Image forming apparatus and image density control method employed by the image forming apparatus

An image forming apparatus comprising:

• a latent image carrier;
• a charging device to charge the latent image carrier to a predetermined charging potential;
• a latent image forming device to irradiate a charged surface of the latent image carrier to form a latent image thereon;
• a developing device including a developer carrier to carry a developer containing at least toner, the developing device transferring the toner carried by the developer carrier onto the latent image formed on the latent image carrier with a developing bias applied to the developer carrier to develop the latent image into a visible toner image;
• a transfer device including a transfer member to transfer the toner image from the latent image carrier onto the transfer member;
• a toner amount detector to detect an amount of toner of the toner image formed on the surface of the latent image carrier or the toner image transferred from the latent image carrier to the transfer member per unit area;
• and
• a control circuit to form a patch pattern including a plurality of patch toner images developed under different imaging conditions, to detect an amount of toner for each of the plurality of patch toner images via the toner amount detector, and to execute an imaging condition determination process at a predetermined time to determine an imaging condition for forming an output image according to a detected amount of toner,
• the control circuit obtaining a linear approximation formula of a developing potential and an amount of toner according to an exposure potential of the patch pattern including the plurality of patch toner images and the detected amount of toner to calculate a developing gamma and a developing start voltage according to a gradient of the linear approximation formula,
• the control circuit determining a target charging potential, a target exposure potential and a target developing bias according to the developing gamma and the developing start voltage,
• the control circuit determining an amount of a background potential to be corrected according to a difference between the developing start voltage and a target developing start voltage obtained according to environmental information, the background potential being a difference between the target charging potential and the target developing bias,
• the control circuit correcting the target charging potential.