U.S. patent application number 09/961322 was filed with the patent office on 2002-01-31 for spindle motor.
This patent application is currently assigned to KABUSHIKI KAISHA SANKYO SEIKI SEISAKUSHO. Invention is credited to Gomyo, Masato, Miura, Kazushi, Narita, Takayuki, Tago, Tokio, Yazawa, Takehiko.
Application Number | 20020012483 09/961322 |
Document ID | / |
Family ID | 26447737 |
Filed Date | 2002-01-31 |
United States Patent
Application |
20020012483 |
Kind Code |
A1 |
Miura, Kazushi ; et
al. |
January 31, 2002 |
Spindle motor
Abstract
A potential-difference alleviating member for alleviating and
lowering the potential difference, which is an energy difference
between a rotating or fixed bearing member and a rotary hub or a
fixing frame which are formed of metals of different types, is
interposed between the two members so as to prevent the occurrence
or advance of potential difference corrosion. Relief portions are
respectively provided at a joining interface between a rotary shaft
and a thrust plate and a joining interface between a bearing member
and the counter plate, and the respective members are welded in the
relief portions so as to be integrated.
Inventors: |
Miura, Kazushi; (Nagano,
JP) ; Gomyo, Masato; (Nagano, JP) ; Narita,
Takayuki; (Nagano, JP) ; Tago, Tokio; (Nagano,
JP) ; Yazawa, Takehiko; (Nagano, JP) |
Correspondence
Address: |
SUGHRUE, MION, ZINN,
MACPEAK & SEAS, PLLC
2100 Pennsylvania Avenue, NW
Washington
DC
20037-3213
US
|
Assignee: |
KABUSHIKI KAISHA SANKYO SEIKI
SEISAKUSHO
|
Family ID: |
26447737 |
Appl. No.: |
09/961322 |
Filed: |
September 25, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09961322 |
Sep 25, 2001 |
|
|
|
09549698 |
Apr 14, 2000 |
|
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Current U.S.
Class: |
384/100 ;
G9B/19.028 |
Current CPC
Class: |
F16C 17/107 20130101;
H02K 5/1677 20130101; F16C 43/02 20130101; F16C 17/045 20130101;
G11B 19/2009 20130101; F16C 2370/12 20130101; F16C 33/107 20130101;
H02K 7/086 20130101 |
Class at
Publication: |
384/100 |
International
Class: |
F16C 032/06 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 15, 1999 |
JP |
P.HEI.11-107724 |
Apr 28, 1999 |
JP |
P.HEI.11-123056 |
Claims
What is claimed is:
1. A spindle motor comprising: a fixed shaft; a cylindrical rotary
bearing member rotatably supported on an outer peripheral face of
the fixed shaft, and made of a first metal material; a rotary hub
integrally joined to the rotary bearing member, and made of a
second metal material different from the first metal material; and
a potential-difference alleviating member provided on the joining
surfaces of the rotary bearing member and the rotary hub, and made
of a third metal material whose ionization tendency in an
electrochemical series is positioned between ionization tendencies
of the first and second metal materials.
2. The spindle motor as set forth in claim 1, wherein the first
metal material is a copper group metal material, the second metal
material is an aluminum group metal material, and the third metal
material is a nickel group metal material.
3. The spindle motor as set forth in claim 1, wherein the
potential-difference alleviating member is formed on at least one
of the joining surfaces of the rotary bearing member and the rotary
hub by any one of plating, vapor deposition and coating.
4. A spindle motor comprising: a fixed shaft; a cylindrical rotary
bearing member rotatably supported on an outer peripheral face of
the fixed shaft, and made of a first metal material; and a rotary
hub integrally joined to the rotary bearing member, and made of a
second metal material different from the first metal material; and
a passivation film formed on the joining surfaces of the rotary
bearing member and the rotary hub.
5. The spindle motor as set forth in claim 4, wherein the
passivation film is made of either the first metal material or the
second metal material.
6. A spindle motor comprising: a fixed frame made of a first metal
material; a cylindrical fixed bearing member integrally joined to
the fixed frame, and made of a second metal material different from
the first metal material; a rotary shaft rotatably supported on an
inner peripheral face of the fixed bearing member; a rotary hub
secured to the rotary shaft; and a potential-difference alleviating
member provided on the joining surfaces of the fixed frame and the
fixed bearing member, and made of a third metal material whose
ionization tendency in an electrochemical series is positioned
between ionization tendencies of the first and second metal
materials.
7. The spindle motor as set forth in claim 6, wherein the first
metal material is a copper group metal material, the second metal
material is an aluminum group metal material, and the third metal
material is a nickel group metal material.
8. The spindle motor as set forth in claim 6, wherein the
potential-difference alleviating member is formed on at least one
of the joining surfaces of the rotary bearing member and the rotary
hub by any one of plating, vapor deposition and coating.
9. A spindle motor comprising: a fixed frame made of a first metal
material; a cylindrical fixed bearing member integrally joined to
the fixed frame, and a second metal material different from the
first metal material; a rotary shaft rotatably supported on an
inner peripheral face of the fixed bearing member; a rotary hub
secured to the rotary shaft; and a passivation film formed on the
joining surfaces of the fixed frame and the fixed bearing
member.
10. The spindle motor as set forth in claim 9, wherein the
passivation film is made of either the first metal material or the
second metal material.
11. A spindle motor comprising: a fixed shaft; a cylindrical rotary
bearing member rotatably supported on an outer peripheral face of
the fixed shaft, and made of a first metal material; a rotary hub
integrally joined to the rotary bearing member, and made of a
second metal material different from the first metal material; and
an insulating resin film formed on the joining surfaces of the
rotary bearing member and the rotary hub.
12. The spindle motor as set forth in claim 11, wherein the resin
film is formed on outer circumferential faces of the rotary bearing
member and the rotary hub continuously from the joining surfaces
such that the rotary bearing member and the rotary hub are partly
conducted.
13. A spindle motor comprising: a fixed frame made of a first metal
material; a cylindrical fixed bearing member integrally joined to
the fixed frame, and made of a second metal material different from
the first metal material; a rotary shaft rotatably supported on an
inner peripheral face of the fixed bearing member; a rotary hub
secured to the rotary shaft; and an insulating resin film formed on
the joining surfaces of the rotary bearing member and the rotary
hub.
14. The spindle motor as set forth in claim 13, wherein the resin
film is formed on outer circumferential faces of the rotary bearing
member and the rotary hub continuously from the joining surfaces
such that the rotary bearing member and the rotary hub are partly
conducted.
15. A spindle motor comprising: a fixed frame having a cylindrical
holder; a cylindrical bearing sleeve having a hydrodynamic bearing
surface on an inner peripheral face thereof, and disposed in the
cylindrical holder; a rotary shaft rotatably supported on an inner
peripheral face of the fixed bearing sleeve via a lubricating fluid
provided therebetween; a rotary hub secured to a first end of the
rotary shaft; an annular thrust plate integrally joined to a second
end of the rotary shaft to constitute a thrust hydrodynamic bearing
portion in the bearing sleeve; a disk-like counter plate for
closing an opened end portion of the bearing sleeve in which the
thrust hydrodynamic bearing portion is provided; and a relief
portion formed on one end portion of joining surfaces of the rotary
shaft and the thrust plate so as to recess in an axial direction of
the rotary shaft at which the rotary shaft and the thrust plate are
welded to be integrated with each other.
16. The spindle motor as set forth in claim 15, further comprising:
a relief portion formed on one end portion of joining surfaces of
the counter plate and the bearing sleeve so as to recess in an
axial direction of the rotary shaft at which the counter plate and
the bearing sleeve are welded to be integrated with each other.
17. The spindle motor as set forth in claim 16, wherein at least
one of materials constituting the joining surfaces is fused to be
joined to the other material.
18. The spindle motor as set forth in claim 15, further comprising:
a relief portion formed on one end portion of the rotary surfaces
of the counter plate and the cylindrical holder of the fixed plate
so as to recess in an axial direction of the rotary shaft at which
the counter plate and the cylindrical holder are welded to be
integrated with each other.
19. The spindle motor as set forth in claim 18, wherein at least
one of materials constituting the joining surfaces is fused to be
joined to the other material.
20. The spindle motor as set forth in claim 15, wherein the rotary
hub and the rotary shaft are secured to each other by welding.
21. The spindle motor as set forth in claim 15, wherein dynamic
pressure generating grooves are formed in the thrust hydrodynamic
bearing portion; and wherein the relief portion is located where is
away from a portion where the dynamic pressure generating grooves
are formed.
22. A spindle motor comprising: a fixed shaft; a cylindrical rotary
bearing sleeve rotatably supported on an outer peripheral face of
the fixed shaft via a lubricating fluid provided therebetween; a
rotary hub integrally joined to the rotary bearing member; a fixed
frame having an opening into which a first end of the fixed shaft
is secured; an annular thrust plate integrally joined to a second
end of the fixed shaft to constitute a thrust hydrodynamic bearing
portion in the bearing sleeve; and a relief portion formed on one
end portion of joining surfaces of the fixed shaft and the thrust
plate so as to recess in an axial direction of the fixed shaft at
which the fixed shaft and the thrust plate are welded to be
integrated with each other.
23. The spindle motor as set forth in claim 22, wherein dynamic
pressure generating grooves are formed in the thrust hydrodynamic
bearing portion; and wherein the relief portion is located where is
away from a portion where the dynamic pressure generating grooves
are formed.
24. The spindle motor as set forth in claim 22, wherein at least
one of materials constituting the joining surfaces is fused to be
joined to the other basic material.
25. The spindle motor as set forth in claim 5, wherein the
passivation film is made of a third metal material which is
different from the first and second metal materials.
26. The spindle motor as set forth in claim 10, wherein the
passivation film is made of a third metal material which is
different from the first and second metal materials.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a spindle motor used as an
apparatus for rotatively driving a hard disk or the like.
[0002] A spindle motor disclosed in, for example, Japanese Patent
Publication No. 8-4769A is known as a spindle motor used as an
apparatus for rotatively driving a recording medium such as a hard
disk. As shown in FIG. 7, this spindle motor is mainly comprised of
a stator assembly 100 and a rotor assembly 120 having driving
magnets 125. The rotor assembly 120 has a hub 122 secured to an
upper end portion of a rotary shaft 121 by means of press-fitting,
shrinkage fitting, or the like. Meanwhile, the stator assembly 100
has stator cores 116 each formed by winding a coil 117 around a
respective salient pole portion. These stator cores 116 are fitted
to an outer peripheral portion of a bearing holder 115.
[0003] A bearing sleeve 113 is fitted in an inner peripheral
portion of the bearing holder 115. Radial bearing portions RBa and
RBb serving as bearing surfaces for generating hydrodynamic
pressure are formed on an inner peripheral surface of the bearing
sleeve 113 in such a manner as to be spaced apart from each other
in the axial direction. A lubricating fluid 105 such as oil
undergoes a pressure rise due to the pumping action of dynamic
pressure generating grooves (not shown) when the rotary shaft 121
rotates, and the rotary shaft 121 and the hub 122 are pivotally
supported by the hydrodynamic pressure generated by the lubricating
fluid 105.
[0004] Further, a thrust plate 126 constituting a thrust
hydrodynamic bearing portion is press-fitted and secured to the
rotary shaft 121. Further, a counter plate 114 is fixed at an open
end of the bearing holder 115 of a frame 111 through a mechanical
coupling means such as fixing screws 106. The thrust plate 126 is
placed between a lower end face of the bearing sleeve 113 and an
inner bottom surface of the counter plate 114, and as the
lubricating fluid 105 is present in this space, the rotary shaft
121 is stably supported in the thrust direction by the hydrodynamic
pressure generated by the lubricating fluid 105.
[0005] In recent years, a trend toward compact and thin spindle
motors for rotatively driving recording medium disks are rapidly
underway. In conjunction with this trend, the bearing member
(bearing sleeve 113) supporting the shaft 121 is formed of a
metallic material different from the metallic material composing
the fixing frame 111. One reason for this is that a metal excelling
in workability is adopted as the metallic material composing the
bearing sleeve 113 so that the inside-diameter portion of the
bearing sleeve 113 can be machined satisfactorily. In this case,
the bearing sleeve 113 formed of a different type of metallic
material is integrally joined to the fixing frame 111 by means of
press-fitting, shrinkage fitting, or the like.
[0006] In a spindle motor in which different types of metallic
material are integrally joined together, if an electrolyte having a
large dielectric constant, such as water, penetrates the joint, a
local battery is formed between these metallic materials of
different types, and anodic dissolution occurs due to the local
battery, resulting in the so-called potential difference corrosion.
The portion where such potential difference corrosion occurs is
scattered in due course of time in the form of dust, and causes
damage to the recording medium disk or the magnetic head.
Accordingly, in the case of an apparatus for which cleanliness is
required, such as a hard disk drive (HDD), it is desirable to
reliably prevent the occurrence of the aforementioned potential
difference corrosion.
[0007] In recent years when motors are required to be thinner, it
has become impossible to secure a sufficient joining length in the
joining of the rotary shaft and the thrust plate and in the joining
of the rotary shaft and the hub. Consequently, there have arisen
problems in that it is difficult to obtain desired shock-resisting
performance (e.g., 1,000 G or more) and joining strength capable of
withstanding an external stress during assembly, thereby making it
difficult to produce a thin motor.
[0008] For instance, in FIG. 7, various joining methods are adopted
in joining the counter plate 114 and the frame 111 or in joining
the counter plate 114 and the bearing sleeve 113. In a case where
the fixing screws 106 shown in FIG. 7 are used to effect fastening,
the heads of the fixing screws 106 hinder the attempt to produce a
thin motor. In a case where the counter plate 114 is fixed by a
calking method, the calked portion must be made to project from the
bottom surface of the counter plate 114, which also hinders the
attempt to produce a thin motor. Further, in a case where the
counter plate 114 is fixed by a press-fitting method, since a
sufficient joining length cannot be obtained, the joining strength
lacks.
SUMMARY OF THE INVENTION
[0009] A primary object of the invention is to provide a spindle
motor which makes it possible to prevent by a simple arrangement
the potential difference corrosion between a bearing member and
another member which are formed of metallic materials of different
types.
[0010] A secondary object of the invention is to provide a spindle
motor which can be made thin by increasing the joining strength
even in the case of a part whose joining length is short.
[0011] In accordance with the invention, the arrangement is
provided such that a potential-difference alleviating member for
alleviating and lowering the potential difference, which is an
energy difference between a rotating or fixed bearing member and a
rotary hub or a fixing frame which are formed of metals of
different types, is interposed between the two members so as to
prevent the occurrence or advance of potential difference
corrosion. Accordingly, the working environment of an apparatus
such as a hard disk drive (HDD), in particular, for which
cleanliness is required, can be made favorable, and the reliability
of the apparatus can be improved.
[0012] Further, in accordance with the invention, the arrangement
is provided such that an insulating resin coating film or a
passivation film is interposed between a rotating or fixed bearing
member and a rotary hub or a fixing frame which are formed of
metals of different types, so as to prevent the occurrence of a
local battery and prevent the occurrence or advance of potential
difference corrosion. Accordingly, the working environment of an
apparatus such as a hard disk drive (HDD), in particular, for which
cleanliness is required, can be made favorable, and the reliability
of the apparatus can be improved.
[0013] Furthermore, in accordance with the invention, the
arrangement is provided such that relief portions are respectively
provided at a joining interface between the rotary shaft and the
thrust plate and a joining interface between the bearing member and
the counter plate or a joining interface between the fixing frame
and the counter plate, and the respective members are welded in the
relief portions so as to be integrated. Accordingly, even if the
joining length of the members is relatively short, it is possible
to obtain a sufficient joining strength and improve the shock
resistance of the motor itself. As a result, the perpendicularity
of the thrust plate with respect to the rotary shaft, for example,
can be maintained stably, and the reliability of the motor can be
improved.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] In the accompanying drawings:
[0015] FIG. 1 is an explanatory cross-sectional view showing a
hard-disk driving motor of a shaft fixed type according to a first
embodiment of the present invention;
[0016] FIG. 2 is an explanatory half cross-sectional view showing a
hard-disk driving motor of a shaft rotating type according to a
second embodiment of the present invention;
[0017] FIG. 3 is an explanatory cross-sectional view showing a
hard-disk driving motor of a shaft fixed type according to a third
embodiment of the present invention;
[0018] FIGS. 4A to 4C are cross-sectional views showing the
structure for joining a rotary shaft and a thrust plate;
[0019] FIG. 5 is a half cross-sectional view showing a spindle
motor according to a fourth embodiment of the present
invention;
[0020] FIG. 6 is a cross-sectional view showing the structure for
joining the fixed shaft and the thrust plate shown in FIG. 1;
and
[0021] FIG. 7 is a half cross-sectional view showing a related
spindle motor.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022] Hereafter, a description will be given of the embodiments of
the invention. First, referring to the drawings, a description will
be given of the structure of a hard disk drive (HDD) to which the
invention is applied.
[0023] The HDD spindle motor of a shaft fixed type, which is a
first embodiment of the present invention, shown in FIG. 1 is
comprised of a stator assembly 10 serving as a fixed member and a
rotor assembly 20 serving as a rotating member which is assembled
to the stator assembly 10 from an upper side thereof in the
drawing. Of these assemblies, the stator assembly 10 has a fixing
frame 11 which is screwed down to an unillustrated fixed base. A
hollow cylindrical bearing holder 12 is formed on a substantially
central portion of the fixing frame 11 in such a manner as to be
integrally provided uprightly, and stator cores 14 are fitted to an
outer peripheral surface of the bearing holder 12. Driving coils 15
are respectively wound around salient pole portions of the stator
cores 14.
[0024] A fixed shaft 16 formed of a stainless steel (SUS 420J2;
indication based on JIS) is fixed in a shaft-fixing hole 11 a of
the fixing frame 11 in such a manner as to project upwardly. This
fixed shaft 16 is disposed concentrically with the bearing holder
12, and an upper end portion of the fixed shaft 16 is also screwed
down to the unillustrated fixed base. A bearing sleeve 21 serving
as a rotating-shaft bearing member making up a part of the rotor
assembly 20 is rotatably fitted on an outer periphery of the fixed
shaft 16, and a rotary hub 22 for mounting an unillustrated
recording medium such as a magnetic disk is joined to an outer
periphery of the bearing sleeve 21.
[0025] A cylindrical large-diameter portion 20a for joining, which
is formed in such a manner as to project outwardly in the radial
direction, is disposed in an upper end portion of the bearing
sleeve 21. A joining hole 22a, which is formed penetratingly in a
central portion of the rotary hub 22, is integrally joined to an
outer peripheral surface of the large-diameter portion 20a for
joining by means of press-fitting or shrinkage fitting. The rotary
hub 22 is formed of an aluminum group material for the purpose of
light weight, and has a cylindrical body 22e. Annular driving
magnets 22c are attached to an outer periphery of the cylindrical
body 22e with a back yoke 22b placed therebetween. These magnets
22c are disposed in such a manner as to annularly oppose outer
peripheral-side end faces of the stator cores 14 in close proximity
thereto. Further, the cylindrical body 22e has a disk-mounting
surface 22d for mounting the recording medium disk on its outer
peripheral portion.
[0026] Meanwhile, the bearing sleeve 21 is formed of a copper group
material or a stainless steel metal to facilitate drilling and the
like. A pair of bearing projections 21a serving as a pair of radial
bearings are formed on an inner periphery of a central hole, which
is provided in the bearing sleeve 21, in such a manner as to be
axially spaced apart a predetermined distance. Further,
hydrodynamic surfaces formed on inner peripheral surfaces of these
bearing projections 21a are disposed in such a manner as to
proximately oppose hydrodynamic surfaces formed on an outer
peripheral surface of the fixed shaft 16, thereby forming a pair of
radial hydrodynamic bearing portions RBa and RBb which are adjacent
to each other in the axial direction. More specifically, the
hydrodynamic surface on the bearing sleeve 21 side and the
hydrodynamic surface on the fixed shaft 16 side in each of the pair
of radial hydrodynamic bearing portions RBa and RBb are opposingly
disposed circumferentially with a very small gap of several microns
therebetween. A lubricating fluid such as oil, a magnetic fluid, or
air is charged in the bearing space having the very small gap in
such a manner as to continue in the axial direction. It should be
noted that oil is used as the lubricating fluid in this
embodiment.
[0027] A fluid storage portion 21b, which is formed by radially
recessing the inner peripheral portion of the central hole in the
bearing sleeve 21, is formed between the pair of radial
hydrodynamic bearing portions RBa and RBb, and a sufficient
quantity of lubricating fluid is stored in the fluid storage
portion 21b.
[0028] At least one of the hydrodynamic surfaces of the bearing
sleeve 21 and the fixed shaft 16 is annually recessed to form
unillustrated radial dynamic pressure generating grooves of, for
example, herringbone shape in such a manner as to be axially
divided into two blocks. Thus the lubricating fluid is pressurized
by the pumping action of the radial dynamic pressure generating
grooves during rotation to generate hydrodynamic pressure, and the
rotary hub 22 is pivotally supported in the radial direction by the
hydrodynamic pressure of the lubricating fluid.
[0029] In the axially opposite end portions of the bearing space
which form the radial hydrodynamic bearing portions RBa and RBb, a
pair of capillary seal portions are respectively disposed in such a
manner as to axially sandwich the radial hydrodynamic bearing
portions RBa and RBb. Each of these capillary seal portions is
formed by gradually enlarging the gap between the bearing sleeve 21
and the fixed shaft 16 in the radially outward direction in a
tapered manner by an inclined surface formed on the bearing sleeve
21. The dimension of the gap of the capillary seal portion disposed
on the inward side of the bearing is set to a range of 20 .mu.m to
300 .mu.m, for example. These capillary seal portions are so
arranged that the level of the lubricating fluid is located there
when the motor either rotates or is at a standstill.
[0030] A disk-shaped thrust plate 23 is secured to an illustrated
upper end portion of the fixed shaft 16. This thrust plate 23 is
disposed so as to be accommodated in a hollow cylindrical recessed
portion formed in a central portion of the upper end of the bearing
sleeve 21. Axially proximately opposing surfaces of the thrust
plate 23 and the bearing sleeve 21 in the recessed portion of the
bearing sleeve 21 are formed as hydrodynamic surfaces, thereby
forming a lower thrust hydrodynamic bearing portion SBa.
[0031] Further, a counter plate 24 formed of a large disk-shaped
member is secured to the upper end portion of the bearing sleeve 21
so as to be located in close proximity to the illustrated upper
hydrodynamic surface of the thrust plate 23. An upper thrust
hydrodynamic bearing portion SBa is formed by the hydrodynamic
surface provided on the lower surface of the counter plate 24 and
the hydrodynamic surface of the thrust plate 23 side.
[0032] Both hydrodynamic surfaces on the thrust plate 23 side in
the pair of thrust hydrodynamic bearing portions SBa and SBb which
are disposed axially adjacent to each other, and both hydrodynamic
surfaces on the bearing sleeve 21 and the counter plate 24 side
which are respectively opposed thereto, are disposed in
face-to-face relation to each other in the axial direction with
very small gaps of several microns therebetween. The lubricating
fluid such as oil, a magnetic fluid, or air is charged in the
bearing spaces having the very small gaps in such a manner as to
continue in the axial direction through outer peripheral-side
passages in the thrust plate 23.
[0033] Further, at least one of the hydrodynamic surfaces of the
thrust plate 23 on the one hand, and the hydrodynamic surfaces of
the bearing sleeve 21 and the fixed shaft 16 on the other hand, is
annually recessed to form unillustrated thrust dynamic pressure
generating grooves of, for example, herringbone shape in such a
manner as to be radially divided into two blocks. Thus the
lubricating fluid is pressurized by the pumping action of the
thrust dynamic pressure generating grooves during rotation to
generate hydrodynamic pressure, and the rotary hub 22 is pivotally
supported in the thrust direction by the hydrodynamic pressure of
the lubricating fluid.
[0034] Next, a description will be given of the technique of the
invention for preventing the potential difference corrosion which
can occur between the bearing member (bearing sleeve) and another
member which are formed of metallic materials of different
types.
[0035] As described above, the bearing sleeve 21 is formed of a
copper group material, e.g., phosphor bronze which is one of copper
alloys, while the rotary hub 22 which is integrally joined to the
bearing sleeve 21 is formed of an aluminum group material, e.g., an
aluminum material. These metals of different types are joined,
thereby forming a one-piece rotating member. A potential-difference
alleviating member A is interposed between the joined surfaces of
the bearing sleeve 21 and the rotary hub 22. This
potential-difference alleviating member A is formed of a metallic
material, such as a nickel material, whose ionization tendency in
the electrochemical series with respect to solution, e.g., plain
water (tap water), is positioned between that of copper and that of
aluminum. This potential-difference alleviating member A is formed
on at least one of the joined surfaces of the bearing sleeve 21 and
the rotary hub 22 in film form by plating processing, vapor
deposition processing, or coating.
[0036] The ionization tendency refers to the tendency whereby a
metal produces cations when coming into contact with a liquid,
particularly water, and can be quantitatively evaluated by the
standard electrode potential of the metal. The list of metals in
which their ionization tendencies with respect to solution are
arranged in the order of their magnitude is referred to as the
electrochemical series.
[0037] In a case where the metallic materials of different types
are copper and aluminum, metallic materials whose ionization
tendencies in the electrochemical series with respect to plain
water are positioned between that of copper and that of aluminum
are Co, Mo, Cr, and Ni, while metallic materials whose ionization
tendencies in the electrochemical series with respect to saline
water are positioned therebetween are Fe, Sn, Co, W, Cr, Mo, and
Ni. The ionization tendencies in the electrochemical series with
respect to solution types are thus known. Accordingly, the material
which is used as the potential-difference alleviating member A is
selected on the basis of the aqueous solution which is considered
to attach to the metals as well as the two metallic materials to be
joined.
[0038] In the above-described embodiment, supposing that the
potential-difference alleviating member A is not provided, since
the rotating member is used in which the bearing sleeve 21 formed
of a copper material and the rotary hub 22 formed of an aluminum
material are joined, if an electrolyte having a large dielectric
constant, such as water, penetrates the joint, a local battery is
formed between the metallic materials of different types. Hence,
anodic dissolution can possibly occur due to the local battery,
resulting in potential difference corrosion. In contrast, in
accordance with the invention, since the nickel film is provided as
the potential-difference alleviating member A between the bearing
sleeve 21 and the rotary hub 22, the potential difference between
the two members 21 and 22 becomes small due to the
potential-difference alleviating member A interposed between the
two members 21 and 22, thereby making it possible to prevent the
generation of the local battery and hamper the occurrence or
advance of the potential difference corrosion. This action of
preventing the potential difference corrosion is effective when one
component part is formed by joining different types of metals as in
the case of the bearing sleeve 21 and the rotary hub 22, and an
energy difference (potential difference) occurs between the joined
members.
[0039] As described above, the metal whose ionization tendency in
the electrochemical series with respect to solution is positioned
between those of two metals to be joined, i.e., the
potential-difference alleviating member A, can be selected from
among a number of materials. Hence, it suffices to select a
material to be formed by taking into consideration a desired
manufacturing method such as plating processing, vapor deposition
processing, or coating. If the material is selected from this
perspective, by merely adding such as a plating process to normal
machining and assembling processes, it becomes possible to easily
provide the potential-difference alleviating member A having a
satisfactory function.
[0040] Although, in the first embodiment, a description has been
given of a case in which a component part formed by joining metals
of different types is formed by a copper material including a
copper alloy and an aluminum material including an aluminum alloy,
the selection of these metals of different types may be changed as
required.
[0041] Meanwhile, the invention is similarly applicable to a
spindle motor of a shaft rotating type whose half cross sectional
view is shown in FIG. 2, which is a second embodiment of the
present invention.
[0042] The overall HDD spindle motor of the shaft rotating type
shown in FIG. 2 is comprised of a stator assembly 30 serving as a
fixed member and a rotor assembly 40 serving as a rotating member
assembled to the stator assembly 30 from an upper side thereof in
the drawing. Of these assemblies, the stator assembly 30 has a
fixing frame 31 which is screwed down to an unillustrated fixed
base. The fixing frame 31 is formed of an aluminum group material
to attain light weight. A bearing sleeve 33 serving as a fixed
bearing member formed in a hollow cylindrical shape is integrally
joined to the inner side of an annular mounting portion 32, which
is formed in such a manner as to be provided uprightly in a
substantially central portion of the fixing frame 31, by
press-fitting or shrinkage fitting.
[0043] The lower outer peripheral surface of the bearing sleeve 33
is formed such that its radial dimension substantially coincides
with the radial dimension of the outer peripheral surface of the
annular mounting portion 32. Stator cores 34 are fitted to an
attaching surface formed by an outer peripheral surface of the
bearing sleeve 33. Driving coils 35 are respectively wound around
salient pole portions provided in the stator cores 34. In the
embodiment shown FIG. 2, although the stator cores 34 are fitted to
the attaching surface formed by the outer peripheral surface of the
bearing sleeve 33, an arrangement may be provided such that the
annular mounting portion 32 is extended upwardly, and the stator
cores 34 are attached to an outer peripheral surface of that
annular mounting portion 32.
[0044] A rotary shaft 41 formed of a stainless steel (SUS 420J2) or
the like and making up a part of the rotor assembly 40 is rotatably
inserted in a central hole provided in the bearing sleeve 33.
Namely, hydrodynamic surfaces formed on the inner peripheral
surface of the bearing sleeve 33 are disposed in such a manner as
to proximately oppose hydrodynamic surfaces formed on the outer
peripheral surface of the rotary shaft 41, thereby forming the pair
of radial hydrodynamic bearing portions RBa and RBb which are
adjacent to each other in the axial direction. The hydrodynamic
surface on the bearing sleeve 33 side and the hydrodynamic surface
on the rotary shaft 41 side in each of the pair of radial
hydrodynamic bearing portions RBa and RBb are opposingly disposed
circumferentially with a very small gap of several microns
therebetween. A lubricating fluid such as oil, a magnetic fluid, or
air can be used in the bearing space.
[0045] The bearing sleeve 33 is formed of a copper group material
or a stainless steel to facilitate machining, and radial dynamic
pressure generating grooves of, for example, herringbone shape are
formed in its inner periphery in such a manner as to be axially
divided into two blocks. Thus a rotary hub 42 together with the
rotary shaft 41 is pivotally supported in the radial direction by
the hydrodynamic pressure of the lubricating fluid during
rotation.
[0046] The substantially cup-shaped hub 42 on which a recording
medium such as a magnetic disk is mounted is secured to one end of
the rotary shaft 41 by means of a joining member which will be
described later. The hub 42 has a hollow cylindrical portion 42a to
which the disk is fitted, as well as a disk mounting surface 42b
which expands outwardly from the lower end of the hollow
cylindrical portion 42a for mounting the disk thereon. Annular
driving magnets 25 having magnetized poles are fitted to an inner
peripheral surface of the hollow cylindrical portion 42a of the hub
42, and inner peripheral surfaces of the driving magnets 25 are
opposed to outer peripheral surfaces of the stator cores 34 with an
appropriate interval therebetween. Here, since the hub 42 is formed
of a magnetic material such as iron, the hub 42 itself can be made
to function as a back yoke for the driving magnets 25. Accordingly,
in this embodiment, since the yoke which is a separate component is
omitted, as compared with a hub 42 having an identical outside
diameter and the yoke, the inner space of the hub 42, i.e., the
space for disposing the armature, can be made large. Accordingly,
it is possible to obtain a relatively large motor torque. It should
be noted that in a case where the hub 42 is formed of a nonmagnetic
material such as an aluminum alloy, a yoke formed of a magnetic
material is interposed between the hub 42 and the driving magnets
25.
[0047] Meanwhile, a disk-shaped thrust plat 43 is secured to the
other end side, i.e., on the lower side in the drawing, of the
rotary shaft 41 by means of a joining member which will be
described later. This thrust plate 43 is disposed so as to be
accommodated in a recessed portion 33a formed in a central portion
of the lower end side of the bearing sleeve 33. The upper thrust
hydrodynamic bearing portion SBa is formed by hydrodynamic surfaces
formed by axially proximately opposing end faces of the thrust
plate 43 and the bearing sleeve 33 in the recessed portion 33a of
the bearing sleeve 33.
[0048] Further, a disk-shaped counter plate 44 larger than the
thrust plate 43 is secured in a lower end-side opening of the
bearing sleeve 33 by a joining member, which will be described
later, in such a manner as to be located in close proximity to the
illustrated upper hydrodynamic surface of the thrust plate 43.
Then, the lower thrust hydrodynamic bearing portion SBb is formed
by the hydrodynamic surface provided on an upper end face of the
counter plate 44 and the hydrodynamic surface on the thrust plate
44 side.
[0049] The hydrodynamic surfaces on the thrust plate 43 side in the
pair of thrust hydrodynamic bearing portions SBa and SBb which are
disposed axially adjacent to each other, and the hydrodynamic
surfaces on the bearing sleeve 33 and the counter plate 44 side
which are respectively opposed thereto, are disposed in
face-to-face relation to each other in the axial direction with
very small gaps of several microns therebetween. A lubricating
fluid 5 is charged in the bearing spaces having the very small gaps
in such a manner as to continue in the entire axial direction
through outer peripheral-side passages in the thrust plate 43.
[0050] At least one of the hydrodynamic surfaces of the thrust
plate 43 on the one hand, and the hydrodynamic surfaces of the
bearing sleeve 33 and the counter plate 44 on the other hand, is
annually recessed in the usual manner to form thrust dynamic
pressure generating grooves of herringbone shape or spiral shape.
Thus, when the thrust plate 43 is rotated in conjunction with the
rotation of the rotor assembly 40, the rotor assembly 40 including
the rotary shaft 41 and the hub 42 is pivotally supported in the
thrust direction by the hydrodynamic pressure of the thrust dynamic
pressure generating grooves.
[0051] As described above, the bearing sleeve 33 is formed of a
copper group material, specifically phosphor bronze, to facilitate
machining, while the fixing frame 31 which is integrally joined to
the bearing sleeve 33 is formed of an aluminum group material,
specifically an aluminum material. These metals of different types
are joined. A potential-difference alleviating member B is
interposed between the joined surfaces of the bearing sleeve 33 and
the fixing frame 31. In the same way as in the already-described
embodiment shown in FIG. 1, this potential-difference alleviating
member B is formed of a metallic material, such as a nickel
material, whose ionization tendency in the electrochemical series
is positioned between that of a copper group material and that of
an aluminum group material. This potential-difference alleviating
member B can be formed by being coated on at least one of the
joined surfaces of the bearing sleeve 33 and the fixing frame 31 in
film form by plating processing, vapor deposition processing, or
coating.
[0052] It should be noted that the potential-difference alleviating
member B may be formed by a passivation film B coated on at least
one of the joined surfaces of the bearing sleeve 33 and the fixing
frame 31.
[0053] This passivation film B is an oxide film excelling in
corrosion resistance, and can be obtained by subjecting the joined
surface of the bearing sleeve 33 or the fixing frame 31 to
electroless nickel-phosphor plating and by oxidizing and giving
passivity to the plated film by being left to stand for a
predetermined duration.
[0054] It should be note that, as for the passivation film B, the
metallic material itself forming the bearing sleeve 33 or the
fixing frame 31 may be used as the passivation film instead of
using a plating material different from the metal to be joined. For
example, an alumite film may be formed on the joined surface of the
fixing frame 31 which is formed of an aluminum material and is
joined to the bearing sleeve 33, and it is possible to prevent the
formation of a local battery in the event that an electrolyte
having a large dielectric constant, such as water, has penetrated
the joined portions of the fixing frame 31 and the bearing sleeve
33.
[0055] In this embodiment as well, the energy difference between
the bearing sleeve 33 and the fixing frame 31 in which metals of
different types are joined, i.e., the potential difference between
the two members 33 and 31, can be alleviated and lowered by the
potential-difference alleviating member B interposed between the
two members 33 and 31, thereby making it possible to prevent the
occurrence or advance of potential difference corrosion.
[0056] Next, in a third embodiment shown in FIG. 3, instead of the
potential-difference alleviating member A in the first embodiment
shown in FIG. 1, an insulating resin coating film C is interposed
between the joined surfaces of the bearing sleeve 21 and the rotary
hub 22. This resin coating film C is continuously formed over the
entire circumferential periphery ranging from the inner joined
portions of the bearing sleeve 21 and the rotary hub 22, to which
water or the like is liable to be attached, to outer exposed
surfaces of the bearing sleeve 21 on the upper and lower sides
thereof in the drawing. In the inner joined portions of the bearing
sleeve 21 and the rotary hub 22, a region is provided where the
resin coating film C is not formed and is left in a notched state,
so that the bearing sleeve 21 and the rotary hub 22 are made
electrically conductive. Accordingly, the joined surfaces of the
bearing sleeve 21 and the rotary hub 22 are made electrically
conductive at the notched portion of the resin coating film C.
[0057] In the embodiment having the above-described configuration,
since the bearing sleeve 21 and the rotary hub 22 formed of metals
of different types are electrically insulated by the resin coating
film C, even if waterdrops are attached, the local battery is not
formed. Consequently, it is possible to prevent the occurrence or
advance of potential difference corrosion. Since the attachment of
the waterdrops cause a problem in the joined portions exposed to
the outside, in this embodiment in which the resin coating film C
is continuously formed up to the outer exposed surfaces of the
bearing sleeve 21 extending continuously at the joined surfaces,
the formation of the local battery can be prevented satisfactorily
even if the electrolyte such as water is attached to the outer
exposed surfaces of the joined surfaces.
[0058] The arrangement in which the potential-difference
alleviating member or the passivation film is formed over the
entire periphery up to the outer exposed surfaces of the bearing
sleeve 21 extending continuously at the joined surfaces can be also
applied to the embodiments already described.
[0059] In this embodiment, since the bearing sleeve 21 and the
rotary hub 22 are electrically insulated by the resin coating film
C, while inside part of the joined surfaces is made electrically
conductive without the resin coating C, an arrangement can be
provided to ground the rotary hub 22 through that conductive
portion. Accordingly, even if static electricity has been generated
in the rotary hub 22, discharging can be effected smoothly, so that
damage or the like to the magnetic head due to the static
electricity can be prevented.
[0060] Such a resin coating film C is similarly applicable to the
spindle motor of the shaft rotating type shown in FIG. 2. If a
similar resin coating film C is formed between the bearing sleeve
33 and the fixing frame 31, it is possible to obtain similar effect
and advantages.
[0061] It should be noted that the invention can be similarly
applied to any portion if it is a portion where metals of different
types are joined. For example, in the embodiment shown in FIG. 2, a
potential-difference alleviating member may be interposed between
the joining portions of the rotary shaft 41 and the rotary hub
42.
[0062] Next, a description will be given of the technique of the
invention for enhancing the joining strength of component parts
even if joining length is small.
[0063] FIGS. 4A to 4C are diagrams explaining the structure for
joining the rotary shaft 41 and the thrust plate 43 of the spindle
motor in accordance with the second embodiment.
[0064] If the spindle motor is made thin and is designed to a
height of, for example, 5 mm or thereabouts, the joining length of
the rotary shaft 41 and the thrust plate 43 becomes less than 1 mm.
Accordingly, the joining strength becomes weak since a sufficient
joining length cannot be obtained even if the joining of the two
members is effected by the press-fitting method or the shrinkage
fitting method. If press-fitting is effected by providing a large
press-fitting allowance, there is a possibility of deterioration of
the perpendicularity of the thrust plate 43 with respect to the
rotary shaft 41, so that a press-fitting allowance of more than a
predetermined amount cannot be provided. Accordingly, in this
embodiment, after the rotary shaft 41 and the thrust plate 43 are
press-fitted or inserted by an appropriate press-fitting force to
such an extent that the deterioration of perpendicularity does not
occur, the joining interface portions of the two members are welded
together. At this juncture, an axially recessed relief portion 70
is annularly formed in advance at the surface portion of the
joining interface portion, and the rotary shaft 41 and the thrust
plate 43 are welded in this relief portion 70.
[0065] The shape of the relief portion 70 at the joining interface
between the rotary shaft 41 and the thrust plate 43 is formed in
one of the shapes shown in FIGS. 4A, 4B, and 4C. Namely, in FIG.
4A, a tapered surface 41 a is formed over the entire periphery
around the outer peripheral edge of a tip of the rotary shaft 41,
while an inner peripheral surface 43a of a central hole of the
thrust plate 43 is adjacent to the tapered surface 41 a.
Accordingly, the relief portion 70 of a wedge-shaped cross section
is formed, and the two members are welded in this relief portion
70. It should be noted that the tapered surface 41a at the tip of
the rotary shaft 41 also functions as a guide portion at the time
the thrust plate 43 is press-fitted to the rotary shaft 41.
[0066] FIG. 4B shows an example in which the tapered surface 41a is
formed over the entire periphery around the outer peripheral edge
of the tip of the rotary shaft 41, while a tapered surface 43b is
also formed around the inner peripheral edge of the central hole of
the thrust plate 43. The two members are welded together in this
relief portion 70.
[0067] In FIG. 4C, the tapered surface 41a is formed over the
entire periphery around the outer peripheral edge of the tip of the
rotary shaft 41, while a flat recess 43c is formed around the
central hole at a bottom surface portion of the thrust plate 43, a
tapered surface 43d being formed around its outer periphery.
Further, the hydrodynamic surface SBb is formed on its outer side.
In the case of this example, a trapezoidal relief portion 70 is
formed, and the two members are welded together in this relief
portion 70.
[0068] Each of the relief portions 30 formed at the joining
interface between the rotary shaft 41 and the thrust plate 43 is
formed at a position offset from the region where the dynamic
pressure generating grooves are formed in the thrust plate 43.
Accordingly, the dynamic pressure generating grooves are not
subjected to limitations by the relief portion 70, and it is
possible to allow desired thrust hydrodynamic pressure to be
demonstrated.
[0069] Further, as for the welding position, the entire periphery
may be welded, or welding may be effected partially at a plurality
of locations, insofar as the welding position or positions are
located in the relief portion 70.
[0070] As the welding process, it is possible to adopt a plasma
welding process, an arc welding process such as TIG welding, an
electron beam welding process typified by laser welding, or the
like. In this embodiment, the laser welding process is adopted in
which the basic materials to be joined are welded together by
fusing the two materials. In this laser welding process, a laser
beam emitted from a laser oscillator is focused by using a
plurality of mirrors, and is radiated to the joining interface to
join the two members. According to such an electron beam welding
process, since a welding rod used in the arc welding process is
made unnecessary, the buildup of the basic material in the joined
interface portions can be minimized. Further, even if a slight
buildup has occurred, since the axially recessed relief portion 70
is provided at the joining interface, the built-up portion is
accommodated in the relief portion 70, and can be prevented from
projecting from the hydrodynamic surface toward the counter plate
44 side (see FIG. 2). Accordingly, it is desirable to set the size
of the relief portion 70 by taking the size of the built-up portion
into consideration.
[0071] If the arrangement is provided such that the built-up
portion is accommodated in the relief portion 70, the built-up
portion is prevented from being located excessively close to the
counter plate 44, and when the rotor assembly 40 including the
thrust plate 43 is rotated, it is possible to prevent the built-up
portion from colliding against the bearing surface of the counter
plate 44. Further, although the joined portions of the rotary shaft
41 and the thrust plate 43 are located in the lubricating fluid 5,
since the two members are joined by welding without using an
organic solvent such as an adhesive agent, the catalytic action
with respect to the lubricating fluid 5 does not occur, so that the
characteristics of the lubricating fluid 5 such as oil do not
deteriorate.
[0072] Next, a description will be given of the structure for
joining the bearing sleeve 33 and the counter plate 44 of the
spindle motor shown in FIG. 2.
[0073] The disk-shaped counter plate 44 is secured in the opening
at the lower end of the bearing sleeve 33 formed in a hollow
cylindrical shape. The counter plate 44 has its outer peripheral
surface press-fitted to the bearing sleeve 33 with an appropriate
press-fitting force, and an outer peripheral edge of its upper end
face abuts against a stepped portion 33b of the bearing sleeve 33.
Further, an axially recessed relief portion 60 is formed in the
portions of the obverse (lower) sides of the joining interface
portions of the bearing sleeve 33 and the counter plate 44, and the
two members are integrated by welding in the relief portion 60. As
the welding process, in the same way as the above-described process
of joining the rotary shaft 41 and the thrust plate 43, it is
possible to use an electron beam welding process typified by laser
welding. Accordingly, at least one of the bearing sleeve 33 and the
counter plate 44 is fused by being irradiated with an electron
beam, thereby joining the two members.
[0074] Further, the shape of the relief portion 60 may be
wedge-shaped, triangular, trapezoidal, or other cross-sectional
shapes in the same way as the shape of the stepped surface of the
relief portion 70 formed at the joining interface between the
rotary shaft 41 and the thrust plate 43 shown in FIGS. 4A to 4C. It
should be noted that a tapered guide portion 33c should preferably
be formed at an inner peripheral edge of the opening of the bearing
sleeve 33 so as to facilitate the press-fitting or insertion of the
counter plate 44. Further, as for the welding position, it is
preferable to weld the entire periphery so as to seal the
opening.
[0075] In the structure for joining the bearing sleeve 33 and the
counter plate 44, the relief portion 60 is provided which is
capable of accommodating the built-up portion formed by joining the
joining interface portions, and welding is effected in this relief
portion 60 to integrate the two members, as described above.
Therefore, even if the built-up portion is formed by joining, the
attempt to make the overall motor thin is not hampered.
Furthermore, since the bearing sleeve 33 and the counter plate 44
are joined by welding, it is possible to reliably prevent the
leakage of the lubricating fluid 5 without using an O-ring or an
adhesive agent.
[0076] Next, a detailed description will be given of the structure
for joining the rotary shaft 41 and the hub 42 of the spindle motor
in accordance with this embodiment. As shown in FIG. 2, the joining
length of the rotary shaft 41 and the hub 42 is longer than the
joining length of the rotary shaft 41 and the thrust plate 43, but
if the overall height of the motor is shortened, the joining length
of the rotary shaft 41 and the hub 42 also inevitably becomes
short. Consequently, since the joining strength of the rotary shaft
41 and the hub 42 declines. Accordingly, in this embodiment, in the
same way as the structure for joining the rotary shaft 41 and the
thrust plate 43, the two members are joined by welding after the
rotary shaft 41 and the hub 42 are press-fitted with an appropriate
press-fitting force.
[0077] Here, if press-fitting is effected by providing a large
press-fitting allowance of the hub 42 with respect to the rotary
shaft 41, distortion occurs in the hub 42 due to the press-fitting
stress. Consequently, the perpendicularity of the hub 42 with
respect to the rotary shaft 41, specifically the perpendicularity
of the disk-mounting surface 42b of the hub 42 with respect to the
rotary shaft 41, becomes deteriorated, so that the problem of
occurrence of runout exceeding an allowable range is liable to
occur when the disk is mounted on the hub 41 and is rotatively
driven.
[0078] Accordingly, in this embodiment, an axially recessed relief
portion 50 is formed at the joining interface between the rotary
shaft 41 and the hub 42, and the two members are joined by laser
welding in this relief portion 50. The relief portion 50 is formed
by a tapered surface 41b formed at a corner of the tip of the
rotary shaft 41 and a tapered surface 42c formed at an inner
peripheral edge of a shaft-attaching hole 28 of the hub 42. Of
these tapered surfaces, the tapered surface 41b of the rotary shaft
41 also functions are a guide portion at the time of press-fitting
the hub 42 to the rotary shaft 41. It should be noted that, in this
embodiment, since a damper guide 29 for guiding a damper (not
shown) for holding the disk is provided on an upper end face of the
hub 42 in such a manner as to axially project slightly from the
joining interface between the rotary shaft 41 and the hub 42, the
attempt to make the motor thin is not hampered even if the relief
portion 50 is not formed. Further, as for the welding position, the
entire periphery of the joining interface may be welded, or welding
may be effected partially at a plurality of locations.
[0079] By virtue of the above-described joining structure, since
the joining strength of the rotary shaft 41 and the hub 42 can be
sufficiently increased without forcibly press-fitting the rotary
shaft 41 and the hub 42, the shock resistance of the motor
improves, and the perpendicularity of the disk mounting surface 42b
of the hub 42 with respect to the rotary shaft 41 can be maintained
with high accuracy.
[0080] FIG. 5 is a half cross-sectional view showing a spindle
motor in accordance with a fourth embodiment of the invention. In
FIG. 5, those arrangements having common functions to those of the
spindle motor shown in FIG. 2 are denoted by the same reference
numerals, and a detailed description thereof will be omitted.
[0081] The stator cores 34 each having the coil 35 wound
therearound are attached to the outer periphery of a tubular holder
32' provided uprightly in the center of the fixing frame 31. This
tubular holder 32' is formed to be axially longer than the tubular
holder 32 shown in FIG. 2, and the bearing sleeve 33 and the
counter plate 44 are fixed to its inner periphery. Namely, although
the counter plate 44 in FIG. 2 is joined to the opening of the
bearing sleeve 33, in FIG. 5, the counter plate 44 is joined to the
opening of the tubular holder 32' of the fixing frame 31 after
being press-fitted thereto with an appropriate press-fitting
force.
[0082] In joining the counter plate 44 to the tubular holder 32',
the axially recessed relief portion 60 is provided at the joining
interface between the two members, and the counter plate 44 and the
tubular holder 32' are welded in this relief portion 60 to
integrate the two members. As the welding process, the arc welding
process or the electron beam welding process is adopted as
described above. Preferably, however, at least one of the counter
plate 44 and the tubular holder 32' is fused by the electron beam
welding process typified by laser welding so as to join the two
members. By joining the two members in the relief portion 60 in
this manner, since a portion projecting from the bottom surface of
the fixing frame 31 or the counter plate 44 is not formed, the
attempt to make the motor thin is not hampered. Further, since the
fixed shaft 31 and the counter plate 44 are firmly joined by
welding, the shock resistance also improves.
[0083] In this embodiment as well, the rotary shaft 41 and the
thrust plate 43 are joined in the same way as in the
above-described embodiments. Namely, one end of the rotary shaft 41
is press-fitted in the central hole of the thrust plate 43, the
relief portion 70 is formed at the joining interface between the
rotary shaft 41 and the thrust plate 43, and the two members are
integrated by welding in the relief portion 70.
[0084] Further, in the joining of the rotary shaft 41 and the hub
42, in the same way as the joining of the rotary shaft 41 and the
thrust plate 43, the rotary shaft 41 is press-fitted in the central
hole of the hub 42, the relief portion 50 is formed at the joining
interface between the rotary shaft 41 and the hub 42, and the two
members are integrated by welding in the relief portion 50.
Incidentally, this relief portion 50 may be omitted depending on
the shape of the hub 42.
[0085] As described above, in accordance with the spindle motor
shown in FIG. 5 as well, it is possible to obtain a sufficient
joining strength even if the joining length of the rotary shaft 41
and the thrust plate 43 and the joining length of the tubular
holder 32' of the fixing frame 31 and the counter plate 44 are
relatively short. Accordingly, it is possible to stably maintain
the perpendicularity of the thrust plate 43 with respect to the
rotary shaft 41. Moreover, even if projections are formed by
welding, since the projections are respectively accommodated in the
relief portions 60 and 70, the attempt to make the overall motor
thin is not hampered. Further, since the rotary shaft 41 and the
thrust plate 43 are joined by welding, even if the lubricating
fluid 5 is oil, catalytic action does not occur, and the
characteristics of the lubricating fluid 5 do not deteriorate.
[0086] Next, a description will be given of the structure for
joining the fixed shaft 16 and the thrust plate 23 in FIG. 1. After
the bearing sleeve 21 formed integrally with the hub 22 is fitted
over the fixed shaft 16 provided uprightly on the fixing frame 11,
the annular thrust plate 23 is press-fitted to the fixed shaft 16
with an appropriate press-fitting force. Subsequently, as the
joining interface portions of the fixed shaft 16 and the thrust
plate 23 are welded together, the two members are joined. As shown
in FIG. 6, the relief portion 70 which is recessed below the
hydrodynamic surface is annularly formed at the peripheral edge of
the central hole corresponding to the joining interface portion on
the thrust plate 23 side. The laser welding process is desirable as
this welding, and the thrust plate 23 formed of a copper group
material, a stainless steel metal, or the like is fused so as to
undergo metallic fusion with the fixed shaft 16. The welding with
the fixed shaft 16 is performed in the relief portion 70, and the
arrangement provided is such that even if a local projection occurs
due to welding, it does not project above the hydrodynamic
surface.
[0087] By virtue of such an arrangement, since a sufficient joining
strength can be obtained even if the joining length of the fixed
shaft 16 and the thrust plate 23 is relatively short, the
perpendicularity of the thrust plate 23 with respect to the fixed
shaft 16 can be maintained stably, so that the reliability of the
motor improves. Moreover, since the axially recessed relief portion
70 is provided at the joining interface, and the two members are
integrated by welding in this relief portion 70, the attempt to
make the overall motor thin is not hampered. Further, since the
joining interface portions located in such a manner as to be
contiguous to the lubricating fluid 5 for generating hydrodynamic
pressure are welded, even if the lubricating fluid 5 is oil,
catalytic action does not occur, and the characteristics of the
lubricating fluid 5 do not deteriorate.
[0088] Although a description has been given above specifically of
the embodiments of the invention devised by the present inventors,
the invention is not limited by the foregoing embodiments, and it
goes without saying that various modifications are possible without
departing from the scope of the invention.
[0089] For example, although, in the above-described embodiment, an
example has been shown in which joining is accomplished by welding
in such a way that the counter plate 44 closes the bearing sleeve
33 or the opening of the tubular holder 32' of the fixing frame 31,
part of the joining interface may be welded to secure joining
strength, and the entire periphery of the joining interface may be
sealed by an adhesive agent. Consequently, it is possible to
reliably prevent the leakage of the lubricating fluid.
[0090] Furthermore, the invention is similarly applicable to a
spindle motor than a hard-disk driving motor, e.g., a CD-ROM
driving motor and a polygon-mirror driving motor.
* * * * *