Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-03-05
2003-04-29
Lavinder, Jack (Department: 3683)
Bearings
Rotary bearing
Fluid bearing
C384S107000, C029S898041
Reexamination Certificate
active
06554476
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a dynamic pressure bearing device applicable to apparatus rotating at high speed, for example hard disk drivers, rotary polygon mirror drivers and so forth and methods of manufacturing such a device, and more particularly to a thrust dynamic pressure bearing device and a method of manufacturing the same.
Among apparatus rotating at high speed such as hard disk drivers, there is one using a dynamic pressure bearing so arranged that rotors can rotate without contacting bearing members by causing dynamic pressure to be generated in lubricating oil lying between the rotors and the bearing members while the rotors are rotating upon the respective bearing members. Such a dynamic pressure bearing includes a radial dynamic pressure bearing for supporting the rotor in the direction in which it rotates and a thrust bearing for supporting the rotor in the axial direction.
As for a known thrust bearing, it is formed by press-fitting a disk-like thrust plate into a rotary shaft in order to secure the thrust plate thereto.
The dynamic pressure bearing device will be briefly described by the use of an example of a hard disk driving motor shown in FIG.
6
. The structure of the thrust bearing shown in
FIG. 6
conforms to what is based on the present invention and though the motor structure is well known, the following description will be given to make clear problems to be solved by the invention.
In
FIG. 6
, a motor frame
8
has a hole for fixing a sleeve
4
and the lower end portion of the sleeve
4
is securely press-fitted into the hole. The sleeve
4
is a cylindrical member having a central shaft hole, and a small-diameter and a large-diameter recessed portions
13
and
14
are formed round the central shaft hole in the lower end portion of the sleeve
4
. The central hole of a stator core
12
is placed in the outer periphery of the sleeve
4
and fixedly bonded thereto or fixed by a proper member. The stator core
12
has a proper number of radially projected poles and a driving coil
23
is wound on each projected pole.
A rotary shaft
1
is inserted into the central hole of the sleeve
4
. A disk-like thrust plate
5
has been secured to the lower end portion of the rotary shaft
1
by press-fitting. The thrust plate
5
is disposed in the small-diameter recessed portion
13
of the sleeve
4
. A counter plate
6
forming a fixed-side dynamic pressure bearing part is fixedly fitted in the large-diameter recessed portion
14
so as to positioned the thrust plate
5
in the small-diameter recessed portion
13
.
Herringbone dynamic pressure grooves are formed on upper and lower surfaces
51
and
52
of the thrust plate
5
in the circumferential direction. There are very small gaps respectively between the upper surface
51
of the thrust plate
5
and the opposed sleeve
4
and between the lower surface
52
of the thrust plate
5
and the opposed counter plate
6
. Lubricating fluid such as lubricating oil lies in these gaps, thus forming a dynamic pressure thrust bearing. When the thrust plate
5
together with the rotary shaft
1
rotates, the lubricating fluid is compressed in the dynamic pressure grooves, so that the dynamic pressure is generated in the thrusting direction. Moreover, a very small gap is also present between the outer periphery of the rotary shaft
1
and the central shaft hole of the sleeve
4
, dynamic pressure grooves are formed in at least one of the outer peripheral face of the rotary shaft
1
and the inner peripheral face of the central shaft hole of the sleeve
4
. Consequently, a radial dynamic pressure bearing part
40
is formed with lubricating fluid lying between the gap above. As the rotary shaft
1
rotates, the lubricating fluid causes dynamic pressure is generated in the radial direction.
The rotary shaft
1
projects from the upper edge face of the sleeve
4
, and the central hole of a rotor hub
2
like a cup placed upside down is secured by press-fitting to the projected portion of the rotary shaft
1
. The outer peripheral wall of the rotor hub
2
covers the stator core
12
, and a cylindrical rotor magnet
7
is secured to the inner periphery of the outer peripheral wall. The central hole of a one or a plurality of hard disks (not shown) is placed with the outer peripheral face of the rotor hub
2
as a guide, and the hard disk(s) is mounted on a flange
21
formed on the outer peripheral face of the rotor hub
2
. The hard disk is fitted integrally to the rotor hub
2
with a proper cramp member.
Supply of power to each driving coil
23
is controlled in accordance with the rotational position of the rotor magnet
7
, whereby the rotor magnet
7
, the rotor hub
1
, the rotary shaft
1
and the thrust plate
5
, these integrally forming rotating parts, are rotated. With their rotation, the aforementioned thrust and radial dynamic pressures are generated and the rotary shaft
1
makes non-contact rotation relative to the sleeve
4
and the counter plate
6
forming the fixed-side dynamic pressure bearing part. Therefore, the frictional resistance is reduced to make possible the smooth and high-speed rotation of the rotary shaft
1
.
With respect to the formation of the thrust dynamic pressure bearing part, the rotary shaft
1
is press-fitted into and integrated with the thrust plate
5
, for example.
FIG. 7
shows how the rotary shaft
1
, the thrust plate
5
and the counter plate
6
are combined together in the related art. As seen from
FIG. 6
, the right angles at which the rotary shaft
1
meets the thrust plate
5
are important and unless the degree of the right angle is satisfactory as shown in
FIG. 8
, the gap in the thrust dynamic pressure bearing part would lack uniformity, thus making the generation of the dynamic pressure unstable. The method heretofore used to increase the degree of the right angle is to raise the precision of jigs when the rotary shaft
1
is press-fitted into the thrust plate
5
.
The degree of the right angle between the rotary shaft and the thrust plate may be considered to be made accurately achievable by shaving the shaft without press-fitting the rotary shaft into the thrust plate. Under this method, the degree of the right angle can be attained precisely and there is no problem arising from causing the thrust plate from warping. However, the disadvantage of the shaving method includes making the working troublesome, requiring a lengthy working time, wasting much raw material and increasing costs.
These problems will be developed from not only the shaft rotating type but also a shaft fixed type.
SUMMARY OF THE INVENTION
An object of the present invention made to solve the foregoing problems concerning the related art is to provide a dynamic pressure bearing device having a shaft and a thrust plate forming a thrust dynamic pressure bearing part which is mounted to the shaft in a direction perpendicular to the shaft, in such a manner as to integrate the shaft and the thrust plate by press-fitting so that the thrust plate can be set free from warping and the gap between the thrust plate and the fixed-side dynamic pressure bearing part is uniformized, whereby a stable thrust dynamic pressure is obtainable, and to provide a method of manufacturing the same.
In order to achieve the above object, according to the present invention, there is provided a dynamic pressure bearing device, comprising:
a shaft member;
a thrust plate, formed with a press-fitting portion into which the shaft member is press-fitted such that the thrust plate extends perpendicular to an axial direction of the shaft member;
a bearing member, being opposed to the thrust plate for forming a thrust dynamic pressure bearing portion; and
at least two relief portions, for absorbing press-fitting stress, the relief portions provided in at least one of the press-fitting portion of the thrust plate and a part of the shaft member which corresponds to the press-fitting portion.
In this configuration, a portion which is equivalent to the press-fitting margin is relieved when the sh
Ishikawa Masayuki
Marumo Hiromasa
Zenisawa Hiroshi
Kabushiki Kaisha Sankyo Seiki Seisakusho
Lavinder Jack
Siconolfi Robert A.
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