Metal working – Method of mechanical manufacture – Process for making bearing or component thereof
Reexamination Certificate
2003-02-18
2003-11-25
Vidovich, Gregory (Department: 3726)
Metal working
Method of mechanical manufacture
Process for making bearing or component thereof
C029S898070
Reexamination Certificate
active
06651340
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates in general to an assembly fixture, and in particular to an improved fixture for assembling pivot bearing assemblies for disk drives. Still more particularly, the present invention relates to a self-aligning fixture for pre-loading and aligning pivot bearing assemblies for disk drives.
2. Description of the Prior Art
Referring to
FIG. 1
, a schematic drawing of an information storage system comprising a magnetic hard disk file or drive
11
for a computer system is shown. Drive
11
has a base
13
containing magnetic disks
15
that are rotated about a hub
17
. A set of actuator arms
21
are pivotally mounted to base
13
on a pivot assembly
23
. A controller
19
is mounted to base
13
for selectively moving arms
21
relative to disks
15
. Each arm
21
comprises a mounting support
25
, a suspension
27
, and a head gimbal assembly
29
having a magnetic read/write head secured to each suspension
27
for reading data from and writing data to disks
15
. A conventional voice coil motor
26
is also mounted to pivot assembly
23
opposite head gimbal assemblies
29
. Movement of an actuator driver
28
(indicated by arrow
30
) moves head gimbal assemblies
29
radially across the disks
15
until the heads settle on the target tracks.
As shown in
FIG. 2
, pivot assembly
23
contains ball bearings
31
, a shaft
33
, and a sleeve
35
. The naturally-occurring, micron scale, machine tolerance inaccuracies in these components and in the tolerances of a conventional fixture
37
used to pre-load pivot
23
(shown greatly exaggerated for clarity) accumulate during the assembly of pivot
23
. The lower end of shaft
33
mounts in a hole
41
in base
43
of fixture
37
. Sleeve
35
is suspended above the upper surface of base
43
as a tubular anvil or rod
45
exerts axial force on the upper face
46
of the inner ring
47
to pre-load pivot
23
. Bearing pre-load is controlled to maintain sufficient stiffness of the pivot assembly. Fixture
37
only has one degree of freedom (up and down) to apply the pre-load to face
46
of inner ring
47
.
The tolerance stack-up of pivot
23
and fixture
37
causes significant angular misalignment between inner and outer rings
47
,
49
. This misalignment or “ring face out-of-parallelism” creates a moment on one side of inner ring
47
, thereby producing a greater localized pre-load force on the ball compliment. The term “ball compliment” is used to describe the array of spaced-apart balls within a bearing. Unfortunately, because fixture
37
is non-compliant, it is unable to compensate for ring face out-of-parallelism, raceway wobble and groove wobble. When a non-uniform, pre-load force is exerted on the ball compliment, one side is pinched tight by the raceways while the opposite side is loose. As pivot
23
rotates, the balls are compressed as they pass through the tight zone, thereby causing torque ripple. This phenomena is an excellent indicator that the actuator itself is dynamically unstable. Torque ripple must be compensated by the servo controller by varying the coil current. This non-uniform, pre-load force around the circumference of the bearing corresponds to a non-uniform stiffness around the circumference. Stiffness variation from pivot to pivot or circumferentially within one pivot can affect the frequencies and gains of the structural resonances of the actuator.
The problem of angular misalignment of the raceways can be prevented by increasing the radial clearance or gap between the shaft and the inner diameter of the bearing. A larger gap allows more compliance between the parts. Unfortunately, this solution creates the problem of increased outgassing arising from the additional adhesive required to fill the larger gap between the bearing and the shaft. Thus, an improved solution for pre-loading pivot assemblies is needed.
SUMMARY OF THE INVENTION
A fixture for pre-loading a pivot assembly has a stationary base and a tool that is axially movable relative to the base. The tool has a platen with a pre-load mass and a cylindrical enclosure. A sphere is suspended within the enclosure but is free to roll and move laterally along three degrees of freedom. The pivot assembly has an external sleeve with a coaxial shaft mounted on bearings. Each ball bearing has an inner ring, an outer ring, and balls in between. The rings are adhesively bonded to the shaft and sleeve.
The pivot is placed on the base of the fixture and the tool is lowered. The sphere is free to “float” within the enclosure until it makes contact with the inner ring of the upper bearing in the pivot. Upon contact, the compliant, rolling sphere automatically self-aligns with the pivot. The pre-load mass applies the desired force against the pivot until the adhesive cures. The sphere ensures that the pre-load force is uniform around the ball compliment circumference of the bearings such that the inner and outer rings of the bearings float and their raceways self-align under the pre-load force. After the adhesive cures, the pivots have negligible torque ripple and consistent dynamic response.
The foregoing and other objects and advantages of the present invention will be apparent to those skilled in the art, in view of the following detailed description of the preferred embodiment of the present invention, taken in conjunction with the appended claims and the accompanying drawings.
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Bracewell & Patterson L.L.P.
International Business Machines - Corporation
Omgba Essama
Vidovich Gregory
LandOfFree
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