JP6578666B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

  The present invention relates to a fixing device that fixes an unfixed toner image on a recording material, and an image forming apparatus including the fixing device. The image forming apparatus includes various apparatuses such as a copying machine, a printer, a facsimile machine, and a multifunction machine having these functions in a complex manner.

  In recent years, in an image forming apparatus employing an electrophotographic system, an unfixed toner image is transferred to a fixing nip portion between a fixing roller that heats an unfixed toner image on a recording material and a pressure roller that is in pressure contact with the fixing roller. It is widely performed to fix a toner image on a recording material by conveying the recording material and heating and pressurizing it. As this type of fixing device, for example, an endless belt is wound around an outer peripheral portion of a fixing roller, and an unfixed toner image on a recording material is heated via the endless belt.

  In this type of belt-type fixing device, the endless belt is not fixed to a support roller such as a fixing roller that stretches the endless belt, and various factors (for example, support The movement of the support roller in the axial direction (meandering or offset) may occur due to the inclination of the roller or the expansion of the support roller. Therefore, a regulating member for restricting such movement of the endless belt is usually provided at both axial ends of the support roller. However, there is a problem that the endless belt is cracked when the end of the endless belt comes into contact with such a regulating member.

  On the other hand, as a prior art, in Patent Document 1, the shape of the meandering detection roller that supports the belt-like web is changed to an inverted crown shape so that the shaft end of the meandering detection roller is displaced according to the meandering of the web. A configured web transport device is disclosed. In this web conveyance device, the amount of meandering of the web is calculated by measuring the change in expansion and contraction of the support springs respectively connected to both ends of the meandering detection roller. In addition, two differential rollers that can rotate independently are mounted on the axis of the meandering detection roller, and the rotational speed of the differential roller is reduced by an electromagnetic brake in accordance with the calculated amount of meandering. Is corrected.

  Patent Document 1 also discloses a configuration in which the rotational speed of the differential roller is changed using a friction member fixedly supported by a frame instead of the electromagnetic brake. In this configuration, as described above, when the shaft end of the meandering detection roller is displaced according to the meandering of the web (that is, the shaft of the meandering detection roller is inclined), the differential roller is fixedly supported on the frame as a result. The friction member approaches and comes into contact, and the rotational speed of the differential roller is reduced.

JP 2002-316756 A

  However, when the technique disclosed in Patent Document 1 is applied to the belt-type fixing device as described above, there are the following problems.

  That is, when the shape of the support roller is an inverted crown shape, a large stress is generated at the end portion of the endless belt, so that the end portion of the endless belt is likely to be damaged.

  In addition, since a gap may be formed between the two differential rollers, the gap prevents the temperature of the endless belt from being uniformed, thereby adversely affecting the image quality (gloss) on the recording material. .

  Further, in the configuration using the electromagnetic brake, there is a concern that the magnetic force is lowered due to the electromagnetic brake being exposed to a high temperature for a long time, and there is a problem that the brake operation becomes unstable. Furthermore, there is a problem that the cost becomes high.

  In addition, it is necessary to configure the shaft of the meandering detection roller so that the shaft of the meandering detection roller can be tilted regardless of the configuration using the electromagnetic brake or the configuration using the friction member fixedly supported by the frame. It cannot be stably supported and may adversely affect the formation of the fixing nip portion. As a result, there is a problem in that the recording material conveyance speed in the fixing nip portion has a left-right difference, causing paper wrinkles and image distortion.

  The present invention has been made in view of the above problems, and includes a fixing device capable of controlling the position of the endless belt in the width direction while suppressing breakage of the endless belt, and the fixing device. It is a technical problem to provide an image forming apparatus.

The invention of claim 1 is a fixing device for fixing an unfixed toner image on a recording material, and has a first roller for forming a fixing nip portion and the same outer diameter provided along a common axis. The first roller unit including a first roller unit, a central roller unit, and a second roller unit that are rotatable independently of each other, and at least two rollers including the first roller and the second roller. An endless belt, detection means for detecting the position or displacement of the endless belt in the width direction, and the first end roller section or the second end roller section selectively based on the detection result of the detection means and a frictional force applying means for applying a frictional force, said central roller unit is configured with respect to the common axis, the area on the endless belt at the fixing nip portion may contact with the recording medium The length and the position of the first end roller portion and the second end roller are determined so as not to exceed the range where the endless belt is positioned while completely covering the corresponding maximum contact range. The portion is provided at a position that contacts the endless belt outside the maximum contact range with respect to the common axis direction .

According to a second aspect of the present invention, there is provided a fixing device for fixing an unfixed toner image on a recording material, the first roller for forming a fixing nip portion, and the same outer diameter provided along a common axis. The first roller unit including a first roller unit, a central roller unit, and a second roller unit that are rotatable independently of each other, and at least two rollers including the first roller and the second roller. An endless belt, detection means for detecting the position or displacement of the endless belt in the width direction, and the first end roller section or the second end roller section selectively based on the detection result of the detection means and a frictional force applying means for applying a frictional force, the frictional force applying means, said shaft member having an axis parallel to the axis of the second roller, on the shaft member, the first end roller Department and Two pressing members fixed in different directions from each other at positions opposite to the second end roller part, and the two pressing members by rotating the shaft member in different directions according to the detection result of the detecting means. Drive means for bringing either one of the members into contact with the corresponding first end roller portion or second end roller portion is provided.

  According to a third aspect of the present invention, in the fixing device according to the first aspect, the frictional force applying means includes a shaft member having an axis parallel to an axis of the second roller, and the shaft member on the shaft member. By rotating two pressing members fixed in different directions at positions facing the first end roller portion and the second end roller portion, respectively, and the shaft member in different directions according to the detection result of the detection means And driving means for bringing either one of the two pressing members into contact with the corresponding first end roller portion or second end roller portion.

A fourth aspect of the present invention, in the fixing device according to any one of claims 1-3, wherein the frictional force applying means, the friction of the recording medium in accordance with the conveyance speed different sizes of in the fixing nip portion Friction force control means for applying force is provided.

  A fifth aspect of the present invention relates to an image forming apparatus, and includes the fixing device according to any one of the first to fourth aspects.

  According to the present invention, a frictional force is selectively applied to the first end roller portion or the second end roller portion based on the detection result of the position or displacement of the endless belt in the width direction, and the rotation speed is reduced. The Therefore, the position of the endless belt in the width direction can be changed by causing a difference in the rotation speed between the first end roller portion and the second end roller portion.

  In addition, since the three roller parts (the first end roller part, the central roller part, and the second end roller part) have the same outer diameter, a large stress does not occur at the end of the endless belt, and the endless Damage to the belt can be suppressed.

It is a schematic explanatory drawing of a printer. FIG. 3 is a side sectional view of the fixing device. FIG. 3 is a front sectional view of the fixing device.

  Hereinafter, an embodiment embodying the present invention will be described with reference to the drawings when applied to a tandem color digital printer (hereinafter referred to as a printer) which is an example of an image forming apparatus. In addition, in the following description, when using a term indicating a specific direction or position (for example, “left / right”, “up / down”, etc.) as necessary, the direction orthogonal to the paper surface in FIG. ing. These terms are used for convenience of explanation, and do not limit the technical scope of the present invention.

(1). Overview of Printer First, an overview of the printer 1 will be described with reference to FIG. As shown in FIG. 1, the printer 1 includes an image process device 3, a paper feeding device 4, a fixing device 5, and the like in a housing 2. Although not shown in detail, the printer 1 is connected to a network such as a LAN, and is configured to execute printing based on the command when receiving a print command from an external terminal (not shown). Yes.

  The paper feeding device 4 located at the lower part in the housing 2 includes a paper feeding cassette 21 that accommodates the recording material P, a pickup roller 22 that feeds the recording material P in the paper feeding cassette 21 from the uppermost layer, and a fed recording material P. A pair of separation rollers 23 for separating the recording materials one by one, a pair of timing rollers 24 for conveying the recording material P separated into one sheet to the image processing apparatus 3 at a predetermined timing, and the like. The recording material P in each paper feed cassette 21 is sent out one by one from the uppermost layer to the transport path 30 by the rotation of the pickup roller 22 and the separation roller 23. The conveyance path 30 includes a nip portion of the timing roller pair 24, a secondary transfer nip portion of the image processing device 3, and a fixing nip portion 33 (see FIG. 2) of the fixing device 5 from the paper feeding cassette 21 of the paper feeding device 4. Then, it reaches the discharge roller pair 26 at the upper part of the housing 2.

  The recording material P in the paper feed cassette 21 is set to a center reference that is transported in the transport direction S toward the transport path 30 with reference to the center of the sheet passing width (width dimension orthogonal to the transport direction S). Although illustration is omitted, the paper feed cassette 21 is provided with a pair of side part regulating plates for bringing the recording material P before paper feeding closer to the center. The pair of side regulating plates are configured to move in close proximity to each other in the sheet passing width direction (direction perpendicular to the transport direction S). By sandwiching the recording material P in the paper feed cassette 21 from both sides in the sheet passing width direction by the pair of side portion regulating plates, the recording material P in the paper feed cassette 21 is set to the center reference regardless of the standard. Therefore, the transfer process in the image processing apparatus 3 and the fixing process in the fixing apparatus 5 are also executed on the basis of the center.

  The image processing device 3 positioned above the paper feeding device 4 plays a role of transferring a toner image formed on a photosensitive drum 13 which is an example of an image carrier to a recording material P, and is an intermediate transfer member. And a total of four image forming sections 7 corresponding to the respective colors of yellow (Y), magenta (M), cyan (C) and black (K).

  The intermediate transfer belt 6 is an endless belt made of a conductive material, and is also an example of an image carrier. The intermediate transfer belt 6 is wound around a driving roller 8 located on the right side of the central part in the housing 2 and a driven roller 9 located on the left side of the central part. The intermediate transfer belt 6 rotates in the counterclockwise direction in FIG. 1 by rotating the driving roller 8 counterclockwise in FIG. 1 by power transmission from a main motor (not shown).

  A secondary transfer roller 10 is disposed on the outer peripheral side of the portion of the intermediate transfer belt 6 that is wound around the drive roller 8. The secondary transfer roller 10 is in contact with the intermediate transfer belt 6, and a portion between the intermediate transfer belt 6 and the secondary transfer roller 10 (contact portion) is a secondary transfer nip portion as a secondary transfer region. . The secondary transfer roller 10 rotates in the clockwise direction in FIG. 1 with the rotation of the intermediate transfer belt 6 or with the movement of the recording material P that is nipped and conveyed by the secondary transfer nip portion. A transfer belt cleaner 12 for removing untransferred toner on the intermediate transfer belt 6 is disposed on the outer peripheral side of the portion of the intermediate transfer belt 6 wound around the driven roller 9. The transfer belt cleaner 12 is in contact with the intermediate transfer belt 6.

  The four image forming units 7 are arranged along the intermediate transfer belt 6 in the order of yellow (Y), magenta (M), cyan (C), and black (K) from the left in FIG. They are arranged side by side. In FIG. 1, for convenience of explanation, symbols Y, M, C, and K are attached to each image forming unit 7 according to the reproduction color. Each image forming unit 7 includes a photosensitive drum 13 as an example of an image carrier that rotates clockwise in FIG. Around the photosensitive drum 13, a charging device 14, an exposure device 19, a developing device 15, a primary transfer roller 16, and a photosensitive cleaner 17 are arranged in this order along the clockwise rotation direction in FIG. 1.

  The photosensitive drum 13 is negatively charged and is configured to rotate clockwise in FIG. 1 by power transmission from the main motor. The charging device 14 uniformly charges the surface of the photosensitive drum. The developing device 15 makes the electrostatic latent image formed on the photosensitive drum 13 visible by reversal development using toner having a negative polarity.

  The primary transfer roller 16 is located on the inner peripheral side of the intermediate transfer belt 6 and faces the photosensitive drum 13 of the corresponding image forming unit 7 with the intermediate transfer belt 6 interposed therebetween. The primary transfer roller 16 also rotates counterclockwise in FIG. 1 as the intermediate transfer belt 6 rotates. Between the intermediate transfer belt 6 and the primary transfer roller 16 (contact portion) is a primary transfer nip portion as a primary transfer region. The photoreceptor cleaner 17 is for removing untransferred toner remaining on the photoreceptor drum 13, and is in contact with the photoreceptor drum 13. An exposure device 19 is disposed below the four image forming units 7. The exposure device 19 forms an electrostatic latent image on each photosensitive drum 13 by laser light based on image information from an external terminal or the like.

  Each image forming unit 7 is a cartridge (integrated structure) in which the photosensitive drum 13, the charging device 14, the exposure device 19, the developing device 15, and the photosensitive cleaner 17 are collectively accommodated in the housing 20. A so-called process cartridge is detachably attached to the housing 2. A hopper (not shown) that accommodates toner to be supplied to each developing device 15 is disposed above the intermediate transfer belt 6.

  In each image forming unit 7, when a laser beam corresponding to an image signal is projected from the exposure device 19 onto the photosensitive drum 13 charged by the charging device 14, an electrostatic latent image is formed. The electrostatic latent image is reversely developed with toner supplied from the developing device 15 and becomes a toner image of each color. The toner images on the respective photosensitive drums 13 are primarily transferred from the photosensitive drum 13 to the outer peripheral surface of the intermediate transfer belt 6 in the order of yellow, magenta, cyan, and black at the corresponding primary transfer nip portions, and are superimposed. . Untransferred toner remaining on the photosensitive drum 13 is scraped off by the photosensitive cleaner 17 and removed from the photosensitive drum 13. When the recording material P passes through the secondary transfer nip portion, the superimposed four color toner images are secondarily transferred onto the recording material P all at once. Untransferred toner remaining on the intermediate transfer belt 6 is scraped off by the transfer belt cleaner 12 and removed from the intermediate transfer belt 6.

  The fixing device 5 positioned above the secondary transfer roller 10 includes a fixing rotating member 31 and a pressure rotating member 32 that is in pressure contact with the fixing rotating member 31. A contact portion between the fixing rotating member 31 and the pressure rotating member 32 is a fixing nip portion 33 which is a fixing region. The recording material P on which the unfixed toner image is placed after passing through the secondary transfer nip portion is heated and pressurized when passing through the fixing nip portion 33 between the fixing rotating member 31 and the pressure rotating member 32. A toner image is fixed on the recording material P. Thereafter, the recording material P is discharged onto the paper discharge tray 27 by the rotation of the discharge roller pair 26.

  A control unit 28 that performs overall control of the printer 1 is disposed between the image processing apparatus 3 and the sheet feeding apparatus 4 in the housing 2. The controller 28 incorporates a controller (not shown) that executes various arithmetic processes, storage, and control.

(2). Next, the structure of the fixing device 5 will be described with reference to FIG. As described above, the fixing device 5 includes the fixing rotation member 31 and the pressure rotation member 32 that extend in the sheet passing width direction and can rotate while being pressed against each other.

  The fixing rotation member 31 includes a fixing roller 41, a tension roller 42, and a fixing belt 43 as a belt body located on the outer peripheral side of the fixing roller 41 and the tension roller 42. Both the fixing roller 41 and the tension roller 42 are formed in a cylindrical shape that is long in the sheet passing width direction. The fixing roller 41 presses the fixing belt 43 from the inside in order to form the fixing nip portion 33. Both ends of the fixing roller 41 in the sheet passing width direction are rotatably supported by a frame in the housing 2. The fixing roller 41 has a Φ 20 mm SUS core coated with a silicone sponge and has an outer diameter of Φ49.8 mm and a width of 350 mm. It is processed in the range of 30 ° to 50 ° at 8N.

  The tension roller 42 is rotatably supported by a frame in the housing 2 via a tension coil spring (not shown) so as to apply tension to the fixing belt 43 to prevent the fixing belt 43 from being bent. The tension roller 42 is supported so as to be parallel to the fixing roller 41. The detailed structure of the tension roller 42 will be described later.

  The fixing belt 43 is an endless belt that forms the outer peripheral portion of the fixing rotating member 31. The fixing belt 43 has a cylindrical shape that is long in the sheet passing width direction, and holds the cylindrical shape by the tension applied by the tension roller 42. The fixing belt 43 has a multi-layer structure, and the multi-layer structure of the fixing belt 43 includes a magnetic metal layer. The fixing belt 43 includes, in order from the outside, a release layer, an elastic elastic layer, and a magnetic metal layer that is a heat generating layer. As an example of the configuration of each layer, the release layer is composed of a fluororesin layer or the like, and the elastic layer is composed of silicone rubber or the like. The magnetic metal layer (heat generation layer) includes a conductive material such as Ni, SUS, or Fe. Specifically, the fixing belt 43 is an endless belt having a diameter of Φ80 mm and a width of 380 mm. As a structure from the inside, the magnetic metal layer is provided with a multilayer plating layer of Cu (10 μm) Ni (1 μm) on Ni (40 μm). There is a magnetic metal layer. A silicone rubber layer is provided from 140 μm to 200 μm outside the magnetic metal layer, and an adhesive layer is applied to the outermost layer to cover PFA tubes 30 μm to 50 μm.

  An end detection sensor 44 that detects an end position of the fixing belt 43 in the sheet passing width direction is disposed outside the fixing belt 43 in the sheet passing width direction. The end detection sensor 44 detects the end position (or displacement) of the fixing belt 43 using, for example, an optical sensor.

  A frictional force applying member 45 is disposed on the inner peripheral side of the fixing belt 43. The frictional force applying member 45 is driven by the control unit 28 based on the detection result of the end detection sensor 44 so as to apply a frictional force to the tension roller 42 as necessary. The detailed structure of the frictional force applying member 45 will be described later.

  As an example of a heating source that heats the fixing belt 43 with the fixing belt 43 sandwiched between the fixing roller 41, a heating unit 60 that is an induction heating member is disposed in a non-contact state with the fixing belt 43. Yes. The heating unit 60 generates heat from the magnetic metal layer of the fixing belt 43 by electromagnetic induction. The heating unit 60 includes an electromagnetic induction coil 62 that generates an eddy current in the magnetic metal layer in the fixing belt 43 against the outer peripheral surface of the fixing belt 43, and a coil storage case 63 that stores the electromagnetic induction coil 62. Yes. By supplying power to the electromagnetic induction coil 62, the electromagnetic induction coil 62 generates a magnetic flux, and the magnetic flux penetrates the magnetic metal layer of the fixing belt 43 to generate an eddy current in the magnetic metal layer. As a result, the magnetic metal layer itself generates heat and the fixing belt 43 is heated. A temperature sensor (not shown) is disposed in contact with or close to the outer peripheral side of the fixing belt 43. The electromagnetic induction coil 62 of the heating unit 60 is on / off controlled in accordance with the detection result of the temperature sensor, and the fixing belt 43 is maintained at a predetermined fixing temperature.

  The pressure rotating member 32 has a roller shape (thus, it may be called a pressure roller). The axis of the pressure rotating member 32 extends in parallel with the axis of the fixing roller 41. The pressure rotating member 32 is movable toward and away from the outer peripheral surface of the fixing belt 43, and the pressure rotating member 32 is in pressure contact with the fixing roller 41 via the fixing belt 43 (the pressure rotating member 32 and the fixing member are fixed). The fixing belt 43 can be clamped by the roller 41). A fixing nip portion 33 serving as a fixing region is between the fixing belt 43 and the pressure rotating member 32 (contact portion). The pressure contact force between the fixing roller 41 and the pressure rotation member 32 can be changed according to the type of the recording material P by a pressure contact means (not shown). The pressure rotating member 32 is a metal cored bar with silicone rubber molded on an outer diameter of Φ40 mm, and the outermost layer is coated with an adhesive layer and covered with PFA tubes of 40 μm to 80 μm. Total Asker C type hardness tester The hardness on the roller is processed in the range of 60 ° to 75 ° with a load of 9.8 N. The outer diameter is Φ50 mm and the width is 360 mm, and the roller shape is an inverted crown shape. The amount of reverse crown is 0 for the outer diameter at the left and right 147 mm positions from the central portion with respect to the outer diameter of the central portion of the pressure roller. It is set in the range of 1 mm to 0.3 mm. The metal cored bar is a hollow pipe for weight reduction and low heat capacity, and the thickness of the cored bar is 2 mm.

  By transmitting rotational power from a drive motor (not shown) as a drive source to the pressure rotation member 32 via a power transmission system such as a gear or a belt, the pressure rotation member 32 rotates in the clockwise direction of FIG. To do. With the rotation of the pressure rotating member 32 or the recording material P passing through the fixing nip 33, the fixing belt 43 rotates in the direction opposite to the rotation direction of the pressure rotating member 32 (counterclockwise in FIG. 2), The fixing roller 41 and the tension roller 42 also rotate counterclockwise in FIG.

(3). Next, the structure of the tension roller 42 and the frictional force applying member 45 will be described with reference to FIG.

  The tension roller 42 is made of an aluminum alloy, and is provided with three roller portions (a central roller portion 46, a first end roller portion 47a, and a second end roller portion 47b) along the axial direction. These three roller portions have the same outer diameter and can be rotated independently of each other. Moreover, the outermost layer of these three roller parts is coat | covered with the fluororesin. The outer diameter of the central roller portion 46 of the tension roller 42 is Φ26 mm, it is made of hollow with a thickness of 1.8 mm, the end is drawn to Φ8 mm, and is held by a bearing (not shown). You may form the axis | shaft processed into the shape of edge part (PHI) 8mm by friction welding. The outer diameters of the first end roller portion 47 a and the second end roller portion 47 are the same as the outer diameter of the central roller portion 46.

  The first end roller portion 47a and the second end roller portion 47b have the same shape and the same configuration. The first end roller portion 47 a and the second end roller portion 47 b have a cylindrical shape and are fitted to the core metal portion 48 of the tension roller 42. The 1st end roller part 47a and the 2nd end roller part 47b are comprised from the inner side by the heat resistant resin layer 471 and the metal layer 472, and the surface layer is coat | covered with the fluororesin. As the heat resistant resin layer 471, a PI or PPS molded product and the metal layer 472 may be coated with a fluorine-based paint to provide a film thickness of 30 μm to 40 μm.

  The central roller portion 46 completely covers a range (hereinafter referred to as a maximum contact range R) corresponding to a region on the fixing belt 43 that can contact the recording material P in the fixing nip portion 33 with respect to the axial direction. , Its length and position are determined. Therefore, since the boundary between the central roller portion 46 and the first end roller portion 47a and the boundary between the central roller portion 46 and the second end roller portion 47b are located outside the maximum contact range R, the maximum Within the contact range R, there is no gap between the roller portions. Therefore, at least within the maximum contact range R, the temperature uniformity of the fixing belt 43 is not hindered due to the gap between the roller portions.

  The frictional force applying member 45 includes a shaft member 49 disposed substantially parallel to the tension roller 42, two pressing members (the pressing member 50 a and the pressing member 50 b) attached to the shaft member 49, and the shaft member 49. It is comprised with the drive motor (illustration omitted) etc. which rotate this to arbitrary directions.

  The pressing member 50a and the pressing member 50b are molded in the same shape with a heat-resistant resin, and are fixed to a metal shaft member 49 using a positioning pin (not shown). The pressing member 50a and the pressing member 50b are substantially cylindrical, but have a shape in which a part of the circumference protrudes as shown in FIG. 2 (hereinafter, this protruding portion is referred to as a protruding portion). ). The pressing member 50a and the pressing member 50b are fixed in different directions, that is, the protruding direction of the protruding portion of the pressing member 50a and the protruding direction of the protruding portion of the pressing member 50b are different directions (for example, directions different by 180 degrees). )It has become. Therefore, when the shaft member 49 is rotated in the first direction (for example, counterclockwise in FIG. 2) by the drive motor described above, only the protruding portion of one pressing member (for example, the pressing member 50a) has a corresponding end. When the shaft member 49 is rotated in the second direction (for example, the clockwise direction in FIG. 2) by the driving motor in contact with the roller unit (for example, the first end roller unit 47a), the other pressing member (for example, the pressing member) Only the protruding portion 50b) comes into contact with the corresponding end roller portion (for example, the second end roller portion 47b).

(4). Next, a method for controlling the position of the fixing belt 43 using the tension roller 42 and the frictional force applying member 45 will be described.

  The control unit 28 controls the drive motor described above to rotate the shaft member 49 in the direction according to the detection result of the end detection sensor 44, thereby causing the first end roller unit 47a or the second end roller unit 47b to move. The corresponding pressing member can be brought into contact. The rotation speed of the end roller part on the side where the pressing member abuts between the first end roller part 47a and the second end roller part 47b is reduced by the frictional force between the pressing member and the other end roller part or It becomes slower than the rotation speed of the central roller portion 46. As a result, a difference occurs in the speeds at both ends of the fixing belt 43, and the fixing belt 43 moves in the width direction.

  Specifically, when the control unit 28 finds from the detection result of the end detection sensor 44 that the fixing belt 43 is offset toward the second end roller unit 47b, the control unit 28 controls the driving motor to change the pressing member 50b. The shaft member 49 is rotated so as to contact the second end roller portion 47b. As a result, the speed of the end portion of the fixing belt 43 on the side contacting the second end roller portion 47b becomes slower than the speed of the end portion of the fixing belt 43 on the side contacting the first end roller portion 47a. 43 moves to the first end roller portion 47a side, that is, the deviation of the fixing belt 43 is corrected.

  Similarly, when the control unit 28 finds from the detection result of the end detection sensor 44 that the fixing belt 43 is offset toward the first end roller unit 47a, the control unit 28 controls the drive motor so that the pressing member 50a is the first. The shaft member 49 is rotated so as to contact the end roller portion 47a. As a result, the speed of the end portion of the fixing belt 43 on the side contacting the first end roller portion 47a becomes slower than the speed of the end portion of the fixing belt 43 on the side contacting the second end roller portion 47b. 43 moves to the second end roller portion 47b side, that is, the deviation of the fixing belt 43 is corrected. Thus, when the fixing belt 43 returns to the desired position, the control unit 28 controls the drive motor to place the shaft member 49, the pressing member 50a, and the pressing member 50b in the original state (that is, all the pressing members to the tension roller 42). Return to the non-contact state.

  The control unit 28 applies a friction force having a magnitude different depending on the conveyance speed (that is, the fixing speed) of the recording material P in the fixing nip portion 33 to the first end roller portion 47a or the second end roller portion 47b. You may do it. Specifically, when the fixing speed is high, it is desirable to correct the position of the fixing belt 43 more quickly than when the fixing speed is low. The pressing member may be brought into contact with the corresponding end roller portion with a larger force so as to be larger.

  As apparent from the above description and FIGS. 2 and 3, the fixing device 5 of the present embodiment is a fixing device that fixes an unfixed toner image on the recording material P, and forms the fixing nip portion 33. The first roller (fixing roller 41) and three roller portions (first end roller portion 47a, central roller portion 46, which are provided along a common axis and have the same outer diameter and can rotate independently of each other) An endless belt stretched between at least two rollers including a second roller (tension roller 42) including the second end roller portion 47b) and at least two rollers including the first roller (fixing roller 41) and the second roller (tension roller 42). Fixing belt 43), detection means (edge detection sensor 44) for detecting the position or displacement of the endless belt (fixing belt 43) in the width direction, and detection means ( And a friction force applying means (friction force applying member 45) for selectively applying a friction force to the first end roller portion 47a or the second end roller portion 47b based on the detection result of the portion detection sensor 44). Thus, based on the detection result of the position or displacement of the endless belt (fixing belt 43) in the width direction, a frictional force is selectively applied to the first end roller portion 47a or the second end roller portion 47b, and the rotation thereof Speed is reduced. Therefore, it is possible to change the position of the endless belt (fixing belt 43) in the width direction by causing a difference in the rotation speed between the first end roller portion 47a and the second end roller portion 47b.

  Further, since the three roller portions (the first end roller portion 47a, the central roller portion 46, and the second end roller portion 47b) have the same outer diameter, the end portion of the endless belt (fixing belt 43) is large. Stress is not generated, and damage to the endless belt (fixing belt 43) can be suppressed.

(5). Others The present invention is not limited to the above-described embodiment, and can be embodied in various forms. For example, a printer has been described as an example of the image forming apparatus. However, the image forming apparatus is not limited thereto, and may be a copier, a facsimile, or a complex machine having these functions in combination. In addition, the configuration of each unit is not limited to the illustrated embodiment, and various modifications can be made without departing from the spirit of the present invention.

P Recording material 1 Printer (image forming device)
5 Fixing Device 31 Fixing Rotating Member 32 Pressing Rotating Member 33 Fixing Nip Portion 41 Fixing Roller 42 Tension Roller 43 Fixing Belt 44 End Detection Sensor 45 Friction Force Applying Member 46 Center Roller 47a First End Roller 47b Second End Roller Part 471 Heat-resistant resin layer 472 Metal layer 48 Core metal part 49 Shaft member 50a Pressing member 50b Pressing member 60 Heating unit

Claims (5)

A fixing device for fixing an unfixed toner image on a recording material,
A first roller for forming a fixing nip,
A second roller including a first end roller portion, a central roller portion, and a second end roller portion, which are provided along a common axis and have the same outer diameter and are rotatable independently of each other;
An endless belt stretched around at least two rollers including the first roller and the second roller;
Detection means for detecting the position or displacement of the endless belt in the width direction;
A friction force applying means for selectively applying a friction force to the first end roller portion or the second end roller portion based on the detection result of the detection means;
The central roller portion completely covers a maximum contact range corresponding to a region on the endless belt that can contact the recording material in the fixing nip portion with respect to the common axis direction. Its length and position are determined so as not to exceed the range where it is located,
The first end roller portion and the second end roller portion are provided at a position where the first end roller portion and the second end roller portion contact the endless belt outside the maximum contact range with respect to the common axis direction.
Fixing device. A fixing device for fixing an unfixed toner image on a recording material,
A first roller for forming a fixing nip,
A second roller including a first end roller portion, a central roller portion, and a second end roller portion, which are provided along a common axis and have the same outer diameter and are rotatable independently of each other;
An endless belt stretched around at least two rollers including the first roller and the second roller;
Detection means for detecting the position or displacement of the endless belt in the width direction;
A friction force applying means for selectively applying a friction force to the first end roller portion or the second end roller portion based on the detection result of the detection means;
The frictional force applying means is
A shaft member having an axis parallel to the axis of the second roller;
On the shaft member, and the two pressing members that are secured in different orientations at a position opposed to each of the first end roller portion and the second end roller portion,
By rotating the shaft member in a different direction according to the detection result of the detection means, either one of the two pressing members is brought into contact with the corresponding first end roller portion or second end roller portion. Drive means
Fixing device. The frictional force applying means is
A shaft member having an axis parallel to the axis of the second roller;
On the shaft member, and the two pressing members that are secured in different orientations at a position opposed to each of the first end roller portion and the second end roller portion,
By rotating the shaft member in a different direction according to the detection result of the detection means, either one of the two pressing members is brought into contact with the corresponding first end roller portion or second end roller portion. Drive means
The fixing device according to claim 1. The frictional force applying means applies a frictional force having a magnitude different depending on a conveyance speed of the recording material in the fixing nip portion;
The fixing device according to claim 1. The fixing device according to claim 1 is provided.
Image forming apparatus.

Images