| 摘要 |
In a diaphragm control apparatus of a camera for opening and closing aperture blades using a stepping motor, a step-out status of the stepping motor is detected if an open detecting switch for detecting a full-open status of the aperture blades does not function after a predetermined number of drive pulses necessary for resetting the aperture blades to a full-open position are supplied to the stepping motor. Normally, the stepping motor is subjected to such a slow-up control that the continuing duration of the energizing step (pulse width of an energizing pulse) is gradually reduced from the time the motor has been activated to increase a pulse rate and a driving speed. When the step-out status is detected, the pulse rate of the energizing pulse is set constant, and the driving speed of the stepping motor thereafter is fixed to a constant low speed to provide high-torque driving, and opening the aperture blades to the full-open position. Thereafter, when the aperture is closed to a given aperture value, the slow-up control is executed again, however, the pulse width of the energizing pulse is set lower than that used before detection of the step-out status, thus increasing the driving torque.
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