Fixing device and image forming apparatus

Abstract

To improve the durability of a fixing belt, prevent inability to eject various types of recording materials, and guarantee a suitable gap between the fixing belt and a separation member.SOLUTION: A fixing device 20 has: a pressure roller 22 that is in contact with a fixing belt 31 to form a fixing nip part N where a recording material S is held and conveyed by first pressure or second pressure obtained by reducing the first pressure; and a separation plate 71 that is provided opposite to the fixing belt 31 in a non-contact manner with a gap therebetween on the downstream side of the fixing nip part N in a conveyance direction of the recording material S, separates the recording material S passing through the fixing nip part N from the fixing belt 31, and when the pressure at the fixing nip part N is the second pressure, moves to the downstream side in the conveyance direction compared to a position when the pressure at the fixing nip part is the first pressure.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a fixing device that fixes an unfixed toner image formed on a recording material onto the recording material, and to an image forming apparatus of an electrophotographic system, an electrostatic recording system, or the like, that is provided with the fixing device. [Background technology]

[0002] Conventionally, in an image forming apparatus using an electrophotographic method, an electrostatic latent image formed on a photosensitive drum as an image carrier is developed with toner in a developing device to form a toner image, and the formed toner image is transferred to a sheet and then fixed to the sheet in a fixing device. Such a fixing device has a heating rotating body such as a fixing belt and a pressure rotating body such as a pressure roller, and forms a fixing nip between the heating rotating body and the pressure rotating body, and heats and presses the sheet in the fixing nip to fix the unfixed toner image to the recording material.

[0003] In addition, in a conventional fixing device, a contact or non-contact separation member is provided downstream in the sheet transport direction of a heating unit equipped with a heating rotor and a heater, for separating a sheet that has stuck to the heating rotor after passing through the fixing nip portion.

[0004] Such a separating member is generally required to be positioned and attached with high accuracy relative to the heating rotor. Patent Document 1 relates to a fixing device having a separating member that separates a sheet from a fixing roller, which is a heating rotor, and discloses a configuration in which a contact member is provided on the separating member that contacts the fixing roller outside the paper passing area in order to ensure a gap between the fixing roller and the separating member. The fixing device of Patent Document 1 also has a configuration in which the separating member is rotated in a direction to separate it from the fixing roller during sleep mode.

[0005] In recent years, in order to form high-quality images on various print media in response to the diversification of print media, fixing devices have adopted a configuration in which the contact pressure between the fixing belt and the pressure roller in the fixing nip is variable. For example, the contact pressure between the fixing belt and the pressure roller when fixing an image on an envelope or the like is reduced to about half of the contact pressure when fixing an image on normal print media in order to reduce deterioration of the fixing member due to wrinkles or edges of the envelope.

[0006] In such a fixing device, the running path of the fixing belt changes with the change in the contact pressure between the fixing belt and the pressure roller in the fixing nip, and therefore the distance between the separating member and the fixing belt also changes. Therefore, in this case, it is necessary to guarantee the gap between the separating member and the fixing roller by moving the separating member in response to the change in the contact pressure between the fixing belt and the pressure roller in the fixing nip. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] JP 2014-202851 A Summary of the Invention [Problem to be solved by the invention]

[0008] However, in Patent Document 1, as the durability progresses, the portion of the fixing roller that the contact member of the fixing roller contacts deteriorates, and image defects may occur at the end of the image. Specifically, the surface of the fixing roller is covered with a PFA tube layer as a release layer, and as the durability progresses, wrinkles or lifting occurs in the PFA tube layer at the portion where the contact member of the fixing roller contacts. Then, the wrinkles or lifting that occur in the PFA tube layer invade the paper passing area from outside the paper passing area into the paper passing area, and image defects may occur at the end of the image.

[0009] Furthermore, in Patent Document 1, as the durability of the fixing roller increases, the contact member in contact with the fixing roller also wears out, making it difficult to guarantee the gap between the fixing roller and the separating member over the long term, which is an issue that hinders the improvement of the durability of the fixing roller.

[0010] Furthermore, in Patent Document 1, the separating member that rotates in a direction away from the fixing belt in a reduced pressure state enters the area through which the recording material discharged from the fixing nip moves. As a result, the fixing device of Patent Document 1 has a problem that when the recording material is discharged from the fixing nip in a reduced pressure state, the recording material may get caught on the separating member and may not be able to be discharged.

[0011] An object of the present invention is to provide a fixing device and an image forming apparatus that can realize high durability of a fixing belt, prevent ejection failure for various types of recording materials, and ensure an appropriate gap between the fixing belt and a separation member. [Means for solving the problem]

[0012] The fixing device of the present invention is a fixing device that fixes an unfixed toner image formed on a recording material to the recording material, and includes a heating rotor that heats the unfixed toner image and is rotatable, a pressure rotor that abuts against the heating rotor to form a fixing nip portion and is rotatable, and a separation member that is arranged opposite the heating rotor with a gap and in a non-contact manner on the downstream side of the fixing nip portion in the recording material transport direction, and separates the recording material that has passed through the fixing nip portion from the heating rotor, wherein the pressure rotor abuts against the heating rotor to form the fixing nip portion that clamps and transports the recording material with a first pressure or a second pressure that is reduced from the first pressure, and the separation member moves downstream in the transport direction when the pressure of the fixing nip portion is the second pressure than when it is the first pressure. Effect of the Invention

[0013] According to the present invention, it is possible to realize high durability of the fixing belt, prevent the inability to eject various types of recording materials, and ensure an appropriate gap between the fixing belt and the separating member. [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention; [Diagram 2] 1 is a block diagram showing a configuration of an image forming apparatus according to an embodiment of the present invention; [Diagram 3] 1 is a schematic diagram of a fixing device according to an embodiment of the present invention. [Figure 4] 4 is a perspective view of a separation unit of the fixing device according to the embodiment of the present invention, as viewed from above. FIG. [Diagram 5] 4 is a perspective view of a separation unit of the fixing device according to the embodiment of the present invention, as viewed from the upstream side in the recording material transport direction. FIG. [Figure 6] 2 is a schematic diagram of a part of a fixing device according to an embodiment of the present invention. [Figure 7] 3 is a schematic diagram of a state in which a fixing belt and a pressure roller of the fixing device according to the embodiment of the present invention are in contact with each other with a normal contact pressure. [Figure 8] 4 is a schematic diagram showing a state in which the fixing belt and the pressure roller of the fixing device according to the embodiment of the present invention are in contact with each other at a contact pressure that is lower than a normal contact pressure; [Figure 9] 5A and 5B are schematic diagrams for explaining the positional relationship between a fixing belt and a contact member of the fixing device according to the embodiment of the present invention. [Figure 10] 5 is an enlarged schematic diagram for explaining the positional relationship between a fixing belt and a contact member of the fixing device according to the embodiment of the present invention. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, the embodiments will be described in detail with reference to the drawings.

[0016] <Configuration of Image Forming Apparatus> The configuration of an image forming apparatus 1 according to an embodiment of the present invention will be described in detail with reference to FIGS.

[0017] Here, a tandem type full-color printer is exemplified as the image forming apparatus 1. Note that the image forming apparatus 1 is not limited to a tandem type full-color printer, and may be an image forming apparatus of another type other than a tandem type full-color printer. Also, the image forming apparatus 1 is not limited to a full-color one, and may be a monochrome or mono-color one. Furthermore, the image forming apparatus 1 can be used for various purposes such as a printer, various printing machines, a copier, a FAX, or a multifunction machine.

[0018] The image forming apparatus 1 forms a four-color full-color image on a recording material S such as a sheet in response to an image signal input from a host device such as a document reading device (not shown), a personal computer, or an external device such as a digital camera or a smartphone. Here, the recording material S is, for example, plain paper on which a toner image is formed, a synthetic resin sheet that is a substitute for plain paper, cardboard, an overhead projector sheet, an envelope, or the like.

[0019] Specifically, the image forming apparatus 1 includes an image forming section 40, a control section 90, and a drive motor M1.

[0020] The image forming unit 40 forms a toner image on a recording material S fed by a sheet feeding unit (not shown) based on an image signal input from a document reading device, a host device, or an external device (all not shown). The image forming unit 40 fixes the toner image to the recording material S by applying heat and pressure to the recording material S on which the toner image has been formed, and then discharges the recording material S on which the toner image has been fixed to the outside of the apparatus main body 10.

[0021] The image forming section 40 includes image forming units 50y, 50m, 50c, and 50k, toner bottles 41y, 41m, 41c, and 41k, exposure devices 42y, 42m, 42c, and 42k, an intermediate transfer unit 44, a secondary transfer section 45, and a fixing device 20. Here, the image forming units 50y, 50m, 50c, and 50k, the toner bottles 41y, 41m, 41c, and 41k, the exposure devices 42y, 42m, 42c, and 42k, the intermediate transfer unit 44, and the secondary transfer section 45 configure the toner image forming section.

[0022] In the full-color image forming apparatus 1, the image forming units 50y, 50m, 50c, and 50k are identically configured and provided separately for each of the four colors, yellow (y), magenta (m), cyan (c), and black (k). The toner bottles 41y, 41m, 41c, and 41k and the exposure devices 42y, 42m, 42c, and 42k are identically configured and provided separately for each of the four colors, yellow (y), magenta (m), cyan (c), and black (k).

[0023] The image forming units 50y, 50m, 50c, and 50k form toner images based on image signals input from a document reading device, a host device, or an external device (not shown). The image forming units 50y, 50m, 50c, and 50k are integrated into a process cartridge as a unit, and are detachably mounted in the apparatus main body 10 to transfer the toner images onto an intermediate transfer belt 44b (described later) of the intermediate transfer unit 44.

[0024] The image forming units 50y, 50m, 50c, and 50k include photosensitive drums 51y, 51m, 51c, and 51k, charging rollers 52y, 52m, 52c, and 52k, and developing devices 53y, 53m, 53c, and 53k.

[0025] The photosensitive drums 51y, 51m, 51c, and 51k are, for example, negatively charged organic photoconductors (OPCs) having an outer diameter of 30 mm, and are rotated by a motor (not shown) at a predetermined process speed (circumferential speed) in the direction of the arrow in Fig. 1. The photosensitive drums 51y, 51m, 51c, and 51k carry electrostatic latent images formed by exposure devices 42y, 42m, 42c, and 42k, or toner images formed by development devices 53y, 53m, 53c, and 53k.

[0026] The charging rollers 52y, 52m, 52c, and 52k are rubber rollers that come into contact with the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k and rotate in accordance with the rotation of the photosensitive drums 51y, 51m, 51c, and 51k. The charging rollers 52y, 52m, 52c, and 52k uniformly charge the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k.

[0027] The developing devices 53y, 53m, 53c, and 53k are equipped with developing sleeves 54y, 54m, 54c, and 54k. The developing devices 53y, 53m, 53c, and 53k contain developers supplied from toner bottles 41y, 41m, 41c, and 41k. The developing devices 53y, 53m, 53c, and 53k develop, with toner, electrostatic latent images formed on the photosensitive drums 51y, 51m, 51c, and 51k by application of a developing bias.

[0028] The developing sleeves 54y, 54m, 54c, and 54k are made of a non-magnetic material such as aluminum or non-magnetic stainless steel. The non-magnetic material constituting the developing sleeves 54y, 54m, 54c, and 54k is exemplified by aluminum here. A roller-shaped magnet roller (not shown) is fixed in a non-rotating state inside the developing sleeves 54y, 54m, 54c, and 54k. The developing sleeves 54y, 54m, 54c, and 54k carry a developer having a non-magnetic toner and a magnetic carrier, and transport the developer to the developing area of ​​the photosensitive drums 51y, 51m, 51c, and 51k.

[0029] The toner bottles 41y, 41m, 41c, and 41k supply the developer to the developing devices 53y, 53m, 53c, and 53k.

[0030] The exposure devices 42y, 42m, 42c, and 42k are laser scanners that irradiate the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k with laser light in accordance with separated color image information input from the control unit 90 to expose the photosensitive drums 51y, 51m, 51c, and 51k.

[0031] The toner images developed on the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k are primarily transferred to the intermediate transfer unit 44. The intermediate transfer unit 44 includes a drive roller 44a, a driven roller 44d, primary transfer rollers 47y, 47m, 47c, and 47k, an intermediate transfer belt 44b, and a belt cleaning device 56.

[0032] The intermediate transfer belt 44b is wound around the drive roller 44a. The drive roller 44a is driven to rotate by a motor (not shown), thereby rotating the intermediate transfer belt 44b.

[0033] The intermediate transfer belt 44b is wound around the driven roller 44d. The driven roller 44d is a tension roller that controls the tension of the intermediate transfer belt 44b to a constant value. The driven roller 44d applies a force to the intermediate transfer belt 44b to push it outward by the biasing force of a biasing spring (not shown).

[0034] Each of the primary transfer rollers 47y, 47m, 47c, and 47k is in contact with the intermediate transfer belt 44b and is disposed opposite the photosensitive drums 51y, 51m, 51c, and 51k via the intermediate transfer belt 44b. When a primary transfer bias is applied to each of the primary transfer rollers 47y, 47m, 47c, and 47k, the toner images on the photosensitive drums 51y, 51m, 51c, and 51k are primarily transferred to the intermediate transfer belt 44b.

[0035] The intermediate transfer belt 44b contacts the photosensitive drums 51y, 51m, 51c, and 51k to form a primary transfer portion between the intermediate transfer belt 44b and the photosensitive drums 51y, 51m, 51c, and 51k. The toner images formed on the photosensitive drums 51y, 51m, 51c, and 51k are primarily transferred onto the intermediate transfer belt 44b at the primary transfer portion. For example, a positive primary transfer bias is applied to the intermediate transfer belt 44b by the primary transfer rollers 47y, 47m, 47c, and 47k, so that the negative toner images on the photosensitive drums 51y, 51m, 51c, and 51k are sequentially transferred in a multi-layer manner. The intermediate transfer belt 44b rotates while carrying the toner images primarily transferred from the photosensitive drums 51y, 51m, 51c, and 51k.

[0036] The belt cleaning device 56 cleans the intermediate transfer belt 44b to remove residual toner therefrom.

[0037] The secondary transfer unit 45 secondarily transfers the toner image, which has been primarily transferred onto the intermediate transfer belt 44b, onto a recording material S fed by a sheet feeding device (not shown). The secondary transfer unit 45 transports the recording material S onto which the toner image has been secondarily transferred, to the fixing device 20. The secondary transfer unit 45 includes an inner secondary transfer roller 45a and an outer secondary transfer roller 45b.

[0038] The outer secondary transfer roller 45b contacts the intermediate transfer belt 44b to form a nip between the intermediate transfer belt 44b and the outer secondary transfer roller 45b. A secondary transfer bias having a polarity opposite to that of the toner is applied to the outer secondary transfer roller 45b, so that the toner images carried by the intermediate transfer belt 44b are secondarily transferred all at once to the recording material S supplied to the nip.

[0039] The fixing device 20 is a belt heating type heating device, and is formed in the shape of a cartridge that is detachably mounted in the apparatus main body 10. The fixing device 20 fixes, to the recording material S, an unfixed toner image that has been secondarily transferred onto the recording material S transported by the secondary transfer section 45. The fixing device 20 discharges the recording material S with the fixed toner image to the outside of the apparatus main body 10. The configuration of the fixing device 20 will be described in detail later.

[0040] The control unit 90 controls the overall operation of the image forming apparatus 1. The control unit 90 includes a CPU 91, a ROM 92, a RAM 93, and an I / F 94.

[0041] The CPU 91 is a microprocessor that controls the overall operation of the image forming apparatus 1 by reading and executing a control program stored in the ROM 92, and is the main part of the system controller. Using the RAM 93, the CPU 91 exchanges signals with an operation unit (not shown), a sheet feeding unit (not shown) or the image forming unit 40 via an I / F 94 to control the operation of the drive motor M1, the operation unit, the sheet feeding unit, the image forming unit 40, etc.

[0042] The ROM 92 stores a control program, an image formation control sequence for forming an image on the recording material S, and the like in advance.

[0043] The RAM 93 temporarily stores data.

[0044] The I / F 94 is an input / output circuit that inputs and outputs signals to and from the outside, and is connected to an operation unit, a sheet feeding unit, the image forming unit 40, and the like.

[0045] The driving motor M 1 is driven under the control of the CPU 91 of the control unit 90 to drive the driving members of the fixing device 20 .

[0046] <Configuration of the fixing device> The configuration of the fixing device 20 according to the embodiment of the present invention will be described in detail with reference to FIGS.

[0047] The fixing device 20 has a housing 21, a fixing frame 23, a guide portion 24, a pressure frame 25, a pressure spring 26, a pressure cam 27, a separation movement lever 28, a separation movement cam 29, and a heating unit 30. The fixing device 20 also has a paper discharge unit 60, a paper discharge unit rotating shaft 81, a paper discharge unit lock shaft 82, a stopper 83, and a torsion coil spring 84.

[0048] The housing 21 is a main body of the fixing device 20 that houses each of the components of the fixing device 20 .

[0049] The fixing frame 23 is fixed to both sides of the housing 21 in the direction of the rotation axis W shown in Fig. 4. Here, the direction of the rotation axis W is a direction parallel to the width direction or the main scanning direction perpendicular to the transport direction (hereinafter simply referred to as the "transport direction") of the recording material S. The fixing frame 23 is provided with a guide portion 24, a pressure frame 25, a pressure spring 26, a pressure cam 27, a separation movement lever 28, a separation movement cam 29, a paper discharge unit rotating shaft 81, a paper discharge unit lock shaft 82, and a stopper 83.

[0050] A stay 35 (described later) of the heating unit 30 is inserted into the guide portion 24, and the stay 35 is fixed by a fixing means (not shown). The guide portion 24 includes a support portion 24a, a positioning portion 24b, and a sliding portion 24c.

[0051] The support portion 24a is formed along the conveying direction on the inner side of the fixing belt 31. When the heating unit 30 is located at the mounting position, the support portion 24a supports the reaction force received by the fixing belt 31 from the pressure roller 22 via a pressure pad 32 and a stay 35 of the heating unit 30, which will be described later.

[0052] The positioning portion 24b is formed on the inner side of the fixing belt 31 along a substantially vertical direction at the innermost part of the guide portion 24 in the insertion direction of the heating unit 30 into the fixing frame 23. The positioning portion 24b abuts against the heating unit 30 located at the mounting position with respect to the fixing frame 23, and positions the heating unit 30 with respect to the fixing frame 23.

[0053] The sliding portion 24c is provided opposite the support portion 24a and is formed along the conveying direction, and guides the stay 35 by sliding it when the heating unit 30 is inserted or removed.

[0054] The pressure frame 25 includes a pressure roller 22. The pressure frame 25 is pressed by a pressure cam 27 and moves toward the heating unit 30 against the urging force of the pressure spring 26, thereby pressing the pressure roller 22 against the pressure pad 32 via the fixing belt 31. The pressure of the pressure frame 25 by the pressure cam 27 is released and the pressure frame 25 moves in a direction away from the heating unit 30, thereby releasing the pressure of the pressure roller 22 against the pressure pad 32 via the fixing belt 31.

[0055] The pressure roller 22 as a pressure rotating body is a roller having an elastic layer on the outer periphery of the shaft, and a release layer on the outer periphery of the elastic layer. The shaft is made of stainless steel. The elastic layer is 3 mm thick and made of conductive silicone rubber. The release layer is 30 μm thick and made of PFA as a fluororesin.

[0056] When the pressure frame 25 is pressed by the pressure cam 27, the pressure roller 22 comes into contact with the fixing belt 31 and presses the pressure pad 32 via the fixing belt 31. The pressure roller 22 presses the pressure pad, and thereby forms a fixing nip portion N that sandwiches and conveys the recording material S together with the fixing belt 31 with a first pressure or a second pressure that is lower than the first pressure. When the pressure of the pressure frame 25 by the pressure cam 27 is released, the pressure roller 22 moves away from the fixing belt 31 due to the urging force of the pressure spring 26.

[0057] The pressure roller 22 is axially supported by the fixing frame 23 of the housing 21, and has a gear (not shown) fixed to one end of the pressure roller 22 in the direction of the rotation axis W, and is connected to the drive motor M1 via the gear. The pressure roller 22 is driven by the drive motor M1 to rotate about a rotation axis parallel to the direction of the rotation axis W.

[0058] The pressure spring 26 biases the pressure frame 25 in a direction away from the heating unit 30 .

[0059] The pressure cam 27 as a pressing member is rotated by being driven by a driving source (not shown). By rotating, the pressure cam 27 moves the pressure frame 25 toward the heating unit 30 against the biasing force of the pressure spring 26, or moves the pressure frame 25 in a direction away from the heating unit 30 by the biasing force of the pressure spring 26. When moving the pressure frame 25 toward the heating unit 30, the pressure cam 27 sets the pressure in the fixing nip portion N to a first pressure or a second pressure that is reduced from the first pressure, depending on the amount of rotation.

[0060] The separation movement lever 28 presses a retraction lever 78 of a separation unit 70 (described later) of the paper discharge unit 60 by the biasing force of the torsion coil spring 84, causing the retraction lever 78 to rotate in the direction of arrow D in Fig. 7 and come into contact with a stopper 83. The separation movement lever 28 is pressed by the separation movement cam 29 and rotates in the direction of arrow E in Fig. 8 against the biasing force of the torsion coil spring 84, thereby releasing the pressure on the retraction lever 78 and causing the retraction lever 78 to rotate in the direction of arrow F in Fig. 8.

[0061] The separation movement cam 29 is provided coaxially with the pressure cam 27. When driven by a drive source (not shown), the separation movement cam 29 rotates together with the pressure cam 27 in conjunction with the rotational movement of the pressure cam 27. When the separation movement cam 29 rotates, it presses the separation movement lever 28, causing the separation movement lever 28 to rotate in the direction of arrow E in FIG. 8 against the biasing force of the torsion coil spring 84. When the separation movement cam 29 rotates, it releases the pressure on the separation movement lever 28, causing the separation movement lever 28 to rotate in the direction opposite to the direction of arrow E in FIG. 8 by the biasing force of the torsion coil spring 84.

[0062] The heating unit 30 heats the recording material S transported by the secondary transfer portion 45. The heating unit 30 includes a fixing belt 31, a pressure pad 32, a heating roller 33, a steering roller 34, a stay 35, a unit side plate 36, and a separation positioning portion 37.

[0063] The fixing belt 31 as a heating rotator is made of a material having thermal conductivity and heat resistance, and is a rotatable belt member having a thin cylindrical shape and an endless shape. The fixing belt 31 rotates following the rotation of the heating roller 33.

[0064] The fixing belt 31 has a three-layer structure, for example, including a base layer, an elastic layer provided on the outer periphery of the base layer, and a release layer provided on the outer periphery of the elastic layer. The base layer is 30 μm thick and made of polyimide resin (PI). The elastic layer is 300 μm thick and made of silicone rubber. The release layer is 30 μm thick and made of PFA as a fluororesin. The fixing belt 31 is stretched by a pressure pad 32, a heating roller 33, and a steering roller 34.

[0065] A lubricating sheet or lubricant (not shown) is interposed between the fixing belt 31 and the pressure pad 32, so that the fixing belt 31 slides smoothly against the pressure pad 32. The fixing belt 31 comes into contact with the recording material S on which an unfixed toner image is formed, and heats the recording material S. The fixing belt 31 is heated by the heating roller 33 based on the temperature detection result by a thermistor (not shown), and is controlled to a predetermined target temperature according to the type of recording material S.

[0066] The pressure pad 32 serving as a nip portion forming member is made of liquid crystal polymer (LCP). The pressure pad 32 is supported by a stay 35, and is pressed against the pressure roller 22 by the stay 35 with the fixing belt 31 sandwiched therebetween, thereby forming the fixing nip portion N. The pressure pad 32 is provided with a curved portion 32a (see FIG. 6) at the end portion on the downstream side in the conveying direction of the fixing nip portion N, which curves the fixing belt 31 to separate the recording material S from the fixing belt 31. The pressure pad 32 has a crown shape in which the center portion in the rotation axis direction W is more convex in the conveying direction than the ends.

[0067] The heating roller 33 is a stainless steel pipe with a thickness of 1 mm, and has a halogen heater (not shown) disposed therein, which can generate heat up to a predetermined temperature. A gear (not shown) is fixed to one end of the heating roller 33 in the direction of the rotation axis W, and the heating roller 33 is connected to a driving motor M1 via the gear. The heating roller 33 is rotated by the driving motor M1, so that it rotates about a rotation axis parallel to the direction of the rotation axis W.

[0068] The steering roller 34 has a substantially vertical oscillation center near one end or the center of the rotation axis direction W, and is capable of oscillating about this oscillation center. The steering roller 34 rotates about a rotation axis parallel to the rotation axis direction W with respect to the fixing belt 31, thereby generating a tension difference in the rotation axis direction W, and adjusts the position of the fixing belt 31 in the rotation axis direction W. The steering roller 34 is a tension roller that is biased in a direction to apply a predetermined tension to the fixing belt 31 by a biasing spring supported by a frame (not shown) of any of the heating units 30.

[0069] The stay 35 is made of stainless steel, and both ends in the direction W of the rotation axis are supported by the fixing frame 23 of the housing 21.

[0070] The unit side plate 36 integrates the fixing belt 31, the pressure pad 32, the heating roller 33, the steering roller 34 and the stay 35 into a cartridge shape.

[0071] The separation positioning portion 37 is provided on the stay 35. A guide groove 37b is formed in the separation positioning portion 37 from its tip in the conveying direction toward the opposite direction to the conveying direction. The separation positioning portion 37 positions a separation plate 71 of a separation unit 70 (described later) of the paper discharge unit 60. The separation positioning portion 37 guides the movement of a separation plate 71, a separation plate support member 72, and a separation plate regulating portion 73 (described later) of the separation unit 70 in the conveying direction or the direction opposite to the conveying direction by the guide groove 37b, and regulates the movement in the direction opposite to the conveying direction.

[0072] The paper discharge unit 60 is provided downstream of the fixing nip N in the transport direction, and discharges the recording material S that has passed through the fixing nip N to the outside of the fixing device 20. The paper discharge unit 60 is rotatable about a paper discharge unit rotation shaft 81 of the fixing frame 23, and when the recording material S becomes clogged at the outlet of the fixing nip N, it rotates in the direction of arrow A in FIG. 3 to expose the fixing nip N and make it possible to remove the clogged recording material S. The paper discharge unit 60 includes a paper discharge lower guide 61, a pair of discharge rollers 62, a paper discharge unit locking member 63, and a separation unit 70.

[0073] The lower discharge guide 61 is a guide on the lower side of the conveyance path of the recording material S conveyed from the fixing nip portion N to the pair of discharge rollers 62 .

[0074] The discharge roller pair 62 is disposed on the downstream side in the conveying direction by about 40 mm from the fixing nip portion N. The discharge roller pair 62 discharges the recording material S separated by the separation unit 70 to the outside of the fixing device 20.

[0075] The discharge unit lock member 63 engages with a discharge unit lock shaft 82 of the fixing frame 23 to position the discharge unit 60 relative to the fixing frame 23 .

[0076] The separation unit 70 separates the recording material S from the fixing belt 31, and guides the recording material S separated from the fixing belt 31 to be conveyed to the discharge roller pair 62. The configuration of the separation unit 70 will be described in detail later.

[0077] The paper discharge unit rotation shaft 81 supports the paper discharge unit 60 so as to be rotatable.

[0078] A discharge unit locking member 63 (to be described later) of the discharge unit 60 engages with the discharge unit locking shaft 82 to position the discharge unit 60 relative to the fixing frame 23 .

[0079] The stopper 83, against which the separation movement lever 28 abuts, restricts the rotation of the separation movement lever 28 in the direction opposite to the direction of arrow E in FIG.

[0080] The torsion coil spring 84 biases the separation movement lever 28 in a direction in which the separation movement lever 28 abuts against the stopper 83. Note that the torsion coil spring 84 is omitted in Figs. 3 and 6.

[0081] In the fixing nip N formed by the contact between the fixing belt 31 and the pressure roller 22 of the fixing device 20 having the above-mentioned configuration, the recording material S is heated while being sandwiched and conveyed in the conveying direction. As a result, the unfixed toner image formed in the image forming section 40 and transferred to the recording material S is heated and pressurized in the fixing nip N and fixed to the recording material S.

[0082] In this way, the fixing device 20 needs to have both the function of applying heat and pressure and the function of transporting the recording material S.

[0083] <Configuration of separation unit> The configuration of the separation unit 70 of the fixing device 20 according to the embodiment of the present invention will be described in detail with reference to FIGS.

[0084] The separation unit 70 includes a separation plate 71, a separation plate support member 72, a separation plate regulating portion 73, a separation guide 74, a coil spring 75, a retraction arm 76, a retraction arm shaft 77, a retraction lever 78, and a torsion coil spring 79.

[0085] Separation plate 71 as a separating member is a metal plate that can slide in the conveying direction C in Fig. 8, or in the opposite direction to the conveying direction B in Fig. 7. Fluorine-based tape is attached to the surface of separation plate 71 to prevent toner from the recording material S from adhering due to sliding or damage to the image formed on the recording material S. Separation plate 71 is provided facing fixing belt 31 with a gap therebetween without contacting it, and separates recording material S that has passed through fixing nip portion N from fixing belt 31.

[0086] The separation plate support member 72 is provided with a separation plate 71 and a separation plate regulating portion 73 .

[0087] The separation plate restricting portions 73 are provided as a pair on both sides in the direction of the rotation axis W, and are supported by the separation positioning portion 37 and the separation guide 74 together with the separation plate support member 72 so as to be relatively movable. Here, the separation plate support member 72 and the separation plate restricting portions 73 form a positioning member that is movable together with the separation plate 71. The separation plate restricting portion 73 includes a first guide shaft 73a, a second guide shaft 73b, a spring hook portion 73c, and a side surface portion 73d.

[0088] The first guide shaft 73a protrudes outward from the side surface portion 73d and is provided so that the center of the rotation shaft coincides with the rotation axis direction W. The first guide shaft 73a slidably engages with the guide groove 37b of the separation positioning portion 37 and the guide groove 74a of the separation guide 74. The first guide shaft 73a abuts against the abutment portion 37a, which is the inner wall of the end portion of the guide groove 37b opposite to the conveying direction, by the biasing force of the coil spring 75.

[0089] The second guide shaft 73b protrudes outward from the side surface portion 73d and is provided so that the center of the rotation shaft coincides with the rotation axis direction W. The second guide shaft 73b slidably engages with the guide groove 37b of the separation positioning portion 37. The second guide shaft 73b engages with the guide groove 37b to stop the separation positioning portion 37 from rotating. The second guide shaft 73b abuts against the inner wall of the end of the guide groove 74a of the separation guide 74 in the conveying direction.

[0090] The first guide shaft 73a and the second guide shaft 73b are provided on the side surface portion 73d with a gap therebetween in the conveying direction.

[0091] The spring hook portion 73 c supports one end of the coil spring 75 .

[0092] The side surface portions 73d are provided substantially vertically at both ends of the separation plate support member 72 in the direction W of the rotation axis.

[0093] The separation guide 74 movably supports the separation plate support member 72. The separation guide 74 guides and regulates the movements of the separation plate 71, the separation plate support member 72, and the separation plate regulating portion 73. The separation guide 74 includes a guide groove 74a and a fastening portion 74b.

[0094] The guide groove 74a is an elliptical through hole penetrating in the plate thickness direction. The guide groove 74a slidably engages with the first guide shaft 73a and the second guide shaft 73b to guide the movement of the separation plate 71, the separation plate support member 72, and the separation plate regulating portion 73 in the conveying direction or the direction opposite to the conveying direction. The guide groove 74a regulates the movement of the separation plate 71, the separation plate support member 72, and the separation plate regulating portion 73 in the conveying direction by the second guide shaft 73b abutting against the inner wall of the end of the guide groove 74a in the conveying direction.

[0095] The fastening portion 74b is fastened to the housing of the paper discharge unit 60.

[0096] The coil spring 75 is a torsion coil spring that biases the separation plate restricting portion 73 in the direction of the arrow B in Figures 5 and 7. The coil spring 75 biases the separation plate restricting portion 73 in the direction of the arrow B, thereby causing the first guide shaft 73a to abut against the abutment portion 37a of the separation positioning portion 37.

[0097] The retracting arms 76 are provided at both ends of the separation guide 74 in the direction of the rotation axis W, and are fixed to retracting arm shafts 77. The retracting arms 76 are pressed by the retracting lever 78 and rotate together with the retracting arm shaft 77 in the clockwise direction in Fig. 8, thereby moving the separation plate restricting portion 73 in the direction of arrow C in Fig. 5 and Fig. 8 against the biasing force of the coil spring 75. The retracting arms 76 are released from the pressure of the retracting lever 78 and rotate together with the retracting arm shaft 77 in the counterclockwise direction in Fig. 8, thereby moving the separation plate restricting portion 73 in the direction of arrow B in Fig. 5 and Fig. 7 by the biasing force of the coil spring 75.

[0098] The retracting arm shaft 77 is rotatably supported by the separation guide 74 .

[0099] The retraction lever 78 is rotatably supported on the housing of the paper discharge unit 60. The retraction lever 78 is pressed by the separation movement lever 28 and rotates in the direction of arrow D in Fig. 7 against the biasing force of the torsion coil spring 79, thereby releasing the pressure on the retraction arm 76. When the pressure from the separation movement lever 28 is released, the retraction lever 78 rotates in the direction of arrow F in Fig. 8 due to the biasing force of the torsion coil spring 79, causing the retraction arm 76 to rotate clockwise in Fig. 8.

[0100] The torsion coil spring 79 biases the retraction lever 78 in the direction of the arrow F in Fig. 8. Note that the torsion coil spring 79 is omitted in Figs. 3 and 6.

[0101] <Image Forming Operation of Image Forming Apparatus> The image forming operation of the image forming apparatus 1 according to the embodiment of the present invention will be described in detail with reference to FIGS.

[0102] The image forming apparatus 1 starts an image forming operation when an image signal is input from a document reading device, a host device, or an external device.

[0103] When the image forming apparatus 1 starts an image forming operation, it rotates the photosensitive drums 51y, 51m, 51c, and 51k, and charges the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k with the charging rollers 52y, 52m, 52c, and 52k.

[0104] Next, the image forming apparatus 1 irradiates the photosensitive drums 51y, 51m, 51c, and 51k with laser light from the exposure devices 42y, 42m, 42c, and 42k based on image information, thereby forming electrostatic latent images on the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k.

[0105] Next, the image forming apparatus 1 causes the toner supplied from the developing devices 53y, 53m, 53c, and 53k to adhere to the electrostatic latent images formed on the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k. By causing the toner to adhere to the electrostatic latent images, the image forming apparatus 1 forms toner images on the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k, thereby visualizing the electrostatic latent images.

[0106] Next, the image forming apparatus 1 sequentially transfers the toner images formed on the surfaces of the photosensitive drums 51y, 51m, 51c, and 51k onto the intermediate transfer belt 44b.

[0107] In parallel with the above operations, the image forming apparatus 1 transports the recording material S to the secondary transfer portion 45 in accordance with the transport timing of the toner image on the intermediate transfer belt 44b.

[0108] Next, the image forming apparatus 1 causes the secondary transfer section 45 to transfer the toner image transferred onto the intermediate transfer belt 44b onto the recording material S.

[0109] Next, the image forming apparatus 1 fixes the unfixed toner image transferred to the recording material S to the recording material S by applying heat and pressure to the unfixed toner image by the fixing device 20.

[0110] Next, the image forming apparatus 1 discharges the recording material S on which the toner image has been fixed to the outside of the apparatus main body 10.

[0111] <Operation of the fixing device> The operation of the fixing device 20 according to the embodiment of the present invention will now be described in detail.

[0112] First, the positional relationship between the fixing belt 31 and the separation plate 71 in the case where the contact pressure between the fixing belt 31 and the pressure roller 22 is made variable will be described with reference to Figures 9 and 10. Note that in Figures 9 and 10, the illustration of a part of the fixing device 20 is omitted.

[0113] The second pressure at which the pressure in the fixing nip portion N is reduced is approximately half of the first pressure, so that the amount of bending of the central portion in the rotation axis direction W of the stay 35 that holds the pressure pad 32 is reduced. As a result, when the pressure in the fixing nip portion N becomes the second pressure, the central portion in the rotation axis direction W of the fixing belt 31 moves in a direction approaching the separation plate 71, as shown by the dashed line in Fig. 10(b). Accordingly, when the pressure in the fixing nip portion N is the second pressure, it is necessary to move the separation plate 71 in a direction away from the fixing belt 31.

[0114] The operation of the fixing device 20 taking into consideration the above positional relationship will be described in detail with reference to Fig. 3 to Fig. 8. First, the operation of the fixing device 20 in the normal pressure state where the pressure of the fixing nip N is the first pressure will be described with reference to Fig. 7. Note that the fixing nip N in this case will be referred to as fixing nip N1.

[0115] The pressure frame 25 is pressed by a pressure cam 27 that is rotated by a drive source (not shown) and moves to the heating unit 30 side. As a result, the pressure roller 22 is pressed against the pressure pad 32 via the fixing belt 31, forming the fixing nip N1. The fixing device 20 adjusts the contact pressure of the pressure roller 22 by the crown-shaped pressure pad 32, so that the fixing nip N1 is substantially flat over the entire area in the rotation axis direction W.

[0116] Moreover, the separation movement lever 28 is in contact with a stopper 83 provided on the fixing frame 23 by the biasing force of the torsion coil spring 84. As a result, the retraction lever 78 is pressed by the separation movement lever 28 and rotates in the direction of arrow D. Moreover, the separation plate regulating portion 73 is moved in the direction of arrow B by the biasing force of the torsion coil spring 75, and the first guide shaft 73a is in contact with the contact portion 37a of the separation positioning portion 37.

[0117] In this state, the fixing belt 31 and the separation plate 71 are positioned, and a gap (gap) G1 is formed between the fixing belt 31 and the separation plate 71. The size of the gap G1 is approximately flat over the entire area in the direction of the rotation axis W at the fixing nip portion N1, so that a gap of approximately 500 μm can be guaranteed over the entire area in the direction of the rotation axis W. This allows the fixing device 20 to guide various recording materials S peeled off from the fixing belt 31 from the exit of the fixing nip portion N1 to the discharge roller pair 62 without clogging the gap G1 between the fixing belt 31 and the separation plate 71.

[0118] Next, the operation of the fixing device 20 in the reduced pressure state where the pressure in the fixing nip portion N is set to a second pressure in order to fix an unfixed toner image on a recording material S such as an envelope will be described with reference to Fig. 8. The fixing nip portion N in this case will be referred to as a fixing nip portion N2.

[0119] First, the pressure frame 25 is pressed by the pressure cam 27 that is rotated by a drive source (not shown) and moves to the heating unit 30 side. As a result, the pressure roller 22 is pressed against the pressure pad 32 via the fixing belt 31, and the fixing nip portion N2 is formed.

[0120] In the fixing nip portion N2, the pressure is reduced to a second pressure that is about half of the first pressure in order to reduce deterioration of the fixing member of the fixing device 20 due to wrinkles or edges of the envelope. Therefore, the amount of deflection of the center of the pressure pad 32 in the rotation axis direction W is smaller than when the pressure of the fixing nip portion N2 is the first pressure. Also, the running trajectory of the fixing belt 31 moves downstream in the conveying direction as shown by the dashed line in FIG. 8, because the nip position of the center of the rotation axis direction W of the fixing belt 31 in the fixing nip portion N2 moves downward, compared to when the pressure of the fixing nip portion N is the first pressure.

[0121] In addition, the separation movement lever 28 is pressed by the separation movement cam 29 provided coaxially with the pressure cam 27 and rotates in the direction of the arrow E. The separation movement lever 28 rotates in the direction of the arrow E. As a result, the retraction lever 78 rotates in the direction of the arrow F by the biasing force of the torsion coil spring 79.

[0122] 8 against the biasing force of the torsion coil spring 75, causing the separation plate restricting portion 73 to move in the direction of arrow C. As the separation plate restricting portion 73 moves in the direction of arrow C, the first guide shaft 73a and the second guide shaft 73b also move in the direction of arrow C while engaging with the guide groove 37b, and the first guide shaft 73a moves away from the contact portion 37a. The distance between the first guide shaft 73a and the contact portion 37a is exemplified as 1000 μm here.

[0123] In addition, as the separation plate regulating portion 73 moves in the direction of the arrow C, the separation plate 71 moves in the downstream direction of the conveying direction, that is, in the direction of the arrow C. In this manner, the separation plate 71 moves in conjunction with the pressing operation of the pressure cam 27 against the pressure frame 25.

[0124] In this state, the fixing belt 31 and the separation plate 71 are positioned, and the gap between the fixing belt 31 and the separation plate 71 becomes G2. The size of the gap G2 can be guaranteed to be 500 μm at the center in the direction of the rotation axis W and 1000 μm at both ends in the direction of the rotation axis W at the fixing nip portion N2.

[0125] Further, the separation plate 71, by the separation positioning portion 37 and the guide groove 74a, moves in an area on the fixing belt 31 side of the nip line L (an area above the nip line L in FIG. 7) as the discharge trajectory of the recording material S discharged from the fixing nip portion N. As a result, the separation plate 71 does not enter the discharge trajectory of the recording material S discharged from the outlet of the fixing nip portion N2, so that the recording material S discharged from the outlet of the fixing nip portion N2 can be conveyed to the discharge roller pair 62 without being caught by the separation plate 71.

[0126] As described above, the separation positioning portion 37 and the separation guide 74 movably hold the separation plate support member 72 and the separation plate regulating portion 73. Furthermore, the separation positioning portion 37 and the separation guide 74 set the position of the separation plate 71 with respect to the fixing belt 31 by regulating the movements of the separation plate support member 72 and the separation plate regulating portion 73. The separation positioning portion 37 and the separation guide 74 constitute a regulating means.

[0127] 8 is in a reduced pressure state where the pressure in the fixing nip portion N2 is the second pressure, contact between the fixing belt 31 and the separation plate 71 can be avoided by ensuring that the size of the gap G2 between the fixing belt 31 and the separation plate 71 is 500 to 1000 μm. Also, the recording material S peeled off from the fixing belt 31 can be guided from the exit of the fixing nip portion N2 to the pair of discharge rollers 62 without being clogged in the gap G2.

[0128] Furthermore, when the running path of the fixing belt 31 changes between the normal pressure state and the reduced pressure state, the fixing device 20 moves the position of the separation plate 71 relative to the fixing belt 31 in accordance with the pressure of the fixing nip N. This ensures a suitable gap between the fixing belt 31 and the separation plate 71 for various types of recording materials S, making it possible to provide a fixing device 20 that is compatible with various types of recording materials S. Furthermore, by keeping the fixing belt 31 and the separation plate 71 in a non-contact state, it is possible to achieve high durability of the fixing belt 31.

[0129] Furthermore, by positioning the separation plate 71 with respect to the fixing belt 31 using the separation plate support member 72 and the separation plate regulating portion 73, the separation plate 71 can be positioned in a non-contact state with respect to the fixing belt 31.

[0130] In this embodiment, there is a pressure roller 22 that contacts the fixing belt 31 and forms a fixing nip N that holds and conveys the recording material S with a first pressure or a second pressure that is lower than the first pressure. There is also a separation plate 71 that is provided facing the fixing belt 31 with a gap therebetween on the downstream side of the fixing nip N in the conveying direction of the recording material S and that separates the recording material S that has passed through the fixing nip N from the fixing belt 31. When the pressure of the fixing nip N is the second pressure, the separation plate 71 moves downstream in the conveying direction more than when it is the first pressure.

[0131] This makes it possible to realize high durability of the fixing belt 31, and prevents various types of recording materials S from being unable to be discharged, while also ensuring an appropriate gap between the fixing belt 31 and the separation plate 71.

[0132] The present invention is not limited to the above-described embodiment, and it goes without saying that various modifications are possible without departing from the spirit and scope of the present invention.

[0133] Specifically, in the above embodiment, the coil spring 75 and the torsion coil spring 79 are used, but this is not limiting, and other biasing means such as a tension spring or a compression spring may be used.

[0134] In the above embodiment, the coil spring 75 and the torsion coil spring 79 are provided in the separation unit 70. However, the present invention is not limited to this, and they may be provided outside the separation unit 70, such as on the fixing frame 23.

[0135] In the above embodiment, the guide groove 37b of the separation positioning portion 37 is slidably engaged with the first guide shaft 73a and the second guide shaft 73b to guide the movement of the separation plate 71. However, the present invention is not limited to this, and the movement of the separation plate 71 can be guided by any configuration.

[0136] In addition, in the above embodiment, the fixing nip portion N is formed by pressing the pressure roller 22 against the pressure pad 32 via the fixing belt 31, but this is not limited to the above, and the fixing nip portion N may also be formed by the pressure roller 22 and a heating rotating body such as a heating roller. [Explanation of symbols]

[0137] 20 Fixing device 22 Pressure roller 24 Guide section 25 Compression Frame 27 Pressure Cam 28 Separation movement lever 29 Separate moving cam 30 Heating unit 31 Fixing belt 32 Pressure Pad 32a Curved section 33 Heating roller 35 Stay 40 Image forming section 60 Paper ejection unit 70 Separation Unit 71 Separation plate 72 Separator plate support member 73 Separation plate control part 73a Guide shaft 73b Guide shaft 74 Separation Guide 74a Guide groove 76 Retractable Arm 78 Retract lever 83 Stopper

Claims

1. A fixing device that fixes an unfixed toner image formed on a recording material to the recording material, a heating rotor that heats the unfixed toner image and is rotatable; a rotatable pressure rotating body that is in contact with the heating rotating body to form a fixing nip portion; a separating member provided opposite to the heating rotary body with a gap therebetween on a downstream side of the fixing nip portion in a recording material conveying direction, the separating member separating the recording material that has passed through the fixing nip portion from the heating rotary body; having The pressurizing rotor is a fixing nip portion is formed in which the recording material is nipped and conveyed by a first pressure or a second pressure that is lower than the first pressure by contacting the heating rotary member; The separating member is When the pressure of the fixing nip portion is the second pressure, the fixing nip portion moves to a downstream side in the conveying direction compared to when the pressure is the first pressure. A fixing device comprising:

2. The separating member is the recording material is discharged from the fixing nip portion, and the recording material moves in a region closer to the heating rotor than a path of the recording material is discharged from the fixing nip portion; 2. The fixing device according to claim 1,

3. a nip portion forming member for forming the fixing nip portion, The heating rotor is An endless belt member, The nip portion forming member is a curved portion for curving the belt member at an end portion on the downstream side in the conveying direction of the fixing nip portion to separate the recording material from the belt member, and the fixing nip portion is formed by pressing the belt member against the pressure rotating body on the inner side of the belt member while sandwiching the belt member therebetween; 3. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

4. a pressing member that presses the pressure rotating member against the heating rotating member to form the fixing nip portion with the first pressure or the second pressure, The separating member is Moves in conjunction with the pressing operation of the pressing member.

3. The fixing device according to claim 1, wherein the fixing member is a fixing member having a fixing surface.

5. a positioning member movable together with the separating member; a restricting means for movably holding the positioning member and restricting the movement of the positioning member to set a position of the separating member with respect to the heating rotator; 3. The fixing device according to claim 1, further comprising:

6. The fixing device according to claim 1 or 2, a toner image forming section that forms the unfixed toner image on a recording material and conveys the recording material on which the unfixed toner image has been formed to the fixing device; An image forming apparatus comprising:

Images