PHOTOSENSITIVE DRUM UNIT AND IMAGE FORMING APPARATUS CAPABLE OF SUPPRESSING REGISTRATION ERROR

摘要

A photosensitive drum unit includes a frame and a plurality of photosensitive drums. The plurality of photosensitive drums is supported by the frame and has a shape identical with one another. Each of the plurality of photosensitive drums is rotatable about a rotational axis. The plurality of photosensitive drums is arranged such that a distance between rotational axes of adjacent photosensitive drums is a constant distance P. Each of the plurality of photosensitive drums has a circumferential reference position that is common to all of the plurality of photosensitive drums. Each of the plurality of photosensitive drums has a plurality of marks at circumferential positions that are defined relative to the circumferential reference position. Adjacent two positions of the circumferential positions are spaced by a central angle of {(S-P)/S}x 360 ° where S is a circumferential length of each of the plurality of photosensitive drums.