Electrophotography – Control of electrophotography process – Responsive to copy media characteristic
Reexamination Certificate
2000-03-09
2001-11-06
Brase, Sandra (Department: 2852)
Electrophotography
Control of electrophotography process
Responsive to copy media characteristic
C399S068000, C399S069000
Reexamination Certificate
active
06314252
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus for fixing a developer image formed on a transfer medium with a fixing unit, thereby forming an image, and to a method of forming an image.
An image forming apparatus such as a copying machine or a printer has a fixing unit for heating and fusing a developer image formed on a transfer sheet, thereby fixing the developer image on the transfer sheet. This fixing unit generally has a heating roller incorporating a heat 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.
In the fixing unit having the above arrangement, in order to sufficiently fix the developer image on the transfer sheet, the heating roller and press roller must be maintained at a predetermined temperature. For this purpose, usually, the surface temperature of the heating roller is detected by a temperature sensor such as a thermistor, and the heat source is controlled in accordance with the detection result.
According to a device disclosed in Jpn. Pat. Appln. KOKAI Publication No. 9-179437, a reference temperature for a heating roller is set in advance in accordance with the size of a transfer sheet to be used, and the temperature of the heating roller is controlled on the basis of the reference temperature.
In a copying machine, various types of transfer sheets are prepared in accordance with the sizes of images to be formed, and transfer sheets having sizes corresponding to the images are selectively supplied. The widths, i.e., the axial lengths, of the heating roller and press roller of the fixing unit are set in accordance with the maximum-size transfer sheet to be used.
Therefore, in this fixing unit, when fixing is to be performed on a small-width sheet as a transfer sheet, a paper passing region where the transfer sheet passes and which comes into contact with the transfer sheet, and a paper non-passing region which does not come into contact with the transfer sheet, i.e., where the transfer sheet does not pass, are generated in a press contact portion between the heating roller and the press roller. When continuous copying operation is performed by using a plurality of these small-width sheets, the heat consumption amount differs between the paper passing region and the paper non-passing region, and the paper non-passing region is heated to a temperature higher than a predetermined temperature. In the subsequent copying operation, when a large-width transfer sheet is used, it partly passes the excessively heated paper non-passing region in the fixing unit. This leads to an image defect such as a high-temperature offset, or a paper passing defect such as a paper separation defect.
According to an apparatus disclosed in Jpn. Pat. Appln. KOKOKU Publication No. 5-5112, when continuous copying operation is performed on a predetermined number of transfer sheets or more, the predetermined temperature of a heating roller is gradually decreased during the continuous copying operation, so that an excessive temperature increase of a paper non-passing region is prevented.
In recent years, a composite image forming apparatus, in which a plurality of functions such as those of a copying machine, a printer, and a facsimile are combined, has been proposed as an image forming apparatus. In this image forming apparatus, various types of image data are input from an external device such as a personal computer or from a communication line. These image data are subjected to mixing and processed by an interrupt to form an image. Accordingly, in the composite image forming apparatus of this type, small-width transfer sheets and large-width transfer sheets are mixedly used more often than in an analog copying machine, and an image defect and a paper passing defect in the fixing unit described above tend to occur.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in view of the above situation, and has as its object to provide an image forming apparatus and a method of forming image in which occurrence of a fixing defect can be prevented and an image forming efficiency is improved.
In order to achieve the above object, according to the present invention, there is provided an image forming apparatus comprising: image forming means for forming a developer image on a recording sheet; fixing means for heating and pressing the developer image formed by the image forming means to fix the developer image on the recording sheet; a paper feed section for selectively feeding various types of recording media having different sizes; convey means for conveying the recording sheet fed from the paper feed section through the image forming unit and the fixing unit; a size detector for detecting a size of the recording sheet fed from the paper feed section; a temperature detector for detecting a surface temperature of the fixing means; and control means for controlling a fixing temperature of the fixing means in accordance with a predetermined reference temperature, and controlling image forming operation of the image forming means and recording sheet convey operation of the convey means in accordance with a size of a recording sheet to be fed next and the surface temperature of the fixing means which is detected by the temperature detector.
A method of forming image according to the present invention comprises the steps of: selectively supplying a recording medium with a size corresponding to an image to be formed; forming a developer image on the supplied recording medium; and heating and pressing the developer image formed on the recording medium by fixing means, thereby fixing the developer image on the recording medium;
the step of fixing the developer image including: detecting a surface temperature of the fixing means; and controlling a fixing temperature of the fixing means in accordance with a predetermined reference temperature, and controlling image forming operation of the developer image and recording medium supplying operation in accordance with a size of a recording medium to be supplied next and the detected surface temperature of the fixing means.
According to the image forming apparatus and the image forming method having the above arrangement, upon continuous image forming operation on a plurality of small-size copy media, when the temperature at the end of the heating roller becomes higher than usual, the image forming operation of the image forming means and the convey operation of the convey means are controlled in accordance with the size of a recording sheet to be fed next and the temperature of the fixing means. More specifically, when image formation is to be successively performed on a small-size recording sheet, the image forming operation of the image forming means and the convey operation of the convey means are continued. When image formation is to be performed on a larger-size recording sheet, the image forming operation of the image forming means and the convey operation of the convey means are set in the standby state until the temperature of the fixing means decreases to a predetermined temperature. As a result, a fixing defect can be prevented, and a standby time for the image forming operation can be shortened, thereby improving the efficiency.
According to the present invention, there is also provided an image forming apparatus comprising: a storage portion for storing various types of input image data; image forming means for forming a developer image on a recording sheet in accordance with the image data sent from the storage portion; fixing means for heating and pressing the recording sheet where the developer image has been formed by the image forming means, thereby fixing the developer image on the recording sheet; a paper feed section containing various typ
Brase Sandra
Foley & Lardner
Toshiba Tec Kabushiki Kaisha
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