Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
1999-02-05
2002-03-19
Bucci, David A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S107000, C384S112000, C384S123000, C310S090000
Reexamination Certificate
active
06357916
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a hydrodynamic bearing device for use in an office automation system and an audio-visual system.
BACKGROUND OF THE INVENTION
Hydrodynamic bearing devices are generally used in rotary head cylinders for tabletop VTRs and camera-incorporated VTRs, in polygon scanner motors for laser copiers, and in recording medium rotation drivers for floppy disk devices and hard disk devices.
Specifically, the hard disk devices have higher memory capacities and higher data transfer speeds. This requires a disk rotating device for use in a recording apparatus of this type to be capable of high-speed and high-precision rotation.
To this end, a hydrodynamic bearing device as disclosed in U.S. Pat. No. 5,504,637 is used for a rotary main shaft of the recording apparatus.
The hydrodynamic bearing device has a construction as shown in FIG.
5
.
The hydrodynamic bearing device includes a stationary shaft
1
and a rotary sleeve
2
supported around the stationary shaft
1
. The stationary shaft
1
has a proximal end fixed to a lower casing
3
. Hard disks
4
are fitted around the rotary sleeve
2
.
Dynamic pressure generating grooves
6
are provided in an outer circumferential portion of the stationary shaft
1
in a radial-side dynamic pressure generating portion
5
defined between the stationary shaft
1
and the rotary sleeve
2
.
A stationary thrust ring
9
is attached to a distal end of the stationary shaft
1
by an extension shaft
8
formed with a male thread portion
7
threaded with the stationary shaft
1
.
The rotary sleeve
2
has a recessed portion
10
provided in association with the stationary thrust ring
9
. An opening of the recessed portion
10
is virtually closed by a rotary thrust ring
12
which has at its center a center hole
11
of a diameter greater than the outer diameter of the extension shaft
8
. The rotary thrust ring
12
is fixed to the rotary sleeve
2
by a screw
13
.
In a thrust-side dynamic pressure generating portion
14
defined by the recessed portion
10
of the rotary sleeve
2
, the stationary thrust ring
9
and the rotary thrust ring
12
, dynamic pressure generating grooves
15
,
16
are provided in upper and lower faces of the stationary thrust ring
9
. The thrust-side dynamic pressure generating portion
14
and the radial-side dynamic pressure generating portion
5
are filled with a lubricating fluid.
A stator winding
17
is disposed around a proximal end portion of the stationary shaft
1
on the lower casing
3
. A magnet
18
is provided on an inner circumferential surface of the rotary sleeve
2
as opposing to the stator winding
17
. The extension shaft
8
is fixed to an upper casing
19
by a screw
20
.
In the hydrodynamic bearing device having the aforesaid construction, the hard disks
4
are rotated at a high speed via the rotary sleeve
2
in a sealed space defined between the lower casing
3
and the upper casing
19
upon energization of the stator winding
17
.
The rotation of the rotary sleeve
2
about the stationary shaft
1
pumps the lubricating fluid so that the rotary sleeve
2
can maintain non-contact rotation.
DISCLOSURE OF THE INVENTION
However, the aforesaid arrangement has the following drawback.
Due to expansion of the lubricating fluid and a centrifugal force, the lubricating fluid
21
is liable to scatter out of the radial-side dynamic pressure generating portion
5
as indicated by
22
in
FIG. 6
, or scatter out of a gap between the extension shaft
8
and the rotary thrust ring
12
as indicated by
23
, thereby causing lockup or seizure of a motor.
Particularly, where the scattered lubricating fluid adheres onto the hard disks
4
, erroneous data reproduction may result.
More specifically, a conventional technical approach to the prevention of the scattering of the lubricating fluid from the open end of the thrust-side dynamic pressure generating portion is to reduce the radial spacing of the gap as much as possible.
Further, improvement in shock resistance with respect to the thrust direction is currently demanded. This demand is directed not only to a hydrodynamic bearing device constructed such that a stationary shaft is fixed at its opposite ends as described above, but also to a hydrodynamic bearing device constructed such that the stationary shaft is fixed only at its proximal end.
It is therefore an object of the present invention to provide a hydrodynamic bearing device which has an improved construction to prevent a lubricating fluid from scattering out of a dynamic pressure generating portion.
The hydrodynamic bearing device of the present invention is characterized in that a radial spacing of a gap at an open end of a thrust-side dynamic pressure generating portion is set greater than a spacing of the thrust-side dynamic pressure generating portion as measured with respect to the thrust direction.
With this arrangement, the scattering of the lubricating fluid from the open end of the thrust-side dynamic pressure generating portion can be prevented even when the hydrodynamic bearing device is operated at a high rotation speed in a high temperature environment.
In accordance with a first aspect of the present invention, there is provided a hydrodynamic bearing device which comprises a stationary shaft having opposite ends at least one of which is fixed and a rotary sleeve supported rotatably about the stationary shaft and is adapted to pump a lubricating fluid between the stationary shaft and the rotary sleeve for non-contact rotation of the device, wherein the stationary shaft is provided with a stationary thrust ring, wherein the rotary sleeve has a recessed portion defined by faces thereof opposed to upper and lower faces and outer circumferential surface of the stationary thrust ring, wherein the lubricating fluid is filled in a gap defined between the stationary thrust ring and the recessed portion, wherein the following expression is satisfied:
&Dgr;L=t+10 &mgr;m to 30 &mgr;m [10 &mgr;m≦&Dgr;L−t≦30 &mgr;m]
wherein t is a thickness of the stationary thrust ring and &Dgr;L is a height of the recessed portion.
In accordance with a second aspect of the present invention, the hydrodynamic bearing device is characterized in that the stationary shaft is supported at its fixed opposite ends, that a radial-side dynamic pressure generating portion is defined between the stationary shaft and the rotary sleeve and a thrust-side dynamic pressure generating portion is defined between the stationary thrust ring and the recessed portion and disposed on one side of the radial-side dynamic pressure generating portion, that the radial-side dynamic pressure generating portion and the thrust-side dynamic pressure generating portion are filled with the lubricating fluid, and that a radial spacing &Dgr;d of a gap at an open end of the thrust-side dynamic pressure generating portion satisfies the following expression:
&Dgr;d>&Dgr;L−t
In accordance with a third aspect of the present invention, there is provided a hydrodynamic bearing device which comprises a stationary shaft supported at its fixed opposite ends and a rotary sleeve supported rotatably about the stationary shaft and is adapted to pump a lubricating fluid between the stationary shaft and the rotary sleeve for non-contact rotation of the device, wherein the stationary shaft is provided with a stationary thrust ring, wherein the rotary sleeve has a recessed portion defined by faces thereof opposed to upper and lower faces and outer circumferential surface of the stationary thrust ring, wherein a radial-side dynamic pressure generating portion is defined between the stationary shaft and the rotary sleeve and a thrust-side dynamic pressure generating portion is defined between the stationary thrust ring and the recessed portion and disposed on one side of the radial-side dynamic pressure generating portion, wherein the radial-side dynamic pressure generating portion and the thrust-side dynamic pressure generating portion are filled with the lubricating f
Fukutani Hideshi
Saeki Yasuo
Sakuragi Katsunori
Yoshitsugu Takao
Joyce William C
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
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