Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
1999-02-24
2001-10-02
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
Reexamination Certificate
active
06296390
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the field of hydrodynamic bearing assemblies, and especially to such assemblies adapted to have improved stiffness, reduced power consumption, and long useful life.
BACKGROUND OF THE INVENTION
Many motors, spindles and the like are based on bearing cartridges comprising a shaft and sleeve and bearings supporting these two elements for relative rotation. For example, a shaft may be mounted by means of two ball bearings to a sleeve rotating around the shaft. One of the bearings is typically located at each end of the shaft/sleeve combination. These bearings allow for rotational movement between the shaft and the hub while maintaining accurate alignment of the sleeve to the shaft. The bearings themselves are normally lubricated by grease or oil.
The conventional bearing system described above is prone, however, to several shortcomings. First is the problem of vibration generated by the balls rolling on the raceways. Ball bearings in such cartridges frequently run under conditions that result in physical contact between raceways and balls; this occurs in spite of the lubrication layer provided by the bearing oil or grease. Hence, bearing balls running on the generally even and smooth, but microscopically uneven and rough raceways, transmit this surface structure as well as heir imperfections in sphericity in the form of vibration to the rotating element. This vibration results in misalignment between whatever device is supported for rotation and the surrounding environment. This source of vibration limits therefore the accuracy and the overall performance of the system incorporating the cartridge.
Another problem is related to damage caused by shocks and rough handling. Shocks create relative acceleration between stationary and rotating parts of a system which in turn shows up as a force across the bearing system. Since the contact surfaces in ball bearings are very small, the resulting contact pressures may exceed the yield strength of the bearing material and leave permanent deformation and damage on raceways and balls, which would also result in tilt, wobble, or unbalanced operation of the bearing.
Moreover, mechanical bearings are not always scalable to smaller dimensions. This is a significant drawback since the tendency in the high technology industry has been to continually shrink the physical dimensions.
As an alternative to conventional ball bearing spindle systems, researchers have concentrated much of their efforts on developing a hydrodynamic bearing. In these types of systems, lubricating fluid—either gas or liquid (which may even include air)—as the actual bearing surface between two relatively rotating parts. As used in a typical motor, these comprise a shaft and a surrounding sleeve or hub. Exemplary liquid lubricants comprising oil, more complex ferro-magnetic fluids, or even air have been utilized for use in hydrodynamic bearing systems. Such bearings scale well to small sizes without being prone to many of the defects of ball bearings outlined above. Because of the lack of metal-to-metal contact, the bearing has a long life. Because of the stiffness of the bearing, it is highly stable and useful as a reference in devices such as optical encoders and the like.
However, it is apparent that a difficulty with such a hydrodynamic bearing design is their sensitivity both to machining tolerances and the temperature ranges across which they are utilized. Both of these issues are critical in hydrodynamic bearings, because the very narrow gaps between the rotating and stationary parts. In known designs, it is important to have a very small gap to establish a very stiff bearing which does not allow for any tilting of the rotating part relative to the stationary part. However, greater stiffness in known bearings leads to greater power consumption, also because of the closeness of the relatively rotating bearing surfaces.
Thus it is clear that a number of considerations must be balanced in designing an effective hydrodynamic bearing cartridge.
SUMMARY OF THE INVENTION
It is therefore a primary objective of the present invention to provide a hydrodynamic bearing which is simple in design, and highly adaptable and scalable for use in many different environments.
It is a further objective of the invention to provide a hydrodynamic bearing having a reliable, repeatable design so that the bearing has the necessary stiffness to be used in applications which have no tolerance for tilt, wobble, or other inaccuracies.
It is a further and related objective of the present invention to provide a hydrodynamic bearing in which gap tolerances are widened so that power consumption is reduced. A related objective of the invention is to provide a hydrodynamic bearing design having diminished sensitivity to temperature and machining tolerances, thereby providing a greater consistency in the dynamic performance of the invention.
These and other objectives are achieved by providing a hydrodynamic bearing having a shaft relatively rotatable with respect to a surrounding sleeve and having a thrust plate of or near one end thereof. The shaft and sleeve define a journal bearing extending substantially the full length of the two relatively rotating parts. The groove pattern, which is preferably on the sleeve of the journal bearing, is constant over the length of the single journal, rather than interrupted near the center to form upper and lower bearings. This substantially enhances the bearing stiffness, allowing the gap between shaft and sleeve to be widened. The thrust plate is supported on the outer surface of the shaft, and grooves or openings extend axially between the radially inner surface of the thrust plate and the outer surface of the shaft so that the fluid path over both surfaces of the thrust plate and coupled to the journal bearing, maintaining fluid supply over all bearing surfaces without providing an internal reservoir in the shaft.
Preferably, the ratio of journal bearing length to shaft width is about 1:1; the groove pattern is sinusoidal; and the center of the pattern is offset toward the thrust plate to create a pressure differential toward the thrust plate and away from the end of the bearing distal from the thrust plate so no fluid is lost.
Other features and advantages of the present invention will be apparent to a person of skill in the art who studies the present invention disclosure. Therefore, the scope of the present invention is to be limited only by the following claims.
REFERENCES:
patent: 2397124 (1946-03-01), Buffington et al.
patent: 5415476 (1995-05-01), Onishi
patent: 5685647 (1997-11-01), Leuthold et al.
patent: 5956204 (1999-09-01), Dunfield et al.
Leuthold Hans
Murthy Samnathan
Parsoneault Norbert Steven
Wolff Etoli
Footland Lenard A.
Seagate Technology LLC
Thomason Moser & Patterson LLP
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