Abstract: A fixing device which can be employed in an image forming apparatus controls energization of a heater which heats a fixing device, and a detector for detecting the condition of fixing operations such as the temperature of the fixing device, energizing time of the heater, types of transfer sheets to be used, and the number of previously performed fixing operations. A controller selects from plural kinds of temperature control on the basis of the condition detected by the detector, and controls energization and temperature of the heater during fixing operation including a backward revolution of the fixing device which is performed after an image is fixed. With the above constitution, both an excellent fixing property of a thick transfer sheet in low temperature environment and prevention against curls and wrinkles of thin transfer sheets in high temperature environment can be realized.

Abstract: Disclosed is a fixing device using fuzzy inference, which is used for copying machine, optical printer, or the like. The fixing device is provided with a fixing heater drive circuit 13 for controlling a heater 8 arranged in a fixing roller 9 on the basis of signals from CPU 1. The CPU 1 executes fuzzy inference so as to maintain the heat amount within predetermined value.