Fixing apparatus, image forming apparatus and fixing method

An image forming apparatus comprising a fixing apparatus to perform a temperature control by using a heater wherein the fixing apparatus comprises:

• a heating roller having a center part and a peripheral part;
• a first heater included in the heating roller heating the center part of the heating roller;
• a second heater included in the heating roller, heating the peripheral part of the heating roller;
• a fixing roller;
• a fixing belt heated by the heating roller wound around the heating roller and the fixing roller, and circulating between the heating roller and the fixing roller;
• a pressing roller pressing the fixing roller through the fixing belt;
• a first non-contact sensor spaced from the fixing belt detecting a temperature of a first surface area of the fixing belt the first surface area corresponding to the center part of the heating roller;
• a second non-contact sensor spaced from the fixing belt detecting a temperature of a second surface area of the fixing belt, the second surface area corresponding to the peripheral part of the heating roller;
• and
• a temperature control unit configured to:
• control a temperature of the heating by an on/off control of the first heater and the second heater based on a first temperature detected by the first non-contact sensor and a second temperature detected by the second non-contact sensor, the temperature control unit performing the on/off control in which when one of the first heater and the second heater is turned on, the other is off, and
• to further control the temperature of the heating such that a sum of an on and an off time of at least one of the first or second heater is set to a first repetition period when a speed of the fixing belt is set to a first speed, and the sum of the on and off time is set to a second repetition period shorter than the first repetition period when the speed of the fixing belt is set to a second speed lower than the first speed.

A fixing method comprising:

• heating a center part of a heating roller by a first heater included in the heating roller;
• heating a peripheral part of the heating roller by a second heater included in the heating roller;
• heating a fixing belt by the heating roller, the fixing belt being wound around the heating roller and a fixing roller, and circulating between the heating roller and the fixing roller;
• pressing a pressing roller against the fixing roller through the fixing belt;
• detecting a temperature of a first surface area of the fixing belt by a first non-contact sensor spaced from the fixing belt, the first surface area corresponding to the center part of the heating roller;
• detecting a temperature of a second surface area of the fixing belt by a second non-contact sensor spaced from the fixing belt, the second surface area corresponding to the peripheral part of the heating roller;
• controlling a temperature of the heating by an on/off control of the first heater and the second heater based on a first temperature detected by the first non-contact sensor and a second temperature detected by the second non-contact sensor, while performing the on/off control in which when one of the first heater and the second heater is turned on, the other is off, and
• further controlling the temperature of the heating such that a sum of an on and an off time of at least one of the first or second heater is set to a first repetition period when a speed of the fixing belt is set to a first speed, and the sum of the on and off time is set to a second repetition period shorter than the first repetition period when the speed of the fixing belt is set to a second speed lower than the first speed.