JP2015055709A - Fixing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably convey a recording medium and to maintain excellent image quality by preventing the local wear of a belt member.SOLUTION: A fixing device includes an endless fixing belt 21 heated by a heat source and rotated, a pressure roller 31 rotated in contact with the fixing belt 21, and a stationary member 26 disposed inside the fixing belt 21 and coming into contact with the pressure roller 31 through the fixing belt 21, to form a nip part between the fixing belt 21 and the pressure roller 31. In the longitudinal direction of the nip part, pressure outside a recording medium conveyance area is made higher than that inside the recording medium conveyance area and a friction coefficient between the fixing belt 21 and the stationary member 26 is reduced.

Description

  The present invention relates to a fixing device and an image forming apparatus. More specifically, the present invention relates to a fixing device and an image forming apparatus that are mounted on an electrophotographic image forming apparatus such as a copying machine, a facsimile machine, a printer, or a complex machine thereof.

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

  Various types of fixing devices have been proposed. In a heat roller fixing device, a heat source such as a halogen heater is provided inside, and two rotating bodies (fixing roller, rotating while being pressed against each other while being heated). A recording medium on which an unfixed toner image is placed is passed through a nip portion (fixing nip portion) of a pressure roller), where the toner image is melted and fixed on the recording medium.

  In recent years, there has been a growing demand for energy-saving devices and shorter waiting times for heating. By using an endless belt member such as a belt or thin film instead of a fixing roller, the heat capacity of the fixing device can be reduced. In addition, a so-called on-demand type fixing device is widely adopted in which the heat transfer efficiency to the recording medium is improved and the waiting time required for heating (warm-up time and first print time) is greatly reduced.

  As this type of fixing device, a fixing member is provided on the inner peripheral surface of the belt member, and the fixing member is pressed against the rotating body via the belt member, thereby forming a nip portion between the belt member and the rotating body. A system for conveying a recording medium to the nip portion and fixing a toner image on the recording medium is already known.

  Further, in the fixing device, when the recording medium passes through the nip portion, the recording medium may move toward the center side in the longitudinal direction of the roller or belt, and thus wrinkles may occur. That is, it is known that the roller diameter at the center in the longitudinal direction is reduced and the roller diameter at the end is increased (for example, Patent Document 1). In the case of a belt member, it is known that the inner diameter of the belt at the center in the longitudinal direction is reduced and the inner diameter of the belt at the end is increased.

  In this way, when the recording medium passes through the nip portion, the speed (circumferential speed) can be increased from the center side to the end side in the longitudinal direction, and an outward opening force acts on the recording medium. Thus, the generation of wrinkles can be suppressed.

  However, increasing the diameter on the end side increases the load on the end side. For example, in the case of a belt member, the sliding load on the inner sliding surface of the belt increases and wears locally. There was a problem that. Due to the extreme wear, the uniformity of the nip portion cannot be maintained, and there is a possibility that the image is disturbed or the paper transportability is impaired.

  Further, Patent Document 2 discloses a pivotable rotation member, an endless belt movable while contacting the rotation member, a pressure member disposed inside the endless belt and forming a nip portion, and an endless belt. A low friction member that reduces the frictional resistance with respect to the sliding direction between the pressure member and the pressure member, and the endless belt is formed with a groove or a convex portion on the inner peripheral surface in the moving direction of the endless belt, As the low friction member, there is disclosed a fixing device in which convex portions or grooves that fit into the grooves or convex portions of the endless belt are formed. In Patent Document 2, the frictional force between the inside of the endless belt and the sliding surface of the endless belt is reduced to prevent the belt from being damaged.

  However, even in the technique of Patent Document 2, similarly to Patent Document 1, the sliding load on the inner sliding surface of the belt becomes large and wears locally. Therefore, there is a possibility that the image quality may not be maintained, and the image may be disturbed or the paper transportability may be impaired.

  Accordingly, the present invention provides a fixing device capable of stably conveying a recording medium and maintaining good image quality by stabilizing the behavior of the belt member and preventing the belt member from being worn at an extreme place. For the purpose.

  In order to achieve such an object, a fixing device according to the present invention includes an endless belt member that is heated and rotated by a heat source, a pressure rotator that rotates while contacting the belt member, and the belt member. A fixing member that is disposed inside the belt member and abuts against the pressure rotator through the belt member to form a nip portion between the belt member and the pressure rotator. In the longitudinal direction of the portion, the pressure outside the recording medium conveyance area is higher than that inside the recording medium conveyance area, and the friction coefficient between the belt member and the fixed member is small.

  According to the present invention, with a simple configuration, it is possible to stably convey the recording medium and maintain good image quality by preventing the extreme wear of the belt member.

1 is a cross-sectional view illustrating an embodiment of an image forming apparatus according to the present invention. 1 is a side cross-sectional view illustrating a configuration of an embodiment of a fixing device according to the present invention. It is a schematic perspective view of a fixing member. FIG. 3 is a longitudinal sectional view (1) of the fixing device. It is sectional drawing (2) of the longitudinal direction of a fixing device. FIG. 4 is a longitudinal sectional view (3) of the fixing device. It is sectional drawing (4) of the longitudinal direction of a fixing device. It is a schematic perspective view which shows the modification of a fixing belt and a pressure roller. FIG. 6 is a cross-sectional view illustrating a configuration of another embodiment of a fixing device. FIG. 6 is a cross-sectional view of the configuration of another embodiment of the fixing device, (A) an axial end portion and (B) an axial central side.

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

<First Embodiment>
(Image forming device)
[Constitution]
FIG. 1 is a schematic configuration diagram illustrating the overall configuration of a tandem type color copier that is an embodiment of an image forming apparatus according to the present invention. The outline and operation of the internal configuration of the image forming apparatus will be described with reference to FIG.

  As shown in FIG. 1, the image forming apparatus 1 according to the present embodiment is configured by a tandem color printer. The image forming apparatus 1 has a bottle accommodating portion 101 above the main body, and four toner bottles 102Y, 102M, 102C, and 102K are detachably installed in the bottle accommodating portion 101. The toner bottles 102Y, 102M, 102C, and 102K contain toners of corresponding colors (yellow, magenta, cyan, and black).

  An intermediate transfer unit 85 is disposed below the bottle storage unit 101. The intermediate transfer unit 85 includes an intermediate transfer belt 78, four primary transfer bias rollers 79Y, 79M, 79C, and 79K, a secondary transfer backup roller 82, a cleaning backup roller 83, a tension roller 84, and an intermediate transfer cleaning unit 80. ing. The intermediate transfer unit 85 has image forming units 4Y, 4M, 4C, and 4K that face the intermediate transfer belt 78 and correspond to the respective colors (yellow, magenta, cyan, and black).

  Photosensitive drums 5Y, 5M, 5C, and 5K are disposed in the image forming units 4Y, 4M, 4C, and 4K, respectively. Further, around each of the photosensitive drums 5Y, 5M, 5C, and 5K, a charging unit 75, a developing unit 76, a cleaning unit 77, and a charge eliminating unit (not shown) are disposed.

  The photosensitive drums 5Y, 5M, 5C, and 5K are formed in a cylindrical shape and are driven to rotate by a driving source (not shown). The photosensitive drums 5Y, 5M, 5C, and 5K are provided with photosensitive layers on the outer peripheral surface portions, and the light beams indicated by broken lines emitted from the exposure apparatus are spotted on the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K. By irradiation, electrostatic latent images corresponding to image information read by the document reading unit or image information acquired from the terminal via the network are written on the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K. .

  The charging unit 75 is configured to uniformly charge the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K, and is a contact type that charges the photosensitive drums 5Y, 5M, 5C, and 5K by contact. The thing is adopted.

  The developing unit 76 supplies toner to the photosensitive drums 5Y, 5M, 5C, and 5K, and the supplied toner adheres to the electrostatic latent image written on the outer peripheral surface of the photosensitive drums 5Y, 5M, 5C, and 5K. As a result, the electrostatic latent images on the photosensitive drums 5Y, 5M, 5C, and 5K are visualized as toner images, and the toner is not brought into contact with the photosensitive drums 5Y, 5M, 5C, and 5K. A non-contact type is used.

  The cleaning unit 77 is configured to remove residual toner adhering to the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K, and a brush is applied to the outer peripheral surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K. A brush contact method is used.

  The intermediate transfer belt 78 is stretched and supported by the secondary transfer backup roller 82, the cleaning backup roller 83, and the tension roller 84, and is endlessly moved in the direction of the arrow shown in FIG. The

  The intermediate transfer belt 78 is constituted by an endless belt formed using a resin film or rubber as a base, and a toner image formed on the photosensitive drums 5Y, 5M, 5C, and 5K is transferred. It has become. Further, the toner image transferred to the intermediate transfer belt 78 is transferred to the recording medium P as an unfixed image.

  Each of the photosensitive drums 5Y, 5M, 5C, and 5K is subjected to an image forming process including a charging process, an exposure process, a developing process, a primary transfer process, and a cleaning process. Images of each color are formed on 5M, 5C, and 5K.

  The primary transfer bias rollers 79Y, 79M, 79C, and 79K respectively sandwich the intermediate transfer belt 78 with the photosensitive drums 5Y, 5M, 5C, and 5K to form primary transfer nips. Further, a transfer bias having a polarity opposite to the polarity of the toner is applied to the primary transfer bias rollers 79Y, 79M, 79C, and 79K.

[Image creation process]
Next, the image forming process will be described. First, in the charging step, the photosensitive drums 5Y, 5M, 5C, and 5K are rotationally driven clockwise in FIG. 1 by a drive motor (not shown). The surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K are uniformly charged at the position of the charging unit 75.

  In the exposure process, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the irradiation position of the laser beam emitted from the exposure unit 3, and the electrostatic latent images corresponding to the respective colors by the exposure scanning at this position. Is formed.

  Next, in the development process, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach a position facing the developing unit 76, and the electrostatic latent image is developed at this position to form toner images of each color. The

  Next, in the primary transfer process, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach the positions facing the intermediate transfer belt 78 and the first transfer bias rollers 79Y, 79M, 79C, and 79K, and this position is reached. Thus, the toner images on the photosensitive drums 5Y, 5M, 5C, and 5K are transferred onto the intermediate transfer belt 78. At this time, a small amount of untransferred toner remains on the photosensitive drums 5Y, 5M, 5C, and 5K.

  Next, in the cleaning process, the surfaces of the photoconductor drums 5Y, 5M, 5C, and 5K reach a position facing the cleaning unit 77, and the unremained portions on the photoconductor drums 5Y, 5M, 5C, and 5K at this position. The transferred toner is mechanically collected by the cleaning blade of the cleaning unit 77.

  Then, the surfaces of the photosensitive drums 5Y, 5M, 5C, and 5K reach a position facing a neutralization unit (not shown), and the residual potential on the photosensitive drums 5Y, 5M, 5C, and 5K is removed at this position. . Thereby, the image forming process in the photosensitive drums 5Y, 5M, 5C, and 5K is completed.

  The toner images of the respective colors formed on the respective photosensitive drums through the above development process are transferred onto the intermediate transfer belt 78 in an overlapping manner. As a result, a color image is formed on the intermediate transfer belt 78.

[Transfer process]
Next, the transfer process will be described. The intermediate transfer belt 78 travels in the direction of the arrow in FIG. 1 and sequentially passes through the primary transfer nips of the primary transfer bias rollers 79Y, 79M, 79C, and 79K. As a result, the toner images of the respective colors on the photosensitive drums 5Y, 5M, 5C, and 5K are primarily transferred while being superimposed on the intermediate transfer belt 78.

  The intermediate transfer belt 78 reaches a position facing the secondary transfer roller 89 in a state where the toner images of the respective colors are transferred in an overlapping manner. At this position, the secondary transfer backup roller 82 sandwiches the intermediate transfer belt 78 between the secondary transfer roller 89 and forms a secondary transfer nip. The four color toner images formed on the intermediate transfer belt 78 are transferred onto the recording medium P conveyed to the position of the secondary transfer nip. At this time, untransferred toner that has not been transferred to the recording medium P remains on the intermediate transfer belt 78.

  Thereafter, the intermediate transfer belt 78 reaches the position of the intermediate transfer cleaning unit 80. At this position, the untransferred toner on the intermediate transfer belt 78 is collected. Thereby, the transfer process in the intermediate transfer belt 78 is completed.

[Image formation process]
Next, the image forming process will be described. The recording medium P is conveyed from the paper supply unit 12 disposed below the image forming apparatus 1 to the position of the secondary transfer nip via the paper supply roller 97, the registration roller pair 98, and the like. A plurality of recording media P such as transfer paper are stored in the paper supply unit 12 in an overlapping manner. When the paper feed roller 97 is rotationally driven in the counterclockwise direction in FIG. 1, the uppermost recording medium P is fed between the rollers of the registration roller pair 98.

  The recording medium P conveyed to the registration roller pair 98 is temporarily stopped at the position of the roller nip of the registration roller pair 98 that has stopped rotating. Then, the registration roller pair 98 is rotationally driven in synchronization with the color image on the intermediate transfer belt 78, and the recording medium P is conveyed toward the secondary transfer nip. In this way, a desired color image is transferred onto the recording medium P.

  Thereafter, the recording medium P on which the color image is transferred at the position of the secondary transfer nip is conveyed to the position of the fixing device 20. At this position, the color image transferred on the surface is fixed on the recording medium P by heat and pressure generated by the fixing belt 21 and the pressure roller 31.

  Thereafter, the recording medium P is discharged out of the apparatus through a pair of paper discharge rollers 99. The recording medium P discharged out of the apparatus by the discharge roller pair 99 is sequentially stacked on the stack unit 100 as an output image. Thereby, the image forming process is completed. Further, a sheet reversing device 90 is provided that reverses the recording medium P so as to record images on both sides of the recording medium P, and again conveys the recording medium P toward the secondary transfer nip.

[Control unit]
The image forming apparatus 1 includes a main body control unit and an operation input unit (not shown). The main body control unit is constituted by a microcomputer including a CPU, ROM, RAM, I / O interface, and the like, and a program stored in advance in the ROM is executed by the CPU.

  The main body control unit is connected to the operation input unit and various sensors and motors provided in the image forming apparatus 1. The main body control unit includes a drive motor for driving the above-described photosensitive drums 5Y, 5M, 5C, and 5K, a drive mechanism for rotationally driving the pressure roller 31, and the like based on detection signals input from various sensors. While controlling each motor, the electricity supply control with respect to a heat source is performed.

  The operation input unit is provided in the main body of the image forming apparatus 1 and has various keys such as a numeric keypad and a print start key and various displays, and outputs input signals input through the various keys to the main body control unit. It is supposed to be.

(Fixing device)
Next, the fixing device 20 installed in the image forming apparatus 1 will be described. The fixing device (fixing device 20) according to the present embodiment includes an endless belt member (fixing belt 21) that is heated and rotated by a heat source (heater 25), and a rotary member that rotates while contacting the belt member. A pressure rotator (pressure roller 31) and a fixing member disposed inside the belt member and abutting the pressure rotator through the belt member to form a nip portion between the belt member and the pressure rotator. In the longitudinal direction of the nip portion, the pressure outside the recording medium conveyance area is higher than that in the recording medium conveyance area, and the friction coefficient between the belt member and the fixing member is higher in the longitudinal direction of the nip portion. It is a small one. In addition, the code | symbol in embodiment and the example of application are shown in a parenthesis.

[Basic configuration]
FIG. 2 is a side cross-sectional view illustrating a configuration of an embodiment of the fixing device. The basic configuration of the fixing device 20 will be described with reference to FIG. The fixing device 20 includes a fixing belt 21 as a belt member, a heat transfer member 22, a reinforcing member 23, a heater 25 as a heat source, a fixing member 26, a pressure roller 31, a temperature sensor 40, and a pressure. Mechanism 50.

  The fixing belt 21 is a thin and flexible endless belt, and rotates in the direction of the arrow in FIG. 2 as the pressure roller 31 rotates. The fixing belt 21 has a base material layer, an elastic layer, and a release layer sequentially laminated from the inner peripheral surface side, and the total thickness is set to 1 mm or less.

  The base material layer of the fixing belt 21 has a layer thickness of 30 to 100 μm, and is formed of, for example, a metal material such as nickel or stainless steel or a resin material such as polyimide.

  The elastic layer of the fixing belt 21 has a layer thickness of 100 to 300 μm and is formed of a rubber material such as silicone rubber, foamable silicone rubber, or fluororubber. By providing the elastic layer, when the color image is fixed on the recording medium P at the nip portion formed between the fixing belt 21 and the pressure roller 31, minute irregularities on the surface of the fixing belt 21 are not formed. Then, heat is uniformly transmitted to the toner image T on the recording medium P.

  As a result, the fixing device 20 can suppress the occurrence of a cocoon skin image on the recording medium P. Here, the cocoon skin image means an image in which a number of minute irregularities are formed on the surface.

  The release layer of the fixing belt 21 has a layer thickness of 10 to 50 μm. For example, PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, It is made of a material such as PES (polyether sulfide).

  By providing the release layer, the fixing belt 21 is secured with respect to the toner image T on the recording medium P. Further, the diameter of the fixing belt 21 is set to be 15 to 120 mm. In the present embodiment, the diameter of the fixing belt 21 is set to about 30 mm. Moreover, the mold release means that the bonded objects are peeled off, and the mold release property means the ease of peeling between the objects.

  The pressure roller 31 as a pressure rotating body that contacts the outer peripheral surface of the fixing belt 21 at the nip portion has a diameter of about 30 to 40 mm, and an elastic layer 33 is provided on a hollow cored bar 32. Formed. The elastic layer 33 of the pressure roller 31 is made of a material such as foamable silicone rubber, silicone rubber, or fluorine rubber. A thin release layer made of PFA, PTFE or the like can be provided on the surface layer of the elastic layer 33. Moreover, you may make it have a drum shape by making the difference of the diameter of the center and edge part of the pressure roller 31 into 0.05-0.25 mm. The pressure roller 31 is pressed against the fixing belt 21 to form a desired nip portion between both members.

  The fixing member 26 is made of a heat resistant resin material such as a liquid crystal polymer, and has a concave cross section so that the surface on the pressure roller 31 side follows the curvature of the pressure roller 31. As a result, the recording medium P is fed out from the nip portion so as to follow the curvature of the pressure roller 31, so that the recording medium P after the fixing process is not attracted to the fixing belt 21 and separated. Can be deterred.

  FIG. 3 shows a schematic perspective view of the fixing member 26. As shown in FIG. 3, the fixing member 26 has a contact portion 26 a that comes into contact with the recording medium P via the fixing belt 21 in the recording medium conveyance area where the recording medium P is conveyed, and an outer side in the longitudinal direction from the recording medium conveyance area ( Hereinafter, it has a protruding portion 26b protruding in the thickness direction of the recording medium P. As a result, the slip generated between the fixing belt 21 and the pressure roller 31 can be prevented without increasing the number of parts, which contributes to downsizing of the fixing device 20 and can be easily manufactured, thereby reducing the manufacturing cost. Can be done.

  In FIG. 2, the cross-sectional shape of the fixing member 26 that forms the nip portion is formed in a concave shape. However, the shape of the fixing member 26 that forms the nip portion is formed in a flat shape, or continuously from the flat shape to the concave shape. It can also be formed to change. By setting the nip shape to an arbitrary shape, when the shape of the nip portion is substantially parallel to the image surface of the recording medium P, there is an effect of preventing the recording medium P from being wrinkled. Further, by bringing the shape close to the concave cross-sectional shape, the adhesion between the fixing belt 21 and the recording medium P is increased, and the fixing property is improved. Further, since the curvature of the fixing belt 21 on the exit side of the nip portion is increased, the recording medium P sent from the nip portion can be easily separated from the fixing belt 21.

  The heat transfer member 22 is a guide member for uniformly transferring heat from the heat source to the fixing belt 21. Both ends in the width direction of the heat transfer member 22 are fixedly supported by side plates (not shown) of the fixing device 20 and are pipe-like members having a wall thickness of 0.2 mm or less. As a material of the heat transfer member 22, for example, a metal having thermal conductivity such as aluminum, iron, and stainless steel can be used.

  By setting the wall thickness of the heat transfer member 22 to 0.2 mm or less, the fixing device 20 can improve the heating efficiency of the fixing belt 21. The heat transfer member 22 is formed so as to be close to or in contact with the inner peripheral surface of the fixing belt 21 at a position excluding the nip portion. At the position of the nip portion, a concave shape is formed inside and an opening is formed. A recess is provided.

  Here, the gap A between the fixing belt 21 and the heat transfer member 22 at a position excluding the nip portion at room temperature is preferably greater than 0 mm and 1 mm or less (0 mm <A ≦ 1 mm). As a result, the fixing device 20 can suppress a problem that the area where the heat transfer member 22 and the fixing belt 21 are in sliding contact with each other and the wear of the fixing belt 21 accelerates.

  Further, the fixing device 20 can suppress a problem that the heating efficiency of the fixing belt 21 is lowered due to the heat transfer member 22 and the fixing belt 21 being too far apart. Further, the fixing device 20 is provided with the heat transfer member 22 near the fixing belt 21 so that the circular posture of the fixing belt 21 having flexibility is maintained to some extent. Can be reduced.

  Further, in order to reduce the sliding resistance between the heat transfer member 22 and the fixing belt 21 (friction resistance when moving while sliding), the fixing device 20 uses a material with a low friction coefficient for the sliding contact surface of the heat transfer member 22. Alternatively, a surface layer made of a material containing fluorine can be formed on the inner peripheral surface of the fixing belt 21.

  The heat transfer member 22 is heated by the radiant heat and radiant light (hereinafter simply referred to as “radiant heat”) of the heater 25 to heat the fixing belt 21. That is, the fixing device 20 is configured such that the heat transfer member 22 is directly heated by the heater 25 and the fixing belt 21 is indirectly heated by the heater 25 via the heat transfer member 22.

  The output control of the heater 25 is performed based on the detection result of the surface temperature of the fixing belt 21 by the temperature sensor 40 facing the surface of the fixing belt 21. Further, by such output control of the heater 25, the fixing temperature of the fixing belt 21 for fixing the color image on the recording medium P can be set to a desired temperature. Here, the temperature sensor 40 is configured by a thermistor or the like.

  Further, by providing a plurality of heaters 25 and changing the axial heat generation region for each heater 25, the fixing belt 21 can be heated in a range corresponding to various paper widths.

  As described above, the fixing device 20 is configured such that not only a part of the fixing belt 21 is locally heated but the fixing belt 21 is almost entirely heated in the circumferential direction by the heat transfer member 22. Yes. As a result, the fixing device 20 can suppress the occurrence of fixing failure by sufficiently heating the fixing belt 21 even when the speed of the device is increased.

  The reinforcing member 23 reinforces and supports the fixing member 26 that forms the nip portion. The reinforcing member 23 is formed so that the length in the width direction is equal to that of the fixing member 26, and is formed on the inner peripheral surface side of the fixing belt 21. Is provided. Both ends of the reinforcing member 23 in the width direction are fixedly supported by side plates (not shown) of the fixing device 20.

  The reinforcing member 23 comes into contact with the pressure roller 31 via the fixing member 26 and the fixing belt 21, thereby preventing a problem that the fixing member 26 is greatly deformed by the pressure applied by the pressure roller 31 in the nip portion. doing.

  The reinforcing member 23 is preferably formed of a metal material having high mechanical strength such as stainless steel or iron alloy in order to satisfy the above-described function.

  Further, when the heater 25 is a heat source that uses radiant heat, such as a halogen heater, a heat insulating member is provided on a part or all of the surface of the reinforcing member 23 facing the heater 25, or BA ( It is also preferable to apply a bright annealing process or a mirror polishing process.

  As a result, the radiant heat from the heater 25 toward the reinforcing member 23 is insulated or reflected and used for heating the heat transfer member 22, and the heating efficiency of the heat transfer member 22 is further improved. Efficiency will be further improved.

  The pressure roller 31 is provided with a gear that meshes with a drive gear of a drive mechanism (not shown), and the pressure roller 31 is rotationally driven in the direction of the arrow in FIG. In addition, the pressure roller 31 is rotatably supported at both ends in the width direction on a side plate (not shown) of the fixing device 20 via a bearing.

  The elastic layer 33 is formed of a material such as foamable silicone rubber, silicone rubber, or fluororubber. Further, a thin release layer made of PFA, PTFE or the like is provided on the surface layer of the elastic layer 33.

  Further, when the elastic layer 33 is formed of a sponge-like material such as foamable silicone rubber, the applied pressure acting on the nip portion can be reduced, so that the bending that occurs in the fixing member 26 can be reduced. . In this case, the heating efficiency of the fixing belt 21 is improved because the heat of the fixing belt 21 becomes difficult to move to the pressure roller 31 side.

  A heat source such as a halogen heater can be provided inside the pressure roller 31. Further, when the elastic layer 33 of the pressure roller 31 is formed of a sponge-like material such as foamable silicone rubber, the pressure applied to the nip portion can be reduced. Can be reduced. Furthermore, since the heat insulation of the pressure roller 31 is enhanced and the heat of the fixing belt 21 is difficult to move to the pressure roller 31 side, the heating efficiency of the fixing belt 21 is improved.

  In FIG. 2, the diameter of the fixing belt 21 is formed to be equal to the diameter of the pressure roller 31, but the diameter of the fixing belt 21 may be formed to be smaller than the diameter of the pressure roller 31. it can. In that case, since the curvature of the fixing belt 21 in the nip portion is smaller than the curvature of the pressure roller 31, the recording medium 107 sent out from the nip portion is easily separated from the fixing belt 21.

  Further, the fixing belt 21 can be formed so that the diameter thereof is larger than the diameter of the pressure roller 31. The fixing device 20 according to each embodiment described above is configured such that the pressure applied by the pressure roller 31 does not act on the heat transfer member 22 regardless of the relationship between the diameter of the fixing belt 21 and the diameter of the pressure roller 31. Has been.

  The fixing device 20 is provided with a pressure mechanism 50 that contacts and separates the pressure roller 31 from the fixing belt 21. The pressure mechanism 50 includes a pressure lever 51, an eccentric cam 52, and a pressure spring 53.

  The pressure lever 51 is rotatably supported on a side plate of the fixing device 20 (not shown) around a support shaft 51a provided on one end side. The central portion of the pressure lever 51 is in contact with a bearing (not shown) of the pressure roller 31 movably held in a long hole formed in a side plate of the fixing device 20 (not shown).

  A pressure spring 53 is connected to the other end side of the pressure lever 51. The pressure spring 53 has an eccentric cam 52 attached to its holding plate. The eccentric cam 52 is configured to be rotatable by a drive motor (not shown).

  With such a configuration, the pressure lever 51 rotates around the support shaft 51a by the rotation of the eccentric cam 52 during the normal fixing operation, and the posture of the eccentric cam 52 becomes the state shown in FIG. The pressure roller 31 presses the fixing belt 21 to form a desired nip portion.

  On the other hand, in cases other than the normal fixing operation, such as during jam processing or standby, the eccentric cam 52 rotates 180 degrees from the state shown in FIG. 2, and the pressure roller 31 is detached from the fixing belt 21. Alternatively, the fixing belt 21 is decompressed.

[basic action]
Hereinafter, the basic operation of the fixing device according to the present embodiment will be described with reference to FIG. When the power switch of the image forming apparatus 1 is turned on, power is supplied to the heater 25, and the rotational driving of the pressure roller 31 in the direction of the arrow in FIG.

  Thereby, the fixing belt 21 is also driven to rotate in the direction of the arrow in FIG. 2 by the frictional force with the pressure roller 31. Thereafter, the recording medium P is fed from the paper feeding unit 12, and the unfixed toner image T is transferred onto the recording medium P at the position of the secondary transfer roller 89.

  The recording medium P onto which the unfixed toner image T has been transferred is conveyed in the direction of arrow Y10 in FIG. 2 while being guided by a guide plate (not shown), and is pressed between the fixing belt 21 and the pressure roller 31 in a pressed state. It is carried into the nip part.

  The toner on the surface of the recording medium P is heated by the fixing belt 21 heated by the heater 25 via the heat transfer member 22 and the pressing force of the fixing member 26 reinforced by the reinforcing member 23 and the pressure roller 31. The image T is fixed on the recording medium P. Thereafter, the recording medium P sent out from the nip portion is conveyed in the direction of arrow Y11.

(Fixing member)
As described above, the fixing member 26 has the contact portion 26a in the recording medium conveyance region and the protruding portion 26b that protrudes toward the pressure roller 31 outside the recording medium conveyance region (FIG. 3).

  FIG. 4 is a longitudinal sectional view of the fixing device 20 in a state where the recording medium P is carried into the nip portion of the fixing device 20 and is nipped. In the fixing device 20, a fixing member 26 urged by the pressure lever 51 presses the fixing belt 21 against the pressure roller 31 to form a nip portion.

  Here, since the fixing member 26 has the shape shown in FIG. 3, the fixing belt 21 is attached to the protruding portion 26 b located outside the fixing member 26 in the longitudinal direction (outside the recording medium conveyance area) more than the recording medium conveyance area. The fixing belt 21 is pressed against the pressure roller 31 with a high pressure against the pressure roller 31. That is, the pressure outside the recording medium conveyance area is higher than in the recording medium conveyance area.

  According to such a configuration, the frictional force acting between the fixing belt 21 and the pressure roller 31 is a region where the pressure roller 31 faces the contact portion 26a of the fixing member 26 located in the recording medium conveyance region. In contrast, the protrusion 26b located outside the recording medium conveyance area and the pressure roller 31 act more strongly in the area facing each other. However, on the other hand, there is a risk that the friction between the inner side of the fixing belt 21 and the fixing member 26 outside the recording medium conveyance area (on the end side) will be large and that local wear may occur.

  Accordingly, the fixing device 20 according to the present embodiment is configured to reduce the friction coefficient between the fixing belt 21 and the fixing member 26 outside the recording medium conveyance region where the pressure is high.

  In other words, in order to reduce the space between the fixing belt 21 and the fixing member 26, a coating process is applied to make the surface layer on the inner peripheral side of the fixing belt 21 of the protruding portion 26b of the fixing member 26 low in friction. In this embodiment, as shown in FIG. 4, a low friction coat 26d such as a fluorine coat is applied. In place of the coating process, a low friction member such as a fluororesin sheet may be provided between the inner peripheral side of the fixing belt 21 and the protruding portion 26b.

  According to the fixing device 20 according to the present embodiment, when the recording medium P is nipped by the nip portion in the process of fixing the unfixed toner image T on the recording medium P, the friction coefficient with the pressure roller 31 is small. The surface of the recording medium P obstructs the frictional force between the fixing belt 21 and the pressure roller 31, and the fixing belt 21 and the pressure roller 31 easily slip in the recording medium conveyance region. In the region, since the fixing belt 21 is pressed against the pressure roller 31 at a high pressure by the protrusion 26b, a high frictional force is secured between the surfaces of the pressure roller 31 and the fixing belt 21, and both slips are prevented. can do.

  Furthermore, since the protrusion 26b is provided with a low friction coating 26d, it is possible to reduce the frictional load between the inside of the fixing belt 21 and the fixing member 26, and to prevent extreme wear.

  That is, the portion where the friction coefficient in the longitudinal direction of the sliding surface between the fixing belt 21 and the fixing member 26 corresponds to the pressing force pressing the fixing belt 21 of the pressure roller 31 is high. In order to prevent the wear of the poles at the portion where the load inside the belt end portion is increased.

  Therefore, even when the pressure inside the belt is larger than the central portion, the recording medium P can be prevented by stabilizing the behavior of the fixing belt 21 and preventing the local wear of the fixing belt 21 with a simple configuration. In addition to preventing wrinkles and paper jams, the recording medium P can be stably conveyed, and image noise can be suppressed to maintain good image quality.

<Second Embodiment>
Hereinafter, other embodiments of the fixing device according to the present invention will be described. In addition, the description about the same point as the said embodiment is abbreviate | omitted suitably.

  FIG. 5 is a longitudinal sectional view of the fixing device 20 in a state in which the recording medium P is carried into and held between the nip portions of the fixing device 20 of the second embodiment.

  In the present embodiment, the fixing member 26 is configured to have a slope portion 26c in which the protruding amount in the thickness direction of the recording medium P continuously increases toward the outside in the longitudinal direction in an area outside the recording medium conveyance area. Has been. Further, a low friction coat 26d is applied to the surface of the inclined portion 26c.

  Further, the fixing belt 21 is configured such that the inner diameter continuously increases toward the end in the longitudinal direction in the region outside the recording medium conveyance region. In other words, the fixing belt 21 has a so-called reverse crown shape in which the circumferential length in the recording medium conveyance area is the shortest, and the circumferential length continuously increases toward the end in the longitudinal direction outside the recording medium conveyance area.

  As a result, the fixing device 20 allows the fixing belt 21 that contacts the inclined surface portion 26c outside the recording medium conveyance area to be pressed against the pressure roller 31 without excessive deformation. The cost for replacement can be reduced by lengthening the length of the battery.

  Further, since the inclined portion 26c is provided with the low friction coat 26d, it is possible to reduce the friction load between the inside of the fixing belt 21 and the fixing member 26, and it is possible to prevent extreme wear.

<Third Embodiment>
FIG. 6 is a longitudinal sectional view of the fixing device 20 in a state in which the recording medium P is carried into and held in the nip portion of the fixing device 20 of the third embodiment.

  In the present embodiment, the frictional resistance generated between the fixing belt 21 and the fixing member 26 is reduced between the inner peripheral surface of the fixing belt 21 and the surfaces of the contact portion 26a and the protruding portion 26b of the fixing member 26. The sliding member (low friction member) 28 (28a, 28b) is provided.

  The sliding member 28 is formed, for example, in the form of a sheet having fine irregularities on the surface, and at least on the surface in contact with the fixing belt 21, a material having a small friction coefficient and excellent wear resistance and heat resistance (for example, , A fluororesin sheet or the like).

  Furthermore, in the present embodiment, the friction coefficient of the sliding member 28 is not uniform, but varies depending on the pressure distribution in the longitudinal direction of the nip portion. That is, the sliding member 28 is provided so that the friction coefficient is low at a position where the pressure is high and the friction coefficient is high at a position where the pressure is low.

  That is, the protruding portion 26b corresponding to the outside of the recording medium conveyance area where the pressure is high uses a sliding member 28b having high performance (a large amount of frictional resistance is reduced), and the contact portion 26a corresponding to the recording medium conveyance area where the pressure is low. Then, the sliding member 28a having a reduced amount of frictional resistance is used as compared with the sliding member 28b used for the protruding portion 26b. By using a plurality of sliding members 28a and 28b in this way, it is not necessary to use expensive members that are uniformly highly effective in reducing frictional resistance, and those having relatively low performance can be applied to the sliding member 28a. Therefore, an inexpensive configuration is possible.

  Further, instead of the sliding member 28 in the present embodiment, a low friction coat 26d may be applied so as to have different friction coefficients between the contact portion 26a and the protruding portion 26b. Further, the low friction coat 26d and the sliding member 28 may be used together.

  Further, the fixing device 20 preferably applies a lubricant such as fluorine grease or silicone oil that reduces sliding resistance to the contact surface between the fixing belt 21 and the sliding member 28.

  Since the sliding member 28 has fine irregularities on the surface, the lubricant is applied to the concave portion of the sheet by applying the lubricant, and wear of the sliding member 28 can be prevented.

  Further, since the lubricant applied to the sliding member 28 diffuses between the fixing belt 21 and the heat transfer member 22 as a result of the rotation of the fixing belt 21, the fixing device 20 fixes the heat transfer member 22 and the fixing member 20. Wear of the fixing belt 21 when the belt 21 comes into contact is reduced.

  Here, when compared with the blending consistency representing the hardness of the grease, generally the lubricant as described above has a higher blending consistency (consistency) as the oil component contained in the lubricant increases. Here, the consistency represents the hardness of the paste-like object, and the higher the consistency, the softer the object.

  In general, it has been experimentally known that the higher the mixing consistency, the higher the effect of reducing the load due to the frictional resistance between the fixing belt 21 and the heat transfer member 22, and therefore in the lubricant according to this embodiment, It is desirable to set the mixing consistency at 300 or more.

  However, the absolute amount of lubricant over time decreases as the lubricant scatters due to the rotation of the fixing belt 21 or the oily component gradually evaporates due to the heat of the fixing device 20. Therefore, it is necessary to select a lubricant suitable for the system in consideration of retention of the lubricant that can remain between the fixing belt 21 and the heat transfer member 22.

<Fourth Embodiment>
FIG. 7 is a longitudinal sectional view of the fixing device 20 in a state in which the recording medium P is carried into the nip portion of the fixing device 20 of the fourth embodiment and is sandwiched.

  In the present embodiment, the elastic member 29 is provided between the fixed member 26 and the sliding member 28, and is configured to follow the fixing belt 21 with the unevenness of the recording medium P.

  The elastic member 29 is formed of an elastic body such as silicone rubber or fluorine rubber, and has a contact portion 29a that contacts the recording medium P via the fixing belt 21 in the recording medium conveyance area, and a recording medium outside the recording medium conveyance area. A protrusion 29b protruding in the thickness direction of P is provided.

  In general, when a recording medium with low smoothness (coarse recording medium) is used, if irregularities due to the roughness of the recording medium remain on the surface of the image after fixing the toner image, light is irregularly reflected and the concave portions appear black. It is easy to generate a cocoon skin image that appears as uneven luster. In particular, in an on-demand type fixing device that employs a heating device using an endless belt member such as a belt or a thin film on the image surface side, the cocoon skin image tends to be significantly deteriorated.

  In the fixing device 20 according to the present embodiment, the elastic member 29 is provided on the surface of the fixing member 26 so that the fixing belt 21 can follow the surface of the recording medium. On the other hand, the toner image can be copied to uniformly heat the toner image. Thereby, the fixing device 20 can suppress fine gloss unevenness on the image, and can prevent the occurrence of a cocoon skin image.

  However, the prevention of the cocoon skin image by using the elastic member 29 means that the unevenness of the toner image on the recording medium is eliminated by the pressure, which means that the nip portion has a high pressure. Therefore, even in the case of this configuration, the cocoon skin image is obtained by using the sliding member 28 or the low friction coat 26d so that the end of the nip portion has a lower friction coefficient than the center portion. It is possible to prevent the belt member from being worn at the extreme places. In the example of FIG. 7, the sliding members 28a and 28b are provided as in the third embodiment.

  In the present embodiment, the elastic member 29 is formed to have the protruding portion 29b protruding in the thickness direction of the recording medium P. However, the present invention is not limited to this, and the contact portion 29a and the protruding portion 29b are on the same plane. It may be formed so that the hardness outside the recording medium conveyance area is higher than that inside the recording medium conveyance area.

  In this embodiment, since the elastic member 29 is provided with the protruding portion 29b protruding in the thickness direction of the recording medium P, the fixing member 26 may have a uniform height in the width direction.

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

  In each of the embodiments described above, the fixing belt 21 and the pressure roller 31 are each configured to have a release layer. However, the present invention is not limited thereto, and the release layer is removed outside the recording medium conveyance area. It is also preferable.

  Here, the case where the release layer outside the recording medium conveyance area of each of the fixing belt 21 and the pressure roller 31 is removed will be described. As shown in FIG. 8, the fixing belt 21 has a high friction portion 21b that peels off the release layer outside the recording medium conveyance area and exposes an elastic layer having a surface friction coefficient larger than that of the release layer on the surface. . The pressure roller 31 has a high friction portion 31b that peels off the release layer outside the recording medium conveyance area and exposes an elastic layer having a surface friction coefficient larger than that of the release layer on the surface.

  As a result, the fixing device 20 causes a high frictional force to act between the fixing belt 21 and the pressure roller 31 outside the recording medium conveyance area without adding another member, thereby increasing the grip force between the two members. Therefore, it is possible to prevent slippage between the two members.

  In FIG. 8, the fixing belt 21 and the pressure roller 31 are configured such that both members have a high friction portion outside the recording medium conveyance region, but it is not always necessary to provide the high friction portion on both members. .

  That is, in the fixing device 20, if either the fixing belt 21 or the pressure roller 31 has a high friction part, a high frictional force acts between the fixing belt 21 and the pressure roller 31, so Sufficient grip force is prevented to prevent the occurrence of slip. Further, by improving the grip force, the protruding portion 26b of the fixing member 26 can be lowered and the pressure can be reduced. As a result, the sliding load on the parts is reduced, so that the life can be extended.

  For example, in the above-described embodiment, an example in which a halogen heater provided inside the fixing belt 21 is provided as a heat source has been described. However, the heat source is not limited to the halogen heater. Further, the heat source does not need to be provided on the inner peripheral side of the fixing belt 21 and may heat the fixing belt 21 from the outer peripheral side of the fixing belt 21.

  For example, the heat source may be composed of a coil and an inverter, and a non-contact heating method using an electromagnetic induction heating method (IH method) may be used. In this IH system, a configuration in which a large number of heating coils are arranged in the longitudinal direction, or a configuration in which a heating region and a heating amount in the longitudinal direction are controlled by arranging a large number of members that cancel the magnetic flux can be achieved. . Further, in the electromagnetic induction heating method (IH method), magnetic members may be provided inside and outside the fixing belt 21.

  Although not shown, a fixing device in which shielding members for shielding heat from the heater 25 are disposed between the fixing belt 21 and the heater 25 at both axial ends of the fixing belt 21 may be used. preferable. 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.

  Moreover, in each embodiment mentioned above, although the cross-sectional shape of the heat-transfer member 22 was formed so that it might become substantially circular, you may form so that it may become not only this but a polygon.

  In the case where a means for uniformly transferring the heat from the heat source to the fixing belt 21 and ensuring the running stability of the fixing belt 21 during driving is prepared separately, the fixing device 20 includes the heat transfer member 22. The fixing belt 21 may be directly heated.

  According to the fixing device 20 that can directly heat the fixing belt 21 as described above, the heat capacity of the heat transfer member 22 is excluded from the heat capacity of the entire fixing device, so that the temperature easily rises and the fixing has excellent energy saving performance. It can be configured as a device.

  FIG. 9 shows another example of a fixing device provided with the fixing member 26 shown in FIG. FIG. 9 is a cross-sectional view of the center side in the axial direction of the fixing device 20. The fixing device 20 shown in FIG. 9 includes one heater 25 and includes a reflection member 24 that reflects radiant heat from the heater 25. As the reflecting member 24, for example, a reflecting plate can be used. As shown in FIG. 9, the reflecting member 24 covers the surface of the reinforcing member 23 on the heater 25 side and has a shape in which a bent portion 24 a is formed, and reflects the radiant heat of the heater 25 to the heat transfer member 22. The heating efficiency of the fixing belt 21 is improved.

  In addition, protrusions 23 a are formed at both ends of the reinforcing member 23 in the axial direction, and the protrusions 23 a of the reinforcing member 23 come into contact with a side plate (not shown) when pressed by the pressure roller 31. Thus, the reinforcing member 23 and the fixing member 26 are supported from the opposite side of the nip portion.

  FIG. 10 shows another example of the fixing device including the fixing member 26 shown in FIG. 10A is a cross-sectional view of the fixing device 20 on the end side in the axial direction, and FIG. 10B is a cross-sectional view of the fixing device 20 on the center side in the axial direction.

  The fixing device 20 illustrated in FIG. 10 includes two heaters 25 and a reflection member 24 that reflects radiant heat from the heaters 25. As shown in FIG. 10, the reflecting member 24 covers the surface of the reinforcing member 23 on the heater 25 side and is formed with a bent portion 24 a, and reflects the radiant heat of the heater 25 to the heat transfer member 22, thereby fixing the fixing belt. The heating efficiency of 21 is improved. Further, as shown in FIG. 10A, the reflecting member 24 is bent at the end portion side so that the lower portion in the vertical direction of the reinforcing member 23 has a thick shape and extends to the lower portion side of the heater 25 in the drawing. It is comprised so that it may have the part 24b.

  Note that the configuration of the fixing device 20 illustrated in FIGS. 9 and 10 may be configured without the heat transfer member 22.

  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. .

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 3 Exposure part 4Y, 4M, 4C, 4K Image forming part 5Y, 5M, 5C, 5K Photosensitive drum 12 Paper feed part 20 Fixing apparatus 21 Fixing belt (belt member)
21b High friction part 22 Heat transfer member 23 Reinforcement member 23a Protrusion part 24 Reflection member 24a, 24b Bending part 25 Heater (heat source)
26 Fixing member 26a Contact portion 26b Protruding portion 26c Slope portion 26d Low friction coat 28, 28a, 28b Sliding member (low friction member)
29 Elastic member 29a Contact part 29b Protrusion part 31 Pressure roller (Pressure rotating body)
31b High friction part 32 Core metal 33 Elastic layer 40 Temperature sensor 50 Pressure mechanism 51 Pressure lever 51a Support shaft 52 Eccentric cam 53 Pressure spring 75 Charging part 76 Developing part 77 Cleaning part 78 Intermediate transfer belts 79Y, 79M, 79C, 79K Primary transfer bias roller 80 Intermediate transfer cleaning unit 82 Secondary transfer backup roller 83 Cleaning backup roller 84 Tension roller 85 Intermediate transfer unit 89 Secondary transfer roller 90 Sheet reversing device 97 Paper feed roller 98 Registration roller pair 99 Paper discharge roller pair 100 Stack unit 101 Bottle storage unit 102Y, 102M, 102C, 102K Toner bottle P Paper (recording medium)
T Toner image

JP 09-244448 A JP 2005-266716 A

Claims (10)

An endless belt member that is heated and rotated by a heat source;
A pressure rotator that rotates while contacting the belt member;
A fixing member that is disposed inside the belt member and that abuts against the pressure rotator through the belt member to form a nip portion between the belt member and the pressure rotator. ,
In the longitudinal direction of the nip portion, the pressure outside the recording medium conveyance area is higher than that in the recording medium conveyance area, and the friction coefficient between the belt member and the fixing member is small.   The fixing device according to claim 1, further comprising a low friction member that reduces sliding resistance between the inside of the belt member and the surface of the fixing member outside the recording medium conveyance region.   3. The fixing device according to claim 1, wherein a coating treatment is applied to a surface of the fixing member on the belt member side outside the recording medium conveyance area to reduce sliding resistance therebetween. . Provided between the inner surface of the belt member and the surface of the fixing member in the recording medium conveyance region, a low friction member that reduces the sliding resistance of both,
The fixing device according to claim 2, wherein the low friction member in the recording medium conveyance region is a member having a lower effect of reducing sliding resistance than the low friction member outside the recording medium conveyance region. On the surface of the fixing member in the recording medium conveyance area on the side of the belt member, a coating treatment for reducing the sliding resistance of both is performed.
The fixing device according to claim 3, wherein the film treatment performed in the recording medium conveyance area has a lower effect of reducing sliding resistance than the film treatment performed outside the recording medium conveyance area.   6. The fixing device according to claim 1, wherein the fixing member has a portion that protrudes outside the recording medium conveyance area from the inside of the recording medium conveyance area. 7.   The fixing device according to claim 2, wherein an elastic member is provided between the fixing member and the low friction member.   The high friction part which raises sliding resistance with respect to the opposing member is provided in the surface outside the recording medium conveyance area | region of the said belt member and / or the said pressurization rotary body, The any one of Claim 1 to 7 characterized by the above-mentioned. A fixing device according to claim 1.   The fixing device according to claim 8, wherein the high friction portion is formed by peeling a release layer on a surface of the belt member or the pressure rotating body.   An image forming apparatus comprising the fixing device according to claim 1.