FILM FRAME LOCATION DEVICE COMPRISING MEANS FOR DETECTING BOTH LEADING AND TRAILING EDGES OF FRAME

1290371 Photo-electric investigation of film strips AGFA GEVAERT A G 29 Sept 1969 [27 Sept 1968] 47795/69 Addition to 1183223 Heading G1A The apparatus of the Parent is modified in that a further photo-electric scanning device with associated computer circuitry is provided for investigating the positions of trailing edges of picture areas. A feature of the embodiment described is that two similar analog computer circuits are used, in contrast to the digital computer circuit of the Parent Specification. These circuits, provided to process the outputs of two photo-electric scanners spaced apart by a picture area length utilize storing of the current maximum transparency and comparison of this with incoming detector outputs. Each circuit feeds a counter 13 and 43 having a capacity approximating the number of steps in a picture area length, and supplied from pulse generator 15 which drives the film stepping motor. Each counter can via OR- gate 44 cause marking by punch 18 of the position of the spacing zone, or control locating of the picture area within the printing apparatus, when the counter reaches the end of its capacity. A further counter 32 counts the number of times a measured transparency value is considerably lower, e.g. by 10%, than the maximum. This prevents, via flip flop 33 and amplifier 17, marking, if this number does not exceed 16 since the area is then a blank. The device determining this condition is an operational amplifier 30 comparing the current measured value with the current stored value. The 10% factor is decided by the values of the resistors 6, 29 in the inputs to the storage operational amplifier 8. These resistors and that 7 act in setting the predetermined amount between stored and current transparency values which has to be exceeded in the comparison operational amplifier 5 before counter 13 is erased, this arrangement dealing with leading picture edges. For trailing picture edge location, a similar arrangement of resistors 40, 41 is provided in the circuit of the other detector 28. Each storage circuit comprises a capacitor isolated by a diode from the operational amplifier 8 or 36 and having a feedback loop via field effect transistor 12 or 39.