US Patent 7565096 Image forming apparatus and image carrier unit

An image forming apparatus includes an image carrier unit, a unit containing portion, driving units, driving sources, and a phase change matching unit. The image carrier unit integrally has image carriers that respectively carry images, and respectively have rotational shafts. The unit containing portion removably contains the image carrier unit. Each of the driving units includes at least one driving gear, and transmits driving force by the driving gear to the rotational shaft of one of the image carriers that corresponds thereto. The driving sources apply the driving force to the driving gears of the driving units. The phase change matching unit matches phase changes in the driving gears of the driving units when no image is formed.