U.S. patent application number 11/229537 was filed with the patent office on 2006-03-23 for method for assembling bearing of spindle motor.
This patent application is currently assigned to Nidec Corporation. Invention is credited to Yasuaki Hada, Takayuki Ishino, Hironori Itsusaki, Akira Kagata, Isao Misu, Toshiya Tsujita.
Application Number | 20060059689 11/229537 |
Document ID | / |
Family ID | 36072311 |
Filed Date | 2006-03-23 |
United States Patent
Application |
20060059689 |
Kind Code |
A1 |
Kagata; Akira ; et
al. |
March 23, 2006 |
Method for assembling bearing of spindle motor
Abstract
A method for assembling a bearing structure is provided. The
bearing structure includes a housing of a cylindrical shape with
one closed end, made up of a cylindrical portion and a cap portion.
The method includes the steps of inserting a shaft integrated with
a rotor hub into a sleeve and fixing a stopper member to the distal
end of the shaft so as to make a hub assembly, inserting the sleeve
into the housing, exerting a force on the sleeve to move toward the
bottom of the housing until an end surface of the sleeve abuts the
stopper member, pulling one of the housing and the hub assembly
from the other relatively in the axial direction by a predetermined
distance, and fixing the sleeve to the housing.
Inventors: |
Kagata; Akira; (Minami-ku,
JP) ; Misu; Isao; (Minami-ku, JP) ; Itsusaki;
Hironori; (Minami-ku, JP) ; Tsujita; Toshiya;
(Minami-ku, JP) ; Hada; Yasuaki; (Minami-ku,
JP) ; Ishino; Takayuki; (Minami-ku, JP) |
Correspondence
Address: |
WESTERMAN, HATTORI, DANIELS & ADRIAN, LLP
1250 CONNECTICUT AVENUE, NW
SUITE 700
WASHINGTON
DC
20036
US
|
Assignee: |
Nidec Corporation
Kyoto
JP
|
Family ID: |
36072311 |
Appl. No.: |
11/229537 |
Filed: |
September 20, 2005 |
Current U.S.
Class: |
29/898.02 |
Current CPC
Class: |
H02K 15/00 20130101;
F16C 17/107 20130101; Y10T 29/49639 20150115; F16C 35/02 20130101;
H02K 7/085 20130101; F16C 33/107 20130101; F16C 17/02 20130101 |
Class at
Publication: |
029/898.02 |
International
Class: |
B21K 1/10 20060101
B21K001/10 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 22, 2004 |
JP |
2004-274862 |
Claims
1. A method for assembling a bearing of a spindle motor, the
bearing comprising: a housing of a cylindrical shape with one
closed end, made up of a cylindrical portion and a cap portion for
closing one end of the cylindrical portion; a sleeve of a hollow
cylindrical shape fixed to the inner surface of the housing; a
shaft inserted in the sleeve in a rotatable manner; a rotor hub
having substantially a disk shape formed integrally with the shaft
and connected to the proximal end of the shaft at the middle
portion; and a stopper member fixed to the distal end of the shaft
so as to be positioned at the bottom side of the housing, wherein a
radial gap is formed between the sleeve and the shaft, and an axial
gap is formed between the opening end surface of the housing and
the rotor hub as well as between the stopper member and an end
surface of the sleeve, the method comprising the steps of: (a)
inserting the shaft integrated with the rotor hub into the sleeve
and fixing the stopper member to the distal end of the shaft so as
to make a hub assembly; (b) inserting the sleeve into the housing;
(c) exerting a force on the sleeve to move toward the bottom of the
housing until an end surface of the sleeve abuts the stopper
member; (d) pulling one of the housing and the hub assembly from
the other relatively in the axial direction by a predetermined
distance; and (e) fixing the sleeve to the housing.
2. The method according to claim 1, wherein the housing is formed
to have a wall thickness that is thinner at the cap portion than at
the cylindrical portion.
3. The method according to claim 1, wherein lubricating oil is kept
between the opening end surface of the housing and the rotor hub so
that a thrust fluid dynamic pressure bearing is formed.
4. The method according to claim 1, wherein lubricating oil is kept
between the opening end surface of the housing and the rotor hub as
well as between the stopper member and the end surface of the
sleeve so that thrust fluid dynamic pressure bearings are
formed.
5. The method according to claim 1, wherein the step (b) includes
inserting the sleeve into the housing until the opening end surface
of the housing abuts the rotor hub, and the step (d) includes
pulling one of the housing and the hub assembly from the other
relatively in the axial direction by a distance that is equal to an
axial gap between the opening end surface of the housing and the
rotor hub plus an axial gap between the stopper member and an end
surface of the sleeve after assembling.
6. The method according to claim 1, wherein the sleeve is made of a
ferromagnetic material or a material containing a ferromagnetic
material, and the step (c) includes placing a magnet outside the
bottom of the housing so as to exert the force on the sleeve.
7. The method according to claim 1, wherein the step (c) includes
applying an inertial force to the housing and the hub assembly as a
lump so as to exert the force on the sleeve.
8. The method according to claim 1, wherein the step (b) includes
applying an adhesive to the outer surface of the sleeve or the
inner surface of the housing before inserting the sleeve into the
housing, and the steps (c) and (d) are performed before the
adhesive is cured, and the step (e) includes curing the adhesive to
fix the sleeve to the housing.
9. The method according to claim 8, further comprising the step,
between the steps (d) and (e), of curing a part of the adhesive
between the outer surface of the sleeve and the inner surface of
the housing as temporary fixing.
10. The method according to claim 8, wherein the step (b) includes
applying an adhesive that is cured in a short time for temporary
fixing to a part and applying an adhesive that is cured in a long
time to the other part of the outer surface of the sleeve or the
inner surface of the housing.
11. The method according to claim 1, further comprising the step,
after the step (e), of filling lubricating oil in a space including
a radial gap formed between the sleeve and the shaft and an axial
gap between the opening end surface of the housing and the rotor
hub as well as between the stopper member and an end surface of the
sleeve.
12. The method according to claim 9, further comprising the step,
after the step (e), of filling lubricating oil in a space including
a radial gap formed between the sleeve and the shaft and an axial
gap between the opening end surface of the housing and the rotor
hub as well as between the stopper member and an end surface of the
sleeve.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a method for assembling a
bearing of a spindle motor that is used for driving a recording
medium such as a hard disk.
[0003] 2. Description of the Prior Art
[0004] A bearing structure utilizing fluid dynamic pressure has
become a mainstream as a bearing of a spindle motor for driving and
rotating a recording medium in a hard disk driving device or a
removable disk driving device. A fluid dynamic pressure bearing,
e.g., a radial fluid dynamic pressure bearing has a structure in
which lubricating oil as a fluid is filled in a gap between a shaft
and a sleeve, and a pressure of the fluid (dynamic pressure) is
generated when the shaft rotates. In addition, it is also common to
adopt a thrust fluid dynamic pressure bearing as a thrust bearing
in the axis direction, in which lubricating oil is filled in a gap
between a stator and a rotor in the axis direction, and a dynamic
pressure is generated when the shaft rotates.
[0005] In addition, miniaturization of a spindle motor has been
realized along with downsizing of a hard disk driving device or the
like. As a bearing structure of the spindle motor, one-piece design
of the shaft and the rotor hub has been proposed and studied to
make products. FIG. 8 shows an example of a miniaturized spindle
motor. Its bearing includes a housing that has a cylindrical shape
with one closed end made up of a cylindrical member 101 and a cap
member 102 combined with each other, a sleeve 103 having a hollow
cylindrical shape fixed to the inner surface of the cylindrical
member 101, a shaft 104 disposed inside the sleeve 103 in a
rotatable manner, a rotor hub 105 having substantially a disk shape
formed integrally with the shaft 104 and connected to the proximal
end of the shaft 104 at the middle portion, and a stopper member
106 fixed to the distal end of the shaft so as to be positioned at
the bottom side of the housing.
[0006] A radial gap is formed between the sleeve 103 and the shaft
104, while an axial gap is formed between an opening end surface of
the housing and the rotor hub 105 as well as between a stopper
member 106 and an end surface of the sleeve 103. A space including
these gaps is filled with lubricating oil (fluid).
[0007] The outer surface of the shaft 104 or the inner surface of
the sleeve 103 is provided with grooves for gathering lubricating
oil arranged in the rotation direction (for example, a plurality of
herringbone grooves having a doglegged shape). These grooves make
up a structure for generating a dynamic pressure of the lubricating
oil when the shaft 104 rotates (i.e., a radial fluid dynamic
pressure bearing 109). Two radial fluid dynamic pressure bearings
109 are disposed separately in the axial direction.
[0008] In addition, a first thrust fluid dynamic pressure bearing
111 is formed between the opening end surface of the housing and
the rotor hub 105 for generating a dynamic pressure of the
lubricating oil by similar grooves. A second thrust fluid dynamic
pressure bearing 112 is formed between the stopper member 106 and
the end surface of the sleeve 103 for generating a dynamic pressure
of the lubricating oil by similar grooves. There are various forms
and combinations that can be adopted as the fluid dynamic pressure
bearing. There is a case where only the radial fluid dynamic
pressure bearing 109 is provided. In another case, the radial fluid
dynamic pressure bearing 109 and one of the thrust fluid dynamic
pressure bearings 111 and 112 are provided. In still another case,
each of the upper and the lower sides of the stopper member 106 is
provided with the thrust fluid dynamic pressure bearing.
[0009] The bearing having the structure described above is
assembled in the following procedure. First, the sleeve 103 is
inserted in the cylindrical member 101 of the housing, and the
sleeve 103 is fixed to the inner surface of the cylindrical member
101 by adhesive or other means. In this step, a tool is used for
precise registration between the cylindrical member 101 and the
sleeve 103 in the axial direction. This registration is important
for securing an appropriate axial gap between the stopper member
106 and the end surface of the sleeve 103 when the axial gap
between the opening end surface of the housing and the rotor hub
105 is adjusted appropriately.
[0010] Next, the shaft 104 integrated with the rotor hub 105 is
inserted in the sleeve 103, and the stopper member 106 is fixed to
the distal end of the shaft 104. For example, an external thread
formed on the outer surface of a shank portion of the stopper
member 106 engages an internal thread formed on the inner surface
of the shaft 104 at the distal end so that they are fixed
precisely. Finally, the cap member 102 is fixed to the cylindrical
member 101 and they are sealed by laser welding or other means so
that a housing of a cylindrical shape with one closed end is made
up of the cylindrical member 101 and the cap member 102. Then,
lubricating oil is filled in a space that includes a radial gap
between the sleeve 103 and the shaft 104, an axial gap between the
opening end surface of the housing and the rotor hub 105, and an
axial gap between the stopper member 106 and the sleeve 103.
[0011] The above-mentioned conventional bearing structure of the
spindle motor adopts the shaft and the rotor hub that are
integrated as one member. For the purpose of precise registration
of the housing (the cylindrical member 101) and the sleeve 103 in
the axial direction, it is necessary to assemble them in the
following order. The cylindrical member 101 must be fixed to the
sleeve 103 first by using a tool. After the shaft 104 is inserted
in the sleeve 103, the stopper member 106 is fixed to the shaft
104. Then, the cap member 102 is seamed to the cylindrical member
101. Therefore, the housing of the cylindrical shape with one
closed end (like a cup) must be made up of two separate members,
i.e., the cylindrical member 101 and the cap member 102.
[0012] However, the structure of the housing made up of two
separate members that are the cylindrical member 101 and the cap
member 102 is disadvantageous in cost and administration because of
its increased number of components compared with the housing of a
cup shape in which the cylindrical member and the cap member are
integrated. In addition, facilities and steps of laser welding or
bonding are necessary for seaming the cylindrical member 101 with
the cap member 102 in the assembly process. Moreover, if the seamed
state (sealed state) of the cylindrical member 101 with the cap
member 102 is incomplete, lubricating oil may leak from the
incomplete portion. Therefore, an inspection step such as a helium
leak test is necessary for checking the sealed state of the seamed
portion.
SUMMARY OF THE INVENTION
[0013] An object of the present invention is to provide a method
for assembling a bearing having a novel structure including a
component of integrated rotor hub and shaft and a housing of a
cylindrical shape with one closed end made up of integrated
cylindrical portion and cap portion.
[0014] A bearing structure of a spindle motor according to the
present invention includes a housing of a cylindrical shape with
one closed end, made up of a cylindrical portion and a cap portion
for closing one end of the cylindrical portion, a sleeve of a
hollow cylindrical shape fixed to the inner surface of the housing,
a shaft inserted in the sleeve in a rotatable manner, a rotor hub
having substantially a disk shape formed integrally with the shaft
and connected to the proximal end of the shaft at the middle
portion, and a stopper member fixed to the distal end of the shaft
so as to be positioned at the bottom side of the housing, in which
a radial gap is formed between the sleeve and the shaft, and an
axial gap is formed between the opening end surface of the housing
and the rotor hub as well as between the stopper member and an end
surface of the sleeve.
[0015] According to this structure, the housing of a cylindrical
shape with one closed end can be formed as one body of component by
press molding, for example, which is advantageous in cost and
administration compared with the conventional housing made up of
the cylindrical member and the cap member. In addition, it is not
necessary to seam the cylindrical member with the cap member in the
assembling process, and an inspection step for checking a sealed
state of the seamed part is not necessary too, unlike the
conventional structure.
[0016] A method according to the present invention for assembling
the bearing having the above-described structure includes the steps
of (a) inserting the shaft integrated with the rotor hub into the
sleeve and fixing the stopper member to the distal end of the shaft
so as to make a hub assembly, (b) inserting the sleeve into the
housing, (c) exerting a force on the sleeve to move toward the
bottom of the housing until an end surface of the sleeve abuts the
stopper member, (d) pulling one of the housing and the hub assembly
from the other relatively in the axial direction by a predetermined
distance, and (e) fixing the sleeve to the housing.
[0017] According to this method, a distance of separating the
housing from the hub assembly in the step (d) can be controlled
precisely. Therefore, high accuracy of at least the axial gap
between the stopper member and an end surface of the sleeve can be
secured.
[0018] In addition, the assembling method of the present invention
is applied preferably to a bearing structure in which the housing
is formed to have a wall thickness that is thinner at the cap
portion than at the cylindrical portion. If the housing of a
cylindrical shape with one closed end is formed by a press molding
as described above, it is easy to realize a wall thickness that is
thinner at the cap portion of the bottom than at the cylindrical
portion. Thus, a dimension of the entire spindle motor in the axial
direction can be reduced (to be lower profile). Alternatively, if
the dimension of the entire spindle motor in the axial direction is
restricted, a length of the radial bearing in the axial direction
can be increased as much as possible so that rigidity against a
load that causes inclination of the bearing can be enhanced.
[0019] Moreover, the assembling method of the present invention is
used preferably for a bearing structure in which lubricating oil is
kept between the opening end surface of the housing and the rotor
hub so that a thrust fluid dynamic pressure bearing is formed.
According to this structure, the thrust fluid dynamic pressure
bearing can improve durability of the entire bearing.
[0020] Moreover, the assembling method of the present invention is
used preferably for a bearing structure in which lubricating oil is
kept between the opening end surface of the housing and the rotor
hub as well as between the stopper member and the end surface of
the sleeve so that thrust fluid dynamic pressure bearings are
formed. This structure is a so-called double thrust structure,
which can further improve durability of the entire bearing. In
addition, it is necessary to secure high accuracy of the axial gap
between the opening end surface of the housing and the rotor hub as
well as between the stopper member and an end surface of the sleeve
in this structure. The assembling method of the present invention
enables to secure high accuracy even if the one body of housing of
a cylindrical shape with one closed end is used.
[0021] Moreover, in the method of the present invention for
assembling a bearing as described above, the step (b) preferably
includes inserting the sleeve into the housing until the opening
end surface of the housing abuts the rotor hub, and the step (d)
preferably includes pulling one of the housing and the hub assembly
from the other relatively in the axial direction by a distance that
is equal to an axial gap between the opening end surface of the
housing and the rotor hub plus an axial gap between the stopper
member and an end surface of the sleeve after assembling. According
to this method, the axial gap between the opening end surface of
the housing and the rotor hub plus the axial gap between the
stopper member and an end surface of the sleeve can be controlled
precisely, so that high accuracy of the axial gap can be
secured.
[0022] Moreover, in the method of the present invention for
assembling a bearing as described above, it is preferable that the
sleeve be made of a ferromagnetic material or a material containing
a ferromagnetic material, and that the step (c) include placing a
magnet outside the bottom of the housing so as to exert the force
on the sleeve. This shows an example of means for exerting the
force on the sleeve, in which an attraction force of a magnet is
utilized for moving the sleeve toward the bottom of the
housing.
[0023] Moreover, in the method of the present invention for
assembling a bearing as described above, the step (c) preferably
includes applying an inertial force to the housing and the hub
assembly as a lump so as to exert the force on the sleeve. An
example of a method for applying an inertial force may include
fixing the housing and the hub assembly as a lump to a rotating
tool so that a centrifugal force due to the rotation is applied to
them as an inertial force. By fixing them to the rotating tool with
the housing toward the outside, the inertial force is applied to
the sleeve in the direction toward the bottom of the housing. Thus,
the sleeve can be moved toward the bottom of the housing.
[0024] Moreover, in the method of the present invention for
assembling a bearing as described above, it is preferable that the
step (b) include applying an adhesive to the outer surface of the
sleeve or the inner surface of the housing before inserting the
sleeve into the housing, and that the steps (c) and (d) be
performed before the adhesive is cured, and that step (e) include
curing the adhesive to fix the sleeve to the housing. According to
this method, viscosity of the adhesive before curing can be
utilized for performing registration of the sleeve with the housing
effectively and precisely.
[0025] Moreover, it is preferable that the method of the present
invention for assembling a bearing further includes the step,
between the steps (d) and (e), of curing a part of the adhesive
between the outer surface of the sleeve and the inner surface of
the housing as temporary fixing. When a thermosetting adhesive is
used for example, a part of an area to which the adhesive is
applied is heated rapidly for curing and temporary fixing. Then,
the entire assembly is put in a curing oven so that the entire
adhesive is cured. In this way, the temporary fixing can prevent
the relative position between the sleeve and the housing in the
axial direction after the registration from shifting before the
adhesive is cured.
[0026] Moreover, in the method of the present invention for
assembling a bearing as described above, the step (b) preferably
includes applying an adhesive that is cured in a short time for
temporary fixing to a part and applying an adhesive that is cured
in a long time to the other part of the outer surface of the sleeve
or the inner surface of the housing. According to this method, the
relative position between the sleeve and the housing in the axial
direction after the registration is fixed temporarily by the
adhesive for temporary fixing and then is fixed securely by the
adhesive that is cured in a long time. Therefore, similarly to the
effect described above, the relative position between the sleeve
and the housing in the axial direction after the registration can
be prevented from shifting before the adhesive (for production
fixing) is cured.
[0027] Moreover, it is preferable that the method of the present
invention for assembling a bearing preferably further include the
step, after the step (e), of filling lubricating oil in a space
including a radial gap formed between the sleeve and the shaft and
an axial gap between the opening end surface of the housing and the
rotor hub as well as between the stopper member and an end surface
of the sleeve. Thus, it is possible to realize a bearing structure
with high durability, in which a radial bearing and a thrust
bearing are filled with lubricating oil.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] FIG. 1 is a cross section showing a bearing structure of a
spindle motor according to an example of the present invention.
[0029] FIGS. 2(a) and 2(b) show examples of a cross-sectional shape
of a housing.
[0030] FIG. 3 shows assembling steps sequentially of the bearing
structure according to the present invention.
[0031] FIGS. 4(a) and 4(b) show examples of a force that is exerted
on the sleeve.
[0032] FIG. 5 shows an example of a method for adjusting an axial
gap.
[0033] FIGS. 6(a) and 6(b) show a preferred example in which the
sleeve is fixed to the housing by adhesive.
[0034] FIG. 7 shows another example in which the sleeve and the
housing are fixed to each other by adhesive.
[0035] FIG. 8 shows a conventional bearing structure of a spindle
motor.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0036] Hereinafter, examples of the present invention will be
described with reference to the attached drawings. Note that when a
position or a direction of each member is expressed by up, down,
right and left in the following description, it merely means a
position or a direction in a drawing and does not mean a position
or a direction in a real apparatus.
[0037] FIG. 1 is a cross section showing a bearing structure of a
spindle motor according to an example of the present invention.
This bearing structure includes a housing 11 of a cylindrical shape
with one closed end, a sleeve 12 of a hollow cylindrical shape
fixed to the inner surface of the housing 11, a shaft 13 that is
inserted in the sleeve 12 in a rotatable manner, a rotor hub 14
having substantially a disk shape formed integrally with the shaft
13 and connected to the proximal end of the shaft 13 at the middle
portion, and a stopper member 15 fixed to the distal end of the
shaft 13 so as to be positioned at the bottom side of the housing
11.
[0038] The housing 11 has a cylindrical shape with one closed end
(like a cup) and is made up of a cylindrical portion and a cap
portion for closing one end of the cylindrical portion. The housing
11 can be formed by press molding of a sheet metal, for example. It
is advantageous in cost and administration compared with the
conventional housing made up of the cylindrical member and the cap
member. In addition, it is not necessary to seam the cylindrical
member with the cap member in the assembling process, and an
inspection step for checking a sealed state of the seamed part is
not necessary too, unlike the conventional structure.
[0039] FIGS. 2(a) and 2(b) show examples of a cross-sectional shape
of a housing 11. In the example shown in FIG. 2(a), a wall
thickness of the cap portion 11a is substantially the same as a
wall thickness of the cylindrical portion 11b (at the part close to
the cap portion 11a except the upper part). In the example shown in
FIG. 2(b), on the contrary, a wall thickness of the cap portion 11a
is smaller than a wall thickness of the cylindrical portion 11b.
When the housing 11 is formed by press molding, it is easy to make
a wall thickness of the cap portion 11a smaller than a wall
thickness of the cylindrical portion 11b as shown in FIG. 2(b).
Thus, an axial direction of the entire spindle motor can be reduced
to respond a request for a low profile. Alternatively, if the
dimension of the entire spindle motor in the axial direction is
restricted, a length of the radial bearing in the axial direction
can be increased as much as possible so that rigidity against a
load that causes inclination of the bearing can be enhanced. Note
that a wall thickness of the upper portion of the cylindrical
portion 11b increases gradually toward the upper end (opening end),
and the reason of it is to constitute a capillary seal portion for
preventing lubricating oil from leaking as described later.
[0040] The sleeve 12 is preferably a porous sintered body made of
metal powder or metal oxide powder, which is molded and sintered,
and then impregnated with lubricating oil. In particular, it is
preferable that the sleeve 12 is made of a ferromagnetic material
or a material containing a ferromagnetic material in order that the
sleeve 12 is forced to move by a magnet in an assembling process
that will be described later. The sleeve 12 is fixed to the inner
surface of the housing 11 by means of adhesive or the like. On this
occasion, precise registration between the housing 11 and the
sleeve 12 in the axial direction is necessary.
[0041] The shaft 13 is formed integrally with the rotor hub 14
having substantially a disk shape and extends from the middle
portion of the rotor hub 14 perpendicularly. Therefore, it is
possible to improve accuracy of perpendicularity and the like of
the shaft 13 with respect to the rotor hub 14. In addition, the
entire spindle motor can be adapted to be small and compact. It is
also advantageous in cost and administration compared with the
structure made up of separated bodies of the shaft and the rotor
hub. In addition, it is not necessary to connect them in the
assembling process so that the number of man-hour can be
reduced.
[0042] The rotor hub 14 includes a disk portion 14a of a disk-like
shape extending in the radial direction from the proximal end
(upper end) of the shaft 13, a cylindrical wall portion 14b
extending in the axial direction from the rim portion of the disk
portion 14a coaxially with the shaft 13 and a flange portion 14c
extending in a step shape outward in the radial direction further
from the cylindrical wall portion 14b. This spindle motor is used
for a hard disk driving device, so a recording medium (hard disk)
to be driven to rotate is put on and fixed to the upper surface of
the rotor hub 14 (the upper surface of the disk portion 14a and the
flange portion 14c). In addition, a rotor magnet 16 of a ring shape
is fixed to the outer surface of the cylindrical wall portion 14b
and the lower surface of the flange portion 14c by means of
adhesive or the like. A stator armature 17 is arranged so as to
face the rotor magnet 16 with a predetermined gap in the radial
direction.
[0043] The stopper member 15 includes a shank portion 15a that is
inserted in and fixed to the distal end (lower end) of the shaft 13
and a flange portion 15b of a disk-like shape extending in the
radial direction from the proximal end of the shank portion 15a,
which are formed integrally. The distal end of the shaft 13 is
provided with an internal thread while the shank portion 15a of the
stopper member 15 is provided with an external thread, which are
engaged with each other so that the stopper member 15 is fixed to
the distal end of the shaft 13. Alternatively, it is possible to
use means of adhesive or the like for fixing them to each
other.
[0044] The stopper member 15 has a function of preventing the shaft
13 and the rotor hub 14 from being off (detached) upward from the
sleeve 12 and the housing 11 by abutting the lower end surface of
the sleeve 12 at the upper surface of the flange portion 15b. The
shaft 13 and the rotor hub 14 are integrated to be one component,
and the disk portion 14a of the rotor hub 14 covers the upper
opening of the housing 11. In addition, the cap portion 11a and the
cylindrical portion 11b of the housing 11 are integrated to be one
component. Therefore, assembling order of the housing 11, the
sleeve 12, the shaft 13 (the rotor hub 14) and the stopper member
15 has a restriction, and it is necessary to devise a method of
assembling them as being described later in detail.
[0045] A radial gap is formed between the sleeve 12 and the shaft
13 of the bearing structure. In addition, an axial gap is formed
between the opening end surface of the cylindrical portion 11b of
the housing 11 and the lower surface of the disk portion 14a of the
rotor hub 14. Furthermore, another axial gap is formed between the
upper surface of the flange portion 15b of the stopper member 15
and the end surface of the sleeve 12 as well as between the lower
surface of the flange portion 15b and the upper surface of the cap
portion 11a of the housing 11. A space including these gaps is
filled with lubricating oil (fluid).
[0046] Therefore, the lubricating oil filled mainly inside the
housing 11 migrates from the opening end surface of the cylindrical
portion 11b to the outside of the housing 11, and a surface of the
lubricating oil is positioned in the gap between the outer surface
of the cylindrical portion 11b and the inner surface of the
cylindrical wall portion 14b of the rotor hub 14. As understood
from FIG. 1 and FIGS. 2(a) and 2(b), the housing 11 is formed so
that a wall thickness of the cylindrical portion 11b increases
gradually toward the upper end (opening end) at the upper portion.
Therefore, the gap between the outer surface of the cylindrical
portion 11b and the inner surface of the cylindrical wall portion
14b of the rotor hub 14 increases gradually from the upper end
toward the lower end. Thus, a capillary seal portion is formed for
preventing leakage of the lubricating oil. In other words, leakage
of the lubricating oil from the gap between the outer surface of
the cylindrical portion 11b and the inner surface of the
cylindrical wall portion 14b of the rotor hub 14 to the outside
(downward) can be prevented by surface tension of the lubricating
oil and atmospheric pressure.
[0047] The outer surface of the shaft 13 or the inner surface of
the sleeve 12 is provided with grooves for gathering the
lubricating oil arranged in the rotation direction (herringbone
grooves). More specifically, a plurality of grooves having a
doglegged shape is formed sequentially in the circumferential
direction. When the shaft 13 rotates, the lubricating oil is led
into both ends of the doglegged groove and gathered to middle
portion (inflection point) of the doglegged groove so that a
pressure of the lubricating oil (a dynamic pressure) is generated
at this point. Thus, a fluid dynamic pressure bearing is realized,
in which the shaft 13 is retained by the sleeve 12 via the
lubricating oil so that the shaft 13 can rotate at high speed. Two
of such radial fluid dynamic pressure bearings 19 are disposed at
two positions separated in the axial direction.
[0048] In addition, a first thrust fluid dynamic pressure bearing
20 that has a function similar to that of the radial fluid dynamic
pressure bearing 19 is formed between the opening end surface of
the cylindrical portion 11b of the housing 11 and the lower surface
of the disk portion 14a of the rotor hub 14. Grooves that are
formed on the opening end surface of the cylindrical portion 11b of
the housing 11 or on the lower surface of the disk portion 14a of
the rotor hub 14 may be the herringbone grooves like the radial
fluid dynamic pressure bearing 19 or a helical groove. The helical
groove has a function of gathering the lubricating oil inward in
the radial direction against a centrifugal force that is exerted on
the lubricating oil when the rotor hub 14 rotates. A second thrust
fluid dynamic pressure bearing 21 that has a structure and a
function similar to those of the first thrust fluid dynamic
pressure bearing 20 is formed between the upper surface of the
flange portion 15b of the stopper member 15 and an end surface of
the sleeve 12.
[0049] Note that there are various forms and combinations of
structures concerning these fluid dynamic pressure bearings 19, 20
and 21. There is a case where only the radial fluid dynamic
pressure bearing 19 is provided. In another case, the radial fluid
dynamic pressure bearing 19 plus one of the thrust fluid dynamic
pressure bearings 20 and 21 are provided. In addition, there is
another case in which each of the upper and the lower sides of the
stopper member 15 is provided with the thrust fluid dynamic
pressure bearing. The present invention can be applied to any of
these various forms of the fluid dynamic pressure bearings.
[0050] Next, a method for assembling the above-mentioned bearing
structure will be described. First, an outline of the assembling
method will be described with reference to FIG. 3. FIG. 3 shows
assembling steps sequentially of the bearing structure according to
an example of the present invention. Note that FIG. 3 shows the
components of the bearing structure upside down with respect to
FIG. 1, for matching with the real assembling works.
[0051] In the first step (a), the shaft 13 integrated with the
rotor hub 14 is inserted in the sleeve 12, and the stopper member
15 is fixed to the distal end of the shaft 13 to be a hub assembly
23. In the actual work, the sleeve 12 is engaged with the shaft 13
of the rotor hub 14 that is placed so that the distal end of the
shaft 13 faces upward, and then the stopper member 15 is fixed to
the distal end of the shaft 13 by means of thread engagement,
adhesive or the like. Note that lipophobic liquid is applied to a
predetermined portion of the rotor hub 14 in advance.
[0052] In the next step (b), the sleeve 12 of the hub assembly 23
is inserted in the housing 11. In the actual work, the housing 11
is engaged with the sleeve 12 of the hub assembly 23 that is placed
so that the stopper member 15 faces upward. Note that the housing
11 and the sleeve 12 are formed with accuracy in dimensions so that
the inner surface of the housing 11 (the cylindrical portion 11b)
can make substantially an intimate contact with the outer surface
of the sleeve 12. In order to fix them to each other with adhesive,
the sleeve 12 is inserted into the housing 11 after adhesive is
applied to the inner surface of the housing 11 or the outer surface
of the sleeve 12.
[0053] In the next step (c), the sleeve 12 is moved toward the
bottom of the housing 11 (upward in FIG. 3) by exerting a force on
the sleeve 12 utilizing a magnetic force or an inertial force that
will be described later. This movement is stopped when an end
surface of the sleeve 12 (the upper end surface in FIG. 3) abuts
the stopper member 15 (the flange portion 15b). If adhesive exists
between the inner surface of the housing 11 and the outer surface
of the sleeve 12, this step has to be done before the adhesive is
cured.
[0054] In the next step (d), the housing 11 is pulled relatively
from the hub assembly 23 in the axial direction by a predetermined
distance. In the example shown in FIG. 3, the housing 11 is held by
a tool and pulled upward by a predetermined distance from the hub
assembly 23 that is fixed to the lower side. This step also has to
be done before adhesive is cured if it exists between the inner
surface of the housing 11 and the outer surface of the sleeve 12.
This step enables precise adjustment of the axial gap between the
rotor (the rotor hub 14 and the stopper member 15) and the stator
(the sleeve 12).
[0055] After that, the sleeve 12 is fixed to the housing 11 in the
step (e). If adhesive exists between them, they are fixed to each
other by curing the adhesive. For example, if thermosetting
adhesive is used, the entire assembly is put in a curing oven and
is baked at a predetermined temperature. Instead of the fixing
method using adhesive, a laser welding method can be used for
fixing the sleeve 12 to the housing 11. In this case, for example,
plural small through holes for passing a laser beam are formed in
the disk portion 14a of the rotor hub 14, and the laser beam
passing through the holes can irradiate a seaming portion of the
sleeve 12 with the housing 11. Finally, lubricating oil is filled
in a space including the radial gap between the sleeve 12 and the
shaft 13, the axial gap between the opening end surface of the
housing 11 and the rotor hub 14, and the axial gap between the
stopper member 15 and the end surface of the sleeve 12 (mainly
inside the housing 11).
[0056] FIGS. 4(a) and 4(b) show examples of a force that is exerted
on the sleeve 12 in the step (c). In the example shown in FIG.
4(a), a magnetic force is used for exerting on the sleeve 12. In
order to use this method, the sleeve 12 must be made of a
ferromagnetic material or a material containing a ferromagnetic
material. Then, a magnet MG is placed outside the bottom of the
housing 11, so that the sleeve 12 is attracted to move toward the
bottom of the housing. The state before the magnet MG is placed
where the lower end surface of the sleeve 12 abuts the rotor hub 14
becomes the state after the magnet MG is placed where the upper end
surface of the sleeve 12 abuts the stopper member 15 as shown in
FIG. 4(a).
[0057] In the example shown in FIG. 4(b), a centrifugal force
(inertial force) is utilized for exerting on the sleeve 12. More
specifically, the entire assembly of the housing 11 and the hub
assembly 23 is fixed to the rotating tool RT, which is rotated at a
predetermined angular velocity .omega.. In this case, the entire
assembly is fixed so that the housing 11 faces outside of the
rotation. A centrifugal force that is proportional to a mass and a
radius of rotation and a square of the angular velocity .omega. is
exerted on each member, but the housing 11 and the hub assembly 23
are fixed to the rotating tool RT. Therefore, only the sleeve 12 is
forced to move toward the bottom of the housing. As a result, the
state where the upper end surface of the sleeve 12 abuts the
stopper member 15 is obtained as shown in FIG. 4(b). Note that
after the rotating tool RT stops the above-mentioned state of the
relative position is maintained by a frictional force between the
inner surface of the housing 11 and the outer surface of the sleeve
12 or by viscosity of the adhesive that exists between them.
[0058] FIG. 5 shows an example of a method for adjusting an axial
gap in the step (d). In this example, the hub assembly 23 is placed
on a table and fixed to the same so that the housing 11 faces
upward, and the bottom of the housing 11 (the cap portion 11a) and
the outer surface of the cylindrical portion 11b are held by a
vacuum chuck VC. In the example shown in FIG. 5, the magnet MG
placed on the outside of the bottom surface of the housing 11 is
held together. Then, the housing 11 held by the vacuum chuck VC is
pulled up by a predetermined distance corresponding to a desired
axial gap AG so that the housing 11 is away from the hub assembly
23.
[0059] In a preferred embodiment of the adjusting method, the
sleeve 12 is inserted into the housing 11 until the opening end
surface of the housing 12 abuts the disk portion 14a of the rotor
hub 14 in the step (b). This state is a reference position (start
position), and from this reference position the housing 12 is
pulled away from the hub assembly 23 in the axial direction in the
step (d) by a distance corresponding to the axial gap between the
opening end surface of the housing 11 and the rotor hub 14 plus the
axial gap between the stopper member 15 and the end surface of the
sleeve 12 after assembling. Thus, the sum of these two axial gaps
is adjusted precisely as the axial gap AG that is a predetermined
distance mentioned above.
[0060] FIGS. 6(a) and 6(b) show a preferred example in which the
sleeve 12 is fixed to the housing 11 by adhesive. FIG. 6(b) is an
enlarged view of FIG. 6(a). In this example, when adhesive is
applied to the inner surface of the housing 11 or the outer surface
of the sleeve 12 in the step (b) mentioned above, adhesive that is
cured in a short time for temporary fixing is applied to a part of
the applied area while adhesive that is cured in a long time is
applied to the other part of the area. More specifically, anaerobic
adhesive (e.g., an acrylic adhesive) that is cured in a short time
(approximately 2-3 minutes) is applied to a minor part area AR1
that is closer to the bottom of the housing 11 within the
adhesive-applied area AR between the sleeve 12 and the housing 11,
while thermosetting adhesive (e.g., an epoxy adhesive) is applied
to the other major part area AR2.
[0061] In step (d), the state where the axial gap is adjusted is
maintained 1-3 minutes, so that the adhesive for temporary fixing
applied to a part area AR1 is cured. After that, the vacuum chuck
VC can be removed from the housing 11 while the relative position
between the sleeve 12 and the housing 11 is maintained by the
temporary fixing. Then, the entire assembly is put in the curing
oven and baked. Thus, the thermosetting adhesive applied to the
major part area AR2 is cured so that the sleeve 12 and the housing
11 are fixed to each other.
[0062] FIG. 7 shows another example in which the sleeve 12 and the
housing 11 are fixed to each other by adhesive. The FIG. 7
corresponds to the enlarged view of shown in FIG. 6(b). In this
example, when adhesive is applied to the inner surface of the
housing 11 or the outer surface of the sleeve 12 in the
above-mentioned step (b), thermosetting adhesive (e.g., an epoxy
adhesive) is applied to the entire adhesive-applied area AR. Then,
a heater HT is disposed at the inner surface of vacuum chuck VC at
the distal end portion that contacts the outer surface of the
cylindrical portion 11b of the housing 11.
[0063] In the step (d), electric power is supplied to the heater HT
of the vacuum chuck VC at the distal end portion in the state where
the axial gap is adjusted. Then, the cylindrical portion 11b of the
housing 11 is heated by the heater HT, and the heat conducts to the
thermosetting adhesive. As a result, a part of the thermosetting
adhesive is rapidly heated and cured as to work for temporary
fixing. After that, the vacuum chuck VC can be removed from the
housing 11 while the relative position between the sleeve 12 and
the housing 11 is maintained by the temporary fixing. Then, the
entire assembly is put in the curing oven and baked. Thus, the
thermosetting adhesive is completely cured so that the sleeve 12
and the housing 11 are fixed to each other.
[0064] Although examples of the present invention are described
together with some variations above, the present invention can be
embodied variously without being limited to the above-described
examples and variation. In addition, materials and shapes of each
member that are shown in the above description of examples are
merely examples, and it should not be interpreted that a structure
of the present invention is limited to those materials and
shapes.
* * * * *