Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-04-27
2001-05-08
Grimley, Arthur T. (Department: 2852)
Electrophotography
Image formation
Fixing
C118S060000, C219S216000, C399S122000, C399S328000, C399S330000
Reexamination Certificate
active
06229982
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a fixing apparatus for use in, for example, electrophotographic copier, which is designed to fixing an image transferred on a paper sheet, and also to a fixing method and an image forming apparatus.
An electrophotographic copier forms a toner image on the photosensitive drum and transfers the toner image to a paper sheet. The paper sheet with the toner image transferred to it is supplied to the fixing apparatus. The fixing apparatus fixes the toner image on the paper sheet.
The fixing apparatus comprises a heat roller and a press set in press contact with the heat roller. As the paper sheet having a toner image transferred to it passes through the contact portion between the heat roller and the press roller, it is heated and pressed. The toner image is thereby fixed.
At the time of fixing the toner image, dirt such as toner may stick to the surface of the press roller. A cleaning roller made of metal is pressed onto the press roller, thereby to remove the dirt from the press roller.
To enhance the efficiency of transporting the paper sheet, the press roller of the fixing apparatus is shaped like a so-called “reversed crown,” having its diameter gradually decreasing toward the middle portion from either end.
Hitherto, the cleaning roller, which is shaped straight, is pressed onto the press roller that is shaped like an reversed crown. The cleaning roller fails to contact the press roller at its middle portion, though it well contacts the press roller at its end portions.
It is therefore impossible to removed the dirt from the middle portion of the press roller. Consequently, the paper sheet may gets dirty in the process of fixing the image.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in consideration of the foregoing. The object of the invention is to provide a fixing apparatus, a fixing method and an image forming apparatus, in which a cleaning roller is made to contact a fixing roller to remove dirt.
A fixing apparatus according to the invention comprises: fixing means having a pair of fixing rollers and designed to fix a developer image on a medium as the medium having the developer image transferred passes through a nip between the fixing rollers, one of the fixing rollers having a smaller diameter at a middle portion than at either end portion; and a cleaning roller set in contact with the one of the fixing rollers, for removing, from the one of the fixing rollers, dirt stuck to the one of the fixing rollers during a process of fixing the developer image on the medium, the cleaning roller having a larger diameter at a middle portion than at either end portion.
A fixing method according to the invention comprises the steps of: fixing a developer image on a medium as the medium having the developer image transferred passes through a nip between a pair of fixing rollers one of which has a smaller diameter at a middle portion than at either end portion; and cleaning the one of the fixing rollers, by removing dirt from the one of the fixing rollers by using a cleaning roller set in contact with the one of the fixing rollers and having a larger diameter at a middle portion than at either end portion.
An image forming apparatus according to the invention comprises: image forming means for forming an electrostatic latent image on an image carrier; developing means for applying developer to the electrostatic latent image formed by the image forming means, thereby to develop a developer image; transferring means for transferring the developer image formed by the developing means, to a medium; and fixing means for fixing the developer image transferred to the medium by the transferring means. The fixing means comprises: a pair of fixing rollers for fixing the developer image on the medium as the medium passes through a nip between the fixing rollers, one of the fixing rollers having a smaller diameter at a middle portion than at either end portion; and a cleaning roller set in contact with the one of the fixing rollers, for removing the developer from the one of the fixing rollers, the cleaning roller having a larger diameter at a middle portion than at either end portion.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.
REFERENCES:
patent: 4682878 (1987-07-01), Takizawa et al.
patent: 5450181 (1995-09-01), Tsukida et al.
patent: 5655201 (1997-08-01), Islam et al.
patent: 5689789 (1997-11-01), Moser
patent: 5749037 (1998-05-01), Takayuki
Eguchi Yoshihiko
Yamauchi Shin
Foley & Lardner
Grimley Arthur T.
Ngo Hoang
Toshiba Tec Kabushiki Kaisha
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