Rolling bearing unit

Details Rolling bearing unit Rolling bearing unit

2001-12-06

2004-03-23

Hannon, Thomas R. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C029S898070, C029S898090

Reexamination Certificate

active

06709162

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a rolling-bearing unit, and more particularly to a rolling-bearing unit that is used in a location where there is high-speed and minute-rocking motion, for example, as in the bearing unit for the swing arm of a magnetic disk apparatus such as a Hard Disk Drive Apparatus (HDD), Flexible Disk Drive Apparatus (FDD), and also to a rolling-bearing unit with its radial rigidity controlled to a desired value for use in the magnetic disk apparatus.
2. Description of the Prior Art
As shown in Japanese Patent Publication No. TokuKai Hei 7-1 11053, the HDD for use in the memory device of computers etc. has a structure as shown in FIG.
1
. When the HDD is used, the hard disk
101
is rotated at a high speed by an electric motor of the direct drive type. The swing arm
103
has a head
102
at its tip end, and is supported at its base end by a rolling bearing unit
104
as shown in
FIG. 2
so that it swings with respect to the support shaft parallel to the rotation shaft of the hard disk
1
.
The rolling bearing unit
104
as shown in
FIG. 2
comprises an inner member or inner tube
5
in a cylindrical shape, an outer member or outer tube
6
in a cylindrical shape provided around the inner tube
5
, and a pair of ball bearings
7
for supporting the inner tube
5
and the outer tube
6
such that they rotate relative to each other. The ball bearings
7
have an inner race
9
having an inner ring raceway
8
of a deep groove type or angular type formed on its outer peripheral surface, an outer race
11
having an outer ring raceway
10
of a deep groove type or angular type formed on its inner peripheral surface, and a plurality of rolling elements or balls
12
rotatively provided between the inner ring raceway
8
and the outer ring raceway
10
. The balls
12
are rollably retained by a cage (not shown). In addition, although not illustrated, as required, the outer race
11
is formed with an attachment groove at the opposite ends of the inner peripheral surface generally along the circumference, and a shield plate is provided to have its outer peripheral edge attached to the attachment groove, so that the grease is prevented from leaking out of the space where the balls
12
are provided.
As shown in
FIG. 3
, a conventional bearing unit for the swing arm comprises a pair of ball bearings
100
,
110
which are filled with grease, wherein a swing arm (not shown in the figure) is driven in a minute-rocking motion by a drive motor (not shown in the figure) having a rotor and a stator, and this swing arm is attached to a shaft
1
that is fastened on the inner periphery of the inner races
100
A,
110
A of the pair of ball bearings
100
,
110
, and a housing
2
is fastened around the outer periphery of the outer races
100
B,
110
B of the pair of ball bearings
100
,
110
.
This conventional rolling bearing unit is assembled such that it is possible to apply a pre-load to the pair of ball bearings
100
,
110
in order to give them a specified radial rigidity, and such that it is possible to control runout of the shaft and achieve a specified positioning precision.
As shown in
FIG. 3
, in the assembly method for such a conventional rolling bearing unit, the lower end surface of the inner race
110
A is supported by a jig
4
, and a specified load from dead weight or spring force is applied to the upper end surface of the inner race
100
A, then using a spacer
3
, the position on the outer races
100
B,
110
B is fixed, and in this way a specified pre-load is applied by bringing the inner race
100
A relatively close to the inner race
100
A.
In this state, it is then possible to attach the outer peripheral portion of the shaft
1
with the inner peripheral surfaces
100
a
,
100
a
of the inner races
100
A,
110
A using adhesive or the like, as well as it is possible to attach the inner peripheral portion of the housing
2
with the outer peripheral surfaces
100
b
,
110
b
of the outer races
100
B,
110
B, also using adhesive or the like.
However, recently, there is an increasing demand for higher density magnetic disk apparatus.
Therefore, the width of the tracks on which signals are recorded on the disk has become narrower, and thus there is an even larger demand that the swing arm, in which the head for recording or reproducing the signals is mounted, be able to move at higher access speed to the target track and with improved positioning precision (faster and more precise control in positioning).
Therefore, together with an increasing demand for more rigidity of the ball bearing (rolling bearing) that supports the swing arm, there is a need to decrease the variation in rigidity between individual parts.
However, for a conventional rolling bearing unit for a swing arm, two bearings were selected from a bearing group, which were manufactured to fit within the tolerance range for a typical radial clearance, and with the method described above, the rolling bearing unit was assembled such that specified dead weight or spring force was applied in order to obtain the desired radial rigidity, however, there was a relatively large variation in the radial clearance and in the rate of curvature of the groove in the inner and outer races, so a relatively large variation in the rigidity between individual parts occurred.
It is thought to be possible to further increase the processing precision, so as to reduce the variation in the radial clearance and in the rate of curvature of the groove in the inner and outer races, and control the variation in the radial rigidity with a specified range, however, to at the present time, to actually do so would increase costs, that it is hard to adopt this way.
The ball bearings
7
in FIG.
2
and ball bearings in
FIG. 3
have a similar structure. And, the following is a description referring to
FIG. 2
only.
The ball bearings
7
as shown in
FIG. 2
have a spacer
13
held between the outer races
11
which are fitted into the inner peripheral surface of the outer tube
6
and fixed with adhesion at two locations axially spaced apart from each other. In addition, the inner races
9
are fitted onto the outer peripheral surface of the inner tube
5
and fixed with adhesion at two locations axially spaced apart from each other in the state where a dead weight
14
is mounted on the vertically upper one of the inner races
9
or in the state where an axial load is applied to the inner races
9
in order that they come to each other. Accordingly, a pre-load is applied to the balls
12
at a contact angle in the opposite directions (face-to-face or back-to-back combination). The reason of applying the pre-load to the ball bearings
7
is to secure the rigidity of the ball bearings
7
and to improve the rotation precision.
In order to produce the rolling bearing unit with the pre-load controlled at an optimum value, the dead weight
14
or a spring, or a method as shown in
FIG. 5
, detailed later, is used to apply the predetermined axial load to the inner races
9
. In the method of
FIG. 5
, the ball bearings
7
of the rolling bearing unit
4
a
are pressed in between the inner tube
5
and the outer tube
6
while the axial resonance frequency of the rolling bearing unit
4
a
is measured. And, at the point when the axial resonance frequency has reached a predetermined value, the ball bearings
7
are fixed between the inner tube
5
and the outer tube
6
.
Specifically, the inner races
9
of the ball bearings
7
are pressed by a minute-motion feeding apparatus
15
so that they come close to each other while vibration is applied to the inner races
9
and the inner tube
5
by vibrators
17
provided between the lower surface of the minute-motion feeding apparatus
15
and the upper surface of a stage
16
provided with a load cell. Simultaneously, the axial resonance frequency of the rolling bearing unit
4
a
is measured by a sensor
18
which is provided in contact with or adjacent to a side surface of the outer tube
6
. When the axial resonance frequency has

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