Aperture driving apparatus and projection type image display apparatus

1. An aperture driving apparatus comprising:

a swing unit and a stationary unit, wherein:

said swing unit comprises:

an aperture plate that partially blocks a light;

a coil that is a part of a voice coil motor for obtaining a driving force for driving said aperture driving plate, and

a swing arm that supports said aperture plate and said coil, and has a bearing portion between said aperture plate and said coil, and

said stationary unit comprises:

a swing shaft that engages said bearing portion and swingably supports said swing arm about a swing axis, and

a magnet and a yoke that constitute said voice coil motor together with said coil, said magnet applying said driving force to said coil;

an angle sensor that detects the swing angle of said swing arm;

an evaluating unit that determines an evaluation value used for determining the swing angle by which said swing arm is to be swung; and

a control unit that determines the swing angle by which said swing arm is to be swung according to an output of said angle sensor and said evaluation value, to thereby control the swing angle of said swing arm using a closed-loop control technique,

wherein, in the direction of said swing axis, the position of a center of gravity of said swing unit is substantially aligned with a position at which said driving force is applied to said coil, and

wherein said magnet is disposed on only one side of said coil in the direction of said swing axis, such that the position at which said driving force is applied to said coil is displaced from the center of said coil toward said one side in the direction of said swing axis.

2. The aperture driving apparatus according to claim 1 , wherein said bearing portion of said swing arm includes a bearing and a bearing mounting portion to which said bearing is mounted, and

wherein, in said bearing mounting portion, said bearing is mounted to a portion protruding to the side on which said magnet is disposed.

3. The aperture driving apparatus according to claim 2 , wherein said bearing is made of metal.

4. The aperture driving apparatus according to claim 1 , wherein a balancer is mounted to said swing arm on the side on which said magnet is disposed in the direction of said swing axis, said balancer being provided for substantially aligning said position of said center of gravity with said position at which said driving force is applied to said coil in the direction of said swing axis.

5. The aperture driving apparatus according to claim 4 , wherein said balancer is a cylindrical member mounted to said swing arm in the vicinity of said swing axis.

6. The aperture driving apparatus according to claim 1 , wherein a portion of said swing arm from said bearing portion to said aperture plate protrude to the side on which the magnet is disposed.

7. The aperture driving apparatus according to claim 1 , wherein said coil includes first and second coil parts extending perpendicular to said swing axis and facing each other in the direction of said swing axis;

wherein said first coil part is closer to said magnet than said second coil part is, and

wherein said position at which said driving force is applied to said coil is in said first coil part.

8. The aperture driving apparatus according to claim 7 , wherein said yoke includes a center yoke disposed between said first and second coil parts, and a back yoke disposed to sandwich said magnet with said first coil part.

9. A projection type image display device comprising:

said aperture driving apparatus according to claim 1 ;

a light modulating unit that modulates said light whose amount is adjusted by said aperture driving apparatus, in accordance with image information, and

a projection unit that projects said light modulated by said light modulating unit.