U.S. patent application number 10/042691 was filed with the patent office on 2002-07-25 for ball bearing device for a swing arm.
This patent application is currently assigned to NSK, Ltd.. Invention is credited to Endo, Shigeru, Muraki, Hiromitsu, Sato, Chuichi, Tanaka, Katsuhiko.
Application Number | 20020097938 10/042691 |
Document ID | / |
Family ID | 27280377 |
Filed Date | 2002-07-25 |
United States Patent
Application |
20020097938 |
Kind Code |
A1 |
Muraki, Hiromitsu ; et
al. |
July 25, 2002 |
BALL BEARING DEVICE FOR A SWING ARM
Abstract
The locus of the displacement of the centers of the balls of a
ball bearing is made elliptical and the radial bearing rigidity of
the ball bearing in one radial direction is made greater than the
radial bering rigidity in the other radial direction orthogonal to
the one radial direction, or at least one of the axial length of
the portion on the inner diametral surface of the inner race of the
ball bearing which is fitted to a shaft and the axial length of the
portion on the outer diametral surface of the outer race of the
ball bearing which is fitted to a housing is made 1/2 or less of
the bearing width of the ball bearing, whereby the radial rigidity
of a ball bearing device is made greatly small as compared with the
radial rigidity in the prior art and as the result, the stability
of a swing arm system can be enhanced and the higher speed and
higher accuracy of control become possible.
Inventors: |
Muraki, Hiromitsu;
(Fujisawa-shi, JP) ; Tanaka, Katsuhiko;
(Yamato-shi, JP) ; Endo, Shigeru; (Kanagawa-ken,
JP) ; Sato, Chuichi; (Fujisawa-shi, JP) |
Correspondence
Address: |
Mitchell W. Shapiro
Miles & Stockbridge P.C.
Suite 500
1751 Pinnacle Drive
McLean
VA
22102-3833
US
|
Assignee: |
NSK, Ltd.
|
Family ID: |
27280377 |
Appl. No.: |
10/042691 |
Filed: |
January 2, 2002 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
10042691 |
Jan 2, 2002 |
|
|
|
09532944 |
Mar 22, 2000 |
|
|
|
09532944 |
Mar 22, 2000 |
|
|
|
09014167 |
Jan 27, 1998 |
|
|
|
6053638 |
|
|
|
|
Current U.S.
Class: |
384/513 |
Current CPC
Class: |
F16C 11/04 20130101;
Y10T 29/49696 20150115; F16C 27/04 20130101; F16C 35/077 20130101;
F16C 2370/12 20130101; Y10T 29/49682 20150115 |
Class at
Publication: |
384/513 |
International
Class: |
F16C 033/58 |
Foreign Application Data
Date |
Code |
Application Number |
Jan 28, 1997 |
JP |
9-013722 |
Sep 11, 1997 |
JP |
9-246442 |
Dec 4, 1997 |
JP |
9-334098 |
Claims
What is claimed is:
1. A ball bearing device for a swing arm, comprising: a plurality
of ball bearings each including balls, an inner race, an outer race
and a retainer; a shaft fitted to the inner diametral surface of
said inner race of each said ball bearing; and a housing fitted to
the outer diametral surface of said outer race of each said ball
bearing, wherein, for each said ball bearing, at least one of (1)
the axial length of the portion on the inner diametral surface of
said inner race which is fitted to the shaft and (2) the axial
length of the portion on the outer diametral surface of said outer
race which is fitted to the housing is {fraction (1/2)} or less of
the bearing width of said ball bearing.
2. A ball bearing device according to claim 1, wherein said housing
is formed with a plurality of recesses in an inner diametral
surface thereof, the outer race of each said ball bearing being
mounted to a corresponding one of said recesses.
3. A ball bearing device according to claim 1, wherein each said
ball bearing is such that radial bearing rigidity in one radial
direction is greater than radial bearing rigidity in a direction
orthogonal to said one radial direction.
4. A ball bearing device according to claim 2, wherein each said
recess includes diametrically opposed escapes having a clearance to
the outer diametral surface of the outer race of the corresponding
ball bearing to allow elliptical deformation of that outer
race.
5. A ball bearing device according to claim 2, said housing is
formed with recesses in its outer diametral surface near said ball
bearings to reduce radial rigidity of said housing near said ball
bearings.
6. A ball bearing device according to claim 5, wherein said
recesses in said outer diametral surface of said housing are
slits.
7. A ball bearing device for a swing arm, comprising: a ball
bearing including balls, an inner race, an outer race and a
retainer; a shaft fitted to the inner diametral surface of said
inner race of said ball bearing; and a housing having an inner
diametral surface and a recess formed in said inner diametral
surface at an axial end thereof, wherein said outer race is mounted
to said recess such that the axial length of the portion on the
outer diametral surface of said outer race which is fitted to the
inner diametral surface of said recess is {fraction (1/2)} or less
of the bearing width of said ball bearing.
8. A ball bearing device according to claim 7, said housing is
formed with a recesses in its outer diametral surface near said
ball bearing to reduce radial rigidity of said housing near said
ball bearing.
9. A ball bearing device according to claim 8, wherein said recess
in said outer diametral surface of said housing is a slit.
10. A ball bearing device according to claim 8, wherein said recess
includes diametrically opposed escapes having a clearance to the
outer diametral surface of said outer race to allow elliptical
deformation of said outer race.
11. A method of stabilizing the high-speed control of a ball
bearing device for a swing arm in which a plurality of ball
bearings are mounted between a shaft and a housing, wherein, for
each said ball bearing, at least one of (1) the axial length of the
portion of the shaft which is fitted to the inner diametral surface
of the inner race of the ball bearing and (2) the axial length of
the portion of the housing which is fitted to the outer diametral
surface of the outer race of the ball bearing is made 1/2 or less
of the bearing width of the ball bearing, thereby reducing the
radial bearing rigidity of the ball bearing device.
12. A method according to claim 11, wherein the outer race of each
said ball bearing is mounted to a corresponding recess formed in
the inner diametral surface of the housing.
13. A method according to claim 11, wherein the radial bearing
rigidity of each ball bearing in one radial direction thereof is
made greater than the radial bearing rigidity thereof in a
direction orthogonal to said one radial direction.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to a ball bearing device for the
swing arm of a disc driving apparatus for a magnetic disc, an
optical disc or the like.
[0003] 2. Related Background Art
[0004] The bearing portion of a ball bearing device for a swing arm
according to the prior art, as shown in FIG. 12A of the
accompanying drawings, has ball bearings 1 and 11 having grease
enclosed therein, and the ball bearings are used under a pre-load
at predetermined positions. FIG. 12B of the accompanying drawings
shows the surface pressure distribution 14 of the ball bearing 11
in a cross-section taken along the line 12B-12B of FIG. 12A, and
the surface pressure distribution 14 is indicated by a circle, and
the radial bearing rigidity of all portions in the circumferential
direction thereof is constant.
[0005] As shown, there are fitting portions on both of the inner
diametral surface of the inner race of the ball bearing fitted to a
shaft 5 and the outer diametral surface of the outer race fitted to
a housing 10.
[0006] These fitting portions are adhesively secured to the shaft 5
and the housing 10 over the entire bearing width of the ball
bearings 1 and 11.
[0007] FIG. 12C of the accompanying drawings schematically shows
the actually used state of the ball bearing device for a swing arm
according to the prior art.
[0008] Recently, higher and higher density has been required of
magnetic disc apparatuses. Therefore, the width of tracks for
recording signals on the disc has become narrower and narrower, and
the higher speed of access to a target track and the higher
accuracy of positioning performance have been required of a swing
arm carrying thereon a head for recording and reproducing
signals.
[0009] Accordingly, in order to satisfy the higher speed and higher
accuracy of control, the freedom from a torque fluctuation such as
a torque spike, a low torque, etc. are required of the ball
bearings 1 and 11 supporting the swing arm 9. Also, the high
stability and low torque of the control of the swing arm system
when controlled at a high speed are desired.
[0010] Heretofore, in the ball bearing device for the swing arm, as
shown in FIG. 12A, the two ball bearings 1 and 11 have been
accurately assembled together with a pre-load applied in the axial
direction thereof to thereby achieve the higher accuracy of the
bearing device. The present invention has as its object to provide
a ball bearing device for a swing arm in which the stability of a
swing arm system is enhanced and the higher speed and higher
accuracy of control are possible.
SUMMARY OF THE INVENTION
[0011] In the present invention, in order to enhance the stability
of the swing arm and the swing arm system and achieve the higher
speed and higher accuracy of the control of the swing arm,
attention has been paid to the rigidity of the ball bearing device
in the radial direction thereof and it has been confirmed that it
is effective to vary the rigidity in the radial direction in
accordance with the following methods.
[0012] 1) During the operation of the ball bearing device, the
locus of the displacement of the centers of the balls is made
elliptical, whereby the rigidity of the ball bearing device in the
radial direction thereof is made to differ between two directions
orthogonal to each other in the radial direction.
[0013] Particularly in the case of a straight swing arm, it is
preferable that the rigidity in a radial direction parallel to the
axis of the arm be made great relative to the rigidity in a radial
direction orthogonal to the direction, and further it is preferable
in enhancing the stability of the control of the swing arm to make
the magnitude thereof greater by 5% or more.
[0014] 2) The rigidity of the ball bearing device in the radial
direction thereof is greatly reduced as compared with the rigidity
of the ball bearing device of the prior-art construction in the
radial direction thereof.
[0015] It is particularly preferable in enhancing the stability of
the control of the swing arm that the rigidity in the radial
direction be reduce to 50% or less relative to the rigidity of the
ball bearing device of the prior-art construction in the radial
direction thereof.
[0016] According to one aspect of the present application, the ball
bearing of the present invention has a difference between the
radial bearing rigidities of the ball bearing in two directions
orthogonal to each other.
[0017] In the present invention, the locus of the displacement of
the centers of the balls of the ball bearing is made elliptical,
whereby the amount of elastic deformation of the balls and raceway
surface is made to differ between the major axis side and the minor
axis side of the ellipse. As the result, the contact surface
pressure differs between the major axis direction and the minor
axis direction of the ellipse and the radial bearing rigidity
differs. Or further, if the radial bearing gap in the other radial
direction is made larger than the radial bearing gap in one radial
direction orthogonal to the other radial direction, the balls and
the raceway surface do not contact with each other in the other
radial direction, and the radial bearing rigidity in the other
radial direction can be made small as compared with the radial
bearing rigidity in one radial direction. As the result, the radial
bearing rigidities of the ball bearing in the two directions
orthogonal to each other can be made to have a difference
therebetween.
[0018] Specifically, in the ball bearing according to the present
invention, it is preferable that balls be disposed between one
raceway surface provided on an inner member and the other raceway
surface provided on an outer member and at least one of one raceway
surface and the other raceway surface be elliptical in its
cross-section by a radial plane. Or further, it is preferable that
the radial bearing gap in one radial direction be smaller than the
other radial bearing gap orthogonal to the one radial direction.
For example, in the ball bearing according to the present
invention, the inner member may fit to a shaft and in one radial
direction, the inner member may be pressed into the shaft, and in
the other radial direction, a gap may be provided between the inner
member and the shaft. Or in the ball bearing according to the
present invention, the outer member may fit to a housing and in one
radial direction, the outer member may be pressed into the housing,
and in the other radial direction, a gap may be provided between
the outer member and the housing.
[0019] Or further, in the ball bearing according to the present
invention, the inner member may fit to the shaft and the outer
member may fit to the housing, and a plane containing the centers
of a plurality of balls disposed between one raceway surface of the
inner member and the other raceway surface of the outer member may
be inclined with respect to a plane perpendicular to the center
axis of the rocking member of one of the shaft and the housing.
[0020] According to one aspect of the present application, the ball
bearing according to the present invention is characterized in that
at least one of the axial length of the portion fitting to the
shaft in the inner diametral surface of an inner race and the axial
length of the portion fitting to the housing in the outer diametral
surface of an outer race is {fraction (1/2)} or less of the bearing
width of the ball bearing. Thereby, the rigidity of the ball
bearing device in the radial direction thereof is greatly reduced
as the rigidity of the ball bearing device of the prior-art
construction in the radial direction thereof.
[0021] According to one aspect of the present application, the ball
bearing device of the present invention is characterized in that
the radial bearing rigidities in two directions orthogonal to each
other have a difference therebetween and at least one of the axial
length of the portion fitted to the shaft in the inner diametral
surface of the inner race and the axial length of the portion
fitted to the shaft in the outer diametral surface of the outer
race is {fraction (1/2)} or less of the bearing width of the ball
bearing.
[0022] Other modes of the present invention will become apparent
from the embodiments of the invention which will be shown and
described below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] FIG. 1A is a cross-sectional view showing a ball bearing
device according to a first embodiment of the present
invention.
[0024] FIG. 1B shows the surface pressure distribution of the
portion of contact between a raceway surface and balls in the first
embodiment of the present invention.
[0025] FIG. 2 is a cross-sectional view showing a ball bearing
device according to a second embodiment of the present
invention.
[0026] FIGS. 3A, 3B and 3C are cross-sectional views showing a ball
bearing device according to a third embodiment of the present
invention.
[0027] FIG. 4A is a cross-sectional view showing a ball bearing
device according to a fourth embodiment of the present
invention.
[0028] FIG. 4B shows the surface pressure distribution of the
portion of contact between a raceway surface and balls in the
fourth embodiment of the present invention.
[0029] FIG. 5A is a cross-sectional view showing a ball bearing
device according to a fifth embodiment of the present
invention.
[0030] FIG. 5B shows the surface pressure distribution of the
portion of contact between a raceway surface and balls in the fifth
embodiment of the present invention.
[0031] FIG. 6A is a cross-sectional view showing a ball bearing
device according to a sixth embodiment of the present
invention.
[0032] FIG. 6B shows the surface pressure distribution of the
portion of contact between a raceway surface and balls in the sixth
embodiment of the present invention.
[0033] FIG. 7A is a schematic cross-sectional view of a ball
bearing device according to a seventh embodiment of the present
invention.
[0034] FIG. 7B is a schematic longitudinal cross-sectional view of
the ball bearing device according to the seventh embodiment of the
present invention when the device is used in an outer race turning
type actuator having a voice coil motor.
[0035] FIG. 8 is a schematic longitudinal cross-sectional view of a
ball bearing device according to an eighth embodiment of the
present invention in which the rigidity of a housing is
reduced.
[0036] FIG. 9 is a schematic cross-sectional view of a ball bearing
device according to a ninth embodiment of the present
invention.
[0037] FIG. 10 is a schematic longitudinal cross-sectional view of
a ball bearing device according to a tenth embodiment of the
present invention.
[0038] FIG. 11A is a schematic longitudinal cross-sectional view of
a ball bearing device according to an eleventh embodiment of the
present invention.
[0039] FIG. 11B is a cross-sectional view of the ball bearing
device of FIG. 11A taken along the line 11B-11B of FIG. 11A.
[0040] FIG. 12A is a cross-sectional view showing a ball bearing
device according to the prior art.
[0041] FIG. 12B shows the surface pressure distribution of the
portion of contact between a raceway and balls in the prior
art.
[0042] FIG. 12C is a schematic longitudinal cross-sectional view of
the ball bearing device according to the prior art when the device
is used in an outer race turning type actuator having a voice coil
motor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0043] A first embodiment of the present invention will hereinafter
be described with reference to the drawings. Like constituents in
various embodiments are designated by like reference numerals.
[0044] Means for making the locus of the displacement of the center
of a ball elliptical and making the rigidity of a ball bearing in
the radial direction thereof differ between two radial directions
orthogonal to each other includes the following means:
[0045] 1. To work the raceway surface of at least one of an inner
race and an outer race into an elliptical shape in advance.
[0046] 2. During the incorporation of the ball bearing, to incline
a plane containing the centers of a plurality of balls with respect
to a plane perpendicular to the center axis of the rocking member
of at least one of a shaft and a housing.
[0047] 3. In the other radial direction, there is a gap between the
ball bearing and the housing or the shaft, and in one radial
direction orthogonal to the other direction, to deform the raceway
surface of one of the outer race and the inner race into an
elliptical shape by the effect of the gap when the ball bearing is
pressed into the housing or the shaft.
[0048] 4. To apply additional working by which thermal deformation
is created in the outer diametral surface or the inner diametral
surface of the ball bearing, and deform the raceway surface of one
of the outer race and the inner race.
[0049] Description will hereinafter be made in accordance with the
drawings.
[0050] FIG. 1A shows a first embodiment of shaft fixing using a
ball bearing according to a first aspect of the present invention.
In a deep groove ball bearing 1 (hereinafter referred to as the
ball bearing), a plurality of balls 15 retained by a retainer are
disposed between one raceway surface provided on the inner races 3,
13 of an inner member (hereinafter referred to as one raceway
surface) and the other raceway surface provided on the outer races
2, 12 of an outer member (hereinafter referred to as the other
raceway surface). One raceway surface is such that its
cross-section by a radial plane is circular, and the other raceway
surface is such that its cross-section by a radial plane is
elliptical. As the result, the ball bearings 1, 11 are such that
the radial bearing gap in one radical direction is smaller than the
other radial bearing gap orthogonal to the one radial
direction.
[0051] The ball bearings 1, 11 have their outer diametral surfaces
fixedly fitted to the inner diametral surface of the cylindrical
housing 10 of a magnetic disc apparatus at an axial interval and
have their inner diametral surfaces fixedly fitted to a shaft 5
fixed to a base 16. The minor axis of the ellipse of the other
raceway surface provided on the outer races 2, 12 is incorporated
so as to become parallel to the axial direction of a swing arm 9
fixedly fitted to the outer diametral surface of the housing 10.
The shapes and direction of the minor axis of the ellipses of the
raceway surfaces are made coincident with each other in the ball
bearings 1 and 11. When with the shaft thus fixed, the housing 10
is used as a rocking member, if the raceway surfaces of the outer
races 2, 12 on that side of the magnetic disc apparatus which is
mounted on the housing 10 are worked into an elliptical shape, the
axial direction of the swing arm 9 and the minor axis of the
ellipse of the raceway surface will always become parallel to each
other even if the swing arm 9 effects rocking movement.
[0052] When the raceway surfaces are thus worked into an elliptical
shape in advance, the raceway surfaces can be made into an
elliptical shape even if the ball bearings 1, 11 are used while
being loosely fitted to the housing 10 and the shaft 5.
[0053] FIG. 1B shows a cross-section taken along the line 1B-1B of
FIG. 1A and the surface pressure distribution 14 of the portion of
contact between the balls 15 and raceway surface of the ball
bearing used in the cross-section. The dimensions of the major axis
and the minor axis are set such that the surface pressure of the
ellipses of the raceway surfaces of the outer races in the
direction of the minor axis thereof is about twice as great as the
surface pressure in the direction of the major axis. As described
above, the ball bearing according to the first embodiment of the
present invention is such that the locus of the displacement of the
centers of the balls 15 is elliptical, and as the result, the
radial bearing rigidity in one radial direction, i.e., the
direction of the minor axis, is greater than the radial bearing
rigidity in the other radial direction orthogonal to the one radial
direction, i.e., the direction of the major axis.
[0054] FIG. 2 shows a second embodiment of the present invention in
which the shaft 5 is a rocking member. The ball bearings 1, 11 in
which in advance, the raceway surface of one of the inner members,
i.e., the inner races 3, 13, is worked so that its cross-section by
a radial plane may become elliptical and the raceway surface of the
other of the outer races 2, 12 is worked so that its cross-section
by a radial plane may become circular are incorporated in the
housing 10 fixed to the base 16 of the magnetic disc apparatus, in
a direction in which the major axis of the ellipses of the raceway
surfaces of the inner races 3, 13 is parallel to the axial
direction of the swing arm 9 fixed to the shaft 5. The shapes and
directions of the major axes of the ellipses of the raceway
surfaces are made coincident with each other by the two upper and
lower ball bearings 1 and 11. As the result, the ball bearings are
such that the radial bearing gap in one radial direction is smaller
than the other radial bearing gap orthogonal to the one radial
direction.
[0055] When the raceway surfaces are thus worked into an elliptical
shape in advance, the raceway surfaces can be made elliptical even
if the ball bearings 1, 11 are used while being loosely fitted to
the housing 10 and the shaft 5. As described above, the ball
bearing according to the second embodiment of the present invention
is such that the locus of the displacement of the centers of the
balls 15 is elliptical and as the result, the radial bearing
rigidity in one radial direction is greater than the radial bearing
rigidity in the other radial direction orthogonal to the one radial
direction.
[0056] FIGS. 3A to 3C show a third embodiment of the present
invention. The swing arm in this embodiment is such that the ball
bearings 1, 11 in which the raceway surface of one of the inner
races 3, 13 and the raceway surface of the other of the outer races
2, 12 are worked into an ordinary standard are assembled to the
shaft 5 and the housing 10 in a state in which a plane containing
the centers of a plurality of balls 15 is inclined with respect to
a plane perpendicular to the center axis of the rocking member of
one of the shaft 5 and the housing 10, whereby the locus of the
displacement of the centers of the balls 15 is made elliptical.
That is, as in the ordinary standard ball bearing, one raceway
surface and the other raceway surface are circular in their
cross-section by a radial plane. In the present embodiment, by the
standard ball bearings 1, 11 being inclined and mounted, the balls
15 are displaced in the axial bearing gaps of the ball bearings 1,
11 in the axial direction of the ball bearings 1, 11, whereby the
locus of the displacement of the centers of the balls 15 is made
elliptical. The inner diametral surfaces of the inner races 3, 13
are parallel to the center axis of the shaft 5, and the outer
diametral surfaces of the outer races 2, 12 are perpendicular to a
plane containing the centers of the plurality of balls 15.
[0057] FIG. 3A shows a case where the upper and lower ball bearings
1 and 11 have been symmetrically inclined and mounted and
thereafter a constant position pre-load has been applied thereto.
The center axis of the shaft 5 is concentric with the center axis
of the housing 10.
[0058] FIG. 3B shows a case where the upper and lower ball bearings
1 and 11 have been inclined in the same direction and mounted and
thereafter a pre-load has been applied thereto. The center axis of
the shaft 5 is concentric with the center axis of the housing
10.
[0059] FIG. 3C shows a case where the upper and lower ball bearings
1 and 11 have been inclined in the same direction and mounted and
thereafter a constant position pre-load has been applied thereto.
The center axis of the shaft 5 is inclined with respect to the
center axis of the housing 10.
[0060] In any of the above-described three examples, the plane
containing the centers of the plurality of balls become inclined
with respect to the plane perpendicular to the center axis of the
rocking member of one of the shaft 5 and the housing 10, and as the
result, the tack locus becomes elliptical. As described above, in
the present embodiment, the radial bearing rigidity of the ball
bearings in one radial direction becomes greater than the radial
bearing rigidity in the other radial direction orthogonal to the
one radial direction, and the radial bearing gap in one radial
direction becomes smaller than the radial bearing gap in the other
radial direction orthogonal to the one radial direction. As the
result, again in the present embodiment, there is obtained an
effect similar to that of the first embodiment.
[0061] In the case of this third embodiment, at least one of the
ordinary ball bearings 1, 11, the shaft 5 and the housing 10 can be
slightly worked and used and therefore, the cost is low.
[0062] FIGS. 4A and 4B show a fourth embodiment of the present
invention. FIG. 4B shows a cross-section taken along the line 4B-4B
of FIG. 4A and the surface pressure distribution in the
cross-section, and in this embodiment, two ordinary ball bearings
are pressed into the housing 10 to thereby make the outer diametral
surfaces and raceway surfaces of the outer races elliptical. On the
inner diametral surface of the housing 10, escapes 25 are formed in
advance on the opposite sides of the center axis of the ball
bearings 1, 11 in one radial direction. When this is done, the
portion of the escapes 25 in the ball bearings 1, 11 becomes
loosely fitted and the pressed-in portion in the other radial
direction orthogonal to one radial direction linking the escapes 25
together becomes tightly fitted, and a compression load acts on the
outer races 2, 12 of the ball bearings 1, 11 in the pressed-in
portion. As the result, the outer diametral surfaces and raceway
surfaces of the outer races 2, 12 are deformed into an elliptical
shape in which the cross-section by the radial plane has the
portion of the escapes 25 as the major axis. If these escapes 25
are provided in a direction orthogonal to the axial direction of
the swing arm 9 mounted on the shaft 5, the radial bearing rigidity
in a direction parallel to the axial direction of the swing arm can
be made greater than in a direction orthogonal to the axial
direction of the swing arm 9. The raceway surface of one of the
inner races 3, 13 is circular in its cross-section by the radial
plane. The effect thereafter is substantially similar to that of
the aforedescribed embodiments. This embodiment enables ordinary
ball bearings to be used and therefore is low in cost. Also, the
housing 10 can only be provided with the escapes 25 and therefore,
the factors for an increased cost are few in the working of the
housing as well.
[0063] FIGS. 5A and 5B show a fifth embodiment of the present
invention. FIG. 5B shows a cross-section taken along the line 5B-5B
of FIG. 5A and a surface pressure distribution in the
cross-section, and in this embodiment, as in the fourth embodiment,
the ball bearings 1, 11 are pressed into the housing 10 to thereby
make the raceway surfaces of the outer races 2, 12 elliptical. The
difference of the present embodiment from the fourth embodiment is
that the escapes 25 are provided not on the housing 10 but on the
outer diametral surfaces of the outer races 2, 12.
[0064] FIGS. 6A and 6B show a sixth embodiment of the present
invention. FIG. 6B shows a cross-section taken along the line 6B-6B
of FIG. 6A and a surface pressure distribution in the
cross-section, and in this embodiment, an energy beam such as a
laser beam is locally applied to the outer races 2, 12 of ordinary
ball bearings 1, 11 to thereby cause thermal deformation, thus
deforming (thermally deformed portions 26) the outer diametral
surfaces and the other raceway surface of the outer races 2, 12 so
that the cross-section by a radial plane may become elliptical. In
the present embodiment, the laser is applied to two portions of the
outer diametral surface of the outer races 2, 12 which are spaced
apart by 180.degree. from each other to thereby deform the outer
diametral surfaces and raceway surfaces of the outer races 2, 12
into an ellipse, whereafter the ball bearings 1, 11 are mounted on
the housing 10 as by loose fitting. One raceway surface of the
inner races 3, 13 is circular in its cross-section by a radial
plane. In the other points, the effect of the present embodiment is
substantially similar to that of the embodiments hitherto
described.
[0065] Both of one raceway surface and the other raceway surface
may be elliptical in their cross-sections by a radial plane, and
the major axis of the ellipse of one raceway surface and the major
axis of the ellipse of the other raceway surface may be orthogonal
to each other.
[0066] Also, even if in one radial direction, the inner member is
pressed into the shaft 5 and in the other radial direction
orthogonal to the one radial direction, there is a gap between the
inner member and the shaft 5, one raceway surface of the inner
races 3, 13 of the inner member becomes elliptical in its
cross-section by a radial plane. In this case, the other raceway
surface of the outer member may be circular or elliptical in its
cross-section by a radial plane.
[0067] As regards the ball bearings 1, 11, if the radial bearing
rigidity in one radial direction is greater than the radial bearing
rigidity in the other radial direction orthogonal to the one radial
direction, the radial bearing gap becomes larger in the other
radial direction than in the one radial direction and a low torque
is provided. Accordingly, there can be provided a ball bearing in
which the radial bearing rigidity in the necessary radial direction
is made great and which is of a low torque as a whole.
[0068] Also, other embodiment in which the raceway surfaces of the
ball bearings are elliptical than the above-described embodiments
will do, and an embodiment in which the locus of the displacement
of the centers of the balls is elliptical will also do, and any of
these embodiments can provide an effect similar to that of the
present invention.
[0069] As regards the ball bearings 1, 11, with the inner member as
a shaft, one raceway surface may be provided on the shaft, and with
the outer member as a housing, the other raceway surface may be
provided on the housing.
[0070] A second aspect of the present invention will now be
described.
[0071] FIG. 7A shows a seventh embodiment of a ball bearing device
according to a second aspect of the present invention. The ball
bearings 1, 11 have a plurality of balls retained by a retainer
between outer races 2, 12 and inner races 3, 13.
[0072] These ball bearings 1, 11 are incorporated in the axially
opposite end portions of the inner diametral surface of a housing
10 on which the swing arm 9 of a magnetic disc apparatus is
mounted. The upper and lower ball bearings 1 and 11 are fixed to
the housing 10 by light press-in fit on the outer diametral
surfaces 2a and 12a of the respective outer races 2 and 12. Both of
the two outer races 2, 12 have their axially inner sides in contact
with a stepped surface perpendicular to the axis of the housing
10.
[0073] The ball bearings 1, 11 have the axial lengths 2l and 12l of
their portions fitted to the housing 10 on the outer diametral
surfaces 2a and 12a of the outer races 2 and 12 set to {fraction
(1/2)} or less of the bearing widths 1l and 11l of the ball
bearings 1 and 11. The inner race 13 of the lower ball bearing 11
has a shaft 5 fixed to its inner diametral surface by light
press-in. The portions of the two ball bearings 1, 11 which are
fitted to the housing 10 on the outer diametral surfaces 2a and 12a
of the outer races are axially inner portions, i.e., the inside
portions of the housing 10.
[0074] Also, as regards the shaft 5, a flange portion 6 provided at
the axially central portion is larger in diameter than the axially
opposite portions of the flange portion 6 and further, for the ease
of assembly and the enlargement of a pair of bearing spans, the
inner race 13 of the lower ball bearing has its axially inner side
in contact with the stepped surface of the flange portion 6. The
inner diametral surface 3a of the inner race 3 of the upper ball
bearing 1 is fixed to the shaft 5 by light press-in while pre-load
setting by a resonance frequency is effected. Furthermore, for the
prevention of the slippage by a shock load, an adhesive agent is
applied to the upper side 13b of the inner race 13 of the lower
ball bearing, which is thus fixed to the shaft 5.
[0075] For the reduction of the radial rigidity and the ease of
washing, the shaft 5 is a hollow shaft having a hole axially
extending through the central portion of the shaft 5 and further,
threaded grooves are formed from the upper and lower opening end
portions of the hole so that mounting screws can be mounted in the
shaft 5. The material of the shaft may be stainless steel, but it
is preferable to use a material having a small modulus of
longitudinal elasticity such as aluminum in order to reduce the
radial rigidity.
[0076] Further, as in an eighth embodiment shown in FIG. 8, slits
10a can be formed in the outer diametral surface of the housing 10
in the portions between the two ball bearings 1 and 11 which are
near the two ball bearings to thereby reduce the radial rigidity of
the housing 10. In this case, the housing 10 has the outer diameter
of its portions located on the ball bearing 1, 11 sides axially
outward of those portions formed with the slits 10a made smaller
than the outer diameter of the portion between the upper and lower
slits 10a at the center of the housing 10 and a level difference A
is provided on the housing 10.
[0077] Accordingly, the housing 10 is elastically deformable
without its portions axially outward of the slits 10a contacting
with a swing arm 9 which will be described later. An escape portion
may be provided on the swing arm 9 mounted on the housing 10 so
that the portions of the housing 10 which are axially outward of
the slits 10a may not contact with the swing arm 9.
[0078] As the ball bearings 1, 11, use may be made of a combination
of balls of bearing steel and grease lubrication, but preferably,
the material of the balls may be ceramics and oil may be used as a
lubricant and further, a slight quantity of oil may preferably be
poured into the raceway surfaces of the outer races 2, 12 and the
inner races 3, 13 in advance. Alternatively, use may be made of the
so-called oil plating which is a lubricating method of thinly
applying a slight quantity of oil to the raceway surfaces of the
outer races 2, 12 and the inner races 3, 13 in advance.
[0079] By using the ball bearings 1, 11 having their raceway
surfaces subjected to the oil plating, the initial scattering of
the lubricant from the ball bearings 1, 11 can be reduced and
torque fluctuation can also be reduced as compared with the case of
grease lubrication. Also, since the material of the balls is
ceramics, there can be provided ball bearings 1, 11 which are low
in wear and excellent in fretting durability.
[0080] It is preferable to design the ball bearings 1, 11 so as to
be reduced in radial rigidity by choosing at least one of groups
comprising making the radial gap greater than 15 .mu.m exceeding
the standard of 6 to 14 .mu.m, or reducing the number of balls to
six or less which is smaller than the standard of 7 to 8, and
making the pre-load applied to the ball bearings 1, 11 less than
0.5 Kgf smaller than the standard of 0.5 to 1.0 Kgf. As the ball
bearings 1, 11 used in the present invention, use can be made of
standard ball bearings and therefore, the ball bearing device for a
swing arm can be made inexpensively.
[0081] While the material of the retainer of the ball bearings 1,
11 may be stainless steel, iron, nylon or like material, it is more
preferable to use a polymer member containing lubricating oil
formed with synthetic resin containing lubricating oil. When a
retainer comprising the polymer member containing lubricating oil
is used, torque and torque fluctuation become small and further,
the lubricating oil contained in the retainer oozes for a long time
and therefore, good lubrication is effected for a long time and
excellent durability is obtained.
[0082] FIG. 7B shows the seventh embodiment as it is actually
incorporated into an apparatus. In this embodiment, the upper and
lower end portions of the shaft 5 are fixed to a body case 8 by
means of upper and lower bolts 7. When it is desired to further
reduce the radial rigidity of the shaft 5, there may be adopted a
cantilever structure in which only the lower portion of the shaft 5
is fixed to the body case 8 and the upper portion of the shaft 5 is
not supported.
[0083] While the housing 10 is fitted and adhesively secured to the
inner diametral surface of the swing arm 9, it may be fixed to the
swing arm 9 by means of a bolt. When the housing 10 is to be
adhesively secured, a circumferential groove-like adhesive
reservoir 20 provided in the outer diametral surface of the housing
10 is filled with an adhesive agent.
[0084] FIG. 9 shows a ninth embodiment of the present invention. In
this embodiment, the axial lengths 3l and 13l of the portions of
the inner diametral surfaces of the inner races 3 and 13 of the
upper and lower ball bearings 1 and 11 which are fitted to the
shaft 5 are {fraction (1/2)} or less of the bearing widths 1l and
11l of the ball bearings 1 and 11. Unlike the seventh embodiment,
the width of the housing 10 can be made the same as the width in
the prior art and the housing 10 can secure the same mounting width
as the mounting width for the swing arm 9 in the prior art.
[0085] FIG. 10 shows a tenth embodiment of the present invention.
In this embodiment, the axial lengths 2l and 12l of the portions of
the outer diametral surfaces of the outer races 2, 12 of the ball
bearings 1, 11 which are fitted to the housing 10 are {fraction
(1/2)} or less of the bearing widths 1l and 11l of the ball
bearings 1, 11. The difference of the present embodiment from the
seventh embodiment is that the axially inside portions of the outer
diametral surfaces 2a and 12a of the outer races are not in contact
with the housing 10.
[0086] That is, in both of the two ball bearings 1 and 11, the
portions of the outer diametral surfaces of the outer races 2 and
12 which are fitted to the housing 10 are axially outside portions.
Therefore, the axial length of the housing 10 is enlarged and the
moment rigidity thereof is improved.
[0087] Also, in the present embodiment, as in the ninth embodiment,
the housing 10 can secure the same mounting width as the mounting
with for the swing arm 9 in the prior art.
[0088] The ball bearings 1, 11 may be such that both of the axial
length 3l, 13l of the portions of the inner diametral surfaces 3a,
13a of the inner races which are fitted to the shaft 5 and the
axial lengths 2l, 12l of the portions of the outer diametral
surfaces 2a, 12a of the outer races which are fitted to the housing
10 are {fraction (1/2)} or less of the bearing widths 1l, 11l of
the ball bearings.
[0089] Also, in the present invention, the radial rigidity of the
ball bearing device may be reduced by the combination of the ball
bearings 1, 11 are the housing 10, or radial rigidity of the ball
bearing device may be reduced by the combination of the ball
bearings 1, 11 and the shaft 5, or the radial rigidity of the ball
bearing device may be reduced by the combination of the ball
bearings 1, 11, the housing 10 and the shaft 5.
[0090] A third aspect of the present invention will now be
described.
[0091] FIGS. 11A and 11B show an eleventh embodiment of a ball
bearing device according to the third aspect of the present
invention.
[0092] FIG. 11B is a cross-sectional view taken along the line
11B-11B of FIG. 11A, and in this embodiment, two ordinary ball
bearings 1 and 11 are pressed into the housing 10 to thereby make
the outer diametral surfaces and raceway surfaces of the outer
races 2, 12 elliptical. On the inner diametral surface of the
housing 10, escapes 25 are formed in advance on the opposite sides
of the center axis of the ball bearings 1, 11 in one radial
direction. If this is done, the ball bearings 1, 11 are loosely
fitted in the portions of the escapes 25 and are tightly fitted in
the pressed-in portion in the other radial direction orthogonal to
the one radial direction, and a compression load acts on the outer
races 2, 12 of the ball bearings in the pressed-in portion.
[0093] As the result, the outer diametral surfaces and raceway
surfaces of the outer races 2, 12 have their cross-sections by a
radial plane deformed into an elliptical shape in which the
portions of the escapes 25 are the major axis. If these escapes 25
are provided in a direction orthogonal to the axial direction of a
swing arm 9 mounted on the housing 10, the radial bearing rigidity
in a direction parallel to the axial direction of the swing arm can
be made greater than in a direction orthogonal to the axial
direction of the swing arm. The raceway surfaces of the inner races
3, 13 are circular in their cross-sections by a radial plane.
[0094] The above-described construction is similar to the
construction of the fourth embodiment, and the other portions of
the illustrated embodiment are constructed substantially similarly
to the seventh embodiment.
[0095] The ball bearings 1, 11 and the ball bearing device in the
present embodiment not only have their rigidity in the radial
direction greatly reduced as compared with the rigidity in the
radial direction in the prior art, but also the rigidities of the
ball bearings 1, 11 in the radial direction are made to differ
between two directions orthogonal to each other and as the result,
the stability of the swing arm system can be enhanced and the
higher speed and higher accuracy of control are possible.
* * * * *