When crank 1 rotates about fixed axis A, the tip of claw a of connecting rod 2 describes a complex connecting-rod curve. At one portion of this 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 At another portion of the curve, claw a is withdrawn from the perforation. The required shape of the path of claw a is obtained by properly profiling the part of connecting-rod 2 that contacts roller 3 which rotates about fixed axis B, and by proper selection of the dimensions of links 1 and 2 and the profile of flat spring 4.
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