Film transport mechanism having automatic stroke adjustment

Abstract

A film transport mechanism for transporting film having perforations including a motor that drives sprockets for transporting the film in increments defined by a pull down stroke. In addition, the mechanism includes a pin element having at least one pin, the pin element being rotatable to a first position wherein the pin is inserted into an associated perforation to stabilize the film without contacting a perforation edge to generate a first sound level when the pull down stroke substantially equals a perforation pitch. Further, when the pitch is not equal to the pull down stroke, the pin contacts a perforation edge to generate a second sound level. The mechanism also includes a microphone positioned adjacent the pin element and the film for detecting a range of sound levels. An acoustic analyzing circuit is provided for comparing a sound level detected by the microphone to an acoustic signature indicative of contact between the pin and a perforation edge wherein when the detected sound level substantially matches the acoustic signature, the circuit controls the drive means to adjust the pull down stroke until the first sound level is detected wherein the pull down stroke is substantially equal to the pitch and thus the pin is inserted into a perforation without contacting a perforation edge.