Metal working – Method of mechanical manufacture – Process for making bearing or component thereof
Reexamination Certificate
2000-07-28
2002-06-04
Hughes, S. Thomas (Department: 3726)
Metal working
Method of mechanical manufacture
Process for making bearing or component thereof
C029S898070, C029S603030, C029S598000
Reexamination Certificate
active
06397470
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a dynamic pressure bearing apparatus applicable to a motor for a hard disk drive as well as a method for manufacturing such dynamic pressure bearing apparatus. More particularly, the present invention related to a dynamic pressure bearing apparatus used to increase the rotational accuracy of a hub to which a rotational body such as a disk is mounted.
As is known, a dynamic pressure bearing apparatus includes a shaft and a sleeve which rotate in relation to each other. As the apparatus starts rotating at a high speed, dynamic pressure is generated by the dynamic pressure generating grooves that are formed, for example, on the bearing surface. The rotor rotates with high accuracy due to the stiffness of the bearing. By applying such an apparatus as a bearing apparatus in a motor for a hard disk drive, high recording density can be obtained. However, further improvement in recording density is demanded and therefore an increase in rotational accuracy is desired.
A conventional method for manufacturing a dynamic pressure bearing apparatus is described with reference to
FIGS. 6 and 7
. As shown in
FIG. 6
, a ring-shaped thrust plate
22
is fixed to the outer circumference at the bottom of rotatable shaft
21
to form a shaft assembly by integrating the two parts. Then, rotatable shaft
21
is inserted through the center hole of sleeve
23
from the bottom. Thrust plate
22
fits in a concavity at the bottom of sleeve
23
with a given space. Counter plate
24
is engaged into another concavity having a diameter larger than the previous concavity at the bottom of sleeve
23
. Counter plate
24
is fixed to sleeve
23
, and an adhesive is used for sealing such that a sleeve assembly is provided.
Rotatable shaft
21
is rotatable in relation to sleeve
23
wherein a bearing assembly is formed by inserting oil as a lubricant fluid between rotatable shaft
21
and sleeve
23
. Dynamic pressure generating grooves are formed on at least one of the outer surface of rotatable shaft
21
and the inner surface of sleeve
23
. A dynamic pressure bearing is formed by placing the oil between the dynamic pressure generating grooves, rotatable shaft
21
and sleeve
23
.
On the other hand, a core assembly is formed by winding drive coil
26
around each of projecting poles of laminated core
25
. A center hole of laminated core
25
of the core assembly is engaged to the outer circumference of sleeve
23
of the bearing assembly and is fixed thereto by an adhesive. Oil absorbent fabric
27
is placed on the laminated core from the upper end of rotatable shaft
21
and cover
28
is engaged thereto. As shown in
FIG. 7
, the laminated core is mounted to the upper surface of sleeve to form a stator assembly.
Further, in a separate process, as shown in
FIG. 7
, cylindrical rotor magnet
33
is engaged to the inside ceiling of hub
30
, with a reversed-cup shape, via seal
32
to form a rotor assembly. Rotor magnet
33
is magnetized, alternating the N and S poles with a given distance, in a circumferential direction. It is fixed to the inner surface of hub
30
with an adhesive or the like. Hub
30
has disk mounting surface
31
which projects as a flange to the outer circumference. The rotor assembly is placed on the top of the stator assembly to form a motor assembly by fixing the top end of rotatable shaft
21
to the center hole hub
30
.
The center hole of base
34
is engaged to the outer circumference at the bottom of sleeve
23
, forming the motor assembly, and is fixed with an adhesive and the like. Insulator
29
is placed between the stator portion of the motor assembly and base
34
. Flexible print wiring substrate
35
is placed at a concavity formed on the bottom surface of base
34
. Each drive coil
26
and a feeder circuit are connected by flexible print wiring substrate
35
.
A current flow to each drive coil
26
is controlled while detecting the rotational position of rotor magnet
33
, causing magnetic attraction / repulsion between rotor magnet
33
and the projecting pole of the stator. As a result, a force is applied to the rotor, which is formed together with rotor magnet
33
, in the circumferential direction such that the rotor rotates. Dynamic pressure is generated, by rotation of rotatable-shaft
21
as a part of the rotor, between the outer surface of rotatable shaft
21
and the inner surface of sleeve
23
due to viscous resistant of the oil. Then, rotatable shaft
21
is supported in the radial direction without having its outer surface mechanically contact the inner surface of sleeve
23
. Also, a thrust dynamic pressure bearing is formed between thrust plate
22
, sleeve
23
and counter plate
24
; the thrust load of rotatable shaft
21
is supported without mechanically contacting the other parts.
According to a conventional method for manufacturing a dynamic pressure bearing apparatus as described above, hub
30
and rotatable shaft
21
are assembled to each other at the end of the manufacturing process. Therefore, one may not be able to obtain high accuracy of disk mounting surface
31
of hub
30
for vibration or deviation in the axial direction in relation to the rotational center of rotatable shaft
21
. This is due to the space between rotatable shaft
21
and sleeve
23
, which is sufficient for generating dynamic pressure; because when hub
30
is fixed to rotatable shaft
21
at the end of the manufacturing process, rotatable shaft
21
may be assembled to hub
30
with leaning by an amount of the space therein.
Also, the length of a shaft in the axial direction tends to be shortened along with a decrease in the thickness of apparatus in recent years. In the case of a short length in the axial direction with a thin bearing, according to the conventional method for manufacturing a dynamic pressure bearing apparatus, sufficient length for connecting hub
30
and rotatable shaft
21
cannot be obtained. This is another reason why it is difficult to provide accuracy of disk mounting surface
31
for vibration in the axial direction.
Further, in the case of a short length in the axial direction with a thin bearing, it is difficult to obtain sufficient length for connecting hub
30
and rotatable shaft
21
. As a result, bonding strength is not sufficient, when impact is applied, the product is deformed such that desired characteristics are not obtained.
When accuracy of disk mounting surface
31
for vibration or deviation in the axial direction is not sufficiently obtained, in general, after hub
30
is fixed to rotatable shaft
21
, then disk mounting surface
31
of hub
30
is cutting processed to reduce vibration or deviation while hub
30
is rotated. However, resolving the problem of vibration or deviation by cutting while rotating with an outside drive after assembling the dynamic pressure bearing as described above causes shortening of the life of the bearing due to contacts among parts thereof.
OBJECTS AND SUMMARY OF THE INVENTION
It therefore is an object of the present invention to provide a dynamic pressure bearing apparatus and a method for manufacturing thereof in which vibration of a hub can be recognized and controlled in the first stage of an assembly process such that accuracy therein is increased and the yield is increased for a lower cost.
It is a further object to provide a dynamic pressure bearing apparatus and a method for manufacturing thereof in which oil as a lubricant fluid can be easily inserted and oil leakage is minimized.
To achieve the above objects, a dynamic pressure bearing apparatus is provided in which a hub is fixed to a rotatable shaft and a disk mounting surface of the hub is processed, wherein the rotatable shaft is inserted into a sleeve. The apparatus is provided with high accuracy as compared to conventional technology in which the vibration of the hub is adjusted at the end of the assembly process. Yield is improved, and the accuracy is guaranteed in the pre-process so that assembly errors and manufacturing cost can be decreased.
In accordance wit
Gomyo Masato
Saichi Masayoshi
Compton Eric
Hughes S. Thomas
Reed Smith LLP
Sankyo Seiki Mfg. Co. Ltd.
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