Fixing device and image forming apparatus

Abstract

To provide a fixing device that, with a simple configuration, can prevent a reduction in the temperature of part of a heater in contact with a temperature detection unit.SOLUTION: A fixing device comprises: a fixing belt that heats toner on a sheet; a pressure roller that applies pressure to the toner on the sheet passing through a pressure area; a heater 33 that is in contact with an inner face of the fixing belt and applies heat to the fixing belt; and a temperature detection unit 47 that is provided in contact with the heater 33 and detects the temperature of the heater 33. The heater 33 has a substrate 36 that extends in an axial direction corresponding to the fixing belt, and a plurality of resistance heating elements 40 that are arranged side by side in the axial direction with a gap therebetween on one face of the substrate 36 in contact with the inner face of the fixing belt, and generate heat upon energization. The temperature detection unit 47 is provided corresponding to an intensified heating element 40A that is any one of the plurality of resistance heating elements 40 on the other face of the substrate 36. The intensified heating element 40A has a larger calorific value than the other resistance heating elements 40.SELECTED DRAWING: Figure 5

Description

[Technical field]

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

[0002] An electrophotographic image forming apparatus is equipped with a fixing device that has a heater in contact with the inner surface of a cylindrical film and thermally fixes toner on a medium. The fixing device is provided with a thermal element that cuts off the flow of electricity to the heater in the event of an abnormal temperature rise. When the thermal element is in contact with the heater, the temperature of the heater drops at the contact point, and this can make it difficult to properly thermally fix the toner on the paper.

[0003] Therefore, a fixing device (image heating device) in which the thermal element is not in contact with the heater (heating body) is known (Patent Document 1). A resin spacer is provided between the heating body and the thermal element, and the spacer has an opening, a frame, and legs extending inward from the frame. The heating body is held by a resin heating body holding member, and the softening point of the spacer is set lower than the heat resistance temperature of the heating body holding member. When the temperature of the heating body rises abnormally, the spacer softens, causing the thermal element to come into contact with the heating body, cutting off the flow of electricity to the heating resistor. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 4546233 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the image heating device described above, a spacer must be manufactured and installed between the heater and the thermal element, which increases manufacturing costs and complicates the structure. Also, in order for the thermal element to function during an abnormal temperature rise, strong restrictions are imposed on the selection of material and shape (thickness, diameter of opening, etc.) of the spacer, which also increases manufacturing costs and complicates the structure.

[0006] In consideration of the above problems, the present invention provides a fixing device and an image forming apparatus that can suppress a temperature drop in a part of a heater with which a temperature detection portion comes into contact, with a simple structure. [Means for solving the problem]

[0007] The fixing device according to the present invention includes a fixing belt formed in a cylindrical shape and rotating about its axis to heat toner on a medium, a pressure roller rotating about its axis to form a pressure area between the fixing belt and the pressure roller, and pressurizing the toner on the medium passing through the pressure area, a heater that contacts the inner surface of the fixing belt facing the pressure area and heats the fixing belt, and a temperature detection unit that is provided in contact with the heater and detects the temperature of the heater, wherein the heater has a substrate that extends in the axial direction corresponding to the fixing belt, and a plurality of resistance heating elements that are arranged with gaps in between in the axial direction on one side of the substrate that is the inner surface side of the fixing belt and generate heat when electricity is passed through them, and the temperature detection unit is provided on the other side of the substrate in correspondence with a reinforced heating element that is at least one of the plurality of resistance heating elements, and the reinforced heating element has a larger heat generation amount than the other resistance heating elements.

[0008] In this case, the reinforced heating element may be formed to be wider in the axial direction than the other resistive heating elements.

[0009] In this case, the reinforced heating element, which is made up of a single resistive heating element, may be formed wider than the axial dimension of the temperature detection portion, and the temperature detection portion may be arranged to be located within the range of the reinforced heating element.

[0010] The image forming apparatus according to the present invention includes the fixing device described above. Effect of the Invention

[0011] According to the present invention, a temperature drop in a part of the heater with which the temperature detection portion comes into contact can be suppressed with a simple structure. [Brief description of the drawings]

[0012] [Figure 1] FIG. 1 is a schematic diagram (front view) illustrating a printer according to an embodiment of the present invention. [Diagram 2] 1 is a cross-sectional view illustrating a fixing device according to an embodiment of the present invention. [Diagram 3] FIG. 4 is a bottom view illustrating a heater of the fixing device according to one embodiment of the present invention. [Figure 4] FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. [Diagram 5] FIG. 2 is a plan view illustrating a heater of a fixing device according to an embodiment of the present invention. [Figure 6] 4 is a graph showing a relationship between the axial position and temperature of a heater in a fixing device according to an embodiment of the present invention. [Figure 7] FIG. 2 is an enlarged plan view showing a part of a heater of a fixing device according to an embodiment of the present invention. [Figure 8] 10 is an enlarged plan view showing a part of a heater of a fixing device according to a first modified example of one embodiment of the present invention. FIG. [Figure 9] 5 is a graph showing a temperature difference between a resistance heating element of a heater in a fixing device according to an embodiment of the present invention and a gap. [Figure 10] FIG. 11 is an enlarged plan view showing a part of a heater of a fixing device according to a second modified example of the embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Hereinafter, an embodiment of the present invention will be described with reference to the attached drawings. Note that Fr, Rr, L, R, U, and D shown in the drawings indicate front, rear, left, right, top, and bottom. Terms indicating directions and positions are used in this specification, but these terms are used for convenience of explanation and do not limit the technical scope of the present invention.

[0014] [Printer overall configuration] A printer 1 as an example of an image forming apparatus will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (front view) showing the printer 1.

[0015] The printer 1 includes a device main body 2 that has a generally rectangular parallelepiped exterior. A paper feed cassette 3 that stores paper P (medium) is provided at the bottom of the device main body 2. A paper output tray 4 is provided on the top surface of the device main body 2. Note that the paper P is not limited to being made of paper, and may be made of resin or the like.

[0016] Inside the device body 2, a transport path 8 is formed as a passage for the paper P. The transport path 8 is formed in a substantially S-shape between the paper feed cassette 3 and the paper discharge tray 4. At the upstream end of the transport path 8, a paper feeder 5 that takes out the paper P from the paper feed cassette 3 is provided. An image forming device 6 is provided in the middle of the transport path 8, and a fixing device 20 is provided downstream of the transport path 8.

[0017] The imaging device 6 includes a toner container 10, a drum unit 11, and an optical scanning device 12. The toner container 10 contains, for example, black toner (developer). The drum unit 11 includes a photoconductor drum 13, a charging device 14, a developing device 15, and a transfer roller 16. The charging device 14, the developing device 15, and the transfer roller 16 are arranged around the photoconductor drum 13 in the order of the image formation process. The transfer roller 16 contacts the photoconductor drum 13 from below to form a transfer nip. The toner may be a two-component developer in which a toner and a carrier are mixed, or a one-component developer made of a magnetic toner.

[0018] A control device (not shown) of the printer 1 appropriately controls each device to execute an image forming process as follows. The charging device 14 charges the surface of the photoconductor drum 13. The photoconductor drum 13 receives scanning light emitted from the optical scanning device 12 and carries an electrostatic latent image. The developing device 15 develops the electrostatic latent image on the photoconductor drum 13 into a toner image using toner supplied from the toner container 10. The paper P is sent from the paper feed cassette 3 to the transport path 8 by the paper feed device 5, and the toner image on the photoconductor drum 13 is transferred to the paper P passing through the transfer nip. The fixing device 20 thermally fixes the toner image to the paper P. The paper P is then discharged to the paper output tray 4.

[0019] [Fixing device] Next, the fixing device 20 will be described with reference to Figs. 2 to 7. Fig. 2 is a cross-sectional view showing the fixing device 20. Fig. 3 is a bottom view showing the heater 33. Fig. 4 is a cross-sectional view taken along line IV-IV in Fig. 3. Fig. 5 is a plan view showing the heater 33. Fig. 6 is a graph showing the relationship between the axial position and the temperature of the heater 33. Fig. 7 is a plan view showing an enlarged portion of the heater 33.

[0020] 2, the fixing device 20 includes a fixing belt 31, a pressure roller 32, a heater 33, and a temperature detection unit 47. The fixing belt 31 and the pressure roller 32 are provided inside a housing 30 (see FIG. 1). The heater 33 and the temperature detection unit 47 are provided inside the fixing belt 31.

[0021] <Fixing belt> The fixing belt 31 is an endless belt, and is formed in a generally cylindrical shape that is long in the front-rear direction (axial direction). The surface layer of the fixing belt 31 is made of a synthetic resin material having heat resistance and elasticity, such as polyimide resin. The fixing belt 31 is disposed in the upper part of the inside of the housing 30. A pair of generally cylindrical caps (not shown) are attached to both ends of the fixing belt 31 in the axial direction. Note that a belt guide (not shown) for maintaining the generally cylindrical shape of the fixing belt 31 may be provided inside the fixing belt 31.

[0022] (Pressing member, holding member) A pressing member 34 and a holding member 35 are provided inside the fixing belt 31. The pressing member 34 is formed in an axially long, approximately rectangular tube shape made of a metal material such as an aluminum alloy or stainless steel. The pressing member 34 penetrates the fixing belt 31 (and the cap) in the axial direction (front-rear direction), and both front and rear ends of the pressing member 34 protruding from the fixing belt 31 are supported by the housing 30. The fixing belt 31 described above is supported rotatably relative to the pressing member 34. The holding member 35 is formed in an axially long, approximately semi-cylindrical shape made of a heat-resistant resin material, for example. The holding member 35 is formed slightly shorter in the axial direction than the fixing belt 31, and is disposed inside the fixing belt 31. The holding member 35 is fixed to the lower surface of the pressing member 34, and has a curved surface that fits along the lower inner surface of the fixing belt 31. A fitting portion 35A into which the heater 33 is fitted is recessed in the lower portion of the holding member 35.

[0023] <Pressure roller> The pressure roller 32 is formed in a generally cylindrical shape that is long in the front-rear direction (axial direction). The pressure roller 32 is disposed at the lower inside of the housing 30. The pressure roller 32 has a core 32A made of an aluminum alloy, stainless steel, or the like, and an elastic layer 32B made of silicone sponge or the like laminated on the outer circumferential surface of the core 32A. Both axial ends of the core 32A are rotatably supported by the housing 30. A drive motor (not shown) is connected to the core 32A via a gear train or the like, and the pressure roller 32 is rotationally driven by the drive motor.

[0024] The fixing device 20 also has a pressure adjustment unit (not shown) that adjusts the contact pressure of the pressure roller 32 against the fixing belt 31 by raising and lowering the pressure roller 32. The pressure roller 32 is pressed against the fixing belt 31, forming a pressure area N between the fixing belt 31 and the pressure roller 32. The fixing belt 31 heats the toner on the paper P passing through the pressure area N while rotating around its axis, and the pressure roller 32 presses the toner on the paper P passing through the pressure area N while rotating around its axis. The toner image is fixed on the paper P by the paper P passing through the pressure area N. The pressure area N refers to an area from an upstream position in the conveying direction of the paper P where the pressure is 0 Pa, through a position where the pressure is maximum, to a downstream position in the conveying direction of the paper P where the pressure is 0 Pa again. In this specification, the direction in which the paper P passes through the pressure area N is called the "passing direction". The passing direction is the same direction as the conveying direction of the paper P and is perpendicular to the axial direction (front-rear direction). In this specification, the terms "upstream" and "downstream" and similar terms refer to "upstream" and "downstream" and similar concepts in the passing or conveying direction.

[0025] The paper P is transported with the center of its front-to-rear width generally coinciding with the center of the pressure area N in the front-to-rear direction (axial direction). For this reason, the fixing belt 31 (or the pressure area N) has a passing area A1 in the axial center that contacts the paper P, and non-passing areas A2 on both sides in the axial direction that do not contact the paper P (see FIG. 3). The transported paper P always contacts the vicinity of the axial center of the passing area A1, regardless of the size of the paper P (dimension in the front-to-rear direction). In contrast, normal size paper P (e.g. A4 size) contacts both sides of the passing area A1 in the axial direction, but small and medium size paper P (e.g. A5, B5 size, etc.) do not contact them.

[0026] <Heater> 2, the heater 33 is provided inside the fixing belt 31. Specifically, the heater 33 is fitted into the fitting portion 35A of the holding member 35, and is in contact with the inner surface of the fixing belt 31 facing the pressure region N. The heater 33 heats the fixing belt 31 from the inside.

[0027] As shown in FIGS. 3 and 4, the heater 33 has a substrate 36 and a heat generating portion 37.

[0028] (substrate) The substrate 36 is made of an electrically insulating material such as ceramic. The substrate 36 is formed in a substantially rectangular plate shape that is elongated in the axial direction to correspond to the fixing belt 31. The substrate 36 is formed to be slightly shorter than the fixing belt 31 in the axial direction, and is disposed inside the fixing belt 31.

[0029] (heat generating part) The heat generating section 37 is provided on the lower surface (one surface) of the substrate 36, which is the inner surface side of the fixing belt 31 (see FIG. 4). As shown in FIG. 3, the heat generating section 37 is composed of five divided heat generating sections 41-45 arranged in a row in the axial direction. Each divided heat generating section 41-45 is composed of a plurality of resistance heating elements 40 arranged in a row with a gap 46 in the axial direction. Each resistance heating element 40 is made of a metal material with a high electric resistance value and is formed in a substantially rectangular shape that is elongated in the passing direction. The heat generating section 37 is formed to be shorter than the entire axial length of the fixing belt 31 and longer in the axial direction than the passing area A1 of the fixing belt 31. In other words, some of the resistance heating elements 40 of the divided heat generating sections 44, 45 located on both outer sides in the axial direction face the non-passing area A2 of the fixing belt 31.

[0030] The divided heat generating section 41 located in the center in the axial direction corresponds to the front-to-rear width of a small-sized (e.g., A5 size) sheet of paper P passing through the pressurized area N. The divided heat generating section 41 and the two divided heat generating sections 42, 43 adjacent to it correspond to the front-to-rear width of a medium-sized (e.g., B5 size) sheet of paper P passing through the pressurized area N. All of the divided heat generating sections 41-45 correspond to the front-to-rear width of a normal-sized (e.g., A4 size) sheet of paper P passing through the pressurized area N.

[0031] Five individual electrodes 51-55 and a common electrode 56 are formed on the lower surface of the substrate 36 (see FIGS. 3 and 4). The five individual electrodes 51-55 and the common electrode 56 are formed, for example, from a metal material having a lower electric resistance value than the resistance heating element 40. In this specification, the five individual electrodes 51-55 and the common electrode 56 will be referred to simply as "electrode portions 51-56" in the description that is common to both.

[0032] As shown in FIG. 3, the individual electrode 51 is connected to the downstream end (right end) of the divided heat generating portion 41 (resistance heating element 40) located in the center in the axial direction. The other individual electrodes 52-55 are connected to the downstream ends of the divided heat generating portions 42-45, respectively. The common electrode 56 is connected to the upstream ends (left ends) of all the resistance heating elements 40. Each of the multiple electrode portions 51-56 extends from a portion connected to the heat generating portion 37 to both outsides of the heat generating portion 37 in the axial direction. The multiple electrode portions 51-56 are electrically connected to external devices (not shown), such as a power source, on both sides of the substrate 36 in the axial direction.

[0033] The heat generating portion 37 and the electrode portions 51-56 are covered with a coating layer 57 (see FIG. 4). The coating layer 57 is made of a material, such as ceramic, that has electrical insulation properties and has a small sliding friction force with respect to the fixing belt 31. The coating layer 57, the heat generating portion 37, and the electrode portions 51-56 can be formed with high precision on the substrate 36 by, for example, a film formation technique such as sputtering, a printed circuit board manufacturing technique, a screen printing technique, or a combination of these techniques.

[0034] The heater 33 is fitted into the fitting portion 35A of the holding member 35 with the heat generating portion 37 (coat layer 57) facing the pressure roller 32, and the coat layer 57 is brought into contact with the inner surface of the fixing belt 31 (see FIGS. 2 and 4). The heater 33 receives the fixing belt 31 pressed against the pressure roller 32, so that a pressure region N is formed at the contact portion between the fixing belt 31 and the pressure roller 32.

[0035] <Temperature detection section> The temperature detection unit 47 is, for example, a heat-sensitive element such as Thermocut, and is provided in contact with the heater 33 (see FIG. 4). In detail, the temperature detection unit 47 is attached to the top surface of the fitting portion 35A of the holding member 35, and the lower part of the temperature detection unit 47 is in contact with the upper surface (the other surface) of the substrate 36 (see FIG. 2). The temperature detection unit 47 is in contact with the substrate 36 slightly rearward of the center in the axial direction (see FIG. 5). The temperature detection unit 47 detects the temperature of the heater 33, and cuts off the power supply to the heater 33 if the temperature is abnormal.

[0036] [Function of the fixing device] Here, a brief description will be given of the operation (fixing process) of the fixing device 20. The electrodes 51 to 56 of the heater 33, the drive motor, etc. are electrically connected to a power source (not shown) and a control device via various drive circuits (not shown).

[0037] The control device drives and controls the drive motor and heater 33. The pressure roller 32 rotates by receiving the driving force of the drive motor, and the fixing belt 31 rotates following the pressure roller 32 (see the solid thin arrow in FIG. 2). The heat generating section 37 (each resistance heating element 40) generates heat when electricity is applied via the electrode sections 51 to 56, and the fixing belt 31 (pressure region N) heats up.

[0038] At this time, the control device changes the divided heating sections 41-45 to be heated (powered) according to the size of the paper P. For example, when a normal-sized paper P passes through the pressurizing region N, the control device supplies power to all divided heating sections 41-45, causing all divided heating sections 41-45 to generate heat. Also, for example, when a medium-sized paper P passes through the pressurizing region N, the control device causes the divided heating sections 41-43 to generate heat, and when a small-sized paper P passes through the pressurizing region N, the control device causes the divided heating section 41 to generate heat. This makes it possible to heat only the necessary parts of the fixing belt 31 (pressurizing region N) according to the size of the paper P. As a result, the power used can be kept to a minimum. Also, it is possible to prevent excessive temperature rise at both ends of the fixing belt 31 in the axial direction.

[0039] When the fixing belt 31 reaches the set temperature, the image forming process described above starts. While the paper P onto which the toner image has been transferred passes through the pressure region N, the toner image is heated and pressed, and is fixed to the paper P.

[0040] However, depending on the material and size of the temperature detection section 47, the heat capacity of the temperature detection section 47 may become large, and the heat of the heater 33 may be taken by the temperature detection section 47. For this reason, as shown by the dashed line in Fig. 6, a part (contact part) of the substrate 36 in contact with the temperature detection section 47 becomes lower in temperature than the other part (non-contact part) of the substrate 36 not in contact with the temperature detection section 47. Then, the temperature of the heater 33 becomes non-uniform along the axial direction, and the temperature of the fixing belt 31 (pressure region N) also becomes non-uniform, which may prevent proper thermal fixing. In Fig. 6, the dashed line and the solid line are assumed to coincide with each other except for the contact part (contact position) of the temperature detection section 47.

[0041] [Reinforced heating element] 5 and 7, in the fixing device 20 according to the present embodiment, a temperature detection unit 47 is provided on the upper surface of the substrate 36 in correspondence with one of the multiple resistance heating elements 40 (40A), and the one resistance heating element 40 (40A) has a larger heat value (kJ / kg) than the other resistance heating elements 40. In this specification, the one resistance heating element 40 corresponding to the temperature detection unit 47 is referred to as the "enhanced heating element 40A."

[0042] The reinforced heating element 40A is formed wider in the axial direction (front-rear direction) than the other resistance heating elements 40. The other resistance heating elements 40, excluding the reinforced heating element 40A, are formed to be approximately the same size. As a specific example, the axial dimension (front-rear direction) of the other resistance heating elements 40 is about 2 mm, and the axial dimension of the reinforced heating element 40A is about 4 mm. In addition, the interval (gap 46 exposing the substrate 36) between the adjacent resistance heating elements 40 (including the reinforced heating element 40A) in the axial direction is about 0.2 mm. The reinforced heating element 40A is configured to have a wider heat generating range (area) and to be high in temperature compared to the other resistance heating elements 40. All the resistance heating elements 40, including the reinforced heating element 40A, are formed to be the same size in the passing direction (left-right direction).

[0043] The temperature detection section 47 faces the reinforced heating element 40A across the substrate 36. The axial dimension of the temperature detection section 47 is larger (longer) than the axial dimension of the reinforced heating element 40A, and the dimension of the temperature detection section 47 in the passing direction is shorter than the dimension of the reinforced heating element 40A (resistance heating element 40) in the passing direction. When the temperature detection section 47 is viewed from above (or the bottom surface of the heater 33), the middle region in the axial direction (front-rear direction) of the temperature detection section 47 is arranged so as to overlap the reinforced heating element 40A, and both sides of the temperature detection section 47 in the axial direction are arranged so as to overlap a pair of gaps 46 adjacent to the reinforced heating element 40A. In other words, both sides of the temperature detection section 47 in the axial direction protrude to both outsides in the axial direction of the reinforced heating element 40A.

[0044] In the fixing device 20 according to the present embodiment described above, the reinforced heating element 40A is formed wide in the axial direction in consideration of the temperature detection unit 47 taking heat from the heater 33. According to this configuration, the amount of heat generated by the reinforced heating element 40A corresponding to the contact portion of the temperature detection unit 47 is reinforced (increased), so that, as shown by the solid line in FIG. 6, it is possible to suppress (reduce) the temperature drop of a part (contact portion) of the heater 33 (substrate 36) that is in contact with the temperature detection unit 47. This makes it possible to make the temperature of the heater 33 uniform along the axial direction, and ensure proper thermal fixing. In addition, by forming one reinforced heating element 40A, the temperature drop of the contact portion of the temperature detection unit 47 is suppressed, so that the temperature drop of the contact portion can be suppressed with a low-cost and simple structure compared to the case where a spacer or the like is provided to keep the temperature detection unit 47 out of contact with the heater 33. In this specification, the term "uniform" does not mean only a completely constant state, but means that some error is allowed.

[0045] [Variations] In the fixing device 20 according to the present embodiment described above, one of the multiple resistance heating elements 40 is the reinforced heating element 40A, but the present invention is not limited to this. For example, as shown in Fig. 8, two of the multiple resistance heating elements 40 may be the reinforced heating element 40A (first modified example). That is, it is sufficient that the temperature detection unit 47 is provided on the upper surface of the substrate 36 in correspondence with the reinforced heating element 40A, which is at least one of the multiple resistance heating elements 40.

[0046] In the fixing device 20 according to the present embodiment described above, the temperature detection section 47 is disposed so as to protrude from the reinforced heating element 40A on both sides in the axial direction and to face the gaps 46 (substrate 36) between the adjacent resistance heating elements 40. In this case, as shown in FIG. 9, the temperature of the gaps 46 is significantly lower than the temperature of the resistance heating element 40 (reinforced heating element 40A), so that the temperature of the pair of gaps 46 adjacent to the reinforced heating element 40A at the contact position of the temperature detection section 47 may be lower than the temperature of the other gaps 46. If a temperature difference (unevenness) occurs between the multiple gaps 46 of the heater 33, a temperature difference (unevenness) in the axial direction may also occur in the fixing belt 31, and there is a risk that the toner on the paper P may not be properly thermally fixed. For this reason, it is not preferable to dispose the temperature detection section 47 so as to face the gaps 46 of the heater 33.

[0047] Therefore, as shown in FIG. 10, the reinforced heating element 40B consisting of a single resistance heating element 40 may be formed wider than the axial dimension of the temperature detection section 47, and the temperature detection section 47 may be provided so as to be located within the range of the reinforced heating element 40B (second modification). That is, when the temperature detection section 47 is viewed from above (or the heater 33 is viewed from the bottom), both sides of the temperature detection section 47 in the axial direction do not protrude to both outsides in the axial direction of the reinforced heating element 40B, and the temperature detection section 47 may be arranged so as to overlap the reinforced heating element 40B in its entirety. According to the fixing device 20 of the second modification, since the entire temperature detection section 47 faces the reinforced heating element 40B, the temperature of the pair of gaps 46 adjacent to the reinforced heating element 40B is prevented from being lower than the temperature of the other gaps 46. This makes it possible to uniformize the temperature of all the gaps 46 in the heater 33, and ensures proper thermal fixing.

[0048] In the fixing device 20 according to this embodiment (including the first and second modified examples, the same applies below), the heat generating section 37 is divided into five divided heat generating sections 41-45 to correspond to three different sizes of paper P, but the present invention is not limited to this. The heat generating section 37 may be divided into three divided heat generating sections to correspond to two or more different sizes of paper P, or it may not be divided (neither is shown).

[0049] In addition, in the fixing device 20 according to the present embodiment, the paper P passes through the center of the pressure region N in the axial direction, but this is not limiting, and the paper P may pass through a position closer to one side in the axial direction of the pressure region N. In this case, the non-passage region A2 is set only on one side in the axial direction of the fixing belt 31 (or the pressure region N).

[0050] In addition, in the fixing device 20 according to the present embodiment, the pressure roller 32 is rotationally driven and the fixing belt 31 is rotated accordingly, but the present invention is not limited to this, and the fixing belt 31 may be rotationally driven and the pressure roller 32 may be rotated accordingly. In addition, the pressure roller 32 is raised and lowered (moved in a direction approaching or separating) relative to the fixing belt 31, but the present invention is not limited to this, and the fixing belt 31 may be moved in a direction approaching or separating relative to the pressure roller 32 (not shown).

[0051] In addition, in the description of this embodiment, a case where the present invention is applied to a monochrome printer 1 has been shown as an example, but the present invention is not limited to this, and may be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device, etc.

[0052] The above embodiment shows one aspect of the fixing device and image forming apparatus according to the present invention, and the technical scope of the present invention is not limited to the above embodiment. The present invention may be modified, substituted, or altered in various ways without departing from the spirit of the technical idea, and the claims include all embodiments that may be included within the scope of the technical idea. [Explanation of symbols]

[0053] 1. Printer (image forming device) 20 Fixing device 31 Fixing belt 32 Pressure roller 33 Heater 36 Substrate 40 Resistance heating element 40A, 40B Reinforced heating element 46 Gap 47 Temperature detection unit N pressure area P Paper (medium)

Claims

1. a fixing belt formed in a cylindrical shape and rotating about an axis to heat the toner on the medium; a pressure roller that rotates around an axis to form a pressure area between the pressure roller and the fixing belt and pressurizes the toner on the medium passing through the pressure area; a heater that contacts an inner surface of the fixing belt facing the pressure region and heats the fixing belt; a temperature detection unit provided in contact with the heater and detecting a temperature of the heater; The heater is a substrate extending in an axial direction corresponding to the fixing belt; a plurality of resistance heating elements that are arranged with gaps between them in the axial direction on one surface of the substrate that is the inner surface side of the fixing belt, and generate heat when electricity is applied thereto; the temperature detection unit is provided on the other surface of the substrate in correspondence with at least one of the plurality of resistance heating elements, that is, a reinforced heating element; The enhanced heating element has a larger heat generation amount than the other resistive heating elements.

2. The fixing device according to claim 1 , wherein the reinforced heating element is formed wider in the axial direction than the other resistive heating elements.

3. The reinforced heating element, which is a single resistive heating element, is formed to be wider than the axial dimension of the temperature detection portion, 3. The fixing device according to claim 2, wherein the temperature detection unit is disposed within a range of the enhanced heating element.

4. 4. An image forming apparatus comprising the fixing device according to claim 1.

Images