Device for standing projection of single photograms in a cinematographic projector

Claim 1

In a cinematographic projector comprising a motor, a shaft coupled to and driven by said motor, a sector diaphragm coupled to said shaft and cutting off the projection during transport of a film, a current supply line, a tachometric speed regulating circuit connected between said motor and said supply line, said speed regulating circuit comprising a tachometer generator coupled to said motor and supplying a tachometric voltage that varies with the motor speed, a source of reference voltage, means connected to said source for changing said Reference voltage, means for comparing said reference and tachometric voltages and means for controlling the motor speed according to the difference between said reference and tachometric voltages; the improvement comprising means for providing the still projection of any desired frame of the film and comprising stop control means connected to said means for changing the reference voltage, said stop control means acting on said source to lower substantially said reference voltage, switch-off means for cutting off the current supply to the motor connected to and operated by said stop control means, a photoresistance connected to said switchoff means allowing operation of said switch-off means only when said photoresistance is in a lighted condition, a lamp illuminating said photoresistance, and between said lamp and said photo-resistance a disk having an apertured slit, said disk being coupled to said shaft and being so timed with reference to said sector diaphragm that said slit opens the light path between said lamp and said photoresistance when said sector diaphragm leaves the projected frame entirely uncovered, whereby upon operation of said stop control means said motor is firstly slowed down to a reduced speed under control of said speed regulating circuit, and then the motor is stopped in a position corresponding to a correct projection position of said sector diaphragm.