A color image forming apparatus including: multiple imaging units (18Y, 18C, 18M, 18K) configured to perform electrophotographic image formation, each imaging unit (18Y, 18C, 18M, 18K) including: a photoconductor; toner supply motors (94Y, 94M, 94C, 94K), photoconductor drive motors (95Y, 95M, 95C, 95K) and solenoids (96Y, 96M, 96C, 96K); a charging device configured to charge the photoconductor for forming an electrostatic latent image thereon; a developing device configured to develop the electrostatic latent image; a retractable cleaner configured to clean the charging device when in contact with the charging device; and a cleaner retraction mechanism configured to bring the retractable cleaner into contact with the charging device, the charging device and the photoconductor being installed and replaced in conjunction with each other; and a controller configured to calculate a photoconductor usage of each of the multiple imaging units (18Y, 18C, 18M, 18K), and individually control the cleaner retraction mechanism in each of the multiple imaging units (18Y, 18C, 18M, 18K) according to the calculated photoconductor usage, characterized in that the controller is further configured to control operation of the toner supply motors (94Y, 94M, 94C, 94K), the photoconductor drive motors (95Y, 95M, 95C, 95K) and the solenoids (96Y, 96M, 96C, 96K), respectively, while storing data on the operation of each individual imaging unit (18Y, 18M, 18C, 18K) in a non-volatile memory on which is based the calculation of the photoconductor usage, wherein said data include length of time each photoconductor drive motor (95Y, 95M, 95C, 95K) is activated, length of time each toner supply motor (94Y, 94M, 94C, 94K) is activated, number of pixels of each primary color contained in printed images, and environmental conditions under which the image forming apparatus and/or each imaging unit (18Y, 18C, 18M, 18K) is operated, wherein the cleaner retraction mechanism is arranged to be triggered by the solenoid (96Y, 96M, 96C, 96K), wherein the controller is configured to actuate the solenoid (96Y, 96M, 96C, 96K) to bring the retractable cleaner into contact with the charging device, wherein the controller is configured to increment a distance count by the calculated distance travelled by each photoconductor surface during image formation from the activation time of each photoconductor drive motor (95Y, 95M, 95C, 95K), which indicates the photoconductor usage, wherein the stored data is used by the controller to adjust this distance count. multiple imaging units (18Y, 18C, 18M, 18K) configured to perform electrophotographic image formation, each imaging unit (18Y, 18C, 18M, 18K) including: a photoconductor; toner supply motors (94Y, 94M, 94C, 94K), photoconductor drive motors (95Y, 95M, 95C, 95K) and solenoids (96Y, 96M, 96C, 96K); a charging device configured to charge the photoconductor for forming an electrostatic latent image thereon; a developing device configured to develop the electrostatic latent image; a retractable cleaner configured to clean the charging device when in contact with the charging device; and a cleaner retraction mechanism configured to bring the retractable cleaner into contact with the charging device, the charging device and the photoconductor being installed and a photoconductor; toner supply motors (94Y, 94M, 94C, 94K), photoconductor drive motors (95Y, 95M, 95C, 95K) and solenoids (96Y, 96M, 96C, 96K); a charging device configured to charge the photoconductor for forming an electrostatic latent image thereon; a developing device configured to develop the electrostatic latent image; a retractable cleaner configured to clean the charging device when in contact with the charging device; and a cleaner retraction mechanism configured to bring the retractable cleaner into contact with the charging device, the charging device and the photoconductor being installed and replaced in conjunction with each other; and a controller configured to calculate a photoconductor usage of each of the multiple imaging units (18Y, 18C, 18M, 18K), and individually control the cleaner retraction mechanism in each of the multiple imaging units (18Y, 18C, 18M, 18K) according to the calculated photoconductor usage, characterized in that the controller is further configured to control operation of the toner supply motors (94Y, 94M, 94C, 94K), the photoconductor drive motors (95Y, 95M, 95C, 95K) and the solenoids (96Y, 96M, 96C, 96K), respectively, while storing data on the operation of each individual imaging unit (18Y, 18M, 18C, 18K) in a non-volatile memory on which is based the calculation of the photoconductor usage, wherein said data include length of time each photoconductor drive motor (95Y, 95M, 95C, 95K) is activated, length of time each toner supply motor (94Y, 94M, 94C, 94K) is activated, number of pixels of each primary color contained in printed images, and environmental conditions under which the image forming apparatus and/or each imaging unit (18Y, 18C, 18M, 18K) is operated, wherein the cleaner retraction mechanism is arranged to be triggered by the solenoid (96Y, 96M, 96C, 96K), wherein the controller is configured to actuate the solenoid (96Y, 96M, 96C, 96K) to bring the retractable cleaner into contact with the charging device, wherein the controller is configured to increment a distance count by the calculated distance travelled by each photoconductor surface during image formation from the activation time of each photoconductor drive motor (95Y, 95M, 95C, 95K), which indicates the photoconductor usage, wherein the stored data is used by the controller to adjust this distance count.