Fixing device and image forming apparatus

Abstract

To provide a fixing device that can appropriately detect a temperature of a heater while reducing a diameter of a fixing belt.SOLUTION: A fixing device 7 comprises: a fixing belt 20 that heats toner on a sheet; a pressure roller 21 that forms a pressure area N with the fixing belt 20 to apply pressure to the toner on the sheet passing through the pressure area; a heater 23 that is in contact with an inner face of the fixing belt 20 facing the pressure area N to heat the fixing belt 20; a soaking member 26 that is in contact with one face of the heater 23 that is on the opposite side of the fixing belt 20, and absorbs heat generated from the heater 23 to move the heat in an axial direction; and a temperature detection unit 27 that is in contact with one face of the soaking member 26 that is on the opposite side of the heater 23, and detects a temperature of the heater 23 with the soaking member 26 therebetween. The heater 23 and the soaking member 26 expose one end in the axial direction axially outward from the fixing belt 20, and the temperature detection unit 27 is provided to be in contact with the soaking member 26 exposed from the fixing belt 20.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a fixing device that fixes a toner image on a medium and an image forming apparatus. [Background technology]

[0002] Electrophotographic image forming apparatuses are equipped with a fixing device that thermally fixes toner on a recording material (medium). For example, the fixing device has a cylindrical film, a heater that contacts the inner surface of the film, a metal plate that contacts the heater, and a thermistor that contacts the metal plate (Patent Document 1). The thermistor is located within the space surrounded by the film, near the center of the heat-generating area of ​​the heater, and detects the temperature of the heater via the metal plate. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2016-95433 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in the fixing device described above, since the thermistor (temperature detection unit) is placed in a space surrounded by a film (fixing belt), the diameter (outer diameter) of the film tends to become large (its curvature tends to become small), which causes a problem of the fixing device becoming large. Also, in the fixing device described above, since the thermistor is wrapped in a film, it is easily affected by the temperature of the space within the film, and there is a risk that the heater temperature may not be detected properly.

[0005] In consideration of the above circumstances, the present invention provides a fixing device and an image forming apparatus that can properly detect the temperature of the heater while reducing the diameter of the fixing belt. [Means for solving the problem]

[0006] a pressure member that forms a pressure region between the fixing belt and the pressure member and applies pressure to the toner on the medium as the pressure member rotates around its axis; a heater that extends in the axial direction of the fixing belt and contacts the inner surface of the fixing belt facing the pressure region to heat the fixing belt; a heat equalizing member that extends in the axial direction and contacts one side of the heater opposite the fixing belt to absorb heat generated by the heater and transfer it in the axial direction; and a temperature detection unit that contacts one side of the heat equalizing member opposite the heater and detects the temperature of the heater via the heat equalizing member, wherein at least one of both sides in the axial direction of the heater and the heat equalizing member is exposed from the fixing belt to the outside in the axial direction, and the temperature detection unit is provided to contact the heat equalizing member exposed from the fixing belt.

[0007] In this case, the temperature detection unit may be disposed along the outer edge of the fixing belt in the axial direction when viewed from the outside in the radial direction.

[0008] In this case, it is preferable that the fixing member further includes a fixing member having one end fixed to the heater exposed from the fixing belt and the other end brought into contact with the temperature detection unit, and pressing the temperature detection unit against the heat equalizing member.

[0009] An image forming apparatus according to the present invention includes the fixing device described above. [Effects of the Invention]

[0010] According to the present invention, it is possible to appropriately detect the temperature of the heater while reducing the diameter of the fixing belt. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram (side view) showing the internal structure of an image forming apparatus according to one embodiment of the present invention. [Figure 2] FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention. [Figure 3] FIG. 3 is a cross-sectional view taken along the line III-III in FIG. 2. [Figure 4] FIG. 2 is a bottom view schematically illustrating a heater of a fixing device according to an embodiment of the present invention. [Figure 5] FIG. 5 is a cross-sectional view of FIG. 4 . [Figure 6] FIG. 1 is a front view showing a fixing device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. In the drawings, Fr, Rr, L, R, U, and D indicate front, rear, left, right, top, and bottom. The front-to-back direction, left-to-right direction (axial direction), and top-to-bottom direction are perpendicular to one another. 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. Furthermore, the terms "upstream," "downstream," and similar terms refer to "upstream" and "downstream" in the transport direction of paper P (medium) and similar concepts. In each drawing, the dimensions and angles of components are not accurate and are shown schematically for the purpose of explanation.

[0013] An image forming apparatus 1 according to an embodiment will be described with reference to Fig. 1. Fig. 1 is a schematic diagram (side view) showing the image forming apparatus 1.

[0014] The image forming apparatus 1 is an electrophotographic printer. The image forming apparatus 1 has an apparatus main body 2 that has a substantially rectangular parallelepiped appearance. A paper feed cassette 3 that stores, for example, paper P (medium) is detachably provided at the bottom of the apparatus main body 2. A paper output tray 4 is provided on the top surface of the apparatus main body 2. Note that the paper P, which is an example of a medium, is not limited to being made of paper, and may be a resin sheet or the like.

[0015] The image forming apparatus 1 includes a paper feeder 5, an imaging device 6, and a fixing device 7. The paper feeder 5 is provided at the upstream end of a transport path 9A that extends from the paper feed cassette 3 to the paper output tray 4, and sends out paper P stored in the paper feed cassette 3 one sheet at a time to the transport path 9A. The imaging device 6 is provided in the middle of the transport path 9A, and forms a toner image on the transported paper P. The fixing device 7 is provided downstream of the transport path 9A, and thermally fixes the toner image to the paper P.

[0016] The conveying path 9A is provided with a pair of registration rollers 10A that temporarily block the conveyed paper P to correct (skew correct) the inclination of the paper P. Below the conveying path 9A, a reversing conveying path 9B is provided that branches off on the downstream side of the conveying path 9A and merges with the upstream side of the conveying path 9A. The reversing conveying path 9B is provided with a plurality of pairs of conveying rollers 10B that convey the paper P.

[0017] The image forming device 6 includes a toner container 11, a drum unit 12, and an optical scanning device 13. The toner container 11 is located at the upper front of the device main body 2 and contains, for example, black toner (developer). The drum unit 12 includes a photosensitive drum 14, a charging device 15, a developing device 16, and a transfer roller 17. The photosensitive drum 14 is formed in a substantially cylindrical shape and is driven to rotate about its axis by a motor (not shown). The charging device 15, the developing device 16, and the transfer roller 17 are arranged around the photosensitive drum 14 in the order of the image formation process. The transfer roller 17 contacts the photosensitive drum 14 from below to form a transfer nip. The optical scanning device 13 is located above the photosensitive drum 14 and emits scanning light toward the surface of the photosensitive drum 14.

[0018] The image forming apparatus 1 is provided with a control device 8 that controls the entire apparatus. The control device 8 may be configured with a processor, or may be configured with a logic circuit (hardware) formed on an integrated circuit or the like. When configured with a processor, the processor reads and executes programs stored in memory to perform various processes. For example, a CPU (Central Processing Unit) is used as the processor. The memory is configured with one or more storage devices such as ROM (Read Only Memory) and RAM (Random Access Memory) depending on the application.

[0019] [Image formation processing] The following describes the operation of the image forming apparatus 1. The control device 8, which controls the image forming apparatus 1, executes the image forming process as follows based on image data input from an external terminal.

[0020] The charging device 15 charges the surface of the photosensitive drum 14, and the optical scanning device 13 emits scanning light based on image data to form an electrostatic latent image on the photosensitive drum 14. The developing device 16 develops a toner image on the photosensitive drum 14 using toner supplied from the toner container 11. The paper feeder 5 feeds paper P one sheet at a time from the paper feed cassette 3 to the transport path 9A. The paper P is transported along the transport path 9A, skew-corrected by a pair of registration rollers 10A, and enters the transfer nip. The transfer roller 17 transfers the toner image on the photosensitive drum 14 to the surface of the paper P as it passes through the transfer nip. The fixing device 7 thermally fixes the toner image to the paper P. In the case of single-sided printing, the paper P that has passed through the fixing device 7 is discharged to the paper output tray 4.

[0021] In the case of double-sided printing, the paper P that has passed through the fixing device 7 switches back at the downstream end of the conveying path 9A and is sent to the reverse conveying path 9B. The paper P is conveyed by the conveying roller pair 10B, returned from the reverse conveying path 9B to the conveying path 9A again, and after skew correction by the registration roller pair 10A, is sent to the transfer nip. Thereafter, the toner image is transferred onto the paper P and thermally fixed, and the double-sided printed paper P is discharged onto the paper output tray 4.

[0022] [Fusing device] Next, the fixing device 7 will be described with reference to Figures 2 to 6. Figure 2 is a perspective view showing the fixing device 7. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a bottom view schematically showing the heater 23. Figure 5 is a cross-sectional view taken along line VV in Figure 4. Figure 6 is a front view showing the fixing device 7.

[0023] The fixing device 7 includes a fixing belt 20, a pressure roller 21, a heater 23, a heat equalizing member 26, and a temperature detection unit 27. The fixing belt 20 and the pressure roller 21 are supported by a frame (not shown), and the frame is fixed to the device body 2.

[0024] <Fixing belt> As shown in Figures 2 and 3, the fixing belt 20 is an endless belt formed in a generally cylindrical shape that is long in the left-right direction (axial direction). The fixing belt 20 is made of a heat-resistant and flexible material (polymer resin, metal, or a combination of polymer resin and metal). A pair of holding members 24 (see Figure 2) is inserted into both left and right ends of the fixing belt 20. The pair of holding members 24 guide the fixing belt 20 to rotate around its axis while maintaining its generally cylindrical shape. The fixing belt 20 is supported by a frame (not shown) via the pair of holding members 24.

[0025] As shown in FIG. 3, a support member 25 and a heater holder 22 are provided in the space surrounded by the fixing belt 20. The support member 25 is formed, for example, from a metal material such as stainless steel into a generally rectangular cylindrical shape that is elongated in the left-right direction (axial direction), and is installed between a pair of holding members 24. The heater holder 22 is fixed to the lower part of the support member 25. The heater holder 22 is formed, for example, from a heat-resistant and abrasion-resistant synthetic resin into a generally semi-cylindrical shape that is elongated in the left-right direction. The heater holder 22 curves along the inner surface of the fixing belt 20 and contacts the lower side of the inner surface of the fixing belt 20 (the side of the pressure region N). A fitting portion 22A into which the heater 23 is fitted is recessed in the lower part of the heater holder 22.

[0026] <Pressure roller> As shown in FIGS. 2 and 3, pressure roller 21, an example of a pressure member, is formed in a generally cylindrical shape that is long in the left-right direction. Pressure roller 21 has a metal core 21A and an elastic layer 21B, such as a silicone sponge, laminated on the outer circumferential surface of the metal core 21A (see FIG. 3). A drive motor M is connected to the left end of core 21A via a gear train (not shown) (see FIG. 2). Pressure roller 21 contacts fixing belt 20 from below, forming a pressure region N between itself and fixing belt 20. A toner image is fixed onto paper P as it passes through pressure region N. Note that pressure region N refers to the region extending from an upstream position where the pressure is 0 Pa, through a position where pressure is applied, to a downstream position where the pressure returns to 0 Pa.

[0027] The paper sheet P is transported with the center of its width in the left-right direction roughly aligned with the center of the pressure area N in the left-right direction (axial direction). For this reason, the fixing belt 20 (or the pressure area N) has a passing area A1 in the axial center that contacts the paper sheet P, and non-passing areas A2 on both sides in the axial direction that do not contact the paper sheet P (see FIG. 4). The transported paper sheet P always contacts the passing area A1 near the axial center, regardless of the size (left-right dimension) of the paper sheet P. In contrast, normal-sized paper sheets P (e.g., A4 size) contact both sides of the passing area A1 in the axial direction, but small-sized paper sheets P (e.g., A5, B5 size, etc.) do not contact the passing area A1.

[0028] <Heater> 3 and 4, heater 23 extends in the left-right direction (axial direction) of fixing belt 20 and is fitted into fitting portion 22A of heater holder 22. Heater 23 comes into contact with the inner surface of fixing belt 20 facing pressure region N, and heats fixing belt 20. As shown in FIGS. 4 and 5, heater 23 has a substrate 30 and a heat generating portion 31.

[0029] (substrate) The substrate 30 is made of an insulator (electrically insulating material) such as ceramic. The substrate 30 is formed in a substantially rectangular plate shape that extends in the left-right direction (axial direction) to correspond to the fixing belt 20. As shown in Fig. 6, the substrate 30 is formed to be longer in the left-right direction (axial direction) than the fixing belt 20, penetrates the fixing belt 20 in the axial direction, and extends outward from both ends of the fixing belt 20 in the axial direction. In other words, both ends of the substrate 30 (heater 23) in the axial direction are exposed outward from the fixing belt 20 in the axial direction.

[0030] (heat generating part) The heat generating section 31 is provided on the lower surface of the substrate 30, which faces the inner surface of the fixing belt 20 (see FIG. 5). As shown in FIG. 4, the heat generating section 31 is composed of three resistance heating elements 32A to 32C arranged in a row in the left-right direction (axial direction) with a gap G therebetween. In this specification, in descriptions common to the three resistance heating elements 32A to 32C, only Arabic numerals are used for the reference numerals. The gap G is set to an insulation distance (creepage distance) that can prevent creepage discharge between adjacent resistance heating elements 32.

[0031] The resistance heating element 32 is formed in a substantially rectangular shape from a metal material with high electrical resistance. The entire heat generating section 31 is shorter than the overall length of the fixing belt 20 in the left-right direction (axial direction) and is longer in the axial direction than the passing area A1 of the fixing belt 20 (see FIG. 4). In other words, both axial sides of the resistance heating elements 32B and 32C located on both outer sides in the axial direction face the non-passing area A2 of the fixing belt 20 (see FIG. 4). The resistance heating element 32A located in the center in the axial direction corresponds to the left-right width of a small-size paper P, and all of the resistance heating elements 32A to 32C correspond to the left-right width of a normal-size paper P.

[0032] Three individual electrodes 33A to 33C and a common electrode 33D are formed on the lower surface of the substrate 30. The three individual electrodes 33A to 33C and the common electrode 33D are formed, for example, from a metal material having a lower electrical resistance value than the resistance heating element 32. In this specification, when describing the three individual electrodes 33A to 33C and the common electrode 33D in common, they will be simply referred to as "electrode portion 33" and will be indicated by Arabic numerals only.

[0033] As shown in FIG. 4, the individual electrode 33A is connected to the downstream end (rear end) of the resistance heating element 32A located in the center in the axial direction. The other individual electrodes 33B and 33C are connected to the downstream ends of the resistance heating elements 32B and 32C, respectively. The common electrode 33D is connected to the upstream ends (front ends) of all of the resistance heating elements 32A to 32C. Each of the multiple electrode portions 33 extends from a portion connected to the heat generating element 31 to both outer sides of the heat generating element 31 in the axial direction. The multiple electrode portions 33 are electrically connected to devices (not shown) such as a power supply on both sides of the substrate 30 in the axial direction.

[0034] The heat generating portion 31 and the electrode portion 33 are covered with a coating layer 34 (see FIG. 5). The coating layer 34 is made of a material, such as ceramic, that has electrical insulation properties and exhibits low sliding friction against the inner surface of the fixing belt 20. The coating layer 34, the heat generating portion 31, and the electrode portion 33 can be formed with high precision on the substrate 30 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.

[0035] The heater 23 is fitted into the fitting portion 22A of the heater holder 22 with the heat generating portion 31 (coating layer 34) facing the pressure roller 21, and the coating layer 34 is in contact with the inner surface of the fixing belt 20 (see FIG. 5). The heater 23 receives the fixing belt 20 pressed against the pressure roller 21, thereby forming a pressure region N at the contact portion between the fixing belt 20 and the pressure roller 21.

[0036] <Heat-equalizing member> Incidentally, since the fixing belt 20 has a smaller heat capacity than a roller or the like, the fixing device 7 that employs the fixing belt 20 has the advantage of requiring less time to warm up. However, for example, when small-sized sheets of paper P are continuously fixed, the paper P (toner image) absorbs heat in most of the passing area A1 of the fixing belt 20, preventing excessive temperature rise. However, the axial ends of the passing area A1 where the paper P does not pass and the non-passing area A2 may experience excessive temperature rise. Therefore, in the fixing device 7 according to this embodiment, a heat equalizing member 26 is provided in the heater 23 to prevent excessive temperature rise in the non-passing area A2 of the fixing belt 20 and the like.

[0037] The temperature equalizing member 26 is made of a metal material such as an aluminum alloy. The temperature equalizing member 26 is formed in a substantially rectangular plate shape elongated in the axial direction to correspond to the fixing belt 20. As shown in FIGS. 5 and 6, the temperature equalizing member 26 is provided on (in contact with) the upper surface (one surface) of the heater 23 (substrate 30) opposite the fixing belt 20 (pressure region N). The temperature equalizing member 26 is formed to be shorter in the axial direction than the substrate 30 and longer in the axial direction than the fixing belt 20 (heat generating section 31). As shown in FIG. 6, the temperature equalizing member 26 penetrates the fixing belt 20 in the axial direction and extends outward from one side (for example, the right side) of the fixing belt 20 in the axial direction. The temperature equalizing member 26 is disposed so as to cover the three resistance heating elements 32A to 32C, with the right side in the axial direction exposed outward from the fixing belt 20.

[0038] A lubricant (not shown), such as silicone grease, is applied between the heat equalizing member 26 and the substrate 30. The lubricant not only brings the heat equalizing member 26 and the substrate 30 into close contact with each other, but also facilitates the transfer of heat from the heater 23 to the heat equalizing member 26. The heat equalizing member 26 absorbs the heat generated by the heater 23 and transfers it in the axial direction. In other words, the heat equalizing member 26 equalizes the temperature of the heater 23 along the axial direction. As a result, the temperature of the fixing belt 20 is also equalized along the axial direction, preventing excessive temperature rise in the non-passage area A2. In this specification, the term "uniform" does not refer only to a completely constant state, but also allows for a slight margin of error.

[0039] [Function of the fixing device] Here, the operation (fixing process) of the fixing device 7 will be described. As will be described in detail later, the fixing device 7 is provided with a temperature detection unit 27 that detects the temperature of the heater 23. The heater 23, temperature detection unit 27, drive motor M, etc. are electrically connected to a control device 8, a power source (not shown), etc. The control device 8 controls the power source, heater 23, etc. as appropriate.

[0040] The control device 8 controls the drive motor M to rotate the pressure roller 21 around its axis. The fixing belt 20 rotates following the rotation of the pressure roller 21 (see the arrow in FIG. 2). The control device 8 also receives a detection signal from the temperature detection unit 27 and controls the heater 23 (or power supply) to maintain a preset target temperature. The heater 23 (heat generating unit 31) generates heat when energized, and heats the fixing belt 20 (pressure region N).

[0041] At this time, the control device 8 changes which of the three resistance heating elements 32A to 32C is heated (energized) depending on the size of the paper P. For example, when a normal-sized paper P passes through the pressure region N, the control device 8 executes control to cause all three resistance heating elements 32A to 32C to generate heat. On the other hand, when a small-sized paper P passes through the pressure region N, the control device 8 executes control to cause only one resistance heating element 32A to generate heat. This makes it possible to heat only the necessary portion of the fixing belt 20 (pressure region N) in accordance with the size of the paper P. As a result, it is possible to minimize the amount of power used. It is also possible to prevent excessive temperature rise at both ends of the fixing belt 20 in the axial direction.

[0042] When the fixing belt 20 (heater 23) reaches the target temperature, the control device 8 starts the image formation process already described. The paper P onto which the toner image has been transferred enters the pressure area N. The fixing belt 20 heats the toner (toner image) on the paper P as it passes through the pressure area N while rotating around its axis. The pressure roller 21 pressurizes the toner on the paper P as it passes through the pressure area N while rotating around its axis. The toner image is then fixed to the paper P, forming a fixed image on the paper P. The paper P with the fixed image is then discharged to the paper output tray 4.

[0043] Incidentally, the temperature detection unit 27 that detects the temperature of the heater 23 may be disposed in a space surrounded by the fixing belt 20. For example, if the temperature detection unit 27 is disposed on the upper surface of the heat equalizing member 26 at approximately the center in the axial direction, a large fitting portion 22A must be formed in the heater holder 22 to accommodate the temperature detection unit 27, resulting in a larger heater holder 22. This requires a larger diameter for the fixing belt 20, which increases the size of the fixing device 7. Furthermore, if the temperature detection unit 27 is disposed so as to be surrounded by the fixing belt 20, it is susceptible to the temperature of the space within the fixing belt 20, and there is a risk that the temperature of the heater 23 may not be detected properly. Therefore, the fixing device 7 according to this embodiment has a structure that properly detects the temperature of the heater 23 while reducing the diameter of the fixing belt 20.

[0044] <Temperature detection section> The temperature detection unit 27 is disposed outside the fixing belt 20 adjacent to the outer end of the fixing belt 20 in the axial direction (see FIG. 6). As shown in FIGS. 5 and 6, the temperature detection unit 27 is in contact with the upper surface (one surface) of the heat equalizing member 26, which is on the opposite side from the heater 23. More specifically, the temperature detection unit 27 is provided so as to be in contact with (the upper right surface of) the heat equalizing member 26 exposed from the fixing belt 20. The temperature detection unit 27 is, for example, a heat-sensitive element such as a thermo-cut, and detects the temperature of the heater 23 via the heat equalizing member 26, and if the detected temperature is abnormal, cuts off the power supply to the heater 23.

[0045] The temperature detection unit 27 is fixed to the substrate 30 via a fixing member 28. The fixing member 28 is, for example, a leaf spring made of a metal material such as stainless steel, and is provided in the form of a cantilever with one end fixed to the heater 23. One end (right end) of the fixing member 28 is fixed via a screw to the heater 23 (substrate 30) exposed from the fixing belt 20. The fixing member 28 extends from the right end while slanting upward toward the left, and the other end (left end) of the fixing member 28 is in contact with the upper surface of the temperature detection unit 27 (see FIG. 6 ). The other end of the fixing member 28 is in contact with the temperature detection unit 27, pressing the temperature detection unit 27 against the soaking member 26. Note that the one end of the fixing member 28 may be fixed to the substrate 30 not only by a screw but also by an adhesive or the like, for example.

[0046] In the fixing device 7 according to the present embodiment described above, the heater 23 and the heat equalizing member 26 are exposed at one axial end to the outside of the fixing belt 20, and the temperature detection unit 27 is provided to contact the heat equalizing member 26 exposed from the fixing belt 20. With this configuration, the temperature detection unit 27 is disposed outside the fixing belt 20 in the axial direction, so the diameter (outer diameter) of the fixing belt 20 can be made smaller (the curvature can be increased) compared to when the temperature detection unit 27 is disposed in the space surrounded by the fixing belt 20. Furthermore, because the temperature detection unit 27 is disposed outside the fixing belt 20 in the axial direction, it can be made less susceptible to the temperature of the space inside the fixing belt 20. As described above, the diameter of the fixing belt 20, and therefore the fixing device 7, can be made smaller, while still properly detecting the temperature of the heater 23.

[0047] Furthermore, in the fixing device 7 according to this embodiment, the temperature detection unit 27 is pressed against the heat equalizing member 26 by the fixing member 28, so that the temperature of the heater 23 can be detected properly via the heat equalizing member 26.

[0048] Incidentally, in order to properly thermally fix the toner onto the paper P, it is necessary to maintain the surface of the fixing belt 20 at an appropriate temperature (target temperature). Therefore, it is preferable that the temperature detection unit 27 directly detects the surface temperature of the fixing belt 20 and controls (controls the power supply to) the heater 23 based on the detection result. However, since it is difficult to bring the temperature detection unit 27 into contact with the surface of the rotating fixing belt 20, the temperature detection unit 27 detects the temperature of the heater 23 and controls the heater 23 based on the detection result. In other words, the surface temperature of the fixing belt 20 is estimated (predicted) from the temperature of the heater 23. If the temperature detection unit 27 is disposed in a space within the fixing belt 20 or if the temperature detection unit 27 is located far away from the right end of the fixing belt 20 in the axial direction, the detection result of the temperature detection unit 27 may deviate significantly from the actual surface temperature of the fixing belt 20, and it may be impossible to accurately estimate (predict) the surface temperature of the fixing belt 20 from the detection result of the temperature detection unit 27.

[0049] Therefore, in the fixing device 7 according to the present embodiment, as shown in FIG. 6 , the temperature detection unit 27 is disposed along the outer axial edge of the fixing belt 20 when viewed from the radial outside (front or rear) of the fixing belt 20. The left end of the temperature detection unit 27 may coincide with the outer axial edge of the fixing belt 20 when viewed from the radial outside, or may be slightly separated (by several millimeters to several tens of millimeters) from the outer axial edge of the fixing belt 20. This configuration reduces the discrepancy between the detection result of the temperature detection unit 27 (the temperature of the heater 23) and the surface temperature of the fixing belt 20. This allows the surface temperature of the fixing belt 20 to be accurately estimated (predicted) based on the detection result of the temperature detection unit 27. As a result, the toner can be appropriately thermally fixed to the paper P.

[0050] In the fixing device 7 according to the present embodiment, both axial ends of the heater 23 (substrate 30) are exposed axially outward from the fixing belt 20, and one axial end (the right side) of the heat equalizing member 26 is exposed axially outward from the fixing belt 20, but the present invention is not limited to this. It is sufficient that at least one of both axial ends of the heater 23 and the heat equalizing member 26 is exposed axially outward from the fixing belt 20.

[0051] In the fixing device 7 according to the present embodiment, one temperature detector 27 is provided on the upper right surface of the heat equalizing member 26, which is exposed from the right end of the fixing belt 20. However, the present invention is not limited to this. For example, the heat equalizing member 26 may be provided so as to be exposed outward from the left end of the fixing belt 20 in the axial direction, and one temperature detector 27 may be provided on the upper left surface of the exposed heat equalizing member 26 (not shown). Alternatively, the heat equalizing member 26 may be provided so as to be exposed outward from both ends of the fixing belt 20 in the axial direction, and two temperature detectors 27 may be provided on the upper surfaces of both sides of the heat equalizing member 26 in the axial direction (not shown). Even in these cases, each temperature detector 27 may be arranged along the outer edge of the fixing belt 20 in the axial direction, as viewed from the outside in the radial direction. When two temperature detectors 27 are provided, the control device 8 may calculate an average of the detection results of the two temperature detectors 27 and control the heater 23 based on the calculated average.

[0052] Furthermore, in the fixing device 7 according to this embodiment, the temperature detection unit 27 is fixed to the substrate 30 via the cantilever-type fixing member 28, but the present invention is not limited to this. For example, the middle portion of a band-shaped fixing member may be in contact with the upper surface of the temperature detection unit 27, and the fixing member may be fixed to the substrate 30 in a state in which both sides of the fixing member are elastically deformed (not shown). Alternatively, the fixing member 28 may be omitted, and the temperature detection unit 27 may be fixed to the substrate 30 via an adhesive or the like (not shown).

[0053] Furthermore, in the fixing device 7 according to this embodiment, the temperature detection unit 27 is a thermo-cut, but is not limited to this and may be, for example, a contact-type temperature sensor such as a thermocouple, a platinum resistance thermometer, a thermistor thermometer, or a bimetal thermometer.

[0054] Furthermore, in the fixing device 7 according to this embodiment, the heat generating section 31 is divided into three resistance heating elements 32A to 32C, but this is not limiting and the heat generating section 31 may be divided into two, four or more, or may not be divided at all (all of which are not shown). Additionally, the heat generating section 31 may be a single resistance heating element extending from one side to the other in the axial direction, or a U-shaped resistance heating element extending from one side to the other in the axial direction and then folding back to extend from the other side to one side in the axial direction (all of which are not shown).

[0055] Furthermore, in the fixing device 7 according to this 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 (not shown). In this case, the non-passing region A2 is set only on one side in the axial direction of the fixing belt 20 (or the pressure region N).

[0056] Furthermore, in the fixing device 7 according to this embodiment, the pressure roller 21 is driven to rotate, and the fixing belt 20 is driven to rotate, but this is not limited to this, and the fixing belt 20 may be driven to rotate, and the pressure roller 21 may be driven to rotate.

[0057] Furthermore, in the description of the above embodiment, the present invention has been applied to a monochrome image forming device 1 as an example, but this is not limiting and the present invention may also be applied to, for example, a color printer, a copier, a facsimile, or a multifunction device.

[0058] The above-described 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-described embodiment. The present invention may be variously changed, substituted, or modified without departing from the spirit of the technical concept, and the claims include all embodiments that may fall within the scope of the technical concept. [Explanation of symbols]

[0059] 1. Image forming device 7 Fixing device 20 Fixing belt 21 Pressure roller (pressure member) 23 Heater 26 Heat-equalizing member 27 Temperature detection unit 28 Fixing member N pressure area P Paper (medium)

Claims

1. a fixing belt formed in a cylindrical shape and rotating around its axis to heat the toner on the medium; a pressure member that forms a pressure region between itself and the fixing belt and that pressurizes the toner on the medium that passes through the pressure region while rotating around its axis; a heater extending in the axial direction of the fixing belt, contacting the inner surface of the fixing belt facing the pressure region, and heating the fixing belt; a heat equalizing member that extends in the axial direction, contacts one surface of the heater opposite to the fixing belt, absorbs heat emitted from the heater, and transfers the heat in the axial direction; a temperature detection unit that is in contact with one surface of the temperature equalizing member opposite to the heater and detects the temperature of the heater via the temperature equalizing member, the heater and the heat equalizing member are exposed at least on either side in the axial direction from the fixing belt to the outside in the axial direction; The fixing device is characterized in that the temperature detection unit is provided so as to be in contact with the heat equalizing member exposed from the fixing belt.

2. 2. The fixing device according to claim 1, wherein the temperature detection unit is disposed along an outer edge of the fixing belt in the axial direction when viewed from the outside in the radial direction.

3. 3. The fixing device according to claim 1, further comprising a fixing member having one end fixed to the heater exposed from the fixing belt, the other end brought into contact with the temperature detection unit, and pressing the temperature detection unit against the heat equalizing member.

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

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