JP2008175908A - Fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device or the like where a fixing member is hardly scratched. <P>SOLUTION: The fixing device 60 is equipped with a fixing roller 70 and a pressure module 80 arranged so as to press-contact with the fixing roller 70 and forming a nip part N for performing pressuring and heating action to paper on which a toner image is held between the fixing roller 70 and the pressure module 80. The pressure module 80 is equipped with a support frame 81, a pressure pad 82, a first coil spring 83, a pad for peeling 84, a second coil spring 85 and a pressure belt 86. The unit pressure applied, when the pad for peeling 84 presses an elastic layer 71 through the pressure belt 86, is larger than the unit pressure applied when the pressure pad 82 presses the elastic layer 71 through the pressure belt 86. The spring constant of the second coil spring 85 is smaller than the spring constant of the first coil spring 83. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fixing device used in an image forming apparatus such as a copying machine, a printer, and a facsimile.

  In an image forming apparatus such as a copying machine or a printer, for example, a fixing device may be provided that heats and presses a recording material on which a toner image is held to fix the image on the recording material. Such a fixing device includes, for example, a belt that is stretched between a plurality of rollers and heated by a heat source, and a pressure roller that is provided to face the rollers with the belt interposed therebetween. There is known a technique in which a material is sandwiched and conveyed between the belt and a pressure roller for heating (for example, see Patent Document 1).

JP 2004-234951 A

  By the way, in the fixing device, when a fixing process is performed on a thick sheet, the end (edge) of the sheet is strongly pressed against the fixing member, and the fixing member may be scratched. If a flaw or the like occurs in the fixing member, an image defect such as unevenness or streak flaw is caused in the fixed image.

  SUMMARY An advantage of some aspects of the invention is to provide a fixing device or the like that makes it difficult to cause scratches on a fixing member.

  For this purpose, a fixing device to which the present invention is applied includes a fixing member that is rotatably arranged, and a nip portion that is rotatably arranged in contact with the fixing member and through which a recording material holding an image is inserted. A belt-like member formed between the fixing member and a plurality of pressing members that are provided inside the belt-like member and press the belt-like member with different unit pressures toward the nip portion. Among the members, one pressing member that presses the belt-shaped member with a unit pressure higher than that of the other pressing members can move forward and backward according to the thickness of the recording material passing through the nip portion.

  Here, a first spring member that supports the other pressing member so as to be movable forward and backward with respect to the nip portion, and a second spring member that supports the one pressing member so as to be movable forward and backward with respect to the nip portion, The spring constant of the second spring member may be smaller than the spring constant of the first spring member. One pressing member presses the belt-shaped member at a predetermined position inside the belt-shaped member, and the other pressing member presses the belt-shaped member on the upstream side in the rotation direction of the belt-shaped member relative to the one pressing member. It can be characterized by.

  From another point of view, the fixing device to which the present invention is applied is provided with a fixing member that is rotatably arranged, a belt-like member that is rotatably arranged, and an inner side of the belt-like member. A first disposing member, a first spring member that presses the first disposing member against the fixing member via the belt-shaped member, and a second disposing member disposed inside the belt-shaped member. And a second spring member having a spring constant different from that of the first spring member and pressing the second arrangement member against the fixing member via the belt-like member.

  Here, the second disposing member is disposed downstream of the first disposing member in the rotation direction of the belt-shaped member, and the spring constant of the second spring member is the spring constant of the first spring member. Smaller than that.

  Further, when the present invention is regarded as an image forming apparatus, the image forming apparatus to which the present invention is applied is arranged such that the fixing member that is rotatably arranged and the fixing member are rotatably contacted to hold the image. A belt-like member that forms a nip portion for inserting the recording material between the fixing member, a pressing member that is disposed inside the belt-like member and presses the belt-like member toward the nip portion, and is inserted into the nip portion. Grasping means for grasping the type of the recording material to be recorded, and advancing / retreating means for advancing / retreating the pressing member with respect to the fixing member based on the type of the recording material grasped by the grasping means.

  Here, the advancing / retreating means can be characterized in that when the thickness as the type of the recording material grasped by the grasping means exceeds a predetermined threshold, the pressing member is retracted with respect to the fixing member. The pressing member includes a member for fixing the image held on the recording material to the recording material and a member for peeling the recording material inserted through the nip portion from the fixing member or the belt-like member. The means may be characterized by advancing and retracting a member for peeling. Further, the advancing / retreating means can be characterized by advancing and retracting the pressing member that presses the belt-like member with the highest unit pressure when a plurality of pressing members are provided.

According to the first aspect of the present invention, it is possible to provide a fixing device that makes it difficult to cause scratches on the fixing member as compared with the case where the present configuration is not provided.
According to the second aspect of the present invention, the one pressing member that easily causes scratches to the fixing member is more easily retracted from the nip portion than the other pressing members. As compared with the case where there is no defect, it is possible to reduce the occurrence of scratches on the fixing member.
According to the invention of claim 3, when the recording material is inserted through the nip portion, the other pressing member that may be provided with the fixing function is less likely to move backward than the first pressing member. The fixing performance can be ensured as compared with the case where this configuration is not provided.

According to the invention which concerns on Claim 4, compared with the case where it does not have this structure, the fixing device which makes it hard to produce the crack to a fixing member can be provided.
According to the fifth aspect of the present invention, when the recording material is inserted through the nip portion, the first disposing member that may be provided with a fixing function is less likely to retreat than the second disposing member. Therefore, the fixing performance can be ensured as compared with the case where the present configuration is not provided.

According to the sixth aspect of the present invention, it is possible to provide an image forming apparatus that makes it difficult to cause scratches on the fixing member as compared with the case where the present configuration is not provided.
According to the seventh aspect of the present invention, it is possible to make it more difficult to cause a flaw on the fixing member as compared with the case where the present configuration is not provided.
According to the eighth aspect of the invention, since the member for peeling is advanced and retracted, the fixing performance by the member for fixing can be maintained.
According to the ninth aspect of the present invention, the pressing member that is most likely to cause scratches with respect to the fixing member advances and retreats. Therefore, compared with the case where the present configuration is not provided, the fixing member is not damaged. It becomes possible to make it harder to occur.

-First embodiment-
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram showing an image forming apparatus to which the present invention is applied. The image forming apparatus shown in FIG. 1 is an intermediate transfer type image forming apparatus generally called a tandem type. The image forming apparatus includes a plurality of image forming units 1Y, 1M, 1C, and 1K that form toner images of respective color components by electrophotography. Further, a primary transfer unit 10 that sequentially transfers (primary transfer) the color component toner images formed by the image forming units 1Y, 1M, 1C, and 1K to the intermediate transfer belt 15 is provided.

  Further, the image forming apparatus includes a secondary transfer unit 20 that collectively transfers (secondary transfer) the superimposed toner image transferred onto the intermediate transfer belt 15 onto a sheet P that is a recording material (recording paper). Yes. Various rollers such as a driving roller 31 are provided inside the intermediate transfer belt 15 so as to stretch the intermediate transfer belt 15 from the inside and to be rotated by a motor (not shown) having excellent constant speed. ing. Further, a fixing device 60 for fixing the secondary transferred image on the paper P is provided. In addition, a control panel (not shown) that receives input from the user or the like regarding the number of sheets on which image formation is performed or the type of sheet on which image formation is performed, and a start button (not shown) that receives an instruction to start image formation from the user or the like And a control unit 40 that controls the operation of each device (each unit).

  In the present embodiment, the following electrophotographic devices are sequentially arranged in each of the image forming units 1Y, 1M, 1C, and 1K. First, a charger 12 for charging the photosensitive drums 11 is disposed around the photosensitive drums 11 rotating in the arrow A direction. Further, a laser exposure device 13 (an exposure beam is indicated by a symbol Bm in the drawing) for writing an electrostatic latent image on the photosensitive drum 11 is provided. Further, a developing device 14 is provided that stores toner of each color component and visualizes the electrostatic latent image on the photosensitive drum 11 with the toner. Further, a primary transfer roller 16 is provided for transferring each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15 by the primary transfer unit 10. A drum cleaner 17 for removing residual toner on the photosensitive drum 11 is also provided.

The primary transfer unit 10 includes a primary transfer roller 16 disposed to face the photosensitive drum 11 with the intermediate transfer belt 15 interposed therebetween.
The secondary transfer unit 20 includes a secondary transfer roller 22 disposed on the toner image holding surface side of the intermediate transfer belt 15 and a backup roller 25. The secondary transfer roller 22 is disposed in pressure contact with the backup roller 25 with the intermediate transfer belt 15 interposed therebetween.
The control unit 40 includes a CPU (Central Processing Unit) that controls the operation of each device (each unit), a ROM (Read Only Memory) that stores a program, and a RAM (Random Access Memory) that temporarily stores various data. Etc.

Next, a basic image forming process of the image forming apparatus according to the present embodiment will be described. In the image forming apparatus according to the present embodiment, image data is output from an image reading device (not shown) or the like. This image data is subjected to predetermined image processing by an image processing device (not shown), and converted into color material gradation data of four colors of Y (yellow), M (magenta), C (cyan), and K (black). And output to the laser exposure unit 13.
The laser exposure unit 13 irradiates the photosensitive drums 11 of the image forming units 1Y, 1M, 1C, and 1K, for example, with an exposure beam Bm emitted from a semiconductor laser in accordance with the input color material gradation data. After the surface of each photoconductive drum 11 is charged by the charger 12, the surface is scanned and exposed by the laser exposure unit 13 to form an electrostatic latent image.

The formed electrostatic latent images are developed as toner images of Y, M, C, and K colors by the developing devices 14 of the respective image forming units 1Y, 1M, 1C, and 1K.
On the other hand, the intermediate transfer belt 15 is circulated and driven at a predetermined speed in the direction of arrow B shown in FIG. 1 by various rollers such as a driving roller 31. The toner images formed on the photosensitive drums 11 are sequentially electrostatically attracted onto the intermediate transfer belt 15 in the primary transfer unit 10 where the photosensitive drums 11 and the intermediate transfer belt 15 come into contact with each other. A toner image superimposed thereon is formed. After the superimposed toner image is formed on the surface of the intermediate transfer belt 15, the intermediate transfer belt 15 moves and the toner image is conveyed to the secondary transfer unit 20. In the secondary transfer unit 20, the secondary transfer roller 22 is pressed against the backup roller 25 via the intermediate transfer belt 15. At this time, the sheet P conveyed by the conveying roller 52 and the like at the same timing is sandwiched between the intermediate transfer belt 15 and the secondary transfer roller 22 in the secondary transfer unit 20.

  In the secondary transfer unit 20, a secondary transfer bias is applied between the secondary transfer roller 22 and the backup roller 25, and a secondary transfer electric field is formed between both members. The unfixed toner image held on the intermediate transfer belt 15 is electrostatically transferred collectively onto the paper P in the secondary transfer unit 20. Thereafter, the sheet P on which the toner image has been electrostatically transferred is conveyed by the secondary transfer roller 22 to a conveyance belt 55 provided downstream of the secondary transfer roller 22 in the sheet conveyance direction. The transport belt 55 transports the paper P to the fixing device 60 at an optimal transport speed. In the fixing device 60, the paper P on which the toner image is transferred is heated and pressed, and the toner image is fixed on the paper P. Then, the sheet P that has been fixed is discharged outside the image forming apparatus.

Next, the fixing device 60 will be described.
FIG. 2 is a side sectional view showing a schematic configuration of the fixing device 60 to which the present invention is applied.
The fixing device 60 is disposed in pressure contact with the fixing roller 70 and forms a nip portion N that pressurizes and heats the sheet on which the toner image is held between the fixing roller 70. And a pressurizing module 80. The fixing device 60 includes a support housing (not shown) that supports the fixing roller 70 and the pressure module 80, and a drive source (not shown) that drives the fixing roller 70 to rotate.

  A fixing roller 70 as a fixing member is rotatably arranged with respect to the support housing. The fixing roller 70 includes a cylindrical core 72 made of aluminum or the like, an elastic layer 71 made of silicone rubber or the like provided around the cylindrical core 72, and the cylindrical core 72 and the elastic layer provided inside the cylindrical core 72. And a heater 73 such as a halogen lamp for heating 71 from the inside. Further, the fixing roller 70 includes a release layer (not shown) made of tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA) or the like on the outer peripheral surface of the elastic layer 71.

The pressure module 80 includes a support frame 81, a pressure pad 82, a first coil spring 83, a peeling pad 84, a second coil spring 85, and a pressure belt 86.
The support frame 81 is disposed inside the pressure belt 86 and is fixed to the support housing (not shown) so as to be disposed at a predetermined position of the fixing device 60. The support frame 81 includes an accommodating portion 81a having an opening on the side facing the fixing roller 70. The accommodating portion 81a accommodates the first coil spring 83 and the second coil spring 85. It has become. Further, the pressure part 82 and the peeling pad 84 are accommodated in the accommodating part 81a in a state where the tops are exposed.

  The pressure pad 82 (pressing member, other pressing member, first disposing member) is formed in a block shape that does not rotate itself, and the surface of the fixing roller 70 that contacts the elastic layer 71 is the elastic layer 71. The shape follows the outer surface. The pressure pad 82 is disposed inside the pressure belt 86 and has a function of forming a part of the nip portion N by pressing the elastic layer 71 via the pressure belt 86. Yes.

  The peeling pad 84 (pressing member, one pressing member, second disposing member) is provided on the downstream side in the rotation direction of the pressure belt 86 with respect to the pressure pad 82 and is disposed on the inner side of the pressure belt 86. The pressure belt 86 is pressed toward the fixing roller 70 to form a part of the nip portion N. Further, the peeling pad 84 is formed in a block shape that does not rotate itself, like the pressure pad 82.

Further, the peeling pad 84 has a function of peeling the paper adhering to the elastic layer 71 by melting the toner image from the elastic layer 71.
The peeling pad 84 is formed in an arc shape with a rounded surface pressed against the elastic layer 71. Then, the peeling pad 84 formed in such a shape is disposed in pressure contact so that the elastic layer 71 is indented inward.

  As a result, the paper introduced into the nip portion N causes micro-slip with the elastic layer 71 in a region where the peeling pad 84 and the elastic layer 71 are in pressure contact with each other via the pressure belt 86. Further, since the sheet moves along the arc-shaped portion of the peeling pad 84, the traveling direction of the sheet and the surface of the elastic layer 71 is different at the exit portion of the nip portion N. As a result, the sheet is peeled from the elastic layer 71 by passing through the pressure contact portion between the peeling pad 84 and the elastic layer 71.

  In the present embodiment, since the elastic layer 71 is recessed as described above in the vicinity of the outlet portion of the nip portion N, the unit pressure (when the peeling pad 84 presses the elastic layer 71 via the pressure belt 86 ( The pressure load per unit area) is larger than the unit pressure (pressure load per unit area) when the pressure pad 82 presses the elastic layer 71 via the pressure belt 86.

The first coil spring 83 as the first spring member is formed with a predetermined spring constant, and is disposed between the pressure pad 82 and the bottom surface of the accommodating portion 81a of the support frame 81, and pressurizes. The pad 82 is pressed toward the fixing roller 70.
The second coil spring 85 as the second spring member is formed with a predetermined spring constant, and is disposed between the peeling pad 84 and the bottom surface of the accommodating portion 81a of the support frame 81 for peeling. The pad 84 is pressed toward the fixing roller 70. In the present embodiment, the spring constant of the second coil spring 85 is smaller than the spring constant of the first coil spring 83.
Note that the pressure module 80 can also be pressed against the fixing roller 70 by a third coil spring 91 and a frame 92, as shown in FIG. At this time, the spring constant of the second coil spring 85 is set smaller than the spring constant of the third coil spring 91.

  The pressure belt 86 as a belt-like member is a flexible endless belt (endless belt). The pressure belt 86 has a three-layer structure, and is composed of a base layer made of polyimide or the like, an elastic layer made of silicone rubber or the like laminated on the surface side (outer peripheral surface side) of the base layer, and an elastic layer. And a surface layer (release layer) made of a fluororesin formed so as to cover the layer.

  In this embodiment, a part of the fixing device 60 is configured by the fixing roller 70. However, the fixing roller 70 may be configured to include, for example, a belt-shaped member. Further, in this embodiment, no member for stretching the pressure belt 86 is provided inside the pressure belt 86, but a member for stretching the pressure belt 86, such as a rotatable roller-shaped member. Can also be arranged. Further, a guide member for guiding the pressure belt 86 can be provided inside the pressure belt 86.

Next, the operation of the fixing device 60 will be described.
When fixing is performed by the fixing device 60, first, the sheet on which the toner image is held is conveyed to the nip portion N formed between the pressure module 80 and the elastic layer 71 by the conveyance belt 55 (see FIG. 1). be introduced. At this time, the fixing roller 70 rotates in the direction of arrow C in response to a driving force from a driving source (not shown). Further, the pressure belt 86 is rotated in the direction of arrow D following the fixing roller 70 as the fixing roller 70 rotates. Further, when fixing is performed, power is supplied to the heater 73 from a power supply unit (not shown), and the fixing roller 70 and the pressure belt 86 are adjusted to a predetermined temperature.

  In this state, the paper introduced into the nip N is first pressurized and heated in a region of the nip N where the elastic layer 71 and the pressure pad 82 are in pressure contact with each other via the pressure belt 86. Receive. Next, the sheet is pressurized and heated in a region of the nip N where the elastic layer 71 and the peeling pad 84 are in pressure contact with each other via the pressure belt 86. As a result, the toner image held on the paper is fixed to the paper. On the other hand, the sheet is peeled from the elastic layer 71 by being peeled by the peeling pad 84 in the vicinity of the exit portion in the nip portion N. Then, the sheet peeled from the elastic layer 71 is discharged out of the apparatus by a discharge guide (not shown) and a discharge roller (not shown), and the fixing process is completed.

  Note that the tip of the peeling pad 84 in this embodiment has an arc shape, and this tip shape is similar to the elastic layer 71 of the fixing roller 70 like the pressure pad 82. You can also. In such a case, even if the pressure pad 82 and the peeling pad 84 are retracted from the fixing roller 70, the size (distance) of the nip portion N is almost the same as that before the retracting, so that deterioration of the fixing property is avoided. can do.

  By the way, in the conventional fixing device, one in which the peeling pad 84 is disposed in a state where it cannot be retracted (retracted) from the fixing roller 70 has been proposed. In the case of such a fixing device, there is not much problem when a thin sheet is passed. However, when a thick sheet is passed, the sheet is strongly pressed against the elastic layer 71 and the pressure belt 86 and elastic. There is a possibility that scratches may occur at locations where the layer 71 and the pressure belt 86 are in contact with the edge portion (end portion) of the paper. If such a scratch occurs, when fixing a sheet on which a large image is formed later, the scratch and the image may come into contact with each other and an image defect such as uneven gloss may occur in the fixed image. is there.

  Therefore, in the present embodiment, a configuration in which the second coil spring 85 is provided between the peeling pad 84 and the support frame 81 so that the peeling pad 84 can be retracted from the elastic layer 71 of the fixing roller 70. In this configuration, the pressing force acting on the paper when the thick paper is passed is reduced as compared with the prior art. As a result, scratches are less likely to occur than in the past, and image defects such as uneven gloss are less likely to occur than in the past.

  Note that when the cardboard is passed, the peeling pad 84 is retracted, so there is a concern that the stripping performance is deteriorated. However, the cardboard itself has a certain degree of rigidity, and the elastic layer is formed by the so-called stiffness. 71 is easy to peel off. For this reason, even if it is set as the structure which retracts the peeling pad 84, peeling performance can be maintained. In the case of thin paper, the amount of retraction of the peeling pad 84 is small, and the relationship between the elastic layer 71 and the peeling pad 84 is almost the same as before (before retraction). Even the peeling performance is maintained.

In the present embodiment, the spring constant of the second coil spring 85 is made lower than the spring constant of the first coil spring 83 as described above.
By the way, it is possible to lower the spring constant of the second coil spring 85 and lower the spring constant of the first coil spring 83. However, if the spring constant of the first coil spring 83 is lowered, the nip pressure may be lowered and the fixing performance may be lowered. Therefore, in the present embodiment, the spring constant of the first coil spring 83 is made large enough to ensure the fixing performance, and the spring constant of the second coil spring 85 is made lower than that of the first coil spring 83. It is said. As a result, it is possible to suppress the generation of scratches on the elastic layer 71 and the like while maintaining the fixing performance.

-Second Embodiment-
Next, a second embodiment will be described.
FIG. 3 is a schematic configuration diagram showing the second embodiment. In addition, about the function similar to 1st Embodiment, the same code | symbol is used and the description is abbreviate | omitted here.
In the present embodiment, as shown in FIG. 3A, in addition to the fixing roller 70 and the pressure module 80, a moving module 90 is further provided.

Similar to the first embodiment, the pressure module 80 includes a support frame 81, a pressure pad 82, a first coil spring 83, a peeling pad 84, and a pressure belt 86.
In this embodiment, the support frame 81 is fixed to a support housing (not shown) of the fixing device 60 as in the first embodiment, but the peeling pad 84 is the first embodiment. Unlike the form, it is fixed to a frame 92 described later in the moving module 90.

The moving module 90 includes a third coil spring 91, a frame 92, a support shaft 93, and a driving module 94.
The third coil spring 91 is disposed between the main body side of the image forming apparatus and the frame 92, and has a function of pressing the frame 92 toward the fixing roller 70.
The frame 92 is rotatably supported by the support shaft 93 at one end, and is pressed by the third coil spring 91 at the other end. The frame 92 supports the peeling pad 84 between the one end and the other end.

The support shaft 93 is supported on the main body side of the image forming apparatus and supports the frame 92 rotatably.
The driving module 94 includes a motor M as a driving source, and a cam (not shown) that transmits the driving force generated by the motor M to the frame 92 and swings the frame 92 about the support shaft 93. . In the present embodiment, the motor M and the cam are exemplified as members constituting the drive module 94, but various drive sources and mechanisms that have been conventionally used can also be used.

  As a result, in this embodiment, the separation pad 84 is moved back and forth with respect to the fixing roller 70 by the moving module 90 (see arrow G in the figure). As described above, the support frame 81 that supports the pressure pad 82 is fixed to a support housing (not shown) of the fixing device 60. For this reason, even if the peeling pad 84 is advanced or retracted by the moving module 90, the position of the pressure pad 82 with respect to the fixing roller 70 remains unchanged.

In this embodiment, when a start button (not shown) is pressed, information from a user input on a control panel (not shown) is input to the control unit 40.
The control unit 40 to which information from the user is input grasps, for example, the thickness of the sheet on which fixing is performed, and determines whether or not this thickness exceeds a predetermined threshold. . When it is determined that the thickness exceeds a predetermined threshold value, a decision is made to retract the peeling pad 84 from the fixing roller 70, and the retracting amount is determined. Further, the control unit 40 can determine the save amount based on the paper type input by the user with reference to, for example, a memory in which a table in which the relationship between the paper type and the save amount is defined in advance is stored. Note that the control unit 40 can determine the retraction amount based on, for example, an output from a sensor that detects the thickness of a sheet provided in the image forming apparatus.

Next, the control unit 40 drives the motor M provided in the driving module 94 based on the determined retraction amount, thereby rotating the frame 92 by a predetermined amount around the support shaft 93. As a result, the peeling pad 84 follows the rotation of the frame 92 and moves to the position of the retraction amount determined by the control unit 40.
Thereafter, the control unit 40 causes each device or the like to execute an image forming operation or the like, and causes the fixing device 60 to perform a fixing process. Then, the sheet for which the fixing process has been completed by the fixing device 60 is discharged to the outside of the image forming apparatus.

In the present embodiment, as described above, the peeling pad 84 is positively moved according to information from the user or the like, and the position of the peeling pad 84 is controlled. As a result, it is possible to more reliably ensure the peeling performance when performing fixing processing on thin paper, and it is possible to more reliably suppress the occurrence of scratches when performing fixing processing on thick paper. .
In this embodiment, the peeling pad 84 can be advanced and retracted by using the frame 92, the support shaft 93, and the like. However, as shown in FIG. It is also possible to make it.

-Third embodiment-
Next, a third embodiment will be described.
FIG. 4 is a schematic configuration diagram illustrating the third embodiment.
In the fixing device 60 in the first embodiment and the second embodiment, the pressure pad 82 and the peeling pad 84 that do not rotate themselves are used, but the pressure pad 82 and the peeling pad 84 are as follows. It is also possible to adopt a configuration using a rotatable member as shown in FIG. It is also possible to provide a member for stretching the pressure belt 86 as shown below. Even with such a configuration, the same effects as those of the first embodiment can be obtained. Further, by using the driving module 94 shown in the second embodiment, the same effects as those of the second embodiment can be obtained. In addition, the same code | symbol is used about the function similar to 1st Embodiment and 2nd Embodiment, The description is abbreviate | omitted here.

For example, as shown in FIG. 4A, the peeling pad 84 can be configured by a rotatable roller member.
Further, for example, as shown in FIG. 4B, it is possible to provide a peeling roller 84 with a rotatable roller member and to provide a tension roller 87 for tensioning the pressure belt 86.
Furthermore, for example, as shown in FIG. 4C, both the pressure pad 82 and the peeling pad 84 can be constituted by a rotatable roller member.

1 is a schematic configuration diagram illustrating an image forming apparatus to which the present invention is applied. 1 is a side sectional view showing a schematic configuration of a fixing device to which the present invention is applied. It is the schematic block diagram which showed 2nd Embodiment. It is the schematic block diagram which showed 3rd Embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 40 ... Control part, 70 ... Fixing roller, 82 ... Pressure pad, 83 ... 1st coil spring, 84 ... Stripping pad, 85 ... 2nd coil spring, 86 ... Pressure belt, 90 ... Module for movement, N ... Nip part

Claims (9)

A fixing member disposed rotatably;
A belt-like member that is rotatably arranged on the fixing member and forms a nip portion between the fixing member and a recording material on which an image is held;
A plurality of pressing members provided on the inner side of the belt-shaped member and pressing the belt-shaped member with different unit pressures toward the nip portion;
One pressing member that presses the belt-shaped member with a unit pressure higher than that of the other pressing members among the plurality of pressing members can advance and retreat according to the thickness of the recording material passing through the nip portion. A fixing device. A first spring member that supports the other pressing member so as to be movable back and forth with respect to the nip portion;
A second spring member that supports the one pressing member so as to be movable back and forth with respect to the nip portion;
The fixing device according to claim 1, wherein a spring constant of the second spring member is smaller than a spring constant of the first spring member. The one pressing member presses the belt-shaped member at a predetermined position inside the belt-shaped member,
The fixing device according to claim 2, wherein the other pressing member presses the belt-like member on the upstream side in the rotation direction of the belt-like member with respect to the one pressing member. A fixing member disposed rotatably;
A belt-like member disposed rotatably;
A first disposing member disposed inside the belt-shaped member;
A first spring member that presses the first disposing member against the fixing member via the belt-shaped member;
A second disposing member disposed inside the belt-shaped member;
A second spring member having a spring constant different from that of the first spring member and pressing the second arrangement member against the fixing member via the belt-shaped member;
Including a fixing device. The second disposing member is disposed downstream of the first disposing member in the rotation direction of the belt-shaped member,
The fixing device according to claim 4, wherein a spring constant of the second spring member is smaller than a spring constant of the first spring member. A fixing member disposed rotatably;
A belt-like member that is rotatably arranged on the fixing member and forms a nip portion between the fixing member and a recording material on which an image is held;
A pressing member disposed inside the belt-shaped member and pressing the belt-shaped member toward the nip portion;
Grasping means for grasping the type of the recording material inserted into the nip portion;
Based on the type of recording material grasped by the grasping means, advance / retreat means for advancing / retreating the pressing member relative to the fixing member;
An image forming apparatus.   7. The advancing / retreating unit retreats the pressing member with respect to the fixing member when the thickness as the type of the recording material grasped by the grasping unit exceeds a predetermined threshold value. The image forming apparatus described. The pressing member includes a member for fixing the image held on the recording material to the recording material, and a member for peeling the recording material inserted through the nip portion from the fixing member or the belt-shaped member. Become
The image forming apparatus according to claim 6, wherein the advance / retreat unit moves the member for peeling off and forward.   The image forming apparatus according to claim 6, wherein the advancing / retreating unit advances and retracts the pressing member that presses the belt-shaped member with the highest unit pressure when a plurality of the pressing members are provided.

Images