Heating device, fixing device, and image forming apparatus

Abstract

To detect an increase in temperature in an area through which a sheet does not pass.SOLUTION: A heating device comprises: a pair of rotating bodies 21, 22 that are in contact with each other to form a nip part allowing sheets P1, P2 to pass through; a heat source 23 that has a heating area 60 in which resistance heating elements are arranged, and heats at least one of the pair of rotating bodies 21, 22; and a temperature detection member 27B that detects the temperature of the heat source 23 or a member in contact with the heat source 23, or one of the pair of rotating bodies 21, 22. The center z of the heating area 60 in a longitudinal direction X of the heat source 23 is arranged shifted in the longitudinal direction X with respect to the center c of a sheet passage width. The temperature detection member 27B is arranged outside the sheet passage width on a side where the center z of the heating area 60 is shifted in the longitudinal direction from the center c of the sheet passage width.SELECTED DRAWING: Figure 6

Description

Technical Field

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

Background Art

[0002] As an example of a heating device mounted in an image forming apparatus such as a copying machine or a printer, a fixing device is known that fixes an unfixed image on a sheet by heating the sheet carrying the unfixed image.

[0003] Generally, a fixing device includes a pair of rotators that form a nip portion through which a sheet passes while contacting each other, and a heat source that heats at least one of these rotators. In a state where one or both of the rotators are heated to a predetermined temperature by the heat source, when a sheet carrying an unfixed image is conveyed to the nip portion between the pair of rotators, the sheet is heated and pressed in the nip portion, so that the unfixed image on the sheet is fixed.

[0004] Here, in the region where the sheet contacts the rotator, the heat of the rotator is consumed by the passage of the sheet. On the other hand, in the region where the sheet does not pass, it is difficult for the heat to be consumed by the sheet. Therefore, in the region where the sheet does not pass, the rotator is likely to increase in temperature. And when the rotator partially thermally expands due to the temperature rise of the rotator in the region where the sheet does not pass, there is a problem that the rotator is twisted and damaged due to the thermal expansion difference. In particular, such a problem of partial temperature rise of the rotator tends to become more prominent when the sheet is conveyed with a misalignment in its width direction.

[0005] Therefore, in Patent Document 1 (Japanese Patent No. 5924867), a displacement detection unit that detects the displacement of the sheet in the width direction is provided, and when the displacement of the sheet is detected by the displacement detection unit, a countermeasure for eliminating the twist of the rotator is proposed.

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, the temperature rise of the rotating body in areas where the sheet described above does not pass can also be determined by the detection information from a temperature sensing element that detects the temperature of the rotating body or heat source.

[0007] However, the pattern of temperature rise in the rotating body in areas not covered by the sheet can change if the sheet's transport position shifts. Specifically, when the sheet is transported at a predetermined position, the temperature rise will be similar in the non-passing areas on both sides of the area through which the sheet passes. However, when the sheet is transported shifted to one side in the width direction from the predetermined area through which the sheet passes, the temperature rise of the rotating body will be more pronounced on the side opposite to the side where the sheet shifted. Therefore, depending on the direction in which the sheet shifts, the side on which the temperature rise is most pronounced will also differ.

[0008] When detecting such a temperature rise, if a temperature sensing element is placed in one of the non-passing regions on either side of the area through which the sheet passes, there is a risk that the temperature rise of the rotating body may not be detected if the temperature rise becomes significant in the other non-passing region. [Means for solving the problem]

[0009] To solve the above problems, the present invention provides a heating device comprising: a pair of rotating bodies that contact each other to form a nip portion through which a sheet passes; a heating source having a heating region on which a resistance heating element is arranged and which heats at least one of the pair of rotating bodies; and a temperature sensing member that detects the temperature of the heating source, a member in contact with the heating source, or one of the pair of rotating bodies, wherein the center of the heating region in the longitudinal direction of the heating source is offset in the longitudinal direction from the center of the sheet passage width, and the temperature sensing member is arranged outside the sheet passage width on the side where the center of the heating region is offset in the longitudinal direction from the center of the sheet passage width. [Effects of the Invention]

[0010] According to the present invention, it is possible to detect a temperature rise in an area that the sheet does not pass through. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. [Figure 2] This is a schematic diagram of the fixing device according to this embodiment. [Figure 3] This is a cross-sectional view of the fixing belt according to this embodiment. [Figure 4] This is a plan view of the heater according to this embodiment. [Figure 5] This is a perspective view showing the heater according to this embodiment with a connector, which serves as a power supply component, connected to it. [Figure 6] This diagram shows the positional relationship between the heater, temperature sensor, and paper sensor with respect to each paper feeding area in an embodiment of the present invention. [Figure 7] This diagram shows a state where paper is being transported with a shift to one side in its width direction. [Figure 8] This diagram shows a state in which paper is transported while shifted to the other side in the width direction. [Figure 9] This figure shows an example where the arrangement of the edge-side temperature sensor and paper sensor is configured to accommodate paper with a width smaller than the maximum paper feeding width. [Figure 10] This is a schematic diagram of a fixing device according to another embodiment of the present invention. [Figure 11] This is a perspective view of the heater, heating plate, and heater holder according to the other embodiment described above. [Figure 12] This diagram shows the positional relationship between the heater, temperature sensor, and paper sensor of the other embodiment described above, with respect to each paper feeding area. [Figure 13] This figure shows an example where the bottom plate of the paper feed cassette is tilted. [Figure 14] This figure shows an example in which a paper sensor is installed on the main body of the image forming apparatus. [Figure 15] This is a cross-sectional view of a fixing belt without an elastic layer. [Figure 16]It is a diagram showing the configuration of a fixing device different from the above embodiment. [Figure 17] It is a diagram showing the configuration of a fixing device different from the above embodiment. [Figure 18] It is a diagram showing the configuration of a fixing device different from the above embodiment. [Figure 19] It is a diagram showing the configuration of a fixing device different from the above embodiment. [Figure 20] It is a diagram showing the configuration of an image forming apparatus different from the above embodiment. [Figure 21] It is a diagram showing the configuration of the fixing device shown in FIG. 20. [Figure 22] It is a plan view of the heater shown in FIG. 21. [Figure 23] It is a perspective view of the heater and the heater holder shown in FIG. 21. [Figure 24] It is a diagram showing the method of attaching the connector to the heater shown in FIG. 21. [Figure 25] It is a diagram showing the arrangement of the temperature sensor and the thermostat provided in the fixing device shown in FIG. 20. [Figure 26] It is a diagram showing the groove portion of the flange shown in FIG. 24. [Figure 27] It is a plan view of the heater showing another example of the arrangement of the heat sink. [Figure 28] It is a plan view of the heater showing yet another example of the arrangement of the heat sink. [Figure 29] It is a plan view of the heater showing the enlarged divided area. [Figure 30] It is a diagram showing the configuration of a fixing device different from the above embodiment. [Figure 31] It is a perspective view of the heater, the heat sink, the second high thermal conductivity member, and the heater holder shown in FIG. 30. [Figure 32] It is a plan view of the heater showing the arrangement of the heat sink and the second high thermal conductivity member. [Figure 33] It is a plan view of the heater showing another example of the arrangement of the heat sink and the second high thermal conductivity member. [Figure 34] It is a plan view of the heater showing yet another example of the arrangement of the second high thermal conductivity member. [Figure 35] This figure shows a configuration of a fixing device that differs from the embodiment described above. [Figure 36] This is a diagram showing the atomic crystal structure of graphene. [Figure 37] This is a diagram showing the atomic crystal structure of graphite. [Figure 38] This diagram shows the configuration of a conventional fixing device. [Figure 39] This diagram shows the state in which paper is transported with a misalignment in the width direction in a conventional fixing device. [Modes for carrying out the invention]

[0012] The present invention will be described below with reference to the attached drawings. In each drawing used to explain the present invention, components such as members and parts having the same function or shape will be given the same reference numerals to the extent possible so that they can be distinguished, and their description will be omitted after they have been described once.

[0013] Figure 1 is a schematic diagram of an image forming apparatus according to one embodiment of the present invention. Here, "image forming apparatus" in this specification includes printers, copiers, facsimile machines, printing presses, or multifunction devices that combine two or more of these. Furthermore, "image forming" as used in the following description means not only forming images that have meaning, such as characters and figures, but also forming images that do not have meaning, such as patterns. First, the overall configuration and operation of the image forming apparatus according to this embodiment will be described with reference to Figure 1.

[0014] As shown in Figure 1, the image forming apparatus 100 according to this embodiment includes an image forming unit 200 for forming an image on a sheet-like recording medium such as paper, a fixing unit 300 for fixing the image on the recording medium, a recording medium supply unit 400 for supplying the recording medium to the image forming unit 200, and a recording medium discharge unit 500 for discharging the recording medium outside the apparatus.

[0015] The image forming unit 200 includes four process units 1Y, 1M, 1C, and 1Bk as image forming units, an exposure apparatus 6 that forms an electrostatic latent image on the photoreceptor 2 provided in each process unit 1Y, 1M, 1C, and 1Bk, and a transfer apparatus 8 that transfers the image to a recording medium.

[0016] Each process unit 1Y, 1M, 1C, and 1Bk has essentially the same configuration, except that they contain toners (developers) of different colors: yellow, magenta, cyan, and black, which correspond to the color separation components of a color image. Specifically, each process unit 1Y, 1M, 1C, and 1Bk includes a photoreceptor 2 as an image carrier that carries an image on its surface, a charging member 3 that charges the surface of the photoreceptor 2, a developing device 4 that supplies toner as a developer to the surface of the photoreceptor 2 to form a toner image, and a cleaning member 5 that cleans the surface of the photoreceptor 2.

[0017] The transfer device 8 comprises 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 and 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 photoreceptor 2 via the intermediate transfer belt 11, thereby forming a primary transfer nip between the intermediate transfer belt 11 and each photoreceptor 2. The secondary transfer rollers 13 contact the outer circumferential surface of the intermediate transfer belt 11, forming a secondary transfer nip.

[0018] In the fixing section 300, a fixing device 20 is provided. 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 contact each other on their respective outer surfaces, forming a nip section (fixing nip).

[0019] The recording medium supply unit 400 is provided with a paper feed cassette 14, which serves as a sheet storage unit for accommodating paper P as a recording medium, and a paper feed roller 15 for feeding paper P from the paper feed cassette 14. Hereinafter, "recording medium" will be described as "paper," but "recording medium" is not limited to paper. "Recording medium" includes not only paper but also OHP sheets or fabrics, metal sheets, plastic films, or prepreg sheets made by pre-impregnating carbon fibers with resin. Furthermore, "paper" includes not only plain paper but also cardboard, postcards, envelopes, thin paper, coated paper (such as coated paper and art paper), tracing paper, etc.

[0020] The recording medium discharge unit 500 is provided with a pair of paper discharge rollers 17 for discharging the paper P to the outside of the image forming apparatus, and a paper discharge tray 18 for placing the paper P discharged by the paper discharge rollers 17.

[0021] Next, the printing operation of the image forming apparatus 100 according to this embodiment will be described with reference to Figure 1.

[0022] When printing is started in the image forming apparatus 100, the photoreceptors 2 of each process unit 1Y, 1M, 1C, 1Bk and the intermediate transfer belt 11 of the transfer device 8 begin to rotate. At the same time, the paper feed roller 15 begins to rotate, and paper P is fed out from the paper feed cassette 14. The fed paper P comes to rest upon contact with a pair of timing rollers 16, and the transport of paper P is temporarily stopped until the image to be transferred to paper P is formed.

[0023] In each process unit 1Y, 1M, 1C, and 1Bk, first, the surface of the photoreceptor 2 is charged to a uniform high potential by the charging member 3. Next, based on the image information of the original document read by the document reader or the print image information instructed to print from the terminal, the exposure unit 6 exposes the surface (charged surface) of each photoreceptor 2. As a result, the potential of the exposed area decreases, and an electrostatic latent image is formed on the surface of each photoreceptor 2. Then, the developing unit 4 supplies toner to this electrostatic latent image, and a toner image is formed on each photoreceptor 2. As the toner image formed on each photoreceptor 2 reaches the primary transfer nip (position of the primary transfer roller 12) as the photoreceptor 2 rotates, it is transferred sequentially onto the rotating intermediate transfer belt 11. Thus, a full-color toner image is formed on the intermediate transfer belt 11. Furthermore, in the image forming apparatus 100, a monochrome image can be formed using any one of the process units 1Y, 1M, 1C, or 1Bk, or a two-color or three-color image can be formed 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, residual toner and other contaminants on each photoreceptor 2 are removed by the cleaning member 5.

[0024] The toner image transferred onto the intermediate transfer belt 11 is transported to the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates, and is transferred onto the paper P that has been transported by the timing roller 16. The paper P is then transported to the fuser unit 20, where the toner image on the paper P is heated and pressurized by the fuser belt 21 and the pressure roller 22, thereby fixing the toner image to the paper P. The paper P is then transported to the recording medium discharge unit 500 and discharged into the paper discharge tray 18 by the paper discharge roller 17. This completes the series of printing operations.

[0025] Next, the configuration of the fixing device according to this embodiment will be described in detail based on Figure 2.

[0026] As shown in Figure 2, the fixing device 20 according to this embodiment includes a fixing belt 21 and a pressure roller 22, as well as a heater 23, a heater holder 24, a stay 25, a guide member 26, a temperature sensor 27, and the like.

[0027] The fixing belt 21 is a rotating body (first rotating body or fixing member) that contacts the unfixed toner-carrying surface of the paper P to fix the unfixed toner (unfixed image) to the paper P, and is composed 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.

[0028] As shown in Figure 3, the fixing belt 21 is constructed by laminating a base material 210, an elastic layer 211, and a release layer 212 in order from the inner circumferential surface to the outer circumferential surface, with an overall thickness of 1 mm or less. The base material 210 has a layer 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 layer thickness of 100 to 300 μm and is made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber. Because the fixing belt 21 has an elastic layer 211, minute irregularities are not formed on the surface of the fixing belt 21 in the nip portion, making it easier for heat to be uniformly transferred to the toner image on the paper P. The release layer 212 has a layer thickness of 10 to 50 μm and is made of materials such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyether sulfide). The fixing belt 21 has a release layer 212, which ensures release properties (peelability) from the toner (toner image).

[0029] As shown in Figure 2, the pressure roller 22 is a rotating body (second rotating body or opposing member) positioned opposite the outer circumferential surface of the fixing belt 21. The pressure roller 22 contacts the heater 23 via the fixing belt 21 and forms a nip portion N between itself and the fixing belt 21.

[0030] The pressure roller 22 is, for example, a roller with an outer diameter set to 25 mm, and has a hollow iron core material 220, an elastic layer 221 provided on the outer surface of the core material 220, and a release layer 222 provided on the outer surface of the elastic layer 221. The elastic layer 221 has a thickness of, for example, 3.5 mm and is made of silicone rubber or the like. The release layer 222 has a thickness of, for example, about 40 μm and is made of fluororesin or the like.

[0031] The heater 23 is a heating source that heats the fixing belt 21 from the inside. The heater 23 is a planar or plate-shaped heater that extends longitudinally along the longitudinal direction of the fixing belt 21 (the paper width direction intersecting the paper transport direction), and is positioned to contact the inner circumferential surface of the fixing belt 21. The heater 23 according to this embodiment includes a base material 55, a resistance heating element 56 provided on the base material 55, and an insulating layer 57 covering the resistance heating element 56.

[0032] As shown in Figure 2, in this embodiment, the resistance heating element 56 is provided on the surface of the base material 55 on the pressure roller 22 side (nip portion N side), but it may also be provided on the opposite side. In that case, since the heat from 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.

[0033] The heater holder 24 is a heating source holding member positioned inside the fixing belt 21 and holding the heater 23. Since the heater holder 24 is prone to becoming hot due to the heat from the heater 23, it is preferable that it be made of a heat-resistant material. 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 suppressing heat transfer from the heater 23 to the heater holder 24, thereby efficiently heating the fixing belt 21.

[0034] The stay 25 is a support member that supports the heater holder 24. The stay 25 supports the side of the heater holder 24 opposite to the side facing the pressure roller 22 along the longitudinal direction of the fixing belt 21, thereby suppressing the bending of the heater holder 24 due to the pressure applied by the pressure roller 22, and forming a nip portion N of uniform width between the fixing belt 21 and the pressure roller 22. To ensure its rigidity, the stay 25 is preferably made of an iron-based metal material such as SUS or SECC.

[0035] The guide member 26 is a member that guides the anchoring belt 21 from the inside. The guide member 26 has an arc-shaped cross-section that follows the inner circumferential surface of the anchoring belt 21 and is positioned on the upstream and downstream sides of the heater 23 in the rotational direction of the anchoring belt 21 (direction of the arrow in Figure 2), respectively. In this embodiment, each guide member 26 is configured integrally with the heater holder 24, but they may be configured as separate parts.

[0036] The temperature sensor 27 is a temperature sensing member that detects the temperature of the heater 23. Known temperature sensors such as thermopiles, thermostats, thermistors, or NC sensors 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 side of the heater 23 opposite to the pressure roller 22 side. Furthermore, the temperature sensor 27 is not limited to a contact-type temperature sensor; it may also be a non-contact type temperature sensor that is positioned without contact with the heater 23 and detects the ambient temperature near the heater 23.

[0037] The fixing device 20 according to this embodiment operates as follows.

[0038] As shown in Figure 2, when the pressure roller 22 is driven to rotate, the driving force is transmitted to the fixing belt 21, causing the fixing belt 21 to rotate in response. The fixing belt 21 is then heated by the heater 23. The temperature of the heater 23 at this time is detected by the temperature sensor 27, and the amount of heat generated by the heater 23 is controlled based on the detected temperature. This maintains the temperature of the fixing belt 21 at a temperature at which the image can be fixed (fixing temperature). When the paper P carrying the unfixed image is transported between the fixing belt 21 and the pressure roller 22 (nip section N), the toner image on the paper P is heated and pressurized by the fixing belt 21 and the pressure roller 22, and the image is fixed to the paper P.

[0039] Figure 4 is a plan view of the heater according to this embodiment.

[0040] As shown in Figure 4, the heater 23 according to this embodiment has a plate-shaped base material 55 extending in one direction (in the direction of arrow X in Figure 4). The base material 55 is arranged such that its longitudinal direction X is oriented in the longitudinal direction of the fixing belt 21 or in the axial direction of the pressure roller 22. On the surface of the base material 55, two resistance heating elements 56 are arranged side by side in the longitudinal direction Y of the base material 55, extending in the longitudinal direction X of the base material 55. The "short direction" refers to the direction perpendicular to the longitudinal direction X along the surface of the base material 55 on which the resistance heating elements 56 are provided, and is the same direction as the paper transport direction in which the paper is transported.

[0041] As shown in Figure 4, a pair of electrode portions 58 are provided on one end of the base material 55 in the longitudinal direction X. Each electrode portion 58 is connected to each resistance heating element 56 via a power supply line 59. The ends of each resistance heating element 56 opposite to the ends connected to the electrode portions 58 are connected to each other via another power supply line 59. Each resistance heating element 56 and each power supply line 59 are covered with an insulating layer 57 to ensure insulation. In contrast, each electrode portion 58 is exposed and not covered by the insulating layer 57 so that a connector, which will be used as a power supply terminal as described later, can be connected to it.

[0042] The base material 55 is made of a material with excellent heat resistance and insulation properties, such as ceramics like alumina or aluminum nitride, glass, mica, or polyimide. Alternatively, the base material 55 may be a metal material (conductive material) such as stainless steel (SUS), iron, or aluminum, with an insulating layer formed on top. In particular, if the base material 55 is a highly thermally conductive material such as aluminum, copper, silver, graphite, or graphene, the uniformity of heating the heater 23 can be improved, enhancing image quality. The insulating layer 57 is made of a material with excellent heat resistance and insulation properties, such as ceramics like alumina or aluminum nitride, glass, mica, or polyimide. The resistive heating element 56 is formed, for example, by coating the surface of the base material 55 with a paste made of silver palladium (AgPd) and glass powder by screen printing, and then firing the base material 55. It is also possible to use a resistive material such as silver alloy (AgPt) or ruthenium oxide (RuO2) as the material for the resistive heating element 56. Furthermore, the electrode portion 58 and the power supply line 59 are formed by screen printing silver (Ag) or silver-palladium (AgPd).

[0043] Figure 5 is a perspective view showing the state in which the connector 40, which serves as a power supply component, is connected to the heater 23.

[0044] As shown in Figure 5, the connector 40 has a resin housing 41, a plurality of contact terminals 42 provided on the housing 41, and a power supply harness 43 connected to each contact terminal 42. Each contact terminal 42 is made of an elastically deformable member such as a leaf spring.

[0045] As shown in Figure 5, the connector 40 is attached so as to sandwich the heater 23 and the heater holder 24 together. In this way, the heater 23 and the heater holder 24 are held together by the connector 40. In this state, the tip (contact portion 42a) of each contact terminal 42 of the connector 40 elastically contacts (pressure contact) the corresponding electrode portion 58, thereby electrically connecting each contact terminal 42 and each electrode portion 58. This makes it possible to supply power to the heater 23 (each resistance heating element 56) from the power supply of the image forming apparatus via the connector 40.

[0046] Here, we will explain the challenges of conventional fixing devices.

[0047] Figure 38 shows the paper feeding area (sheet feeding area) through which the paper passes in the nip section in a conventional fixing device.

[0048] As shown in Figure 38, this configuration employs a so-called central reference transport method in which paper P1 and P2 of various widths are transported with their respective widths centered c as the reference point. In Figure 38, the symbol W1 indicates the maximum paper feed width (maximum sheet pass width) through which the widest paper P1 passes among the various papers fed into the fuser, and the symbol W2 indicates the minimum paper feed width (minimum sheet pass width) through which the narrowest paper P2 passes.

[0049] Generally, the heating area 60 of the heater 23 is arranged symmetrically with respect to the center c in the width direction of the paper, and is positioned over an area equal to or larger than the maximum paper feed width W1 so that it can heat paper of various widths that are transported to the fuser. Therefore, when paper with a width smaller than the maximum paper feed width W1 (for example, the smallest width paper P2) is transported, there is a problem that the heater 23 and fuser belt 21, etc., will heat up in the non-paper feed area where the small width paper P2 does not pass. Since such a temperature rise in the non-paper feed area may cause damage to the fuser belt 21, etc., it is necessary to reduce the print speed to suppress the temperature rise in the non-paper feed area before damage occurs. However, reducing the print speed leads to a decrease in productivity.

[0050] Therefore, in order to improve the problem of temperature rise in the non-paper-feeding area, some conventional fixing devices are equipped with a temperature sensor that detects the temperature in the non-paper-feeding area, and measures are taken to reduce the print speed only when the temperature detected by the temperature sensor approaches a predetermined temperature (a temperature at which damage may occur). In this case, since the print speed is reduced only when necessary, unnecessary productivity reductions can be avoided. Furthermore, in the central reference transport system, the temperature rise in the non-paper-feeding areas on both sides is about the same, so as shown in Figure 38, if there is a temperature sensor 27 that detects the temperature of the heater 23 or fixing belt 21 in at least one of the non-paper-feeding areas (for example, outside the maximum paper-feeding width W1), the temperature rise in the non-paper-feeding area can be detected.

[0051] However, when replenishing paper, if the paper is set in a position shifted from its pre-set position, the paper may be transported off-center c of the transport reference. In this case, the temperature sensor 27, which is positioned in the non-feed area on one side, may not be able to accurately detect the temperature rise in the non-feed area. That is, as shown in Figure 39, if the paper P is shifted to one side in the width direction (left side in the figure) from the pre-set passage area W, the area where the temperature sensor 27 is positioned becomes the feed area, not the non-feed area, and therefore the temperature rise is not detected by the temperature sensor 27. However, on the opposite side from where the paper P is shifted (right side in the figure), the temperature rise is significant. As a result, the temperature rise on the opposite side from where the paper P is shifted cannot be detected, and consequently, a temperature rise occurs.

[0052] One solution to this problem is to place temperature sensors in the non-paper-feeding areas on both sides. However, this increases the number of temperature sensors required, leading to higher costs. Furthermore, even if temperature sensors are placed in the non-paper-feeding areas on both sides, it takes some time for the sensors to detect a rise in temperature in those areas. Therefore, image formation is performed on the misaligned paper until the misalignment is detected based on the temperature sensor's detection. In other words, if paper misalignment is detected based solely on temperature sensor information, it becomes difficult to detect the misalignment early, resulting in wasted paper and toner.

[0053] Furthermore, in addition to the above issues, the fixing device also has a problem where, when a paper P1 of the maximum width is fed through, sufficient heat is not applied to both ends of the paper P1 in the width direction, resulting in fixing failure. That is, immediately after the temperature of the fixing belt 21 rises to a predetermined fixing temperature, the amount of heat stored in the fixing belt 21 is insufficient, so when a paper P1 of the maximum width passes through, the temperature of the fixing belt 21 drops at both ends of the maximum paper feed width W1, which may result in fixing failure.

[0054] As described above, conventional fixing devices have various problems, including temperature rise in non-paper-feed areas, paper misalignment detection, cost issues, and poor fixing at both ends in the width direction of the paper. Therefore, in the embodiments of the present invention described below, the following configuration is adopted to solve these various problems in fixing devices while reducing costs. The characteristic features of the embodiments of the present invention will be described below.

[0055] Figure 6 shows the positional relationship between the heater 23, temperature sensor 27, and paper sensor 30 with respect to the respective paper feeding areas P1 and P2 in an embodiment of the present invention.

[0056] As shown in Figure 6, in this embodiment, one temperature sensor 27 for detecting the temperature of the heater 23 is located inside the minimum paper feed width W2 and one outside the maximum paper feed width W1.

[0057] In this invention, "maximum paper width" refers to a predetermined area where it is assumed that the widest paper will pass, regardless of whether the widest paper actually passes through. Specifically, in this embodiment, a central reference transport system is employed in which paper of various widths is transported based on the center c in the width direction of each paper. Therefore, the various papers are transported symmetrically with respect to the longitudinal center of the fixing belt 21 indicated by the symbol m in Figure 6, or the axial center of the roller portion 62 (elastic layer 221 portion) of the pressure roller 22. For this reason, in this embodiment, the maximum paper width W1 is the range from the longitudinal center of the fixing belt 21 or the axial center (m) of the roller portion 62 of the pressure roller 22 to a distance of half the maximum width of the paper, extending toward both ends. For example, if the widest paper is A4 size (width: 210 mm), the maximum paper width is the range from the longitudinal center of the fixing belt 21 or the axial center of the roller portion 62 of the pressure roller 22 to a distance of 105 mm, which is half the width of A4, extending toward both ends. Furthermore, in this invention, "minimum paper feed width" refers to a predetermined area where it is assumed that a sheet of paper of the minimum width will pass, regardless of whether such a sheet actually passes through. Therefore, the minimum paper feed width W2 is the range from the longitudinal center of the fixing belt 21 or the axial center of the roller portion 62 of the pressure roller 22 toward both ends, at a distance of half the minimum width of the paper.

[0058] Of the two temperature sensors 27 described above, the temperature sensor 27A, which is positioned inside the minimum paper feeding width W2, is located at the center c of the paper feeding width for various types of paper, in other words, at the longitudinal center of the fixing belt 21 or at the axial center of the roller portion 62 of the pressure roller 22. More specifically, the temperature detection unit of the temperature sensor 27A is located at the center c of the paper feeding width for various types of paper. In this way, by positioning one temperature sensor 27A at the center c of the paper feeding width for various types of paper, this temperature sensor 27A can detect the temperature of the heater 23 within the paper feeding width for various types of paper. Based on the detected temperature, the heater 23 is controlled to maintain the fixing belt 21 at a predetermined temperature. Note that the temperature sensor 27A, which is positioned inside the minimum paper feeding width W2, is not necessarily limited to being positioned at the center c of the paper feeding width, but may also be positioned at a location offset from the center c of the paper feeding width.

[0059] In contrast, the temperature sensor 27B, which is located outside the maximum paper feed width W1, is positioned in one of the non-paper feed areas on either side of the maximum paper feed width W1, that is, on one end side of the fixing belt 21 or pressure roller 22. More specifically, the temperature detection unit of the temperature sensor 27B is positioned in the non-paper feed area on one side of the maximum paper feed width W1. Hereinafter, the temperature sensor 27A (first temperature detection member) positioned in the center c of the paper feed width will be conveniently referred to as the "center temperature sensor," and the temperature sensor 27B (second temperature detection member) positioned on one end side of the fixing belt 21 or pressure roller 22 will be conveniently referred to as the "end-side temperature sensor." The function and role of the end-side temperature sensor 27B will be described later.

[0060] Furthermore, as shown in Figure 6, the fixing device 20 according to this embodiment is provided with a paper sensor 30 as a sheet detection member. The paper sensor 30 is a non-contact type sensor that detects paper passing through the nip section, and is positioned on the opposite side from the side where the end-side temperature sensor 27B is provided, with reference to the center c of the paper feeding width. The paper sensor 30 is also positioned outside the minimum paper feeding width W2 and inside the maximum paper feeding width W1. Specifically, the detection part of the paper sensor 30 that detects paper is positioned outside the minimum paper feeding width W2 and inside the maximum paper feeding width W1.

[0061] In this embodiment, the fixing device 20, like conventional fixing devices, has a heating region 60 of the heater 23 that extends over a wide area on both sides in the longitudinal direction of the heater 23, beyond the maximum paper feed width W1. However, unlike conventional devices, the heating region 60 is not arranged symmetrically with respect to the center c of the paper feed width. That is, in this embodiment, as shown in Figure 6, the center z of the heating region 60 in the longitudinal direction X of the heater 23 is shifted relative to the center c of the paper feed width towards the side where the end-side temperature sensor 27B is located (the left side in Figure 6). Therefore, in this embodiment, the paper sensor 30 is located on the opposite side (the right side in Figure 6) from the side where the center z of the heating region 60 of the heater 23 is shifted relative to the center c of the paper feed width. In this invention, the term "heat-generating region" refers to the region in the longitudinal direction X of the heater 23 where the resistance heating element 56 is arranged. As shown in the example below (see Figure 22), when multiple resistance heating elements 56 are arranged, it refers to the range from one end to the other in the longitudinal direction (arrow X direction) of the region where all the resistance heating elements 56 are arranged.

[0062] As described above, in this embodiment, the center z of the heating region 60 of the heater 23 is offset to one side in the longitudinal direction X of the heater 23 (towards the end-side temperature sensor 27B) relative to the center c of the paper feed width. Therefore, when various types of paper are transported along a predetermined paper feed width, the temperature rise becomes more pronounced in the non-paper feed region on the side where the heating region 60 is located, i.e., the side of the end-side temperature sensor 27B (the left side in Figure 6). Consequently, even if the paper transport position varies somewhat in the width direction, the temperature rise in the non-paper feed region on the end-side temperature sensor 27 side is generally more pronounced than the temperature rise in the non-paper feed region on the opposite side. Furthermore, in this embodiment, since the end-side temperature sensor 27B is located in the non-paper feed region on the side where the temperature rise is more pronounced, the end-side temperature sensor 27B can accurately detect the temperature rise in the non-paper feed region. Furthermore, if the temperature detected by the end-side temperature sensor 27 exceeds a preset upper limit, control measures such as reducing the print speed (productivity) or decreasing the heat output of the heater 23 are implemented to avoid damage to the fuser belt 21 due to the temperature rise.

[0063] Thus, in this embodiment, by shifting the center z of the heat-generating region 60 relative to the center c of the paper-feeding width, the temperature rise is basically made more pronounced on the side where the center z of the heat-generating region 60 is shifted (the left side in Figure 6), thus avoiding fluctuations in the side where the temperature rise is pronounced due to variations in the paper-feeding position. Furthermore, in this embodiment, by placing the end-side temperature sensor 27B on the side where the temperature rise is pronounced, it becomes possible to accurately detect the temperature rise in the non-paper-feeding region. This solves the problem of not being able to accurately detect the temperature rise in the non-paper-feeding region due to variations in the paper-feeding position. In addition, in this embodiment, since the side where the temperature rise is pronounced is limited to one non-paper-feeding region, it is not necessary to provide temperature sensors in both non-paper-feeding regions, thus reducing costs.

[0064] Furthermore, as shown in Figure 7, if the maximum width of paper P1 is transported significantly to the right of the preset paper feed width W1, the temperature rise becomes increasingly pronounced in the non-feeding area on the opposite side of the shifted paper P1 (the left side in Figure 7). In this case, the temperature detected by the edge-side temperature sensor 27B will be higher than normal (when there is no paper misalignment), allowing the paper misalignment to be determined based on the temperature detected by the edge-side temperature sensor 27B. The determination of paper misalignment based on the temperature detected by the edge-side temperature sensor 27B is performed by a control unit provided in the image forming apparatus. Specifically, the control unit compares the temperature detected by the edge-side temperature sensor 27B with the temperature stored in advance for normal conditions, and determines that paper misalignment has occurred if the detected temperature exceeds the normal temperature. If paper misalignment is determined to have occurred, paper feeding and image formation are stopped to avoid image formation on the misaligned paper. This reduces the wasteful consumption of paper and toner.

[0065] Furthermore, as shown in Figure 8, conversely, if the paper P1 with the maximum width is transported significantly to the left of the preset paper feed width W1, the paper P1 will not pass the position of the paper sensor 30. As a result, the paper sensor 30 will no longer detect the paper P1. The control unit and other components can then detect the misalignment of the paper P1 by sensing the detection signal from the paper sensor 30 at this time. In this case as well, to avoid the wasteful consumption of paper and toner due to continued image formation, paper feeding and image formation are stopped. In particular, in this case, since the presence or absence of paper misalignment can be detected when the first sheet of paper is transported, paper feeding and image formation can be stopped at an early stage, effectively suppressing the wasteful consumption of paper and toner. It is also possible to detect paper misalignment by using a temperature sensor instead of the paper sensor 30, but in this embodiment, the paper sensor 30, which is less expensive than a temperature sensor, is used to reduce costs.

[0066] Furthermore, in this embodiment, the problem of temperature drop at the end of the fixing belt 21 associated with paper feeding when the maximum width of paper P1 is fed through can also be improved. Here, the temperature drop at the end of the fixing belt 21 associated with paper feeding can be determined by detecting the temperature of the fixing belt 21 at the end within the maximum paper feeding width W1, but in this embodiment, a temperature sensor is not provided at the end within the maximum paper feeding width W1. Therefore, in this embodiment, an end-side temperature sensor 27B, which is positioned outside the maximum paper feeding width W1, is used as a temperature sensor to detect the temperature drop at the end of the fixing belt 21. That is, by inferring the temperature of the fixing belt 21 at the end within the maximum paper feeding width W1 from the temperature of the non-paper feeding area detected by the end-side temperature sensor 27B, it is possible to confirm whether the temperature at the end of the fixing belt 21 has risen sufficiently. Then, by confirming that the temperature of the fixing belt 21 at the end within the maximum paper feeding width W1 has risen sufficiently based on the temperature detected by the end-side temperature sensor 27B, paper feeding can be started, thereby suppressing the temperature drop at the end associated with paper feeding. This makes it possible to avoid the occurrence of fixing failures due to a decrease in temperature at the end of the fixing belt 21 in this embodiment.

[0067] As described above, in this embodiment, by offsetting the center z of the heat-generating area 60 in the longitudinal direction X relative to the center c of the paper width, and by arranging the end-side temperature sensor 27B and the paper sensor 30 in the above-mentioned positions, it becomes possible to resolve not only the problems associated with temperature rise and paper misalignment in the non-paper-feeding area, but also the temperature drop at the widthwise end of the paper, and various other problems related to cost.

[0068] Furthermore, the central temperature sensor 27A and the end-side temperature sensors 27B may not only detect the temperature of the heater 23, but may also detect the temperature of the fixing belt 21 or the pressure roller 22. Even when these temperature sensors 27A and 27B detect the temperature of the fixing belt 21 or the pressure roller 22, the same operation and effects as in the above embodiment can be achieved.

[0069] Furthermore, although the above embodiment described the temperature rise and positional shift in the non-paper-feed area when the widest paper P1 is fed, the present invention is also applicable when feeding paper with a width smaller than the widest paper P1. Therefore, the arrangement of the end-side temperature sensor 27B and the paper sensor 30 is not limited to the positions shown in Figure 6 and can be changed.

[0070] For example, as shown in the example in Figure 9, the end-side temperature sensor 27B and the paper sensor 30 may be positioned to correspond to a paper P3 with a paper width W3 smaller than the maximum paper width W1. In this case, the end-side temperature sensor 27B is positioned inside the maximum paper width W1 and outside the paper width W3 smaller than the maximum paper width W1, and the paper sensor 30 is positioned at the end within the paper width W3 smaller than the maximum paper width W1. This makes it possible to detect temperature rise and positional displacement in the non-paper-feeding area when a paper P3 with a paper width W3 smaller than the maximum paper width W1 is fed. Furthermore, the present invention is also applicable when feeding paper of other specific width sizes.

[0071] Next, another embodiment of the present invention (second embodiment), which differs from the above embodiment (first embodiment), will be described. The following description will mainly focus on the parts that differ from the above embodiment, and explanations of the same parts will be omitted as appropriate.

[0072] The fixing device 20 shown in Figure 10 includes a heat transfer assisting member or a high thermal conductivity member, a heat equalizing plate 89, between the heater 23 and the heater holder 24. Otherwise, it has basically the same configuration as the fixing device according to the above embodiment (see Figure 2). The heat equalizing plate 89 is made of a material with a higher thermal conductivity than the heater holder 24 (for example, copper, aluminum, silver, etc.) and extends in the longitudinal direction X of the heater 23, thereby transferring the heat from the heater 23 in the longitudinal direction of the fixing belt 21 to equalize the heat.

[0073] As shown in Figure 11, the heat equalization plate 89 is a plate-shaped member having a certain thickness, for example, its thickness is set to 0.3 mm, its length in the longitudinal direction to 222 mm, and its width in the longitudinal intersection direction to 10 mm. In this embodiment, the heat equalization plate 89 is made of a single plate material, but it may be made of multiple members. Note that in Figure 10, the guide member 26 shown in Figure 9 is omitted.

[0074] Furthermore, as shown in Figure 11, the heat equalizing plate 89 is fitted into the recess 24a of the heater holder 24, and the heater 23 is mounted on top of it, so that the heat equalizing plate 89 is held in place by being sandwiched between the heater holder 24 and the heater 23. In this embodiment, the longitudinal width of the heat equalizing plate 89 is set to be approximately the same as the longitudinal width X of the heater 23. The movement of the heat equalizing plate 89 and the heater 23 in the direction intersecting the longitudinal direction (paper transport direction) is restricted by the side walls 24b and 24c, which are arranged in the longitudinal direction of the recess 24a of the heater holder 24. In addition, the movement of the heat equalizing plate 89 and the heater 23 in the longitudinal direction is also restricted by the side walls 24d and 24e, which are arranged in a direction intersecting the longitudinal direction of the recess 24a of the heater holder 24. In this way, by restricting the longitudinal displacement of the heat equalizing plate 89 within the fixing device, the heat conduction efficiency can be improved over the target range in the longitudinal direction.

[0075] Figure 12 shows the positional relationship between the heater 23, the heat distribution plate 89, the temperature sensor 27, and the paper sensor 30 in this embodiment with respect to the respective paper feeding areas P1 and P2.

[0076] As shown in Figure 12, in this embodiment, unlike the above embodiment, the center z of the heating region 60 of the heater 23 is not shifted in the longitudinal direction X of the heater 23 with respect to the center c of the paper width, but is located at the same position as the center c of the paper width. That is, the heating region 60 is arranged symmetrically with respect to the center c of the paper width. In contrast, the longitudinal center v of the heat distribution plate 89 is shifted in the longitudinal direction X of the heater 23 with respect to the center c of the paper width.

[0077] As described above, in this embodiment, the longitudinal center v of the heat equalizing plate 89 is offset to one side in the longitudinal direction X of the heater 23 relative to the center c of the paper feed width. Therefore, when various types of paper are transported along a predetermined paper feed width, the temperature rise in the non-paper feed region on the side where more heat equalizing plates 89 are placed (the left side in Figure 12) becomes more pronounced than the temperature rise in the other non-paper feed region. That is, on the side where the longitudinal center v of the heat equalizing plate 89 is offset, heat from the heater 23 is more easily transferred to the fixing belt 21 via the heat equalizing plate 89, resulting in a significant temperature rise in the fixing belt 21 in the non-paper feed region. Thus, in this embodiment, by offsetting the longitudinal center v of the heat equalizing plate 89 relative to the center c of the paper feed width, the side where the temperature rise is more pronounced is specified to be one of the non-paper feed regions (the left side in Figure 12). Furthermore, if multiple heat equalization plates 89 are arranged along the longitudinal direction X of the heater 23, the center v of the heat equalization plate 89 is defined as the longitudinal center of the region where all of these heat equalization plates 89 are arranged, that is, the region from the heat equalization plate 89 at one end to the heat equalization plate 89 at the other end. The center v of this region should be positioned such that it is offset to one side in the longitudinal direction X of the heater 23 relative to the center c of the paper width.

[0078] Therefore, in this embodiment as well, by arranging the end-side temperature sensor 27B in the non-paper-feeding area on the side where the temperature rise is significant, the end-side temperature sensor 27B can accurately detect the temperature rise in the non-paper-feeding area. In order to detect such a temperature rise in the non-paper-feeding area, in this embodiment the end-side temperature sensor 27B is arranged in the non-paper-feeding area (outside the maximum paper-feeding width W1) on the side where the longitudinal center v of the heat equalizing plate 89 is shifted. On the other hand, the paper sensor 30 is arranged within the paper-feeding area (maximum paper-feeding width W1) on the side opposite to where the end-side temperature sensor 27B is provided, with reference to the center c of the paper-feeding width.

[0079] As a result, in this embodiment as well, in addition to the problems associated with temperature rise and paper misalignment in the non-paper-feeding area, various problems related to temperature drop at both ends in the width direction of the paper and costs can be resolved, just as in the above embodiment.

[0080] Furthermore, in this embodiment, the central temperature sensor 27A and the end-side temperature sensor 27B may detect the temperature of the fixing belt 21, or they may detect the temperature of the pressure roller 22 or the heat distribution plate 89. Also, the arrangement of the end-side temperature sensor 27B and the paper sensor 30 is not limited to positions corresponding to the maximum paper feed width W1 as shown in Figure 12, but may be arranged to correspond to any paper feed width smaller than the maximum paper feed width W1, as in the example shown in Figure 9.

[0081] In the embodiments of the present invention described above, a configuration was described in which either the center z of the heating region 60 of the heater 23 or the center v of the heat equalization plate 89 is offset with respect to the center c of the paper width. However, both the center z of the heating region 60 of the heater 23 and the center v of the heat equalization plate 89 may be offset in the same direction with respect to the center c of the paper width.

[0082] Next, modifications or additional components in each embodiment of the present invention described above will be explained.

[0083] As described above, in each embodiment of the present invention, a unidirectional misalignment in the width direction of the paper is detected by the paper sensor 30, allowing the misalignment to be identified at an early stage. However, depending on how the paper is incorrectly loaded, it may be impossible to know in which direction the paper will be misaligned in the width direction.

[0084] Therefore, as shown in the example in Figure 13, the sheet mounting surface 31a of the bottom plate 31 provided in the paper feed cassette 14 may be tilted downward on the side where the end-side temperature sensor 27B is located (left side in Figure 13) from the center c of the paper feed width. By tilting the bottom plate 31 of the paper feed cassette 14 in this way, the misalignment of the paper P can be identified in one direction. That is, as shown in Figure 13, even if the distance between the pair of regulating members 32 that regulate the positions of both ends of the paper P in the width direction is set to be wider than the width of the paper P, because the bottom plate 31 (sheet mounting surface 31a) is tilted, the paper P on the bottom plate 31 will be positioned towards the left side in Figure 13 along the tilt of the sheet mounting surface 31a due to gravity. In this case, when the paper P is transported, the paper P will be transported with a misalignment from the preset paper feed width, but the direction of this misalignment will be the misalignment on the side of the end-side temperature sensor 27B, so the misalignment can be detected based on whether or not the paper sensor 30 detects the paper, as shown in the example in Figure 8. Therefore, misalignment of the paper can be detected at an early stage.

[0085] Furthermore, as shown in the example in Figure 14, the paper sensor 30 may be provided on the image forming apparatus body instead of the fuser unit 20. In this case, when the fuser unit 20 is replaced, the paper sensor 30 does not need to be replaced along with the fuser unit 20, thus reducing replacement costs.

[0086] Furthermore, as shown in the example in Figure 15, the fixing belt 21 may be a belt consisting of a base material 210 and a surface layer (release layer) 212 provided on the outer periphery of the base material 210. In this case, since there is no elastic layer such as a rubber layer between the surface layer (release layer) 212 and the base material 210, the heat insulation is lower and the thermal conductivity from the heater to the fixing belt surface (outer surface) is better compared to a fixing belt having an elastic layer. However, on the other hand, it is conceivable that the temperature rise of the fixing belt 21 in the non-paper-feeding area will be significant. For this reason, it is preferable to apply the present invention to fixing devices equipped with a fixing belt 21 that does not have such an elastic layer. By applying the present invention, the temperature rise in the non-paper-feeding area can be accurately detected, so that damage to the fixing belt 21 can be suppressed more reliably.

[0087] Although the present invention has been described above, the present invention is not limited to the above embodiments and examples, and the design can be modified as appropriate without departing from the spirit of the invention.

[0088] For example, the present invention can also be applied to fixing devices with configurations as shown in Figures 16 to 19. The configurations of each fixing device shown in Figures 16 to 19 will be described below.

[0089] The fuser 20 shown in Figure 16 differs from the fuser 20 shown in Figure 2 in the position of the temperature sensor 27 that detects the temperature of the heater 23. Other than that, the configuration is the same. In the fuser 20 shown in Figure 16, the temperature sensor 27 is positioned upstream of the center M of the nip section N in the paper feeding direction (nip inlet side). On the other hand, in the fuser 20 shown in Figure 2, the temperature sensor 27 is positioned at the center M of the nip section N. As shown in Figure 16, when the temperature sensor 27 is positioned upstream of the center M of the nip section N in the paper feeding direction, the temperature sensor 27 can accurately detect the temperature on the nip inlet side. Since the nip inlet side is a region where heat from the fuser belt 21 is particularly easily lost by the paper P entering the nip section N, accurately detecting the temperature on the nip inlet side with the temperature sensor 27 ensures image fixation and effectively suppresses the occurrence of fixation offset (a state where the toner image cannot be sufficiently heated).

[0090] Next, in the embodiment shown in Figure 17, a heating nip section N1 that heats the fixing belt 21 with a heater 23 and a fixing nip section N2 that allows the paper P to pass through are formed at separate locations. Specifically, in this embodiment, a nip forming member 68 is placed 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 section N1 and the fixing nip section N2. In this case, the fixing belt 21 is heated at the heating nip section N1, and the heat from the fixing belt 21 is applied to the paper P at the fixing nip section N2, thereby fixing the unfixed image to the paper P.

[0091] Next, the fixing device 20 shown in Figure 18 is an example in which the pressure roller 69 on the heater 23 side is omitted from the fixing device shown in Figure 17, and the heater 23 is formed in an arc shape to match the curvature of the fixing belt 21. Otherwise, the configuration is the same as shown in Figure 17. In this case, because 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 secured, and the fixing belt 21 can be heated efficiently.

[0092] Next, the fixing device 20 shown in Figure 19 is an example in which a roller 73, as another rotating body, is positioned between a pair of rotating bodies, belts 71 and 72. In this example, a heater 23 is positioned within the left belt 71 in Figure 19, and a nip forming member 74 is positioned within the right belt 72. The heater 23 contacts the roller 73 via the left belt 71, and the nip forming member 74 contacts the roller 73 via the right belt 72, thereby forming a heating nip portion N1 and a fixing nip portion N2. In this case, the heater 23 heats the roller 73 via the left belt 71.

[0093] Furthermore, the image forming apparatus according to the present invention is not limited to the color image forming apparatus shown in Figure 1, but is also applicable to image forming apparatuses with configurations such as those shown in Figure 20. The configurations of other image forming apparatuses to which the present invention can be applied will be described below.

[0094] The image forming apparatus 100 shown in Figure 20 comprises an image forming means 80 consisting of a photosensitive drum and the like, a paper transport unit consisting of a pair of timing rollers 81 and the like, a paper feeder 82, a fuser 83, a paper discharger 84, and a reading unit 85. The paper feeder 82 has multiple paper trays, each of which accommodates paper of a different size.

[0095] The reading unit 85 reads the image of the original document Q. The reading unit 85 generates image data from the read image. The paper feeder 82 receives multiple sheets of paper P and feeds the paper P to the transport path. The timing roller 81 transports the paper P on the transport path to the image forming means 80.

[0096] The image forming means 80 forms a toner image on the paper P. Specifically, the image forming means 80 includes a photoreceptor drum, a charging roller, an exposure device, a developing device, a replenishment device, a transfer roller, a cleaning device, and a static elimination device. The fixing device 83 heats and pressurizes the toner image to fix it 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 to the outside of the image forming device 100.

[0097] Next, the fixing device 83 according to this embodiment will be described based on Figure 21. In the configuration shown in Figure 21, parts that are common with the fixing device 20 of the above embodiment shown in Figure 2 are denoted by the same reference numerals, and their descriptions are omitted.

[0098] As shown in Figure 21, 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.

[0099] A nip section N is formed between the fixing belt 21 and the pressure roller 22. The nip width of the nip section N is 10 mm, and the linear speed of the fixing device 83 is 240 mm / s.

[0100] The fixing belt 21 comprises a polyimide substrate and a release layer, and does not have an elastic layer. The release layer is formed from a heat-resistant film material, for example, a fluororesin. The outer diameter of the fixing belt 21 is approximately 24 mm.

[0101] The pressure roller 22 includes a core metal, an elastic layer, and a release layer. The outer diameter of the pressure roller 22 is 24-30 mm, and the thickness of the elastic layer is 3-4 mm.

[0102] The heater 23 includes a base material, an insulating layer, a conductor layer containing a resistive heating element, and an insulating layer, with an overall thickness set to 1 mm. The width of the heater 23 in the paper transport direction is 13 mm.

[0103] As shown in Figure 22, the conductor layer of the heater 23 comprises a plurality of resistive heating elements 56, a power supply line 59, and electrode sections 58A to 58C. The plurality of resistive heating elements 56 are arranged at intervals from each other in the longitudinal direction (arrow X direction) of the heater 23. Here, the portion between each resistive heating element 56 is called a "divided region," and as shown in the enlarged view of Figure 22, a divided region B is formed between each resistive heating element 56 (in Figure 22, divided region B is only shown in the enlarged view, but in reality, divided region B is provided between all resistive heating elements 56). Also, in Figure 22, the direction of arrow Y is a direction that intersects or is perpendicular to the longitudinal direction X of the heater 23 (longitudinal intersection direction), and is a different direction from the thickness direction of the base material 55. Furthermore, the direction of arrow Y is the same as the direction that intersects the arrangement direction of the multiple resistance heating elements 56 (arrangement intersection direction), or the direction that follows the surface of the base material 55 on which the resistance heating elements 56 are provided, which is the short-side direction of the heater 23, or the same direction as the transport direction of the paper fed through the fixing device.

[0104] Furthermore, multiple resistive heating elements 56 constitute a central heating element 35B and heating elements 35A and 35C at both ends that can generate heat independently of it. For example, when current is applied to the leftmost electrode 58A and the central electrode 58B of the three electrode elements 58A to 58C in Figure 22, the heating elements 35A and 35C at both ends will generate heat. Also, when current is applied to the electrode elements 58A and 58C at both ends, the central heating element 35B will generate heat. For example, when performing a fixing operation on small-sized paper, only the central heating element 35B will be heated, and when performing a fixing operation on large-sized paper, all heating elements 35A to 35C will be heated, allowing for heating according to the size of the paper.

[0105] Furthermore, as shown in Figure 23, the heater holder 24 according to this embodiment has a recess 24a for housing and holding 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 rectangular surface (bottom surface) 24f formed in the shape of approximately the same size as the heater 23, and four wall portions (sides) 24b, 24c, 24d, and 24e provided along the four sides forming the outer perimeter of the surface 24f so as to intersect with the surface 24f. Note that in Figure 37, the right wall portion 24e is omitted from the illustration. Alternatively, one of the pair of wall portions 24d and 24e that intersect with the longitudinal direction X of the heater 23 (the arrangement direction of the resistance heating elements 56) may be omitted, and the recess 24a may be configured to open at one end of the heater 23 in the longitudinal direction.

[0106] As shown in Figure 24, 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 (e.g., LCP) and a plurality of contact terminals provided inside the housing.

[0107] The connector 86 is attached to the heater 23 and heater holder 24 in a direction intersecting the longitudinal direction X of the heater 23 (the direction of arrangement of the resistance heating elements 56) (see the direction of the arrow from the connector 86 in Figure 24). The connector 86 is attached to the heater 23 and heater holder 24 on one end side of the heater 23 in the longitudinal direction X (the direction of arrangement of the resistance heating elements 56), on the side opposite to the side where the drive motor for the pressure roller 22 is provided. When attaching the connector 86 to the heater holder 24, a protrusion provided on one of the connector 86 or heater holder 24 may engage with a recess provided on the other, and the protrusion may move relative to the other within the recess.

[0108] With the connector 86 attached, the heater 23 and heater holder 24 are held in place by the connector 86 from both their front and back sides. In this state, each contact terminal makes contact (pressure contact) with each electrode portion of the heater 23, thereby electrically connecting each resistive heating element 56 to the power supply provided in the image forming apparatus via the connector 86. This makes it possible to supply power from the power supply to each resistive heating element 56.

[0109] Furthermore, the flanges 87 shown in Figure 24 are belt retaining members provided at both ends in the longitudinal direction of the anchoring belt 21, and hold both ends of the anchoring 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 which are frame members of the anchoring device.

[0110] Figure 25 shows the arrangement of the temperature sensor 27 and the thermostat 88, which is an electrical cutoff member, according to this embodiment.

[0111] As shown in Figure 25, the temperature sensor 27 according to this embodiment is positioned to face the inner circumferential surfaces of the central Xm side and the end side of the fixing belt 21 in the longitudinal direction (arrow X direction). In addition, one of these temperature sensors 27 is positioned in a location corresponding to the divided region B (see Figure 22) between the resistance heating elements of the heater 23.

[0112] Furthermore, thermostats 88, which act as power-cutting members, are positioned at the central Xm side and the end side of the fixing belt 21 so as 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. If the temperature detected by the thermostat 88 exceeds a preset threshold, the power supply to the heater 23 is cut off.

[0113] Furthermore, as shown in Figures 25 and 26, the flanges 87 that hold both ends of the fixing belt 21 are provided with slide grooves 87a. The slide grooves 87a extend in the direction in which the fixing belt 21 moves toward and toward the pressure roller 22. The engaging portion of the fixing device housing engages with the slide grooves 87a. By the relative movement of these engaging portions within the slide grooves 87a, the fixing belt 21 is configured to move toward and toward the pressure roller 22.

[0114] Furthermore, the area in which the heat equalization plate 89 is placed is not limited to the area shown in Figure 11.

[0115] For example, as shown in the example in Figure 27, the heat equalizer 89 may be placed only over the entire area corresponding to the spacing (divided region) B between each resistance heating element 56. In Figure 27, for convenience, the resistance heating elements 56 and the heat equalizer 89 are shown offset vertically in Figure 27, but they are placed at approximately the same position in the longitudinal intersection direction (arrow Y direction). The heat equalizer 89 may also be placed over a portion of the longitudinal intersection direction (arrow Y direction) of the resistance heating elements 56, or, as shown in the example in Figure 28, the heat equalizer 89 may be placed over the entire longitudinal intersection direction (arrow Y direction) of the resistance heating elements 56. Furthermore, as shown in Figure 28, the heat equalizer 89 may be placed not only at the position corresponding to the longitudinal spacing B, but also across the resistance heating elements 56 on both sides of the spacing B. "Placing the heat equalizer 89 across the resistance heating elements 56 on both sides" means that the heat equalizer 89 overlaps with the resistance heating elements 56 on both sides in the longitudinal direction, at least partially. Furthermore, the heat equalizer 89 may be placed at positions corresponding to all of the spacing B of the heater 23, or it may be placed at positions corresponding to only some of the spacing B (in this case, one location), as shown in the example in Figure 28. Here, "placing the heat equalizer 89 at positions corresponding to spacing B" means that at least a portion of the spacing B and the heat equalizer 89 overlap in the longitudinal direction.

[0116] The pressure applied by the pressure roller 22 causes the heat equalization plate 89 to be sandwiched between the heater 23 and the heater holder 24, making close contact with these components. The contact of the heat equalization plate 89 with the heater 23 improves the heat conduction efficiency of the heater 23 in the longitudinal direction. Furthermore, by positioning the heat equalization plate 89 at a position corresponding to the interval B of the heater 23 in the longitudinal direction, the heat conduction efficiency at interval B can be improved, increasing the amount of heat transferred to interval B and raising the temperature at interval B. This suppresses temperature unevenness in the longitudinal direction of the heater 23 and suppresses temperature unevenness in the longitudinal direction of the fixing belt 21. As a result, uneven fixing and gloss unevenness of the image fixed to the paper can be suppressed. In addition, it is no longer necessary to increase the heat output of the heater 23 to ensure sufficient fixing performance at interval B, thereby achieving energy savings in the fixing device. In particular, when the uniform heating plate 89 is placed over the entire longitudinal area where the resistance heating element 56 is located, the heat transfer efficiency of the heater 23 can be improved over the entire main heating area (i.e., the image forming area of ​​the paper being fed through), and temperature unevenness in the longitudinal direction of the heater 23 and, consequently, the fixing belt 21 can be suppressed.

[0117] Furthermore, the combination of the heat distribution plate 89 and the resistance heating element 56 having PTC characteristics can more effectively suppress overheating in the non-paper-feeding area when small-sized paper is fed. PTC characteristics refer to the characteristic that the resistance value increases as the temperature rises (the heater output decreases when a constant voltage is applied). In other words, because the resistance heating element 56 has PTC characteristics, the amount of heat generated by the resistance heating element 56 in the non-paper-feeding area can be effectively suppressed, and the heat distribution plate 89 can efficiently transfer the heat from the non-paper-feeding area, where the temperature has risen, to the paper-feeding area. As a result of these synergistic effects, overheating in the non-paper-feeding area can be effectively suppressed.

[0118] Furthermore, in the vicinity of interval B, the temperature of the heater 23 is lower due to the small amount of heat generated at interval B, so it is preferable to place a heat equalizing plate 89. For example, by placing a heat equalizing plate 89 at a position corresponding to the enlarged division region C, which includes the area around interval B shown in Figure 29, the longitudinal heat transfer efficiency in and around interval B can be improved, and longitudinal temperature unevenness of the heater 23 can be suppressed more effectively. In addition, if the heat equalizing plate 89 is placed over the entire longitudinal direction of the region where all resistance heating elements 56 are arranged, longitudinal temperature unevenness of the heater 23 (fixing belt 21) can be suppressed more reliably.

[0119] Next, we will describe yet another embodiment of the fixing device.

[0120] The fixing device 20 shown in Figure 30 has a second high-thermal-conductivity member 90 between the heater holder 24 and the heat equalization plate 89. The second high-thermal-conductivity member 90 is provided at a different position from the heat equalization plate 89 in the stacking direction (left-right direction in Figure 30) of the components such as the heater holder 24, the stay 25, and the heat equalization plate 89, which is the first high-thermal-conductivity member. More specifically, the second high-thermal-conductivity member 90 is provided superimposed on the heat equalization plate 89. In this embodiment, a temperature sensor (thermistor) 27 is provided, as in the embodiment shown in Figure 10, but Figure 30 shows a cross-section where the temperature sensor 27 is not located.

[0121] The second high thermal conductivity member 90 is made of a material with a higher thermal conductivity than the base material 55, such as graphene or graphite. In this embodiment, the second high thermal conductivity member 90 is made of a graphite sheet with a thickness of 1 mm. Alternatively, the second high thermal conductivity member 90 may be made of a plate material such as aluminum, copper, or silver.

[0122] As shown in Figure 31, multiple second high-heat-conductivity members 90 are arranged in the recess 24a of the heater holder 24, with longitudinal spacing between each second high-heat-conductivity member 90. The portion of the heater holder 24 where the second high-heat-conductivity members 90 are provided has a recess that is deeper than the rest of the heater holder 24. The second high-heat-conductivity members 90 have gaps between them and the heater holder 24 on both longitudinal sides. This suppresses heat transfer from the second high-heat-conductivity members 90 to the heater holder 24, allowing the heater 23 to efficiently heat the fixing belt 21. Note that the guide member 26 shown in Figure 10 is omitted in Figure 31.

[0123] As shown in Figure 32, the second high-heat-conductivity member 90 (see hatched area) is positioned in the longitudinal direction (arrow X direction) at a location corresponding to the interval B, overlapping at least a portion of the adjacent resistance heating elements 56. In particular, in this embodiment, the second high-heat-conductivity member 90 is positioned over the entire interval B. Note that Figure 32 (and Figure 34 described later) shows the case where the heat equalizing plate 89 is positioned over the entire longitudinal direction of the area where all the resistance heating elements 56 are arranged, but the arrangement range of the heat equalizing plate 89 is not limited to this.

[0124] As in this embodiment, in addition to the heat equalization plate 89, the second high heat conductive member 90 is positioned at a location corresponding to the longitudinal spacing B, overlapping at least a portion of the adjacent resistance heating elements 56. This further improves the longitudinal heat transfer efficiency at the spacing B, and more effectively suppresses longitudinal temperature unevenness of the heater 23. Most preferably, as shown in Figure 33, the heat equalization plate 89 and the second high heat conductive member 90 are provided only over the entire area at the location corresponding to spacing B. This makes it possible to particularly improve the heat transfer efficiency at the location corresponding to spacing B compared to other areas. In Figure 33, for convenience, the resistance heating elements 56, the heat equalization plate 89, and the second high heat conductive member 90 are shown offset in the vertical direction of the figure, but they are positioned at approximately the same location in the longitudinal intersection direction (arrow Y direction). However, this is not the only option, and the heat equalization plate 89 and the second high heat conductive member 90 may be positioned in a portion of the longitudinal intersection direction of the resistance heating elements 56, or they may be positioned to cover the entire longitudinal intersection direction.

[0125] Furthermore, both the heat distribution plate 89 and the second high-thermal-conductivity member 90 may be made of the graphene sheet. In this case, the heat distribution plate 89 and the second high-thermal-conductivity member 90 can be formed with high thermal conductivity in a predetermined direction along the surface of the graphene, that is, in the longitudinal direction rather than the thickness direction. This effectively suppresses temperature unevenness in the longitudinal direction of the heater 23 and the fixing belt 21.

[0126] Graphene is a flaky powder. As shown in Figure 36, graphene consists of a planar hexagonal lattice structure of carbon atoms. A graphene sheet is a sheet of graphene, usually a single layer. A graphene sheet may also contain impurities in the single layer of carbon, or it may have a fullerene structure. A fullerene structure is generally recognized as a compound in which an equal number of carbon atoms form a polycyclic structure fused in a cage-like manner with 5-membered and 6-membered rings, such as C60, C70, and C80 fullerenes, or other closed cage-like structures having 3-coordinate carbon atoms.

[0127] Graphene sheets are artificial materials and can be fabricated, for example, by chemical vapor deposition (CVD).

[0128] Commercially available graphene sheets can be used. The size and thickness of the graphene sheet, as well as the number of layers of the graphite sheet described later, can be measured, for example, by a transmission electron microscope (TEM).

[0129] Furthermore, graphite with multiple layers of graphene exhibits high thermal conductivity anisotropy. As shown in Figure 37, graphite has a crystalline structure in which layers of condensed six-membered rings of carbon atoms are spread out in a planar manner, and these layers are stacked multiple times. In this crystalline structure, adjacent carbon atoms within a layer form covalent bonds, while carbon atoms between layers form van der Waals bonds. The covalent bonds have a stronger bonding force than van der Waals bonds, and there is a large anisotropy between the bonds within a layer and the bonds between layers. In other words, by constructing the heat equalization plate 89 or the second high thermal conductivity member 90 from graphite, the heat transfer efficiency in the longitudinal direction of the heat equalization plate 89 or the second high thermal conductivity member 90 becomes larger than in the thickness direction (i.e., the stacking direction of the members), and heat transfer to the heater holder 24 can be suppressed. Therefore, temperature unevenness in the longitudinal direction of the heater 23 can be efficiently suppressed, and the heat flowing out to the heater holder 24 can be minimized. Furthermore, by constructing the heat distribution plate 89 or the second high heat conductivity member 90 from graphite, the heat distribution plate 89 or the second high heat conductivity member 90 can be given excellent heat resistance, such as not oxidizing up to about 700 degrees Celsius.

[0130] The physical properties and dimensions of the graphite sheet can be appropriately changed according to the functions required of the heat distribution plate 89 or the second high-thermal-conductivity member 90. For example, the anisotropy of its thermal conductivity can be increased by using high-purity graphite or single-crystal graphite, or by increasing the thickness of the graphite sheet. In addition, to increase the speed of the fixing device, a thinner graphite sheet may be used to reduce the heat capacity of the fixing device. Furthermore, if the width of the nip section N and the heater 23 is large, the longitudinal width of the heat distribution plate 89 or the second high-thermal-conductivity member 90 may be increased accordingly.

[0131] From the viewpoint of increasing mechanical strength, it is preferable that the graphite sheet has 11 or more layers. Furthermore, the graphite sheet may partially consist of single-layer and multi-layer sections.

[0132] The second high-heat-conductivity member 90 may be provided in the longitudinal direction at a position corresponding to the interval B (further expanded division region C) and overlapping with at least a portion of the adjacent resistance heating element 56, and is not limited to the arrangement shown in Figure 32. For example, as shown in the example in Figure 34, the second high-heat-conductivity member 90A may be provided extending outwards on both sides of the base material 55 in the longitudinal intersection direction (arrow Y direction). The second high-heat-conductivity member 90B may be provided in the longitudinal intersection direction within the range where the resistance heating element 56 is provided. The second high-heat-conductivity member 90C may be provided in a portion of the interval B.

[0133] In another embodiment shown in Figure 35, a gap in the thickness direction (left-right direction in Figure 35) is provided between the heat equalization plate 89 and the heater holder 24. That is, a relief portion 24g acting as an insulating layer is provided in a part of the recess 24a (see Figure 48) of the heater holder 24 where the heater 23, heat equalization plate 89, and second high heat conductive member 90 are arranged. The relief portion 24g is provided in a part of the longitudinal direction other than the part where the second high heat conductive member 90 (not shown in Figure 35) is provided. Furthermore, the relief portion 24g is formed by making the depth of the recess 24a of the heater holder 24 deeper than the other parts. As a result, the contact area between the heater holder 24 and the heat equalization plate 89 can be minimized, so that heat transfer from the heat equalization plate 89 to the heater holder 24 is suppressed, and the heater 23 can efficiently heat the fixing belt 21. In the cross-section where the second high-heat-conducting member 90 in the longitudinal direction is provided, the second high-heat-conducting member 90 abuts against the heater holder 24, as shown in the embodiment in Figure 30.

[0134] Furthermore, in this embodiment, the relief portion 24g is provided over the entire area where the resistance heating element 56 is installed in the longitudinal direction (vertical direction in Figure 35). This effectively suppresses heat transfer from the uniform heat plate 89 to the heater holder 24, improving the heating efficiency of the fixing belt 21 by the heater 23. In addition to the configuration of providing a space as in the relief portion 24g, the insulating layer may also be configured with an insulating material having a lower thermal conductivity than the heater holder 24.

[0135] Furthermore, in this embodiment, the second high heat conductivity member 90 is provided as a different member from the heat equalization plate 89, but this is not limited to this. For example, the portion of the heat equalization plate 89 corresponding to the spacing B may be made thicker than the other portions so that the heat equalization plate 89 also functions as the second high heat conductivity member 90.

[0136] Although the configurations of other fixing devices and image forming apparatuses to which the present invention can be applied have been described above, the same effects as those of the above embodiments can be obtained by applying the present invention to fixing devices and image forming apparatuses with such configurations.

[0137] Furthermore, in the above description, the present invention has been explained using the case of application to a fixing device, which is an example of a heating device. However, the present invention is not limited to fixing devices, but can also be applied to heating devices such as drying devices for drying liquids such as ink applied to paper, laminators for heat-pressing a film as a covering member onto the surface of a sheet such as paper, and heat sealers for heat-pressing the sealing portion of packaging materials.

[0138] To summarize the embodiments of the present invention described above, the present invention includes a heating device, a fixing device, and an image forming apparatus having at least the following configurations.

[0139] [First Structure] The first configuration is a heating device comprising: a pair of rotating bodies that contact each other to form a nip portion through which a sheet passes; a heating source having a heating region where a resistance heating element is arranged and which heats at least one of the pair of rotating bodies; and a temperature sensing member that detects the temperature of the heating source, a member in contact with the heating source, or one of the pair of rotating bodies, wherein the center of the heating region in the longitudinal direction of the heating source is offset in the longitudinal direction from the center of the sheet passage width, and the temperature sensing member is positioned outside the sheet passage width on the side where the center of the heating region is offset in the longitudinal direction from the center of the sheet passage width.

[0140] [Second Structure] The second configuration is a heating device comprising: a pair of rotating bodies that contact each other to form a nip portion through which a sheet passes; a heating source having a heating region where a resistance heating element is arranged and which heats at least one of the pair of rotating bodies; a heat transfer assisting member that contacts the heating source; and a temperature sensing member that detects the temperature of the heating source, or a member that contacts the heating source, or one of the pair of rotating bodies, wherein the center of the heat transfer assisting member in the longitudinal direction of the heating source is offset in the longitudinal direction from the center of the sheet passage width, and the temperature sensing member is positioned outside the sheet passage width on the side where the center of the heat transfer assisting member is offset in the longitudinal direction from the center of the sheet passage width.

[0141] [The third structure] The third configuration is a heating device in which, in the first or second configuration, the rotating body heated by the heating source is a belt having a base material and a surface layer provided on the outer circumference side of the base material, and there is no elastic layer between the surface layer and the base material.

[0142] [Fourth component] The fourth configuration is a heating device in which, in any one of the first to third configurations, the heating source has a plurality of heating elements arranged at intervals in the sheet width direction, and the conductive member support is arranged to overlap the areas between the heating elements in the sheet width direction.

[0143] [Fifth Structure] The fifth configuration is a fixing device that fixes the unfixed image onto a sheet using a heating device of any one of the first to fourth configurations.

[0144] [The sixth component] The sixth configuration is an image forming apparatus comprising a heating device of any one of the first to fourth configurations, or a fixing device of the fifth configuration.

[0145] [The seventh component] The seventh configuration is an image forming apparatus provided in the image forming apparatus body, wherein the sixth configuration includes a sheet detection member for detecting a sheet passing through the nip portion, the sheet detection member is located on the side opposite to the side where the temperature detection member is provided with respect to the center of the sheet passage width, and is located inside the sheet passage width, and the sheet detection member is located in the image forming apparatus body.

[0146] [The eighth component] The eighth configuration is an image forming apparatus that, in the sixth or seventh configuration, includes a sheet housing section in which the sheet is housed, wherein the sheet housing section has a sheet mounting surface that is inclined downward on the side where the temperature sensing member is located, relative to the center of the sheet passage width. [Explanation of Symbols]

[0147] 14. Paper feed cassette (sheet storage section) 20 Fixing device (heating device) 21 Fixing belt (first rotating body) 22 Pressure roller (second rotating body) 23 Heater (heat source) 27 Temperature sensor (temperature sensing component) 30. Paper sensor (sheet detection component) 31 Bottom plate 31a Sheet mounting surface 37. Heating plate (heat transfer assisting member) 56 Resistive heating element 60 Heat-generating area 100 Image forming apparatus 210 Base material 212 Surface layer N Nip section P Paper (sheet) W1 Maximum paper feed width (maximum sheet passage width) W2 Minimum paper feed width (minimum sheet passage width) X Longitudinal direction [Prior art documents] [Patent Documents]

[0148] [License 1] Patent No. 5924867

Claims

1. A pair of rotating bodies that come into contact with each other to form a nip section through which the sheet passes, A heating source having a heating region on which a resistance heating element is arranged, and which heats at least one of the pair of rotating bodies, The aforementioned heating source, or a member in contact with the heating source, or a temperature sensing member that detects the temperature of one of the pair of rotating bodies, A heating device comprising, The center of the heating region in the longitudinal direction of the heating source is offset in the longitudinal direction from the center of the sheet passage width. The heating device is characterized in that the temperature sensing member is positioned on the outside of the sheet passage width on the side where the center of the heating region is offset in the longitudinal direction from the center of the sheet passage width.

2. A pair of rotating bodies that come into contact with each other to form a nip section through which the sheet passes, A heating source having a heating region on which a resistance heating element is arranged, and which heats at least one of the pair of rotating bodies, A heat transfer assisting member that comes into contact with the aforementioned heating source, The aforementioned heating source, or a member in contact with the heating source, or a temperature sensing member that detects the temperature of one of the pair of rotating bodies, A heating device comprising, The center of the heat transfer assisting member in the longitudinal direction of the heating source is offset in the longitudinal direction from the center of the sheet passage width. The heating device is characterized in that the temperature sensing member is positioned on the outside of the sheet passage width on the side where the center of the heat transfer assisting member is offset in the longitudinal direction from the center of the sheet passage width.

3. The system includes a sheet detection member that detects the sheet passing through the nip portion, The heating device according to claim 1 or 2, wherein the sheet detection member is positioned on the side opposite to the side on which the temperature detection member is provided, with reference to the center of the sheet passage width, and is positioned inside the sheet passage width.

4. The heating device according to claim 1 or 2, wherein the rotating body heated by the heating source is a belt having a base material and a surface layer provided on the outer circumference side of the base material, and having no elastic layer between the surface layer and the base material.

5. A fixing device characterized by fixing an unfixed image onto a sheet using the heating device described in claim 1 or 2.

6. An image forming apparatus characterized by comprising the heating device described in claim 1 or 2.

7. The system includes a sheet detection member that detects the sheet passing through the nip portion, The sheet detection member is positioned on the side opposite to the side on which the temperature detection member is provided, with reference to the center of the sheet passage width, and is located inside the sheet passage width. The image forming apparatus according to claim 6, wherein the sheet detection member is provided on the main body of the image forming apparatus.

8. It has a seat storage compartment in which the seat is stored, The image forming apparatus according to claim 6, wherein the sheet receiving section has a sheet mounting surface that is inclined downward on the side where the temperature sensing member is positioned, relative to the center of the sheet passage width.

Images