Heating device, fixing device, and image forming apparatus

Abstract

To ensure good responsiveness of a temperature sensor.SOLUTION: A heating device comprises: a heater 23 that heats a belt member; a heat transfer auxiliary member 24 that is in contact with a surface 23b of the heater 23 on an opposite side of a belt contact surface 23a in contact with an inner peripheral surface of the belt member; a holder 25 that holds the heater 23 and the heat transfer auxiliary member 24; and a temperature sensor 27 that is in contact with the surface 23b of the heater 23 on the opposite side of the belt contact surface 23a, and detects a temperature of the heater 23. When a direction of rotation of the belt member on the belt contact surface 23a is defined as a belt movement direction Y, a size A of the minimum gap S1 between an upstream end 27a of the temperature sensor 23 and an opposing surface 40a of the heat transfer auxiliary member 24 facing the upstream end in the belt movement direction Y, and a size B of the minimum gap S2 between a downstream end 24b of the heat transfer auxiliary member 24 and an opposing surface 30b of the holder 25 in the belt movement direction Y, satisfy a relationship of A>B.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 technology]

[0002] 2. Description of the Related Art As an example of a heating device mounted in an image forming apparatus such as a copying machine or a printer, a fixing device that heats a sheet to fix an image onto the sheet is known.

[0003] Generally, a fixing device includes a pair of rotating bodies that come into contact with each other to form a nip portion, a heat source that heats at least one of the pair of rotating bodies, etc. When a sheet enters between the rotating bodies (the nip portion) in a state in which one or both of the rotating bodies are heated to a predetermined temperature by the heat source, an unfixed image on the sheet is heated and pressurized, and the unfixed image is fixed to the sheet. In addition, in the fixing device, a temperature sensor that detects the temperature of the heat source is used to properly maintain the temperature of the heat source and prevent excessive temperature rise.

[0004] The temperature sensor is preferably arranged so as to be in direct contact with the heat source in order to detect the temperature of the heat source with good responsiveness. For example, Patent Document 1 (JP 2014-102429 A) describes a configuration in which a temperature sensor is arranged in a portion cut out of a graphite sheet and the temperature sensor is in direct contact with the heater.

[0005] However, if the cut-out part of the graphite sheet comes into contact with the temperature sensor due to misalignment of parts, etc., heat will flow from the temperature sensor to the graphite sheet, making it impossible to detect temperature quickly and accurately, and there is a risk that the responsiveness of the temperature sensor will decrease. Summary of the Invention [Problem to be solved by the invention]

[0006] Therefore, an object of the present invention is to ensure good responsiveness of a temperature sensor. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention provides a heating device for heating a sheet, comprising a rotating endless belt member, a heater in contact with the inner surface of the belt member and heating the belt member, a heat transfer auxiliary member in contact with the surface of the heater opposite to the belt contact surface that contacts the inner surface of the belt member, a holder for holding the heater and the heat transfer auxiliary member, and a temperature sensor in contact with the surface of the heater opposite to the belt contact surface and detecting the temperature of the heater, wherein when the rotation direction of the belt member at the belt contact surface is defined as the belt movement direction, a minimum gap size A between the upstream end of the temperature sensor in the belt movement direction and the opposing surface of the heat transfer auxiliary member facing the upstream end of the temperature sensor, and a minimum gap size B between the downstream end of the heat transfer auxiliary member in the belt movement direction and the opposing surface of the holder facing the downstream end of the heat transfer auxiliary member satisfy the relationship A>B. Effect of the Invention

[0008] According to the present invention, good responsiveness of the temperature sensor can be ensured. [Brief description of the drawings]

[0009] [Figure 1] 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment of the present invention. [Diagram 2] 1 is a schematic configuration diagram of a fixing device according to a first embodiment of the present invention. [Diagram 3] 1 is a perspective view of a fixing device according to a first embodiment of the present invention. [Figure 4] FIG. 2 is a plan view of the heater according to the first embodiment of the present invention. [Diagram 5] FIG. 2 is a plan view showing a heat transfer assistance member, a holder, and a temperature sensor according to the first embodiment of the present invention. [Figure 6] 6 is a cross-sectional view of the heat transfer assistant member and the holder taken along line ZZ in FIG. 5. [Figure 7]5A and 5B are diagrams illustrating a state in which a heat transfer assistant member moves in a belt moving direction in the first embodiment of the present invention. [Figure 8] 10A and 10B are diagrams showing an aspect in which a heat transfer assistant member moves in a direction opposite to the belt moving direction in the first embodiment of the present invention. [Figure 9] FIG. 11 is a plan view showing a heat transfer assistance member, a holder, and a temperature sensor according to a second embodiment of the present invention. [Figure 10] FIG. 1 is a diagram showing an example of a configuration in which the first embodiment and the second embodiment of the present invention are combined. [Figure 11] FIG. 11 is a diagram showing another example of a configuration in which the first embodiment and the second embodiment of the present invention are combined. [Figure 12] FIG. 11 is a plan view showing a heat transfer assistance member, a holder, and a temperature sensor according to a third embodiment of the present invention. [Figure 13] 11 is a diagram showing the configuration of another fixing device to which the present invention can be applied. [Figure 14] 11 is a diagram showing the configuration of another fixing device to which the present invention can be applied. [Figure 15] FIG. 13 is a diagram showing the configuration of still another fixing device to which the present invention can be applied. [Figure 16] FIG. 11 is a reference diagram for explaining a problem related to the responsiveness of a temperature sensor. [Figure 17] FIG. 11 is a reference diagram for explaining a problem related to the responsiveness of a temperature sensor. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

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

[0011] <Overall configuration of image forming apparatus> FIG. 1 is a schematic diagram of an image forming apparatus 1000 according to a first embodiment of the present invention. In this specification, the term "image forming apparatus" includes a printer, a copier, a facsimile, a printing machine, or a multifunction machine that combines two or more of these. In addition, "image formation" used in the following description means not only forming an image having meaning such as characters and figures, but also forming an image having no meaning such as a pattern. First, the overall configuration and operation of the image forming apparatus according to the first embodiment of the present invention will be described with reference to FIG. 1.

[0012] As shown in FIG. 1, an image forming apparatus 1000 according to the first embodiment of the present invention includes an image forming section 100, a fixing section 200, a sheet supply section 300, and a sheet discharge section 400.

[0013] (Image forming section) The image forming section 100 is a section that forms an image on a sheet as a recording medium. The image forming section 100 includes four imaging units 1Y, 1M, 1C, and 1Bk, an exposure device 6, and a transfer device 8.

[0014] Each of the four imaging units 1Y, 1M, 1C, and 1Bk includes an electrostatic latent image carrier 2, a charging member 3, a developing device 4, and a cleaning member 5.

[0015] The electrostatic latent image carrier 2 is a rotating body that carries an electrostatic latent image on its surface. As the electrostatic latent image carrier 2, for example, a drum-shaped photoconductor as shown in FIG. 1 or an endless belt-shaped photoconductor can be used.

[0016] The charging member 3 is a member that charges the surface of the electrostatic latent image carrier 2. There are no particular limitations on the charging member 3 as long as it can apply a voltage to the surface of the electrostatic latent image carrier 2 to uniformly charge it, and it can be appropriately selected depending on the purpose. Specific examples of the charging member 3 include contact-type charging members such as conductive or semiconductive charging rollers, magnetic brushes, fur brushes, films, and rubber blades, as well as non-contact-type charging members that utilize corona discharge.

[0017] The developing device 4 is a device that forms a toner image by supplying toner as a developer to the electrostatic latent image on the electrostatic latent image carrier 2. The developing device 4 contains toner (developer) of different colors such as yellow, magenta, cyan, and black, which correspond to the color separation components of the color image, for each of the imaging units 1Y, 1M, 1C, and 1Bk.

[0018] The cleaning member 5 is a member that removes toner and other foreign matter remaining on the electrostatic latent image carrier 2. As the cleaning member 5, for example, a cleaning blade that is arranged so as to come into contact with the surface of the electrostatic latent image carrier 2 is used.

[0019] The exposure device 6 is a device that forms an electrostatic latent image by exposing the charged surface of the electrostatic latent image carrier 2. The exposure device 6 is not particularly limited as long as it can expose the charged surface of the electrostatic latent image carrier 2, and can be appropriately selected depending on the purpose. Specific examples of the exposure device include various exposure devices such as a copying optical system, a rod lens array system, a laser optical system, a liquid crystal shutter optical system, and an LED optical system.

[0020] The transfer device 8 is a device that transfers an image onto a sheet. The transfer device 8 includes an intermediate transfer belt 11, a primary transfer roller 12, and a secondary transfer roller 13. The intermediate transfer belt 11 is an endless belt member, 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 electrostatic latent image carrier 2 via the intermediate transfer belt 11, thereby forming a primary transfer nip between the intermediate transfer belt 11 and each electrostatic latent image carrier 2. Meanwhile, the secondary transfer roller 13 contacts the outer peripheral surface of the intermediate transfer belt 11. As a result, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11.

[0021] (Fixing part) The fixing section 200 has a fixing device 20 that heats the sheet to fix an image onto the sheet. The fixing device 20 includes a pair of rotating bodies 19A and 19B that contact each other, and a heater that heats at least one of the pair of rotating bodies 19A and 19B.

[0022] (Sheet supply section) The sheet supply unit 300 is a part that supplies sheets to the image forming unit 100. The sheet supply unit 300 has a paper feed cassette 14 that stores paper P as a sheet, and a paper feed roller 15 that feeds paper P from the paper feed cassette 14. It should be noted that the "sheet" is not limited to paper (paper). In addition to paper, the "sheet" also includes overhead projector sheets or fabrics, metal sheets, plastic films, and prepreg sheets in which carbon fibers are pre-impregnated with resin. In addition to plain paper, the "paper" also includes cardboard, postcards, envelopes, thin paper, coated paper (coated paper, art paper, etc.), tracing paper, and the like.

[0023] (Sheet ejection section) The sheet discharge section 400 is a section that discharges the paper P to the outside of the apparatus. The sheet discharge section 400 has a pair of paper discharge rollers 17 that discharge the paper P, and a paper discharge tray 18 on which the paper P discharged by the paper discharge rollers 17 is placed.

[0024] <Image formation operation> Next, the operation of the image forming apparatus 1000 according to the first embodiment of the present invention will be described with reference to FIG.

[0025] When an instruction to start image formation is given from the operation panel or an external terminal, the electrostatic latent image carrier 2 starts to rotate in each of the imaging units 1Y, 1M, 1C, and 1Bk, and the surface of the electrostatic latent image carrier 2 is charged to a uniform high potential by the charging member 3. Next, the exposure device 6 exposes the surface (charged surface) of each electrostatic latent image carrier 2 based on the image information of the document read by the document reading device or the print image information instructed from the external terminal. As a result, the potential of the exposed portion is reduced and an electrostatic latent image is formed on the surface of each electrostatic latent image carrier 2. Then, toner is supplied from the developing device 4 to each electrostatic latent image. As a result, a toner image of a different color is formed on each electrostatic latent image carrier 2.

[0026] Thereafter, the toner images on the electrostatic latent image carriers 2 reach the primary transfer nip (the position of the primary transfer roller 12) as the electrostatic latent image carriers 2 rotate, and are transferred from the electrostatic latent image carriers 2 to the intermediate transfer belt 11, which is rotating, in the primary transfer nip so as to be superimposed on each other. Thus, a full-color toner image is formed on the intermediate transfer belt 11. Note that the image formation is not limited to the case where a full-color image is formed using all four imaging units 1Y, 1M, 1C, and 1Bk, but it is also possible to form a monochromatic image using any one of the imaging units 1Y, 1M, 1C, and 1Bk, or to form a two-color or three-color image using any two or three imaging units. After the toner images are transferred to the intermediate transfer belt 11, foreign matter such as residual toner on the electrostatic latent image carriers 2 is removed by a cleaning member 5.

[0027] 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 at the secondary transfer nip. This paper P is supplied from the sheet supply unit 300. When an instruction to start image formation is given, the sheet supply unit 300 starts rotating the paper feed roller 15, and the paper P is sent out from the paper feed cassette 14. The sent out paper P comes into contact with the timing roller pair 16 on the way to the secondary transfer nip, and the transport is temporarily stopped. Thereafter, the timing roller pair 16 starts rotating at a predetermined timing, and the paper P is transported to the secondary transfer nip in time with the toner image on the intermediate transfer belt 11 reaching the secondary transfer nip. As a result, the toner image on the intermediate transfer belt 11 is transferred to the paper P at the secondary transfer nip.

[0028] Next, the paper P is transported to the fixing section 200. In the fixing section 200, the toner image on the paper P is heated and pressurized by a pair of rotating rotors 19A, 19B, and the toner image is fixed to the paper P. The paper P is then transported to the sheet discharge section 400, and discharged to the paper discharge tray 18 by the paper discharge rollers 17. In this manner, a series of image forming operations is completed.

[0029] <Configuration of the fixing device> FIG. 2 is a schematic diagram of a fixing device 20 according to the first embodiment of the present invention.

[0030] As shown in FIG. 2, the fixing device 20 includes a pair of rotating bodies 19A and 19B, as well as a heater 23, a heat transfer auxiliary member 24, a holder 25, a stay 26, a temperature sensor 27, a separating member 28, and the like.

[0031] Of the pair of rotors 19A, 19B, the first rotor 19A is a fixing belt 21 that is disposed on the unfixed image bearing surface side of the paper P. The other, second rotor 19B, is a pressure roller 22 that is disposed to face the fixing belt 21. The fixing belt 21 and the pressure roller 22 are pressurized by a pressure member such as a spring so as to come into contact with each other. As a result, a nip portion N is formed between the fixing belt 21 and the pressure roller 22.

[0032] The fixing belt 21 is composed of an endless belt member having, for example, a base material, an elastic layer, a release layer, etc., in this order from the inside. The base material of the fixing belt 21 is made of a metal material such as nickel or stainless steel, or a resin material such as polyimide. The elastic layer of the fixing belt 21 is made of a rubber material such as silicone rubber, foamed silicone rubber, or fluororubber. Since the fixing belt 21 has an elastic layer, minute irregularities are less likely to be formed on the surface of the fixing belt 21, so that heat is more easily transferred uniformly to the toner image on the paper P, improving the fixing quality. The release layer of the fixing belt 21 is made of a material such as PFA (tetrafluoroethylene-perfluoroalkylvinylether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyether sulfide). Since the fixing belt 21 has a release layer, the separation of the toner image from the fixing belt 21 is improved, and the wrapping of the paper P around the fixing belt 21 is suppressed.

[0033] The pressure roller 22 has, for example, a hollow or solid core material, an elastic layer provided on the outer peripheral surface of the core material, and a release layer provided on the outer peripheral surface of the elastic layer. The core material of the pressure roller 22 is made of a metal material such as iron. The elastic layer of the pressure roller 22 is made of silicone rubber, foamed silicone rubber, fluororubber, etc. The release layer of the pressure roller 22 is made of a fluororesin such as PFA or PTFE.

[0034] The heater 23 is a planar or plate-shaped heating source that contacts the inner circumferential surface of the fixing belt 21 at the nip portion N. The heater 23 contacts the pressure roller 22 via the fixing belt 21, so that the fixing belt 21 is pressed between the heater 23 and the pressure roller 22, forming the nip portion N. The heater 23 has a resistance heating element 51 that generates heat when electricity is applied. The resistance heating element 51 is provided on a base material 50 and is covered with an insulating layer 52. When the resistance heating element 51 generates heat, the heat is transferred to the inner circumferential surface of the fixing belt 21 via the insulating layer 52, and the fixing belt 21 is heated. The heater 23 may be turned so that the base material 50 contacts the inner circumferential surface of the fixing belt 21. In that case, since the heat of the resistance heating element 51 is transferred to the fixing belt 21 via the base material 50, it is preferable that the base material 50 is formed of a material with high thermal conductivity.

[0035] Specifically, the substrate 50 is formed of a non-metallic material such as ceramics, glass, or mica, such as alumina or aluminum nitride, which have excellent heat resistance and insulation. In addition, the substrate 50 can be formed of a conductive material such as metal by interposing a separate insulating layer between the substrate 50 and the resistance heating element 51. As the metal material, aluminum or stainless steel is preferable in terms of low cost. In addition, in order to suppress temperature unevenness of the heater 23 and improve image quality, the substrate 50 may be formed of a material with high thermal conductivity, such as copper, graphite, or graphene. Graphene is a sheet-like substance formed by bonding carbon atoms.

[0036] The resistance heating element 51 is formed by a method such as screen printing. Specifically, a paste made of silver palladium (AgPd) and glass powder is applied to the base material 50 by screen printing, and then the base material 50 is fired to form the resistance heating element 51. In addition to silver palladium, other resistive materials such as silver alloy (AgPt) or ruthenium oxide (RuO2) may be used as the material for the resistance heating element 51. The insulating layer 52 is formed of, for example, heat-resistant glass.

[0037] The heat transfer assistant member 24 is a member that assists the transfer of heat generated from the heater 23. The heat transfer assistant member 24 is formed of a material having a higher thermal conductivity than the holder 25 and the like. For example, copper, aluminum, graphene, or the like is used as the material of the heat transfer assistant member 24. The heat transfer assistant member 24 is arranged so as to contact a surface 23b of the heater 23 opposite to a belt contact surface 23a that contacts the inner circumferential surface of the fixing belt 21. This allows the heat of the heater 23 to be effectively dispersed via the heat transfer assistant member 24, thereby suppressing temperature unevenness and localized temperature rise in the heater 23. Note that the heat transfer assistant member 24 is not limited to being a single-layer member made of a single material, and may be a multi-layer member made of multiple materials.

[0038] The holder 25 is a member that holds the heater 23 and the heat transfer assistant member 24. The holder 25 has a concave accommodation portion 30 that accommodates the heater 23 and the heat transfer assistant member 24. By accommodating the heater 23 and the heat transfer assistant member 24 in the accommodation portion 30, the movement of the heater 23 and the heat transfer assistant member 24 in the vertical direction and the direction perpendicular to the paper surface in FIG. 2 is restricted. The holder 25 is preferably made of a heat-resistant material since it is likely to become hot due to the heat of the heater 23. In particular, when the holder 25 is made of a heat-resistant resin with low thermal conductivity such as LCP, unnecessary heat transfer from the heater 23 to the holder 25 is suppressed, and the heating efficiency of the heater 23 is improved.

[0039] Also, the height of the edge of the storage section 30 may be made larger than the thickness of the heater 23, and the edge of the storage section 30 may protrude further toward the nip N than the heater 23. In this case, it becomes possible to prevent damage to the fixing belt 21 due to contact with the edge of the heater 23. Also, since the curvature of the fixing belt 21 on the exit side of the nip N can be increased, it is possible to improve the separation property of the paper P from the fixing belt 21. Note that, if there is no risk of damage to the fixing belt 21 due to contact with the edge of the heater 23, the height of the edge of the storage section 30 may be made smaller than the thickness of the heater 23.

[0040] The stay 26 is a support member that supports the holder 25. The stay 26 supports the holder 25 from the side opposite to the pressure roller 22, thereby suppressing the deflection of the heater 23 due to the pressure force of the pressure roller 22, and obtaining a uniform width of the nip portion N. The material of the stay 26 is preferably an iron-based metal material such as SUS or SECC in order to ensure rigidity.

[0041] The temperature sensor 27 is a contact-type detection means that comes into contact with the surface 23b of the heater 23 opposite to the belt contact surface 23a and detects the temperature of the heater 23. In the first embodiment of the present invention, a thermostat is used as the temperature sensor 27. The thermostat is a temperature sensor that functions as a power cut-off means that cuts off the power supply to the heater 23 when the detected temperature of the heater 23 becomes equal to or higher than a predetermined temperature. The temperature sensor 27 is disposed so as to be in direct contact with the heater 23 through a hole 31 provided in the holder 25 and a hole 40 provided in the heat transfer assistance member 24.

[0042] The separating member 28 is a member that separates the paper P that has passed through the nip portion N from the outer circumferential surface of the fixing belt 21. The separating member 28 is disposed downstream of the nip N in the paper conveying direction. The separating member 28 is fixed to a frame member such as a side plate of the fixing device 20. This allows the leading end of the separating member 28 to be held in a proximate position where it does not come into contact with the outer circumferential surface of the fixing belt 21. The separating member 28 may be attached so as to be displaceable so as to approach and move away from the outer circumferential surface of the fixing belt 21. When the paper P that has passed through the nip portion N comes into contact with the leading end of the separating member 28, the leading end of the separating member 28 enters between the paper P and the fixing belt 21, and the paper P is separated from the outer circumferential surface of the fixing belt 21.

[0043] FIG. 3 is a perspective view of the fixing device 20 according to the first embodiment of the present invention.

[0044] 3, fixing belt 21 is rotatably supported by a pair of rotating body support members 29 arranged on both ends of fixing belt 21 in its longitudinal direction X. Note that the "longitudinal direction" here means a direction perpendicular to the rotation direction of fixing belt 21 and along the outer circumferential surface of fixing belt 21. In other words, the "longitudinal direction" is the direction indicated by arrow X in FIG. 3, and is the same as the longitudinal direction or rotation axis direction of pressure roller 22, or the width direction of a paper sheet passing through nip portion N (a direction intersecting the paper conveyance direction).

[0045] The rotating body support member 29 has a support portion 29a having a C-shaped cross section, a regulating portion 29b, and a fixed portion 29c. The support portion 29a is inserted into an end portion of the fixing belt 21 in the longitudinal direction X and supports the fixing belt 21 from the inside. For this reason, the outer diameter of the support portion 29a is formed to be smaller than the inner diameter of the fixing belt 21. In contrast, the outer diameter of the regulating portion 29b is formed to be larger than the inner diameter of the fixing belt 21. As a result, even if the fixing belt 21 is displaced in one direction in the longitudinal direction X, the one end portion of the fixing belt 21 in the longitudinal direction X abuts against the regulating portion 29b, thereby regulating the shift of the fixing belt 21 in the longitudinal direction X. The fixed portion 29c is a portion fixed to a frame member of the fixing device 20. The fixing portion 29c is fixed to the frame member, so that the fixing belt 21 is rotatably supported by the rotating body support member 29.

[0046] FIG. 4 is a plan view of the heater 23 according to the first embodiment of the present invention.

[0047] 4, the heater 23 has a longitudinal base material 50, and a resistance heating element 51, an insulating layer 52, an electrode portion 53, and a power supply line 54 provided on the base material 50. The heater 23 is disposed so as to extend continuously in the longitudinal direction X of the fixing belt 21 when assembled in the fixing belt 21.

[0048] The resistance heating elements 51 are arranged at intervals along the longitudinal direction of the base material 50. The gap between adjacent resistance heating elements 51 is preferably 0.2 mm or more, more preferably 0.4 mm or more, from the viewpoint of ensuring insulation between the resistance heating elements 51. However, if the gap between the resistance heating elements 51 is too large, the temperature is likely to decrease in the gap, so the gap is preferably 5 mm or less, more preferably 1 mm or less, from the viewpoint of suppressing temperature unevenness along the longitudinal direction. In addition, the resistance heating elements 51 are connected to a pair of electrode parts 53 via a power supply line 54. In the example shown in FIG. 4, a pair of electrode parts 53 is provided at both ends of the base material 50 in the longitudinal direction, and each resistance heating element 51 is electrically connected in parallel to each electrode part 53. The arrangement, number, shape, etc. of the resistance heating elements 51, the electrode parts 53, and the power supply line 54 are not limited to the example shown in FIG. 4.

[0049] The resistance heating element 51 and the power supply line 54 are covered with an insulating layer 52 to ensure insulation and durability. On the other hand, the electrode parts 53 are exposed and not covered with the insulating layer 52 because a connector serving as a power supply member is connected to the electrode parts 53. When the connector is connected to each electrode part 53, power can be supplied to each resistance heating element 51.

[0050] <Operation of the fixing device> The fixing device 20 according to the first embodiment of the present invention operates as follows.

[0051] When the image forming operation is started, the pressure roller 22 starts to rotate in the direction of the arrow in FIG. 2, and the fixing belt 21 starts to rotate in accordance with the rotation. At this time, a lubricant is applied to the inner peripheral surface of the fixing belt 21 in order to reduce the sliding resistance of the fixing belt 21 against the heater 23. In addition, the heater 23 starts to be energized, and when the resistance heating element 51 generates heat by the energization, the fixing belt 21 is heated. Then, when the temperature of the fixing belt 21 reaches a predetermined target temperature at which the image can be fixed, the paper P carrying the unfixed image is conveyed between the fixing belt 21 and the pressure roller 22 (nip portion N), and the toner image on the paper P is heated and pressurized. As a result, the toner image is fixed to the paper P. Thereafter, the paper P is separated from the fixing belt 21 by the separating member 28 and discharged from the fixing device 20.

[0052] <Issues regarding temperature sensor responsiveness> Here, the problem regarding the responsiveness of the temperature sensor will be described using the configuration according to the first embodiment of the present invention as an example.

[0053] In a configuration using a planar heater 23 with a small thermal capacity as a heating source as in the first embodiment of the present invention, the heater 23 quickly rises in temperature, shortening the first print time and saving energy. On the other hand, if a sudden temperature rise causes a large temperature difference between the heat-generating and non-heat-generating parts of the heater 23, there is a risk that the base material 50 of the heater 23 will be damaged due to a stress difference caused by thermal expansion. For this reason, in the first embodiment of the present invention, a temperature sensor 27 is provided to detect the temperature of the heater 23, and when the temperature of the heater 23 reaches or exceeds a predetermined temperature, the power supply to the heater 23 is cut off to stop heat generation.

[0054] In addition, in general, in a fixing device, when a paper sheet having a width smaller than the heating area of ​​the heater passes through, there is a problem that the temperature of the non-passing area where the paper sheet does not pass through rises. In particular, when multiple papers are fixed continuously, the temperature rise in the non-passing area becomes significant, and the temperature of the rotating body such as the fixing belt rises excessively, and there is a risk that the rotating body may be deteriorated or damaged. Therefore, in the first embodiment of the present invention, the heat transfer auxiliary member 24 is brought into contact with the heater 23, and the heat of the heater 23 in the non-passing area is dispersed to the surroundings via the heat transfer auxiliary member 24. In addition, the heat of the heater 23 in the non-passing area can be transferred to the passing area where the paper sheet passes through and effectively utilized as heat for the fixing process, so that improvement in energy saving can be expected.

[0055] However, if the heat transfer assistant member 24 is interposed between the temperature sensor 27 and the heater 23 in order to bring the heat transfer assistant member 24 into contact with the heater 23, the temperature sensor 27 will detect the temperature of the heater 23 via the heat transfer assistant member 24, and the responsiveness of the temperature sensor 27 will decrease. In that case, the temperature sensor 27 will not be able to quickly detect a temperature rise in the heater 23, and there is a risk that damage to the heater 23 due to the temperature rise will not be prevented. For this reason, in the first embodiment of the present invention, a hole 40 is provided in the heat transfer assistant member 24, and the temperature sensor 27 is made to directly contact the heater 23 through the hole 40. This allows the temperature sensor 27 to quickly detect a temperature rise in the heater 23, and effectively prevents damage to the heater 23 due to the temperature rise.

[0056] Incidentally, the accommodation section 30 of the holder 25 in which the heater 23 and the heat transfer assistant member 24 are accommodated is formed to be slightly larger than the heater 23 and the heat transfer assistant member 24 in order to avoid interference between the heater 23 and the heat transfer assistant member 24 when they thermally expand. Therefore, as shown in Fig. 16, there are gaps S between the heater 23 and the inner wall surfaces 30a, 30b of the accommodation section 30, and between the heat transfer assistant member 24 and the inner wall surfaces 30a, 30b of the accommodation section 30, respectively, and the heater 23 and the heat transfer assistant member 24 are accommodated in the accommodation section 30 so as to be able to move.

[0057] 17, when the fixing belt 21 rotates, the heater 23 and the heat transfer assistant member 24 move in the rotation direction of the fixing belt 21 in accordance with the rotation of the fixing belt 21. On the other hand, since the temperature sensor 27 is fixed to the holder 25 or the like, when the heat transfer assistant member 24 moves, the inner surface 40a of the hole 40 of the heat transfer assistant member 24 may come into contact with the temperature sensor 27, which may reduce the responsiveness of the temperature sensor 27. In other words, when the inner surface 40a of the hole 40 comes into contact with the temperature sensor 27, heat flows from the temperature sensor 27 to the heat transfer assistant member 24, which may prevent the temperature rise of the heater 23 from being detected quickly and accurately.

[0058] In this configuration, the temperature sensor 27 contacts the heater 23 through the hole 40 of the heat transfer assistant member 24, and the temperature sensor 27 comes into contact with the heat transfer assistant member 24 due to misalignment of the heat transfer assistant member 24, resulting in a problem of reduced responsiveness of the temperature sensor 27. As a method for solving this problem, there is a method for making the hole 40 larger so that the hole 40 does not come into contact with the temperature sensor 27 when the heat transfer assistant member 24 moves. However, the method for making the hole 40 larger may reduce the contact area between the heat transfer assistant member 24 and the heater 23 as the area of ​​the hole 40 increases, and there is a concern that the heat dispersion effect of the heat transfer assistant member 24 may be difficult to obtain. Therefore, simply making the hole 40 larger makes it difficult to ensure good responsiveness of the temperature sensor 27 while maintaining good function of the heat transfer assistant member 24. Therefore, in the first embodiment of the present invention, the following measures are taken to ensure good responsiveness of the temperature sensor 27 while maintaining good function of the heat transfer assistant member 24.

[0059] <Configuration according to the first embodiment of the present invention> Hereinafter, a configuration according to the first embodiment of the present invention will be described with reference to FIGS.

[0060] FIG. 5 is a plan view showing the heat transfer assisting member 24, the holder 25, and the temperature sensor 27 according to the first embodiment of the present invention. FIG. 6 is a cross-sectional view taken along the line Z-Z in FIG. 5, showing the heat transfer assisting member 24 and the holder 25 cut. The arrow Y in FIGS. 5 and 6 indicates the rotation direction of the fixing belt 21 on the belt contact surface 23a of the heater 23. In the following description, the rotation direction of the fixing belt 21 on the belt contact surface 23a is referred to as the "belt moving direction".

[0061] As shown in FIG. 5, like the heater 23, the heat transfer assisting member 24 is formed in a plate shape that continuously extends in the longitudinal direction X of the fixing belt 21. A hole portion 40 in which the temperature sensor 27 is disposed is formed at the longitudinal center portion of the heat transfer assisting member 24. In the first embodiment of the present invention, since the temperature sensor 27 is disposed within the passing region W1 through which the paper passes, the hole portion 40 is also disposed within the passing region W1.

[0062] Further, the heat transfer assisting member 24 is formed such that the width in the belt moving direction Y becomes larger at both longitudinal ends (E1 < E2). For this reason, the heat transfer assisting member 24 has protruding portions 41A and 41B that protrude from the upstream side 24a and the downstream side 24b in the belt moving direction Y at both longitudinal ends, which are non-passing regions W2 where the paper does not pass. That is, the width E2 in the belt moving direction Y of the protruding portions 41A and 41B is formed to be larger than the width E1 in the belt moving direction Y of the other portions.

[0063] On the other hand, the accommodating portion 30 of the holder 25 is formed to have the same width F in the longitudinal direction X. Therefore, the upstream end 30a and the downstream end 30b in the belt moving direction Y, which are the inner wall surfaces of the accommodating portion 30, are formed in straight lines parallel to each other.

[0064] Here, when the fixing belt 21 rotates, the heat transfer assistant member 24 moves in the belt movement direction Y, and therefore, as the heat transfer assistant member 24 moves, the downstream end 24b of the heat transfer assistant member 24 in the belt movement direction Y approaches the downstream end 30b of the accommodation section 30, which is the opposing surface facing the heat transfer assistant member 24. Also, as the heat transfer assistant member 24 moves, the hole 40 of the heat transfer assistant member 24 moves, and the upstream end 40a of the hole 40 in the belt movement direction Y approaches the upstream end 27a of the temperature sensor 27, which is the opposing surface facing the hole 40. At this time, if the upstream end 40a of the hole 40 comes into contact with the upstream end 27a of the temperature sensor 27, the responsiveness of the temperature sensor 27 decreases, and there is a risk that the temperature rise of the heater 23 cannot be detected quickly and accurately.

[0065] Therefore, in the first embodiment of the present invention, the size A of the gap S1 and the size B of the gap S2 shown in Figures 5 and 6 are set to have a relationship of A > B so that the upstream end 40a of the hole 40 does not contact the upstream end 27a of the temperature sensor 27.

[0066] The gap S1 is the minimum gap between the upstream end 27a of the temperature sensor 27 and the upstream end 40a of the hole 40 facing it. On the other hand, the gap S2 is the minimum gap between the downstream end 24b of the heat transfer assistant member 24 and the downstream end 30b of the storage unit 30 facing it. In this case, the gap between the downstream end 24b of the heat transfer assistant member 24 and the downstream end 30b of the storage unit 30 is formed to be smaller at the protruding parts 41B on both ends of the heat transfer assistant member 24 in the longitudinal direction, so the minimum gap S2 is the gap between the protruding parts 41B and the storage unit 30. In contrast, the gap between the upstream end 27a of the temperature sensor 27 and the upstream end 40a of the hole 40 is the same size at any position, so the gap at any position is taken as the minimum gap S1. The minimum gaps S1 and S2 change depending on the position of the heat transfer assistant member 24 within the storage section 30, but the sizes A and B of the minimum gaps S1 and S2 only need to be the size of the gap between the heat transfer assistant member 24 placed at any position and the temperature sensor 27 or the storage section 30.

[0067] In this way, in the first embodiment of the present invention, the size A of the minimum gap S1 and the size B of the minimum gap S2 are configured to satisfy the relationship A>B, so that even if the heat transfer assistant member 24 moves with the rotation of the fixing belt 21, contact between the heat transfer assistant member 24 and the temperature sensor 27 is avoided. That is, as shown in FIG. 7, even if the heat transfer assistant member 24 moves in the belt movement direction Y with the rotation of the fixing belt 21, the downstream end 24b of the protruding portion 41B of the heat transfer assistant member 24 contacts the downstream end 30b of the accommodation portion 30 before the upstream end 40a of the hole portion 40 contacts the upstream end 27a of the temperature sensor 27, so that the movement of the heat transfer assistant member 24 in the belt movement direction Y is restricted. This prevents contact between the upstream end 40a of the hole portion 40 and the upstream end 27a of the temperature sensor 27. Therefore, according to the configuration according to the first embodiment of the present invention, it is possible to prevent a decrease in the responsiveness of the temperature sensor 27 due to contact between the heat transfer assistant member 24 and the temperature sensor 27, and good responsiveness can be obtained. Furthermore, damage to the heater 23 due to an increase in temperature can be prevented, improving reliability.

[0068] Furthermore, according to the configuration of the first embodiment of the present invention, since the hole 40 does not need to be so large to avoid contact between the heat transfer assistant member 24 and the temperature sensor 27, the heat dispersion effect of the heat transfer assistant member 24 can be maintained well. In other words, since it is sufficient to set the size of the hole 40 so that the sizes A and B of the minimum gaps S1 and S2 satisfy the relationship A>B, the size of the hole 40 can be made the minimum size, and deterioration of the function of the heat transfer assistant member 24 due to making the hole 40 larger than necessary can be suppressed. Therefore, according to the configuration of the first embodiment of the present invention, it is possible to ensure good responsiveness of the temperature sensor 27 while maintaining good function of the heat transfer assistant member 24.

[0069] Furthermore, in the first embodiment of the present invention, in addition to avoiding contact between the heat transfer assistant member 24 and the temperature sensor 27 when moving in the belt movement direction Y, it is also possible to avoid contact between the heat transfer assistant member 24 and the temperature sensor 27 when moving in the direction opposite to the belt movement direction Y.

[0070] Specifically, the size C of the gap S3 and the size D of the gap S4 shown in Figs. 5 and 6 are set to have a relationship of C>D. Here, the gap S3 is the minimum gap between the downstream end 27b of the temperature sensor 27 in the belt moving direction Y and the downstream end 40b of the hole 40, which is the opposing surface facing the downstream end 27b. On the other hand, the gap S4 is the minimum gap between the upstream end 24a of the heat transfer assistant member 24 and the upstream end 30a of the storage unit 30, which is the opposing surface facing the upstream end 24a. The minimum gap S4 between the upstream end 24a of the heat transfer assistant member 24 and the upstream end 30a of the storage unit 30 is the gap between the protrusion 41A and the storage unit 30, just like the minimum gap S2. On the other hand, the gap between the downstream end 27b of the temperature sensor 27 and the downstream end 40b of the hole 40 is the same size at any position, so the gap at any position is set to the minimum gap S3. In addition, the minimum gaps S3, S4 also change depending on the position of the heat transfer assistant member 24 within the storage section 30, but the sizes C, D of the minimum gaps S3, S4 may also be the size of the gap between the heat transfer assistant member 24 placed at any position and the temperature sensor 27 or the storage section 30.

[0071] Since the size C of the minimum gap S3 and the size B of the minimum gap S4 satisfy the relationship C>D, contact between the heat transfer assistant member 24 and the temperature sensor 27 can be avoided even if the heat transfer assistant member 24 moves in the opposite direction to the belt movement direction Y. That is, as shown in FIG. 8, even if the heat transfer assistant member 24 moves in the opposite direction to the belt movement direction Y, the upstream end 24a of the protrusion 41A of the heat transfer assistant member 24 contacts the upstream end 30a of the accommodation section 30 before the downstream end 40b of the hole 40 contacts the downstream end 27b of the temperature sensor 27, so that the movement of the heat transfer assistant member 24 in the opposite direction to the belt movement direction Y is restricted. As a result, contact between the downstream end 40b of the hole 40 and the downstream end 27b of the temperature sensor 27 is avoided, so that a decrease in the responsiveness of the temperature sensor 27 due to contact between the heat transfer assistant member 24 and the temperature sensor 27 can be prevented.

[0072] Thus, according to the configuration of the first embodiment of the present invention, the contact between the heat transfer assistant member 24 and the temperature sensor 27 can be avoided not only when the heat transfer assistant member 24 moves in the belt moving direction Y, but also when it moves in the opposite direction to the belt moving direction Y, so that the deterioration of the responsiveness of the temperature sensor 27 due to the contact between the heat transfer assistant member 24 and the temperature sensor 27 can be highly prevented. Furthermore, by making it possible to avoid the contact between the heat transfer assistant member 24 and the temperature sensor 27 whether the heat transfer assistant member 24 moves in the belt moving direction Y or the opposite direction, it becomes possible to attach the heat transfer assistant member 24 and the holder 25 without worrying about the upstream and downstream directions. In other words, even if the heat transfer assistant member 24 and the holder 25 are attached with their upstream and downstream directions reversed, the contact between the heat transfer assistant member 24 and the temperature sensor 27 caused by the movement of the heat transfer assistant member 24 in the belt moving direction Y or the opposite direction can be avoided, so that the occurrence of abnormalities due to incorrect assembly can be prevented. Therefore, according to the configuration of the first embodiment of the present invention, it becomes possible to provide a fixing device and an image forming device with high reliability.

[0073] In the first embodiment of the present invention, when the heat transfer assistant member 24 moves in the belt moving direction Y or the opposite direction, the heat transfer assistant member 24 is positioned by contacting only a part of the heat transfer assistant member 24 and the storage section 30 in the belt moving direction Y, rather than contacting the entire part of the heat transfer assistant member 24 and the storage section 30 facing each other in the belt moving direction Y. This improves the positioning accuracy of the heat transfer assistant member 24. That is, the heat transfer assistant member 24 and the storage section 30 contact only the protrusions 41A and 41B, which are a part of the heat transfer assistant member 24, and the part facing the protrusions 41A and 41B, rather than the entire part of the heat transfer assistant member 24 and the storage section 30 facing each other in the belt moving direction Y. This reduces the contact area, and reduces the influence of positioning variations due to dimensional tolerances of parts. In this way, according to the configuration of the first embodiment of the present invention, the positioning accuracy of the heat transfer assistant member 24 is improved, so that it is possible to more reliably avoid contact between the hole 40 and the temperature sensor 27. In addition, the area for ensuring the dimensional accuracy of the heat transfer assistant member 24 and the storage section 30 for positioning can be reduced, which also reduces the manufacturing cost. The heat transfer assistant member 24 and the container 30 are not necessarily limited to a configuration in which only a part of the portion facing the belt moving direction Y is in contact with each other, but may be a configuration in which the entire facing portion is in contact with each other.

[0074] Furthermore, in the first embodiment of the present invention, the positioning protrusions 41A, 41B are disposed in the non-passage area W2, so that the function of the heat transfer assistant member 24 in the passage area W1 can be achieved as intended. That is, in the passage area W1 of the heat transfer assistant member 24, there is no need to change the shape for positioning, so that it is possible to avoid any effect on the function of the heat transfer assistant member 24 due to the shape change. As a result, the heat dispersion effect of the heat transfer assistant member 24 can be achieved as intended in the passage area W1, so that the paper can be heated uniformly.

[0075] Furthermore, since the projections 41A, 41B for positioning are disposed in the non-passage region W2, the posture of the heat transfer assistant member 24 during positioning can be stabilized. That is, since the projections 41A, 41B are disposed not in the pass-through region W1 but in the non-passage region W2 away from both ends in the longitudinal direction, rotation of the heat transfer assistant member 24 within the housing section 30 can be suppressed, and the posture of the heat transfer assistant member 24 can be stabilized.

[0076] <Configuration of other embodiments> Next, another embodiment of the present invention that is different from the first embodiment will be described. Below, the differences from the first embodiment of the present invention will be mainly described, and the same parts will not be described as appropriate.

[0077] Second embodiment of the present invention FIG. 9 is a plan view showing a heat transfer assistance member 24, a holder 25, and a temperature sensor 27 according to the second embodiment of the present invention.

[0078] As shown in FIG. 9, in the second embodiment of the present invention, the holder 25 has a plurality of protrusions 32A, 32B for positioning the heat transfer assistant member 24. The plurality of protrusions 32A, 32B are provided at the upstream end 30a and downstream end 30b of the storage section 30 in the longitudinal direction. On the other hand, the heat transfer assistant member 24 does not have a protrusion for positioning. Since the protrusions 32A, 32B of the holder 25 are provided so as to protrude from the upstream end 30a and downstream end 30b of the storage section 30, the width of the storage section 30 in the belt movement direction Y is smaller in the portion where each protrusion 32A, 32B is provided than in the other portion (F1>F2). Therefore, the minimum gaps S2, S4 are formed between each protrusion 32A, 32B and the heat transfer assistant member 24.

[0079] Therefore, in the second embodiment of the present invention, similarly to the first embodiment of the present invention, the relationship of the minimum gaps S1, S2, S3, and S4 is set to A>B and C>D, so that contact between the heat transfer assistant member 24 and the temperature sensor 27 can be avoided. That is, when the heat transfer assistant member 24 moves in the belt movement direction Y or the opposite direction, the downstream protrusion 32B or the upstream protrusion 32A comes into contact with the heat transfer assistant member 24 before the hole 40 comes into contact with the temperature sensor 27, and the movement of the heat transfer assistant member 24 is restricted, so that contact between the hole 40 and the temperature sensor 27 can be avoided. Furthermore, the protrusions 32A and 32B come into contact with the heat transfer assistant member 24, so that the heat transfer assistant member 24 is positioned in the belt movement direction Y or the opposite direction.

[0080] In this way, the protrusion for positioning the heat transfer assistant member 24 is not limited to being provided on the heat transfer assistant member 24, but may be provided on the storage section 30 of the holder 25. Furthermore, by providing a protrusion on at least one of the heat transfer assistant member 24 and the holder 25, the gap between the heat transfer assistant member 24 and the storage section 30 can be reduced, and the protrusion can be brought into contact with the other member before the heat transfer assistant member 24 and the temperature sensor 27 come into contact, thereby preventing the heat transfer assistant member 24 and the temperature sensor 27 from contacting each other. Therefore, the minimum gaps S2 and S4 for preventing such contact between the heat transfer assistant member 24 and the temperature sensor 27 can be formed by making some of the portions where the heat transfer assistant member 24 and the holder 25 face each other closer than the other portions in the belt movement direction Y. That is, the minimum gaps S2 and S4 may be formed by making the width E2 of a portion of the heat transfer assistant member 24 larger than the width E1 of the other portions as in the first embodiment of the present invention, or by making the width F2 of a portion of the storage section 30 smaller than the width F1 of the other portions as in the second embodiment of the present invention.

[0081] In particular, when the width of the accommodation section 30 is changed to form the minimum gaps S2, S4 as in the second embodiment of the present invention, the heat transfer assistant member 24 can be made to have the same width E over its length, so that the heat transfer assistant member 24 can be formed in a simple shape. In this case, there is an advantage that the yield is improved when the heat transfer assistant member 24 is manufactured by cutting it out from a large plate material, and the manufacturing cost can be reduced.

[0082] Also in the second embodiment of the present invention, when the heat transfer assistant member 24 moves in the belt movement direction Y or the opposite direction, the heat transfer assistant member 24 comes into contact with the protrusions 32A, 32B of the storage section 30, so that the contact area between the heat transfer assistant member 24 and the storage section 30 can be reduced. This reduces the effects of positioning variations due to dimensional tolerances of parts, so that the heat transfer assistant member 24 can be positioned with high precision, and it becomes possible to more reliably avoid contact between the hole 40 and the temperature sensor 27. Furthermore, since the area required to ensure dimensional precision between the heat transfer assistant member 24 and the storage section 30 for positioning is small, manufacturing costs can be reduced.

[0083] Also in the second embodiment of the present invention, the protrusions 32A, 32B for positioning the heat transfer assistant member 24 are arranged in the non-passage areas W2 on both ends in the longitudinal direction, so that the heat transfer assistant member 24 can be positioned at separate locations on both ends in the longitudinal direction. This makes it possible to stabilize the posture of the heat transfer assistant member 24 when it is positioned.

[0084] <Combination of the first and second embodiments of the present invention> Moreover, the configuration according to the first embodiment of the present invention and the configuration according to the second embodiment may be combined.

[0085] For example, as shown in FIG. 10, a protrusion 41A may be formed on the heat transfer assistant member 24 on the upstream side of the belt movement direction Y, and a protrusion 32B may be formed on the storage section 30 on the downstream side of the belt movement direction Y.

[0086] In addition, as in the example shown in FIG. 11, protrusions 41A, 41B may be formed on the heat transfer assistance member 24 at one end side (right end side) in the longitudinal direction X, and protrusions 32A, 32B may be formed on the accommodating section 30 at the other end side (left end side) in the longitudinal direction X.

[0087] In this way, the configuration according to the first embodiment of the present invention may be combined with the configuration according to the second embodiment, so that the shapes of the heat transfer assistant member 24 and the accommodating portion 30 are asymmetric on the upstream and downstream sides in the belt movement direction Y, or on one end side and the other end side in the longitudinal direction. In this case, erroneous assembly in which the heat transfer assistant member 24 and the holder 25 are assembled in the wrong orientation is less likely to occur.

[0088] Third embodiment of the present invention FIG. 12 is a plan view showing a heat transfer assistance member 24, a holder 25, and a temperature sensor 27 according to the third embodiment of the present invention.

[0089] As shown in FIG. 12, in the third embodiment of the present invention, the width E3 of the heat transfer assistant member 24 in the belt movement direction Y at the portion where the hole portion 40 is provided is formed larger than the width E1 of the heat transfer assistant member 24 in the belt movement direction Y at the portion other than the hole portion 40 within the passing area W1 (E3>E1).

[0090] In the portion where the holes 40 are provided, the contact area between the heat transfer assistant member 24 and the heater 23 in the belt movement direction Y is reduced, and there is a concern that the heat dispersion effect of the heat transfer assistant member 24 may be difficult to obtain. Therefore, in the third embodiment of the present invention, the width E3 in the portion where the holes 40 are provided is made larger than the width E1 in the portion other than the holes 40 in the passing area W1, thereby suppressing a decrease in the heat dispersion effect in the portion where the holes 40 are provided. As a result, the heat dispersion effect of the heat transfer assistant member 24 can be obtained well even in the portion where the holes 40 are provided, and uniform heating of the paper becomes possible.

[0091] In this case, the positioning of the heat transfer assistant member 24 is performed by contact between the projections 41A, 41B arranged in the non-passage area W2 and the accommodation section 30. Therefore, the portion of the heat transfer assistant member 24 where the hole 40 is provided does not function as a positioning portion. For this reason, the width E3 of the portion where the hole 40 is provided is formed smaller than the width E2 of the portion where the projections 41A, 41B are provided (E3 <E2)。

[0092] The above describes each embodiment of the present invention. In each of the above embodiments, the size of the gap between the members is set to A>B and C>D so that the contact between the heat transfer assistant member 24 and the temperature sensor 27 can be avoided not only when the heat transfer assistant member 24 moves in the belt moving direction Y but also when the heat transfer assistant member 24 moves in the opposite direction to the belt moving direction Y. However, the present invention is not limited to the case where both the relationships A>B and C>D are satisfied, and it may be the case where only the relationship A>B is satisfied. That is, since an excessive temperature rise of the heater 23 is likely to occur during operation when the heater generates heat and the fixing belt 21 rotates, if the contact between the heat transfer assistant member 24 and the temperature sensor 27 can be avoided at least when the heat transfer assistant member 24 moves with the rotation of the fixing belt 21, it is possible to largely prevent damage to the heater 23 due to the temperature rise. Therefore, only the relationship A>B may be adopted so that the contact between the heat transfer assistant member 24 and the temperature sensor 27 can be avoided at least when the heat transfer assistant member 24 moves in the belt moving direction Y. In order to more reliably prevent damage to the heater 23 due to a rise in temperature and further improve reliability, it is preferable to satisfy the relationship C>D in addition to the relationship A>B as in the above embodiment.

[0093] The present invention is also applicable to a configuration including a temperature sensor other than a thermostat. For example, the temperature sensor may be a thermopile, a thermistor, an NC sensor, or the like, in addition to a thermostat.

[0094] Furthermore, the shape of the hole 40 of the heat transfer assistant member 24 in which the temperature sensor 27 is arranged may be a rectangular or circular hole shape, or may be a notch shape that opens in the belt movement direction Y. Even when the hole 40 has a notch shape that opens in the belt movement direction Y, there is a risk that the opposing surface of the hole 40 may come into contact with the temperature sensor 27 when the heat transfer assistant member 24 moves in the belt movement direction Y, so it is meaningful to apply the present invention.

[0095] The configuration for positioning the heat transfer assistant member 24 with respect to the accommodation portion 30 can also be changed as appropriate. For example, a hole can be provided in the holder 25, and a part of the heat transfer assistant member 24 can be bent and inserted into the hole, thereby positioning the heat transfer assistant member 24.

[0096] The present invention is also applicable to fixing devices having configurations other than that shown in Fig. 2. Below, some examples of fixing devices to which the present invention can be applied are illustrated. Note that the same components as those in the fixing device shown in Fig. 2 are given the same reference numerals as in Fig. 2, and their explanations are omitted.

[0097] First, in the example shown in FIG. 13, the heating nip portion N1 and the fixing nip portion N2 are formed at different positions. Specifically, two pressure rollers, large and small, 151 and 152 are arranged on opposite sides of the fixing belt 21, and the pressure rollers 151 and 152 contact the outer circumferential surface of the fixing belt 21 to form the heating nip portion N1 and the fixing nip portion N2. In detail, the pressure roller 151 contacts the heater 23 via the fixing belt 21 to form the heating nip portion N1, and the other pressure roller 152 contacts the nip forming member 150 via the fixing belt 21 to form the fixing nip portion N2. In this case, when the heater 23 generates heat, the fixing belt 21 is heated in the heating nip portion N1. Then, heat is applied from the fixing belt 21 to the unfixed image on the paper P in the fixing nip portion N2, so that the image is fixed to the paper P.

[0098] Next, the example shown in Fig. 14 is an example in which the pressure roller 151 on the heater 23 side in the fixing device 20 shown in Fig. 13 is omitted, and the heater 23 is formed in an arc shape to match the curvature of the fixing belt 21. Other than that, it is the same as the configuration shown in Fig. 13. In this case, since the heater 23 is formed in an arc shape, a long contact area between the fixing belt 21 and the heater 23 in the belt rotation direction is ensured, so that the fixing belt 21 can be heated efficiently.

[0099] 15 shows an example in which a roller 163 is disposed between a pair of belts 161 and 162. In this case, the heater 23 disposed in the left belt 161 contacts the central roller 163 via the belt 161 to form a heating nip N1. Also, the nip forming member 153 disposed in the right belt 162 contacts the central roller 163 via the belt 162 to form a fixing nip N2. When the heater 23 generates heat, the central roller 163 is heated in the heating nip N1, and heat is applied from the central roller 163 to an unfixed image on the paper P entering the fixing nip N2, thereby fixing the image to the paper P.

[0100] The present invention is also applicable to a fixing device, which is an example of a heating device that heats a sheet, as well as other heating devices. For example, the present invention is also applicable to a heating device such as a drying device that is installed in an inkjet image forming device and dries a liquid such as ink applied to paper, a laminator that thermocompresses a covering member such as a film onto the surface of a sheet such as paper, or a heat sealer that thermocompresses a seal portion of a packaging material.

[0101] Furthermore, to summarize the aspects of the present invention, the present invention includes at least the following aspects.

[0102] [First aspect] The first aspect is a heating device for heating a sheet, comprising a rotating endless belt member, a heater in contact with the inner surface of the belt member and heating the belt member, a heat transfer auxiliary member in contact with the surface of the heater opposite the belt contact surface that contacts the inner surface of the belt member, a holder for holding the heater and the heat transfer auxiliary member, and a temperature sensor in contact with the surface of the heater opposite the belt contact surface and detecting the temperature of the heater, wherein when the rotation direction of the belt member at the belt contact surface is defined as the belt movement direction, the size A of the minimum gap between the upstream end of the temperature sensor in the belt movement direction and the opposing surface of the heat transfer auxiliary member opposing the upstream end of the temperature sensor, and the size B of the minimum gap between the downstream end of the heat transfer auxiliary member in the belt movement direction and the opposing surface of the holder opposing the downstream end of the heat transfer auxiliary member satisfy the relationship A>B.

[0103] [Second aspect] The second aspect is a heating device of the first aspect, wherein the size C of the minimum gap between the downstream end of the temperature sensor in the belt movement direction and the opposing surface of the heat transfer assistant member facing the downstream end of the temperature sensor, and the size D of the minimum gap between the upstream end of the heat transfer assistant member in the belt movement direction and the opposing surface of the holder facing the upstream end of the heat transfer assistant member satisfy the relationship C>D.

[0104] [Third aspect] A third aspect is a heating device according to the first or second aspect, wherein the minimum gap between the heat transfer assistant member and the opposing surface of the holder is formed by bringing some of the portions where the heat transfer assistant member and the holder face each other closer together in the belt movement direction than other portions.

[0105] [Fourth aspect] A fourth aspect is a heating device in any one of the first to third aspects, wherein the minimum gap between the heat transfer assistance member and the opposing surface of the holder is formed in a non-passage area through which the sheet does not pass.

[0106] [Fifth aspect] A fifth aspect is a heating device according to any one of the first to fourth aspects, wherein the minimum gap between the heat transfer assistant member and the opposing surface of the holder is formed by making the width of a part of the heat transfer assistant member in the belt movement direction larger than the width of the other part.

[0107] [Sixth aspect] A sixth aspect is a heating device which is any one of the first to fifth aspects, wherein the holder has a storage section in which the heater and the heat transfer assistant member are stored, and the minimum gap between the heat transfer assistant member and the opposing surface of the holder is formed by making the width of a part of the storage section in the belt movement direction smaller than the width of the other part.

[0108] [Seventh aspect] A seventh aspect is a heating device in which, in any one of the first to eighth aspects, the heat transfer assistant member has a hole in which the temperature sensor is arranged within a passing area through which the sheet passes, and the width of the heat transfer assistant member in the belt movement direction at the part where the hole is provided is larger than the width of the heat transfer assistant member in the belt movement direction at the part other than the hole within the passing area.

[0109] [Eighth aspect] The eighth aspect is a heating device of the seventh aspect, wherein the width of the heat transfer assistant member in the belt movement direction at the portion where the hole is provided is smaller than the width of the heat transfer assistant member in the belt movement direction at a non-passage area where the sheet does not pass through.

[0110] [Ninth aspect] A ninth aspect is a fixing device that fixes an unfixed image onto a sheet using the heating device according to any one of the first to eighth aspects.

[0111] [Tenth aspect] A tenth aspect is an image forming apparatus including the heating device according to any one of the first to eighth aspects or the fixing device according to the ninth aspect. [Explanation of symbols]

[0112] 20 Fixing device (heating device) 21 Fixing belt (first rotating body) 22 Pressure roller (second rotating body) 23 Heater 23a Belt contact surface 24 Heat transfer auxiliary material 25 Holder 27 Temperature Sensor 30 Storage unit 40 Hole 1000 Image forming device P Paper (sheet) S1 Minimum gap S2 Minimum gap S3 Minimum gap S4 Minimum clearance W1 passing area W2 non-passing area Y Belt movement direction [Prior art documents] [Patent documents]

[0113] [Patent Document 1] JP 2014-102429 A

Claims

1. A heating device for heating a sheet, comprising: A rotating endless belt member; a heater that contacts an inner circumferential surface of the belt member and heats the belt member; a heat transfer assistance member that contacts a surface of the heater opposite to a belt contact surface that contacts the inner circumferential surface of the belt member; a holder for holding the heater and the heat transfer assistance member; a temperature sensor that is in contact with a surface of the heater opposite to the belt contact surface and detects a temperature of the heater; When the rotation direction of the belt member on the belt contact surface is defined as the belt movement direction, a minimum gap size A between an upstream end of the temperature sensor in the belt moving direction and an opposing surface of the heat transfer assistance member opposing the upstream end of the temperature sensor; The minimum gap size B between the downstream end of the heat transfer assistant member and the opposing surface of the holder opposing the downstream end of the heat transfer assistant member in the belt moving direction is A heating device characterized in that the relationship A>B is satisfied.

2. a minimum gap size C between a downstream end of the temperature sensor in the belt moving direction and an opposing surface of the heat transfer assistance member opposing the downstream end of the temperature sensor; The minimum gap size D between the upstream end of the heat transfer assistant member and the opposing surface of the holder opposing the upstream end of the heat transfer assistant member in the belt moving direction is The heating device according to claim 1 , wherein the relationship C>D is satisfied.

3. 3. The heating device according to claim 1, wherein the minimum gap between the heat transfer assistant member and the opposing surface of the holder is formed by bringing some of the portions where the heat transfer assistant member and the holder face each other in the belt movement direction closer together than other portions.

4. 3. The heating device according to claim 1, wherein the minimum gap between the heat transfer assistance member and the opposing surface of the holder is formed in a non-passage area through which the sheet does not pass.

5. 3. The heating device according to claim 1, wherein the minimum gap between the heat transfer assistant member and the opposing surface of the holder is formed by making a width of a portion of the heat transfer assistant member in the belt movement direction larger than a width of another portion.

6. the holder has a housing portion in which the heater and the heat transfer assistance member are housed, 3. The heating device according to claim 1, wherein the minimum gap between the heat transfer assistance member and the opposing surface of the holder is formed by making a width of a portion of the accommodating portion in the belt movement direction smaller than a width of the remaining portion.

7. the heat transfer assistance member has a hole in which the temperature sensor is disposed within a passage area through which the sheet passes, 3. The heating device according to claim 1, wherein the width of the heat transfer assistant member in the belt movement direction at the portion where the hole is provided is larger than the width of the heat transfer assistant member in the belt movement direction at the portion other than the hole within the passing area.

8. The heating device according to claim 7 , wherein the width of the heat transfer assistant member in the belt movement direction at the portion where the hole is provided is smaller than the width of the heat transfer assistant member in the belt movement direction at a non-passage area where the sheet does not pass through.

9. A fixing device, comprising: a heating device according to claim 1 or 2, for fixing an unfixed image onto a sheet.

10. An image forming apparatus comprising the heating device according to claim 1 or 2.

Images