Image forming apparatus capable of correcting the upper value of a DC voltage used to adjust a development voltage containing a DC voltage

An image forming apparatus comprising:

• an image forming unit configured to perform image formation using toner, the image forming unit including
• an image carrier having a surface on which a photosensitive layer is formed,
• a charging device configured to charge the surface of the image carrier, and
• a development device including a developer carrier configured to carry developer containing the toner, so as to develop an electrostatic latent image formed on the image carrier into a toner image;
• an exposure device configured to expose the surface of the image carrier charged by the charging device, so as to form the electrostatic latent image whose charge is attenuated;
• an image density sensor configured to detect density of the toner image formed by the image forming unit;
• a development voltage power supply configured to apply a development voltage, in which an AC voltage is superimposed on a DC voltage, to the developer carrier;
• and
• a control unit configured to control the development voltage power supply, the control unit being capable of performing calibration, in which density of a plurality of reference images formed by the image forming unit while varying the DC voltage is detected by the image density sensor, and the development voltage is adjusted on the basis of a detection result, so as to adjust the density of the toner image, wherein
• the image forming apparatus further comprises a layer thickness detection mechanism configured to detect thickness of the photosensitive layer based on an accumulated operation distance of the image carrier, and
• along with a decrease in the thickness of the photosensitive layer detected by the layer thickness detection mechanism, the control unit stepwisely decreases an upper limit value of the DC voltage from a reference value to adjust the DC voltage within a range up to the upper limit value, when adjusting the development voltage in the calibration.