Electrophotography – Image formation – Fixing
Reexamination Certificate
2000-03-09
2001-06-05
Royer, William (Department: 2852)
Electrophotography
Image formation
Fixing
C015S256510, C399S327000
Reexamination Certificate
active
06243558
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates a fixing device for fixing a developer image formed on a transfer medium, an image forming apparatus with the fixing device, and a method of fixing the developer image.
An image forming apparatus such as a copying machine or a printer has a fixing device for heating and fusing a developer image formed on a transfer sheet, thereby fixing the developer image on the transfer sheet. This fixing device generally has a heating roller incorporating a heating source such as a heater, and a press roller in rolling contact with the heating roller with a predetermined pressure. The transfer sheet formed with the developer image is conveyed through a portion between the heating roller and press roller. During conveyance, the developer image is fixed to the transfer sheet by the heat and pressure respectively applied by the heating roller and press roller.
The fixing device has a cleaning roller for removing contamination attaching to the heating roller and press roller. The cleaning roller is in rolling contact with the outer surface of at least the heating roller and is urged against the heating roller with a predetermined pressure. As the cleaning roller, a felt roller is mainly used. Felt rollers are roughly classified into those impregnated with silicone oil to supply it, and those not using silicone oil. Felt rollers of either type perform cleaning by wiping out contamination on the heating roller.
When the pressure acting on the cleaning roller is large, although the cleaning performance of the cleaning roller increases, the cleaning roller becomes dirty at an early stage to shorten its service life. To the contrary, when the pressure acting on the cleaning roller is small, although the service life prolongs, the cleaning performance of the cleaning roller degrades. Then, contamination on the heating roller and the press roller cannot be removed sufficiently, and undesirably attaches to a transfer sheet.
When the heating roller and the press roller are cleaned, contamination such as the removed toner, paper dust, and the like attach to the felt roller. If a large amount of contamination attaches to the felt roller over a long-term use, for example, at the start of the fixing operation of the fixing device, contamination attaching to the felt roller is sometimes transferred from the felt roller to the heating roller and the press roller. In this case, contamination attaches to the transfer sheet to cause an image defect. Contamination transfer as described above tends to occur particularly when the pressure acting on the cleaning roller is large.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in view of the above situation, and has as its object to provide a fixing device, an image forming apparatus, and a method of fixing a developer image, which can improve the cleaning performance without shortening the service life of the cleaning roller, and can reduce the amount of contamination transfer from the cleaning roller.
In order to achieve the above object, according to the present invention, there is provided a fixing device comprising: fixing means having a pair of rollers which are in rolling contact with each other, for fixing a developer image formed on a recording sheet passing between the pair of rollers; a cleaning mechanism having a cleaning roller provided in rolling contact with at least one of the pair of rollers, for cleaning contamination on an outer surface of the one roller; and a pressure changing mechanism for changing a pressure applied by the cleaning roller to the one roller at a predetermined period in a fixing operation with respect to one recording sheet.
An image forming apparatus according to the present invention comprises: an image forming section for forming a developer image on a recording sheet; a fixing device for heating and pressing the recording sheet where the developer image has been formed by the image forming section, thereby fixing the developer image on the recording sheet; a paper supply section for selectively supplying various types of recording sheets having different sizes; and a convey mechanism for conveying the recording sheet fed from the paper feed section through the image forming section and the fixing device;
the fixing device including: fixing means having a pair of rollers which are in rolling contact with each other, for fixing a developer image formed on a recording sheet passing between the pair of rollers; a cleaning mechanism having a cleaning roller provided in rolling contact with at least one of the pair of rollers, for cleaning contamination on an outer surface of the one roller; and a pressure changing mechanism for changing a pressure applied by the cleaning roller to the one roller at a predetermined period in a fixing operation with respect to one recording sheet.
Further, according to the present invention, the predetermined period is shorter than a passing time of the recording sheet passing through the pair of rollers. The pair of rollers includes a heating roller having a heating portion therein, and a press roller provided in rolling contact with the heating roller and cooperating with the heating roller to heat and press the recording sheet passing between the heating roller and press rollers.
According to the fixing device and the image forming apparatus, the pressure changing mechanism has a cam arranged in contact with a rotating shaft of the cleaning roller, and a driving source for rotating the cam.
With the fixing device and the image forming apparatus having the above-mentioned arrangement, the pressure applied by the cleaning roller to the roller of the cleaning means is changed by the pressure changing mechanism within a predetermined period, when fixing is performed on one recording sheet. If the change range of the pressure is appropriately set, improvement in both the cleaning performance and the service life of the cleaning roller can be achieved more than in a case wherein the pressure is fixed. Simultaneously, the amount of contamination transfer from the cleaning roller to the heating roller, occurring at the operation start of the fixing device, decreases.
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: 5978640 (1999-11-01), Segawa
patent: 6014538 (2000-01-01), Imamiya et al.
patent: 8-227246 (1996-09-01), None
Foley & Lardner
Royer William
Toshiba Tec Kabushiki Kaisha
Tran Hoan
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