Fixing device

Abstract

To provide a fixing device that can avoid the influence of a singular point in temperature and perform appropriate temperature control by solving the problem in which: when a long side of a plane heater cannot make a straight line within a range corresponding to the width of a fixing belt, a singular point in temperature in the direction of the long side of the plane heater is generated at a portion where the long side cannot make a straight line; and appropriate temperature control of the fixing device may not be performed based on the temperature at the singular point.SOLUTION: A fixing device comprises: a cylindrical body; a heater unit that has a substrate having, within a range of the width of the cylindrical body in an axial direction of the cylindrical body with the axial direction as a longitudinal direction, a first range in which the shape of a cross section orthogonal to the axial direction is a first shape and a second range that is narrower than the first range and in which the shape of the cross section is a second shape different from the first shape, and a heating element that is carried on the substrate, the heater unit heating the cylindrical body; and a temperature transducer that measures the temperature of the cylindrical body at a position of the cylindrical body avoiding the second range in the axial direction.SELECTED DRAWING: Figure 13

Description

[Technical Field]

[0001] FIELD An embodiment of the present invention relates to a fixing device. [Background technology]

[0002] Some image forming apparatuses in homes and workplaces such as offices are equipped with a fixing unit. Some fixing devices include a fixing belt that contacts the paper on which the toner image is formed, and a planar heater that heats the fixing belt. The fixing unit has a heater holder that supports the planar heater. The heater holder supports the planar heater so that the longitudinal direction of the planar heater is aligned with the direction perpendicular to the paper transport direction. A typical configuration is one in which a temperature-sensing element (such as a thermistor) for controlling the temperature of the planar heater is in contact with a substrate of the planar heater. There is also a configuration in which a member with high thermal conductivity, such as copper or graphite, is placed between the temperature-sensitive element and the substrate.

[0003] There is also a configuration in which the planar heater is in direct sliding contact with the inner peripheral surface of the fixing belt. There is also a configuration in which a metal protective member is sandwiched between the planar heater and the inner peripheral surface of the fixing belt. In either configuration, in order to ensure uniform heat transfer to the fixing belt or the protective member, It is preferable that both the upstream and downstream long sides of the planar heater in the paper transport direction are linear at least within the range of the length of the fixing belt in the direction perpendicular to the paper transport direction (i.e., the width of the fixing belt).

[0004] However, for various reasons, it may not be possible to align the long side of the planar heater in a straight line within a range corresponding to the width of the fixing belt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2020-052347 [Patent Document 2] Japanese Patent Application Laid-Open No. 2000-010435 Summary of the Invention [Problem to be solved by the invention]

[0006] If the long side of the sheet heater cannot be aligned in a straight line within the range corresponding to the width of the fixing belt, a temperature singularity occurs in the long side direction of the sheet heater near the point where the alignment is not possible. If the temperature at the singularity point is used, it may not be possible to properly control the temperature of the fixing device. The problem that the present invention aims to solve is to avoid the influence of the temperature singularity and properly control the temperature of the fixing device. [Means for solving the problem]

[0007] A fixing device according to one embodiment comprises: a cylindrical body; a substrate having a longitudinal axis in the axial direction of the cylindrical body, and within the width of the cylindrical body in the axial direction, the substrate having a first region in which the cross-sectional shape perpendicular to the axial direction is a first shape, and a second region in the axial direction having a second shape different from the first shape and narrower than the first region; a heating element carried on the substrate, and a heater unit for heating the cylindrical body; and a temperature-sensing element for measuring the temperature of the cylindrical body at a position in the axial direction that avoids the second region. A fixing device according to one embodiment comprises a cylindrical body; a substrate having a longitudinal axis in the axial direction of the cylindrical body, and within the width of the cylindrical body in the axial direction, a first region having a first shape in a cross section perpendicular to the axial direction, and a second region having a second shape different from the first shape and narrower than the first region in the axial direction, and a heating element carried on the substrate, a heater unit for heating the cylindrical body; and a temperature-sensing element for measuring the temperature of the heater unit at a position on the cylindrical body in the axial direction that avoids the second region. A fixing device according to one embodiment comprises: a cylindrical body; a substrate having a longitudinal axis in the axial direction of the cylindrical body, and within the width of the cylindrical body in the axial direction, a cross-sectional shape perpendicular to the axial direction having a first region with a first shape and a second region with a second shape different from the first shape and narrower than the first region in the axial direction, and a heating element carried on the substrate; a heater unit for heating the cylindrical body; a heat transfer member in contact with the heater unit; and a temperature-sensing element for measuring the temperature of the heat transfer member at a position on the cylindrical body avoiding the second region in the axial direction. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram illustrating the configuration of an image processing device. [Figure 2] FIG. 2 is a cross-sectional view of the fixing device according to the first embodiment, as viewed from the +Y direction. [Figure 3] View of the planar heater from the +z direction. [Figure 4] FIG. 4 is a cross-sectional view of the sheet heater taken along line III-III in FIG. [Figure 5] FIG. 10 is a diagram showing a temperature distribution when a planar heater generates heat. [Figure 6] FIG. 1 is a view of the planar heater as seen from the −z direction. [Figure 7] 10A to 10C are diagrams showing variations of recesses on the long sides of the substrate. [Figure 8] 10A to 10C are diagrams showing variations of recesses on the long sides of the substrate. [Figure 9] 10A to 10C are diagrams showing variations of recesses on the long sides of the substrate. [Figure 10] 10A to 10C are diagrams showing variations of recesses on the long sides of the substrate. [Figure 11] 10A to 10C are diagrams showing variations of recesses on the long sides of the substrate. [Figure 12] 10A to 10C are diagrams showing variations of planar heaters. [Figure 13] A view of the sheet heater fitted into the holder from the +z direction. [Figure 14] FIG. 10 is a front cross-sectional view of a fixing device according to a second embodiment. [Figure 15] FIG. 10 is a front cross-sectional view of a fixing device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] The fixing device of the first embodiment will be described below with reference to the drawings. FIG. 1 is a schematic diagram of an image forming apparatus. The image forming apparatus 1 performs a process of forming an image on a sheet S. The sheet S may be paper. The image forming apparatus 1 includes a housing 10, a scanner section 2, an image forming unit 3, a sheet supply section 4, a conveyance section 5, a reversing unit 9, a tray 7, a control panel 8, a control section 6, and a fixing device 30.

[0010] The housing 10 forms the outer shape of the image forming apparatus 1 . The scanner unit 2 reads image information of the object to be copied as light and darkness, and generates an image signal. The scanner unit 2 outputs the generated image signal to the image forming unit 3. The image forming unit 3 forms a toner image based on an image signal from the scanner unit 2 or an external device. The toner image is an image formed with toner or other materials. The image forming unit 3 transfers the toner image onto the surface of the sheet S. The image forming unit 3 applies heat and pressure to the toner image on the surface of the sheet S to fix the toner image to the sheet S.

[0011] The sheet supply section 4 supplies the sheets S one by one to the conveyance section 5 in synchronization with the timing at which the image forming unit 3 forms a toner image. The sheet supply section 4 includes a sheet storage section 20 and a pickup roller . The sheet storage section 20 stores sheets S of a predetermined size and type. The pickup roller 21 picks up the sheets S one by one from the sheet storage unit 20. The pickup roller 21 supplies the picked-up sheets S to the conveying unit 5.

[0012] The conveying section 5 conveys the sheet S supplied from the sheet supplying section 4 to the image forming unit 3. The conveying section 5 includes a conveying roller 23 and a registration roller 24. The conveying roller 23 conveys the sheet S supplied from the pickup roller 21 to the registration roller 24. The conveying roller 23 abuts the leading edge of the sheet S in the conveying direction against the nip RN of the registration roller 24. The registration rollers 24 bend the sheet S at the nip RN to adjust the position of the leading edge of the sheet S in the conveying direction. The registration rollers 24 convey the sheet S in accordance with the timing at which the image forming unit 3 transfers a toner image onto the sheet S.

[0013] 2 is a front cross-sectional view of the fixing device 30. The fixing device 30 includes a pressure roller 31 and a heating roller 34. A nip N is formed between the pressure roller 31 and the heating roller 34. In this application, the z-direction, x-direction, and y-direction are defined as follows. The z direction is the thickness direction of the sheet heater 40, and is the direction in which the heating roller 34 and the pressure roller 31 are aligned. In the z direction, the direction from the heating roller 34 toward the pressure roller 31 is defined as the positive direction. The x direction is the widthwise direction of the sheet heater 40, and is the conveyance direction of the sheet S in the nip N. In the x direction, the downstream side of the conveyance direction of the sheet S is defined as the positive direction. The y direction is the longitudinal direction of the sheet heater 40 and the axial direction of the fixing belt 35 of the heating roller 34.

[0014] The pressure roller 31 applies pressure to the toner image on the sheet S that has entered the nip N. The pressure roller 31 includes a core metal 32 and an elastic layer 33. The core metal 32 is formed into a cylindrical shape from a metal material such as stainless steel. The elastic layer 33 is made of an elastic material such as silicone rubber, etc. The elastic layer 33 has a constant thickness on the outer circumferential surface of the core metal 32. A release layer made of a resin material such as PFA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer) may be provided on the outer peripheral surface of the elastic layer 33 .

[0015] The pressure roller 31 is driven to rotate by a motor. When the pressure roller 31 rotates with the nip N formed, the fixing belt 35 of the heating roller 34 is rotated accordingly. The pressure roller 31 rotates with the sheet S in the nip N, thereby conveying the sheet S in the conveying direction W.

[0016] The heating roller 34 heats the toner image on the sheet S that has entered the nip N. The heating roller 34 includes a fixing belt 35, a planar heater 40, a heat transfer member 48, a holder 50, a frame 36, and temperature-sensitive elements 371, 372, 381, 382, ​​391, 392, and 393.

[0017] The fixing belt 35 is cylindrical. The fixing belt 35 has, in order from the inner periphery, a base layer, an elastic layer, and a release layer. The base layer is made of a resin material such as polyimide (PI) to reduce heat capacity. The elastic layer is made of an elastic material such as silicone rubber. The release layer is made of a material such as PFA resin.

[0018] The planar heater 40 is located inside the fixing belt 35. The surface of the planar heater 40 in the +z direction is in contact with the inner surface of the fixing belt 35 via grease. Fig. 3 is a view of the planar heater as seen from the +z direction. Fig. 4 is a cross-sectional view of the planar heater taken along line III-III in Fig. 3. Planar heater 40 has a substrate 41, a heating element 45, and wiring 46.

[0019] The substrate 41 is made of a metal material such as stainless steel or a ceramic material such as aluminum nitride. As shown in Fig. 3, the substrate 41 is a long, narrow rectangular plate. The longitudinal direction of the substrate 41 is the axial direction of the fixing belt 35. As shown in Figure 4, An insulating layer 42 made of a glass material or the like is formed on the surface of the substrate 41 in the +z direction. An insulating layer 47 is formed on the surface of the substrate 41 in the −z direction.

[0020] Heating element 45 is made of a silver-palladium alloy or the like. Heating element 45 generates heat when electricity is applied. Heating element 45 is connected to wiring 46. Wiring 46 has a common electrode 461, a central electrode 462, and an end electrode 463. Heating element 45 and wiring 46 are arranged on the surface in the +z direction of substrate 41 with insulating layer 42 interposed therebetween. A protective layer 43 is formed of a glass material or the like so as to cover heating element 45 and the portion of wiring 46 excluding common electrode 461, central electrode 462, and end electrode 463.

[0021] As shown in FIG. 3, the heating element 45 has a central heating element 451 and a pair of end heating elements 452 and 453. The end heating element 452 is on the +y side of the central heating element 451 . The end heating element 453 is on the −y side of the central heating element 451 . The heat generation of the central heating element 451 and the pair of edge heating elements 452, 453 is controlled independently of each other. The heat generation of the pair of edge heating elements 452, 453 is controlled in the same manner. The central heating element 451 generates heat when electricity is passed between the common electrode 461 and the central electrode 462. The pair of edge heating elements 452, 453 generate heat when electricity is passed between the common electrode 461 and the edge electrode 463.

[0022] The heat transfer member 48 shown in FIG. 2 is made of a material with high thermal conductivity, such as a metal such as copper or graphite. The outer shape of the heat transfer member 48 is the same as that of the substrate 41 of the sheet heater 40. The heat transfer member 48 contacts the surface of the sheet heater 40 facing in the -z direction.

[0023] The holder 50 is made of a resin material such as a liquid crystal polymer. The holder 50 covers both sides of the planar heater 40 in the x direction and the surface in the −z direction. The holder 50 supports the planar heater 40 in the −z direction of the planar heater 40 via the heat transfer member 48 . The holder 50 supports the inner circumferential surface of the fixing belt 35 at both ends of the planar heater 40 in the x direction.

[0024] The holder 50 has an upstream rib 51 and a downstream rib 52 . The upstream rib 51 extends upstream in the rotation direction of the fixing belt 35 . The downstream rib 52 extends downstream in the rotation direction of the fixing belt 35 . The upstream rib 51 and the downstream rib 52 are capable of contacting the inner surface of the fixing belt 35 . The upstream rib 51 and the downstream rib 52 maintain the fixing belt 35 in a predetermined shape. The upstream rib 51 and the downstream rib 52 are plate-shaped with the thickness direction aligned in the y direction. A plurality of upstream ribs 51 and a plurality of downstream ribs 52 are aligned in the y direction. The upstream rib 51 and the downstream rib 52 may be located at different positions in the y direction, thereby suppressing temperature variations in the fixing device 30.

[0025] The frame 36 is formed from a steel plate material or the like. The frame 36 is located inside the fixing belt 35 . The frame 36 is attached to the −z direction surface of the holder 50 . The frame 36 extends in the y direction. Both ends of the frame 36 in the y direction are fixed to the housing 10 of the image forming apparatus 1. The frame 36 supports the planar heater 40 via a holder 50 and a heat transfer member 48 .

[0026] The temperature sensing elements 371 and 372 are, for example, thermistors. The temperature sensing elements 381 and 382 are, for example, thermostats. The temperature sensing elements 391, 392, and 393 are, for example, thermistors. The temperature sensitive elements 371 and 372 are located on the −z side of the sheet heater 40 with the heat transfer member 48 interposed therebetween. The temperature sensing elements 371 and 372 measure the temperature of the sheet heater 40 via the heat transfer member 48 . The temperature-sensing elements 381 and 382 cut off the power supply to the heating element 45 when the temperature of the planar heater 40 detected via the heat transfer member 48 exceeds a predetermined temperature. The temperature-sensing elements 391, 392, and 393 are in contact with the inner circumferential surface of the fixing belt 35 and measure the temperature of the fixing belt 35. In order to ensure electrical insulation, a coating layer for ensuring electrical insulation or an electrically insulating sheet such as polyimide may be provided between the −z direction surface of the heat transfer member 48 and the temperature sensitive elements 371, 372, 381, and 382. In this embodiment, the electrically insulating coating layer or sheet on the −z direction surface of the heat transfer member 48 is also referred to as the heat transfer member 48.

[0027] The long side 481 on the -x side of the substrate 41 is substantially straight in the range corresponding to the inner circumferential surface of the fixing belt 35, but has one recess 4811 recessed in the +x direction. The long side 482 on the +x side of the substrate 41 is substantially straight in the range corresponding to the inner circumferential surface of the fixing belt 35, but has one recessed portion 4821 recessed in the -x direction. The recess 4811 and the recess 4821 are at the same position in the y direction. The recesses 4811 and 4821 are positioned so as to overlap the central heating element 451 in the y direction.

[0028] The recesses 4811 and 4821 are intended for abutting tools such as clips or straps to secure the planar heater 40 during the manufacturing process of the planar heater 40. By abutting the tools against the recesses 4811 and 4821, the planar heater 40 can be stably and reliably secured, and the long sides 481 and 482 of the substrate 41 other than the recesses 4811 and 4821 are not damaged. Recesses 4811 and 4821 may be provided, for example, during the manufacturing process of substrate 41, to increase the clearance between other substrates 41 arranged side by side so that a tool can be inserted between them. Recesses 4811 and 4821 are, for example, locations for setting runners when manufacturing substrate 41 by casting or injection molding, and are intended to prevent so-called burrs that remain after the runners are cut off from protruding from long sides 481 and 482 of substrate 41. The recesses 4811 and 4821 are provided to prevent burrs that may be generated when the substrate 41 is manufactured by press working from protruding from the long sides 481 and 482 of the substrate 41, for example. As described above, due to the manufacturing process, it may not be possible to align the long sides 481 and 482 of the substrate 41 of the sheet heater 40 in a straight line within a range corresponding to the width of the fixing belt 35, resulting in the formation of the recesses 4811 and 4821.

[0029] FIG. 5 shows the temperature distribution in the y direction when the sheet heater 40 having the recessed portions 4811 and 4821 generates heat by being energized. In Figure 3 the position Lpf of the end of the end heating element 452 on the +y side; Position Lpg2 between the end heating element 452 and the central heating element 451; a position Lpm overlapping the central heating element 451 and being the center of the recess 4811 or the recess 4821; Position Lpg3 between the end heating element 453 and the central heating element 451; The position Lpr of the end of the end heating element 453 on the -y side, correspond to the positions of the same symbols in FIG. At the position Lpf of the end of the end heating element 452 on the +y side and the position Lpr of the end of the end heating element 453 on the −y side, a drop in temperature occurs toward the outside. Temperature dips also occur at locations between heating elements. Furthermore, at the position Lpm where the cross-sectional area of ​​the XZ cross section of the substrate 41 is reduced due to the provision of the recesses 4811 and 4821, the temperature drops near the y-direction ends of the recesses 4811 and 4821, and conversely, the temperature rises at the y-direction center of the recesses 4811 and 4821.

[0030] FIG. 6 is a view of the sheet heater 40 as seen from the −z direction. Temperature-sensing elements 371, 372 and temperature-sensing elements 381, 382 are located at positions that avoid areas where the temperature distribution is not flat and becomes locally high or low when the central heating element 451, the end heating element 452 and the end heating element 453 generate heat due to the application of electricity, such as at positions Lpg2, Lpg3 and around position Lpm. in particular, The temperature sensitive element 371 abuts against the heat transfer member 48 at a position close to the end heating element 452 within the range of the central heating element 451 in the y direction. The temperature sensitive element 372 abuts against the heat transfer member 48 at a position close to the central heating element 451 within the range of the end heating element 452 in the y direction. The temperature sensitive element 381 abuts against the heat transfer member 48 at a position close to the end heating element 453 within the range of the central heating element 451 in the y direction. The temperature sensitive element 382 abuts against the heat transfer member 48 at a position close to the central heating element 451 within the range of the end heating element 453 in the y direction.

[0031] Since the temperature sensors 371, 372, 381, and 382 are arranged at position Lpm in the y direction, i.e., at positions that avoid the centers of the recesses 4811 and 4821, it is possible to prevent the temperature sensors 371, 372, and the temperature sensors 381 and 382 from being affected by temperature singularities that arise due to changes in the cross-sectional area of ​​the XZ cross section of the substrate 41. Furthermore, since the temperature sensors 371, 372, 381, and 382 are arranged in positions that avoid the areas of the recesses 4811 and 4821 in the y direction, it is possible to prevent the temperature sensors 371, 372, and the temperature sensors 381 and 382 from being affected by the unique temperature range that occurs due to changes in the cross-sectional area of ​​the XZ cross section of the substrate 41.

[0032] The recesses on the long sides of the substrate 41 have a variety of variations. For example, as shown in Figure 7, With respect to the recess 4811 on the long side 481 on the −x side of the substrate 41, A long side 482 on the +x side of the substrate 41 may have a recess 4822 at a position displaced from the recess 4811 in the y direction. The recesses 4811 and 4822 are positioned to overlap the central heating element 451 in the y direction. Also, With respect to the recess 4811 on the long side 481 on the −x side of the substrate 41, A long side 482 on the +x side of the substrate 41 may have a plurality of recesses such as recesses 4822 and 4823 at positions shifted from recess 4811 in the y direction. In the y direction, the recessed portion 4811 and the recessed portions 4822 and 4823 are positioned to overlap with the central heating element 451 .

[0033] For example, as shown in Figure 8, With respect to the recess 4821 of the long side 482 on the +x side of the substrate 41, In some cases, a recess 4812 that is longer in the y direction than the recess 4821 is present on the long side 481 on the -x side of the substrate 41 at a position that overlaps with the recess 4821 in the y direction. The recesses 4812 and 4821 are positioned so as to overlap the central heating element 451 in the y direction.

[0034] For example, as shown in Figure 9, With respect to the recess 4821 of the long side 482 on the +x side of the substrate 41, The long side 481 on the -x side of the substrate 41 may have a recess 4813 at a position displaced from the recess 4821 in the y direction. The recessed portion 4821 and the recessed portion 4813 are positioned so as to overlap with the central heating element 451 in the y direction. Also, With respect to the recess 4821 of the long side 482 on the +x side of the substrate 41, Long side 481 on the -x side of substrate 41 may have a plurality of recesses such as recesses 4813 and 4814 at positions offset from recess 4821 in the y direction. In the y direction, the recessed portion 4821 and the recessed portions 4813 and 4814 are positioned to overlap with the central heating element 451 .

[0035] For example, as shown in Figure 10, The recess 4815 on the long side 481 on the -x side of the substrate 41 and the recess 4825 on the long side 482 on the +x side of the substrate 41 are at the same position in the y direction, but also overlap with the position between the end heating element 452 and the central heating element 451. Also, The recess 4816 on the long side 481 on the -x side of the substrate 41 and the recess 4826 on the long side 482 on the +x side of the substrate 41 are at the same position in the y direction, but also overlap with the position between the end heating element 453 and the central heating element 451.

[0036] For example, as shown in Figure 11, There is a recess 4822 on the long side 482 on the +x side of the substrate 41. There may be cases where the long side 481 on the −x side of the substrate 41 does not have a recess. Naturally, the shapes of the +x side and the −x side in FIGS. 7 to 11 and the presence or absence and number of recesses on the long side of the substrate 41 are not limited to the above variations. The reason for providing recesses on the long sides of the substrate 41 is not just for convenience in the manufacturing process. For example, recesses may be provided on the long sides of the substrate 41 to receive engagement parts that prevent the planar heater 40 from moving in the y direction relative to the holder 50.

[0037] Regardless of the shape, if the thermosensitive element is positioned in a position that avoids the recessed area in the y direction, the thermosensitive element can be prevented from being affected by the unique temperature range that occurs due to changes in the cross-sectional area of ​​the XZ cross section of the substrate 41. Note that even if convex portions, rather than concave portions, are provided on the long sides of the substrate 41, there is a risk that the cross-sectional area of ​​the XZ cross section of the substrate 41 will increase at the position of the convex portion in the y direction, resulting in temperature non-uniformity. If the thermosensitive element is provided at a position that avoids the range of the convex portions in the y direction, it is possible to prevent the thermosensitive element from being affected by the unique temperature range that occurs due to the influence of the change in the cross-sectional area of ​​the XZ cross section of the substrate 41.

[0038] Furthermore, the heating element 45 is not limited to being arranged in the y direction with a central heating element 451 and a pair of end heating elements 452, 453. For example, as shown in Fig. 12, a configuration may be adopted in which an intermediate auxiliary heating element 456 with a high heat generation amount in both end ranges in the y direction is provided between an upstream heating element 454 and a downstream heating element 455 with a high heat generation amount in the central range in the y direction. A configuration may also be adopted in which the heat generation of the upstream heating element 454 and the downstream heating element 455 is controlled in the same way, and the heat generation of the intermediate auxiliary heating element 456 is controlled independently of the upstream heating element 454 and the downstream heating element 455.

[0039] FIG. 13 is a view of the sheet heater 40 fitted in the holder 50 as viewed from the +z direction. Temperature-sensing elements 391, 392, and 393 are located at positions that avoid the +x direction (downstream in terms of the rotation direction of the fixing belt 35) of the central heating element 451, the end heating element 452, and the end heating element 453, such as at positions Lpg2, Lpg3, and around position Lpm, where the temperature distribution is not flat when the heating element is energized and the temperature becomes locally high or low. in particular, The temperature sensitive element 391 contacts the fixing belt 35 on the downstream side in the rotation direction of the fixing belt 35 within the range of the central heating element 451 in the y direction. The temperature sensitive element 392 contacts the fixing belt 35 at a position close to the central heating element 451 within the range of the end heating element 452 in the y direction, on the downstream side in the rotation direction of the fixing belt 35. The temperature sensitive element 393 contacts the fixing belt 35 at a position far from the central heating element 451 within the range of the end heating element 453 in the y direction, downstream in the direction of rotation of the fixing belt 35.

[0040] Since the thermosensors 391, 392, and 393 are arranged at position Lpm in the y direction, i.e., at a position that avoids the center of the recesses 4811 and 4821, the thermosensors 391, 392, and 393 can be prevented from being affected by temperature singularities that arise due to changes in the cross-sectional area of ​​the XZ cross section of the substrate 41. Furthermore, since the temperature-sensing elements 391, 392, and 393 are arranged in positions that avoid the areas of the recesses 4811 and 4821 in the y direction, the temperature-sensing elements 391, 392, and 393 can be prevented from being affected by the unique temperature range that occurs due to changes in the cross-sectional area of ​​the XZ cross section of the substrate 41.

[0041] As described above, by arranging all the thermosensitive elements at position Lpm in the y direction, i.e., at a position that avoids the center of recesses 4811 and 4821, it is possible to prevent all the thermosensitive elements from being affected by temperature singularities that arise due to changes in the cross-sectional area of ​​the XZ cross section of substrate 41, and ultimately to appropriately control the fixing device. Furthermore, by arranging all the thermosensitive elements in positions that avoid the ranges of recesses 4811 and 4821 in the y direction, it is possible to prevent all the thermosensitive elements from being affected by the unique temperature range that occurs due to changes in the cross-sectional area of ​​the XZ cross section of substrate 41, and ultimately to appropriately control the fixing device.

[0042] Both the thermistor and the thermostat may be provided as temperature-sensing elements at position Lpm in the y direction, that is, at a position that avoids the center of recess 4811 or recess 4821. A thermosensitive element that functions only as a so-called safety device, such as a thermostat, where the thermosensitive element itself cuts off power when a specific temperature is exceeded, may be excluded from the group of thermosensitive elements that are provided at position Lpm in the y direction, that is, at a position that avoids the centers of recesses 4811 and 4821, if it has a role that must be activated when an abnormally high temperature occurs even at a singular point. One approach is to provide a thermosensitive element that functions only as a safety device, such as a thermostat, at a position that avoids position Lpm in the y direction, because it should not be activated at the temperature of a singular point. At least a temperature-sensing element such as a thermistor that functions as a thermometer for controlling the amount of current flowing through the sheet heater 40 should be provided at position Lpm in the y direction, that is, at a position that avoids the center of the recess 4811 or the recess 4821.

[0043] 14 is a front cross-sectional view of a fixing device according to the second embodiment. The same components as those in the first embodiment are denoted by the same reference numerals and will not be described. The fixing device of the second embodiment has a cover 60 between the planar heater 40 and the fixing belt 35. The +z surface of the planar heater 40 contacts the −z surface of the cover 60, and the +z surface of the cover 60 slides against the inner surface of the fixing belt 35. The cover 60 covers the entire heating element 45 in the y direction. The cover 60 covers the entire heating element 45 in the y direction. It is preferable that the cover 60 can cover the planar heater 40 from outside the end of the fixing belt 35 in the +y direction to outside the end of the fixing belt 35 in the -y direction. The cover 60 is made of a metal material such as stainless steel.

[0044] When the sheet heater 40 is energized and generates heat, the unevenness of the temperature distribution in the y direction is alleviated by heat diffusion inside the cover 60 and is then transmitted to the fixing belt 35 . Since the locally peculiar temperature is somewhat equalized, the expected effect is not as high as that of the first embodiment, but in the second embodiment, By arranging the thermosensitive elements 391, 392, and 393 at position Lpm in the y direction, i.e., at a position that avoids the center of the recesses 4811 and 4821, it is useful to prevent the thermosensitive elements 391, 392, and 393 from being affected by temperature singularities that arise due to changes in the cross-sectional area of ​​the XZ cross section of the substrate 41.

[0045] 15 is a front cross-sectional view of a fixing device according to the third embodiment. The same components as those in the first embodiment are denoted by the same reference numerals and will not be described. In the fixing device of the third embodiment, the heat transfer member 48 is not sandwiched between the sheet heater 40 and the holder 50. The temperature sensitive elements 371, 372, 381, and 382 abut on the surface of the sheet heater 40 in the -z direction. In the first embodiment, when the sheet heater 40 generates heat by being energized, the unevenness of the temperature distribution in the y direction is alleviated by thermal diffusion inside the heat transfer member 48 and then transferred to the temperature-sensing elements 371, 372, 381, and 382. In a configuration in which the heat transfer member 48 is not sandwiched as in this third embodiment, the uneven temperature distribution in the y direction of the planar heater 40 is not alleviated and has a greater impact on the temperature-sensing elements 371, 372, 381, and 382. Therefore, by arranging the temperature-sensing elements 371, 372, 381, and 382 at position Lpm in the y direction, i.e., at a position avoiding the center of the recess 4811 and the recess 4821, it is possible to prevent the temperature-sensing elements 371, 372, 381, and 382 from being affected by the temperature singularities that arise due to the change in the cross-sectional area of ​​the XZ cross section of the substrate 41.

[0046] Although several embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be embodied in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included within the scope and spirit of the invention, and are also included in the scope of the invention and its equivalents as defined in the claims. [Explanation of symbols]

[0047] 1 image forming apparatus, 2 scanner section, 3 image forming unit, 4 sheet supply section, 5 transport section, 6 control section, 7 tray, 8 control panel, 9 reversing unit, 10 housing, 10 housing, 20 sheet storage section, 21 pickup roller, 23 transport roller, 24 registration roller, 30 fixing device, 31 pressure roller, 32 core metal, 33 elastic layer, 34 heating roller, 35 fixing base 36···Frame, 36···Frame, 40···Plane heater, 41···Substrate, 42···Insulating layer, 43···Protective layer, 45···Heat generating element, 46···Wiring, 47···Insulating layer, 48···Heat transfer member, 50···Holder, 51···Upstream rib, 52···Downstream rib, 60···Cover, 451···Central heating element, 452, 453···End heating element, 371, 372, 381, 382, ​​391, 392, 393···Thermo-sensing element, N···Nip, RN···Nip, S···Sheet.

Claims

1. a cylindrical body; a substrate having a longitudinal direction in the axial direction of the cylindrical body, and having, within a width range of the cylindrical body in the axial direction, a first range in which a cross-sectional shape perpendicular to the axial direction is a first shape, and a second range in which a second shape different from the first shape is narrower than the first range in the axial direction; a first heating element overlapping the second area of ​​the substrate in the axial direction; a second heating element overlapping the first area of ​​the substrate in the axial direction; a heater unit that contacts the inside of the cylindrical body and heats the cylindrical body; a heat transfer member arranged so that the heater unit is positioned between the heat transfer member and the cylindrical body; a first temperature sensing element that measures the temperature of the heat transfer member at a position that overlaps with the first heating element in the axial direction but avoids the second range; a second temperature sensing element that measures the temperature of the heat transfer member at a position that overlaps with the second heating element in the axial direction but avoids the second range; A fixing device comprising:

2. a cylindrical body; a substrate having a longitudinal direction in the axial direction of the cylindrical body, the substrate having a cross-sectional shape perpendicular to the axial direction, the cross-sectional shape of which is a first region having a first shape and a second region having a second shape different from the first shape and narrower than the first region in the axial direction; a first heating element overlapping the second area of ​​the substrate in the axial direction; a second heating element overlapping the first area of ​​the substrate in the axial direction; a heater unit for heating the cylindrical body; a first temperature-sensing element that measures the temperature of the cylindrical body at a position that overlaps with the first heating element in the axial direction but avoids the second range; a second temperature-sensing element that measures the temperature of the cylindrical body at a position that overlaps with the second heating element in the axial direction but avoids the second range; A fixing device comprising:

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