Abstract: In a print control method of an electrophotograph and an image formation apparatus thereof, a surface potential sensor is placed in a post-transfer area and at the position, the potential on the photoconductor drum surface at the developing point is detected. When the potential on the photoconductor drum surface is detected, the developing bias is avoided at the optimum timing and the potential is detected at the position after transfer. The correction potential amount grasped based on the in-machine humidity and the photoconductor drum film thickness previously measured is added to the detected potential and the potential on the photoconductor drum surface at the developing point is reproduced. Feedback control is applied to the potential on the photoconductor drum surface, whereby the developing potential on the photoconductor drum surface is kept stable.

Abstract: An image forming apparatus restricts disturbance of a potential patch in the case where a potential sensor for detecting the potential patch is provided downstream side of a developing device of a multiple developing roller type to enable stable reproduction of a high quality image for a long period. The apparatus includes a potential sensor provided downstream side of moving direction of the image carrier relative to the developing means for detecting a potential on the image carrier, and controller setting the developing bias to a value restricting disturbance of a potential portion as an object for potential detection by the potential sensor by the developer when the potential portion passes across the developing means.

Abstract: In an electrophotographic apparatus, regions having at least three different potential levels Vc, Vw, and Vr are formed on a photosensitive member by using an exposing device, and developing processes respectively using colored particles of different kinds are performed by normal development and reversal development on two potential levels Vc and Vr excluding the intermediate potential level Vw. The apparatus has an auxiliary exposing unit for forming a fringe development preventing potential in an edge of an image forming region in order to prevent fringe development from occurring. The auxiliary exposing unit sets an auxiliary exposure amount by performing pulse-width modulation on a laser driver.

Abstract: An image memory for storing input image data by plural lines, a horizontal scanning fringe correction exposure determining section for determining a fringe between close vertical lines in a horizontal scanning direction in the image data, a vertical scanning fringe correction exposure determining section for determining a fringe at the lower end of an image in a vertical scanning direction and a switch for selecting at least three laser drivers are provided.

Abstract: An electrophotographic printing apparatus using electric potential dividing development processing without the occurrence of primary fringe and fringe caused by auxiliary exposure has reverse electric fields causing primary fringe and fringe caused by auxiliary exposure adjusted to be nearly equal to each other. The auxiliary exposure is applied to an area surrounding one image, and an electric potential of an intermediate electric potential zone is brought close to a bias electric potential of another image which is not subjected to auxiliary exposure.

Abstract: In a two-color image forming apparatus, correction exposure of creating an area having a potential between an image area potential and a white area potential is made for a decided white area on the periphery of the image area. A potential difference between the image area and white area is reduced to attenuate an edge effect, thereby preventing the fringe development. This is accomplished by varying the light amount for the white areas of the intermediate potential areas as a function of the following: surface potentials measured, change in the developing bias voltage and rotating speed of a developing roll, adjustment of the amount of toners by a toner sensor, changing the resistance of a developer, and/or development of raster image processing.