Patent ID: 7437100

Claim:
An image forming apparatus, comprising: a conveyor belt that conveys paper; an intermediate transfer belt that transfers a toner image; a plurality of photosensitive drums of the same shape adjacently arranged facing said intermediate transfer belt; an image forming unit that forms a monochromatic toner image on each of said photosensitive drums; rotational speed detection means that detects individually the rotational speed of said photosensitive drums and said intermediate transfer belt; control means that controls individually the rotational speed of said intermediate transfer belt and said photosensitive drums, using the detected value of rotational speed; transfer means that transfers toner images of various colors formed on said photosensitive drums onto said intermediate transfer belt in sequentially superimposed fashion; drive means that rotates said photosensitive drums with a constant target speed when power is switched on; speed unevenness detection means that detects speed unevenness of said photosensitive drums from the rotational speed detection means of said photosensitive drums; phase correction means that performs phase correction on the speed of the photosensitive drum of largest speed unevenness; and target speed value calculation means that obtains a target speed value of said photosensitive drums by subtracting the speed unevenness of the other photosensitive drums from the speed value after phase correction.