Patent ID: 8005400

Claim:
An image formation apparatus comprising: a first photoreceptor drum which carries a first electrostatic latent image; a second photoreceptor drum which carries a second electrostatic latent image; a third photo receptor drum which carries a third electrostatic latent image; a fourth photo receptor drum which carries a fourth electrostatic latent image; a first developer which develops the first electrostatic latent image to a first toner image; a second developer which develops the second electrostatic latent image to a second toner image; a third developer which develops the third electrostatic latent image to a third toner image; a fourth developer which develops the fourth electrostatic latent image to a fourth toner image; a transfer unit which transfers the first toner image and the second toner image to a medium; a first drum gear having a first cyclic mesh error and a first rib on a side face, and being provided coaxially with the first photoreceptor drum; a second drum gear which rotates, has a second cyclic mesh error and a second rib on a side face, and is provided coaxially with the second photoreceptor drum; a third drum gear provided coaxially with the third photoreceptor drum; a first extra idler gear which meshes with the second drum gear and the third drum gear, wherein the transfer unit further transfers the third toner image to the medium; a fourth drum gear provided coaxially with the fourth photoreceptor drum; a second extra idler gear which meshes with the third drum gear and the fourth drum gear, wherein the transfer unit further transfers the fourth toner image to the medium; a first photo interrupter configured to detect the first rib; and a second photo interrupter configured to detect the second rib.