U.S. patent application number 11/630410 was filed with the patent office on 2008-11-27 for shaft member for fluid lubrication bearing apparatuses and a method for producing the same.
Invention is credited to Kunihiro Hayashi, Toshiyuki Mizutani, Natsuhiko Mori, Takeshi Shimazaki, Kiyoshi Shimizu, Koji Yamagata, Nobuyoshi Yamashita.
Application Number | 20080292228 11/630410 |
Document ID | / |
Family ID | 36036400 |
Filed Date | 2008-11-27 |
United States Patent
Application |
20080292228 |
Kind Code |
A1 |
Yamashita; Nobuyoshi ; et
al. |
November 27, 2008 |
Shaft Member for Fluid Lubrication Bearing Apparatuses and a Method
for Producing the Same
Abstract
A shaft member for hydrodynamic bearing apparatuses which can
restore the pressure balance in a thrust bearing gap formed on both
axial sides of the flange portion in an early stage is provided at
low costs. A shaft material 10 integrally having a shaft portion 11
and a flange portion 12 is formed as a through-hole 19 opening to
its both end faces 12a, 12b on the flange portion 12 of the shaft
material 10 is formed in a common forging step. As a result, the
through-hole 29 is formed to open to the inner diameter side of
these bearing gap W1, W2 avoiding thrust bearing gaps W1, W2 formed
on both end faces of the flange portion 22 of the shaft member 2 as
a finished product.
Inventors: |
Yamashita; Nobuyoshi;
(Kuwana-shi, JP) ; Mori; Natsuhiko; (Kuwana-shi,
JP) ; Mizutani; Toshiyuki; (Kuwana-shi, JP) ;
Shimazaki; Takeshi; (Awara-shi, JP) ; Yamagata;
Koji; (Awara-shi, JP) ; Shimizu; Kiyoshi;
(Awara-shi, JP) ; Hayashi; Kunihiro; (Awara-shi,
JP) |
Correspondence
Address: |
WENDEROTH, LIND & PONACK, L.L.P.
2033 K STREET N. W., SUITE 800
WASHINGTON
DC
20006-1021
US
|
Family ID: |
36036400 |
Appl. No.: |
11/630410 |
Filed: |
September 7, 2005 |
PCT Filed: |
September 7, 2005 |
PCT NO: |
PCT/JP05/16399 |
371 Date: |
June 13, 2007 |
Current U.S.
Class: |
384/107 |
Current CPC
Class: |
F16C 35/02 20130101;
B21K 1/12 20130101; F16C 17/107 20130101; F16C 33/107 20130101;
F16C 2220/46 20130101; F16C 3/02 20130101; B24B 7/16 20130101; F16C
2226/12 20130101; Y10T 29/49348 20150115; F16C 2226/60 20130101;
F16C 33/14 20130101; B24B 5/01 20130101; F16C 2220/70 20130101 |
Class at
Publication: |
384/107 |
International
Class: |
F16C 32/00 20060101
F16C032/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 8, 2004 |
JP |
2004-261436 |
Sep 8, 2004 |
JP |
2004-261457 |
Claims
1. A shaft member for hydrodynamic bearing apparatuses comprising a
flange portion, and being supported in a non-contact manner in the
thrust direction by the pressure produced by hydrodynamic effect of
a fluid which occurs in a thrust bearing gap on both axial sides of
the flange portion, a through-hole opening to both end faces of the
flange portion being formed on the flange portion, and the inner
periphery of the through-hole being processed by plastic
processing.
2. A shaft member for hydrodynamic bearing apparatuses according to
claim 1 further comprising a shaft portion formed integrally with
the flange portion by forging.
3. A shaft member for hydrodynamic bearing apparatuses according to
claim 1, wherein the through-hole is formed in the vicinity of the
shaft portion.
4. A hydrodynamic bearing apparatus comprising a shaft member
according to claim 1; a bearing sleeve into which the shaft member
is inserted at its inner periphery; a radial bearing portion which
produces pressure by the hydrodynamic effect of a fluid which
occurs in a radial bearing gap between the outer periphery of the
shaft portion and the inner periphery of the bearing sleeve to
support the shaft portion in the radial direction in a non-contact
manner; a first thrust bearing portion which produces pressure by
the hydrodynamic effect of a fluid occurring in the thrust bearing
gap on one end side of the flange portion to support the flange
portion in the thrust direction in a non-contact manner; and a
second thrust bearing portion which produces pressure by the
hydrodynamic effect of the fluid occurring in the thrust bearing
gap on the other end side of the flange portion to support the
flange portion in the thrust direction in a non-contact manner.
5. A hydrodynamic bearing apparatus according to claim 4, wherein
hydrodynamic grooves for producing the hydrodynamic effect of the
fluid are formed asymmetrically in the axial direction on one of
the outer circumferential surface of the shaft portion facing the
radial bearing gap and the inner periphery face of the bearing
sleeve opposing this outer circumferential surface.
6. A motor comprising a hydrodynamic bearing apparatus according to
claim 4; a rotor magnet and a stator coil.
7. A method for producing a shaft member for hydrodynamic bearing
apparatuses which comprises a shaft portion and a flange portion
and is supported in a non-contact manner by the pressure produced
by hydrodynamic effect of a fluid which occurs in a thrust bearing
gap on both axial sides of the flange portion in the thrust
direction, the method comprising integrally forming the shaft
portion and the flange portion by forging, and forming a
through-hole opening to both end faces of the flange portion on the
flange portion by forging, and these forging being performed
simultaneously.
8. A metallic shaft member for fluid lubrication bearing
apparatuses in which a threaded hole is formed on its one end
portion and a radial bearing face facing a radial bearing gap is
formed on the outer periphery, wherein said threaded hole is formed
by plastic processing.
9. A shaft member for fluid lubrication bearing apparatuses
according to claim 8, wherein said threaded hole has a prepared
hole formed by a forging process; and a thread portion formed on
the opening side of said prepared hole by a rolling process.
10. A shaft member for fluid lubrication bearing apparatuses
according to claim 9, wherein said prepared hole comprises a
conical surface; and a cylinder face which is disposed on the
opening side of said conical surface and is smoothly continuous
with said conical surface via a radially curved surface.
11. A shaft member for fluid lubrication bearing apparatuses
according to claim 10, wherein said conical surface has a shape
with its top removed.
12. A shaft member for fluid lubrication bearing apparatuses
according to claim 8, wherein the shaft portion and the flange
portion are integrally formed by forging.
13. A shaft member for fluid lubrication bearing apparatuses
according to claim 8, wherein the coaxiality of the center line of
the pitch circle of said thread portion is 0.2 mm or lower.
14. A fluid lubrication bearing apparatus comprising a shaft member
for fluid lubrication bearing apparatuses according to claim 13;
and a sleeve member into which said shaft member is inserted at its
inner periphery and which forms the radial bearing gap between
itself and said shaft member, the fluid lubrication bearing
apparatus retaining the shaft member and the sleeve member in a
non-contact manner by a lubricating film of a fluid produced in
said radial bearing gap.
15. A motor comprising a fluid lubrication bearing apparatus
according to claim 14; a rotor magnet and a stator coil.
16. A method for producing a shaft member for fluid lubrication
bearing apparatuses which comprises a threaded hole formed on its
one end and a radial bearing face formed on its outer periphery
facing a radial bearing gap, the method comprising forming a
prepared hole of the threaded hole by forging on a metallic shaft
material, and then forming a thread portion in the prepared hole by
rolling to form said threaded hole.
17. A method for producing a shaft member for fluid lubrication
bearing apparatuses according to claim 16, wherein said shaft
material is formed and said prepared hole is formed in a common
forging step.
18. A metallic shaft member for fluid lubrication bearing
apparatuses which comprises a shaft portion and a flange portion,
at least the shaft portion being formed by forging, and the shaft
portion having a concave formed on its tip face, the concave
comprising a plastically processed surface.
19. A shaft member for fluid lubrication bearing apparatuses
according to claim 18, wherein the concave has a shape whose
diameter gradually decreases from the tip of the shaft portion
toward the center of the shaft portion.
20. A fluid lubrication bearing apparatus comprising a shaft member
for fluid lubrication bearing apparatuses according to claim 18;
and a radial bearing gap formed between the outer circumferential
surface of the shaft portion and the face facing the same, the
apparatus relatively rotatably supporting said shaft member by a
lubricating film of a fluid which occurs in a radial bearing
gap.
21. A method for producing a metallic shaft member for fluid
lubrication bearing apparatuses which comprises a shaft portion and
a flange portion, the method comprising forming the shaft portion
by forging, and forming a concave at the tip portion of the shaft
portion by plastic processing during the forging process to cause
the tip portion of the shaft portion to overhang by a plastic
flow.
22. A method for producing a shaft member for fluid lubrication
bearing apparatuses according to claim 21, wherein the concave is
formed by plastic processing to cause the tip portion of the shaft
portion to overhang until the tip portion reaches at least a final
finished shape.
23. A method for producing a shaft member for fluid lubrication
bearing apparatuses according to claim 22, wherein the final
finished shape of the tip portion of the shaft portion is defined
by the outer circumferential surface of the tip of the shaft
portion, the tip face of the shaft portion and a chamfer between
the two faces.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a shaft member for fluid
lubrication bearing apparatuses which relatively rotatably supports
a shaft member in the radial direction by a lubricating film of a
fluid which occurs in a radial bearing gap and a method for
producing the same.
[0002] Fluid lubrication bearings of this type are roughly
classified into two groups: a hydrodynamic bearing comprising a
hydrodynamic pressure producing means for producing hydrodynamic
pressure in a lubricating oil in a bearing gap; and so-called
cylindrical bearings (bearings comprising a perfectly circular
bearing face) not comprising a hydrodynamic pressure producing
means.
[0003] For example, a fluid lubrication bearing apparatus
incorporated in a spindle motor of a disk drive unit such as HDD is
provided with a radial bearing portion which rotatably supports a
shaft member in the radial direction in a non-contact manner; and a
thrust bearing portion which rotatably supports the shaft member in
the thrust direction in a non-contact manner. a bearing
(hydrodynamic bearing) which is provided with grooves for producing
a hydrodynamic pressure (hydrodynamic groove) on the inner
periphery face of a bearing sleeve or on the outer circumferential
surface of the shaft member is used as a radial bearing portion. As
a thrust bearing portion, for example, both end faces of the flange
portion of the shaft member or a hydrodynamic bearing provided with
hydrodynamic grooves on the face facing it (an end face of the
bearing sleeve, an end face of a bottom member fixed on a housing,
the inner bottom face of the bottom of the housing or the like) is
used (for example, refer to patent document 1: Japanese Unexamined
Patent Publication No. 2002-61641). Alternatively, as the thrust
bearing portion, a bearing having the structure in which one end
face of the shaft member is supported in a contact manner by a
bottom member (so-called pivot bearing) is used in some cases (for
example, refer to patent document 2: Japanese Unexamined Patent
Publication No. 1999-191943).
[0004] In a spindle motor of this type, a clamper for clamping a
disk-shaped information recording medium such as magnetic disks
(hereinafter referred to simply as a disk) between a disk hub and
itself is attached to the edge of the shaft member. The clamper is
attached on the shaft member by screwing into a threaded hole
formed on one edge of the shaft member through the clamper (for
example, refer to patent document 3: Japanese Unexamined Patent
Publication No. 2000-235766).
[0005] Recently, to deal with increased information recording
density and higher rotational speed in information appliances,
higher rotational accuracy is required for the above spindle motor
for information appliances. To meet this demand, higher rotational
accuracy is also required for a fluid lubrication bearing apparatus
incorporated into the above spindle motor. At the same time, with
the demand for lower price of information appliances, reduced
production costs of the above fluid lubrication bearing apparatus
are strongly desired recently.
[0006] By the way, in order to stably exert the rotational
performance of a fluid lubrication bearing apparatus (hydrodynamic
bearing apparatus) for a long term, it will be important to control
the radial bearing gap and thrust bearing gap in which the pressure
of the fluid for supporting the shaft member occurs highly
accurately. For example, when the thrust bearing gap is formed on
both side of the flange portion in the axial direction as mentioned
above, to maintain the thrust support of the shaft member in a
stable state, the pressure for the thrust support on one end face
side of the flange portion and the pressure for thrust support on
the other end face side need to be brought into balance so that the
sliding contact of the end face of the flange portion and the face
facing it is avoided as much as possible. Higher accuracy of the
thrust bearing gap can be achieved by processing the end face of
the flange portion facing this, hydrodynamic grooves and the like
highly accurately, but merely increasing processing accuracy will
inappropriately result in higher costs.
[0007] Moreover, examples of methods for forming a threaded hole on
the shaft member include a method comprising forming a prepared
hole of the threaded hole on the shaft material by cutting, and a
thread cutting is worked relative to this prepared hole. However,
by this method, cutting powders produced when the prepared hole is
cut are accumulated at the bottom of the threaded hole, and cutting
powders cannot be completely removed even if the threaded hole is
cleaned after the process. Accordingly, the cutting powders
remaining inside the threaded hole deposit to other components as
contaminants when other components are mounted or a bearing
apparatus is assembled, and may get in the fluid (for example,
lubricating oil, etc.) filling the inside of the bearing apparatus
after being assembled. Alternatively, if the cutting powders
deposited to other components (contamination) are further
transferred to disks, they may cause disk crash. Moreover, removal
of cutting powders requires complicated and numerous cleaning
steps, leading to an increase in costs.
[0008] Moreover, to deal with cost reduction required for the above
fluid lubrication bearing apparatus, various cost reducing measures
are examined for the component parts of fluid lubrication bearing
apparatuses. For example, as for the shaft member, an article
comprising the shaft portion and the flange portion integrally
formed by forging to produce a near net shape is known (for
example, refer to patent document 4: Japanese Unexamined Patent
Publication No. 2004-347126).
BRIEF SUMMARY OF THE INVENTION
[0009] On one hand, forging is a method having excellent
processability and cost performance as mentioned above, but on the
other hand, due to its characteristics, required dimensional
accuracy may not be obtained depending on the shape of the shaft
member.
[0010] More specifically, the forging process includes compressing
a material to deform it in a specific direction into a
predetermined shape. For example, when the pressing direction in
forging is the same as the longitudinal direction of the material,
compressive force imparted to one end of the material is not
sufficiently transmitted to the other end, and thus plastic flow at
the other end may be rendered insufficient. This prevents the
deformation enough to attain a desired shape, preventing to obtain
high forming accuracy.
[0011] In particular, with recent demand for increased capacity
disk apparatuses, a fluid lubrication bearing apparatus
(hydrodynamic bearing apparatus) which can load a plurality of
disks and is integrated in a spindle motor, the use of an elongated
shaft member compared to those known is examined to cope with an
increase in moment load. However, its elongation tends to cause
problems in the plastic flow abobe mentioned more evidently.
Therefore, it is difficult to produce a shaft member having both
elongated length and high dimensional accuracy at low costs at the
moment.
[0012] A first object of the present invention is to provide a
shaft member for hydrodynamic bearing apparatuses which can restore
the pressure balance in a thrust bearing gap formed on both side of
a flange portion in the axial direction in an early stage at low
costs.
[0013] A second object of the present invention is to provide a
shaft member for fluid lubrication bearing apparatuses which can
prevent contaminants from depositing to bearing component parts and
prevent contaminants from getting inside a bearing apparatus as
much as possible at low costs.
[0014] A third object of the present invention is to provide a
shaft member for fluid lubrication bearing apparatuses which has
high dimensional accuracy and can be elongated at low costs.
[0015] To achieve the first object, the present invention provides
a shaft member for hydrodynamic bearing apparatuses, the shaft
member comprising a flange portion and being supported in a
non-contact manner in the thrust direction by the pressure produced
by hydrodynamic effect of a fluid which occurs in a thrust bearing
gap on both axial sides of the flange portion, a through-hole
opening to its both end faces being formed on the flange portion,
and the inner periphery of the through-hole being processed by
plastic processing.
[0016] In the present invention, as stated above, a through-hole
opening to its both end faces is formed on the flange portion.
Hence, when the fluid pressure in the thrust bearing gap on an
axial end side is extremely increased for any reason, the fluid
(for example, lubricating oil) flows into the thrust bearing gap on
the other axial end side via the through-hole formed on the flange
portion. Accordingly, pressure balance in both thrust bearing gaps
is restored at an early stage to maintain the width of the thrust
bearing gaps appropriately, and the sliding friction between the
end face of the flange portion and the face facing it can be
prevented beforehand.
[0017] An example of the methods of forming the through-hole on the
flange portion includes cutting. However, cutting suffers a long
cycle time, whereby processing efficiency is lowered and costs are
increased. Moreover, cutting inevitably produces cutting powders,
which may get in the fluid as contaminants. In order to prevent
that, a cleaning process of the shaft member needs to be
additionally performed after cutting, resulting in increased costs.
In particular, as the diameter of the flange portion is several
millimeters in the above hydrodynamic bearing apparatus used in
information appliances, the diameter of the through-hole will be as
minute as several tens to several hundreds micrometers accordingly.
In this case, it is difficult to completely remove cutting powders
after cutting, and therefore a careful cleaning step or other
process is necessary, which inevitably raises the costs.
[0018] In contrast, plastic processing typically including forging
have shorter cycle time compared to cutting in general, and can
process very efficiently. Moreover, since cutting powders are not
produced unlike in cutting, cleaning step is unnecessary.
Therefore, forming the through-hole by plastic processing can
greatly reduce the costs. In this case, the inner periphery of the
through-hole will be a face subjected to plastic processing. As a
face subjected to plastic processing has a good roughness, smooth
flow of the fluid in the through-hole without performing a special
post-treatment can be ensured.
[0019] The through-hole is desirably formed in the vicinity of the
shaft portion. By forming the through-hole in the vicinity of the
shaft portion, the passage of the fluid between the two thrust
bearing gaps is also ensured on the inner diameter side of the
flange portion. The regulating function of the pressure balance
between the two thrust bearing gaps can be increased, as well as
the fluid passage (an annular gap between the outer circumferential
surface of the flange portion and the inner periphery face of the
housing) on the outer diameter side of the flange portion which is
originally there. From this perspective, the through-hole desirably
opens to the inner diameter side of the radial center of the thrust
bearing gap. In this case, the through-hole is desirably disposed
so that it opens at a position avoiding the thrust bearing gap
between the region in which the hydrodynamic grooves are formed and
the face facing it (the inner diameter side of the thrust bearing
gap) to prevent the so-called drop of the hydrodynamic pressure
(loss of the hydrodynamic pressure). If it is difficult to make the
through-hole open to said position due to a spatial limit or any
other factor, it may open to a position overlapping the thrust
bearing gap. However, it is desirable to avoid, if possible, a drop
in the hydrodynamic pressure also in this case.
[0020] The above a shaft member for hydrodynamic bearing
apparatuses, for example, can be provided as a hydrodynamic bearing
apparatus comprising a shaft member; a bearing sleeve into which
this shaft member is inserted at its inner periphery; a radial
bearing portion which produces pressure by the hydrodynamic effect
of a fluid which occurs in a radial bearing gap between the outer
periphery of the shaft portion and the inner periphery of the
bearing sleeve to support the shaft portion in the radial direction
in a non-contact manner; a first thrust bearing portion which
produces pressure by the hydrodynamic effect of a fluid which
occurs in a thrust bearing gap on one end side of the flange
portion to support the flange portion in the thrust direction in a
non-contact manner; and a second thrust bearing portion which
produces pressure by the hydrodynamic effect of the fluid occurring
in the thrust bearing gap on the other end side of the flange
portion to support the flange portion in the thrust direction in a
non-contact manner.
[0021] The fluid is caused to flow in the axial direction in the
radial bearing gap by forming hydrodynamic grooves asymmetrically
in the axial direction for producing the hydrodynamic effect of the
fluid on one of the outer circumferential surface of the shaft
portion facing the radial bearing gap and the inner periphery face
of the bearing sleeve opposing this outer circumferential surface.
If this flow is directed to the flange portion, the occurrence of
negative pressure in the bearing apparatus can be avoided, and the
function of the through-hole to regulate the pressure balance
equilibrates high pressure caused by pushing to the flange
portion.
[0022] The above hydrodynamic bearing apparatus can be also
presented as a motor which comprises a hydrodynamic bearing
apparatus, rotor magnet and stator coil.
[0023] Moreover, to achieve the first object, the present invention
provides a method for producing a shaft member for hydrodynamic
bearing apparatuses which comprises a shaft portion and a flange
portion and is supported in the thrust direction in a non-contact
manner by the hydrodynamic effect of a fluid which occurs in the
thrust bearing gap on both axial sides of the flange portion, the
method comprising integrally forming the shaft portion and the
flange portion by forging and forming a through-hole opening to its
both end faces on the flange portion by forging, and these forging
being performed simultaneously. As mentioned above, forming of the
through-hole is performed by a forging process so that cutting
powders and the like associated with the process can be prevented,
a cleaning step after the process can be omitted or simplified.
Moreover, forming of the through-hole and forming of the shaft
material comprising the shaft portion and the flange portion
integrally are both performed simultaneously by forging, whereby
the processing steps can be simplified and the time for the process
can be greatly shortened.
[0024] To achieve the second object, the present invention provides
a metallic shaft member for fluid lubrication bearing apparatuses
in which a threaded hole is formed on its one end and a radial
bearing face facing the radial bearing gap is formed on the outer
periphery, the threaded hole being formed by plastic processing.
Herein, the radial bearing face may be any that faces the radial
bearing gap which produces a hydrodynamic effect, regardless of
whether or not the hydrodynamic grooves for producing the
hydrodynamic effect are formed.
[0025] As mentioned above, the threaded hole is formed by plastic
processing in the present invention. Therefore, cutting needs not
be performed to form the threaded hole, cutting powders produced by
cutting can be prevented. Accordingly, cutting powders do not
remain inside the threaded hole. Furthermore, cutting powders can
be prevented from depositing to other components as contaminants
when other components are mounted or a bearing apparatus is
assembled and from getting in a lubricating oil or the like filling
the inside of the bearing apparatus after being assembled.
Moreover, unlike in cutting, since cutting powders are not produced
in a large amount, the cleaning step can be simplified and related
forming costs can be reduced.
[0026] The threaded hole can be, for example, so constructed that
it has a prepared hole formed by a forging process and a thread
portion formed by rolling process on the opening side of the
prepared hole. In this case, as plastic processing, a forging
process is performed on the prepared hole, and a rolling process is
performed on the thread portion. The prepared hole by the forging
process is formed in a series from the shaft ends. After this
prepared hole is formed, the opening side of the prepared hole is
partially subjected to screw rolling so that the final threaded
hole is constituted by the thread portion on the opening side and
the unrolled prepared hole remaining on the bottom side of the
hole. Because this threaded hole is formed only by plastic
processing, production of cutting powders can be prevented and the
problem of contamination can be solved. Moreover, a shaft material
having a shape corresponding to the shaft member, for example, the
shaft material which integrally has the shaft portion and flange
portion can be formed by forging.
[0027] Moreover, since the above threaded hole is for fixing other
components on the shaft member, the accuracy of the
perpendicularity of the shaft member and other components
screw-fixed on the shaft member varies depending on how the
threaded hole is inclined relative to the shaft member. An example
of the methods for suppressing the inclination of the threaded hole
relative to the shaft member is increasing the processing accuracy
of the prepared hole which serves as the reference in processing
the thread portion of the threaded hole. When the prepared hole is
formed by a forging process as in the present invention, the method
by which a pin for forming the prepared hole is pushed into the
shaft material to cause the pushing portion to undergo plastic
deformation is employed. However, if an edge is formed between a
conical end face of the pin tip and a cylindrical outer
circumferential surface positioned on its proximal end side
(connecting portion), when the pin is pushed, a great amount of
stress is concentrated at a portion corresponding to the edge of
the shaft material (for example, a portion which is deformed in
conformity with the edge formed at the connecting portion between
the pin tip face and the outer circumferential surface of the shaft
material). If a raw material forming the shaft material is, for
example, stainless steel or like material with poor ductility, this
trend becomes more evident. In its worst case, cracks are formed at
the portion where stress is concentrated. In consideration of this
problem, the prepared hole of the threaded hole is shaped so that
it has a conical surface and a cylinder face which is disposed on
the opening side of this conical surface and is smoothly continuous
with the conical surface via a radially curved surface in the
present invention.
[0028] Since the shape of the prepared hole is correspondent to the
shape deformed in conformity with the surface shape of the pin for
forming the prepared hole, such a constitution means that the tip
portion of the pin is in a conical surface shape, and that the
conical surface of the tip portion of the pin is smoothly
continuous with the cylindrical outer circumferential surface via
the radially curved surface. Therefore, when the pin having the
above-mentioned shape is pushed into the shaft material, a portion
corresponding to the connecting portion between the pin tip face of
the shaft material and the outer circumferential surface of the
cylinder is deformed in conformity with the smooth connecting
portion of the pin, and the concentrated stress at the portion
corresponding to this connecting portion is mitigated. This can
increase the yield rate of products in forming of the prepared
hole, ensuring the formation of the prepared hole. Moreover, since
the pushing direction of the pin is stabilized by forming the tip
of the pin in a conical shape, runout of the tip can be prevented
for accurate pushing of the pin into the shaft material, the
dimensional accuracy of the prepared hole, in particular the
inclination of the axis of the prepared hole relative to the axis
of the shaft member can be suppressed to a low level.
[0029] Examples of more preferable shapes of the prepared hole
include such a shape that the top of the conical surface formed at
the bottom of the prepared hole is removed. The shape of a pin
forming the material to be processed into this shape may be in such
a shape that the tip portion of the pin in the form of a sharp cone
is removed (for example, radially curved surface or a flat face).
Accordingly, when the prepared hole is formed, not only at the
portion corresponding to the connecting portion between the pin tip
face of the shaft material and the outer circumferential surface of
the cylinder, but also the stress concentrated at a portion
corresponding to the pin tip face top can be mitigated, further
ensuring forming of the prepared hole.
[0030] Moreover, when the shaft member is in rotation, high
perpendicularity relative to the shaft member for a component is
required fixed on the shaft member of the fluid lubrication bearing
apparatus to avoid contact with components on the fixed side of the
bearing apparatus, runout or prevent other problems. Accordingly,
in the present invention, the coaxiality of the center line of the
pitch circle of the thread portion in the threaded hole formed on
the shaft member is set to 0.2 mm or lower. Herein, the coaxiality
refers to the dimension of the deviation from the datum axis
straight line of an axis (referring to the center line of the pitch
circle of the thread portion herein) which is to be on the same
straight line as the datum axis straight line (theoretically
correct axis line as a geometric reference. Moreover, the term axis
line used herein refers to an axis which is a geometrically correct
straight line of the shaft member), and its dimension is
represented by the diameter of the smallest geometrically correct
cylinder which includes the entire above axis (pitch circle center
line) and is coaxial with the datum axis straight line.
[0031] Accordingly, for example, the clamper for clamping the disk
between the disk hub and itself is screw fixed on the shaft member
with its clamping face perpendicularly intersecting the axis of the
shaft member, the disk is fixed with its disk plane remaining
parallel to the clamper and the clamping face of the disk hub.
Accordingly, the disk can be fixed while the value of the
perpendicularity relative to the shaft member is suppressed to a
low level, and runout of the disk relative to the shaft member when
the shaft member is in rotation can be suppressed.
[0032] Moreover, to achieve the second object, the present
invention provides a method for producing a shaft member for fluid
lubrication bearing apparatuses, the shaft member comprising a
threaded hole formed on its one end and a radial bearing face
facing a radial bearing gap formed on its outer periphery, the
method comprising forming a prepared hole of the threaded hole by
forging on a metallic shaft material, and then forming a thread
portion in the prepared hole by rolling to form the threaded
hole.
[0033] According to such a producing method, since forming of the
threaded hole does not require cutting, cutting powders produced by
cutting can be prevented. The cutting powders thus do not remain
inside the threaded hole. In addition, the cutting powders are
prevented from being deposited to other components as contaminants
when other components are mounted or a bearing apparatus is
assembled, causing disk crash or getting in a lubricating oil or
the like filling the inside of the bearing apparatus after being
assembled. Moreover, as mentioned above, instead of cutting, a
forging process or a rolling process can be also used to shorten
the cycle time and reduce material costs with an improved ratio of
the amount of the material prior to the forming process to that
after the process.
[0034] Moreover, the shaft material and the prepared hole can be
formed in a common forging step. According to this method, because
forming of the prepared hole and forming of the shaft material are
performed both by forging, such a process can be performed at a
time so that the forming step can be simplified.
[0035] The above shaft member for fluid lubrication bearing
apparatuses can be provided as a fluid lubrication bearing
apparatus comprising, for example, a shaft member for fluid
lubrication bearing apparatuses; and a sleeve member into which
this shaft member is inserted at its inner periphery and which
forms the radial bearing gap between itself and the shaft member,
the apparatus retaining the shaft member and sleeve member in a
non-contact manner by a lubricating film of a fluid produced in the
radial bearing gap.
[0036] Moreover, the above fluid lubrication bearing apparatus can
be provided as a motor comprising this fluid lubrication bearing
apparatus, a rotor magnet and a stator coil.
[0037] To achieve said third object, the present invention provides
a metallic shaft member for fluid lubrication bearing apparatuses
which comprises a shaft portion and a flange portion, at least the
shaft portion being formed by forging, the shaft portion having a
recess formed on its tip face, and the recess comprising a
plastically processed surface.
[0038] Examples of means for achieving said object include a method
of increasing the pressing pressure in forging. However, simply
increasing pressing pressure may cause increased strain in the mold
and raw materials, reduced mold life, cracks in raw materials, and
various other problems. In contrast, in the present invention,
since a concave comprising a plastically processed surface on the
tip face of the shaft portion is formed, that is, the concave is
formed by the plastic deformation of the tip portion of the shaft
portion, the material which was originally in the concave is pushed
out to the outer diameter side and the tip side by forming of the
concave. Accordingly, the tip portion can be formed by minimizing
the occurrence of shortage of the deformation amount at the tip
portion by performing the forging process of the shaft portion and
plastic processing of the concave. Therefore, when the shaft member
is elongated, the deformation amount at the tip portion of the
shaft portion can be ensured and high forming accuracy can be
obtained throughout the length of the shaft portion. In addition,
as mentioned above, since forming accuracy can be increased without
increasing the pressing pressure, it is economical that no concern
about reduced mold life, etc., is necessary.
[0039] A preferred concave formed on the tip face of the shaft
portion, for example, has a shape whose diameter gradually
decreases from the tip of the shaft portion toward the center of
the shaft portion. This constitution has been created based on the
tendency that its deformation shortage grows larger as it gets
closer to the shaft end side when deformation is insufficient at
the tip of the shaft portion. Accordingly, by forming a concave
having such a shape, deformation shortage at the tip portion of the
shaft portion can be efficiently compensated to form such a tip
portion more accurately.
[0040] The shaft member having the above constitution can be
provided as, for example, a fluid lubrication bearing apparatus
comprising this shaft member; and a radial bearing gap formed
between the outer circumferential surface of the shaft portion and
the face facing it, the apparatus relatively rotatably supporting
the shaft member by a lubricating film of a fluid which occurs in a
radial bearing gap.
[0041] Moreover, to achieve said third object, the present
invention provides a method for producing a metallic shaft member
for fluid lubrication bearing apparatuses which comprises a shaft
portion and a flange portion, the shaft portion being formed by
forging, the process of the forging comprising forming a concave by
plastic processing on the tip face of the shaft portion to cause
the tip portion of the shaft portion to overhang by a plastic
flow.
[0042] As mentioned above, in the process of the forging of the
shaft portion, when the concave is formed by plastic processing,
for example, the tip portion of the shaft portion is preferably
caused to overhang until it reaches at least final finished shape.
Normally, the shaft member of this type is finished by grinding or
like shaving process only at the portions where dimensional
accuracy (shape accuracy) is required, among forging formed
articles. Accordingly, at the forging stage, the tip portion of the
shaft portion is caused to overhang until at least a final finished
shape is reached so that the cutting process at the tip portion is
enabled, and the shaft member having high dimensional accuracy can
be thus obtained.
[0043] Various shapes are possible as a final finished shape of the
tip of the shaft portion. For example, a shape defined by the outer
circumferential surface of the tip of the shaft portion, the tip
face of the shaft portion and a chamfer between these two faces is
possible.
[0044] According to the present invention, when the shaft member is
in rotation, the pressure balance in the thrust bearing gap formed
on both side of the flange portion in the axial direction can be
restored in an early stage and the thrust bearing gaps can be
always maintained at a predetermined interval. Therefore, the
rotational performance of the bearing can be exerted stably for a
long term. Moreover, such a function can be obtained at low costs,
and mass productivity can be dramatically improved.
[0045] According to the present invention, the production of
cutting powders associated with cutting is prevented. This prevents
the deposition of contaminants to bearing component parts, disk
crash, and contaminants from getting inside a bearing apparatus as
much as possible, maintaining the cleanliness of the fluid
lubrication bearing apparatus at low costs. Moreover, since the pin
forming the prepared hole can be surely and accurately pushed into
the shaft material, the cylindricity of the thread portion can be
maintained highly accurately, and the mounting accuracy of other
component screw fixed on the shaft member relative to the shaft
member can be improved.
[0046] According to the present invention, a shaft member for fluid
lubrication bearing apparatuses which has high dimensional accuracy
and can be elongated can be provided at low costs.
BRIEF DESCRIPTION OF SEVERAL VIEWS OF THE DRAWING
[0047] FIG. 1 is a side elevational view of a shaft member for
hydrodynamic bearing apparatuses according to the first embodiment
of the present invention.
[0048] FIG. 2 is a cross-sectional view of a spindle motor for an
information appliance integrating a hydrodynamic bearing apparatus
comprising a shaft member.
[0049] FIG. 3 is a longitudinal sectional view of a hydrodynamic
bearing apparatus.
[0050] FIG. 4 is a longitudinal sectional view of a bearing
sleeve.
[0051] FIG. 5 is a lower end view of a bearing sleeve.
[0052] FIG. 6 is a side elevational view of a shaft material formed
by a forging process.
[0053] FIG. 7 is a schematic illustration showing an example a
grinding apparatus according to the width grinding step of a shaft
material.
[0054] FIG. 8 is a partial cross-sectional view showing an example
of a grinding apparatus according to the width grinding step.
[0055] FIG. 9 is a schematic illustration showing an example of a
grinding apparatus according to the full face grinding process step
of a shaft material.
[0056] FIG. 10 is a schematic illustration showing an example of a
grinding apparatus according to the grinding finish step of a shaft
material.
[0057] FIG. 11 is a side elevational view of a shaft member for
fluid lubrication bearing apparatuses according to the second
embodiment of the present invention.
[0058] FIG. 12 is an expanded sectional view of the vicinity of the
bottom of a threaded hole formed on the end of a shaft member.
[0059] FIG. 13 is a cross-sectional view of a spindle motor for
information appliances integrating a fluid lubrication bearing
apparatus comprising a shaft member.
[0060] FIG. 14 is a longitudinal sectional view of a fluid
lubrication bearing apparatus.
[0061] FIG. 15 is a side elevational view of a shaft material
formed by a forging process.
[0062] FIG. 16 is an expanded sectional view of the vicinity of the
bottom of a prepared hole of a threaded hole formed the end of a
shaft material.
[0063] FIG. 17 is a side elevational view of a shaft member for a
fluid lubrication bearing apparatus according to the third
embodiment of the present invention.
[0064] FIG. 18 is a cross-sectional view of a spindle motor for
information appliances integrating a fluid lubrication bearing
apparatus.
[0065] FIG. 19 is a cross-sectional view of a fluid lubrication
bearing apparatus.
[0066] FIG. 20 is a side elevational view of a shaft material
formed by a forging process.
[0067] FIG. 21 is a schematic illustration of an example of a mold
used in a forging process.
[0068] FIG. 22 is an expanded view which conceptionally shows a
known forming forging manner of a shaft material.
[0069] FIG. 23 is an expanded view which conceptionally shows a
forming forging manner of a shaft material according to the present
invention.
DETAILED DESCRIPTION OF THE INVENTION
[0070] A first embodiment of the present invention will be
described below with reference to FIGS. 1-10.
[0071] FIG. 2 conceptionally shows an example of the constitution
of a spindle motor for information appliances incorporating a
hydrodynamic bearing apparatus 1 according to the first embodiment
of the present invention. This spindle motor for an information
appliance is used for disk drive units such as HDDs. It comprises
the hydrodynamic bearing apparatus 1 which rotatably supports a
shaft member 2 in a non-contact manner; a disk hub 3 which is
mounted on the shaft member 2; for example, a stator coil 4 and a
rotor magnet 5 facing each other across a gap in the radial
direction; and a bracket 6. The stator coil 4 is mounted on the
outer periphery of the bracket 6, and the rotor magnet 5 is mounted
on the inner periphery of the disk hub 3. The bracket 6 has the
hydrodynamic bearing apparatus 1 mounted on its inner periphery.
Moreover, disk hub 3 retains one or more disk-shaped information
recording media such as magnetic disks (hereinafter referred to
simply as a disk) D on its outer periphery. In the thus constructed
spindle motor for information appliances, when the stator coil 4 is
energized, the rotor magnet 5 is rotated by the excitation between
the stator coil 4 and rotor magnet 5. This causes the disk hub 3
and the disk D retained on the disk hub 3 to rotate unitarily with
the shaft member 2.
[0072] FIG. 3 shows an example of the hydrodynamic bearing
apparatus 1. This hydrodynamic bearing apparatus 1 is constituted
of a housing 7 having a bottom 7b at its one end; a bearing sleeve
8 fixed on to the housing 7; a shaft member 2 inserted into the
inner periphery of the bearing sleeve 8; and a sealing member 9 as
its main components. For the sake of explanation, the bottom 7b
side of the housing 7 is referred to as the lower side, and the
side opposite to the bottom 7b is referred to as the upper side in
the following description.
[0073] As shown in FIG. 3, the housing 7 is constituted of, for
example, a side portion 7a formed of a resin material such as LCP,
PPS, or PEEK in the form of a cylinder, and a bottom 7b located at
one end side of the side portion 7a and, for example, formed of a
metallic material. In this embodiment, the bottom 7b is formed
separately from the side portion 7a and is retrofitted on the lower
inner periphery of the side portion 7a. In a part of the annular
region of the upper end face 7b1 of the bottom 7b, for example, a
region in which a plurality of hydrodynamic grooves are arranged
spirally is formed as a portion for producing hydrodynamic
pressure, although not shown in the Figs. Note that in this
embodiment, the bottom 7b is formed separately from the side
portion 7a, and fixed on the lower inner periphery of the side
portion 7a. It can be, however, formed integrally with the side
portion 7a, for example, from a resin material. At this time, the
hydrodynamic grooves provided on the upper end face 7b1 can be
die-formed simultaneously with the injection molding of the housing
7 comprising the side portion 7a and bottom 7b, which can dispense
with the trouble of forming the hydrodynamic grooves on the bottom
7b.
[0074] The bearing sleeve 8 is formed, for example, of a porous
body made of a sintered metal, especially a porous body of a
sintered metal comprising copper as a main ingredient in the form
of a cylinder, and is fixed at a predetermined position the inner
periphery face 7c of the housing 7.
[0075] Throughout the inner periphery face 8a of the bearing sleeve
8 or in part of its cylinder face region, a hydrodynamic pressure
producing part is formed. In this embodiment, for example, as shown
in FIG. 4, the region, in which a plurality of hydrodynamic grooves
8a1, 8a2 are arranged in a herringbone shape, is formed at two
axially separated positions. In the region where of the upper
hydrodynamic groove 8a1 is formed, the hydrodynamic groove 8a1 is
formed asymmetrically in the axial direction relative to the axial
center m (the axial center of the region between the upper and
lower slanted grooves), the axial dimension X1 of the region above
the axial center m is larger than the axial dimension X2 of the
region therebelow. Therefore, when the shaft member 2 is in
rotation, the lubricating oil in the radial bearing gap by the
asymmetric hydrodynamic groove 8a1 is pushed downward.
[0076] On the outer circumferential surface 8b of the bearing
sleeve 8, one or more axial direction grooves 8b1 are formed
throughout its axial length. In this embodiment, three axial
direction grooves 8b1 are formed at an equal interval in the
circumferential direction.
[0077] In the entire annular region of the lower end face 8C of the
bearing sleeve 8 or a part thereof, a region in which a plurality
of hydrodynamic grooves 8c1 are arranged in a spiral shape is
formed as a portion for producing hydrodynamic pressure, for
example, as shown in FIG. 5.
[0078] A sealing member 9 as a sealing means is formed, as shown in
FIG. 3, for example, of a soft metallic material such as brass and
other metallic materials, or a resin material separately from the
housing 7 and in an annular shape, and fixed by means of press
fitting, adhesion or the like into the upper inner periphery of the
side portion 7a of the housing 7. In this embodiment, the inner
periphery face 9a of the sealing member 9 is formed in the form of
a cylinder, and the lower end face 9b of the sealing member 9 is in
contact with the upper end face 8D of the bearing sleeve 8.
[0079] The shaft member 2 is, for example, formed of a metallic
material such as stainless steel, and has a T-shaped cross section
integrally comprising a shaft portion 21 and a flange portion 22
provided at the lower end of the shaft portion 21, as shown in FIG.
1. At the outer periphery of the shaft portion 21, as shown in FIG.
3, radial bearing faces 23a, 23b facing the region in which two
hydrodynamic grooves 8a1, 8a2 are formed on the inner periphery
face 8a of the bearing sleeve 8 are formed at two axially separated
positions. Above one of the radial bearing faces, the face 23a, a
tapered face 24 whose diameter gradually decreases toward the shaft
tip is formed adjacently. Further thereabove, a cylinder face 25,
which serves as a mounting portion of the disk hub 3, is formed.
Annular recess portions 26, 27, 28 are formed between the two
radial bearing faces 23a, 23b, between the other radial bearing
face 23b and flange portion 22, and between the tapered face 24 and
cylinder face 25, respectively.
[0080] On the upper end face of the flange portion 22, for example,
a thrust bearing face 22a of a first thrust bearing portion T1
facing the thrust bearing gap is formed, as shown in FIG. 3. On the
lower end face of the flange portion 22, a thrust bearing face 22b
of a second thrust bearing portion T2 facing thrust bearing gap is
formed, as shown in FIG. 3. In addition, on the inner diameter side
(in the vicinity of the shaft portion 21) of the flange portion 22,
a through-hole 29 opening to both end faces of the flange portion
22 is formed. In this embodiment, the through-hole 29 opens to a
portion on the inner diameter side of the thrust bearing faces 22a,
22b of both end faces of the flange portion 22.
[0081] Between the tapered face 24 of the shaft portion 21 and the
inner periphery face 9a of the sealing member 9 facing the tapered
face 24, an annular sealing space S, whose radial dimension is
gradually increased upwardly from the bottom 7b side of the housing
7, is formed. In the hydrodynamic bearing apparatus 1 after being
assembled (refer to FIG. 3), the inner space of the housing 7
containing the radial bearing gap and thrust bearing gap is
completely filled with a lubricating oil, and its oil level is
maintained to be within the range of the sealing space S.
[0082] In the thus constructed hydrodynamic bearing apparatus 1,
when the shaft member 2 is rotated, the pressures of lubricating
oil films formed in the radial bearing gap between the regions
(upper and lower) where the hydrodynamic grooves 8a1, 8a2 of the
inner periphery face 8a of the bearing sleeve are formed and the
radial bearing faces 23a, 23b of the shaft portion 21 facing the
region where these hydrodynamic grooves 8a1, 8a2 are formed,
respectively, are increased by the hydrodynamic effect of the
hydrodynamic grooves 8a1, 8a2. A first radial bearing portion R1
and a second radial bearing portion R2 which rotatably support the
shaft member 2 in the radial direction in a non-contact manner by
the pressure of these oil films are then formed. Moreover, the
pressure of the lubricating oil films formed in a first thrust
bearing gap W1 (refer to FIG. 3) and in a second thrust bearing gap
W2 (refer to FIG. 3) is increased by the hydrodynamic effect of the
hydrodynamic grooves. The first thrust bearing gap W1 is between a
hydrodynamic groove 8c1 region formed on the lower end face 8C of
the bearing sleeve 8 and the upper (the shaft portion side) thrust
bearing face 22a of the flange portion 22 facing this hydrodynamic
groove 8c1 region, while the second thrust bearing gap W2 is
between the hydrodynamic groove region formed on the upper end face
7b1 of the bottom 7b and the thrust bearing face 22b on the lower
side (opposite to the shaft portion side) of the flange portion 22
facing this hydrodynamic groove region. In addition, a first thrust
bearing portion T1 and a second thrust bearing portion T2, which
rotatably support the shaft member 2 in a non-contact manner in the
thrust direction, are formed by the pressure of these oil
films.
[0083] When the shaft member 2 is in rotation, the lubricating oil
circulates in the above the radial bearing gap W1 and thrust
bearing gap W2, or between the abobe gaps and the inside of the
bearing sleeve 8 made of a porous body, and the lubricating oil is
appropriately provided for supporting the shaft member in the
bearing gaps. However, for some reason, the circulation of the oil
is sometimes disturbed. Also in that case, the through-hole 29
provided on the flange portion 22 adjusts the pressure balance
between the thrust bearing gaps W1, W2, whereby one thrust bearing
gap (first thrust bearing gap W1) and the other thrust bearing gap
(second thrust bearing gap W2) can be maintained at appropriate
intervals. Accordingly, the shaft member 2 can be stably supported
in the thrust direction, enabling to stably exert such bearing
performance for a long term.
[0084] A method for producing the shaft member 2 constituting the
hydrodynamic bearing apparatus 1 will be described below.
[0085] The shaft member 2 is produced mainly in the following two
steps: a (A) forming step and a (B) grinding step. The (A) forming
step in this procedure comprises a shaft material forming process
(A-1); a through-hole forming process (A-2); and a shaft portion
correcting process (A-3). Moreover, the (B) grinding step comprises
a width grinding process (B-1); a full face grinding process (B-2);
and a finish grinding process (B-3).
(A) Forming Step
(A-1) Shaft Material Forming Process and (A-2) Through-Hole Forming
Process
[0086] To begin with, a metallic material such as stainless steel
which will be a material of the shaft member 2 to be formed is
compression-formed (forging process) by using molds, for example,
in a cold state so that, for example, the shaft material 10
integrally having the region corresponding to the shaft portion
(hereinafter referred to simply as a shaft portion) 11 and the
region corresponding to the flange portion (hereinafter referred to
simply as a flange portion.) 12 is formed (shaft material forming
process (A-1)) as shown in FIG. 6. In this embodiment, a mold used
in forging of this shaft material 10 also serves as the mold for
forming the through-hole 19 on the flange portion 12. Accordingly,
by compression-forming the metal material with this mold, a
through-hole 19 passing between the side end face 12a of the shaft
portion of the flange portion 12 and the end face on the side
opposite to the shaft portion 12b is formed (through-hole forming
process (A-2)) on the inner diameter side (in the vicinity of the
shaft portion 11) of the flange portion 12 as the shaft material 10
is formed by forging, as shown in FIG. 6.
[0087] As mentioned above, performing the forming of the
through-hole 19 on the flange portion 12 by a forging process can
prevent cutting powders and the like produced by processing, and
dispense with or simplify a cleaning step after the process.
Moreover, the forming of the through-hole 19 and the forming of the
shaft material 10 integrally comprising the shaft portion 11 and
flange portion 12 are performed both by forging and simultaneously,
whereby such a processing step can be simplified, and machining
time can be greatly shortened.
[0088] A method of cold-forging employed in the above forming step
may be, extrusion, upsetting, heading or the like, or combinations
of them. In the examples shown in FIG. 6, the outer circumferential
surface 11a of the shaft portion 11 after being subjected to the
forging process is in a different diameter shape comprising a
tapered face 14 and a cylinder face 15 which is continuous upwardly
with the tapered face 14 and has a smaller diameter than other
portions disposed therebetween, but may be formed to have a uniform
diameter throughout its length by dispensing with the tapered face
14. Note that in this embodiment, described is the case where the
forming of the shaft material 10 and the forming of the
through-hole 19 are performed both by a forging process
simultaneously, both steps need not necessarily be performed
simultaneously and the through-hole 19 may be formed by forging
after forming the shaft material 10 by forging.
(A-3) Shaft Portion Correcting Process
[0089] The shaft portion 11 of the shaft material 10 formed by
forging in the previous step is nipped with pressure, for example,
with a pair of rolling die (for example, flat dies and round dies,
etc.) and said pair of rolling dies are reciprocated in the
directions opposite to each other to perform a rolling process for
correcting cylindricity on the outer circumferential surface 11a of
the shaft portion 11 (shaft portion correcting process (A-3)),
although not shown in the Figs. This improves the cylindricity of
the face 13 subjected to the correcting process, of the outer
circumferential surface 11a of the shaft portion of the shaft
material 10 so that it falls within a required range (for example,
10 .mu.m or lower). Examples of the correcting processes of the
cylindricity employed include a rolling process, drawing compound,
ironing, sizing by pressing split-cavity molds (nipping) and
various other processing methods. Moreover, the correcting process
is performed not only throughout the length of the outer
circumferential surface 11a of the shaft portion 11, but also on a
part of the outer circumferential surface 11a, as long as it
includes the portions corresponding to the radial bearing faces
23a, 23b of the shaft member 2 as a finished product.
(B) Grinding Step
(B-1) Width Grinding Process
[0090] The end face 11b of the shaft portion and end face 12b of
the flange portion 12 on the opposite side of the shaft portion,
which will be the end faces of the shaft material 10 after being
subjected to the forming step, are ground relative to the corrected
face 13 mentioned above. A grinding apparatus 40 used in this
grinding step comprises, for example, a carrier 41 which retains a
plurality of the shaft material 10 as workpiece; and a pair of
grind stones 42, 42 which grinds the end face 11b of the shaft
portion and end face 12b of the flange portion 12 on the opposite
side of the shaft portion of the shaft material 10 retained by the
carrier 41, as shown in FIG. 7.
[0091] As shown in FIG. 7, a plurality of notches 43 is provided on
part of the circumferential region of the outer periphery of the
carrier 41 at an equal pitch in the circumferential direction. The
shaft material 10 is contained in the notch 43 with its correcting
process face 13 in angular contact with the inner face 43a of the
notch 43. The correcting process face 13 of the shaft material 10
protrudes slightly from the outer circumferential surface of the
carrier 41, and a belt 44 is provided on the outer diameter side of
the carrier in a tensioned state to bind the protruding portions of
the shaft material 10 from the outer diameter side. On both axial
end sides of the carrier 41 where the shaft material 10 is
contained in the notch 43, for example, a pair of grind stones 42,
42 are coaxially disposed with their end faces (grinding surfaces)
facing each other at a predetermined interval, as shown in FIG.
8.
[0092] As the carrier 41 rotates, the shaft material 10 is
sequentially loaded into the notch 43 from a determined position.
The loaded shaft material 10 traverses the end faces of the
rotating grind stones 42, 42 from their outer diameter edge toward
the inner diameter edge in such a state that it is prevented from
falling off from the notch 43 by binding of the belt 44.
Accordingly, both end faces of the shaft material 10, i.e., the end
face 11b of the shaft portion and the end face 12b of the flange
portion 12 on the side opposite to the shaft portion are ground by
the end faces of the grind stones 42, 42 (refer to FIG. 8). At this
time, the corrected face 13 of the shaft material 10 is supported
by the carrier 41 and this corrected face 13 has high cylindricity.
Therefore, if the perpendicularity of the rotation axis of the
grind stone 42 and the grinding surface of the grind stone 42 and
the parallelism of the rotation axis of the grind stone 42 and the
rotation axis of the carrier 41, etc. are highly accurately
controlled in advance, both end faces 11b, 12b of the shaft
material 10 can be highly accurately finished with reference to
this corrected face 13, enabling to suppress the value of the
perpendicularity relative to the corrected face 13. Moreover, the
width of the shaft material 10 in the axial direction (the overall
length including the flange portion 12) can be finished to have a
predetermined size.
(B-2) Full Face Grinding Process
[0093] Subsequently, the outer circumferential surface 10a of the
shaft material 10 and the side end face 12a of the flange portion
12 on the shaft portion side are ground relative to both end faces
(the end face 11b of the shaft portion, the end face 12b of the
flange portion 12 on the side opposite to the shaft portion) of the
ground shaft material 10. The grinding apparatus 50 used in this
grinding step performs, for example, plunge-grinding by the grind
stone 53 with the back plate 54 and pressure plate 55 pressed to
both end faces of the shaft material 10, as shown in FIG. 9. The
corrected face 13 of the shaft material 10 is rotatably supported
by a shoe 52.
[0094] The grind stone 53 is a formed grind stone which comprises a
grinding surface 56 corresponding to the outer circumferential
surface shape of the shaft member 2 as a finished product. The
grinding surface 56 comprises a cylinder grinding portion 56a which
grinds the outer circumferential surface 11a through the length of
the shaft portion 11 in the axial direction and the outer
circumferential surface 12c of the flange portion 12; and a plane
grinding portion 56b which grinds the side end face 12a of the
shaft portion of the flange portion 12. The grind stone 53 in the
example shown in FIG. 9 comprises, as the cylinder grinding portion
56a, portions 56a1, 56a2, which grind the regions corresponding to
the radial bearing faces 23a, 23b of the shaft member 2, a portion
56a3, which grinds the region corresponding to the tapered face 24,
a portion 56a4, which grinds the region corresponding to the
cylinder face 25, portions 56a5-56a7, which grind the recess
portions 26-28, respectively, and a portion 56a8, which grinds a
region corresponding to the outer circumferential surface 22c of
the flange portion 22.
[0095] Grinding in the grinding apparatus 50 of the above
constitution is performed in the following procedure. To begin
with, the grind stone 53 is fed obliquely (the direction of arrow 1
in FIG. 9) with the shaft material 10 and grind stone 53 rotating,
and a plane grinding portion 56b of grind stone 53 is pressed
against the side end face 12a on the shaft portion side of the
flange portion 12 to grind the side end face 12a on the shaft
portion side of the flange portion 12. The finishing process of the
end face of the flange portion 22 of the shaft member 2 on the
shaft portion side is thus completed, forming the thrust bearing
face 22a facing a first thrust bearing portion T1. Subsequently,
the grind stone 53 is fed in the direction perpendicular to the
rotation axis of the shaft material 10 (the direction of arrow 2 in
FIG. 9), and the cylinder grinding portion 56a of the grind stone
53 is pressed to the outer circumferential surface 11a of the shaft
portion 11 of the shaft material 10 and the outer circumferential
surface 12c of the flange portion 12 to grind the faces 11a, 12c.
Accordingly, out of the outer circumferential surface of the shaft
portion 21 of the shaft member 2, the regions corresponding to
radial bearing faces 23a, 23b and cylinder face 25 are ground
respectively, and the tapered face 24, the outer circumferential
surface 22c of the flange portion 22, and the recess portions 26-28
are formed. Note that in the above grinding, for example, it is
preferred to perform grinding while measuring the remaining
grinding allowance by a measurement gauge 57, as shown in FIG.
9.
[0096] In this full face grinding process step, since the accuracy
setting of the perpendicularity of both end faces 11b, 12b of the
shaft material 10 has been performed beforehand in the width
grinding, each of the to-be-ground surfaces can be ground highly
accurately.
(B-3) Finish Grinding Process
[0097] (B-2) Among the faces which have been ground in full face
grinding process, the radial bearing faces 23a, 23b of the shaft
member 2 and the region corresponding to the cylinder face 25 are
subjected to the final finish grinding process. An example of the
grinding apparatus used in this grinding is a cylinder grinder
shown in FIG. 10. It performs plunge grinding by the grind stone
63, while rotating the shaft material 10 held between the back
plate 64 and pressure plate 65. The shaft material 10 is rotatably
supported by a shoe 62. A grinding surface 63a of the grind stone
63 comprises a first cylinder grinding portion 63a1 which grinds
regions corresponding to the radial bearing faces 23a, 23b of the
shaft member 2 (the regions 13a, 13b in FIG. 10), and a second
cylinder grinding portion 63a2 which grinds a region corresponding
to the cylinder face 25 (region 15 in FIG. 10).
[0098] In the grinding apparatus 60 having the above constitution,
by providing the rotating grind stone 63 with the feed in the
radial direction, the regions 13a, 13b, and 15 corresponding to the
radial bearing faces 23a, 23b and cylinder face 25, respectively,
are ground, and these regions are finished to have the final
surface accuracy.
[0099] After the above (A) forming step and (B) grinding step are
finished, heat treatment and cleaning process, if necessary, can be
performed to complete the shaft member 2 shown in FIG. 1.
Accordingly, in the vicinity of the shaft portion 21, a
through-hole 29 opening to both end faces of the flange portion 22
is formed. Since the inner periphery face of the through-hole 29 is
formed by a forging process, its surface roughness becomes
high.
[0100] According to the above production method, the cylindricity
of the radial bearing faces 23a, 23b formed on the outer periphery
of the shaft portion 21 can be finished highly accurately. Because
of this, for example, the circumferential or axial variation of the
radial bearing gap formed between the inner periphery face 8a of
the inner periphery of the bearing sleeve 8 of in the hydrodynamic
bearing apparatus 1 and itself is suppressed to be in a
predetermined range, and bearing performance can be thus prevented
from being adversely affected by the variation of the above radial
bearing gap. Moreover, relative to the radial bearing faces 23a,
23b formed on the outer periphery of the shaft portion 21, the
shaft member 2 whose values of the perpendicularity of both end
faces 22a, 22b of the flange portion 22 (thrust bearing face) are
suppressed can also be formed. Because the thrust bearing faces
22a, 22b formed on both end faces of the flange portion 22 form the
thrust bearing gap between themselves and the faces facing them
(the lower end face 8C of the bearing sleeve 8, the upper end face
7b1 of the bottom 7b of the housing 7, etc.), the numerical value
of such perpendicularity can be thus suppressed to a low level,
whereby variation in the above thrust bearing gap can be reduced.
Moreover, the end face of the shaft portion 21b can also serve as
the reference plane for setting the above thrust bearing gap.
Accordingly, by suppressing the numerical value of the
perpendicularity of the end face 21b of the shaft portion to a low
level, the thrust bearing gap can be controlled with high
accuracy.
[0101] Moreover, in this embodiment, since a finish grinding
process (refer to FIG. 10) is performed in the region corresponding
to the cylinder face 25 of the shaft portion 21, the cylindricity
of the cylinder face 25 can also be finished highly accurately, the
mounting accuracy in mounting components such as the disk hub 3 to
the shaft member 2 can be increased. Because of this, the accuracy
when clampers or the like for retaining the disk D on the disk hub
3 is fixed on the shaft member 2 can be increased, and the mounting
accuracy relative to the shaft member 2 of the disk D clamped
between the clamper and disk hub 3 can be further increased,
thereby further improving the motor performance.
[0102] Described In the above embodiment is the case where the
through-hole 29 is formed so that it opens to the inner diameter
side of these bearing face 22a, 22b to prevent a drop in the
pressure in the thrust bearing gaps W1, W2, avoiding the thrust
bearing faces 22a, 22b of the flange portion 22 (thrust bearing
gaps W1, W2). However, when the hydrodynamic grooves and thrust
bearing gaps can be set considering some pressure drop, the
through-hole 29 can also be formed in such positions on the thrust
bearing faces 22a, 22b.
[0103] A second embodiment of the present invention will be
described below with reference to FIGS. 11-16. Note that portions
and components having the same constitution and actions as the
constitutions shown in FIGS. 1-10 (first embodiment) are referred
to by the same reference numerals, and their repeated explanations
are omitted.
[0104] FIG. 13 conceptionally shows an example of the constitution
of a spindle motor for information appliances incorporating a fluid
lubrication bearing apparatus (hydrodynamic bearing apparatus) 101
according to the second embodiment of the present invention. This
spindle motor for information appliances is used for disk drive
units such as HDDs, and comprises a fluid lubrication bearing
apparatus 101 which rotatably supports a shaft member 102 in a
non-contact manner; a disk hub 3 mounted on the shaft member 102, a
stator coil 4 and a rotor magnet 5 which, for example, face each
other across a gap in the radial direction; and a bracket 6. The
stator coil 4 is mounted on the outer periphery of the bracket 6,
and the rotor magnet 5 is mounted on the inner periphery of the
disk hub 3. The bracket 6 has a fluid lubrication bearing apparatus
101 attached on its inner periphery. Moreover, the disk hub 3
retains one or more disk D such as magnetic disks on its outer
periphery, and the disk D is held between the disk hub 3 and a
clamper 110. In this spindle motor for an information appliance,
when the stator coil 4 is energized, the rotor magnet 5 is rotated
by the magnetic force between the stator coil 4 and rotor magnet 5,
whereby the disk hub 3, shaft member 102 and the disk D held
between the disk hub 3 and clamper 110 are rotated unitarily.
[0105] FIG. 14 shows an example of the fluid lubrication bearing
apparatus 101. This fluid lubrication bearing apparatus 101 is
constituted of a housing 7 having a bottom 7b at its one end; a
bearing sleeve 8 fixed on the housing 7 as a sleeve member; a shaft
member 102 inserted into the inner periphery of the bearing sleeve
8; and a sealing member 9, as its main components. For the sake of
explanation, the bottom 7b side of the housing 7 is referred to as
the lower side, and the side opposite to the bottom 7b is referred
to as the upper side in the following description.
[0106] The shaft member 102 is formed, for example, of a metallic
material such as stainless steel, and has a T-shaped cross section
integrally comprising a shaft portion 121 and a flange portion 122
provided at the lower end of the shaft portion 121, as shown in
FIG. 11. On the outer periphery of the shaft portion 121, as in the
first embodiment, radial bearing faces 123a, 123b facing the region
in which two hydrodynamic grooves 8a1, 8a2 are formed on the inner
periphery face 8a of the bearing sleeve 8 are formed at two axially
separated positions, as shown in FIG. 4. Above one them, the radial
bearing face 123a, a tapered face 124, of which diameter gradually
decreases toward the shaft tip, is formed adjacently, and a
cylinder face 125, which serves as a mounting portion of the disk
hub 3, is formed further thereabove. Annular recess portions 126,
127, 128 are formed between the two radial bearing faces 123a,
123b, between the other radial bearing face 123b and flange portion
122, and between the tapered face 124 and the cylinder face 125,
respectively.
[0107] In the shaft portion 121, on the axis of the end face 121b
on the side opposite to the flange portion 122, a threaded hole 131
for screwing the clamper 110 on the shaft member 2 is formed. A
thread portion 132 which screws together with screw 111 for fixing
the clamper 110 on the inner periphery on the opening side of the
hole 131 is formed, and for example, a prepared hole 133 formed
prior to the formation of the thread portion 132 at the bottom of
the threaded hole 131 as shown in FIG. 12 is remaining.
[0108] The disk hub 3 is fixed on the cylinder face 125 formed on
the upper end of the shaft portion 121 of the above shaft member
102 by, for example, adhesion, press fitting or other means. In
addition, the screw 111 is screwed into the threaded hole 131
formed on the shaft portion 121 via the clamper 110 so that the
clamper 110 is fixed on the disk hub 3, and the disk is held
between the clamping faces 3a, 110a formed on the outer diameter
side the upper face of the disk hub 3 and on the outer diameter
side of the lower surface of the clamper 110.
[0109] In such a manner mentioned above, the fluid lubrication
bearing apparatus 101 retaining the disk D on the disk hub 3 is
constituted as shown in FIG. 14. At this time, an annular sealing
space S, whose size in the radial direction is gradually increased
upwardly from the bottom 7b side of the housing 7, is formed
between the tapered face 124 of the shaft portion 121 and the inner
periphery face 9a of a sealing member 9 facing the tapered face
124. In the fluid lubrication bearing apparatus 101 after being
assembled (refer to FIG. 14), the oil level is retained within the
range of the sealing space S.
[0110] In The thus constructed fluid lubrication bearing apparatus
101, when the shaft member 102 is rotated, the pressures of
lubricating oil films formed in the radial bearing gaps between the
radial bearing faces 123a, 123b of the shaft portion 121 facing the
regions (upper and lower) where the hydrodynamic grooves 8a1, 8a2
are formed on the inner periphery of the bearing sleeve 8 face 8a
and the region where these hydrodynamic grooves 8a1, 8a2 are
formed, respectively are increased by the hydrodynamic effect of
the hydrodynamic grooves 8a1, 8a2. In addition, a first radial
bearing portion R11 and a second radial bearing portion R12 which
rotatably support the shaft member 102 in the radial direction in a
non-contact manner are formed by the pressure of these oil films.
Moreover, the pressures of lubricating oil films formed in a first
thrust bearing gap between the thrust bearing face 122a of the
upper side (the shaft portion side) of the flange portion 122
facing the region where the hydrodynamic groove 8c1 is formed on
the lower end face 8C of the bearing sleeve 8 and the region where
this hydrodynamic groove 8c1 is formed, and in a second thrust
bearing gap between the region where the hydrodynamic groove is
formed on the upper end face 7b1 of the bottom 7b, the thrust
bearing face 122b on the lower side (opposite to the shaft portion
side) the flange portion 122 facing this face are increased by the
hydrodynamic effect of the hydrodynamic grooves. In addition, a
first thrust bearing portion T11 and a second thrust bearing
portion T12 which rotatably support the shaft member 102 in the
thrust direction in a non-contact manner are formed by the pressure
of these oil films.
[0111] The production method of the shaft member 102 constituting
the above fluid lubrication bearing apparatus 101 will be described
below.
[0112] The shaft member 102 is produced in mainly two steps: a (C)
forming step and a (D) grinding step. In this procedure, the (C)
forming step comprises a forging process (C-1), a thread portion
rolling process (C-2) and a correcting process (C-3). The (D)
grinding step comprises a width grinding (D-1), a full face
grinding process (D-2), and a finish grinding process (D-3).
(C) Forming Step
(C-1) Forging Process
[0113] To begin with, a material of the shaft member 102 to be
formed, i.e., a metal material such as stainless steel is subjected
to compression-forming (plastic deformation) with a mold, for
example, in a cold state, whereby, for example, the shaft material
112 integrally having the region corresponding to the shaft portion
(hereinafter referred to simply as a shaft portion) 113 and the
region corresponding to the flange portion (hereinafter referred to
simply as a flange portion.) 114 is formed (forging process), as
shown in FIG. 15. Moreover, the prepared hole 133 for forming the
threaded hole 131 is formed by forging (for example, backward
extrusion) on the edge of the shaft portion 113 as the shaft
material 112 is formed by the forging process mentioned above
(refer to FIG. 11).
[0114] At this time, on the inner periphery of the prepared hole
133 formed by forging simultaneously with the shaft material 112, a
cylinder face 134 whose diameter is constant is formed as shown in
FIG. 15, and a conical surface 135 which is continuous with the
cylinder face 134 is formed at its bottom. In a connecting portion
134a Between The conical surface 135 and cylinder face 134, a
radially curved surface which smoothly connects the conical surface
135 and cylinder face 134 as shown in FIG. 16 is formed. Moreover,
at a top 135a of the conical surface 135, a radially curved surface
is formed similarly. From a different perspective, these are
plastically deformed in conformity with the tip shape of the pin
pushed into the metallic material in forging of the prepared hole
133. That is, although not shown in the Figs., a conical surface is
formed at the tip of the pin, and a cylinder face is formed on the
outer periphery of the pin, the connecting portion between the
conical surface and the outer circumferential surface of the
cylinder and the top of the conical surface has the shape of a
rounded edge (both have a radially curved surface shape
herein).
[0115] Such a pin shape (in this embodiment, the connecting portion
between the conical surface and cylinder face of the pin and the
top of the conical surface are each caused to be a radially curved
surface), when the pin is pushed into the metallic material,
concentrated stress at a portion corresponding to the connecting
portion 134a of the metallic material (shaft material 112) or a
portion corresponding to top 135a is mitigated. This can increase
the yield rate in forming of the prepared hole 133 (in the forging
process), and ensure the forming of the prepared hole 133.
Moreover, for example, a radially curved surface is formed at the
connecting portion 134a or top 135a, the diameter of the radially
curved surface can be large enough to maintain the guide function
of the pin of the conical surface 135 when the pin is pushed in.
Because of this, the stress at a portion corresponding to the
connecting portion 134a or a portion corresponding to the top 135a
when the pin is pushed in can be mitigated, while the guide
function of the conical surface formed at the tip of the pin when
it is pushed into the processed material regarding the pushing
direction is provided, enabling secure and accurate forming of the
prepared hole 133.
[0116] As mentioned above, when the prepared hole is formed by
forging, its reduction of are should be also noted. Reduction of
area refers to the ratio of a cross section area of a material
after being processed to that of the material before being
processed. As in this embodiment, when the prepared hole 133 is
formed by forging (mainly extrusion) on the bar metallic material
(shaft material 112), assuming that the edge outer diameter of the
shaft portion 113 in the shaft material 112 is d1 and the hole
diameter of the prepared hole 133 formed by forging is d2,
reduction in excess RA is, for example, represented by
RA=(.pi.d2.sup.2/4)/(.pi.d1.sup.2/4).times.100[%], as shown in FIG.
15.
[0117] Since the forging basically performs compression forming of
the material which will be the target to be processed, required
processing pressure, or processable processing pressure is affected
by the ductility and strength of the processed material, durability
(wear resistance, strength, etc.) of the mold. Therefore, to obtain
sufficient dimensional accuracy while ensuring moldability under
this condition, a dimensional limit of processing inevitably
occurs. From these perspectives, for example, when a steel material
such as stainless steel is used as a raw material of the processed
material (shaft material 112), the reduction in excess RA is
preferably within the range of 20%-75%. The upper limit of this is
preferably 70%, while the lower limit value is more preferably 25%.
Moreover, there is also an appropriate range of the axial length of
the prepared hole 133 formed for the reason mentioned above. For
example, the dimension of the prepared hole 133 (aspect ratio) is
preferably set so that the axial length (depth) E falls within the
range of 2.0.times.d2-3.0.times.d2 at its maximum.
[0118] Moreover, in the forging process of the shaft material 112,
depending on the shape of the shaft material 112 and the manner
that it is formed, compressive force is not sufficiently
transmitted to the tip portion of the shaft material 112,
deformation may be insufficient at the tip portion. In contrast, in
this embodiment, the prepared hole 133 of the threaded hole 131 is
formed by forging at the tip portion of the shaft portion 113
simultaneously with forging of the shaft material 112, the material
which was previously in the prepared hole 133 is pushed out to the
surrounding of the prepared hole 133 to cause the tip portion to
overhang on the outer diameter side and shaft end side.
Accordingly, the tip portion can be formed preventing deformation
shortage at the tip portion of the shaft material 112 as much as
possible in forging.
[0119] Note that a method of cold forging employed in the above
forming step may be extrusion mentioned above (forward extrusion
and backward extrusion), upsetting, heading or the like, or
combinations of them. In the examples shown in FIG. 15, the outer
circumferential surface 113a of the shaft portion 113 after the
forging process is in a different diameter shape which comprises a
tapered face 115 and a cylinder face 15 continuous upwardly with
the tapered face 115 and having a diameter than other portions
disposed therebetween, but the tapered face 115 may be dispensed
with and formed to have a uniform diameter throughout its
length.
(C-2) Thread Portion Rolling Process
[0120] In the prepared hole 133 of the shaft material 112 formed by
forging in the preceding step, for example, while a rolling tool
such as a rolled tap is relatively rotated between the shaft
material 112 and the tap itself is pushed into the prepared hole
133, although not shown in the Figs. Because of this, the outer
peripheral shape of the rolled tap is rolled to the cylinder face
134 of the inner periphery of the prepared hole 133, whereby the
valley 132a of the thread portion 132 is formed and the material
portion pushed out by the rolling of the valley 132a bulges on its
adjacent region, the peak 132b of the thread portion 132 is formed
(refer to FIG. 15 or 16).
[0121] As mentioned above, the prepared hole 133 to form the
threaded hole 131 is formed by forging so that the thread portion
132 can be formed by rolling on the inner periphery of the prepared
hole 133 formed by forging, that is, the threaded hole 131 is
formed by plastic processing. Therefore, chips (cutting powders,
etc.) caused by cutting or like machining can be greatly reduced.
Accordingly, it is possible to prevent chips from being deposited
on other parts constituting the bearing (including constitutional
parts of the motor) as contaminants in assembly, for example,
getting in the lubricating oil filling the inside of the fluid
lubrication bearing apparatus 101 while in use, or being
transferred to the disk D to cause disk crash. Moreover, since the
shaft material 112 and the prepared hole 133 of the threaded hole
131 are formed in a common forging step, such a forming step can be
simplified and processing costs can be reduced. In addition, chips
or other waste can be prevent before and after the forming process,
whereby materials can be efficiently used to greatly cut on
material costs. Alternatively, cycle time can be shortened by
employing forging processes and rolling processes, improving the
productivity.
(C-3) Correcting Process
[0122] To increase the dimensional accuracy of the shaft material
112 formed by a forging process, in particular the cylindricity of
the face corresponding to the outer circumferential 113a surface of
the shaft portion the shaft member 102 as a finished product
(hereinafter simply referred to as the outer circumferential
surface of the shaft portion), the outer circumferential surface
113a of the shaft portion of the shaft material 112 is subjected to
a plastic processing for correcting the cylindricity after the
forging process. Because of this, out of the outer circumferential
surface 113a of the shaft portion of the shaft material 112, the
outermost diameter surface 117 of the shaft portion 113 is
corrected, the cylindricity of the face 117 subjected to the
correcting process is improved to be in a desired range (for
example, 10 .mu.m or lower). Simultaneously, the cylinder face 116
of the upper end of the shaft portion 113 is also subjected to a
correcting process, whereby the cylindricity of the cylinder face
116 is improved similarly. Note that as the correcting process of
the cylindricity, rolling, drawing, ironing, sizing by pressing
split-cavity molds (nipping) or various other processing methods
can be employed.
(D) Grinding Step
(D-1) Width Grinding
[0123] both end faces of the shaft material 112 which have been
subjected to the correcting process, i.e., the end face 113b of the
shaft portion and the end face 114b of the flange portion 114 on
the side opposite to the shaft portion (refer to FIG. 15) are
ground relative to the outermost diameter surface 117 subjected to
said correcting process out of the outer circumferential surface
113a of the shaft portion (the first grinding step). The grinding
apparatus used in this grinding step comprises, as in the first
embodiment, a carrier 41 retaining a plurality of the shaft
materials 112 as workpieces; and a pair of grind stones 42, 42
which grind the end face 113b of the shaft portion of the shaft
material 112 retained by the carrier 41 and the end face 114b of
the flange portion 114 on the side opposite to the shaft portion,
as shown in FIGS. 7 and 8. Note that other constitutions of the
grinding apparatus 40 than this are based on the first embodiment,
and their explanations are thus omitted.
[0124] As the carrier 41 rotates, the shaft material 112 is loaded
into the notch 43a sequentially from a certain position. The loaded
shaft material 112 traverses the end faces of the rotating grind
stones 42, 42 from their outer diameter edge toward the inner
diameter edge in such a state that it is prevented from falling off
from the notch 43 by binding of the belt 44. Accordingly, both end
faces of the shaft material 112, namely the end face 113b of the
shaft portion an the end face 114b of the flange portion 114 on the
side opposite to the shaft portion, are ground by the end face s of
the grind stones 42, 42. Moreover, the width of the shaft material
112 in the axial direction (the entire length including the flange
portion 114) is finished to have a predetermined size.
(D-2) Full Face Grinding Process
[0125] Subsequently, the outer circumferential surface 112a of the
shaft material 112 and the end face 114a of the flange portion 114
on the shaft portion side are ground relative to the ground end
faces 113b, 114b of the shaft material 112 (both end faces 121b,
122b of the shaft member 102) (the second grinding step). As in the
first embodiment, the grinding apparatus used in this grinding step
performs plunge-grinding by the grind stone 53 with the back plate
54 and pressure plate 55 pressed against both end faces of the
shaft material 112, as shown in FIG. 9. The correcting process face
117 of the shaft material 112 is rotatably supported by a shoe 52.
Note that other constitutions of the grinding apparatus 50 than
this is based on the first embodiment, and their explanations are
thus omitted.
[0126] Grinding in the grinding apparatus 50 of the above
constitution is performed in the following procedure. To begin
with, while the shaft material 112 and the grind stone 53 are in
rotation, the grind stone 53 is fed obliquely (the direction of
arrow 1 in FIG. 9), a plane grinding portion 56b of the grind stone
53 is pressed against the end face 114a of the flange portion on
the shaft portion side of the shaft material 112 to grind mainly
the end face 114a on the shaft portion side. The shaft portion side
end face 122a in the flange portion 122 of the shaft member 102 is
thus formed. Subsequently, the grind stone 53 is fed in the
direction perpendicularly intersecting the rotation axis of the
shaft material 112 (the direction of arrow 2 in FIG. 9), and then
the cylinder grinding portion 56a of the grind stone 53 is pressed
against the outer circumferential surface 113a of the shaft portion
113 of the shaft material 112 and the outer circumferential surface
114C of the flange portion 114 to grind the faces 113a, 114C.
Accordingly, out of the outer circumferential surface of the shaft
portion 121 of the shaft member 102, the radial bearing faces 123a,
123b and the region corresponding to the cylinder face 125 are
ground and the tapered face 124, the outer circumferential surface
122C of the flange portion 122, and the recess portions 126-128 are
further formed.
(D-3) Finish Grinding Process
[0127] (D-2) Among the faces which have been ground in the full
face grinding process, the radial bearing faces 123a, 123b of the
shaft member 102 and the region corresponding to the cylinder face
125 are subjected to the final finish grinding process. As in the
first embodiment, a grinding apparatus used in this grinding
performs plunge grinding on the rotating shaft material 112 held
between the back plate 64 and pressure plate 65 by the grind stone
63 with the cylinder grinder shown in FIG. 10. Note that other
constitutions of the grinding apparatus 60 are based on the first
embodiment, and their explanations are thus omitted.
[0128] In the grinding apparatus 60 having the above constitution,
the radial bearing faces 123a, 123b and the region corresponding to
the cylinder face 125 are ground by providing the rotating grind
stone 63 with the feed in the radial direction, and these regions
are finished to have the final surface accuracy.
[0129] After the above (C) forming step and (D) grinding step, heat
treatment and cleaning process, if necessary, are performed so that
the shaft member 102 shown in FIG. 11 is completed.
[0130] The shaft member 102, as long as it is produced by the above
production method, by forming the prepared hole 133 with high
accuracy, the forming accuracy of the threaded hole 131, for
example, the coaxiality of the center line of the pitch circle of
the thread portion relative to the axis of the shaft member 102 can
be suppressed to 0.2 mm or lower. Moreover, according to the above
production method, relative to the radial bearing faces 123a, 123b
formed on the outer periphery of the shaft portion 121, it is also
possible to form the shaft member 102 with suppressed
perpendicularity of both end faces 122a, 122b of the flange portion
122 (thrust bearing face) and suppressed value of the
perpendicularity of the end face 121b of the of the shaft portion.
Among these, the end face 121b of the shaft portion not only serves
as a reference plane for grinding the outer circumferential surface
of the shaft portion 121 and the upper end face of the flange
portion 122 (thrust bearing face 122a side), but also serves as a
contact surface when the clamper 110 which holds the disk D between
the disk hub 3 and itself to fix it is fixed on the shaft member
102 (screw fixing).
[0131] Accordingly, as mentioned above, the forming accuracy of the
threaded hole 131 (in particular, the coaxiality of the thread
portion 132) can be increased, and the value of the
perpendicularity of the end face 121b of the of the shaft portion
can be also suppressed to a low level, whereby the mounting
accuracy on the shaft member 102 of the clamper 110 can be
increased. As a result, the disk D can be fixed with the value of
the perpendicularity relative to the shaft member 102 suppressed to
a low level, and runout of the disk D relative to the shaft member
102 when the shaft member 102 is in rotation can be suppressed.
Hence, excellent disk rotation can be obtained.
[0132] According to the above production method, the cylindricity
of the radial bearing faces 123a, 123b formed on the outer
periphery of the shaft portion 121 can also be finished highly
accurately. Because of this, for example, variation in the
circumferential or axial dimension of the radial bearing gap formed
between the inner periphery of the bearing sleeve 8 in the fluid
lubrication bearing apparatus 101 and the outer periphery of the
shaft portion 121 can be suppress to be in a predetermined range,
and the bearing performance can be thus prevented from being
adversely affected by the variation of the above radial bearing
gap. Furthermore, the region corresponding to the cylinder face 125
of the shaft portion 121 is subjected to the finish grinding
process (refer to FIG. 10) so that the cylindricity of the cylinder
face 125 can also be finished highly accurately, increasing the
mounting accuracy in mounting the disk hub 3 or other components on
the shaft member 102. This can further increase the mounting
accuracy of the clamper 110 and the disk D clamped between the
clamper 110 and disk hub 3 relative to shaft member 102, thereby
further improving the motor performance.
[0133] Note that the example described in the above embodiment is
so constructed that a radially curved surface is formed in the
prepared hole 133 at the connecting portion 134a between the
conical surface 135 and cylinder face 134 and that a radially
curved surface is formed on the top 135a of the conical surface
135, but it is not limited to this configuration. For example, as
for the connecting portion 134a, there may be formed any face as
long as the it smoothly connects the conical surface 135 and the
cylinder face 134. Moreover, as for the top 135a, there may be
formed any face as long as the top 135a is removed from the top
135a, for example, a flat face where the top 135a is removed
(truncated conical surface) may be formed in stead of a radially
curved surface.
[0134] A third embodiment of the present invention will be
described below with reference to FIGS. 17-23.
[0135] FIG. 18 conceptionally shows one constitutional example of a
spindle motor for information appliances incorporating a fluid
lubrication bearing apparatus 201 according to the third embodiment
of the present. This spindle motor is used for Disk drive units
such as HDDs, and comprises a fluid lubrication bearing apparatus
(hydrodynamic bearing apparatus) 201 which rotatably supports the
shaft member 202 fixing the hub 203 in a non-contact manner; for
example, a stator coil 204 and a rotor magnet 205 opposing each
other across a gap in the radial direction; and a bracket 206. The
stator coil 204 is mounted on the outer diameter side of the
bracket 206, and the rotor magnet 205 is mounted on outer periphery
of the hub 203. The bearing component 207 of the fluid lubrication
bearing apparatus 201 is fixed on the inner periphery of the
bracket 206. Moreover, one or more of the disk D is retained on the
hub 203. In FIG. 18, two of the disk D is retained on the hub 203.
In the thus constructed spindle motor, when the stator coil 204 is
energized, the rotor magnet 205 is rotated by the excitation
produced between the stator coil 204 and rotor magnet 205, whereby
the disk D retained on the shaft member 202 and the hub 203 which
is fixed on shaft member 202 are rotated unitarily with the shaft
member 202.
[0136] FIG. 19 shows the fluid lubrication bearing apparatus 201.
This fluid lubrication bearing apparatus 201 mainly comprises a
bearing component 207 whose one end opens, a shaft member 202 which
is inserted at the inner periphery of the bearing component 207 and
rotates relative to the bearing component 207. Note that for the
sake of explanation, the side of a bottom 209b of the housing
portion 209 constituting the bearing component 207 is referred to
as the lower side, while the side opposite to the bottom 209b is
referred to as the upper side in the description below.
[0137] The bearing component 207 has such a shape that it opens at
least at one axial end, and separately comprises an approximately
cylindrical sleeve portion 208 and a housing portion 209 positioned
on the outer diameter side of the sleeve portion 208 in this
embodiment.
[0138] The sleeve portion 208 is, for example, formed in the form
of a cylinder with a metallic non-porous body or a porous body made
of a sintered metal. In this embodiment, the sleeve portion 208 is
formed in the form of a cylinder form with a porous body made of a
sintered metal comprising copper as a main ingredient, and is fixed
on the inner periphery face (large diameter face 209C) of the
housing portion 209 by, for example, adhesion (including loose
adhesion and press fitting adhesion), press fitting, welding (for
example, ultrasonic welding) or other suitable means. Of course,
the sleeve portion 208 can be also formed from non-metallic
materials such as resins, ceramics, etc.
[0139] On the entire surface of the inner periphery face 208a of
the sleeve portion 208 or a part thereof a cylinder region, a
region in which a plurality of hydrodynamic grooves are arranged is
formed. In this embodiment, for example, a region in which a
plurality of hydrodynamic grooves is arranged in a herringbone
shape is formed at two axially separated positions, as in FIG.
4.
[0140] In the entire annular region of the lower end face 208b of
the sleeve portion 208 or a part thereof, a region in which a
plurality of hydrodynamic groove are spirally arranged as a portion
for producing thrust hydrodynamic pressure, for example, as in FIG.
5, is formed. This region in which the hydrodynamic grooves are
formed faces the upper end face 222a of the flange portion 222 as a
thrust bearing face. While the shaft member 202 is in rotation, the
region forms the thrust bearing gap of a first thrust bearing
portion T21 described later between the itself and the upper end
face 222a (refer to FIG. 19).
[0141] The housing portion 209 is formed of a metal or a resin, and
has a cylinder part 209a, and a bottom 209b integrally or
separately formed at the lower end of the cylinder part 209a. In
this embodiment, the bottom 209b is formed integrally with the
cylinder part 209a.
[0142] In the entire annular region of the upper end face 209b1 of
the bottom 209b or a part thereof, a region in which a plurality of
hydrodynamic groove are spirally (the spiral direction is opposite
to that in FIG. 5) arranged as a portion for producing thrust
hydrodynamic pressure, for example, as in FIG. 5, is formed. This
the region in which the hydrodynamic grooves are formed faces the
lower end face 222b of the flange portion 222 as a thrust bearing
face. While the shaft member 202 is in rotation, the region forms
the thrust bearing gap of a second thrust bearing portion T22
described later between itself and the lower end face 222b (refer
to FIG. 19).
[0143] The inner periphery face of the housing portion 209 is
mainly constituted of a large diameter face 209C where the sleeve
portion 208 is fixed, a small diameter face 209D which is provided
at the lower end of the large diameter face 209C and has a diameter
smaller than that of the large diameter face 209C. In this
embodiment, the upper end face 209E is formed on the shoulder
between the large diameter face 209C and small diameter face 209D.
In the state that the lower end face 208b of the sleeve portion 208
is in contact with the upper end face 209E, the width in the axial
direction from the lower end face 208b of the sleeve portion 208 to
the upper end face 209b1 of the bottom 209b is set to be equal to
the axial dimension of the small diameter face 209D. Accordingly,
(the sum of) the thrust bearing gap described later can be obtained
highly accurately by controlling the axial dimension of the small
diameter face 209D highly accurately.
[0144] A sealing portion 210 as a sealing means is formed, for
example, of a metallic material or a resin material separately from
the housing portion 209, and is fixed by press fitting, adhesion,
deposition, welding or other means on the inner periphery of the
upper end portion of the cylinder part 209a of the housing portion
209. In this embodiment, fixing of the sealing portion 210 is
conducted with the lower end face 210b of the sealing portion 210
in contact the upper end face 208D of the sleeve portion 208 (for
example, refer to FIG. 19).
[0145] A tapered face is formed on the inner periphery face 210a of
the sealing portion 210. Between this tapered face and the outer
circumferential surface of the shaft portion 221 facing the tapered
face, an annular sealing space S2 whose radial dimension upwardly
and gradually increases is formed. A lubricating oil is placed in
the inner space of the housing portion 209 sealed by the sealing
portion 210, and the inside of the housing portion 209 is filled
with the lubricating oil (dotted region in FIG. 19). In this state,
the oil level of the lubricating oil is maintained within the range
of the sealing space S2.
[0146] As shown in FIG. 17, the shaft member 202 is formed of a
metallic material such as stainless steel, and has a T-shaped cross
section integrally comprising the shaft portion 221 and the flange
portion 222 provided at the lower end of the shaft portion 221. On
the outer periphery of the shaft portion 221, radial bearing faces
223a, 223b facing regions on the inner periphery face 208a of the
sleeve portion 208 where upper and lower hydrodynamic grooves are
formed, respectively, are formed at two axially separated
positions.
[0147] A concave 225 is formed on the tip face 224a of the tip
portion 224. In this embodiment, the concave 225 consists a
plastically processed surface 225a, and is so configured that its
diameter gradually decreases from the tip face 224a side toward the
center of the shaft portion 221. A cylindrical outer
circumferential surface 224b is provided at the tip portion 224 of
the shaft portion 221 positioned on the opposite side in the axial
direction of the flange portion 222, and a hub 203 is fixed on this
outer circumferential surface 224b by press fitting, adhesion or
other means. Note that annular recess portions 226, 227, 228 are
formed between the two radial bearing faces 223a, 223b, between the
lower radial bearing face 223b and the flange portion 222, and
between the upper radial bearing face 223a and outer
circumferential surface 224b, respectively.
[0148] In the fluid lubrication bearing apparatus 201 having the
above constitution, while the shaft member 202 is in rotation, a
hydrodynamic groove formation region formed on the inner periphery
face 208a of the sleeve portion 208 forms a radial bearing gap
between itself and the radial bearing faces 223a, 223b of the shaft
portion 221 facing it. In addition, as the shaft member 202
rotates, the lubricating oil in the above radial bearing gap is
pushed to the axial center side of the hydrodynamic groove (refer
to FIG. 4), and its pressure is increased. As mentioned above, a
first radial bearing portion R21 and a second radial bearing
portion R22 which support the shaft portion 221 in a non-contact
manner in the radial direction are constituted, respectively, by
the hydrodynamic effect of the lubricating oil produced by the
hydrodynamic grooves.
[0149] Simultaneously, the pressure of the lubricating oil film
formed in the thrust bearing gap between the lower end face 208b of
the sleeve portion 208 (hydrodynamic groove formation region) and
the upper end face 222a of the flange portion 222 facing it, and
the pressure in the thrust bearing gap between a region formed on
the upper end face 209b1 of the bottom of the housing portion 209
where the hydrodynamic grooves are formed and the lower end face
222b of the flange portion 222 facing it are increased by the
hydrodynamic effect of the hydrodynamic grooves. In addition, a
first thrust bearing portion T21 and a second thrust bearing
portion T22 which support the flange portion 222 (shaft member 202)
in the thrust direction in a non-contact manner are constituted by
the pressure of these oil films, respectively.
[0150] The production method of the shaft member 202 constituting
the above fluid lubrication bearing apparatus 201 will be described
below.
[0151] The shaft member 202 is produced mainly in the following two
steps: a forming step (E), and a grinding step (F). In this
procedure, the (E) forming step comprises a shaft material forging
process (E-1) and a shaft portion correcting process (E-2).
Moreover, the (F) grinding step comprises a width grinding process
(F-1), a full face grinding process (F-2), and finish grinding
process (F-3). In this embodiment, the (E-1) shaft material forging
process is mainly described.
(E) Forming Step
(E-1) Shaft Material Forging Process
[0152] To begin with, a material of the shaft member 202 to be
formed, i.e., a bar material made of metal such as stainless steel
is compression-formed (forging process) by using molds, for
example, in a cold state, so that, for example, the shaft material
212 integrally having the region corresponding to the shaft portion
(hereinafter referred to simply as a shaft portion) 213 and the
region corresponding to the flange portion (hereinafter referred to
simply as a flange portion.) 214 is formed {shaft material forging
process (E-1)} as shown in FIG. 20.
[0153] As mentioned above, if the shaft material 212 is formed by
forging, no cutting powders are produced by processing, wasted of
the material can be reduced, and a cleaning step after the process
can also be simplified. Moreover, since it is a pressing operation,
the cycle time per one piece of the shaft material 212 can be
shortened, improving the productivity.
[0154] Methods which can be employed as the above forging process
include extrusion, upsetting process and other various processes,
and a processing method suitable for the shape of the processed
article is selected. For example, in the shaft material 212 in the
shape shown in FIG. 20, to increase the forming accuracy of the
shaft portion 213, for example, it is possible to employ a method
comprising roughly forming the shaft material 212 from a wire by a
different forging, and then compressing the shaft material 212 by
mold clamping with molds 216, 217 in the axial direction to cause
the shaft portion 213 to overhang in the radial direction, as shown
in FIG. 21.
[0155] In this case, although sufficient compressive force can be
applied to the portions in the vicinity of the dividing face of the
molds 216, 217 such as the flange portion 214 and the end on the
flange portion 214 side of the shaft portion 213, compressive force
is not sufficiently transmitted to the portions which are far from
the dividing face such as the tip portion 215 of the shaft portion
213 on the side opposite to the flange portion 214. Consequently,
deformation in the radial direction associated with compression
becomes insufficient in particular at the tip portion 215. For
example, as shown in FIG. 22, the closer to the tip face 215a, the
tip portion 215 of the shaft portion 213 tends to be tapered.
[0156] In contrast, for example, if a protrusion 218 of the shape
shown in FIG. 23 is provided at the center portion of a formed
surface 217a corresponding to the tip face 215a of the mold 217, a
concave 225 having the shape corresponding to the protrusion 218a
is formed on the tip face 215a of the tip of the shaft portion 215.
Since this concave 225 is formed by pushing the protrusion 218 into
the tip face 215a to cause the corresponding region to undergo
plastic deformation, the tip portion 215 is caused to overhang by
such plastic deformation, whereby the shortage of plastic
deformation at the tip portion 215 can be compensated. In this
embodiment, plastic flow in the outer radial direction occurs
uniformly in the axial direction and the outer circumferential
surface 215b overhang to the shape corresponding to the inner
periphery face 217a of the mold 217, whereby tapering of the tip
portion 215 can be prevented and the tip portion 215 having a
constant diameter can be formed.
[0157] Note that in the example shown in FIG. 23, described is the
case where the concave 225 is formed on the tip face 215a so that
the tip portion 215 is caused to overhang and the tip portion 215
is deformed until the shape in which the diameter of the outer
circumferential surface 215b becomes constant is reached, but it is
not necessarily be caused to overhang to such a degree. For
example, the shape of the concave 225 (protrusion 218) and its size
can be set in a grinding step described later so that the tip
portion 215 is caused to overhang until the final finished shape is
reached. In this embodiment, the final finished shape of the tip
portion 224 of the shaft member 202 as a finished product is
defined by the outer circumferential surface 224b of the tip
portion 224, tip face 224a and a chamfer 224C provided between the
faces 224a, 224b. Therefore, In this case, the following grinding
step is enabled by causing it to overhang somewhat larger than the
shape defined by the faces 224a, 224b, 224C, obtaining the shaft
member 202 having high dimensional accuracy.
[0158] Moreover, in this embodiment, since the concave 225 is in
such a shape that its diameter gradually decreases from the tip
face 224a side to center of the shaft portion 221, the closer to
the tip face 215a side in plastic processing of the concave 225,
the greater the amount of deformation in the outer radial
direction. Therefore, tapering of the tip portion 215 can be
prevented and the shaft portion 213 can be formed more accurately
by forming the concave 225 in such a shape.
[0159] The forming forging step can be performed, as mentioned
above, separately in two or more forging steps, or for example, a
wire having constant diameter can be formed in one forging step.
Moreover, in this embodiment, the case where forming of the shaft
material 212 and forming of the concave 225 are performed with a
common mold is described, but forming of both is not necessarily
performed simultaneously. For example, after forming the shaft
material 212 by forging, the same action as that mentioned above
can be obtained as above by forming the concave 225 by forging.
(E-2) Correcting Process
[0160] To increase the dimensional accuracy of the shaft material
212 formed by a forging process, in particular the cylindricity of
the face corresponding to the outer circumferential surface 213a of
the shaft portion of the shaft member 2 as a finished product
(hereinafter referred to simply as the outer circumferential
surface of the shaft portion), a plastic processing for correcting
the cylindricity is performed on the outer circumferential surface
213a of the shaft portion of the shaft material 212 after being
subjected to the forging process. Accordingly, the outer
circumferential surface 213a of the shaft portion of the shaft
material 212 is corrected, the cylindricity of the face 213
subjected to the correcting process is improved to be in a desired
range (for example, 10 .mu.m or lower). When the outer
circumferential surface 215b of the tip portion 215 is formed to
have the same diameter as the outer circumferential surface 213a of
the shaft portion, the outer circumferential surface 215b is also
subjected to a correcting process, and the cylindricity of the
outer circumferential surface 215b is improved similarly.
(F) Grinding Step
(F-1) Width Grinding
[0161] Both end faces of the shaft material 212 which has been
subjected to the correcting process, i.e., the tip face 215a of the
shaft portion and the end face 214b of the flange portion 214 on
the side opposite to the shaft portion (refer to FIG. 20) is ground
relative to the outermost diameter surface 217 subjected to said
correcting process of the outer circumferential surface 213a of the
shaft portion (The first grinding step). A grinding apparatus used
in this grinding step is, for example, similar to the grinding
apparatus 40 shown in FIGS. 7 and 8. Since other constitutions,
arrangements and processing manners are based on the first
embodiment, their explanations will be omitted.
[0162] By such a grinding step, the tip face 215a of the shaft
portion and the end face 214b of the flange portion 214 on the side
opposite to the shaft portion are ground. At this time, because the
corrected face 213a of the shaft material 212 is supported by the
carrier 41 and this corrected face 213a have high cylindricity, if
the perpendicularity of the rotation axis of the grind stone 42 and
the grinding surface of the grind stone 42, and the parallelism of
the rotation axis of the grind stone 42 and the rotation axis of
the carrier 41, etc. are highly accurately controlled in advance,
said both end faces 215a, 214b of the shaft material 212 can be
highly accurately finished relative to this corrected face 213a,
and the value of the perpendicularity relative to the corrected
face 213a can be suppressed to a low level. Moreover, the axial
width of the shaft material 212 (the entire length including the
flange portion 214) is finished to have a predetermined size.
(F-2) Full Face Grinding Process
[0163] Subsequently, the outer circumferential surface 213a and the
end face 214a of the flange portion 214 on the shaft portion side
of the shaft material 212 relative to both end faces 215a, 214b of
the ground shaft material 212 are ground (second grinding step).
The grinding apparatus used in this grinding step is, for example,
similar to the grinding apparatus 50 shown in FIG. 9.
[0164] Moreover, a grind stone used in this grinding is a formed
grind stone comprising a grinding surface corresponding to the
outer circumferential surface shape of the shaft member 202 as a
finished product, and, although not shown in the Figs., comprises
radial bearing faces 223a, 223b; outer circumferential surface 224b
of the tip portion; a chamfer 224C; recess portions 226-228, outer
circumferential surface 222C of the flange portion 222; and a
grinding surface which grinds a region corresponding to upper end
face 222a of the flange portion 222. Since other constitutions,
arrangements and processing manners are based on the first
embodiment, their explanations are omitted.
[0165] By such a grinding process, out of the outer circumferential
surface of the shaft portion 221 of the shaft member 202, the
radial bearing faces 223a, 223b and the outer circumferential
surface 224b of the tip portion, and the region corresponding to
the chamfer 224C are ground, and the outer circumferential surface
222C of the flange portion 222 and the recess portions 226-228, the
upper end face 222a of the flange portion 222 are further formed.
In this grinding step, since the accuracy setting of the
perpendicularity of both end faces 215a, 214b of the shaft material
212 (both end faces 224a, 222b of the shaft member 202) has been
conducted previously in the width grinding, each of the
to-be-ground surfaces can be ground highly accurately.
(F-3) Finish Grinding Process
[0166] Among the faces which have been ground in full face grinding
process, the radial bearing faces 223a, 223b of the shaft member
202, and the region corresponding to the outer circumferential
surface 224b of the tip portion are subjected to the final finish
grinding process. A grinding apparatus used in this grinding is,
for example, similar to the grinding apparatus 60 shown in FIG. 10.
Since other constitutions, arrangements and processing manners are
based on the first embodiment, their explanations will be
omitted.
[0167] By such a grinding process, the radial bearing faces 223a,
223b and the region corresponding to the outer circumferential
surface 224b of the tip portion are ground, and these regions are
finished to have the final surface accuracy.
[0168] After the above (E) forming step and (F) grinding step, heat
treatment and cleaning process, if necessary, are performed to
complete the shaft member 202 shown in FIG. 17.
[0169] The shaft member 202, as long as it is produced by the
production method mentioned above, can be formed so that the shaft
portion 221, in particular the tip portion 224 of the shaft portion
221 is caused to overhang until at least a final finished shape is
reached, and said outer circumferential surface 215b can be
finished highly accurately by the following grinding. Accordingly,
a fixing area between the hub 203 and said outer circumferential
surface 215b can be ensured to obtain high fixing strength and
fixing accuracy between the hub 203 and the outer circumferential
surface 215b. Moreover, according to such a constitution, it is
possible to readily deal with the elongation of the shaft member
202 by adjusting the size of the concave 225 formed on the tip face
224a of the shaft portion or the like.
[0170] In the above embodiment (first embodiment), the case where
the radial bearing faces 23a, 23b of the shaft member 2 and thrust
bearing faces 22a, 22b are all smooth surface having no
hydrodynamic grooves was exemplified, but hydrodynamic grooves may
be formed on these bearing faces. In this case, the radial
hydrodynamic groove can be formed by rolling or forging, and the
thrust hydrodynamic grooves can be formed by pressing or forging at
the stage preceding the full face grinding process shown in FIG. 8.
Similarly, hydrodynamic grooves can be also formed on the shaft
member 102 according to the second embodiment and the shaft member
202 according to third embodiment.
[0171] Moreover, in the embodiments described above, as the
hydrodynamic bearing constituting the radial bearing portions R1,
R2 and the thrust bearing portions T1, T2, for example, bearings
using hydrodynamic pressure producing parts comprising hydrodynamic
grooves arranged in a herringbone shape and a spiral shape are
shown as examples, but the constitution of the hydrodynamic
pressure producing parts are not limited to these. Examples of the
radial bearing portions R1, R2 used include a multirobe bearing,
step bearing, taper bearing, taper flat bearing or the like.
Examples of the thrust bearing portions T1, T2 used include a step
pocket bearing, tapered pocket bearing, tapered flat bearing or the
like. Hydrodynamic bearings having similar constitutions can be
used for the radial bearing portions R11, R12 and the thrust
bearing portions T11, T12 according to the second embodiment and
the radial bearing portions R21, R22 and thrust bearing portions
T21, T22 according to the third embodiment.
[0172] Moreover, as for the second and third embodiments, the
radial bearing portions R11, R12 and thrust bearing portions T11,
T12 can be also constituted of bearings other than hydrodynamic
bearings, for example, a pivot bearing can be used as the thrust
bearing portion, and a cylindrical bearing as a radial bearing
portion.
[0173] Moreover, in the embodiments described above, a lubricating
oil is mentioned as an example of a fluid which fills the inside of
the hydrodynamic bearing apparatus 1, and produces hydrodynamic
effect in the radial bearing gap between the bearing sleeve 8 and
the shaft member 2 and in the thrust bearing gaps W1, W2 between
the bearing sleeve 8 and housing 7 and the shaft member 2. However,
such a fluid is not particularly limited to this fluid. As a fluid
which can produce hydrodynamic effect in the bearing gaps having
hydrodynamic grooves, for example, a gas such as air and a
lubricant having fluidity such as a magnetic fluid may be used. Of
course, similar kind of fluids may be used for the fluid
lubrication bearing apparatus 101, 201 according to the second and
third embodiments.
[0174] The fluid lubrication bearing apparatus according to the
present invention is suitable for information appliances, for
example, Magnetic disk apparatuses such as HDD, optical disk
apparatuses such as CD-ROM, CD-R/RW and DVD-ROM/RAM, spindle motors
for magneto-optic disk apparatuses such as MD and MO, polygon
scanner motors of laser beam printers (LBP), color wheel motors of
projectors, or small motors such as fan motors.
* * * * *