Three-lobe constant-breadth cam 1 rotates about fixed axis A. The contour of cam 1 is enclosed by the square opening in follower 2 which has claw a. Follower 2 has straight slot b whose axis passes through point A and which slides along fixed pin 3. When cam 1 rotates, follower 2 has a complex motion in which claw a is inserted into a perforation of the film, advances the film and is withdrawn from the perforation.
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