Image forming apparatus including fixing device and controller for driving fixing device, including heating process to raise temperature of heating unit of fixing device

An image forming apparatus comprising:

• a fixing device comprising:
• a heating unit comprising a heater;
• an endless belt;
• a pressure roller configured to, in cooperation with the heating unit, nip the endless belt between the pressure roller and the heating unit;
• and
• a first temperature sensor configured to detect a temperature of the heating unit;
• a motor for rotating the pressure roller;
• a second temperature sensor different from the first temperature sensor;
• and
• a controller configured to perform driving the fixing device, the driving the fixing device including a heating process to raise the temperature of the heating unit to a target temperature,
• wherein the controller is further configured to perform, during the heating process:
• a first control operation in which the controller rotates the motor at a first rotational speed and adjusts a duty cycle of electric power supplied to the heater to a higher value as a deviation between the target temperature and a temperature detected by the first temperature sensor becomes greater;
• and
• a second control operation in which the controller rotates the motor at a second rotational speed lower than the first rotational speed and restricts the duty cycle within a range lower than or equal to a restricted value, the restricted value being lower than an upper limit of the duty cycle in the first control operation, and
• wherein the controller is further configured to perform the second control operation when a temperature detected by the second temperature sensor at a start of the driving the fixing device is lower than or equal to a first threshold.