JP2007003998A - Fixing device and image forming apparatus using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress a defect in conveyance, such as wrinkling, at a fixation section in a fixing device and an image forming apparatus by properly detecting rise in temperature, within a paper non-passing range, when a narrow-width paper is passed to suppress defects in transport, at continuous passing of the narrow-width paper. <P>SOLUTION: The fixing device, which fixes a toner image on a form 40 at a nip part 7c of two rollers (a heat roller (fixing roller 7a) and a pressure roller 7b), at least one of which is heated by a heat source, is provided with a first temperature detecting means 41 for detecting temperature at a nearly width-directional center part of conveyable area width of the two rollers and a second temperature detecting means 42 for detecting temperature at a position ≥65% toward the outside from the center of the conveyance area width. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a fixing device and an image forming apparatus used in an image forming apparatus such as a FAX, a printer, and a copying machine using an electrophotographic system, an electrostatic recording system, and the like.

  In recent years, electrophotographic image forming apparatuses have been widely used, and have come to cope with various changes in sheet types and sizes. Especially when it is used as an industrial image forming apparatus, a large-sized sheet of A0 or more may be used, and types of sheets such as plain paper, polyester film and tracing paper suitable for the second original drawing can also be used. is there.

  The fixing device of an electrophotographic copying apparatus is generally composed of a transfer sheet on which a toner image is transferred from a photoreceptor, and a pair of heated rollers and a pressure roller having an elastic body made of silicon rubber on the surface layer that is in pressure contact therewith. The toner image is fixed on the transfer paper by passing the transfer paper through the fixing nip.

  In addition, in a wide copying machine capable of passing A0 size transfer paper, A2 size transfer paper having a narrow width may be passed continuously. In such a case, the non-sheet passing portion is more than half in the width direction of the fixing nip portion, and the transfer paper passes through the central portion of the fixing nip portion, which is the sheet passing portion, so heat is taken away, so the predetermined control temperature is maintained. Is done.

  In such a case, since the transfer paper is not passed on the end side which is a non-sheet passing portion, the temperature is considerably higher than the control temperature, and the temperature distribution difference in the fixing nip portion in the axial direction is increased. For this reason, a difference occurs in the amount of heat from the fixing nip portion in the width direction of the transfer paper, causing uneven fixing and image quality. Further, since the speed difference is caused by the expansion of each roller diameter, wrinkles and the like are easily generated, and the conveyance quality is deteriorated.

  For this reason, for example, in Patent Document 1, the first heater that is a light distribution of only a small size and the second heater that is the light distribution of the other end are divided and installed within a paper passing range. , The temperature rise at the edge of the small size paper is suppressed. However, in the case of a wide-width copying machine, the difference in transfer paper size increases, the number of heaters increases to divide the heater, and the diameter of the heating roller inevitably increases. Therefore, during operation, the temperature maintenance becomes disadvantageous due to an increase in the surface area of the heating roller.

  Further, in Patent Document 2, a heat pipe is built in the heating roller to suppress a temperature rise in a non-sheet passing portion during small size continuous sheet passing. However, since the heat pipe is built in the heating roller, the heating roller is increased in thickness and weight, and therefore the rise time of the entire apparatus cannot be shortened. At the same time, the cost is also increased.

  In addition, Patent Document 3 discloses a fixing device for an image forming apparatus that can prevent uneven glossiness of large sizes and uniformly heat-fix the paper even when the paper of different sizes is thermally fixed. In Cited Document 3, for example, in a fixing device that sandwiches and conveys a sheet having an unfixed toner image and heat-presses the sheet to heat-fix the sheet, a heat generation part having a heating element inside the heating roller, and a heating roller A temperature detecting means having a first temperature sensor for measuring a temperature of a paper passing portion of a paper having a small width size and a second temperature sensor for measuring a temperature of a non-paper passing portion of a paper having a small width size in the heating roller; If the temperature difference between the paper-passing part and the non-paper-passing part is greater than or equal to a predetermined value after passing a small sheet, the heating roller and the pressure roller are idled by temporarily stopping energization to the heat generation part for a predetermined time. Control means for controlling the heat generation, and when the temperature difference between the paper passing portion and the non-paper passing portion is greater than or equal to a predetermined value after passing the small width paper, the energization to the heat generation portion is temporarily stopped for a predetermined time. Heating roller So as to control to idle pressure roller. Accordingly, the temperature difference between the paper passing portion and the non-paper passing portion is reduced, and even if the paper having a large width is fixed after the paper having a small width is passed, fixing unevenness is hardly caused.

  Patent Document 4 discloses a fixing device and an image forming apparatus excellent in economy that enable stable fixing without causing damage to peripheral members and fixing failure due to excessive heating. In Patent Document 4, for example, a first thermistor (68) that detects the temperature of the central portion of the heating roller (58) and a second thermistor (69) that detects the temperature of one end of the pressure roller (60). ) And are provided. The reference temperatures of the heating roller and the pressure roller are determined in advance according to the size of the paper on which the developer image is fixed. The control unit sets the reference temperature of the heating roller and the pressure roller corresponding to the detected paper size, and compares the actual temperature detected by the first and second thermistors with the reference temperature. The optimum control temperature of the heating roller is set according to the comparison result, and the heating roller is maintained at the control temperature by controlling the heater lamp (61). In this way, the fixing device is excellent in economic efficiency that prevents excessive heating of the heating roller and the pressure roller, and can obtain a good image without causing damage and fixing failure due to heat of the peripheral members. An image forming apparatus is realized.

  In Patent Document 5, in a fixing device that fixes a developer onto a medium by transporting a medium having a developer held on the surface between the rollers as the heating roller and the pressure roller rotate. First detection means for detecting at least two surface temperatures on the heating roller, second detection means for detecting at least two surface temperatures on the pressure roller, and the first detection means When the surface temperature of the heating roller detected by the second detection unit is within a predetermined range and the surface temperature of the pressure roller detected by the second detection unit is within the predetermined range, the heating roller Control means for controlling so that fixing is possible only when the absolute value of the difference between the average value of the surface temperature of the pressure roller and the average value of the surface temperature of the pressure roller is within a predetermined range. The fixing device (claim 1), and the like have been disclosed to. According to the invention according to Patent Document 5, since the surface temperature of several places of the heating roller and the pressure roller is detected and the temperature difference is within an appropriate temperature range, the fixing is possible. It is said that the surface temperature of the pressure roller becomes uniform and problems such as curling, wrinkling, and deterioration in image quality can be solved.

  In Patent Document 6, a temperature detection device is provided at the center and the end in the width direction of the pressure roller, and the system is stopped by a fan by stopping the mechanical drive due to the detected temperature difference. However, this is intended to ensure the transport quality to the wide paper after passing the narrow paper. Moreover, the installation space of a cooling fan and the passage of an airflow are required. At the same time, since the driving is stopped during cooling, the nip is difficult to cool, and the roller surface is not uniform in the circumferential direction.

JP-A-8-220932 JP-A-8-314326 JP 2003-167472 A JP-A-9-179437 Japanese Patent No. 3109322 Japanese Patent No. 3398500

  As described above, in a wide-width copying machine capable of passing A0 size transfer paper, when A2 size transfer paper having a narrow width is continuously passed, it passes from the boundary of the non-sheet passing portion within each roller. Since heat is conducted to the paper portion, a difference occurs in the amount of heat from the fixing nip portion in the width direction of the transfer paper.

  At the same time, since the temperature inside the apparatus also rises, the amount of heat is increased from the end of the transfer paper and the speed difference is caused by the expansion of the diameter of each roller, so that the conveyance quality such as wrinkles is deteriorated. This is a common problem in a copying apparatus capable of passing a plurality of transfer paper sizes, but the problem becomes particularly noticeable in a wide-width copying machine because the number of sizes and the size difference increase.

  Therefore, in the fixing device and the image forming apparatus of the present invention, in order to suppress a conveyance failure such as wrinkles during continuous passage of narrow paper, the temperature rise in the non-paper passing range can be appropriately detected during narrow paper passage. An object of the present invention is to suppress a conveyance failure at the fixing unit.

  The fixing device according to the present invention is a fixing device that fixes a toner image on a sheet at a nip portion of two rollers, at least one of which is heated by a heat source, at a substantially central portion in the width direction of the transportable region width of the two rollers. First temperature detecting means for detecting temperature, and second temperature detecting means for detecting a temperature of a portion 65% or more outside from the center of the transportable region width are provided.

The fixing device of the present invention can convey the two rollers in the fixing device for fixing the toner image on the paper passing through the center of the nip portion at the nip portion of the two rollers heated at least one by the heat source. A first temperature detecting means for detecting a temperature at a substantially central portion in the width direction of the region width, and an outside of a paper passing range determined corresponding to the fixing paper width set or detected at the central portion of the transportable region width A second temperature detecting means for detecting the temperature of the part of
The heating state by the heat source is controlled based on the difference between the detected temperatures of the first temperature detecting means and the first temperature detecting means.

  Further, in the fixing device as described above, when the difference between the detected temperatures of the first temperature detecting means and the second temperature detecting means exceeds a preset temperature difference, the apparatus shifts to the apparatus standby state to the heater as a heat source. Is turned off and the two rollers are controlled to rotate until the temperature difference decreases to a preset value.

  As described above, when the temperature difference detected between the heating roller and the pressure roller exceeds a preset temperature difference, the machine is put in a standby state, the power supply to the heater is turned off, and the temperature difference is cooled to a preset temperature difference. By rotating the fixing unit until the heating roller and the pressure roller can be uniformly cooled in the circumferential direction. In another aspect of the invention, an image forming apparatus is configured using any one of the fixing devices.

  By such a heating roller thermistor installation position, it is possible to appropriately detect the temperature rise in the non-sheet passing range during continuous feeding of narrow paper, and to suppress transport problems, and to obtain optimal transport quality at any paper width It becomes possible. In addition, when the machine is cooled, the heating roller is used efficiently for heat diffusion, and by rotating the roller uniformly in the circumferential direction, the temperature rise in the non-sheet-passing range can be made more quickly and appropriately. It is possible to detect, and it is possible to obtain the optimum transport quality with any paper width.

  The fixing unit (fixing device) of the following embodiment generally includes a heating roller having a built-in heat source heater and a pressure roller having a surface formed of an elastic layer and pressure-bonded to the heating roller. In the fixing device for fixing a toner image, a temperature detection unit is provided at a central portion in the width direction of the heating roller, and a temperature detection unit is provided at an end portion corresponding to only the maximum sheet passing width in the pressure roller width direction. The temperature rise in the non-sheet passing range is detected when the width is passed. When the temperature difference detected by the heating roller and pressure roller exceeds a preset temperature difference, the machine is put on standby, the energization of the heater is turned off, and the fixing unit is rotated until it is cooled to a preset temperature difference. By doing so, the heating roller and the pressure roller are uniformly cooled in the circumferential direction.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a longitudinal front view schematically showing an image forming apparatus according to the present invention. This apparatus is a wide-width image forming apparatus capable of passing a standard A0 size sheet using each electrophotographic sheet width based on a central reference.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment is an example of a copying machine that includes an image forming unit 3 inside a printer main body 2 and a document reading device 4 at the top. The apparatus 4 does not necessarily have to be provided. The image forming unit 3 forms a plurality of process units (not shown) such as charging, latent image forming, development, toner cleaning, and charge removal on the outer periphery of the photosensitive member 5 and a developed image on the photosensitive member 5 (transferred). The transfer unit 6 is arranged on a sheet), and the fixing unit 7 is arranged on the downstream side of the transfer unit 6.

  The fixing unit (fixing device) 7 is pressed against a heating roller (fixing roller) 7a having two rollers, that is, a coiled heater (heating roller heater) 7d, which is a heat source that generates heat when energized, is built in the shaft core. The nip portion 7c is formed by the pressure roller 7b. As shown in FIG. 2, the thermistor 41 as a first temperature detecting means for detecting the temperature in the central portion (substantially the central portion in the width direction of the transportable region width of the roller) that passes through any paper width in the heating roller 7 a. The pressure roller 7b has a 841 width (standard size, A0 size) only corresponding to an end portion (for example, a portion of 65% or more outside the center of the transportable region width) for detecting the temperature of this portion. A thermistor 42 as temperature detecting means 2 is arranged. The second temperature detecting means may be provided at a part where the temperature of the part outside the sheet passing range determined corresponding to the fixing sheet width set or detected at the center of the transportable area width can be detected. For example, you may make it provide in site | parts other than this.

  Between the photosensitive member 5 and the transfer unit 6, there is provided a sheet conveyance path 10 whose upstream side is connected to the feeding paths 8 and 9. A conveying roller 9 a is arranged in the feeding path 9, a registration roller 11 is disposed on the upstream side of the photosensitive member 5 in the sheet conveying path 10, and a roller 12 that presses a sheet (paper) upstream of the fixing unit 7. The discharge roller 13 is disposed downstream of the fixing unit 7. A discharge port 14 for discharging the sheet to a discharge tray (not shown) is formed at the downstream end of the sheet conveyance path 10. The photoreceptor 5, the fixing unit 7, the registration roller 11, and the paper discharge roller 13 arranged in the sheet conveyance path 10 have a function as a sheet conveyance system member that conveys roll papers 22 and 23 as sheets, The photosensitive member 5, the heating roller 7a of the fixing unit 7, the driving side of the registration roller 11 and the paper discharge roller 13 receive rotational force from a common conveying motor 15 via a transmission device (not shown). Driven by rotation. In the present embodiment, the driving side of the conveying roller 9 a in the feeding path 9 is also configured to receive the rotational force from the conveying motor 15.

  In the present embodiment, since it becomes difficult to handle A0 size sheets one by one, it is possible to feed paper with roll-shaped sheets 22 and 23, and productivity can be increased. A roll paper feeding device 20 is provided below the printer main body 2. A roll main body 21 of the roll paper feeder 20 includes a roll paper storage unit 24 that stores a plurality of roll papers 22 and 23, and a printer main body 2 from the roll paper storage unit 24 through the feed paths 25 and 26. A feed discharge port 27 for discharging to the feed passage 9 is formed. Feed rollers 28 and 29 as feed portions are disposed near the entrances of the feed passages 25 and 26, and a transport roller 30 as a feed portion is disposed near the upstream side of the feed discharge port 27. The rollers on the driving side of the feeding rollers 28 and 29 and the conveying roller 30 are rotationally driven by receiving the rotational force of a common feeding motor 31 via a transmission (not shown).

  Further, a cutter 32 for cutting the roll papers 22 and 23 and a carrier 33 for supporting the cutter 32 are provided in the vicinity of the downstream side of the feed discharge port 27. The cutter 32 is moved along the width direction of the roll paper 22 or 23 together with the carrier 33, and is driven in the rotational direction during the movement to cut the roll paper 22 or 23.

  Different types of roll papers 22 and 23 are prepared and are selected by the operator. A sheet type recognizing unit is provided for setting the type of roll paper 22, 23 when the type is selected. Although not shown, this sheet type recognition means is realized by the CPU or the like determining the type of key operated by the operator to select the sheet type. Alternatively, a display corresponding to the type of the roll papers 22 and 23 may be provided in the roll paper storage unit 24, and the display may be read and recognized. Furthermore, the types of the roll papers 22 and 23 may be automatically detected. The automatic detection method can also be performed by measuring characteristics such as waist strength and light transmittance of the roll papers 22 and 23, for example. The types of roll papers 22 and 23 are, for example, (a) plain paper (b) film (c) tracing paper and the like. Further, the roll papers 22 and 23 are cut into a desired length unit by a cutter 32 to determine the length of the sheet. The length information is, for example, in the sub-scanning direction (sheet conveyance direction). It can be recognized by the amount of print data.

  Here, the image forming apparatus 1 includes a microcomputer (not shown). This microcomputer includes a CPU for recognizing input of operation keys for setting the types of the roll papers 22 and 23 described above. The microcomputer has a storage device such as a RAM for temporarily storing print data read by the document reading device 4. Further, the microcomputer executes a program corresponding to the set type of roll paper 22 and 23.

  In such a configuration, when the roll paper 22 is selected, the roll paper 22 is cut into a sheet having a desired length by the cutter 32, and is fed from the feed path 25 by the feed roller 28 and the transport roller 30. One feed passage 9 is passed through. When the roll paper 23 is selected, the roll paper 23 is passed through the feeding path 9 of the image forming apparatus 1 through the feeding path 26 and the feeding path 25 by the feeding roller 29 and the conveying roller 30. In the image forming apparatus 1, charging, latent image formation, and development are performed on the surface of the photoreceptor 5 by each electrophotographic process unit, and the toner image on the photoreceptor 5 is transferred to the roll paper 22 or 23 by the transfer unit 6. Is transcribed. The roll paper 22 or 23 onto which the image has been transferred is conveyed to the fixing unit 7 where the toner image is fixed and discharged from the discharge port 14 to the discharge tray by the discharge roller 13.

  Next, the operation of the fixing unit 7 will be described. In FIG. 1, after the toner image is formed on the photoconductor 5, the toner image is transferred to the paper 40 that has entered the photoconductor 5 and the transfer unit 6, and the toner image is transferred from the photoconductor 5 to the paper 40 by the separation unit 6a. Separated in a transcribed state. The sheet (transfer sheet) 40 on which the unfixed toner image is formed is composed of two rollers, that is, a pair of heated heating rollers 7a and a pressure roller 7b formed by an elastic layer on the surface pressed against the rollers. It is conveyed to the nip portion 7c.

  As a basic temperature control for the fixing unit, when the pressure roller temperature rises in order to suppress the conveyance quality deterioration such as wrinkles due to the excessive amount of heat in the fixing unit 7 to the transfer paper, A proper heating amount is obtained by changing the set temperature of the heating roller in stages and dynamically changing it. The target temperature (set temperature) is switched depending on the paper type and paper thickness for the heating roller temperature and the pressure roller temperature. The paper used can be set by manual operation, but the paper type and paper thickness are automatically detected, and in conjunction with this, automatic switching control is performed to an appropriate target temperature setting suitable for the paper used. For example, the following control is performed corresponding to the set temperature.

A = initial pressure roller temperature, B = initial heat roller temperature C = current pressure roller temperature, D = current heat roller control temperature x: number of control steps x = (C−A) / 3
D = B−x (D is a constant temperature after 20 steps),
As a temperature control.

By the way, in order to fix the toner image on the transfer paper, the melting point of the toner must be secured. Therefore, the temperature of the heating roller that directly heats the toner cannot be lowered below a certain temperature even if the pressure roller temperature rises. Here, the heating roller 7a has a release layer of 20 to 30 μm on the surface, but the core metal itself is aluminum having good thermal conductivity, and its thermal expansion coefficient is 23.9 × 10 ⁻⁶ . Therefore, the thermal diffusivity in the axial direction is good although it varies depending on the thickness. On the other hand, the pressure roller 7b has a silicon rubber layer having a thickness of 5 to 10 mm as an elastic body on the surface. Since the coefficient of thermal expansion is 5 × 10 ⁻⁴ , the thermal conductivity is poor unlike metal, and the thermal expansion is larger than that of metal. For this reason, especially during continuous paper feeding, the change in the roller diameter in the axial direction is more greatly affected by the temperature difference between the pressure roller 7b and the paper feeding range than the heating roller 7a.

  FIG. 3 shows the temperature distribution in the width direction of the heating roller 7a and the pressure roller 7b when A0 size transfer paper is continuously fed, obtained by experiments with the apparatus of the embodiment. The non-sheet passing portion is also small, and the end side has a heat loss to the outside, so that each roller has a lower temperature than the central portion. There is no temperature difference between the heating roller and the non-sheet passing portion because the core metal is aluminum and the heat diffusibility is good. The temperature difference between the end of the transfer paper and the non-sheet passing portion is 20 ° C., but there is no conveyance failure such as wrinkles.

  FIG. 4 shows the temperature distribution in the width direction of the heating roller 7a and the pressure roller 7b when A2 size transfer paper is continuously passed through the apparatus according to the embodiment. More than half of the fixing unit becomes a non-sheet passing portion, and heating continues to maintain the sheet passing portion of the heating roller 7a at a constant temperature. Becomes prominent. As for the heating roller temperature, the core metal is aluminum and the thermal diffusibility is good, but the temperature difference between the end portion of the transfer paper and the non-sheet passing portion is 5 ° C. The temperature difference between the end of the transfer paper and the non-sheet passing portion is 40 ° C.

  In consideration of this point, in the wide-width image forming apparatus according to the embodiment capable of passing up to A0 size paper, the pressure roller thermistor is located at the center of the transportable area width so as to be in the non-sheet passing range except when fixing 841 width paper. When the detected heating roller temperature exceeds the lower limit control temperature and the pressure roller temperature rises to a certain temperature, the heater is turned off and the entire device is If the function is controlled to stop once, it is possible to suppress problems caused by a temperature rise in the non-sheet passing range when sheets of various widths that are normally used are continuously used (continuous sheet passing).

  However, when the fixing unit is held in a stopped state (heater OFF, roller drive stopped) as described above, the cooling of the non-sheet passing range becomes partial, and the uneven temperature distribution continues for a long time. Therefore, in the exemplary apparatus, only the fixing unit roller is idly rotated simultaneously with turning off the heater. By maintaining the rotation in this way, it is possible to use a heat roller with good thermal diffusibility as a means for heat dissipation and to uniformly cool the whole around the nip portion 7c in the circumferential direction.

In this way, when the thermistor 42 detects that the pressure roller temperature has been cooled to a certain temperature, the heating roller heater 7d is turned on while the roller is still rotating, and the apparatus can be used when it reaches the set temperature. Specifically, during the temperature control process described above,
When x> 26, JOB after that is stopped, the heater is turned off, and the two rollers (heating roller 7a and pressure roller 7b) of the fixing unit are rotated to enter the cooling mode.
The message “Please wait” is displayed.
When x <3, the heater is turned on and heated again, and when the current heating roller control temperature: D reaches a predetermined control temperature (initial setting heating roller temperature: B),
A message “available” is displayed and a fixing operation request is accepted.

  In this way, by detecting the temperature at the heating roller thermistor installation position, the toner image is fixed on the paper at an appropriate temperature by controlling the target temperature regardless of the paper width, and the temperature at the pressure roller thermistor installation position is adjusted. By detecting and controlling based on the temperature difference between this and the heating roller temperature (temperature at the heating roller thermistor installation position), an undesired excessive temperature rise at the fixing unit is detected during continuous feeding of narrow paper. A conveyance defect can be suppressed.

  In the embodiment, one second temperature detecting means is provided on one end side of the roller, but it is also provided on the other end symmetrical position, and the average value of both detected temperatures is used as the control temperature. It may be used. In addition, a plurality of temperature detection means are appropriately arranged on one end side so as to be separated from each other in the axial direction, an appropriate temperature detection means is selected according to the paper width to be used, and the detected temperature of the selected temperature detection means is set. You may make it use for control. Although the thermistor is used as the temperature detecting means in the embodiment, the temperature of a predetermined portion of the roller may be detected using a non-contact type temperature detector. In this case, it is conceivable that the temperature detection region is changed by a single narrow directivity non-contact temperature detector so that optimum temperature detection and roller temperature control are performed for various paper widths.

1 is a longitudinal front view schematically showing an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a cross-sectional view of a main part for explaining a fixing unit (fixing device) in an embodiment of the present invention. It is a figure explaining the width direction temperature distribution of the heating roller and pressure roller at the time of continuous paper passing (A0 size transfer paper) in the apparatus of the embodiment. It is a figure explaining the width direction temperature distribution of the heating roller and pressure roller at the time of continuous paper passing (A2 size transfer paper) in the apparatus of the embodiment.

Explanation of symbols

3 ... Image forming section 5 ... Photoconductor 7 ... Fixing section (fixing device), sheet conveyance system member 7a ... Heating roller (fixing roller)
7b: Pressure roller 7c: Fixing nip 7d: Heating roller heater (heat source)
DESCRIPTION OF SYMBOLS 10 ... Sheet conveyance path 11, 13 ... Sheet conveyance system member 15 ... Conveyance motors 22, 23 ... (roll form) Sheets 28, 29, 30 ... Feed section 31 ... Feed motor 40 ... Paper (transfer paper)
41. Thermistor (first temperature detecting means)
42 ... Thermistor (second temperature detecting means)

Claims (4)

In a fixing device for fixing a toner image on a sheet at a nip portion of two rollers, at least one of which is heated by a heat source,
A first temperature detecting means for detecting a temperature at a substantially central portion in the width direction of the transportable area width of the two rollers; and a temperature of a portion of 65% or more outside from the center of the transportable area width. And a second temperature detecting means. In a fixing device for fixing a toner image on a sheet passing through the center of a nip portion at a nip portion of two rollers at least one of which is heated by a heat source,
A first temperature detecting means for detecting a temperature at a substantially central portion in the width direction of the transportable region width of the two rollers, and a fixing paper width set or detected at the central portion of the transportable region width; A second temperature detecting means for detecting the temperature of a portion outside the determined sheet passing range;
A fixing device that controls a heating state by the heat source based on a difference between detected temperatures of the first temperature detecting unit and the first temperature detecting unit.   When the difference between the detected temperatures of the first temperature detecting means and the second temperature detecting means exceeds a preset temperature difference, the apparatus shifts to an apparatus standby state and turns off the energization to the heater as the heat source, The fixing device according to claim 1, wherein the two rollers are controlled to rotate until the temperature difference decreases to a preset value. An image forming apparatus comprising the fixing device according to claim 1.

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