Image heating apparatus changing set temperature in accordance with temperature of heater

An image heating apparatus comprising:

• a heater;
• temperature detecting means for detecting a temperature of said heater;
• electric power supply control means for controlling electric power supply to said heater during image heating, so that the temperature detected by said temperature detecting means is maintained at a predetermined set temperature;
• and
• temperature determining means for determining the set temperature on the basis of a time period required for the temperature detected by said temperature detecting means to change from a first temperature to a second temperature, said determining means determining the set temperature for each image heating operation.

An image heating apparatus comprising:

• a heater;
• temperature detecting means for detecting a temperature of said heater;
• electric power supply control means for controlling electric power supply to said heater during image heating, so that the temperature detected by said temperature detecting means is maintained at a predetermined set temperature;
• and
• temperature determining means for determining the set temperature on the basis of a lowering rate of the temperature detected by said temperature detecting means during an interval between adjacent recording materials in continuous image heating operations.

An image heating apparatus comprising:

• a heater;
• temperature detecting means for detecting a temperature of said heater;
• and
• electric power supply control means for controlling electric power supply to said heater so that the temperature detected by said temperature detecting means is maintained at a predetermined temperature during an interval between adjacent recording materials in continuous image heating operations,
• wherein during a power supply control operation of said control means in the interval, there is a time period in which heat generation by said heater is shut-off or decreased.

An image heating apparatus comprising:

• a heater;
• temperature detecting means for detecting a temperature of said heater;
• electric power supply control means for controlling electric power supply to said heater during image heating, so that the temperature detected by said temperature detecting means is maintained at a predetermined set temperature;
• and
• temperature determining means for determining the set temperature on the basis of a changing rate of the temperature detected by said temperature detecting means in a predetermined time period in which the temperature of the heater is increased,
• wherein said predetermined period is not less than a unit time period of electric power supply control.