Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1997-08-25
2001-03-13
Tamai, Karl (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C384S112000, C029S898020, C029S898041
Reexamination Certificate
active
06201328
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a spindle motor utilizing a dynamic pressure bearing for use in optical disks, magnetic disks and the like.
In recent years, optical and magnetic disk apparatuses have been developed to have a small size, a light weight, and a large capacity. In accordance with the popularization of notebook-type personal computers, spindle motors have been compelled to comply with the miniaturization and reduction in thickness of the computers, and have been demanded to have improved impact resistance and high precision. As a bearing for use in conventional spindle motors, a small-size ball bearing has been frequently used. However, when such a small-size ball bearing is used in accordance with the reduction in outer diameter of the spindle motors, a sufficient rotational accuracy cannot be obtained. The above has caused difficulty in achieving a large capacity, a significantly reduced impact resistance performance, and deterioration of the ball bearing, incurring a noise problem.
Lately, because the capacity increase cannot be achieved with the rotational accuracy of the ball bearing, a spindle motor utilizing a fluid dynamic pressure bearing filled with lubricating oil has been developed.
An exemplary construction of a spindle motor for use in a fixed magnetic disk drive (referred to as an HDD hereinafter) utilizing the conventional fluid dynamic pressure bearing will be described with reference to
FIGS. 10 and 11
. In
FIGS. 10 and 11
, there are shown a motor housing
31
, a rotor hub section
32
, a sleeve section
33
, a shaft
34
, and a thrust plate
35
. There are further shown a magnet
36
fixed to the rotor hub section
32
, a stator core
37
, and a coil
38
.
The motor housing
31
is provided with a cylindrical section
31
a
and a flange section
31
b
. The sleeve section
33
is mounted to an inner peripheral surface of the cylindrical section
31
a
, while a peripheral portion of the flange section
31
b
is mounted to a chassis of the HDD. Around the cylindrical section
31
a
is secured the stator core
37
around which the coil
38
is wound. The rotor hub section
32
is formed into a cup-like configuration with a disk receiving surface
32
a
and a disk inner diameter regulating cylindrical section
32
b
, and it rotates about the shaft
34
, which is fixed to the center of the section
32
b
. To an inner peripheral portion of the cup-shaped rotor hub section
32
is secured the cylindrical magnet
36
that is circumferentially magnetized alternately with north poles and south poles.
The motor having the above construction is a radial type brushless motor. A current flows through the coil
38
to generate magnetic fields at salient poles of the stator core
37
and consequently generate a torque between the stator core
37
and the field-forming magnet
36
provided opposite to the stator core
37
, thereby rotating the rotor hub section
32
. By this operation, a magnetic disk (not shown) clamped on the rotor hub section
32
rotates.
Furthermore, a fluidic substance is filled inside the sleeve section
33
fixed to the cylindrical section
31
a
at the inner peripheral portion of the motor housing
31
, while the thrust plate
35
is formed with spiral grooves. With this arrangement, the shaft
34
is rotatably supported in the direction of thrust by a dynamic pressure generated between the thrust plate
35
and the end surface of the shaft
34
according to the rotation of the shaft
34
, and is also rotatably supported in the radial direction by a dynamic pressure generated at the fluidic substance in a non-contact manner with respect to the sleeve section
33
.
Next, an outline of a manufacturing process of the thrust plate
35
will be described. A rod material (often made of stainless steels) is finished to a specified outer diameter, and then cut into sliced pieces. Each of the disk-shaped sliced pieces to be processed is designed to have a thickness greater by about 0.3 mm than the intended thickness. Then, the disk-shaped materials are each subjected to a heat treatment process to have an increased hardness and then to a lapping process to have an improved surface flatness through elimination of warp generated in the material due to the heat treatment process. Spiral grooves are formed on the lapped surface by etching.
However, according to the above-mentioned prior art spindle motor, for the manufacturing of the thrust plate
35
, the material pieces are positioned one by one for the etching process, and therefore, a seriously degraded manufacturing efficiency results. Furthermore, since the material pieces are processed one by one, a large variation in depth of the spiral grooves occurs in the etching process. Therefore, it is required to perform again the lapping process while measuring the groove depth, and this has further degraded the manufacturing efficiency.
For the above reasons, the thrust plate
35
provided with the spiral grooves to be used as the dynamic pressure bearing in the direction of thrust within the dynamic pressure bearing structure becomes expensive because of the manufacturing method, and this also pushes up the cost of the spindle motor.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a spindle motor provided with a fluid bearing having a thrust plate at low cost.
In accomplishing these and other aspects, according to a first aspect of the present invention, there is provided a spindle motor comprising a housing, a rotor hub section arranged rotatably with respect to the housing, a sleeve section, a shaft fit rotatably in the sleeve section, a thrust plate mounted to the sleeve section opposite to an end surface of the shaft and a thrust dynamic pressure bearing having a dynamic pressure bearing groove formed on the thrust plate. The thrust dynamic pressure bearing includes lubricating oil at a relative slide interface between the thrust plate and the end surface of the shaft. The dynamic pressure bearing groove and a circumferential portion of the thrust plate are formed by etching. A radial dynamic pressure bearing includes lubricating oil at a peripheral interface between the shaft and the sleeve section.
According to a second aspect of the present invention, there is provided the spindle motor as defined in the first aspect, wherein one hole for escaping air trapped in a space defined by the sleeve section, the shaft, and the thrust plate is formed through the thrust plate by etching.
According to a third aspect of the present invention, there is provided the spindle motor as defined in the first aspect, wherein a seal groove for a seal ring for sealing the thrust plate and the sleeve section is formed on the thrust plate by etching.
According to a fourth aspect of the present invention, there is provided the spindle motor as defined in the first aspect, wherein the sleeve section is fixed to the housing and the shaft is fixed to the rotor hub section.
According to a fifth aspect of the present invention, there is provided the spindle motor as defined in the fourth aspect, wherein the circumferential portion of the thrust plate is etched from both sides of the thrust plate in its thickness direction to form a circumferential etching portion on a side of a groove surface where the dynamic pressure bearing groove is formed and a circumferential etching portion opposite from the groove surface. A boundary edge formed by the etching from both sides and located between the circumferential etching portions is made to be located in a position within a range from one half of a thickness of the thrust plate to a surface opposite to the groove surface. Then the thrust plate is caulked with the sleeve section while a gap formed between the circumferential etching portion on the groove surface side and the sleeve section does not disappear and the circumferential etching portion on the side opposite to the groove surface is stuffed with a material of the sleeve section and the boundary edge abuts on the sleeve section without any gap and bites into the s
Matsushita Electric - Industrial Co., Ltd.
Tamai Karl
Wenderoth , Lind & Ponack, L.L.P.
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