JP2009139778A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of attaining shortening of a print time of large-sized or small-sized recording material and capable of reducing power consumption and also improving the productivity. <P>SOLUTION: The fixing device 30 is equipped with a heating body 3 which is energized to generate heat, a fixing belt 1 which has low heat capacity and is freely rotatable, and a pressure roller 2 which rotates in press-contact with the fixing belt 1. The heating body 3 has a first resistance heating element 3a, whose heating value is high at the center part and a second resistance heating element 3b whose heating value is high at the ends in a longitudinal direction, and the first resistance heating element 3a and the second resistance heating element 3b are provided with temperature detecting elements 6a and 6b detecting their temperatures. Then, the ratio of energizing the first resistance heating element 3a and the second resistance heating element 3b is varied, according to the result of detection by the temperature detecting elements 6a and 6b and the result of the detection of the width in a longitudinal direction of the recording material 21 which is to be printed next. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device for fixing an image on a recording material by heating and pressing in an image forming apparatus such as a copying machine employing an electrophotographic system.

  Conventionally, as a fixing method for fixing an unfixed toner image on a recording material, a heat fixing method in which an unfixed toner image is heated and melted and fixed on a recording material is generally used from the viewpoint of safety and fixing property. Yes.

  In particular, because of the high thermal efficiency and ease of miniaturization, the heat that presses and heats the unfixed toner image by nipping and transporting the recording material in the fixing area where the heating rotary member and the pressure rotary member are pressed against each other. The fixing device is most frequently used.

  In this type of fixing device, a heat-resistant belt (fixing belt) that is a heating rotator is brought into close contact with a heating rotator (elastic roller) and is slid and conveyed to a heating element. Then, a transfer material carrying an unfixed image is introduced into a pressure nip formed by a heating heater and a pressure member with the heat resistant fixing film interposed therebetween, and is conveyed along with the heat resistant belt. In this way, the unfixed image is fixed on the recording material as a permanent image by the heat from the heating heating element applied via the heat-resistant belt and the pressing force of the pressure nip portion.

  The belt heating type heating device can use a low heat capacity linear heating element as a heating element and a thin film with a low heat capacity as a belt, thus saving power and shortening the wait time (quick start property) Improvement) is possible.

  In recent years, in fixing devices, for example, recording materials of various sizes from a relatively large size recording material such as A3 size to a commonly used small size recording material such as A4R and B5 sizes have been passed. The diversification that enables it is progressing. For this reason, it is necessary to configure the width in the longitudinal direction of the heating rotary member and the pressure rotary member so as to correspond to a relatively large size such as A3 size.

  However, when a recording material of a small size such as A4R or B5 passes through the fixing device when the configuration as described above is adopted, the non-sheet passing region where the recording material does not pass in the effective fixing region of the heating rotating member. Will increase.

  When a small-size recording material is continuously passed, the surface temperature of the non-sheet passing region becomes very high because the recording material does not remove heat from the surface of the heating rotating member corresponding to the non-sheet passing region. In other words, a so-called non-sheet passing portion temperature rise phenomenon occurs. For this reason, it becomes easy to cause thermal damage to each member, and in order to prevent it, productivity of a small-sized recording material has to be reduced.

  In addition, when a recording material having a wide longitudinal direction is passed after the small size recording material has passed, only the non-sheet passing region of the small size recording material becomes hot at the heating element, heating member, and pressure member. For this reason, hot offset is likely to occur in this portion, and in order to prevent this phenomenon, a pause time must be provided before printing on a large size paper after passing a small size.

  In view of this, various methods have been proposed in which a plurality of heating elements having different heat generation distributions in the longitudinal direction are provided on the substrate, and the drive ratio of each heating element is appropriately controlled.

  For example, in Patent Document 1, a method of changing the energization ratio of each heating element according to the longitudinal width of the recording material used, or the energization ratio of each heating element according to the output of the temperature detection element of the non-sheet passing portion. A method of changing the number has been proposed.

  Further, in Patent Document 2, when a recording material having a long longitudinal width is printed within a predetermined time after a recording material having a narrow longitudinal width is printed, the energization ratio to the heating element having a large end heating value is usually set. A method of making it smaller has been proposed.

  Further, Patent Document 3 proposes a method of driving at a predetermined energization ratio according to the longitudinal width of the recording material and changing the energization ratio according to the number of processed sheets or the temperature of the non-sheet passing area.

JP 10-177319 JP2003-345175 JP2001-183929

  However, in the conventional fixing device, in order to minimize the temperature rise of the non-sheet passing portion, it is necessary to set an optimum energization ratio at an earlier stage. Also, in the low heat capacity fixing device, since the history of longitudinal temperature distribution from the previous printing operation remains, always performing the same start-up operation will lead to excessive power consumption and promotion of temperature rise in the non-sheet passing portion. There is.

  The technical problem of the present invention has been made in view of the circumstances as described above, and the purpose thereof is to reduce the printing time and power consumption of large and small recording materials and to improve productivity. It is an object of the present invention to provide a fixing device capable of achieving the above.

  In order to achieve the above object, a typical configuration according to the present invention includes a heating element that generates heat when energized, a fixing member that is rotatable with a low heat capacity, and a pressure member that rotates while being pressed against the fixing member. In the fixing device for fixing the unfixed toner image on the recording material by heating and pressing the recording material while nipping and conveying the recording material by the press nip formed by the fixing member and the pressure member, The first resistance heating element having a high heat generation amount at the portion and the second resistance heating element having a high heat generation amount at the end portion in the longitudinal direction are detected, and the longitudinal temperature distribution of the heating body is detected at the center and the longitudinal end portion of the heating body. A temperature detection element is provided, and the first resistance heating element and the second resistance at the time of starting up the fixing device according to the detection result by the temperature detection element and the detection result of the longitudinal width of the recording material of the next print Energize the heating element And changes the rate.

  A pressure contact nip formed by the fixing member and the pressure member; and a heating member that generates heat when energized, a fixing member that is rotatable with a low heat capacity, and a pressure member that rotates in pressure contact with the fixing member. In the fixing device for fixing the unfixed toner image on the recording material by heating and pressing while the recording material is nipped and conveyed by the section, the heating body includes a first resistance heating element having a high calorific value in the central portion and a longitudinal end. A second resistance heating element that generates a large amount of heat, and a temperature detection element that detects the longitudinal temperature distribution of the heating element is provided at the center and longitudinal ends of the heating element, and the number of recording materials in the previous print job The first resistance heating element and the second resistance heating element are energized when the fixing device is started up according to the detection result of the longitudinal width and elapsed time and the detection result of the longitudinal width of the recording material of the next print. Ratio to Characterized in that it further.

  According to the present invention, the temperature distribution in the longitudinal direction of the fixing device at the start of the printing operation is detected based on the history of the previous printing operation, and the lighting ratio of each heating element is changed to an optimal ratio according to the detection result. Then start up the fixing device. As a result, the printing time can be shortened and the power consumption can be reduced.

  In addition, by providing a means for detecting the longitudinal width of the recording material, it is possible to detect the longitudinal width (image width) that needs to be fixed. This makes it possible to further optimize the lighting ratio when the fixing device is started up. Fixing failure at the time of a size recording material and non-sheet passing portion temperature rise at the time of a small size recording material can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. 1 is a cross-sectional view showing the configuration of the main part of an image forming apparatus according to an embodiment of the present invention, FIG. 2 is a schematic diagram of the fixing device of FIG. 1, and FIG. 3 is a heating element of FIG. FIG.

[Embodiment 1]
In FIG. 1, an image forming apparatus is a tandem color image forming apparatus that employs an intermediate transfer member 27 that is an example of an electrophotographic color image forming apparatus. This color image forming apparatus includes an image forming unit and an image processing unit (not shown).

  The image forming unit forms an electrostatic latent image with exposure light that is turned on based on the exposure time converted by the image processing unit. Then, the electrostatic latent image is developed to form a single color developer image, and the single color developer images are superimposed to form a multicolor developer image. Further, the multicolor developer image is transferred to the recording material 21, and the multicolor developer image on the recording material 21 is fixed.

  The image forming unit includes a feeding unit 11, photoconductors 22Y, 22M, 22C, and 22K for each station arranged in parallel for development colors, and injection charging units 23Y, 23M, 23C, and 23K as primary charging units. Yes. Further, developer cartridges 25Y, 25M, 25C, and 25K, developing devices 26Y, 26M, 26C, and 26K, an intermediate transfer member 27, a transfer roller 28, a cleaning unit 29, and a fixing device 30 are provided.

  The photosensitive drums 22Y, 22M, 22C, and 22K are configured by applying an organic photoconductive layer to the outer periphery of an aluminum cylinder. Then, the driving force of a driving motor (not shown) is transmitted and rotated, and the driving motor rotates the photosensitive drums 22Y, 22M, 22C, and 22K in the counterclockwise direction according to the image forming operation.

  The primary charging means includes four injection chargers 23Y, 23M, 23C, and 23K for charging yellow (Y), magenta (M), cyan (C), and black (K) photoreceptors for each station. I have. Each injection charger 23Y, 23M, 23C, 23K has a sleeve 23YS, 23MS, 23CS, 23KS.

  Exposure light to the photosensitive drums 22Y, 22M, 22C, and 22K is sent from the scanner units 24Y, 24M, 24C, and 24K, and the electrostatic latent image is selectively exposed by exposing the surfaces of the photosensitive drums 22Y, 22M, 22C, and 22K. An image is formed.

  The developing units 26Y, 26M, 26C, and 26K are detachably attached and develop yellow (Y), magenta (M), cyan (C), and black (K) for each station in order to visualize the electrostatic latent image. Individually. The developing units 26Y, 26M, 26C, and 26K are provided with sleeves 26YS, 26MS, 26CS, and 26KS.

  The intermediate transfer member 27 is in contact with the photosensitive drums 22Y, 22M, 22C, and 22K, rotates clockwise when forming a color image, and rotates with the rotation of the photosensitive drums 22Y, 22M, 22C, and 22K. A single color developer image is transferred.

  Thereafter, a transfer roller 28 (to be described later) comes into contact with the intermediate transfer member 27 to sandwich and convey the recording material 21, and the multicolor developer image on the intermediate transfer member 27 is transferred to the recording material 21.

  The transfer roller 28 contacts the recording material 21 at a position 28a while transferring the multicolor developer image onto the recording material 21, and is separated to a position 28b after the printing process.

  The fixing device 30 melts and fixes the transferred multi-color developer image while transporting the recording material 21, and the recording material 21 holding the multi-color developer image is transported as well as heat and pressure. Is added to fix the developer on the surface.

  The recording material 21 after fixing the developer image is then discharged onto a discharge tray (not shown) by a discharge roller (not shown) to complete the image forming operation.

  The cleaning means 29 is for cleaning the developer remaining on the intermediate transfer member 27, and is disposed after the four-color multicolor developer images formed on the intermediate transfer member 27 are transferred to the recording material 21. Developer is stored in a cleaner container.

  In the fixing device 30 shown in FIG. 2, reference numeral 1 denotes a fixing belt which is an endless and rotatable fixing member. The fixing belt 1 is externally fitted to the arc-shaped guide member 7 with a margin in the circumference, and the guide member 7 is provided with a heating body 3.

  The fixing belt 1 is a resin having a high heat transfer and high strength metal layer, an elastic layer such as rubber having a high thermal conductivity, and a toner having high peelability in order to reduce heat capacity and improve quick start performance. Consists of layers.

  Reference numeral 2 denotes a pressure roller as a pressure rotating body. The pressure roller 2 is disposed so as to face the heating body 3 with the fixing belt 1 interposed therebetween, and has a silicon rubber layer as an elastic layer on a core metal such as iron or aluminum, and a release layer thereon. Of PFA tube layers.

  At the time of image fixing, the fixing belt 1 is driven by the rotation of the pressure roller 2. That is, the fixing belt 1 is in close contact with the surface of the heating member 3 and slides on the surface of the heating member 3 while sliding at a predetermined peripheral speed, that is, a recording material 21 carrying an unfixed toner image T conveyed from the image forming unit (not shown). It is rotationally driven without wrinkles at substantially the same peripheral speed as the transport speed.

  As shown in FIG. 3, the heating element 3 includes a first resistance heating element 3a and a second resistance heating element 3b as heat generation sources that generate heat by supplying power, and the first and second resistance heating elements 3a, 3b. The temperature rises due to heat generation. At this time, the temperature of the fixing belt 1 is controlled by the CPU 8 so as to be maintained at a predetermined temperature.

  In the process of passing the fixing nip portion of the recording material 21, thermal energy is applied from the heating body 3 to the recording material 21 via the fixing belt 1, and the unfixed toner image T on the recording material 21 is heated and melted and fixed. Passes through the fixing nip.

  Thereafter, when the recording material 21 is separated and discharged from the fixing belt 1, the rotation driving of the pressure roller 2 is stopped and the energization to the heating body 3 is stopped. During multiple printing, the temperature of the fixing belt is controlled until a series of printing operations is completed.

  The fixing belt 1 used in the fixing device 30 uses 50 μm SUS as a metal layer as a base layer, a rubber layer having a thermal conductivity of 1.0 W / m · K is provided on the SUS, and a PFA of 30 μm as a surface release layer. Use a tube. The inner diameter of the belt is φ25.

  The core of the pressure roller 2 is made of aluminum, the diameter of the core is φ10, the thickness of the rubber layer is 3 mm, the thickness of the tube layer is 50 μm, and the outer diameter is φ25.

  The heating element 3 which is a heater for heating forms the first and second resistance heating elements 3a and 3b by printing a thick film of Ag · Pd paste on the Al 2 O 3 substrate 4 and baking it. Here, the resistance value of the first resistance heating element 3a is continuously changed, that is, the area of the heating element is continuously changed so that the heat generation amount in the central portion in the longitudinal direction is increased.

  On the contrary, the resistance value of the second resistance heating element 3b is continuously changed so that the amount of heat generated at the end in the longitudinal direction is increased.

  Further, as means for detecting the longitudinal temperature distribution, temperature detection elements 6 a and 6 b are provided on the side opposite to the surface on which the heating body 3 slides with the fixing belt 1. The temperature detection element 6 a is provided at the center of the heating body 3 that is the center of passage of the recording material 21. The temperature detection element 6b is provided at a position of 147 mm on the left and right from the center of the heating body 3.

  Here, when a member having a low heat capacity such as the fixing belt 1 is used, a temperature distribution history in the longitudinal direction by the previously performed printing operation remains. For example, when a plurality of sheets of small size recording materials 21 such as A4R and B5 are continuously printed, the temperature of the non-sheet passing portion region at the end in the longitudinal direction becomes high.

  In such a temperature distribution state, if the normal start-up operation is performed, the temperature at the end becomes higher than necessary, and image defects such as hot offset occur. Therefore, the timing of the start-up operation until the temperature at the end decreases. Need to delay.

  Further, when the heating operation 3 is turned off after the printing operation is completed, the heat at the end in the longitudinal direction is large, so that the temperature at the center is high and the temperature at the end is low. In such a temperature distribution state, when a normal startup operation is performed, fixing failure at the end portion may occur, or the rising time of the fixing device 30 may be increased by turning on the power to the center more than necessary. .

  Therefore, in this embodiment, the temperature difference between the center temperature detecting element 6a and the end temperature detecting element 6b when a print job is received is detected, and the longitudinal width of the recording material 21 is detected. The lighting ratio for energizing the first resistance heating element 3a and the second resistance heating element 3b at the time of start-up is determined from the detection result. FIG. 4 shows the relationship between the optimum lighting ratio with respect to the temperature difference between the temperature detecting elements 6a and 6b at the center and the end and the longitudinal width of the recording material 21 passing in the next job.

  In the case where the longitudinal width passing through the next job is 292 to 297 mm as an example, if the temperature difference between the temperature detecting elements 6a and 6b at the center and the end is within 10 ° C., the first start-up operation is normal. Resistance heating element 3a: Energization is performed with second resistance heating element 3b = 100: 100.

  When the temperature at the center is 11 to 30 ° C. higher than the end portion, the first resistance heating element 3a is changed to the second resistance heating element 3b = 100: 80. When the temperature at the center is 31 ° C. higher than the end portion, the first resistance heating element 3a: second resistance heating element 3b is changed to 100: 60. On the other hand, when the temperature of the end portion is 11 ° C. or more higher than the center, the first resistance heating element 3a is changed to the second resistance heating element 3b = 80: 100.

  By performing the optimal control of the lighting ratio at the time of startup as described above, it is possible to suppress excess power consumption and shorten the printing time.

  Hereinafter, a procedure for changing the resistance heating element lighting ratio at the start-up according to the temperature difference between the temperature detection elements 6a and 6b at the time of print reception will be described with reference to the flowchart of FIG.

  First, a print job is received (see STEP 1). Then, the temperature of the temperature detection elements 6a and 6b at the center and the end is detected (see STEP 2). Next, the longitudinal width of the recording material 21 is detected (see STEP 3).

  From the detection results of STEP2 and STEP3, the lighting ratio for energizing the first resistance heating element 3a and the second resistance heating element 3b is determined with reference to the table of FIG. 4 (see STEP4). Printing is started when the central temperature detection elements 6a and 6b reach the target temperature (see STEP 5).

  As described above, in this embodiment, the temperature distribution in the longitudinal direction of the fixing device 30 at the start of the printing operation is detected based on the history of the previous printing operation. Then, the start-up operation of the fixing device 30 is performed by changing the lighting ratio of each of the first and second resistance heating elements 3a and 3b to an optimal ratio according to the detection result. As a result, the printing time can be shortened and the power consumption can be reduced.

  In addition, by detecting the longitudinal width of the recording material 21, it is possible to detect the longitudinal width that needs to be fixed, which enables further optimal selection of the lighting ratio when the fixing device 30 is started up. Fixing failure and temperature rise of the non-sheet passing portion at the time of a small size recording material can be reduced.

  The embodiment of the present invention has been described in detail above, but the present invention is not limited to the above-described embodiment, and the scope does not depart from the spirit of the invention described in the claims of the present invention. Thus, various changes can be made.

  For example, in the present embodiment, the ratio of energizing the heating element 3 is changed to a constant ratio, but the temperatures of the plurality of temperature detection elements 6a and 6b are sequentially detected, and the heating element 3 is energized stepwise. The ratio may be changed sequentially.

  Further, it is possible to use the history of the print job performed immediately before in order to detect the longitudinal temperature distribution at the time of print reception. Accordingly, the first resistance heating element 3a and the second resistance heating element 3b are energized at the time of start-up according to the information on the longitudinal width, the number of recording materials 21 and the print job interval of the recording material 21 that has passed through the fixing device 30 in the immediately preceding print job. A method for changing the ratio will be described.

  As a longitudinal temperature distribution detecting means at the time of receiving a print job, it has means for detecting information on the longitudinal width and number of recording materials 21 that have passed through the fixing device 30 in the previous print job, and information on the print job interval. And the lighting ratio which supplies with electricity to 1st and 2nd resistance heating element 3a, 3b at the time of start-up is changed according to a detection result.

  Generally, the longitudinal temperature distribution changes depending on the contents of the print job performed immediately before. For example, when a plurality of small-sized recording materials 21 such as A4R and B5 are printed, the temperature at the end in the longitudinal direction (non-sheet passing area) increases. The paper section temperature rises. In addition, the temperature distribution changes due to the movement of heat in the longitudinal direction and the heat radiation from the end depending on the elapsed time from the previous job.

  Therefore, it is possible to detect the longitudinal temperature distribution from these information and determine the lighting ratio of the first and second resistance heating elements 3a and 3b at the time of start-up. 6 to 11 show the relationship between the longitudinal width of the recording material 21 in the previous job, the number of sheets, the print job interval, and the optimum lighting ratio. When the elapsed time from the previous job is 30 s or less, the lighting ratio at startup is changed with reference to the tables of FIGS.

  The longitudinal width of the recording material 21 is set to three levels of 277 mm or less, 278 to 292 mm, 293 mm or more, and the number of sheets is set to four levels of 1 to 20, 21 to 60, 61 to 120, 121 or more. .

  For example, when the recording material width of the next job is 292 to 297 mm and the recording material width of the previous job is 277 mm or less, the first resistance heating element 3a and the second resistance heating element 3b are set to 100: 40 with 1 to 20 sheets. change. 21 to 60 sheets are changed to the first resistance heating element 3a: second resistance heating element 3b = 100: 20. With 61 sheets or more, the first resistance heating element 3a: second resistance heating element 3b is changed to 100: 0.

  When the elapsed time from the previous job is 31 s to 120 s, the lighting ratio at startup is changed with reference to the tables of FIGS. Further, when the elapsed time from the previous job is 121 s or more, energization is performed with a normal startup operation, first resistance heating element 3a: second resistance heating element 3b = 100: 100.

  Hereinafter, a procedure for changing the heating element lighting ratio at the start-up according to the information of the longitudinal width and number of recording materials 21 and the print job interval in the previous print job will be described with reference to the flowchart of FIG.

  First, a print job is received (see STEP 1). Thereafter, the longitudinal width and number of recording materials 21 in the previous print job and the print job interval are detected (see STEP 2). Next, it is determined whether or not the print job interval is 121 s or more (see STEP 3). When the print job interval is 121 s or more, the first resistance heating element 3a: second resistance heating element 3b = 100: 100 is energized (see STEP 7). When it is 120 s or less, the longitudinal width of the recording material 21 of the next print job is detected (see STEP 4).

  With reference to the tables of FIGS. 6 to 8 and FIGS. 9 to 11 from the previous print job information, the lighting ratio for energizing the first resistance heating element 3a and the second resistance heating element 3b is determined (see STEP 5). Thereafter, when the central temperature detecting element 6a reaches the target temperature, printing is started (see STEP 6).

  Note that the method of detecting the history information of the previous print job performed in the present embodiment and the method of detecting the temperature difference between the temperature detection elements 6a and 6b at the center and the end may be performed simultaneously. Thereby, the longitudinal temperature distribution is determined with higher accuracy.

1 is a cross-sectional view illustrating a main configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a schematic diagram of the fixing device in FIG. 1. It is a schematic diagram of the heating body of FIG. It is a relationship diagram of the temperature difference of the temperature detection element of a center and an edge part, and the optimal lighting ratio. 2 is a flowchart illustrating control of a fixing unit in FIG. 1. FIG. 6 is a relationship diagram of a recording material longitudinal width, the number of sheets, and a print job interval in a previous job and an optimum lighting ratio (print job interval: 30 s or less). FIG. 6 is a relationship diagram of a recording material longitudinal width, the number of sheets, and a print job interval in a previous job and an optimum lighting ratio (print job interval: 30 s or less). FIG. 6 is a relationship diagram of a recording material longitudinal width, the number of sheets, and a print job interval in a previous job and an optimum lighting ratio (print job interval: 30 s or less). FIG. 6 is a diagram illustrating the relationship between the longitudinal width of a recording material, the number of sheets, and the print job interval in the previous job and the optimum lighting ratio (print job interval: 31 to 120 s). FIG. 6 is a diagram illustrating the relationship between the longitudinal width of a recording material, the number of sheets, and the print job interval in the previous job and the optimum lighting ratio (print job interval: 31 to 120 s). FIG. 6 is a diagram illustrating the relationship between the longitudinal width of a recording material, the number of sheets, and the print job interval in the previous job and the optimum lighting ratio (print job interval: 31 to 120 s). 6 is a flowchart illustrating another control of the fixing unit in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Fixing belt 2 Pressure roller 3 Heating body 3a 1st resistance heating element 3b 2nd resistance heating element 6a, 6b Temperature detection element 7 Guide member 8 CPU
11 Feeding department
21 Recording material
22Y, 22M, 22C, 22K Photosensitive drum
23Y, 23M, 23C, 23K Injection charger
24Y, 24M, 24C, 24K Scanner section
25Y, 25M, 25C, 25K Developer cartridge
26Y, 26M, 26C, 26K Developer
27 Intermediate transfer member
30 Fixing device T Toner image

Claims (3)

A heating member that generates heat when energized; a fixing member that is rotatable with a low heat capacity; and a pressure member that rotates in pressure contact with the fixing member; and a pressure nip formed by the fixing member and the pressure member. In a fixing device for fixing an unfixed toner image on the recording material by heating and pressing while sandwiching and conveying the recording material,
The heating element has a first resistance heating element having a high calorific value at the center and a second resistance heating element having a high calorific value at the longitudinal end, and the heating element has a heating element at the center and the longitudinal end of the heating element. A temperature detection element for detecting a temperature distribution in the longitudinal direction is provided, and the first resistance at the time of starting up the fixing device is determined according to a detection result by the temperature detection element and a detection result of a longitudinal width of the recording material of the next print. A fixing device, wherein a ratio of energizing the heating element and the second resistance heating element is changed. 2. The fixing according to claim 1, wherein a ratio of energizing the first resistance heating element and the second resistance heating element at the time of starting the fixing device is sequentially changed according to a detection result by the temperature detection element. apparatus. A heating member that generates heat when energized; a fixing member that is rotatable with a low heat capacity; and a pressure member that rotates in pressure contact with the fixing member; and a pressure nip formed by the fixing member and the pressure member. In a fixing device for fixing an unfixed toner image on the recording material by heating and pressing while sandwiching and conveying the recording material,
The heating element has a first resistance heating element having a high calorific value at the center and a second resistance heating element having a high calorific value at the longitudinal end, and the heating element has a heating element at the center and the longitudinal end of the heating element. A temperature detection element for detecting the longitudinal temperature distribution is provided, and according to the detection result of the number of recording materials, the longitudinal width and the elapsed time in the previous print job, and the detection result of the longitudinal width of the recording material of the next print The fixing device is characterized in that a ratio of energizing the first resistance heating element and the second resistance heating element when the fixing device is started is changed.