| 摘要 |
<p>PURPOSE:To straighten a curl surely in forecasting a degree of the curl on recording paper in response to a broad type tober image by changing a straightened variable of the curl according to the detected result of a black-and- white ratio of the toner image being fixed to the recording paper. CONSTITUTION:Exposure scanning of an original takes place prior to copying action, and then a black-and-white ratio of the original is found out of an output signal of an AE sensor 80 detecting the exposure value. In regard to the black- and-white ratio 6-8% of a normal document original, conditions including heating temperature or the like of a fixing device are preset so as not to produce a curl. However, an actual original is wide in a range as black-and-white ratio 9-100%. Therefore, it is the higher in the black-and-white ratio, the more in a fixing area of toner to a paper ground part, so that paper is easy to be stuck to a fixing roller, thus a face curl is produced. In this curl straightening method, there are three processes: 1) A change of speed ratio of a roller pair, 2) a change of a bending angle in a pressing part, 3) a change of surface temperature of this pressing part.</p> |
