JP2005215601A - Belt-fixing apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a belt-fixing apparatus capable of surely separating a transfer paper, and also of preventing deterioration of a fixing belt. <P>SOLUTION: Regarding the belt fixing apparatus, provided with the fixing belt 15 stretched to be laid between a fixing roller 12 and a separation roller 14, and a pressure roller 17 which is brought into press contact with the fixing roller 12 via the fixing belt 15, and wherein an unfixed toner image 25 on the transfer paper 24 carried by the fixing belt 15, is heated and pressurized at a fixation nip part 18 formed by the fixing belt 15 and the pressure roller 17, a cam roller with a shaft 20 which is driven by a stepping motor, for forming a curved part, while pressurizing a part of the fixing belt 15 against outward from the inner peripheral side of the fixing belt 15 is arranged between the fixing roller 12, and the separation roller 14 inside the fixing belt 15, and an apex part 22a whose curvature is larger than that of the peripheral part of the separation roller 14 and which projects outside in a radial direction is arranged on the outer surface of the cam roller 20 with the shaft 20. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a belt fixing device applied to an image forming apparatus such as a copying machine, a printer, a facsimile, or a combination machine combining these.

  Conventionally, as a method for fixing an unfixed toner image formed on a transfer paper, a heat fixing method using heat and pressure is generally used. In the heat fixing method, a transfer paper having an unfixed toner image on its inner surface is sandwiched between fixing nips between a heating member and a pressure roller, and heat is applied to the unfixed toner to cause melting, and at the same time, contact surface pressure To fix the unfixed toner image on the transfer paper.

  The thermal fixing method has a problem that a so-called toner offset (hot offset) occurs in which the melted unfixed toner is transferred to the heating member when the fixing temperature is high. When the toner offset occurs, the transfer paper is stuck to the heating member, so that the transfer paper is not smoothly conveyed and a transfer paper jam occurs.

  There are various methods for separating the transfer paper in the fixing device. For example, the transfer paper is mechanically forcibly separated using a separation claw or a curved portion having a large curvature (small radius of curvature) is used. A method of separating by rigidity (waist) is widely known.

  In the fixing device using the mechanical separation method, the separation claw is brought into contact with the heating roller as a heating member at the timing when the transfer paper is conveyed (discharged) from the fixing nip portion, and at other times, the separation claw is removed from the heating roller. Some have been separated to suppress wear of the heating roller (Patent Document 1). The separation claw is rotatably supported around the support shaft in the vicinity of the periphery of the heating roller. One swinging end of the separation claw is connected with a spring imparted with a habit of pressing the claw tip against the peripheral surface of the heating roller, and the other swinging end is imparted with a habit of separating the claw tip from the heating roller. To be connected. The other end of the spring is locked by a slide member that slides with a pressure lever. The end of the pressure lever is displaced according to the thickness of the transfer paper, so that the separation claw is controlled so as to be in contact with and away from the heating roller.

In the fixing device using the curvature separation method, a convex deformed portion having a large curvature is formed at least at the exit end in the width direction of the fixing nip portion of the fixing roller and the pressure roller (Patent Document 2). Some fixing belts 33 spanned between a fixing roller 31 having a halogen heater 31a and a separation roller 32 have a curved portion 33a having a large curvature (FIG. 5). In FIG. 5, the sheet-like transfer paper 34 on which the unfixed toner image 35 is formed passes through a pressure contact portion formed by a fixing belt 33 and a pressure roller 36 that travels by the rotation of the fixing roller 31, and is transferred. An unfixed toner image 35 is fixed on the paper 34. Then, the transfer paper 34 that has passed through the pressure contact portion is separated in curvature by the curved portion 33 a of the fixing belt 33 that is in contact with the separation roller 32.
JP-A-4-291384 (page 3-4) JP 2000-206815 (page 4)

  However, the conventional fixing device has the following problems to be solved.

  In the first conventional fixing device, the separation claw is configured to be able to contact and separate from the heating roller so that the separation claw is not always in contact with the fixing belt. There is a problem that the nail marks cannot be completely removed as long as they come into contact.

  The conventional second fixing device has a problem in that wear on the fixing roller side having the elastic layer is accelerated because the pressure contact portion between the fixing roller and the pressure roller is always in contact with a constant contact surface pressure. In addition, the contact area at the press contact portion is increased, the load for driving the roller is increased, and there is a concern that the transfer paper cannot be smoothly conveyed.

  In the conventional third fixing device, if the radius of curvature of the separation roller 32 is decreased, the curvature of the fixing belt 33 is increased, so that the separation effect of the transfer paper 34 is enhanced. However, since the fixing belt 33 is bent slightly, the fixing belt is bent. There was a possibility that the deterioration of 33 was accelerated. Further, in the case of a color image, the amount of toner used is increased, and there is a concern that the transfer paper 34 cannot be separated by the separation roller 32 alone and transfer paper jam occurs.

  In view of the above, the present invention can reliably separate the recording material while smoothly running the fixing belt without applying an unnecessary load on the roller, and can prevent deterioration of the fixing belt. It is an object to provide a belt fixing device.

  In order to achieve the above object, the invention described in claim 1 comprises a fixing belt spanned between a fixing roller and a separation roller, and a pressure roller pressed against the fixing roller via the fixing belt. Then, the unfixed toner image formed on the sheet-like recording material conveyed by the fixing belt is heated and pressed at a fixing nip formed by the fixing belt and the pressure roller to be fixed on the recording material. In the belt fixing device, a shaft that is rotatably supported by a rotating shaft between the fixing roller and the separation roller on the downstream side of the fixing nip portion, and that forms a curved portion protruding outward from the fixing belt. It is characterized in that an attached piece member is provided.

  According to the above configuration, the sheet-like recording material on which the unfixed toner image is formed passes through the fixing nip portion formed by the fixing belt and the pressure roller that travels by the rotation of the fixing roller, and the unfixed toner image Is heated and pressed to be fixed on the recording material. Then, by rotating the shaft-mounted piece member supported by the rotation shaft, the inner surface of the fixing belt is pushed outward at the peripheral portion of the shaft-mounted piece member to form a curved portion. Since the inner surface of the fixing belt is pressed, it is possible to prevent the outer surface on which the unfixed toner image is fixed from being scratched. The recording material conveyed to the downstream side passes through the curved portion, rises in the direction away from the fixing belt while riding on the curved portion due to its own weight and rigidity, conveyed to the downstream side, and fixed before the separation roller. Separate the curvature from the belt.

  According to a second aspect of the present invention, in the belt fixing device according to the first aspect, the shaft-mounted piece member is provided with a top portion that has a larger curvature than the peripheral portion of the separation roller and protrudes radially outward. It is characterized by that.

  According to the above configuration, since the top portion with a large curvature is provided in the shaft piece member, when the piece member rotates, the top portion pushes the inner surface of the fixing belt outward, and the fixing belt has a curved portion with a large curvature. Will be formed.

  According to a third aspect of the present invention, in the belt fixing device according to the first or second aspect, a plurality of frames scattered in the width direction of the fixing belt are provided on the shaft of the shaft-mounted piece member. It is characterized by.

  According to the above configuration, the force pushing the fixing belt is distributed, unnecessary load is reduced, and the fixing belt runs smoothly without meandering or skewing.

  According to a fourth aspect of the present invention, in the belt fixing device according to the third aspect, the plurality of frames are provided at positions corresponding to a plurality of sizes of the recording material.

  According to the above configuration, by arranging the plurality of frames so as to correspond to the plurality of sizes of the recording material, it is possible to reliably separate even the recording materials of different sizes.

  According to a fifth aspect of the present invention, in the belt fixing device according to any one of the first to fourth aspects, the shaft-shaped piece member is rotated in synchronization with the conveyance timing of the recording material, and A drive control means for stopping the rotation of the piece member with the shaft is provided.

  According to the above configuration, the fixing belt is pushed in accordance with the conveyance timing of the recording material, and unnecessary contact between the frame member and the fixing belt can be prevented. The drive control means includes, for example, a controller that receives an input signal from a sensor that detects conveyance of the recording material and transmits a drive pulse, and a stepping motor as an actuator that is controlled by the drive pulse from the controller. You can apply what you have.

  According to a sixth aspect of the present invention, in the belt fixing device according to the fifth aspect, the rotation stop position of the piece with a shaft is a position where the piece and the fixing belt are not in contact with each other.

  According to the above configuration, the frame can be prevented from always contacting the fixing belt, and deterioration due to wear of the fixing belt can be suppressed.

  As described above, according to the first aspect of the invention, the recording material is lifted in the direction away from the fixing belt by the curved portion formed on the fixing belt. Therefore, the recording material that has been lifted by the separation roller can be reliably separated. In addition, deterioration of the fixing belt can be prevented.

  According to the second aspect of the present invention, since the top portion having a large curvature is provided on the piece member, when the piece member rotates together with the rotation shaft, the top portion pushes the inner surface of the fixing belt outward. Thus, a curved portion having a large curvature is formed on the fixing belt. Therefore, it is possible to provide a fixing device that has a simple configuration and excellent recording material separation without increasing the size of the fixing device.

  According to the third aspect of the invention, the fixing belt is partially pushed by the plurality of frames, the pushing force is dispersed, and conveyance failure due to skewing and meandering of the fixing belt is prevented.

  According to the fourth aspect of the present invention, even recording materials of different sizes can be reliably separated from the fixing belt, the application range of the recording material is expanded, and versatility is increased.

  According to the fifth aspect of the present invention, since the operation of pushing the fixing belt by the piece member can be performed in synchronization with the recording material conveyance timing, it is possible to avoid applying an unnecessary load to the fixing belt, Incorrect conveyance and deterioration of the fixing belt are prevented.

  According to the sixth aspect of the present invention, it is possible to prevent the frame from coming into contact with the fixing belt. Therefore, it is possible to prevent the fixing belt and the frame from being deteriorated and to improve the life of the fixing belt.

  Specific examples of embodiments of the present invention will be described below with reference to the drawings. 1 to 4 show an embodiment of a belt fixing device according to the present invention.

  The belt fixing device 10 is applied to a copying machine, a facsimile, a printer, or the like as an image forming apparatus. The image forming apparatus is an apparatus that forms an image on a transfer sheet 24 as a recording material by an image forming process including an electrostatic latent image forming process and a fixed image forming process.

  The belt fixing apparatus 10 according to the present embodiment can reliably separate the transfer paper 24 and can prevent the fixing belt 15 from being deteriorated. A cam roller with a shaft (a frame member with a shaft) that is driven by a stepping motor (not shown) downstream of the fixing nip portion 18 and forms a curved portion 15c when a part of the fixing belt 15 is pushed outward from the inner peripheral side. 20, and a top portion 22 a that has a larger curvature than the peripheral portion of the separation roller 14 and protrudes outward in the radial direction is provided on the outer surface of the cam 22 of the cam cam 20 with a shaft.

  Hereinafter, the schematic configuration and operation of the belt fixing device 10 will be described. As shown in FIG. 1, a belt fixing device 10 has a heating source in the center, a large-diameter fixing roller 12 that is rotationally driven, a small-diameter separation roller 14 that is driven to rotate and separates a transfer sheet 24, and a fixing An endless fixing belt 15 that is stretched around the roller 12 and the separation roller 14 and fixes the unfixed toner image 25 onto the transfer paper 24, is positioned opposite the fixing roller 12, and is interposed via the fixing belt 15. A pressure roller 17 pressed against the fixing roller 12 and a shaft-equipped cam roller 20 rotatably supported by a rotation shaft of a stepping motor are provided between the fixing roller 12 and the separation roller 14.

  The fixing roller 12 includes a hollow pipe-shaped metal core 12a having a reinforcing internal rib (not shown) and a halogen heater 12b as a heating source. Since the core metal 12a is formed to have an outer diameter of 30 mm and a barrel thickness of 0.4 mm, the rise time until the temperature is raised to a fixable temperature is fast. The cored bar 12a is heated by radiant heat from the halogen heater 12b, but a heating coil using an electromagnetic induction phenomenon can be used instead of the halogen heater 12b. The core metal 12a is made of an aluminum alloy having a good thermal conductivity, but is not limited to an aluminum alloy, and a copper alloy, stainless steel, or the like can also be made of a material having good thermal efficiency.

  The temperature of the fixing roller 12 is measured by a thermistor (not shown) as temperature detecting means, and the halogen heater 12b is on / off controlled by a controller (not shown) according to the measured temperature at that time. The temperature of the fixing roller 12 is controlled to about 160 ° C.

  A journal portion (not shown) of the fixing roller 12 that has been reduced in diameter by the drawing process by the squeezing roller is formed with a thickness of 1 mm or more in order to emphasize strength. The journal roller is driven by a motor (not shown) as a driving source, so that the fixing roller 12 rotates in the clockwise direction. The journal portion is elastically supported by a spring (not shown), and the fixing belt 15 spanned between the separation roller 14 and the fixing roller 12 is stretched with a tension of about 0.1 to 0.3 N (1 to 3 kgf). It is in a state. By fixing the fixing belt 15, the fixing belt 15 slips or loosens so that no meandering occurs.

  The fixing belt 15 is made of PI (polyimide) having high heat resistance (200 ° C. or higher) and excellent in flexibility, silicone rubber (rubber hardness is about 25 °) as an elastic layer, and fluorine resin as a release layer. It has a three-layer structure. Note that the present invention is not limited to such a three-layer structure, and a four-layer structure can be provided by providing an intermediate layer between the elastic layer and the release layer.

  The base is formed to a thickness of 50 to 90 μm, and the silicone rubber of the elastic layer is formed to a thickness of 200 to 300 μm. By using silicone rubber, variations in film thickness and non-uniformity in contact are absorbed, and the unfixed toner image 25 is fixed uniformly.

  The release layer is made of PTFE (tetrafluoroethylene resin), PFA (ethylene tetrafluoride / perfluoroalkyl vinyl ether copolymer resin), FEP (tetrafluoroethylene / hexafluoropropylene copolymer resin), etc. Or a mixture of these resins, or a resin in which these fluorine resins are dispersed in a heat resistant resin, is formed to a thickness of about 10 to 30 μm. If the release layer is too thick, the elasticity of the silicone rubber is lost and gloss unevenness is caused in the image, so that the dimensions are set.

  Since the fixing belt 15 is wound around the fixing roller 12 at a predetermined winding angle, heat is easily conducted. The larger the wrapping angle, the easier the heat is transmitted to the fixing belt 12, and the thermal efficiency is improved.

  The separation roller 14 is a roller that separates the transfer paper 24 by a curvature separation method, and is configured integrally with a roller main body 14a and journal portions 14b at both ends. The roller body 14a is formed to have a diameter of 8 mm or more in order to suppress deterioration due to deformation of the fixing belt 15. The outer peripheral surface of the roller body 14a is covered with silicone rubber as an elastic layer. In order to prevent the fixing belt 15 from coming off, both ends of the roller main body 14a are provided with a guide groove (not shown) and a non-illustrated stop ring (not shown) following the guide groove.

  The silicone rubber can be coated with a fluorine resin such as PFA. PFA has higher wear resistance than fluororubber, fluorolatex, and the like, and therefore prevents scratch marks on the roller portion 14a. Further, by using a conductive type PFA, the charge amount of the fixing belt 15 is reduced, and the separation of the transfer paper 24 is improved.

  The pressure roller 17 is composed of a roller body 17a and a journal portion 17b. The roller body 17 a is made of a metal having good thermal conductivity such as an aluminum alloy or iron, like the core 12 a of the fixing roller 12, and is formed with higher rigidity than the fixing roller 12. The roller body 17a is covered with silicone rubber having a thickness of about 1 mm, but the pressure applied to the fixing belt 15 is not lowered. The pressure roller 17 is biased in a direction to press the fixing belt 15 by a spring (not shown), and a fixing nip portion 18 that heats and presses the unfixed toner image 25 between the fixing belt 15 and the pressure roller 17 is provided. Is formed.

  The shaft-equipped cam roller 20 includes a plurality of cams 22 and a rotating shaft 21, and is disposed inside the fixing belt 15 on the downstream side of the fixing nip portion 18. The cam 22 is made of a hollow aluminum alloy in order to keep the heat capacity small. The rotating shaft 21 is supported by the rotating shaft of the stepping motor and can rotate independently without being affected by the separation roller 14 and the pressure roller 17. The rotating shaft 21 is formed to have a diameter of 3 mm or more and has a rigidity that does not bend by the force received from the fixing belt 15.

  On the outer surface of the cam 22, a top portion 22 a that protrudes radially outward and has a curvature larger than the curvature of the separation roller 14 is formed to protrude, and when the cam 22 rotates, the inner surface 15 b of the fixing belt 15 is pushed outward. A curved portion 15c having a large curvature is formed. The curved portion 15 c is not always formed on the fixing belt 15, but is formed in a timely manner in accordance with the transfer timing of the transfer paper 24.

  At the time of image formation, when the fixing roller 12 is driven to rotate in the clockwise direction, the separation roller 14 is driven to rotate in the clockwise direction, and accordingly, the fixing belt 15 is rotated in the clockwise direction. The fixing roller 12 is heated by the halogen heater 12b, and the fixing belt 15 wound around the fixing roller 12 is maintained at a temperature suitable for fixing the unfixed toner image 25 by this heat. The transfer sheet 24 supplied from the lower side of the fixing roller 12 is conveyed together with the fixing belt 15, and a fixing nip portion formed by the fixing belt 15 and the pressure roller 17 with the unfixed toner image 25 facing inward. 18 is passed. The unfixed toner receives heat from the fixing belt 15 and pressure from the fixing nip portion 18, whereby the toner is melted and a complete image is fixed on the transfer paper 24. When the transfer paper 24 is conveyed downstream, the stepping motor is driven to rotate the cam roller 20 with the shaft counterclockwise, and the fixing belt 15 is pushed outward by the top 22a of the cam 22 to fix the fixing belt. 15 is formed with a curved portion 15c having a large curvature. The transfer paper 24 rides on the curved portion 15c, and the transfer paper 24 is conveyed to the downstream side while being lifted from the fixing belt 15 by its own weight and rigidity, and the transfer paper 24 is surely separated by curvature by the separation roller 14. It is like that.

  Next, embodiments of each claim will be described in detail. FIG. 2 shows a state in which a plurality of cams (frames) 22 of the cam roller 20 with a shaft supported by the rotation shaft of the stepping motor are arranged in a balanced manner at equal intervals throughout the width direction of the fixing belt 15. And the features of the invention of claim 3 or 4 are indicated.

  By interposing a plurality of cams 22, the force for pushing the fixing belt 15 outward is dispersed, and the fixing belt 15 can be run in a stable state. Further, since the plurality of cams 22 are arranged in a balanced manner in the width direction of the fixing belt 15, the rotation of the fixing belt 15 becomes smooth, and the meandering and skewing of the fixing belt 15 are prevented. .

  The plurality of cams 22 are positioned so as to correspond to the ends of transfer papers 24a to 24b of different sizes. That is, the widths of the transfer papers 24a to 24b used vary depending on the specifications of the apparatus, but in order to ensure separation of the transfer papers 24a to 24b, the image forming range on the transfer papers 24a to 24b. The cam 22 is arranged so as to fit the end. Thereby, even in the case of transfer papers 24a to 24b of different sizes, it is possible to reliably separate them.

  The present invention is not limited to arranging the plurality of cams 22 at regular intervals. If the running stability of the fixing belt 15 is not impaired, the cams 22 are brought into close contact with the rotating shaft 21. Or a wide cam can be arranged. When the cams 22 are arranged in close contact with each other, the area of the curved portion 15c formed in the width direction of the fixing belt 15 is widened, and the separation property of the transfer paper 24 is improved. Also in this case, since the top portion 22a of the cam 22 contacts the fixing belt 15 in a timely manner, an increase in load or deterioration of the fixing belt 15 is suppressed.

  The schematic configuration of the belt fixing device 10 is as described above. The belt fixing device 10 is provided with a drive control means (not shown) to start / stop the cam roller 20 with the shaft in accordance with the transfer timing of the transfer paper 24. The configuration to be applied is a feature of the present invention described in claim 5 or 6.

  The drive control means includes a controller that receives an input signal from a sensor or the like that detects conveyance of the transfer paper 24 and transmits a drive pulse, and a stepping motor as an actuator that is controlled by the drive pulse from the controller. Things can be applied. By providing the drive control means, it is possible to avoid the cam 22 from constantly contacting the fixing belt 15 and to suppress deterioration due to wear or the like of the fixing belt 15.

  The origin (reference position) of the cam 22 in the rotation stopped state is set to a position where the top portion 22a does not contact the fixing belt 15 (FIG. 3). Since the top portion 22 a escapes from the fixing belt 15, unnecessary contact between the cam 22 and the fixing belt 15 is avoided.

  The cam 22 in the rotation stopped state rotates in accordance with the timing at which the transfer paper 24 that has passed through the fixing nip portion 18 is conveyed in front of the cam 22 (FIG. 4). The cam 22 rotates counterclockwise by a fixed rotation angle based on the drive pulse transmitted from the controller. The cam 22 is curved on the fixing belt 15 while the transfer paper 24 is running below the cam 22. The speed is controlled so that the portion 15c is formed.

  That is, the rotation speed of the cam 22 is determined by the relationship with the size of the transfer paper 24. The number of drive pulses is such that the cam 22 rotates faster when the transfer paper 24 size is small, and rotates slower when the transfer paper 24 size is large. The interval is set. It is also possible to change the rotational speed of the cam 22 depending on the material of the recording material. In this way, it is possible to respond to the strength of the adhesion between the recording material and the fixing belt 15 and to expand the application range of the belt fixing device 10.

  If the rotational speed of the cam 22 is slower than the transfer speed of the transfer paper 24, the number of the top portions 22a of the cam 22 is set to two or more to increase the number of contact between the cam 22 and the fixing belt 15, or fixing. It is also possible to provide two or more cam rollers 20 with shafts along the running direction of the belt 15.

  The material of the cam 22 is arbitrary, and is set in combination with the material of the fixing belt 15 to be used. In order to reduce the frictional force between the fixing belt 15 and the cam 22, it is also effective to cover the outer peripheral surface of the cam 22 with a low friction layer such as a fluororesin. The rotation direction of the cam 22 is also arbitrary, and when the belt fixing device 10 is small and the rotation torque of the stepping motor is small, the cam 22 is rotated in the same direction as the traveling direction of the fixing belt 15. Is also effective.

  As described above, according to the present embodiment, the fixing belt 15 is pushed outward by the cam 22, whereby the curved portion 15 c is formed on the fixing belt 15, and the transfer paper 24 rides on the curved portion 15 c and is fixed. The transfer paper 24 attached to the belt 15 is separated from the fixing belt 15 by its own weight and rigidity. By performing the operation of pushing the fixing belt 15 by the cam 22 in synchronization with the conveyance timing of the transfer paper 24, it is possible to avoid applying an unnecessary load to the fixing belt 15.

In addition, this invention is not limited to the said embodiment, In the range which does not deviate from the main point of this invention, it can deform | transform and implement as follows.
(1) The cam 22 of the shaft-equipped cam roller 20 that is pivotally supported by the rotation shaft of the stepping motor is changed to a ring having a circular cross section, and the rotation shaft 21 is moved in a predetermined manner so that the ring contacts and separates from the fixing belt 15. Rotate eccentrically with amplitude. According to this structure, when the ring comes into contact with the fixing belt 15, a curved portion having a large curvature is formed in the fixing belt 15, and the same effect as that of the second aspect of the invention can be achieved.

1 is a schematic configuration diagram of a belt fixing device according to the present invention. It is explanatory drawing which shows the cam roller with a shaft shown in FIG. It is explanatory drawing which similarly shows the rotation stop state of a cam roller with a shaft. It is explanatory drawing which similarly shows the rotation state of a cam roller with a shaft. It is a figure which shows an example of the conventional belt fixing device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Belt fixing device 12 Fixing roller 14 Separation roller 15 Fixing belt 15c Curved part 17 Pressure roller 18 Fixing nip part 20 Cam roller with shaft (frame member with shaft)
22 Cam
22a Top 24 Transfer paper (recording material)
25 Unfixed toner image

Claims (6)

A fixing belt spanned between a fixing roller and a separation roller; and a pressure roller pressed against the fixing roller via the fixing belt, and formed on a sheet-like recording material conveyed by the fixing belt. In a belt fixing device that heats and presses an unfixed toner image at a fixing nip formed by the fixing belt and the pressure roller, and fixes the image on the recording material.
A shaft-shaped piece member is provided on the downstream side of the fixing nip portion between the fixing roller and the separation roller so as to be rotatably supported by a rotation shaft and to form a curved portion protruding outward on the fixing belt. A belt fixing device.   The belt fixing device according to claim 1, wherein the shaft-mounted piece member is provided with a top portion that has a larger curvature than a peripheral portion of the separation roller and protrudes radially outward.   The belt fixing device according to claim 1, wherein a plurality of pieces that are scattered in a width direction of the fixing belt are provided on the shaft of the piece with the shaft.   4. The belt fixing device according to claim 3, wherein the plurality of frames are arranged so as to correspond to a plurality of sizes of the recording material.   5. A drive control means for rotating the shafted piece member in synchronization with the recording material transport timing and stopping the rotation of the shafted piece member. 2. A belt fixing device according to item 1.   6. The belt fixing device according to claim 5, wherein the rotation stop position of the piece with a shaft is a position where the piece and the fixing belt are not in contact with each other.

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