Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
1997-12-17
2001-01-16
Enad, Elvin (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S06700R, C310S06800R, C310S090000
Reexamination Certificate
active
06175174
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic bearing, and more particularly, to a magnetic bearing of a drive motor which drives an optical deflector used in an electrophotographic device such as a laser printer, digital copying machine, and the like.
2. Description of the Related Art
Normally, an image forming device includes an optical deflector
60
shown in
FIG. 10
as means for scanning an optical beam such as a laser and the like. The optical deflector
60
is formed by a rotary polygon mirror
12
, in which a plurality of reflecting mirrors are formed at the outer periphery, and a dynamic pressure air bearing type drive motor
62
which rotates rapidly the rotary polygon mirror
12
(see Japanese Patent Application Laid-Open (JP-A) No. 60-55316, Japanese Patent Application Laid-Open (JP-A) No. 60-244913, and Japanese Patent Application Laid-Open (JP-A) No. 62-85216).
The drive motor
62
includes a stationary shaft
66
, at which grooves
64
for generating dynamic pressure are provided, and a sleeve
68
, which is rotatably provided at the outer peripheral surface of the stationary shaft
66
with a predetermined gap therebetween. The drive motor
62
has a so-called radial dynamic pressure air bearing mechanism, i.e., the sleeve
68
rotates without abutting the stationary shaft
66
due to the dynamic pressure effect generated at the time of rotation.
Further, the supporting structure of the sleeve
68
in the axial direction thereof is the one in which the sleeve
68
is levitated by magnetic attracting force generated between a ring-shaped permanent magnet
72
for lift (hereinafter, “levitational permanent magnet”) and a stationary permanent magnet
74
. The levitational permanent magnet
72
is mounted to a pedestal
70
, on which the rotary polygon mirror
12
is disposed, outwardly in the radial direction thereof, and the stationary permanent magnet
74
is disposed at the outer peripheral portion of the levitational permanent magnet
72
.
On the other hand, a magnetic circuit which is required for the rotation of the sleeve
68
is formed between a yoke
78
and a permanent magnet
76
for rotation (hereinafter, “rotational permanent magnet”) which is fixed to the outer peripheral portion of the pedestal
70
. Moreover, as a plurality of magnetic poles of the rotational permanent magnet
76
are detected by a magnetic detection element
80
and a drive coil
84
provided on a circuit board
82
is energized at a predetermined timing logic, the torque of the sleeve
68
is obtained.
However, in the drive motor
62
, because the levitational permanent magnet
72
and the stationary permanent magnet
74
are provided outwardly in the radial direction of the sleeve
68
, a housing that accommodates the components projects outwardly. As a result, the drive motor
62
becomes large.
Further, because the magnetic circuit for rotational drive and the magnetic circuit for magnetic bearing are formed separately, the number of components cannot be reduced. Furthermore, since the borderline region of the magnetic poles of the stationary permanent magnet
74
at a fixed side and that of the levitational permanent magnet
72
at a rotational side face to each other, when one of the permanent magnets is formed thinner than the other, a portion in which magnetic force is small is generated and the magnetic attracting force may be thereby decreased.
SUMMARY OF THE INVENTION
With the aforementioned in view, an object of the present invention is to provide a magnetic bearing in which a drive motor can be made compact and the number of components can be reduced.
In a primary aspect of the present invention, a rotating body is provided around a stationary shaft so as to be rotatable. Further, a rotational permanent magnet is fixed to the outer peripheral portion of the rotating body, and torque is generated by energizing a drive coil disposed at a base at a predetermined timing logic. In this way, the rotating body rotates with the rotational permanent magnet.
On the other hand, a levitational permanent magnet is disposed at the axial direction end portion of the rotating body in an annular shape. A yoke serving as a magnetic body is disposed so as to face the outer peripheral portion of the levitational permanent magnet with a predetermined gap therebetween. The rotating body is supported in a levitated state due to the magnetic attracting force generated between the yoke and the levitational permanent magnet.
Namely, compared to a structure in which a levitational permanent magnet is fixed to the outer peripheral portion of a rotating body, the magnetic bearing can be designed more compact as the levitational permanent magnet is placed nearer to the central portion of the rotating body. Thus, the drive motor can be made compact.
Further, because the yoke, which originally forms a magnetic circuit between the yoke and the rotational permanent magnet, is used as a magnetic body which generates magnetic attracting force between the yoke and the levitational permanent magnet, the number of components for the drive motor can be decreased.
In the above structure, the inner peripheral surface or the outer peripheral surface of the levitational permanent magnet is polarized to a single pole, and the plate thickness of the yoke is thinner than the plate thickness of the levitational permanent magnet.
Namely, because the borderline region of the magnetic poles of the levitational permanent magnet runs along the axial direction of the rotating body and does not face the yoke, there is no such portion exist in which magnetic force is small with respect to the yoke, the magnetic force is concentrated on the yoke having thin plate thickness, and strong magnetic attracting force can be thus obtained.
Further in another structure slightly different from the above, the upper surface or the lower surface of the levitational permanent magnet is polarized to a single pole, and the plate thickness of the yoke is equal to or thicker than the plate thickness of the levitational permanent magnet.
Namely, as the yoke having a thick plate thickness faces the borderline region of the magnetic poles of the levitational permanent magnet and the curvature of the leakage flux with respect to the magnetic body is increased, strong magnetic force can be obtained.
In a secondary aspect of the present invention, a rotating body is rotatably provided around a stationary shaft fixed to a base and a levitational permanent magnet is disposed at the axial direction end portion of the rotating body in an annular shape. The levitational permanent magnet faces a magnetic body disposed at the base side with a predetermined gap therebetween, and the rotating body is levitated due to the magnetic attracting force generated between the magnetic body and the levitational permanent magnet.
Namely, compared to a structure in which a levitational permanent magnet is fixed to the outer peripheral portion of a rotating body, the magnetic body can be placed nearer to the rotating body as the levitational permanent magnet is placed nearer to the central portion of the rotating body. As a result, the magnetic bearing can be designed compact.
REFERENCES:
patent: 4357555 (1982-11-01), Gerkema et al.
patent: 4523800 (1985-06-01), Yamashita et al.
patent: 4717223 (1988-01-01), Ishida et al.
patent: 4726640 (1988-02-01), Iwama et al.
patent: 4958098 (1990-09-01), Sarraf
patent: 5280208 (1994-01-01), Komura et al.
patent: 5289067 (1994-02-01), Tanaka et al.
patent: 5453650 (1995-09-01), Hashimoto et al.
patent: 5675201 (1997-10-01), Komura et al.
patent: 5731831 (1998-03-01), Murabe et al.
patent: 60-55316 (1985-03-01), None
patent: 60-244913 (1985-12-01), None
patent: 62-85216 (1987-04-01), None
Enad Elvin
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Fuji 'Xerox Co., Ltd.
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