| 摘要 |
PURPOSE:To apply the attracting force only at a place near the full-close position and to reduce the power consumption, by setting properly the form, size and position of a soft magnetic iron member which coacts with a movable magnet and adding an energy storing element to apply an aperture blade full-close current to a control circuit. CONSTITUTION:An energy storing element (capacitor) C is charged with connection of a main power supply S, and the proper aperture value is held with the control of a driving motor 4' and in response to the luminance information signal B. When the power supply is cut off, a switching circuit SW is turned on. Then the output of an operational amplifier P1 is reduced by the discharge of the capacitor C, and the aperture blade is stopped down to the full-close position. While the form and the size of a soft magnetic iron member 11 as well as its relative position to a rotary magnet 7 which moves the aperture blade are set respectively so that the attracting force that is generated by the magnet 7 only when the aperture blade is actuated at a place near the full-close position can actuate the aperture blade in the stop-down direction. |
