Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
1998-12-18
2001-01-23
Hannon, Thomas R. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S112000, C384S132000
Reexamination Certificate
active
06176618
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a dynamic pressure bearing, a spindle motor using the dynamic pressure bearing, and a rotary device having the spindle motor as a driving source and, more specifically, to a spindle motor in which a rotor is supported by a stator through the dynamic pressure bearing.
Dynamic pressure bearings are suitable as bearings of a rotary device in the fields of computers and copy machines because they can be miniaturized and can operate with smooth, high speed revolution. Particularly, as an air dynamic pressure bearing does not use a lubricant such as oil, a rotator such as a magnetic disk is never soiled. As a result, the air dynamic pressure bearing is adopted widely for a rotator device. However, the air dynamic pressure bearing has disadvantages, including that stiffness of the bearing is very low and that production is difficult because it requires a bearing gap of several micron order. In view of the foregoing disadvantages, a liquid dynamic pressure bearing having high stiffness and which is easy to produce has been developed.
The prior art is disclosed in U.S. Pat. No. 5,487,608. The device is a shaft rotation type spindle motor having a liquid dynamic pressure bearing in which lower end of the bearing is closed end, upper end of the bearing is opened end, and a radial bearing portion is formed at upper portion and a thrust bearing portion is formed at lower portion. When the spindle motor rotates at high speed, the radial bearing portion and the thrust bearing portion are constructed so that net flow of lubricating oil by dynamic pressure orients to the closed end direction at the radial bearing portion, net flow of lubricating oil by dynamic pressure orients to radial bearing portion direction, and net flow connected with these flows orients to the closed end of the bearing. Therefore, lubricating oil does not leak from the bearing when the motor rotates at high speed. A capillary seal is provided at the opened end so that lubricating oil does not leak out of the bearing when the motor stops.
A prior art bearing assembly is disclosed in U.S. Pat. No. 5,487,608 which is incorporated herein by reference. FIG. 4 of U.S. Pat. No. 5,487,608 has been replicated herein as FIG.
9
. The bearing assembly comprises a shaft rotation-type spindle motor having a liquid dynamic pressure bearing. The bearing assembly comprises a stationary sleeve
70
has a lower portion
40
, an interior surface forming a bushing
72
, a tapered surface
162
, a vertical surface
181
, and an outer circumferential surface
182
. A rotating shaft
52
constituting a cylindrical radial bearing member is mounted for rotation relative to the stationary sleeve
70
. The rotating shaft
52
has hubs
174
and
180
and defines a radial bearing portion. Upper and lower journal bearings
130
,
132
are disposed between the stationary sleeve
70
and the rotating shaft
52
. A thrust plate
74
and a counterplate
76
define a thrust bearing portion of the bearing assembly. The thrust plate
74
has bearing surfaces
120
,
122
and is stepped at
75
into a lower end of the rotating shaft
52
and extends into a recess
90
defined by a lower end of the bushing
72
and an upper surface of the counterplate
76
. The counterplate
76
is pressed against the lower portion of the stationary sleeve
70
and sits in against a step as shown at
78
. Immediately below the counterplate
76
is located a shield
84
which is provided to close the bearing assembly from the outside. The bearing assembly is further provided with gaps
92
,
94
,
96
, recesses
80
,
90
, a bores
102
,
134
, a groove
104
, a reservoir
100
, equipressure grooves
136
,
150
, a capillary seal
160
, a gas trap
170
, and a labyrinth seal
172
. A lower end of the bearing assembly is closed, an upper end of the bearing assembly is opened, the radial bearing portion is formed at the upper end, and the thrust bearing portion is formed at the lower end.
When a spindle motor of the bearing assembly rotates at a high speed, the radial bearing portion and the thrust bearing portion are constructed so that the net flow of lubricating oil by dynamic pressure orients in the closed end direction at the radial bearing portion, the net flow of lubricating oil by dynamic pressure orients in the radial bearing portion direction, and the net flow connected with these flows orients to the closed end of the bearing. Therefore, lubricating oil does not leak from the bearing when the motor rotates at high speed. The capillary seal
160
is provided at the opened end so that lubricating oil does not leak out of the bearing when the rotor stops.
The spindle motor disclosed in U.S. Pat. No. 5,487,608 is a useful liquid dynamic pressure bearing which has high stiffness and which is easy to produce as compared to an air dynamic pressure bearing. However, construction of the liquid dynamic pressure bearing is complex. As shown in
FIG. 9
, two members, namely the thrust plate
74
and the counterplate
76
are needed to form the thrust bearing portion. A dynamic pressure generating groove which does not function properly due to its construction must be formed at the radial bearing portion and the thrust bearing portion. Furthermore, the bores
102
,
134
, a radial dynamic pressure generating portion, and a thrust dynamic pressure generating portion must be formed respectively at the rotating shaft
52
. As a result, it is difficult to miniaturize and manufacture the liquid dynamic pressure bearing having the foregoing construction.
SUMMARY OF THE INVENTION
In view of the foregoing problems in the conventional art, it is an object of the present invention to prevent generation of over drawing of oil at an oil suction side of a dynamic pressure generating groove of a thrust bearing portion during high speed revolution of a spindle motor having a liquid dynamic pressure bearing with a disc-shaped thrust bearing member having no balance hole. This can be accomplished by providing a liquid dynamic pressure bearing comprising a rotational shaft mounted for undergoing rotation and having a disc-shaped thrust bearing portion at a central part thereof and a radial bearing portion, and a cylindrical bearing member for rotatably supporting the rotational shaft, the cylindrical bearing member having a closed end forming a small diameter cylinder portion for receiving the radial bearing portion of the rotational shaft and an open end forming a large diameter cylinder portion for receiving the disc-shaped thrust bearing portion so that a plurality of first gaps for receiving a lubricating oil are formed between the rotational shaft and the cylindrical bearing member.
Another object of the present invention is to insure that lubricating oil is not drawn much at the oil suction side of the dynamic pressure generating groove of a radial bearing portion during high speed revolution of the spindle motor having the rotational shaft and the cylindrical bearing member as set forth above.
Another object of the present invention is to provide a spindle motor having a liquid dynamic pressure bearing comprising the rotational shaft and the cylindrical bearing member, as set forth above, in which unstableness of revolution caused by a half whirl instability phenomenon is decreased and stable revolution is obtained while supporting a high load even at high speed revolution.
The foregoing and other objects of the present invention are achieved by a spindle motor in which a rotor is supported relative to a stator through a liquid dynamic pressure bearing. The spindle motor comprises a rotational shaft mounted for undergoing rotation and having a disc-shaped thrust bearing portion at a central part thereof and a radial bearing portion, a cylindrical bearing member for rotatably supporting the rotational shaft, the cylindrical bearing member having a closed end forming a small diameter cylinder portion for receiving the radial bearing portion of the rotational shaft and an open end forming a large diameter cyl
Kawawada Naoki
Takehara Isamu
Adams & Wilks
Hannon Thomas R.
Seiko Instruments Inc.
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