| 摘要 |
PURPOSE:To have an iris blade return to an expected position without using a return spring by a method wherein a permanent magnet is actuated to turn in a direction of leaving a gap formed in a yoke by a repulsion force produced by the magnetic action of the gap. CONSTITUTION:A gap 62 perpendicular to the end surface of a yoke 36 is formed in the axial direction of the yoke 36. The stand-by position (SBP) (in other words, the maximum closing position of a photography opening with an iris blade) of a rotor 28 is set at an angle position where a position deflected from a diameter D1 which passes through a center P0 in the circumferential direction of the gap 2 by a predetermined acute angle agrees with the magnetizing direction D2 of a permanent magnet of which a rotor main part 50 is composed. When the rotor 28 is turned counterclockwise from the SBP following the current application to a driving coil, the pole of the rotor 28 is far from the far-side end of the SBP of the gap 62. Therefore, the action of the attracting force to the rotor 28 is small, so that the rotor 28 is mainly actuated to turn toward the SBP by a repulsion force caused by a leakage flux. |
