Image forming apparatus and image forming unit with an improved phase adjustment means

摘要

A clutch (32) drives a first transmission system for color printing, including photosensitive drums (9a to 9c), and a second transmission system for monochrome printing, including a photosensitive drum (9d). The clutch stops the first system when both sensors (63, 61) detect marks (72) on the drum (9c) and its driving gear (A3). Next, when both sensors (64, 62) detect marks (72) on the drum (9d) and its driving gear (A4), the clutch redrives. Consequently, positionings of all the drums (9a to 9d) are performed without causing positional differences by inertia at the time of stop. <IMAGE>