or when a large number of pores of small diameter are present on the rotary surface, adhesion easily occurs between the rotary surfaces of the spindle and the bearing, so that seize-up may occur when the spindle or the bearing is formed of a metal.
In the above first aspect of the present invention, because the surface porosity of the rotary surface formed of a ceramic is set to 10 to 60%, the size and number of pores become proper, so that occurrence of vibration or seize-up can be prevented. Further, in a dynamic-pressure bearing having a structure such that a rotation body (i.e., bearing member) is sandwiched between thrust plates, the occurrence of linking can be avoided.
The term “surface porosity” means the ratio of the total cross-sectional area of pores (the total area of cross sections of pores taken along a rotary surface) to the area of the rotary surface. When known dynamic-pressure grooves are formed on the rotary surface, the area of the dynamic-pressure grooves is omitted for calculation of the surface porosity. That is, in such case, the surface porosity is represented by (the total cross-sectional area of pores present on the rotary surface excluding a region where the dynamic-pressure grooves are formed)/(the area of the rotary surface excluding the region where the dynamic-pressure grooves are formed). This definition for surface porosity will be applied to the following description in the present specification.
(2) The ceramic dynamic-pressure bearing as described in (1) above, wherein the surface porosity of the rotary surface is 20 to 50%.
This embodiment of the invention limits the surface porosity to a more desirable range within the range defined in (1). Within the limited range, the above-described variation, seize-up, and linking can be prevented more effectively.
The above-described second object of the present invention has been achieved by providing a ceramic dynamic-pressure bearing comprising a dynamic-pressure gap formed between a first member and a second member, which undergo relative rotation about a predetermined axis o
Ishikawa Hironobu
Moribe Junya
Yogo Tetsuji
Bucci David A.
NGK Spark Plug Co. Ltd.
Smith Julie K.
Sughrue & Mion, PLLC
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