Electromagnetic actuator

1. An electromagnetic actuator comprising:

a bobbin made of a non-magnetic material which includes a hollow cylindrical portion and two disk flanges fixed to opposite ends of said hollow cylindrical portion, respectively;

a coil formed between said two disk flanges by winding insulated wire around said hollow cylindrical portion;

a power supply which supplies a current to said coil;

a movable member pivoted on said hollow cylindrical portion; and

at least one stationary member made of a permanent magnet and fixed to at least one of said two disk flanges,

wherein said movable member is made of a magnetic material and comprises a shaft portion and at least one rotating portion,

wherein said shaft portion is pivoted about said hollow cylindrical portion,

wherein said rotating portion is fixed to said shaft portion, lies on said disk flange, and extends in a radial direction of said shaft portion,

wherein, when said power supply supplies said current to said coil in a predetermined direction, said rotating portion is magnetized to a predetermined polarity and rotates on said disk flange by a magnetic force of said permanent magnet, and

wherein said stationary member includes a stopper for stopping rotation of said movable member at a predetermined rotational position.

2. The electromagnetic actuator according to claim 1 , wherein said rotating portion of said movable member is formed into a sector-shaped core centered about an axis of said shaft portion,

wherein said stationary member is provided so as to lie in a plane in which said sector-shaped core of said movable member rotates, and

wherein radial-edge faces of said stationary member are magnetized as one and the other of an S-pole and an N-pole.

3. The electromagnetic actuator according to claim 2 , wherein two of said rotating portions are joined to both ends of said shaft portion, respectively, and are magnetized as opposite polarities, respectively, when said power supply supplies said current to said coil,

wherein two of stationary members are positioned to correspond to said two sector-shaped portions, and

wherein radial-edge faces of each of said two stationary members are magnetized as one and the other of an S-pole and an N-pole.

4. The electromagnetic actuator according to claim 3 , wherein said electromagnetic actuator is used as a drive source of a mirror drive device for rotating a main mirror of an SLR camera reciprocatively.

5. The electromagnetic actuator according to claim 2 , wherein the following equation is satisfied:

θ a+θb+θr= 2π,

wherein θa designates a central angle of said sector-shaped core,

θb designates a central angle of said stationary member, and

θr designates a maximum angle of rotation of said sector-shaped core.

6. The electromagnetic actuator according to claim 1 , wherein said electromagnetic actuator is used as a drive source of a mirror drive device for rotating a main mirror of an SLR camera reciprocatively.

7. The electromagnetic actuator according to claim 6 , wherein said rotating portion is provided on each lateral end of said main mirror at a rotational axis thereof,

wherein each of said rotating portion is formed into a sector-shaped core centered about an axis of said shaft portion, coaxial with said rotational axis of said main mirror,

wherein said stationary member is provided at each of said sector-shaped core so as to lie in a plane in which said sector-shaped core of said movable member rotates,

wherein radial-edge faces of said stationary member are magnetized as one and the other of an S-pole and an N-pole, and

wherein upon said mirror being driven in an up/down direction, one of two radial edge faces of each of said sector-shaped core abut against one of said radial-edge faces of each corresponding said stationary member.

8. The electromagnetic actuator according to claim 1 , wherein said electromagnetic actuator is used as a drive source of a shutter device for making shutter blades perform an opening/shutting operation.

9. The electromagnetic actuator according to claim 1 , wherein said stationary member is formed as a semi-circular plate.

10. The electromagnetic actuator according to claim 9 , wherein said semi-circular plate is substantially identical in radius to said one of said two disk flanges.

11. An electromagnetic actuator comprising:

a bobbin made of a non-magnetic material which includes a hollow cylindrical portion and two disk flanges fixed to opposite ends of said hollow cylindrical portion, respectively;

a coil wound around said hollow cylindrical portion;

a rotatable member which is supported by said bobbin to be freely rotatable about an axis of said hollow cylindrical portion; and

a permanent magnet fixed to one of said two disk flanges,

wherein said rotatable member is made of a soft magnetic material and includes a shaft portion and a swingable portion,

wherein said shaft portion is fitted into said hollow cylindrical portion to be freely rotatable about said axis,

wherein said swingable portion lies on said one disk flange and extends in a radial direction of said shaft portion,

wherein, when current is supplied to said coil in a predetermined direction, said swingable portion is magnetized as a predetermined polarity and rotates on said disk flange by a magnetic force of said permanent magnet, and

wherein at least one of radial-edge faces of said permanent magnet serves as a stopper for stopping rotation of said rotatable member at a predetermined rotation position, said radial-edge faces constituting one and the other of an N-Pole and an S-Pole.

12. An SLR camera, to which a photographing lens is detachably attached, comprising:

a quick-return mirror provided in a camera body of said camera; and

at least one electromagnetic actuator provided on said quick-return mirror and configured to reciprocatively rotate said quick-return mirror between an upward position and a downward position;

said electromagnetic actuator comprising:

a bobbin made of a non-magnetic material which includes a hollow cylindrical portion and two disk flanges fixed to opposite ends of said hollow cylindrical portion, respectively;

a coil formed between said two disk flanges by winding insulated wire around said hollow cylindrical portion;

a power supply which supplies a current to said coil.,

a movable member pivoted on said hollow cylindrical portion; and

at least one stationary member made of a permanent magnet and fixed to at least one of said two disk flanges,

wherein said movable member is made of a magnetic material and includes a shaft portion which is connected with said quick return mirror so as to integrally rotate with said quick-return mirror, and at least one rotating portion,

wherein said shaft portion is pivoted about said hollow cylindrical portion,

wherein said rotating portion is fixed to said shaft portion, lies on said disk flange, and extends in a radial direction of said shaft portion,

wherein, when said power supply supplies said current to said coil in a predetermined direction, said rotating portion is magnetized to a predetermined polarity and rotates on said disk flange by a magnetic force of said permanent magnet, to thereby rotate said quick-return mirror via said shaft portion, and

wherein said stationary member includes a stopper for stopping rotation of said movable member at a predetermined rotational position.