Ceramic bearing ball

Details Ceramic bearing ball Ceramic bearing ball

2000-03-03

2001-11-13

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S907100

Reexamination Certificate

active

06315454

ABSTRACT:

FIELD OF THE INVENTION
This invention relates to bearing balls of the type which find use in, for example, computer hard disk drives, semiconductor wafer transfer devices, a HDD carriage arm and other devices which require low vibration operation.
BACKGROUND OF THE INVENTION
Bearing devices which make use of balls or rollers arranged between outer and inner races are widely used for the smooth running of rotary components in equipment of the most diverse sizes from heavy industrial equipment to electronic devices. Traditionally, such bearing balls and rollers have been manufactured from steel but, in recent years, ceramic materials, such as, for example, silicon nitride also have been used.
Steel and super-steel have heretofore been the material of choice for bearing balls in, for example, hard disk drives for computers. However, with improvements in computer performance, higher rotational frequencies have been demanded, and, accordingly, it has become necessary to make use of ceramic materials (ball manufacturing material) for the manufacture of bearing balls. One type of hard disk drive of the nature incorporating ceramic bearing balls is described and illustrated in U.S. Pat. No. 5,485,331 to Dunfield et al., issued Jan. 16, 1996.
Since the density of ceramic materials is generally lower than that of steel, the weight and hence the frictional resistance of ceramic bearing balls is correspondingly lower. Also, since the thermal expansion coefficient of ceramic materials is lower than that of steel, the dimensional accuracy can be improved. A ceramic material also has the advantage of requiring less lubricant.
However, merely selecting a ceramic material for a bearing ball is not necessarily sufficient in itself. For example, in a computer hard disk drive, irregular bearing vibrations during the storage (writing) and reading of data constitutes a potentially fatal performance drawback. Balls for such a bearing therefore demand a greater performance accuracy than that of the bearing balls used in a machine tool, for example.
It is therefore an object of the present invention to provide a ceramic bearing ball which is capable of preventing irregular vibration of, for example, a hard disk drive incorporating the ceramic bearing ball.
SUMMARY OF THE INVENTION
In accordance with a first aspect of the invention, a ceramic ball is provided characterized by a sphericity of not more than 0.08 &mgr;m, a surface roughness of not more than 0.012 &mgr;m and a maximum surface pore size of 5&mgr;m.
According to the another aspect of the invention, a disk drive bearing is provided having inner and outer races, and accommodated between the races, a plurality of ceramic bearing balls. The bearing has a raceway run-out of less than the pitch of a hard disk memory track, preferably less than one-half, more preferably less than one-third the pitch of a hard disk drive memory track.
It will be understood that if the pitch or width between memory tracks on the surface of the hard disk that is rotated by the disk drive motor is smaller than the sphericity tolerance, then there is a great risk that reading information/data recorded on the surface of the hard disk will not be achieved by a laser or magnetic head reader. The reason for this is that the raceway run-out in the motor bearing directly affects reading accuracy of data in the memory track. This is because the hard disk is located by the inner or outer race of the disk drive motor bearing.
A ceramic ball according to the present invention having the above characteristics has an excellent surface condition and high dimensional accuracy. Accordingly, when such a ceramic ball is used in a bearing in, for example, a computer hard disk drive, irregular bearing vibration rarely occurs. As a result, the writing and reading of data can be achieved accurately and reliably.


REFERENCES:
patent: 4831471 (1989-05-01), Tsujisawa
patent: 5485331 (1996-01-01), Dunfield et al.
patent: 5524985 (1996-06-01), Dunfield
patent: 5581420 (1996-12-01), Chainer et al.
patent: 5642947 (1997-07-01), Akamatsu et al.
patent: 42 01 615 A1 (1993-07-01), None
patent: 2 219 359 A (1989-12-01), None
H.J. Boving et al., “Properties and Performance of Chemical-Vapour-Deposited TiC-Coated Ball-Bearing Components,”Thin Solid Films, vol. 153, No. 1, Oct. 26, 1987, pp. 253-266.

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