A program shutter has a shutter mechanism comprised of at least one sector movable in opening and closing directions in response to forward and reverse rotation of a step motor to form a lens aperture. A control unit automatically controls the shutter operation and comprises an exposure quantity storage circuit for storing exposure quantity data corresponding to the brightness of a subject being photographed, a motor control data storage circuit for storing step drive number data proportional to the exposure quantity data and interpolation quantity data corresponding to the exposure quantity data, a pulse generator circuit for generating step drive pulses and clock pulses, a first presettable counter preset with the step drive number data before opening of the sector and downcounted to zero by the drive pulses, a second presettable counter preset with the interpolation quantity data and downcounted to zero by the clock pulses beginning at a time after the first counter has downcounted to zero, a reverse drive circuit for detecting when the second counter has counted down to zero and thereafter effecting rotation of the step motor in the reverse direction, and a motor drive circuit for rotationally driving the step motor according to the drive pulses generated by the pulse generator circuit means.
A strain relieving channel 32 is provided between the hub 31 of a multifaceted scanwheel 15 and the bearing assembly 13 on which the hub 31 is mounted. Compression of the bearing assembly 13 and distortion of the scanwheel facets 29 due to thermally induced compression of the scanwheel web 33 are both reduced by bowing of the hub 31, made possible by the strain relieving channel 32.
A shutter for a camera comprises sectors for opening and closing a shutter opening by reciprocal pivotal movement, a motor for reciprocally and pivotally moving the sectors by forwardly and reversely rotating a rotor of the motor by forward and reverse electricity conduction to a coil, a memory circuit having stored therein electricity conduction data of the coil corresponding to operational characteristics of the motor and the sectors, and a control circuit for controlling electricity conduction to the coil in accordance with a brightness of an object to be photographed and executing exposure control in accordance with the brightness of the object. The electricity conduction data includes reverse pulses for rotating the rotor in a direction reverse to a direction of opening the sectors for reducing acceleration of the sectors during opening movement thereof, and forward pulses for rotating the rotor in the direction of opening the sectors for continuing the opening movement of the sectors.
There is disclosed a program shutter for use in a camera. The program shutter consists of a shutter mechanism and a control portion. The shutter mechanism has sectors for defining an opening and a stepper motor for driving the sectors. The control portion produces pulses having pulse width conforming to the operating characteristic of the shutter mechanism. These pulses are used to step the motor forward or backward according to the exposure corresponding to the luminance of the subject.
An exposure control system for a camera having a scanning type shutter mechanism for forming a range of aperture areas through which a photographic image is formed includes a stepper motor and a regulator or open loop control system therefor, to actuate the shutter mechanism between its open and closed positions in correspondence with a predetermined set of aperture area defining curves selected in accordance with sensed scene brightness and subject reflectivity levels. The stepper motor is operated at a relatively low rate of speed in order to avoid shutter blade mechanism overshoot and to achieve substantially the same shutter mechanism positioning accuracy as that achieved with a closed loop control system. Employing a stepper motor together with an open loop control system for scanning shutter mechanism actuation in the above member, results in a simplified exposure control system that is both compact and relatively inexpensive.
To prevent rebounding motion of sectors caused in stopping the sectors and achieve small-sized formation of a shutter, there is provided a shutter for a camera including sectors for opening and closing a shutter opening by reciprocal and pivotal movement, a motor for reciprocally and pivotally moving the sectors by forwardly and reversely rotating a rotor of the motor by applying current to a coil in forward and reverse directions, a control circuit for controlling current applied to the coil for exposure control in accordance with a brightness of an object to be photographed and a memory circuit for outputting data used for applying current to the control circuit in correspondence with operational characteristics of the motor and the sectors. The memory circuit is provided with current data for applying current to the coil for rotating the rotor in a direction reverse to a rebounding direction of the sectors to prevent a rebounding motion of the sectors.
