U.S. patent application number 11/629910 was filed with the patent office on 2007-12-06 for shaft member for hydrodynamic bearing apparatuses and a method for producing the same.
Invention is credited to Syoichi Kodera, Hideaki Kubota, Natsuhiko Mori, Keiji Nagasaki, Masato Utiumi, Nobuyoshi Yamashita.
Application Number | 20070278881 11/629910 |
Document ID | / |
Family ID | 36036271 |
Filed Date | 2007-12-06 |
United States Patent
Application |
20070278881 |
Kind Code |
A1 |
Yamashita; Nobuyoshi ; et
al. |
December 6, 2007 |
Shaft Member For Hydrodynamic Bearing Apparatuses And A Method For
Producing The Same
Abstract
A shaft member for hydrodynamic bearing apparatuses having
higher dimensional accuracy produced at low costs and a method for
producing the same are provided. Moreover, a shaft member for
hydrodynamic bearing apparatuses having hydrodynamic grooves
processed with high accuracy and a method for producing the same
are provided without a large increase in the processing costs. A
shaft material 10 integrally having a shaft portion 11 and a flange
portion 12 is formed by a forging process, and the cylindricity of
a part or the entire outer circumferential surface 11a of the shaft
portion 11 is corrected. The end face 11b of the shaft portion of
the shaft material 10 and the end face 12b of the flange portion 12
on the opposite side of the shaft portion are ground relative to
the corrected face 13 mentioned above, and the outer
circumferential surface 10b of the shaft material 10 is ground
relative to these end faces 11b, 12b. This renders the cylindricity
of the radial bearing faces 23a, 23b formed on the outer periphery
of the shaft portion 21 of the produced shaft member 2 to be 3
.mu.m or lower. Moreover, in a common forging step, a shaft
material 110 integrally having the shaft portion 111 and flange
portion 112 is formed, while simultaneously thrust hydrodynamic
groove regions 112a, 112b are formed on both end faces of the
flange portion 112. After the forging process, in a common rolling
step, radial hydrodynamic groove regions 113a, 113b are formed on
the outer circumferential surface 111a of the shaft portion 111. In
a grinding step following the rolling process, the radial
hydrodynamic groove regions 113a, 113b and the thrust hydrodynamic
groove regions 112a, 112b are ground.
Inventors: |
Yamashita; Nobuyoshi;
(Kuwana-shi, JP) ; Kubota; Hideaki; (Kuwana-shi,
JP) ; Mori; Natsuhiko; (Kuwana-shi, JP) ;
Nagasaki; Keiji; (Awara-shi, JP) ; Kodera;
Syoichi; (Awara-shi, JP) ; Utiumi; Masato;
(Awara-shi, JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W.
SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
36036271 |
Appl. No.: |
11/629910 |
Filed: |
August 31, 2005 |
PCT Filed: |
August 31, 2005 |
PCT NO: |
PCT/JP05/15952 |
371 Date: |
June 13, 2007 |
Current U.S.
Class: |
310/90 ;
29/603.03; 384/227 |
Current CPC
Class: |
Y10T 29/49025 20150115;
Y10T 29/49565 20150115; Y10T 29/49639 20150115; F16C 17/107
20130101; F16C 33/107 20130101; F16C 2370/12 20130101; F16C 33/14
20130101; B24B 7/162 20130101; B24B 5/18 20130101; F16C 3/02
20130101; Y10T 29/4956 20150115 |
Class at
Publication: |
310/090 ;
029/603.03; 384/227 |
International
Class: |
H02K 7/08 20060101
H02K007/08 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2004 |
JP |
2004-261446 |
Sep 8, 2004 |
JP |
2004-261452 |
Claims
1. A shaft member for hydrodynamic bearing apparatuses comprising a
shaft portion and a flange portion each formed by forging, a radial
bearing face which faces a radial bearing gap and is formed on the
outer periphery of the shaft portion, and said radial bearing face
having a cylindricity of 3 .mu.m or lower.
2. A shaft member for hydrodynamic bearing apparatuses according to
claim 1, wherein the perpendicularity of both end faces of the
flange portion and the perpendicularity of an end face of the shaft
portion relative to said radial bearing face are each 5 .mu.m or
lower.
3. A shaft member for hydrodynamic bearing apparatuses according to
claim 1, wherein said shaft portion and flange portion are
integrally formed by forging.
4. A shaft member for hydrodynamic bearing apparatuses according to
claim 1, wherein both end faces of said shaft member are grinding
surfaces.
5. A shaft member for hydrodynamic bearing apparatuses according to
claim 1, wherein a slanting recess portion is formed at the corner
between said shaft portion and flange portion.
6. A hydrodynamic bearing apparatus comprising a shaft member for
hydrodynamic bearing apparatuses according to claim 1; a bearing
sleeve into which said shaft member is inserted at its inner
surface; a radial bearing portion which produces pressure by the
hydrodynamic effect of a fluid which occurs in a radial bearing gap
between the outer periphery of the shaft portion and the inner
surface of the bearing sleeve to support the shaft portion in the
radial direction in a non-contact manner; a first thrust bearing
portion which produces pressure by the hydrodynamic effect of a
fluid which occurs in a thrust bearing gap on one end side of the
flange portion to support the flange portion in the thrust
direction in a non-contact manner; and a second thrust bearing
portion which produces pressure by the hydrodynamic effect of a
fluid occurring in the thrust bearing gap on the other end side of
the flange portion to support the flange portion in the thrust
direction in a non-contact manner.
7. A hydrodynamic bearing apparatus according to claim 6, wherein
hydrodynamic grooves for producing the hydrodynamic effect of the
fluid are formed asymmetrically in the axial direction on one of
the outer circumferential surface of the shaft portion facing the
radial bearing gap and the inner surface of the bearing sleeve
facing this outer circumferential surface.
8. A motor comprising the hydrodynamic bearing apparatus according
to claim 6, a rotor magnet and a stator coil.
9. A method for producing a shaft member for hydrodynamic bearing
apparatuses, the method comprising the step of forming the shaft
material which integrally has the shaft portion and the flange
portion by a forging process; and the step of correcting the
cylindricity of a part or the entire outer circumferential surface
of the shaft portion.
10. A method for producing a shaft member for hydrodynamic bearing
apparatuses according to claim 9, wherein said correcting step is
performed by rolling.
11. A method for producing a shaft member for hydrodynamic bearing
apparatuses according to claim 9, wherein a first grinding process
is performed on both end faces of the shaft material relative to
said corrected face, and a second grinding process is performed on
at least the outer circumferential surface of the shaft material
relative to said both end faces.
12. A method for producing a shaft member for hydrodynamic bearing
apparatuses according to claim 11, wherein the first grinding
process is performed on the other hand end face of the flange
portion and on the end face of the shaft portion.
13. A method for producing a shaft member for hydrodynamic bearing
apparatuses according to claim 11, wherein said second grinding
process is performed on at least a portion which serves as a radial
bearing face facing a radial bearing gap on the outer periphery of
the shaft portion of the shaft material.
14. A method for producing a shaft member for hydrodynamic bearing
apparatuses according to claim 13, wherein the other end face of
the flange portion is ground further in the second grinding
process.
15. A metallic shaft member for hydrodynamic bearing apparatuses
which integrally comprises a shaft portion and a flange portion,
and a radial hydrodynamic groove region which comprises a plurality
of hydrodynamic grooves and demarcation portions demarcating each
hydrodynamic groove being formed on the outer periphery of said
shaft portion by plastic processing, and said outer circumferential
surfaces of the demarcation portions in the radial hydrodynamic
groove region being grinding surfaces.
16. A shaft member for hydrodynamic bearing apparatuses according
to claim 15, wherein a thrust hydrodynamic groove region comprising
a plurality of the hydrodynamic grooves and demarcation portions
demarcating each hydrodynamic groove is formed by plastic
processing on both end faces of said flange portion, and the end
face in the axial direction of the demarcation portion in said
thrust hydrodynamic groove region is a grinding surface.
17. A shaft member for hydrodynamic bearing apparatuses according
to claim 15, wherein said radial hydrodynamic groove region is
formed by a rolling process or a forging process.
18. A shaft member for hydrodynamic bearing apparatuses according
to claim 16, wherein said thrust hydrodynamic groove region is
formed by a forging process.
19. A shaft member for hydrodynamic bearing apparatuses according
to claim 15, wherein said shaft portion and said flange portion are
integrally formed by forging.
20. A hydrodynamic bearing apparatus comprising a shaft member for
hydrodynamic bearing apparatuses according to claim 15; and a
sleeve member into which said shaft member is inserted at its inner
surface to form a radial bearing gap between itself and said shaft
member, wherein said shaft member and said sleeve member being
retained in a non-contact manner by said hydrodynamic effect of the
fluid occurring in the radial bearing gap.
21. A hydrodynamic bearing apparatus according to claim 20, wherein
the sleeve member is formed of an oil-containing sintered
metal.
22. A hydrodynamic bearing apparatus according to claim 20, wherein
hydrodynamic grooves for producing the hydrodynamic effect of the
fluid are formed asymmetrically in the axial direction on the outer
circumferential surface of the shaft portion facing the radial
bearing gap.
23. A motor comprising a hydrodynamic bearing apparatus according
to claim 20, a rotor magnet and a stator coil.
24. A method for producing a shaft member for hydrodynamic bearing
apparatuses comprising a shaft portion and a flange portion
integrally, and a radial hydrodynamic groove region which comprises
a plurality of hydrodynamic grooves and demarcation portions
demarcating each hydrodynamic groove being formed on the outer
periphery of said shaft portion, the method comprising forming said
radial hydrodynamic groove region by plastic processing on the
outer periphery of the shaft portion of the shaft material, and
then grinding a portion including the outer diameter portion of the
demarcation portion in said radial hydrodynamic groove region.
25. A method for producing a shaft member for hydrodynamic bearing
apparatuses according to claim 24, the method comprising forming
said shaft material and said radial hydrodynamic groove region both
by forging, and simultaneously performing forging of both.
26. A method for producing a shaft member for hydrodynamic bearing
apparatuses according to claim 24, wherein forming said radial
hydrodynamic groove region and correcting said cylindricity of a
portion including the radial hydrodynamic groove region of the
shaft portion are both performed by rolling, and the rolling
process of both are simultaneously performed.
27. A method for producing a shaft member for hydrodynamic bearing
apparatuses according to claim 24, wherein forming said shaft
material and forming the thrust hydrodynamic groove region
comprising the hydrodynamic grooves and demarcation portions
demarcating each hydrodynamic groove on both end faces of the
flange portion are both performed by forging, and the forging
process of both is performed simultaneously.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a shaft member for
hydrodynamic bearing apparatuses which relatively rotatably
supports the shaft member in the radial direction in a non-contact
manner by the hydrodynamic effect which occurs in a radial bearing
gap, and a method for producing the same.
[0002] A hydrodynamic bearing rotatably supports a shaft member by
the hydrodynamic effect of lubricating oil which occurs in a
bearing gap in a non-contact manner. For example, it is used in the
spindle motor of disk-shaped recording medium drive units such as
HDDs incorporated therein. Hydrodynamic bearing apparatuses of this
type are provided with a radial bearing portion which rotatably
supports a shaft member in the radial direction in a non-contact
manner, and a thrust bearing portion which rotatably supports the
shaft member in the thrust direction in a non-contact manner.
Grooves for producing a hydrodynamic pressure (hydrodynamic
grooves) are formed on the inner surface of a bearing sleeve or the
outer surface of the shaft member, which constitutes the radial
bearing portion. Moreover, hydrodynamic grooves are formed on both
end faces of a flange portion of a shaft member which constitutes a
thrust bearing portion, or on the face facing it (an end face of
the bearing sleeve or an end face of a thrust member fixed on the
housing, or the inner bottom face of the bottom of the housing,
etc.) (for example, refer to patent document 1: Japanese Unexamined
Patent Publication No. 2002-61641).
[0003] Moreover, the above hydrodynamic grooves are formed, for
example, on the outer surface of the shaft member in a herringbone
arrangement or a spiral arrangement. Known examples of methods for
forming the hydrodynamic grooves of this type include cutting (for
example, refer to patent document 2: Japanese Unexamined Patent
Publication No. H08-196056), etching (for example, refer to patent
document 3: Japanese Unexamined Patent Publication No. H06-158357),
among others.
BRIEF SUMMARY OF THE INVENTION
[0004] Recently, in order to deal with an increase in the
information recording density and rotation speed of information
appliances, there is a demand for higher rotational accuracy of
spindle motors for the above information appliances. To meet this
demand, higher rotational accuracy is required for hydrodynamic
bearing apparatuses incorporated into the above spindle motor.
[0005] By the way, to increase the rotational accuracy of
hydrodynamic bearing apparatuses, it will be important to highly
accurately control the accuracy of a radial bearing gap and thrust
bearing gap, in which hydrodynamic pressure occurs. To control this
gap appropriately, high dimensional accuracy is required for the
shaft member of the hydrodynamic bearing apparatus relating to the
formation of the bearing gaps mentioned above. In contrast, further
increase in accuracy by conventional processing methods is
difficult since they suffer significantly high processing costs.
Therefore, the presentation of a new processing method of a shaft
member is desired, which has both satisfactory processing accuracy
and processing costs.
[0006] When hydrodynamic grooves are formed on the shaft member
side (for example, on the outer surface of the shaft portion or
both end faces of the flange portion), highly accurate processing
of the hydrodynamic grooves is required since the processing
accuracy of the hydrodynamic grooves affects the accuracy of the
bearing gaps. However, to improve the processing accuracy of the
hydrodynamic grooves by employing conventional processing methods
(for example, etching, cutting, etc.), the processing costs
significantly increase.
[0007] A first object of the present invention is to provide a
shaft member for hydrodynamic bearing apparatuses having higher
dimensional accuracy at low costs and a method for producing the
same.
[0008] A second object of the present invention is to provide a
shaft member for hydrodynamic bearing apparatuses having
hydrodynamic grooves processed with high accuracy without a large
increase in the processing costs and a method for producing the
same.
[0009] To achieve the first object, the present invention provides
a shaft member for hydrodynamic bearing apparatuses which comprises
a shaft portion and a flange portion both formed by forging, and a
radial bearing face facing a radial bearing gap and formed on the
outer periphery of the shaft portion, and the radial bearing face
having a cylindricity of 3 .mu.m or lower. Herein, the cylindricity
is defined as follows: when a cylindrical face (the target face of
the cylindricity. Herein, it refers to the radial bearing face of
the shaft portion) is placed between two geometrically correct
coaxial cylindrical faces, the cylindricity is represented by the
difference between the radii of the two coaxial cylindrical faces
in the case where the interval between the two coaxial cylindrical
faces (inscribed cylindrical face and circumscribed cylindrical
face) is rendered minimum. The radial bearing face can be any face
facing the radial bearing gap which produces hydrodynamic effect,
regardless of whether it has hydrodynamic grooves for producing
hydrodynamic effect.
[0010] The cylindricity of the radial bearing face formed on the
outer periphery of the shaft portion considerably affects the
accuracy of particularly the radial bearing gap formed between the
outer periphery of the shaft portion and the bearing component
(bearing sleeve, housing, etc.) facing the outer periphery of the
shaft portion. That is, if the value of the cylindricity becomes
higher, the above radial bearing gap will not be constant in the
circumferential direction or axial direction, making the difference
between the widely gapped portions and narrowly gapped portions
obvious. Accordingly, the rotational torque of the shaft member at
the narrowly gapped bearing portions becomes higher than at other
portions, which leads to increased bearing loss, while the
stiffness of the bearing becomes lower at the above widely gapped
bearing portions than at other portions, which leads greater runout
of the shaft. Moreover, if the gap is not constant in the axial
direction, an undesired flow of a lubricating fluid in the axial
direction may occur and the appropriate circulation of the
lubricating fluid may be adversely affected. From these
perspectives, in the present invention, the cylindricity of the
radial bearing face is defined to be 3 .mu.m or lower. Accordingly,
dimensional variation of the radial bearing gap in the
circumferential direction or axial direction is suppressed, thereby
suppressing the above bearing loss. This can also ensure the high
stiffness of the bearing mentioned above. Therefore, the radial
bearing gap between this shaft member and the bearing component
facing the shaft member can be controlled with high accuracy to
realize the high rotational accuracy of a bearing apparatus
comprising the shaft member and bearing component.
[0011] In this shaft member, the perpendicularity of both end faces
of the flange portion and the perpendicularity of an end face of
the shaft portion, relative to the radial bearing face formed on
the outer periphery of the shaft portion, are preferably 5 .mu.m or
lower, respectively. Herein, the term "perpendicularity" is defined
as follows: in the combination of a predetermined plane and a
reference plane which should be perpendicular to each other, the
perpendicularity is represented by the maximum value of the
difference between the predetermined plane (an end face of the
flange portion or an end face of the shaft portion herein) and a
geometric plane which is geometrically perpendicular relative to
the reference plane (the radial bearing face herein). When the
value of the perpendicularity of the end face of the flange portion
is higher than 5 .mu.m, a variation is generated in a thrust
bearing gap formed between the end face and that facing it, which
may adversely affect the bearing performance including an increased
bearing loss. Moreover, when the value of the perpendicularity of
the end face of the shaft portion is higher than 5 .mu.m, it will
be difficult to set the thrust bearing gap accurately, or when the
end face of the shaft portion serves as the reference plane for
grinding the outer surface of the shaft portion and the end face of
the flange portion, the processing accuracy of these grinding
surfaces may be lowered.
[0012] The above shaft member is formed of the shaft portion and
flange portion respectively by forging. Using both end faces of the
shaft member (an end face of the shaft portion and an end face of
the flange portion located on both end faces of the shaft member)
as the grinding surfaces enables to perform precise grinding of the
outer surface of the shaft member using these faces as the
reference planes. Accordingly, the shaft member having the radial
bearing faces whose values of cylindricity and perpendicularity are
suppressed can be obtained at low costs. The shaft portion and
flange portion of the above shaft member can be also integrally
formed by forging for further cost reduction.
[0013] Forming a slanting recess portion at the corner of the shaft
portion and flange portion can ensure the undercut of the grind
stone in grinding both the outer surface of the shaft portion and
the end face of the flange portion. Although various methods can be
usable as a method for forming this recess portion, forming by
plastic processing is preferred from the perspective of inhibiting
the production of burrs, impurities, etc., after processing.
[0014] Moreover, to achieve the first object, the present invention
provides a method for producing a shaft member for hydrodynamic
bearing apparatuses which comprises a step of forming a shaft
material having the shaft portion and flange portion integrally by
forging; and a step of correcting the cylindricity of a part or the
entire outer surface of the shaft portion. More preferably, the
present invention provides a method for producing a shaft member
for hydrodynamic bearing apparatuses, wherein a first grinding is
performed on both end faces of the shaft material relative to the
corrected face mentioned above, and a second grinding is then
performed on at least the outer surface of the shaft material
relative to the both end faces.
[0015] In the present invention, as stated above, the cylindricity
of the outer surface of the shaft portion is corrected after
roughly forming of the shaft member (shaft material) having the
shaft portion and flange portion integrally by forging. Therefore,
highly accurate grinding (width grinding) can be performed relative
to the corrected face in the first grinding step described
later.
[0016] For the correcting process of the cylindricity mentioned
above, various plastic processing, for example, rolling with round
dies, flat dies, etc., can be used, as well as drawing compound,
ironing, sizing by pressing (clipping) of split-cavity molds or the
like.
[0017] In the first grinding step, both end faces located at both
ends of the shaft material in the axial direction, specifically an
end face of the shaft portion and an end face of the flange portion
are ground. At this time, since the end faces are ground relative
to the outer circumferential surface of the shaft portion which has
been subjected to the correcting process as mentioned above, these
two end faces of the shaft material can be finished with highly
accurate perpendicularity and flatness.
[0018] The second grinding is then performed on the outer surface
of the shaft material relative to these two ground end faces of the
shaft material. Both end faces of the shaft material, which are the
reference planes, have been highly accurately finished in the first
grinding step. Hence, the target to be processed, i.e., the outer
circumferential surface of the shaft material can also be finished
highly accurately. The second grinding process is performed on at
least a portion which will be the radial bearing face of the outer
circumferential surface of the shaft material. Additionally, the
process can also be performed on the outer circumferential surface
of the flange portion. Furthermore, it can be performed on the
other (on the shaft portion side) end face of the unground flange
portion. In this second grinding step, these to-be-ground faces can
be finished at a time by using grind stones (formed grind stone)
having the outline shapes corresponding to these to-be-ground faces
of the shaft material.
[0019] By following the above-mentioned procedure, the shaft member
in which the radial bearing face has the cylindricity of 3 .mu.m or
lower and both end faces of the flange portion and the end face of
the shaft portion have the perpendicularity of 5 .mu.m or lower,
respectively, can be produced at low costs.
[0020] The above shaft member for hydrodynamic bearing apparatuses
can be provided as a hydrodynamic bearing apparatus which comprises
a bearing sleeve into which the shaft member is inserted at its
inner surface; a radial bearing portion which produces pressure by
the hydrodynamic effect which occurs in a radial bearing gap
between the outer periphery of the shaft portion and the inner
periphery of the bearing sleeve to support the shaft portion in the
radial direction in a non-contact manner; a first thrust bearing
portion which produces pressure by the hydrodynamic effect of a
fluid which occurs in a thrust bearing gap on one end side of the
flange portion to support the flange portion in the thrust
direction in a non-contact manner; and a second thrust bearing
portion which produces pressure by the hydrodynamic effect of the
fluid occurring in the thrust bearing gap on the other end side of
the flange portion to support the flange portion in the thrust
direction in a non-contact manner.
[0021] In this case, for example, hydrodynamic grooves for
producing the hydrodynamic effect of the fluid can be formed
asymmetrically in the axial direction on one of the outer
circumferential surface of the shaft portion facing the radial
bearing gap and the inner periphery face of the bearing sleeve
opposing this outer circumferential surface.
[0022] The above hydrodynamic bearing apparatus can be provided as
a motor which comprises a hydrodynamic bearing apparatus, a rotor
magnet and a stator coil.
[0023] To achieve the second object, the present invention provides
a shaft member for hydrodynamic bearing apparatuses which is a
metallic shaft member for hydrodynamic bearing apparatuses which
integrally comprises the shaft portion and the flange portion, in
which a radial hydrodynamic groove region comprising the
hydrodynamic grooves and demarcation portions demarcating each
hydrodynamic groove is formed by plastic processing on the outer
periphery of the shaft portion, and the outer circumferential
surfaces of the demarcation portions in the radial hydrodynamic
groove region are grinding surfaces. The demarcation portions
herein refer to the portions which demarcate the hydrodynamic
grooves, including the so-called ridges between the hydrodynamic
grooves. Moreover, when the hydrodynamic grooves are formed with a
slant arrangement in the axial direction, so-called smooth portions
which divide those slanting hydrodynamic grooves in the axial
direction are also included in the demarcation portions.
[0024] In the present invention, as stated above, the radial
hydrodynamic groove region comprising the hydrodynamic grooves and
demarcation portions demarcating each hydrodynamic groove is formed
by plastic processing on the outer periphery of the shaft portion
of the shaft member. Hence, for example, cutting powders are not
produced unlike in cutting, thereby saving materials. Compared to
processing methods by etching, the trouble of performing masking
preliminarily for preventing of corrosion can be dispensed with,
and processing costs can be thus greatly reduced on the whole.
Moreover, the present invention is characterized in that the outer
circumferential surfaces of the demarcation portions in the radial
hydrodynamic groove region are grinding surfaces. These grinding
surfaces are obtained by grinding the outer diameter portions of
the demarcation portions (the top portions adjacent to the
hydrodynamic grooves) demarcating the hydrodynamic grooves of the
radial hydrodynamic groove regions formed by plastic processing.
Accordingly, precise processing of the hydrodynamic groove region,
which cannot be achieved only by plastic processing, is enabled,
and the dimensional accuracy of the outer diameter and surface
roughness can be accurately obtained. Therefore, according to the
present invention, improved processing accuracy and reduced
processing costs can be both achieved, such radial bearing gap in
hydrodynamic bearing apparatuses can be controlled highly
accurately.
[0025] Such a hydrodynamic groove region can be formed, for
example, on both end faces of the flange portion formed integrally
with the shaft portion by plastic processing. In this case, the
flange portion is so constructed that thrust hydrodynamic groove
regions comprising the hydrodynamic grooves and demarcation
portions demarcating each hydrodynamic groove are formed on its
both end faces and the end face in axial direction of the
demarcation portions in these thrust hydrodynamic groove regions
are grinding surfaces.
[0026] The radial hydrodynamic groove region can be formed, for
example, by a rolling process or a forging process. Alternatively,
both the radial hydrodynamic groove region and thrust hydrodynamic
groove region can be formed by a forging process. Alternatively,
the shaft portion and flange portion, in which these hydrodynamic
groove regions are formed, respectively, can be formed, for
example, integrally by forging.
[0027] To achieve the second object, the present invention also
provides a method for producing a shaft member for hydrodynamic
bearing apparatuses which comprises a shaft portion and a flange
portion integrally, and a radial hydrodynamic groove region
comprising hydrodynamic grooves and demarcation portions
demarcating each hydrodynamic groove on the outer periphery of the
shaft portion, the method comprising forming a radial hydrodynamic
groove region by plastic processing on the outer periphery of the
shaft portion of the shaft material, and then grinding a portion
including an outer diameter portion of the demarcation portion in
the radial hydrodynamic groove region.
[0028] According to such a producing method, both an improvement in
the processing accuracy of the radial hydrodynamic groove region
and reduction of the processing costs can be achieved. Moreover,
forming the shaft material which integrally has the shaft portion
and the flange portion by forging can realize further reduction of
processing costs, or reduction of the cycle time per product.
[0029] Examples of the plastic processing of the radial
hydrodynamic groove region employed include a forging process. In
this case, both the shaft material and radial hydrodynamic groove
region can be formed by forging, and forging of them can be
performed simultaneously. Accordingly, such a processing step can
be simplified and the cycle time required for processing can be
even reduced.
[0030] In the shaft portion of the shaft material, it is possible
to perform a rolling process for correcting the cylindricity of a
portion including the radial hydrodynamic groove region of the
shaft portion. In this case, for example, both the formation of the
radial hydrodynamic groove region and the correction of the
cylindricity of a portion including the radial hydrodynamic groove
region of the shaft portion can be performed by rolling
simultaneously so that such a processing step can be simplified and
the cycle time can be shortened. Thus, the mass productivity of the
product can be dramatically improved.
[0031] Alternatively, it is possible to perform forming the shaft
material and forming the thrust hydrodynamic groove region
comprising the hydrodynamic grooves and demarcation portions
demarcating each hydrodynamic groove on both end faces of the
flange portion both by forging, and to simultaneously perform
forging of both. Accordingly, the processing steps relating to the
formation of the shaft material and thrust hydrodynamic groove
region can be simplified to shorten the machining time.
[0032] The above shaft member for hydrodynamic bearing apparatuses
can be presented, for example, as a hydrodynamic bearing apparatus
which comprises a shaft member for hydrodynamic bearing
apparatuses; and a sleeve member into which this shaft member is
inserted at its inner surface and which forms a radial bearing gap
between itself and the shaft member, which retains the shaft member
and sleeve member in a non-contact manner by the hydrodynamic
effect of a fluid occurring in the radial bearing gap. The bearing
sleeve can be formed, for example, from an oil-containing sintered
metal, and a thrust hydrodynamic groove region can be formed on an
end face in the axial direction of the sleeve instead of the end
face of the flange portion.
[0033] The above hydrodynamic bearing apparatus can be provided as
a motor comprising this hydrodynamic bearing apparatus, a rotor
magnet and a stator coil.
[0034] According to the present invention, the outer
circumferential surface of the shaft portion and the end face of
the flange portion of the shaft member involved in the formation of
the radial bearing gap and thrust bearing gap can be processed
highly accurately at low costs. Therefore, these bearing gaps of
the hydrodynamic bearing apparatus incorporating the shaft member
can be controlled highly accurately. As a result, high rotational
accuracy can be imparted to the above hydrodynamic bearing
apparatus.
[0035] Moreover, according to the present invention, the
hydrodynamic grooves formed on the shaft member can be processed
accurately without an increase in such processing costs. Moreover,
the bearing performance of the hydrodynamic bearing apparatus
integrating this shaft member can be exerted stably for a long term
by controlling the bearing gap in the hydrodynamic bearing
apparatus highly accurately.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING
[0036] FIG. 1 is a side elevational view of a shaft member for the
hydrodynamic bearing apparatus according to the first embodiment of
the present invention.
[0037] FIG. 2 is a cross-sectional view of a spindle motor for an
information appliance integrating a hydrodynamic bearing apparatus
comprising a shaft member.
[0038] FIG. 3 is a longitudinal sectional view of a hydrodynamic
bearing apparatus.
[0039] FIG. 4 is a longitudinal sectional view of a bearing
sleeve.
[0040] FIG. 5 is a side elevational view of a shaft material formed
by a forging process.
[0041] FIG. 6 is a schematic illustration of a correcting process
(rolling process) by round dies.
[0042] FIG. 7 is a schematic illustration of a correcting process
(rolling process) by flat dies.
[0043] FIG. 8 is a schematic illustration showing an example a
grinding apparatus according to the width grinding step of a shaft
material.
[0044] FIG. 9 is a partial cross-sectional view showing an example
of a grinding apparatus according to the width grinding step.
[0045] FIG. 10 is a schematic illustration showing an example of a
grinding apparatus according to the full-face grinding step of a
shaft material.
[0046] FIG. 11 is a schematic illustration showing an example of a
grinding apparatus according to the grinding finishing step of a
shaft material.
[0047] FIG. 12 is an expanded sectional view of the vicinity of the
corner between the shaft portion and flange portion of a shaft
member.
[0048] FIG. 13 is a side elevational view of a shaft member for a
hydrodynamic bearing apparatus according to the second embodiment
of the present invention.
[0049] FIG. 14 is a top view of the flange portion of a shaft
member seen from the direction of arrow A.
[0050] FIG. 15 is a bottom view of the flange portion of a shaft
member seen from the direction of arrow B.
[0051] FIG. 16 is a longitudinal sectional view of a hydrodynamic
bearing apparatus comprising a shaft member.
[0052] FIG. 17 is a side elevational view of a shaft material
formed by a forging process.
[0053] FIG. 18 is a top view of the flange portion of a shaft
material seen from the direction of arrow A.
[0054] FIG. 19 is a bottom view of the flange portion of a shaft
material seen from the direction of arrow B.
[0055] FIG. 20 is an expanded sectional view of a thrust
hydrodynamic groove region formed on the end face of a flange
portion on the side opposite to the shaft portion prior to
grinding.
[0056] FIG. 21 is an expanded sectional view of a thrust
hydrodynamic groove region after being ground.
DETAILED DESCRIPTION OF THE INVENTION
[0057] A first embodiment of the present invention will be
described below with reference to FIGS. 1-12.
[0058] FIG. 2 conceptionally shows a constitutional example of a
spindle motor for an information appliance incorporating a
hydrodynamic bearing apparatus 1 according to the first embodiment
of the present invention. This spindle motor for an information
appliance is used for disk drive units such as HDDs, and comprises
the hydrodynamic bearing apparatus 1 which rotatably supports a
shaft member 2 in a non-contact manner, a disk hub 3 which is
mounted on the shaft member 2, for example, a stator coil 4 and a
rotor magnet 5 facing each other across a gap in the radial
direction, and a bracket 6. The stator coil 4 is mounted on the
outer periphery of the bracket 6, and the rotor magnet 5 is mounted
on the inner periphery of the disk hub 3. The bracket 6 has the
hydrodynamic bearing apparatus 1 mounted on its inner periphery.
Moreover, the disk hub 3 retains one or more disks D such as
magnetic disks on its outer periphery. In this spindle motor for an
information appliance, when the stator coil 4 is energized, the
rotor magnet 5 is rotated by the excitation between the stator coil
4 and rotor magnet 5, whereby the disk hub 3 and the disk D
retained by the disk hub 3 is rotated unitarily with the shaft
member 2.
[0059] FIG. 3 shows the hydrodynamic bearing apparatus 1. This
hydrodynamic bearing apparatus 1 is mainly constituted of a housing
7 having a bottom 7b at its one end, a bearing sleeve 8 fixed on
the housing 7, and a shaft member 2 inserted at the inner periphery
of the bearing sleeve 8. For the sake of explanation, the bottom 7b
side of the housing 7 is referred to as the lower side, and the
side opposite to the bottom 7b is referred to as the upper side in
the following description.
[0060] As shown in FIG. 3, the housing 7 is constituted of, for
example, a side portion 7a formed of a resin material such as LCP,
PPS and PEEK in the form of a cylinder, and a bottom 7b located at
one end side of the side portion 7a and, for example, formed of a
metallic material. In this embodiment, the bottom 7b is formed
separately from the side portion 7a, is retrofitted on the lower
inner periphery of the side portion 7a. In a part of the annular
region os the upper end face 7b1 of the bottom 7b, hydrodynamic
grooves are formed, for example, in the form of a spiral, as a
portion for producing hydrodynamic pressure, although not shown in
the Figs. In this embodiment, the bottom 7b is formed separately
from the side portion 7a, and is fixed on the lower inner periphery
of the side portion 7a. It can be, however, formed integrally with
the side portion 7a, for example, from a resin material. At this
time, the hydrodynamic grooves provided on the upper end face 7b1
can be molded simultaneously with the injection molding of the
housing 7 comprising the side portion 7a and bottom 7b, which can
dispense with the trouble of forming the hydrodynamic grooves on
the bottom 7b.
[0061] The bearing sleeve 8 is formed of, for example, a porous
body made of a sintered metal, especially a porous body of a
sintered metal comprising copper as a main ingredient in the form
of a cylinder, and is fixed at a predetermined position on an inner
surface 7c of the housing 7.
[0062] Throughout an inner surface 8a of the bearing sleeve 8 or in
a part of its cylindrical face region, a radial hydrodynamic
pressure producing part is formed. In this embodiment, for example,
as shown in FIG. 4, a region, in which a plurality of hydrodynamic
grooves 8a1, 8a2 are arranged in a herringbone shape, is formed at
two axially separated positions. The upper hydrodynamic groove 8a1
is formed asymmetrically in the axial direction relative to the
axial center m (the axial center of the region between the upper
and lower slanted grooves), the axial dimension X1 of the region
above the center m in the axial direction is larger than the axial
dimension X2 of the region therebelow.
[0063] Although not shown in the Figs., for example, a region in
which a plurality of hydrodynamic grooves are arranged spirally is
formed throughout the lower end face 8b of the bearing sleeve 8 or
in a part of annular region, as a portion for producing thrust
hydrodynamic pressure.
[0064] A sealing member 9 as a sealing means is formed of, for
example, a soft metallic material such as brass and other metallic
materials, or a resin material in a ring shape, as shown in FIG. 3.
The sealing member 9 is press-fitted to the upper inner periphery
of the side portion 7a of the housing 7, and is fixed by means of
adhesion or the like. In this embodiment, the inner surface 9a of
the sealing member 9 is formed in the shape of a cylinder, and the
lower end face 9b of the sealing member 9 is in contact with the
upper end face 8C of the bearing sleeve 8.
[0065] As shown in FIG. 1, the shaft member 2 is formed of a
metallic material such as stainless steel, and has a T-shaped cross
section integrally comprising a shaft portion 21 and a flange
portion 22 provided at the lower end of the shaft portion 21. On
the outer periphery of the shaft portion 21, as shown in FIG. 3,
radial bearing faces 23a, 23b facing the formation region of two
hydrodynamic grooves 8a1, 8a2 formed on the inner surface 8a of the
bearing sleeve 8 are formed at two axially separated positions.
Above one of the radial bearing faces, the face 23a and a tapered
face 24 whose diameter gradually decreases toward the shaft tip are
formed adjacently. Further thereabove, a cylinder face 25, which
serves as a mounting portion of the disk hub 3, is formed. Annular
recess portions 26, 27, 28 are formed between the two radial
bearing faces 23a, 23b, between the other radial bearing face 23b
and flange portion 22, and between the tapered face 24 and cylinder
face 25, respectively.
[0066] On both end faces of the flange portion 22, thrust bearing
faces 22a, 22b facing the hydrodynamic groove regions formed on the
lower end face 8b of the bearing sleeve and the upper end face 7b1
of the bottom 7b, respectively, are formed.
[0067] Between the tapered face 24 of the shaft portion 21 and the
inner surface 9a of the sealing member 9 facing the tapered face
24, an annular sealing space S, whose radial dimension gradually
increases upwardly from the bottom 7b side of the housing 7, is
formed. In the hydrodynamic bearing apparatus 1 after being
assembled (refer to FIG. 3), the oil level is within the range of
the sealing space S.
[0068] In the thus constructed hydrodynamic bearing apparatus 1,
when the shaft member 2 is rotated, the pressure of a lubricating
oil film formed in the radial bearing gap between the formation
regions (two positions: upper and lower) of the hydrodynamic
grooves 8a1, 8a2 of the inner periphery of the bearing sleeve 8 and
the radial bearing faces 23a, 23b of the shaft portion 21 facing
these regions, respectively, is increased by the hydrodynamic
effect of the hydrodynamic grooves 8a1, 8a2. A first radial bearing
portion R1 and a second radial bearing portion R2 which rotatably
support the shaft member 2 in the radial direction in a non-contact
manner by the pressure of these oil films are then formed. The
pressures of a first thrust bearing gap between the hydrodynamic
groove region formed on the lower end face 8b of the bearing sleeve
8 and the thrust bearing face 22a of the upper side (the shaft
portion side) of the flange portion 22 facing this hydrodynamic
groove region and a lubricating oil film formed on a second thrust
bearing gap between the hydrodynamic groove region formed on the
upper end face 7b1 of the bottom 7b and the thrust bearing face 22b
of the lower side (opposite to the shaft portion side) of the
flange portion 22 facing this face are increased by the
hydrodynamic effect of the hydrodynamic grooves. A first thrust
bearing portion T1 and a second thrust bearing portion T2 which
rotatably support the shaft member 2 in the thrust direction in a
non-contact manner by the pressures of these oil films are then
formed.
[0069] The method for producing the shaft member 2 constituting the
above hydrodynamic bearing apparatus 1 will be described below.
[0070] The shaft member 2 is produced in mainly two steps: (A)
forming step and (B) grinding step. In this embodiment, one of
these steps, the (A) forming step includes a forging process (A-1)
and a correcting process (A-2), and the (B) grinding step includes
width grinding (B-1), full-face grinding (B-2) and finish grinding
(B-3).
[0071] (A) Forming Step
[0072] (A-1) Forging Process
[0073] To begin with, a bar material made of metal such as
stainless steel which is a material of the shaft member 2 to be
formed is cold-forged to form the shaft material 10 having a
T-shaped cross section and integrally having the shaft portion 11
and flange portion 12, as shown in FIG. 5. The cold-forging method
used may be any of extrusion, upsetting, heading or the like, or
combinations of them. In the examples shown in FIG. 5, the outer
circumferential surface 11a of the shaft portion 11 after being
subjected to the forging process has such a different diameter
shape that the tapered face 14 is disposed therebetween, but may be
formed to have a uniform diameter throughout its length by
dispensing with the tapered face 14.
[0074] As mentioned above, forming the shaft material 10 by forging
does not produce cutting allowance and can reduce wasted materials
compared with forming the shaft material 10 having a similar shape
by, for example, cutting or the like. Moreover, since it is a
pressing operation, the cycle time per piece of the shaft material
10 can be improved, thereby improving the productivity.
[0075] (A-2) Correcting Process
[0076] Subsequently, the outer circumferential surface 11a of the
shaft portion of the shaft material 10 after being subjected to the
forging process is subjected to a plastic processing for correcting
the cylindricity. This improves the cylindricity of the face 13
subjected to the correcting process, of the outer circumferential
surface of the shaft portion 11a of the shaft material 10 so that
it falls within a required range (for example, 10 .mu.m or lower).
At this time, the correcting process of the cylindricity employed
may be, for example, a rolling process by using round dies 34, flat
dies 35, etc., as shown in FIG. 6 or FIG. 7. Various other
processing methods such as drawing, ironing, sizing process by
pressing (clipping) split-cavity molds, etc., can be employed. The
correcting process is conducted throughout the length of the outer
circumferential surface of the shaft portion 11, or can be
conducted on a part thereof. When only a part thereof is corrected,
its processed region includes at least the region which will be the
radial bearing faces 23a, 23b of the shaft member 2.
[0077] (B) Grinding Step
[0078] (B-1) Width Grinding Process
[0079] The end face 11b of the shaft portion and the end face 12b
of the flange portion 12 on the opposite side of the shaft portion
(refer to FIG. 5), which will be the end faces of the shaft
material 10 subjected to the correcting process, is ground relative
to the corrected face 13 mentioned above of the outer
circumferential surface of the shaft portion 11a (first grinding
step). A grinding apparatus 40 used in this grinding step
comprises, for example, a carrier 41 which retains a plurality of
the shaft material 10 as workpieces, and a pair of grind stones 42,
42 which grinds the end face 11b of the shaft portion of the shaft
material 10 retained by the carrier 41 and the end face 12b of the
flange portion 12 on the side opposite to the shaft portion, as
shown in FIG. 8.
[0080] As shown in FIG. 8, a plurality of notches 43 are provided
on a part of the circumferential region of the outer
circumferential edge of the carrier 41 at an equal pitch in the
circumferential direction. The shaft material 10 is contained in
the notch 43 with its correcting process face 13 in angular contact
with the inner face 43a of the notch 43. The correcting process
face 13 of the shaft material 10 protrudes slightly from the outer
circumferential surface of the carrier 41, and on the outer
diameter side of the carrier, a belt 44 is provided in a tensioned
state to bind the protruding portions of the shaft material 10 from
the outer diameter side. On both end sides of the carrier 41 of the
shaft material 10 contained in the notch 43 in the axial direction,
a pair of grind stones 42, 42 are coaxially disposed with their end
faces (grinding surfaces) facing each other at a predetermined
interval.
[0081] As the carrier 41 rotates, the shaft material 10 is
sequentially loaded into the notch 43 from a determined position.
The loaded material 10 traverses the end faces of the rotating
grind stones 42, 42 from their outer diameter edge toward the
inside diameter edge, while being prevented from falling off from
the notch 43 by binding of the belt 44. Accordingly, both end faces
of the shaft material 10, i.e., the end face 11b of the shaft
portion and the end face 12b of the flange portion 12 on the side
opposite to the shaft portion are ground by the end faces of the
grind stones 42, 42. At this time, since the corrected face 13 of
the shaft material 10 is supported by the carrier 41 and this
corrected face 13 has high cylindricity. Therefore, if the
perpendicularity of the rotation axis of the grind stone 42 and the
grinding surface of the grind stone 42 and the parallelism of the
rotation axis of the grind stone 42 and the rotation axis of the
carrier 41, etc., are controlled in advance with highly accuracy,
relative to this corrected face 13, the above-mentioned both end
faces 11b, 12b of the shaft material 10 can be finished with high
accuracy, enabling to suppress the value of the perpendicularity
relative to the corrected face 13. Moreover, the width of the shaft
material 10 in the axial direction (the overall length including
the flange portion 12) can be finished to have a predetermined
size.
[0082] (B-2) Full-Face Grinding Process
[0083] Subsequently, the outer circumferential surface 10b of the
shaft material 10 and the end face 12a on the shaft portion side of
the flange portion 12 are ground relative to both end faces 11b,
12b of the ground shaft material (second grinding step). The
grinding apparatus used in this grinding step is, for example,
plunge-ground by the grind stone 53 with the back plate 54 and
pressure plate 55 pressed against both end faces of the shaft
material 10, as shown in FIG. 10. The corrected face 13 of the
shaft material 10 is rotatably supported by a shoe 52.
[0084] The grind stone 53 is a formed grind stone which comprises a
grinding surface 56 corresponding to the outer circumferential
surface shape of the shaft member 2 as a finished product. The
grinding surface 56 comprises a cylinder grinding portion 56a which
grinds the outer circumferential surface 11a throughout the axial
length of the shaft portion 11 and the outer circumferential
surface 12c of the flange portion 12; and a plane grinding portion
56b which grinds the end face 12a on the shaft portion side of the
flange portion 12. In the example shown in FIG. 10, the grind stone
53 comprises, as the cylinder grinding portion 56a, portions 56a1,
56a2, which grind the regions corresponding to the radial bearing
faces 23a, 23b of the shaft member 2, a portion 56a3, which grinds
the region corresponding to the tapered face 24, a portion 56a4,
which grinds the region corresponding to the cylinder face 25,
portions 56a5-56a7, which grind the recess portions 26-28,
respectively, and a portion 56a8, which grinds the outer
circumferential surface 12c of the flange portion 12.
[0085] Grinding in the grinding apparatus 50 of the above
constitution is performed in the following procedure. To begin
with, the grind stone 53 is fed in a diagonal direction (the
direction of arrow 1 in FIG. 10) with the shaft material 10 and
grind stone 53 rotating, and the plane grinding portion 56b of the
grind stone 53 is pressed against the end face 12a on the shaft
portion side of the flange portion of the shaft material 10, to
mainly grind the end face 12a on the shaft portion side. This
causes the end face 12a on the shaft portion side in the flange
portion 22 of the shaft member 2 to be ground. Subsequently, the
grind stone 53 is fed in the direction perpendicular to the
rotation axis of the shaft material 10 (the direction of arrow 2 in
FIG. 10), and the cylinder grinding portion 56a of the grind stone
53 is pressed against the outer circumferential surface 11a of the
shaft portion 11 of the shaft material 10 and the outer
circumferential surface 12c of the flange portion 12 to grind the
faces 11a, 12c. Accordingly, out of the outer circumferential
surface of the shaft portion 21 of the shaft member 2, the regions
13a, 13b corresponding to the radial bearing faces 23a, 23b of the
shaft material 10, the tapered face 24 and the region 15
corresponding to the cylinder face 25, and the outer
circumferential surface 22c of the flange portion 22 are ground,
and the recess portions 26-28 are formed. Note that in the above
grinding, for example, as shown in FIG. 10, it is preferable to
perform grinding while measuring the remaining grinding allowance
by a measurement gauge 57.
[0086] In this second grinding step, since the accuracy setting has
been performed of the perpendicularity of both end faces 11b, 12b
of the shaft material 10 beforehand in the width grinding, each of
the to-be-ground surfaces can be ground highly accurately.
[0087] (B-3) Finish Grinding Process
[0088] (B-2) Among the faces which have been ground in full-face
grinding, the radial bearing faces 23a, 23b of the shaft member 2
and regions 13s, 13b, 15 corresponding to the cylinder face 25 are
subjected to final finish grinding. A grinding apparatus used in
this grinding, for example, performs plunge grinding by the grind
stone 63, while rotating the shaft material 10 held between the
back plate 64 and pressure plate 65 by the cylinder grinder shown
in FIG. 11. The shaft material 10 is rotatably supported by a shoe
62. A grinding surface 63a of the grind stone 63 comprises the
first cylinder grinding portion 63a1, which grinds the regions 13a,
13b corresponding to the radial bearing faces 23a, 23b, and the
second cylinder grinding portion 63a2, which grinds the region 15
corresponding to the cylinder face 25.
[0089] In the thus constructed grinding apparatus 60, the rotating
grind stone 63 is provided with the feed in the radial direction so
that the radial bearing faces 23a, 23b and the regions 13a, 13b, 15
corresponding to the cylinder face 25 are ground respectively and
these regions are finished with a final surface accuracy. In this
embodiment, the regions corresponding to the radial bearing face
23a, 23b and the region corresponding to the cylinder face 25 are
both subjected to finish grinding, the grinding of the region
corresponding to the cylinder face 25 may be dispensed with.
[0090] After performing the (A) forming step and (B) grinding step
discussed the above, heat treatment and cleaning process, if
necessary, can be performed to complete the shaft member 2 shown in
FIG. 1.
[0091] The shaft member 2, as long as it is produced by the
production method mentioned above, can be finished to have the
cylindricity of the radial bearing faces 23a, 23b formed on the
outer periphery of the shaft portion 21 of, for example, 3 .mu.m or
lower (desirably 1.5 .mu.m or lower). This allows, for example,
variation in the radial bearing gap formed between itself and the
inner periphery of the bearing sleeve 8 of in the hydrodynamic
bearing apparatus 1 in the circumferential direction or axial
direction to fall within a predetermined range, preventing bearing
performance from being adversely affected by the variation of the
above radial bearing gap. Therefore, such a radial bearing gap can
be controlled with high accuracy, and the rotational accuracy of
hydrodynamic bearing apparatuses of this type can be maintained at
a high level. Note that in this embodiment, not only the radial
bearing face 23a, 23b but also the region corresponding to the
cylinder face 25 are subjected to finish grinding (refer to FIG.
11), the cylinder face 25 is also finished to have the above
cylindricity. Therefore, the mounting accuracy (perpendicularity,
etc.) of mounting components such as the disk hub 3 on the shaft
member 2 is increased, contributing to the improvement in the motor
performance.
[0092] It is possible to form the shaft member 2 in which the
perpendicularity of both end faces of the flange portion 22 (thrust
bearing faces) 22a, 22b and the perpendicularity of the end face
21b of the shaft portion are both 5 .mu.m or lower, relative to the
radial bearing faces 23a, 23b formed on the outer periphery of the
shaft portion 21 according to the above production method. Among
them, the thrust bearing faces 22a, 22b formed on both end faces of
the flange portion 22 form the thrust bearing gap between the face
opposing them (the lower end face 8b of the bearing sleeve 8 and
the upper end face 7b1 of the bottom 7b of the housing 7, etc.) and
themselves. Therefore, the numerical value of such perpendicularity
can be thus suppressed to a low level, whereby variation in of the
above thrust bearing gap can be reduced. Moreover, the end face 21b
of the shaft portion serves not only as the reference plane for
grinding the outer circumferential surface of the shaft portion 21
and the upper end face of the flange portion 22 (thrust bearing
face 22a side), but also as the reference plane for setting the
above thrust bearing gap. Accordingly, by suppressing the numerical
value of the perpendicularity of the end face 21b of the shaft
portion to a low level, and such a grinding face, as well as the
thrust bearing gap, can be controlled highly accurately.
[0093] Note that in the above description, in the full-face
grinding shown in FIG. 10, the cylinder grinding of the outer
circumferential surface 10b of the shaft material 10 and the plane
grinding of the end face 12a on the shaft portion side of the
flange portion 12 are performed by the common grind stone 53, but
both grinding may be performed by different grind stones.
[0094] In the above description, the case where the recess portions
26-28 of the shaft member 2 are formed in the full-face grinding
(B-2) shown in FIG. 10 was exemplified. However, these recess
portions 26-28 may be subjected to the plastic processing (for
example rolling) simultaneously in correcting process shown in
FIGS. 6 and 7. In this case, in particular the recess portion 27 of
the corner between the shaft portion 21 and flange portion 22 is
formed obliquely as shown in FIG. 12. This allows the recess
portion 27 to also serve as an undercut of the grind stone 53 for
grinding the end face 12a on the shaft portion side of the flange
portion 12 and the outer circumferential surface of the shaft
portion 11a simultaneously in the full-face grinding (refer to FIG.
10).
[0095] In the embodiments described above, the case where the
radial bearing faces 23a, 23b of the shaft member 2 and thrust
bearing faces 22a, 22b are all smooth surfaces having no
hydrodynamic grooves was exemplified, but hydrodynamic grooves may
be formed on these bearing faces. In this case, the radial
hydrodynamic grooves can be formed by rolling or forging, and the
thrust hydrodynamic groove can be formed by pressing or forging, at
the stage preceding the full-face grinding shown in FIG. 10.
[0096] A second embodiment of the present invention will be
described below with reference to FIGS. 13-21. Note that the parts
and components having the same constitution and action as the
constitution (first embodiment) shown in FIGS. 1-12 are denoted by
the identical reference numerals, and repeated explanations are
omitted.
[0097] FIG. 16 shows a hydrodynamic bearing apparatus 101 according
to the second embodiment of the present invention. This
hydrodynamic bearing apparatus 101 is also used in a spindle motor
for disk drive units shown in FIG. 2 incorporated therein, and
constitutes a motor together with, for example, a disk hub 3,
stator coil 4, rotor magnet 5 and bracket 6 shown in the same Figs
(FIG. 2). The hydrodynamic bearing apparatus 101 comprises a
housing 7 having a bottom 7b at its one end, a bearing sleeve 8
fixed on to the housing 7, a shaft member 102 inserted at the inner
periphery of the bearing sleeve 8, and a sealing member 9 as its
main components. Note that also in this embodiment, for the sake of
explanation, the side of the bottom 7b of the housing 7 is referred
to as the lower side, and the side opposite to the bottom 7b is
referred to as the upper side in the description below.
[0098] As shown in FIG. 13, the shaft member 102 is formed of, for
example, a metallic material such as stainless steel, and has a
T-shaped cross section integrally comprising a shaft portion 121
and a flange portion 122 provided at the lower end of the shaft
portion 121. In a part of the outer periphery of the shaft portion
121, a cylinder region, radial hydrodynamic groove regions 123a,
123b are formed at two axially separated positions. Accordingly, in
this embodiment, an inner surface 8a of a bearing sleeve 8 facing
the radial hydrodynamic groove regions 123a, 123b is a cylindrical
face having no hydrodynamic grooves and having a circular cross
section.
[0099] These two upper and lower hydrodynamic groove regions 123a,
123b comprise a plurality of hydrodynamic grooves 123a1, 123b1 and
demarcation portions 123a2, 123b2 demarcating the hydrodynamic
grooves 123a1, 123b1, respectively. In this embodiment, as shown in
FIG. 1, they are both in a herringbone shape. Among them, the upper
radial hydrodynamic groove region 123a is formed asymmetrically in
the axial direction relative to the axial center m (the center in
the axial direction of the region between the upper and lower
slanted grooves), and the axial dimension X1 of the region above
the axial center m is larger than the axial dimension X2 of the
region therebelow.
[0100] Throughout the upper end face of the flange portion 122 or
in a part of its annular region, for example, as shown in FIG. 14,
a thrust hydrodynamic groove region 122a is formed. Moreover, in a
part of its annular region of the lower end face of the flange
portion 122, for example, as shown in FIG. 15, a thrust
hydrodynamic groove region 122b is formed. These thrust
hydrodynamic groove regions 122a, 122b comprise respectively a
plurality of hydrodynamic grooves 122a1, 122b1 and demarcation
portions 122a2, 122b2 demarcating the hydrodynamic groove 122a1,
122b1. In this embodiment, as shown in FIGS. 14 and 15, each of the
region forms a spiral shape. Note that the thrust hydrodynamic
groove regions 122a, 122b may be in the shape, for example, of a
herringbone shape or the like, without being limited to the shape
shown particularly. Alternatively, each of the upper and lower
faces may have different hydrodynamic groove shapes.
[0101] Above one of the hydrodynamic groove regions, the radial
hydrodynamic groove region 123a, a tapered face 124, of which
diameter gradually decreases toward the shaft tip, is formed
adjacently, and a cylinder face 125, which will be a mounting
portion of the disk hub 3, is formed further thereabove. Annular
recess portions 126, 127, 128, are formed between the two radial
hydrodynamic groove regions 123a, 123b, between the other radial
hydrodynamic groove region 123b and the flange portion 122, and
between the tapered face 124 and the cylinder face 125,
respectively.
[0102] Between the tapered face 124 of the shaft portion 121 and
the inner surface 9a of a sealing member 9 facing the tapered face
124, an annular sealing space S, whose size in the radial direction
is gradually increased upwardly from the bottom 7b side of the
housing 7 is formed. In the hydrodynamic bearing apparatus 1 after
being assembled (refer to FIG. 16), the oil level is maintained
within the range of the sealing space S.
[0103] In the thus constructed hydrodynamic bearing apparatus 101,
when the shaft member 102 is rotated, the pressure of a lubricating
oil film formed the radial bearing gap between a cylinder face 8a
formed on the inner periphery of the bearing sleeve 8 and the
radial hydrodynamic groove regions 123a, 123b of the shaft portion
121 facing the cylinder face 8a is increased by the hydrodynamic
effect of the hydrodynamic grooves 123a1, 123b1. Subsequently, a
first radial bearing portion R11 and a second radial bearing
portion R12 which rotatably support the shaft member 102 in the
radial direction in a non-contact manner are formed by the pressure
of these oil films. Moreover, the pressure of the lubricating oil
films formed the thrust bearing gap between the lower end face 8b
of the bearing sleeve 8 and the thrust hydrodynamic groove region
122a of the upper side (the shaft portion side) of the flange
portion 122 facing the lower end face 8b, and the thrust bearing
gap between the upper end face 7b1 of the bottom 7b and the thrust
hydrodynamic groove region 122b of the lower side (opposite to the
shaft portion side) of the flange portion 122 facing the upper end
face 7b1 is increased by the hydrodynamic effect of the
hydrodynamic grooves 122a1, 122b1. Subsequently, a first thrust
bearing portion T11 and a second thrust bearing portion T12 which
rotatably support the shaft member 102 in the thrust direction in a
non-contact manner are formed by the pressure of these oil
films.
[0104] A method for producing of the shaft member 102 constituting
the above hydrodynamic bearing apparatus 101 will be described
below.
[0105] The shaft member 102 is produced in mainly two steps: (C)
forming step and (D) grinding step. Among them, the (C) forming
step comprises a shaft material forming process (C-1), a thrust
hydrodynamic groove region forming process (C-2), a radial
hydrodynamic groove region forming process (C-3), and a shaft
portion correcting process (C-4). The (D) grinding step comprises a
width grinding process (D-1), a full-face grinding process (D-2),
and a finish grinding process (D-3).
[0106] (C) Forming Step
[0107] (C-1) Shaft Material Forming Process and (C-2) Thrust
Hydrodynamic Groove Region Forming Process
[0108] To begin with, a material of the shaft member 102 to be
formed, i.e., a metal material such as stainless steel is
compression-formed (forging process) by using molds, for example,
as shown in FIG. 17, in a cold state, whereby the shaft material
110 integrally having the region 111 corresponding to the shaft
portion (hereinafter referred to simply as a shaft portion) and the
region 112 corresponding to the flange portion (hereinafter
referred to simply as a flange portion) is formed (shaft material
forming process (C-1)). The molds used in the forge forming of this
shaft material 110 also serves as the molds for forming thrust
hydrodynamic groove regions 112a, 112b on the flange portion 112 in
this embodiment. Accordingly, simultaneously with the forge forming
of the shaft material 110, plastic processing is performed in the
positions corresponding to both end faces of the flange portion
112. For example, as shown in FIGS. 18 and 19, thrust hydrodynamic
groove regions 112a (the shaft portion side), 112b (opposite to the
shaft portion side) comprising a plurality of hydrodynamic groove
112a1, 112b1 and demarcation portions 112a2, 112b2 demarcating
these hydrodynamic grooves 112a1, 112b1 are formed (thrust
hydrodynamic groove region formation process (C-2)).
[0109] A method of cold-forging employed in the above forming step
may be extrusion, upsetting, heading or the like, or combinations
of them. In the example shown in FIG. 17, the outer circumferential
surface lila of the shaft portion 111 after the forging process has
a different diameter shape in which a tapered face 114 and a
cylinder face 115, which is upwardly continuous with the tapered
face 114 and has a diameter smaller than other portions, are
disposed therebetween, and the tapered face 114 may be dispensed
with and formed to have a uniform dimer throughout its length. Note
that described in this embodiment is the case where the forming of
the shaft material 110 and the forming of the thrust hydrodynamic
groove regions 112a, 112b are conducted simultaneously by the
forging process. However, both steps need not necessarily be
performed simultaneously, and the thrust hydrodynamic groove
regions 112a, 112b may be formed by plastic processing, for
example, a forging process, pressing process or the like after
forming the shaft material 110 by forging.
[0110] (C-3) Radial Hydrodynamic Groove Region Forming Process and
(C-4) Shaft Portion Correcting Process
[0111] The shaft portion 111 of the shaft material 110 formed by
forging in the previous step is pressurized a pair of rolling dies
(for example, round dies, flat dies, etc.), for example, in the
shape shown in FIGS. 6 or 7 and the pair of rolling dies are
reciprocated in the directions opposite to each other so that a
hydrodynamic groove transcription face previously formed on the
holding face of either of the pair of rolling dies are transcribed
(radial hydrodynamic groove region forming process (C-3)) on the
outer circumferential surface 111a of the shaft portion 111. Since
the above pair of rolling dies in this embodiment also serves as a
correcting tool for correcting the shaft portion 111 of the shaft
material 110, a rolling process for correcting cylindricity is
conducted (shaft portion correcting process (C-4)) on the outer
circumferential surface 111a of the shaft portion 111
simultaneously with transcription of the above hydrodynamic
grooves.
[0112] As a result, for example, radial hydrodynamic groove regions
113a, 113b having the shape shown in FIG. 17 are formed at two
axially separated positions on the outer circumferential surface
111a of the shaft portion 111, while out of the outer
circumferential surface 111a of the shaft portion, a face 113
including radial hydrodynamic groove regions 113a, 113b (for
example, the bottom faces of hydrodynamic grooves 113a1, 113b1 and
the outer circumferential surfaces of demarcation portions 113a2,
113b2 demarcating the hydrodynamic grooves 113a1, 113b1) is
corrected, and the cylindricity of the face 113 subjected to the
correcting process is improved to be within a desired range (for
example, 10 .mu.m or lower). Simultaneously, the cylinder face 115
of the upper end of the shaft portion 111 is also subjected to a
correcting process, and the cylindricity of the cylinder face 115
is improved similarly.
[0113] As mentioned above, forming of the radial hydrodynamic
groove regions 113a, 113b and correction of the outer
circumferential surface 111a of the shaft portion can be both
performed simultaneously by rolling. Additionally, for example,
after a correcting process is performed on the outer
circumferential surface 111a of the shaft portion 111, a procedure
to perform a rolling process of the radial hydrodynamic groove
regions 113a, 113b on the face subjected to the correcting process
can be also employed. In that case, various processing methods
including a rolling process, drawing, ironing, sizing by pressing
split-cavity molds (clipping) and the like, can be employed in the
correcting process of the cylindricity. Moreover, the correcting
process is performed throughout the length of the outer
circumferential surface 111a of the shaft portion 111, or can be
conducted on a part of the outer circumferential surface 111a as
long as the part includes the radial hydrodynamic groove regions
113a, 113b.
[0114] As mentioned above, the forming of the shaft material 110
integrally comprising the shaft portion 111 and flange portion 112
and the forming of the thrust hydrodynamic groove regions 112a,
112b on both end faces of the flange portion 112 are simultaneously
performed both by forging, and in addition, the forming of the
radial hydrodynamic groove regions 113a, 113b and the correcting
process of the outer circumferential surface 111a of the shaft
portion are performed simultaneously both by rolling, whereby such
processing steps can be simplified and machining time can be
greatly shortened. Moreover, compared to cutting or etching, etc.,
employing forging processes and rolling processes in which the
cycle time per processed item is shorter can further shorten the
machining time, enabling further cost reduction and improvement in
mass productivity.
[0115] At the stage where the above forming step (C) has been
completed, for example, as shown in FIG. 20, the height h1 from the
bottom face 112b3 of the hydrodynamic groove 112b1 to the axial end
face 112b4 of the demarcation portion 112b2 in the thrust
hydrodynamic groove region 112b is set to a suitable value
considering the forming accuracy in the above forging process and
the grinding allowance in the width grinding (D-1) of the shaft
material 110 described later. The height (not shown) from the
bottom faces of the hydrodynamic grooves 113a1, 113b1 in the radial
hydrodynamic groove regions 113a, 113b to the outer circumferential
surfaces of the demarcation portions 113a2, 113b2, and the height
(not shown) from the bottom faces of the hydrodynamic groove 112a1
in the thrust hydrodynamic groove region 112a on the shaft portion
111 side to the axial end faces of the demarcation portion 112a2
are set to suitable values considering the forming accuracy in the
above forging process, and the full-face grinding (D-2) of the
shaft material 110 described later and the grinding allowance in
the finish grinding (D-3).
[0116] (D) Grinding Step
[0117] (D-1) Width Grinding
[0118] The end face on the side opposite to the shaft portion on
the side on which the end face 111b of the shaft portion and the
thrust hydrodynamic groove region 112b of the flange portion 112,
which will be the two end faces of the shaft material 110 after
being subjected to the forming step are formed (refer to FIG. 19)
is ground relative to the corrected face 113 mentioned above. A
grinding apparatus used in this grinding step comprises, as shown
in FIGS. 8 and 9, a carrier 41 retaining a plurality of the shaft
materials 110 as workpieces; and a pair of grind stones 42, 42
which grind the end face opposite to the shaft portion side
comprising the end face 111b of the shaft portion of the shaft
material 110 retained by the carrier 41 and the thrust hydrodynamic
groove region 112b of the flange portion 112, as in the first
embodiment. Note that other constitutions of the grinding apparatus
40 than this are based on the first embodiment, and their
explanations are thus omitted.
[0119] As the carrier 41 rotates, the shaft material 110 is
sequentially loaded into the notch 43 from a fixed position. The
loaded shaft material 110 traverses the end faces of the rotating
grind stones 42, 42 from their outer diameter edge toward the
inside diameter edge, while being prevented from falling off from
the notch 43 by binding of the belt 44. Accordingly, both end faces
of the shaft material 110, namely the end face 111b of the shaft
portion and the end face of the flange portion 112 on the side
opposite to the shaft portion comprising the thrust hydrodynamic
groove region 112b are ground by the end faces of the grind stones
42, 42 (refer to FIG. 9). Moreover, the width of the shaft material
110 in the axial direction (the entire length including the flange
portion 112) is finished to have a predetermined size.
[0120] In this grinding step, as mentioned above, the thrust
hydrodynamic groove region 112b of the flange portion 112 is
ground, for example, in such a manner that the demarcation portion
112b2 is ground by a predetermined grinding allowance (h1-h2 in
FIG. 21) from the height h1 at the time of forging, as shown in
FIG. 21. This renders the height of the demarcation portion 112b2
(the depth of the hydrodynamic groove 112b1) to be the same as the
predetermined value h2 (for example, 3 .mu.m-15 .mu.m). Therefore,
the thrust bearing gap between the component facing it (in this
embodiment, the bottom 7b of the housing 7) and itself can be
controlled highly accurately at the interval of a several
micrometers to several ten micrometers.
[0121] (D-2) Full-Face Grinding Process
[0122] Subsequently, relative to the ground two end faces of the
shaft material 110 (the end face 111b of the shaft portion, the end
face of the flange portion 112 on the side opposite to the shaft
portion comprising the thrust hydrodynamic groove region 112b), the
outer circumferential surface 110a of the shaft material 110 and
the end face of the flange portion 112 on the shaft portion side
comprising the thrust hydrodynamic groove region 112a are ground. A
grinding apparatus used in this grinding step conduct
plunge-grinding by the grind stone 53, with the back plate 54 and
pressure plate 55 pressed against both end faces of the shaft
material 110, as in the first embodiment shown in FIG. 10. The
corrected face 13 of the shaft material 110 is rotatably supported
by a shoe 52. Note that other constitutions of the grinding
apparatus 50 than this is based on the first embodiment and their
explanations are thus omitted.
[0123] Grinding in the grinding apparatus 50 of the above
constitution is performed in the following procedure. To begin
with, while the shaft material 110 and the grind stone 53 are in
rotation, the grind stone 53 is fed obliquely (the direction of
arrow 1 in FIG. 10), the plane grinding portion 56b of the grind
stone 53 is pressed against the end face of the flange portion 112
on the shaft portion side of the shaft material 110, the end face
of the flange portion 112 on the shaft portion side (on the thrust
hydrodynamic groove region 112a side) comprising the thrust
hydrodynamic groove region 112a is ground. Accordingly, the end
face of the flange portion 122 of the shaft member 102 on the shaft
portion side is formed, and grinding of the thrust hydrodynamic
groove region 112a is completed, and the thrust hydrodynamic groove
region 122a of the shaft member 102 is formed. Subsequently, the
grind stone 53 is fed in the direction perpendicularly intersecting
the rotation axis of the shaft material 110 (the direction of arrow
2 in FIG. 10), the cylinder grinding portion 56a of the grind stone
53 is pressed against the outer circumferential surface 111a of the
shaft portion 111 of the shaft material 110 and the outer
circumferential surface 112c of the flange portion 112 to grind the
faces 111a, 112c. Accordingly, out of the outer circumferential
surface of the shaft portion 121 of the shaft member 102, the
radial hydrodynamic groove region 123a, 123b and the region
corresponding to the cylinder face 125 are ground, while the
tapered face 124, the outer circumferential surface 122c of the
flange portion 122, and the recess portions 126-128 are further
formed.
[0124] In this grinding step (full-face grinding process), the
demarcation portion 112a2 of the thrust hydrodynamic groove region
112a formed on the end face of the flange portion 112 on the shaft
portion side is ground, for example, by a predetermined grinding
allowance from the height at the time of forging, similarly to the
case of the thrust hydrodynamic groove region 112b, although not
shown in the Figs. This renders the height of the demarcation
portion 112a2 (the depth of the hydrodynamic groove 112a1) to have
a predetermined value, whereby the thrust bearing gap between the
component facing it (the lower end face 8b of the bearing sleeve 8
in this embodiment) and itself is highly accurately controlled. In
this embodiment, since the accuracy setting of the perpendicularity
of both end faces of the shaft material 110 (the end face 111b of
the shaft portion, the end face of the flange portion 112 on the
side opposite to the shaft portion) has been performed previously
in the width grinding process, grinding of the thrust hydrodynamic
groove region 112a can be conducted more precisely.
[0125] (D-3) Finish Grinding Process
[0126] (D-2) Among the faces which have been ground in full-face
grinding process, the radial hydrodynamic groove regions 123a, 123b
of the shaft member 102 and the region corresponding to the
cylinder face 125 are subjected to the final finish grinding. As in
the first embodiment, a grinding apparatus used in this grinding is
a cylinder grinder shown in FIG. 11. It performs plunge grinding by
the grind stone 63 while rotating the shaft material 110 held
between the back plate 64 and the pressure plate 65. Note that
other constitutions of the grinding apparatus 60 are based on the
first embodiment, and their explanations are thus omitted.
[0127] In the grinding apparatus 60 having the above constitution,
the rotating grind stone 63 is provided with the feed in the radial
direction so that the radial hydrodynamic groove regions 123a, 123b
and the regions 113a, 113b and 115 corresponding to the cylinder
face 125 are ground, and these regions are finished to have the
final surface accuracy. In this grinding step, similarly to the
case of the thrust hydrodynamic groove regions 112a, 112b, the
demarcation portions 113a2, 113b2 of the radial hydrodynamic groove
regions 113a, 113b is ground, for example, by a predetermined
grinding allowance from the height at the time of rolling, although
not shown in the Figs. This renders the heights of the demarcation
portions 113a2, 113b2 (the depth of hydrodynamic grooves 113a1,
113b1) to have a predetermined value, enabling to highly accurately
control the radial bearing gap between the component facing it (in
this embodiment, the cylinder face 8a of the bearing sleeve 8) and
itself.
[0128] After being subjected to the above (C) forming step and (D)
grinding step, the shaft member 102 shown in FIG. 13 is completed
by performing, if necessary, heat treatment and cleaning
process.
[0129] The shaft member 102 produced by the above production method
has the radial hydrodynamic groove regions 123a, 123b formed at two
separate upper and lower portions on the outer periphery of the
shaft portion 121 by a rolling process, and has such a structure
that the outer circumferential surfaces of the demarcation portions
123a2, 123b2 of the radial hydrodynamic groove regions 123a, 123b
are the grinding surfaces. It also has the thrust hydrodynamic
groove regions 122a, 122b formed by a forging process on both end
faces of the flange portion 122, and has such a structure that the
axial end faces of the thrust hydrodynamic groove regions 122a,
122b are the grinding surfaces. The grinding surfaces of the
demarcation portions 123a2, 123b2 in the radial hydrodynamic groove
regions 123a, 123b are formed in the (D-2) full-face grinding
process and (D-3) finish grinding process. Moreover, the grinding
surface of the demarcation portion 122a2 in the thrust hydrodynamic
groove region 122a is formed in the (D-2) full-face grinding
process, and the grinding surface is formed in the (D-1) width
grinding process of the demarcation portion 122b2 in the thrust
hydrodynamic groove region 122b.
[0130] As mentioned above, the radial hydrodynamic groove regions
113a, 113b of the shaft material 110 are formed by a rolling
process, and among the radial hydrodynamic groove regions 113a,
113b, the outer diameter portions of the demarcation portions
113a2, 113b2 are ground, whereby the hydrodynamic grooves region
123a, 123b can be formed at reduced costs, while the dimensional
accuracy of their outer diameters and surface roughness can be
highly accurately finished. As for the thrust hydrodynamic groove
regions 122a, 122b, low-cost forming and high-accuracy finish can
be achieved at the same time for the same reason. This allows the
radial bearing gap and thrust bearing gap in the hydrodynamic
bearing apparatus 101 to be controlled highly accurately, enabling
to produce stable bearing performance.
[0131] According to the above production method, it is also
possible to highly accurately finish the cylindricity of the radial
hydrodynamic groove regions 123a, 123b formed on the outer
periphery of the shaft portion 121. Accordingly, for example
pressure, variation of the radial bearing gap formed between the
cylinder face 8a of the inner periphery of the bearing sleeve 8 in
the bearing apparatus 101 and the hydrodynamic groove regions in
the circumferential direction or axial direction is suppressed to
fall within a predetermined range, and bearing performance can be
prevented from being adversely affected by the variation of the
above radial bearing gap. Moreover, the grinding allowance of the
demarcation portion in grinding (h1-h2 in FIG. 21) varies depending
on the forming accuracy in forging or rolling. As shown in this
embodiment, the cylindricity of the shaft portion 121 is corrected
so that in particular the forming accuracy of the demarcation
portions 123a2, 123b2 in the radial hydrodynamic groove region
123a, 123b can be improved and the grinding allowance in grinding
can be reduced. This enables to further shorten machining time and
reduce processing costs. Alternatively, the forming accuracy of the
hydrodynamic groove region in forging or rolling is preliminarily
increased, whereby the grinding allowance in grinding can be
reduced.
[0132] As mentioned above, if the radial hydrodynamic groove
regions 123a, 123b are formed on the outer periphery of the shaft
member 102, hydrodynamic grooves need not be processed on the inner
periphery of the bearing sleeve 8. The inner periphery of the
bearing sleeve 8 can serve as the cylinder face 8a, reducing such
related costs. Moreover, if hydrodynamic grooves need not be
processed on the inner periphery of the bearing sleeve 8, it is
unnecessary to form the bearing sleeve 8 and the housing 7 as
separate components. Therefore, these components can be unified
(with a resin or the like), although not shown in the Figs. This
can reduce the number of parts and related production costs.
[0133] In the second embodiment described above, the case where the
radial hydrodynamic groove regions 113a, 113b are formed by a
rolling process is described, but alternatively, for example, the
forging of the shaft material 110 and the thrust hydrodynamic
groove regions 112a, 112b can be conducted simultaneously with the
forming of the radial hydrodynamic groove regions 113a, 113b by
forging. In this case, the shape of the hydrodynamic grooves by
forging is not particularly limited, and may be, for example, a
herringbone shape, a spiral shape, or other various hydrodynamic
groove shapes.
[0134] In the second embodiment, described was the case where the
thrust hydrodynamic groove regions 122a, 122b are formed on both
end faces of the flange portion 122. However, it is not
particularly limited to this form, and, for example, the thrust
hydrodynamic groove regions may be formed on the side of the lower
end face 8b of the bearing sleeve 8 and the upper end face 7b1 of
the bottom 7b facing the two end faces of the flange portion 122,
respectively.
[0135] In the embodiments described above (the first and second
embodiments), for example, bearings using hydrodynamic pressure
producing parts comprising hydrodynamic grooves arranged in a
herringbone shape and a spiral shape are shown as examples of the
hydrodynamic bearing which constitutes the radial bearing portions
R1, R2, R11, R12 and the thrust bearing portions T1, T2, T11, T12.
However, the constitution of the hydrodynamic pressure producing
parts is not limited to these. As the radial bearing portions R1,
R2, R11, R12, for example, multirobe bearing, step bearing, taper
bearing, taper flat bearing or the like may be used. As the thrust
bearing portions T1, T2, T11, T12, step pocket bearing, taper
pocket bearing, taper flat bearing and the like may be used.
[0136] In the embodiments described above, a lubricating oil is
mentioned as an example of a fluid which fills the inside of the
hydrodynamic bearing apparatus 1, 101 and produces hydrodynamic
effect in the radial bearing gap between the bearing sleeve 8 and
the shaft member 2, 102 and the thrust bearing gap between the
bearing sleeve 8 and housing 7 and the shaft member 2, 102.
However, it is not particularly limited to this fluid. A fluid
which can produce hydrodynamic effect in the bearing gaps having
hydrodynamic groove regions, for example, a gas such as air and a
lubricant having fluidity such as a magnetic fluid may be used.
[0137] The hydrodynamic bearing apparatus according to the present
invention is suitable for spindle motors of information appliances,
for example, magnetic disk apparatuses such as HDD, optical disk
apparatuses such as CD-ROM, CD-R/RW, DVD-ROM/RAM, magneto-optic
disk apparatuses such as MD and MO, etc., polygon scanner motors of
laser beam printers (LBP), and other small motors.
* * * * *