Electrophotography – Image formation – Development
Reexamination Certificate
1999-12-23
2001-07-17
Beatty, Robert (Department: 2852)
Electrophotography
Image formation
Development
C399S235000
Reexamination Certificate
active
06263178
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an electrophotographic copier, printer, facsimile apparatus or similar image forming apparatus and more particularly to a method of applying a bias voltage for development and a method of switching it in an image forming apparatus.
2. Discussion of the Background
A color image forming apparatus of the type including two image forming units is conventional. The image forming units are spaced from each other by a preselected distance along the same running surface of an intermediate image transfer belt. Each image forming unit includes a single photoconductive element and a plurality of developing sections each for developing a particular latent image formed on the drum with toner of particular color. This type of image forming apparatus is disclosed in, e.g., Japanese Patent Laid-Open Publication No. 10-177286.
The above conventional color image forming apparatus has some problems left unsolved, as follows. In each image forming unit, a plurality of developing sections each develops a particular latent image formed on a single photoconductive drum with toner of particular color in contact with the drum, as stated above. It is therefore necessary to prevent toner of different colors from being mixed by selectively rendering the toner of different colors inoperative by sophisticated control. Moreover, a particular bias voltage for development is assigned to each of developing rollers included in the developing sections. This scales up a bias power source and therefore increases the overall size of the apparatus.
SUMMARY OF THE INVENTION
An image forming apparatus of the present invention includes a plurality of image forming units each including a single image carrier, a single writing device and a plurality of developing means each including a single developing roller for developing a latent image formed on the image carrier by the writing device with a developer to thereby produce a toner image. The image forming units are spaced by a preselected distance along the same surface of an intermediate image transfer belt to which the toner image is to be transferred from the image carrier. A selecting device causes the developing means to selectively perform development. A single bias power source applies a bias voltage for development to the developing means. A bias switching device applies the bias voltage output from the bias power source to one of the developing means selected by the selecting device.
It is therefore an object of the present invention to provide a bias applying method and a bias switching method for an image forming apparatus of the type including two image forming units capable of obviating the sophisticated control over the condition of toner and thereby reducing the overall size of the apparatus.
REFERENCES:
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patent: 62-212673 (1987-09-01), None
Takeyama Yoshinobu
Yanagawa Nobuyuki
Beatty Robert
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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