Electricity: motive power systems – Phasing or angular or linear positional control of movable...
Reexamination Certificate
2002-03-11
2004-04-27
Leykin, Rita (Department: 2837)
Electricity: motive power systems
Phasing or angular or linear positional control of movable...
C318S685000, C318S696000, C318S640000, C318S254100, C310S049030, C359S227000, C359S230000
Reexamination Certificate
active
06727672
ABSTRACT:
BACKGROUND OF THE PRESENT INVENTION
1. Field of the Present Invention
The present invention relates to a driving device having an extremely compact size, and a light amount controller and a shutter using the driving device.
2. Description of the Related Art
Conventionally, motors that can be designed to be compact in size include a brushless motor. Brushless motors with simple driving circuits include a stepper motor, described below.
FIG. 9
shows an example of a small-sized hollow cylindrical stepper motor. The stepper motor includes two stators
102
each comprised of a bobbin
101
having a stator coil
105
concentrically wound thereon, two stator yokes
106
axially fixedly holding the bobbin
101
in a sandwiching fashion, the stator yokes
106
each having stator teeth
106
a
and
106
b
alternately arranged circumferentially about an inner peripheral surface of the bobbin
101
, and a casing
103
to which are secured the stator yokes
106
formed integrally with the respective stator teeth
106
a
and
106
b.
One of the two casings
103
has a flange
115
and a bearing
108
fixed thereto, while the other casing
103
has another bearing
108
fixed thereto. A rotor
109
is comprised of a rotor magnet
111
rigidly fitted on a rotor shaft
110
. The rotor magnet
111
defines radial gaps between the same and the stator yokes
106
of the stators
102
. The rotor shaft
110
is rotatably supported by the two bearings
108
on opposite ends thereof.
A light controller using a variation of the stepper motor constructed as above has been proposed in Japanese Patent Publication (Kokoku) No. 53-2774. The light controller controls the quantity of passing light by opening and closing shutter blades connected to the stepper motor, in a stepwise fashion. Another variation is a hollow motor proposed in Japanese Laid-Open Patent Publication (Kokai) No. 57-166847. The hollow motor is a ring-shaped stepper motor which allows light to pass through a cavity formed in a central portion thereof.
In the above conventional small-sized stepper motor shown in
FIG. 9
, however, the casings
103
, the bobbins
101
, the stator coils
105
and the stator yokes
106
are concentrically arranged around the rotor
109
, which inevitably results in increased outer dimensions of the motor. Further, magnetic flux generated by energization of the stator coils
105
mainly flows between the end faces
106
a
1
of the stator teeth
106
a
and the end faces
106
b
1
of the stator teeth
106
b
as shown in
FIG. 10
, and hence the magnetic flux does not effectively act on the rotor magnet
111
.
Similarly, the light controller proposed in Japanese Patent Publication (Kokoku) No. 53-2774 and the hollow motor proposed in Japanese Laid-Open Patent Publication (Kokai) 57-166847 each have stator coils and stator yokes arranged around a rotor magnet, so that the outer dimensions of the motor are increased, and magnetic flux generated by energization of the stator coils does not effectively act on the rotor magnet.
Further, a coin-shaped brushless motor as shown in
FIG. 11
has been proposed, e.g., in Japanese Laid-Open Patent Publications (Kokai) No. 7-213041 and No. 2000-50601. The brushless motor is comprised of a plurality of coils
301
,
302
,
303
and a disk-shaped magnet
304
. As shown in
FIG. 11
, each of the coils has a thin coin-like shape, and is disposed such that the axis thereof extends parallel with that of the magnet. The disk-shaped magnet is magnetized in the axial direction thereof, and is disposed such that the magnetic surface (inner peripheral surface) of the magnet faces in a direction perpendicular to the axis of each of the coils.
In this motor, as illustrated by arrows in
FIG. 12
, magnetic flux generated by the coils cannot fully effectively act on the magnet. Further, the center of a rotational force or torque generated by the magnet is away from the outer periphery of the motor by a distance of L, so that the torque generated by the motor is small for the size of the motor. In addition, since a central portion of the motor is occupied by the coils and the magnet, it is difficult to utilize this portion for some other purposes.
SUMMARY OF THE PRESENT INVENTION
It is a first object of the present invention to provide a small-sized and slim driving device which is easy to manufacture and capable of producing high output.
It is a second object of the present invention to provide a light amount controller using a small-sized and slim driving device which is easy to manufacture and capable of producing high output.
To attain the first object, in a first aspect of the present invention, there is provided a driving device comprising a magnet having a hollow cylindrical shape and having an outer peripheral surface and an inner peripheral surface, at least the outer peripheral surface being circumferentially divided into n sections magnetized so as to have alternately different poles, the magnet being rotatable about a rotational axis of the hollow cylindrical shape thereof, a coil arranged axially of the magnet and parallel thereto, an outer magnetic pole portion disposed to be magnetized by the coil, the outer magnetic pole portion having a plurality of hair comb tooth-shaped portions opposed to the magnet and arranged around the magnet such that an angle corresponding to a circumferential width of each of the hair comb tooth-shaped portions opposed to the magnet about the rotational axis of the hollow cylindrical shape of the magnet is equal to a predetermined angle A, and an inner magnetic pole portion disposed to be magnetized by the coil, the inner magnetic pole portion having a hollow cylindrical shape opposed to the inner peripheral surface of the magnet, wherein the predetermined angle A is set to such a value that a rotational force acts on the magnet to return to a position in which a boundary between adjacent ones of the n sections having alternately different poles is opposed to a circumferential center of a corresponding one of the hair comb tooth-shaped portions of the outer magnetic pole portion, when the boundary shifts from the position.
To attain the second object, in a second aspect of the present invention, there is provided a light amount controller comprising a magnet having a hollow cylindrical shape and having an outer peripheral surface and an inner peripheral surface, at least the outer peripheral surface being circumferentially divided into n sections magnetized so as to have alternately different poles, the magnet being rotatable about a rotational axis of the hollow cylindrical shape thereof, a coil arranged axially of the magnet and parallel thereto, an outer magnetic pole portion disposed to be magnetized by the coil, the outer magnetic pole portion having a plurality of hair comb tooth-shaped portions opposed to the magnet and arranged around the magnet such that an angle corresponding to a circumferential width of each of the hair comb tooth-shaped portions opposed to the magnet about the rotational axis of the hollow cylindrical shape of the magnet is equal to a predetermined angle A, and an inner magnetic pole portion disposed to be magnetized by the coil, the inner magnetic pole portion having a hollow cylindrical shape opposed to the inner peripheral surface of the magnet, and a light amount control member disposed for rotation in a manner interlocked to the magnet, wherein the predetermined angle A is set to such a value that a rotational force acts on the magnet to return to a position in which a boundary between adjacent ones of the n sections having alternately different poles is opposed to a circumferential center of a corresponding one of the hair comb tooth-shaped portions of the outer magnetic pole portion, when the boundary shifts from the position.
To attain the second object, in a third aspect of the present invention, there is provided a light amount controller comprising a magnet having a hollow cylindrical shape and having an outer peripheral surface and an inner peripheral surface, at least the outer peripheral surface being
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Leykin Rita
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