Fixing device and image forming apparatus

Abstract

A fixing device and an image forming apparatus are provided, the fixing device including: an endless conveyor belt that is heated and circularly movable; a fixing part which is in contact with the inner peripheral surface of the conveyor belt and is fixed; a pressure roller that presses the conveyor belt against the fixed portion to form a fixing portion through which the recording material on which the unfixed image is formed passes, and that rotates and drives the pressure roller; and a support roller that is disposed upstream of the fixing portion in a moving direction of the conveyor belt and rotatably supports the conveyor belt, the fixing portion forming a first curved surface of an arcuate curved surface upstream of a position where the fixing portion is formed in the moving direction, and the fixing portion forming a second curved surface of an arcuate curved surface upstream of a position where the fixing portion is formed in the moving direction. A second curved surface which is an arc-shaped curved surface is formed on the upstream side of the first curved surface in the moving direction, and if the curvature radius of the first curved surface is set to be r1 (mm) and the curvature radius of the second curved surface is set to be r2 (mm), the condition that r1 > r2 is satisfied, and the conveyor belt is erected on the support roller and the first curved surface in a state where tension is applied.

Description

Technical Field

[0001] The present invention relates to a fixing device and an image forming device. Background Art

[0002] In Patent Document 1, a fixing device is disclosed. Regarding a fixing member, when forming a fixing portion, a contact portion where its conveyor belt contacts a pressure roller is formed into an arcuate curved surface that bends away from the pressure roller, and an insertion portion adjacent to the insertion side where a recording material is inserted in the contact portion is formed into an arcuate curved surface that bends in a direction opposite to the contact portion. When the thickness of the conveyor belt is set to t (mm), the radius of curvature of the curved surface of the entrance portion is set to r1 (mm), and the radius of curvature of the curved surface of the contact portion is set to r2 (mm), the conditions of t(1 / r1 + 1 / r2) ≤ 0.130 and r1 ≤ r2 are satisfied.

[0003] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2014 - 182256 Summary of the Invention

[0004] There is a fixing device having a fixing portion fixed to the inner peripheral side of an annular conveyor belt that can move in a loop. By a pressure roller that rotates while applying pressure to the fixing portion, an unfixed toner image formed on a recording material is fixed. In this fixing device, if the posture of the conveyor belt is disordered, the unfixed toner image is disordered. In order to suppress this disorder, a technique of providing a support roller that contacts and rotates with the conveyor belt on the upstream side of the fixing portion to correct the posture of the conveyor belt is adopted.

[0005] However, in a case where the degree of freedom of the posture of the conveyor belt is restricted due to, for example, a shortening of the distance from the support roller to the fixing portion, the fixing portion is displaced due to vibration or the like, and it is easy to generate friction between the end portion of the fixing portion and the conveyor belt, thereby easily causing wear of the conveyor belt.

[0006] An object of the present invention is to suppress wear of the conveyor belt when correcting the posture of the conveyor belt by a support roller provided on the upstream side of the fixing portion.

[0007] The invention according to Solution 1 is a fixing device, characterized by comprising: an annular conveyor belt, which is heated and can move in a cycle; a fixing part, which is fixed in contact with the inner peripheral surface of the conveyor belt; a pressure roller, which presses the conveyor belt against the fixing part to form a fixing part through which a recording material with an unfixed image passes, and is rotationally driven; and a support roller, which is arranged on the upstream side of the fixing part in the moving direction of the conveyor belt and rotatably supports the conveyor belt. The fixing part forms a first curved surface with an arc-shaped surface on the upstream side of the position where the fixing part is formed in the moving direction, and forms a second curved surface with an arc-shaped surface on the upstream side of the first curved surface in the moving direction. If the radius of curvature of the first curved surface is set as r1 (mm) and the radius of curvature of the second curved surface is set as r2 (mm), the condition of r1>r2 is satisfied. The conveyor belt is installed on the support roller and the first curved surface in a state where tension is applied.

[0008] The invention according to Solution 2 is the fixing device according to Solution 1, characterized in that

[0009] The first curved surface and the second curved surface are formed at the end of the fixing part, and the second curved surface is continuously formed with the first curved surface.

[0010] The invention according to Solution 3 is the fixing device according to Solution 2, characterized in that

[0011] The first curved surface and the second curved surface are smoothly continuous.

[0012] The invention according to Solution 4 is the fixing device according to any one of Solutions 1 to 3, characterized in that

[0013] The radius of curvature of the second curved surface is greater than the radius of curvature at which the conveyor belt starts to deteriorate when the conveyor belt is bent.

[0014] The invention according to Solution 5 is the fixing device according to any one of Solutions 1 to 4, characterized in that

[0015] The radius of curvature of the second curved surface is determined to be a radius of curvature such that the conveyor belt does not contact the second curved surface even if the conveyor belt has jitter.

[0016] The invention according to Solution 6 is an image forming device, comprising: an image forming unit, which forms an unfixed image on a recording material; and the fixing device according to any one of Solutions 1 to 5, which fixes the unfixed image formed by the image forming unit on the recording material.

[0017] Invention effect

[0018] According to the first aspect of the present invention, when correcting the posture of the conveyor belt by the support roller provided on the upstream side of the fixing portion, wear of the conveyor belt can be suppressed.

[0019] According to the second aspect of the present invention, compared with the case where the second curved surface is not continuously provided with the first curved surface, the contact area between the conveyor belt and the fixing portion can be reduced.

[0020] According to the third aspect of the present invention, compared with the case where the first curved surface and the second curved surface are not smoothly continuous, wear of the conveyor belt can be suppressed.

[0021] According to the fourth aspect of the present invention, the lower limit value of the radius of curvature of the second curved surface can be determined.

[0022] According to the fifth aspect of the present invention, the upper limit value of the radius of curvature of the second curved surface can be determined.

[0023] According to the sixth aspect of the present invention, there is provided an image forming apparatus that suppresses wear of the conveyor belt when correcting the posture of the conveyor belt by a support roller provided on the upstream side of the fixing portion in a fixing device. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The embodiments of the present invention will be described in detail with reference to the following drawings.

[0025] Figure 1 is a diagram showing an image forming apparatus to which the present embodiment is applied;

[0026] Figure 2 is a diagram showing the structure of a fixing device;

[0027] Figure 3 is a diagram showing the shape of a contact member;

[0028] Figure 4 is a diagram showing a state in which a fixing belt is pressed against a fixing portion by a pressure roller;

[0029] Figure 5 is a diagram showing a comparative example.

[0030] REFERENCE SIGNS

[0031] 1 - Image forming apparatus, 10 - Image forming unit, 20 - Transfer unit, 50 - Fixing device, 51 - Fixing belt, 52 - Fixing portion, 53, 54a to 54c - Inner support roller, 55 - Outer support roller, 58 - Pressure roller, 523 - Contact surface, 524 - Large diameter surface, 525 - Small diameter surface. DETAILED DESCRIPTION OF THE INVENTION

[0032] 〔Image forming apparatus 1〕

[0033] Hereinafter, the image forming apparatus to which the present embodiment is applied will be described in detail with reference to the accompanying drawings.

[0034] Figure 1 It is a diagram showing the image forming apparatus 1 according to the present embodiment.

[0035] The image forming apparatus 1 exemplifies, for example, an electrophotographic image forming apparatus that forms a toner image on a recording material.

[0036] The image forming apparatus 1 includes: image forming units 10Y, 10M, 10C, and 10K (hereinafter, sometimes simply referred to as "image forming unit 10") that form toner images; a transfer unit 20 that transfers the toner images formed by the image forming unit 10 onto a recording material; a conveyance unit 40 that conveys the recording material; a fixing device 50 that fixes the unfixed toner images, which are unfixed images, onto the recording material; and a control unit 100 that controls each unit of the image forming apparatus 1.

[0037] [Control Unit 100]

[0038] The control unit 100 includes: a CPU (Central Processing Unit) 101 that controls the entire image forming apparatus 1; a RAM (Random Access Memory) 102 that is used as a work area during operation; and a ROM (Read Only Memory) 103 that is a memory storing various programs and various settings executed by the CPU 101.

[0039] [Image Forming Unit 10]

[0040] Figure 1 A plurality of the illustrated image forming units 10 are provided to form toner images for each color. In the present embodiment, four image forming units 10 of yellow (Y), magenta (M), cyan (C), and black (K) are provided. Figure 1 10Y, 10M, 10C, and 10K shown represent the components corresponding to the above respective colors. In addition, since the image forming units 10 of each color have the same structure except for the toner used, the components of the image forming unit 10K are denoted by symbols in Figure 1

[0041] Each color image forming unit 10 has while Figure 1The photosensitive drum 11 rotates in the clockwise direction (the direction of arrow A) to form an electrostatic latent image. Each color image forming section 10 includes: a charger 12 that charges the surface of the photosensitive drum 11; an exposure device 13 that forms an electrostatic latent image on the photosensitive drum 11; a developing device 14 that develops the electrostatic latent image formed on the photosensitive drum 11; a primary transfer roller 15 that transfers the toner image formed on the photosensitive drum 11 to the intermediate transfer belt 21; and a drum cleaner 16 that removes the developer remaining on the photosensitive drum 11. Then, by applying a primary transfer electric field between the primary transfer roller 15 and the photosensitive drum 11, at the primary transfer position T1, the toner image formed on the photosensitive drum 11 is transferred to the intermediate transfer belt 21.

[0042] 〔Transfer section 20〕

[0043] The transfer section 20 includes: an intermediate transfer belt 21 onto which the toner images of respective colors formed by the photosensitive drums 11 of the respective image forming sections 10 are transferred; and conveyor belt support rollers 22a to 22f provided on the inner peripheral side of the intermediate transfer belt 21. The transfer section 20 includes a secondary transfer roller 23 that transfers the toner images transferred onto the intermediate transfer belt 21 onto the recording material all at once. Further, the transfer section 20 includes a cleaner 24 that removes toner and the like on the surface of the intermediate transfer belt 21.

[0044] In the intermediate transfer belt 21, the toner images are transferred from the photosensitive drums 11 of respective colors to the outer peripheral surface. As Figure 1 shown, the intermediate transfer belt 21 is annular and wound around a plurality of conveyor belt support rollers 22a to 22f. The intermediate transfer belt 21 is circulated in the direction of arrow B by rotationally driving at least one of the plurality of conveyor belt support rollers 22a to 22f.

[0045] The secondary transfer roller 23 is disposed opposite to the conveyor belt support roller 22e with the intermediate transfer belt 21 therebetween. The secondary transfer roller 23 presses the intermediate transfer belt 21 against the conveyor belt support roller 22e and rotates.

[0046] As Figure 1 shown, the cleaner 24 is disposed on the outer peripheral side of the intermediate transfer belt 21. The cleaner 24 is disposed on the downstream side of the secondary transfer roller 23 and on the upstream side of the image forming section 10 in the circulation direction of the intermediate transfer belt 21.

[0047] 〔Conveyor section 40〕

[0048] The conveying unit 40 includes: a housing unit 41 that houses the recording material; and a feeding device 42 that feeds out the recording material housed in the housing unit 41 one by one. Further, the conveying unit 40 includes a pair of paper conveying rollers 43a to 43c that convey the recording material from the housing unit 41 to the secondary transfer position T2 of the transfer unit 20. Moreover, the conveying unit 40 includes paper conveyor belts 45 and 46 that convey the recording material from the secondary transfer position T2 to the fixing device 50. Further, the conveying unit 40 includes a pair of paper discharge rollers 47a and 47b that discharge the recording material sent out from the fixing device 50 to the outside of the image forming apparatus 1.

[0049] 〔Fixing Device 50〕

[0050] Hereinafter, Figure 2 , the fixing device 50 to which this embodiment is applied will be described.

[0051] Figure 2 is a diagram showing the structure of the fixing device 50.

[0052] The fixing device 50 includes: a fixing belt 51, which is a ring-shaped conveyor belt that is heated and can move in a cycle; a fixing portion 52 that contacts and fixes to the inner peripheral surface of the fixing belt 51; inner support rollers 53, 54a to 54c that are provided in contact with the inner peripheral surface of the fixing belt 51 and rotatably support the fixing belt 51; and an outer support roller 55 that is provided in contact with the outer peripheral surface of the fixing belt 51 and rotatably supports the fixing belt 51. Further, the fixing device 50 includes: a pressure roller 58 provided at a position opposed to the fixing portion 52; a displacement mechanism 63 that displaces the position of the pressure roller 58; and a pressing mechanism 64 that applies a force pressing toward the fixing portion 52 to the pressure roller 58. Moreover, the fixing device 50 includes: a coating device 69 that coats a lubricant on the inner peripheral surface of the fixing belt 51; introducing guide members 65a and 65b that introduce the recording material into the fixing device 50; and discharging guide members 66a and 66b that guide the recording material fixed by the fixing device 50 to the conveying path.

[0053] The fixing belt 51 is composed of a plurality of layers, and in this embodiment, it is composed of 3 layers. In this embodiment, the fixing belt 51 is composed of, for example, a base material of a ring-shaped conveyor belt, an elastic layer formed on the surface (outer peripheral surface) side of the base material, and a release layer formed on the elastic layer. The base material is formed of a material such as polyimide resin. Further, the elastic layer is formed of an elastic member such as silicone rubber. Further, the release layer is formed of a material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer).

[0054] Furthermore, the width of the fixing belt 51 is set to a dimension greater than the maximum value of the width when transporting the recording material. Also, the belt length of the fixing belt 51 is set to a dimension required to be wound around the fixing portion 52, the plurality of internal support rollers 53, 54a to 54c, and the external support roller 55.

[0055] The fixing portion 52 includes: a corner tube-shaped support body 521 disposed in a fixed state; and a contact member 522 that contacts the inner peripheral surface of the fixing belt 51.

[0056] The support body 521 is disposed along the inner side from the front of the apparatus in the length direction (the direction in which the corner tube extends), which is orthogonal to the transport direction of the recording material. Also, the support body 521 is disposed opposite to the pressure roller 58. The support body 521 is formed of a material such as metal like iron or aluminum, or liquid crystal polymer.

[0057] The contact member 522 is mounted on the surface of the support body 521 opposite to the pressure roller 58. Also, the contact member 522 is formed of a material such as fluororesin like polytetrafluoroethylene (PTFE) or PFA. Additionally, regarding the shape of the contact member 522, it will be described later. Figure 3 It will be described later.

[0058] The internal support roller 53 is a cylindrical roller made of aluminum or the like and is rotatably disposed at the position farthest from the fixing portion 52. Also, a halogen heater 56 is provided in the internal space of the internal support roller 53. By heating the internal support roller 53 with this halogen heater 56, the internal support roller 53 heats the fixing belt 51 from the inner peripheral surface side. Moreover, a temperature detector 67 for detecting the surface temperature of the internal support roller 53 is provided on the internal support roller 53. Also, the internal support roller 53 is configured as a tension applying roller that applies tension to the fixing belt 51 by supporting the fixing belt 51 in a state of elastically pressing it from the inner peripheral surface side toward the outer peripheral surface side.

[0059] The internal support roller 54a is disposed on the upstream side of the fixing portion 52 in the moving direction (arrow C direction) of the fixing belt 51 and rotatably supports the fixing belt 51. Then, the internal support roller 54a corrects the posture of the fixing belt 51 before contacting the fixing portion 52.

[0060] The internal support roller 54b is disposed on the downstream side of the fixing portion 52 in the moving direction of the fixing belt 51 and rotatably supports the fixing belt 51. Then, the internal support roller 54b corrects the posture of the fixing belt 51 away from the fixing portion 52.

[0061] The internal support roller 54c is rotatably disposed between the internal support roller 53 and the internal support roller 54a in the moving direction of the fixing belt 51. Then, the internal support roller 54c corrects the posture of the fixing belt 51 when it travels.

[0062] The outer support roller 55 is a cylindrical roller made of aluminum or the like, contacts the outer peripheral surface of the fixing belt 51, and is arranged in a rotatable state. The outer support roller 55 is disposed between the inner support roller 54b and the inner support roller 53 in the moving direction of the fixing belt 51. A halogen heater 57 is provided in the inner space of the outer support roller 55. The outer support roller 55 is heated by the halogen heater 57, and thus the outer support roller 55 heats the fixing belt 51 from the outer peripheral surface side. Further, a temperature detector 68 for detecting the surface temperature thereof is provided on the outer support roller 55. Moreover, a first driving device 61 composed of a driving motor or the like is provided on the outer support roller 55. The first driving device 61 is configured to be able to rotationally drive the outer support roller 55 at a required time. Thereby, the outer support roller 55 rotationally drives the fixing belt 51 in the direction of arrow C.

[0063] Regarding the pressure roller 58, the rotation axis of the pressure roller 58 is arranged along the inner side from the front of the image forming apparatus 1 with the direction orthogonal to the conveyance direction of the recording material as the longitudinal direction. The pressure roller 58 is a roller having a structure in which an elastic layer 582 made of silicone rubber or the like and a release layer 583 made of PFA or the like are sequentially laminated on the outer peripheral surface of a cylindrical roller base 581 made of aluminum or the like. The elastic layer 582 is a layer that elastically deforms when the pressure roller 58 presses the fixing belt 51 against the fixing portion 52 to form a fixing area NP. For example, its hardness is set to a value that is harder than the hardness of the fixing portion 52. Here, the fixing area NP refers to the area where the pressure roller 58 presses the fixing belt 51 against the fixing portion 52, and is indicated by the symbol NP in Figure 2 In this, a fixing portion 59 through which the recording material on which an unfixed image is formed passes is formed in the fixing area NP.

[0064] The pressure roller 58 includes a second driving device 62 for rotating the pressure roller 58, and the pressure roller 58 is rotationally driven. The second driving device 62 is composed of a driving motor or the like. Thereby, the pressure roller 58 contacts the outer peripheral surface of the fixing belt 51 pressed against the fixing portion 52 and is rotationally driven, thereby rotating the fixing belt 51 in the direction indicated by arrow C.

[0065] The displacement mechanism 63 moves the pressure roller 58 to a first position in contact with the fixing portion 52 and a second position separated from the fixing portion 52. In Figure 2 The state where the pressure roller 58 is located at the second position is shown. As the displacement mechanism 63, for example, a mechanism having the following structure is used: a support frame that rotatably supports the pressure roller 58 is displaced by a displacement driving member such as a cam.

[0066] The pressing mechanism 64 applies a force to the pressing roller 58 toward the fixing portion 52. As the pressing mechanism 64, a mechanism constituted by a spring member or the like is applied, and it is configured to function in combination with the displacement mechanism 63.

[0067] The introduction guide member 65 is disposed at a position near the upstream side of the fixing area NP in the conveyance direction of the recording material. The introduction guide member 65 guides the recording material toward the entrance of the fixing area NP.

[0068] The discharge guide member 66 is disposed at a position near the downstream side of the fixing area NP in the conveyance direction of the recording material. The discharge guide member 66 guides the fixed recording material toward the paper discharge roller pair 47a (refer to Figure 1 ). The discharge guide member 66b disposed on the side closer to the pressing roller 58 among the discharge guide members 66 is disposed in a state where a conical separation claw (not shown) that peels the recording material discharged from the fixing area NP from the outer peripheral surface of the pressing roller 58 slightly contacts the outer peripheral surface of the pressing roller 58. Further, the discharge guide member 66b is attached to a frame of the displacement mechanism 63 or the like, and is displaced in linkage with the displacement operation of the displacement mechanism 63.

[0069] 〔Contact member 522〕

[0070] Next, Figure 3 is used to describe the shape of the contact member 522 to which this embodiment is applied.

[0071] Figure 3 is a diagram showing the shape of the contact member 522 that contacts the inner peripheral surface of the fixing belt 51.

[0072] The contact member 522 is formed with a contact surface 523 that contacts the fixing belt 51 pressed by the pressing roller 58 (refer to Figure 3 ) within the range shown in the fixing area NP of Figure 2 . Further, the contact member 522 is formed with a large-diameter surface 524 that supports the fixing belt 51 from the inner support roller 54a within the range shown by H1 in Figure 3 . Moreover, the contact member 522 is formed with a small-diameter surface 525 that avoids contact with the fixing belt 51 within the range shown by H2 in Figure 3 . Moreover, the contact member 522 is formed with a downstream side surface 526 within the range shown by H3 in Figure 3 , and the downstream side surface 526 is provided with a so-called R shape to reduce the friction applied to the fixing belt 51 away from the contact member 522. The large-diameter surface 524 formed within the range shown by H1 is an example of the first curved surface, and the small-diameter surface 525 formed within the range shown by H2 is an example of the second curved surface.

[0073] The contact surface 523 is a concave portion that curves away from the pressure roller 58 and is an arcuate surface. The contact surface 523 is designed such that the magnitude of the curvature of its arc becomes approximately the same as the magnitude of the curvature of the outer diameter of the pressure roller 58. Thus, the pressure roller 58 presses the fixing area NP of the fixing belt 51 to have the width of the contact surface 523 in the conveyance direction of the recording material.

[0074] The large-diameter surface 524 is continuous with the contact surface 523 in the moving direction of the fixing belt 51 and is formed on the upstream side of the contact surface 523. The large-diameter surface 524 is a convex portion that protrudes toward the fixing belt 51 and is an arcuate curved surface. The center of the arc of the large-diameter surface 524 is shown as point P1 in Figure 3 FIG. And, the radius of curvature of the arc of the large-diameter surface 524 is shown as r1 (mm) in Figure 3 FIG.

[0075] The large-diameter surface 524 is arranged such that any one of its tangents contacts the outer diameter of the inner support roller 54a. Thus, in a state where tension is applied to the fixing belt 51, the fixing belt 51 is stretched from the inner support roller 54a over the large-diameter surface 524.

[0076] The small-diameter surface 525 is formed on the upstream side of the large-diameter surface 524 in the moving direction of the fixing belt 51. The small-diameter surface 525 is a convex portion that protrudes toward the fixing belt 51 and is an arcuate curved surface. The center of the arc of the small-diameter surface 525 is shown as point P2 in Figure 3 FIG. And, the radius of curvature of the arc of the small-diameter surface 525 is shown as r2 (mm) in Figure 3 FIG.

[0077] The radius of curvature r2 of the small-diameter surface 525 is formed to satisfy the condition of r1 > r2.

[0078] And, in the present embodiment, the magnitude of the radius of curvature r2 of the small-diameter surface 525 can be set to be greater than the radius of curvature at which the fixing belt 51 starts to deteriorate when the fixing belt 51 is bent. Here, the deterioration of the fixing belt 51 refers to an irreversible change that occurs when the fixing belt 51 is bent, for example, cracks generated in the polyimide resin of the base material used for the fixing belt 51. The radius of curvature at which the fixing belt 51 starts to deteriorate varies depending on various conditions such as the material used for the fixing belt 51 and the environment in which it is used, and the radius of curvature at which the fixing belt 51 starts to deteriorate is determined through experiments, simulations, etc.

[0079] Further, in the present embodiment, the size of the radius of curvature r2 can be determined to be a size of the radius of curvature such that even if the fixing belt 51 vibrates, the fixing belt 51 does not contact the small-diameter surface 525. For example, when the radius of curvature r2 of the small-diameter surface 525 is large, when the fixing belt 51 contacting the large-diameter surface 524 vibrates, it is likely to contact the small-diameter surface 525. Therefore, the size of the radius of curvature r2 is determined to be a value less than the value at which the fixing belt 51 does not contact the small-diameter surface 525. Here, the vibration of the fixing belt 51 refers to the disorder of the fixing belt 51 generated when the fixing belt 51 moves in a loop, for example, the state in which the fixing belt 51 undulates.

[0080] Further, in the present embodiment, the large-diameter surface 524 and the small-diameter surface 525 are formed at the end of the fixing portion 52, and the large-diameter surface 524 and the small-diameter surface 525 are continuously formed. In addition, the large-diameter surface 524 may not be continuous with the small-diameter surface 525. For example, a flat surface or a curved surface may be formed between the large-diameter surface 524 and the small-diameter surface 525.

[0081] Further, in the present embodiment, the large-diameter surface 524 and the small-diameter surface 525 are smoothly continuous. Here, being smoothly continuous means that the tangent line is determined to be one at the boundary between the large-diameter surface 524 and the small-diameter surface 525. In addition, the large-diameter surface 524 and the small-diameter surface 525 may not be smoothly continuous and may have corners.

[0082] The downstream side surface 526 is on the downstream side of the contact surface 523 in the moving direction of the fixing belt 51 and is formed at the end of the contact member 522.

[0083] 〔Processing performed in the fixing device 50〕

[0084] Next, use Figure 2 and Figure 4 to describe the operation of the fixing device 50 in the present embodiment.

[0085] Figure 4 is a diagram showing a state in which the fixing belt 51 is pressed against the fixing portion 52 by the pressure roller 58. The pressure roller 58 presses the fixing belt 51 against the contact surface 523 of the contact member 522 and rotates in the clockwise direction in the figure.

[0086] In the fixing device 50 in the present embodiment (refer to Figure 1 ), when the main power supply of the image forming apparatus 1 (refer to Figure 1 ) is turned on, the required power is also supplied to the fixing device 50, and the preheating operation is started.

[0087] In the warm-up operation of the fixing device 50, first, the displacement mechanism 63 operates to separate the pressure roller 58 from the fixing belt 51, and the halogen heaters 56 and 57 operate to heat the inner support roller 53 and the outer support roller 55. If it is determined that the surface temperatures of the halogen heaters 56 and 57 become equal to or higher than a predetermined temperature, the displacement mechanism 63 moves the pressure roller 58 to a position where it presses against the fixing portion 52, and rotates and drives the first drive device 61 and the second drive device 62, respectively. As a result, the fixing belt 51 moves in a cycle, and the entire circumference of the fixing belt 51 is heated.

[0088] During fixing, in the fixing device 50, as Figure 4 shown, a state is formed in which the pressure roller 58 presses the fixing belt 51 against the fixing portion 52 to form a fixing portion 59. At this time, the elastic layer 582 of the pressure roller 58 is elastically deformed in a state of biting into a portion that contacts and passes through the fixing portion 52. Also, in the fixing device 50, the fixing belt 51 receives rotational power from the pressure roller 58 that contacts the outer peripheral surface of the fixing belt 51 and rotates in the direction indicated by arrow C. At this time, the outer support roller 55 is not rotationally driven but is freely rotatable and rotates following the fixing belt 51. Therefore, during the fixing operation, the fixing belt 51 rotates in the direction indicated by arrow C at a required speed by only receiving the rotational power of the pressure roller 58.

[0089] At this time, a recording material on which an unfixed toner image is formed is guided by the lower introduction guide member 65b and passes through the fixing area NP between the fixing belt 51 and the pressure roller 58. When passing through this fixing area NP, it is subjected to heating and pressing processes to fix the unfixed toner image on the recording material. The recording material after fixing is peeled off from the pressure roller 58 by the discharge guide member 66 and discharged from the fixing device 50.

[0090] In the present embodiment, as described above, a large-diameter surface 524 for mounting the fixing belt 51 is formed on the contact member 522, and a small-diameter surface 525 is formed on the upstream side of the large-diameter surface 524 in the moving direction of the fixing belt 51. Thus, when the fixing portion 52 is displaced, the fixing belt 51 is pressed by the large-diameter surface 524 having a large radius of curvature r1, so that the bending of the fixing belt 51 can be suppressed as compared with the case where the radius of curvature of the position where the fixing belt 51 is mounted is small. Thus, even when the fixing portion 52 is displaced, the fixing belt 51 can be suppressed from contacting on the upstream side of the large-diameter surface 524.

[0091] Also, in the present embodiment, the size of the radius of curvature r2 of the small-diameter surface 525 is larger than the radius of curvature at which the fixing belt 51 starts to deteriorate when the fixing belt 51 is bent. Therefore, even when the fixing belt 51 contacts the small-diameter surface 525, deterioration of the fixing belt 51 due to bending can be suppressed.

[0092] 〔Comparative Example〕

[0093] Here, as a comparative example, a case where the contact member 522 of the fixing portion 52 does not have a large-diameter surface 524 will be described.

[0094] Figure 5 It is a diagram showing a comparative example.

[0095] In this comparative example, a fixing portion 92 corresponding to the fixing portion 52 of the present embodiment is shown. This fixing portion 92 is different from the fixing portion 52 of the present embodiment and does not have a portion corresponding to the large-diameter surface 524.

[0096] In Figure 5 the state of the pressure roller 58 during the fixing operation is shown. The pressure roller 58 presses the fixing belt 51 against the fixing portion 92 and rotates clockwise in the figure. The fixing portion 92 has a so-called R-shaped rounded portion 92c at the upstream end in the moving direction of the fixing belt 51. In this comparative example, the fixing belt 51 is mounted on the inner support roller 54a and the rounded portion 92c. When the fixing belt 51 moves, friction is generated between the inner peripheral surface of the fixing belt 51 and the rounded portion 92c.

[0097] In Figure 5 the enlarged view, the position of the fixing portion 92 before displacement is shown by a one-dot chain line, and the state after displacement of the fixing portion 92 under the influence of vibrations of the image forming apparatus or the like is shown by a solid line. After the displacement of the fixing portion 92, the inner peripheral side of the fixing belt 51 contacts the side surface of the fixing portion 92 along the rounded portion 92c. When the rounded portion 92c is displaced, the smaller the curvature of the rounded portion 92c, the easier it is for the fixing belt 51 to bend along the rounded portion 92c. Then, cracks or the like may be generated on the fixing belt 51 due to the bending of the fixing belt 51 along the rounded portion 92c. This crack becomes deterioration of the fixing belt 51. And if the fixing belt 51 moves in a circulating manner while in contact with the side surface of the fixing portion 92, friction is generated between the side surface of the fixing portion 92 and the fixing belt 51, which may cause wear of the fixing belt 51.

[0098] As described above, regarding the shape of the contact member 522 of the fixing device 50 to which the present embodiment is applied, a small-diameter surface 525 is provided at the upstream end of the fixing portion 52 in the moving direction of the fixing belt 51, and a large-diameter surface 524 is provided on the downstream side of the small-diameter surface 525 and is continuous with the small-diameter surface 525. Then, the fixing belt 51 is mounted on the large-diameter surface 524. Therefore, in the fixing device 50 to which the present embodiment is applied, when the fixing portion 52 is displaced, the large-diameter surface 524 having an arc shape with a large radius of curvature r1 presses the fixing belt 51, and compared with the case where the fixing belt 51 is mounted on a curved surface with a small radius of curvature, bending of the fixing belt 51 can be suppressed, and wear of the fixing belt 51 can be suppressed.

[0099] (Supplementary Note) (1)

[0101] A fixing device, characterized in that it has:

[0102] An annular conveyor belt, which is heated and can move in a cycle;

[0103] A fixing part, which is in contact with the inner peripheral surface of the conveyor belt and is fixed;

[0104] A pressure roller, which presses the conveyor belt against the fixing part to form a fixing part through which a recording material with an unfixed image passes, and is rotationally driven; and

[0105] A support roller, which is arranged on the upstream side of the fixing part in the moving direction of the conveyor belt and rotatably supports the conveyor belt,

[0106] The fixing part forms a first curved surface with an arc-shaped surface on the upstream side of the position where the fixing part is formed in the moving direction, and forms a second curved surface with an arc-shaped surface on the upstream side of the first curved surface in the moving direction. If the radius of curvature of the first curved surface is set as r1 (mm) and the radius of curvature of the second curved surface is set as r2 (mm),

[0107] then the condition of r1 > r2 is satisfied,

[0108] The conveyor belt is installed on the support roller and the first curved surface in a state where tension is applied. (2)

[0110] The fixing device according to (1), characterized in that

[0111] The first curved surface and the second curved surface are formed at the end of the fixing part,

[0112] The second curved surface is continuously formed with the first curved surface. (3)

[0114] The fixing device according to (2), characterized in that

[0115] The first curved surface and the second curved surface are smoothly continuous. (4)

[0117] The fixing device according to any one of (1) to (3), characterized in that

[0118] The radius of curvature of the second curved surface is greater than the radius of curvature at which the conveyor belt starts to deteriorate when the conveyor belt is bent. (5)

[0120] The fixing device according to any one of (1) to (4), characterized in that

[0121] The radius of curvature of the second surface is determined to be a radius of curvature such that the conveyor belt does not contact the second surface even if the conveyor belt vibrates. (6)

[0123] An image forming apparatus includes:

[0124] an image forming unit that forms an unfixed image on a recording material; and

[0125] the fixing device according to any one of (1) to (5) that fixes the unfixed image formed by the image forming unit to the recording material.

[0126] According to the fixing device of (1), when the posture of the conveyor belt is corrected by a support roller provided upstream of the fixing portion, wear of the conveyor belt can be suppressed.

[0127] According to the fixing device of (2), compared with a case where the second surface is not continuously provided with the first surface, the contact area between the conveyor belt and the fixing portion can be reduced.

[0128] According to the fixing device of (3), compared with a case where the first surface and the second surface are not smoothly continuous, wear of the conveyor belt can be suppressed.

[0129] According to the fixing device of (4), a lower limit value of the radius of curvature of the second surface can be determined.

[0130] According to the fixing device of (5), an upper limit value of the radius of curvature of the second surface can be determined.

[0131] According to the image forming apparatus of (6), an image forming apparatus can be provided in which wear of the conveyor belt is suppressed when the posture of the conveyor belt is corrected by a support roller provided upstream of the fixing portion in the fixing device.

[0132] The above-described embodiments of the present invention are provided for purposes of illustration and description. In addition, the embodiments of the present invention do not comprehensively and exhaustively include the present invention, and do not limit the present invention to the disclosed manner. Obviously, various modifications and variations are apparent to those skilled in the art to which the present invention pertains. The present embodiment is selected and described in order to most easily explain the principle of the present invention and its applications. Thus, other technicians in the art can understand the present invention through various modified examples optimized for specific uses assumed for various embodiments. The scope of the present invention is defined by the above claims and their equivalents.

Claims

1. A fixing device, characterized in that, having: a ring-shaped conveyor belt, which is heated and capable of circular movement; a fixing portion, which is fixed in contact with the inner peripheral surface of the conveyor belt; a pressure roller, which presses the conveyor belt against the fixing portion to form a fixing portion through which a recording material on which an unfixed image is formed passes, and is rotationally driven; and a support roller, which is disposed on the upstream side of the fixing portion in the moving direction of the conveyor belt and rotatably supports the conveyor belt, the fixing portion forms a first curved surface with an arc-shaped surface on the upstream side of the position where the fixing portion is formed in the moving direction, and forms a second curved surface with an arc-shaped surface on the upstream side of the first curved surface in the moving direction. If the radius of curvature of the first curved surface is set as r1 (mm) and the radius of curvature of the second curved surface is set as r2 (mm), then the condition of r1 > r2 is satisfied, the conveyor belt is installed on the support roller and the first curved surface in a state where tension is applied.

2. The fixing device according to claim 1, wherein the first curved surface and the second curved surface are formed at the end of the fixing portion, the second curved surface is continuously formed with the first curved surface.

3. The fixing device according to claim 2, wherein the first curved surface and the second curved surface are smoothly continuous.

4. The fixing device according to any one of claims 1 to 3, wherein the radius of curvature of the second curved surface is greater than the radius of curvature at which the conveyor belt starts to deteriorate when the conveyor belt is bent.

5. The fixing device according to any one of claims 1 to 4, wherein the radius of curvature of the second curved surface is determined to be a radius of curvature such that even if the conveyor belt has jitter, the conveyor belt will not contact the second curved surface.

6. An image forming apparatus, comprising: an image forming unit, which forms an unfixed image on a recording material; and the fixing device according to any one of claims 1 to 5, which fixes the unfixed image formed by the image forming unit on the recording material.

Images