SE335673B - - Google Patents

Abstract

1,198,040. Control of D.C. motors. TESLA NARODNI PODNIK. 13 Jan., 1969 [12 Jan., 1968 (2)], No. 1917/69. Heading H2J. [Also in Division G2] In feeding equipment for advancing a film strip by a required number of frames in either direction, the strip is moved past a light source and an objective between two reels, the film being coupled to two reversible motors through respective friction drives. Photo-electric sensors for stopping forward or backward movement of the film are located near the film gate, another pair of similar sensors being positioned near the display screen. These sensors detect the passage of synchronizing marks on the film strip. A forward-signal is applied from a bistable circuit to lead 26, whereby transistor T1 is turned-on, transistor T3 is turnedoff and transistors T4, T9, are rendered conductive. Motor 4 receives full positive supply voltage, whilst motor 5 is energized at a lower voltage through resistors R31. Backward movement is started when a signal from a bistablecircuit is applied to lead 27, so turning-on the transistor T2. Transistor T5 is turned-off whilst transistors T8, T10, are made conductive so that the motors 5, 4, are energized in reverse, the motor 4 having a reduced voltage-supply. When, during forward movement, for example, a stopping signal, is applied to the bistable circuit, the motors are switched-off and a monostable circuit becomes effective to apply a pulse to lead 28. Transistors T2, T10, are turned-on whereby the motors are connected for reverse-current braking, the motor 4 being supplied through the resistor R31. The motors are then disconnected from the power supply and transistors T5 and T12 become effective to complete a braking circuit across the motors. During the reverse movement, the braking is effected in a similar manner.