Image forming apparatus and charging bias adjusting method therefor

摘要

An image forming apparatus includes a latent image bearer to rotate, an image forming unit including a charger and a developing device, a charge power supply to output a charging bias applied to a charger, a transfer device, a toner adhesion amount, and a controller. The controller causes the image forming unit to form a background fog pattern in a background area of the latent image bearer while changing a background potential, acquires toner adhesion amount values detected at different positions of the background fog pattern, having different potentials, sorts the toner adhesion amount values in an order of the background potential, determines a relation between the background potential and background fog amount based the toner adhesion amount values except any toner adhesion amount value out of monotonicity, and adjust the charging bias to an optimum value computed based on the determined relation.

主权项

1. An image forming apparatus comprising:
a latent image bearer to rotate; an image forming unit including:
a charger to charge a surface of the latent image bearer; anda developing device including a developer bearer disposed facing the latent image bearer, the developing device to develop the latent image into a toner image; a charge power supply to output a charging bias applied to the charger; a transfer device to transfer the toner image from the latent image bearer onto a transfer medium; a toner adhesion amount detector to detect an amount of toner adhering to one of the latent image bearer and the transfer medium; and a controller configured to:
cause the image forming unit to form a background fog pattern in a background area of the latent image bearer while changing a background potential, which is a potential difference between the background area of the latent image bearer and the developer bearer;acquire a plurality of toner adhesion amount values respectively detected at different positions in the background fog pattern by the toner adhesion amount detector, the different positions having different potentials;sort the plurality of toner adhesion amount values in a magnitude order of the background potential;exclude any toner adhesion amount value out of monotonicity from the plurality of toner adhesion amount values;determine a relation between the background potential and a background fog amount based on a rest of the plurality of toner adhesion amount values; andadjust the charging bias output from the charge power supply to an optimum value computed based on the determined relation between the background potential and the background fog amount.