Patent
1987-12-23
1989-05-30
Perkey, W. B.
G03B 7087, G03B 7097
Patent
active
048355640
ABSTRACT:
A drive current of a motor is controlled by an output of a pulse oscillator having a variable duty ratio in response to a shutter release operation. Shutter blades having the function of the diaphragm blade start to open the aperture for exposure in interlocked relationship with the rotation of the motor. The shutter blades are provided with a plurality of detection marks for use in detection of the shutter blade position, and every time each of the detection marks passes through a predetermined detection point, an aperture value detection circuit produces a detection pulse. Each of the detection pulses is supplied to an operation circuit which calculates a time interval between the detection pulses. The time interval between the detection pulses is compared with a reference time stored previously in a setting device so that the duty ratio of the output signal of the pulse oscillator in the next cycle of the detection pulse is controlled to control the rotational speed of the motor. Further, the duty ratio of the pulse oscillator is made equal to 100% so that the motive power at the initial operation is secured until the aperture value detection circuit produces a first detection pulse.
REFERENCES:
patent: 4280761 (1981-07-01), Ogawa et al.
patent: 4322145 (1982-03-01), Yamada et al.
patent: 4354748 (1982-10-01), Grimes et al.
patent: 4743934 (1988-05-01), Yoshida et al.
Matsumoto Jun-ichi
Nakagawa Norifumi
Copal Company Limited
Perkey W. B.
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