Fixing device

Abstract

To provide a fixing device capable of enhancing the stability of a belt surface on the downstream side from a nip part even when using a steering roller.SOLUTION: A fixing pad 320 is arranged inside the fixing belt 310; a rotatable pressure roller 330 presses a fixing pad 320 through the fixing belt 310 to form a nip part N for sandwiching and conveying a recording material; an auxiliary drive roller 340 provided on the downstream side of the nip part N inside the fixing belt 310 applies a drive force to the fixing belt 310; motors M0 and M1 apply a drive force to each of the pressure roller 330 and the auxiliary drive roller 340 so that the peripheral speed of the auxiliary drive roller 340 is larger than that of the pressure roller 330; and a steering roller 350 for controlling a position of the fixing belt 310 in the width direction is provided on the downstream side of the auxiliary drive roller 340 and on the upstream side of the fixing pad 320.SELECTED DRAWING: Figure 8

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image carried on a recording material onto the recording material. [Background technology]

[0002] A known fixing device configuration includes a fixing belt, which is an endless belt, and a pressure roller that contacts the outer peripheral surface of the fixing belt, forming a nip portion that sandwiches and conveys a recording material, and fixing a toner image to the recording material as it passes through the nip portion (Patent Document 1). In the configuration described in Patent Document 1, a driving force is applied to the fixing belt by rotating the pressure roller. Furthermore, Patent Documents 2, 3, 4, and 5 describe configurations in which, in addition to a configuration in which the pressure roller is rotated, an auxiliary drive roller stretches the fixing belt to improve the rotational stability of the fixing belt. In the configurations of Patent Documents 2, 3, 4, and 5, the fixing belt is stretched by a fixed member or roller that forms the nip portion that sandwiches and conveys the recording material, and the auxiliary drive roller. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-228765 [Patent Document 2] Japanese Patent Application Laid-Open No. 2003-195671 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-4746 [Patent Document 4] Japanese Patent Application Laid-Open No. 2015-135354 [Patent Document 5] Japanese Patent Application Publication No. 2017-223800 Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, a configuration that uses a steering roller with a tilted rotation axis to correct deviation of the fixing belt so that the fixing belt fits within a predetermined range in the width direction of the fixing belt is known. If the twist of the fixing belt caused by the tilt of the steering roller reaches the downstream side of the nip in the recording material conveyance direction, there is a risk of reducing the stability of separating the recording material from the nip. On the other hand, the auxiliary drive roller can eliminate slack in the belt surface upstream of the auxiliary drive roller in the direction of rotation of the fixing belt by using its driving force. Therefore, by positioning the auxiliary drive roller upstream of the steering roller in the direction of rotation, the stability of the belt surface downstream of the nip can be improved.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a fixing device that can improve the stability of the belt surface downstream of the nip portion even when a steering roller is used. [Means for solving the problem]

[0006] a driving source that applies a driving force to the pressure member to rotate the fixing belt; a transmission mechanism that transmits the driving force from the driving source to the auxiliary drive roller; and a steering roller that is disposed downstream of the auxiliary drive roller and upstream of the pad in the rotation direction of the fixing belt so as to stretch the inner surface of the fixing belt and to adjust the position of the fixing belt by tilting the fixing belt so that the fixing belt is positioned within a predetermined range in the width direction of the fixing belt.

[0007] and a steering roller arranged downstream of the auxiliary drive roller and upstream of the pad in the direction of rotation of the fixing belt to stretch the inner surface of the fixing belt and to adjust the position of the fixing belt by tilting the fixing belt so that the fixing belt is positioned within a predetermined range in the width direction of the fixing belt. [Effects of the Invention]

[0008] According to the present invention, even when a steering roller is used, the stability of the belt surface downstream of the nip portion can be improved. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 1 is a cross-sectional view showing a schematic configuration of a fixing device according to a first embodiment. [Figure 3] 5 is a schematic diagram for explaining the trajectory of the fixing belt on the downstream side of the fixing pad. FIG. [Figure 4] 2 is a cross-sectional view of a schematic configuration of a fixing device for explaining the relationship between the amount of wrapping of the fixing belt and the roller that stretches the fixing belt according to the first embodiment. FIG. [Figure 5] FIG. 10 is a cross-sectional view showing the schematic configuration of a fixing device according to a second embodiment. [Figure 6]FIG. 4 is a schematic diagram illustrating a belt length L on the downstream side of the fixing pad. [Figure 7] 1 is a graph showing the relationship between belt length L and belt curvature radius. [Figure 8] FIG. 10 is a cross-sectional view showing the schematic configuration of a fixing device according to a third embodiment. [Figure 9] FIG. 10 is a schematic cross-sectional view showing the main part of a fixing device according to a fourth embodiment. [Figure 10] FIG. 11 is a cross-sectional view of a fixing device according to a fifth embodiment, illustrating the relationship between the amount of wrapping of the fixing belt and the roller that stretches the fixing belt. [Figure 11] FIG. 10 is a schematic cross-sectional view showing the main part of a fixing device according to a sixth embodiment. [Figure 12] FIG. 20 is a schematic cross-sectional view showing the configuration of a main part of a fixing device according to another first example of the sixth embodiment. [Figure 13] FIG. 22 is a schematic cross-sectional view showing the configuration of a main part of a fixing device according to another second example of the sixth embodiment. [Figure 14] FIG. 22 is a schematic cross-sectional view showing the configuration of a main part of a fixing device according to another third example of the sixth embodiment. [Figure 15] FIG. 13 is a cross-sectional view showing a schematic configuration of a fixing device according to a seventh embodiment. [Figure 16] FIG. 13 is a cross-sectional view showing the schematic configuration of a fixing device according to an eighth embodiment. [Figure 17] FIG. 10 is a cross-sectional view showing the schematic configuration of a fixing device according to a comparative example. DETAILED DESCRIPTION OF THE INVENTION

[0010] First Embodiment The first embodiment will be described with reference to Figures 1 to 4. First, the schematic configuration of an image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0011] [Image forming equipment] Image forming apparatus 1 is an electrophotographic full-color printer having four image forming units Pa, Pb, Pc, and Pd corresponding to the four colors of yellow, magenta, cyan, and black. In this embodiment, image forming units Pa, Pb, Pc, and Pd are arranged in tandem along the rotation direction of intermediate transfer belt 204 (described later). Image forming apparatus 1 forms a toner image (image) on a recording material in response to an image signal from an image reading unit (document reading device) 2 connected to image forming apparatus main body 3 or from a host device such as a personal computer connected to image forming apparatus main body 3 so as to be able to communicate with it. Examples of recording materials include sheet materials such as paper, plastic film, and cloth.

[0012] The image forming apparatus 1 comprises an image reading unit 2 and an image forming apparatus main body 3. The image reading unit 2 reads an original placed on a platen glass 21. Light emitted from a light source 22 is reflected by the original and forms an image on a CCD sensor 24 via optical components 23 such as a lens. This optical unit scans in the direction of the arrow, converting the original into a line-by-line electrical signal data stream. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus main body 3, where it is subjected to image processing in accordance with each image forming unit (described later) by a control unit 30. The control unit 30 also receives external inputs as image signals from external host devices such as a print server.

[0013] The image forming apparatus main body 3 includes multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit forms an image based on the image signal. That is, the image signal is converted into a laser beam that is PWM (pulse width modulation) controlled by a control unit 30. A polygon scanner 31 serving as an exposure device scans the laser beam in accordance with the image signal. The laser beam is then irradiated onto photosensitive drums 200a to 200d serving as image carriers of each image forming unit Pa to Pd.

[0014] Note that Pa is a yellow (Y) image forming unit, Pb is a magenta (M) image forming unit, Pc is a cyan (C) image forming unit, and Pd is a black (Bk) image forming unit, each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially identical, the Y image forming unit Pa will be described in detail below, and descriptions of the other image forming units will be omitted. In the image forming unit Pa, a toner image is formed on the surface of the photosensitive drum 200a based on an image signal, as will be described below.

[0015] A charging roller 201a, which serves as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential to prepare for the formation of an electrostatic latent image. A laser beam from a polygon scanner 31 forms an electrostatic latent image on the surface of the photosensitive drum 200a, which has been charged to a predetermined potential. A developing unit 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. A primary transfer roller 203a discharges electricity from the back surface of the intermediate transfer belt 204 and applies a primary transfer bias of opposite polarity to the toner, transferring the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After transfer, the surface of the photosensitive drum 200a is cleaned by a cleaner 207a.

[0016] The toner image on intermediate transfer belt 204 is then conveyed to the next image forming station, where the toner images of each color formed at each image forming station are transferred in the order of Y, M, C, and Bk, forming a four-color image on the surface. The toner image that has passed through Bk image forming station Pd, which is located at the most downstream side in the rotation direction of intermediate transfer belt 204, is conveyed to a secondary transfer station made up of a pair of secondary transfer rollers 205 and 206. In the secondary transfer station, a secondary transfer electric field of opposite polarity to the toner image on intermediate transfer belt 204 is applied, thereby secondarily transferring the toner image onto the recording material.

[0017] The recording material is stored in a cassette 9, and the recording material fed from the cassette 9 is transported to a registration unit 208, which is made up of, for example, a pair of registration rollers, and waits at the registration unit 208. Thereafter, the timing of the registration unit 208 is controlled to align the position of the toner image on the intermediate transfer belt 204 with the position of the paper, and the recording material is transported to a secondary transfer unit.

[0018] The recording material onto which the toner image has been transferred in the secondary transfer section is transported to a fixing device 8, where the toner image carried on the recording material is fixed to the recording material by heating and pressing. The recording material that has passed through the fixing device 8 is discharged onto a discharge tray 7. When forming images on both sides of the recording material, after the toner image has been transferred and fixed onto the first side (front side) of the recording material, the recording material is turned over via a reversing conveyance section 10, and the toner image is transferred and fixed onto the second side (rear side) of the recording material, and the recording material is then stacked on the discharge tray 7.

[0019] As described above, the control unit 30 controls the entire image forming apparatus 1. The control unit 30 can also perform various settings based on input from the operation unit 4 of the image forming apparatus 1. The control unit 30 has a CPU (Central Processing Unit), a ROM (Read Only Memory), and a RAM (Random Access Memory). The CPU controls each unit by reading a program corresponding to a control procedure stored in the ROM. The RAM stores working data and input data, and the CPU performs control by referring to the data stored in the RAM based on the aforementioned programs.

[0020] [Fusing device] Next, the configuration of the fixing device 8 in this embodiment will be described with reference to FIG. 2. This embodiment employs a fixing device of a belt heating type using an endless belt. In FIG. 2, the recording material is conveyed from right to left as indicated by the arrow α. The fixing device 8 has a heating unit 300 having a fixing belt 310 as an endless rotatable belt, and a pressure roller 330 as a pressure rotating body (pressure member) that contacts the fixing belt 310 and forms a nip N together with the fixing belt 310.

[0021] The heating unit 300 includes the above-described fixing belt 310, a fixing pad 320 serving as a nip portion forming member and tension member (pressure pad), an auxiliary driving roller 340 serving as a driving roller, and a tension roller 351 serving as a tension member. The pressure roller 330 rotates in contact with the outer peripheral surface of the fixing belt 310, and is also a driving rotor that applies a driving force to the fixing belt 310.

[0022] The endless fixing belt 310 has thermal conductivity, heat resistance, and the like, and is, for example, a thin-walled cylindrical shape with an inner diameter of 120 mm. In this embodiment, it has a three-layer structure consisting of a base layer, an elastic layer on the outer periphery of the base layer, and a release layer on the outer periphery of the elastic layer. The base layer is 60 μm thick and made of polyimide resin (PI), the elastic layer is 300 μm thick and made of silicone rubber, and the release layer is 30 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The fixing belt 310 is stretched by a fixing pad 320, an auxiliary drive roller 340, and a tension roller 351.

[0023] The fixing pad 320, which serves as a nip portion forming member, is disposed inside the fixing belt 310 so as to face the pressure roller 330 with the fixing belt 310 sandwiched therebetween, and forms a nip portion N between the fixing belt 310 and the pressure roller 330, which sandwiches and conveys the recording material. In this embodiment, the fixing pad 320 is a substantially plate-shaped member that is long along the width direction of the fixing belt 310 (the direction of the rotation axis of the auxiliary drive roller 340). The fixing pad 320 is pressed against the pressure roller 330 with the fixing belt 310 sandwiched therebetween, thereby forming the nip portion N. The fixing pad 320 is made of LCP (liquid crystal polymer) resin.

[0024] The fixing pad 320 is supported by a stay 360 disposed inside the fixing belt 310. The stay 360 is a reinforcing member having long rigidity along the width direction of the fixing belt 310. The stay 360 provides strength to the fixing pad 320 and ensures the pressure force at the nip N when the fixing pad 320 is pressed by the pressure roller 330.

[0025] As shown in FIG. 3, both ends of the nip portion N of the fixing pad 320 in the recording material conveyance direction are formed as curved portions 320a and 320b. The curved portions 320a and 320b are curved in a direction (upward in FIG. 3) away from the nip surface toward the end. The nip surface is formed between the fixing belt 310 and the pressure roller 330 and is a surface along the surface of the fixing pad 320 facing the pressure roller 330 (the lower surface in FIG. 3). In this embodiment, the upstream curved portion 320a is a partial cylindrical surface with a radius of 8 mm, and the downstream curved portion 320b is a partial cylindrical surface with a radius of 6 mm. In other words, the radius of curvature of the downstream curved portion 320b is smaller than the radius of curvature of the upstream curved portion 320a.

[0026] In this manner, in this embodiment, the downstream end of the fixing pad 320 is formed as the curved surface portion 320b, and the curvature of the curved surface portion 320b curves the fixing belt 310. Then, the recording material that has passed through the nip portion N is separated from the fixing belt 310 by the curvature of the fixing belt 310.

[0027] A lubricating sheet 370 is interposed between the fixing pad 320 and the fixing belt 310. In this embodiment, a PTFE (polytetrafluoroethylene) coated PI (polyimide) sheet with a thickness of 100 μm is used as the lubricating sheet 370. The PI sheet has 100 μm protrusions formed at 1 mm intervals, which reduces the contact area with the fixing belt 310 and thereby reduces sliding resistance.

[0028] A lubricant is applied to the inner peripheral surface of fixing belt 310, allowing fixing belt 310 to slide smoothly against fixing pad 320, which is covered with lubricating sheet 370. Silicone oil with a viscosity of 100 cSt is used as the lubricant. In this embodiment, fixing pad 320, which is a non-rotating member that does not rotate even when fixing belt 310 rotates, is used as the nip portion forming member, but a rotating body such as a roller may also be used.

[0029] 2, auxiliary drive roller 340 is disposed inside fixing belt 310, and rotates together with fixing pad 320 while tensioning fixing belt 310, thereby applying a driving force to fixing belt 310. Auxiliary drive roller 340 is formed into a cylindrical shape from a metal such as aluminum or stainless steel, and is provided therein with halogen heater 340a as a heat source for heating fixing belt 310. Auxiliary drive roller 340 is heated to a predetermined temperature by halogen heater 340a.

[0030] In this embodiment, the auxiliary drive roller 340 is formed from an aluminum pipe, for example, with an outer diameter of 40 mm and a thickness of 1 mm, from the viewpoint of thermal conductivity, and the surface is anodized. Although a single halogen heater 340a is sufficient, it is preferable to have multiple heaters in consideration of temperature distribution control in the longitudinal direction (direction of the rotation axis) of the auxiliary drive roller 340. The multiple halogen heaters 340a have different light distributions in the longitudinal direction, and the lighting ratio is controlled according to the size of the recording material. In this embodiment, two halogen heaters 340a are provided. The heat source is not limited to a halogen heater, and may be another heater capable of heating the auxiliary drive roller 340, such as a carbon heater.

[0031] The fixing belt 310 is heated by an auxiliary driving roller 340 heated by a halogen heater 340a, and is controlled to a predetermined target temperature according to the type of recording material based on temperature detection by a thermistor (not shown). The auxiliary driving roller 340 has a gear fixed to one end in the direction of its rotation axis, and is connected to a motor M1, which serves as an auxiliary driving roller driving source (second driving source), via the gear, and is driven to rotate. The fixing belt 310 is provided with a driving force by the rotation of the auxiliary driving roller 340. The force applied to the fixing belt 310 by the auxiliary driving roller 340 is referred to as the auxiliary driving force.

[0032] The rotation of the auxiliary drive roller 340 may be provided by a rotational drive force from a motor M0 serving as a pressure roller drive source (first drive source) that rotationally drives the pressure roller 330, or by a motor M1 that is separate from the motor M0. The drive transmission mechanism from the motor may be a mechanism other than gears, such as a pulley and belt, or a mechanism that presses a roller driven by the motor from the outside.

[0033] The tension roller 351 is disposed inside the fixing belt 310, stretches the fixing belt 310 together with the fixing pad 320 and the auxiliary drive roller 340, and is rotated by the fixing belt 310. In this embodiment, the fixing pad 320, the tension roller 351, and the auxiliary drive roller 340 are disposed in this order with respect to the rotation direction of the fixing belt 310. The tension roller 351 is formed into a cylindrical shape from a metal such as aluminum or stainless steel. In this embodiment, the tension roller 351 is a stainless steel or aluminum pipe with an outer diameter of 40 mm and a thickness of 1 mm, and its ends are rotatably supported by bearings (not shown).

[0034] In this embodiment, the tension roller 351 is biased by a spring supported by the frame of the heating unit 300, and also serves as a tension roller that applies a predetermined tension to the fixing belt 310. In this embodiment, the tension applied by the spring is 50 N. By applying tension to the fixing belt 310 using the tension roller 351 in this manner, the fixing belt 310 is caused to follow the curved portions 320a and 320b of the fixing pad 320. In other words, the fixing belt 310 is curved along the curved portions 320a and 320b.

[0035] The pressure roller 330, which serves as a driving rotor, rotates in contact with the outer circumferential surface of the fixing belt 310, applying a driving force to the fixing belt 310. In this embodiment, the pressure roller 330 is a roller having an elastic layer formed on the outer periphery of its shaft and a release layer formed on the outer periphery of the elastic layer. The shaft is made of stainless steel, the elastic layer is 5 mm thick and made of conductive silicone rubber, and the release layer is 50 μm thick and made of PFA (tetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin. The pressure roller 330 is rotatably supported by the fixing frame 380 of the fixing device 8, and a gear is fixed to one end thereof. The pressure roller 330 is connected to a motor M0, which serves as a pressure roller drive source (first drive source) via the gear, and is driven to rotate.

[0036] The fixing frame 380 is provided with a heating unit positioning portion 381, a pressure frame 383, and a pressure spring 384. The heating unit 300 is positioned on the fixing frame 380 by inserting a stay 360 into the heating unit positioning portion 381 and fixing the stay 360 to the heating unit positioning portion 381 by a fixing means (not shown). The heating unit positioning portion 381 has a pressure direction regulating surface 381a facing the pressure roller 330 and a conveying direction regulating surface 381b that is an abutting surface in the insertion direction of the heating unit 300. The stay 360 is fixed in a state where its movement is restricted by the pressure direction regulating surface 381a and the conveying direction regulating surface 318b. At this time, the pressure roller 330 is separated from the fixing belt 310.

[0037] After the heating unit 300 is positioned by the heating unit positioning portion 381, the pressure roller 330 comes into contact with the fixing belt 310 as a result of the pressure frame 383 being moved by a drive source and a cam (not shown). The pressure roller 330 is then pressed against the fixing pad 320 via the fixing belt 310. In this embodiment, the pressure applied during image formation is 1000 N.

[0038] Furthermore, in this embodiment, a separating member 400 that separates the recording material from the fixing belt 310 is provided downstream of the nip portion N in the recording material conveyance direction. The separating member 400 is disposed with a gap between it and the outer peripheral surface of the fixing belt 310, and separates the recording material that has passed through the nip portion N from the fixing belt. Specifically, the separating member 400 is disposed close to a portion of the outer peripheral surface of the fixing belt 310 that is stretched between the fixing pad 320 and the tension roller 351. The separating member 400 is formed in a blade shape, with its tip facing the outer peripheral surface of the fixing belt 310.

[0039] The fixing device 8 configured as described above sandwiches a recording material carrying a toner image at a nip portion N formed between the fixing belt 310 and the pressure roller 330, and heats the toner image while conveying the recording material. This melts the toner image and fixes it to the recording material. In this embodiment, during image formation, the peripheral speed of the fixing belt 310 is 300 mm / s, the pressure at the nip portion N is 1000 N, and the temperature of the fixing belt 310 is 180°C.

[0040] [Fastening belt conforms to the curved surface of the fixing pad] 2, in the configuration of this embodiment, the angle θ between the nip surface and the path of fixing belt 310 from nip portion N to tension roller 351 is set to 52°. Here, if fixing belt 310 has low rigidity and the tension on fixing belt 310 is sufficiently large, the path of fixing belt 310 at the exit of nip portion N (downstream side of nip portion N in the recording material conveyance direction) will be as shown by the solid line in FIG. 3. However, due to the rigidity of fixing belt 310 and the force applied to fixing belt 310 at nip portion N, the path of fixing belt 310 at the exit of nip portion N during image formation may bulge as shown by the dotted line in FIG. 3.

[0041] That is, the fixing belt 310 receives a rotational driving force from the pressure roller 330. For this reason, if the above-described auxiliary driving roller 340 were a roller that did not apply a driving force to the fixing belt 310, the fixing belt 310 might bend at the exit of the nip N due to the driving force of the pressure roller 330. In this case, the ability of the fixing belt 310 to follow the curvature of the curved portion 320b at the downstream end of the fixing pad 320 would decrease, and the fixing belt would not bend sufficiently at the exit of the nip N, resulting in a bulging path as shown by the dashed line in FIG.

[0042] If the path of the fixing belt 310 expands in this way at the exit of the nip portion N, the separation of the recording material from the fixing belt 310 will be impaired. Also, there is a possibility that the fixing belt 310 will come into contact with the separating member 400 arranged close to the fixing belt 310. If the fixing belt 310 comes into contact with the separating member 400, the surface of the fixing belt 310 will be damaged, and the quality of the toner image fixed by the fixing device 8 may be degraded.

[0043] One possible solution to this problem is to increase the tension of the fixing belt 310. However, if the tension of the fixing belt 310 is increased, there is a risk that adverse effects such as creep deformation of the base layer of the fixing belt 310 may occur.

[0044] Therefore, in this embodiment, as described above, the auxiliary drive roller 340 is provided, which is disposed inside the fixing belt 310 and applies a driving force to the fixing belt 310. In particular, in this embodiment, the peripheral speed of the auxiliary drive roller 340 is set to be faster than the peripheral speed of the pressure roller 330. With this configuration, when a driving force is applied to the auxiliary drive roller 340, the auxiliary drive roller 340 pulls the belt surface upstream of the auxiliary drive roller 340 in the rotation direction of the fixing belt 310. As a result, the belt surface upstream of the auxiliary drive roller 340 and downstream of the nip N in the rotation direction of the fixing belt 310 is pulled by the auxiliary drive roller 340. As a result, it is possible to reduce the bulge of the path of the fixing belt 310 at the exit of the nip N.

[0045] The belt tracking can be improved by applying a driving force to the fixing belt 310 by the auxiliary driving roller 340. In addition, the peripheral speed of the auxiliary driving roller 340 can be made faster than the peripheral speed of the pressure roller 330, thereby further improving the belt tracking.

[0046] The provision of the auxiliary drive roller 340 also proved effective in preventing image misalignment. The fixing belt 310 is rotated by the pressure roller 330. During this rotation, the sliding resistance between the fixing belt 310 and the fixing pad 320 causes the fixing belt 310 to be conveyed with a slight misalignment relative to the recording material passing through the nip N. Meanwhile, by applying an auxiliary drive force from the inner surface of the fixing belt 310 using the auxiliary drive roller 340, the fixing belt 310 receives not only the drive force from the pressure roller 330 but also the drive force from the auxiliary drive roller 340. Therefore, even if the fixing pad 320 increases the rotation load of the fixing belt 310, the fixing belt 310 always receives the drive force from the auxiliary drive roller 340, regardless of whether a recording material is present in the nip N. As a result, the peripheral speed of the pressure roller 330 and the peripheral speed of the fixing belt 310 can be made substantially the same, not only when a recording material is not present in the nip N, but also when a recording material is present in the nip N. In other words, the rotational stability of the fixing belt 310 can be improved.

[0047] More specifically, the fixing belt 310 is sandwiched between the pressure roller 330 and the fixing pad 320 under strong pressure at the nip portion. Because the auxiliary drive roller 340 rotates the fixing belt 310 by friction with the fixing belt 310, it cannot transmit a driving force that moves the fixing belt 310 at a circumferential speed faster than that of the pressure roller 330 against the strong pressure. Therefore, when there is no recording material in the nip portion, the fixing belt 310 and the pressure roller 330 move at the same circumferential speed at the nip portion. At this time, because the fixing belt 310 has a low elastic modulus in the circumferential direction, the auxiliary drive roller 340 rotates while sliding relative to the fixing belt 310. Due to this operation, the circumferential speed of the fixing belt 310 and the circumferential speed of the pressure roller 330 are substantially the same. On the other hand, for the same reason, when the recording material is in the nip portion, the fixing belt 310 receives the driving force of the auxiliary driving roller 340 and the driving force of the pressure roller 330, so that the peripheral speed of the fixing belt 310 and the peripheral speed of the pressure roller 330 can be made substantially the same. Furthermore, the peripheral speeds of the fixing belt 310, the recording material, and the pressure roller 330 can be made substantially the same. As a result, it has been found that it is possible to alleviate misalignment of the fixing belt 310 with respect to the recording material, and this is also effective in suppressing image misalignment. In this way, the peripheral speed of the auxiliary driving roller 340 is set so that the peripheral speed of the fixing belt 310 and the peripheral speed of the pressure roller 330 are substantially the same. Here, "substantially the same" means that the speed difference is within ±5%. In order to obtain the effects described above, it is preferable to satisfy 1.04≦peripheral speed of auxiliary drive roller 340 / peripheral speed of pressure roller 330≦1.20, and it is preferable to satisfy 1.1≦peripheral speed of auxiliary drive roller 340 / peripheral speed of pressure roller 330≦1.2 (the periphery speed of auxiliary drive roller 340 is 110% or more and 120% or less of the periphery speed of pressure roller 330). Therefore, in order to improve image quality, it is preferable to satisfy 1.04≦peripheral speed of auxiliary drive roller 340 / peripheral speed of pressure roller 330≦1.15.

[0048] [Thermal efficiency of auxiliary drive roller] As described above, the auxiliary drive roller 340 has a halogen heater 340a disposed therein as a heat source for heating the fixing belt 310. The auxiliary drive roller 340 rotates at a faster speed than the fixing belt 310. This allows the virtual heat transfer nip to be wider than when the auxiliary drive roller 340 is driven to rotate at a constant speed along with the fixing belt 310. In other words, the contact time between the auxiliary drive roller 340 and the fixing belt 310 can be longer than when the auxiliary drive roller 340 is driven to rotate at a constant speed along with the fixing belt 310. Therefore, by rotating the auxiliary drive roller 340 at a faster peripheral speed than the fixing belt 310, the efficiency of heat transfer from the auxiliary drive roller 340 to the fixing belt 310 can be improved compared to when the auxiliary drive roller 340 is driven to rotate at a constant speed along with the fixing belt 310.

[0049] [Durability of the auxiliary drive roller surface] As described above, belt tracking is improved by increasing the peripheral speed of the auxiliary drive roller 340 relative to the peripheral speed of the fixing belt 310, which is 300 mm / s. However, because the peripheral speed of the auxiliary drive roller 340 is intentionally made faster than the peripheral speed of the fixing belt 310 to apply an auxiliary driving force to the fixing belt 310, the outer peripheral surface of the auxiliary drive roller 340 and the inner peripheral surface of the fixing belt 310 rub against each other. As described above, the auxiliary drive roller 340 is made of aluminum from the perspective of thermal conductivity, and it is conceivable that the outer peripheral surface will wear out due to rubbing. For this reason, it is preferable that the surface layer of the auxiliary drive roller 340 be anodized.

[0050] [Fixing belt wrapping amount] Next, the amount of wrap of the fixing belt 310 around each roller will be explained using FIG. 4. Here, the amount of wrap of the belt refers to the length of wrap around the roller, or more specifically, the length of contact between the belt and the roller. Note that the configuration in FIG. 4 is the same as that shown in FIG. 2, except that angles θa and θd have been added to FIG. 2. However, the halogen heater 340a in FIG. 2 is not shown in FIG. 4.

[0051] 4, the angle formed by the fixing belt 310 wound around the auxiliary driving roller 340 and the center of the roller is defined as a winding angle θd. The angle formed by the fixing belt 310 wound around the tension roller 351 and the center of the roller is defined as a winding angle θa. The winding angle is the angle formed by lines connecting the roller center and both ends of the roller circumferential direction within the range where the belt is in contact with the roller.

[0052] In this embodiment, the winding angle θd around the auxiliary driving roller 340 is set to be larger than the winding angle θa around the tension roller 351. Specifically, the winding angle θd is set to be 120°, and the winding angle θa is set to be 100°. By setting the winding angle θd to be larger than the winding angle θa in this manner, the winding amount of the fixing belt 310 around the auxiliary driving roller 340 is set to be larger than the winding amount of the fixing belt 310 around the tension roller 351.

[0053] Here, even if the winding angle θd is simply made larger than the winding angle θa, if the cross-sectional area of ​​the auxiliary drive roller 340 is too small compared to the cross-sectional area of ​​the tension roller 351, the winding amount around the auxiliary drive roller 340 cannot be made larger than the winding amount around the tension roller 351. For this reason, in this embodiment, for example, the cross-sectional areas, in other words, the outer diameters, of the auxiliary drive roller 340 and the tension roller 351 are made substantially the same, and the winding amount around the auxiliary drive roller 340 is made larger than the winding amount around the tension roller 351. Note that, as long as this relationship is satisfied for the winding amounts, the cross-sectional area of ​​the auxiliary drive roller 340 may be smaller than the cross-sectional area of ​​the tension roller 351. Of course, the cross-sectional area of ​​the auxiliary drive roller 340 may be larger than the cross-sectional area of ​​the tension roller 351.

[0054] Increasing the amount of wrapping of the fixing belt 310 around the auxiliary drive roller 340 in this way increases the contact area between the auxiliary drive roller 340 and the fixing belt 310, thereby improving the efficiency of transmission of driving force from the auxiliary drive roller 340 to the fixing belt 310. Furthermore, if a heat source such as a halogen heater 340a is provided inside the auxiliary drive roller 340, the efficiency of heat transmission from the auxiliary drive roller 340 to the fixing belt 310 can also be improved. The amount of wrapping of the fixing belt 310 around the auxiliary drive roller 340 may be greater than the amount of wrapping of the fixing belt 310 around the fixing pad 320. In other words, the amount of wrapping of the fixing belt 310 around the auxiliary drive roller 340 may be the greatest among all the members that tension the fixing belt 310 from the inside.

[0055] As described above, in this embodiment, the provision of the auxiliary drive roller 340 improves belt tracking. As a result, it is possible to prevent a decrease in the ability of the recording material passing through the nip N to separate from the fixing belt 310. In addition, the separating member 400 is disposed with a gap between it and the fixing belt 310. This gap is set small so as to separate the recording material from the fixing belt 310. Therefore, if the belt tracking decreases and the path of the fixing belt 310 expands at the exit of the nip N, the fixing belt 310 may come into contact with the separating member 400, potentially damaging the fixing belt 310. In contrast, in this embodiment, the provision of the auxiliary drive roller 340 improves belt tracking, making it less likely that the fixing belt 310 will come into contact with the separating member 400.

[0056] <Second embodiment> The second embodiment will be described with reference to Figures 5 to 11. In the first embodiment described above, the auxiliary drive roller 340 was disposed downstream of the tension roller 351 and upstream of the fixing pad 320 with respect to the rotation direction of the fixing belt 310. In contrast, in this embodiment, the auxiliary drive roller 340 is disposed downstream of the fixing pad 320 and upstream of the tension roller 351 with respect to the rotation direction of the fixing belt 310. Specifically, in this embodiment, the positions of the auxiliary drive roller 340 and the tension roller 351 are swapped with respect to the configuration of the first embodiment. Since the other configurations and functions are the same as those of the first embodiment, the same reference numerals are used for overlapping configurations, and their description and illustration will be omitted or simplified. The following description will focus on the differences from the first embodiment.

[0057] The fixing device 8A of this embodiment differs from the first embodiment in the configuration of the heating unit 300A. Specifically, as described above, the auxiliary driving roller 340 is disposed downstream of the fixing pad 320 and upstream of the tension roller 351 with respect to the rotation direction of the fixing belt 310. Furthermore, no member for tensioning the fixing belt 310 is disposed between the fixing pad 320 and the auxiliary driving roller 340. That is, as shown in FIG. 5 , the heating unit 300A is disposed such that the auxiliary driving roller 340 and the tension roller 351 are disposed in this order in the rotation direction of the fixing belt 310 from the exit of the nip N in the recording material conveyance direction, which is the reverse of the configuration in the first embodiment. In this embodiment, by disposing the auxiliary driving roller 340 closer to the nip N, belt tracking performance can be further improved. This point will be described with reference to FIGS. 6 to 11.

[0058] [Relationship between belt length and auxiliary drive roller transport effect] First, the belt length from the exit of the nip N in the conveying direction to the auxiliary drive roller 340 varies greatly depending on whether the auxiliary drive roller 340 or the tension roller 351 is positioned upstream in the rotation direction. FIG. 6 is a diagram for explaining the belt length L. The belt length L indicates the distance from the point where belt tracking is required to the point where force is applied. In this embodiment, the belt length L is the length from the curved surface portion 320b (exit of the nip N) at the downstream end of the fixing pad 320 to the auxiliary drive roller 340.

[0059] The inventors conducted a simple test to see how belt tracking changes when belt length L is changed. The results are shown in Figure 7. In the simple test, the angle θ between the nip surface and the path of fixing belt 310 was set to 52°, and fixing belt 310 was pulled with a force of 50 N while changing belt length L, and belt tracking was observed. Figure 7 shows that shortening belt length L leads to improved belt tracking. This difference is thought to be due to the influence of factors such as the rigidity of the base layer of fixing belt 310 and the shrinkage of the release layer. In the configuration of Example 2, the fixing pad 320 and the auxiliary drive roller 340 are arranged adjacent to each other. Therefore, the belt length between the fixing pad 320 and the auxiliary drive roller 340 in the direction opposite to the rotation direction of the fixing belt 310 in Example 2 is shorter than the belt length between the fixing pad 320 and the auxiliary drive roller 340 in the direction opposite to the rotation direction of the fixing belt 310 in Example 1. Therefore, with the configuration of Example 2, even if the peripheral speed of the auxiliary drive roller 340 is slow, the bulge of the fixing belt 310 at the exit of the nip portion can be reduced.

[0060] As described above, with the configuration of this embodiment, even if the peripheral speed of the auxiliary drive roller 340 is slower than that of the first embodiment, belt tracking can be improved and a decrease in the separation of the recording material from the fixing belt 310 can be suppressed. Also, the fixing belt 310 is less likely to come into contact with the separating member 400. Furthermore, since the peripheral speed of the auxiliary drive roller 340 can be slowed, wear due to friction between the fixing belt 310 and the auxiliary drive roller 340 can be reduced. However, even in this embodiment, when considering belt tracking and thermal conductivity from the auxiliary drive roller 340 to the fixing belt 310, it is preferable to set the peripheral speed of the auxiliary drive roller 340 faster than the peripheral speed of the pressure roller 330.

[0061] 5, auxiliary drive roller 340 is disposed inside fixing belt 310 without any other member provided downstream of nip portion N. However, there is no problem in disposing any member, such as a cleaning member or a member for applying lubricant, between nip portion N and auxiliary drive roller 340 as long as it does not contribute to tensioning fixing belt 310.

[0062] <Third embodiment> The third embodiment will be described with reference to Fig. 8. In this embodiment, the tension roller 351 of the second embodiment described above is replaced with a steering roller 350. Since the other configurations and functions are the same as those of the second embodiment, the same reference numerals are used for the overlapping configurations, and explanations and illustrations thereof will be omitted or simplified. The following description will focus on the points that are different from the second embodiment.

[0063] 8, fixing device 8B of this embodiment differs from the second embodiment in the configuration of heating unit 300B. Specifically, steering roller 350 is disposed inside fixing belt 310 and serves as a tension roller that suspends fixing belt 310 together with fixing pad 320 and auxiliary driving roller 340. Note that in this embodiment as well, auxiliary driving roller 340 is disposed downstream of fixing pad 320 and upstream of steering roller 350 in terms of the rotation direction of fixing belt 310.

[0064] The steering roller 350 tilts relative to the rotational axis direction (longitudinal direction) of the auxiliary drive roller 340, thereby controlling the position (shift position) of the fixing belt 310 relative to this rotational axis direction. That is, the steering roller 350 has a rotation center at the center of the rotational axis direction (longitudinal direction) of the steering roller 350, and tilts relative to the longitudinal direction of the auxiliary drive roller 340 by swinging around this rotation center. This generates a tension difference between one side and the other side of the fixing belt 310 in the longitudinal direction, causing the fixing belt 310 to move in the longitudinal direction.

[0065] The fixing belt 310 tends to shift to one of its ends during rotation, depending on the accuracy of the outer diameter of the rollers that support it and the alignment accuracy between the rollers. Therefore, the steering roller 350 controls this shift. Specifically, the steering roller 350 is a roller that adjusts the position of the fixing belt 310 by tilting it so that the fixing belt 310 is positioned within a predetermined range in the width direction of the fixing belt 310. The steering roller 350 may be swung by a drive source such as a motor, or may be configured to swung by automatic centering. The center of rotation may be the center in the longitudinal direction, as in this embodiment, or it may be an end in the longitudinal direction.

[0066] In this embodiment, the steering roller 350 is biased by a spring supported by the frame of the heating unit 300B, and also serves as a tension roller that applies a predetermined tension to the fixing belt 310. The tension applied by the spring is 50 N, and by applying tension to the fixing belt 310, the fixing belt 310 is caused to follow the curved surface portions 320a and 320b of the fixing pad 320.

[0067] In the configuration of Example 3, the auxiliary driving roller 340 and the steering roller 350 are arranged in this order in the rotation direction from the exit of the nip portion N in the conveying direction. In contrast, in the comparative example, the steering roller 350 and the auxiliary driving roller 340 are arranged in this order in the rotation direction from the exit of the nip portion N in the conveying direction. That is, we will consider the effect on belt tracking performance of whether the steering roller 350 is arranged upstream or downstream of the auxiliary driving roller 340 in the rotation direction. When the steering roller 350 is arranged upstream of the auxiliary driving roller 340, the angle θ at the longitudinal end changes between one end and the other end in the longitudinal direction due to the rotation (inclination) of the steering roller 350. As a result, the distance of the fixing belt 310 from the exit of the nip portion N to the auxiliary driving roller 340 in the longitudinal direction varies, which tends to cause uneven tension in the fixing belt 310. As a result, the amount of swelling of the fixing belt differs between one end and the other end in the longitudinal direction, which reduces the stability of separation performance.

[0068] On the other hand, by arranging the auxiliary driving roller 340 upstream of the steering roller 350 in the rotation direction as in Example 3, the auxiliary driving force of the auxiliary driving roller 340 can be uniformly and efficiently applied to the fixing belt 310. As a result, the belt tracking ability can be improved compared to the comparative example. Therefore, in Example 3, it is possible to improve the separation performance of the recording material from the fixing belt 310 and suppress contact between the fixing belt 310 and the separating member 400.

[0069] In this manner, in the configuration of this embodiment, even if the tension roller is the steering roller 350, the belt tracking ability can be improved and it is possible to prevent a decrease in the separation ability of the recording material from the fixing belt 310. In addition, it is possible to make the fixing belt 310 less likely to come into contact with the separating member 400.

[0070] <Fourth embodiment> The fourth embodiment will be described with reference to FIG. 9. In the above-described embodiments, a configuration was described in which a fixing pad 320, which is a non-rotating member, is used as the nip portion forming member. In contrast, in this embodiment, a roller (fixing roller 395) is used as the nip portion forming member. Also, in this embodiment, unlike the above-described embodiments, fixing belt 310 is stretched only by auxiliary drive roller 340 and fixing roller 395. Since the other configurations and functions are the same as those of the first embodiment, the same reference numerals are used for overlapping configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0071] 9, in a heating unit 300C of a fixing device 8C of this embodiment, a fixing belt 310 is stretched only by an auxiliary drive roller 340 and a fixing roller 395. The fixing roller 395 is disposed inside the fixing belt 310 so as to face the pressure roller 330 with the fixing belt 310 sandwiched therebetween, and forms a nip portion N between the fixing belt 310 and the pressure roller 330, which sandwiches and conveys the recording material. The fixing roller 395 rotates in response to the rotation of the fixing belt 310.

[0072] Furthermore, since the fixing roller 395 is formed in a cylindrical shape, the fixing belt 310 is curved by the curvature of the downstream end in the recording material conveyance direction at the nip N, similar to the curved surface portion 320b on the downstream side of the fixing pad 320. Then, the recording material that has passed through the nip N is separated from the fixing belt 310. Therefore, similar to when the nip portion forming member is the fixing pad 320, in consideration of the separation of the recording material, it is required that the fixing belt 310 has good followability (belt followability) to the curvature of the fixing roller 395.

[0073] That is, even if the nip portion forming member is a rotating body such as the fixing roller 395, as in the above-described embodiments, the fixing belt 310 rotates while receiving a fixing belt driving force from the pressure roller 330 at the nip portion N. Therefore, the fixing belt driving force may cause the fixing belt 310 to swell downstream in the conveyance direction, which may reduce the ability of the fixing belt 310 to follow the fixing roller 395.

[0074] Therefore, in this embodiment as well, in order to satisfy the ability of the fixing belt 310 to follow the fixing roller 395, an auxiliary driving force is applied to the fixing belt 310 by the auxiliary driving roller 340. In this embodiment, the auxiliary driving roller 340 is disposed on the opposite side of the fixing roller 395 from the pressure roller 330.

[0075] The auxiliary driving roller 340 is supported by the frame of the heating unit 300C. The tensioner 312 is biased by a spring (not shown) and applies a predetermined tension to the fixing belt 310. The tension of the spring is 50 N, and it applies tension to the fixing belt 310. This allows the fixing belt 310 to follow the outer circumferential surface of the fixing roller 395 .

[0076] The auxiliary drive roller 340 and the fixing roller 395 are each formed from an aluminum pipe with a thickness of 1 mm, and the surface is anodized. The auxiliary drive roller 340 and the fixing roller 395 may be made of other metals, such as stainless steel. The auxiliary drive roller 340 is provided with a halogen heater 340a as a heat source therein, and is capable of generating heat up to a predetermined temperature. On the other hand, the fixing roller 395 is not provided with a heat source such as a halogen heater. The heat source may be provided only to the fixing roller 395 rather than the auxiliary drive roller 340, or may be provided to both rollers.

[0077] The pressure roller 330 receives a rotational drive force from a motor M0 serving as a pressure roller drive source, and the auxiliary drive roller 340 receives a rotational drive force from a motor M1 serving as an auxiliary drive roller drive source. However, the auxiliary drive roller 340 may also receive a rotational drive force from the motor M0. In this embodiment as well, it is preferable that the peripheral speed of the auxiliary drive roller 340 is faster than the peripheral speed of the pressure roller 330.

[0078] In this embodiment, belt tracking can also be improved by providing the auxiliary drive roller 340. As a result, it is possible to prevent a decrease in the separation ability of the recording material passing through the nip portion N from the fixing belt 310, and it is possible to make it difficult for the fixing belt 310 to come into contact with the separating member 400.

[0079] <Fifth embodiment> The fifth embodiment will be described with reference to FIG. 10. In this embodiment, the belt winding amount described in FIG. 4 is set to be the largest on auxiliary drive roller 340A among the rollers that tension fixing belt 310. Also, in this embodiment, a steering roller 350A is provided, as in the third embodiment. Since the other configurations and functions are the same as those of any of the first to third embodiments, the same reference numerals are used for overlapping configurations, and explanations and illustrations are omitted or simplified. The following description will focus on the points that are different from any of the first to third embodiments.

[0080] Fixing device 8D has fixing belt 310 as an endless rotatable heating rotor, fixing pad 320 as a nip portion forming member, heating unit 300D including auxiliary drive roller 340A and steering roller 350A, and pressure roller 330. In this embodiment as well, auxiliary drive roller 340A is disposed downstream of fixing pad 320 and upstream of steering roller 350A in terms of the rotation direction of fixing belt 310.

[0081] Fixing belt 310 is a thin-walled cylinder with an inner diameter of 120 mm, and has the same basic configuration as that described in the third embodiment, being stretched by fixing pad 320, auxiliary drive roller 340A, and steering roller 350A. Fixing pad 320 is pressed against pressure roller 330 with fixing belt 310 sandwiched therebetween, and lubricating sheet 370 is interposed between fixing pad 320 and fixing belt 310.

[0082] Furthermore, in this embodiment, an oil application roll 361 is provided as a lubricant application member that applies a lubricant to the inner peripheral surface of the fixing belt 310. The oil application roll 361 has an outer diameter of approximately 10 mm and is positioned inside the fixing belt 310, between the fixing pad 320 and the steering roller 350A. The oil application roll 361 is supported by a rotatable support arm (not shown) so as to be biased against the inner peripheral surface of the fixing belt 310 with a force of approximately 10 N.

[0083] The oil application roll 361 contains a heat-resistant aramid felt impregnated with heat-resistant silicone oil having a viscosity of about 100 cSt as a lubricant for lubricating the inner circumferential surface of the belt. The surface of the heat-resistant aramid felt has a sheet-like oil application control film made of a porous PTFE layer. The oil application roll 361 contacts the inner circumferential surface of the fixing belt 310 and supplies silicone oil to the inner circumferential surface of the fixing belt 310 while rotating in accordance with the movement of the fixing belt 310.

[0084] The auxiliary drive roller 340A is an aluminum pipe with an outer diameter of 80 mm and a thickness of 1.5 mm, and has a halogen heater (not shown) disposed inside as a heat source, capable of generating heat up to a predetermined temperature. The fixing belt 310 is heated by the auxiliary drive roller 340, and is controlled to a predetermined target temperature according to the type of recording material based on temperature detection by a thermistor. The auxiliary drive roller 340A also has a gear fixed to one end of its shaft, and is connected to a motor M1 via the gear to rotate in the direction of arrow b.

[0085] In this embodiment, auxiliary drive roller 340A is also driven at a faster peripheral speed than fixing belt 310. Specifically, the driving forces of motors M0 and M1 that drive pressure roller 330 are adjusted so that auxiliary drive roller 340 is driven at a peripheral speed of 357 mm / s and fixing belt 310 is driven at 340 mm / s. At this time, silicone oil, a viscous material, is interposed between auxiliary drive roller 340A and fixing belt 310, which have different peripheral speeds, to absorb the difference in peripheral speed between the inner surface of fixing belt 310 and the surface of auxiliary drive roller 340A. Furthermore, the auxiliary driving force is transmitted from auxiliary drive roller 340A to fixing belt 310 by friction and the shear force of the viscous material.

[0086] The higher the kinematic viscosity of the lubricant, the greater the effect of transmitting the auxiliary driving force. However, in order to ensure smooth sliding between the fixing belt 310 and the fixing pad 320, the kinematic viscosity of the lubricant at room temperature (20° C.) is set to 10,000 mm 2 If the viscosity is too low, the slippage between the fixing belt 310 and the auxiliary driving roller 340 increases, and the auxiliary driving force cannot be transmitted sufficiently. Therefore, the kinematic viscosity of the lubricant at room temperature (20° C.) is preferably 50 mm / s or less. 2 It is desirable that it be / s or higher.

[0087] The steering roller 350A is an aluminum pipe with an outer diameter of 20 mm and a thickness of 1 mm, and its ends are rotatably supported by bearings (not shown). The steering roller 350A is biased by a spring supported by the frame of the heating unit 300D, and also serves as a tension roller that applies a predetermined tension to the fixing belt 310. The tension applied by the spring is, for example, 50 N, and causes the fixing belt 310 to follow the curved portions 320a and 320b of the fixing pad 320. The configuration of this steering roller 350A is the same as that of the third embodiment.

[0088] The surfaces of the auxiliary driving roller 340A and the steering roller 350A are anodized, but the auxiliary driving roller 340A and the steering roller 350A may be rollers made of other metals such as stainless steel.

[0089] The pressure roller 330 is configured in the same manner as in the first embodiment, and is connected to a motor M0 to be driven to rotate in the direction of arrow a. A nip N formed between the fixing belt 310 and the pressure roller 330 sandwiches a recording material carrying a toner image therebetween, and heats the toner image while conveying the recording material.

[0090] [Fixing belt wrapping amount] Here, the angle formed by the fixing belt 310 wound around the auxiliary driving roller 340A and the center of the roller is defined as a winding angle θd. The angles formed by the fixing belt 310 wound around the steering roller 350A and the oil application roll 361 and the center of the roller are defined as winding angles θb and θc. Furthermore, the angle θ between the nip surface and the path of the fixing belt 310 from the nip portion N to the auxiliary driving roller 340A is set to 52°, as in the first embodiment.

[0091] At this time, the auxiliary driving roller 340A and the steering roller 350A are positioned so that the winding angle θd by the auxiliary driving roller 340A is 150° and the winding angle θb by the steering roller 350A is 100°. The winding angle θd by the auxiliary driving roller 340A is set larger than the winding angles θb and θc by the tension members other than the auxiliary driving roller 340A (θd > θb, θd > θc). That is, the winding angle θd by the auxiliary driving roller 340A is set larger than the winding angle θb by the steering roller 350A and the winding angle θs by the oil application roll 361.

[0092] In this embodiment, the cross-sectional area of ​​the auxiliary driving roller 340A is larger than the cross-sectional areas of the steering roller 350A and the oil application roll 361. That is, when the fixing belt 310 is stretched by a plurality of members, the cross-sectional area of ​​the member that performs the auxiliary driving (i.e., the auxiliary driving roller 340A) among the stretching members is maximized, and the wrap angle θd around the member that performs the auxiliary driving is increased.

[0093] This makes it possible to more effectively achieve a belt arrangement that allows a larger proportion of the belt to be wrapped around the auxiliary driving roller 340A. That is, it is possible to more reliably achieve a configuration in which the amount of the fixing belt 310 wrapped around the auxiliary driving roller 340A is greater than the amount of the fixing belt 310 wrapped around the steering roller 350A and the oil application roll 361.

[0094] As a result, the auxiliary driving force can be more efficiently transmitted from auxiliary driving roller 340A to fixing belt 310. Furthermore, if a heating source such as a halogen heater is provided inside auxiliary driving roller 340A, the efficiency of heat transmission from auxiliary driving roller 340A to fixing belt 310 can also be improved. Furthermore, since the inner circumferential surface of fixing belt 310 is coated with silicone oil, which is a viscous lubricant, the contact area between auxiliary driving roller 340A and fixing belt 310 can be increased, and the effect of transmitting the auxiliary driving force by shear force can also be increased.

[0095] Sixth Embodiment The sixth embodiment will be described with reference to FIGS. 11 to 14. This embodiment relates to the arrangement of the oil application roll 361 described in the fifth embodiment. FIG. 11 and FIG. 12, which shows another first example of this embodiment, are similar to the second embodiment except for the presence of the oil application roll 361. FIG. 13, which shows another second example of this embodiment, is similar to the first embodiment except for the presence of the oil application roll 361. FIG. 14, which shows another third example of this embodiment, is similar to the fourth embodiment except for the presence of the oil application roll 361. Therefore, the same reference numerals are used to designate overlapping components in each drawing, and their explanation and illustration will be omitted or simplified. The following description will focus on the differences from any of the first, third to fifth embodiments.

[0096] First, as in the fifth embodiment, this embodiment also has an oil applicator roll 361 as a lubricant applicator member that applies a lubricant to the inner circumferential surface of fixing belt 310. Examples of materials that make up oil applicator roll 361 include organic or inorganic porous materials such as sponges and porous ceramic bodies, and woven or nonwoven fabrics made of organic or inorganic fibers such as cloth or polyester fibers wound around a shaft. The above materials are impregnated with a lubricant in advance, and the lubricant is applied to the inner surface of the belt by allowing the lubricant to seep out little by little.

[0097] The oil application roll 361 is biased toward and in contact with the inner circumferential surface of the fixing belt 310 by a compression spring 361c serving as a biasing means. The biasing means may be, other than a compression spring, a tension spring, a leaf spring, rubber, or other elastic member. However, the position of the oil application roll 361 may be fixed at a position where it contacts the inner circumferential surface of the fixing belt 310. In this embodiment, the oil application roll 361 serving as a lubricant application member is a rotating body, but the lubricant application member may also be a non-rotating body. For example, a member such as a pad or sponge soaked in lubricant may be brought into contact with the inner circumferential surface of the fixing belt 310.

[0098] The oil application roll 361 is made up of a shaft 361a and a lubricant retention layer 361b. Examples of materials that can be used to form the shaft 361a include aluminum, iron, stainless steel, and brass. The lubricant retention layer 361b is a layer that is impregnated with and retains the lubricant to be applied, and the lubricant impregnated in this layer seeps out and is applied to the inner surface of the fixing belt 310. As described above, porous materials and fibrous materials are used as the material. In this embodiment, the amount of lubricant impregnated is 3.6 g.

[0099] Here, if the contact force (or contact pressure) of the oil application roll 361 against the inner circumferential surface of the fixing belt 310 is not stable, there is a risk that the amount of lubricant applied may be excessive or insufficient. For example, if the amount of lubricant applied is too much, the lubricant on the oil application roll 361 will be depleted early. On the other hand, if the amount of lubricant applied is too little, the sliding properties between the inner circumferential surface of the fixing belt 310 and the contacting member will decrease.

[0100] One factor that causes fluctuations in the contact force of the oil application roll 361 on the fixing belt 310 is vibrations that occur when the fixing belt 310 rotates, which act in a direction that reduces the belt tension. For this reason, in this embodiment, the oil application roll 361 is brought into contact with the inner circumferential surface of the fixing belt 310, which is pulled by the auxiliary drive roller 340 or the pressure roller 330, thereby suppressing fluctuations in the contact force of the oil application roll 361. The contact force of the oil application roll 361 on the fixing belt 310 is set to 2 N or more and 3.2 N or less, corresponding to a lubricant application amount of 0.7 g or more and 1.2 g or less per 100 hours (100 h). In the fixing device 8 of this embodiment, the target value of the contact force is set to 2.6 N.

[0101] 11, oil application roll 361 is disposed upstream of auxiliary drive roller 340 and downstream of fixing pad 320 in the rotation direction of fixing belt 310. Here, in heating unit 300E of fixing device 8E, the areas of fixing belt 310 stretched around the respective stretching members are defined as sections 310a, 310b, and 310c. Section 310a is between stretching roller 351 and fixing pad 320, section 310b is between fixing pad 320 and auxiliary drive roller 340, and section 310c is between auxiliary drive roller 340 and stretching roller 351. Note that when the belt lengths of section 310a and section 310b are compared, section 310b is shorter.

[0102] In this case, in this embodiment, the oil application roll 361 is brought into contact with the inner circumferential surface of the fixing belt 310 in section 310b, which is the range in which the fixing belt 310 is stretched between the auxiliary drive roller 340 and the fixing pad 320. As a result, the oil application roll 361 comes into contact with the inner circumferential surface of the fixing belt 310 stretched by the auxiliary drive roller 340, thereby suppressing fluctuations in the contact force.

[0103] 12, an oil application roll 361 is disposed upstream of the fixing pad 320 and downstream of the tension roller 351 in the rotation direction of the fixing belt 310. Sections 310a to 310c in the heating unit 300F of the fixing device 8F are the same as those in FIG.

[0104] In this case, in this embodiment, the oil application roll 361 is brought into contact with the inner circumferential surface of the fixing belt 310 in a section 310a, which is the range in which the fixing belt 310 is stretched between the fixing pad 320 and the tension roller 351. As a result, the oil application roll 361 comes into contact with the inner circumferential surface of the fixing belt 310 stretched by the pressure roller 330, thereby suppressing fluctuations in the contact force.

[0105] Next, in the case of a heating unit 300G of a fixing device 8G shown in FIG. 13 as a second example, the positions of the auxiliary drive roller 340 and the tension roller 351 are swapped compared to the configurations shown in FIGS. 11 and 12. Therefore, an oil application roll 361 is disposed upstream of the auxiliary drive roller 340 and downstream of the tension roller 351 in terms of the rotation direction of the fixing belt 310. In the heating unit 300G, the areas of the fixing belt 310 stretched around the respective tension members are designated as sections 310d, 310e, and 310f. Section 310d is between the auxiliary drive roller 340 and the fixing pad 320, section 310e is between the fixing pad 320 and the tension roller 351, and section 310f is between the tension roller 351 and the auxiliary drive roller 340.

[0106] In this case, in this embodiment, the oil application roll 361 is brought into contact with the inner circumferential surface of the fixing belt 310 in a section 310f, which is the range in which the fixing belt 310 is tensioned between the auxiliary drive roller 340 and the tension roller 351. As a result, the oil application roll 361 comes into contact with the inner circumferential surface of the fixing belt 310 tensioned by the auxiliary drive roller 340, thereby suppressing fluctuations in the contact force. Note that in the configurations of Figures 11 to 13, the same results can be obtained even if the tension roller 351 is replaced with a tension member that tensions the fixing belt 310, such as the steering roller 350.

[0107] 14, a third example of a fixing device 8H, an oil application roll 361 is disposed upstream of the auxiliary drive roller 340 and downstream of the fixing roller 395 in the rotation direction of the fixing belt 310. In the heating unit 300H of the fixing device 8H, the areas of the fixing belt 310 stretched around the stretching members are designated as sections 310g and 310h. Section 310g is the range downstream of the auxiliary drive roller 340 and upstream of the fixing roller 395 in the rotation direction of the fixing belt 310, and section 310h is the range downstream of the auxiliary drive roller 340 and upstream of the fixing roller 395 in the rotation direction of the fixing belt 310.

[0108] In this case, in this embodiment, the oil application roll 361 is brought into contact with the inner circumferential surface of the fixing belt 310 in a section 310h upstream of the auxiliary drive roller 340, which is a range in which the fixing belt 310 is stretched between the auxiliary drive roller 340 and the fixing roller 395. As a result, the oil application roll 361 comes into contact with the inner circumferential surface of the fixing belt 310 pulled by the auxiliary drive roller 340, and fluctuations in the contact force are suppressed.

[0109] In either case, fluctuations in the contact force of the oil application roll 361 against the fixing belt 310 are suppressed, so that the amount of lubricant applied by the oil application roll 361 to the fixing belt 310 can be stabilized.

[0110] Seventh Embodiment The seventh embodiment will be described with reference to Fig. 15. This embodiment relates to the arrangement of a refreshing roller 390 as a rubbing member that rubs against the fixing belt. Other than the presence of the refreshing roller 390, this embodiment is the same as the second embodiment.

[0111] [Refresh Roller] In the case of the heating unit 300I constituting the fixing device 8I of this embodiment, in order to stably maintain the outer peripheral surface of the fixing belt 310 in a desired state, the heating unit 300I has a refreshing roller 390 as a rotating body that abuts against the outer peripheral surface (outer surface) of the fixing belt 310 and rotates by being applied with a driving force without via the fixing belt 310. In this embodiment, the refreshing roller 390 is driven by the motor M1 that drives the auxiliary driving roller 340.

[0112] Further, the refresh roller 390 is a polishing roller that polishes the outer peripheral surface of the fixing belt 310. Here, when a variety of recording materials such as various papers are continuously passed through the nip portion N, the surface of the fixing belt 310 becomes uneven in roughness. When the fixing operation is performed in this state, when the recording material carrying the toner image passes through the nip portion N of the fixing belt 310, the surface state of the fixing belt 310 is transferred to the toner image, and the desired glossiness cannot be obtained in the toner image (output image) after fixing, and there is a risk of gloss unevenness occurring. Therefore, by periodically bringing the refresh roller 390 into contact with the outer peripheral surface of the fixing belt 310 to polish the surface and adjusting the surface property of the fixing belt 310, the gloss unevenness of the output image can be made less noticeable.

[0113] The refresh roller 390 uses a roller made of stainless steel with an outer diameter of 12 mm and an aluminum oxide-based abrasive material adhered to its surface. As the refresh roller, a roller with silicon oxide, titanium oxide, iron oxide, chromium oxide, etc. adhered thereto, or a roller with the surface of a stainless steel roller blasted to form irregularities may also be used. The surface roughness of the refresh roller 390 is preferably about arithmetic mean roughness Ra of 0.1 to 0.2 μm. If the surface is rougher than this, the surface of the fixing belt 310 will be deeply damaged, affecting the output image.

[0114] Also, the refresh roller 390 is pressed against the outer peripheral surface of the fixing belt 310 with a predetermined pressure by a pressing mechanism (not shown) of the fixing belt 310. Further, the refresh roller 390 is rotationally driven with a peripheral speed difference with respect to the fixing belt 310. In the present embodiment, the peripheral speed V1 of the refresh roller 390 is set slower than the peripheral speed V0 of the fixing belt 310 (V1 < V0). However, it may also be V1 > V0. By bringing the refresh roller 390 into contact with the outer peripheral surface of the fixing belt 310 in this way, fine scratches can be made on the surface layer of the fixing belt 310.

[0115] The pressure mechanism that presses the refreshing roller 390 controls the contact and separation of the refreshing roller 390 with the surface of the fixing belt 310 using a pressure spring and a cam (not shown). One end and the other end of the refreshing roller 390 in the width direction of the fixing belt 310 are rotatably fixed to the pressure mechanism. In this embodiment, the pressure that presses the refreshing roller 390 against the fixing belt 310 is set to a total pressure of approximately 40 N.

[0116] The refreshing roller 390, which can be brought into contact with and separated from the outer peripheral surface of the fixing belt 310, is normally on standby at a separated position. The refreshing roller 390 is controlled so that it presses against the fixing belt 310 and rubs the surface of the fixing belt 310 whenever necessary, such as every time a predetermined number of recording materials pass through the nip portion N.

[0117] In this embodiment, in order to achieve the aforementioned difference in peripheral speed, the refreshing roller 390 is driven and controlled independently by a motor (for example, motor M1) separate from the motor M0 that drives the pressure roller 330. Another method for driving the refreshing roller 390 is to provide a peripheral speed ratio with the pressure roller 330 and connect the refreshing roller 390 to the motor M1 with a gear, and switch the rotation speed of the refreshing roller 390 with a clutch. In the image forming apparatus of this embodiment, the peripheral speed of the refreshing roller 390 is set to 100 mm / sec in order to effectively roughen the surface of the fixing belt 310.

[0118] In this embodiment, the refreshing roller 390 is disposed in a position facing the auxiliary driving roller 340 across the fixing belt 310. In other words, the refreshing roller 390 is in contact with the outer circumferential surface of the fixing belt 310 that is stretched around the auxiliary driving roller 340.

[0119] In other words, the following applies: First, with respect to the fixing belt 310, the exit of the nip portion N of the fixing belt 310 in the conveying direction is defined as the belt upstream side, and the entrance of the nip portion N in the conveying direction is defined as the belt downstream side. When multiple members are in contact with the fixing belt 310, the upstream and downstream positions are defined based on the points at which they start to contact the fixing belt 310. For example, in this embodiment, the point at which the auxiliary driving roller 340 contacts the fixing belt 310 is located upstream of the point at which the auxiliary driving roller 340 contacts the fixing belt 310. Therefore, the refreshing roller 390 is located downstream of the upstream point at which the auxiliary driving roller 340 starts to contact the fixing belt 310.

[0120] [Fastening belt conforms to the curved surface of the fixing pad] 3, in the configuration of this embodiment, the angle θ between the nip surface and the path of fixing belt 310 from nip portion N to tension roller 351 is set to 52°. Here, if fixing belt 310 has low rigidity and the tension on fixing belt 310 is sufficiently large, the path of fixing belt 310 at the exit of nip portion N (downstream side of nip portion N in the recording material conveyance direction) will be as shown by the solid line in FIG. 3. However, due to the rigidity of fixing belt 310 and the force applied to fixing belt 310 at nip portion N, the path of fixing belt 310 at the exit of nip portion N during image formation may bulge as shown by the dotted line in FIG. 3.

[0121] That is, the fixing belt 310 receives a rotational driving force from the pressure roller 330. For this reason, if the above-mentioned auxiliary driving roller 340 were a roller that did not apply a driving force to the fixing belt 310, the fixing belt 310 might bend at the exit of the nip N due to the driving force of the pressure roller 330. In this case, the ability of the fixing belt 310 to follow the curvature of the curved portion 320b at the downstream end of the fixing pad 320 would decrease, and the fixing belt would not bend sufficiently at the exit of the nip N, resulting in a bulging path as shown by the dashed line in FIG. 3. In other words, the behavior of the fixing belt 310 would become unstable.

[0122] If the path of the fixing belt 310 expands at the exit of the nip N in this way, the separation of the recording material from the fixing belt 310 will be impaired. Also, there is a possibility that the fixing belt 310 will come into contact with a separating member 401 (FIG. 2) arranged close to the fixing belt 310. If the fixing belt 310 comes into contact with the separating member 401, the surface of the fixing belt 310 will be damaged, and the quality of the toner image fixed by the fixing device 8 may be degraded.

[0123] One possible solution to this problem is to increase the tension of the fixing belt 310. However, increasing the tension of the fixing belt 310 may cause adverse effects such as creep deformation of the base layer of the fixing belt 310. Hereinafter, the ability of the fixing belt 310 to follow the curved surface portion 320b will be referred to as belt followability.

[0124] As described above, in this embodiment, the auxiliary drive roller 340 is disposed inside the fixing belt 310 and applies a driving force to the fixing belt 310. In particular, in this embodiment, the peripheral speed of the auxiliary drive roller 340 is set to be faster than the peripheral speed of the pressure roller 330. When the peripheral speed of the auxiliary drive roller 340 is set to be faster than the peripheral speed of the pressure roller 330 in this manner, tension is generated downstream of the nip portion N of the fixing belt 310 in the conveyance direction, making it easier for the fixing belt 310 to follow the fixing pad 320.

[0125] Based on the same principle, when the refreshing roller 390 is brought into contact with the fixing belt 310, the fixing belt 310 receives a driving force from the refreshing roller 390. For this reason, when the refreshing roller 390 is brought into contact with the fixing belt 310, the belt tracking performance changes. Here, if the refreshing roller 390 is brought into contact with the fixing belt 310 at a position, for example, upstream of the auxiliary driving roller 340 and downstream of the fixing pad 320, the influence of the refreshing roller 390 on the belt tracking performance becomes greater than that of the auxiliary driving roller 340. In particular, when the refreshing roller 390 is brought into contact between the refreshing roller 390 and the fixing pad 320 and the peripheral speed of the refreshing roller 390 is set slower than that of the fixing belt 310, the belt tracking performance decreases.

[0126] Therefore, in this embodiment, the refreshing roller 390 is disposed at a position facing the auxiliary driving roller 340 with the fixing belt 310 sandwiched therebetween. As a result, the auxiliary driving roller 340 has a greater effect on the belt tracking performance than the refreshing roller 390, and it is possible to suppress a decrease in the belt tracking performance. That is, it is possible to suppress the fixing belt 310 from being insufficiently curved at the exit of the nip portion N and causing its path to bulge as shown by the dashed line in FIG. 3. That is, in a configuration having the refreshing roller 390 to which a driving force is applied separately from the auxiliary driving roller 340, it is possible to stabilize the behavior of the fixing belt 310.

[0127] Eighth Embodiment The eighth embodiment will be described with reference to Fig. 16. This embodiment differs from the seventh embodiment described above in the position of the refreshing roller 390. Since the other configurations and functions are the same as those of the seventh embodiment described above, the same components are denoted by the same reference numerals, and their explanation and illustration will be omitted or simplified. The following description will focus on the points that are different from the seventh embodiment.

[0128] In the case of the heating unit 300J constituting the fixing device 8J of this embodiment, the refreshing roller 390 is disposed downstream of the auxiliary driving roller 340 and upstream of the fixing pad 320 in the rotation direction of the fixing belt 310. In particular, in this embodiment, the refreshing roller 390 is disposed downstream of the auxiliary driving roller 340 and upstream of the steering roller 350 in the rotation direction of the fixing belt 310. In other words, the position where the refreshing roller 390 abuts on the outer circumferential surface of the fixing belt 310 is between the auxiliary driving roller 340 and the steering roller 350.

[0129] A backup member 391 is disposed on the inner circumferential surface of the fixing belt 310 at a position facing the refreshing roller 390 with the fixing belt 310 sandwiched therebetween. One end and the other end of the backup member 391 in the width direction of the fixing belt 310 are fixed to the corresponding fixing frame 380. The outer circumferential surface of the backup member 391 is formed into a shape that fits along the inner circumferential surface of the fixing belt 310 in a free state. A 2 mm thick silicone rubber elastic layer is disposed on the surface of the backup member 391 so as to come into contact with the inner circumferential surface of the fixing belt 310.

[0130] In this embodiment, the refreshing roller 390 is disposed downstream of the auxiliary driving roller 340. Therefore, similar to the first embodiment, the auxiliary driving roller 340 has a greater effect on the belt tracking performance than the refreshing roller 390, and the deterioration of the belt tracking performance can be suppressed.

[0131] The refreshing roller 390 may be disposed between the steering roller 350 and the fixing pad 320. In this case, too, a backup member 391 is provided at a position facing the refreshing roller 390 with the fixing belt 310 sandwiched therebetween. The refreshing roller 390 may also be disposed at a position facing the steering roller 350 with the fixing belt 310 sandwiched therebetween. In this case, the refreshing roller 390 may be configured to oscillate in conjunction with the steering roller 350. However, when the refreshing roller 390 is disposed at this position, it is preferable that the opposing tension roller not oscillate.

[0132] Furthermore, in the first embodiment and other embodiments, when the refreshing roller 390 faces the tension roller that stretches the fixing belt 310, the refreshing roller 390 is backed up by the tension roller, so the backup member 391 can be omitted.

[0133] [Comparative Example] Next, a comparative example to be compared with each of the above-described embodiments will be described with reference to FIG. 17. FIG. 17 shows the comparative example. The basic configuration of both comparative examples is the same as that of the seventh embodiment. The heating unit 300K constituting the fixing device 8K of the comparative example differs from that of the seventh embodiment in the position of the refreshing roller 390. The refreshing roller 390 of the comparative example is positioned downstream of the fixing pad 320 and upstream of the auxiliary drive roller 340 in the rotation direction of the fixing belt 310. As with the eighth embodiment, a backup member 391 is positioned opposite the refreshing roller 390 with the fixing belt 310 interposed therebetween.

[0134] [Effect confirmation] Next, the effects of the embodiments will be described by comparing the above-described Comparative Examples 1 and 2 with the above-described seventh and eighth embodiments. The configuration of the seventh embodiment is referred to as Example 7, and the configuration of the eighth embodiment is referred to as Example 8. When the refreshing roller 390 is disposed between the fixing pad 320 and the auxiliary driving roller 340 (Comparative Example), it was found that the refreshing roller 390 inhibits belt tracking. The reason for this is that the refreshing roller 390 and the backup member 391 are disposed so as to sandwich the fixing belt 310, and therefore the effect of the auxiliary driving roller 340 pulling the belt surface does not easily reach the nip portion N.

[0135] In contrast to this, in the seventh and eighth embodiments, the refreshing roller 390 is disposed in a position facing the auxiliary driving roller 340 across the fixing belt 310, or on the downstream side of the auxiliary driving roller 340, thereby ensuring belt tracking.

[0136] <Other embodiments> In the above-described embodiments, a halogen heater is provided on the auxiliary drive roller as a heat source for heating the fixing belt. However, the heat source may be provided on the tension roller or steering roller instead of the auxiliary drive roller. It may also be provided on the nip-forming member. For example, if the nip-forming member is a fixing pad, a plate-shaped heat-generating member such as a ceramic heater may be provided on the fixing belt side of the fixing pad. If the nip-forming member is a roller, a heat source such as a halogen heater may be provided inside the roller. Furthermore, the fixing belt may be heated by electromagnetic induction.

[0137] In the above-described embodiments, a pressure roller is used as the driving rotor. However, the driving rotor may be an endless belt that is tensioned by a plurality of tension rollers and driven by one of the tension rollers. In the above-described embodiments, the pressure roller as the driving rotor presses against the belt to form the nip, but the belt may press against the driving rotor. [Explanation of symbols]

[0138] 8, 8A, 8B, 8C, 8D, 8E, 8F, 8G, 8H, 8I, 8J... Fixing device / 310... Fixing belt / 320... Fixing pad (pad) / 330... Pressure roller (pressure member) / 340, 340A... Auxiliary drive roller / 340a... Halogen heater (heat source) / 350, 350A... Steering roller / 351... Tension roller / 361... Oil application roll (application member) / 390... Refresh roller (rubbing member) / 400... Separation member

Claims

1. A fixing device that fixes a toner image formed on a recording material to the recording material, a rotatable fixing belt that comes into contact with the toner image formed on the recording material to fix the toner image to the recording material; a pad disposed inside the fixing belt; a rotatable pressure member that presses the pad through the fixing belt to form a nip portion that sandwiches and conveys a recording material; an auxiliary driving roller that is provided downstream of the nip portion in the rotation direction of the fixing belt, stretches the inner surface of the fixing belt, and applies a driving force to the fixing belt; a driving source that applies a driving force to the pressure member to rotate the fixing belt; a transmission mechanism that transmits a driving force from the drive source to the auxiliary driving roller and makes the peripheral speed of the auxiliary driving roller faster than the peripheral speed of the pressure member and the peripheral speed of the fixing belt; an application member disposed inside the fixing belt and applying oil to the fixing belt; The fixing device is characterized in that the application member is disposed downstream of the auxiliary drive roller and upstream of the nip portion in the conveying direction of the fixing belt.

2. The fixing device described in Claim 1, characterized in that the transmission mechanism transmits a driving force to the auxiliary drive roller so that the peripheral speed of the fixing belt is substantially equal to the peripheral speed of the pressure member.

3. The fixing device according to claim 1, wherein the ratio of the peripheral speed of the auxiliary drive roller to the peripheral speed of the pressure member satisfies 1.04≦circumferential speed of the auxiliary drive roller / circumferential speed of the pressure member≦1.

20.

4. A fixing device described in any one of claims 1 to 3, characterized in that it has a separation member arranged with a gap between it and the outer peripheral surface of the fixing belt and separates the recording material that has passed through the nip portion from the fixing belt.

5. The fixing device described in Claim 4, characterized in that the separation member is provided downstream of the nip portion in the rotational direction of the fixing belt and is positioned close to the portion of the outer surface of the fixing belt that is stretched between the auxiliary drive roller and the pad.

6. A fixing device as described in any one of claims 1 to 5, characterized in that the auxiliary drive roller has a heat source inside for heating the fixing belt.

7. A fixing device as described in any one of claims 1 to 6, characterized in that the auxiliary drive roller is made of aluminum and has an anodized surface.

8. The fixing belt further comprises a steering roller that is arranged to stretch the inner surface of the fixing belt at a position downstream of the auxiliary drive roller and upstream of the pad in the rotation direction of the fixing belt, and that can be tilted with respect to the width direction of the fixing belt so that the fixing belt is positioned within a predetermined range in the width direction of the fixing belt; 8. The fixing device according to claim 1, wherein the amount of the fixing belt wound around the auxiliary drive roller is greater than the amount of the fixing belt wound around the steering roller.

9. A fixing device described in any one of claims 1 to 8, characterized in that the application member is an oil application roller.

10. The fixing device according to claim 1, wherein the auxiliary drive roller rotates in a sliding manner relative to the fixing belt.

11. A fixing device as described in any one of claims 1 to 10, characterized in that it has a rubbing member that comes into contact with the outer surface of the fixing belt and rubs against the fixing belt.

12. The fixing device according to claim 11, wherein the friction member presses the fixing belt toward the auxiliary drive roller.

Images