| 摘要 |
A light quantity adjusting device is provided with a light blocking member for adjusting a quantity of light by moving the light blocking member and a drive source for driving the light blocking member. The drive source includes at least a rotor having a plurality of poles, a stator, a coil and a limiting part arranged to limit the rotation angle range of the rotor to an angle not exceeding 180 degrees. The drive source is arranged such that a cogging torque existing when the coil is not energized works over the whole rotation angle range to cause the rotor to rotate in one direction and, a coil torque generated when the coil is energized works over the whole rotation angle range to cause the rotor to rotate in the other direction. The peak of the coil torque is set to be obtainable within the rotation angle range, and a torque which is obtained by combining the cogging torque and the coil torque works to cause the rotor to rotate in the other direction.
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