Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-05-22
2003-12-30
Bucci, David A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
C384S107000, C384S112000
Reexamination Certificate
active
06669368
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a spindle motor and a bearing assembly for use in office automation equipment such as a computer and peripheral equipment thereof as a driving device/component for the rotating mechanism thereof, specifically to the spindle motor and the bearing assembly to enhance the run-out accuracy
onrepeatable runout (NRRO) of a motor, and reliability, low noise, acoustic life, and rigidity, etc.
2. Description of the Prior Art
Spindle motors for driving a magnetic disk, e.g., a hard disk drive as a peripheral device of a computer, are classified broadly into two types in terms of the structure: the fixed shaft type in which a fixed shaft is installed upright on a base, and a rotor hub is supported to freely rotate on the fixed shaft through a bearing interposed between the fixed shaft and the rotor hub; and the rotary shaft type in which a rotary shaft is vertically installed on a rotor hub, and the rotary shaft is supported to freely rotate on a base through a bearing interposed between the rotary shaft and the base.
Generally, the fixed shaft type is provided with, as shown in
FIG. 9
, a base (flange)
02
, a fixed shaft
010
that is installed upright on the base
02
, a rotor hub (hub member)
03
that rotates relative to the base
02
, and a bearing means
04
interposed between the fixed shaft
010
and the rotor hub
03
. A recording medium such as a magnetic disk (not shown) is mounted on the rotor hub
03
. A stator
015
is installed on the outer peripheral surface of an inner cylindrical wall
014
of the base
02
, and a permanent magnet
016
is installed on the inner peripheral surface of an outer circumferential wall
013
of the rotor hub
03
so as to face the outer peripheral surface of the stator
015
. A feeder
017
feeds current to the windings of the stator
015
and is connected to a flexible printed circuit board
037
.
The bearing means
04
is a compound ball bearing, and an inner ring
06
thereof is fixed to the outer surface of the fixed shaft
010
, and an outer ring
05
thereof is fixed to the inner peripheral surface of an inner circumferential wall
032
of the rotor hub
03
. A part of the inner ring
06
can be formed integrally with the fixed shaft
010
according to circumstances, as shown in
FIG. 9
; and the outer ring
05
can be formed integrally with the whole structure of the compound ball bearing in certain cases, as shown in the same figure.
The rotary shaft type is also provided with, as shown in
FIG. 10
, the base (flange)
02
, the rotor hub (hub member)
03
that rotates relative to the base, a rotary shaft
020
that is vertically installed on the rotor hub
03
, and the bearing means
04
interposed between the rotary shaft
020
and the base
02
. The recording medium such as a magnetic disk (not shown) is mounted on the rotor hub
03
. The stator
015
is installed on the outer peripheral surface of the inner cylindrical wall
014
of the base
02
, and the permanent magnet
016
is installed on the inner peripheral surface of the outer circumferential wall
013
of the rotor hub
03
so as to face the outer peripheral surface of the stator
015
. The symbol
017
denotes the feeder for feeding current to the windings of the stator
015
, which is connected to a flexible printed circuit board
037
.
The bearing means
04
is a compound ball bearing, and the inner ring
06
thereof is fixed to the outside to the rotary shaft
020
, and the outer ring
05
thereof is fixed to the inner peripheral surface of the cylindrical wall
014
of the base
02
. A part of the inner ring
06
can be formed integrally with the rotary shaft
020
according to circumstances, as shown in
FIG. 10
; and the outer ring
05
can be formed integral with the whole structure of the compound ball bearing in certain cases, as shown in the same figure.
In a certain case, the rotor hub
03
and the rotary shaft
020
each manufactured separately can be assembled into a unit, as shown in
FIG. 10
; and in another case, they can be manufactured as an integral unit from the beginning. In the latter case, a part of the inner ring
06
cannot be formed integrally with the rotary shaft
020
.
In any type of the spindle motor
01
, the rotor hub
03
thereof is supported on the base
02
to freely rotate through the compound ball bearing
04
as a rolling bearing interposed between the base
02
and the rotor hub
03
. And, the inner ring
06
of the compound ball bearing
04
is fixed to the outside of the fixed shaft
010
vertically installed on the base
02
or to the rotary shaft
020
vertically installed on the rotor hub
03
. The outer ring
05
thereof is fixed to the inner peripheral surface of the inner circumferential wall
032
of the rotor hub
03
or to the inner peripheral surface of the inner cylindrical wall
014
of the base
02
.
Now, recent demands of the hard disk drive show a remarkable tendency toward increase in the recording capacity, to enhance the impact resistance, to lower the noises, to increase the data access speed, and so forth. In order to answer these requirements, the roller bearing of a spindle motor has gone through improvements in the material composition, enhancements of the precision of the inner and outer rings and rolling elements, etc.
However, when the inner and outer rings and the balls (rolling elements) are made of steel such as bearing steel, metal-to-metal contact occurs between the rolling surfaces of the inner and outer rings and the surfaces of the balls, which contact effects galling and wear to deteriorate the acoustic characteristic, leading to a problem in the acoustic life (recently, the life of the spindle motor is evaluated not by the fatigue life, but by the acoustic life). Further, fretting corrosions (impressions, dilapidated surfaces) form on the rolling surfaces due to shocks and vibrations during transportation, which also deteriorates the acoustic life and the precision of rotation.
Especially in recent years, the rotational speed of a spindle motor is increased to higher than 7200 rpm, and the sound of rotation of the motor becomes increased to that degree, which tends to shorten the acoustic life. Also, in the future, a need for still further increase of the recording capacity is estimated in view of the demand for recording video images and so forth. In order to answer such demands and estimated future problems, the foregoing improvements in the material composition and enhancements of the working precision and the like will not be sufficient.
In recent years, ball materials have been tested and examined which exceed in the non-agglutination property and in wear resistance, and nitride silicon ceramics have been adopted as the rolling element material. There have been discussions about the limitation of the rolling bearing itself, including the ceramic ball bearing made of such new materials, and employment of a fluid bearing has been suggested as a solution to these problems.
FIG. 11
illustrates a rotary shaft type spindle motor
01
with such a fluid bearing. This spindle motor
01
is provided with a base (flange)
02
, a rotor hub (hub member)
03
that rotates relative to the base
02
, a rotary shaft
020
that is vertically installed on the rotor hub
03
, and a fluid bearing
030
interposed between the rotary shaft
020
and the base
02
.
A sleeve
031
of the fluid bearing
030
sheathes the rotary shaft
020
, and is fixed to the inner peripheral surface of the inner cylindrical wall
014
of the base
02
. Lubricating oil is supplied into the sliding area between the sleeve
031
and the rotary shaft
020
, and herringbones (<-shaped grooves)
033
formed on the circumferential surface of the rotary shaft
020
raise the pressure of the lubricating oil, with the rotation of the rotary shaft
020
, which floats the rotary shaft
020
up in the sleeve
031
.
Although not detailed in the drawing, similar herringbones are formed on an edge surface of a thrust ring
034
fixed to a lower part of t
Bucci David A.
Lorusso, Loud & Kelly
Minebea Co. Ltd.
Smith Julie K.
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