Patent ID: 7359650

Claim:
An image forming apparatus comprising: a photosensitive unit; a static eliminator unit which eliminates static electricity from the surface of the photosensitive unit; a charging unit which charges a surface of the photosensitive unit subjected to the static elimination by the static eliminator unit; an exposure unit which exposes the surface of the photosensitive unit charged by the charging unit; a developing unit which develops the surface of the photosensitive unit exposed by the exposure unit; control means for executing a process to rotate the photosensitive unit and operate the static eliminator unit while charging a predetermined region of the photosensitive unit by the charging unit, at a time when the photosensitive unit has been set and at a periodic time; a potential sensor which detects a residual potential of the surface of the photosensitive unit subjected to the static elimination by the static eliminator unit, and a charging potential of the surface of the photosensitive unit charged by the charging unit; detection means for detecting a difference between the charging potential detected by the potential sensor and the residual potential detected by the potential sensor at the time of the execution of the process by the control means; storage means for storing the difference detected by the detection means as an initial value accompanying the execution of the process by the control means at the time when the photosensitive unit has been set; subtraction means for subtracting the difference detected by the detection means from the stored initial value accompanying the periodic execution of the process by the control means; and judgment means for judging that a lifetime of the photosensitive unit has expired in a case where a subtraction result of the subtraction means is less than a predetermined set value.