Image heating apparatus and image forming apparatus

1. An image heating apparatus, comprising:

a heater that includes a plurality of heat-generating blocks arrayed in a width direction of a recording material that is orthogonal to a conveying direction of the recording material;

a nip forming portion forming a nip that nips the recording material;

a temperature-detecting portion that detects a temperature of the heater; and

a control portion that controls electric power to be supplied to the plurality of heat-generating blocks, based at least on the temperature detected by the temperature-detecting portion,

wherein the image heating apparatus heats an image formed on recording material nipped by the nip, by heat of the heater,

wherein the plurality of heat-generating blocks have a first heat-generating group and a second heat-generating group,

wherein the first heat-generating group includes first and fourth heat-generating blocks symmetrically laid out with a conveyance reference position of the recording material in the width direction as a reference, and the second heat-generating group includes second and third heat-generating blocks symmetrically laid out with the conveyance reference position, placed at positions in the width direction different from the positions at which the first and fourth heat-generating blocks are placed,

wherein the temperature-detecting portion includes at least one first temperature-detecting element for detecting the temperature of at least one of the first and fourth heat-generating blocks included in the first heat-generating group, and at least one second temperature-detecting element for detecting the temperature of at least one of the second and third heat-generating blocks included in the second heat-generating group,

wherein, in a case of heating the image formed on the recording material at the nip forming portion, the control portion supplies electric power via a first switch to the first heat-generating group to maintain a detected temperature detected by only one of the at least one first temperature-detecting element at a control target temperature, and supplies electric power via a second switch to the second heat-generating group to maintain a detected temperature detected by only one of the at least one second temperature-detecting element at a control target temperature,

wherein the only one of the at least one first temperature-detecting element is placed on one side as to the conveyance reference position in the width direction, and

wherein the only one of the at least one second temperature-detecting element is placed on other side as to the conveyance reference position in the width direction.

2. The image heating apparatus according to claim 1 ,

wherein the first heat-generating group and the second heat-generating group are adjacent to each other in the width direction.

3. The image heating apparatus according to claim 1 ,

wherein the nip forming portion includes a cylindrical film on an inner side of which the heater is placed, and a pressure member that comes into contact with an outer face of the film, and

wherein the nip is formed by the heater and the pressure member via the film, between the film and the pressure member.

4. The image heating apparatus according to claim 3 ,

wherein the first temperature-detecting element and the second temperature-detecting element are placed in contact with a face of the heater that is on an opposite side from a face that forms the nip with the pressure member.

5. The image heating apparatus according to claim 1 ,

wherein the first temperature-detecting element and the second temperature-detecting element are thermistors.

6. The image heating apparatus according to claim 1 ,

wherein the heater includes a substrate on which the plurality of heat-generating blocks are formed, and

wherein the first temperature-detecting element and the second temperature-detecting element are printed thermistors formed on the substrate.

7. The image heating apparatus according to claim 1 , wherein each of the first to fourth heat-generating blocks includes a heat-generating resistor that generates heat by electric power, and the image heating apparatus further comprises:

a processor that functions as a resistance distribution acquisition portion that acquires a distribution of resistance of the heat-generating resistor in the width direction of the heater,

wherein the control portion controls electric power to be supplied to the plurality of heat-generating blocks based at least on the distribution acquired by the acquisition portion and the temperature detected by the temperature-detecting portion.

8. The image heating apparatus according to claim 7 ,

wherein the control portion controls electric power to be supplied to the plurality of heat-generating blocks while maintaining a temperature difference of the first heat-generating group and the second heat-generating group within a predetermined value.

9. The image heating apparatus according to claim 1 , further comprising:

a plurality of safety elements for shut off electric power to the first to fourth heat-generating blocks when a temperature of the heater reaches an abnormal temperature,

wherein the plurality of safety elements include

a first safety element placed corresponding to one of heat-generating blocks included in the first heat-generating group, and

a second safety element placed corresponding to one of heat-generating blocks included in the second heat-generating group.

10. The image heating apparatus according to claim 9 ,

wherein the first safety element is placed corresponding to a heat-generating block regarding which the first temperature-detecting element is placed corresponding thereto, out of the heat-generating blocks included in the first heat-generating group, and

wherein the second safety element is placed corresponding to a heat-generating block regarding which the second temperature-detecting element is placed corresponding thereto, out of the heat-generating blocks included in the second heat-generating group.

11. The image heating apparatus according to claim 9 ,

wherein the first safety element is placed corresponding to a heat-generating block which is different from a heat-generating block regarding which the first temperature-detecting element is placed corresponding thereto, out of the heat-generating blocks included in the first heat-generating group, and

wherein the second safety element is placed corresponding to a heat-generating block which is different from a heat-generating block regarding which the second temperature-detecting element is placed corresponding thereto, out of the heat-generating blocks included in the second heat-generating group.

12. The image heating apparatus according to claim 1 ,

wherein the first temperature-detecting element is placed to detect the temperature at a center region in the width direction of one of the heat-generating blocks included in the first heat-generating group, and

wherein the second temperature-detecting element is placed to detect the temperature at a center region in the width direction of one of the heat-generating blocks included in the second heat-generating group.

13. The image heating apparatus according to claim 12 ,

wherein the temperature-detecting portion further includes a temperature-detecting element to detect a temperature at an end-portion region in the width direction of each of the plurality of heat-generating blocks.

14. An image forming apparatus, comprising:

an image forming portion that forms an image on a recording material; and

a fixing portion that fixes the image formed on the recording material onto the recording material,

wherein the fixing portion includes

a heater that includes a plurality of heat-generating blocks arrayed in a width direction of a recording material that is orthogonal to a conveying direction of the recording material;

a nip forming portion forming a nip that nips the recording material;

a temperature-detecting portion that detects a temperature of the heater; and

a control portion that controls electric power to be supplied to the plurality of heat-generating blocks, based at least on the temperature detected by the temperature-detecting portion,

wherein the image heating apparatus heats an image formed on recording material nipped by the nip, by heat of the heater,

wherein the plurality of heat-generating blocks have a first heat-generating group and a second heat-generating group,

wherein the first heat-generating group includes first and fourth heat-generating blocks symmetrically laid out with a conveyance reference position of the recording material in the width direction as a reference, and the second heat-generating group includes second and third heat-generating blocks symmetrically laid out with the conveyance reference position, placed at positions in the width direction different from the positions at which the first and fourth heat-generating blocks are placed,

wherein the temperature-detecting portion includes at least one first temperature-detecting element for detecting the temperature of at least one of the first and fourth heat-generating blocks included in the first heat-generating group, and at least one second temperature-detecting element for detecting the temperature of at least one of the second and third heat-generating blocks included in the second heat-generating group,

wherein, in a case of heating the image formed on the recording material at the nip forming portion, the control portion supplies electric power via a first switch to the first heat-generating group to maintain a detected temperature detected by only one of the at least one first temperature-detecting element at a control target temperature, and supplies electric power via a second switch to the second heat-generating group to maintain a detected temperature detected by only one of the at least one second temperature-detecting element at a control target temperature,

wherein the only one of the at least one first temperature-detecting element is placed on one side as to the conveyance reference position in the width direction, and

wherein the only one of the at least one second temperature-detecting element is placed on other side as to the conveyance reference position in the width direction.

15. An image heating apparatus for heating an image formed on a recording material, comprising:

a cylindrical film;

a heater provided in an inner space of the film, the heater includes a substrate, a first to fourth heat-generating blocks arranged on the substrate in this order in a longitudinal direction of the substrate perpendicular to a conveying direction of the recording material;

a roller contacting an outer peripheral surface of the film and forming a nip for nipping and conveying the recording material together with the heater through the film;

a plurality of switches provided in power supply paths to the first to fourth heat-generating blocks for controlling electric power to be supplied to the first to fourth heat-generating blocks; and

a control portion configured to control the plurality of switches,

wherein, with respect to the longitudinal direction, the first and fourth heat-generating blocks are arranged in a symmetrical position with a conveyance reference position of the recording material as boundary, and the second and third heat-generating blocks are arranged in a symmetrical position with the conveyance reference position of the recording material as boundary,

wherein the plurality of switches includes a first switch for controlling the first and fourth heat-generating block and a second switch for controlling the second and third heat-generating block, and

wherein, in a case of heating the image formed on the recording material at the nip, the control portion controls the first switch so that a temperature of the first heat-generating block is maintained at a target temperature based only on the temperature of the first heat-generating block among temperatures of the first and fourth heat-generating block, and controls the second switch so that a temperature of the third heat-generating block is maintained at a target temperature based only on the temperature of the third heat-generating block among temperatures of the second and third heat-generating block.

16. The image heating apparatus according to claim 15 , wherein the first and second switches are TRIAC.