A fixing device includes a heater, a first rotatable member, a second rotatable member, and a heat equalizing member. In a case that a region including a center of the heat equalizing member with respect to a longitudinal direction is a first region, a region closer to an end of the heat equalizing member than the first region is with respect to the longitudinal direction is a second region, and a region closer to the end of the heat equalizing member than the second region is with respect to the longitudinal direction is a third region. When the heat equalizing member has thermal capacities per unit length in the first region, the second region, and the third region are Cα, Cβ and Cγ, respectively, Cα, Cβ and Cγ satisfy the following relationship:
Cα>Cβ, and Cγ>Cβ.

An example fixing device includes a heating member, a pressing member to form a fixing nip with the heating member, a temperature sensor to sense a temperature at a first point of the heating member, and a processor to set a target temperature lower than a first set temperature at which normal fixing is possible for the entire area of a print medium in a case where a distribution of an image for a first area, which is a certain outer area of the print medium, is less than a certain criterion, and control power supplied to he heating member such that the temperature at the first point sensed by the temperature sensor reaches the set target temperature.

The present invention is characterized in that a control portion respectively sets a heating amount with respect to a region in which an image is formed and a heating amount with respect to a region in which an image is not formed in a single sheet of a recording material, and a difference between the heating amount with respect to the region in which an image is formed and the heating amount with respect to the region in which an image is not formed differs depending on a type of the recording material.

An image heating apparatus includes a heater having a first heating block and a second heating block, a heating rotating member to be heated by the heater, a pressure rotating member forming a nip portion for conveying a recording material between the pressure rotating member and the heating rotating member, first temperature detection elements and second temperature detection elements for detecting temperatures of the first heating block and second heating block respectively at positions farther from a recording material conveyance reference position than the first temperature detection elements. In the image heating apparatus, the first temperature detection elements are arranged on a side downstream of the heater in a recording material conveying direction, and the second temperature detection elements are arranged on upstream of the first temperature detection elements in the recording material conveying direction.

A fixing device includes an endless belt and a pressure rotator disposed opposite an outer circumferential surface of the endless belt. The pressure rotator has a first span in an axial direction of the endless belt. A nip formation pad, which is disposed opposite an inner circumferential surface of the endless belt, forms a fixing nip between the endless belt and the pressure rotator. The nip formation pad includes a belt-side thee disposed opposite the endless belt A radiant heater, which is disposed opposite the inner circumferential surface of the endless belt, heats the endless belt. A thermal conduction aid, which contacts the belt-side face of the nip formation pad, conducts heat in the axial direction of the endless belt. The thermal conduction aid has a second span within which the first span of the pressure rotator is provided at the fixing nip.

A fixing device includes a rotator, a pressure member, a conductor, and a heater. The pressing member presses the rotator to form a nip between the rotator and the pressing member. The conductor is grounded and includes a contact portion having a limiting shape to limit a contact area in which the contact portion is in contact with an inner circumferential surface of the rotator. The heater is in contact with the inner circumferential surface of the rotator to heat the rotator.

An image forming apparatus includes an image forming unit to form an image on a sheet. A fixing device heats the sheet and includes a tubular body that presses against the sheet and rotates, and a heat generator contacts an inside surface of the tubular body. The length dimension of the heat generator is aligned with the axial direction of the tubular body. The heat generator has a first row of first heating elements with a first gap between each adjacent pair of first heating elements and a second row of second heating elements. The first and second rows are offset from one another in a width direction corresponding to the sheet conveyance direction. A second gap is between each adjacent pair of second heating elements in the longitudinal direction. The positions of the first gaps are different from positions of the second gaps.

A heating device includes a substrate, one or more heating elements arranged along the substrate, a heat conductor contacting the substrate, a plurality of thermometers each configured to measure a temperature of the heat conductor, and a plurality of thermostats each configured to measure a temperature of the heat conductor and interrupt electrical power supplied to the heating elements. The thermometers and the thermostats are alternately arranged in a longitudinal direction of the substrate.

A fixing unit includes a tubular film, a pressure roller, a heater including a first heating element and a second heating element, a detector configured to detect a temperature of the heater, a switcher configured to switch which of the first heating element and the second heating element is supplied power from a power supply, and a controller configured to control the switcher. The controller is configured to execute a first control of determining a first electric energy and a second electric energy based on the temperature of the heater detected by the detector and a target temperature of the heater, and a second control of causing the switcher to switch between a state in which power is supplied to the first heating element by the first electric energy and a state in which power is supplied to the second heating element by the second electric energy.

A heating device includes a first temperature sensor and a second temperature sensor that detect a temperature of at least one of a first rotator, a second rotator, and a heater that heats at least one of the first rotator and the second rotator. The first temperature sensor is disposed outboard from an increased conveyance span where an increased size sheet having an increased width in a longitudinal direction of the heater is conveyed. The second temperature sensor is disposed outboard from a decreased conveyance span where a decreased size sheet having a decreased width in the longitudinal direction of the heater is conveyed. The decreased conveyance span is smaller than the increased conveyance span. The second temperature sensor is disposed within the increased conveyance span and disposed opposite the first temperature sensor via a center of the increased conveyance span in the longitudinal direction of the heater.