Patent ID: 7106983
Filing Date: 2006-09-12
Classification: G03G

Abstract:
1. A color image forming apparatus comprising: a plurality of image forming devices each comprising: a photoconductor; a charger for charging the surface of said photoconductor; an exposing unit for exposing the charged surface of said photoconductor to form an electrostatic latent image; a developing unit for developing said electrostatic latent image on said photoconductor by attaching a toner on said photoconductor with a developer carrier to which a developing bias with an AC component superposed is applied; an image density sensor for sensing an image density of an image developed by said developing unit; a developing bias DC component control portion for controlling a DC component of a developing bias applied to said developing unit based on the image density information that the image density of the image developed on said photoconductor due to a parallel electric field is sensed by said image density sensor; a photoconductor surface potential control portion for controlling a surface potential of said photoconductor based on the image density information that the image density of the image developed on said photoconductor due to a parallel electric field is sensed by said image density sensor; an exposure value control portion for controlling an exposure value of said exposure unit based on the image density information that the image density of the image developed on said photoconductor due to a peripheral electric field is sensed by said image density sensor; a developing bias AC component control portion for controlling the amplitude of AC component of a developing bias applied to said developing unit based on the image density information that the image density having a dot occupied area ratio of 50% or more is sensed by said image density sensor; and an exposure value varying unit for switching an exposure value of said exposure unit between an image area having a predetermined number of pixels adjacent to a white paper portion and other image areas; wherein at least one of a DC component of developing bias by said developing bias DC component control portion, a surface potential of said photoconductor by said photoconductor surface potential control portion, an exposure value by said exposure value control portion, and the amplitude of a developing bias AC component by said developing bias AC component control portion is adjusted to reduce a difference in a gradation density curve between each image forming devices.