Photography – With exposure objective focusing means – focusing aid – or... – Lens drive circuit or motor structure
Reexamination Certificate
2002-06-27
2003-07-08
Perkey, W. B. (Department: 2851)
Photography
With exposure objective focusing means, focusing aid, or...
Lens drive circuit or motor structure
C396S463000, C310S049030
Reexamination Certificate
active
06591066
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a motor suitable for a reduction in size and optical apparatus using the motor.
2. Related Background Art
FIG. 16
is a sectional view showing an arrangement of a conventional stepping motor.
FIG. 17
is a partial sectional view simply illustrating magnetic fluxes flowing from the stator of the stepping motor in FIG.
16
.
Referring to
FIG. 16
, two bobbins
101
having stator coils
105
wound therearound are juxtaposed in the axial direction of a rotor
109
. These two bobbins
101
are respectively fixed to different stator yokes
106
. Stator teeth
106
a
and
106
b
are alternately formed on the inner diameter surface of each stator yoke
106
. The stator yokes
106
are respectively fixed to cases
103
. Two stators
102
respectively corresponding to the two excitation stator coils
105
are constituted by these members.
A flange
115
and bearing
108
are fixed to one of the two cases
103
, and the other bearing
108
is fixed to the other case
103
. A rotor
109
is formed from a rotor magnet
111
fixed to a rotor shaft
110
. The rotor shaft
110
is rotatably supported by the two bearings
108
.
In the stepping motor described above, however, since the cases
103
, bobbins
101
, stator coils
105
, and stator yokes
106
are arranged on the outer surface of the rotor
109
, the outer dimension of the motor becomes large. In addition, the magnetic fluxes which are generated when the stator coils
105
are energized mainly pass through an end face
106
a
1
of the stator tooth
106
a
and an end face
106
b
1
of the stator tooth
106
b
, as shown in FIG.
17
. For this reason, much of magnetic flux does not act on the rotor magnet
111
, and hence the motor output does not increase much.
In order to increase the output of a motor while decreasing its size, a motor having an arrangement like the one disclosed in U.S. Pat. No. 5,831,356 has been proposed. In this motor, a rotor is formed by dividing a cylindrical permanent magnet into equal portions in the circumferential direction and alternately magnetizing the portions to different poles, and the first coil, rotor, and second coil are sequentially arranged in the axial direction of the rotor (the axial direction of the motor). The first outer magnetic poles and first inner magnetic poles which are excited by the first coil are arranged to face the outer and inner surfaces of one half portion of the rotor in the axial direction, whereas the second outer magnetic poles and second inner magnetic poles which are excited by the second coil are arranged to face the outer and inner surfaces of the other half portion of the rotor in the axial direction.
FIG. 18
is a sectional view of a motor having the above arrangement. This motor includes a magnet
311
, a first coil
312
, a second coil
313
, a first stator
314
, first outer magnetic poles
314
a
and
314
b
, first inner magnetic poles
314
c
and
314
d
, a second stator
315
, second outer magnetic poles
315
a
and
315
b
, second inner magnetic poles
315
c
and
315
d
, a coupling ring
316
for holding the first stator
314
and second stator
315
, and an output shaft
317
to which the magnet
311
is fixed and which rotates together with the magnet
311
. This output shaft
317
is rotatably supported by bearing portions
314
e
and
315
e
of the first and second stators
314
and
315
.
According to this arrangement, a motor having a high output level and a small diameter can be provided.
Unlike such a motor having a reduced diameter, a motor having a reduced length in the axial direction is disclosed in Japanese Patent Application Laid-Open No. 2000-50601.
FIG. 19
shows this motor. The motor is constituted by a plurality of coils
301
,
302
, and
303
and a disk-like magnet
304
. As shown in
FIG. 19
, each coil has a thin coin-like shape, whose axis is parallel to the axis of the magnet. The disk-like magnet is magnetized in the axial direction of the disk-like shape, and the magnetized surface of the magnet faces the axis of the coil.
According to this arrangement, as indicated by the arrows in
FIG. 20
, a large number of magnetic fluxes generated from the coils do not pass through the magnet. The output level is therefore not high for the size of the motor.
There seems to be room for improvement in providing a motor having a reduced length in the axial direction.
SUMMARY OF THE INVENTION
According to an aspect of the present invention, there is provided a motor comprising a rotor having a cylindrical magnet having an outer surface divided into portions in a circumferential direction which are alternately magnetized to different poles, a first outer magnetic pole which is excited by a first coil and faces the outer surface of the magnet within a first predetermined angular range, a first inner magnetic pole which is excited by the first coil and faces an inner surface of the magnet, a second outer magnetic pole which is excited by a second coil and faces the outer surface of the magnet within a second predetermined angular range, and a second inner magnetic pole which is excited by the second coil and faces the inner surface of the magnet, wherein the first and second outer magnetic poles are positioned on the same circumference centered on the magnet.
According to another aspect of the present invention, there is provided a motor comprising a rotatable rotor having a cylindrical magnet having an outer surface alternately magnetized to different poles in a circumferential, a first outer magnetic pole which is excited by a first coil and faces the outer surface of the magnet, a second outer magnetic pole which is excited by a second coil and faces the outer surface of the magnet, and an inner magnetic pole which faces an inner surface of the magnet, wherein the first and second outer magnetic poles are positioned on the same circumference centered on the magnet, and when the center of one outer magnetic pole faces the center of a region of the magnet, the center of the other outer magnetic pole faces a boundary portion between regions of the magnet.
In addition, there are provided a photographing apparatus which translates a lens holder by using this motor as a driving source and a photographing apparatus which opens shutter blades by using the motor as a driving source.
REFERENCES:
patent: 5831356 (1998-11-01), Aoshima
patent: 2002/0127013 (2002-09-01), Mizumaki et al.
Perkey W. B.
Robin Blecker & Daley
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