JP2013161029A - Fixing device and image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To control belt skew by a belt support member supporting a fixation member and prevent the ends of a belt from damaging to prolong the life span of the fixation member.SOLUTION: A fixing device 20 comprises a fixation belt 21 that is an endless belt rotating while heated by a halogen heater 23, a pressure roller 22 in contact with the outer peripheral surface of the fixation belt 21, a nip forming member 24 that is placed on the inner peripheral side of the fixation belt 21 and that contacts with a pressure roller 22 through the fixation belt 21 to form the nip part, flanges 26 having cylinder-shaped parts 28 supporting the posture of the fixation belt 21 from the inner peripheral surface side of the fixation belt 21 from both end sides to prescribed positions in the direction of the rotation axis of the fixation belt 21. The flanges 26 comprise ribs 29a having a shape in which the outer diameter of the cylinder-shaped parts 28 becomes larger from the center side to both end sides in the direction of the rotation axis of the fixation belt at the position corresponding to the upstream side of a nip part in the rotation direction of the fixation belt 21.

Description

  The present invention relates to a fixing device and an image forming apparatus. More specifically, the present invention relates to a fixing device that fixes a toner image formed on an image carrier onto a recording medium, and an image forming apparatus including the fixing device.

  Various image forming apparatuses using an electrophotographic system and an electrostatic recording system have been devised as image forming apparatuses such as a copying machine, a printer, a facsimile machine, and a composite machine thereof, and are well-known techniques. In the image forming process, an electrostatic latent image is formed on the surface of the photosensitive drum as an image carrier, and the electrostatic latent image on the photosensitive drum is developed with a toner as a developer to be visualized and developed. The image is formed by a process in which the transferred image is transferred onto a recording paper (also referred to as paper, recording material, or recording medium) by a transfer device to carry the image, and a toner image on the recording paper is fixed by a fixing device using pressure, heat, or the like. Yes.

  In the fixing device, a fixing member (fixing means) and a pressure member (pressure means) constituted by opposing rollers or belts or a combination thereof are arranged to contact each other to form a nip portion. The recording paper is sandwiched between the portions, and heat and pressure are applied to fix the toner image on the recording paper.

  For example, Patent Document 1 discloses a belt fixing type fixing device. For example, as shown in FIG. 10, such a belt fixing type fixing device includes a heating roller 74 having a heater 76 as a heat source, and a fixing belt 79 including a fixing roller 72 having a rubber layer on the surface layer. The transferred toner image is heated and pressed and fixed in the process of passing the recording paper P onto which the toner has been transferred through a nip portion (fixing nip portion) formed by the pressure roller 71 in contact with the fixing belt 79. Is.

  Patent Document 2 discloses a film heating type fixing device. For example, as shown in FIG. 11, such a film heating type fixing device has a heat resistant film (fixing film 84) between a ceramic heater 81 as a heating element and a pressure roller 71 as a pressure member. Is formed between the film 84 and the pressure roller 71 in the fixing nip portion, and the recording paper P to which toner has been transferred is interposed between the film 84 and the film 84 so as to be nipped and conveyed. The heat of the ceramic heater 81 is applied to the recording paper through the film 84 at the portion, and the unfixed toner image is fixed to the recording paper surface by heat and pressure with the applied pressure of the fixing nip portion.

  Such a film heating type fixing device can constitute an on-demand type device using a ceramic heater and a low heat capacity member as a film, and a ceramic heater as a heat source only when image forming of the image forming apparatus is executed. It is sufficient to energize the printer and heat it up to the specified fixing temperature. The waiting time from turning on the image forming apparatus to the image forming executable state is short (quick start), and the power consumption during standby is greatly increased. There are advantages such as small (power saving).

  Patent Document 3 discloses a pressure belt type fixing device. This fixing device is disposed with a rotatable heat-fixing roller whose surface is elastically deformed, an endless belt that can run while being in contact with the heat-fixing roller, and a non-rotating state inside the endless belt to heat-fix the endless belt A belt nip that allows the recording paper to pass between the endless belt and the heat fixing roller is provided between the endless belt and the heat fixing roller, and a pressure pad that elastically deforms the surface of the heat fixing roller is provided. By increasing the contact area between the recording paper and the roller, the heat conduction efficiency is greatly improved, energy consumption is reduced, and at the same time, miniaturization is realized.

  However, the film heating type fixing device as in Patent Document 2 has a problem of durability and a problem of belt temperature stability. In other words, the wear resistance due to the sliding of the ceramic heater that is the heat source and the inner surface of the belt is insufficient, and the surface that repeats continuous friction becomes rough and the frictional resistance increases when operated for a long time, and the running of the belt becomes unstable. There is a problem that a phenomenon such as an increase in driving torque of the fixing device occurs. As a result, there has been a problem that the recording paper forming the image slips and the image shifts, or the stress applied to the drive gear increases and the gear is damaged.

  In addition, since the belt is locally heated at the nip portion, the belt temperature becomes the coldest when the rotating belt returns to the nip entrance. There was a problem that it was easy.

  Further, in the pressure belt type fixing device as in Patent Document 3, since the heat capacity of the fixing roller is large and the temperature rise is slow, a warm-up operation (operation until the fixing operation temperature is reached and the sheet passing operation is started). There was a problem that it took a long time.

  As a technique for solving these problems, Patent Document 4 discloses that a pipe-shaped metal heat conductor is provided inside an endless belt (fixing belt) to guide the movement of the endless belt. A fixing device is disclosed in which an endless belt is heated via a metal heat conductor by a heat source provided in the conductor. This fixing device includes a pressure roller that forms a nip portion in contact with a metal heat conductor via an endless belt.

  In the fixing device described in Patent Document 4, the metal heat conductor diffuses heat, can apply uniform heat to the entire endless belt, can reduce the warm-up time, and can rotate at high speed. The lack of heat can be resolved.

  Further, Patent Document 5 discloses a fixing device that does not have a pipe-shaped metal heat conductor and can heat the inner peripheral surface of an endless belt (fixing belt) from a heat source such as a halogen heater. Has been. According to the fixing device described in Patent Document 5, it is possible to further shorten the warm-up time and improve the energy saving performance.

  By the way, when an endless fixing belt (film) is used as a fixing member in a belt heating type fixing device, a deviation of the fixing belt toward one side (hereinafter referred to as a belt) in the rotation axis direction (thrust direction) occurs. In some cases, it is known that it is difficult to strictly control such a belt shift.

  With regard to such belt deviation control, for example, in Patent Document 2, the fixing member is loosely suspended with respect to the guide member for guiding the fixing member, and the belt deviation force is reduced. An image heating apparatus is disclosed in which the end of the belt is received by an end portion restricting surface (hereinafter referred to as a restricting surface) of a flange that supports the fixing member to restrict the belt. Patent Document 6 discloses a heating device having a tapered shape so as to approach the belt end portion as the regulating surface is moved away from the nip portion.

  However, as in the technique described in the above-mentioned patent document, in a configuration in which the end of the fixing belt is restricted by the restriction surface of the flange, if the belt shifting force increases, the fixing belt may be folded depending on the film thickness, material, etc. , Wrinkles, cracks, etc. (also referred to as belt end breakage or belt tearing) may occur.

  When such a phenomenon occurs, there is a risk that a fixed image in the fixing device is deteriorated, a running failure of the fixing belt, a durability life of the fixing belt is decreased, and an abnormal noise is generated when the fixing belt is restricted. . Further, as the performance of the fixing device improves, the rotation speed of the fixing belt tends to increase and the belt shifting force tends to increase. Therefore, reducing the load on the belt end is an important issue.

  Here, the main factor generating the belt offset force is the parallelism accuracy of the nip constituting members (fixing member and pressure member) constituting the nip. If the nip components are free of parallelism deviation, belt deviation can be suppressed to some extent, but in reality, the occurrence of parallelism deviation is completely eliminated due to the accumulation of component errors and assembly variations. Is difficult. Even in a state where there is no deviation in parallelism, belt misalignment may occur due to driving of the fixing device.

  Conventionally, proposals have been made to prevent damage to the belt edge due to belt misalignment, but the parallelism of the nip components is fixed once assembled, so the parallelism shifts due to machine differences. A belt having a large belt has a large belt offset force, and there is a possibility that the end of the fixing belt may be damaged in less than the expected life, leaving room for examination.

  As a result of various investigations by the inventors of the present application, in a belt fixing device in which the nip constituent member is an upper and lower roller type such as a fixing roller and a pressure roller, the parallelism between the rollers constituting the nip affects the belt shifting force. However, there is no roller member on the fixing belt side, and a pressure fixing member (also referred to as a contact member or nip forming member) that supports the fixing belt from the belt inner surface side to the fixing belt inner surface of the nip portion facing the pressure roller. ) (Methods such as Patent Documents 4 and 5), it was found that the parallelism between the pressure roller and the fixing belt, rather than the pressure roller and the pressure fixing member, greatly affects the belt shifting force. Here, as a substitute characteristic of the belt shifting force, FIG. 9 shows a measured belt moving amount (shifting speed: μm / sec) per unit time. FIG. 9 shows that the parallelism of the nip component (fixing belt / pressure roller) and the belt shift speed have a strong correlation.

  Therefore, the present invention is a case where a belt shift occurs due to the influence of a parallelism shift between a fixing member that is an endless belt constituting a nip and a pressure member that contacts an outer peripheral surface of the fixing member. It is an object of the present invention to provide a fixing device capable of preventing the belt end portion from being damaged by regulating the belt by a belt supporting member that supports the fixing member, and an image forming apparatus including the fixing device.

  In order to achieve the above object, a fixing device according to the present invention includes a fixing member that is an endless belt that rotates while being heated by a heating unit, a pressure member that contacts an outer peripheral surface of the fixing member, and the fixing member. An abutting member that is disposed on the inner peripheral side of the fixing member and abuts with the pressure member via the fixing member to form a nip portion; A belt support member having a cylindrical portion that supports the posture of the fixing member from the inner peripheral surface side of the fixing member, and the belt support member is located upstream of the nip portion in the rotation direction of the fixing member. At a corresponding position, the cylindrical portion has a tapered portion having a shape in which the outer diameter increases from the center side to both end sides in the rotation axis direction of the fixing member.

  According to the present invention, it is possible to prevent the belt end portion from being damaged by regulating the belt shift by the belt support member that supports the fixing member, and it is possible to extend the life of the fixing member.

1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment. 1 is a schematic configuration diagram of a fixing device according to an exemplary embodiment. FIG. 3 is an arrow view of the fixing device from the direction of arrow A in FIG. 2. (A) Front view of flange, (B) An example of a side view seen from the nip portion direction. It is explanatory drawing about the relationship between a parallelism shift | offset | difference and a belt shift direction. It is explanatory drawing (1) of belt shift regulation by a flange. It is explanatory drawing (2) of the belt shift regulation by a flange. (A) The front view of a flange, (B) It is another example of the side view seen from the nip part direction. It is a graph which shows the relationship between the parallelism of a nip structural member, and a shift speed. 1 is a schematic configuration diagram of a belt fixing type fixing device. 1 is a schematic configuration diagram of a film heating type fixing device.

  Hereinafter, the configuration according to the present invention will be described in detail based on the embodiment shown in FIGS.

(Configuration / Operation of Image Forming Apparatus)
The configuration and operation of the entire image forming apparatus will be described with reference to FIG. The image forming apparatus shown in FIG. 1 is a color printer using a tandem system in which image forming units for forming a plurality of color images are juxtaposed along the belt extending direction. However, the present invention is not limited to this system. It is also possible to target not only printers but also copying machines and facsimile machines.

  The image forming apparatus 100 includes photosensitive drums 15Y, 15C, 15M, and 15Bk as image carriers that can form images as images corresponding to colors separated into yellow, cyan, magenta, and black, respectively. The installed tandem structure is adopted.

  The image forming apparatus 100 has an endless belt in which the visible images formed on the photosensitive drums 15Y, 15C, 15M, and 15Bk are movable in the direction of arrow A1 while facing the photosensitive drums 15Y, 15C, 15M, and 15Bk. A primary transfer process is performed on an intermediate transfer body 11 (hereinafter referred to as a transfer belt) 11 on which the image is used, and each image is superimposed and transferred. Batch transfer is performed by executing the process.

  Around each photosensitive drum, an apparatus for performing image formation processing is arranged according to the rotation of the photosensitive drum. When the photosensitive drum 15Bk that performs black image formation is described as an object, the rotation direction of the photosensitive drum 15Bk is described. A charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk that perform image forming processing are disposed along the line. For the writing performed after charging, the optical writing device 8 is used.

  In the superimposing transfer to the transfer belt 11, the visible image formed on each photosensitive drum 15 </ b> Y, 15 </ b> C, 15 </ b> M, 15 </ b> Bk is transferred to the same position on the transfer belt 11 while the transfer belt 11 moves in the A <b> 1 direction. As described above, voltage application by the primary transfer rollers 12Y, 12C, 12M, and 12Bk disposed to face the photosensitive drums 15Y, 15C, 15M, and 15Bk with the transfer belt 11 interposed therebetween causes the A1 direction upstream. The timing is shifted toward the downstream side.

  The photosensitive drums 15Y, 15C, 15M, and 15Bk are arranged in this order from the upstream side in the A1 direction. Each of the photosensitive drums 15Y, 15C, 15M, and 15Bk is provided in an image station for forming yellow, cyan, magenta, and black images.

  The image forming apparatus 100 is disposed so as to face four image stations that perform image forming processing for each color and above each of the photosensitive drums 15Y, 15C, 15M, and 15Bk, and the transfer belt 11 and the primary transfer roller 12Y. , 12C, 12M, and 12Bk, a secondary transfer roller 5 that is a transfer roller as a transfer member that is arranged to face the transfer belt 11 and is driven by the transfer belt 11 and rotated. An intermediate transfer belt cleaning device 13 disposed opposite to the transfer belt 11 for cleaning the transfer belt 11, and an optical writing device 8 serving as an optical writing device disposed below these four image stations. And have.

  The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, a rotating polygonal mirror as a deflecting means, and the like, and each photosensitive drum 15Y, 15C, 15M, Write light Lb corresponding to each color with respect to 15 Bk (in FIG. 1, for convenience, the reference is given only to the image station of the black image, but the same applies to the other image stations), and the photoconductor An electrostatic latent image is formed on the drums 15Y, 15C, 15M, and 15Bk.

  The image forming apparatus 100 includes a sheet feeding device 61 as a sheet feeding cassette on which recording sheets S transported between the photosensitive drums 15Y, 15C, 15M, and 15Bk and the transfer belt 11 are stacked, and a sheet feeding device. The transfer section between each of the photosensitive drums 15Y, 15C, 15M, and 15Bk and the transfer belt 11 is moved at a predetermined timing in accordance with the toner image formation timing of the recording medium P conveyed from the feeding device 61. A registration roller pair 4 that is fed out toward the registration roller 4 and a sensor (not shown) that detects that the leading edge of the recording paper S has reached the registration roller pair 4 are provided.

  The image forming apparatus 100 includes a fixing device 20 for fixing the toner image on the recording medium P to which the toner image has been transferred, and a paper discharge roller 7 for discharging the fixed recording medium P to the outside of the main body of the image forming apparatus 100. A paper discharge tray 17 that is disposed in the upper part of the main body of the image forming apparatus 100 and loads the recording medium P discharged to the outside of the main body of the image forming apparatus 100 by the discharge roller 7, and is positioned below the paper discharge tray 17. In addition, toner bottles 9Y, 9C, 9M, and 9Bk filled with yellow, cyan, magenta, and black toners are provided.

  In addition to the transfer belt 11 and primary transfer rollers 12Y, 12C, 12M, and 12Bk, the transfer belt unit 10 includes a drive roller 72 and a driven roller 73 around which the transfer belt 11 is wound.

  The driven roller 73 also has a function as a tension urging unit for the transfer belt 11. For this reason, the driven roller 73 is provided with an urging unit using a spring or the like. Such a transfer belt unit 10, the primary transfer rollers 12Y, 12C, 12M, and 12Bk, the secondary transfer roller 5, and the cleaning device 13 constitute a transfer device 71.

  The sheet feeding device 61 is disposed at the lower part of the main body of the image forming apparatus 100, and includes a feeding roller 3 as a feeding roller that contacts the upper surface of the uppermost recording medium P. 3 is rotated in the counterclockwise direction so that the uppermost recording medium P is fed toward the registration roller pair 4.

  Although not shown in detail, the cleaning device 13 provided in the transfer device 71 has a cleaning brush and a cleaning blade disposed so as to face and contact the transfer belt 11. The transfer belt 11 is cleaned by scraping and removing foreign matter such as residual toner on the top with a cleaning brush and a cleaning blade. Further, the cleaning device 13 has a discharge means (not shown) for carrying out and discarding the residual toner removed from the transfer belt 11.

(Configuration of fixing device)
Next, the configuration and operation of the fixing device 20 installed in the image forming apparatus 100 will be described in detail. As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a fixing member, a pressure roller 22 as a pressure member, a halogen heater 23 as a heat source (heating member), a nip forming member 24 as a contact member, A support member 25, a flange 26 as a belt support member, and the like are included. Moreover, FIG. 3 has shown the arrow view from the arrow A direction in FIG.

[Fixing belt]
The fixing belt 21 as a fixing member is a thin and flexible endless belt (or film), and rotates together with an external roller. In the example shown in FIG. 2, the pressure roller 22 is rotated by a driving unit (not shown), and the driving force is transmitted to the belt at the nip portion, whereby the fixing belt 21 is rotated. Hereinafter, the longitudinal direction of the fixing belt 21 is referred to as an axial direction (rotational axis direction), and the rotational direction (rotating direction) of the fixing belt 21 is referred to as a circumferential direction.

  The fixing belt 21 is formed by sequentially laminating an elastic layer and a release layer on a base material, and the entire thickness thereof is set to 1 mm or less, for example. The base material of the fixing belt 21 has a layer thickness of 30 to 50 μm, for example, and is formed of a metal material such as nickel or stainless steel or a resin material such as polyimide.

  The elastic layer of the fixing belt 21 has a layer thickness of, for example, 100 to 300 μm, and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber.

  The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm, such as PFA (tetrafluoroethylene bar fluoroalkyl vinyl ether copolymer resin), polyimide, polyetherimide, PES (polyether sulfide), and the like. Made of material. By providing the release layer, the releasability (peelability) for the toner image is secured.

  Here, the heat-resistant temperature of the silicone rubber layer is about 230 ° C., and when it exceeds this, oxidation starts. Further, the PFA layer and the PTFA layer have a temperature of about 250 ° C. If the temperature exceeds this, the curing of the rubber and the decrease in the PFA adhesive strength are accelerated, thereby causing deterioration.

  The diameter of the fixing belt 21 is set to 30 mm, for example. Inside the fixing belt 21 (inner peripheral surface side), a halogen heater 23, a nip forming member 24, a support member 25, and the like are fixed. The fixing belt 21 is pressed by the nip forming member 24 to form a nip portion with the pressure roller 22.

[Flange]
As shown in FIG. 3, the fixing device 20 holds the fixing belt 21 by inserting the cylindrical portion 28 of the flange 26 to a predetermined position from both ends in the axial direction to the inside of the fixing belt 21. The posture can be maintained. When the nip portion is pressurized, the nip portion is restrained between the nip forming member 24 and the pressure roller 22.

  The flange 26 includes a cylindrical part 28 having an opening corresponding to the nip part, a plate-like part 27 (regulating surface), and a rib 29a. The outer diameter of the cylindrical part 28 is smaller than the inner diameter of the fixing belt 21. The fixing belt 21 is stretched so that a slight gap is formed. The gap is preferably 1 mm or less. The rib 29a will be described later.

  In the present embodiment, since the nip forming member 24 is disposed at the nip portion, the cylindrical portion 28 of the flange 26 has an opening shape at a position corresponding to the nip portion. In addition, the “outer diameter” of the cylindrical portion 28 is an outer diameter (assuming a complete cylindrical shape) on the assumption that the cylindrical portion 28 is formed with the same curvature as the other portions in the opening shape portion. The outer diameter is also included. The plate-like portion 27 of the flange 26 is fixed to, for example, a side plate of the fixing device 20.

  When the fixing device 20 is not in operation, the flange 26 and the fixing belt 21 are circumferentially formed with the above space, but when in operation (when the belt is rotating), the nip upstream side (in FIGS. 2 and 3). The lower side is pulled in so that there is no gap, and the fixing belt 21 is conveyed along the outer diameter of the flange 26. On the other hand, on the downstream side of the nip (upper side in FIGS. 2 and 3), bending occurs and an outer diameter and a gap of the flange 26 are formed.

  That is, it can be said that the posture of the fixing belt 21 during belt rotation is held by the shape of the flange 26 on the nip upstream side.

[Nip forming member]
The nip forming member 24 is fixed to the inner peripheral surface side of the fixing belt 21 and abuts against the pressure roller 22 via the fixing belt 21 to form a nip portion. Further, both end portions in the axial direction are fixedly supported by side plates (not shown) of the fixing device 20. Note that it is preferable that the slidable contact surface of the nip forming portion 24 is formed of a material having a low friction coefficient so that the wear of the fixing belt 21 is reduced even if the nip forming member 24 and the fixing belt 21 are slidably contacted. Further, a sliding sheet may be provided between the nip forming member 24 and the inner peripheral surface of the fixing belt 21.

  The nip forming member 24 is preferably formed of a nonconductor, specifically, an insulating material such as a resin material, ceramic, or glass. Thereby, heat generation of the nip forming member 24 can be prevented due to the influence of the voltage applied to the halogen heater 23.

  In the example shown in FIG. 2, the shape of the nip portion is concave on the fixing belt 21 side, but may be a flat shape or other shapes. By making the shape of the nip part concave, the discharge direction of the leading edge of the recording paper P is closer to the pressure roller 22, improving the separation property and suppressing the occurrence of jam.

[Support member]
The support member 25 is provided to prevent the nip forming member 24 from being deformed. The support member 25 is formed of a metal material having high mechanical strength such as stainless steel or iron, and the support member 25 causes the nip forming member 24 to bend by receiving pressure from the pressure roller 22. (It is possible to prevent the central portion in the width direction from being greatly bent by the pressure applied to both ends in the width direction).

  In addition, when the support member 25 is heated by the radiant heat of the halogen heater 23 or the like, it is also preferable to heat-insulate or mirror-treat the surface. Thereby, excessive heating can be prevented and useless energy consumption can be suppressed.

[Halogen heater]
Both ends of the halogen heater 23 are fixed to side plates (not shown) of the fixing device 20, and the fixing belt 21 is heated by the radiant heat of the halogen heater 23 whose output is controlled by the power supply unit of the image forming apparatus 100. . Heat is applied to the toner image on the recording medium P from the surface of the heated fixing belt 21.

  The output control of the halogen heater 23 is controlled based on the detection result of the belt surface temperature by a temperature sensor (not shown) such as a thermistor facing the surface of the fixing belt 21, and thereby the temperature of the fixing belt 21 is desired. The temperature is controlled.

  In the example shown in FIG. 2, the halogen heater 23 is used as the heat source. However, the present invention is not limited to this, and an induction heating means (IH coil), a resistance heating element, a carbon heater, or the like may be used as the heat source. good.

[Pressure roller]
The pressure roller 22 as the pressure member has, for example, a diameter of 30 mm, and an elastic layer is formed on a hollow cored bar. The elastic layer of the pressure roller 22 is formed of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber. It is also preferable to provide a thin release layer made of PFA, PTFE or the like on the surface layer of the elastic layer. The pressure roller 22 is pressed against the fixing belt 21 by a spring or the like, and the rubber layer is crushed and deformed to form a predetermined nip width between the two members.

  Further, by forming the fixing belt 21 so that the diameter of the fixing belt 21 is smaller than the diameter of the pressure roller 22, the curvature of the fixing belt 21 at the nip portion is smaller than the curvature of the pressure roller 22. The sent recording medium P is easily separated from the fixing belt 21.

  The pressure roller 22 is rotated by a driving force transmitted from a driving unit such as a motor through a gear. Further, the pressure roller 22 may be a solid roller, but the hollow roller may have a smaller heat capacity. Further, a heat source such as a halogen heater may also be provided on the pressure roller 22 side. The temperature of the nip portion may be controlled by a temperature sensor provided on the pressure roller 22 side. If there is no heater inside the pressure roller, sponge rubber may be used. Sponge rubber is more desirable because it increases heat insulation and makes it difficult for heat of the fixing belt 21 to be taken away.

(Fixing device operation)
The operation of the fixing device 20 will be described. When the image forming apparatus 100 receives the output signal, the driving device (not shown) starts to operate, and the halogen heater 23 starts heating in synchronization therewith. It is not necessary to start the operation of the driving device and the heating of the halogen heater 23 at the same time. In consideration of the through-up of the driving motor and the response of the halogen heater 23, the rotation of the fixing belt 21 is started independently and the heating of the halogen heater 23 is performed. The start timing can be set.

  The driving force of the driving device is transmitted to the pressure roller 22 by a drive transmission device (not shown), and the pressure roller 22 starts to rotate. The rotational force of the pressure roller 22 is transmitted to the fixing belt 21 that is in contact therewith, and the fixing belt 21 starts to rotate. When the fixing belt 21 reaches a predetermined temperature, the recording medium P is fed and conveyed, and passes through the nip portion of the fixing device 20 so that heat and pressure are applied to fix the unfixed image on the recording medium P.

(Belt shift control)
The fixing device 20 according to the present embodiment includes a flange having a cylindrical portion 28 that supports the posture of the fixing belt 21 from the inner peripheral surface side of the fixing belt 21 from both ends in the axial direction of the fixing belt 21 to a predetermined position. 26 (belt support member), and the flange 26 has an outer diameter of the cylindrical portion 28 from the center side in the axial direction of the fixing belt 21 toward both ends at a position corresponding to the upstream side of the nip portion in the circumferential direction. It has a rib 29a (tapered portion) having a shape that becomes larger.

  FIG. 4 is a schematic configuration diagram showing an embodiment of the flange 26. 4A is a front view of the flange 26 provided on the far side in the axial direction in the fixing device 20 shown in FIG. 2 as viewed from the front side in the axial direction, and the cylindrical portion 28 is a position corresponding to the nip portion. Has an opening shape. FIG. 4B shows a side view when FIG. 4A is viewed from the nip portion side.

  Further, the flange 26 includes a rib (tapered portion) 29 a at a position corresponding to the upstream side of the nip portion of the cylindrical portion 28. The rib 29a may be provided on the upstream side of the nip and at a position where the fixing belt 21 slides along the outer periphery of the flange 26 (cylindrical portion 28) during rotation. It is most effective and preferable to change the parallelism of the fixing belt 21 at a position corresponding to a direction perpendicular to (90 °). In addition, it is preferable to increase the circumferential width of the rib 29a as much as possible because stress is not concentrated. Further, the cylindrical portion 28 and the rib 29a may be integrally molded, or may be separately molded and the rib 29a can be attached to the cylindrical portion 28.

  The fixing device 20 according to the present embodiment can prevent the fixing belt 21 from shifting in the axial direction by including the flange 26.

  First, the relationship between the parallelism shift and the belt shift direction will be described with reference to FIG. FIG. 5 is a front view of the fixing device 20 that feeds the recording medium P from the lower side to the upper side in the drawing as viewed from the pressure roller 22 side. Therefore, the pressure roller 22 is on the front side in the figure, and the fixing belt 21 is disposed on the back side so as to be opposed. FIG. 5 shows an example in which the pressure roller 22 is supported by the shaft 22a and is horizontal due to the accumulation of component errors, assembly variation, and the like, but the fixing belt 21 has a left-up parallelism shift. ing.

  During the operation of the fixing device 20 in which such a deviation in parallelism has occurred, the fixing belt 21 is moved to the left (the belt moving direction is left). On the other hand, in a state in which the fixing belt 21 causes a rightward shift in parallelism, the fixing belt 21 moves to the right during operation (the belt moving direction is right).

  Next, the shift control of the fixing belt 21 by the flange 26 will be described with reference to FIG. FIG. 6 shows an example in which the rib 29 a is formed outside the width in the axial direction of the fixing belt 21 when the fixing belt 21 is in a predetermined position. That is, in the fixing belt 21, the cylindrical portion 28 of the flange 26 is supported by a horizontal portion (a portion where the rib 29a is not formed).

  From this state, when the belt shift occurs in any direction as the fixing belt 21 rotates, the fixing belt 21 is applied to the rib 29a to correct the belt parallelism. In the example of FIG. 6, since the effect of only the shape of the one-side flange is achieved, the parallelism correction amount is suppressed. However, since the stress on the fixing belt 21 is reduced, the life is particularly improved in an apparatus with a small offset force. It becomes possible.

  On the other hand, as shown in FIG. 7, when the width of the rib 29 a of the flange 26 in the axial direction is increased and the fixing belt 21 is in a predetermined position, the rib 29 a is within the width of the fixing belt 21 in the axial direction. May be formed.

  From this state, when the belt shift occurs in either direction as the fixing belt 21 rotates, as shown in FIG. 7, when the fixing belt 21 moves to the left (arrow A), the flange 26 The left side of the fixing belt 21 can be lowered by the rib 29a (arrow B), and accordingly, the right side of the fixing belt 21 is raised (arrow C). As a result, the parallelism is corrected to generate a shifting force from the right (arrow D), and the shifting force to the left can be attenuated.

  It is also preferable to increase the height (inclination) of the ribs 29 a of the flange 26 so that the end of the fixing belt 21 does not abut against the restriction surface (plate-shaped portion 27) at the end of the flange 26. .

  In the fixing device 20 having the flange 26 described above, when the fixing belt 21 is moved to one side, the posture is restricted by the rib 29a of the flange 26, and the parallelism of the belt changes to become a reverse force in the reverse direction. Even when the flange 26 does not contact the plate-like portion 27, or even when it contacts, the contact force of the fixing belt 21 can be prevented from being damaged, so that the fixing belt 21 can be prevented from being damaged. Can be planned.

  Further, by forming the rib 29a outside the width in the axial direction of the fixing belt 21, when the fixing belt 21 is at the center position, the fixing belt 21 is formed at the horizontal portion of the flange 26 (cylindrical portion 28 without the rib 29a). By holding and restricting the belt by the rib 29a only when the shifting force is applied and the belt is shifted, damage to the end of the fixing belt 21 can be suitably prevented. Long life can be achieved.

  In addition, by configuring the outer diameter of the cylindrical portion 28 including the rib 29 a of the flange 26 to be smaller than the inner diameter of the fixing belt 21, even if the fixing belt 21 is offset and hits the rib 29 a of the flange 26, Since there is a gap on the inner peripheral surface of the fixing belt 21, the sliding load does not increase, damage to the end of the fixing belt 21 can be prevented, and the life of the fixing belt 21 can be extended.

  FIG. 8 shows another example of the flange 26, in which the rib 29b is formed in a step shape. 8A is a front view of the flange 26 provided on the far side in the axial direction in the fixing device 20 shown in FIG. 2, and FIG. 8B is a nip portion of FIG. 8A. The side view at the time of seeing from the side is shown.

  As shown in FIG. 8, since the rib 29b has a stepped shape, the parallelism of the fixing belt 21 can be changed more greatly. Therefore, the belt shift control is performed more effectively and the fixing is performed. The end portion of the belt 21 can be prevented from being damaged, and the life of the fixing belt 21 can be extended. Further, the sliding load can be further suppressed. In addition, as shown in FIG. 8, the step portion of the staircase may be made vertical to serve as a regulating surface, but the step portion of the staircase is preferably further tapered.

  By forming the image forming apparatus 100 (FIG. 1) including the fixing device 20 having the above-described configuration, image forming that realizes an improvement in the durability of the fixing belt 21 by reducing the shifting force of the fixing belt 21. An apparatus 100 can be provided.

  The above-described embodiment is a preferred embodiment of the present invention, but is not limited thereto, and various modifications can be made without departing from the gist of the present invention.

3 Feed roller 4 Registration roller pair 5 Secondary transfer roller 7 Paper discharge roller 8 Optical writing device 9Y, 9C, 9M, 9Bk Toner bottle 10 Transfer belt unit 11 Transfer belt (intermediate transfer member)
12Y, 12C, 12M, 12Bk Primary transfer roller 13 Intermediate transfer belt cleaning device 15Y, 15C, 15M, 15Bk Photosensitive drum 17 Discharge tray 20 Fixing device 21 Fixing belt 22 Pressure roller 23 Halogen heater 24 Nip forming member 25 Support Member 26 Flange 27 Plate-shaped portion 28 Cylindrical portion 29a, 29b Rib (tapered portion)
30Y, 30C, 30M, 30Bk Charging devices 40Y, 40C, 40M, 40Bk Developing devices 50Y, 50C, 50M, 50Bk Cleaning device 61 Sheet feeding device 72 Drive roller 73 Followed roller 71 Transfer device 100 Image forming device P Recording medium

JP 11-2982 A JP-A-4-44075 JP-A-10-213984 JP 2007-334205 A JP 2008-154822 A JP 2005-234294 A

Claims (7)

A fixing member that is an endless belt that rotates while being heated by a heating unit;
A pressure member in contact with the outer peripheral surface of the fixing member;
An abutting member disposed on an inner peripheral side of the fixing member and abutting the pressure member via the fixing member to form a nip portion;
A belt support member having a cylindrical portion that supports the posture of the fixing member from the inner peripheral surface side of the fixing member from both ends in the rotation axis direction of the fixing member to predetermined positions, respectively.
In the belt support member, the outer diameter of the cylindrical portion is directed from the center side to the both end sides in the rotation axis direction of the fixing member at a position corresponding to the upstream side of the nip portion in the rotation direction of the fixing member. A fixing device having a taper-shaped portion that increases in size.   The fixing device according to claim 1, wherein an outer diameter of the cylindrical portion including the tapered portion is smaller than an inner diameter of the fixing belt.   The fixing device according to claim 1, wherein the tapered portion is formed outside a width in a rotation axis direction of the fixing belt.   The taper-shaped portion is formed so that the outer diameter of the cylindrical-shaped portion increases stepwise from the center side to the both end sides in the rotation axis direction of the fixing member. The fixing device according to any one of 3 to 3.   The fixing device according to claim 1, wherein the cylindrical portion has an opening shape at a position corresponding to a nip portion in a rotation direction of the fixing member.   The taper-shaped portion is formed including a position corresponding to an upstream side of 90 ° from the center position of the nip portion in the rotation direction of the fixing member. The fixing device according to 1.   An image forming apparatus comprising the fixing device according to claim 1.