Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-08-16
2004-03-09
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S115000
Reexamination Certificate
active
06702464
ABSTRACT:
TECHNICAL FIELD
This invention relates to a hydrodynamic bearing assembly incorporated with a spindle motor used for driving a memory device such as a hard disk drive (referred to as a “HDD”, hereinafter), or a bar code scan reader, and in particular, relates to the hydrodynamic bearing assembly, which has an improved activation feature.
BACKGROUND ART
The hydrodynamic bearing assembly for use in a spindle motor of the memory device such as the HDD and a drive unit for driving a polygonal mirror in the bar code reader has been required to attain a high rate, stable rotation under a high load, to have a high bearing rigidity that prevents the rotational member from making contacts with the stationary member even under the existence of external vibrations, thereby to have a reduced starting torque, and to have an improved activation feature with a reduced wear caused by the frictional rotations.
FIG. 8
illustrates one example of a conventional spindle motor. In the drawing, a column shaft
1
and a disk-shaped thrust plate
4
are secured on a base
10
. The thrust plate
4
is attached perpendicularly to the shaft
1
. The shaft includes an outer surface parallel to the axis of the shaft
1
. A cylindrical hollow sleeve
3
is rotatably arranged around the outer surface of the shaft
1
with a predetermined gap so that a hydrodynamic,bearing is defined between the shaft
1
and sleeve
3
. Thus, the radial bearing is defined between the outer surface of the shaft
1
and the inner surface of the sleeve
3
for generating a radial dynamic pressure in the radial direction perpendicular to the axis. Also, a thrust bearing is defined between a bottom surface of the sleeve
3
(which is referred to as a thrust-opposing surface of the sleeve
3
, hereinafter) and the thrust plate
4
for generating a thrust dynamic pressure in the thrust direction parallel to the axis. Grooves
5
for generating the thrust dynamic pressure are formed on a surface of the thrust plate
4
opposing to the thrust-opposing surface of the sleeve
3
. A rotor
17
is attached with the sleeve
3
such that it can rotate together with the shaft
1
around the sleeve
3
. Information media (in case of the HDD) or a polygonal mirror (in case of the bar code scan reader) is mounted on the outer surface of the rotor
17
. A rotor magnet
18
is attached on the inner surface of the rotor
17
and opposes to a stator coil
19
mounted on a base
10
.
FIG. 9
illustrates a detail of the grooves
5
formed on the thrust plate
4
for generating the thrust dynamic pressure. A plurality of spiral grooves is formed on the thrust plate
4
, and each groove is designed to be inclined with a predetermined angle relative to the circle and generally has a width of several microns (approximately 1 to 5 microns). Although
FIG. 9
shows the grooves
5
formed on the thrust plate
4
, the grooves
5
may be formed on the thrust-opposing surface
13
.
In the rotation of the spindle motor so constructed, the stator coil (not shown) energized by the electric flow generates the attraction/repulsion force. This provides a rotation driving force with the rotor
17
having the rotor magnet
18
to rotate both of the rotor
17
and the sleeve
3
secured thereto around the shaft
1
. A relative movement between the shaft
1
and the sleeve
3
due to the rotation generates the radial dynamic pressure through a fluid such as air intervened therebetween. Also, the relative movement between the thrust plate
4
and thrust-opposing surface
13
of the sleeve
3
in cooperation of the grooves
5
generates the thrust dynamic pressure. The radial and thrust dynamic pressures keep the rotational member such as the sleeve
3
and the rotor
17
away from the stationary member such as shaft
1
and the thrust plate
4
during the rotation.
FIG. 10
is an enlarged perspective view of the hydrodynamic bearing assembly in isolation used for the spindle motor of FIG.
8
. In the drawing, the thrust plate
4
is secured on one end of the shaft
1
perpendicular to the axis. The sleeve
3
indicated by a phantom line is rotatably arranged around the outer surface of the shaft
1
. When the spindle motor is energized to activate, the rotational member such as sleeve
3
starts to rotate in contact with the thrust plate
4
due to its own weight. The spiral grooves
5
in cooperation with the rotation of the sleeve
3
indicated by the arrow
6
conducts the fluid such as air into the thrust bearing between the sleeve
3
and the thrust plate
3
and forces the fluid towards the center of the thrust plate
4
along the direction indicated by the arrow
7
. A land portion
9
is defined between the spiral grooves
5
and the outer surface of the shaft
1
, in which the forced fluid are compressed between the land portions
9
and inner end portions of the grooves
5
so as to generate the dynamic pressure for supporting the sleeve
3
. Thus, according to the conventional hydrodynamic bearing assembly, the thrust dynamic pressure to be generated has peaks localized adjacent to the land portion
9
.
FIG. 10
shows another example of the hydrodynamic bearing assembly, having the shaft
1
with another grooves
2
offset to the axis, which are formed on the outer surface and opposes to the inner surfaces of the sleeve
3
. The grooves
2
are not essential to generate the radial dynamic pressure. However, the rotational member such as the sleeve
3
in the drawing rotates around the bearing axis of the stationary member such as the shaft
1
, and also it may whirl (revolve) around another axis offset to the bearing axis, which is referred to as a half-whirl phenomenon. The half-whirl results in whirling of the functional components such as the information media and the polygonal mirror mounted on the rotor
17
, thereby to cause malfunctions in utilizing the components. The grooves
2
formed on the outer surface of the shaft
1
advantageously avoid the half-whirl. The grooves may have various configurations for avoiding the half-whirl, including the offset grooves as shown in the drawing, grooves parallel to the axis, and the herringbone-shaped grooves. However, when the grooves
2
are offset to the axis, advantageously, the rotation of inner surface of the sleeve
3
in the direction indicated by the arrow
8
forces the fluid from the top end to the bottom end due to its viscosity, thereby further increasing the dynamic pressure in the thrust bearing. Also, the grooves
2
may be formed on the inner surface of the sleeve
3
, rather than on the outer surface of the shaft
1
.
The dynamic pressure distribution in the radial bearing is generated similar to that of the thrust bearing. Thus, the rotation of the sleeve
3
in the direction opposing to the grooves as indicated by the arrow
8
, in cooperation with its viscosity, forces the fluid in the grooves from the upper end (right side of the drawing) to the lower end (left side). To this end, it is assumed that the dynamic pressure distribution is uneven, increasing the dynamic pressure adjacent the bottom ends of the groove
2
.
FIG. 11
illustrates the hydrodynamic bearing assembly having the sleeve
3
, which is whirled and inclined relative to the shaft
1
and the thrust plate
4
due to the external factors applied to the bearing assembly. The sleeve
3
is inclined counterclockwise relative to the shaft
1
, the shaft
1
moves closer to the sleeve
3
at the upper right portion A and the lower left portion B in the drawing. Also, the thrust plate
4
moves closer to the thrust-opposing surface at the leftmost portion C.
The parallel lines indicated in the drawing schematically illustrates the dynamic pressure in the radial and thrust bearings when the shaft
1
is inclined relative to the sleeve
3
. As the shaft
1
moves closer to the sleeve
3
adjacent to the portion A, the wedge effect due to the convolution of the fluid therebetween generates the higher dynamic pressure. The same effect is observed adjacent to the portion B. Therefore, the counter forces due to the dynamic pressure adja
Komura Osamu
Murabe Kaoru
Otsuki Makoto
Takeuchi Hisao
Footland Lenard A.
Sumitomo Electric Industries Ltd.
LandOfFree
Dynamic pressure bearing with improved starting characteristics does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Dynamic pressure bearing with improved starting characteristics, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Dynamic pressure bearing with improved starting characteristics will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3193080