US Patent 7756439 Image forming apparatus and process cartridge used therein

An image forming apparatus includes multiple imaging units and a controller. The multiple imaging units each include a photoconductor, a charging device, a developing device, a retractable cleaner, and a cleaner retraction mechanism. The charging device charges the photoconductor for forming an electrostatic latent image thereon. The developing device develops the electrostatic latent image. The retractable cleaner cleans the charging device when in contact with the charging device. The cleaner retraction mechanism is configured to bring the retractable cleaner into contact with the charging device. The charging device and the photoconductor are installed and replaced in conjunction with each other. The controller calculates a photoconductor usage of each of the multiple imaging units, and individually controls the cleaner retraction mechanism in each of the multiple imaging units according to the calculated photoconductor usage.