Fixing device and image forming apparatus

摘要

A fixing device includes a fixing member including a heating unit, and a pressure member, the heating unit includes a sub-heater having a heat generating portion in a region smaller than a minimum paper width, a main heater having a heat generating portion at outside of the sub-heater, a first temperature detector to detect a temperature of the fixing member at the heat generating portion of the main heater, and a second temperature detector to detect the temperature at the heat generating portion of the sub-heater. The main heater and the sub-heater can be switched selectively, and the initial duty ratio at the start of PID temperature control by the sub-heater is determined in accordance with a difference between temperatures detected by the respective temperature detectors at the start of PID temperature control and a target temperature so that the temperature is not overshooting and dropped.

主权项

1. A fixing device comprising:
a fixing member configured to heat a recording medium and including a heating unit to heat regions corresponding to different paper sizes along an axial direction of the fixing member; and a pressure member configured to contact the fixing member firmly, the heating unit including:
a sub-heater having a heat generating portion in a region smaller than a minimum paper width, the sub-heater being closest to the pressure member;a main heater having a heat generating portion at least at a region outside of the sub-heater;a first temperature detector to detect a temperature of the fixing member at the heat generating portion of the main heater; anda second temperature detector to detect a temperature of the fixing member at the heat generating portion of the sub-heater, wherein the heating unit can be selectively switched between the main heater and the sub-heater.