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 to the recording material.

Background Art

[0002] As a fixing device, a configuration is known in which a nip portion for nipping and conveying a recording material is formed between a fixing belt which is an endless belt and a pressure roller in contact with the outer peripheral surface of the fixing belt, and the toner image is fixed to the recording material passing 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 rotationally driving the pressure roller. Further, in Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5, in addition to the configuration in which the pressure roller is rotationally driven, an auxiliary drive roller stretches the fixing belt to improve the rotational stability of the fixing belt. The configurations of Patent Document 2, Patent Document 3, Patent Document 4, and Patent Document 5 are configured such that the fixing belt is stretched by a fixing member or roller for forming a nip portion that nips and conveys the recording material and the auxiliary drive roller.

Prior Art Literature

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Patent Document 3

Patent Document 4

Patent Document 5

Summary of the Invention

Problems to be Solved by the Invention

[0004] In this configuration, there is a coating member that applies lubricant to the inner circumferential surface of the fixing belt. However, if the contact force of the coating member with the inner circumferential surface of the fixing belt is not stable, there is a risk that the amount of lubricant applied may be too much or too little.

Means for Solving the Problems

[0006] One aspect of the present disclosure is a fixing device for fixing a toner image formed on a recording material to the recording material, comprising: a rotatable fixing belt for fixing the toner image to the recording material by contacting the toner image formed on the recording material; a pad disposed inside the fixing belt; a rotatable pressurizing member that presses the pad via the fixing belt and forms a nip portion for gripping and transporting the recording material; an auxiliary drive roller provided downstream of the nip portion in the rotational direction of the fixing belt, which tensions the inner surface of the fixing belt and provides driving force to the fixing belt; a drive source that provides driving force to the pressurizing member for rotating the fixing belt; and a drive source that transmits the driving force from the drive source to the auxiliary drive roller. The fixing device comprises: a transmission mechanism that makes the peripheral speed of the roller faster than the peripheral speed of the pressurizing member and the peripheral speed of the fixing belt; an applicator member disposed inside the fixing belt and applying oil to the fixing belt; and a separation member disposed with a gap between it and the outer circumferential surface of the fixing belt and separating the recording material that has passed through the nip portion from the fixing belt, wherein the applicator member is disposed downstream of the auxiliary drive roller and upstream of the nip portion in the rotational direction of the fixing belt, and the separation member is provided downstream of the nip portion in the rotational direction of the fixing belt and is disposed close to the portion of the outer circumferential surface of the fixing belt stretched between the auxiliary drive roller and the pad. Another aspect of the present disclosure is a fixing device for fixing a toner image formed on a recording material to the recording material, comprising: a rotatable fixing belt for fixing the toner image to the recording material by contacting the toner image formed on the recording material; a pad disposed inside the fixing belt; a rotatable pressurizing member that presses the pad via the fixing belt and forms a nip portion for gripping and transporting the recording material; an auxiliary drive roller provided downstream of the nip portion in the rotational direction of the fixing belt, tensioning the inner surface of the fixing belt and providing driving force to the fixing belt; a drive source that provides driving force to the pressurizing member for rotating the fixing belt; and a device that transmits the driving force from the drive source to the auxiliary drive roller and sets the peripheral speed of the auxiliary drive roller to be greater than the peripheral speed of the pressurizing member and the peripheral speed of the fixing belt. The fixing device further comprises a transmission mechanism to speed up the process, an applicator positioned inside the fixing belt and applying oil to the fixing belt, and a steering roller positioned downstream of the auxiliary drive roller and upstream of the pad in the rotational direction of the fixing belt, so as to stretch the inner surface of the fixing belt, and capable of being inclined with respect to the width direction of the fixing belt so that the fixing belt is located within a predetermined range in the width direction of the fixing belt, wherein the applicator is positioned downstream of the auxiliary drive roller and upstream of the nip portion in the rotational direction of the fixing belt, and the amount of the fixing belt wrapped around the auxiliary drive roller is greater than the amount of the fixing belt wrapped around the steering roller. [Effects of the Invention]

[0008] According to the present invention, Fluctuations in the contact force of the coating material against the inner surface of the fixing belt are suppressed. [Brief explanation of the drawing]

[0009] [Figure 1] A schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 2] A schematic cross-sectional view of the fixing device according to the first embodiment. [Figure 3] A schematic diagram illustrating the trajectory of the anchoring belt downstream of the anchoring pad. [Figure 4] A schematic cross-sectional view of a fixing device for illustrating the relationship between the amount of belt wrapped around a roller that tensions the fixing belt according to the first embodiment. [Figure 5] A schematic cross-sectional view of the fixing device according to the second embodiment. [Figure 6] A schematic diagram illustrating the belt length L downstream of the fixing pad. [Figure 7] A graph showing the relationship between belt length L and belt radius of curvature. [Figure 8] A schematic cross-sectional view of the fixing device according to the third embodiment. [Figure 9] A schematic cross-sectional view showing the main components of the fixing device according to the fourth embodiment. [Figure 10] A schematic cross-sectional view of a fixing device for illustrating the relationship between the amount of belt wrapped around a roller that tensions the fixing belt according to the fifth embodiment. [Figure 11] A schematic cross-sectional view showing the main components of the fixing device according to the sixth embodiment. [Figure 12] A schematic cross-sectional view showing the main components of a fixing device according to another first example of the sixth embodiment. [Figure 13]Schematic cross-sectional view showing the main part of a fixing device according to another second example of the sixth embodiment. [Figure 14] Schematic cross-sectional view showing the main part of a fixing device according to another third example of the sixth embodiment. [Figure 15] Schematic cross-sectional view of a fixing device according to the seventh embodiment. [Figure 16] Schematic cross-sectional view of a fixing device according to the eighth embodiment. [Figure 17] Schematic cross-sectional view of a fixing device according to a comparative example. [Modes for Carrying Out the Invention]

[0010] <First Embodiment> The first embodiment will be described with reference to FIGS. 1 to 4. First, the schematic configuration of the image forming apparatus of the present embodiment will be described with reference to FIG. 1.

[0011] [Image Forming Apparatus] The image forming apparatus 1 is an electrophotographic full-color printer having four image forming portions Pa, Pb, Pc, and Pd provided corresponding to four colors of yellow, magenta, cyan, and black. In the present embodiment, a tandem type is adopted in which the image forming portions Pa, Pb, Pc, and Pd are arranged along the rotation direction of an intermediate transfer belt 204 to be described later. The 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 the image forming apparatus main body 3 or a host device such as a personal computer communicatively connected to the image forming apparatus main body 3. Examples of the recording material include sheet materials such as paper, plastic films, and cloth.

[0012] The image forming apparatus 1 comprises an image reading unit 2 and an image forming apparatus body 3. The image reading unit 2 reads a document placed on the document glass 21. Light emitted from a light source 22 is reflected by the document and formed as an image on a CCD sensor 24 via an optical system component 23 such as a lens. By scanning in the direction of the arrow, this optical system unit converts the document into a series of electrical signal data for each line. The image signal obtained by the CCD sensor 24 is sent to the image forming apparatus body 3, where the control unit 30 performs image processing according to each image forming unit, which will be described later. The control unit 30 also receives external input as an image signal from an external host device such as a print server.

[0013] The main body of the image forming apparatus 3 is equipped with multiple image forming units Pa, Pb, Pc, and Pd, and each image forming unit performs image formation based on the image signal described above. That is, the image signal is converted into a laser beam controlled by PWM (pulse width modulation) by the control unit 30. The polygon scanner 31, which acts as an exposure device, scans the laser beam according to the image signal. The laser beam is then irradiated onto the photosensitive drums 200a to 200d, which serve as image carriers for each of the image forming units Pa to Pd.

[0014] Pa is the image forming unit for yellow (Y), Pb is for magenta (M), Pc is for cyan (C), and Pd is for black (Bk), each forming an image of the corresponding color. Since the image forming units Pa to Pd are substantially the same, the details of the Y image forming unit Pa will be explained below, and the explanations 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 the image signal, as described below.

[0015] The charging roller 201a, acting as a primary charger, charges the surface of the photosensitive drum 200a to a predetermined potential, preparing it for electrostatic latent image formation. An electrostatic latent image is formed on the surface of the photosensitive drum 200a, which has been charged to the predetermined potential, by a laser beam from the polygon scanner 31. The developer 202a develops the electrostatic latent image on the photosensitive drum 200a to form a toner image. The primary transfer roller 203a discharges from the back of the intermediate transfer belt 204, applying a primary transfer bias with the opposite polarity to the toner, and transfers the toner image on the photosensitive drum 200a onto the intermediate transfer belt 204. After the transfer, the surface of the photosensitive drum 200a is cleaned by the cleaner 207a.

[0016] Furthermore, the toner image on the intermediate transfer belt 204 is transported to the next image forming section, and the toner images of each color formed in the respective image forming sections are transferred sequentially in the order of Y, M, C, and Bk, forming a four-color image on its surface. The toner image that has passed through the Bk image forming section Pd, which is the furthest downstream in the rotational direction of the intermediate transfer belt 204, is transported to a secondary transfer section consisting of a pair of secondary transfer rollers 205 and 206. In the secondary transfer section, a secondary transfer electric field with the opposite polarity to the toner image on the intermediate transfer belt 204 is applied, and the image is secondary transferred to the recording material.

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

[0018] The recording material onto which the toner image has been transferred in the secondary transfer unit is transported to the fuser unit 8, where it is heated and pressurized to fix the toner image onto the recording material. The recording material that has passed through the fuser unit 8 is discharged to the discharge tray 7. When image formation is performed on both sides of the recording material, once the transfer and fixing of the toner image to the first side (front) of the recording material is complete, the front and back sides of the recording material are reversed via the inversion transport unit 10, and the toner image is transferred and fixed to the second side (back) of the recording material, which is then loaded onto the discharge tray 7.

[0019] The control unit 30 controls the entire image forming apparatus 1 as described above. The control unit 30 can also perform various settings based on input from the operation unit 4 of the image forming apparatus 1. This control unit 30 includes a CPU (Central Processing Unit), ROM (Read Only Memory), and RAM (Random Access Memory). The CPU controls each part while reading programs corresponding to control procedures stored in the ROM. The RAM stores working data and input data, and the CPU controls the apparatus 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 using Figure 2. In this embodiment, a belt heating type fixing device using an endless belt is employed. In Figure 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 and rotatable belt, and a pressure roller 330 as a pressure rotating body (pressure member) that contacts the fixing belt 310 and forms a nip portion N together with the fixing belt 310.

[0021] The heating unit 300 includes the aforementioned fixing belt 310, a fixing pad 320 as a nip-forming member and tensioning member (pressure pad), an auxiliary drive roller 340 as a drive roller, and a tension roller 351 as a tensioning member. The pressure roller 330 is also a drive rotating body that rotates in contact with the outer circumferential surface of the fixing belt 310 and imparts driving force to the fixing belt 310.

[0022] The fixing belt 310, which is an endless belt, has thermal conductivity and heat resistance, and for example, it is a thin-walled cylindrical shape with an inner diameter of 120 mm. In this embodiment, it has a three-layer structure with a base layer, an elastic layer on the outer circumference of the base layer, and a release layer on the outer circumference of the release 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. This 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 the nip-forming member, is positioned inside the fixing belt 310, facing the pressure roller 330 with the fixing belt 310 in between, and forms a nip portion N that grips and transports the recording material between the fixing belt 310 and the pressure roller 330. In this embodiment, the fixing pad 320 is a substantially plate-shaped member that is long in the width direction of the fixing belt 310 (the direction of the rotation axis of the auxiliary drive roller 340). The nip portion N is formed when the fixing pad 320 is pressed against the pressure roller 330 with the fixing belt 310 in between. The fixing pad 320 is made of LCP (liquid crystal polymer) resin.

[0024] The fixing pad 320 is supported by a stay 360 positioned inside the fixing belt 310. The stay 360 is a rigid reinforcing member that is long along the width direction of the fixing belt 310. The stay 360 provides strength to the fixing pad 320 when it is pressed by the pressure roller 330, ensuring the applied pressure at the nip portion N.

[0025] Furthermore, as shown in Figure 3, the ends of the nip portion N of the fixing pad 320 in the recording material transport direction are curved surfaces 320a and 320b, respectively. The curved surfaces 320a and 320b are curved surfaces that curve away from the nip surface towards the ends (upper part of Figure 3). The nip surface is formed between the fixing belt 310 and the pressure roller 330 and is a surface that follows the surface of the fixing pad 320 on the pressure roller 330 side (lower part of Figure 3). In this embodiment, the upstream curved surface 320a is a partial cylindrical surface with a radius of 8 mm, and the downstream curved surface 320b is a partial cylindrical surface with a radius of 6 mm. That is, the radius of curvature of the downstream curved surface 320b is smaller than the radius of curvature of the upstream curved surface 320a.

[0026] In this embodiment, the downstream end of the fixing pad 320 is made into a curved surface portion 320b, and the curvature of the curved surface portion 320b causes the fixing belt 310 to curve. 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 PI (polyimide) sheet coated with PTFE (polytetrafluoroethylene) is used as the lubricating sheet 370, with a thickness of 100 μm. The PI sheet has protrusions of 100 μm in size formed at 1 mm intervals, which reduces sliding resistance by reducing the contact area with the fixing belt 310.

[0028] Furthermore, a lubricant is applied to the inner circumferential surface of the fixing belt 310, so that the fixing belt 310 slides smoothly against the fixing pad 320, which is covered with a lubricating sheet 370. A silicone oil with a viscosity of 100 cSt is used as the lubricant. In this embodiment, the fixing pad 320, which is a non-rotating member that does not rotate even when the 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] As shown in Figure 2, the auxiliary drive roller 340 is positioned inside the fixing belt 310 and rotates together with the fixing pad 320, tensing the fixing belt 310 and providing driving force to the fixing belt 310. The auxiliary drive roller 340 is formed in a cylindrical shape from a metal such as aluminum or stainless steel, and a halogen heater 340a is disposed inside it as a heat source for heating the fixing belt 310. The auxiliary drive roller 340 is then heated to a predetermined temperature by the halogen heater 340a.

[0030] In this embodiment, the auxiliary drive roller 340 is formed from, for example, an aluminum pipe with an outer diameter of 40 mm and a thickness of 1 mm, with an anodized surface, from the viewpoint of thermal conductivity. While one halogen heater 340a may suffice, it is desirable to have multiple halogen heaters 340a to control the temperature distribution along the longitudinal direction (rotation axis direction) of the auxiliary drive roller 340. Multiple halogen heaters 340a have different light distributions along their 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 heating source is not limited to halogen heaters; other heaters capable of heating the auxiliary drive roller 340, such as carbon heaters, may also be used.

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

[0032] The rotation of the auxiliary drive roller 340 may be driven by a motor M0, which serves as the pressure roller drive source (first drive source) that rotates the pressure roller 330, or by a motor M1 separate from motor M0. Furthermore, the drive transmission mechanism from the motor may be other than gears, such as a pulley and belt, or a mechanism that presses a roller driven by an external motor against it.

[0033] The tension roller 351 is positioned inside the fixing belt 310 and, together with the fixing pad 320 and the auxiliary drive roller 340, tensions the fixing belt 310 and rotates in accordance with the fixing belt 310. In this embodiment, with respect to the rotation direction of the fixing belt 310, the fixing pad 320, tension roller 351, and auxiliary drive roller 340 are arranged in that order. The tension roller 351 is formed in 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 end is rotatably supported by a bearing (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 acts as a tension roller that applies a predetermined tension to the fixing belt 310. The tension from the spring is 50N in this embodiment. By applying tension to the fixing belt 310 with the tension roller 351 in this way, the fixing belt 310 is made to follow the curved shapes 320a and 320b of the fixing pad 320. That is, the fixing belt 310 is curved along the curved shapes 320a and 320b.

[0035] The pressure roller 330, acting as a driving rotating body, rotates in contact with the outer surface of the fixing belt 310, thereby providing driving force to the fixing belt 310. In this embodiment, the pressure roller 330 is a roller with an elastic layer formed on the outer circumference of its shaft and a release layer formed on the outer circumference of the elastic layer. The shaft is made of stainless steel, the elastic layer is made of conductive silicone rubber with a thickness of 5 mm, and the release layer is made of PFA (polytetrafluoroethylene-perfluoroalkoxyethylene copolymer resin) as a fluororesin with a thickness of 50 μm. 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 of it. The gear is connected to a motor M0, which serves as the pressure roller drive source (first drive source), and the roller is rotated.

[0036] The fixing frame 380 is provided with a heating unit positioning section 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 section 381 and fixing the stay 360 to the heating unit positioning section 381 by fixing means (not shown). Here, the heating unit positioning section 381 has a pressure direction restricting surface 381a facing the pressure roller 330 and a transport direction restricting surface 381b which is the abutment 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 restricting surface 381a and the transport direction restricting surface 318b. At this time, the pressure roller 330 is separated from the fixing belt 310.

[0037] The pressure roller 330 comes into contact with the fixing belt 310 after the heating unit 300 is positioned in the heating unit positioning section 381, as the pressure frame 383 moves due to a drive source (not shown) and a cam. Then, the pressure roller 330 pressurizes the fixing pad 320 via the fixing belt 310. In this embodiment, the pressure applied during image formation is 1000N.

[0038] In this embodiment, a separation member 400 is provided on the downstream side of the nip section N in the recording material transport direction to separate the recording material from the fixing belt 310. The separation member 400 is positioned with a gap between it and the outer surface of the fixing belt 310, separating the recording material that has passed through the nip section N from the fixing belt. Specifically, the separation member 400 is positioned close to the portion of the outer surface of the fixing belt 310 that is stretched between the fixing pad 320 and the tension roller 351. The separation member 400 is also formed in a blade shape, with its tip facing the outer surface of the fixing belt 310.

[0039] In this configuration, the fixing device 8 holds the recording material carrying the toner image in a nip section N formed between the fixing belt 310 and the pressure roller 330, and heats the toner image while transporting it. As a result, the toner image melts and is fixed to the recording material. In this embodiment, during image formation, the peripheral speed of the fixing belt 310 is 300 mm / s, the pressure applied in the nip section N is 1000 N, and the temperature of the fixing belt 310 is 180 °C.

[0040] [Conformability of the fixing belt's fixing pad to curved shapes] As shown in Figure 2, in the configuration of this embodiment, the angle θ between the nip surface and the trajectory of the fixing belt 310 from the nip section N to the tension roller 351 is set to 52°. Here, if the rigidity of the fixing belt 310 is small and the tension on the fixing belt 310 is sufficiently large, the trajectory of the fixing belt 310 at the exit of the nip section N (downstream side of the nip section N in the recording material transport direction) will be as shown by the solid line in Figure 3. However, due to the rigidity of the fixing belt 310 and the force that the fixing belt 310 receives at the nip section N, the trajectory of the fixing belt 310 at the exit of the nip section N during image formation may bulge as shown by the dotted line in Figure 3.

[0041] In other words, the fixing belt 310 receives rotational driving force from the pressure roller 330. Therefore, if the auxiliary drive roller 340 described above is a roller that does not provide driving force to the fixing belt 310, there is a risk that the fixing belt 310 will bend at the exit of the nip section 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 surface portion 320b at the downstream end of the fixing pad 320 will decrease, and the fixing belt will not bend sufficiently at the exit of the nip section N, causing the track to bulge as shown by the dashed line in Figure 3.

[0042] If the trajectory of the fixing belt 310 bulges at the exit of the nip section N in this way, the separation of the recording material from the fixing belt 310 will decrease. In addition, there is a possibility that the fixing belt 310 may come into contact with the separating member 400 which is positioned 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 may be damaged, which may reduce the image quality of the toner image fixed by the fixing device 8.

[0043] One possible solution to this problem is to increase the tension of the anchoring belt 310. However, increasing the tension of the anchoring belt 310 may cause adverse effects such as creep deformation of the base layer of the anchoring belt 310.

[0044] Therefore, in this embodiment, as described above, an auxiliary drive roller 340 is provided, which is positioned inside the fixing belt 310 and applies 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 driving force is applied to the auxiliary drive roller 340, the auxiliary drive roller 340 pulls on the belt surface upstream of the auxiliary drive roller 340 in the rotational direction of the fixing belt 310. As a result, the belt surface that is upstream of the auxiliary drive roller 340 in the rotational direction of the fixing belt 310 and downstream of the nip section N is pulled by the auxiliary drive roller 340. As a result, the bulge of the trajectory of the fixing belt 310 at the exit of the nip section N can be reduced.

[0045] By applying driving force to the anchoring belt 310 with the auxiliary drive roller 340, belt tracking performance can be improved. Furthermore, by making the peripheral speed of the auxiliary drive roller 340 faster than the peripheral speed of the pressure roller 330, belt tracking performance can be further improved.

[0046] Furthermore, the provision of the auxiliary drive roller 340 was found to be effective in preventing image misalignment. The fixing belt 310 rotates under the force applied by the pressure roller 330, but at that time, due to the sliding resistance with the fixing pad 320, the fixing belt 310 is transported while slightly misaligned with the recording material passing through the nip section N. On the other hand, by providing auxiliary driving force from the inner surface of the fixing belt 310 by the auxiliary drive roller 340, the fixing belt 310 receives driving force not only from the pressure roller 330 but also from the auxiliary drive roller 340. Therefore, even if the fixing pad 320 is configured to increase the rotational load on the fixing belt 310, the fixing belt 310 always receives driving force from the auxiliary drive roller 340, regardless of whether the recording material is in the nip section or not. 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 the recording material is in the nip section but also when it is not. In other words, the rotational stability of the fixing belt 310 can be improved.

[0047] More specifically, the fixing belt 310 is held tightly between the pressure roller 330 and the fixing pad 320 at the nip. The auxiliary drive roller 340 rotates the fixing belt 310 by frictional force, and therefore cannot transmit the driving force necessary to move the fixing belt 310 at a faster peripheral speed than the pressure roller 330 against the strong pressure. As a result, when there is no recording material at the nip, the fixing belt 310 and the pressure roller 330 move at the same peripheral speed at the nip. In this case, because the fixing belt 310 has a low modulus of elasticity in the circumferential direction, the auxiliary drive roller 340 rotates in a sliding motion relative to the fixing belt 310. Due to this operation, the peripheral speed of the fixing belt 310 and the peripheral speed of the pressure roller 330 are substantially the same. On the other hand, even when the recording material is in the nip section, for similar reasons, the fixing belt 310 receives the driving force of the auxiliary drive roller 340 and the pressure roller 330, allowing the peripheral speed of the fixing belt 310 and the peripheral speed of the pressure roller 330 to be substantially the same. Furthermore, the peripheral speed of the recording material, the fixing belt 310, and the pressure roller 330 can be made substantially the same. As a result, the displacement of the fixing belt 310 relative to the recording material can be mitigated, and it has been found to be effective in suppressing image displacement. Thus, the peripheral speed of the auxiliary drive 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%. To obtain the effects shown above, it is preferable that 1.04 ≤ peripheral speed of auxiliary drive roller 340 / peripheral speed of pressure roller 330 ≤ 1.20 be satisfied, and it is preferable that 1.1 ≤ peripheral speed of auxiliary drive roller 340 / peripheral speed of pressure roller 330 ≤ 1.2 (the peripheral speed of the auxiliary drive roller 340 is 110% or more and 120% or less of the peripheral speed of the pressure roller 330) be satisfied. To further improve image quality, it is preferable that 1.04 ≤ peripheral speed of auxiliary drive roller 340 / peripheral speed of pressure roller 330 ≤ 1.15 be satisfied.

[0048] [Thermal efficiency of auxiliary drive rollers] As described above, the auxiliary drive roller 340 has a halogen heater 340a inside it, which serves as a heat source for heating the fixing belt 310. Here, the auxiliary drive roller 340 rotates at a faster speed than the fixing belt 310. Therefore, compared to when the auxiliary drive roller 340 rotates driven by the fixing belt 310 at a constant speed, the heat transfer nip can be virtually widened. In other words, the contact time between the auxiliary drive roller 340 and the fixing belt 310 can be increased compared to when the auxiliary drive roller 340 rotates driven by the fixing belt 310 at a constant speed. Therefore, by rotating the auxiliary drive roller 340 at a peripheral speed faster than the fixing belt 310, the heat transfer efficiency from the auxiliary drive roller 340 to the fixing belt 310 can be improved compared to when it rotates driven at a constant speed.

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

[0050] [Amount of fixing belt wrapped around] Next, the amount of winding of the fixing belt 310 around each roller will be explained using Figure 4. Here, the amount of winding of the belt refers to the length that is wound around the roller, or more precisely, the length that the belt is in contact with the roller. Note that the configuration of Figure 4 is the same as that shown in Figure 2, with only angles θa and θd added. However, the halogen heater 340a shown in Figure 2 is omitted in Figure 4.

[0051] As shown in Figure 4, the angle that the anchoring belt 310 makes with the center of the auxiliary drive roller 340 when it is wrapped around the roller is defined as the wrapping angle θd. Similarly, the angle that the anchoring belt 310 makes with the center of the tension roller 351 when it is wrapped around the roller is defined as the wrapping angle θa. The wrapping angle is the angle formed by the lines connecting the ends of the circumferential direction of the roller in the area where the belt is in contact with the roller, and the roller center.

[0052] In this embodiment, the winding angle θd with respect to the auxiliary drive roller 340 is made larger than the winding angle θa with respect to the tension roller 351. Specifically, the winding angle θd is set to 120° and the winding angle θa is set to 100°. By making the winding angle θd larger than the winding angle θa in this way, the amount of winding of the anchoring belt 310 with respect to the auxiliary drive roller 340 is made larger than the amount of winding of the anchoring belt 310 with respect to the tension roller 351.

[0053] Here, simply making the winding angle θd larger than the winding angle θa will not allow the amount of winding on the auxiliary drive roller 340 to be greater than the amount of winding on the tension roller 351 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. For this reason, in this embodiment, for example, the cross-sectional areas, or in other words, the outer diameters, of the auxiliary drive roller 340 and the tension roller 351 are made approximately the same, and the amount of winding on the auxiliary drive roller 340 is made greater than the amount of winding on the tension roller 351. Note that if the amount of winding is in this relationship, 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 also be larger than the cross-sectional area of ​​the tension roller 351.

[0054] By increasing the amount of the fixing belt 310 wrapped around the auxiliary drive roller 340 in this way, the contact area between the auxiliary drive roller 340 and the fixing belt 310 can be increased, improving the efficiency of power transmission from the auxiliary drive roller 340 to the fixing belt 310. Furthermore, if there is a heating source such as a halogen heater 340a inside the auxiliary drive roller 340, the heat transfer efficiency from the auxiliary drive roller 340 to the fixing belt 310 can also be improved. Note that the amount of the fixing belt 310 wrapped around the auxiliary drive roller 340 may be greater than the amount of the fixing belt 310 wrapped around the fixing pad 320. In other words, the amount of the fixing belt 310 wrapped around the auxiliary drive roller 340 may be the largest among all the members that tension the fixing belt 310 from the inside.

[0055] As described above, in this embodiment, the belt following performance can be improved by providing the auxiliary drive roller 340. As a result, a decrease in the separation performance of the recording material from the fixing belt 310 as it passes through the nip section N can be suppressed. In addition, the separation member 400 is positioned on the fixing belt 310 with a gap between them. This gap is set small in order to separate the recording material from the fixing belt 310. Therefore, if the belt following performance decreases and the trajectory of the fixing belt 310 bulges at the exit of the nip section N, the fixing belt 310 may come into contact with the separation member 400, potentially damaging the fixing belt 310. In contrast, in this embodiment, the belt following performance can be improved by providing the auxiliary drive roller 340, making it less likely for the fixing belt 310 to come into contact with the separation member 400.

[0056] <Second Embodiment> A second embodiment will be described using Figures 5 to 11. In the first embodiment described above, with respect to the rotation direction of the fixing belt 310, the auxiliary drive roller 340 was positioned downstream of the tension roller 351 and upstream of the fixing pad 320. In contrast, in this embodiment, with respect to the rotation direction of the fixing belt 310, the auxiliary drive roller 340 is positioned downstream of the fixing pad 320 and upstream of the tension roller 351. Specifically, in this embodiment, the positions of the auxiliary drive roller 340 and the tension roller 351 are swapped compared to the configuration of the first embodiment. Other configurations and operations are the same as in the first embodiment, so the same reference numerals are used for redundant components, and their description and illustration are 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, with respect to the rotation direction of the fixing belt 310, the auxiliary drive roller 340 is positioned downstream of the fixing pad 320 and upstream of the tension roller 351. Furthermore, no member for tensioning the fixing belt 310 is positioned between the fixing pad 320 and the auxiliary drive roller 340. That is, as shown in Figure 5, the heating unit 300A is arranged in the order of auxiliary drive roller 340 and tension roller 351 in the rotation direction of the fixing belt 310, starting from the recording material transport direction exit of the nip section N, which is the reverse of the configuration order of the first embodiment. In this embodiment, by positioning the auxiliary drive roller 340 closer to the nip section N, the belt tracking performance can be further improved. This point will be explained using Figures 6 to 11.

[0058] [Relationship between belt length and the conveying effect of auxiliary drive rollers] First, the belt length from the exit point in the conveying direction of the nip section N to the auxiliary drive roller 340 changes significantly depending on whether the auxiliary drive roller 340 or the tension roller 351 is positioned on the upstream side in the direction of rotation. Figure 6 is a diagram illustrating the belt length L. The belt length L represents the distance from the point where belt followability is required to the point where force is applied. In this embodiment, the belt length L is defined as the length from the curved surface portion 320b (exit point of the nip section N) at the downstream end of the fixing pad 320 to the auxiliary drive roller 340.

[0059] The inventors conducted a simple test to observe how the belt's followability changes when the belt length L is varied. The results are shown in Figure 7. In the simple test, the angle θ between the nip surface and the trajectory of the fixing belt 310 was set to 52°, and the belt's followability was observed when the fixing belt 310 was pulled with a force of 50N while varying the belt length L. From Figure 7, it can be seen that shortening the belt length L leads to an improvement in belt followability. This difference is thought to be due to the influence of the rigidity of the base layer of the fixing belt 310 and the shrinkage of the release layer. The configuration of Example 2 is such that the fixing pad 320 and the auxiliary drive roller 340 are arranged next to each other. Therefore, the belt length between the fixing pad 320 and the auxiliary drive roller 340 in the opposite direction of rotation 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 opposite direction of rotation of the fixing belt 310 in Example 1. As a result, 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 section 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 in the configuration of the first embodiment, good belt following performance can be achieved, and a decrease in the separation performance of the recording material from the fixing belt 310 can be suppressed. In addition, the fixing belt 310 can be made less likely to come into contact with the separation 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 following performance and heat conduction 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] In the example shown in Figure 5, the auxiliary drive roller 340 is positioned inside the fixing belt 310, without any components downstream of the nip section N. However, if the components do not contribute to the tensioning of the fixing belt 310, such as cleaning components or components for applying lubricant, they can be placed between the nip section N and the auxiliary drive roller 340 without any particular problem.

[0062] <Third Embodiment> A third embodiment will be described with reference to Figure 8. In this embodiment, the tension roller 351 of the second embodiment described above is replaced with a steering roller 350. The other configurations and operations are the same as in the second embodiment, so the same reference numerals are used for redundant components, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from the second embodiment.

[0063] As shown in Figure 8, the fixing device 8B of this embodiment differs from the second embodiment in the configuration of the heating unit 300B. Specifically, the tension roller that is positioned inside the fixing belt 310 and tensions the fixing belt 310 together with the fixing pad 320 and the auxiliary drive roller 340 is the steering roller 350. In this embodiment as well, the auxiliary drive roller 340 is positioned downstream of the fixing pad 320 and upstream of the steering roller 350 with respect to the rotational direction of the fixing belt 310.

[0064] The steering roller 350 controls the position (closer position) of the anchoring belt 310 in relation to the rotation axis direction (longitudinal direction) of the auxiliary drive roller 340 by tilting. That is, the steering roller 350 has a pivot point at the center of the rotation axis direction (longitudinal direction) of the steering roller 350, and tilts relative to the longitudinal direction of the auxiliary drive roller 340 by oscillating around this pivot point. This creates a tension difference between one side and the other side of the anchoring belt 310 in the longitudinal direction, causing the anchoring belt 310 to move in the longitudinal direction.

[0065] The anchoring belt 310 tends to shift towards one end during rotation due to factors such as the outer diameter accuracy of the tensioning rollers and the alignment accuracy between the rollers. Therefore, the steering roller 350 controls this shifting. Specifically, the steering roller 350 is a roller that adjusts the position of the anchoring belt 310 by tilting so that the anchoring belt 310 is located within a predetermined range in the width direction of the anchoring belt 310. The steering roller 350 may be oscillated by a drive source such as a motor, or it may be configured to oscillate by self-alignment. Furthermore, the center of rotation may be the center in the longitudinal direction, as in this embodiment, or it may be one of the ends in the longitudinal direction.

[0066] Furthermore, in this embodiment, the steering roller 350 is biased by a spring supported by the frame of the heating unit 300B, and also acts as a tension roller that applies a predetermined tension to the fixing belt 310. The tension from the spring is 50N, and by applying tension to the fixing belt 310, the fixing belt 310 is made to follow the curved shapes 320a and 320b of the fixing pad 320.

[0067] In Example 3, the configuration is such that the auxiliary drive roller 340 and the steering roller 350 are arranged in the order of the outlet in the conveying direction of the nip section N and the rotational direction. In contrast, in the comparative example, the steering roller 350 and the auxiliary drive roller 340 are arranged in the order of the outlet in the conveying direction of the nip section N and the rotational direction. In other words, we will examine the effect on belt tracking performance depending on whether the steering roller 350 is placed upstream or downstream of the auxiliary drive roller 340 in the rotational direction. If the steering roller 350 is placed upstream of the auxiliary drive roller 340, the angle θ changes between one end and the other end in the longitudinal direction due to the rotation (tilting) of the steering roller 350 at the longitudinal end. As a result, there is a longitudinal unevenness in the distance of the anchoring belt 310 from the outlet of the nip section N to the auxiliary drive roller 340 in the longitudinal direction, and tension unevenness in the anchoring belt 310 is likely to occur. Consequently, the amount of bulging of the anchoring 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 positioning the auxiliary drive roller 340 upstream of the steering roller 350 in the rotational direction, as in Example 3, the auxiliary driving force from the auxiliary drive roller 340 to the fixing belt 310 can be applied to the fixing belt 310 evenly and efficiently. As a result, the belt following performance was improved compared to the comparative example. Therefore, in Example 3, the separation performance of the recording material from the fixing belt 310 is improved, and contact between the fixing belt 310 and the separation member 400 is suppressed.

[0069] In this configuration of the embodiment, even if the tension roller is a steering roller 350, good belt tracking performance can be achieved, and a decrease in the separation of the recording material from the fixing belt 310 can be suppressed. In addition, the fixing belt 310 can be made less likely to come into contact with the separation member 400.

[0070] <Fourth Embodiment> A fourth embodiment will be described with reference to Figure 9. In the embodiments described above, a configuration was described in which a non-rotating fixing pad 320 was 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 embodiments described above, the fixing belt 310 is tensioned by only the auxiliary drive roller 340 and the fixing roller 395. The other configurations and operations are the same as in the first embodiment, so the same reference numerals are used for redundant components, and their description and illustration are omitted or simplified. The following description will focus on the differences from the first embodiment.

[0071] As shown in Figure 9, in this embodiment, the heating unit 300C of the fixing device 8C tensions the fixing belt 310 using only the auxiliary drive roller 340 and the fixing roller 395. The fixing roller 395 is positioned inside the fixing belt 310, facing the pressure roller 330 with the fixing belt 310 in between, and forms a nip portion N that grips and conveys the recording material between the fixing belt 310 and the pressure roller 330. The fixing roller 395 rotates in accordance with the rotation of the fixing belt 310.

[0072] Furthermore, since the fixing roller 395 is formed in a cylindrical shape, it curves the fixing belt 310 due to the curvature of the downstream end in the recording material transport direction at the nip section N, similar to the curved surface portion 320b downstream of the fixing pad 320. This separates the recording material that has passed through the nip section N from the fixing belt 310. For this reason, as with the case where the nip section forming member is the fixing pad 320, good followability of the fixing belt 310 to the curvature of the fixing roller 395 (belt followability) is required when considering the separation of the recording material.

[0073] In other words, even if the nip-forming member is a rotating body such as the fixing roller 395, the fixing belt 310 rotates in the nip portion N while receiving fixing belt driving force from the pressure roller 330, similar to the embodiments described above. As a result, the fixing belt 310 may bulge downstream in the conveying direction due to this fixing belt driving force, potentially reducing its ability to follow the fixing roller 395.

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

[0075] Furthermore, the auxiliary drive roller 340 was supported by the frame of the heating unit 300C. A tensioner biased by a spring (not shown) that applies a predetermined tension to the anchoring belt 310. It also functions as a roller. The tension from the spring is 50N, which applies tension to the fixing belt 310. This causes the fixing belt 310 to follow the outer surface of the fixing roller 395.

[0076] Furthermore, the auxiliary drive roller 340 and the fixing roller 395 are each formed from aluminum pipes with a thickness of 1 mm, and their surfaces are anodized. The auxiliary drive roller 340 and the fixing roller 395 may also be made of other metals such as stainless steel. The auxiliary drive roller 340 has a halogen heater 340a installed inside as a heat source, capable of generating heat to a predetermined temperature. On the other hand, the fixing roller 395 does not have a heat source such as a halogen heater. The heat source may be provided in the fixing roller 395 only, or in both rollers.

[0077] Furthermore, the pressure roller 330 is supplied with rotational driving force from motor M0, which serves as the pressure roller drive source, and the auxiliary drive roller 340 is supplied with rotational driving force from motor M1, which serves as the auxiliary drive roller drive source. However, the rotation of the auxiliary drive roller 340 may also be supplied with rotational driving force from motor M0. In this embodiment as well, it is preferable to make the peripheral speed of the auxiliary drive roller 340 faster than the peripheral speed of the pressure roller 330.

[0078] In this embodiment as well, the belt tracking performance can be improved by providing the auxiliary drive roller 340. As a result, a decrease in the separation of the recording material passing through the nip section N from the fixing belt 310 can be suppressed, and the fixing belt 310 can be made less likely to come into contact with the separation member 400.

[0079] <Fifth Embodiment> The fifth embodiment will be described with reference to Figure 10. In this embodiment, the amount of belt winding described in Figure 4 is made largest on the auxiliary drive roller 340A among the rollers that tension the fixing belt 310. Also, in this embodiment, a steering roller 350A is provided, similar to the third embodiment. The other configurations and operations are the same as in any of the first to third embodiments, so the same reference numerals are used for overlapping components, and their descriptions and illustrations are omitted or simplified. The following description will focus on the differences from any of the first to third embodiments.

[0080] The fixing device 8D includes a fixing belt 310 as an endless, rotatable heating rotating body, a fixing pad 320 as a nip-forming member, a heating unit 300D including an auxiliary drive roller 340A and a steering roller 350A, and a pressure roller 330. In this embodiment as well, the auxiliary drive roller 340A is positioned downstream of the fixing pad 320 and upstream of the steering roller 350A with respect to the rotational direction of the fixing belt 310.

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

[0082] Furthermore, in this embodiment, there is an oil application roll 361 as a lubricant application member that applies lubricant to the inner circumferential surface of the fixing belt 310. The oil application roll 361 has an outer diameter of about 10 mm and is located 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 bias the inner circumferential surface of the fixing belt 310 with an force of about 10 N.

[0083] The oil application roll 361 contains a heat-resistant aramid felt impregnated with a heat-resistant silicone oil having a viscosity of approximately 100 cSt, which serves as a lubricant for lubricating the inner 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 surface of the fixing belt 310 and rotates in accordance with the movement of the rotating fixing belt 310, supplying silicone oil to the inner surface 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. A halogen heater (not shown) is installed inside as a heat source and is capable of generating heat up to a predetermined temperature. The fixing belt 310 is heated by the auxiliary drive roller 340 and 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 the motor M1 via the gear to be rotationally driven in the direction of arrow b.

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

[0086] The higher the kinematic viscosity of the lubricant, the greater the effect of transmitting auxiliary driving force. However, in order to ensure smooth friction between the fixing belt 310 and the fixing pad 320, the kinematic viscosity of the lubricant at room temperature (20°C) should be 10,000 mm². 2 It is desirable that the viscosity be less than / s. Also, if the viscosity is too low, the slippage between the fixing belt 310 and the auxiliary drive roller 340 will increase, and the auxiliary drive force will not be transmitted sufficiently. Therefore, the kinematic viscosity of the lubricant at room temperature (20°C) should be 50 mm². 2 A value of / s or higher is desirable.

[0087] The steering roller 350A is an aluminum pipe with an outer diameter of 20 mm and a thickness of 1 mm, and its end is rotatably supported by a bearing (not shown). The steering roller 350A is also biased by a spring supported by the frame of the heating unit 300D, and acts as a tension roller that applies a predetermined tension to the fixing belt 310. For example, the tension from the spring is 50 N, and by applying tension to the fixing belt 310, the fixing belt 310 is made to follow the curved shapes 320a and 320b of the fixing pad 320. The configuration of this steering roller 350A is the same as in the third embodiment.

[0088] The auxiliary drive roller 340A and the steering roller 350A are each anodized on their surface. However, the auxiliary drive 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 the motor M0 and rotated in the direction of arrow a. The nip portion N formed between the fixing belt 310 and the pressure roller 330 grips the recording material carrying the toner image and heats the toner image while transporting it.

[0090] [Amount of fixing belt wrapped around] Here, the angle that the fixing belt 310 makes with the center of the auxiliary drive roller 340A when it is wrapped around it is defined as the wrapping angle θd. Similarly, the angles that the fixing belt 310 makes with the center of the steering roller 350A and the oil application roll 361 when it is wrapped around them are defined as the wrapping angles θb and θc, respectively. Furthermore, the angle θ between the nip surface and the trajectory of the fixing belt 310 from the nip section N to the auxiliary drive roller 340A is set to 52°, as in the first embodiment.

[0091] At this time, the auxiliary drive roller 340A and the steering roller 350A are positioned such that the winding angle θd by the auxiliary drive roller 340A is 150° and the winding angle θb by the steering roller 350A is 100°. Furthermore, the winding angle θd by the auxiliary drive roller 340A is greater than the winding angles θb and θc by the tensioning members other than the auxiliary drive roller 340A (θd>θb, θd>θc). In other words, the winding angle θd by the auxiliary drive roller 340A is greater than the winding angle θb by the steering roller 350A and the winding angle θs by the oil application roll 361.

[0092] Furthermore, in this embodiment, the cross-sectional area of ​​the auxiliary drive roller 340A is made larger than the cross-sectional area of ​​the steering roller 350A and the oil application roll 361. That is, when the fixing belt 310 is tensioned by multiple members, the cross-sectional area of ​​the member that performs auxiliary driving (i.e., the auxiliary drive roller 340A) among the tensioning members is maximized, and the winding angle θd on the member that performs auxiliary driving is increased.

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

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

[0095] <Sixth Embodiment> The sixth embodiment will be described using Figures 11 to 14. This embodiment relates to the arrangement of the oil application roll 361 described in the fifth embodiment. Figure 11 and Figure 12, which shows another first example of this embodiment, are the same as the second embodiment except that the oil application roll 361 is present. Figure 13, which shows another second example of this embodiment, is the same as the first embodiment except that the oil application roll 361 is present. Figure 14, which shows another third example of this embodiment, is the same as the fourth embodiment except that the oil application roll 361 is present. Therefore, in each figure, the same reference numerals are used to indicate overlapping components, and their description and illustration are omitted or simplified. The following description will focus on the differences from the first, third to fifth embodiments.

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

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

[0098] The oil application roll 361 consists of a shaft 361a and a lubricant-retaining layer 361b. Examples of materials that make up the shaft 361a include aluminum, iron, stainless steel, and brass. The lubricant-retaining layer 361b is a layer that impregnates 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 mentioned above, porous materials and fibrous materials are used as the material. The amount of lubricant to be impregnated is 3.6 g in this embodiment.

[0099] If the contact force (or contact pressure) between the oil application roll 361 and the inner surface of the fixing belt 310 is not stable, there is a risk of excessive or insufficient lubricant application. For example, if too much lubricant is applied, the lubricant on the oil application roll 361 will be depleted prematurely. Conversely, if too little lubricant is applied, the sliding properties between the inner surface of the fixing belt 310 and the contacting member will decrease.

[0100] One factor causing fluctuations in the contact force of the oil application roll 361 against the fixing belt 310 is that vibrations generated during the rotation of the fixing belt 310 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 against the fixing belt 310 is set to 2N to 3.2N, corresponding to a lubricant application amount of 0.7g to 1.2g per 100 hours (100h). In the fixing device 8 of this embodiment, the target value of the contact force is set to 2.6N.

[0101] Specifically, in the case of the fixing device 8E shown in Figure 11, the oil application roll 361 is positioned upstream of the auxiliary drive roller 340 and downstream of the fixing pad 320 with respect to the rotational direction of the fixing belt 310. Here, the heating unit 300E of the fixing device 8E designates the areas stretched over each tensioning member of the fixing belt 310 as sections 310a, 310b, and 310c. Section 310a is between the tensioning roller 351 and the fixing pad 320, section 310b is between the fixing pad 320 and the auxiliary drive roller 340, and section 310c is between the auxiliary drive roller 340 and the tensioning roller 351. When comparing the belt lengths of section 310a and section 310b, section 310b is shorter.

[0102] 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 area where the fixing belt 310 is stretched by 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 that is pulled by the auxiliary drive roller 340, thus suppressing fluctuations in the contact force.

[0103] Next, in the case of the fixing device 8F shown in Figure 12, another first example, the oil application roll 361 is positioned upstream of the fixing pad 320 and downstream of the tension roller 351 with respect to the rotational direction of the fixing belt 310. Sections 310a to 310c in the heating unit 300F of the fixing device 8F are the same as in Figure 11.

[0104] In this embodiment, the oil application roll 361 is brought into contact with the inner circumferential surface of the fixing belt 310 in section 310a, which is the area where the fixing belt 310 is stretched by 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 that is pulled by the pressure roller 330, thus suppressing fluctuations in the contact force.

[0105] Next, in the case of the heating unit 300G of the fixing device 8G shown in Figure 13, which is another second example, the positions of the auxiliary drive roller 340 and the tension roller 351 are swapped compared to the configurations in Figures 11 and 12. For this reason, the oil application roll 361 is positioned upstream of the auxiliary drive roller 340 and downstream of the tension roller 351 with respect to the rotational direction of the fixing belt 310. The heating unit 300G defines the areas stretched on each tension member of the fixing belt 310 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 embodiment, the oil application roll 361 is brought into contact with the inner circumferential surface of the anchoring belt 310 in section 310f, which is the area where the anchoring belt 310 is stretched by 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 anchoring belt 310 that is pulled by the auxiliary drive roller 340, thus suppressing fluctuations in the contact force. In the configurations shown in Figures 11 to 13, the tension roller 351 can be replaced with a tensioning member that stretches the anchoring belt 310, such as a steering roller 350, and the result will be the same.

[0107] Furthermore, in the case of the fixing device 8H shown in Figure 14, which is another third example, the oil application roll 361 is positioned upstream of the auxiliary drive roller 340 and downstream of the fixing roller 395 with respect to the rotational direction of the fixing belt 310. The heating unit 300H of the fixing device 8H designates the areas stretched over each tensioning member of the fixing belt 310 as sections 310g and 310h. Section 310g is the area downstream of the auxiliary drive roller 340 and upstream of the fixing roller 395 with respect to the rotational direction of the fixing belt 310, and section 310h is the area downstream of the fixing roller 395 and upstream of the auxiliary drive roller 340.

[0108] In this embodiment, the oil application roll 361 is brought into contact with the inner circumferential surface of the fixing belt 310 in the section 310h, which is upstream of the auxiliary drive roller 340 and is the area 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 that is pulled by the auxiliary drive roller 340, thus suppressing fluctuations in the contact force.

[0109] In either configuration, fluctuations in the contact force of the oil application roll 361 with respect to the fixing belt 310 are suppressed, thereby stabilizing the amount of lubricant applied to the fixing belt 310 by the oil application roll 361.

[0110] <Seventh Embodiment> A seventh embodiment will be described with reference to Figure 15. This embodiment concerns the arrangement of the refresh roller 390 as a sliding member that slides against the fixing belt. It is the same as the second embodiment except for the presence of the refresh roller 390.

[0111] [Refresh Roller] In the case of the heating unit 300I that constitutes the fixing device 8I of this embodiment, in order to stably maintain the outer surface of the fixing belt 310 in a desired state, there is a refresh roller 390 which is a rotating body that contacts the outer surface (outer surface) of the fixing belt 310 and rotates when a driving force is applied to it without going through the fixing belt 310. In this embodiment, the refresh roller 390 is driven by the motor M1 that drives the auxiliary drive 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 wide variety of recording materials such as paper are continuously passed through the nip portion N, the surface of the fixing belt 310 becomes uneven in roughness. If a fixing operation is performed in this state, when the recording material carrying the toner image passes through the nip portion N, the surface state of the fixing belt 310 is transferred to the toner image, so that a desired glossiness cannot be obtained in the toner image (output image) after fixing, and there is a risk that gloss unevenness will occur. Accordingly, the refresh roller 390 is periodically brought into contact with the outer peripheral surface of the fixing belt 310 to polish the surface, and the surface property of the fixing belt 310 is adjusted, whereby gloss unevenness in the output image can be made less noticeable.

[0113] As the refresh roller 390, a stainless steel roller having an outer diameter of 12 mm with an aluminum oxide-based abrasive grain material adhered to its surface was used. The refresh roller may be a roller to which silicon oxide, titanium oxide, iron oxide, chromium oxide or the like is adhered, or a stainless steel roller whose surface is blasted to form irregularities. The surface roughness of the refresh roller 390 is preferably an arithmetic average roughness Ra of about 0.1 to 0.2 μm. If the surface is rougher than this, the surface of the fixing belt 310 will be deeply scratched, affecting the output image.

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

[0115] The pressurizing mechanism that pressurizes the refresh roller 390 controls the contact and separation from the surface of the fixing belt 310 by a pressurizing spring and cam (not shown). The refresh roller 390 is rotatably fixed to the pressurizing mechanism at one end and the other end in the width direction of the fixing belt 310. In this embodiment, the pressure applied to press the refresh roller 390 against the fixing belt 310 is set to a total pressure of approximately 40 N.

[0116] The refresh roller 390, which can contact and separate from the outer surface of the fixing belt 310, is normally in a separated position. The refresh roller 390 is controlled to press against the fixing belt 310 when necessary, such as each time a predetermined number of recording materials pass through the nip section N, thereby performing a sliding motion on the surface of the fixing belt 310.

[0117] In this embodiment, in order to create the aforementioned peripheral speed difference, the refresh roller 390 is independently driven and controlled by a motor (for example, motor M1) separate from the motor M0 that drives the pressure roller 330. Alternatively, as another driving method for the refresh roller 390, the motor M1 may be gear-coupled to the pressure roller 330 with a peripheral speed ratio, and the rotational speed of the refresh roller 390 may be switched by a clutch. In the image forming apparatus of this embodiment, the peripheral speed of the refresh roller 390 is set to 100 mm / sec in order to effectively roughen the surface of the fixing belt 310.

[0118] Furthermore, in this embodiment, the refresh roller 390 is positioned opposite the auxiliary drive roller 340, with the fixing belt 310 in between. In other words, the refresh roller 390 is in contact with the outer circumferential surface of the fixing belt 310 stretched over the auxiliary drive roller 340.

[0119] To put it another way, it is as follows: First, in the fixing belt 310, the exit point in the conveying direction of the nip portion N of the fixing belt 310 is defined as the upstream of the belt, and the inlet point in the conveying direction of the nip portion N is defined as the downstream of the belt. When multiple members are in contact with the fixing belt 310, the upstream and downstream positions are defined with respect to the point where contact with the fixing belt 310 begins. For example, in this embodiment, the point where the auxiliary drive roller 340 contacts the fixing belt 310 is upstream of the point where it contacts the refresh roller 390. Therefore, the refresh roller 390 is located downstream of the point upstream where the auxiliary drive roller 340 begins to contact the fixing belt 310.

[0120] [Conformability of the fixing belt's fixing pad to curved shapes] As shown in Figure 3, in the configuration of this embodiment, the angle θ between the nip surface and the trajectory of the fixing belt 310 from the nip section N to the tension roller 351 is set to 52°. Here, if the rigidity of the fixing belt 310 is small and the tension on the fixing belt 310 is sufficiently large, the trajectory of the fixing belt 310 at the exit of the nip section N (downstream side of the nip section N in the recording material transport direction) will be as shown by the solid line in Figure 3. However, due to the rigidity of the fixing belt 310 and the force that the fixing belt 310 receives at the nip section N, the trajectory of the fixing belt 310 at the exit of the nip section N during image formation may bulge as shown by the dotted line in Figure 3.

[0121] In other words, the fixing belt 310 receives rotational driving force from the pressure roller 330. Therefore, if the auxiliary drive roller 340 described above is a roller that does not provide driving force to the fixing belt 310, there is a risk that the fixing belt 310 will bend at the exit of the nip section 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 surface portion 320b at the downstream end of the fixing pad 320 will decrease, and the fixing belt will not bend sufficiently at the exit of the nip section N, causing the track to bulge as shown by the dashed line in Figure 3. In other words, the behavior of the fixing belt 310 becomes unstable.

[0122] If the trajectory of the fixing belt 310 bulges at the exit of the nip section N in this way, the separation of the recording material from the fixing belt 310 will decrease. In addition, there is a possibility that the fixing belt 310 may come into contact with the separating member 401 (Figure 2) which is positioned 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 may be damaged, which may reduce the image quality of the toner image fixed by the fixing device 8.

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

[0124] In this embodiment, as described above, an auxiliary drive roller 340 is provided, which is positioned inside the fixing belt 310 and applies 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, tension is generated downstream in the conveying direction of the nip portion N of the fixing belt 310, making it easier for the fixing belt 310 to follow the fixing pad 320.

[0125] Similarly, when the refresh roller 390 is brought into contact with the fixing belt 310, the fixing belt 310 receives a driving force from the refresh roller 390. Therefore, when the refresh roller 390 is brought into contact with the fixing belt 310, the belt tracking performance changes. Here, if the refresh roller 390 is brought into contact with the fixing belt 310, for example, upstream of the auxiliary drive roller 340 and downstream of the fixing pad 320, the influence of the refresh roller 390 on the belt tracking performance becomes greater than that of the auxiliary drive roller 340. In particular, if the refresh roller 390 is brought into contact with the fixing pad 320 and the peripheral speed of the refresh roller 390 is slower than the peripheral speed of the fixing belt 310, the belt tracking performance decreases.

[0126] Therefore, in this embodiment, the refresh roller 390 is positioned opposite the auxiliary drive roller 340, with the fixing belt 310 in between. As a result, the auxiliary drive roller 340 has a greater influence on belt tracking performance than the refresh roller 390, and a decrease in belt tracking performance can be suppressed. In other words, it is possible to suppress the fixing belt 310 from not curving sufficiently at the exit of the nip section N, and the trajectory from bulging as shown by the dashed line in Figure 3. That is, in a configuration having a refresh roller 390 to which driving force is applied separately from the auxiliary drive roller 340, the behavior of the fixing belt 310 can be stabilized.

[0127] <Eighth Embodiment> The eighth embodiment will be described with reference to Figure 16. In this embodiment, the position of the refresh roller 390 differs from that of the seventh embodiment described above. The other configurations and operations are the same as those of the seventh embodiment described above, so the same reference numerals are used for similar configurations, and their description and illustration are omitted or simplified. The following description will focus on the differences from the seventh embodiment.

[0128] In the case of the heating unit 300J that constitutes the fixing device 8J of this embodiment, the refresh roller 390 is positioned downstream of the auxiliary drive roller 340 and upstream of the fixing pad 320 with respect to the rotational direction of the fixing belt 310. In particular, in this embodiment, the refresh roller 390 is positioned downstream of the auxiliary drive roller 340 and upstream of the steering roller 350 with respect to the rotational direction of the fixing belt 310. That is, the position where the refresh roller 390 contacts the outer circumferential surface of the fixing belt 310 is between the auxiliary drive roller 340 and the steering roller 350.

[0129] Furthermore, a backup member 391 is positioned on the inner circumferential surface of the fixing belt 310 at a location facing the refresh roller 390 across the fixing belt 310. With respect to the width direction of the fixing belt 310, one end and the other end of the backup member 391 are fixed to the corresponding fixing frame 380, respectively. The outer circumferential surface of the backup member 391 is formed to conform to the inner circumferential surface of the fixing belt 310 in its free state. In addition, a 2 mm thick silicone rubber is placed on the surface of the backup member 391 as an elastic layer so as to be in contact with the inner circumferential surface of the fixing belt 310.

[0130] In this embodiment, the refresh roller 390 is positioned downstream of the auxiliary drive roller 340. Therefore, similar to the first embodiment, the auxiliary drive roller 340 has a greater impact on belt tracking performance than the refresh roller 390, thus suppressing a decrease in belt tracking performance.

[0131] Alternatively, the refresh roller 390 may be positioned between the steering roller 350 and the fixing pad 320. In this case as well, a backup member 391 is provided at a position opposite the refresh roller 390, with the fixing belt 310 in between. Alternatively, the refresh roller 390 may be positioned opposite the steering roller 350, with the fixing belt 310 in between. In this case, the refresh roller 390 may be configured to swing in conjunction with the steering roller 350. However, when the refresh roller 390 is provided at this position, it is preferable that the opposing tension roller does not swing.

[0132] Furthermore, including in the first embodiment, when the refresh roller 390 faces the tension roller that tensions the fixing belt 310, the refresh roller 390 is backed up by the tension roller, so the backup member 391 described above can be omitted.

[0133] [Comparative Example] Next, comparative examples that are comparable to each of the above embodiments will be described using Figure 17. Figure 17 shows the comparative examples. The basic configuration of the comparative examples is set to be the same as that of the seventh embodiment. The heating unit 300K that constitutes the fixing device 8K of the comparative examples differs from that of the seventh embodiment in the position of the refresh roller 390. The position of the refresh roller 390 in the comparative examples is downstream of the fixing pad 320 and upstream of the auxiliary drive roller 340 with respect to the rotation direction of the fixing belt 310. Also, similar to the eighth embodiment, a backup member 391 is placed opposite the refresh roller 390 and the fixing belt 310, with the refresh roller 390 in between.

[0134] [Effect confirmation] Next, the effects of the embodiments will be explained by comparing the above-described Comparative Examples 1 and 2 with the above-described Seventh and Eighth embodiments. The configuration of the Seventh embodiment will be referred to as Example 7, and the configuration of the Eighth embodiment will be referred to as Example 8. When the refresh roller 390 is placed between the fixing pad 320 and the auxiliary drive roller 340 (Comparative Example), it was found that the belt following performance is hindered by the refresh roller 390. The reason for this is that, as a result of the refresh roller 390 and the backup member 391 being positioned to sandwich the fixing belt 310, the effect of the auxiliary drive roller 340 pulling the belt surface does not easily reach the nip portion N.

[0135] In contrast, in Examples 7 and 8, the refresh roller 390 can be positioned opposite the auxiliary drive roller 340 and the fixing belt 310, or downstream of the auxiliary drive roller 340, thereby ensuring belt tracking performance.

[0136] <Other Embodiments> In the embodiments described above, a configuration was described in which 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 heating element 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] Furthermore, in the embodiments described above, a configuration using a pressure roller as the driving rotating body was explained. However, the driving rotating body may also be an endless belt that is stretched by a plurality of tension rollers and driven by any of the tension rollers. Also, in the embodiments described above, the pressure roller as the driving rotating body is pressed against the belt in order to form the nip portion, but the belt may be pressed against the driving rotating body instead. [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 (coating member) / 390... Refresh roller (rubbing member) / 400... Separation member

Claims

1. A fixing device for fixing a toner image formed on a recording material to the recording material, A rotatable fixing belt for contacting and fixing a toner image formed on a recording material to the recording material, A pad positioned inside the aforementioned fixing belt, A rotatable pressurizing member that presses the pad via the fixing belt and forms a nip portion for gripping and transporting the recording material, An auxiliary drive roller is provided downstream of the nip portion in the rotational direction of the fixing belt, stretches the inner surface of the fixing belt, and applies driving force to the fixing belt. A drive source that applies a driving force to the pressurizing member to rotate the fixing belt, A transmission mechanism that transmits driving force from the drive source to the auxiliary drive roller, and makes the peripheral speed of the auxiliary drive roller faster than the peripheral speed of the pressurizing member and the peripheral speed of the fixing belt, An applicator member is positioned inside the fixing belt and applies oil to the fixing belt, The system includes a separating member that is positioned with a gap between it and the outer surface of the fixing belt, and separates the recording material that has passed through the nip portion from the fixing belt, The coating member is positioned downstream of the auxiliary drive roller and upstream of the nip portion in the rotational direction of the fixing belt. The fixing device is characterized in that the separating 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 circumferential surface of the fixing belt that is stretched between the auxiliary drive roller and the pad.

2. The fixing device according to 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 pressurizing member.

3. The fixing device according to claim 1 or 2, characterized in that 1.04 ≤ peripheral speed of the auxiliary drive roller / peripheral speed of the pressurizing member ≤ 1.

20.

4. The fixing device according to any one of claims 1 to 3, characterized in that it has a heating source for heating the fixing belt inside the auxiliary drive roller.

5. The fixing device according to any one of claims 1 to 4, characterized in that the auxiliary drive roller is made of aluminum and its surface is anodized.

6. A fixing device for fixing a toner image formed on a recording material to a recording material, A rotatable fixing belt for contacting and fixing a toner image formed on a recording material to the recording material, A pad positioned inside the aforementioned fixing belt, A rotatable pressurizing member that presses the pad via the fixing belt and forms a nip portion for gripping and transporting the recording material, An auxiliary drive roller is provided downstream of the nip portion in the rotational direction of the fixing belt, stretches the inner surface of the fixing belt, and applies driving force to the fixing belt. A drive source that applies a driving force to the pressurizing member to rotate the fixing belt, A transmission mechanism that transmits driving force from the drive source to the auxiliary drive roller, and makes the peripheral speed of the auxiliary drive roller faster than the peripheral speed of the pressurizing member and the peripheral speed of the fixing belt, An applicator member is positioned inside the fixing belt and applies oil to the fixing belt, The system further includes a steering roller that is positioned downstream of the auxiliary drive roller and upstream of the pad in the rotational direction of the fixing belt, so as to stretch the inner surface of the fixing belt, and which can be inclined with respect to the width direction of the fixing belt so that the fixing belt is located within a predetermined range in the width direction of the fixing belt, The coating member is positioned downstream of the auxiliary drive roller and upstream of the nip portion in the rotational direction of the fixing belt. A fixing device characterized in that the amount of the fixing belt wrapped around the auxiliary drive roller is greater than the amount of the fixing belt wrapped around the steering roller.

7. The fixing device according to any one of claims 1 to 6, characterized in that the coating member is an oil coating roller.

8. The fixing device according to any one of claims 1 to 7, characterized in that the auxiliary drive roller performs a sliding rotation relative to the fixing belt.

9. The fixing device according to any one of claims 1 to 8, characterized in that it has a sliding member that contacts the outer surface of the fixing belt and slides against the fixing belt.

10. The fixing device according to claim 9, characterized in that the friction member presses the fixing belt toward the auxiliary drive roller.

Images