JP2012189721A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fixing device and an image forming apparatus which do not generate failure for various recording sheets having different properties and images for which different amounts of toner are used.SOLUTION: The fixing device comprises: a pressurizing member; a fixing belt rotating at the periphery of the pressurizing member; and a columnar pressing member which biases the fixing belt from the inside of the circumference of the fixing belt to a surface of the pressurizing member to form a nip part for fusing and fixing toner to a recording sheet by making the recording sheet pass through the nip part, between the pressurizing member and the fixing belt. The pressing member is rotatably supported, and has at least one of a recess part and a flat part on a circumference of a cross section orthogonal to a rotation axis direction. There is also provided the image forming apparatus having the fixing device.

Description

  The present invention relates to a fixing device that heats and fixes a toner image formed on a recording sheet on a recording medium in an image forming apparatus such as a copying machine, a printer, a facsimile machine, and a multifunction machine of these, and an image forming apparatus using the fixing device. About.

  Generally, the fixing device includes a rotatable heating roller and a pressure roller that is in pressure contact with the heating roller and rotates. In the fixing device, a nip portion is formed between a heating roller and a pressure roller, and a recording sheet on which unfixed toner is placed is inserted into the nip portion and heated and pressed to fix the toner. Creating an image.

  In such a fixing device, a plurality of fixing methods and the like for improving the toner fixing property and the recording sheet peeling property have been proposed.

  For example, Patent Document 1 proposes a method of forming a nip width in an area for transporting a recording paper between a rotating heat-resistant belt and a guide plate that is variably provided. According to this method, it is possible to heat and fix the toner image by controlling the pressure applied to the guide plate so that the nip width can be varied.

  Further, in Patent Literature 2 and Patent Literature 3, a heating roll whose surface is heated and rotated, an endless pressure belt driven in contact with the surface of the heating roll, and the circumference of the pressure belt There has been proposed a method of forming a nip portion that includes a pressing member that urges the surface of the heating roll and is capable of inserting a recording sheet between the heating roll and the pressure belt. According to the method, it is possible to optimize the pressure state by controlling the shape of the nip portion according to the shape and position of the pressing member.

  However, in the fixing device of Patent Document 1, the nip width is increased in order to suppress the curling of the recording sheet and to maintain good fixing properties, and the pressure in the flat nip portion formed wide is kept uniform. It was difficult. For this reason, depending on the type of recording sheet and the amount of unfixed toner, problems such as toner adhesion to the fixing member and wrinkling of the recording sheet may occur.

  Further, in the fixing devices of Patent Documents 2 and 3, by providing a pressing member that protrudes toward the recording sheet exit side of the nip portion, the curvature of the nip exit is locally increased, and at the same time, the recording sheet covers this portion. The pressure when passing is increased. According to this method, it is possible to improve the releasability between the recording sheet and the fixing member, but there is a case where the load applied to the recording sheet is large and excessive curling may occur depending on the type of the recording sheet. there were.

  Furthermore, in recent years, it has been demanded that a single apparatus can handle a wide variety of recording sheets and images, and it is extremely difficult to satisfactorily fix toner on a recording sheet without causing any of the above problems in all situations. It is difficult to.

  Therefore, an object of the present invention is to provide a fixing device that does not cause the above problem even in various recording sheets having different characteristics and images having different amounts of toner used.

  In order to solve the above-described problems, a fixing device according to the present invention includes a fixing belt that rotates and moves, a pressure member that contacts the fixing belt, and urges the fixing belt from the circumference to the surface of the pressure member. And a columnar pressing member that forms a nip portion that melts and fixes the toner to the recording sheet by passing the recording sheet between the pressing member and the fixing belt, and the pressing member rotates. It is supported so that it has at least one of a recessed part and a plane part in the outer periphery of the cross section orthogonal to a rotating shaft direction.

  In the fixing device according to the present invention having such a configuration, the pressing member is rotatably installed, and the position in contact with the pressure member via the fixing belt is controlled, so that the shape of the nip portion can be freely controlled. Is possible. Therefore, the shape of the nip portion can be selected and formed in accordance with the type of recording sheet or the amount of unfixed toner on the recording sheet, so that it is possible to prevent the occurrence of the above problems in the fixing device.

  According to the present invention, the releasability from the fixing belt is good and the recording sheet is wrinkled and excessively curled even under various conditions such as the type of recording sheet and the amount of unfixed toner on the recording sheet. It is possible to provide a fixing device without any problem.

1 is a schematic diagram illustrating an example of an image forming apparatus according to an exemplary embodiment. FIG. 2 is a diagram illustrating a configuration example of a fixing device according to the present embodiment. It is sectional drawing orthogonal to the rotating shaft direction of the press roller which concerns on this Embodiment. It is a figure which shows the shape of the nip part formed with the press roller which concerns on this Embodiment. It is a rotating shaft direction sectional drawing which passes along the axial center of the press roller which concerns on this Embodiment. FIG. 6 is a diagram illustrating a state in which a pressing roller rotates while a recording sheet passes through a nip portion in the present embodiment.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention (hereinafter referred to as “embodiments”) will be described in detail with reference to the drawings.
[First Embodiment]
<Outline of image forming apparatus>
FIG. 1 is a schematic configuration diagram illustrating an example of an image forming apparatus to which the fixing device of the present embodiment is applied. In the figure, reference numeral 100 denotes a tandem intermediate transfer type image forming apparatus main body as an image forming apparatus, and 200 denotes a paper feed table on which the image forming apparatus main body 100 is placed. Further, inside the image forming apparatus main body 100, a tandem type intermediate transfer type image forming unit (hereinafter referred to as a tandem type image forming unit) 20 in which a plurality of image forming units 1Y, 1M, 1C, and 1K are arranged in parallel. Is provided. Subscripts Y, M, C, and K attached to the above symbols indicate yellow, magenta, cyan, and black colors, respectively.

  The image forming apparatus main body 100 is provided with an endless belt-shaped intermediate transfer member (hereinafter referred to as an intermediate transfer belt) 10 near the center. The intermediate transfer belt 10 is wound around a plurality of support rollers 14, 15, 16 and the like and can be rotated and conveyed clockwise in the drawing.

  In this embodiment, a cleaning device 17 for the intermediate transfer belt is provided on the left of the support roller 16. The cleaning device 17 removes residual toner remaining on the intermediate transfer belt 10 after image transfer.

  On the intermediate transfer belt 10 stretched between the support roller 14 and the support roller 15, four image forming units 1Y, 1M, 1C, and 1K of yellow, magenta, cyan, and black are arranged horizontally along the conveyance direction. The tandem type image forming unit 20 is arranged side by side. Each of the image forming units 1Y, 1M, 1C, and 1K of the tandem type image forming unit 20 includes photosensitive drums 2Y, 2M, 2C, and 2K as image carriers that carry toner images of the respective colors.

  Two exposure devices 4 are provided above the tandem image forming unit 20. Each exposure device 4 corresponds to two image forming units (1Y and 1M, 1C and 1K). For example, it is composed of two light source devices (semiconductor laser, semiconductor laser array, or multi-beam light source) and a coupling optical system, a common optical deflector (polygon mirror, etc.), two scanning imaging optical systems, etc. This is an optical scanning exposure apparatus. Each of the photosensitive drums 2Y, 2M, 2C, and 2K is exposed according to image information of each color of yellow, cyan, magenta, and black to form an electrostatic latent image.

  The following devices are provided around the photosensitive drums 2Y, 2M, 2C, and 2K of the image forming units 1Y, 1M, 1C, and 1K. First, there are charging devices 3Y, 3M, 3C, and 3K that uniformly charge the photosensitive drums prior to exposure. Next, developing devices 5Y, 5M, 5C, and 5K that develop the electrostatic latent image formed by the exposure device 4 with toner of each color. Further, photoconductor cleaning devices 7Y, 7M, 7C, and 7K are provided for removing transfer residual toner on the photoconductor drum. Further, primary transfer rollers 6Y, 6M, 6C, and 6K that transfer toner images from the photosensitive drums 2Y, 2M, 2C, and 2K to the intermediate transfer belt 10 are provided. The primary transfer rollers 6Y, 6M, 6C, and 6K are provided to face the photosensitive drums 2Y, 2M, 2C, and 2K with the intermediate transfer belt 10 interposed therebetween.

  Among the plurality of support rollers that support the intermediate transfer belt 10, the support roller 14 is a drive roller that rotationally drives the intermediate transfer belt 10. The support roller 14 is connected to the motor via a drive transmission mechanism (gear, pulley, belt, etc.) not shown. When a black single color image is formed on the intermediate transfer belt 10, the support rollers 15 other than the driving roller 14 are moved so that the photosensitive drums 2 Y, 2 M, and 2 C that do not form an image are transferred to the intermediate transfer belt 10. It is possible to move away from Thereby, the life of the photosensitive drums 2Y, 2M, 2C and the intermediate transfer belt 10 can be extended.

  A secondary transfer device 22 is provided on the lower side of the intermediate transfer belt 10 on the side opposite to the tandem image forming unit 20. In the illustrated example, the secondary transfer device 22 presses the secondary transfer counter roller 16 and applies a transfer electric field to transfer the image on the intermediate transfer belt 10 to a recording sheet as a transfer medium.

  A fixing device 25 for fixing the transferred image on the recording sheet is provided next to the secondary transfer device 22. The fixing device 25 is configured by bringing a pressure roller 27 into contact with a fixing belt 26 that is an endless belt. The fixing belt 26 is suspended from a driving roller 31, a tension roller 32, and a pressing member 29. Heating means (a heater, a lamp, an electromagnetic induction heating device, or the like) is provided inside the tension roller 32 in this embodiment.

  The recording sheet on which the image has been transferred by the secondary transfer device 22 is conveyed to the fixing device 25 by a conveyance belt 24 supported by two rollers 23. The conveyance belt 24 may be a fixed guide member, or may be a conveyance roller, a conveyance roller, or the like.

  In the present embodiment, the recording sheet is reversed under the secondary transfer device 22 and the fixing device 25 so as to record images on both sides of the recording sheet in parallel with the tandem image forming unit 20 described above. A sheet reversing device 28 is provided.

  When image data is sent to the image forming apparatus main body 100 and an image formation start signal is received, the tandem image forming unit 20 rotates the support roller 14 with a drive motor (not shown) to drive the other plurality of support rollers. Following the rotation, the intermediate transfer belt 10 is rotated and conveyed in the direction of the arrow in the figure. At the same time, in each of the image forming units 1Y, 1M, 1C, and 1K, first, the photosensitive drums 2Y, 2M, 2C, and 2K start to rotate counterclockwise by a drive motor (not shown). Next, charging by the charging devices 3Y, 3M, 3C, and 3K and exposure (latent image formation) by the exposure device 4 are performed. Thereafter, through development processes of the developing devices 5Y, 5M, 5C, and 5K, monochrome images of yellow, cyan, magenta, and black are formed on the photosensitive drums 2Y, 2M, 2C, and 2K, respectively. Thereafter, as the intermediate transfer belt 10 is conveyed, the single color images are sequentially transferred to the intermediate transfer belt 10 by the primary transfer rollers 6Y, 6M, 6C, and 6K to form a composite color image on the intermediate transfer belt 10.

  The recording sheet after the image transfer is transported by the transport belt 24 and sent to the fixing device 25, and heat and pressure are applied by the fixing device 25 to fix the transferred image. The recording sheet after fixing is switched by a switching claw (not shown), discharged by a discharge roller 56, and stacked on a discharge tray 57. Alternatively, it is switched by a switching claw (not shown) and put into the sheet reversing device 28, where it is reversed and guided again to the paper feed path in the image forming apparatus main body 100, reversed and conveyed to record an image on the back surface, and then discharged The paper is discharged onto a paper discharge tray 57 by a roller 56.

On the other hand, the photoconductor drums 2Y, 2M, 2C, and 2K after image transfer remain on the photoconductor drums 2Y, 2M, 2C, and 2K after image transfer by the photoconductor cleaning devices 7Y, 7M, 7C, and 7K. Residual toner is removed. The intermediate transfer belt 10 after image transfer is removed by the intermediate transfer belt cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 10 after image transfer. Then, after the above-described cleaning process, the image forming apparatus is prepared for another image formation by the tandem type image forming unit 20.
<Configuration of fixing device>
Next, the fixing device 25 according to the present embodiment will be described in detail with reference to FIGS.

FIG. 2 shows a fixing device 25 according to the present invention. The fixing device 25 in the present embodiment includes a pressure roller 27 as the pressure member and a pressure roller 29 as the pressure member. Further, the fixing belt 26, the driving roller 31, and a tension roller 32 having a halogen heater 33 therein are included. The nip portion 35 is formed by the contact between the fixing belt 26 and the pressure roller 27. When the recording sheet passes through the nip portion 35, the toner on the recording sheet can be melted and fixed.
<Pressurizing member>
The pressing member may be a roller having an elastic material on the surface or a member on a flat plate having an elastic member, and the elastic member is configured so as to press the fixing belt 26 from the inner periphery of the endless belt. Can also be used. In any case, any material can be used as long as the nip portion 35 is formed in a shape corresponding to the surface shape of the pressing member described later.

In this embodiment, a pressure roller 27 that is rotationally driven is used as the pressure member. The pressure roller 27 is made of a metal such as iron, stainless steel, aluminum, or an alloy thereof, for example, stainless steel, and the surface is made by integrally molding a foamable resin, for example, as an elastic material. It has been. Further, on the surface, as a rubber material having heat resistance and elasticity, for example, silicon rubber, and on the fluororesin such as PFA (perfluoroalkyl vinyl ether copolymer resin) and PTFE (polytetrafluoroethylene), For example, PFA is coated to prevent melted toner from adhering to the surface easily. In the present embodiment, the surface of the pressure roller 27 is heated by a heating means (not shown). As a result, the temperature difference between both sides of the recording sheet passing through the nip portion 35 can be reduced, and the occurrence of curling and wrinkling of the recording sheet can be further suppressed. Further, the pressure roller 27 is supported so as to be movable in the direction of the pressing roller 29, and can adjust the pressure applied to the recording sheet passing through the nip portion 35. In the present embodiment, the pressure roller 29 is movably supported, but the pressure applied to the recording sheet passing through the nip portion 35 can also be controlled by supporting the pressure roller 29 so as to be movable. it can.
<About fixing belt>
The fixing belt 26 is an endless belt, and is urged by a pressing member from the periphery to come into contact with the pressure roller 27. The fixing belt 26 rotates at the same speed as the recording sheet conveyance speed while the surface in contact with the recording sheet is heated, and melts and fixes unfixed toner on the recording sheet at the nip portion 35.

In this embodiment, the fixing belt 26 rotates while being suspended between the driving roller 31, the tension roller 32, and the pressing member. Holes with a diameter of 3 mm are provided at both ends of the fixing belt, and are configured to engage with protrusions provided at the axial end of the driving roller 31, and move according to the rotation of the driving roller 31. . The fixing belt 26 is slid while being in contact with the surface of the tension roller 32 and the pressing member without being bent by being suspended on the tension roller 32. The fixing belt 32 is heated to a temperature at which the toner is melted and fixed by a halogen heater 33 provided in the tension roller 32.
The fixing belt 26 of this embodiment is an endless belt, and an elastic layer and a release layer are formed on the surface of a base material. As the base material, for example, a polyimide film is used as the base material, and the surface thereof is coated with an elastomer material having a thickness of about 2 mm and excellent in heat resistance and elasticity, for example, silicon rubber, and the inner and outer peripheral surfaces are release layers. For example, PFA is coated with a fluororesin material excellent in heat resistance and releasability.

The driving roller 31 and the tension roller 32 may be integrated, and the fixing belt 26 may be suspended by one roller and a driving force may be applied. Further, as a means for heating the fixing belt 26, the surface of the fixing belt 26 may be heated from the outside of the fixing belt 26.
<Pressing member>
The columnar pressing member is provided so as to urge the fixing belt 26 from the inside to the pressure roller 27 to form a nip portion 35 corresponding to the surface shape. The pressing member is fixedly held while the recording sheet passes through the nip portion 35 except for a case described later, and forms a nip portion 35 having a fixed shape. The fixing belt 26 that slides on the pressing member rotates and moves so as to pass through the nip portion 35 together with the recording sheet while contacting the surface of the pressing member.

  The pressing member is rotatably provided and has a flat portion or a concave portion on the outer periphery of a cross section perpendicular to the rotation axis direction, and a portion that presses the pressure roller 27 via the fixing belt 26 at the time of fixing. By changing, various nip portions 35 can be formed according to conditions such as the type of recording sheet and the amount of unfixed toner.

The pressing roller 29 used as the pressing member is formed into a columnar shape using, for example, stainless steel as a base material among heat-resistant metal materials such as aluminum and iron, and the surface is coated with a fluororesin such as PFA having excellent heat resistance and releasability. Has been.
The pressure roller 29 is pressed by a pressure mechanism 38 using a spring spring 37 in the direction of the pressure roller 27, and urges the fixing belt 26 to come into pressure contact with the pressure roller 27. As a result, the foamable resin portion near the surface of the pressure roller 27 is deformed, and the nip portion 35 corresponding to the surface shape of the pressure roller 29 is formed.

  The pressing roller 29 is rotatably supported and can be freely rotated and stopped by a driving source (not shown), and the position thereof can be controlled by an encoder (not shown) attached to the end of the pressing roller 29. ing.

  In the present embodiment, the pressing roller 29 has a length in the rotation axis direction of 230 to 370 mm, and preferably has a maximum length from the axis to the outer edge in a cross section orthogonal to the rotation axis direction of 15 to 40 mm. Moreover, as shown in FIG. 3, it has the convex circular arc part a, flat part b1, b2 of different length, and the recessed part c in the outer periphery of the cross section orthogonal to an axial direction. The arc portion a preferably has a semicircular shape with a radius of 10 to 40 mm, and the concave portion c preferably has a shape recessed along a circle with a radius (outer diameter of the pressure roller 27/2 + 5 to 30) mm. In addition to the circular arc part, it is sufficient to form at least one of a flat part and a concave part on the outer periphery of the cross section of the pressing member. It is more preferable to form a recess. This is because by having a plurality of different portions, it is possible to create various nip widths and shapes.

  The nip portion 35 formed by the pressing roller 29 in the present embodiment is shown in FIG. 4A shows a state in which the nip portion 35 is formed by the arc portion of the pressing roller 29. FIGS. 4B and 4C show the nip portion 35 by the flat portion and the concave portion of the pressing roller 29, respectively. It shows the state of being formed. As described above, in the present embodiment, the shape of the nip portion 35 is controlled by rotating the pressing roller 29. Furthermore, in this embodiment, it is possible to control the pressure applied to the nip portion 35 by moving the pressure roller 27 in the direction of the pressure roller 29.

  FIG. 5 is a sectional view in the axial direction passing through the axis of the pressing roller 29. 5A is a cross-sectional view taken along the line II ′ of FIG. 3, and FIG. 5B is a cross-sectional view taken along the line of FIG. As shown in FIGS. 5A and 5B, the pressing roller 29 has a drum shape in which the central portion in the rotational axis direction is depressed in the axial section. Further, the amount of depression in the central portion differs depending on the circumferential direction.

  Specifically, as shown in FIGS. 5A and 5B, the length L1 from the axial center to the outer edge of the central portion of the pressing roller 29 is smaller than the length L2 from the axial center to the outer edge of the peripheral portion. Further, the lengths L1 and L2 are continuously changed in the circumferential direction so that the lengths L1 and L2 are different from each other in the cross section along the line II.

  The difference between L1 and L2 of each part of the pressing roller 29 in this embodiment varies in the circumferential direction from 0.05 mm to 0.15 mm in the arc part a in FIG. 3, and is 0.15 mm in the flat part b1 and 0 in b2. .05 mm, and the recess c is 0.05 mm.

The internal memory of the image forming apparatus 100 combines information such as the size and thickness of the recording sheet, the type of special paper such as glossy paper and envelopes, and the amount of unfixed toner formed on the recording sheet, for good fixing. The optimum state of the nip portion 35 for obtaining an image is held in advance. Based on this information, the position where the pressure roller 27 is pressed through the fixing belt 26 of the pressure roller 29 is controlled to form an optimum nip portion, thereby obtaining an image having no problem under various conditions. It becomes possible.
<Operation of the fixing device>
According to the present embodiment, as described below, it is possible to effectively prevent the recording sheet from being wrinkled or excessively curled, and to improve the peelability between the recording sheet and the fixing belt 26.
≪Record sheet wrinkle prevention≫
For example, if the pressure in the nip portion 35 is not uniform in the direction of the rotation axis of the pressing roller, there arises a problem that a local difference occurs in the conveyance speed of the recording sheet, and the recording sheet is likely to be wrinkled. This phenomenon is particularly noticeable in the case of a recording sheet that is weak.

  As described above, the pressing roller 29 of the present embodiment has a length L1 from the axial center to the outer edge at the center portion smaller than the length L2 at the peripheral portion in the axial section passing through the axial center. When the pressing roller 29 has such a shape, the pressure at the end in the width direction of the recording sheet passing through the nip portion 35 becomes larger than the pressure at the center portion. Accordingly, the recording sheet is always given a force spreading from the central portion toward both ends, and a fixed image can be obtained without causing wrinkles on not only general paper but also a recording sheet with low stiffness. it can.

  Further, the pressure roller 29 in the present embodiment has a shape in which the difference in length (L2−L1) between the central portion and the peripheral portion in the axial section is different in the circumferential direction. With such a shape, wrinkles can be effectively prevented even in recording sheets having different sizes and different sheet widths. For example, when fixing at the arc portion of the pressure roller 29, the nip portion 35 is formed at a portion where the difference (L2-L1) is large when the paper width is large, and the difference (L2) when the paper width is small. The nip portion 35 may be formed at a portion where -L1) is small. As a result, the generation of wrinkles can be effectively prevented regardless of the width of the paper.

Further, when the recording sheet is an envelope, when passing through the nip portion 35, a difference in linear velocity occurs between the front surface and the back surface of the envelope, and thus wrinkles may occur at the joint portion between the front and back surfaces. However, if the flat portion of the pressing roller 29 is used, the difference in linear velocity between the front and back of the envelope is reduced, so that the generation of wrinkles can be suppressed.
≪Releasability between recording sheet and fixing belt 1≫
In order to fix the unfixed toner on the recording sheet, it is necessary to apply sufficient heat and pressure to the toner and the recording sheet while the recording sheet passes through the nip portion 35. This is because if either of them is insufficient, the recording sheet is wound around the fixing member and the toner adheres to the fixing member. Even when either heat or pressure is excessive, problems such as toner adhesion to the fixing member and occurrence of curling of the recording sheet are likely to occur. In particular, when the recording sheet is weak and the amount of toner is small, winding or excessive curling is remarkable.

However, even when the recording sheet is weak and the amount of toner is small, the occurrence of the above-described problem can be suppressed by forming the nip portion 35 with the flat portion or the concave portion of the pressing roller 29. This is because the nip width can be formed wider at a lower pressure than when the arc portion is used, so that sufficient heat and pressure can be applied to the toner and the recording sheet. Therefore, the recording sheet is not wound around the fixing member and the toner is not attached to the fixing member, and it is possible to prevent the recording sheet from being excessively curled.
≪Releasability between recording sheet and fixing belt 2≫
Further, by rotating the pressing roller 29 while the recording sheet passes through the nip portion 35, the releasability between the recording sheet and the fixing belt 26 can be kept better.

  FIG. 6 shows the operation of the pressing roller 29 when the recording sheet passes through the nip portion 35 by forming the nip portion 35 using the flat portion of the pressing roller 29.

In particular, when the recording sheet is weak and the image area is large and the amount of unfixed toner is large, the peelability between the fixing belt 26 and the recording sheet is lowered. In such a case, the nip part 35 is first formed using the flat part or recessed part of the pressing roller 29 (FIG. 6A). Next, while the leading edge of the recording sheet passes through the nip portion 35, the pressing roller 29 is rotated counterclockwise in the drawing to apply a large pressure locally to the recording sheet (FIG. 6B). Further, after the leading end of the recording sheet has passed through the nip portion 35, control is performed to restore the original state (FIG. 6C). Specifically, the above effect can be obtained by rotating the rotation angle of the pressing roller 29 by about 3 ° to 10 °.
By controlling the rotation of the pressing roller 29 in this way, it is possible to improve the peelability between the recording sheet and the fixing belt while preventing the occurrence of curling over the entire recording sheet. Such an operation of the pressing roller 29 is particularly effective when performed using a flat portion or a concave portion of the pressing roller 29. Further, even when the nip portion 35 is formed by the arc portion of the pressing roller 29, the same effect can be obtained by performing the operation of reducing the distance between the pressing roller 27 and the pressing roller 29 while the recording sheet passes. You can also
<Summary>
As described above, according to the fixing device of the present embodiment, the position and operation of the pressure roller 29, the position of the pressure roller 27, and the like under various conditions caused by combinations of the type of recording sheet and the amount of toner on the recording sheet. Since the optimum nip portion 35 can be formed by controlling the above, the occurrence of wrinkles and excessive curling of the recording sheet is prevented, the peelability between the recording sheet and the fixing belt 26 is improved, and a good fixed image is obtained. Obtainable.

  Finally, the present invention is not limited to the requirements shown here, such as combinations of other elements with the shapes and configurations described in the above embodiments. These points can be changed without departing from the gist of the present invention, and can be appropriately determined according to the application form.

25 Fixing Device 26 Fixing Belt 27 Pressure Roller (Pressure Member)
29 Pressing roller (pressing member)
35 Nip part

JP-A-8-115003 JP-A-10-228200 JP 2004-12682 A

Claims (8)

A fixing belt that rotates and rotates, a pressure member that contacts the fixing belt, and a force between the pressure member and the fixing belt that biases the fixing belt from the circumference to the surface of the pressure member. And a columnar pressing member that forms a nip portion that melts and fixes the toner to the recording sheet by passing the recording sheet, and the pressing member is rotatably supported. A fixing device having at least one of a concave portion and a flat portion on an outer periphery of a cross section perpendicular to the surface. The fixing device according to claim 1, wherein a shape of the nip portion formed by the pressure member and the fixing belt is formed according to a surface shape of the pressing member. The fixing device according to claim 2, wherein a distance between the pressing member and the pressing member is variably supported. The axial difference passing through the axial center of the pressing member, the difference in length from the axial center to the outer edge in the central part and the peripheral part changes continuously in the circumferential direction. Fixing device. The pressing member is any one of the type of recording sheet, the amount of unfixed toner held on the recording sheet, the pressure member, the fixing belt, the recording sheet, or the ambient temperature in the fixing device, or The fixing device according to claim 1, wherein the fixing device rotates based on two or more pieces of information. The distance between the pressing member and the pressure member is the type of the recording sheet, the amount of unfixed toner held on the recording sheet, the pressure member, the fixing belt, the recording sheet, or the atmosphere in the fixing device. 6. The fixing device according to claim 3, wherein the fixing device changes based on any one or two or more information of the temperatures. The fixing device according to claim 1, wherein the shape of the nip portion changes while the recording sheet passes through the nip portion. An image forming apparatus comprising the fixing device according to claim 1.

Images