U.S. patent application number 09/413229 was filed with the patent office on 2002-02-14 for anti friction bearing and a motor including such a bearing.
This patent application is currently assigned to Minebea Kabushiki - kaisha (Minebea Co., Ltd.). Invention is credited to MATSUOKA, HIDEKI, YAJIMA, HIROYUKI.
Application Number | 20020018607 09/413229 |
Document ID | / |
Family ID | 17695471 |
Filed Date | 2002-02-14 |
United States Patent
Application |
20020018607 |
Kind Code |
A1 |
YAJIMA, HIROYUKI ; et
al. |
February 14, 2002 |
ANTI FRICTION BEARING AND A MOTOR INCLUDING SUCH A BEARING
Abstract
An anti-frictional bearing which is reduced in its asynchronous
rotational run out so that the cumbersome analyzing operation of
the raceway surface and selecting operation of inner and/or outer
races are not required. The bearing will contribute for the high
packaging density and high speed operation of the hard disk device.
An anti-frictional bearing including an inner race way 1a formed on
an outer peripheral surface of an inner race 1, an outer race way
2a formed on an inner peripheral surface of an outer race 2, and a
plurality of rotating bodies 3 interposed between the race ways and
retained by retainers 4 in a predetermined distance with each
other, wherein an out of roundness of a raceway surface 1a, 2a of
at least one of said inner and outer races 1, 2 is equal to or less
than 0.05 .mu.m.
Inventors: |
YAJIMA, HIROYUKI;
(NAGANO-KEN, JP) ; MATSUOKA, HIDEKI; (NAGANO-KEN,
JP) |
Correspondence
Address: |
FRISHAUF HOLTZ GOODMAN
LANGER & CHICK PC
767 THIRD AVENUE 25TH FLOOR
NEW YORK
NY
100172023
|
Assignee: |
Minebea Kabushiki - kaisha (Minebea
Co., Ltd.)
|
Family ID: |
17695471 |
Appl. No.: |
09/413229 |
Filed: |
October 6, 1999 |
Current U.S.
Class: |
384/490 |
Current CPC
Class: |
F16C 19/18 20130101;
F16C 2240/40 20130101; F16C 33/585 20130101; F16C 2370/12 20130101;
F16C 19/06 20130101; F16C 19/08 20130101 |
Class at
Publication: |
384/490 |
International
Class: |
F16C 019/04 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 7, 1998 |
JP |
10-285742 |
Claims
What is claimed is,
1. An anti-frictional bearing including an inner race way formed on
an outer peripheral surface of an inner race, an outer race way
formed on an inner peripheral surface of an outer race, and a
plurality of rotating bodies interposed between the race ways and
retained by retainers in a predetermined distance with each other,
wherein an out of roundness of a raceway surface of at least one of
said inner and outer races is equal to or less than 0.05 .mu.m.
2. The anti-frictional bearing in accordance with claim 1 wherein;
the out of roundness of the raceway surface of the inner race is
equal to or less than 0.05 .mu.m.
3. The anti-frictional bearing in accordance with claim 1 wherein;
the out of roundness of the raceway surface of the outer race is
equal to or less than 0.05 .mu.m.
4. The anti-frictional bearing in accordance with claim 1 wherein;
the out of roundness of the raceway surfaces of the inner race and
the outer race are both equal to or less than 0.05 .mu.m.
5. A compound anti-frictional bearing including; a stepped shaft
including an enlarged diameter shaft portion on the outer
peripheral surface thereof an inner race way is formed directly and
a reduced diameter shaft portion around which an inner race is
fitted; a cylindrical sleeve surrounding the stepped shaft, on the
inner peripheral surface of which first outer race way
corresponding to the inner race way provided around the outer
peripheral surface of the enlarged diameter shaft portion, and
second outer race way corresponding to an inner race way provided
around the outer peripheral surface of the inner race are formed
directly; a first row of rotating bodies retained by retainers in a
predetermined distance with each other between the inner race way
provided around the outer peripheral surface of the enlarged
diameter shaft portion and the first outer race way of said
cylindrical sleeve; and a second row of rotating bodies retained by
retainers in a predetermined distance with each other between the
inner race way provided around the inner race and the second outer
race way of said cylindrical sleeve; said compound anti-frictional
bearing characterized in that: an out of roundness of the raceway
surface of at least one of the inner race way of the enlarged
diameter shaft portion, the inner race way of said inner race, the
first outer race way of the cylindrical sleeve, or the second outer
race way of the cylindrical sleeve is equal to or less than 0.05
.mu.m.
6. A motor in which a rotor hub is journalled rotatably on the base
by means of an anti-frictional bearing characterized in that a
plurality of rotating bodies retained by retainers in the
predetermined spacing are interposed between an inner race way
formed on an outer peripheral surface of a inner race and an outer
race way formed on an inner peripheral surface of an outer race,
wherein a out of roundness of a raceway surface of either of the
inner race way or outer race way is equal to or less than 0.05
.mu.m.
7. The motor in accordance with claim 6 wherein; the out of
roundness of the raceway surface of the inner race is equal to or
less than 0.05 .mu.m.
8. The motor in accordance with claim 6 wherein; the out of
roundness of the raceway surface of the outer race is equal to or
less than 0.05 .mu.m.
9. The motor in accordance with claim 6 wherein; the out of
roundness of both raceway surfaces of the inner and outer races are
equal to or less than 0.05 .mu.m.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Technical Field
[0002] The present invention relates to an anti-frictional bearing
constituting a rotationally supporting portion of a spindle rotor
of a hard disk drive device, VTR, and so on. The present invention
further relates to a motor into which such a bearing is
incorporated.
[0003] 2. Description of the Prior Art
[0004] The compact hard disk device to be incorporated into a
personal computer includes magnetic disk or disks driven by means
of spindle motor in high rotational speed. The rotational member of
such motor is adapted to be journalled through an anti-friction
bearing having an inner diameter of 4-6 mm and an outer diameter of
8-15 mm.
[0005] Recently, a remarkable development or improvement is
achieved in the hard disk device regarding the miniaturization and
high packaging density. Especially for the hard disk device the
size of which is equal to or less than 3.5 inch, the packaging
density is increased rapidly. More recently, the hard disk device
of the size of 2.5 inch to be incorporated into the hand held
personal computer of the note book type is also demanded to have
substantially the same memory capacity as that of the hard disk
device of 3.5 inch in spite of its small size.
[0006] In order to enlarge the memory capacity of the hard disk
device of the size of 2.5 inch, it is necessary to increase both of
the track recording density and the track density. The presently
demanded track density from 10 KTPI to 14 KTPI (TPI: Track Per
Inch) can be satisfied by the track pitch less than 2.54 .mu.m.
This value of the track pitch corresponds with the track density of
10 KTPI.
[0007] In either hard disk device the size of which is 3.5 inch or
2.5 inch, it is necessary to increase the number of revolution of
the magnetic disk or disks to increase the data transfer rate of
the hard disk device. For example, the hard disk device of 3.5 inch
requires the number of revolution from 5400 rpm to 7200 rpm, and
the hard disk device of 2.5 inch requires the number of revolution
from 4000 rpm to 5000 rpm.
[0008] When it is intended to read or write datum accurately into
the magnetic disk of increased track density, it is necessary to
reduce the rotational run out of the magnetic disk. The rotational
run out is apt to increase in proportion to the number of
revolution of the magnetic disk. It is therefore important in the
high packaging density of the hard disk device to improve the
precision of the rotational run out of the magnetic disk.
[0009] In order to reduce the rotational run out of the magnetic
disk, it is necessary to reduce the run out attributable to the
anti-frictional bearing itself of the spindle motor for driving the
magnetic disk. The counter measures having been taken for the
problem of the rotational run out of the magnetic disk are to
improve the sphericity of the rotational bodies of the
anti-frictional bearing and to effect the high precision working on
the raceway surface of the inner and/or outer races to reduce the
working tolerance to the minimum.
[0010] However, an microscopic undulation formed inevitably during
working or processing on the raceway surface of the inner and/or
outer race will change the relative position of the inner and outer
races during the operation of the bearing. This changing of the
relative position will cause the rotational run out. This
rotational run out can be observed as an irregular run out in which
the positional relationship between the inner race and the outer
race is asynchronous with the rotation of the bearing. This run out
is known as an asynchronous rotational run out referred to as NRRO
(non-repeatable run out).
[0011] When the asynchronous rotational run out is increased beyond
the allowable maximum extent, the magnetic head for reading and/or
waiting datum can not be moved accurately relative to the magnetic
disk of high tracking density. This will cause an error in
effecting the reading and/or writing datum into disk. In
conclusion, the asynchronous rotational run out will fail the
reliability of the hard disk device.
[0012] In other words, the asynchronous rotational run out of the
anti-frictional bearing to be incorporated into the spindle motor
will interfere the high packaging density and the high speed of the
hard disk device, i.e. the reduction of the asynchronous rotational
run out of the anti-frictional bearing to be incorporated into the
spindle motor is extraordinarily important in achieving the high
packaging density and the high speed of the hard disk device.
[0013] The asynchronous rotational run out is influenced by the
shape of the undulation on the raceway surface of the inner and/or
outer races and the number of rotational bodies interposed
therebetween. In order to reduce the asynchronous rotational run
out, it is necessary to measure the out of roundness of the raceway
surface accurately, to make a harmonic analysis on thus obtained
value of measurement as described below, and to select the inner
and/or outer races which are suitable for the nether of rotating
bodies to be interposed therebetween. The harmonic analysis will
now be described as follows.
[0014] Each of the inner and/or outer races has a raceway surface
representing a complex undulation. This undulation can be seized as
a function, the frequency of which is one revolution, i.e. the
function is a composite of a plurality of harmonic vibrations.
[0015] In concretely, the shape of raceway surface as shown in FIG.
19(a) can be seized as a composite of a harmonic vibration of the
frequency of 1/3 revolution (tertiary vibration) as shown in FIG.
19(b), a harmonic vibration of the frequency of {fraction (1/7)}
revolution (seventh vibration) as shown in FIG. 19(c), and a
harmonic vibration of the frequency of {fraction (1/50)} revolution
(fifty vibration) as shown in FIG. 19(d).
[0016] In this connection, the undulation presented on the raceway
surface can be expressed as a following function f(t) including a
plurality of frequencies .omega.,2.omega.,3.omega. . . .
f(t)=C.sub.0+C.sub.2 cos (.omega.t+.phi..sub.2)+C.sub.2 cos
(2.omega.t+.phi..sub.2)+C.sub.2 cos (3.omega.t+.phi..sub.3)+ . .
.
[0017] In the harmonic analysis, the constant C.sub.0, C.sub.2,
C.sub.2, . . . , .phi..sub.2, .phi..sub.2, . . . are
determined.
[0018] In the harmonic analysis effected on the shape of the
raceway surface of the inner and/or outer races, the harmonic
vibration of 1/n revolution forms a shape of an undulation
including crests the number of which is n. In this connection, the
harmonic vibration of 1/n revolution is referred to as the
undulation including crests the number of which is n. The medial
magnitude (C.sub.2, C.sub.2, . . . ) of the displacement amplitude
of the shape varying in a sinusoidal manner is referred to as
unilateral amplitude of each number of crests.
[0019] The shape of the raceway surface of each inner race ways,
the out of roundness of which are 0.13 .mu.m, 0.096 .mu.m, 0.084
.mu.m, and 0.055 .mu.m is shown in FIGS. 20-23 respectively in the
magnification of 100,000. The results of the harmonic analysis made
on each shapes of the raceway surface are shown in FIGS. 24-27
respectively.
[0020] The numbers put on the left column of each table are basic
number N, the numbers to be added to the basic number N are put on
the upper row of each table, and the values listed on the table are
the values of unilateral amplitude.
[0021] For example, in the table of FIG. 24, the value put on the
field of N+0 of the second row (N=7) means that the component of
vibration of {fraction (1/7)} revolution of the shape of the
raceway surface as shown in FIG. 20 is 0.002 .mu.m, that is the
unilateral amplitude in the case that the number of crests are
seven is also 0.002 .mu.m. The value put on the field of N+1 of the
second row means that the unilateral amplitude in the case that the
number of crests are eight is 0.006 .mu.m, and the value put on the
field of N+2 of the second row means that the unilateral amplitude
in the case that the number of crests are eight is 0.005 .mu.m. The
designation ______ put on the fields of the table means that the
unilateral amplitude can not be measured, i.e. there are
substantially no unilateral amplitude.
[0022] The asynchronous rotational run out of the anti-frictional
bearing relates to the shape of the undulation represented on the
raceway surfaces of the inner and/or outer race and the number of
rotating bodies as mentioned above. Particularly, it is known that
the value of unilateral amplitude in the number of crests of aZ and
aZ.+-.1 (a is positive integer, and Z is the number of rotating
bodies) will influence on the rotational run out.
[0023] This is caused by the run out due to the deflection between
the rotating bodies and the positions of the crests. In this
connection, when the anti-frictional bearing, including rotating
bodies the number of which is Z, is intended to be manufactured,
the inner or outer races greater in its value of unilateral
amplitude can not be employed, since they will cause the rotational
run out of the anti-frictional bearing.
[0024] Concretely, the number of rotating bodies to be utilized for
the anti-frictional bearing of the spindle motor of the hard disk
device of the size equal to or smaller than 3.5 inch is normally
from 8 to 12. Explaining on the most general case that the number
of rotating bodies is eight, the values of the unilateral amplitude
put on each field of N+0 (the number of crest is seven), N+1 (the
number of crest is eight), and N+2 (the number of crest is nine) of
the second row of each of FIGS. 24-27 will influence on the
rotational run out, so that it is necessary to reduce these values
to 0.002 .mu.m or less than 0.002 .mu.m.
[0025] However, in each table of FIGS. 24-27, the values of the
unilateral amplitude on the number of crest from seven to nine does
not satisfy the above mentioned condition, so that the inner race
representing the shape of the raceway surface as illustrated in
FIGS. 20-23 are unsuitable for using in the anti-frictional bearing
including eight rotating bodies.
[0026] As mentioned above, it is necessary in the prior art to make
following cumbersome operations to obtain the anti-frictional
bearing reduced in its asynchronous rotational run out and thus
suitable for the spindle motor of the hard disk device. The
above-mentioned operations are to make a measurement on the out of
roundness of the inner and/or outer races, to make the harmonic
analysis thereon, and to select the inner and/or outer races based
on the relationship between the unilateral amplitude obtained by
the harmonic analysis and the number of crests.
[0027] Accordingly the object of the present invention is to solve
the problems of the prior art. In other words, the object of the
present invention is to provide an anti-frictional bearing in which
the asynchronous rotational run out is reduced substantially, the
complex analyzing operation and the selecting operation to be
carried on the inner and/or outer races are unnecessary, and high
packaging density and high speed of the hard disk device can be
assured when it is incorporated into the spindle motor of the hard
disk device. Another object of the present invention is to provide
a motor including such anti-frictional bearing.
SUMMARY OF THE INVENTION
[0028] These and other objects are achieved by an anti-frictional
bearing including an inner race way formed on an outer peripheral
surface of an inner race, an outer race way formed on an inner
peripheral surface of an outer race, and a plurality of rotating
bodies interposed between the race ways and retained by retainers
in a predetermined distance with each other, wherein an out of
roundness of a raceway surface of at least one of said inner and
outer races is equal to 0.051 .mu.m or less than 0.05 .mu.m.
BRIEF DESCRIPTION OF THE DRAWINGS
[0029] Further feature of the present invention will become
apparent to those skilled in the art to which the present invention
relates from reading the following specification with reference to
the accompanying drawings, in which:
[0030] FIG. 1 is a vertical cross sectional view showing the
anti-frictional bearing to which the present invention will be
applied;
[0031] FIG. 2 is a partially sectional plan view of the
anti-frictional bearing of FIG. 1;
[0032] FIG. 3 is a schematic diagram of the shape of the undulation
of the inner race way of the anti-frictional bearing in accordance
with the present invention;
[0033] FIG. 4 is a schematic diagram of the shape of the undulation
of the inner race way of the other anti-frictional bearing in
accordance with the present invention;
[0034] FIG. 5 is a schematic diagram of the shape of the undulation
of the inner race way of the further anti-frictional bearing in
accordance with the present invention;
[0035] FIG. 6 is a table representing the result of the harmonic
analysis effected on the inner race way of the anti-frictional
bearing as shown in FIG. 3;
[0036] FIG. 7 is a table representing the result of the harmonic
analysis effected on the inner race way of the anti-frictional
bearing as shown in FIG. 4;
[0037] FIG. 8 is a table representing the result of the harmonic
analysis effected on the inner race way of the anti-frictional
bearing as shown in FIG. 5;
[0038] FIGS. 9-11 are the graphs showing the results of the
measurement on the value of the asynchronous rotational run out
(NRRO) of the bearing into which the inner race of the present
invention having the out of roundness of its inner race way equal
to or less than 0.05 .mu.m is incorporated. Also shown in these
figures as relatives are the results obtained in the measurement on
the value of the asynchronous rotational run out of the bearing
into which the inner race having the out of roundness of its inner
race way from 0.07 .mu.m to 0.08 .mu.m is incorporated, and results
of the bearing into which the inner race having the out of
roundness of its inner race way more than 0.10 .mu.m respectively
is incorporated.
[0039] FIG. 12 is the graph showing the result obtained from the
measurement test on the value of the rotational torque of the
bearing of the present invention into which the inner race having
the out of roundness of its inner race way equal to or less than
0.05 .mu.m is incorporated. Also measured in this test as relatives
are the results obtained in the measurement on the value of the
rotational torque of the bearing into which the inner race having
the out of roundness of its inner race way from 0.075 .mu.m to 0.10
.mu.m is incorporated, and that of the bearing into which the inner
race having the out of roundness of its inner race way more than
0.15 .mu.m respectively is incorporated.
[0040] FIG. 13 is a vertical cross sectional view showing an
example of the motor in accordance with the present invention;
[0041] FIG. 14 is a vertical cross sectional view showing another
example of the motor in accordance with the present invention;
[0042] FIG. 15 is a vertical cross sectional view showing another
example of the anti-frictional bearing to which the present
invention will be applied;
[0043] FIG. 16 is a cross sectional view along the line of XVI-XVI
in FIG. 15;
[0044] FIG. 17 is a cross sectional view along the line of
XVII-XVII in FIG. 15;
[0045] FIG. 18 is a vertical cross sectional view showing the
spindle motor including the anti-frictional bearing as shown in
FIG. 15;
[0046] FIG. 19 is schematic diagrams for explaining the principle
of the harmonic analysis;
[0047] FIG. 20 is a schematic diagram of the shape of the
undulation of the inner race way of the anti-frictional bearing in
accordance with the prior art;
[0048] FIG. 21 is a schematic diagram of the shape of the
undulation of the inner race way of the anti-frictional bearing in
accordance with the prior art;
[0049] FIG. 22 is a schematic diagram of the shape of the
undulation of the inner race way of the other anti-frictional
bearing in accordance with the prior art;
[0050] FIG. 23 is a schematic diagram of the shape of the
undulation of the inner race way of the further anti-frictional
bearing in accordance with the prior art;
[0051] FIG. 24 is a table representing the result of the harmonic
analysis effected an the inner race way of the anti-frictional
bearing of prior art as shown in FIG. 20;
[0052] FIG. 25 is a table representing the result of the harmonic
analysis effected on the inner race way of the anti-frictional
bearing of prior art as shown in FIG. 21;
[0053] FIG. 26 is a table representing the result of the harmonic
analysis effected on the inner race way of the anti-frictional
bearing of prior art as shown in FIG. 22; and
[0054] FIG. 27 is a table representing the result of the harmonic
analysis effected on the inner race way of the anti-frictional
bearing of prior art as shown in FIG. 23.
DETAILED DESCRIPTION OF THE PRESENT INVENTION
[0055] The anti-frictional bearing of the present invention will
now be described with reference to the attached drawings.
[0056] The anti-frictional bearing which is the subject of the
present invention is shown in FIGS. 1 and 2. The balls 3 as
rotating bodies of the bearing are interposed between the inner
race way 1a provided on the outer peripheral surface of the inner
race 1 and the outer race way 2a provided on the inner peripheral
surface of the outer race 2. The balls 3 are equidistantly retained
around the shaft by means of retainers 4.
[0057] The shape of the undulation of the inner race way 1a of the
anti-frictional bearing is shown in FIGS. 3, 4, and 5 respectively
in the magnification of 100,000. The out of roundness of each shape
shown in FIGS. 3, 4, and 5 is 0.048 .mu.m, 0.0371 .mu.m, and 0.0331
.mu.m respectively. The number of crests and the unilateral
magnitude of each inner race way having such shape in its raceway
surface derived from the harmonic analysis are listed in FIGS. 6,
7, and 8 respectively.
[0058] In each inner race way shown in FIGS. 3, 4, and 5, the out
of roundness is equal to or less than 0.059 .mu.m, and the
relationship between the number of crest and the unilateral
amplitude in the number of crest equal to or above 7(N+0) is equal
to or less than 0.001 .mu.m (N means a number of the rotating
bodies included in the bearing) as shown in the table of 6, 7, and
8.
[0059] In other words, in the case that the out of roundness of the
inner race way is equal to or less than 0.05 .mu.m, the unilateral
amplitude in the number of crest above 7 are all equal to or less
than 0.001 .mu.m. In this connection, when the number of rotating
bodies are either of the number from eight to twelve, the
unilateral amplitude in the number of crest from 7 to 13 will be
equal to or less than 0.001 .mu.m. This means that the effect on
the run out of the bearing will be reduced to a minimum.
[0060] In the case that the out of roundness of the inner race way
is equal to or less than 0.05 .mu.m, it is unnecessary to analyze
the unilateral amplitude in the number of crest included on the
inner race way to select the inner race to the number of rotating
bodies, i.e. such inner race can be incorporated into the bearing
irrespective of the number of the rotating bodies. In other words,
it is only necessary to measure the out of roundness, and the
harmonic analyzing operation can also be eliminated.
[0061] The graphs shown in FIGS. 9-11 are the results of the
measurement on the value of the asynchronous rotational run out
(NRRO) of the bearing into which the inner race of the present
invention having the out of roundness of its inner race way equal
to or less than 0.05 .mu.m is incorporated.
[0062] Also shown in these figures as relatives are the results
obtained in the measurement on the value of the asynchronous
rotational run out of the bearing into which the inner race having
the out of roundness of its inner race way from 0.07 .mu.m to 0.08
.mu.m is incorporated, and results of the bearing into which the
inner race having the out of roundness of its inner race way more
than 0.10 .mu.m respectively is incorporated.
[0063] As shown in these figures, it is evident that the one having
the out of roundness equal to or less than 0.05 .mu.m is reduced in
its NRRO components of both outer and inner races.
[0064] Shown in FIG. 12 the result obtained from the measurement
test on the value of the rotational torque of the bearing of the
present invention into which the inner race having the out of
roundness of its inner race way equal to or less than 0.05 .mu.m is
incorporated.
[0065] Also measured in this test as relatives are the results
obtained in the measurement on the value of the rotational torque
of the bearing into which the inner race having the out of
roundness of its inner race way from 0.075 .mu.m to 0.10 .mu.m is
incorporated, and that of the bearing into which the inner race
having the out of roundness of its inner race way more than 0.15
.mu.m respectively is incorporated.
[0066] This measurement test is affected by employing the ball
bearing having following features:
1 Outer diameter; 15 mm Inner diameter; 5 mm Number of balls; 8 pcs
Rotational speed; 2 rpm Pre-load; 350 gf
[0067] The bearing is of oil lubricating outer race rotating
type.
[0068] The reduction of the rotational run out equal to or less
than 0.05 .mu.m will also reduce the frictional torque of the
anti-frictional bearing.
[0069] Further, it can be ensured that the anti-frictional bearing
of the present invention is also reduced in its value of andelon,
and that the required drive power can also be reduced, when using
such bearing in the spindle motor.
[0070] Although in the above-mentioned embodiment, the relationship
between the out of roundness and the unilateral amplitude of the
inner race is explained, this relationship can also be obtained in
the case of the outer race. If it is intended to reduce further the
asynchronous rotational run out, it is desirable to make the out of
run out of both of the inner and outer races equal to or less than
0.05 .mu.m.
[0071] Although the ball bearing using balls as rotating bodies is
described, the present invention can also be applied equally to the
other anti-frictional bearing such as roller bearings.
[0072] The anti-frictional bearing having an arrangement as
described above is adapted to be used by incorporating into the
spindle motor as shown in FIG. 13.
[0073] The spindle motor shown in FIG. 13 is of outer rotor type in
which a pair of upper and lower ball bearings are interposed
between the outer peripheral surface of the spindle shaft 6 secured
on the base 5 to extend vertically therefrom and the inner
peripheral surface of the vertical bore 8 of the rotor hub 7 so as
to support the rotor hub 7 rotatably.
[0074] In other words, the motor of the type as shown in FIG. 13,
the inner race of each ball bearings 9 is stational, and the outer
race is rotatable.
[0075] In FIG. 13, the reference numeral 10 is added to the rotor
magnets provided on the inner surface of the downwardly depending
flange of the rotor hub 7, and the reference numeral 11 is added to
the stator positioned opposite to the magnets. The rotor hub 7 is
adapted to be rotated by providing the electric power to the coils
wound around the stator 11. In the case of hard disk drive device,
magnetic disk or disks (not shown) are mounted on the outer
peripheral surface of the rotor hub 7.
[0076] The spindle motor shown in FIG. 14 is an example of the
spindle motor of the inner rotor type in which the spindle shaft 14
is supported through a pair of ball bearings 9 fitted within the
sleeve 13 extending vertically from the base 12. The spindle shaft
14 is formed integrally with the rotor hub 15.
[0077] In other words, the motor of the type as shown in FIG. 14,
the outer race of each ball bearings 9 is stational whereas the
inner race is rotatable.
[0078] In the above-mentioned embodiment, although a ball bearing
of generic type in which balls as rotational bodies are interposed
between the inner and outer races, the anti-frictional bearing of
different type such as the compound bearing including two rows of
balls as illustrated in FIGS. 15, 16, and 17 can also be
employed.
[0079] The anti-frictional bearing shown in FIGS. 15, 16, and 17,
spindle shaft 16 is a stepped shaft including an enlarged diameter
shaft portion 16a and a reduced diameter shaft portion 16b, an
outer race is formed by cylindrical sleeve 17, balls 20 as lower
rotating bodies are interposed between the inner race way 18 formed
around the outer peripheral surface of the enlarged diameter shaft
portion 16a and the first outer race way 19a formed on the inner
peripheral surface of the cylindrical sleeve 17, balls 23 as upper
rotating bodies are interposed between the inner race way 22 formed
on inner race 21 fitted around the reduced diameter shaft portion
16b and the second outer race way 19a formed on the inner
peripheral surface of the cylindrical sleeve 17, and the balls 23,
20 of the upper and lower rows are retained equidistantly around
the shaft with each other by means of retainer 24.
[0080] In the anti-frictional bearing having a structure as
mentioned above, the enlarged diameter shaft portion 16a included
in the spindle shaft will enhance the rigidity of the shaft, so
that the durability and anti-vibration property of the shaft is
excellent. Further, the inner race of the lower bearing and outer
races of upper and lower bearing are unnecessary so that an
advantage that the number of the parts can be reduced will surely
be obtained.
[0081] An example of the motor including the anti-frictional
bearing of the structure as mentioned above is shown in FIG. 18. In
such motor, anti-frictional bearing 25 is mounted within the
central cylindrical portion 7a of the rotor hub 7, the rotor hub 7
is journalled rotatably around the spindle shaft 16, the shaft 16
and inner race 21 are stational, and the cylindrical sleeve 17 is
rotatable.
The Advantages or Effects to be Derived from the Present
Invention
[0082] In accordance with the present invention, the unilateral
amplitude can be reduced by making the out of roundness of the
raceway surface equal to or less than 0.05 .mu.m. In this
connection, the cumbersomeness inherent in the prior art that the
number of crest and the value of unilateral amplitude of inner and
outer races are to be analyzed and selection of the races is to be
made to the number of rotating bodies can be eliminated, the
production cost for the bearing can be reduced, and the
asynchronous rotational run out of the bearing can be improved.
[0083] The reduction of the asynchronous rotational run out will
also reduce the frictional torque produced within the bearing. This
also leads to the reduction of the electric power consumed on the
spindle motor of the present invention.
[0084] In the hard disk device including the motor of the present
invention as a rotational drive means for magnetic disk or disks,
high packaging density of the magnetic disk or disks, or enlarged
capacity and fast speed of the hard disk drive device can be
realized.
[0085] Making the packaging density of the magnetic disk or disks
higher, the number of magnetic disks to be included within the hard
disk device can be reduced, the diameter of each magnetic disk can
be reduced, the size of the hard disk device itself can be reduced,
and the amount of materials used in the magnetic disk or the casing
of the hard disk device can also be reduced to save resources.
[0086] In conclusion, reducing of the electric power required in
the spindle motor and saving of the resources used for
manufacturing the hard disk device will be able to contribute to
solving the problem of the environmental disruption or
pollution.
[0087] While particular embodiments of the present invention have
been illustrated and described, it should be obvious to those
skilled in the art that various changes and modifications can be
made without departing from the spirit and scope of the
invention.
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