JP6682891B2 - Fixing device and image forming apparatus - Google Patents

Description

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

  An image forming apparatus such as a copying machine or a printer includes a fixing device including a heater, and various size sheets are used for image formation. For this reason, if the heater length of the fixing device is set to a length corresponding to the maximum size paper, the temperature rise at the edge of the non-paper passing part becomes large when the small size paper is passed. We need to slow down and reduce productivity. In order to deal with this problem, a first halogen heater having a dense light distribution in the central portion and a second halogen heater having a dense light distribution near the end portion are provided inside the fixing roller, and A fixing device is known in which only the first halogen heater is turned on when a sheet of a size is used.

  Further, although the frequency of use on the entire sheet is very low, there is a case where a special large size sheet such as an A3 flat sheet or 13 inches, which is slightly larger than the A3 size sheet, is used. Even if it is attempted to separately provide a halogen heater having a light distribution corresponding to such a large size sheet, there is a problem that it is difficult because the diameter size of the fixing roller based on the miniaturization is restricted.

  Therefore, a nip forming unit is provided inside a thin and flexible endless belt member that quickly rises to the fixing temperature, and a contact pressure is applied between the belt member, a pressure roller for pressing the belt member, and the nip forming unit. A fixing device that forms a nip is known (see, for example, "Patent Document 1"). In this fixing device, a plurality of halogen heaters having different light distributions are disposed inside the belt member, and a large size heater is provided at both ends in the width direction of the belt member and on the upstream side of the nip in the rotation direction of the belt member. The end heat source compatible with the paper is arranged so as to contact the inner surface or the outer surface of the belt member. By arranging this end heat source, it is possible to handle large-sized paper with a simple configuration without adding a halogen heater dedicated to large-sized paper.

In the configuration described in "Patent Document 1," since the end heat sources are arranged at positions corresponding to both ends of the belt member in the width direction, it is necessary to control the end heat sources at the same time. However, there is a problem that it becomes complicated. Therefore, by electrically connecting each end heat source in series and performing on / off control, electric control can be simplified as compared with a configuration in which each end heat source is individually on / off controlled, and a temperature sensor and a safety device are provided. Can be simplified. However, this configuration has a problem that fine temperature control is difficult and an image defect or high temperature abnormality occurs due to a temperature drop or an excessive temperature rise.
SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned problems and provide a fixing device capable of preventing image defects and high temperature abnormalities by performing fine temperature control.

According to the present invention, an endless belt member having flexibility, a pressure member arranged to face the belt member, and a nip formed by being pressed by the pressure member via the belt member. a nip forming member, and a second heat source for heating the first heat source for heating the axially central portion of the belt member, the axially outer side of the belt member than the first heat source, the second heat source a third heat source for heating the near both ends of the belt member a axially outer side of the belt member than a power supply for driving the respective heat source, the temperature of the axial position corresponding to the first heat source a first temperature detection means for detecting a second temperature detecting means for detecting the temperature of the axial position corresponding to the second heat source, the temperature of the axial position corresponding to the third heat source detection and a third temperature detecting means for, in the third heat source A first control mode so as not to drive, a and a second control mode for driving the second heat source and the third all the heat source connected in series with the heat source can be selected, the second control the drive control of the second heat source and the third heat source in the mode, have a control means for executing by feeding back the temperature information detected by said second temperature sensing means and said third temperature detecting means When the second control mode is selected, the control means starts sheet feeding when the third temperature detecting means reaches or exceeds a first predetermined temperature, and after the sheet feeding, the third temperature is passed. When the detection unit reaches a second predetermined temperature higher than the first predetermined temperature, the target temperature of the second temperature detection unit is lowered, and after the paper has passed, the third temperature detection unit sets the first temperature to the first predetermined temperature. When a third predetermined temperature lower than the predetermined temperature is reached, Characterized in that to raise the target temperature of the second temperature sensing means.

  According to the present invention, all the heat sources can be connected in series and simultaneously controlled when a large-sized sheet is passed, the control circuit and the temperature sensor can be simplified, and the third temperature detecting means can be used as the third temperature detecting means. By arranging at a position corresponding to the heat source and performing auxiliary monitoring, it is possible to reliably prevent the occurrence of image defects and high temperature abnormalities.

1 is a schematic diagram of an image forming apparatus to which an embodiment of the present invention can be applied. 1 is a schematic view of a fixing device used in an embodiment of the present invention. FIG. 3 is a schematic view in the vicinity of a nip portion of a fixing device used in an embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a support structure of a fixing belt used in an embodiment of the present invention. FIG. 3 is a schematic diagram showing a light distribution of a halogen heater and a positional relationship of end heaters used in an embodiment of the present invention. It is a schematic diagram showing a nip formation unit used for one embodiment of the present invention. FIG. 3 is a schematic diagram illustrating a contact state between an end heater and a nip forming member used in an embodiment of the present invention and a fixing belt. FIG. 7 is a schematic diagram illustrating another example of the contact state between the fixing heater and the end heater and the nip forming member used in the embodiment of the present invention. FIG. 7 is a schematic diagram illustrating still another example of the contact state between the fixing heater and the end heater and the nip forming member used in the embodiment of the present invention. 1 is a circuit configuration diagram of a halogen heater and an end heater to which an embodiment of the present invention is applied. It is a schematic diagram explaining the 1st, 2nd, and 3rd temperature sensing means used for one embodiment of the present invention. It is a block diagram of a control means used for one embodiment of the present invention. It is a diagram which shows the temperature control curve in one Embodiment of this invention. 6 is a flowchart illustrating an operation during sheet passing according to the embodiment of the present invention. It is a schematic diagram of an end heater used for one embodiment of the present invention. FIG. 3 is a diagram illustrating a positional relationship between a resistance heating element and a fixing belt used in an embodiment of the present invention. It is a figure which shows the nip formation unit used for other embodiment of this invention.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, before describing the present embodiment, the background of the proposal of the technique described in the above-mentioned "Patent Document 1" will be described. When the recording medium is small, the halogen heater with a dense light distribution in the center is turned on, and when it is large, the halogen heater with a dense light distribution near the edges is turned on together with appropriate on / off distribution. By doing so, various sizes of paper can be supported.

  Here, referring to the paper size and the frequency of use, most of the commonly used papers are up to A3 size, and A3 size papers are passed in the vertical direction. In particular, A4 or LT size paper, which is frequently used, is often passed in the lateral direction to improve productivity. Therefore, if the heating width of the fixing device is set to about 300 mm, 99% or more of recording media can be covered depending on the model in most cases. On the other hand, although the usage frequency for the whole is very low, it is required to support paper of a size larger than A3 width such as A3 flat or 13 inches.

  In the case of a heating method using a halogen heater, since a plurality of heaters corresponding to small-sized paper are provided inside the fixing roller having a diameter of about 30 mm, the number of heaters cannot be easily increased. For this reason, it is inevitable to lengthen the halogen heater having a dense end light distribution in accordance with the paper width larger than the A3 width. As described above, when considering the frequency of use, heating of about 300 mm width is overwhelmingly large, but when the above long halogen heater is used, it is heated up to around 330 mm width, and the energy consumption of the difference is wasted. . Furthermore, when passing A3 or A4 landscape (A4Y) size paper, the temperature near the edge of the 330 mm width rises, and it is necessary to reduce productivity or install a fan to cool it. It was When the reflection plate is provided, there is a problem that the temperature of the end of the heater is abnormally increased. The device described in Patent Document 1 has been proposed in order to deal with such a problem.

  Hereinafter, a first embodiment of the present invention capable of solving the above-mentioned problems of the conventional technology will be described. First, based on FIG. 1, an outline of the configuration of an image forming apparatus to which this embodiment is applicable will be described. The image forming apparatus 100 is a tandem type color printer in which image forming units that form a plurality of color images are arranged in parallel along the moving direction of the intermediate transfer belt.

  The image forming apparatus 100 includes a photosensitive drum 20Y as an image carrier capable of forming images corresponding to the colors separated into yellow (Y), cyan (C), magenta (M), and black (Bk). , 20C, 20M, 20Bk. The toner image as a visible image formed on each photoconductor drum 20 is superposed on the intermediate transfer belt 11 as an intermediate transfer body that is movable and movable in the direction of arrow A1 while facing each photoconductor drum 20 and is primary. Transcribed. After that, the sheets S as a recording medium are collectively transferred in a secondary transfer process. Around the photosensitive drums 20, devices for performing image forming processing according to the rotation of the photosensitive drums 20 are arranged.

  An apparatus for performing an image forming process will be described on behalf of the photoconductor drum 20Bk that forms a black image. Around the photosensitive drum 20Bk, a charging device 30Bk for performing image forming processing, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk are sequentially arranged along the rotation direction of the photosensitive drum 20Bk. After charging by the charging device 30Bk, the optical writing device 8 performs optical writing on the surface of the photosensitive drum 20Bk based on image information to form an electrostatic latent image. The electrostatic latent image is visualized as a toner image by the developing device 40Bk.

  The toner images formed on the respective photoconductor drums 20 are primarily transferred to the same position on the intermediate transfer belt 11 in an overlapping manner while the intermediate transfer belt 11 moves in the A1 direction. This primary transfer shifts the timing from the upstream side to the downstream side in the A1 direction by the voltage application by the primary transfer rollers 12 arranged to face the photoconductor drums 20 with the intermediate transfer belt 11 interposed therebetween. Is done. The photoconductor drums 20Y, 20C, 20M, and 20Bk are arranged in this color order from the upstream side in the moving direction of the intermediate transfer belt 11. The photoconductor drums 20Y, 20C, 20M, and 20Bk are provided in the image stations for forming yellow, cyan, magenta, and black images, respectively.

  The image forming apparatus 100 is arranged to face four image stations for performing image forming processing for each color and above the respective photoconductor drums 20, and the intermediate transfer belt 11 and the respective primary transfer rollers 12Y, 12C, 12M. , 12Bk, and the intermediate transfer belt unit 10. Further, the image forming apparatus 100 has a secondary transfer roller 5 as a secondary transfer unit that is disposed so as to face the intermediate transfer belt 11 and rotates along with the intermediate transfer belt 11. The image forming apparatus 100 also includes an intermediate transfer belt cleaning device 13 that is disposed so as to face the intermediate transfer belt 11 and cleans the intermediate transfer belt 11. The optical writing device 8 is arranged below the four image stations so as to face them.

  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, and a rotating polygon mirror as a deflecting means. The optical writing device 8 emits writing light Lb corresponding to each color to each photoconductor drum 20, and forms an electrostatic latent image on each photoconductor drum 20. In FIG. 1, for convenience, only the image station of the black image is targeted, and the reference light Lb is attached to the writing light, but the same applies to other image stations.

  Below the image forming apparatus 100, a sheet feeding device 61 is provided as a paper feeding cassette on which the sheets S conveyed toward the space between the photosensitive drums 20 and the intermediate transfer belt 11 are stacked. The sheet S conveyed from the sheet feeding device 61 is transferred between the intermediate transfer belt 11 and the secondary transfer roller 5 by the registration roller pair 4 at a predetermined timing corresponding to the toner image formation timing of the image station. It is fed toward the secondary transfer portion. The arrival of the leading edge of the sheet S at the registration roller pair 4 is detected by a sensor (not shown).

  The sheet S on which the toner image has been transferred is sent to the fixing device 150, where heat and pressure are applied to fix the toner image on the sheet S. The fixed paper S is ejected by the paper ejection roller pair 7 onto the upper surface of the image forming apparatus main body as a paper ejection tray. Below the upper surface of the main body of the image forming apparatus, toner bottles 9Y, 9C, 9M, and 9Bk filled with toners of yellow, cyan, magenta, and black are provided.

The intermediate transfer belt unit 10 includes, in addition to the intermediate transfer belt 11 and each primary transfer roller 12, a drive roller 72 and a driven roller 73 around which the intermediate transfer belt 11 is wound. The driven roller 73 also has a function as a tension applying means for the intermediate transfer belt 11, and therefore the driven roller 73 is provided with a biasing means using a spring or the like. The intermediate transfer belt unit 10, each primary transfer roller 12, the secondary transfer roller 5, and the intermediate transfer belt cleaning device 13 constitute a transfer device 71.
The sheet feeding device 61 has the feeding roller 3 that comes into contact with the upper surface of the uppermost sheet S, and the uppermost sheet S is moved by rotating the feeding roller 3 counterclockwise. The sheet is fed toward the registration roller pair 4.

  The intermediate transfer belt cleaning device 13 provided in the transfer device 71 has a cleaning brush and a cleaning blade that are arranged so as to face and contact the intermediate transfer belt 11. The intermediate transfer belt cleaning device 13 removes foreign matter such as residual toner on the intermediate transfer belt 11 by scraping it with a cleaning brush and a cleaning blade. The intermediate transfer belt cleaning device 13 also has a discharge unit (not shown) for carrying out and discarding the residual toner removed from the intermediate transfer belt 11.

  As shown in FIG. 2, the fixing device 150 includes a fixing belt 80 as a thin and flexible endless belt member, and a pressure roller 84 as a pressure member that is disposed so as to face the fixing belt 80. have. Inside the fixing belt 80, a nip forming unit 86 is provided between the fixing belt 80 and the pressure roller 84 to form a nip portion N that holds and conveys the sheet S as a recording medium. . The nip forming unit 86 is arranged inside the fixing belt 80 so as to face the pressure roller 84, and a stay member that holds the nip forming member 88 against the pressure applied from the pressure roller 84. 90 and. The nip forming member 88 slides on the inner surface of the fixing belt 80 via a low friction sheet as a sliding sheet. Further, sliding torque can be reduced by applying a lubricant such as fluorine grease or silicone oil to the sliding sheet. Further, the nip forming member 88 may directly contact the inner surface of the fixing belt 80.

  The stay member 90 has a box shape having an opening on the side opposite to the nip portion N side. Inside the stay member 90, a halogen heater 82a as a first heat source and a halogen heater 82b as a second heat source are arranged. There is. The fixing belt 80 is directly heated by radiant heat from the inner surface side by the halogen heaters 82a and 82b on the opening side of the stay member 90. In order to increase the heating efficiency of the halogen heaters 82a and 82b, a plate-shaped reflecting member 94 that reflects the light emitted from the halogen heaters 82a and 82b to the fixing belt 80 is provided on the inner surface of the stay member 90. The reflecting member 94 is provided to suppress unnecessary energy consumption due to the stay member 90 being heated by the radiant heat from the halogen heaters 82a and 82b. The same effect can be obtained by performing heat insulation or mirror surface treatment on the inner surface of the stay member 90 instead of the reflecting member 94.

  As shown in FIG. 3, the pressure roller 84 has a hollow metal roller 84a provided with a silicone rubber layer 84b. In order to obtain releasability, a release layer made of PFA (perfluoroalkoxy fluororesin) or PTFE (polytetrafluoroethylene) and having a layer thickness of 5 to 50 μm is provided on the surface of the rubber layer 84b. The pressure roller 84 rotates by receiving a driving force from a driving source such as a motor provided in the image forming apparatus 100 via a gear. Further, the pressure roller 84 is pressed toward the fixing belt 80 by a spring or the like, and the rubber layer 84b is crushed and deformed, so that a predetermined nip width Nw is formed in the paper transport direction. The pressure roller 84 may be a solid roller, but a hollow roller is preferable because it has a small heat capacity. The pressure roller 84 may have a heating source such as a halogen heater inside. The rubber layer 84b may be solid rubber, but sponge rubber may be used when there is no heater inside the pressure roller. The sponge rubber is more preferable because the heat insulating property is improved and the heat of the fixing belt 80 is less likely to be taken away.

  The fixing belt 80 is a metal belt such as nickel or SUS having a layer thickness of 30 to 50 μm, an endless belt using a resin material such as polyimide, or a film. The surface layer of the belt has a releasing layer such as a PFA or PTFE layer and has a releasing property so that the toner does not adhere thereto. An elastic layer formed of a silicone rubber layer or the like may be provided between the base material of the belt and the PFA or PTFE layer. If there is no silicone rubber layer, the heat capacity will be smaller and the fixability will be improved.However, when the unfixed image is crushed and fixed, the subtle unevenness of the belt surface is transferred to the image and uneven fixing (glossy) occurs on the solid part of the image. This causes a problem that unevenness) remains.

  In order to improve the above problems, it is necessary to provide a silicone rubber layer of 100 μm or more. As a result, the silicone rubber layer is deformed to absorb subtle unevenness, thus improving fixing unevenness. The fixing belt 80 is rotated by contact friction with the rotation of the pressure roller 84. Although the fixing belt 80 is sandwiched and rotated by the nip portion N, both ends of the fixing belt 80 are held in a cylindrical shape except the nip portion N, so that the cross-sectional shape of the fixing belt 80 is stably maintained in a circular shape. As shown in FIG. 2, a separating member 32 for separating the sheet S from the fixing belt 80 is provided on the downstream side of the nip portion N in the sheet conveying direction.

  In the present embodiment, as shown in FIGS. 1 and 3, the shape of the nip portion N is flat, but it may be a concave shape that is convex on the fixing belt 80 side when viewed from the pressure roller 84 side or another shape. It may be. With respect to the shape of the nip portion N, the concave shape causes the discharge direction of the leading end of the paper to be closer to the pressure roller 84, and the separability is improved, so that the occurrence of jam is suppressed. In this case, the nip forming surface of the nip forming member 88 is formed in a concave shape. In this case, contact between the end heaters 112a and 112b, which is a third heat source to be described later and is provided integrally with the nip forming member 88. The surface may also have a shape along the nip forming surface.

  By the function of the stay member 90, the bending of the nip forming member 88 that receives pressure from the pressure roller 84 can be prevented, and a uniform nip width can be obtained in the axial direction. In the present embodiment, the pressure roller 84 is pressed toward the fixing belt 80 to form the nip portion N, but the nip forming unit 86 is pressed toward the pressure roller 84 side to form the nip portion N. May be The stay member 90 has sufficient flexural strength to support the nip forming member 88. Examples of the material include metal materials such as stainless steel and iron, metal oxides such as ceramics, and the like.

  As shown in FIG. 4, the fixing belt 80 is rotatably supported on both end sides in the axial direction by flanges 36 as supporting members projecting from the side plates 34 in the axial direction. Although FIG. 4 shows the supporting structure on one side in the axial direction of the fixing belt 80, the other side has the same structure. The flanges 36 that guide both ends of the fixing belt 80 have an outer diameter that is substantially equal to the inner diameter of the fixing belt 80, and have a length that is 5 to 10 mm inward from both ends of the fixing belt 80. The fixing belt 80 is guided by the flange 36, so that the cross-sectional shape of the fixing belt 80 is maintained to be circular even during traveling (while rotating). A portion of the flange 36 corresponding to the nip portion N is opened to dispose the nip forming unit 86 at a predetermined position. The stay member 90 has a length extending over the entire axial direction of the fixing belt 80, and both sides thereof are fixed to the side plates 34 and supported in a positioned state.

  As shown in FIG. 5, the halogen heater 82a is a halogen heater corresponding to a small size sheet S having a dense light distribution in the central portion in the longitudinal direction which is the axial direction of the fixing belt 80. The halogen heater 82b is a halogen heater corresponding to the sheet S of A3 size or the like in which the light distributions at both ends in the same longitudinal direction are dense. When the paper S is of a small size, only the halogen heater 28a is turned on to prevent unnecessary heating of the non-paper passing portion.

  The difference between the width of the A3 size and the width of the A4Y in which the A4 size is set sideways and the A3 novi (329 mm) and 13 inches (330 mm) is 32 to 33 mm. Therefore, if only the both ends of the fixing belt 80 in the axial direction are heated, if the both ends can be heated by the width of 16 to 16.5 mm, which is the above-mentioned half, as shown in FIG. It is possible to widen the width corresponding to the paper such as obi. In other words, if it is possible to heat the portions of the halogen heater 82b where the light distribution is not dense at both ends, it is possible to handle large-sized paper S such as A3 non-woven paper. Therefore, as the end heaters 112a and 112b used as the third heat source which is the end heat source, it is sufficient to use a small heater having an axial length of about 20 mm.

  When passing a large-sized sheet S such as A3 flat or 13 inch, the halogen heaters 82a and 82b and the end heaters 112a and 112b are energized. When passing a sheet of A3 size or smaller, only the halogen heaters 82a and 82b or the halogen heater 82a is energized, and the end heaters 112a and 112b are not energized. When the halogen heater 82b has a heating structure capable of handling a large-sized sheet S such as A3 paper, even if the large-sized sheet S is not fed, that portion is heated and wasteful energy is consumed. become. According to the configuration of the present embodiment, the above problem can be solved by adding a simple configuration in which the end heaters 112a and 112b are added to both ends of the fixing belt 80 or in the vicinity of both ends.

  Further, in the present embodiment, both the end heaters 112a and 112b may have PTC characteristics. If it has PTC characteristics, the resistance value increases at a set temperature or higher, so that the temperature does not rise above the set temperature, and it is possible to realize a safe fixing device without fear of burning or belt damage. Further, in this embodiment, since the end heaters 112a and 112b are provided inside the fixing belt 80, the belt end can be heated from the inside without hindering the traveling movement of the fixing belt 80. Further, by forming the belt contact surfaces of the end heaters 112a and 112b by another member made of a smooth material, it is possible to reduce sliding resistance and stabilize belt running.

  As shown in FIG. 6, on the side surface 90 a of the stay member 90 on the pressure roller 84 side, two protrusions 90 b and 90 c extending in the longitudinal direction of the fixing belt 80 are formed. The rectangular parallelepiped nip forming member 88 is housed and positioned between the protrusions 90b and 90c, and is fixed to the side surface 90a by means such as adhesion. Recesses 88a and 88b as stepped portions are formed at both ends of the nip forming member 88 in the longitudinal direction, and end heaters 112a and 112b are housed in these recesses and fixed by means such as bonding. The surface of the nip forming member 88 facing the pressure roller 84 forms a nip forming surface 88c.

  As shown in FIG. 7A, the surfaces of the end heaters 112a and 112b contacting the inner surface of the fixing belt 80 and the nip forming surface 88c are in the arrow F direction (the direction of the drag force) that is the direction of pushing the inner surface of the fixing belt 80. ) Are configured to have the same height. In other words, the surfaces of the end heaters 112a and 112b that come into contact with the inner surface of the fixing belt 80 are configured to be extension surfaces of the nip forming surface 88c in the longitudinal direction. In the present embodiment, since the end heaters 112a and 112b are integrally provided with the nip forming member 88 necessary for forming the nip, the end heaters 112a and 112b are provided inside the fixing belt 80. It can be arranged and space can be saved.

  Further, since the surfaces of the end heaters 112a and 112b, which come into contact with the inner surface of the fixing belt 80, and the nip forming surface 88c are located at the same height (on the same plane), a sufficient pressure force by the pressure roller 84 is applied to the fixing belt. 80 between the end heaters 112a and 112b. As a result, the belt running can be realized in a state where the fixing belt 80 and the end heaters 112a and 112b are in close contact with each other, and the good heating efficiency of the end heaters 112a and 112b can be maintained by improving the heat transfer property. Further, since the heating portion for the fixing belt 80 by the end heaters 112a and 112b exists in the nip region, there is a problem of re-melting of untransferred toner due to heating at a portion different from the nip portion N as in Patent Document 1. Does not occur. Further, since the pressure roller 84 also serves as the urging means for bringing the end heaters 112a, 112b and the fixing belt 80 into close contact with each other in order to improve the heat transfer property, there is no need to press only the end heaters 112a, 112b. Therefore, the configuration can be simplified compared to the conventional one. In other words, since the end heaters 112a and 112b and the fixing belt 80 are brought into close contact with each other by utilizing the pressure applied to form the nip portion N, the traveling property and the heat transfer in the configuration disclosed in Patent Document 1 are performed. The problem of trade-off with defects does not occur.

  In the present embodiment, the shape of the recess formed in the nip forming member 88 is such that the end in the axial direction is open, but as shown in FIG. 7B, the recesses 88a and 88b surrounded on all sides are formed. Good. Further, the front and rear in the axial direction may be closed and both sides orthogonal to the axial direction may be opened.

  Further, as shown in FIG. 8, the end heaters 112a and 112b may be supported by the elastic member 38 in the recesses 88a and 88b. As shown in FIG. 8A, the surfaces of the end heaters 112a and 112b, which come into contact with the inner surface of the fixing belt 80, and the nip forming surface 88c have the same height when the pressure roller 84 does not apply pressure. Not in However, as shown in FIG. 8B, when the nip portion N is formed by the pressure applied by the pressure roller 84, the elastic member 38 is deformed and comes into contact with the inner surface of the fixing belt 80. , 112b have the same height as the nip forming surface 88c. As the elastic member 38, a rubber material or a spring can be adopted.

  As described above, since the end heaters 112a and 112b are fixedly positioned on the nip forming member 88 which is a separate member, the contact surfaces of the end heaters 112a and 112b with respect to the inner surface of the fixing belt 80 and the nip forming surface 88c are fixed. There is a possibility that the height and the height may shift during the assembling stage. Even in such a case, if the end heaters 112a and 112b are supported by the elastic member 38, a manufacturing error can be absorbed and the surface height can be made the same when forming the nip.

  In this embodiment, the end heaters 112a and 112b are integrally provided in the nip forming unit 86, but the present invention is not limited to this. As shown in FIG. 9, the end heaters 112 a and 112 b may be provided in the nip region independently of the nip forming unit 86. For example, it is possible to adopt a configuration in which the support members 42a and 42b fixed to the side plate 34 are fixed. Also in this case, the surfaces of the end heaters 112a and 112b, which come into contact with the inner surface of the fixing belt 80, and the nip forming surface 88c are set at the same height. Also in this example, the end heaters 112a and 112b may be displaced by the elastic member 38.

  In addition, in the present embodiment, the stay member 90 and the halogen heaters 82a and 82b are integrally provided as the nip forming unit 86, but a single piece including the nip forming member 88 and the end heaters 112a and 112b is integrally formed. It is a nip forming unit according to the invention.

  When a heater having a PTC characteristic is used as the end heaters 112a and 112b, it usually takes a longer heating time than a halogen heater. For this reason, if the end heaters 112a, 112b and the halogen heaters 82a, 82b are heated at the same timing, only the inner side of the central portion is heated first, resulting in wasted energy consumption. Further, when heat is taken away by passing the paper, the end heaters 112a and 112b require a longer heating time to return to the target temperature than the halogen heaters 82a and 82b due to the characteristics of PTC.

Therefore, by reducing the productivity according to the heating cycle of the end heaters 112a and 112b to cope with the heating cycle, it becomes possible to perform heating control without temperature variation between the central portion and the end portions. That is, when the end heaters 112a and 112b for heating both ends or the vicinity of both ends of the fixing belt 80 are used, the halogen heaters 82a and 82b corresponding to other normal size papers are heated and controlled according to the temperature rise of the ends. To do. As a result, when the amount of heat generated by the end heaters 112a and 112b is low, only the heater heating unit corresponding to the normal size paper is heated first, and it is possible to prevent energy from being consumed more than necessary. In addition, the transport speed when transporting the paper S of a size that uses the end heaters 112a and 112b is set to be slower than the transport speed of the paper S of other sizes. By thus reducing the productivity of the large-sized paper S which is rarely used, the heaters at both ends (the end heaters 112a and 112b) can be simplified and the cost can be reduced, and the efficiency can be improved.
In the present embodiment, a configuration having two halogen heaters as a heat source for fixing is shown, but the present invention is not limited to this, and a configuration having three or more halogen heaters for small size paper may be used.

  The electrical connection configuration of the halogen heaters 82a and 82b and the end heaters 112a and 112b in each of the above embodiments is shown in FIG. 10 as a first embodiment. In the circuit shown in FIG. 10, the halogen heaters 82a, 82b and the end heaters 112a, 112b are connected to a power supply 115, and a main switch 116 is provided between the power supply 115 and each heater 82a, 82b, 112a, 112b. Has been. A triac 121a is arranged between the main switch 116 and the halogen heater 82a, and a triac 121b and a switch 120 are arranged between the main switch 116 and the halogen heater 82b and the end heaters 112a and 112b. Has been done.

  When the switch 120 is connected to the terminal S1, the first control mode is set in which the halogen heaters 82a and 82b are energized but the end heaters 112a and 112b are turned off. When the switch 120 is connected to the terminal S2, the second control mode is set, and all the heaters 82a, 82b, 112a, 112b are energized. The amount of electricity supplied to each heater 82a, 82b, 112a, 112b is controlled by the control means 130 described later via the triacs 121a, 121b. In the present embodiment, in the second control mode, the halogen heater 82b and the end heaters 112a and 112b are always driven simultaneously by the triac 121b, so that the control can be simplified.

  As shown in FIG. 11, a thermopile 125a as a first temperature detecting means is provided near the outer peripheral surface of the fixing belt 80 and at an axial position corresponding to the heat generating portion of the halogen heater 82a. Further, a thermopile 125b as a second temperature detecting means is arranged near the outer peripheral surface of the fixing belt 80 and at an axial position corresponding to the heat generating portion of the halogen heater 82b. Further, at a position in contact with the outer peripheral surface of the pressure roller 84 and at an axial position corresponding to any one of the end heaters (the end heater 112b in this embodiment), a thermistor as a third temperature detecting means. 125c is provided. The end heaters 112a and 112b are in direct contact with the fixing belt 80, but since the pressure roller 84 is in pressure contact with the fixing belt 80, the temperature of the pressure roller 84 is detected as a result of the heat transfer action. By doing so, heating control by the end heaters 112a and 112b can be performed. The temperature information detected by the thermopiles 125a and 125b and the thermistor 125c is output to the control means 130 described later.

  FIG. 12 is a block diagram of the control means used in this embodiment. The control unit 130 including a well-known microcomputer having a CPU, a ROM, a RAM, and the like is provided in the main body of the image forming apparatus 100. The control unit 130 selects the connection terminal of the switch 120 when the main switch 116 is turned on. Then, the control means 130 controls the energization amount to the halogen heaters 82a and 82b and the end heaters 112a and 112b by the triacs 121a and 121b based on the temperature information from the thermopiles 125a and 125b and the thermistor 125c.

Here, the end heaters 112a and 112b will be described. The end heaters 112a and 112b used in this embodiment are the same, and FIG. 15 shows the end heater 112a as a representative.
The end heater 112a is configured by patterning a resistance heating element 52, which is a heating member, on a ceramic base material 51 having an outer shape of about 10 mm × 20 mm, and laminating an insulating layer 53 of a thin glass layer on the resistance heating element 52. A terminal 54 connected to a power supply and a switching element is provided at the end of the end heater 112a.

As described above, the end heaters 112a and 112b have the resistance heating element 52 on one surface side thereof, and one surface side having the resistance heating element 52 mainly generates heat and the other surface side does not have much. It is constructed so that heat does not reach.
The end heaters 112a and 112b used in the present embodiment have a resistance heating element 52 on the side in contact with the recesses 88a and 88b, and terminals 54 are provided on the surface sides thereof, respectively.
As shown in FIG. 16, the end heaters 112 a and 112 b have the resistance heating element 52 disposed on the side not in contact with the fixing belt 80, so that even if the insulating layer 53 is damaged, the electric power supplied is fixed. Is configured not to reach.

Next, the operation at the time of sheet passing for each sheet size will be described based on FIG.
When the job signal is received (ST01), it is first confirmed whether the paper size is A3 or smaller (ST02). When the job signal of A3 size or smaller is received, the first control mode is selected (ST03), and the switch 120 is connected to the terminal S1 (ST04).

  Then, it is determined whether or not the temperature of the thermopile 125a, 125b has reached the paper passing target temperature (for example, 150 ° C.) (ST05), and when the temperature of the thermopile 125a, 125b becomes the paper passing target temperature, the paper is not passed. It is started (ST06). After passing the paper, the control unit 130 controls the triacs 121a and 121b to control the energization amount of the halogen heaters 82a and 82b so that the thermopiles 125a and 125b maintain the target paper passing temperature (ST07).

  In step ST01, when a job signal having a size larger than A3 size (A3 size, 13 inches, etc.) is received, the second control mode is selected (ST08), and the switch 120 is connected to the terminal S2 (ST09). . Then, it is judged whether or not the temperatures of the thermopiles 125a and 125b have reached the sheet passing target temperature and the temperature detected by the thermistor 125c has reached the first predetermined temperature (for example, 100 ° C.) (ST10). The paper is started (ST11).

  When the detected temperature of the thermistor 125c reaches a second predetermined temperature (for example, 110 ° C.) higher than the first predetermined temperature after passing the sheet (ST12), the target temperature of the thermopile 125b is lowered (for example, to 145 ° C.). (ST13). After that, when the control means 130 determines that the temperature of the thermistor 125c becomes equal to or higher than the fourth predetermined temperature (for example, 150 ° C.) higher than the second predetermined temperature (ST14), the switch 120 is connected from the terminal S1 to the terminal S2. Is automatically switched to (ST15). As a result, the second control mode is forcibly shifted to the first control mode (ST16), and the end heaters 112a and 112b are turned off (ST17).

  In step ST12, when the detected temperature of the thermistor 125c becomes equal to or lower than the third predetermined temperature (for example, 90 ° C.) lower than the first predetermined temperature (ST18), the control unit 130 sets the target temperature of the thermopile 125b to ( For example, the temperature is raised to 155 ° C. (ST19), and the process returns to step ST12. As a result, even when a temperature difference occurs between the halogen heaters 82a and 82b and the end heaters 112a and 112b, the paper can be passed after the temperature of the end heaters 112a and 112b exceeds the predetermined temperature. It is possible to prevent image defects from occurring. Further, even if the temperature of the end heaters 112a and 112b rises and falls above a predetermined temperature during a job, it is possible to prevent the occurrence of image defects by raising and lowering the target temperature of the halogen heaters 82a and 82b. Further, when the temperature of the end heaters 112a and 112b rises too much, the control means 130 forcibly shifts from the second control mode to the first control mode, so various problems due to high temperatures of the end heaters 112a and 112b. It is possible to reliably prevent the occurrence of. The temperature control curve at this time is shown in FIG.

  With the above configuration, the halogen heaters 82a and 82b and the end heaters 112a and 112b can be connected in series for simultaneous control when a large size sheet S is passed, and the control circuit and the temperature sensor can be simplified. it can. Further, by placing the thermistor 125c at a position corresponding to the end heaters 112a and 112b and performing auxiliary monitoring, it is possible to reliably prevent the occurrence of image defects and high temperature abnormalities. Further, since the thermistor 125c makes contact with the outer peripheral surface of the pressure roller 84 to detect the temperature, the influence on the image can be eliminated and the cost can be reduced. Furthermore, in the first control mode, the heat storage amount and other factors can be reduced. It can also be used for the purpose.

  Further, as failure detection, it is desirable to provide a safety device such as a thermostat 126 near the outer peripheral surface of the fixing belt 80 in order to prevent runaway when the thermopiles 125a and 125b fail (see FIG. 2). In the second control mode, the end heaters 112a and 112b are always driven simultaneously with the halogen heater 82b. Therefore, if the thermostat 126 is provided near the halogen heater 82b and near the outer peripheral surface of the fixing belt 80, abnormality of the end heaters 112a and 112b can be prevented at the same time, and the safety device can be simplified.

FIG. 17 shows a modification of the nip forming unit. The nip forming unit 63 includes a nip forming member 88, end heaters 112 a and 112 b, and a stay member 64 that holds the nip forming member 88 against the pressure applied from the pressure roller 84.
The stay member 64 integrally includes a receiving portion 64a configured similarly to the stay member 90 to receive the nip forming member 88, and a leg portion 64b having a substantially triangular cross-sectional shape. Between the leg portion 64b and the fixing belt 14, halogen heaters 82a and 82b as first heat sources for directly heating the fixing belt 14 from the inner surface side by radiant heat are arranged.
In order to increase the heating efficiency of the halogen heaters 82a and 82b, the reflecting member 65, which is an arc-shaped plate material that reflects the light emitted from the halogen heaters 82a and 82b to the fixing belt 14, is provided with the leg portions 64b and the halogen heaters 82a and 82b. It is provided between.

Even when the nip forming unit 63 described above is used in place of the nip forming unit 86, the same operational effect as that of the above-described embodiment can be obtained.
Instead of providing the reflection member 65, the outer surface of the leg portion 64b may be heat-insulated or mirror-finished. In this case, the heating efficiency is slightly reduced as compared with the case where the reflecting member 65 is provided.

  Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these specific embodiments, and unless otherwise specified in the above description, the present invention described in the claims is disclosed. Various modifications and changes are possible within the scope of the spirit. The effects described in the embodiments of the present invention merely exemplify the most preferable effects that result from the present invention, and the effects according to the present invention are limited to those described in the embodiments of the present invention. is not.

80 Belt member (Fixing belt)
82a First heat source (halogen heater)
82b Second heat source (halogen heater)
84 Pressure member (pressure roller)
88 Nip forming member 100 Image forming apparatus 112a, 112b Third heat source (end heater)
115 power source 125a first temperature detecting means (thermopile)
125b Second temperature detecting means (thermopile)
125c Third temperature detecting means (thermistor)
130 Control Unit 150 Fixing Device S Recording Medium (Paper)

JP, 2014-178370, A

Claims (5)

An endless belt member having flexibility,
A pressing member arranged to face the belt member,
A nip forming member that forms a nip by being pressed by the pressure member via the belt member,
A first heat source for heating the central portion in the axial direction of the belt member;
A second heat source for heating the outer side of the belt member in the axial direction with respect to the first heat source;
A third heat source that heats the vicinity of both end portions of the belt member, which is outside the second heat source in the axial direction of the belt member,
A power source for driving each heat source,
A first temperature detecting means for detecting the temperature of the axial position corresponding to the first heat source,
A second temperature detecting means for detecting the temperature of the axial position corresponding to the second heat source,
And a third temperature detecting means for detecting the temperature of the axial position corresponding to the third heat source,
Selectable in the first control mode so as not to drive only the third heat source, and a second control mode for driving the second heat source and the third all the heat source connected in series with the heat source Yes,
Wherein the drive control of the second heat source and the third heat source in the second control mode, said second temperature sensing means and said third feedback temperature information detected by the temperature detecting means of the control to be executed have a means,
When the second control mode is selected, the control means starts sheet feeding when the third temperature detecting means reaches or exceeds the first predetermined temperature, and after the sheet feeding, the third temperature detecting When the temperature of the means reaches a second predetermined temperature higher than the first predetermined temperature, the target temperature of the second temperature detecting means is lowered, and after the paper has passed, the third temperature detecting means causes the third predetermined temperature detecting means to reach the first predetermined temperature. A fixing device that raises the target temperature of the second temperature detecting means when the temperature reaches a third predetermined temperature lower than the temperature . The fixing device according to claim 1,
When the third temperature detecting means reaches a fourth predetermined temperature higher than the second predetermined temperature after passing the paper, the control means forcibly changes from the second control mode to the first control mode. A fixing device characterized by being transferred . The fixing device according to claim 1 or 2,
The fixing device, wherein the third temperature detecting means detects the temperature by contacting the pressing member . The fixing device according to any one of claims 1 to 3 ,
The first control mode is selected when using a recording medium having a paper passage width equal to or less than the highest print ratio, and the second control mode has a wider paper passage width than the highest print ratio. A fixing device, which is selected when a recording medium is used . An image forming apparatus comprising the fixing device according to claim 1 .

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