Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2002-09-24
2004-08-24
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
Reexamination Certificate
active
06779924
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a dynamic pressure bearing, and particularly to a dynamic pressure bearing having dynamic pressure grooves formed on the inner peripheral surface of a sleeve in which a shaft is fitted, which has high precision, reduces the manufacturing cost and has a lower bearing damage rate, and a method of manufacturing the dynamic pressure bearing.
A dynamic pressure bearing, in which a shaft is fitted in a sleeve and relatively rotated and herringbone type or spiral type grooves are formed on at any one of the inner peripheral surface of the sleeve and the outer peripheral surface of the shaft, is used as a bearing apparatus for a spindle motor rotating at high speed in information equipment or the like.
For example, as shown in
FIG. 9
, there is used such a dynamic pressure bearing that herringbone type dynamic pressure grooves
23
are formed on the inner peripheral surface of a sleeve
21
on which a stator coil
21
is mounted, a shaft
25
is fitted in the sleeve
21
so that a ferromagnetic material (not shown) is disposed to face the stator coil
20
and the stator coil
20
is supplied with current to rotate the shaft
25
at high speed. Such a dynamic pressure bearing is used in an apparatus in which a polygon mirror or optical disc (not shown) is fixed to the shaft
25
and a laser beam is reflected therefrom to record or read out information.
On the inner peripheral surface
21
b
of the sleeve
21
, a bearing portion
22
is equipped at a step portion
21
a
having a slightly reduced diameter, and herringbone type or spiral type V-shaped dynamic pressure grooves
23
are formed on the inner surface of the bearing portion
22
of the step portion
21
a
as shown in
FIGS. 10 and 11
. Alternatively, dynamic pressure grooves may be formed on the outer peripheral surface of the shaft
25
in place of formation of the dynamic pressure grooves
23
on the inner peripheral surface of the sleeve
21
. Such dynamic pressure grooves
23
are usually formed by plastic working based on form rolling. Further, there is known an example of forming dynamic pressure grooves by using an electrolytic etching working in order to satisfy recent requirements for high precision and increase of working speed. In the case of stainless steel, etc., etching working on these materials needs much time. Therefore, there has been proposed a dynamic pressure-bearing achieved by subjecting a bearing face of a sleeve of aluminum alloy to plastic working based on ball form rolling and carrying out an alumite treatment after honing working, thereby forming an anode oxidation coating (Japanese Laid-open Patent Application No. Hei-8-247138).
To overcome lack of lubricating oil in bearing gaps to enhance durability and bearing rigidity, such a dynamic pressure bearing is proposed that it includes dynamic pressure grooves formed on the inner peripheral surface of the sleeve, lubricating oil or grease is impregnated in the bearing body
31
, and dynamic pressure grooves
33
are formed to be inclined with respect to the bearing face of the bearing body as shown in
FIG. 12A
(Japanese Laid-open Patent Application No. Hei-11-82479). According to the bearing apparatus thus constructed, the rotational shaft is supported under a non-contact state by dynamic pressure films of the lubricating oil formed in the bearing gaps, and the lubricating oil is circulated between the inside of the bearing body
32
and each bearing gap through opening portions of the bearing face. In this case, as shown in
FIG. 12B
, each dynamic pressure groove
33
comprises one oblique groove
33
a
, the other oblique groove
33
b
and a smoothing portion
34
formed between the oblique grooves
33
a
and
33
b.
As described above, the dynamic pressure grooves
23
of the bearing portion
22
equipped at the step portion
21
a
of the inner peripheral surface of the conventional sleeve
21
are formed over the whole width D from one end portion
21
c
of the step portion
21
c
to the other end portion of the step portion
21
c
. Therefore, as shown in
FIG. 11
, particularly when the shaft
25
is rotated in a bell-shaped mode (conical mode or precession mode) at the start or stop time of the motor, the shaft
25
damages the end portions
21
c
of the step portion
21
a
. If the end portions
21
c
of the step portion
21
a
at which the bearing portion
22
is equipped are repetitively damaged due to rotation of the shaft
25
in such a conical mode as described above, the performance as the dynamic pressure bearing is degraded, and finally it adversely affects the performance and lifetime of equipment equipped with such a dynamic pressure bearing.
According to the conventional technique, after dynamic pressure grooves
23
are formed on the inner peripheral surface of a sleeve by the plastic working based on the form rolling as described above, it is required to carry out finish machining by reaming, balling, horning or the like, so that the manufacturing cost is high.
The etching process used as a work to form dynamic pressure grooves has high precision, however, it still needs a high manufacturing cost. Further, dynamic pressure grooves may be formed by the electrolytic etching processing. However, the conventional processing has a problem that pattern symmetry is lost unless the positioning to a work is not performed at high precision, so that fluid flow occurs.
SUMMARY OF THE INVENTION
The present invention has been implemented to overcome the foregoing problem, and has an object to provide a dynamic pressure bearing which can reduce damages of dynamic pressure grooves even when a shaft has a swinging motion in a conical mode, simplify the positioning (precision) to keep symmetry in an electrolytic etching process and exhibit high performance, and a method of manufacturing the dynamic pressure bearing.
In order to solve the aforesaid object, the invention is characterized by having the following arrangement.
(1) A dynamic pressure bearing comprising:
a sleeve;
a bearing portion formed on an inner peripheral surface of the sleeve, wherein a diameter of an inner peripheral surface of the bearing portion is smaller than the inner diameter of the sleeve; and
dynamic pressure grooves formed on a part of the inner peripheral surface of the bearing portion, wherein the dynamic pressure groove is not formed at opposite end portions of the bearing portion.
(2) A method of manufacturing a dynamic pressure bearing including a sleeve; a bearing portion formed on an inner peripheral surface of the sleeve, having a predetermined width, wherein the diameter of the inner peripheral surface of the bearing portion is smaller than the inner diameter of the sleeve; and dynamic pressure grooves formed on a part of the inner peripheral surface of the bearing portion, wherein the dynamic pressure groove is not formed at opposite end portions of the bearing portion, the method comprising the step of:
subjecting the sleeve to electrolytic etching to form the dynamic pressure groove.
(3) A dynamic pressure bearing comprising:
a sleeve;
a bearing portion formed on an inner peripheral surface of the sleeve, having a first width in an axial direction, wherein a diameter of an inner peripheral surface of the bearing portion is smaller than an inner diameter of the sleeve; and
dynamic pressure groove formed on the inner peripheral surface of the bearing portion, having a second width in the axial direction smaller than the first width.
(4) The dynamic pressure bearing according to (3), wherein the dynamic pressure groove is not formed at opposite end portions of the bearing portion.
(5) The dynamic pressure bearing according to (3), wherein a center line of the first width is coincident with a center line of the second width.
REFERENCES:
patent: 08-247138 (1996-09-01), None
patent: 11-082479 (1999-03-01), None
patent: 2001-099159 (2001-04-01), None
patent: 2001-200846 (2001-07-01), None
Footland Lenard A.
Koyo Seiko Co. Ltd.
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