JP2013037159A - Image heating device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image heating device capable of preventing an abnormal rise of a temperature in a paper non-passing section on one end side of a longitudinal direction and heating a large number of images at a high speed even when there are displacements (continuous displacements, for instance) in the longitudinal direction of a recording material to be conveyed to a nip section.SOLUTION: The image heating device includes: displacement recognition means for recognizing that the paper non-passing section displaces by the displacements in the longitudinal direction of the recording material to be conveyed to the nip section; and heating means capable of independently heating the one end side and the other end side of the longitudinal direction corresponding to the nip section. When the displacements to the one end side is recognized, a heating control is performed so that the other end side has relatively small heating amount to the one end side.

Description

  The present invention relates to an image heating apparatus mounted on an image forming apparatus capable of forming a toner image on a recording material such as a copying machine, a printer, or a facsimile employing an electrophotographic system. Examples of the image heating device include a fixing device that fixes an unfixed image formed on a recording material, and a gloss processing heating device that improves the glossiness of an image by heating the image fixed on the recording material.

  As a fixing device for heating and fixing an unfixed toner image carried on a recording material as a fixed image in an image forming apparatus, a film heating method has been widely used. A film heating type fixing device forms a fixing nip portion by sandwiching a heat resistant film (fixing film, fixing belt) between a ceramic heater as a heating element and a pressure roller as a pressure member. is there. A recording material on which an unfixed toner image is formed and supported is introduced into the fixing nip, and is nipped and conveyed together with the fixing film.

  As a result, the heat of the ceramic heater is applied to the recording material through the fixing film at the fixing nip portion, and the unfixed toner image is fixed on the recording material surface by the applied pressure of the fixing nip portion. A characteristic of the above-described film heating type fixing device is that a member having a small heat capacity is used as the fixing film. In this case, there is an advantage that the time (warm-up time) required for the fixing device to fix the recording material carrying the unfixed toner image can be shortened and the power consumption is small.

  On the other hand, when the fixing film as described above is used, since the fixing film is thin and has a small heat capacity, the heat conduction in the direction orthogonal to the recording material conveyance direction (hereinafter referred to as the longitudinal direction) is deteriorated. To do. When a recording material having a narrow width relative to the length in the longitudinal direction of the fixing nip portion is passed, heat is taken away by the recording material by the recording material. On the other hand, since heat is not taken away from the non-sheet passing portion, the temperature of the non-sheet passing portion increases. The narrow recording material is a so-called small size recording material. For example, in the case of an image forming apparatus of LTR size and A4 size longitudinal conveyance, the recording material is A5 and B5 size width or less.

  Therefore, in a conventional fixing film type fixing device, a plurality of rows of heating resistance layers having different lengths in the longitudinal direction are installed on the ceramic heater at the nip portion in the film rotation direction (paper passing direction) to pass the paper. There has been proposed a method of generating heat in a heating resistor layer having a length that matches the width of the recording material. In this way, even when a small-size recording material is passed, temperature rise in the non-passing region can be suppressed (Patent Document 1).

JP 2000-162909 A

  However, the above-described conventional example is an example of countermeasures against edge temperature rise in the case of so-called small size paper. In recent years, with an increase in the speed of image forming apparatuses and a large amount of continuous printing, there has been a problem of edge temperature rise when an A4 size paper (paper width 210 mm) passes through an LTR size (paper width 216 mm) machine.

  With the recent increase in the speed of image forming apparatuses, the recording material conveyance speed in the fixing apparatus has become very high. For this reason, the heating member is in a very high temperature state in order to apply heat to the recording material and ensure the fixing property of the toner image to the recording material. In addition, due to the increase in speed, the interval between the previous recording material and the next recording material becomes very short, and the heating member in the fixing device continues to be heated.

  As a result, the recording material takes heat away in the paper passing portion, whereas the recording material does not take heat away in the non-paper passing portion. Therefore, in the LTR size machine, only in the case of a small size recording material such as A5 or B5 size. Even A4 size tends to be hot. When a large amount of paper is passed, the temperature of the non-paper passing portion becomes very high. For example, in a heating member typified by a ceramic heater or the like, a length in the longitudinal direction is required to ensure the fixability of LTR size paper (216 mm) as a heating element in the heating member. At the same time, it is also required to suppress the temperature rise in the non-sheet passing portion of the heating element when A4 size paper (210 mm) is passed, and the length in the longitudinal direction is adjusted to balance that.

  However, in recent years, there has been an increasing number of cases in which a large amount is continuously printed due to mass printing. For this reason, the number of image forming apparatuses that can set a large amount of recording material in the paper feed unit is increasing. When a large amount of recording material is set in the paper feed unit, as shown in FIG. 10, depending on mechanical factors or the way the user sets the recording material, the state is biased in the direction (longitudinal direction) perpendicular to the conveyance direction. There is a risk of setting.

  As described above, when the recording material set with a bias is continuously fed in the paper feeding unit, the paper is continuously biased to the right side with respect to the heating member in the fixing device, for example. Or, conversely, there is a case where the paper is fed to the left side. When the paper is continuously passed in such a state, the paper passing area is shifted in the longitudinal direction with respect to the heating member, and when the paper is passed to the left, the non-paper passing portion on the right side is widened. On the contrary, when the paper is passed to the right side, the non-sheet passing portion on the left side becomes wide, and the temperature rises greatly, causing a large left-right difference in the temperature of the fixing member of the fixing device, and one side greatly increases in the longitudinal direction. It gets warm.

  FIG. 11 shows an example of an increase in the temperature of a non-sheet passing portion region of a heater as a heating body when an A4 size recording material is continuously fed with a shift of 1 mm from the sheet passing center in an LTR size machine. . The recording material is heated in a non-sheet passing portion opposite to the side where the recording material is transported away, and the temperature of the recording material increases greatly as the number of sheets passed increases. When the heat resistance temperature of the constituent member of the fixing device is exceeded, the constituent member may be deteriorated, resulting in poor durability or damage. In addition, even when the constituent members do not deteriorate, when the recording material is passed with the temperature being high only on one side in the longitudinal direction, image adverse effects such as hot offset and roughness may occur.

  As described above, in consideration of the influence of the minute shift of the sheet passing position of the recording material, in the LTR machine, in order to cope with the recent increase in the speed of the image forming apparatus and a large amount of continuous printing, the length of the heating member in the longitudinal direction. It is not possible to support A4 size only by adjusting the size. That is, it has become difficult to suppress the temperature rise of the non-sheet passing portion during A4 size paper passing. In addition, it is difficult to deal with the influence of the minute shift of the recording material conveyance position by the expansion and contraction of the heating body according to the recording material width as in the conventional example.

  For this reason, particularly in a high-speed image forming apparatus for LTR size, when A4 size paper is continuously passed, in order to suppress the temperature of the non-sheet passing portion, for example, paper passing during A4 size paper passing is performed. The temperature detection element detects the temperature of the heating element at the end of the region. Before the temperature of the non-sheet passing portion of the heating body predicted from the detected temperature reaches the heat resistant temperature of the fixing member, the printing operation is stopped for a certain period of time, and the temperature of the non paper passing portion is higher than the heat resistant temperature. Wait until it drops sufficiently. Alternatively, the interval between the trailing edge of the previous recording material and the leading edge of the next recording material (hereinafter referred to as “paper interval”) is increased, and the temperature adjustment temperature of the fixing device is reduced during the interval between the papers. It is necessary to prevent problems from occurring.

  However, there is a problem that the throughput is greatly reduced and the productivity is lowered. In the present invention, even when there is a displacement (for example, continuous displacement) in the longitudinal direction of the recording material conveyed to the nip portion, the temperature of the non-sheet passing portion on one end side in the longitudinal direction is abnormally increased. An object of the present invention is to provide an image heating apparatus that can prevent a large amount of images and heat a large amount of images at high speed.

  In order to achieve the above object, the present invention forms a nip portion that is rotatable and can be heated in a longitudinal direction that intersects the rotation direction, and a heating nip member that is in pressure contact with the heating rotation member. An image heating apparatus that heats the image by sandwiching and transporting a recording material carrying an image in the nip portion, wherein the recording material is transported to the nip portion in the longitudinal direction. Displacement recognition means for recognizing that the non-sheet passing portion is displaced by the displacement, and heating means for independently heating one end side and the other end side in the longitudinal direction corresponding to the nip portion, When the displacement recognizing unit recognizes that the non-sheet passing portion is displaced toward the one end side in the longitudinal direction, the other end side with respect to the heating unit is relative to the one end side. Heating control to control heating so that the heating amount becomes smaller And having a stage, a.

  According to the present invention, even when there is a displacement (for example, continuous displacement) in the longitudinal direction of the recording material conveyed to the nip portion, the non-sheet passing portion on one end side in the longitudinal direction is abnormally heated. Therefore, it is possible to provide an image heating apparatus that heats a large amount of images at a high speed.

It is a block diagram of a heater (fixing heater) in the image heating apparatus according to the embodiment of the present invention. 1 is a schematic cross-sectional view of an image forming apparatus equipped with an image heating apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional view of a fixing device as an image heating device according to an embodiment of the present invention. 1 is a perspective model view of a fixing device as an image heating device according to an embodiment of the present invention. FIG. 6 is a diagram illustrating a positional relationship in a longitudinal direction of a fixing nip portion when a recording material is passed in an embodiment of the present invention. It is a figure which shows the temperature transition of the heating body in embodiment of this invention. FIG. 6 is a relationship diagram between a heating body temperature and a recording material conveyance position according to a second embodiment of the present invention. It is a block diagram of the heater (fixing heater) in the 3rd Embodiment of this invention. The temperature transition of the heating body in a prior art example is shown, (a) is a diagram showing a case where paper is passed on the basis of paper passing, and (b) is a diagram showing a case where paper is passed while being displaced to one end side. It is. It is a model figure of the recording material loading state of the paper feed section in the conventional example. It is a figure which shows the temperature transition of the non-sheet passing part in a prior art example.

  Exemplary embodiments of the present invention will be described below in detail with reference to the drawings.

<< First Embodiment >>
(Image forming device)
FIG. 2 is a schematic configuration diagram showing a color image forming apparatus equipped with an image heating apparatus according to an embodiment of the present invention. This image forming apparatus is an electrophotographic tandem type full color printer. The configuration of the image forming apparatus includes four image forming units (image forming units), and these four image forming units are arranged in a line at regular intervals. The image forming unit forms an image forming unit 1Y that forms a yellow image, an image forming unit 1M that forms a magenta image, an image forming unit 1C that forms a cyan image, and a black image. The image forming unit 1Bk.

  Photosensitive drums 2a, 2b, 2c, and 2d are installed in the image forming units 1Y, 1M, 1C, and 1Bk, respectively. Around each photosensitive drum 2a, 2b, 2c, 2d, charging rollers 3a, 3b, 3c, 3d, developing devices 4a, 4b, 4c, 4d, transfer rollers 5a, 5b, 5c, 5d, drum cleaning device 6a, 6b, 6c, 6d are installed. Exposure devices 7a, 7b, 7c, and 7d are installed above the charging rollers 3a, 3b, 3c, and 3d and the developing devices 4a, 4b, 4c, and 4d, respectively. Each developing device 4a, 4b, 4c, 4d contains yellow toner, magenta toner, cyan toner, and black toner, respectively.

  An endless belt-shaped intermediate transfer member 40 as a transfer medium is in contact with each primary transfer portion N of each of the photosensitive drums 2a, 2b, 2c, and 2d of the image forming portions 1Y, 1M, 1C, and 1Bk. The intermediate transfer belt 40 is stretched between a drive roller 41, a support roller 42, and a secondary transfer counter roller 43, and is rotated (moved) in the arrow direction (clockwise) by the drive of the drive roller 41.

  The transfer rollers 5a, 5b, 5c, and 5d for primary transfer are in contact with the photosensitive drums 2a, 2b, 2c, and 2d via the intermediate transfer belt 40 at the primary transfer nip portions 27, respectively. The secondary transfer counter roller 43 is in contact with the secondary transfer roller 44 via the intermediate transfer belt 40 to form a secondary transfer portion M. A belt cleaning device 45 that removes and collects transfer residual toner remaining on the surface of the intermediate transfer belt 40 is installed in the vicinity of the drive roller 41 outside the intermediate transfer belt 40.

A fixing device 12 is installed on the downstream side of the secondary transfer portion M in the conveyance direction of the recording material P.
When the image forming operation start signal is issued, the photosensitive drums 2a, 2b, 2c, and 2d that are rotationally driven at a predetermined process speed are uniformly charged by the charging rollers 3a, 3b, 3c, and 3d, respectively (in this embodiment, Negative polarity).

  The exposure devices 7a, 7b, 7c, and 7d respectively convert input color-separated image signals into optical signals at a laser output unit (not shown). Laser light, which is a converted optical signal, is scanned and exposed on each of the charged photosensitive drums 2a, 2b, 2c, and 2d to form an electrostatic latent image.

  Then, yellow toner is charged on the surface of the photosensitive member by the developing device 4a in which a developing bias having the same polarity as the charging polarity (negative polarity) of the photosensitive drum 2a is applied on the photosensitive drum 2a on which the electrostatic latent image is formed. Electrostatic adsorption is performed according to the potential. By this electrostatic adsorption, the electrostatic latent image is visualized to be a developed image. This yellow toner image is primary transferred onto the rotating intermediate transfer belt 40 by the transfer roller 5a to which a primary transfer bias (polarity opposite to the toner (positive polarity)) is applied at the primary transfer portion N. Is done. The intermediate transfer belt 40 to which the yellow toner image has been transferred is rotated toward the image forming unit 1M.

  Also in the image forming unit 1M, the magenta toner image formed on the photosensitive drum 2b in the same manner as described above is superimposed on the yellow toner image on the intermediate transfer belt 40 and transferred by the primary transfer unit N. . In the same manner, cyan and black toner images formed by the photosensitive drums 2c and 2d of the image forming units 1C and 1Bk on the yellow and magenta toner images superimposed and transferred onto the intermediate transfer belt 40 in the same manner are respectively used as the primary. The images are sequentially overlapped at the transfer portion N. As a result, a full-color toner image is formed on the intermediate transfer belt 40.

  Then, the recording material (transfer material) P is conveyed to the secondary transfer portion M by the registration roller 46 in accordance with the timing when the front end of the full color toner image on the intermediate transfer belt 40 is moved to the secondary transfer portion M. Full-color toner images are collectively transferred to the recording material P by the secondary transfer roller 44 to which a secondary transfer bias (opposite polarity (positive polarity) from the toner) is applied. The recording material P on which the full-color toner image is formed is conveyed to the fixing unit 12 and is full-color toner at the fixing nip portion between the fixing sleeve 20 as a heating rotation member and the pressure roller 22 that is driven to rotate. The image is heated and pressed to melt and fix it on the surface of the recording material P. Thereafter, the image is discharged to the outside and becomes an output image of the image forming apparatus. Then, a series of image forming operations is completed.

  In the primary transfer described above, the primary transfer residual toner remaining on the photosensitive drums 2a, 2b, 2c, and 2d is removed and collected by the drum cleaning devices 6a, 6b, 6c, and 6d. Further, the secondary transfer residual toner remaining on the intermediate transfer belt 40 after the secondary transfer is removed and collected by the belt cleaning device 45.

(Image heating device)
FIG. 3 is a schematic configuration model diagram of the fixing device 12 as the image heating device. The fixing device 12 of the present embodiment is a fixing belt heating method and a pressure rotating body driving method (tensionless type). FIG. 4 is a perspective model diagram showing the positional relationship between the fixing heater 16, the main thermistor 18, and the sub-thermistors 19a and 19b in the fixing device 12 of the present embodiment.

(Overall configuration of image heating device)
The fixing device 12 serving as an image heating device heats and fixes a toner image on a recording material. The fixing device 12 serves as a heating body having an energized heat generating resistance layer and a first rotating body that moves together with the recording material. And a sleeve 20. The fixing sleeve 20 is provided so as to be rotatable and capable of being heated in a longitudinal direction intersecting the rotation direction. The fixing device 12 further includes a pressure roller 22 as a second rotating body that is in pressure contact with the fixing sleeve 20, and a toner image on the recording material at a fixing nip 27 formed by the fixing sleeve 20 and the pressure roller 22. Is configured to heat and fix.

  The fixing sleeve 20 is a cylindrical (endless belt-shaped) member in which an elastic layer is provided on a belt-shaped member. For example, a film is used. The heater 16 is held by the heater holder 17. The heater holder 17 is a heat resistant and rigid member having a substantially semicircular arc shape in cross section, and the heater 16 is disposed on the lower surface of the heater holder 17 along the longitudinal direction of the holder. The heater 16 and the heater holder 17 constitute a backup member. The fixing sleeve 20 is loosely fitted on the heater holder 17.

  Here, the fixing heater 16 as the heating body uses a ceramic heater in the present embodiment, and the details of the configuration will be described later. The heater holder 17 is formed of a liquid crystal polymer resin having high heat resistance, plays a role of holding the fixing heater 16 and guiding the fixing sleeve 20.

  The pressure roller 22 is formed by forming a silicone rubber layer on a stainless steel core by injection molding and coating a PFA resin tube thereon. The pressure roller 22 is disposed such that both ends of the core bar are rotatably supported by bearings between a side plate (not shown) and a front side plate of the apparatus frame 24. On the upper side of the pressure roller 22, the fixing sleeve unit composed of the heater 16, the heater holder 17, the fixing sleeve 20 and the like is disposed in contact with the pressure roller 22 in parallel with the heater 16 facing downward.

  Both ends of the heater holder 17 are urged in the axial direction of the pressure roller 22 with a force of 12.5 kgf on one side and a total pressure of 25 kgf by a pressure mechanism (not shown). As a result, the downward surface (hereinafter referred to as a surface) of the fixing heater 16 is pressed against the elastic layer of the pressure roller 22 via the fixing sleeve 20 with a predetermined pressing force against the elasticity of the elastic layer. . Thus, a fixing nip portion 27 having a predetermined width necessary for heat fixing is formed. The pressurization mechanism has a pressure release mechanism, and is configured such that the pressurization is released at the time of jam processing and the recording material P can be easily removed.

In the present embodiment, as shown in FIG. 4, the sub-thermistor 19 a that is the first temperature detection unit and the sub-thermistor 19 b that is the second temperature detection unit are orthogonal to the conveyance direction of the recording material P. It arrange | positions in a different position regarding a direction (longitudinal direction), and detects the temperature of the heater 16. FIG.
As a specific arrangement, the nip portion is provided at a first position on one side and a second position on the other side across the longitudinal center position.

  In FIG. 3, since the two sub thermistors 19a and 19b are on the same line of sight, only one is shown. In the present embodiment, the main thermistor 18 is in elastic contact with the inner surface of the fixing sleeve 20 above the heater holder 17 and detects the temperature of the inner surface of the fixing sleeve 20. The sub-thermistors 19a and 19b are disposed closer to the fixing heater 16 that is a heat source than the main thermistor 18 is. In the present embodiment, the sub-thermistors 19a and 19b are in contact with the upward surface (hereinafter referred to as the back surface) in FIGS. 3 and 4 of the fixing heater 16, and the back surface of the fixing heater at the end of the heating resistor layer. Detect the temperature.

  In the main thermistor 18, a thermistor element is attached to the tip of a stainless steel arm 25 fixedly supported by the heater holder 17. As the arm 25 elastically swings, the thermistor element is always kept in contact with the inner surface of the fixing sleeve 20 even when the movement of the inner surface of the fixing sleeve 20 becomes unstable.

  The main thermistor 18 is disposed in the vicinity of the center of the fixing sleeve 20 in the longitudinal direction, and the sub-thermistors 19a and 19b are disposed in the vicinity of the end portion at an equal distance from the center of the fixing heater 16, respectively. It is arrange | positioned so that it may contact the back surface of. That is, the sub-thermistor 19a and the sub-thermistor 19b are arranged at the same distance from the center in the direction (longitudinal direction) perpendicular to the recording material conveyance direction of the energized heat generating resistance layer of the heater 16.

  The main thermistor 18 and the sub-thermistors 19a and 19b are connected to an energization control means 21 as a heating control means. The energization control means 21 determines the temperature control content of the fixing heater 16 based on the detection results of the main thermistor 18 and the sub-thermistors 19a and 19b. Further, the energization control means 21 determines the energization ratio to the energization heat generating resistance layer based on the detection results of the sub-thermistors 19a and 19b during continuous paper feeding. In the present specification, the energization ratio is the ratio of the time during which the heater is energized with respect to the period of voltage change of the AC waveform of the commercial power supply. The determination of the energization ratio for each energization heat generating resistance layer will be described later.

  Reference numerals 23 and 26 in FIG. 3 denote an entrance guide and a fixing paper discharge roller assembled to the apparatus frame 24. The entrance guide 23 serves to guide the transfer material so that the recording material P that has passed through the secondary transfer nip is accurately guided to the fixing nip portion 27. The entrance guide 23 of the present embodiment is made of polyphenylene sulfide (PPS) resin.

  The pressure roller 22 is rotationally driven in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed by a driving unit (not shown). A rotational force acts on the cylindrical fixing sleeve 20 by the pressure frictional force in the fixing nip portion 27 between the outer surface of the pressure roller 22 and the fixing sleeve 20 by the rotational driving of the pressure roller 22. The fixing sleeve 20 is rotated in the clockwise direction indicated by the arrow around the outer circumference of the heater holder 17 while the inner surface of the fixing sleeve 20 is in close contact with the downward surface of the fixing heater 16 and slides. Grease is applied to the inner surface of the fixing sleeve 20 to ensure slidability between the heater holder 17 and the inner surface of the fixing sleeve 20.

  In this manner, the pressure roller 22 is rotationally driven, and accordingly, the cylindrical fixing sleeve 20 is driven and rotated, and the fixing heater 16 is energized. In a state where the temperature of the fixing heater 16 is raised and raised to a predetermined temperature, the recording material P carrying the unfixed toner image is guided and introduced along the entrance guide 23 into the fixing nip portion 27. . In the fixing nip portion 27, the toner image carrying surface side of the recording material P is in close contact with the outer surface of the fixing sleeve 20, and the fixing nip portion 27 is nipped and conveyed together with the fixing sleeve 20.

  In this nipping and conveying process, heat of the fixing heater 16 is applied to the recording material P through the fixing sleeve 20, and an unfixed toner image on the recording material P is heated and pressurized on the recording material P to be melted and fixed. . The recording material P that has passed through the fixing nip 27 is separated from the fixing sleeve 20 by the curvature, and is discharged by the fixing discharge roller 26.

(Heater configuration)
FIG. 1 shows the configuration of the fixing heater 16 in the present embodiment. The fixing heater 16 of this embodiment has a back surface heating type structure. That is, 100 is a high thermal conductive substrate formed of a ceramic material such as alumina or aluminum nitride. The substrate 100 has a shape elongated in the longitudinal direction, and is formed wider than the width of the fixing nip portion 27 formed between the pressure roller 22 and the substrate 100.

  Further, an energization heating resistance layer made of a conductive material such as silver palladium (Ag / Pd) is formed along the longitudinal direction on the opposite side to the fixing nip portion 27 of the high thermal conductive substrate 100. In the present embodiment, a plurality of rows of energization heating resistors (two rows of energization heating resistors having centers displaced in different directions from the center in the longitudinal direction) are provided in the rotation direction (paper passing direction) in the nip portion. Specifically, two series of energization heating resistor layers (first energization heating resistor layer 101 and second energization heating resistor layer 102) are formed on the substrate by means such as screen printing. Further, an insulating protective layer 106 made of glass or the like is formed on the energization heat generating resistance layers 101 and 102.

  In the present embodiment, the energization heating resistance layers 101 and 102 each have a longitudinal length of 219.5 mm. However, as shown in FIG. 1, the positions in the longitudinal direction are shifted. Specifically, assuming that the sheet passing reference position of the recording material is the longitudinal center, the energized heat generating resistance layer 101 is displaced by 1.75 mm to the left and the energized heat generating resistance layer 102 is displaced by 1.75 mm to the right.

  For this reason, in the longitudinal direction, the region where both the energization heating resistance layers 101 and 102 are present is a region of 108 mm from the longitudinal center toward the left and right ends, and the entire longitudinal direction is 216 mm. The region where only one of the energization heat generating resistance layers 101 and 102 exists is 3.5 mm on both the left and right sides at the end in the longitudinal direction. In addition, when a region where at least one of the energization heat generation resistance layers 101 and 102 exists in the longitudinal direction is defined as a heat generation region, the length of the heat generation region is 223 mm. The longitudinal center of the heat generating area is the same as the sheet passing standard of the recording material.

  In order to make the explanation in the future easy to understand, let X be the center of conveyance of the recording material, that is, the center when the energized heat generating resistance layers 101 and 102 are considered together. Further, the longitudinal left end position of the energization heating resistor layer 101 shifted to the left side is Y1, and the right end position is Y2. The longitudinal left end position of the energization heating resistor layer 102 shifted to the right is defined as Z1 and the right end position is defined as Z2. Using this definition, the distance between Y1 and Z2 is 223 mm, and the distance between Y1 and Z1 and between Z2 and Y2 is 3.5 mm.

  Further, both of the energization heat generating resistance layers 101 and 102 have the same resistance value in the entire longitudinal direction, and the resistance value per unit length in the longitudinal direction is substantially uniform. Further, sub thermistors 19 a and 19 b are provided on the back surface of the heater 16. The sub-thermistor 19a is located 99 mm to the left of the heat generating center and 19b is located 99 mm to the right, and detects the temperature of the heater 16.

(Heat heat distribution)
In FIG. 1, when the recording material is passed, the energization heat generation resistance layer 101 is supplied with power from an unillustrated power source between the electrode portions 103 and 104, and the energization heat generation resistance layer 102 is also not illustrated between the electrode portions 103 and 105. Power is supplied from each and generates heat. By appropriately controlling the duty ratio and wave number of the voltage applied to the electrode section, the temperature of the fixing sleeve 20 is maintained at a desired temperature, and the toner image on the recording material is heated. That is, the energization to the energization heat generating resistor layers 101 and 102 is controlled so that the temperature of the main thermistor 18 maintains the target temperature. Here, power supplies for supply (not shown) to the respective energization heat generation resistance layers 101 and 102 are independent, and the energization ratios to the energization heat generation resistance layers 101 and 102 can be changed.

  When the energization heat generating resistance layers 101 and 102 are both energized at the same energization ratio, the respective energization heat generation resistance layers generate the same heat. Therefore, the heater 16 has a heat generation distribution that is symmetrical with respect to the heat generation center X in the longitudinal direction. On the other hand, for example, when the energization ratio to the energization heat generating resistance layer 102 is increased with respect to the energization ratio to the energization heat generation resistance layer 101, the energization heat generation resistance layer 102 generates a larger amount of heat. In this case, the amount of heat generated between Y2 and Z2 where only the energized heat generating resistance layer 102 exists is larger than the amount of heat generated between Y1 and Z1 where only the energized heat generating resistance layer 101 exists.

  Moreover, if the relationship between the energization ratios is reversed, the amount of heat generated between Y1 and Z1 can be increased. That is, the amount of heat generated at the end in the longitudinal direction can be controlled by changing the energization ratio of the other energization heat generation resistance layer to the other energization heat generation resistance layer.

(Control of energization ratio to energization heating resistance layer)
1) Sub-thermistor detection temperature and non-sheet passing portion temperature First, the detected temperature of the sub thermistors 19a and 19b and the temperature of the non-sheet passing portion with respect to the sheet passing position of the recording material will be described. Here, when the recording material is fed, the energization heat generating resistance layers 101 and 102 are energized at the same energization ratio. That is, assuming that the energization ratio to the energization heating resistor layer 101 determined so that the detected temperature of the main thermistor 18 becomes the target temperature is D1, and the energization ratio to the energization heating resistor layer 102 is D2, the control is performed with D1 = D2. Is going.

  FIG. 5 shows a state in which A4 size paper is passed through the fixing nip portion. Reference numeral 16 denotes a fixing heater as the heating body, and reference numerals 101 and 102 denote heating resistance layers provided on the back surface of the fixing heater 16. When A4 size paper is passed centered on X according to the paper passing standard (in the case of a solid line), in the configuration of the present embodiment, the energization heat is generated from the region of 6.5 mm from both ends of the A4 paper, that is, from the paper edge. A region up to the end of the resistance layer is a non-sheet passing portion.

  In the left-right direction (longitudinal direction) in FIG. 5, with respect to the left side in FIG. 5, the portion from the end of the recording material to the end Y <b> 1 of the energization heating resistor layer 101 is a non-sheet passing portion. On the right side, the end of the recording material to the end Z2 of the energization heating resistance layer 102 is a non-sheet passing portion. In this case, since the length of the non-sheet passing portion in the left-right direction (longitudinal direction) is the same, the temperature rise of the non-sheet passing portion is the same on the left and right.

  On the other hand, a case where the recording material is passed through to one side (in the case of the broken line in FIG. 5), specifically, a case where A4 size paper is shifted to the right by 1.5 mm will be described. In this case, the longitudinal center of the recording material is shifted by 1.5 mm with respect to the longitudinal center X of the heat generating region, and the length of the region of the non-sheet passing portion is different on the left and right. The distance from the end of the recording material to the energized heating resistance layer end Y1 is 8 mm. Further, the distance from the end of the recording material to the end Z2 of the energization heating resistor layer 102 is 5 mm. Therefore, the temperature on the Y1 side where the area of the non-sheet passing portion is wide rises, which may cause the problem described in the conventional example.

  FIG. 9 shows the monitoring results of the detection results Ta and Tb of the sub-thermistors 19a and 19b and the temperature of the non-sheet passing portion when A4 size paper and paper having a basis weight of 80 g / mm are continuously passed. The non-sheet-passing portion was measured by installing a K-type thermocouple on the heating resistor at the same distance from the paper edge (this result is 3 mm from the paper edge). Hereinafter, regarding the non-sheet passing portion temperature measured by the thermocouple, the temperature on the same side as the sub-thermistor 19a is denoted as Ha, and the temperature on the same side as the sub-thermistor 19b is denoted as Hb. Here, the energization ratio to the energization heat generating resistance layers 101 and 102 was controlled to be equal (D1 = D2).

  FIG. 9A shows the result when A4 paper is passed according to the paper passing standard, and FIG. 9B shows the result when the paper is passed 1.5 mm to the right with respect to the paper passing standard. Is the result of As shown in FIG. 9A, when A4 paper is continuously passed, Ta and Tb have the same temperature rise curve when passed according to the paper passing reference. On the other hand, as shown in FIG. 9B, when the sheet passing position shift amount in the longitudinal direction is large, the temperature of the non-sheet passing portion on one side increases rapidly.

  As shown in FIG. 9B, when the paper is passed by 1.5 mm to the right side with respect to the reference, the side where the non-sheet passing portion area becomes wider than when the paper is passed based on the paper passing reference. The temperature Ta on the sub-thermistor 19a side and the temperature Ha of the non-sheet passing portion are high. In addition, it can be seen that the rising curves of the temperature detection results Ta and Tb of the sub-thermistors 19a and 19b correspond to the temperature rising curves of the temperatures Ha and Hb of the non-sheet passing portions on the respective sides. From these results, the temperatures Ha and Hb of the non-sheet passing portions on both sides can be predicted from the detected temperatures Ta and Tb of the sub-thermistors 19a and 19b.

2) Change of energization ratio with respect to energization heat generation resistance layer Hereinafter, energization control to the energization heat generation resistance layer in this embodiment is demonstrated in detail. In FIG. 3, the control circuit unit 21 calculates the difference Ta−Tb from the temperature detection results Ta and Tb of the sub-thermistors 19a and 19b. And the control circuit part 21 as a heating control means performs the heating control mentioned above, when the difference of the temperature detected by the sub thermistors 19a and 19b reaches a predetermined value. That is, when the absolute value of the temperature difference detected by the sub-thermistors 19a and 19b is 10 degrees or more (| Ta−Tb | ≧ 10 ° C.), the other energization with respect to the energization ratio to one energization heating resistance layer Change the ratio of the energization ratio to the heating resistor layer.

  Hereinafter, a case where the sheet passing position of the recording material is shifted to the right by 1.5 mm with respect to the sheet passing reference X will be described in detail. As the recording material is continuously fed, the value of | Ta−Tb | increases, so that the temperature of the sub-thermistor 19a, which is the wider side of the non-sheet-passing area, greatly increases. Therefore, in order to prevent the temperature from being increased greatly only on one side, it is necessary to reduce the heat generation amount on the sub-thermistor 19a side, and the heat generation amount between Y1 and Z1 is made smaller than the heat generation amount between Y2 and Z2. It is preferable.

  If the energization ratio of the energization heat generation resistance layer 101 to the energization heat generation resistance layer 102 is reduced, the heat generation amount between Y1 and Z1 can be made smaller than the heat generation amount between Y2 and Z2. In the present embodiment, when Ta−Tb ≧ 10 ° C., the amount of power input to the energized heat generating resistor layer 101 is reduced by 10% with respect to the amount of power input to the energized heat generating resistor layer 102.

More specifically, it is assumed that at the initial stage of continuous recording material feeding, the energization heating resistance layer 101 is energized at the energization ratio D1 and the energization ratio 102 is energized at the same value D2. That is, it is assumed that D1 = D2 and both of the powers are applied with 300 W and a total power of 600 W is applied. Next, when Ta−Tb ≧ 10 ° C., the energization ratio to the energization heating resistor layer 101 is D1-5%, and the power input amount is about 285 W.
Further, the energization ratio to the energization heat generating resistance layer 102 is set to D2 + 5%, and the power input amount is set to 315W. By doing in this way, the emitted-heat amount of the energization heat-generation resistance layer 101 reduces, and the emitted-heat amount between Y1-Z1 can be reduced. In addition, since the power input amount as the heater 16 remains 600 W, the temperature at the longitudinal center of the fixing sleeve 20 remains constant.

  These are shown in FIG. When the longitudinal position of the recording material (paper) is conveyed toward one side with respect to the sheet passing reference, the difference between Ta and Tb gradually increases as the number of sheets passed increases. However, when the difference between Ta and Tb reaches 10 ° C., the energization ratio to the energization heat generation resistance layer 101 is decreased by 5% in order to reduce the heat generation amount between Y1 and Z1 on the sub-thermistor 19a side. Reduce the amount of power. In addition, the energization ratio to the energization heat generating resistance layer 102 is increased by 5% to increase the input power amount. By doing so, as shown by the solid line in FIG. 6, the temperature difference between Ta and Tb changes from the next recording material passing sheet so as to decrease.

  As described above, when the difference between Ta and Tb reaches a specified value, the energization amount to the energization heat generating resistance layers 101 and 102 is changed. Thereby, even when the recording material is continuously displaced in the direction (longitudinal direction) orthogonal to the conveying direction, it is possible to prevent a large difference in right and left in the heat generation distribution of the fixing heater 16. In addition, in the fixing nip 27, it is possible to prevent only one of the recording material conveyance directions from being heated significantly.

  In the present embodiment, the case where the detected temperature Ta of the sub-thermistor 19a is higher than the detected temperature Tb of the sub-thermistor 19b has been described. That is, the recording material passing position is shifted to the right side from the sheet passing reference X. On the contrary, when the sheet passing position of the recording material is shifted to the left with respect to the sheet passing reference, it goes without saying that the detected temperature Tb of the sub-thermistor 19b is higher. In this case, the energization ratio to the energization heat generating resistor 102 may be reduced, the input power amount may be decreased, the energization ratio to the energization heat generation resistance layer 101 may be increased, and the input power amount may be increased.

  Further, as described above, Ta−Tb ≧ 10 ° C. is satisfied, and Ta−Tb ≧ 10 ° C. is again achieved as the recording material passes through in spite of the reduction in the amount of power applied to the energization heating resistor layer 101. There is a case. For example, this is a case where the sheet passing position of the recording material is closer to the right than expected. In this case, when Ta−Tb ≧ 10 ° C. again, the energization ratio to the energization heat generating resistor layer 101 may be reduced again to reduce the input power amount. That is, every time | Ta−Tb | ≧ 10 ° C., the amount of electric power supplied to the energized heat generating resistor layers 101 and 102 is changed so as to reduce the amount of heat generated on the side where the high temperature is detected. Just do it.

  Further, in the present embodiment, an example in which the temperature of the non-sheet passing portion is predicted based on the detected temperature of the sub-thermistors 19a and 19b provided on the heater 16, is not limited to this. . That is, for example, a temperature detection element that monitors the temperature near the longitudinal end of the fixing sleeve 20 may be provided. The same effect can be obtained by changing the energization ratio in the same manner as in the present embodiment based on the temperature difference between the left and right sides of the fixing sleeve 20. In addition, for example, a temperature detecting element capable of monitoring a temperature difference between the longitudinal and lateral directions of the pressure roller 22 may be provided.

  Further, the configuration on the heater 16 is not limited to the configuration of the present embodiment. That is, a plurality of energized heat generating resistance layers are formed, and at least one of them may be a heat distribution that is asymmetrical in the left and right with respect to the sheet passing reference, which is the center in the longitudinal direction. In addition, as long as the plurality of energization heating resistance layers can be independently energized, the same effects as in the present embodiment can be obtained.

<< Second Embodiment >>
In this embodiment, the energization ratio of the energization heat generating resistance layer is changed based on the difference between Ta and Tb every five sheets. Note that the configuration of the image forming apparatus and the configuration of the fixing device 12 are the same as those in the first embodiment, and thus detailed description thereof is omitted.

  FIG. 7 shows the difference between the detected temperatures Ta and Tb of the sub-thermistors 19a and 19b when five recording materials are continuously fed in the conventional example. Further, the difference between the temperature Ha and Hb of the non-sheet passing portion at the position of the same distance from the end of the recording material on each of the sub-thermistor 19a side and 19b side (in this embodiment, 3 mm from the end portion of the paper) and the recording material. The relationship of the deviation | shift amount from the reference | standard position (center) of a conveyance position is shown.

  FIG. 7 shows the results when paper having an A4 size and a basis weight of 80 / gm2 is passed in an environment of 25 ° C./60%. The vertical axis of the graph is the value of Ta-Tb and Ha-Hb. When the paper is passed to the right, the temperature of Ta increases, so when the paper is passed to the left, the value is positive. The temperature of Tb increases. Therefore, it is a negative value. Further, the temperatures Ha and Hb on the back surface of the fixing heater in the non-sheet passing portion were measured by installing a thermocouple on the back surface of the fixing heater 16.

  As shown in FIG. 7, the difference between Ta and Tb and the difference between Ha and Hb have a one-to-one relationship with the deviation of the A4 paper conveyance position from the reference position, and the temperature difference increases as the recording material conveyance position shifts. You can see that it is getting bigger. When the paper passing position is in the center, the difference is 0 for both Ta and Tb, and Ha and Hb.

In the present embodiment, the energization ratio to the energization heat generation resistance layers 101 and 102 at the time of passing the next five sheets is set every time five recording materials are passed based on the result shown in FIG. . Hereinafter, Table 1 shows the amount of change in the energization ratio to the energization heating resistance layers 101 and 102 every five sheets when A4 size paper having a basis weight of 80 g / m 2 is continuously fed.

  Here, in Table 1, when the values of Ta-Tb and Ha-Hb are positive, the recording material is shifted to the right side, indicating that the temperature on the sub-thermistor 19a side is high. On the other hand, when it is negative, it indicates that the recording material is shifted to the left side and the temperature on the sub-thermistor 19b side is high. When the recording material starts to pass, the energization heat generation resistance layer 101 is energized at an energization ratio D1 and the energization heat generation resistance layer 102 is energized at an energization ratio D2. At this time, D1 = D2, and the temperature of the main thermistor 18 is determined to be the target temperature. In this state, Ta-Tb is obtained after five recording materials are passed.

  At this time, according to Table 1, for example, when Ta-Tb = 10 ° C., during the passage of the next five recording materials, the energization heating resistance layer 101 is energized at a ratio of D1-10%. The energization heat generating resistance layer 102 is energized at an energization ratio of D2 + 10%. For example, when Ta-Tb = 5 ° C., the energization heat generation resistance layer 102 is supplied to the energization heat generation resistance layer 101 at a ratio of D1-5% during the passage of the next five recording materials. Is energized at an energization ratio of D2 + 5%. Here, the case of Ta-Tb = 10 ° C. after passing 5 recording materials is a case where the recording material is shifted 2 mm to the right according to FIG. The case of Ta−Tb = 5 ° C. is a case where the recording material is shifted to the right by 1 mm and passed.

  In the present embodiment, the control circuit unit 21 serving as a heating control unit determines whether the temperature difference has reached a predetermined value for every certain number of sheets to be passed, and when the temperature difference reaches a predetermined value, the control circuit unit 21 applies to the energization heating resistor layers 101 and 102. The heating control for changing the energization ratio is executed. And a heating control is performed so that the change of an energization ratio may differ according to a temperature difference.

  As described above, in this embodiment, by changing the energization ratio to the energization heat generation resistance layers 101 and 102 according to Table 1 above, the energization heat generation increases as the recording material sheet passing position greatly deviates from the sheet passing reference. The amount of change in the energization ratio to the resistance layers 101 and 102 is increased. As a result, it is possible to control the distribution of heat generation to an appropriate heat distribution according to the amount of deviation of the recording material passing position from the sheet passing reference.

  After the start of continuous feeding of the recording material, five sheets are passed, and after the first energization ratio change, the detected temperature difference Ta− of the sub-thermistors 19a and 19b is Ta− even after the next five sheets are passed. Tb may not be zero. In this case, according to Table 1, the energization ratio to the energization heat generating resistance layers 101 and 102 may be changed again according to the value of Ta-Tb. Thereafter, this change is repeated. If | Ta−Tb | <1 after passing five sheets, the energization ratio to the energization heat generating resistance layers 101 and 102 is not changed when the next five recording materials are passed.

  As described so far, the energization ratio to the energization heating resistance layers 101 and 102 is changed for every five sheets of recording material according to Ta-Tb, which is the difference between the detected temperatures of the sub-thermistors 19a and 19b. . By doing so, it is possible to prevent a large difference between right and left in the heat generation distribution of the fixing heater 16 even when the recording material is conveyed continuously shifted in the direction orthogonal to the conveying direction. Further, in the fixing nip portion 27, it is possible to prevent only one of the recording material conveyance directions from being heated significantly. Further, since the energization ratio is changed at a high frequency of every five sheets of recording material, the heat generation distribution of the fixing heater 16 can be controlled more accurately.

  Therefore, it is possible to continuously pass the recording material in a state where not only the heater 16 but also the fixing sleeve 20 and the end portions in the longitudinal direction of the pressure roller 22 are the same on the left and right. As a result, the life of the fixing device is increased. In addition, problems such as hot offset and image defects such as raggedness occurring only on one side of the longitudinal end of the recording material can be more effectively prevented.

  In the present embodiment, an example in which the energization ratio to the energization heat generation resistance layers 101 and 101 is changed every five sheets when the recording material is continuously fed. However, what is meant by this configuration is to change the energization ratio for every fixed number of sheets. That is, for example, the energization ratio may be changed every three sheets of recording material.

<< Third Embodiment >>
In the present embodiment, a case where the fixing heater 16 has three energization heat generating resistance layers will be described. The configuration of the image forming apparatus is the same as that of the first embodiment (FIG. 2), and the configuration of the fixing device 12 other than the fixing heater 16 is also the same as that of the first embodiment (FIG. 2). The configuration of the fixing heater 16 in this embodiment is shown in FIG. The arrangement of the sub-thermistors 19a and 19b is also shown in FIG. Reference numeral 200 denotes a high thermal conductive substrate formed of a ceramic material such as alumina or aluminum nitride, which is formed wider than the width of the fixing nip portion 27 formed between the pressure roller 22 and the substrate.

  The fixing heater 16 in this embodiment has three systems of energizing heat generating resistance layers on the substrate 200. That is, on the side opposite to the fixing nip portion 27 of the high thermal conductive substrate 200, there are three systems of heat generating resistance layers made of a conductive material such as silver palladium (Ag / Pd) along the longitudinal direction. . Specifically, the first row includes a first energization heating resistor 201 centered in the longitudinal direction as the first row, and one end side and the other end side in the longitudinal direction as the second row. Are provided with a second energization heating resistor portion 202 and a third energization heating resistor portion 203 provided independently of each other.

  In the present embodiment, the first energization heating resistor layer 201, the second energization heating resistor layer 202, and the third energization heating resistor layer 203 are formed on the substrate by means such as screen printing. Further, an insulating protective layer 206 made of glass or the like is formed on the energization heat generating resistance layers 201, 202, and 203. The energization heat generation resistance layer 201 is formed with a length of 220 mm, and is 110 mm in both longitudinal end directions with respect to the sheet passing reference position X of the recording material in FIG. The energization heat generating resistance layer 202 and the energization heat generation resistance layer 203 are both 20 mm in length.

  The energization heat generation resistance layer 202 is formed in the region from the position of 92.5 mm to the position of 112.5 mm to the left side with respect to the sheet passing reference X. The energization heat generation resistance layer 203 is formed on the right side with respect to the sheet passing reference X from a position of 92.5 mm to a position of 112.5 mm. That is, the energization heat generating resistance layers 202 and 203 are formed symmetrically with respect to the sheet passing reference X. The power supplies for supply (not shown) to the energization heat generation resistance layers 201, 202, and 203 are independent, and the energization ratios to the energization heat generation resistance layers 201, 202, and 203 can be changed.

  When the recording material is passed, each energization heating resistance layer is energized independently so that the detected temperature of the main thermistor 18 is maintained at the target. In the case of the present embodiment, the energization heating resistance layer 201 is mainly energized during recording material passing. The energization heat generating resistance layers 202 and 203 are energized supplementarily in order to compensate for the shortage of heat at the longitudinal end of the recording material. That is, when the LTR size recording material is continuously passed, the energization heat generating resistance layers 202 and 203 are energized at a relatively large energization ratio to prevent fixing failure of the longitudinal end portion of the recording material. When the A4 size recording material is continuously fed, the energization heat generating resistance layers 202 and 203 are energized at a relatively small energization ratio to prevent abnormal temperature rise in the non-sheet passing portion.

  When the recording material starts to pass, the energization heat generation resistance layers 202 and 203 are energized at the same energization ratio, and the heater 16 generates heat equally on the left and right. In this case, as described above, when the recording material is fed out of the paper feeding reference X, only one side of the heater 16 is heated significantly. That is, only one of the detection temperatures Ta and Tb of the sub-thermistor detects a high temperature. In such a case, the energization ratio to the energization heat generating resistor layer on the side where a high temperature is detected may be reduced.

  For example, when the recording material is passed to the right and the detection temperature Ta of the sub-thermistor 19a is high, the energization ratio to the energization heat generating resistance layer 202 is reduced. By doing in this way, it can prevent that only the left side of the heater 16 raises temperature significantly.

  As a feature of this embodiment, unlike the first and second embodiments, the heat generation amount at the longitudinal end portion of the heater 16 is controlled by independently controlling the energization ratio of the energization heat generation resistance layers 202 and 203. It can be controlled by the target. Even if the energization ratio of the energization heat generating resistance layers 202 and 203 is changed, the energization ratio to the energization heat generation resistance layer 201 is not changed, so that the central portion in the longitudinal direction can be controlled at a stable temperature.

  Furthermore, if the fixing heater 16 of this configuration is used, the detected temperature of the sub-thermistors 19a and 19b can be controlled to be always constant even if the recording material is fed out of the paper feeding reference. Is possible. That is, the detection temperatures Ta and Tb of the sub-thermistors 19a and 19b are constantly monitored during the recording material passing, and the energization ratio to the energization heat generating resistance layer is set so that Ta and Tb are constant.

  By doing so, the temperature of the heater 16 can be controlled so that the detected temperatures Ta and Tb of the sub-thermistor are constant, so that the temperatures Ha and Hb of the non-sheet passing portion do not rise above a certain level. As a result, even when the recording material is continuously passed with a deviation from the sheet passing reference, it is possible to suppress the occurrence of image defects such as hot offset and roughness due to the high temperature only on one side in the longitudinal direction.

  As described above, by using the fixing heater 16 having the configuration shown in FIG. 8 according to the present embodiment, even when the recording material is passed from the sheet passing reference, there is a difference between the left and right in the heat generation distribution of the heater 16. It can be prevented from occurring.

(Modification 1)
In the above-described embodiment, the heating means is provided with a plurality of rows of energization heat generating resistance portions in the rotation direction of the nip portion. However, the present invention is not limited to this, and a single row of energization heat generation in the rotation direction of the nip portion is shown. A resistor may be provided. In this case, for example, the first energization heating resistor portion is formed in a region excluding both ends in the longitudinal direction, the second energization heating resistor portion is disposed at one end portion in the longitudinal direction, and the third energization heat generation portion is disposed in the other end portion in the longitudinal direction. The resistance portions are provided independently so as to form a line.

(Modification 2)
In the above-described embodiment, as the displacement recognition means for recognizing that the non-sheet passing portion is displaced by the displacement in the longitudinal direction of the recording material conveyed to the nip portion, the first position in the longitudinal direction in the nip portion, the second position The temperature detection means provided at the position was used. That is, with respect to the temperature of the first position on one side and the second position on the other side, if the second position is detected as having a higher temperature than the first position, one end Although it has been recognized that there is a displacement toward the part side, the present invention is not limited to this. For example, the displacement in the longitudinal direction of the recording material or the displacement in the longitudinal direction of the non-sheet passing portion may be directly detected optically before the nip portion.

(Modification 3)
In the above-described embodiment, when changing the heating ratio, the energization time as the heating time is changed, that is, the energization ratio is changed. However, the present invention is not limited to this, and for example, the heating current may be changed.

(Modification 4)
In the embodiment described above, when the non-sheet passing portion is recognized as being displaced toward one end in the longitudinal direction by the displacement recognizing unit, the heating control unit sets the other end side of the heating unit to one end. Heating control was performed so that the heating amount was relatively small with respect to the part side. Here, to reduce the heating amount includes the case where the heating is set to zero (heating stop), and the heating amount on the other end side is not changed without changing the heating amount on the one end side. It is also possible to turn off the power so that is zero.

(Modification 5)
In the embodiment described above, the heater as the heating means is used as a backup member that abuts inside the rotating film member. However, the present invention is not limited to this, and the heating means and the backup member are provided separately. Also good. For example, a heating means using an electromagnetic induction method using an exciting coil may be used independently of the backup member.

(Modification 6)
In the above-described embodiment, a rotatable pressure roller is used as the pressure member that forms the nip portion, but a fixed pressure pad may be used.

(Modification 7)
In the embodiment described above, a rotating film is used as the fixing member, but a so-called fixing roller (for example, made of metal) may be used.

12 .... Fusing device, 16 .... Ceramic heater, 18 .... Main thermistor, 19a, 19b ... Sub-thermistor, 20 .... Fusing sleeve, 22 .... Pressure roller, 27 ... Fusing nip, P ... Recording Material

Claims (16)

A heating rotation member which is rotatable and can be heated in a longitudinal direction intersecting the rotation direction;
A pressure member that presses against the heating rotation member to form a nip portion;
An image heating apparatus that heats the image by sandwiching and conveying a recording material carrying an image in the nip portion,
Displacement recognition means for recognizing that the non-sheet passing portion is displaced by the displacement in the longitudinal direction of the recording material conveyed to the nip portion;
Heating means for independently heating one end side and the other end side in the longitudinal direction corresponding to the nip portion;
When the displacement recognizing unit recognizes that the non-sheet passing portion is displaced toward the one end side in the longitudinal direction, the other end side with respect to the heating unit is relative to the one end side. Heating control means for controlling the heating so that the heating amount is small,
An image heating apparatus comprising:   The displacement recognizing means includes temperature detecting means provided at a first position on one side and a second position on the other side across the longitudinal center position in the nip portion, 2. The image heating apparatus according to claim 1, wherein when the position 2 is detected as having a higher temperature than the first position, it is recognized that there is a displacement toward the one end side.   The image heating apparatus according to claim 2, wherein the heating control unit performs the heating control when a temperature difference between the first position and the second position reaches a predetermined value.   The heating control means determines whether the temperature difference between the first position and the second position has reached a predetermined value for every fixed number of sheets passed, and executes the heating control when the predetermined value has been reached. The image heating apparatus according to claim 3.   When the non-sheet passing portion is recognized as being displaced toward the one end in the longitudinal direction by the displacement recognizing unit, the heating control unit sets the heating ratio of the other end with respect to the heating unit. The image heating apparatus according to claim 1, wherein the image heating apparatus is set to be relatively small with respect to a heating ratio on one end side.   The image heating apparatus according to claim 5, wherein the heating ratio is an energization ratio as a ratio of time during which the heating unit is energized with respect to a voltage change period of an AC waveform of a commercial power supply.   The image heating apparatus according to claim 6, wherein the sum of the energization ratio on the one end side and the energization ratio on the other end side is constant.   8. The image heating apparatus according to claim 1, wherein the heating unit includes a plurality of rows of energized heat generating resistance portions in the rotation direction of the nip portion. 9.   The image heating apparatus according to claim 8, wherein the heating unit includes two rows of energized heat generating resistance portions having centers displaced in different directions from the center in the longitudinal direction.   The heating means includes, as a first row, a first energization heating resistor portion having the center in the longitudinal direction as the center, and as one second row, the one end side and the other end side in the longitudinal direction. The image heating apparatus according to claim 8, further comprising: a second energization heating resistor portion and a third energization heating resistor portion provided independently of each other. The displacement recognition means includes a temperature detection means provided at a first position on one side and a second position on the other side across the longitudinal center position in the nip portion,
The image heating apparatus according to claim 10, wherein the heating unit performs heating control so that a temperature detected by the temperature detection unit is constant. The heating rotation member is a film member, and has a backup member in contact with the inside,
The image heating apparatus according to claim 1, wherein the pressure member is outside the film member and presses the film member to form a nip portion together with the backup member. .   The image heating apparatus according to claim 12, wherein the heating unit is a heater, and the heater also serves as the backup member.   The image heating apparatus according to claim 12, wherein the pressure member is a pressure roller that is driven and rotated.   The image heating apparatus according to claim 12, wherein the pressure member is a fixed pressure pad.   3. The image heating apparatus according to claim 2, wherein the first position and the second position are arranged at a position having an equal distance from a center in the longitudinal direction.