Image heating apparatus

An image forming apparatus comprising:

• an image forming portion configured to form a toner image on a recording material;
• and
• an image heating device configured to heat the recording material having the toner image formed thereon while conveying the recording material, in a nip;
• and
• said image heating device including:
• a rotatable member;
• a plurality of heat generating elements including a first heat generating element and a second heat generating element, configured to heat said rotatable member, said heat generating elements extending in a longitudinal direction of said rotatable member, wherein the ratio of a heat generation amount of said second heat generating element at an end portion thereof to that at a central portion thereof with respect to the longitudinal direction is larger than the ratio of a heat generation amount of said first heat generating element at an end portion thereof to that at a central portion thereof with respect to the longitudinal direction;
• a back-up member contacting said rotatable member to form the nip;
• a temperature detecting portion configured to detect the temperature of said rotatable member or said heater;
• and
• a controller configured to control electric power supplied to said heater so that the detected temperature detected by said temperature detecting portion is at a target temperature, and said controller is configured to control the electric power supplied to said first heat generating element and the electric power supplied to said second heat generating element, independently from each other,
• wherein said controller switches the ratio of the electric power supplied to said second heat generating element to the electric power supplied to said first heat generating element from a first ratio to a second ratio, which is smaller than the first ratio, while small size recording materials are being conveyed through said image heating device, the small size recording materials having the same size, and
• wherein said controller controls said heater so that the sum of the electric power supplied to said first heat generating element and the electric power supplied to said second heat generating element in the second ratio is the same as the sum in the first ratio at the timing of the switching.

An image forming apparatus comprising:

• an image forming portion configured to form a toner image on a recording material;
• and
• an image heating device configured to heat the recording material having the toner image formed thereon while conveying the recording material, in a nip;
• and
• said image heating device including:
• a rotatable member;
• a plurality of heat generating elements including a first heat generating element and a second heat generating element, configured to heat said rotatable member, said heat generating elements extending in a longitudinal direction of said rotatable member, wherein the ratio of a heat generation amount of said second heat generating element at an end portion thereof to that at a central portion thereof with respect to the longitudinal direction is larger than the ratio of a heat generation amount of said first heat generating element at an end portion thereof to that at a central portion thereof with respect to the longitudinal direction;
• a back-up member contacting said rotatable member to form the nip;
• a temperature detecting portion configured to detect the temperature of said rotatable member or said heater, and
• a controller configured to control a duty cycle of an electric power supplied to said heater on the basis of a detected temperature of said temperature detecting portion, said controller being configured to control the duty cycle for said first heat generating element and the duty cycle for said second heat generating element, independently from each other,
• wherein said controller switches the ratio of the electric power supply duty cycle of said second heat generating element to the duty cycle of said first heat generating element from a first ratio to a second ratio, which is smaller than the first ratio, while small size recording materials are being conveyed through said image heating device, the small size recording materials having the same size, and
• wherein the duty cycle relative to the detected temperature of said first heat generating element in the second ratio is larger than that in the first ratio.