Bearings – Rotary bearing – Antifriction bearing
Reexamination Certificate
2000-01-31
2001-09-25
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Antifriction bearing
C384S611000, C384S612000, C384S613000
Reexamination Certificate
active
06293705
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to spindle bearing assemblies, and more particularly to those including a plurality of raceways containing rolling members compressed with a controlled preload force.
BACKGROUND OF THE INVENTION
Although the use of such bearings is common in devices incorporating small electric motors, such as disc drives, preload force variations in such bearings are difficult to control in practice. Variations that reduce the preload force can cause play between the rotating and stationary members and/or undesired oscillations. Variations that increase the preload force can cause other problems, such as excessive or uneven wear in the bearings and/or balls.
Although some control mechanisms exist within the systems that apply the preload force, the need for spindle bearings having an internal control mechanism remains to be satisfied.
SUMMARY OF THE INVENTION
Spindle bearings are assembled with at least one annular gimbal to compensate for undesired components of bearing compression force. Spindle bearings are provided with a pair of coaxial raceways that are separated so that a first assembly can rotate with respect to a second. Balls rollingly engage the inner and outer races to maintain the races in coaxial alignment, typically with an offset preload so that the balls are kept in compression.
A preferred gimbal of the present invention has a somewhat oblong cross section along a radial half-plane and is formed integral to the assembly by cutting at least one groove about a rigid portion to make a deformable layer about 0.5 millimeters thick. Alternatively, the gimbals may be pre-formed and affixed to a rigid member to form the assembly.
Type I embodiments of the present invention compensate for operational force variations such as those caused by temperature variation. Type I devices include gimbals on one or both assemblies, compensating for variations in these forces that might otherwise become excessive. Some Type I devices are disc drives using stainless steel spindle bearings with balls made of ceramic. Ceramic balls typically have a thermal coefficient of expansion less than a fourth that of steel, often resulting in unacceptably large force variations in response to thermal variations less than 40 degrees Centigrade. Ceramic balls are much harder than stainless steel, however, resulting in favorable durability characteristics for applications such as disc drives.
A “rigid” element as used herein is a continuous mass of hard material (such as steel) of which no portion will be displaced from the rest by more than a few nanometers by ball bearing preloads less than 6 pounds. An “annular gimbal” as used herein is an annular mass of resilient material(s) such as steel arranged about an axis of symmetry. Gimbals of the present invention typically have a thickness Less than the diameter of the balls. Preferred disc drives of the present invention feature at least one spindle bearing gimbal with a spring constant 1 to 4 times larger (stiffer) than the balls in the spindle bearing assembly, under nominal normal operating conditions.
Type II embodiments of the present invention compensate for force variations that can occur during assembly, such as those caused by misalignment during the application of a preload. Gimbals of the present invention, when partially compressed or stretched, exert a restoring force that tends to equalize the preload force about the bearings. Virtually all conventional preload application mechanisms have enough give that this restorative force provides a helpful repositioning mechanism.
Additional features and benefits will become apparent to those skilled in the art upon reviewing the following figures and the accompanying detailed description.
REFERENCES:
patent: 4896239 (1990-01-01), Ghose
patent: 5102241 (1992-04-01), Pflunger
patent: 5157295 (1992-10-01), Stefansky et al.
patent: 5421088 (1995-06-01), Kawamura
patent: 5458422 (1995-10-01), Zernickel et al.
patent: 5697708 (1997-12-01), Leuthold et al.
Elsing John William
Jennings David John
Footland Lenard A.
Heller III Edward P.
Minisandram Raghunath S.
Seagate Technology LLC
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