JP5930281B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that fixes an image on a recording medium, and an image forming apparatus including the fixing device.

  As a fixing device used in various image forming apparatuses such as a copying machine, a printer, a facsimile, or a composite machine thereof, a fixing device having a thin fixing belt made of a metal base and an elastic rubber layer is known. In this way, by providing a thin fixing belt with a low heat capacity, the energy required for heating the fixing belt can be greatly reduced, and warm-up time (printing from room temperature such as when the power is turned on) can be performed. It is possible to shorten the time required until a predetermined temperature (reload temperature) and the first print time (the time from when a print request is received to when the printing operation is performed and the paper discharge is completed).

  Conventionally, as shown in FIG. 8, this type of fixing device includes an endless belt (fixing belt) 100, a pipe-shaped metal heat conductor 200 disposed inside the endless belt 100, and a metal heat conductor. Some include a heat source 300 disposed in the interior 200 and a pressure roller 400 that forms a nip portion N in contact with the metal heat conductor 200 via the endless belt 100 (see Patent Document 1). In this case, the endless belt 100 is rotated by the rotation of the pressure roller 400, and at this time, the metal heat conductor 200 guides the movement of the endless belt 100. Further, the endless belt 100 is heated by the heat source 300 in the metal heat conductor 200 via the metal heat conductor 200, so that the entire endless belt 100 can be heated. This makes it possible to shorten the first print time from the heating standby time and to solve the shortage of heat during high-speed rotation.

  Further, a fixing device that directly heats an endless belt (not via a metal heat conductor) has been proposed for further energy saving and first print time improvement (see Patent Document 2).

  In the example shown in FIG. 9, the pipe-shaped metal heat conductor is removed from the inside of the endless belt 100, and instead, a plate-shaped nip forming member 500 is provided at a position facing the pressure roller 400. In this case, since the endless belt 100 can be directly heated by the heat source 300 at a place other than where the nip forming member 500 is disposed, the heat transfer efficiency is greatly improved and the power consumption is reduced. For this reason, it is possible to further shorten the first print time from the heating standby time. Moreover, the cost reduction by not providing a metal heat conductor can also be anticipated.

  Further, in Patent Document 3, in a fixing device using a thin fixing roller or a fixing belt, a heater having a heat generation range different according to the paper size is provided, and the heater is selectively driven according to the paper size, thereby improving efficiency. A technique for generating heat and saving energy is disclosed.

  As described above, by directly heating the endless belt, it becomes possible to further improve the energy saving and the first print time, but on the other hand, because heat is transmitted without going through a metal heat conductor, There is a problem in that heat transfer from the endless belt passing area to the non-passing area is accelerated, and overheating of the non-sheet passing area is likely to occur. As a method for preventing this, there is a method of reducing the rotational speed of the endless belt. In this case, however, a problem that productivity (printing speed) decreases is newly generated.

  Accordingly, in view of such circumstances, the present invention intends to provide a fixing device capable of suppressing an excessive temperature rise in a non-sheet-passing region without reducing productivity, and an image forming apparatus including the fixing device. It is.

To solve the above problems, the present invention according to claim 1, formed with the fixing belt rotatable endless around the axis, and a heating source for heating the fixing belt, the contact with the nip portion in the fixing belt And a nip forming member that forms the nip portion in contact with the opposing member via the fixing belt, and includes a first passage width through which a recording medium passes, and the first passage width. A fixing device having a second passage width that is larger and includes the first passage width, and a third passage width that is smaller than the first passage width and is contained in the first passage width, the heating source Is a first heat generating portion disposed corresponding to the first passage width, and a second portion disposed on an end side of the second passage width that does not overlap the first passage width. a heating unit, and a third heat generating portions which are arranged corresponding to the third bandpass possess, the first And the second heat generating portion so as to be directly opposed to the fixing belt at a place other than the nip portion, and the third heat generating portion is disposed to the first and second heat generating portions. It is arranged on the back side opposite to the front side directly facing the fixing belt .

According to the first aspect of the present invention, the fixing belt can be heated in a range that matches each passing width. Specifically, when heating a range corresponding to the first passage width, only the first heat generating portion is heated, and when heating a range corresponding to the second passage width, the first and second portions are heated. The exothermic part is heated. Further, when heating the range corresponding to the third passage width, only the third heat generating portion needs to generate heat. As described above, since the fixing belt can be heated in a range suitable for each passing width, it is possible to suppress an excessive temperature increase of the fixing belt in the non-passing area of the recording medium without reducing the productivity.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a schematic configuration diagram of a fixing device mounted on the image forming apparatus. 2A and 2B are diagrams illustrating a configuration of an end portion of the fixing belt, in which FIG. 3A is a perspective view, FIG. 2B is a plan view, and FIG. It is a figure which shows the relationship between the heat_generation | fever area | region of each halogen heater, and a paper passing area | region. FIG. 10 is a schematic configuration diagram of a fixing device according to another embodiment. FIG. 2 is a schematic configuration diagram of a fixing device in which a fixing belt is stretched between a fixing roller and a heating roller. FIG. 2 is a schematic configuration diagram of a fixing device using a fixing roller instead of a fixing belt. It is a schematic block diagram of the conventional fixing device. It is a schematic block diagram of another conventional fixing device.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In each of the drawings for explaining the embodiments of the present invention, constituent elements such as members and components having the same function or shape are described once by giving the same reference numerals as much as possible. Then, the explanation is omitted.

First, an overall configuration and operation of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG.
An image forming apparatus 1 shown in FIG. 1 is a color laser printer, and four image forming units 4Y, 4M, 4C, and 4K are provided in the center of the apparatus main body. Each of the image forming units 4Y, 4M, 4C, and 4K contains developers of different colors of yellow (Y), magenta (M), cyan (C), and black (K) corresponding to the color separation components of the color image. The configuration is the same except that.

  Specifically, each of the image forming units 4Y, 4M, 4C, and 4K has a drum-shaped photoconductor 5 as a latent image carrier, a charging device 6 that charges the surface of the photoconductor 5, and a surface of the photoconductor 5. A developing device 7 for supplying toner and a cleaning device 8 for cleaning 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 denoted by reference numerals. The reference numerals are omitted.

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

  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. Further, a power source (not shown) is connected to each primary transfer roller 31 so that 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, a power source (not shown) is also connected to the secondary transfer roller 36, and a predetermined DC voltage (DC) and / or AC voltage (AC) is applied to the secondary transfer roller 36. It has become so.

  The belt cleaning device 35 includes a cleaning brush and a cleaning blade disposed so as to contact the intermediate transfer belt 30. A waste toner transfer hose (not shown) extending from the belt cleaning device 35 is connected to an entrance of a waste toner container (not shown).

  A bottle container 2 is provided in the upper part of the printer main body, and four toner bottles 2Y, 2M, 2C, and 2K containing replenishing toner are detachably attached to the bottle container 2. A replenishment path (not shown) is provided between each toner bottle 2Y, 2M, 2C, 2K and each developing device 7, and each development from each toner bottle 2Y, 2M, 2C, 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 that stores paper P as a recording medium, a paper feed roller 11 that carries the paper P out of the paper feed tray 10, and the like are provided. Here, the recording medium includes thick paper, postcard, envelope, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, OHP sheet and the like in addition to plain paper. Although not shown, 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. A discharge tray 14 for stocking sheets discharged outside the apparatus is provided on the upper surface of the printer main body.

Next, a basic operation of the printer according to the present embodiment will be described with reference to FIG.
When the image forming operation is started, the respective photoconductors 5 in the respective image forming units 4Y, 4M, 4C, and 4K are rotationally driven clockwise by a driving device (not shown), and the surface of each photoconductor 5 is charged by the charging device 6. Are uniformly charged to a predetermined polarity. The surface of each charged photoconductor 5 is irradiated with laser light from the exposure device 9 to form an electrostatic latent image on the surface of each photoconductor 5. At this time, the image information to be exposed on each photoconductor 5 is single-color image information obtained by separating a desired full-color image into color information of yellow, magenta, cyan, and black. In this way, toner is supplied to each electrostatic latent image formed on each photoconductor 5 by each developing device 7, whereby the electrostatic latent image is visualized (visualized) as a toner image. .

  When the image forming operation is started, the secondary transfer backup roller 32 is driven to rotate counterclockwise in the figure, and the intermediate transfer belt 30 is caused to run in the direction indicated by the arrow in the figure. Then, a constant voltage or a constant current controlled voltage having a polarity opposite to the charging polarity of the toner is applied to each primary transfer roller 31. As a result, a transfer electric field is formed in the primary transfer nip between each primary transfer roller 31 and each photoconductor 5.

  Thereafter, when each color toner image on the photoconductor 5 reaches the primary transfer nip as each photoconductor 5 rotates, the toner image on each photoconductor 5 is generated by the transfer electric field formed in the primary transfer nip. Are sequentially superimposed and transferred onto the intermediate transfer belt 30. Thus, a full color toner image is carried on the surface of the intermediate transfer belt 30. Further, the toner on each photoconductor 5 that could not be transferred to the intermediate transfer belt 30 is removed by the cleaning device 8. Thereafter, the surface of each photoconductor 5 is neutralized by a neutralizing device (not shown), and the surface potential is initialized.

  In the lower part of the image forming apparatus, the paper feed roller 11 starts to rotate, and the paper P is sent out from the paper feed tray 10 to the transport path R. The sheet P sent to the transport path R is timed by the registration roller 12 and sent to the secondary transfer nip between the secondary transfer roller 36 and the secondary transfer backup roller 32. At this time, a transfer voltage having a polarity opposite to the toner charge polarity of the toner image on the intermediate transfer belt 30 is applied to the secondary transfer roller 36, thereby forming a transfer electric field in the secondary transfer nip.

  Thereafter, when the toner image on the intermediate transfer belt 30 reaches the secondary transfer nip as the intermediate transfer belt 30 rotates, the transfer electric field formed in the secondary transfer nip causes a transfer on the intermediate transfer belt 30. The toner images are transferred onto the paper P all at once. At this time, the residual toner on the intermediate transfer belt 30 that could not be transferred onto the paper P is removed by the belt cleaning device 35, and the removed toner is conveyed to a waste toner container (not shown) and collected.

  Thereafter, the paper P is conveyed to the fixing device 20, and the toner image on the paper P is fixed to the paper P by the fixing device 20. Then, the paper P is discharged out of the apparatus by the paper discharge roller 13 and stocked on the paper discharge tray 14.

  The above description is an image forming operation when a full-color image is formed on a sheet. A single color image can be formed using any one of the four image forming units 4Y, 4M, 4C, and 4K. Two or three image forming units can be used to form a two-color or three-color image.

Next, the configuration of the fixing device 20 will be described with reference to FIG.
As shown in FIG. 2, the fixing device 20 includes a fixing belt 21 as a rotatable fixing member, a pressure roller 22 as a facing member that is rotatably provided facing the fixing belt 21, and a fixing belt 21. Three halogen heaters 23a, 23b, 23c as heating sources for heating the nip, a nip forming member 24 disposed inside the fixing belt 21, and a stay 25 as a support member for supporting the nip forming member 24, A reflection member 26 that reflects the light emitted from each of the halogen heaters 23 a, 23 b, and 23 c to the fixing belt 21, a temperature sensor 27 that detects temperature of the fixing belt 21, and a sheet from the fixing belt 21 are separated. A separating member 28 for pressing, and a pressing means (not shown) for pressing the pressure roller 22 to the fixing belt 21.

  The fixing belt 21 is composed of a thin and flexible endless belt member (including a film). Specifically, the fixing belt 21 includes 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 (PI), and a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA). Or it is comprised by the release layer of the outer peripheral side formed with polytetrafluoroethylene (PTFE) etc. Further, 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.

  The pressure roller 22 includes a cored bar 22a, an elastic layer 22b made of foamable silicone rubber, silicone rubber, or fluororubber provided on the surface of the cored bar 22a, and a PFA provided on the surface of the elastic layer 22. Alternatively, it is constituted by a release layer 22c made of PTFE or the like. The pressure roller 22 is pressed toward the fixing belt 21 by a pressure unit (not shown) and is in contact with the nip forming member 24 via the fixing belt 21. At the place where the pressure roller 22 and the fixing belt 21 are in pressure contact, the elastic layer 22b of the pressure roller 22 is crushed to form a nip portion N having a predetermined width. The pressure roller 22 is configured to be rotationally driven by a drive source such as a motor (not shown) provided in the printer main body. When the pressure roller 22 is rotationally driven, the driving force is transmitted to the fixing belt 21 at the nip portion N, and the fixing belt 21 is driven to rotate.

  In the present embodiment, the pressure roller 22 is a solid roller, but may be a hollow roller. In that case, a heating source such as a halogen heater may be disposed inside the pressure roller 22. In addition, when there is no elastic layer, the heat capacity is reduced and the fixability is improved, but when the unfixed toner is crushed and fixed, minute irregularities on the belt surface are transferred to the image, and uneven glossiness is formed on the solid portion of the image. It can happen. In order to prevent this, it is desirable to provide an elastic layer having a thickness of 100 μm or more. By providing an elastic layer having a thickness of 100 μm or more, minute unevenness can be absorbed by elastic deformation of the elastic layer, so that occurrence of uneven gloss can be avoided. The elastic layer 22b may be solid rubber, but if there is no heat source inside the pressure roller 22, 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. Further, the fixing member and the facing member are not limited to being brought into pressure contact with each other, and may be configured to simply contact each other without applying pressure.

  The halogen heaters 23a, 23b, and 23c are fixed to side plates (not shown) of the fixing device 20 at both ends. Each of the halogen heaters 23a, 23b, and 23c is configured to generate heat by being output-controlled by a power supply unit provided in the printer body, and the output control is performed by detecting the surface temperature of the fixing belt 21 by the temperature sensor 27. Based on the results. By such output control of the heater 23, the temperature of the fixing belt 21 (fixing temperature) can be set to a desired temperature. Further, a heating source other than the halogen heater may be used as a heating source for heating the fixing belt 21.

  The nip forming member 24 includes a base pad 241 and a sliding sheet (low friction sheet) 240 provided on the surface of the base pad 241. The base pad 241 is disposed in a longitudinal shape over the axial direction of the fixing belt 21 or the axial direction of the pressure roller 22, and determines the shape of the nip portion N by receiving the pressure applied by the pressure roller 22. is there. The base pad 241 is fixedly supported by the stay 25. In this case, a sheet metal 250 is provided so as to surround the nip forming member 24, and the nip forming member 24 is supported by the stay 25 via the sheet metal 250. Thus, the nip forming member 24 is prevented from being bent by the pressure of the pressure roller 22, and a uniform nip width is obtained in the axial direction of the pressure roller 22. The stay 25 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron in order to satisfy the function of preventing the nip forming member 24 from bending. The base pad 241 is also preferably made of a material that is hard to some extent to ensure strength. As a material for the base pad 241, a resin such as a liquid crystal polymer (LCP), a metal, a ceramic, or the like can be used.

  The base pad 241 is made of a heat resistant member having a heat resistant temperature of 200 ° C. or higher. This prevents the nip forming member 24 from being deformed by heat in the toner fixing temperature range and ensures a stable state of the nip portion N, thereby stabilizing the output image quality. For the base pad 241, general materials such as polyethersulfone (PES), polyphenylene sulfide (PPS), liquid crystal polymer (LCP), polyethernitrile (PEN), polyamideimide (PAI), polyetheretherketone (PEEK), etc. It is possible to use a heat resistant resin.

  The sliding sheet 240 may be disposed on at least the surface of the base pad 241 that faces the fixing belt 21. As a result, when the fixing belt 21 rotates, the fixing belt 21 slides with respect to the low friction sheet, so that the driving torque generated in the fixing belt 21 is reduced, and the load due to the frictional force on the fixing belt 21 is reduced. The In addition, it is also possible to set it as the structure which does not have a sliding sheet.

  The reflection member 26 is disposed between the stay 25 and the halogen heaters 23a, 23b, and 23c. In the present embodiment, the reflecting member 26 is fixed to the stay 25. Examples of the material of the reflecting member 26 include aluminum and stainless steel. By arranging the reflection member 26 in this way, the light emitted from the halogen heaters 23 a, 23 b, 23 c to the stay 25 side is reflected to the fixing belt 21. As a result, the amount of light applied to the fixing belt 21 can be increased, and the fixing belt 21 can be efficiently heated. Further, since it is possible to suppress the radiant heat from the halogen heaters 23a, 23b, and 23c from being transmitted to the stay 25 and the like, energy saving can be achieved.

In addition, the fixing device 20 according to the present embodiment is devised in various configurations in order to further improve energy saving and first print time.
Specifically, the halogen heaters 23a, 23b, and 23c are arranged so as to directly face the fixing belt 21, so that the fixing belt 21 can be directly heated at a place other than the nip portion N (direct heating method). ). In the present embodiment, nothing is interposed between the halogen heaters 23a, 23b, and 23c and the left portion of the fixing belt 21 in FIG. 2, and the radiant heat from the halogen heaters 23a, 23b, and 23c is transferred to the fixing belt at that portion. 21 is given directly.

  Further, in order to reduce the heat capacity of the fixing belt 21, the fixing belt 21 is made thinner and smaller in diameter. Specifically, 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, and the overall thickness is set. It is set to 1 mm or less. The diameter of the fixing belt 21 is set to 20 to 40 mm. In order to further reduce the heat capacity, the thickness of the entire fixing belt 21 is desirably 0.2 mm or less, and more desirably 0.16 mm or less. The diameter of the fixing belt 21 is desirably 30 mm or less.

  In this embodiment, the diameter of the pressure roller 22 is set to 20 to 40 mm, and the diameter of the fixing belt 21 and the diameter of the pressure roller 22 are configured to be equal. However, it is not limited to this configuration. For example, the fixing belt 21 may be formed so that the diameter thereof is smaller than the diameter of the pressure roller 22. In that case, since the curvature of the fixing belt 21 at the nip portion N is smaller than the curvature of the pressure roller 22, the recording medium discharged from the nip portion N is easily separated from the fixing belt 21.

  As described above, as a result of reducing the diameter of the fixing belt 21, the space inside the fixing belt 21 is reduced. However, the stay 25 is formed in a concave shape bent at both ends, and the inside of the portion formed in the concave shape. By accommodating all or part of the three halogen heaters 23a, 23b, and 23c, the stay 25 and the halogen heaters 23a, 23b, and 23c can be disposed even in a small space.

  Further, in order to dispose the stay 25 as large as possible even in a small space, the nip forming member 24 is formed compact on the contrary. Specifically, the width of the base pad 241 in the sheet conveyance direction is formed to be smaller than the width of the stay 25 in the sheet conveyance direction. Further, in FIG. 2, the heights of the base pad 241 at the upstream end and the downstream end in the sheet conveyance direction with respect to the nip portion N or the virtual extension line E are h1 and h2, respectively. If the maximum height of the base pad 241 other than the end portion with respect to the nip portion N or its virtual extension line E is h3, h1 ≦ h3 and h2 ≦ h3. With this configuration, the upstream end and the downstream end of the base pad 241 are not interposed between the bent portions on the upstream and downstream sides of the stay 25 in the sheet conveying direction and the fixing belt 21. Each bent portion can be disposed close to the inner peripheral surface of the fixing belt 21. As a result, the stay 25 can be disposed as large as possible in a limited space in the fixing belt 21, and the strength of the stay 25 can be ensured. As a result, it is possible to prevent the nip forming member 24 from being bent by the pressure roller 22 and to improve the fixing property.

  Further, in order to ensure the strength of the stay 25, in this embodiment, the stay 25 comes into contact with the nip forming member 24 and extends in the paper transport direction (vertical direction in FIG. 2), and the base portion 25a. And a rising portion 25b extending in the contact direction of the pressure roller 22 (left side in FIG. 2) from the upstream and downstream ends of the sheet conveyance direction. That is, by providing the stay 25 with the rising portion 25b, the stay 25 has a horizontally long cross section extending in the pressure direction of the pressure roller 22, and the section modulus is increased, so that the mechanical strength of the stay 25 is increased. Can be improved.

  In addition, the strength of the stay 25 is improved by forming the rising portion 25b longer in the contact direction of the pressure roller 22. Therefore, it is desirable that the leading end of the rising portion 25 b is as close as possible to the inner peripheral surface of the fixing belt 21. However, during rotation, the fixing belt 21 may be shaken (disturbance in behavior) regardless of whether it is large or small. Therefore, if the leading end of the rising portion 25b is too close to the inner peripheral surface of the fixing belt 21, the fixing belt 21 is moved to the leading end of the rising portion 25b. There is a risk of contact. In particular, in the configuration using the thin fixing belt 21 as in the present embodiment, since the swinging width of the fixing belt 21 is large, care must be taken in setting the position of the leading end of the rising portion 25b.

  Specifically, in the case of this embodiment, the distance d in the contact direction of the pressure roller 22 between the tip of the rising portion 25b and the inner peripheral surface of the fixing belt 21 is at least 2.0 mm, preferably 3.0 mm or more. It is preferable to set. On the other hand, when the fixing belt 21 has a certain thickness and almost no vibration, the distance d can be set to 0.02 mm. When the reflecting member 26 is attached to the tip of the rising portion 25b as in the present embodiment, it is necessary to set the distance d so that the reflecting member 26 does not contact the fixing belt 21.

  In this way, the rising portion 25b is disposed long in the contact direction of the pressure roller 22 by disposing the leading end of the rising portion 25b as close as possible to the inner peripheral surface of the fixing belt 21. Can do. Accordingly, the mechanical strength of the stay 25 can be improved even in the configuration using the small-diameter fixing belt 21.

  FIG. 3 is a diagram illustrating a configuration of an end portion of the fixing belt. In the figure, (a) is a perspective view, (b) is a plan view, and (c) is a side view as seen from the rotation axis direction of the fixing belt. 3 (a) to 3 (c), only the configuration of one end is shown, but the opposite end also has the same configuration. Only the configuration of the end portion of this will be described.

  As shown in FIG. 3A or 3B, a belt holding member 40 is inserted into the end of the fixing belt 21, and the end of the fixing belt 21 is rotatably held by the belt holding member 40. Has been. As shown in FIG. 3C, the belt holding member 40 is formed in a C-shape that is open at the position of the nip portion (position where the nip forming member 24 is disposed). The end of the stay 25 is fixed to the belt holding member 40 and positioned.

  Further, as shown in FIG. 3A or 3B, a protective member that protects the end portion of the fixing belt 21 between the end surface of the fixing belt 21 and the opposing surface of the belt holding member 40 facing the fixing belt 21. A slip ring 41 is provided. As a result, when the fixing belt 21 is displaced in the axial direction, the end portion of the fixing belt 21 can be prevented from coming into direct contact with the belt holding member 40, and the end portion can be prevented from being worn or damaged. it can. Further, the slip ring 41 is fitted to the belt holding member 40 with a margin with respect to the outer periphery. For this reason, when the end of the fixing belt 21 comes into contact with the slip ring 41, the slip ring 41 can be rotated with the fixing belt 21, but the slip ring 41 does not rotate and is stationary. I do not care. As a material of the slip ring 41, it is preferable to apply a so-called super engineering plastic excellent in heat resistance, for example, PEEK, PPS, PAI, PTFE and the like.

  Although not shown in the drawings, shielding members that shield heat from the halogen heater 23 are disposed between the fixing belt 21 and the halogen heater 23 at both ends in the axial direction of the fixing belt 21. Thereby, in particular, an excessive temperature rise in the non-sheet passing region of the fixing belt during continuous sheet feeding can be suppressed, and deterioration and damage of the fixing belt due to heat can be prevented.

FIG. 4 is a diagram illustrating the relationship between the heat generation area and the sheet passing area of each halogen heater.
The fixing device of this embodiment has at least three paper passage widths of different sizes. Here, as shown in FIG. 4, as the first passage width, a medium size passage width W1 (width 210 mm) that allows A4 size paper to pass vertically, and as the second passage width, A3 size paper is used. There is a large size passage width W2 (width 297 mm) that passes in the vertical direction and a third size passage width W3 (width 105 mm) that allows the A6 size paper to pass in the vertical direction.

  The medium size passage width W1 is included in the larger size passage width W2, and the small size passage width W3 is included in the medium A4 size passage width W1 and the large size passage width W2. Has been. In the present exemplary embodiment, a system (center reference system) is employed in which the central portions in the width direction of various sizes of paper are aligned at the central position in the axial direction of the fixing belt 21. However, the present invention is not limited to this, and can be applied to a fixing device that employs a system (edge reference system) that transports paper of various sizes based on the axial end of the fixing belt. Is possible.

  In FIG. 4, the three halogen heaters 23 a, 23 b, and 23 c that are shown side by side in the vertical direction are different in position, length, and power of each heat generating portion. Specifically, in the medium size heater 23a shown in the center of the figure as the first halogen heater, the heat generating portion is disposed corresponding to the medium size passage width W1, and the maximum power is 700W. . Further, in the large size heater 23b shown at the top of the drawing as the second halogen heater, the heat generating portion is disposed on the end side that does not overlap the medium size passage width W1 in the large size passage width W2. The maximum power is 500W. Moreover, in the heat generating part of the small size heater 23c shown at the bottom of the figure as the third halogen heater, a heat generating part is arranged corresponding to the small size passing width W3, and the maximum power is It is 647W.

  In the present invention, the “large size”, “medium size”, and “small size” are not limited to the A3 vertical size, A4 vertical size, and A6 vertical size, but may be other sizes. Good.

  By the way, the halogen heater has a tendency that the light emission intensity is weakened on the end side, and if the light emission length is set in the same range as the paper passing area, a sufficient amount of heat cannot be obtained on the end side of the paper passing area, and the temperature drops. This may cause a fixing failure. For this reason, in this embodiment, the light emission length of each light emitting unit is longer than the corresponding paper passage width. Specifically, the length of the heat generating portion of the medium size heater 23a is set to 217 mm with respect to the medium size passage width W1 having a width of 210 mm. For the large size passage width W2 having a width of 297 mm, the combined length of the heat generating portions of the medium size heater 23a and the large size heater 23b is set to 324 mm. For the small size passage width W3 having a width of 105 mm, the length of the heat generating portion of the small size heater 23c is set to 133 mm. In addition, the length of the heat generating part of only the large size heater 23b is 56 mm.

Hereinafter, the operation of the fixing device according to the present embodiment will be described with reference to FIGS. 2 and 4.
When the power switch of the printer main body is turned on, power is supplied to the halogen heater according to the paper size to be passed. Specifically, when passing A4 size paper vertically, only the medium size heater 23a is energized. When passing A3 size paper vertically, the medium size heater 23a and the large size end are passed. Energizes the heater 23b. When passing A6 size paper vertically, only the small size heater 23c is energized. Thereby, the fixing belt 21 can be heated in a range suitable for each paper width size.

  At the same time as the energization of the halogen heater is started, the pressure roller 22 starts to rotate clockwise in FIG. As a result, the fixing belt 21 is driven to rotate counterclockwise in FIG. 2 by the frictional force with the pressure roller 22.

  Thereafter, the sheet P carrying the unfixed toner image T in the image forming process described above is conveyed in the direction of the arrow in FIG. It is fed into the nip N of the pressure roller 22. Then, the toner image T is fixed on the surface of the paper P by heat from the heated fixing belt 21 and pressure applied between the fixing belt 21 and the pressure roller 22.

  The paper P on which the toner image T is fixed is carried out from the nip portion N. At this time, the paper P is separated from the fixing belt 21 by the leading edge of the paper P coming into contact with the leading edge of the separation member 28. Thereafter, the separated paper P is discharged out of the apparatus by the paper discharge roller as described above, and stocked on the paper discharge tray.

  As described above, in the fixing device according to the present embodiment, the heat generation range can be made different according to the passage widths of “large size”, “medium size”, and “small size”. The fixing belt 21 can be heated within a range suitable for. For example, when the sheet is continuously passed through the small size passage width W3, if the medium size heater 23a generates heat, the fixing belt 21 may overheat in the non-sheet passing region. As described above, by causing the small size heater 23c corresponding to the small size passage width W3 to generate heat, an excessive temperature rise in the non-sheet passing region can be suppressed.

  As a result, the excessive temperature rise of the fixing belt 21 in the non-sheet-passing region can be suppressed without reducing the productivity (printing speed), so that the fixing belt 21 can be prevented from being deteriorated or damaged by heat. It is possible to maintain its function well over a long period of time. In particular, in the configuration in which the fixing belt 21 is thinly formed to reduce the heat capacity as in the present embodiment, the temperature of the fixing belt 21 is likely to rise, and thus a great effect can be expected.

  Further, in the present embodiment, the temperature sensor 27 is disposed corresponding to the location where the fixing belt 21 is directly heated, so that the temperature of the most easily heated portion of the fixing belt 21 can be accurately detected. I have to. As a result, the accuracy of temperature control of the fixing belt 21 is improved, and deterioration and damage of the fixing belt 21 due to heat can be prevented more reliably.

  In the present embodiment, as shown in FIG. 2, the small size heater 23 c is replaced with the fixing belt 21 with respect to the medium size heater 23 a and the large size heater 23 b when viewed from the axial direction of the fixing belt 21. It is arranged on the back side opposite to the front side facing directly. This is to prevent the radiant heat from the medium size heater 23a and the large size heater 23b, which are frequently used, to the fixing belt 21 from being obstructed by the small size heater 23c, which is less frequently used. In particular, in the present embodiment, since the concave stays 25 are arranged around the halogen heaters 23a, 23b, and 23c, the medium size heater 23a and the large size heater 23b that are frequently used are connected to the stay 25. The small-sized heater 23c that is less frequently used is disposed in the stay 25 so as to be accommodated inside the stay 25. As described above, by arranging the halogen heaters 23a, 23b, and 23c, it is possible to prevent the radiant heat from the frequently used heaters 23a and 23b to the fixing belt 21 from being hindered by the less frequently used heater 23c. It is possible to improve the thermal efficiency.

  Further, in the configuration in which the fixing belt 21 is reduced in diameter as in the present embodiment, since the installation space in the fixing belt 21 is reduced, the three halogen heaters 23a, 23b, and 23c are brought close to each other, so that The halogen heaters 23a, 23b, and 23c are arranged in a compact manner. That is, as shown in FIG. 2, the medium size heater 23a and the large size heater 23b are disposed close to each other, and the small size heater 23c is disposed on the back side of the medium size heater 23a and the large size heater 23b. So that they are close to each other. Also, by arranging in this way, the distance of the small size heater 23c with respect to the fixing belt 21 can be set short, and the temperature increase of the fixing belt 21 when the small size heater 23c is operated can be accelerated.

  In the present embodiment, the medium size heater 23a and the large size heater 23b are arranged in parallel to the axial direction of the fixing belt 21 and close to each other, so that the temperature in the belt axial direction during heating can be reduced. Variation is suppressed.

  In addition, a heat generating portion (first heat generating portion) disposed corresponding to the medium size passage width W1, and a heat generating portion (second heat generating portion) disposed on the end side of the large size passage width W2. The heat generating portions (third heat generating portions) disposed corresponding to the small size passage width W3 may not be configured by separate heat generating elements. For example, reflecting members are provided at both ends of the halogen heater so as to have a temperature control function on the center side and the end side, so that both the medium size heater 23a and the large size heater 23b can be functioned by one halogen heater. It is also possible to achieve this.

FIG. 5 is a diagram showing an embodiment in which the configuration of the present invention is applied to a fixing device including two halogen heaters 23d and 23e.
In FIG. 5, one upper halogen heater 23d is a large / medium size combined heater having the functions of both a medium size heater 23a and a large size heater 23b, and the lower halogen heater 23e is a small size paper heater. It is a small size heater. Here, the two halogen heaters 23d and 23e are arranged vertically so as to directly face the fixing belt. That is, in this embodiment, unlike the above embodiment, since there are only two halogen heaters, a small size heater 23e with low usage frequency is arranged on the back side of the large / medium size combined heater 23d with high usage frequency. Even if not, sufficient radiant heat from the large / medium size combined heater 23d to the fixing belt 21 can be secured. However, in the configuration shown in FIG. 5, when the opening width of the stay 25 and the reflection member 26 is large enough to arrange only one halogen heater, a small size heater 23e with low use frequency is used. It is necessary to dispose on the back side of the high large / medium size combined heater 23d. In the embodiment shown in FIG. 5, the other configurations are the same as those in the above embodiment, and thus the description thereof is omitted.

  As described above, the embodiment of the present invention has been described. However, as illustrated in FIG. 6, the present invention is a fixing device in which the fixing belt 21 is stretched by a heating roller 64 including a fixing roller 63 and a heating source 23, and FIG. As shown in FIG. 7, the present invention can be applied to a fixing device using a fixing roller 63 instead of the fixing belt 21. In these fixing devices, similarly to the above-described embodiment, the medium size heater 23a, the large size heater 23b, and the small size heater 23c are provided as heating sources, so that the fixing belt 21 or the like within a range suitable for each passing width. The fixing roller 63 can be heated, and an excessive temperature rise in the non-passing region can be suppressed without reducing productivity.

  In addition, the fixing device according to the present invention is not limited to the color laser printer shown in FIG. 1, and can be mounted on a monochrome image forming apparatus, other printers, copiers, facsimiles, or complex machines thereof. .

20 Fixing device 21 Fixing belt (fixing member)
22 Pressure roller (opposing member)
23a Medium size heater 23b Large size heater 23c Small size heater 24 Nip forming member 25 Stay (support member)
27 Temperature sensor (temperature detection means)
N nip P Paper (recording medium)
W1 Medium size passage width W2 Large size passage width W3 Small size passage width

JP 2007-334205 A Japanese Patent Laid-Open No. 2007-233011 Japanese Patent No. 4077499

Claims (7)

An endless fixing belt that can rotate around its axis;
A heating source for heating the fixing belt ;
An opposing member that contacts the fixing belt to form a nip portion ;
A nip forming member that contacts the opposing member via the fixing belt to form the nip portion ;
A first passage width through which the recording medium passes, a second passage width that is larger than the first passage width and includes the first passage width, and a first passage width that is smaller than the first passage width and smaller than the first passage width. A fixing device having a third passage width included,
The heating source is disposed on a first heat generating portion disposed corresponding to the first passage width and on an end portion side of the second passage width that does not overlap with the first passage width. a second heating unit, and said third third heating portion disposed in correspondence with the passage width possess,
The first and second heat generating portions are disposed so as to directly face the fixing belt at locations other than the nip portion, and the third heat generating portion is used as the first and second heat generating portions. On the other hand , the fixing device is provided on the back side opposite to the front side directly facing the fixing belt . An endless fixing belt that can rotate around its axis ;
A heating source for heating the fixing belt;
An opposing member that contacts the fixing belt to form a nip portion;
A nip forming member that contacts the opposing member via the fixing belt to form the nip portion;
A first passage width through which the recording medium passes, a second passage width that is larger than the first passage width and includes the first passage width, and a first passage width that is smaller than the first passage width and smaller than the first passage width. A fixing device having a third passage width included,
The heating source is disposed on a first heat generating portion disposed corresponding to the first passage width and on an end portion side of the second passage width that does not overlap with the first passage width. A second heat generating portion, and a third heat generating portion disposed corresponding to the third passage width,
The first and second heat generating portions are disposed so as to directly face the fixing belt at locations other than the nip portion, and the third heat generating portion is used as the first and second heat generating portions. On the other hand, these are arranged on the back side opposite to the front side directly facing the fixing belt,
The first and second heat generating portions are disposed close to each other, and the third heat generating portion is located on the back side of the first and second heat generating portions, and the first and second heat generating portions. A fixing device, which is disposed so as to be close to each other . A support member for supporting the nip forming member;
Forming the support member in a concave shape;
While disposing the first and second heating portions to the concave opening side of the support member, the third aspect of the heat generating portion is disposed so as to accommodate the interior of the support member 1 or 2 The fixing device according to 1. 4. The fixing device according to claim 1, wherein the third heat generating unit is a heat generating unit that is used less frequently than the first and second heat generating units. 5. A temperature detecting means for detecting the temperature of the fixing belt;
It said temperature sensing means, the fixing device according to any one of the first and second heating portions claim 1 which is disposed in correspondence with the position of heating the fixing belt directly 4. Wherein the first and second heating portions, the respective parallel to the axial direction of the fixing belt and fixing device according to any one of claims 1 to 5 which is arranged to be close to each other. An image forming apparatus comprising the fixing device according to claim 1.

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