Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-07-07
2001-12-25
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Transfer
C399S299000, C399S306000
Reexamination Certificate
active
06334039
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, etc., and more particularly to an image forming apparatus having a plurality of recording units and a belt to convey a sheet-formed medium.
2. Discussion of the Background
A technology for a full color image forming method to form a full color image by transferring plural color images one after another using a plurality of electrostatic recording units in an electrophotographic color image forming apparatus is described in Japanese Patent Laid-Open Publication No. 10-333398.
A technology for separating a transfer belt from photoconductive elements used for color image formation in a black and white image forming mode to avoid unnecessary depletion of the photoconductive elements is described in Japanese Patent Laid-Open Publication No. 11-95619. A technology for preventing deformation of a transfer belt is described in Japanese Patent Laid-Open Publication No. 11-95516.
The above-mentioned technologies make it possible to prevent deformation of a transfer belt and unnecessary depletion of the photoconductive elements used for color image formation caused by rotating the transfer belt in a black and white image forming mode, in a warm-up state, or in a stand-by position. However, the transfer belt is always in contact with the photoconductive elements used for color image formation in a full color image forming mode. In order to measure a toner density of a developing unit or to detect displacement of toner images among the photoconductive elements, sensor patterns of toner images are formed on the transfer belt by being directly transferred from the photoconductive elements. When the sensor patterns are detected by a sensor disposed at a downstream side of the transfer belt, the sensor pattern, for example formed on the photoconductive element located at the most upstream side, may not be accurately detected due to, for example, a decrease in an amount of adhered toner of the sensor pattern and a mixture of background fouling toner on photoconductive elements with the sensor pattern caused by a reverse transfer of the sensor pattern to other photoconductive elements, and scattered toner in a nip formed between the transfer belt and the photoconductive element because the sensor pattern contacts three other photoconductive elements before the sensor pattern is detected.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-discussed and other problems and addresses the above-discussed and other problems.
The present invention advantageously provides a novel image forming apparatus forming a full color image with good color balance without displacements of images by detecting information about density and placements of toner images transferred onto a belt.
According to an embodiment of the present invention, an image forming apparatus includes a belt member to convey a sheet-formed medium, a belt supporting device to support the belt member, and a plurality of recording units including rotating image bearing members. The plurality of recording units are arranged in a conveying direction of the sheet-formed medium by the belt to perform the processes of (1) forming a latent image on a surface of each image bearing member, (2) developing each latent image into a toner image with toner, and (3) then transferring each toner image onto the sheet-formed medium carried on the belt. The image forming apparatus also includes a detection device to detect arbitrary toner images formed at the plurality of recording units and then directly transferred onto the belt, and a contact and separation device which enables the belt to contact and separate from the image bearing members. The contact and separation device is configured to be driven so as to separate the belt from the image bearing members before each toner image contacts the respective following recording unit.
REFERENCES:
patent: 5659843 (1997-08-01), Takano et al.
patent: 5719684 (1998-02-01), Ohkaji et al.
patent: 6-95474 (1994-04-01), None
patent: 7-311532-A (1995-11-01), None
patent: 8-328395-A (1996-12-01), None
patent: 10-282783 (1998-10-01), None
patent: 11-65315 (1999-03-01), None
Ozawa Yoshinori
Sato Masumi
Takehara Atsushi
Yoshinaga Hiroshi
Yuuki Kazuhiko
Grainger Quana M.
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ricoh & Company, Ltd.
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