Heating device, fixing device, and image forming apparatus

Abstract

To easily check an assembled state of an urging member.SOLUTION: A heating device 20 comprises: a first rotating body 21; a second rotating body 22 that is in contact with an outer peripheral surface of the first rotating body 21 to form a nip part N; a heat source 23 that heats the first rotating body 21; a temperature sensor 26 that detects a temperature of the heat source 23; an urging member 30 that urges the temperature sensor 26 in a direction of the heat source 23; and a bearing member 25 that bears an end 30b of the urging member 30 on the opposite side of an end 30a on the side of the temperature sensor 26. The bearing member 25 covers the circumference of the urging member 30. The urging member 30 is arranged not to expose to the outside of the bearing member 25. The bearing member 25 has hole parts 25a that are provided on a contact surface contacting with the end 30b of the urging member 30 and communicate the inside and the outside of the bearing member 25 with each other. The hole parts 25a allow checking, by visual observation, of a position of the urging member 30 on the contact surface in a longitudinal direction of the bearing member 25 and in a direction intersecting the longitudinal direction.SELECTED DRAWING: Figure 5

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 on an image forming apparatus such as a copying machine or a printer, a fixing device that heats a sheet to fix an image on the sheet is known.

[0003] Generally, a fixing device includes a pair of rotators that contact each other to form a nip portion, a heater that heats at least one of the pair of rotators, and the like. When a sheet enters between the rotators (nip portion) with one or both of the rotators heated to a predetermined temperature by the heater, the unfixed image on the sheet is heated and pressed, and the unfixed image is fixed on the sheet. Further, in the fixing device, a temperature sensor such as a thermistor or a thermostat that detects the temperature of the heater or the rotator is provided for the purpose of appropriately maintaining the temperature of the heater or preventing excessive temperature rise.

[0004] For example, in Patent Document 1 (Japanese Patent Application Laid-Open No. 2018-112669), a configuration is disclosed in which a temperature sensor is biased against a positioning sheet metal by a biasing member in order to easily and accurately position the temperature sensor.

[0005] By the way, when the biasing member that biases the temperature sensor is assembled, due to assembly errors or the like, the biasing member may be assembled in a tilted state with respect to the temperature sensor, or the biasing member may be assembled in a state shifted from a predetermined position. If the biasing member is not assembled in the correct posture or the correct position, there is a possibility that the desired function of the biasing member cannot be obtained. Therefore, it is required to check the assembly state of the biasing member in a manufacturing process or the like.

[0006] However, in a configuration where the surroundings of the biasing member are covered by other members when the biasing member is assembled, it is impossible or difficult to visually check the biasing member from the outside. Therefore, it has been impossible to easily confirm the assembly state including the quality of the posture and position of the biasing member, as well as the presence or absence of the biasing member.

Summary of the Invention

Problems to be Solved by the Invention

[0007] Therefore, an object of the present invention is to enable easy confirmation of the assembled state of the biasing member.

Means for Solving the Problems

[0008] To solve the above problems, a heating device according to the present invention includes a first rotating body, a second rotating body that contacts an outer peripheral surface of the first rotating body to form a nip portion, a heating source that heats at least one of the first rotating body and the second rotating body, a temperature sensor that detects a temperature of the heating source, a biasing member that biases the temperature sensor in a direction of the heating source, and a receiving member that receives an end portion of the biasing member opposite to a side of the temperature sensor. The receiving member covers the periphery of the biasing member, the biasing member is arranged so as not to be exposed to the outside of the receiving member, the receiving member has a hole portion that communicates an inside and an outside of the receiving member on a contact surface that contacts an end portion of the biasing member, and a position of the biasing member in a longitudinal direction of the receiving member and in a direction intersecting the longitudinal direction on the contact surface can be visually confirmed from the hole portion.

Effects of the Invention

[0009] According to the present invention, the assembled state of the biasing member can be easily confirmed.

Brief Description of the Drawings

[0010]

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MODE FOR CARRYING OUT THE INVENTION

[0011] Hereinafter, the present invention will be described based on 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 much as possible, and the description thereof will be omitted after being explained once.

[0012] <Overall Configuration of Image Forming Apparatus> FIG. 1 is a schematic configuration diagram of an image forming apparatus 1000 according to a first embodiment of the present invention. Here, the "image forming apparatus" in this specification includes a printer, a copier, a facsimile machine, a printing machine, or a multifunction machine combining two or more of these. Further, the "image formation" used in the following description means not only forming an image having meanings such as characters and figures but also forming an image having no meaning such as a pattern. First, with reference to FIG. 1, the overall configuration and operation of the image forming apparatus according to the first embodiment of the present invention will be described.

[0013] As shown in FIG. 1, the image forming apparatus 1000 according to the first embodiment of the present invention includes an image forming unit 100, a fixing unit 200, a sheet feeding unit 300, and a sheet discharging unit 400.

[0014] (Image Forming Unit) The image forming unit 100 is a part that forms an image on a sheet as a recording medium. The image forming unit 100 includes four image forming units 1Y, 1M, 1C, 1Bk, an exposure device 6, and a transfer device 8.

[0015] The four image forming units 1Y, 1M, 1C, and 1Bk each include an electrostatic latent image carrier 2, a charging member 3, a developing device 4, and a cleaning member 5.

[0016] 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, in addition to a photosensitive drum, an endless photosensitive belt or the like is used. As the photosensitive drum, for example, an inorganic photosensitive material such as amorphous silicon or selenium, or an organic photosensitive material such as titanyl phthalocyanine can be used. As the organic photosensitive material, a layer in which a charge generation material such as metal-free phthalocyanine or titanyl phthalocyanine is dispersed in a binder resin (charge generation layer) and a layer in which a charge transport material is dispersed in a binder resin (charge transport layer) are stacked on a support such as an aluminum drum. In addition to the laminated photosensitive member having a laminated structure, a single-layer photosensitive member having a photosensitive layer with a single-layer structure in which both a charge generation material and a charge transport material are dispersed in a binder resin on a support can be mentioned. In the single-layer photosensitive member, a hole transport agent and an electron transport agent can also be added as charge transport materials to the photosensitive layer. Further, an undercoat layer may be provided between the support and the laminated charge generation layer or the single-layer photosensitive layer.

[0017] The charging member 3 is a member that charges the surface of the electrostatic latent image carrier 2. The charging member 3 is not particularly limited as long as it can apply a voltage to the surface of the electrostatic latent image carrier 2 to uniformly charge it, and can be appropriately selected according to the purpose. Specifically, in addition to contact charging members such as conductive or semiconductive charging rollers, magnetic brushes, fur brushes, films, and rubber blades, non-contact charging members using corona discharge can be mentioned.

[0018] The developing device 4 is a device that supplies toner as a developer to the electrostatic latent image on the electrostatic latent image carrier 2 to form a toner image. The developing device 4 stores different colors of toner (developer) such as yellow, magenta, cyan, and black corresponding to the color separation components of the color image for each of the image forming units 1Y, 1M, 1C, and 1Bk.

[0019] The cleaning member 5 is a member for removing toner and other foreign matters remaining on the electrostatic latent image carrier 2. As the cleaning member 5, a cleaning blade or the like arranged to contact the surface of the electrostatic latent image carrier 2 is used.

[0020] The exposure device 6 is a device for exposing the charged surface of the electrostatic latent image carrier 2 to form an electrostatic latent image. 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 according to the purpose. Specifically, 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 can be mentioned.

[0021] The transfer device 8 is a device for transferring 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. When each primary transfer roller 12 contacts each electrostatic latent image carrier 2 via the intermediate transfer belt 11, a primary transfer nip is formed between the intermediate transfer belt 11 and each electrostatic latent image carrier 2. On the other hand, the secondary transfer roller 13 contacts the outer peripheral surface of the intermediate transfer belt 11. Thereby, a secondary transfer nip is formed between the secondary transfer roller 13 and the intermediate transfer belt 11. Further, an elastic intermediate transfer belt can also be used as the intermediate transfer belt 11. As the elastic intermediate transfer belt, for example, one in which a flexible elastic layer is laminated on a rigid base layer that can obtain relatively good flexibility can be used. Further, in order to prevent the intermediate transfer belt 11 from meandering, a stop guide member may be provided on the inner peripheral surface of the intermediate transfer belt 11.

[0022] (Fixing section) The fixing section 200 has a fixing device 20 for heating the sheet to fix the image on the sheet. The fixing device 20 includes a pair of rotating bodies 19A, 19B that contact each other, a heating source for heating at least one of the pair of rotating bodies 19A, 19B, and the like.

[0023] (Sheet Feeding Unit) The sheet feeding unit 300 is a part that supplies sheets to the image forming unit 100. The sheet feeding unit 300 includes a paper feed cassette 14 that accommodates the paper P as a sheet, and a paper feed roller 15 that feeds out the paper P from the paper feed cassette 14. Note that the "sheet" includes, in addition to paper, OHP sheets, cloth, metal sheets, plastic films, or prepreg sheets in which carbon fibers are impregnated with resin in advance. Also, the "paper" includes, in addition to plain paper, thick paper, postcards, envelopes, thin paper, coated paper (such as coated paper and art paper), tracing paper, and the like.

[0024] (Sheet Discharge Unit) The sheet discharge unit 400 is a part that discharges the paper P outside the apparatus. The sheet discharge unit 400 includes 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.

[0025] <Image Forming Operation> Next, with reference to FIG. 1, the operation of the image forming apparatus 1000 according to the first embodiment of the present invention will be described.

[0026] When the image forming operation is started by an instruction from the operation panel or an external terminal, the rotation of the electrostatic latent image carrier 2 is started in each image forming unit 1Y, 1M, 1C, 1Bk. Next, each charging member 3 charges the surface of each electrostatic latent image carrier 2 to a uniform high potential. Subsequently, based on the image information of the document read by the document reading device or the print image information instructed from an external terminal, the exposure device 6 exposes the surface (charged surface) of each electrostatic latent image carrier 2. As a result, the potential of the exposed portion decreases, and an electrostatic latent image is formed on the surface of each electrostatic latent image carrier 2. Thereafter, toner is supplied from each developing device 4 to each electrostatic latent image carrier 2, whereby toner images of different colors are formed on each electrostatic latent image carrier 2.

[0027] The toner images on each electrostatic latent image carrier 2 reach the primary transfer nip (the position of the primary transfer roller 12) as the electrostatic latent image carrier 2 rotates. Then, at the primary transfer nip, the toner images are sequentially transferred from each electrostatic latent image carrier 2 onto the rotationally driven intermediate transfer belt 11 so as to overlap. Thus, a full-color toner image is formed on the intermediate transfer belt 11. Note that image formation is not limited to forming a full-color image using all four image forming units 1Y, 1M, 1C, and 1Bk. It is also possible to form a monochromatic image using any one of the image forming units 1Y, 1M, 1C, and 1Bk, or to form a two-color or three-color image using any two or three of the image forming units. Further, after the toner image is transferred onto the intermediate transfer belt 11, a cleaning operation of the electrostatic latent image carrier 2 is performed by the cleaning member 5. Thereby, foreign matter such as residual toner is removed from the surface of each electrostatic latent image carrier 2.

[0028] The toner image transferred onto the intermediate transfer belt 11 is conveyed to the secondary transfer nip (the position of the secondary transfer roller 13) as the intermediate transfer belt 11 rotates. Then, at the secondary transfer nip, the toner image is transferred from the intermediate transfer belt 11 onto the paper P. This paper P is supplied from the sheet supply unit 300. The paper P is fed out from the paper feed cassette 14 by the rotation of the paper feed roller 15 after the start of the image forming operation. The fed-out paper P contacts the timing roller pair 16 on the way to the secondary transfer nip, and the conveyance is temporarily stopped. Then, when the timing roller pair 16 rotates at a predetermined timing, the paper P is conveyed to the secondary transfer nip in synchronization with the toner image on the intermediate transfer belt 11, and the toner image is transferred onto the paper P.

[0029] The paper P onto which the toner image has been transferred is conveyed to the fixing unit 200. In the fixing unit 200, as the paper P passes between the pair of rotating members 19A and 19B, the toner image on the paper P is heated and pressurized, and the toner image is fixed to the paper P. Then, the paper P is conveyed to the sheet discharge unit 400 and discharged to the paper discharge tray 18 by the paper discharge roller 17. Thereby, a series of image forming operations is completed.

[0030] <Basic Configuration of Fixing Device> FIG. 2 is a diagram showing the basic configuration of a fixing device 20 according to a first embodiment of the present invention.

[0031] As shown in FIG. 2, the fixing device 20 includes, in addition to a pair of rotators 19A and 19B, a heater 23, a heater holder 24, a stay 25, and the like.

[0032] Of the pair of rotators 19A and 19B, one first rotator 19A is a fixing belt 21 disposed on the unfixed image-bearing surface side of the paper P. The other second rotator 19B is a pressure roller 22 disposed to face the fixing belt 21. The fixing belt 21 and the pressure roller 22 are pressed against each other by a pressing member such as a spring. Thereby, a nip portion N is formed between the fixing belt 21 and the pressure roller 22.

[0033] The fixing belt 21 is composed of a cylindrical base material and an endless belt member having a release layer provided on the outer peripheral surface of the base material. The base material is formed of, for example, a metal material such as nickel or stainless steel, or a resin material such as polyimide. The release layer is formed of, for example, a material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), PTFE (polytetrafluoroethylene), polyimide, polyetherimide, or PES (polyether sulfide). Since the fixing belt 21 has a release layer, the separability of the toner image with respect to the fixing belt 21 is improved, and the winding of the paper P around the fixing belt 21 is suppressed. Further, the fixing belt 21 may have an elastic layer between the base material and the release layer. As the material of the elastic layer, for example, rubber materials such as silicone rubber, foamed silicone rubber, and fluororubber are used. When the fixing belt 21 has an elastic layer, it becomes difficult to form minute irregularities on the surface of the fixing belt 21, so that heat is easily transmitted uniformly to the toner image on the paper P, and the fixing quality is improved.

[0034] The pressing roller 22 is composed of a roller having a hollow or solid core material, an elastic layer provided on the outer peripheral surface of the core material, a release layer provided on the outer peripheral surface of the elastic layer, and the like. The core material is formed of a metal material such as iron. As the material of the elastic layer, silicone rubber, foamed silicone rubber, fluororubber, or the like is used. The release layer is formed of a fluororesin such as PFA or PTFE.

[0035] The heater 23 is a heat source for heating the fixing belt 21. In this case, the heater 23 is composed of a planar or plate-like heater that contacts the inner peripheral surface of the fixing belt 21. Further, at the position where the fixing belt 21 and the pressing roller 22 face each other, when the heater 23 contacts the inner peripheral surface of the fixing belt 21, a nip portion N is formed between the fixing belt 21 and the pressing roller 22. In addition to the case where the heater 23 directly contacts the inner peripheral surface of the fixing belt 21, the heater 23 may indirectly contact via a low-friction sliding sheet. Further, in this specification, "contact" includes not only direct contact in which contact is made without passing through other members but also indirect contact in which contact is made through other members unless otherwise specified.

[0036] Specifically, the heater 23 has a base material 50, a resistance heating element 51, an insulating layer 52, and the like. The resistance heating element 51 is provided on the base material 50 and is covered with the insulating layer 52. When the resistance heating element 51 generates heat by energization, the heat is transmitted to the inner peripheral surface of the fixing belt 21 through the insulating layer 52, and the fixing belt 21 is heated. Further, the orientation of the heater 23 may be changed so that the base material 50 contacts the inner peripheral surface of the fixing belt 21. In that case, since the heat of the resistance heating element 51 is transmitted to the fixing belt 21 through the base material 50, the base material 50 is preferably formed of a material having a high thermal conductivity.

[0037] The base material 50 is formed of, for example, a ceramic such as alumina or aluminum nitride excellent in heat resistance and insulation, a non-metallic material such as glass or mica. Further, by separately interposing an insulating layer between the base material 50 and the resistance heating element 51, it is also possible to form the base material 50 of a conductive material such as metal. As the metal material, aluminum or stainless steel is preferable in terms of low cost. Further, in order to suppress temperature unevenness of the heater 23 and improve image quality, the base material 50 may be formed of a material having a high thermal conductivity such as copper, graphite, or graphene. Graphene is a sheet-like substance formed by bonding carbon atoms.

[0038] The resistance heating element 51 is formed by a method such as screen printing. For example, a paste prepared by mixing silver palladium (AgPd) and glass powder or the like 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. Further, as the material of the resistance heating element 51, in addition to silver palladium, a resistance material such as a silver alloy (AgPt) or ruthenium oxide (RuO2) may be used. The insulating layer 52 is formed of, for example, heat-resistant glass or the like.

[0039] The heater holder 24 is a heat source holding member that holds the heater 23. By housing the heater 23 in the recess 24a of the heater holder 24, the movement of the heater 23 in the vertical direction and the direction perpendicular to the paper surface in FIG. 2 is restricted. Since the heater holder 24 is likely to become high temperature due to the heat of the heater 23, it is preferably formed of a heat-resistant material. In particular, when the heater holder 24 is formed of a heat-resistant resin having low thermal conductivity such as LCP, unnecessary heat transfer from the heater 23 to the heater holder 24 is suppressed, so that the heating efficiency of the heater 23 is increased.

[0040] The stay 25 is a support member that supports the heater holder 24. By the stay 25 supporting the surface of the heater holder 24 on the side opposite to the surface on the pressure roller 22 side, the bending of the heater 23 due to the pressure from the pressure roller 22 is suppressed, and a nip portion N with a uniform width can be obtained. As the material of the stay 25, in order to ensure rigidity, an iron-based metal material such as SUS or SECC is preferable.

[0041] <Operation of the fixing device> The fixing device 20 according to the first embodiment of the present invention operates as follows.

[0042] When the image forming operation is started, the pressure roller 22 starts rotational driving in the direction of the arrow in FIG. 2, and accordingly, the fixing belt 21 rotates passively. Also, when energization to the heater 23 is started, the fixing belt 21 is heated. Then, when the temperature of the fixing belt 21 reaches a predetermined target temperature, the sheet P carrying the unfixed image is conveyed to the nip portion N between the fixing belt 21 and the pressure roller 22. Thereby, the toner image on the sheet P is heated and pressurized and fixed to the sheet P. Thereafter, the sheet P is discharged from the nip portion N and conveyed to the sheet discharge portion 400.

[0043] <Configuration of the heater> FIG. 3 is a plan view of the heater 23 according to the first embodiment of the present invention.

[0044] As shown in FIG. 3, the heater 23 according to the first embodiment of the present invention includes a base material 50, a resistance heating element 51, an insulating layer 52, a pair of electrode portions 53, and a plurality of power supply lines 54. Here, the base material 50 is a longitudinal plate material arranged so as to extend in the longitudinal direction X of the fixing belt 21. The plurality of resistance heating elements 51 are arranged at intervals in the longitudinal direction (X direction) of the base material 50. Further, 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, temperature drop is likely to occur in the gap portion, so from the viewpoint of suppressing temperature unevenness in the longitudinal direction, it is preferably 5 mm or less, more preferably 1 mm or less. The pair of electrode portions 53 are provided at both longitudinal ends of the base material 50. Each electrode portion 53 is connected to the plurality of resistance heating elements 51 via a plurality of power supply lines 54. In this case, the plurality of resistance heating elements 51 are electrically connected in parallel to each electrode portion 53. Note that the arrangement, number, shape, etc. of each of the resistance heating element 51, the electrode portion 53, and the power supply line 54 are not limited to the example shown in FIG. 3 and can be changed as appropriate.

[0045] The power supply line 54 is covered by the insulating layer 52 in the same manner as the resistance heating element 51 in order to ensure insulation and durability. On the other hand, since a connector as a power supply member is connected to the electrode portion 53, it is not covered by the insulating layer 52 and is exposed. When a connector is connected to each electrode portion 53, power can be supplied from a power source (AC power source) provided in the image forming apparatus main body to the plurality of resistance heating elements 51.

[0046] <Temperature control mechanism> FIG. 4 is a diagram showing the configuration of the temperature control mechanism of the heater 23 according to the first embodiment of the present invention.

[0047] As shown in FIG. 4, the fixing device 20 according to the first embodiment of the present invention includes a thermistor 27, a thermostat 28, a triac 10, and a control unit 7 as a temperature control mechanism for controlling the temperature of the heater 23.

[0048] The thermistor 27 is a temperature sensor for temperature control provided to maintain the temperature of the heater 23 at a predetermined temperature. On the other hand, the thermostat 28 is a temperature sensor for preventing overheating provided to prevent abnormal temperature rise of the heater 23, which is different from the thermistor 27. The thermistor 27 and the thermostat 28 are arranged to contact the back surface of the heater 23, that is, the surface opposite to the surface of the heater 23 that contacts the fixing belt 21, through the through hole 24b provided in the heater holder 24. Note that the thermistor 27 and the thermostat 28 may be in direct contact with the heater 23 or may be in indirect contact via a high heat conduction member or the like.

[0049] The triac 10 is energization control means for controlling the energization duty from the AC power supply 30 to the heater 23 according to an instruction from the control unit 7. Note that the "energization duty" is the ratio of the energization time to the heater 23 per control cycle. The control unit 7 is composed of a microcomputer including a CPU, a ROM, a RAM, an I / O interface, etc. By the control unit 7 outputting a control signal for controlling the triac 10 based on the detected temperature of the thermistor 27, the triac 10 controls the energization duty based on the control signal, and the temperature of the heater 23 is maintained to be a predetermined target temperature. Also, when the thermostat 28 detects an abnormal temperature rise of the heater 23, the thermostat 28 operates and the energization to the heater 23 is cut off.

[0050] In the example of FIG. 4, the thermistor 27 is arranged at the center and one end side in the longitudinal direction of the heater 23, and the thermostat 28 is arranged on the other end side of the heater 23 from the center in the longitudinal direction. However, the arrangement and number of the thermistor 27 and the thermostat 28 are not limited to the example of FIG. 4 and can be appropriately changed.

[0051] <Problems related to component assembly> Here, based on the configuration of a comparative example different from the present invention, problems related to component assembly will be described.

[0052] FIG. 20 is a diagram showing the configuration of a fixing device 60 according to a comparative example.

[0053] The fixing device 60 according to the comparative example includes a fixing belt 61, a pressure roller 62, a heater 63, a heater holder 64, a stay 65, and a temperature sensor 66. Since these members constituting the fixing device 60 have the same basic configuration and functions as the respective constituent members of the fixing device 20 according to the first embodiment of the present invention, the description of their respective configurations and functions will be omitted. The temperature sensor 66 is a thermistor or a thermostat that detects the temperature of the heater 63.

[0054] The temperature sensor 66 is held by a sensor holder 69 as a temperature sensor holding member. Further, a metal coil spring 70 as a biasing member is disposed in a compressed state between the sensor holder 69 and the stay 65. For this reason, the temperature sensor 66 is biased toward the heater 63 by the coil spring 70 and is held in a state of being pressed against the heater 63.

[0055] The sensor holder 69 is provided with a protrusion 69a into which one end portion 70a of the coil spring 70 is fitted. By fitting one end portion 70a of the coil spring 70 into the protrusion 69a of the sensor holder 69, one end portion 70a of the coil spring 70 is positioned with respect to the sensor holder 69. On the other hand, the other end portion 70b of the coil spring 70 only contacts the inner surface of the stay 65. For this reason, when the coil spring 70 is assembled, if there is an assembly error or the like, the other end portion 70b of the coil spring 70 may be displaced with respect to the stay 65. If, as shown in FIG. 21, as a result of the other end portion 70b of the coil spring 70 being displaced, the coil spring 70 is inclined with respect to the temperature sensor 66, a predetermined biasing force of the coil spring 70 cannot be obtained, and thus the temperature sensor 66 cannot be pressed against the heater 63 with the target pressure.

[0056] In order to prevent the occurrence of such assembly defects, it is necessary to confirm whether the coil spring 70 is correctly assembled after the assembly of the coil spring 70. However, in the comparative example, since the stay 65 is arranged to cover the periphery of the coil spring 70, there is a problem that the assembled state of the coil spring 70 cannot be easily confirmed from the outside of the stay 65. If, by any chance, the fixing device and the image forming apparatus are provided in a state where the coil spring 70 is not correctly assembled or in a state where the coil spring 70 has not been assembled at all (missing part), the temperature detection function by the temperature sensor 26 may not be properly exerted, and there is a risk that the temperature of the fixing device rises excessively.

[0057] Therefore, in the present invention, it is an object to make it possible to easily confirm the assembled state of the biasing member that biases the temperature sensor. For this purpose, in the present invention, a fixing device having the following configuration is proposed. Hereinafter, the characteristic parts of the present invention will be described by taking the configuration according to the first embodiment of the present invention as an example.

[0058] <Configuration of the characteristic part of the present invention> FIG. 5 is a diagram showing the configuration of the characteristic part of the fixing device 20 according to the first embodiment of the present invention. First, the holding structure of the temperature sensor 26 will be described with reference to FIG. 5.

[0059] The fixing device 20 according to the first embodiment of the present invention includes, in the same manner as the fixing device 60 according to the comparative example, a sensor holder 29 as a temperature sensor holding member and a metal coil spring 30 as a biasing member. Here, the temperature sensor 26 is a thermistor 27 or a thermostat 28.

[0060] The sensor holder 29 has a concave holding portion 29a for holding the temperature sensor 26. When the temperature sensor 26 is fitted into the holding portion 29a of the sensor holder 29, the temperature sensor 26 is held by the sensor holder 29. Also, a coil spring 30 is disposed in a compressed state between the sensor holder 29 and the stay 25. For this reason, the temperature sensor 26 is biased toward the heater 23 by the coil spring 30 and is held in a state of being pressed against the heater 23. Note that in FIG. 5, the cross-sectional shape of the heater 23 is simplified.

[0061] Further, the sensor holder 29 has a protrusion 29b into which one end portion 30a on the temperature sensor 26 side of the coil spring 30 is fitted. When one end portion 30a of the coil spring 30 is fitted into the protrusion 29b of the sensor holder 29, one end portion 30a of the coil spring 30 is positioned with respect to the sensor holder 29. On the other hand, since the other end portion 30b on the side opposite to one end portion 30a of the coil spring 30 only contacts the inner surface of the stay 25, it is not positioned with respect to the stay 25. Particularly in the first embodiment of the present invention, since the inner surface of the stay 25 that functions as a receiving member for receiving the other end portion 30b of the coil spring 30 is a flat surface having no protrusions or the like, the other end portion 30b of the coil spring 30 is held in a state where it can be displaced along the inner surface of the stay 25. Therefore, similar to the comparative example, the other end portion 30b of the coil spring 30 is in a state where it is likely to be displaced.

[0062] Also, in the first embodiment of the present invention, similar to the comparative example, the periphery of the coil spring 30 is covered by the stay 25, and the coil spring 30 is arranged so as not to be exposed outside the stay 25. Therefore, it is difficult to visually observe the entire coil spring 30 from the outside of the stay 25. Note that "not being exposed" outside the stay 25 means that the coil spring 30 does not protrude outside the outer surface of the stay 25. Specifically, in the first embodiment of the present invention, the stay 25 includes a first wall portion 251 and a second wall portion 252 that extend from the heater holder 24 to the side opposite to the pressure roller 22, and a third wall portion 253 that extends in a direction orthogonal or intersecting with the first wall portion 251 and the second wall portion 252, and two bent portions 254 and 255 that connect the first wall portion 251 and the third wall portion 253 and the second wall portion 252 and the third wall portion 253. In other words, the stay 25 includes a third wall portion 253, two bent portions 254 and 255 provided at opposite ends of the third wall portion 253, and a first wall portion 251 and a second wall portion 252 that extend from each of the bent portions 254 and 255 toward the pressure roller 22 side. In this case, as shown in FIG. 5, when the fixing device 20 is viewed from one end side in the longitudinal direction of the fixing belt 21, the first wall portion 251 and the second wall portion 252 are arranged so as to face each other with the coil spring 30 interposed therebetween, and the third wall portion 253 is arranged so as to face the heater holder 24 with the coil spring 30 interposed therebetween. Therefore, the vertical direction and the left direction of the coil spring 30 are covered by the stay 25. Further, since the stay 25 is a longitudinal member provided continuously over the longitudinal direction of the fixing belt, when the stay 25 is assembled to cover the coil spring 30, it becomes difficult to visually observe the entire coil spring 30 from the outside of the stay 25.

[0063] Therefore, in the first embodiment of the present invention, the stay 25 is provided with a hole portion 25a for easily visually observing the coil spring 30. The hole portion 25a is provided in the third wall portion 253 of the stay 25 that receives the end portion 30b of the coil spring 30. Further, the hole portion 25a is provided so as to communicate the inside and the outside of the stay 25.

[0064] In the first embodiment of the present invention, at both ends in the longitudinal direction of the stay 25 (the direction perpendicular to the plane of FIG. 5), the coil spring 30 is not covered by the stay 25. Thus, the stay 25 does not necessarily cover the entire periphery of the coil spring 30 except for the heater holder 24 side. That is, the stay 25 may cover at least three directions in the vertical direction and the left direction of the coil spring 30 in FIG. 5 that intersect the longitudinal direction of the stay 25.

[0065] FIG. 6 is a view of the hole 25a of the stay 25 according to the first embodiment of the present invention as seen from the outside of the stay 25.

[0066] As shown in FIG. 6, in the first embodiment of the present invention, two holes 25a are provided. Each hole 25a is provided at a position facing the end 30b of the coil spring 30. The "position facing the end 30b of the coil spring 30" here means the position of the end 30b of the coil spring 30 when the coil spring 30 is correctly assembled. For example, in the case of the first embodiment of the present invention, a state where one end 30a of the coil spring 30 is fitted into the protrusion 29b of the sensor holder 29 and the coil spring 30 is assembled in a direction perpendicular to the third wall portion 253 is the correct assembled state of the coil spring 30. Note that the position of the end 30b when the coil spring 30 is correctly assembled is not limited to the case of showing only an ideal single position, and may include a plurality of positions considering allowable positional deviations.

[0067] Thus, in the first embodiment of the present invention, since the stay 25 has the hole 25a at a position facing the end 30b of the coil spring 30 on the contact surface (the third wall portion 253) that contacts the end 30b of the coil spring 30, the assembled state of the coil spring 30 can be easily confirmed through the hole 25a. That is, since the hole 25a is provided at a position close to the end 30b of the coil spring 30 instead of a position away from the end 30b of the coil spring 30, it becomes easy to visually observe the end 30b of the coil spring 30 through the hole 25a.

[0068] For example, as shown in FIG. 6, when the coil spring 30 is assembled in the correct position, the end portion 30b of the coil spring 30 can be visually observed through the two holes 25a. In particular, in the first embodiment of the present invention, since the two holes 25a are symmetrically arranged with respect to the center O of the end portion 30b of the coil spring 30 assembled in the correct position, when the coil spring 30 is assembled in the correct position, in each hole 25a, the coil spring 30 does not shift in the vertical or horizontal direction of the figure and is visually observed to the same extent.

[0069] On the other hand, when the coil spring 30 is assembled at a position deviated from the correct position, as shown in FIG. 7, since the end portion 30b of the coil spring 30 shifts toward one of the holes 25a or shifts upward in the figure, etc., the direction and degree of the displacement of the coil spring 30 can be grasped by the visibility of the end portion 30b of the coil spring 30 in each hole 25a. Thereby, it is possible to confirm in which direction and to what extent the coil spring 30 is tilted, so that it is also possible to judge whether the posture of the coil spring 30 is good or not. Further, when the coil spring 30 is not assembled at all (in the case of a shortage), since the end portion 30b of the coil spring 30 cannot be visually observed from any of the holes 25a, the presence or absence of the coil spring 30 can also be confirmed.

[0070] As described above, according to the first embodiment of the present invention, by providing the hole 25a for visually observing the end portion 30b of the coil spring 30 in the member (stay 25) that receives the end portion 30b of the coil spring 30, it becomes possible to easily confirm the assembly state including the presence or absence of the coil spring 30 through the hole 25a. Thereby, the occurrence of poor assembly of the coil spring 30 can be reduced, and the reliability is improved.

[0071] The shape of the hole 25a is not limited to a circular shape as shown in FIG. 6, and may be an elliptical shape, a polygonal shape such as a quadrangular shape, or other shapes.

[0072] Further, the width D2 of the hole 25a shown in FIG. 6 is preferably smaller than the width D1 of the end portion 30b of the coil spring 30. Here, the "width D1 of the end portion 30b of the coil spring 30" and the "width D2 of the hole 25a" mean the outer diameter of the end portion 30b of the coil spring 30 and the inner diameter of the hole 25a, respectively. By making the width D2 of the hole 25a smaller than the width D1 of the end portion 30a of the coil spring 30 in this way, it becomes possible to prevent the coil spring 30 from coming out of or falling off from the hole 25a. Further, when the hole 25a is a hole other than a circular hole, or when the biasing member has an end portion with a shape other than an annular end portion such as the coil spring 30, and the dimensions of the respective widths D1 and D2 are not uniquely determined, it is preferable to make the minimum width of the hole 25a smaller than the maximum width of the end portion of the biasing member.

[0073] Also, as shown in FIG. 6, the distance E from one edge to the other edge of adjacent holes 25a is preferably smaller than the width D1 of the end portion 30b of the coil spring 30. Thereby, when the coil spring 30 is assembled at the correct position (the position between the two holes 25a), the end portion 30b of the coil spring 30 can be visually observed through each hole 25a. Here, the "distance E" means the shortest distance. Further, when the biasing member has an end portion with a shape other than an annular end portion such as the coil spring 30, and the width D1 of the biasing member is not uniquely determined, it is preferable to make the distance E smaller than the minimum width of the end portion of the biasing member.

[0074] Further, as shown in FIG. 6, when a plurality of holes 25a are provided so as to be arranged in the longitudinal direction of the stay 25 (the horizontal direction in FIG. 6), in particular, the displacement of the coil spring 30 in the longitudinal direction of the stay 25 becomes easily visible. For example, as shown in FIG. 8, when the stay 25 is assembled by being rotated about the engaging portion 24c of the heater holder 24, the coil spring 30 tends to tilt in the longitudinal direction of the stay 25 as the stay 25 rotates (see the two-dot chain line in FIG. 8). Therefore, in such a configuration, it is preferable to adopt the configuration as shown in FIG. 6. That is, by arranging the plurality of holes 25a so as to be arranged in the longitudinal direction of the stay 25, it becomes easier to confirm the inclination of the coil spring 30 when the coil spring 30 is inclined in the longitudinal direction of the stay 25.

[0075] Also, from the viewpoint of ensuring the dimensional accuracy of the hole 25a, the surface of the stay 25 that receives the end portion 30b of the coil spring 30 is preferably a flat surface. The surface of the stay 25 that receives the end portion 30b of the coil spring 30 may be a surface other than a flat surface, such as a surface having irregularities, but a flat surface is preferable because the hole 25a can be machined with higher accuracy. As a method for machining the hole 25a, a method such as cutting using a drill can be adopted.

[0076] Also, in FIG. 9, when the distance from each bent portion 254, 255 of the stay 25 to the hole 25a is L and the thickness of the stay 25 is T, it is preferable that L and T satisfy the relationship of the following formula (1).

[0077] L > 1 / 2T ··· Formula (1)

[0078] If the distance L from each bending portion 254, 255 to the hole portion 25a becomes too small, when the metal plate is bent to form the stay 25, the hole portion 25a is deformed, and it becomes difficult to form the hole portion 25a with high precision. That is, when the distance L is small, when the hole portion 25a is formed in the metal plate and then the metal plate is bent, the hole portion 25a is easily deformed under the influence of the bending process, so that high dimensional accuracy of the hole portion 25a cannot be obtained. Therefore, by making the distance L satisfy the relationship of the above formula (1), the distance L can be ensured to be large, and the hole portion 25a can be formed with high precision.

[0079] In addition, the biasing member may be an elastic member such as rubber in addition to the metal coil spring 30. Even if the biasing member is an elastic member such as rubber, by making the end portion of the elastic member visible through the hole portion 25a, the assembling state of the elastic member can be easily confirmed.

[0080] Subsequently, another embodiment of the present invention will be described. Hereinafter, mainly the parts different from the first embodiment of the present invention will be described, and the same parts will be omitted as appropriate.

[0081] <Second Embodiment of the Present Invention> FIG. 10 is a view of the hole portion 25a of the stay 25 according to the second embodiment of the present invention as viewed from the outside of the stay 25.

[0082] As shown in FIG. 10, the hole portion 25a may be one. However, in this case, it is necessary to make the inner diameter (width D2) of the circular hole portion 25a smaller than the outer diameter (width D1) of the coil spring 30 so that the coil spring 30 does not come out or fall off from the hole portion 25a. That is, when only one circular hole portion 25a is provided, the hole portion 25a needs to be formed on the inner diameter side of the end portion 30b of the coil spring 30 on the contact surface of the stay 25 that contacts the end portion 30b of the coil spring 30.

[0083] When there is one hole portion 25a, in a state where the coil spring 30 is assembled at the correct position, as shown in FIG. 10, the end portion 30b of the coil spring 30 is located on the outer diameter side of the hole portion 25a. For this reason, the end portion 30b of the coil spring 30 at the correct position cannot be visually observed. On the other hand, when the coil spring 30 is assembled at a position deviated from the correct position, since the end portion 3b of the coil spring 30 is arranged at a position overlapping the hole portion 25a, the end portion 30b of the coil spring 30 can be visually observed through the hole portion 25a. Therefore, in the second embodiment of the present invention, when the coil spring 30 is displaced, the displaced state of the coil spring 30 can be visually observed. Thereby, when the coil spring 30 is assembled at a displaced position, its assembled state can be easily confirmed.

[0084] In the second embodiment of the present invention, although the end portion 30b of the coil spring 30 assembled at the correct position cannot be visually observed, it is possible to visually observe portions other than the end portion 30b of the coil spring 30 through the hole portion 25a. Therefore, the presence or absence of the coil spring 30 can also be confirmed. However, compared with the case where the end portion 30b of the coil spring 30 assembled at the correct position can be visually observed as in the first embodiment of the present invention, since it is difficult to confirm the presence or absence of the coil spring 30, the presence or absence of the coil spring 30 may be confirmed by another method such as confirming the repulsive force of the temperature sensor 26 after assembling the stay 25.

[0085] <The Third Embodiment of the Present Invention> FIG. 11 is a view of the hole portion 25a of the stay 25 according to the third embodiment of the present invention as viewed from the outside of the stay 25.

[0086] In the third embodiment of the present invention shown in FIG. 11, the shape of the hole portion 25a is a rectangle such as a square or a rhombus. By making the shape of the hole portion 25a rectangular in this way, even if there is only one hole portion 25a, the end portion 30b of the coil spring 30 at the correct position can be visually observed through the hole portion 25a while preventing the coil spring 30 from coming out of the hole portion 25a. For this reason, compared with the configuration in which only one circular hole portion 25a is provided (FIG. 10), it becomes possible to more accurately grasp the quality of the assembled state of the coil spring 30.

[0087] <Fourth Embodiment of the Present Invention> FIG. 12 is a view of the hole portion 25a of the stay 25 according to the fourth embodiment of the present invention as viewed from the outside of the stay 25.

[0088] As shown in FIG. 12, the shape of the hole portion 25a may be a cross shape. Also in this case, although there is only one hole portion 25a, by forming the hole portion 25a in a cross shape, the end portion 30b of the coil spring 30 at the correct position can be visually observed through the hole portion 25a while preventing the coil spring 30 from coming out of the hole portion 25a.

[0089] <Fifth Embodiment of the Present Invention> FIG. 13 is a view of the hole portion 25a of the stay 25 according to the fifth embodiment of the present invention as viewed from the outside of the stay 25.

[0090] As shown in FIG. 13, there may be more than two hole portions 25a. In this case, four hole portions 25a are provided so as to be located at the respective vertices of a square. Also, the number of the hole portions 25a may be three or five or more, and the shape of the hole portions 25a may also be a shape other than a circular shape.

[0091] <Sixth Embodiment of the Present Invention> FIG. 14 is a view of the hole portion 25a of the stay 25 according to the sixth embodiment of the present invention as viewed from the outside of the stay 25.

[0092] In the sixth embodiment of the present invention shown in FIG. 14, a plurality of hole portions 25a are provided on the outer diameter side of the end portion 30b of the coil spring 30 that is assembled at the correct position. In this case, when the coil spring 30 is assembled at the correct position, the end portion 30b of the coil spring 30 is arranged at a position that does not overlap with the plurality of hole portions 25a, so the end portion 30b of the coil spring 30 cannot be visually observed from each hole portion 25a. On the other hand, when the coil spring 30 is assembled at a position deviated from the correct position, the end portion 3b of the coil spring 30 is arranged at a position overlapping with the hole portion 25a, so that the end portion 30b of the coil spring 30 can be visually observed through the hole portion 25a. Therefore, the misaligned state of the coil spring 30 can be confirmed.

[0093] In this case as well, similar to the second embodiment of the present invention in FIG. 10, the end portion 30b of the coil spring 30 assembled at the correct position cannot be visually observed, but it is possible to visually observe portions other than the end portion 30b of the coil spring 30 through the hole portion 25a. Therefore, it is also possible to confirm the presence or absence of the coil spring 30.

[0094] As described above, in the first to sixth embodiments of the present invention, by providing the stay 25 with the hole portion 25a that communicates the inner side and the outer side thereof as a receiving member for receiving the other end portion 30b of the coil spring 30, the coil spring 30 can be visually observed from the hole portion 25a. The "being able to be visually observed" as used herein includes not only the case where the end portion 30b of the coil spring 30 can be visually observed when the coil spring 30 is assembled at the correct position, but also the case where portions other than the end portion 30b of the coil spring 30 can be visually observed. In this way, by providing the hole portion 25a at a position where the coil spring 30 can be visually observed, the position of the coil spring 30 in the longitudinal direction (lateral direction in FIG. 6, etc.) and the short-side direction (vertical direction in FIG. 6, etc.) of the stay 25 can be confirmed.

[0095] Note that even if the hole portion 25a is provided on a surface other than the contact surface of the stay 25 that contacts the end portion 30b of the coil spring 30, it is possible to visually check the coil spring 30 from the outside through the hole portion 25a. For example, even when the hole portion 25a is provided in the first wall portion 251, the second wall portion 252, or the bent portions 254 and 255 of the stay 25 in FIG. 5, the coil spring 30 can be visually checked through the hole portion 25a. However, in that case, since the coil spring 30 is viewed from the lateral direction (a direction intersecting the length direction of the coil spring 30), there is a problem that the position cannot be confirmed when the coil spring 30 is displaced in the direction (lateral direction) approaching or separating from the hole portion 25a.

[0096] In contrast, in the first to sixth embodiments of the present invention, the hole portion 25a is not provided in the first wall portion 251, the second wall portion 252, or the bent portions 254 and 255, but is provided in the third wall portion 253 having a contact surface with the end portion 30b of the coil spring 30. Therefore, even if the coil spring 30 is displaced laterally, its position can be confirmed. That is, in FIGS. 6, 7, 10 to 14, on the contact surface with the end portion 30b of the coil spring 30, the direction in which the stay 25 extends long (lateral direction in FIG. 6) is defined as the "longitudinal direction", and the direction intersecting the longitudinal direction (vertical direction in FIG. 6) is defined as the "lateral direction". In the first to sixth embodiments of the present invention, since the hole portion 25a is provided in the third wall portion 253 having a contact surface, the position of the coil spring 30 in the longitudinal direction and the lateral direction can be visually confirmed from the hole portion 25a. For this reason, according to each embodiment of the present invention, it becomes possible to more accurately grasp the displacement of the coil spring 30.

[0097] <The Seventh Embodiment of the Present Invention> FIG. 15 is a diagram showing the configuration of the fixing device 20 according to the seventh embodiment of the present invention.

[0098] In the seventh embodiment of the present invention shown in FIG. 15, the edge of the hole portion 25a is formed as a protruding portion 25b that protrudes toward the inside of the stay 25 (the side of the coil spring 30). For example, when the hole portion 25a is formed from the outside to the inside of the stay 25 using a cutting tool such as a drill, a burr that protrudes inward is generated at the edge of the hole portion 25a. Such a burr may be used as the protruding portion 25b. Further, as shown in FIG. 15, by inserting the protruding portion 25b into the end portion 30b of the coil spring 30 and attaching the end portion 30b of the coil spring 30 to the protruding portion 25b, it is also possible to position the coil spring 30.

[0099] <Eighth Embodiment of the Present Invention> FIG. 16 is a diagram showing the configuration of the fixing device 20 according to the eighth embodiment of the present invention.

[0100] In the eighth embodiment of the present invention shown in FIG. 16, the coil spring 30 is supported not by the stay 25 but by a part of the heater holder 24. That is, in the eighth embodiment of the present invention, instead of the stay 25, the heater holder 24 functions as a receiving member that receives the end portion 30b of the coil spring 30.

[0101] Further, in this case, the coil spring 30 is covered by the heater holder 24. Specifically, the heater holder 24 includes a base portion 240 that holds the heater 23, a first wall portion 241 and a second wall portion 242 that extend from the base portion 240 to the side opposite to the pressure roller 22 side, a third wall portion 253 that extends in a direction orthogonal or intersecting with the first wall portion 251 and the second wall portion 252, and two bent portions 244 and 245 that connect the first wall portion 241 and the third wall portion 243 and the second wall portion 242 and the third wall portion 243.

[0102] Then, as shown in FIG. 16, when the fixing device 20 is viewed from one end side in the longitudinal direction of the fixing belt 21, the first wall portion 241 and the second wall portion 242 of the heater holder 24 are arranged to face each other with the coil spring 30 interposed therebetween, and the third wall portion 243 is arranged to face the base portion 240 with the coil spring 30 interposed therebetween. Therefore, the vertical and horizontal directions of the coil spring 30 in FIG. 16 are covered by the heater holder 24. Also, in this state, the coil spring 30 is arranged so as not to be exposed to the outside of the heater holder 24.

[0103] Therefore, also in the eighth embodiment of the present invention, a hole portion 24d for visually recognizing the end portion 30b of the coil spring 30 is provided. The hole portion 24d is provided at a position facing the end portion 30b of the coil spring 30 on the contact surface of the heater holder 24 that contacts the end portion 30b of the coil spring 30. Thereby, since the end portion 30b of the coil spring 30 can be visually recognized through the hole portion 24d, the assembled state can be easily confirmed. Note that the configuration of the hole portion 24d provided in the heater holder 24 may be the configuration of any of the embodiments shown in FIGS. 6 and 10 to 15.

[0104] Further, the present invention is applicable not only to the fixing device 20 shown in FIG. 2 but also to fixing devices having configurations different from those of FIG. 2 as shown in FIGS. 17 to 19. Hereinafter, the fixing devices having the respective configurations shown in FIGS. 17 to 19 will be described. In FIGS. 17 to 19, portions having the same components as those in FIG. 2 are denoted by the same reference numerals as those in FIG. 2, and the description thereof will be omitted.

[0105] First, in the example shown in FIG. 17, the nip portion N1 for heating and the nip portion N2 for fixing are formed at different positions. Specifically, two pressure rollers 151 and 152 of different sizes located on opposite sides of each other via the fixing belt 21 contact the heater 23 and the nip forming member 150 via the fixing belt 21, thereby forming the nip portion N1 for heating and the nip portion N2 for fixing. In this case, when the heater 23 generates heat, the fixing belt 21 is heated at the heating nip portion N1 where the heater 23 and the fixing belt 21 are in contact. Further, when the paper P enters the fixing nip portion N2 where the fixing belt 21 and the heating roller 152 are in contact, the unfixed image on the paper P is heated and pressed, and the image is fixed on the paper P.

[0106] Also, in the fixing device 20 of FIG. 17, a temperature sensor 26 for detecting the temperature of the heater 23 and a coil spring 30 as a biasing member for biasing the temperature sensor 26 in the direction of the heater 23 are provided. Further, the coil spring 30 is covered by the stay 25. Therefore, also in the example shown in FIG. 17, similar to the above-described embodiment, a hole portion 25a for visually observing the end portion of the coil spring 30 is provided on the surface of the stay 25 that receives the end portion of the coil spring 30. Thereby, the assembled state of the coil spring 30 can be easily confirmed through the hole portion 25a.

[0107] Subsequently, the example shown in FIG. 18 is an example in which the left pressure roller 151 in FIG. 17 is omitted and further the heater 23 is formed in an arc shape in accordance with the curvature of the fixing belt 21. Otherwise, it has the same configuration as the fixing device 20 shown in FIG. 17. In this case, since the heater 23 is formed in an arc shape, a long contact region in the belt rotation direction between the fixing belt 21 and the heater 23 is ensured, so that the fixing belt 21 can be efficiently heated. Also, in this example, by providing a hole portion 25a for visually observing the end portion of the coil spring 30 on the surface of the stay 25 that receives the end portion of the coil spring 30, the assembled state of the coil spring 30 can be easily confirmed through the hole portion 25a.

[0108] Next, the example shown in FIG. 19 is an example in which two belts 161 and 162 are arranged on opposite sides of each other with the central roller 163 interposed therebetween. In this case, the heater 23 disposed within the left belt 161 in FIG. 19 contacts the central roller 163 via the belt 161, thereby forming a heating nip portion N1. Further, the nip forming member 153 disposed within the right belt 162 in FIG. 19 contacts the central roller 163 via the belt 162, thereby forming a fixing nip portion N2. When the heater 23 generates heat, the central roller 163 is heated at the heating nip portion N1, and when the sheet P enters the fixing nip portion N2, the unfixed image on the sheet P is heated and pressed, and the image is fixed to the sheet P. Also in this example, by providing a hole portion 25a for visually observing the end portion of the coil spring 30 on the surface of the stay 25 that receives the end portion of the coil spring 30, the assembled state of the coil spring 30 can be easily confirmed through the hole portion 25a.

[0109] Further, the image forming apparatus according to the present invention is not limited to a color image forming apparatus including a plurality of image forming units as shown in FIG. 1, and may be a monochrome image forming apparatus including only one image forming unit.

[0110] Further, the present invention is not limited to being applied to a fixing device which is an example of a heating device mounted on an image forming apparatus, and can also be applied to heating devices other than the fixing device. For example, the present invention can also be applied to a drying device for drying a liquid such as ink applied to a sheet in an inkjet type image forming apparatus, a laminator for thermocompression bonding a film as a coating member to the surface of a sheet such as a sheet, or a heat sealer for thermocompression bonding a seal portion of a packaging material, etc.

[0111] Summarizing the aspects of the present invention described above, the present invention includes at least the following aspects.

[0112] [First aspect] The first aspect includes a first rotating body, a second rotating body that contacts the outer peripheral surface of the first rotating body to form a nip portion, a heating source that heats at least one of the first rotating body and the second rotating body, a temperature sensor that detects the temperature of the heating source, a biasing member that biases the temperature sensor in the direction of the heating source, and a receiving member that receives an end portion of the biasing member opposite to the end portion on the side of the temperature sensor. The receiving member covers the periphery of the biasing member, and the biasing member is arranged so as not to be exposed to the outside of the receiving member. The receiving member has a hole portion that communicates the inside and the outside of the receiving member on a contact surface that contacts the end portion of the biasing member, and the position of the biasing member in the longitudinal direction of the receiving member and in a direction intersecting the longitudinal direction on the contact surface can be visually confirmed from the hole portion. This is a heating device.

[0113] [Second Aspect] The second aspect is, in the first aspect, the receiving member has the hole portion at a position facing the end portion of the biasing member on the surface that contacts the end portion of the biasing member, or on the inner diameter side of the end portion of the biasing member on the surface that contacts the end portion of the biasing member. Note that each of the embodiments in FIGS. 10 to 13 satisfies the second aspect.

[0114] [Third Aspect] The third aspect is, in the first or second aspect, the biasing member is a coil spring.

[0115] [Fourth Aspect] The fourth aspect is, in any one of the first to third aspects, the width of the hole portion is smaller than the width of the end portion of the biasing member.

[0116] [Fifth Aspect] The fifth aspect is, in any one of the first to fourth aspects, a plurality of the hole portions are provided at positions facing the end portion of one biasing member.

[0117] [Sixth Aspect] The sixth aspect is, in the fifth aspect, the plurality of hole portions are provided so as to be arranged in the longitudinal direction of the receiving member.

[0118] [Aspect 7] In Aspect 7, in Aspect 5 or 6, the distance from one edge to the other edge of the adjacent hole portions is smaller than the width of the end portion of the biasing member.

[0119] [Aspect 8] In Aspect 8, in any one of Aspects 1 to 7, the surface of the receiving member that receives the end portion of the biasing member is a flat surface.

[0120] [Aspect 9] In Aspect 9, in any one of Aspects 1 to 8, the receiving member has a bent portion, and when the distance from the bent portion to the hole portion is L and the thickness of the receiving member is T, L and T satisfy the relationship L > 1 / 2T.

[0121] [Aspect 10] In Aspect 10, in any one of Aspects 1 to 9, the receiving member has a wall portion having the contact surface and two bent portions provided at opposite ends of the wall portion, the hole portion is provided in the wall portion, and is not provided in the bent portions.

[0122] [Aspect 11] Aspect 11 is a fixing device that fixes an unfixed image on a sheet using the heating device of any one of Aspects 1 to 10.

[0123] [Aspect 12] Aspect 12 is an image forming apparatus including the heating device of any one of Aspects 1 to 10, or the fixing device of Aspect 11.

Explanation of Reference Numerals

[0124] 20 Fixing device (heating device) 21 Fixing belt (first rotating body) 22 Pressing roller (second rotating body) 23 Heater (heating source) 24 Heater holder (heating source holding member) 25 stays (receiving member) 25a hole portion 26 temperature sensor 27 thermistor 28 thermostat 29 sensor holder (temperature sensor holding member) 30 coil spring (biasing member) 1000 image forming apparatus P paper (sheet)

Prior Art Documents

Patent Documents

[0125]

Patent Document 1

Claims

1. a first rotating body; a second rotating body that contacts an outer peripheral surface of the first rotating body to form a nip portion; a heat source that heats at least one of the first rotating body and the second rotating body; a temperature sensor that detects a temperature of the heat source; a biasing member that biases the temperature sensor in a direction of the heat source; a receiving member that receives an end portion of the biasing member opposite to an end portion on a side of the temperature sensor; comprising: the receiving member covers a periphery of the biasing member; the biasing member is arranged so as not to be exposed to an outside of the receiving member; the receiving member has a hole portion that communicates an inside and an outside of the receiving member on a contact surface that contacts an end portion of the biasing member; a heating device, wherein a position of the biasing member in a longitudinal direction of the receiving member and in a direction intersecting the longitudinal direction on the contact surface can be visually confirmed from the hole portion.

2. The heating device according to claim 1, wherein the receiving member has the hole portion at a position facing an end portion of the biasing member on a surface that contacts the end portion of the biasing member, or on an inner diameter side of the end portion of the biasing member on the surface that contacts the end portion of the biasing member.

3. The heating device according to claim 1, wherein the biasing member is a coil spring.

4. The heating device according to claim 1, wherein a width of the hole portion is smaller than a width of an end portion of the biasing member.

5. The heating device according to claim 1, wherein a plurality of the hole portions are provided at positions facing an end portion of one biasing member.

6. The heating device according to claim 5, wherein the plurality of hole portions are provided so as to be arranged in a longitudinal direction of the receiving member.

7. The heating device according to claim 5, wherein a distance from one edge to another edge of adjacent hole portions is smaller than a width of an end portion of the biasing member.

8. The heating device according to claim 1, wherein a surface of the receiving member that receives an end portion of the biasing member is a flat surface.

9. The receiving member has a bent portion; when a distance from the bent portion to the hole portion is L and a thickness of the receiving member is T, L and T satisfy a relationship of L > 1 / 2T. The heating device according to claim 1.

10. The receiving member has a wall portion having the contact surface and two bent portions provided at opposite end portions of the wall portion; the hole portion is provided in the wall portion and not provided in the bent portion. The heating device according to claim 1.

11. A fixing device, characterized in that an unfixed image is fixed on a sheet using the heating device according to claim 1.

12. An image forming apparatus comprising the heating device according to claim 1.

Images