| 摘要 |
Apparatus for stepwise transport of exposed and developed photographic films through a copying machine so as to place selected film frames, namely those film frames which are to be imaged onto photographic paper and are designated by holes or other types of indices, into register with the copying station has two photoelectronic detectors the first of which transmits signals to the forward input and the second of which transmits signals to the reverse input of a forward and reverse counter in a circuit which regulates the speed of the film transporting motor. The second detector is located downstream of the first detector and both detectors transmit signals on detection of indices denoting the film frames to be copied. The circuit decelerates the motor, either stepwise or abruptly, in response to detection of indices by the first detector, arrests the motor for a given interval of time in response to detection of indices by the second detector, and ensures that the motor is driven at a maximum speed in the absence of indices between the first and second detectors. The speed of the motor can be increased from zero to maximum speed in a single stage, in several stages, or continuously. This can be accomplished by connecting the operational amplifier for the motor in circuit with a voltage divider wherein one or more resistors are connected in parallel with switching transistors which are energizable with appropriate delays by a timer receiving impulses from the second detector. |
