Sprocket wheel and lens-fitted photo film unit with the same

摘要

A sprocket wheel is used with photo film which includes a plurality of perforation groups arranged in a longitudinal direction thereof and cyclically at a pitch predetermined for one frame. Each of the perforation groups includes first and second perforations arranged at a predetermined distance. The sprocket wheel is rotated by a predetermined amount while the photo film is wound per one frame. The sprocket wheel includes a wheel portion. Four teeth are arranged on a periphery of the wheel portion. A first one of the teeth is meshed with the first perforation. Then a second one of the teeth is meshed with the second perforation. The first and second teeth split the periphery of the wheel portion into first and second arc-shaped faces. The first arc-shaped face is determined in association with the predetermined distance. The second arc-shaped face has a radius greater than a radius of the first arc-shaped face, to push the photo film. The wheel portion, after the second tooth is moved away from the second perforation, is rotated by the photo film with friction between the second arc-shaped face and the photo film.