Three-lobe constant-breadth cam 1 is enclosed by the square opening of slide 2 which reciprocates vertically along guides b-b of slide 3 and has claw a. Slide 3 reciprocates horizontally along fixed guides c. When cam 1 rotates, claw a of slide 2 is inserted into a perforation of the film, advances the film and is withdrawn from the perforation.
$3110$SmC,OC$