Bearings – Rotary bearing – Plain bearing
Reexamination Certificate
2001-12-28
2003-05-06
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Plain bearing
C384S478000, C277S410000
Reexamination Certificate
active
06558042
ABSTRACT:
BACKGROUND OF THE INVENTION
The following invention relates to a bearing guided ferrofluid seals and unique seal carriers for use in electric spindle motors having bearing assemblies with an outer annular ring surface.
Conventional electric spindle motors of the type used in disk drives conventionally use ball bearing assemblies to facilitate movement between a rotary member and a stationary member. As shown in
FIGS. 2 and 3
, bearing assemblies
18
generally include metallic or ceramic ball bearings
24
that are positioned between an inner bearing race or ring
20
and an outer bearing race or ring
22
. Bearing assemblies
18
may be either inner or outer rotators depending on whether the shaft
28
(which is substantially adjacent the inner bearing ring
20
) is stationary or whether a combination of the shaft
28
and hub
32
rotate together. Inner rotators have an inner bearing ring
20
that rotates with the shaft
28
. Outer rotators have an outer bearing ring
22
that rotates with the hub
32
. The ball bearings
24
are preferably evenly spaced within the inner and outer bearing rings
20
,
22
. The hub
32
has an inner surface
30
that may have a single circumference (
FIGS. 2 and 3
) or two circumferences
34
,
36
(FIGS.
4
and
5
).
Arguably, ferrofluid seals
40
are used on the majority of spindle motors produced today for hard disk drives. Further, ferrofluid seals
40
are now being used in other areas of the disk drive such as in the head-stack bearing cartridge assemblies, in other types of motors, and in the pivoting sections of machines that are used in high cleanliness environments. Accordingly, there is a great demand for effective ferrofluid seals
40
.
Ferrofluid seals
40
are commonly used to provide a hermetic seal against gas and other contaminates in applications where a seal is needed between a shaft and its surroundings. In other words, ferrofluid seals
40
are capable of withstanding relative rotation between a shaft and its surroundings. Ferrofluid seals
40
may also be used in single seal motors in which there is a ferrofluid seal
40
at one end and a labyrinth seal or some alternative seal is at the other end.
Ferrofluid seals
40
are generally constructed of two O-shaped pole pieces
42
a,
42
b
sandwiching an O-shaped magnet
44
. The Ferrofluid
46
is positioned between the seal inner diameter
48
a
of the magnet sandwich and the outer diameter of a shaft
28
. Magnetic flux holds the ferrofluid
46
in place. In other words, a ferrofluid seal
40
is an apparatus that includes magnetic fluid holding means for storing a magnetically permeable fluid between an inner element and an outer element, which are relatively rotated. The magnetic fluid holding means has a storage section for storing a part of the magnetic fluid that extends out of the magnetic fluid means. One exemplary ferrofluid seal apparatus is disclosed in U.S. Pat. No. 5,238,254 to Takii et al. Ferro Technologies, Inc., of Pittsburgh, Pa. produces other conventional ferrofluid seals
40
. Ferro Technologies, Inc. produces several embodiments of ferrofluid seals
40
including, but not limited to, a Z-seal (FIG.
2
), an OZ-seal (FIG.
3
), a P-seal (not shown), and a U-seal (not shown).
Unfortunately, almost all ferrofluid seals are not perfect. The seal inner diameter
48
a
is not always a perfect circle and the seal outer diameter
48
b
is not always a perfect circle. Further, the center point of the seal inner diameter
48
a
and the center point of the seal outer diameter
48
b
are not always aligned. When the center points are not aligned then the seal inner diameter
48
a
and the seal outer diameter
48
b
are not concentric. A lack of concentricity between the seal inner diameter
48
a
and the seal outer diameter
48
b
can be referred to as runout.
The ferrofluid seals
40
are effective, but they are delicate and prone to splash and burst problems when they are installed incorrectly or contaminated due to particles or serious out-gassing. The likelihood of splash and burst problems is increased by the introduction of eccentricity between the ferrofluid seal inner diameter
48
a
(also called the seal operating face) and the shaft outer diameter (the surface against which the ferrofluid
46
runs). A splash or a burst is catastrophic because it ejects ferrofluid
46
into a clean environment. Further, a splash or burst may cause a complete seal failure that will then allow particles or out-gassing to pass into the same clean environment.
Ferrofluid seals
40
are generally held in or part of known traditional seal carriers
50
,
52
such as those shown in
FIGS. 2 and 3
.
FIG. 2
shows a ferrofluid seal
40
held in one example of a conventional seal carrier
50
. Conceptually this conventional seal carrier
50
would be substantially washer shaped with a central annular cutout or clearance into which the ferrofluid seal
40
would fit.
FIG. 3
shows an alternative example of a conventional seal carrier
52
that is an extended pole piece
42
b
and, therefore, is an integral part of the ferrofluid seal
40
. Specifically, the pole piece
42
b
of the alternative carrier
52
acts as the carrier itself and drops into the bearing bore (or hub inner surface
30
) or bore that is, under ideal circumstances, concentric with the axis of rotation.
Both examples of conventional carriers
50
,
52
are difficult to accurately place in a motor. Further, because the ferrofluid seals are typically placed into conventional carriers
50
,
52
using a clearance or slip-fit, the ferrofluid seal can fit anywhere within the clearance and, most likely will be off-center. Accordingly, the seal carriers' additional clearances contribute to eccentricity and runout (where the seal inner diameter
48
a
is not concentric with the outer diameter of the carrier
50
) problems.
Using the bearing for positioning is not unknown. For example, U.S. Pat. No. 5,876,126, to Marshall et al. (the “Marshall Patent”), which is assigned to the same assignee as the present invention and incorporated herein by reference, is directed to a motor incorporating a bearing guided labyrinth system. The motor includes a shaft, a hub, a bearing assembly, and a bearing guided labyrinth. The bearing assembly includes an inner bearing ring and an outer bearing ring separated by a plurality of ball bearings. The inner bearing ring has an inner annular ring surface and the outer bearing ring has an outer annular ring surface. The bearing guided labyrinth has an inner prong and an outer prong. The inner prong is at least partially positionable between the inner ring surface and the shaft. The outer prong is at least partially positionable between the outer ring surface and the hub. The outer prong grips the bearing assembly and specifically the outer annular ring surface of the outer bearing ring. Because the purpose of the bearing guided labyrinth system is to reduce particle emission, using the bearing to position the bearing guided labyrinth system, which allows for a tighter fit, is quite effective.
U.S. Pat. No. 5,227,686 to Ogawa includes a spindle motor embodiment in which a lower magnetic fluid sealing means is held in a holder that appears to be guided by an annular member. The lower sealing means is secured to the inner surface of the holder that is then attached to the annular member. The holder includes an annular leg that is positioned within an annular groove of the annular member. The annular groove would have to be a precision surface because it holds the holder and the lower sealing means. Accordingly, the annular groove would be difficult and expensive to produce in the annular member. The purpose of the lower sealing means is to seal the gap between the shaft and the holder and, most likely, to reduce particle emission.
BRIEF SUMMARY OF THE INVENTION
The present invention is directed to bearing guided ferrofluid seals and seal carriers that substantially reduce a motor's ferrofluid seals system's operating eccentricity and runout without significantly reducing t
Hannon Thomas R.
Oster Karen Dana
SAE Magnetics(H. K.) Ltd.
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