[0001]
The present invention relates to: a pivot bearing that allows a precise swing
motion at low torque or with small variations in torque; and a magnetic recording
apparatus using the pivot bearing.
BACKGROUND ART
[0002]
In a pivot bearing of this type, a plurality of ball bearings are conventionally
located axially (in a tandem manner) with respect to a shaft conforming to inner rings of
the ball bearings, thus allowing a swing motion around the shaft with high precision and
at low torque. Meanwhile, a pivot bearing is often used as a bearing for a swing arm
(swing motion) type head access mechanism in a magnetic recording apparatus such as
in a hard disk drive (hereinafter denoted by the acronym "HDD") in particular. In an
HDD, an areal recording density is continually increased and is now about to reach 1
Tbpsi (1 Tera Bit Per Square Inch) due to increases in linear recording density and track
density. Hence, a desire for precision of micro-positioning is also growing, and there
is an increasing demand for higher precision of a pivot bearing.
[0003]
According to Patent Literature 1, an inner ring of one of two bearings included
in a pivot bearing is formed at a pivot shaft, thus making it possible to reduce the
number of components and torque variations. Moreover, Patent Literature 1 discloses
1
fixation of an arm of an HDD and the pivot bearing via a tolerance ring. Patent
Literature 1 further discloses that the tolerance ring is located in a gap between an arm
hole and the pivot bearing, and is thus compressed to exert a reaction force so that the
pivot bearing can be elastically supported with respect to the arm hole. Furthermore,
Patent Literature 2 discloses that when a pivot bearing is fixed in an arm hole via a
tolerance ring, protruded portions (projections) of the tolerance ring are plastically
deformed, thereby reducing a stress applied to an outer ring of the pivot bearing,
reducing the influence associated with deformation of the outer ring, and obtaining a
higher removing force. Besides, Patent Literature 2 also discloses that an allowable
range of variations in a gap between the arm hole and an outer diameter of the pivot
bearing can be increased, and an increase in torque can be prevented in a state where the
pivot bearing is mounted.
PRIOR ART REFERENCE
PATENT LITERATURE
[0004]
[Patent Literature 1] JP-A-2002-106554 (see page 4, paragraphs [0024] to
[0026], FIG. 5 and FIG. 7)
[Patent Literature 2] US 2008/0199254 Al (see page 1, paragraphs [0012] to
[0014], FIG. 2 and FIG. 9)
SUMMARY OF THE INVENTION
PROBLEMS TO BE SOLVED BY THE INVENTION
[0005]
However, in the pivot bearing disclosed in Patent Literature 1, rolling grooves
2
through which balls run have to be formed at part of the shaft; hence, it is conceivable
that there might be no flexibility in selecting a material in terms of bearing
characteristics, and a step for forming the grooves might be different from a normal step
for forming a ball bearing, thus causing a reduction in productivity and an increase in
price.
[0006]
Meanwhile, in assembling the pivot bearing by using the tolerance ring as
disclosed in Patent Literature 2, a higher contact pressure has to be applied between the
tolerance ring and the outer ring of the pivot bearing in order to strengthen fastening of
the pivot bearing to the arm hole. Thus, the deformation of the outer ring of the pivot
bearing is increased, and rolling grooves for balls are deformed, thereby causing an
increase in torque or a reduction in rotational accuracy. This triggers a reduction in
access speed or stop position precision in a recording and/or reproducing apparatus such
as an HDD, which is a factor contributing to performance degradation in the recording
and/or reproducing apparatus.
[0007]
The present invention has been made to solve the above conventional problems,
and enables inexpensive fabrication of a reliable pivot bearing that achieves high
precision with a simple structure, thus providing a reliable high density magnetic
recording apparatus.
MEANS FOR SOLVING THE PROBLEMS
[0008]
To achieve the above object, the present invention provides a pivot bearing
comprising: a shaft; and a plurality of ball bearings which are arranged in an axial
3
direction with respect to the shaft and each of which has an inner ring fixed to the shaft
and an outer ring fixed to a fixing hole of an arm via a tolerance ring, the pivot bearing
being configured to swing around the shaft, wherein the number of balls of each of the
ball bearings and the number of concave portions of the tolerance ring, which are
configured to press the outer ring, are relatively prime to each other, hi this structure,
when the outer ring is a simple ring, deformation will occur due to a stress of the
tolerance ring, and therefore, the outer ring will be deformed into a polygon whose
number of sides is equal to the number of the concave portions of the tolerance ring.
A preload is applied to each ball bearing, an iimer ring raceway surface and an outer
ring raceway surface thereof are brought into contact with the balls, and rigidity of an
iimer ring inner diameter portion of each of the ball bearings is increased by the shaft
inserted and fixed therethrough. Hence, it is conceivable that radial rigidity of the
outer ring may be greatly different between a position at which the ball exists and a
position at which no ball exists with respect the circumferential direction, hi other
words, the outer ring exhibits a characteristic that its rigidity changes repeatedly in
accordance with the number of the balls with respect to the circumferential direction.
Due to these reasons, the outer ring is deformed into a polygon whose number of sides
corresponds to the number of external stresses, i.e., the number of the concave portions
of the tolerance ring, and the rigidity of the outer ring is changed repeatedly in
accordance with the number of the balls. When the number of the concave portions of
the tolerance ring is m and the number of the balls is n, deformation of a raceway
groove of the outer ring is regarded as deformation of the outer ring itself, and it is
conceivable that the outer ring is deformed into a polygon whose number of sides
corresponds to the least common multiple of m and n, i.e., L.C.M.(m, n).
[0009]
4
Since m and n are relatively prime, the outer ring is deformed into a polygon
whose number of sides corresponds to L.C.M.(m, n) = m x n, so that the resulting
polygon can be close to an apparent perfect circle, thus making it possible to reduce
deformation of the raceway groove of the outer ring and to prevent degradation in
characteristics of the pivot bearing.
[0010]
According to another aspect, the concave portions of the tolerance ring,
configured to press the outer ring, are located equidistantly in a circumferential
direction. In this aspect, a polygon obtained when the outer ring is deformed as
mentioned above can be formed into a regular polygon. As a result, deformation
variations can be reduced, thereby making it possible to improve the characteristics of
the pivot bearing.
[0011]
According to still another aspect, the inner ring, outer ring and balls of each of
the ball bearings are made of martensite stainless steel, hi this aspect, as compared with
a case where high-carbon chromium steel such as SUJ2 is used, rust preventmg
capability is increased, thereby making it possible to eliminate the necessity for
application of a rust preventing oil and to reduce contaminants incident to evaporation
of the rust preventing oil.
[0012]
According to yet another aspect, the number of the balls of each of the ball
bearings is either 11 or 13. In this aspect, the number of the balls is akeady a prime
number; therefore, except when the number of the concave portions of the tolerance ring
is equal to the number of the balls of each of the ball bearings, the nimiber of the balls
of each of the ball bearings and the number of the concave portions of the tolerance ring
5
can always be relatively prime, thus making it possible to achieve a higher degree of
design flexibility in deciding the number of the concave portions of the tolerance ring.
[0013]
According to still yet another aspect, the number of the balls of each of the ball
bearings is larger than the number of the concave portions of the tolerance ring
configured to press the outer ring, hi this aspect, when a comparison is made between
precision of the tolerance ring formed by common presswork and precision of
positioning of the balls in each of the ball bearings, the latter precision is generally
higher. Hence, a higher degree of design flexibility can be achieved so as to further
facilitate optimization of, for example, the number or shape of the concave portions
which is likely to absorb precision degradation or variations in each concave portion
caused by springback.
[0014]
According to another aspect, a swing range allowed by the pivot bearing is set
at a mechanical angle of 45° or less, and the number of the balls of each of the ball
bearings is eight or more. In order to reduce variations in the location of each
component in the rotational direction of the ball bearings, the balls may be located so
that the ball pitch of each ball bearing is equal to or less than the mechanical angle.
With the use of the ball bearings whose ball pitch is 45° or less or the ball bearings each
having the eight or more balls, the relative locations of the balls in the circumferential
direction will not be changed in the swing range, and therefore, more stable precision
can be achieved.
[0015]
According to still another aspect, there is provided a magnetic recording
apparatus which uses a pivot bearing comprising: a shaft; and a plurality of ball
6
bearings which are arranged in an axial direction with respect to the shaft and each of
which has an inner ring fixed to the shaft and an outer ring fixed via a tolerance ring to a
fixing hole of an arm having a magnetic head at firont end thereof, the pivot bearing
being configured to swing around the shaft to allow track access of the magnetic head,
wherein the number of balls of each of the ball bearings and the number of concave
portions of the tolerance ring, which are configured to press the outer ring, are relatively
prime to each other. In this aspect, when the number of the concave portions of the
tolerance ring is m and the number of the balls is n as mentioned above, m and n are
relatively prime; therefore, the outer ring is deformed into a polygon whose number of
sides corresponds to L.C.M.(m, n) = m x n, so that the resulting polygon can be close to
an apparent perfect circle, thus making it possible to reduce deformation of a raceway
groove of the outer ring and to prevent degradation in characteristics of the pivot
bearing. Hence, the rotational accuracy of the pivot bearing can be maintained at a
high level for access of the magnetic head in the magnetic recording apparatus, thus
making it possible to improve track positioning accuracy of the high density recording
apparatus in which a track density is high, and to fabricate the magnetic recording
apparatus that has an advantage in high density recording.
EFFECT OF THE INVENTION
[0016]
As described above, according to the present invention, the number of the balls
of each of the ball bearings and the number of the concave portions of the tolerance ring
are relatively prime in the swing motion type pivot bearing in which the outer rings are
fixed via the tolerance ring, thus making it possible to reduce deformation of the
raceway grooves of the outer rings; hence, the pivot bearing that allows a precise swing
7
motion at low torque or with small variations in torque can be fabricated. Moreover,
with the use of this pivot bearing, the magnetic recording apparatus having a higher
track density and capable of performing higher density recording can be fabricated.
BRIEF DESCRIPTION OF THE DRAWINGS
[0017]
FIG. 1 is a schematic plan view of an HDD according to one embodiment of
the present invention;
FIG. 2 is a schematic plan view of an HSA of the HDD according to the
present embodiment;
FIG. 3 is a perspective view illustrating a pivot bearing and an arm according
to the present embodiment;
FIG. 4 is a cross-sectional view illustrating the pivot bearing and tolerance ring
according to the present embodiment;
FIG. 5 A is a front view of the tolerance ring;
FIG. 5B is a cross-sectional view of the tolerance ring;
FIG. 6 is a perspective view of another tolerance ring.
FIG. 7 is a plan view illustrating a relationship between the pivot bearing and
the tolerance ring according to one embodiment of the present invention; and
FIGS. 8A to 8C are characteristic graphs illustrating swing torque to verify
effects of the pivot bearing according to the present invention.
MODE FOR CARRYING OUT THE INVENTION
[0018]
One embodiment of the present invention will be described with reference to
8
the drawings. FIG. 1 is a schematic plan view of an HDD according to one
embodiment of the present invention. FIG. 2 is a schematic plan view of an HSA of
the HDD according to the present embodiment. FIG. 3 is a perspective view
illustrating a pivot bearing and an arm according to the present embodiment. FIG. 4 is
a cross-sectional view illustrating the pivot bearing and tolerance ring according to the
present embodiment. FIG. 5A is a front view of the tolerance ring. FIG. 5B is a
cross-sectional view of the tolerance ring. FIG. 6 is a perspective view of another
tolerance ring. FIG. 7 is a schematic diagram describing a relationship between the
bearing and the tolerance ring according to the present embodiment. FIGS. 8A to 8C
show characteristic graphs illustrating swing torque of the pivot bearing according to
the present invention.
[0019]
The general outlines of the HDD according to the present embodiment are as
follows. The HDD has an areal recording density of about 750 Gbpsi (Giga bit per
square inch) in a 2.5-inch perpendicular magnetic recording method, and is equipped
with two disks to have a storage capacity of 1 TB (Tera Byte). Hereinafter, a structure
of the HDD will first be described with reference to FIGS. 1 and 2.
A magnetic disk 3 serving as a magnetic recording medium is fixed to an
aluminum base plate 2 via not-illustrated spindle and hub which are provided at a
spindle motor 4, so that the magnetic disk 3 is rotatably supported. The magnetic disk 3
is formed by depositing layers such as an under layer, a soft magnetic under layer (SUL),
an Ru intermediate layer, a recording layer and a DLC layer over a glass base material
(substrate) by sputtering. Moreover, a lubricant consisting mainly of perfluoropolyether
(PFPE) is applied as a fluorochemical oil to a surface of the uppermost layer of the
magnetic disk 3. As the recording layer, a Co-Cr-Pt granular filni is used, and a grain
9
boundary is separated by SiOi.
[0020]
The HSA (Head Stack Assembly) 10 is provided at its one end with a magnetic
head 11, and is provided at its other end with a coil 7 included in a VCM (Voice Coil
Motor) for moving the magnetic head 11 in a track direction of the magnetic disk 3 (i.e.,
a radial direction of the magnetic disk 3). At a portion of the HSA 10 adjacent to the
magnetic head 11, a gimbal spring assembly (which is called an "HGA [Head Gimbal
Assembly]") for holding the magnetic head 11 is fixed to an arm 16 by swaging.
Furthermore, at a fi-ont end of the magnetic head 11, there is a region called a tab 15,
and the tab 15 cooperates with a ramp 5 attached to the base plate 2, thereby allowing
the magnetic head 11 to be loaded/unloaded on/from the magnetic disk 3. The magnetic
head 11 used in this embodiment is mounted on a femto slider and is supported by a
high-rigidity suspension; in addition, its flying height is controlled by using thermal
expansion.
[0021]
The HSA 10 is formed so as to be swung around a pivot bearing 13 provided at
a center region of the HSA 10 and serving as a rotation center. A magnet 8 is located
below the coil 7 of the VCM and a magnetic circuit is formed by a not-illustrated yoke,
so that due to an electric current supplied to the coil 7, torque is generated by Fleming's
left-hand rule, thus allowing the HSA 10 to swing around the pivot bearing 13 serving
as the rotation center, and enabling track access.
[0022]
As illustrated in FIG. 3, in the HSA 10, the pivot bearing 13 is fixed in a fixing
hole 18 of the arm 16 (also referred to as an "E-block"), made of an aluminum alloy and
serving as a base of the HSA 10, via a tolerance ring 12. The fixation via the tolerance
10
ring 12 is suitable for execution of rework such as removal of the HSA 10 from an HDA
(Head Disk Assembly) for replacement or correction in the event of failure in the
magnetic head 11 due to an ESD (Electro Static Discharge) or the like.
[0023]
In recent years, the density of an HDD has been fiirther increased, and the
performance of the magnetic head 11 has been further enhanced accordingly; however,
there has been a tendency to complicate a film structure for obtaining a higher MR ratio
and to reduce a withstanding ESD voltage. Further, since the costs of components
have also been increased, workability of HGA rework is preferably improved, and
therefore, workability for the fixation via the tolerance ring 12 is expected to improve
compared with conventional bonding, press-fitting and the like.
[0024]
As illustrated in FIGS. 3 and 4, the pivot bearing 13 includes: a shaft 21; and a
plurality of ball bearings 20 (a pair of ball bearings 20 in the present embodiment)
arranged in an axial direction with respect to the shaft 21, with a spacer 30 interposed
therebetween. The shaft 21 is provided with a screw 22 for fixing the pivot bearing 13
to the base plate 2. The ball bearings 20 each include: an inner ring 27 fixed to the
shaft 21; an outer ring 25 fixed to the fixing hole 18 of the arm 16 via the tolerance ring
12; a plurality of balls 26 located between the inner ring 27 and the outer ring 25; a
retainer 28 for holding the balls 26; and a seal member 29. The ball bearings 20 are
lubricated with grease.
Note that in the present embodiment, the inner rings 27, the outer rings 25 and
the balls 26 are each made of martensite stainless steel. Thus, as compared with a case
where high-carbon chromium steel such as SUJ2 is used, rust preventing capability is
increased, thereby making it possible to eliminate the necessity for application of a rust
11
preventing oil and to reduce contaminants incident to evaporation of the rust preventing
oil.
[0025]
Furthermore, as illustrated in FIG. 5, the tolerance ring 12 is provided by
rolling a steel plate made of a spring material such as SUS304CSP into a tubular shape.
At an axial intermediate portion of the tolerance ring 12, a plurality of convex portions
12a protruded radially outward are located equidistantly in a circumferential direction.
Accordingly, a plurality of concave portions 12b adapted to press the outer rings 25 are
located between the plurality of convex portions 12a so as to be equidistant in the
circumferential direction.
Note that as illustrated in FIG. 6, the tolerance ring 12 may be formed so that
the convex portions 12a are axially divided and the concave portions 12b located
between the divided convex portions 12a press the outer ring 25 of each ball bearing 20.
Moreover, in the present embodiment, each concave portion located between
the adjacent convex portions 12a so as to press the outer ring 25 is intended to provide a
contact surface that abuts against the outer ring 25; thus, each convex portion 12a of the
tolerance ring 12 is deformed between the pivot bearing 13 and the arm 16, thereby
applying a pressing force to the contact surface from the convex portions 12a located on
both sides thereof Accordingly, in the present embodiment, the number of the
concave portions (i.e., the number of the contact surfaces) and the number of the convex
portions 12a are substantially equal to each other.
[0026]
In the present embodiment, the number of the balls of each ball bearing 20 and
the number of the concave portions of the tolerance ring 12, which press the outer ring
25, are set so as to be relatively prime. When the outer ring 25 is a simple ring, the
12
outer ring 25 will be defonned due to a stress of the tolerance ring 12, and therefore, the
outer ring 25 will be deformed into a polygon whose number of sides is equal to the
number of the concave portions of the tolerance ring 12. A preload is applied to each
ball bearing 20, an inner ring raceway surface and an outer ring raceway surface thereof
are brought into contact with the balls 26, and rigidity of an inner ring inner diameter
portion of each ball bearing 20 is increased by the shaft 21 inserted and fixed
therethrough. Hence, it is conceivable that radial rigidity of the outer ring 25 may be
greatly different between a position at which the ball 26 exists and a position at which
no ball 26 exists with respect the circumferential direction. In other words, the outer
ring 25 exhibits a characteristic that its rigidity changes repeatedly in accordance with
the number of the balls 26 with respect to the circumferential direction. Due to these
reasons, the outer ring 25 is deformed into a polygon whose number of sides
corresponds to the number of external stresses, i.e., the number of the concave portions
of the tolerance ring 12, and the rigidity of the outer ring 25 is changed repeatedly in
accordance with the number of the balls 26. When the number of the concave portions
of the tolerance ring 12 is m and the number of the balls 26 is n, deformation of a
raceway groove of the outer ring 25 is regarded as deformation of the outer ring 25 itself,
and it is conceivable that the outer ring 25 is deformed into a polygon whose number of
sides corresponds to the least common multiple of m and n, i.e., L.C.M.(m, n).
[0027]
Since m and n are relatively prime, the outer ring 25 is deformed into a
polygon whose number of sides corresponds to L.C.M.(m, n) = m x n, so that the
resulting polygon can be close to an apparent perfect circle, thus making it possible to
reduce deformation of the raceway groove of the outer ring 25 and to achieve lower
torque of the pivot bearing 13.
13
[0028]
For example, as illustrated in FIG. 7, when the ball 26 is located at a position
corresponding to that of the concave portion of the tolerance ring 12, the concave
portion of the tolerance ring 12, the outer ring 25, the ball 26, the inner ring 27 and the
shaft 21 are substantially radially aligned; therefore, the rigidity of the outer ring is
apparently maximized, and degradation in roundness can be reduced. Conversely, the
rigidity of the outer ring is minimized when the concave portion of the tolerance ring 12
is located at a position corresponding to that of a midpoint between the balls 26. As
illustrated in FIG. 7, when m is 8 and n is 9, i.e., when m and n are relatively prime, the
outer ring 25 is deformed into a polygon whose number of sides corresponds to L.C.M.
= 72, and apparent roundness of the resulting outer ring 25 can be improved.
[0029]
In particular, the concave portions 12b of the tolerance ring 12 are located
equidistantly in the circumferential direction; thus, a polygon obtained when the outer
ring 25 is deformed can be formed into a regular polygon, and deformation variations
are reduced.
[0030]
It should be noted that the number of the balls of each ball bearing 20 can be
set at any number as long as the above-described relationship is established; for
example, the number of the balls of each ball bearing used for the HDD is actually
between 8 and 13. Furthermore, the number of the concave portions of the tolerance
ring 12 can also be set at any number; for example, the number of the concave portions
of the tolerance ring 12 used for the HDD is actually between 7 and 15.
[0031]
Accordingly, when the number n of the balls is 8, for example, the number m
14
of the concave portions of the tolerance ring 12 is 7, 9, 11, 13 or 15, for example, in
order to establish the above-described relationship. Furthermore, when the number n
of the balls is either 11 or 13, the number of the balls is already a prime number; hence,
except when the number of the concave portions of the tolerance ring 12 is equal to the
number of the balls, the number of the concave portions of the tolerance ring 12 and the
number of the balls can always be relatively prime, thus making it possible to achieve a
higher degree of design flexibility in deciding the number of the concave portions of the
tolerance ring 12. Specifically, when the number n of the balls is 11, the number m of
the concave portions may be 7, 8, 9, 10, 12, 13, 14 or 15, for example. Alternatively,
when the nimiber n of the balls is 13, the number m of the concave portions may be 7, 8,
9, 10, 11,12, 14 or 15, for example.
[0032]
When a comparison is made between precision of the tolerance ring 12 formed
by common presswork and precision of positioning of the balls 26 in each ball bearing
20, the latter precision is generally higher. Therefore, the number n of the balls is more
preferably larger than the number m of the concave portions of the tolerance ring 12 so
that design can be performed to provide, for example, the optimal number or shape of
the concave portions which is likely to absorb precision degradation or variations in
each concave portion caused by springback.
[0033]
Furthermore, in the present embodiment, a swing range allowed by the pivot
bearing 13 is set at a mechanical angle of 45° or less, and in order to reduce variations
in the location of each component in the rotational direction of the ball bearings 20, the
balls are located so that the ball pitch of each ball bearing 20 is equal to or less than the
mechanical angle. In other words, with the use of the ball bearings each having the eight
15
or more balls, the relative locations of the balls 26 in the circumferential direction will
not be changed in the swing range, and therefore, more stable precision can be achieved,
thus making it possible to improve reliability of a resulting magnetic recording
apparatus.
[0034]
(Torque Test)
Next, a test for verifying the effects of the present invention will be described
with reference to FIGS. 7 and 8A to 8C. In this test, a pivot bearing such as one
illustrated in FIG. 7, in which the number n of the balls is 8 and the number m of the
concave portions of the tolerance ring 12 is 9, was used as an example of the present
invention, while a pivot bearing in which the number n of the balls is 8 and the number
m of the concave portions of the tolerance ring 12 is 8 was used as a conventional
example. Torque generated when an arm was swung under the same conditions was
measured in each example. Further, the pivot bearing 13 of the example of the present
invention prior to attachment of the tolerance ring 12 thereto was used singly, and
torque measurement results obtained when an arm was swung around this pivot bearing
13 under the same conditions are illustrated in FIG. 8 A.
[0035]
As illustrated in FIG. 8B, in the example of the present invention, there are no
significant variations in the torque although the torque obtained in this example is larger
than the torque obtained in the case of FIG. 8 A in which the pivot bearing 13 was used
singly. Meanwhile, it is found that as illustrated in FIG. 8C, variations in the torque are
significant in the conventional example. Consequently, it is verified that torque
variations are reduced when the number of the balls of each ball bearing 20 and the
number of the concave portions of the tolerance ring 12 are relatively prime.
16
[0036]
The present invention is not limited to the above-described embodiment, but
alterations, modifications may be made as appropriate.
For example, in the present embodiment, the tolerance ring 12 is adapted to
directly press the outer ring 25 of each ball bearing 20; however, when a sleeve having a
thin thickness that allows the tolerance ring 12 to exert a pressing force on the outer
rings 25 is used, the present invention may also be applied to a pivot bearing of a type in
which the outer rings 25 are fixed to the sleeve.
Moreover, in the present embodiment, the convex portions 12a of the tolerance
ring 12 are protruded radially outward in view of assembly properties; however, the
convex portions 12a may be protruded radially inward, and peaks of the convex
portions may be provided as the concave portions 12b of the tolerance ring 12.
[0037]
The present invention is based on Japanese Patent Application No.
2012-078227 filed on March 29, 2012, the contents of which are hereby incorporated by
reference.
DESCRIPTION OF THE REFERENCE CHARACTERS
[0038]
1 HDD
2 base plate
3 disk
4 spindle motor
5 ramp
12 tolerance ring
17
12a convex portion
12b concave portion
13 pivot bearing
16 arm
18 fixing hole
20 ball bearing
21 shaft
25 outer ring
26 ball
27 inner ring
18

CLAIMS
1. A pivot bearing comprising: a shaft; and a plurality of ball bearings which are
arranged in an axial direction with respect to the shaft and each of which has an inner
ring fixed to the shaft and an outer ring fixed to a fixing hole of an arm via a tolerance
ring, the pivot bearing being configured to swing around the shaft,
wherein the number of balls of each of the ball bearings and the number of
concave portions of the tolerance ring, which are configured to press the outer ring, are
relatively prime to each other.
2. The pivot bearing of claim 1, wherein the concave portions of the tolerance
ring, which are configured to press the outer ring, are located equidistantly in a
circumferential direction.
3. The pivot bearing of claim 1 or 2, wherein the iimer ring, outer ring and balls
of each of the ball bearings are made of martensite stainless steel.
4. The pivot bearing of any one of claims 1 to 3, wherein the nimiber of the
balls of each of the ball bearings is either 11 or 13.
5. The pivot bearing of any one of claims 1 to 4, wherein the number of the
balls of each of the ball bearings is larger than the number of the concave portions of the
tolerance ring, which are configured to press the outer ring.
6. The pivot bearing of any one of claims 1 to 5, wherein a swing range allowed
by the pivot bearing is set at a mechanical angle of 45° or less, and the number of the
19
balls of each of the ball bearings is eight or more.
7. A magnetic recording apparatus which uses a pivot bearing comprising: a
shaft; and a plurality of ball bearings which are arranged in an axial direction with
respect to the shaft and each of which has an inner ring fixed to the shaft and an outer
ring fixed via a tolerance ring to a fixing hole of an arm having a magnetic head at fi-ont
end thereof, the pivot bearing being configured to swing around the shaft to allow track
access of the magnetic head, wherein the number of balls of each of the ball bearings
and the number of concave portions of the tolerance ring, which are configured to press
the outer ring, are relatively prime to each other.