JP2019159087A - Fixing device and image forming apparatus - Google Patents

Abstract

To avoid, when a belt with a low heat capacity is used as a fixing member, a situation in which the fixing member enters an excessive temperature rise state and a kink occurs, even when the fixing member is suddenly stopped due to a cause, such as jam.SOLUTION: A fixing device comprises: an endless belt having flexibility; a heat source that heats the belt; a pressure rotating body that is provided outside the belt and opposite to the belt; and a nip forming member that is provided inside the belt and forms a fixing nip between the belt and the pressure rotating body. The relative positional relationship between the belt and the heat source may be different between a state where the belt is heated by the heat source while being rotated and a state where the rotation of the belt and power supply to the heat source are stopped.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a fixing device and an image forming apparatus.

  For image forming apparatuses such as copiers, printers, facsimiles, or multifunction machines having at least two of these functions, there are strong market demands for energy saving and speedup. Among image forming devices, the fixing device consumes a lot of power and has a lot of room for energy saving.Therefore, various proposals have been made.For example, a thin endless belt with a low heat capacity and a metal heat that also serves as a support. There has been known a fixing device that can be directly heated without using a conductor and can obtain good fixability even when mounted on a high-production image forming apparatus. In such a fixing device, the pressure roller arranged on the outer peripheral side of the endless fixing belt and the nip forming member fixedly arranged inside the fixing belt (in the loop) are brought into pressure contact with each other via the fixing belt. A fixing nip is formed.

  On the other hand, in the image forming apparatus, recording materials of various sizes are used. In order to cope with recording materials of various sizes while realizing energy saving while securing productivity, the fixing belt / roller inside the fixing device In addition, a halogen heater having a high light distribution in the center so as to correspond to, for example, the A4 vertical paper width (210 mm) and a portion corresponding to the A4 vertical paper width in the A3 vertical paper width are excluded ( That is, a configuration including a halogen heater having a dense light distribution near the end (excluding the central 210 mm portion of the 297 mm width) is employed. In the case of a recording material of a small size, this fixing device performs fixing by turning on only a halogen heater having a dense light distribution in the center, and in the case of a recording material larger than a small size, turning on both halogen heaters. .

In such a fixing device, two halogen heaters are arranged in parallel, and there is a problem that the radiant heat of one halogen heater heats the other halogen heater. Therefore, for example, in Patent Document 1 and Patent Document 2, by disposing two halogen heaters on both sides sandwiched by a stay member having a reflector and a reflection portion, thermal interference between the plurality of halogen heaters heating each other is caused. A configuration to prevent is disclosed.
Further, Japanese Patent Application Laid-Open No. H10-228561 discloses a configuration in which a movable shielding member for increasing the heating width of the fixing belt is arranged between the heat source and the fixing belt in order to cope with a larger number of recording materials.

  However, since these fixing devices use a thin film-like low heat capacity belt as the fixing member, if the fixing member suddenly stops due to a jam or the like (the rotation of the fixing member stops), the power supply to the heat source is performed. Even if the operation is stopped, the fixing member may be overheated due to residual heat (residual heat) of the heat source. For this reason, plastic deformation (kink) that is recessed inward in the axially central portion of the fixing belt may occur.

  In the present invention, when a low heat capacity belt is used as a fixing member, even if the fixing member suddenly stops due to a jam or the like, the fixing member is overheated and a situation where a kink is generated is avoided. Objective.

  In order to achieve the above object, in the present invention, an endless belt having flexibility, a heat source for heating the belt, a pressure rotating body provided outside the belt and facing the belt, A fixing device provided inside the belt and having a nip forming member that forms a fixing nip between the belt and the pressure rotator, wherein the belt is heated by the heat source while rotating; The relative positional relationship between the belt and the heat source may be different between the rotation of the belt and the state where power supply to the heat source is stopped.

  According to the present invention, the relative positional relationship between the belt and the heat source differs between a state in which the belt is heated while being rotated and a state in which the rotation of the belt and power supply to the heat source are stopped. Therefore, when a low heat capacity belt is used as the fixing member, even if the fixing member suddenly stops due to a jam or the like, it is possible to avoid a situation in which the fixing member becomes overheated and kinks occur. .

1 is a schematic diagram illustrating an image forming apparatus according to an embodiment of the present invention. 1 is a schematic cross-sectional configuration diagram showing a basic embodiment of a fixing device. It is a perspective view which shows the basic composition of a nip formation unit. It is a perspective view which shows the structure of a nip formation unit and a halogen heater. It is a schematic diagram which shows arrangement | positioning of the heat-emitting part of two halogen heaters. FIG. 6A is a diagram showing the relative positional relationship of the halogen heater, the reflecting member, and the stay member, FIG. 6A is a sheet passing paper, FIG. 6B, FIG. 6C, FIG. It shows what has become a state. It is a perspective view which shows the structure of a nip formation unit and a halogen heater, and the arrangement | positioning location of two halogen heaters differs compared with the structure of FIG. FIG. 8 is a diagram showing the relative positional relationship between the halogen heater, the reflecting member, and the stay member, and the arrangement location of the two halogen heaters is different from the configuration of FIG. 6, and FIG. 8b, FIG. 8c, FIG. 8d, FIG. 8e, and FIG. 8f show the belt rotation and heating turned off, respectively. FIG. 9A illustrates an arrangement in which the central light distribution heater is on the upstream side in the belt rotation direction, and FIG. 9B illustrates an arrangement in which the end light distribution heater is on the upstream side in the belt rotation direction. .

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention. The image forming apparatus 1 is a color laser printer. In the center of the printer body, four image forming units 4Y, 4C, 4M, and 4K are provided side by side along the extending direction of the intermediate transfer belt 30. Yes. Each of the image forming units 4Y, 4C, 4M, and 4K stores developers of different colors of yellow (Y), cyan (C), magenta (M), and black (K) corresponding to the color separation components of the color image. Other than that, the configuration is the same.

  Specifically, each of the image forming units 4Y, 4C, 4M, and 4K constituting the image station includes a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and A developing device 7 that supplies toner to the surface of the photoreceptor 5 and a cleaning device 8 that cleans the surface of the photoreceptor 5 are provided. In FIG. 1, only the photoconductor 5, the charging device 6, the developing device 7, and the cleaning device 8 included in the black image forming unit 4 </ b> K are assigned color codes, and the other image forming units 4 </ b> Y, 4 </ b> C, and 4 </ b> M The reference numerals are omitted.

  Below the image forming units 4Y, 4C, 4M, and 4K, an exposure device 9 that exposes the surface of the photoreceptor 5 is disposed. The exposure device 9 includes a light source, a polygon mirror, an f-θ lens, a reflection mirror, and the like, and irradiates the surface of each photoconductor 5 with laser light based on image data.

  A transfer device 3 is disposed above the image forming units 4Y, 4C, 4M, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as a transfer body, four primary transfer rollers 31 as primary transfer means, and a secondary transfer roller 36 as secondary transfer means. Further, the transfer device 3 includes a secondary transfer backup roller 32, a cleaning backup roller 33, a tension roller 34, and a belt cleaning device 35.

  The intermediate transfer belt 30 is an endless belt and is stretched by a secondary transfer backup roller 32, a cleaning backup roller 33, and a tension roller 34. Here, when the secondary transfer backup roller 32 is driven to rotate, the intermediate transfer belt 30 runs (rotates) in the direction indicated by the arrow in the figure.

  Each of the four primary transfer rollers 31 sandwiches the intermediate transfer belt 30 with each photoconductor 5 to form a primary transfer nip. In addition, each primary transfer roller 31 is connected to a power source of a printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to each primary transfer roller 31. .

  The secondary transfer roller 36 sandwiches the intermediate transfer belt 30 with the secondary transfer backup roller 32 to form a secondary transfer nip. Similarly to the primary transfer roller 31, the secondary transfer roller 36 is also connected to the power source of the printer main body, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has come to be.

The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30.
A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2C, 2M, and 2K containing replenishing toner are detachably attached to the bottle container 2. As is well known, a replenishment path is provided between each toner bottle 2Y, 2C, 2M, 2K and each developing device 7, and each development from each toner bottle 2Y, 2C, 2M, 2K is performed via this replenishment path. The toner is supplied to the device 7.

  On the other hand, at the lower part of the printer main body, a paper feed tray 10 containing paper P as a recording material, a paper feed roller 11 for carrying out the paper P from the paper feed tray 10, and the like are provided. Here, the recording material includes, in addition to plain paper, thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet, and the like. Further, as is well known, a manual paper feed mechanism may be provided.

  In the printer main body, a transport path R is provided for discharging the paper P from the paper feed tray 10 through the secondary transfer nip to the outside of the apparatus. In the transport path R, a pair of registration rollers 12 serving as transport means for transporting the paper P to the secondary transfer nip is disposed upstream of the position of the secondary transfer roller 36 in the paper transport direction.

  Further, a fixing device 20 for fixing the unfixed image transferred onto the paper P is disposed downstream of the position of the secondary transfer roller 36 in the paper transport direction. Further, a pair of paper discharge rollers 13 for discharging the paper to the outside of the apparatus is provided downstream of the fixing device 20 in the paper conveyance direction of the conveyance path R. In addition, a paper discharge tray 14 for stocking paper discharged outside the apparatus is provided on the upper surface of the printer main body.

The basic operation of the printer having the above-described configuration is already well known, and a description thereof will be omitted for the sake of brevity.
FIG. 2 is a schematic cross-sectional configuration diagram showing a basic embodiment of the fixing device 20. The fixing device 20 includes an endless fixing belt 21 that is a thin and flexible cylindrical fixing member, and a pressure roller 22 that is a pressure rotating body that abuts from the outer peripheral side of the fixing belt 21. is doing. The fixing belt 21 is heated by the radiant heat of halogen heaters 23A and 23B (hereinafter also referred to as first halogen heater 23A and second halogen heater 23B) as a plurality of fixing heat sources disposed inside (in the loop). The As a heat source, a halogen heater representing a radiation type heat source is generally used, but an induction heating device, a resistance heating element, a carbon heater, or the like may be used.

  Further, a nip forming member 24 that forms a fixing nip N with the pressure roller 22 via the fixing belt 21 and a stay member 25 (support member) that supports the nip forming member 24 are arranged inside the fixing belt 21. Has been. The nip forming member 24 arranged across the width direction of the fixing belt 21 is fixedly supported by the stay member 25, thereby preventing the nip forming member 24 from being bent by the pressure from the pressure roller 22, A uniform nip width is obtained over the axial direction (longitudinal direction) of the pressure roller 22. The nip forming member 24 is a heat-resistant member having high mechanical strength and a heat-resistant temperature of 200 ° C. or more, particularly heat-resistant resins such as polyimide (PI) resin, polyether ether ketone (PEEK) resin, and reinforced them with glass fiber. Is made up of. This prevents deformation of the nip forming member 24 due to heat in the fixing temperature range, ensures a stable fixing nip state, and stabilizes the output image quality. The stay member 25 has its longitudinal ends fixed and held on a side plate of the fixing device 20 or a separately provided holder.

  A heat transfer assisting member 27, which is also referred to as a heat equalizing member that relieves the temperature gradient in the longitudinal direction of the fixing belt, is disposed so as to cover the surface of the nip forming member 24 that faces the inner peripheral surface of the belt. Heat is prevented from staying in the end region of the fixing belt 21 when the paper is passed, and the heat is positively moved in the width direction of the fixing belt 21, that is, in the longitudinal direction of the heat transfer auxiliary member 27. Eliminate temperature unevenness. Therefore, the heat transfer auxiliary member 27 is formed of a material having high thermal conductivity that enables heat transfer in a short time, such as copper or aluminum. In the depiction in FIG. 2, the surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is a surface that directly contacts the fixing belt 21 and is a nip forming surface that is formed flat. However, it may be a concave shape or other shapes. When the nip forming surface has a concave shape, the discharge direction at the front end of the sheet is closer to the pressure roller, the separation is improved, and jamming is suppressed.

  As is well known, a temperature sensor 29 for detecting the belt temperature is provided at an appropriate position on the outer peripheral side of the fixing belt 21, for example, upstream of the fixing nip in the belt rotation direction, and downstream of the fixing device 20 in the sheet conveyance direction. On the side, a separating member 40 for separating the paper P from the fixing belt 21 is disposed. Further, releasable pressure means for pressing the pressure roller 22 to the fixing belt 21 is also provided.

  In order to reduce the heat capacity, the endless fixing belt 21 which is thin like a film and has a small diameter is composed of a base material on the inner peripheral side formed of a metal material such as nickel or SUS, or a resin material such as polyimide, and a PFA. It is comprised by the mold release layer of the outer peripheral side formed with (tetrafluoroethylene perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), etc. An elastic layer formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluorine rubber may be interposed between the base material and the release layer. When the thickness of the elastic layer is about 100 μm, when the unfixed toner is crushed and fixed, minute irregularities on the belt surface can be absorbed by the elastic deformation of the elastic layer, and uneven gloss can be avoided. From the viewpoint of reducing the heat capacity, the fixing belt 21 is set to a thickness of 1 mm or less as a whole. The thicknesses of the base material, the elastic layer, and the release layer constituting the fixing belt 21 are set in a range of 20 to 50 μm, 100 to 300 μm, and 10 to 50 μm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is preferably 0.2 mm or less, and more preferably 0.16 mm or less and 0.02 mm or more. .

  The stay member 25 having a substantially L-shaped cross section and composed of a first member 25A and a second member 25B and having a T-shaped cross section as a whole has an upright portion 25a that stands upright on the side opposite to the fixing nip N side. The halogen heaters 23A and 23B as fixing heat sources are arranged so as to be separated by the standing portion 25a, and also function as a partition member. Reflecting members 28A and 28B are disposed between the stay member 25 and the halogen heaters 23A and 23B. Accordingly, the heating efficiency of the halogen heaters 23A and 23B with respect to the fixing belt 21 can be increased, and wasteful energy consumption due to the stay member 25 being heated by the radiant heat from the halogen heaters 23A and 23B can be suppressed. It should be noted that the halogen heaters 23A and 23B are arranged on the side plates of the fixing device 20 or separately provided holders so that the relative positions of the halogen heaters 23A and 23B can be changed relative to the reflecting members 28A and 28B and the stay member 25. It is held (the displacement will be described later).

  The pressure roller 22 includes a cored bar, an elastic layer made of foamable silicone rubber or fluororubber provided on the surface of the cored bar, and a release layer made of PFA, PTFE, etc. provided on the surface of the elastic layer. It is configured. As is well known, the elastic layer of the pressure roller 22 is crushed at a location where the pressure roller 22 is pressed against the fixing belt 21 by the spring of the pressure means and is in pressure contact with the fixing belt 21, thereby fixing the fixing nip having a predetermined width. N is formed. The pressure roller 22 is rotationally driven by a drive source such as a motor provided in the printer body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the fixing nip N, and the fixing belt 21 rotates with it. The fixing belt 21 is sandwiched and rotated at the fixing nip N, and travels while being guided by side plate flanges disposed at both ends except for the fixing nip N.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heat source such as a halogen heater may be disposed inside the pressure roller 22. The elastic layer may be solid rubber, but if there is no heat source inside the pressure roller, sponge rubber may be used. Sponge rubber is more preferable because heat insulation is enhanced and heat of the fixing belt 21 is less likely to be taken away.

  FIG. 3 is a perspective view showing a basic configuration of the nip forming unit. As shown in FIG. 3, the nip forming unit includes a nip forming member 24, a stay member 25, and a heat transfer assisting member 27. In the nip forming unit, the surface of the nip forming member 24 opposite to the fixing nip N side is integrated with the plane of the stay member 25 on the fixing nip N side. At this time, uneven shapes such as bosses and pins may be formed on the respective surfaces, and these may be fitted in a shape-constrained manner. The heat transfer assisting member 27 is fitted and integrated so as to cover the surface of the substantially rectangular parallelepiped nip forming member 24 facing the inner peripheral surface of the fixing belt 21. The heat transfer assisting member 27 and the nip forming member 24 may be integrated with each other by providing claws or the like, but an adhesive or the like may be used.

  The surface of the heat transfer assisting member 27 that faces the inner peripheral surface of the fixing belt 21 is configured as a belt sliding contact surface 27a. However, in terms of mechanical strength, the nip forming surface is substantially the addition of the nip forming member 24. The surface 24 a faces the pressure roller 22.

  FIG. 4 is a perspective view showing configurations of the nip forming unit and the halogen heater. As shown in FIG. 4 and as described above with reference to FIG. 2, the stay member 25 includes a first member 25 </ b> A and a second member 25 </ b> B having a substantially L-shaped section, and has a substantially T-shaped section. . Therefore, the rigidity is high and the nip forming member 24 can be prevented from being bent by the stress from the pressure roller 22. The stay members 25 (the first member 25 </ b> A and the second member 25 </ b> B) extend linearly in the longitudinal direction of the nip forming member 24 and are fixed to the nip forming member 24. Therefore, a good nip forming surface can be maintained over the entire longitudinal direction of the fixing nip N.

  On both sides of the upright portion 25a in the short direction, the first halogen heater 23A is disposed on the upstream side in the belt rotation direction, and the second halogen heater 23B is disposed on the downstream side in the belt rotation direction. That is, the first halogen heater 23A and the second halogen heater 23B are shielded from each other by the standing portion 25a. The cross-sectional shape of the stay member 25 is not limited to a substantially T shape. The halogen heaters 23A and 23B may be arranged so as to be partitioned from each other with the upright portion 25a interposed therebetween, and the first member 25A and the second member 25B may be curvedly extended in the longitudinal direction of the halogen heater. Further, the first member 25A and the second member 25B may be raised in an oblique direction with respect to the nip forming surface of the nip forming member 24.

  As can be seen from FIGS. 4 and 5, the first halogen heater 23A has a heat generating portion at the center in the longitudinal direction (a portion in which the filament is spirally wound, the light distribution is dense, and the heat generation amount is large). And the center range of the fixing belt 21 is heated to correspond to a small size paper such as A4 vertical size (central light distribution heater). On the other hand, the second halogen heater 23B has heat generating portions at both ends in the longitudinal direction, and heats the side region of the fixing belt 21 (end light distribution heater). For example, when passing a large size paper such as A3 vertical size, not only the first halogen heater 23A but also the second halogen heater 23B is lit to correspond to the large size paper. The halogen heaters 23 </ b> A and 23 </ b> B are configured to generate heat by being output controlled by a power supply unit provided in the printer body. The output control is performed on the belt surface by a temperature sensor 29 provided on the outer periphery of the fixing belt 21. This is performed based on the temperature detection result. By such heater output control, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature.

  In this way, the two halogen heaters 23A and 23B correspond to different sizes of paper. However, when different sizes of paper are used, the paper passing area is deprived of heat by the paper, while the non-paper passing area. In this embodiment, the heat transfer auxiliary member 27 made of a material having high heat conductivity is used to positively fix the fixing belt. The heat is transferred in the width direction 21, that is, in the longitudinal direction of the heat transfer auxiliary member 27, thereby eliminating the temperature non-uniformity in the longitudinal direction.

  However, since the heat transfer assisting member 27 is in sliding contact with the inner peripheral surface of the fixing belt 21, a friction coefficient is increased when a material having high thermal conductivity such as copper or aluminum is brought into sliding contact with the inner peripheral surface of the fixing belt 21 as it is. There are problems such as a large unit torque and a shortened device life. Therefore, it is also desirable that the belt sliding contact surface 27a (see FIG. 3) facing (contacting) the fixing belt 21 of the heat transfer assisting member 27 is smooth and subjected to a low friction process. Specifically, fluorine-based paint or coating such as PFA or PTFE is applied. Further, a sliding resistance is reduced by interposing a lubricant such as fluorine grease or silicone oil between the heat transfer assisting member 27 and the inner peripheral surface of the fixing belt 21.

  A characteristic configuration of the fixing device having the above basic configuration will be described below. This characteristic configuration is that the halogen heaters 23 </ b> A and 23 </ b> B and the reflecting members 28 </ b> A and 28 </ b> B that are heat sources can be displaced inside the fixing belt 21.

  When the fixing device is operated, the fixing belt 21 rotates and the halogen heater 23A (for small size paper) or the halogen heaters 23A and 23B (for large size paper) is turned on to heat the fixing belt 21. By doing so, paper can be passed (FIG. 6a). At this time, the halogen heaters 23A and 23B and the reflecting members 28A and 28B have a relative positional relationship with the best reflection efficiency.

  When the fixing operation is completed, that is, when the sheet passing is completed in the fixing device, the halogen heater is turned off and heating to the fixing belt 21 is stopped, and then the accompanying rotation of the fixing belt 21 is also stopped. By stopping the heating and the accompanying rotation step by step in this way, it is possible to prevent a situation in which the fixing belt is locally overheated and kinks are generated. However, when an abnormality such as a jam occurs and the image forming apparatus stops urgently, the rotation of the fixing belt 21 also immediately stops. In this case, even if the power supply to the halogen heater is stopped, the belt portion facing the halogen heater is heated by the residual heat of the halogen heater, and there is a possibility that a kink is generated in the fixing belt 21 which is thin in film and has a low heat capacity. . In order to avoid this, when the fixing belt 21 stops urgently, the halogen heaters 23A and 23B and the reflecting members 28A and 28B move inside the fixing belt 21.

  FIG. 6b shows a configuration in which only the halogen heaters 23A and 23B move with respect to the positional relationship of FIG. 6a. By changing the relative positional relationship between the inner surface of the fixing belt 21 and the heater so as to increase the distance between them, the heat transfer efficiency to the fixing belt 21 is lowered. In the case of an emergency stop during the passage of small size paper, the two halogen heaters 23A and 23B may be moved together, or only the lit central area heating halogen heater 23A may be moved. Good. The movement of the halogen heaters 23A and 23B is executed by a cam mechanism or a gear mechanism provided on a side plate of the fixing device 20 or a holder provided separately, but these mechanisms are well known and will not be described here.

  FIG. 6c shows a configuration in which the halogen heaters 23A and 23B and the reflecting members 28A and 28B move integrally with respect to the positional relationship of FIG. 6a. By increasing the distance between the inner surface of the fixing belt 21 and the heater, the heat transfer efficiency to the fixing belt 21 is reduced. Since the relative positional relationship between the heater and the reflecting member is not changed, the reflection efficiency does not change. The movement of the halogen heaters 23A, 23B and the reflecting members 28A, 28B are integrally executed by a cam mechanism or a gear mechanism. In FIG. 6c, the reflecting members 28A and 28B are separated from the stay member 25 during the paper passing, and are configured to move so as to contact the stay member 25 at the time of emergency stop. That is, there may be a configuration in which the stay member is in contact with or separated from.

  FIG. 6d also shows a configuration in which the halogen heaters 23A and 23B and the reflecting members 28A and 28B move integrally with respect to the positional relationship of FIG. 6a. By increasing the distance between the inner surface of the fixing belt and the heater, the heat transfer efficiency to the fixing belt 21 is reduced. Since the relative positional relationship between the heater and the reflecting member is not changed, the reflection efficiency does not change. Since the distance of the heater from the inner surface of the fixing belt is smaller than in the case of FIG. 6b, the heat transfer efficiency is not lowered. However, the heater and the reflecting member are moved together, so that the mechanism for this can be simplified.

  FIG. 6e shows a configuration in which the halogen heaters 23A and 23B and the reflecting members 28A and 28B move separately with respect to the positional relationship of FIG. 6a. The movement of the halogen heaters 23A and 23B and the reflecting members 28A and 28B is executed by the respective cam mechanisms and gear mechanisms. By increasing the distance between the inner surface of the fixing belt 21 and the heater, the heat transfer efficiency to the fixing belt 21 is reduced. Furthermore, the reflection efficiency is also lowered by changing the relative positional relationship between the heater and the reflecting member.

  FIG. 6f shows a configuration in which the halogen heaters 23A and 23B and the reflecting members 28A and 28B move separately with respect to the positional relationship of FIG. 6a. The reflection efficiency is lowered by changing the relative positional relationship between the heater and the reflection member. In order to greatly reduce the reflection efficiency, the halogen heaters 23A and 23B are moved so as to change the positional relationship with the reflecting members 28A and 28B, but the distance between the inner surface of the fixing belt 21 and the heater is constant.

  FIG. 7 is a perspective view showing the configuration of the nip forming unit and the halogen heater, and the arrangement location of the two halogen heaters is different from the configuration of FIG. That is, the second halogen heater 23B having heat generating portions at both ends in the longitudinal direction for heating the end range of the fixing belt 21 is arranged in the longitudinal direction to heat the central range of the fixing belt 21 on the upstream side in the belt rotation direction. A first halogen heater 23A having a heat generating portion at the center in the direction is disposed downstream in the belt rotation direction.

  Also in the fixing device having such a positional relationship, the halogen heaters 23 </ b> A and 23 </ b> B and the reflecting members 28 </ b> A and 28 </ b> B are displaced inside the fixing belt 21. The state is shown in FIG. FIGS. 8a, 8b, 8c, 8d, 8e, and 8f correspond to FIGS. 6a, 6b, 6c, 6d, 6e, and 6f, respectively. A description of the movement of the halogen heaters 23A and 23B and the reflecting members 28A and 28B will be given in FIG.

  Note that when the fixing belt in a stopped state is locally heated by the heater, only the belt portion facing the heat generating portion of the heater is heated, and the temperature distribution in the belt circumferential direction becomes non-uniform. Therefore, a difference in thermal expansion occurs between a portion of the fixing belt facing the heater (temperature rising portion) and a portion not facing the heater (non-temperature rising portion). As a result, the temperature rising portion tends to expand in the longitudinal direction (axial direction / belt width direction), but the non-temperature rising portion tends to be maintained. Even in the temperature rising portion heated by the heater, the heat is dissipated in the vicinity of the end portion in the longitudinal direction of the fixing belt, so that the temperature is lower than that in the central portion. For this reason, the center part in the longitudinal direction of the temperature rising portion of the fixing belt is most thermally expanded. Therefore, when heating in a part of the belt in the longitudinal direction, the temperature rising portion of the belt, particularly the central portion thereof, tends to expand greatly outward in the longitudinal direction, but the non-temperature rising portion, particularly the central portion thereof, is to be maintained. The central portion of the temperature rising portion cannot expand outward, and stress that dents inward occurs. As a result, plastic deformation (kink) may occur such that the central portion of the temperature rising portion of the fixing belt is recessed inward.

  From the above, it can be seen that in the configuration in which the stay member 25 is disposed between the two halogen heaters 23A and 23B, the heating method of the fixing belt 21, that is, the thermal expansion in the longitudinal direction differs depending on the heater arrangement. As shown in FIG. 9, the configuration (FIG. 9a; FIG. 4) in which the first halogen heater 23A, which is a central light distribution heater, is arranged on the upstream side in the belt rotation direction prevents thermal expansion in the longitudinal direction. Kink is likely to occur in the center. On the other hand, the configuration (FIG. 9b; FIG. 7) in which the second halogen heater 23B as the end light distribution heater is arranged on the upstream side in the belt rotation direction already has the belt end when the belt center is heated. Heated, the thermal expansion in the longitudinal direction is hardly hindered, and kinks are unlikely to occur at the center. That is, in the configuration in which the end light distribution heater is on the upstream side in the belt rotation direction and the central light distribution heater is on the downstream side in the belt rotation direction as shown in FIG. It can be said that a kink is less likely to occur than a configuration in which such a central light distribution heater is on the upstream side in the belt rotation direction and the end light distribution heater is on the downstream side in the belt rotation direction.

  The present invention has been described based on the embodiments. The present invention is not limited to the embodiments, and can be appropriately changed within the scope of the present invention. The image forming apparatus provided with the fixing device of the present invention is not limited to a copying machine or a printer, but may be a facsimile machine or a multifunction machine having a plurality of functions. In addition, various modifications can be made without departing from the scope of the present invention.

DESCRIPTION OF SYMBOLS 20 Fixing device 21 Fixing belt 22 Pressure roller 23A, 23B Halogen heater 24 Nip forming member 25 Stay member 25A 1st member 25B 2nd member 25a Standing part 27 Heat transfer auxiliary member 27a Nip forming surface 28A, 28B Reflective member 29 Temperature sensor N fixing nip P paper

JP 2017-10004 A JP 2017-167460 A JP 2014-222316 A

Claims (7)

An endless belt having flexibility, a heat source for heating the belt, a pressure rotating body provided outside the belt and facing the belt, provided inside the belt, the belt and the belt In a fixing device having a nip forming member that forms a fixing nip with a pressure rotating body,
The relative positional relationship between the belt and the heat source may be different between a state in which the belt is heated by the heat source while rotating and a state in which the rotation of the belt and power supply to the heat source are stopped. A fixing device. An endless belt having flexibility, a heat source for heating the belt, a pressure rotating body provided outside the belt and facing the belt, provided inside the belt, the belt and the belt In a fixing device having a nip forming member that forms a fixing nip with a pressure rotator, and a reflective member that faces the belt across the heat source,
The relative positional relationship between the heat source and the reflection member may be different between a state in which the belt is heated by the heat source while rotating and a state in which the rotation of the belt and power supply to the heat source are stopped. A fixing device characterized.   The fixing device according to claim 2, wherein the heat source is separated from the belt in a state where the rotation of the belt and the power supply to the heat source are stopped.   The heat source is composed of a heat source having a large calorific value at the center with respect to the end in the longitudinal direction and a heat source having a small calorific value at the center with respect to the end in the longitudinal direction. 2. A heat source having a large amount of heat generation is disposed on the downstream side in the rotation direction of the belt, and a heat source having a small heat generation amount at a central portion with respect to an end portion in the longitudinal direction is disposed on the upstream side in the rotation direction of the belt. Or the fixing device according to 2; An endless belt having flexibility, a heat source for heating the belt, a pressure rotating body provided outside the belt and facing the belt, provided inside the belt, the belt and the belt In a fixing device having a nip forming member that forms a fixing nip with a pressure rotating body,
The heat source is composed of a heat source having a large calorific value at the center with respect to the end in the longitudinal direction and a heat source having a small calorific value at the center with respect to the end in the longitudinal direction. A fixing device, wherein a heat source having a large amount of heat generation is disposed downstream in the rotation direction of the belt, and a heat source having a small heat generation amount at a central portion with respect to an end portion in the longitudinal direction is disposed upstream in the rotation direction of the belt.   The fixing device according to claim 1, further comprising a heat transfer auxiliary member that covers a surface of the nip forming member that faces the belt.   An image forming apparatus comprising the fixing device according to claim 1.

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