Electromagnetic driving unit and light quantity regulating apparatus using the same

摘要

An electromagnetic driving unit includes a rotor having a central shaft and formed of a permanent magnet with a hollow cylindrical shape; an inner yoke disposed on an inner circumferential side of the rotor; an outer yoke disposed on an outer circumferential side of the rotor; and a coil for exciting the inner yoke and outer yoke. The inner yoke has a shaft portion at an end portion thereof inserted into the rotor, and the shaft portion has a circular cross-section or an oval cross-section perpendicular to an axial direction of the shaft portion. The rotor has a bearing recess in an inner circumferential wall thereof, so that the shaft portion of the inner yoke slidably fits in the bearing recess.