Electrical generator or motor structure – Dynamoelectric – Rotary
Reexamination Certificate
2001-07-23
2004-09-28
Mullins, Burton S. (Department: 2834)
Electrical generator or motor structure
Dynamoelectric
Rotary
C310S046000, C310S0400MM
Reexamination Certificate
active
06798093
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ultra-compact motor, and a light amount adjusting apparatus and a lens barrel each of which uses the motor.
2. Related Background Art
FIG. 20
shows a conventional compact cylindrical stepping motor. A stator coil
205
is concentrically wound around a bobbin
201
. The bobbin
201
is clamped and fixed between two stator yokes
206
in the axial direction. On the stator yokes
206
, stator teeth
206
a
and
206
b
are arranged on the inner surface of the bobbin
201
alternately in its circumferential direction. The stator yoke
206
, integrally formed with the stator teeth
206
a
,
206
b
, is fixed to a case
203
to form a stator
202
.
A flange
215
and bearing
208
are fixed to one of two cases
203
, and the other bearing
208
is fixed to the other case
203
. A rotor
209
is formed by a rotor magnet
211
fixed to a rotor shaft
210
. The rotor magnet
211
and the stator yoke
206
of the stator
202
form a radial gap portion therebetween. The rotor shaft
210
is rotatably supported between the two bearings
208
.
In the conventional compact stepping motor shown in
FIG. 20
, however, the cases
203
, bobbins
201
, stator coils
205
, and stator yokes
206
are concentrically arranged around the rotor, and hence the outer dimensions of the motor become large. As shown in
FIG. 21
, the magnetic flux generated upon energization of the stator coil
205
mainly runs through end faces
206
a
1
and
206
b
1
of the stator teeth
206
a
and
206
b
. For this reason, the magnetic flux does not effectively act on the rotor magnet
211
. Consequently, the output level of the motor does not rise remarkably.
The present applicant has proposed a motor that solves such a problem in U.S. Pat. No. 5,831,356.
FIG. 22
shows this motor. In this motor, a rotor
311
formed by a magnet alternately magnetized to different poles at equal intervals in the circumferential direction is formed into a cylindrical shape. A first coil
312
, the rotor
311
, and a second coil
313
are sequentially arranged in the axial direction of the rotor. First outer magnetic poles
314
a
and
314
b
and first inner magnetic poles
314
c
and
314
d
, which are excited by the first coil
312
, are opposed to the outer and inner circumferential surfaces of the rotor
311
, respectively. Second outer magnetic poles
315
a
and
315
b
and second inner magnetic poles
315
c
and
315
d
, which are excited by the second coil
313
, are opposed to the outer and inner circumferential surfaces of the rotor
311
, respectively. A rotating shaft
317
serving as a rotor shaft is joined to the magnet of the cylindrical rotor
311
.
A motor having such an arrangement can be reduced in outer dimensions, and the output level can be raised. In addition, if the magnet of the rotor
311
is formed thin, the distance between the first outer magnetic poles
314
a
and
314
b
and the first inner magnetic poles
314
c
and
314
d
and the distance between the second outer magnetic poles
315
a
and
315
b
and the second inner magnetic poles
315
c
and
315
d
can be reduced. That is, the reluctance of a magnetic circuit which acts on the magnet can be reduced. Therefore, a large amount of magnetic flux can be generated even by supplying small currents to the first and second coils
312
and
313
.
A motor of the type disclosed in U.S. Pat. No. 5,831,356 is designed such that the magnet of the rotor
311
is held via an output shaft
317
and a bearing portion
314
e
(
315
e
) of a stator
314
(
315
) that forms magnetic poles with certain gaps therebetween being ensured with respect to the outer magnetic poles
314
a
and
314
b
(
315
a
and
315
b
) and inner magnetic poles
314
c
and
314
d
(
315
c
and
315
d
) of the stator
314
(
315
). For this reason, when considering distortion of the output shaft, e.g., distortion due to a change in temperature, and the like, the gaps between the magnet and the outer and inner magnetic poles of the stator must be maintained with high precision. There is room for improvement in this point.
SUMMARY OF THE INVENTION
One aspect of this invention is to provide a compact motor including a cylindrical rotor formed by a magnet divided into equal portions in the circumferential direction, which are alternately magnetized with different polarities, first and second coils positioned on two sides of the rotor in the axial direction, first and second outer magnetic pole portions which oppose the outer circumferential surfaces of the coils and magnet and excited by the first and second coils, respectively, and first and second inner magnetic pole portions which oppose the inner circumferential surfaces of the coils and magnet, wherein the gaps between the magnet and the respective magnetic pole portions can be defined with high precision using an annular member fitted on an inner circumferential surface of the magnet and regulating the position of the magnet in the radial direction.
In addition, this motor may include an annular member which is fitted on the outer circumferential surface of the magnet, instead of the inner circumferential surface, and which regulates the position of the magnet in the radial direction.
Furthermore, since the magnet rotatably fits within the annular member, a hollow compact motor can be realized.
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Cuevas Pedro J.
Mullins Burton S.
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