Constant-breadth cam 1 rotates about fixed axis A and its contour a is confined between the flat faces of yoke (follower) 2 which has claw b. Yoke 2 is connected by turning pairs B and E to links 3 and 4 which, in turn, are connected by turning pairs C and F to links 5 and 6. Links 5 and 6 oscillate about fixed axes D and H. The lengths of the links comply with the conditions: B͞C=E͞F, D͞C=H͞F and B͞E-C͞F=D͞H, i.e. figure BEFHDCB is a double parallelogram. When cam 1 rotates, yoke 2 has a complex motion in which claw b is inserted into a perforation of the film, advances the film and is withdrawn from the perforation.
$3210$CmL,OC$