Belt driving device, heating device, fixing device and image forming apparatus

Abstract

To effectively prevent acceleration of wear of a belt.SOLUTION: A belt driving device comprises: an endless belt 21 that has flexibility; a slide member 23 that is arranged to slide with an inner peripheral surface of the belt 21; an opposing member 22 that is in contact with the slide member 23 with the belt 21 therebetween to form a nip part N with the belt 21; and a lubricant that is interposed between the inner peripheral surface of the belt 21 and the slide member 23. The belt 21 is rotatable in the opposite direction D2 to a rotation direction when a sheet is passed through the nip part N. The slide member 23 is movable in a belt surface movement direction at the nip part N in association with the rotation in the opposite direction D2 of the belt 21. The rotation in the opposite direction D2 of the belt 21 is performed within a range equal to or more than the distance of movement of the slide member 23 in association with the rotation in the opposite direction D2 and equal to or less than five rotations.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a belt driving device, a heating device, a fixing device, and an image forming apparatus. [Background technology]

[0002] 2. Description of the Related Art As an example of a belt driving device mounted in an image forming apparatus such as a copying machine or a printer, a fixing device equipped with an endless belt is known.

[0003] In such a fixing device, when the belt rotates, it slides against a sliding member such as a heater disposed inside the belt, generating sliding resistance (friction) between the belt and the sliding member. The sliding resistance generated between the belt and the sliding member accelerates belt wear. Therefore, as a measure to reduce sliding resistance, it is common practice to apply a lubricant such as grease or oil to the inner peripheral surface of the belt.

[0004] However, the amount of lubricant between the belt and the sliding member tends to decrease over time, and as the amount of lubricant decreases, a satisfactory sliding resistance reduction effect cannot be achieved. To address this problem, Patent Document 1 (JP 2018-194696 A) proposes a configuration in which a lubricant reservoir is formed between a plate-shaped member provided on the inside of the belt and the inner peripheral surface of the belt to prevent belt wear due to a lack of lubricant over a long period of time. Patent Document 1 also proposes a method of rotating the belt in the opposite direction from its normal rotation direction (during the fixing process) to return the lubricant that accumulates under the belt due to the influence of gravity to the lubricant reservoir. Summary of the Invention [Problem to be solved by the invention]

[0005] It has been discovered that the following phenomenon occurs when a belt is rotated in the opposite direction from its normal rotation direction. As shown in FIG. 23, the surface of a belt 600 typically has numerous microprotrusions 601, which constitute the surface roughness of the belt 600. Therefore, when the belt 600 rotates in one direction as indicated by the arrow in FIG. 23, the microprotrusions 601 wear away due to sliding against the sliding member 700, and the tips of the microprotrusions 601 are formed so as to face in the opposite direction to the rotation direction of the belt 600 (the direction of movement of the belt surface). Then, as shown in FIG. 24, when the belt 600 rotates in the opposite direction, the tips of the microprotrusions 601 on the belt surface bend in the opposite direction due to the sliding resistance with the sliding member 700. This phenomenon becomes more pronounced as the belt rotates in the opposite direction. Therefore, as the belt rotates in the opposite direction for a longer distance, the tips of the microprotrusions may bend in the opposite direction and chip, accelerating belt wear.

[0006] The above-mentioned Patent Document 1 proposes a method of rotating the belt in the opposite direction to return the accumulated lubricant to the lubricant reservoir, but does not consider at all the adverse effects of rotating the belt in the opposite direction. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention provides a belt drive device including: a flexible endless belt; a sliding member arranged to slide on the inner circumferential surface of the belt; an opposing member that contacts the sliding member via the belt and forms a nip portion between the belt and the opposing member; and a lubricant interposed between the inner circumferential surface of the belt and the sliding member, wherein the belt is rotatable in a direction opposite to a rotation direction when a sheet is passed through the nip portion, and the sliding member is configured to be movable in a belt surface movement direction in the nip portion as the belt rotates in the opposite direction, When the temperature of the belt is 100°C or less, or when one minute or more has passed since the heating of the belt was stopped and the belt was left in a non-heated state, The rotation of the belt in the opposite direction is performed within a range of not less than the movement distance of the sliding member accompanying the rotation in the opposite direction but not more than five rotations. [Effects of the Invention]

[0008] According to the present invention, the acceleration of belt wear can be effectively suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a schematic diagram illustrating the configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a fixing device according to the present embodiment. [Figure 3] FIG. 2 is a cross-sectional view of the fixing belt according to the embodiment. [Figure 4] FIG. 2 is a plan view of the heater according to the embodiment. [Figure 5] FIG. 10 is a diagram illustrating a state in which the fixing belt is rotated in a normal rotation direction. [Figure 6] FIG. 10 is a diagram showing a state in which the fixing belt is rotated in the opposite direction. [Figure 7] 10 is a diagram showing the results of examining the relationship between the reverse rotation speed and rotation torque when the fixing belt is rotated in the reverse direction. [Figure 8] 10A and 10B are diagrams illustrating an example in which the reverse rotation operation of the fixing belt is controlled based on the rotation torque. [Figure 9] 10A and 10B are diagrams illustrating an example in which the reverse rotation operation of the fixing belt is controlled based on any one of the number of sheets of paper passed, the rotation distance, and the elapsed time. [Figure 10] FIG. 2 is a cross-sectional view of a fixing belt that does not have an elastic layer. [Figure 11] FIG. 10 is a diagram showing an example in which resistance heating elements are arranged continuously in the longitudinal direction of the heater. [Figure 12] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 13] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 14] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 15] FIG. 10 is a diagram showing a configuration of a fixing device different from that of the above embodiment. [Figure 16]FIG. 10 is a diagram showing a configuration of an image forming apparatus different from that of the above embodiment. [Figure 17] 17 is a diagram showing the configuration of the fixing device shown in FIG. 16. FIG. [Figure 18] FIG. 18 is a plan view of the heater shown in FIG. 17. [Figure 19] FIG. 18 is a perspective view of the heater and heater holder shown in FIG. 17. [Figure 20] 18A and 18B are diagrams showing a method of attaching a connector to the heater shown in FIG. 17. [Figure 21] 17 is a diagram showing the arrangement of temperature sensors and thermostats included in the fixing device shown in FIG. 16. FIG. [Figure 22] 21 is a view showing a groove portion of the flange shown in FIG. 20. FIG. [Figure 23] 10A and 10B are diagrams showing the state of minute protrusions on the belt surface when the belt is rotated in the normal rotation direction. [Figure 24] FIG. 10 is a diagram showing the state of minute protrusions on the belt surface when the belt is rotated in the opposite direction. DETAILED DESCRIPTION OF THE INVENTION

[0010] The present invention will be described below with reference to the accompanying drawings. In each drawing for explaining the present invention, components such as members and components having the same function or shape are designated by the same reference numerals as far as they can be distinguished, and descriptions thereof will be omitted once they have been described.

[0011] FIG. 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. In this specification, the term "image forming apparatus" includes a printer, a copier, a facsimile, a printing machine, or a multifunction machine that combines two or more of these. Furthermore, the term "image formation" used in the following description refers not only to the formation of meaningful images such as characters and figures, but also to the formation of meaningless images such as patterns. First, the overall configuration and operation of the image forming apparatus according to this embodiment will be described with reference to FIG. 1.

[0012] As shown in FIG. 1, the image forming apparatus 100 according to this embodiment includes an image forming unit 200 that forms an image on a sheet-like recording medium such as paper, a fixing unit 300 that fixes the image on the recording medium, a recording medium supply unit 400 that supplies the recording medium to the image forming unit 200, and a recording medium discharge unit 500 that discharges the recording medium outside the apparatus.

[0013] The image forming section 200 is provided with four process units 1Y, 1M, 1C, and 1Bk as image-forming units, an exposure device 6 that forms an electrostatic latent image on the photosensitive member 2 provided in each of the process units 1Y, 1M, 1C, and 1Bk, and a transfer device 8 that transfers the image onto a recording medium.

[0014] Each of the process units 1Y, 1M, 1C, and 1Bk has basically the same configuration, except that it contains toner (developer) of a different color: yellow, magenta, cyan, or black, which corresponds to the color separation components of a color image. Specifically, each of the process units 1Y, 1M, 1C, and 1Bk includes a photoconductor 2 as an image carrier that carries an image on its surface, a charging member 3 that charges the surface of the photoconductor 2, a developing device 4 that supplies toner as developer to the surface of the photoconductor 2 to form a toner image, and a cleaning member 5 that cleans the surface of the photoconductor 2.

[0015] The transfer device 8 includes an intermediate transfer belt 11, a primary transfer roller 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is an endless belt member that is stretched by a plurality of support rollers. Four primary transfer rollers 12 are provided inside the intermediate transfer belt 11. Each primary transfer roller 12 contacts each photoconductor 2 via the intermediate transfer belt 11, thereby forming a primary transfer nip between the intermediate transfer belt 11 and each photoconductor 2. The secondary transfer roller 13 contacts the outer peripheral surface of the intermediate transfer belt 11, thereby forming a secondary transfer nip.

[0016] The fixing section 300 is provided with a fixing device 20. The fixing device 20 includes a fixing belt 21 made of an endless belt, and a pressure roller 22 as an opposing member facing the fixing belt 21. The fixing belt 21 and the pressure roller 22 come into contact with each other on their outer circumferential surfaces to form a nip portion (fixing nip).

[0017] The recording medium supply unit 400 is provided with a paper feed cassette 14 that stores paper P as a recording medium, and a paper feed roller 15 that feeds paper P from the paper feed cassette 14. Hereinafter, the "recording medium" will be described as "paper," but the "recording medium" is not limited to paper (paper). The "recording medium" includes not only paper (paper), but also transparencies, fabrics, metal sheets, plastic films, and prepreg sheets made of carbon fiber pre-impregnated with resin. Furthermore, "paper" includes not only plain paper, but also cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

[0018] The recording medium ejection section 500 is provided with a pair of ejection rollers 17 for ejecting the paper P outside the image forming apparatus, and an ejection tray 18 on which the paper P ejected by the ejection rollers 17 is placed.

[0019] Next, the printing operation of the image forming apparatus 100 according to this embodiment will be described with reference to FIG.

[0020] When a printing operation is started in the image forming apparatus 100, the photosensitive elements 2 of the process units 1Y, 1M, 1C, and 1Bk and the intermediate transfer belt 11 of the transfer device 8 start to rotate. Also, the paper feed roller 15 starts to rotate, and a sheet of paper P is fed out of the paper feed cassette 14. The fed sheet of paper P comes into contact with a pair of timing rollers 16 and stops, and the transport of the sheet of paper P is temporarily stopped until an image to be transferred onto the sheet of paper P is formed.

[0021] In each process unit 1Y, 1M, 1C, and 1Bk, the surface of the photoconductor 2 is first charged to a uniform high potential by the charging member 3. Next, the exposure device 6 exposes the surface (charged surface) of each photoconductor 2 based on the image information of the original document read by the document reader or the print image information instructed to be printed from a terminal. This reduces the potential of the exposed area, forming an electrostatic latent image on the surface of each photoconductor 2. The developing device 4 then supplies toner to this electrostatic latent image, forming a toner image on each photoconductor 2. As each photoconductor 2 rotates, the toner image formed on each photoconductor 2 reaches the primary transfer nip (the position of the primary transfer roller 12), where it is transferred sequentially onto the rotating intermediate transfer belt 11 so as to overlap one another. In this way, a full-color toner image is formed on the intermediate transfer belt 11. In the image forming apparatus 100, it is possible to form a monochrome image using any one of the process units 1Y, 1M, 1C, and 1Bk, or to form a two-color or three-color image using any two or three of the process units. After the toner image is transferred from the photoreceptor 2 to the intermediate transfer belt 11, the cleaning member 5 removes residual toner and the like from each photoreceptor 2.

[0022] The toner image transferred onto intermediate transfer belt 11 is transported to the secondary transfer nip (position of secondary transfer roller 13) as intermediate transfer belt 11 rotates, and is transferred onto the transported paper P by timing roller 16. Thereafter, paper P is transported to fixing device 20, where the toner image on paper P is heated and pressed by fixing belt 21 and pressure roller 22, thereby fixing the toner image to paper P. Paper P is then transported to recording medium discharge section 500, and is discharged onto paper discharge tray 18 by paper discharge roller 17. This completes the series of printing operations.

[0023] Next, the configuration of the fixing device according to this embodiment will be described in detail with reference to FIG.

[0024] As shown in FIG. 2, the fixing device 20 according to this embodiment includes a fixing belt 21, a pressure roller 22, a heater 23, a heater holder 24, a stay 25, a guide member 26, a temperature sensor 27, and the like.

[0025] The fixing belt 21 is a rotating body (fixing member) that comes into contact with the unfixed toner carrying surface of the paper P to fix the unfixed toner (unfixed image) to the paper P, and is made of a flexible endless belt. The diameter of the fixing belt 21 is set to, for example, 15 to 120 mm. In this embodiment, the inner diameter of the fixing belt 21 is set to 25 mm.

[0026] As shown in FIG. 3, the fixing belt 21 is, for example, formed by laminating a substrate 210, an elastic layer 211, and a release layer 212 in this order from the inner circumferential surface to the outer circumferential surface, with the total thickness set to 1 mm or less. The substrate 210 has a thickness of 30 to 50 μm and is made of a metal material such as nickel or stainless steel, or a resin material such as polyimide. The elastic layer 211 has a thickness of 100 to 300 μm and is made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber. The fixing belt 21 includes the elastic layer 211, which prevents minute irregularities from forming on the surface of the fixing belt 21 at the nip portion, thereby facilitating uniform heat transfer to the toner image on the paper P. The release layer 212 has a thickness of 10 to 50 μm and is made of a material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyether sulfide). The fixing belt 21 has the release layer 212, so that the release properties (peelability) of the toner (toner image) are ensured.

[0027] 2, pressure roller 22 is an opposing member disposed opposite the outer circumferential surface of fixing belt 21. Pressure roller 22 contacts heater 23 via fixing belt 21, forming a nip N between pressure roller 22 and fixing belt 21.

[0028] Pressure roller 22 is a roller with an outer diameter set to, for example, 25 mm, and includes a hollow iron core 220, an elastic layer 221 provided on the outer peripheral surface of core 220, and a release layer 222 provided on the outer peripheral surface of elastic layer 221. Elastic layer 221 has a thickness of, for example, 3.5 mm and is made of silicone rubber or the like. Release layer 222 has a thickness of, for example, about 40 μm and is made of fluororesin or the like.

[0029] The heater 23 is a planar or plate-shaped heat source that heats the inside of the fixing belt 21. The heater 23 extends longitudinally across the length of the fixing belt 21 (the paper width direction that intersects with the paper conveyance direction) and is disposed so as to contact the inner circumferential surface of the fixing belt 21.

[0030] As shown in FIG. 4 , the heater 23 according to this embodiment includes a plate-shaped substrate 55, multiple resistance heating elements 56 provided on the substrate 55, and an insulating layer 57 covering each of the resistance heating elements 56. The multiple resistance heating elements 56 are spaced apart from one another along the longitudinal direction of the substrate 55 (heater 63). The gap between adjacent resistance heating elements 56 is preferably 0.2 mm or more, more preferably 0.4 mm or more, from the viewpoint of ensuring insulation between the resistance heating elements 56. Furthermore, if the gap between adjacent resistance heating elements 56 is too large, a temperature drop is likely to occur in the gap. Therefore, from the viewpoint of suppressing temperature unevenness along the longitudinal direction, the gap is preferably 5 mm or less, more preferably 1 mm or less. Note that multiple resistance heating elements 56 may be arranged along the short side (the direction perpendicular to the longitudinal direction) of the surface of the substrate 55 on which the resistance heating elements 56 are arranged.

[0031] As shown in FIG. 4 , a plurality of electrode portions 58 and a plurality of power supply lines 59 are provided on the surface of the substrate 55 on which each resistance heating element 56 is provided. Each resistance heating element 56 is connected in parallel via the power supply lines 59 to each electrode portion 58 provided at both longitudinal ends of the substrate 55. Each resistance heating element 56 and each power supply line 59 are covered with an insulating layer 57 to ensure insulation. On the other hand, each electrode portion 58 is not covered by the insulating layer 57 but is exposed so that a connector serving as a power supply terminal can be connected. Connecting the connector to each electrode portion 58 enables power to be supplied from a power source to each resistance heating element 56. In this state, power is supplied to each resistance heating element 56, causing each resistance heating element 56 to generate heat.

[0032] The substrate 55 is made of a material with excellent heat resistance and insulation, such as ceramics such as alumina or aluminum nitride, glass, mica, or polyimide. Alternatively, the substrate 55 may be made of a metal (conductive material) such as stainless steel (SUS), iron, or aluminum, on which an insulating layer is formed. In particular, when the substrate 55 is made of a highly thermally conductive material such as aluminum, copper, silver, graphite, or graphene, the heater 23 can be uniformly heated, thereby improving image quality. The insulating layer 57 is made of a material with excellent heat resistance and insulation, such as ceramics such as alumina or aluminum nitride, glass, mica, or polyimide. The resistance heating element 56 is formed by, for example, applying a paste containing silver palladium (AgPd) and glass powder to the surface of the substrate 55 by screen printing or the like, and then firing the substrate 55. Alternatively, each resistance heating element 56 can be made of a resistive material such as silver alloy (AgPt) or ruthenium oxide (RuO). The electrode portion 58 and the power supply line 59 are formed by screen printing silver (Ag) or silver palladium (AgPd).

[0033] 2, in this embodiment, each resistance heating element 56 is provided on the surface of the base material 55 facing the pressure roller 22 (the nip portion N side), but each resistance heating element 56 may also be provided on the opposite surface. In this case, since the heat of each resistance heating element 56 is transferred to the fixing belt 21 via the base material 55, it is preferable that the base material 55 be made of a material with high thermal conductivity, such as aluminum nitride.

[0034] The heater holder 24 is disposed inside the fixing belt 21 and is a holding member that holds the heater 23. The heater holder 24 is preferably made of a heat-resistant material because it is prone to becoming hot due to the heat from the heater 23. For example, if the heater holder 24 is made of a heat-resistant resin with low thermal conductivity, such as LCP or PEEK, the heat resistance of the heater holder 24 is ensured while heat transfer from the heater 23 to the heater holder 24 is suppressed, allowing the fixing belt 21 to be heated efficiently.

[0035] The stay 25 is a support member that supports the heater holder 24. The stay 25 supports the surface of the heater holder 24 opposite to the surface on the pressure roller 22 side across the longitudinal direction of the fixing belt 21, thereby preventing the heater holder 24 from being deflected by the pressure force of the pressure roller 22 and forming a nip portion N of uniform width between the fixing belt 21 and the pressure roller 22. The stay 25 is preferably made of an iron-based metal material such as SUS or SECC to ensure its rigidity.

[0036] The guide member 26 is a member that guides the fixing belt 21 from the inside. The guide member 26 has an arc-shaped cross section that follows the inner circumferential surface of the fixing belt 21, and is disposed upstream and downstream of the heater 23 in the rotation direction (the direction of the arrow in FIG. 2) of the fixing belt 21. In this embodiment, the guide member 26 is configured integrally with the heater holder 24, but may be configured separately.

[0037] The temperature sensor 27 is a temperature detection member that detects the temperature of the heater 23. Known temperature sensors such as a thermopile, thermostat, thermistor, or NC sensor can be used as the temperature sensor 27. In this embodiment, a contact-type temperature sensor is used that detects the temperature by contacting the surface of the heater 63 opposite to the pressure roller 22 side. The temperature sensor 27 is not limited to a contact-type temperature sensor, and may be a non-contact-type temperature sensor that is disposed in a non-contact state with the heater 63 and detects the ambient temperature near the heater 63.

[0038] The fixing device 20 according to this embodiment operates as follows.

[0039] 2, when pressure roller 22 is driven to rotate, the driving force is transmitted to fixing belt 21, causing fixing belt 21 to rotate. Fixing belt 21 is then heated by heater 23. At this time, temperature sensor 27 detects the temperature of heater 23, and the amount of heat generated by heater 23 is controlled based on the detected temperature, thereby heating fixing belt 21 to a temperature at which an image can be fixed (fixing temperature), and maintaining that temperature state. When paper P carrying an unfixed image is transported between fixing belt 21 and pressure roller 22 (nip portion N), paper P is heated and pressed by fixing belt 21 and pressure roller 22, and the unfixed image is fixed to paper P.

[0040] In a configuration in which the heater 23 contacts the inner circumferential surface of the fixing belt 21, as in the present embodiment, when the fixing belt 21 rotates, the fixing belt 21 slides against the heater 23. For this reason, in the present embodiment, a lubricant such as grease or oil is provided between the inner circumferential surface of the fixing belt 21 and the surface of the heater 23 that contacts the inner circumferential surface of the fixing belt 21 (the surface on the pressure roller 22 side), thereby reducing the sliding resistance that occurs between the fixing belt 21 and the heater 23.

[0041] However, in general, the amount of lubricant between the fixing belt and the heater tends to decrease over time because the lubricant gradually volatilizes or flows out from between the fixing belt and the heater as the fixing belt rotates. When the amount of lubricant decreases, the sliding resistance reduction effect is no longer achieved, which raises concerns about an increase in the rotational torque of the fixing belt and the tendency for the fixing belt to wear out.

[0042] To address this issue, methods for maintaining the effectiveness of the lubricant over a long period of time include, for example, providing a plate-shaped member to form a lubricant reservoir on the inner surface of the belt, as proposed in the aforementioned Patent Document 1. However, this method requires the addition of additional components to the fixing belt, which increases costs and hinders device miniaturization. Another method would be to add a mechanism for replenishing the lubricant, but this would complicate the mechanism and increase costs. Therefore, it would be preferable to be able to maintain the effectiveness of the lubricant without adding a new mechanism or component.

[0043] Therefore, when a fixing device that had reached the end of its life was examined, it was found that there was unused lubricant remaining between the fixing belt and the heater. Specifically, as shown in FIG. 5, it was found that unused lubricant 50 remained upstream and downstream of a portion A where the heater 23 and the fixing belt 21 contact each other (hereinafter referred to as the "inner nip") in the sheet passing direction C (the sheet passing direction, or the belt surface movement direction at the nip) in which the paper passes through the nip N. That is, in this embodiment, the width Wa of the inner nip in the sheet passing direction C is smaller than the width Wb of the entire plane of the heater 23 on the pressure roller 22 side in the sheet passing direction C. Therefore, a gap S is generated between the heater 23 and the fixing belt 21 upstream and downstream of the inner nip A. Therefore, the lubricant 50 that has leaked out from the inner nip A accumulates in the gap S. Furthermore, as shown in Figure 5, in a configuration in which the heater 23 is housed in a recess 24a of the heater holder 24, and the upstream and downstream edges 241 of the recess 24a in the paper feed direction C protrude toward the pressure roller 22 beyond the surface of the heater 23 facing the pressure roller 22 in order to avoid contact of the fixing belt 21 with the edge of the heater 23, the above-mentioned gap S is particularly likely to occur due to the step between the surface of the heater 23 and the heater holder 24.

[0044] In this way, there is unused lubricant remaining in the gap between the fixing belt and the heater, and if this remaining lubricant can be effectively utilized, the effectiveness of the lubricant can be sustained.

[0045] It is known that the trajectory of the fixing belt when it rotates differs between the upstream side (hereinafter referred to as the "nip entrance side") and the downstream side (hereinafter referred to as the "nip exit side") of the nip portion in the paper feed direction. Specifically, as shown in FIG. 5 , when fixing belt 21 rotates, at nip entrance side E1 (upstream side in paper feed direction C), a force acts on fixing belt 21 to draw fixing belt 21 into nip portion N, causing fixing belt 21 to rotate along a trajectory that brings fixing belt 21 close to or into contact with the surfaces of heater 23 and heater holder 24. On the other hand, at nip exit side E2 (downstream side in paper feed direction C), fixing belt 21 rotates along a trajectory that moves away from the surfaces of heater 23 and heater holder 24 and bulges outward. Therefore, the lubricant 50 that accumulates in each gap S is formed following the trajectory of fixing belt 21 when it rotates. As long as fixing belt 21 rotates along a similar trajectory, lubricant 50 will not generally adhere to fixing belt 21.

[0046] However, if the trajectory of the fixing belt 21 could be changed, it would be possible to cause the accumulated lubricant 50 to adhere to the fixing belt 21. For this reason, in this embodiment of the present invention, the fixing belt 21 is rotated in the direction opposite to its normal rotation direction. That is, as shown in FIG. 6, the fixing belt 21 is rotated in a direction D2 opposite to the normal rotation direction (rotation direction D1 shown in FIG. 5) when passing a sheet through the nip N. When the fixing belt 21 is rotated in the opposite direction D2 in this way, the fixing belt 21 bulges outward on the nip entrance side E1, as opposed to the case shown in FIG. 5 above, and the fixing belt 21 approaches or comes into contact with the surfaces of the heater 23 and the heater holder 24 on the nip exit side E2.

[0047] Therefore, as shown in Figure 6, when the fixing belt 21 is rotated in the opposite direction D2, the fixing belt 21 approaches the surface of the heater 23, particularly at the nip exit side E2, so that the inner surface of the fixing belt 21 comes into contact with the lubricant 50 remaining at the nip exit side E2.

[0048] 6, in this embodiment, when the fixing belt 21 rotates in the opposite direction D2, the heater 23 moves toward the nip entrance side E1 (the direction in which the belt surface moves in the nip portion N) within the recessed portion 24a of the heater holder 24 due to friction between the heater 23 and the fixing belt 21. That is, in this embodiment, in order to avoid interference with the heater holder 24 due to thermal expansion of the heater 23, the width W1 of the recessed portion 24a in the paper passage direction C is formed larger than the width W2 of the heater 23 in the paper passage direction C, as shown in FIG. 6, and there is a backlash (gap) in the paper passage direction C between the heater 23 and the recessed portion 24a.

[0049] 5, heater 23 moves toward nip exit side E2 as fixing belt 21 rotates and hits side surface 24b of recessed portion 24a on nip exit side E2. In contrast, as shown in FIG. 6, when fixing belt 21 rotates in the opposite direction D2, heater 23 moves toward nip entrance side E1 as fixing belt 21 rotates in the opposite direction D2 and hits side surface 24c of recessed portion 24a on nip entrance side E1. At this time, lubricant 50 remaining on the surface of heater 23 moves as heater 23 moves, and lubricant 50 on nip exit side E2 in particular moves to a position where it is more likely to come into contact with the inner circumferential surface of fixing belt 21.

[0050] As described above, in this embodiment, by rotating the fixing belt 21 in the direction D2 opposite to the normal rotation direction, the rotational trajectory of the fixing belt 21 can be changed to a trajectory that makes it easier for the fixing belt 21 to come into contact with the lubricant 50 on the heater 23, and the position of the heater 23 can be changed to a position where the lubricant 50 can easily come into contact with the fixing belt 21. This allows the lubricant 50 that accumulates on the nip outlet side E2 above the heater 23 to adhere to the inner circumferential surface of the fixing belt 21. Then, the lubricant 50 that has adhered to the inner circumferential surface of the fixing belt 21 can be supplied to the inner nip A between the fixing belt 21 and the heater 23 as the fixing belt 21 moves in the opposite direction D2.

[0051] As described above, in this embodiment, unused and accumulated lubricant 50 can be effectively utilized by being supplied to inner nip A between fixing belt 21 and heater 23, thereby making it possible to suppress an increase in rotational torque and wear of the fixing belt that accompanies a decrease in lubricant over a long period of time. Also, in this embodiment, lubricant can be supplied to inner nip A without adding a new mechanism or part, making it possible to suppress an increase in rotational torque and wear of the fixing belt at low cost.

[0052] In this embodiment, to avoid the adverse effects of the reverse rotation of the fixing belt, the reverse rotation of the fixing belt is controlled as follows. Specifically, if the rotation distance of the fixing belt in the reverse direction becomes long, as shown in FIG. 24, the tips of the minute protrusions 601 on the belt surface bend in the opposite direction to that during normal rotation, accelerating belt wear and increasing rotational torque. Therefore, in this embodiment, the rotation distance of the fixing belt in the reverse direction is limited within a certain range.

[0053] First, the relationship between the reverse rotation speed when the fixing belt rotates in the opposite direction to its normal rotation direction and the rotation torque generated according to the reverse rotation speed will be explained based on Fig. 7. Graphs R0, R1, R5, and R10 in Fig. 7 show the rotation torque of the fixing belt when the reverse rotation speed of the fixing belt is 0, 1, 5, and 10 times, respectively.

[0054] As shown in Figure 7, when the number of reverse rotations of the fixing belt was zero (Graph R0), the rotational torque increased most significantly as the number of sheets passed through the nip increased. In this case, the fixing belt did not reverse, so the lubricant supply to the inner nip due to the reverse rotation described above was not achieved. This is thought to be why the amount of lubricant decreased over time as the number of sheets passed increased, resulting in an increase in rotational torque. In contrast, when the number of reverse rotations was one (Graph R1) and five (Graph R5), the supply of lubricant to the inner nip due to the reverse rotation of the fixing belt was achieved, thereby suppressing the increase in rotational torque. In particular, the increase in rotational torque was most effectively suppressed when the number of reverse rotations was one. In contrast, when the number of reverse rotations was ten (Graph R10), the results were nearly identical to when the fixing belt did not reverse (Graph R0), even though it did reverse. This is thought to be because the longer distance the fixing belt rotated in reverse caused wear on the belt surface, resulting in an increase in rotational torque.

[0055] Based on the above results, in this embodiment, the number of reverse rotations of the fixing belt is limited to five rotations or less (five rotation distances or less), which effectively suppresses the increase in rotational torque. By limiting the number of reverse rotations of the fixing belt to five or less, the accelerated wear of the fixing belt and the increase in rotational torque that accompany an increase in the number of reverse rotations can be suppressed. As a result, the occurrence of wear damage to the heater is also suppressed, and the deterioration of image quality due to the wear damage can be avoided. Furthermore, when the number of reverse rotations of the fixing belt is limited to one rotation or less (one rotation distance or less), the accelerated wear of the fixing belt and the increase in rotational torque can be more effectively suppressed, and further improvements in the durability and reliability of the fixing belt can be expected.

[0056] As described above, in this embodiment, the upper limit of the number of reverse rotations of the fixing belt is set to 5, preferably 1 or less, thereby effectively suppressing accelerated wear of the fixing belt and an increase in rotational torque. However, the rotation distance of the fixing belt during reverse rotation must be equal to or greater than the movement distance of the heater during reverse rotation. That is, as shown in FIG. 6 , by rotating the fixing belt 21 in the opposite direction D2, the heater 23 is moved toward the nip entrance side E1, and the lubricant 50 on the nip exit side E2 is moved to a position where it is likely to come into contact with the fixing belt 21. Therefore, the rotation distance of the fixing belt during reverse rotation is set to be equal to or greater than the movement distance of the heater 23 during this rotation. Therefore, the rotation distance of the fixing belt during reverse rotation is set to be equal to or greater than the movement distance of the heater 23 accompanying the reverse rotation of the fixing belt 21, but equal to or less than the rotation distance of five rotations. Note that the "distance traveled by the heater due to the reverse rotation of the fixing belt" here refers to the distance equivalent to the gap L that occurs between the heater 23 and the opposite side (the side on the nip entrance side E1) when the heater 23 is in contact with the side 24b on the nip exit side E2 of the recess 24a (the state shown in Figure 5).

[0057] As described above, in this embodiment, by rotating the fixing belt in the reverse direction for a distance equal to or greater than the heater travel distance associated with the reverse rotation and no more than five rotations, the accumulated lubricant can be supplied between the heater and the fixing belt while suppressing adverse effects associated with the reverse rotation. As a result, in this embodiment, an increase in rotational torque and wear of the fixing belt can be suppressed over a long period of time, thereby improving the durability and reliability of the fixing belt.

[0058] It is preferable that the rotation speed of the fixing belt during reverse rotation be slower than the rotation speed during normal operation (when paper is passed through the nip N). By slowing the rotation speed during reverse rotation, the rotation torque is reduced and the load on the heater is also reduced, so that wear due to reverse rotation can be more effectively suppressed.

[0059] Furthermore, since the rotational torque of the fixing belt increases as the amount of lubricant between the heater and the fixing belt decreases, for example, as shown in FIG. 8 , a torque sensor 31 that detects the rotational torque of the pressure roller 22 or the fixing belt 21 may be used. In this case, information on the rotational torque detected by the torque sensor 31 is sent to a control unit 30 provided in the image forming apparatus main body, etc., and the control unit 30 determines whether the rotational torque exceeds a predetermined reference value. If the rotational torque exceeds the reference value, the control unit 30 reverses the rotation of the pressure roller 22, thereby rotating the fixing belt 21 in the opposite direction. As a result, the lubricant remaining on the heater 23 is supplied between the heater 23 and the fixing belt 21.

[0060] Furthermore, since the amount of lubricant between the heater and the fixing belt tends to decrease over time as the fixing device is used, the reverse rotation of the fixing belt may be controlled based on the number of sheets of paper that have passed through the nip, the rotation distance (cumulative distance) of the fixing belt, or the elapsed time from a preset timing. For example, as shown in FIG. 9 , a control unit 30 provided in the image forming apparatus main body includes at least one of a paper-passed count recording unit 32 that records the number of sheets of paper that have passed through the nip, a rotation distance recording unit 33 that stores the rotation distance of the fixing belt, and an elapsed time measuring unit 34 that measures the elapsed time from a preset timing. Then, when the number of sheets of paper passed recorded by the paper-passed count recording unit 32, the rotation distance of the fixing belt recorded by the rotation distance recording unit 33, or the elapsed time measured by the elapsed time measuring unit 34 exceeds a preset reference value, the fixing belt 21 is reversed. This allows lubricant to be supplied when the amount of lubricant between the heater and the fixing belt decreases over time. Furthermore, the timing of reverse rotation of the fixing belt may be controlled using the information on the number of sheets passed, the rotation distance, or the elapsed time in combination with the detection result of the rotation torque.

[0061] The reverse rotation of the fixing belt may also be performed after the fixing belt has been left unheated. Specifically, the reverse rotation of the fixing belt is performed when the temperature of the fixing belt is 100°C or lower, or after one minute or more has passed since heating of the fixing belt was stopped. In this case, the temperature of the fixing belt is particularly low and the fixing belt has become non-circular. Therefore, by rotating the fixing belt in the reverse direction in this state, the lubricant is more likely to adhere to the inner surface of the fixing belt.

[0062] The reverse rotation of the fixing belt may also be performed immediately after the fixing belt has completed the fixing process. Specifically, after 30 or more sheets of paper have been continuously passed through the fixing device and the fixing process has been completed (after the paper has been passed through the nip), the reverse rotation of the fixing belt is performed within one minute. In this case, the temperature of the accumulated lubricant is high and the viscosity of the lubricant is reduced, so by rotating the fixing belt in the reverse direction, the lubricant can be more easily supplied between the heater and the fixing belt.

[0063] The lubricant interposed between the heater and the fixing belt may contain fluorine grease or silicone oil. Such lubricants become viscous and gel-like at low temperatures, and therefore tend to adhere to the fixing belt when the fixing belt is rotated in reverse.

[0064] To further reduce the likelihood of wear of the fixing belt, the fixing belt 21 may be a belt made of a substrate 210 and a surface layer (release layer) 212 disposed on the outer periphery of the substrate 210, as shown in the example of FIG. 10 . In this case, since no elastic layer, such as a rubber layer, is disposed between the surface layer (release layer) 212 and the substrate 210, the fixing belt 21 has lower insulation properties and better thermal conductivity from the heater to the fixing belt surface (outer periphery) than a fixing belt having an elastic layer. Therefore, in the fixing belt shown in FIG. 10 , the heater's heat output can be set relatively low. Generally, fixing belts lose strength and become more susceptible to wear as the temperature increases. Therefore, setting the heater's heat output low can suppress the temperature rise of the fixing belt, reducing wear of the fixing belt. Furthermore, heat-induced degradation of the lubricant can be suppressed, thereby maintaining the lubricating function over a long period of time and extending the life of the fixing belt.

[0065] 4, the heater that heats the fixing belt preferably has a configuration in which multiple resistance heating elements 56 are arranged in the longitudinal direction (paper width direction intersecting the paper transport direction) of the heater 23. In this case, the heat output of each resistance heating element 56 can be controlled independently of one another, and by individually controlling the heat output of each resistance heating element 56 according to the width of the paper passing through the nip portion, it is possible to prevent excessive temperature rise in non-paper passing areas where paper does not pass, and to prevent a decrease in durability of the fixing belt and deterioration of the lubricant that accompanies temperature rise.

[0066] The heater is not limited to the configuration shown in FIG. 4, but may have a configuration in which resistance heating elements 56 are arranged continuously in the longitudinal direction of the heater 23 as shown in FIG.

[0067] The resistance heating element may also have a PTC (positive temperature coefficient of resistance) characteristic, which is a characteristic whereby when the temperature of the resistance heating element rises, the resistance value of the resistance heating element rises and the heater output decreases.

[0068] This characteristic suppresses the heater's temperature rise in the non-paper-passing area. Specifically, when a sheet of paper narrower than the entire longitudinal width of the resistance heating elements is passed through the printer, the temperature of the resistance heating elements rises in the non-paper-passing area because the paper does not absorb heat. However, because the voltage applied to the resistance heating elements remains constant, the temperature of the resistance heating elements in the non-paper-passing area rises, resulting in an increase in their resistance value. As a result, the output (heat generation) of the resistance heating elements in the non-paper-passing area decreases relatively, suppressing excessive temperature rise in the fixing belt. Therefore, by using a heater with a resistance heating element having PTC characteristics, temperature rise in the fixing belt in the non-paper-passing area can be effectively suppressed, improving the durability of the fixing belt. Furthermore, as shown in FIG. 4, when the resistance heating elements 56 are electrically connected in parallel, temperature rise in the non-paper-passing area can be suppressed while maintaining printing speed.

[0069] Although the embodiments of the present invention have been described above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the spirit of the present invention.

[0070] For example, the present invention is also applicable to fixing devices having the configurations shown in Figures 12 to 15. The configurations of the fixing devices shown in Figures 12 to 15 will be described below.

[0071] The fixing device 20 shown in FIG. 12 differs from the fixing device 20 shown in FIG. 2 above in the location of the temperature sensor 27 that detects the temperature of the heater 23. The rest of the configuration is the same. In the fixing device 20 shown in FIG. 12, the temperature sensor 27 is located upstream of the center M of the nip N in the paper feed direction (the nip entrance side). On the other hand, in the fixing device 20 shown in FIG. 4, the temperature sensor 27 is located at the center M of the nip N. As shown in FIG. 12, when the temperature sensor 27 is located upstream of the center M of the nip N in the paper feed direction, the temperature sensor 27 can accurately detect the temperature at the nip entrance side. The nip entrance side is an area where heat from the fixing belt 21 is particularly likely to be lost by the paper P entering the nip N. Therefore, by accurately detecting the temperature at the nip entrance side using the temperature sensor 27, image fixability can be ensured and the occurrence of fixing offset (a state in which a toner image cannot be sufficiently heated) can be effectively suppressed.

[0072] 13, a heating nip N1 where the heater 23 heats the fixing belt 21 and a fixing nip N2 where the paper P passes are formed at separate positions. Specifically, in this embodiment, a nip forming member 68 is disposed inside the fixing belt 21 in addition to the heater 23, and pressure rollers 69 and 70 are pressed against the heater 23 and the nip forming member 68, respectively, via the fixing belt 21, thereby forming the heating nip N1 and the fixing nip N2. In this case, the fixing belt 21 is heated at the heating nip N1, and the heat of the fixing belt 21 is applied to the paper P at the fixing nip N2, thereby fixing the unfixed image to the paper P.

[0073] Next, the fixing device 20 shown in Fig. 14 is an example in which the pressure roller 69 on the heater 23 side of the fixing device shown in Fig. 13 is omitted, and the heater 23 is formed in an arc shape to match the curvature of the fixing belt 21. In other respects, it is the same as the configuration shown in Fig. 13. In this case, since the heater 23 is formed in an arc shape, the contact length between the fixing belt 21 and the heater 23 in the belt rotation direction is ensured, and the fixing belt 21 can be heated efficiently.

[0074] 15 shows an example of fixing device 20 in which roller 73 is disposed between a pair of belts 71 and 72. In this example, heater 23 disposed in belt 71 on the left side in FIG. 15 contacts roller 73 via belt 71, and nip forming member 74 disposed in belt 72 on the right side contacts roller 73 via belt 72, thereby forming nip N1 for heating and nip N2 for fixing.

[0075] 13, 14, and 15, nip forming members 68 and 74 are provided in addition to heater 23 as members that slide relatively to the belt. The present invention is also applicable to a configuration in which a lubricant is supplied between such nip forming members 68 and 74 and the belt. Furthermore, the present invention is not limited to a configuration in which a heater is disposed in a nip portion through which paper passes (fixing nip portion N2), but is also applicable to a configuration in which a heater is disposed in a nip portion through which paper does not pass (heating nip portion N1) as shown in FIGS. 13, 14, and 15.

[0076] Furthermore, the image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in FIG. 1, but may also be a monochrome image forming apparatus, a copying machine, a printer, a facsimile, or a combination machine of these.

[0077] For example, the present invention can also be applied to an image forming apparatus configured as shown in Fig. 16. Image forming apparatus 100 shown in Fig. 16 includes image forming means 80 including a photosensitive drum and the like, a paper transport section including a pair of timing rollers 81 and the like, a paper feeder 82, a fixing device 83, a paper discharge device 84, and a reading section 85. Paper feeder 82 includes multiple paper feed trays, each of which stores paper of a different size.

[0078] The reading unit 85 reads an image of the document Q. The reading unit 85 generates image data from the read image. The paper feeder 82 stores a plurality of sheets of paper P and sends the sheets of paper P to a conveyance path. The timing rollers 81 convey the sheets of paper P on the conveyance path to the image forming means 80.

[0079] The image forming means 80 forms a toner image on the paper P. Specifically, the image forming means 80 includes a photosensitive drum, a charging roller, an exposure device, a developing device, a replenishment device, a transfer roller, a cleaning device, and a discharging device. The fixing device 83 applies heat and pressure to the toner image to fix the toner image to the paper P. The paper P with the fixed toner image is transported to the paper discharge device 84 by a transport roller or the like. The paper discharge device 84 discharges the paper P outside the image forming apparatus 100.

[0080] Next, the fixing device 83 according to this embodiment will be described with reference to Fig. 17. In the configuration shown in Fig. 27, components common to the fixing device 20 of the above embodiment shown in Fig. 2 are designated by the same reference numerals and description thereof will be omitted.

[0081] As shown in FIG. 17, the fixing device 83 includes a fixing belt 21, a pressure roller 22, a heater 23, a heater holder 24, a stay 25, a temperature sensor 27, and the like.

[0082] A nip N is formed between the fixing belt 21 and the pressure roller 22. The nip width of the nip N is 10 mm, and the linear speed of the fixing device 83 is 240 mm / s.

[0083] The fixing belt 21 has a polyimide base and a release layer, but does not have an elastic layer. The release layer is formed of a heat-resistant film material made of, for example, fluororesin. The outer diameter of the fixing belt 21 is approximately 24 mm.

[0084] The pressure roller 22 includes a core metal, an elastic layer, and a release layer. The pressure roller 22 has an outer diameter of 24 to 30 mm, and the elastic layer has a thickness of 3 to 4 mm.

[0085] The heater 23 includes a base material, a heat insulating layer, a conductive layer including a resistance heating element, and an insulating layer, and has an overall thickness of 1 mm. The width of the heater 23 in the paper transport direction is 13 mm.

[0086] As shown in FIG. 18, the conductor layer of the heater 23 includes a plurality of resistance heating elements 56, power supply lines 59, and electrode portions 58A to 58C. The plurality of resistance heating elements 56 are arranged at intervals in the longitudinal direction (arrow X direction) of the heater 23. Here, if the portions between the resistance heating elements 56 are referred to as "divided regions," then, as shown in the enlarged view of FIG. 18, divided regions B are formed between each of the resistance heating elements 56 (although FIG. 18 illustrates divided regions B only within the enlarged view, in reality divided regions B are provided between all of the resistance heating elements 56). In addition, in FIG. 18, the direction of arrow Y is a direction intersecting or perpendicular to the longitudinal direction X of the heater 23 (longitudinal intersecting direction) and different from the thickness direction of the substrate 55. In addition, the direction of arrow Y is a direction that intersects with the arrangement direction of the multiple resistance heating elements 56 (arrangement cross direction), or a direction along the surface of the substrate 55 on which the resistance heating elements 56 are provided, which is the same as the short side direction of the heater 23, or the transport direction of the paper passing through the fixing device.

[0087] Furthermore, the multiple resistance heating elements 56 form a central heating section 35B and heating sections 35A and 35C on both ends that can generate heat independently. For example, of the three electrode sections 58A to 58C, when electricity is applied to the leftmost electrode section 58A and the central electrode section 58B in FIG. 18, the heating sections 35A and 35C on both ends generate heat. When electricity is applied to the electrode sections 58A and 58C on both ends, the central heating section 35B generates heat. For example, when fixing small-size paper, only the central heating section 35B generates heat, and when fixing large-size paper, all of the heating sections 35A to 35C generate heat, allowing heating according to the size of the paper.

[0088] 19, the heater holder 24 according to this embodiment has a recess 24a that accommodates and holds the heater 23. The recess 24a is formed on the heater 23 side of the heater holder 24. The recess 24a is composed of a surface (bottom surface) 24f formed in a rectangular shape having approximately the same size as the heater 23, and four walls (side surfaces) 24b, 24c, 24d, and 24e that intersect with the surface 24f along the four sides that form the outline of the surface 24f. Note that the right wall 24e is not shown in FIG. 19. Alternatively, one of the pair of walls 24d and 24e (left and right) that intersect with the longitudinal direction X of the heater 23 (the direction in which the resistance heating elements 56 are arranged) may be omitted, and the recess 24a may be configured to open at one end of the heater 23 in the longitudinal direction.

[0089] 20, the heater 23 and heater holder 24 according to this embodiment are held by a connector 86. The connector 86 has a housing made of resin (for example, LCP) and a plurality of contact terminals provided inside the housing.

[0090] The connector 86 is attached to the heater 23 and the heater holder 24 in a direction intersecting the longitudinal direction X of the heater 23 (the arrangement direction of the resistance heating elements 56) (see the direction of the arrow from the connector 86 in FIG. 20). The connector 86 is attached to the heater 23 and the heater holder 24 at one end side in the longitudinal direction X of the heater 23 (the arrangement direction of the resistance heating elements 56), on the side opposite to the side on which the drive motor of the pressure roller 22 is provided. Note that when the connector 86 is attached to the heater holder 24, a convex portion provided on one of the connector 86 and the heater holder 24 may engage with a concave portion provided on the other, and the convex portion may move relatively within the concave portion.

[0091] With the connector 86 attached, the heater 23 and heater holder 24 are held by being sandwiched between them from the front and back sides by the connector 86. In this state, each contact terminal comes into contact (pressure-welded) with each electrode portion of the heater 23, electrically connecting each resistance heating element 56 to a power supply provided in the image forming apparatus via the connector 86. This enables power to be supplied from the power supply to each resistance heating element 56.

[0092] 20 are belt holding members that are provided on both longitudinal ends of the fixing belt 21 and hold both ends of the fixing belt 21 from the inside. The flanges 87 are inserted into both ends of the stay 25 and fixed to a pair of side plates that are frame members of the fixing device.

[0093] FIG. 21 is a diagram showing the arrangement of the temperature sensor 27 and the thermostat 88, which is a current interrupting member, according to this embodiment.

[0094] 21, the temperature sensors 27 according to this embodiment are disposed so as to face the inner circumferential surfaces of the fixing belt 21 on the center Xm side and the end side in the longitudinal direction X. One of these temperature sensors 27 is disposed at a position corresponding to the divided region B (see FIG. 18) between the resistance heating elements of the heater 23.

[0095] Further, on the center Xm side and end sides of the fixing belt 21, thermostats 88 as current-cutting members are arranged to face the inner circumferential surface of the fixing belt 21. Each thermostat 88 detects the temperature of the inner circumferential surface of the fixing belt 21 or the ambient temperature near the inner circumferential surface. When the temperature detected by the thermostat 88 exceeds a preset threshold value, the current to the heater 23 is cut off.

[0096] 21 and 22, flanges 87 that hold both ends of fixing belt 21 are provided with slide grooves 87a. Slide grooves 87a extend in the direction in which fixing belt 21 approaches and separates from pressure roller 22. An engagement portion of the housing of the fixing device engages with slide groove 87a. This engagement portion moves relatively within slide groove 87a, allowing fixing belt 21 to move in the direction in which fixing belt 21 approaches and separates from pressure roller 22.

[0097] The above has described the configurations of other fixing devices and image forming apparatuses to which the present invention can be applied, but by applying the present invention to fixing devices and image forming apparatuses with such configurations, the same effects as those of the above-described embodiment can be obtained. That is, by applying the present invention, it is possible to supply the accumulated lubricant between the heater and the fixing belt without adding any new mechanism or parts, thereby improving the durability of the fixing belt through resistance stress.

[0098] Furthermore, the present invention is not limited to a fixing device, which is an example of a belt-driven device or a heating device using a belt, but can also be applied to other belt-driven devices and heating devices. For example, the present invention can be applied to a heating device (drying device) that heats paper to dry a liquid such as ink applied to the paper, as well as a laminator that thermocompresses a film as a covering member onto the surface of a sheet such as paper, or a heat sealer that thermocompresses a seal portion of a packaging material. The present invention can also be applied to a belt-driven device that does not have a heat source such as a heater. [Explanation of symbols]

[0099] 20 Fixing device (heating device, belt drive device) 21 Fixing belt (belt) 22 Pressure roller (opposing member) 23 Heater (heat source, sliding member) 24 Heater holder (holding member) 24a Recess 50 Lubricants 56 Resistance heating element (heating element) 100 Image forming device C Paper feed direction (sheet passing direction) N Nip section P Paper (sheet) [Prior art documents] [Patent documents]

[0100] [Patent Document 1] Japanese Patent Application Publication No. 2018-194696

Claims

1. a flexible endless belt; a sliding member disposed so as to slide on an inner circumferential surface of the belt; an opposing member that contacts the sliding member via the belt and forms a nip between the opposing member and the belt; A belt driving device including a lubricant interposed between an inner circumferential surface of the belt and the sliding member, the belt is rotatable in a direction opposite to a direction in which the belt rotates when the sheet passes through the nip portion, the sliding member is configured to be movable in a direction in which the belt surface moves in the nip portion in association with the rotation of the belt in the opposite direction, a belt driving device that rotates the belt in the opposite direction within a range of not more than five rotations but not more than a moving distance of the sliding member accompanying the rotation in the opposite direction when the temperature of the belt is 100°C or less, or after one minute or more has elapsed in an unheated state since heating of the belt was stopped.

2. A flexible endless belt, a sliding member disposed so as to slide on an inner circumferential surface of the belt; an opposing member that contacts the sliding member via the belt and forms a nip between the opposing member and the belt; a holding member having a recess in which the sliding member is accommodated; a lubricant interposed between the inner circumferential surface of the belt and the sliding member; the sliding member is accommodated in a belt driving device so as to be movable in a belt surface movement direction in the nip portion in accordance with the rotation of the belt in the opposite direction, the belt is rotatable in a direction opposite to a direction in which the belt rotates when the sheet passes through the nip portion, the sliding member is configured to be movable in a direction in which the belt surface moves in the nip portion in association with the rotation of the belt in the opposite direction, A belt driving device, characterized in that the rotation of the belt in the opposite direction is performed within a range of not less than a movement distance of the sliding member accompanying the rotation in the opposite direction but not more than five rotations.

3. A belt drive device as described in claim 1 or 2, wherein the rotation of the belt in the opposite direction is performed within a range of one rotation or less that is equal to or greater than the movement distance of the sliding member accompanying the rotation in the opposite direction.

4. A belt drive device described in any one of claims 1 to 3, wherein the rotation speed of the belt in the opposite direction is slower than the rotation speed when passing a sheet through the nip portion.

5. A belt drive device described in any one of claims 1 to 4, wherein the rotation of the belt in the opposite direction is performed based on at least one of the number of sheets that have passed through the nip portion, the rotation distance of the belt, the elapsed time from a predetermined timing, and the rotational torque of the belt or the opposing member.

6. 3. The belt driving device according to claim 2, wherein upstream and downstream edges of the recess in the belt surface movement direction protrude toward the opposing member beyond the opposing member-side surface of the sliding member.

7. 7. The belt drive device according to claim 1, wherein a width of a portion of the sliding member, where the surface of the sliding member facing the opposing member and the inner circumferential surface of the belt, in the direction of movement of the belt surface is smaller than a width of the entire surface of the sliding member facing the opposing member in the direction of movement of the belt surface.

8. The belt driving device according to claim 1 , wherein the lubricant contains fluorine grease or silicone oil.

9. 9. The belt driving device according to claim 1, wherein the belt has a base material and a surface layer provided on an outer peripheral side of the base material, and no elastic layer is provided between the surface layer and the base material.

10. The belt drive device according to any one of claims 1 to 9; A heating device comprising: a heat source for heating the belt provided in the belt driving device.

11. The heating device according to claim 10 , wherein the heat source has a plurality of heating elements arranged in a longitudinal direction of the heat source, the heating elements being capable of being controlled to generate heat independently of each other.

12. A fixing device, comprising: a heating device according to claim 10; and a fixing unit for fixing an unfixed image onto a sheet using the heating device according to claim 10.

13. 13. An image forming apparatus comprising at least one of the belt driving device according to claim 1, the heating device according to claim 10 or 11, and the fixing device according to claim 12.

Images