When crank 1 of three-bar slider-crank linkage ABC rotates about fixed axis A, the tip of claw a of link 2 describes a connecting-rod curve. Pin C of link 2 slides along fixed slot b-b. At one portion of the connecting-rod curve, claw a is inserted into a perforation of the film which it advances. At another portion of the curve, claw a is withdrawn from the perforation.
$1650$SC,OC$