Image heating apparatus and image forming apparatus that control a temperature at which energization to a heater is turned off based on a temperature rise rate per unit time of a detection temperature

1. An image heating apparatus comprising:

an endless belt configured to heat a toner image on a recording material, while feeding the recording material through a nip;

a rotatable member configured to form the nip in cooperation with said endless belt;

a heater including a heat generating element configured to generate heat by energization, said heater being configured to heat said endless belt;

a detecting portion configured to detect a temperature of said heat generating element configured to heat a region outside of a minimum sheet passing region of said endless belt with respect to a longitudinal direction of said endless belt, wherein the minimum sheet passing region is a region of said endless belt in which, with respect to the longitudinal direction, a minimum-size recording material of recording materials to be fed to the nip passes through the region; and

a controller configured to control a temperature, at which energization to said heater is turned off, depending on a detection temperature of said detecting portion,

wherein, when a temperature rise rate per unit time of the detection temperature of said detecting portion is a first rise rate, said controller turns off the energization to said heater in response to the detection temperature reaching a first temperature, and, when the temperature rise rate per unit time is a second rise rate that is less than the first rise rate, said controller turns off the energization to said heater in response to the detection temperature reaching a second temperature that is greater than the first temperature.

2. The image heating apparatus according to claim 1 , wherein, when the temperature rise rate per unit time is the first rise rate, said controller permits the energization to said heater until the detection temperature reaches the first temperature, and, when the temperature rise rate per unit time is the second rise rate, said controller permits the energization to said heater until the detection temperature reaches the second temperature.

3. The image heating apparatus according to claim 1 , further comprising an image forming portion configured to form the toner image on the recording material,

wherein, when the temperature rise rate per unit time is the first rise rate, in response to the detection temperature reaching the first temperature, said controller turns off the energization to said heater in a state in which continuation of an image forming operation by said image forming portion is detected, and, when the temperature rise rate per unit time is the second rise rate, in response to the detection temperature reaching the second temperature, said controller turns off the energization to said heater in the state in which continuation of the image forming operation by said image forming portion is detected.

4. The image heating apparatus according to claim 1 , further comprising an image forming portion configured to form the toner image on the recording material,

wherein the first temperature and the second temperature are less than a predetermined temperature, at which execution of an image forming operation by said image forming portion is prohibited.

5. The image heating apparatus according to claim 1 , wherein said controller sets the temperature, at which the energization to said heater is turned off, at the first temperature when the temperature rise rate per unit time is the first rise rate, and sets the temperature, at which the energization to said heater is turned off, at the second temperature, and then turns off the energization to said heater, in response to that the detection temperature reaching the set temperature, and

wherein, when the temperature, at which the energization to said heater is turned off, is set at the first temperature during passing of the recording material through the nip, said controller sets the temperature, at which the energization to said heater is turned off, at a temperature that is greater than the first temperature in response to passing of a trailing end of the recording material through the nip.

6. The image heating apparatus according to claim 1 , wherein said controller controls the temperature, at which the energization to said heater is turned off, depending on the detection temperature and the temperature rise rate per unit time, and

wherein, when the detection temperature is a first detection temperature and the temperature rise rate is the first rise rate, said controller sets the temperature, at which the energization to said heater is turned off, at the first temperature, and, when the detection temperature is a second detection temperature that is less than the first detection temperature and the temperature rise rate per unit time is the first rise rate, said controller sets the temperature, at which the energization to said heater is turned off, at a third temperature that is greater than the first temperature.

7. The image heating apparatus according to claim 1 , wherein, when the recording material with a first size, with respect to the longitudinal direction, in which the recording material is in non-contact with said endless belt at a position in which said detecting portion is provided with respect to the longitudinal direction, is fed through the nip, said controller turns off, when the temperature rise rate per unit time is the first rise rate, the energization to said heater in response to the detection temperature reaching the first temperature, and turns off, when the temperature rise rate per unit time is the second rise rate, the energization to said heater in response to the detection temperature reaching the second temperature.

8. The image heating apparatus according to claim 1 , wherein, depending on the temperature rise rate per unit time, said controller limits an upper limit of electrical power supplied to said heater in a period until the energization to said heater is turned off.

9. The image heating apparatus according to claim 1 , wherein, depending on the detection temperature and the temperature rise rate per unit time, said controller limits an upper limit of electrical power supplied to said heater in a period until the energization to said heater is turned off.

10. An image forming apparatus comprising:

an image forming portion configured to form a toner image on a recording material;

an endless belt configured to heat the toner image, formed on the recording material by said image forming portion, while feeding the recording material through a nip;

a rotatable member configured to form the nip in cooperation with said endless belt;

a heater including a heat generating element configured to generate heat by energization, said heater being configured to heat said endless belt;

a sensor configured to detect a temperature of said heat generating element configured to heat a region outside of a minimum sheet passing region of said endless belt with respect to a longitudinal direction of said endless belt, wherein the minimum sheet passing region is a region of said endless belt in which, with respect to the longitudinal direction, a minimum-size recording material of recording materials to be fed to the nip passes through the region;

a double feed detecting portion configured to detect feeding of a plurality of recording materials to the nip; and

a controller configured to control a temperature, at which energization to said heater is turned off, depending on a detection result of said double feed detecting portion,

wherein, when the feeding of the plurality of recording materials to the nip is detected by said double feed detecting portion, said controller turns off the energization to said heater in response to the detection temperature of said sensor reaching a first temperature, and, when the feeding of the plurality of recording materials to the nip is not detected by said double feed detecting portion, said controller turns off the energization to said heater in response to the detection temperature reaching a second temperature that is greater than the first temperature.

11. The image forming apparatus according to claim 10 , wherein, when the feeding of the plurality of recording materials to the nip is detected by said double feed detecting portion, said controller permits the energization to said heater until the detection temperature reaches the first temperature, and, when the feeding of the plurality of recording materials to the nip is not detected by said double feed detecting portion, said controller permits the energization to said heater until the detection temperature reaches the second temperature.

12. The image forming apparatus according to claim 10 , further comprising an image forming portion configured to form the toner image on the recording material,

wherein, when the feeding of the plurality of recording materials to the nip is detected by said double feed detecting portion, in response to the detection temperature reaching the first temperature, said controller turns off the energization to said heater in a state in which continuation of an image forming operation by said image forming portion is detected, and, when the feeding of the plurality of recording materials to the nip is not detected by said double feed detecting portion, in response to the detection temperature reaching the second temperature, said controller turns off the energization to said heater in the state in which continuation of the image forming operation by said image forming portion is detected.

13. The image forming apparatus according to claim 10 , further comprising an image forming portion configured to form the toner image on the recording material,

wherein the first temperature and the second temperature are less than a predetermined temperature at which execution of an image forming operation by said image forming portion is prohibited.

14. The image forming apparatus according to claim 10 , wherein, on the basis of an output of said sensor, said double feed detecting portion detects the feeding of the plurality of recording materials to the nip.

15. An image heating apparatus comprising:

an endless belt configured to heat a toner image on a recording material, while feeding the recording material through a nip;

a rotatable member configured to form the nip in cooperation with said endless belt;

a heater including a heat generating element configured to generate heat by energization, said heater being configured to heat said endless belt;

a detecting portion configured to detect a temperature of said endless belt in a region outside of a minimum sheet passing region of said endless belt with respect to a longitudinal direction of said endless belt, wherein the minimum sheet passing region is a region of said endless belt in which, with respect to the longitudinal direction, a minimum-size recording material of recording materials to be fed to the nip passes through the region; and

a controller configured to control a temperature, at which energization to said heater is turned off, depending on the detection temperature of said detecting portion,

wherein, when a temperature rise rate per unit time of the detection temperature of said detecting portion is a first rise rate, said controller turns off the energization to said heater in response to the detection temperature reaching a first temperature, and, when the temperature rise rate per unit time is a second rise rate that is less than the first rise rate, said controller turns off the energization to said heater in response to the detection temperature reaching a second temperature that is greater than the first temperature.