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Category:Internet properties established in 20111. Field of the Invention
The present invention relates to a fixing apparatus mounted on an image forming apparatus such as a copying machine or a printer, and a method of control thereof.
2. Description of the Related Art
Conventionally, an image forming apparatus in which a belt-shaped member is wound around a heating roller to form a fixing nip between a fixing roller and the belt-shaped member has been proposed. In such an image forming apparatus, the heating roller is constantly applied with a predetermined load, and the belt-shaped member is wound around the heating roller at a predetermined rate to form the fixing nip therebetween.
In recent years, an image forming apparatus which controls a sheet being conveyed with high accuracy has been proposed (see Japanese Patent Laid-Open No. 2008-260062).
Incidentally, if the surface of the belt-shaped member formed by winding the belt-shaped member around the heating roller is, for example, significantly uneven, it may cause a change in the width of the fixing nip (hereinafter referred to as “nip width”). As a result, the image bearing surface of the sheet may not be pressed against the belt-shaped member at a desired pressure. If the image bearing surface of the sheet is pressed against the belt-shaped member at an excessively high pressure, the belt-shaped member may be injured. In such a case, the belt-shaped member is required to be replaced, resulting in increased frequency of maintenance.
In a fixing apparatus which has been proposed to solve the above-described problem, a temperature sensor for measuring the temperature of the belt-shaped member is provided, and the temperature of the belt-shaped member is controlled based on the result of the measurement. Specifically, in this fixing apparatus, when the belt-shaped member has a temperature that is higher than the fixing temperature, the amount of displacement of the belt-shaped member is gradually increased by an electrically-driven screw to form the fixing nip between the belt-shaped member and the fixing roller. When the temperature of the belt-shaped member is lower than the fixing temperature, the amount of displacement of the belt-shaped member is gradually decreased by the electrically-driven screw to decrease the width of the fixing nip. In the fixing apparatus, the heating roller is designed to always ac619d1d87
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