Patent ID: 8831457

Claim:
A fixing device comprising: an excitation coil supplied with power and generating an alternating magnetic field; a fixing member heated by electromagnetic induction resulting from the alternating magnetic field; a pressing member forming a nip by pressing against the surface of the fixing member, an unfixed image on a recording sheet being thermally fixed to the recording sheet upon the recording sheet passing through the nip; a magnetic shunt alloy member having a Curie temperature set to be a predetermined temperature higher than a target fixing temperature and arranged so as to suppress, when heated to the Curie temperature and above, a rise in temperature in a non-sheet passing region of the fixing member, the non-sheet passing region being a region through which the recording sheet does not pass; a sheet passing region temperature detector configured to detect a temperature of a sheet passing region of the fixing member, the sheet passing region being a region through which the recording sheet passes; a determiner configured to determine whether a temperature of the non-sheet passing region is about to reach the Curie temperature; a power controller configured to set a parameter for controlling the power supplied to the excitation coil; and a power supply configured to supply the power to the excitation coil in accordance with the set parameter, wherein until the determiner determines that the temperature of the non-sheet passing region is about to reach the Curie temperature, the power controller performs first control to select a target power to be provided to the excitation coil, according to the temperature detected by the sheet passing region temperature detector, and to adjust the parameter so as to maintain the power supplied to the excitation coil at the target power by feedback control, and when the determiner determines that the temperature of the non-sheet passing region is about to reach the Curie temperature, the power controller switches to performing second control to provide power to the excitation coil by switching the parameter to a predetermined fixed parameter, the fixed parameter being set so that a difference between the power supplied when the temperature of the non-sheet passing region is about to reach the Curie temperature and the power supplied after reaching the Curie temperature falls within an allowable range.