Patent ID: 6744995
Filing Date: 2004-06-01
Classification: G03G

Abstract:
An electrophotographic image forming apparatus comprising:a photoreceptor which is rotatable, and a surface of which can be uniformly charged at a voltage level, the surface attracting a toner for printing with an electrostatic force, the toner being transferred to an object to be printed on, such as paper, to perform a printing operation, and said photoreceptor rotating predetermined times during the printing operation; a charging unit for charging the surface of the photoreceptor to be either at a first white background potential or at a second white background potential; an exposing unit for forming an electrostatic print pattern on the surface of said photoreceptor set to be at the second white background potential, to form a latent image; a developing unit having a rotatable development roller, which rotates with a developer adhering to the surface thereof, the developer including a carrier and the toner attracting each other by an electrostatic force, the toner adhering to the latent image on the surface of the photoreceptor by the electrostatic force, a development bias being applied to the development roller, a potential difference between the development bias and the first white background potential being a first contrast potential, a potential difference between the development bias and the second white background potential being a second white background contrast potential, and an absolute value of the second white background contrast potential being greater than an absolute value of the first white background potential; and a control unit for controlling the charging unit so that a part of a total surface area corresponding to all the turns of the photoreceptor during a printing operation is charged to be at the second white background potential, the part corresponding to a predetermined number of turns relevant to the printing operation, and that the rest of the total surface area corresponding to the rest of turns is charged to be at the first white background potential.