Patent ID: 9645533
Date: 2017-05-09
CPC Classifications: G03G

Claim:
1. A fixing device that thermally fixes an unfixed image onto a recording sheet by pressing the recording sheet against a heating rotating body during passage of the recording sheet, the heating rotating body using, as a heat source, a resistance heating element whose electrical resistivity varies with temperature, the fixing device comprising: a temperature monitoring unit configured to monitor temperature in a sheet passing region and in a non-sheet passing region of the heating rotating body; a power supply unit configured to supply power to the resistance heating element so that the temperature in the sheet passing region is maintained at a target temperature during sheet passing with thermal fixing; a cooling unit configured to cool the non-sheet passing region; and a control unit configured to control cooling operation of the cooling unit according to the temperature in the non-sheet passing region during sheet passing with thermal fixing so that (i) the electrical resistivity of the resistance heating element is lower in a region corresponding to the non-sheet passing region than in a region corresponding to the sheet passing region and (ii) an absolute value of a temperature difference between the sheet passing region and the non-sheet passing region does not exceed an allowable temperature difference, wherein the resistance heating element is a positive temperature coefficient (PTC) element, and the control unit controls the cooling operation so that the temperature in the non-sheet passing region is lower than the target temperature.