Heater, heating device, and image forming apparatus

Abstract

To solve the problem in which: when heating elements are different in distance from a thermistor in a short direction of a heater, the temperature responsiveness of the thermistor may vary depending on the heating element that generates heat.SOLUTION: In a short direction of a substrate, the distance from a temperature detection element to a first heating element is a first distance, and the distance from the temperature detection element to a second heating element is a second distance longer than the first distance. When seen in a thickness direction orthogonal to the short direction and a longitudinal direction of the substrate, a conductor overlaps the first heating element and the second heating element.SELECTED DRAWING: Figure 3

Description

[Technical Field]

[0001] The present invention relates to a heater, and more particularly to a heater used in copying machines, printers, facsimiles, etc. that use electrophotographic or electrostatic recording methods. [Background technology]

[0002] In conventional image forming apparatuses using electrophotographic processes, unfixed toner images formed on a sheet are fixed by applying heat and pressure using a fixing device equipped with a heater. Sheets that can be fixed by fixing devices come in a variety of widths, including A4, B5, and A5. When fixing an A4-sized sheet, the difference between the heated area (the area heated by the heater) and the sheet width in the longitudinal direction of the heater is small, so the temperature of the non-sheet-passing area is unlikely to rise. On the other hand, when fixing an A5-sized sheet, which is narrower than an A4-sized sheet, the difference between the heated area and the sheet width in the longitudinal direction of the heater is large, so the temperature of the non-sheet-passing area is likely to rise. An increase in the temperature of the non-sheet-passing area can result in image defects and other problems.

[0003] Therefore, Patent Document 1 discloses that a heater is used that includes a plurality of heating elements with different lengths in the longitudinal direction of the heater, and the heating element to be used is switched depending on the width of the sheet. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-162909 Summary of the Invention [Problem to be solved by the invention]

[0005] 25, multiple heating elements having different lengths in the longitudinal direction of the heater are arranged side by side in the lateral direction of the heater. In such a heater, if there is a difference in the distance between the thermistor and each heating element in the lateral direction of the heater, there is a risk that the temperature responsiveness of the thermistor will vary depending on the heating element that generates heat.

[0006] The present invention has been made in view of the above circumstances, and has an object to suppress fluctuations in the temperature responsiveness of a thermistor. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides: A heater used in an apparatus main body having a control unit, the heater being configured so that the supplied power is controlled by the control unit, an elongated substrate; and a first surface of the substrate; a first heating element, a second heating element, and a third heating element configured to generate heat when supplied with the power; a temperature detection element disposed on a second surface of the substrate opposite the first surface; a conductor disposed on the second surface of the substrate, in contact with the temperature detection element, and configured to be electrically connected to the control unit, wherein the second heating element, the first heating element, and the third heating element are disposed in this order in a short-side direction of the substrate, and a distance from the temperature detection element to the second heating element and a distance from the temperature detection element to the third heating element are both longer than a distance from the temperature detection element to the first heating element in the short-side direction of the substrate, When viewed in the thickness direction of the substrate, the conductor is and, the second heating element and the third heating element, It is characterized by overlapping. [Effects of the Invention]

[0008] According to the configuration of the present invention, fluctuations in the temperature response of the thermistor can be suppressed. [Brief explanation of the drawings]

[0009] [Figure 1] Schematic diagram of an image forming apparatus [Figure 2] Cross-sectional view of the fixing device [Figure 3] Schematic diagram of the heater in the longitudinal direction [Figure 4] Cross section of heater [Figure 5] Schematic diagram of the power control unit [Figure 6] Schematic diagram of a heater of a comparative example in the longitudinal direction [Figure 7] Graph showing temperature transition of the temperature detection element [Figure 8] Table showing the temperature of the temperature detection element [Figure 9] Schematic diagram of the heater in the longitudinal direction [Figure 10] Schematic diagram of the heater in the longitudinal direction [Figure 11] Cross section of heater [Figure 12] Schematic diagram of the power control unit [Figure 13] Schematic diagram of the heater in the longitudinal direction [Figure 14] Cross section of heater [Figure 15] Schematic diagram of the power control unit [Figure 16] Cross section of heater [Figure 17] Schematic diagram of the heater in the longitudinal direction [Figure 18] Cross section of heater [Figure 19] Schematic diagram of the heater in the longitudinal direction [Figure 20] Cross section of heater [Figure 21] Schematic diagram of the power control unit [Figure 22] Schematic diagram of the heater in the longitudinal direction [Figure 23] Cross section of heater [Figure 24] Schematic diagram of the power control unit [Figure 25] Schematic diagram of a conventional heater in the longitudinal direction DETAILED DESCRIPTION OF THE INVENTION

[0010] The following describes embodiments of the present invention with reference to the drawings. Note that the following embodiments do not limit the scope of the invention as claimed, and not all of the combinations of features described in the embodiments are necessarily essential to the solution of the invention.

[0011] (First embodiment) [Image forming equipment] FIG. 1 is a schematic diagram of an image forming apparatus P. The image forming apparatus P has four image forming stations that form images of the respective colors: yellow, magenta, cyan, and black. These four image forming stations are arranged in a row at regular intervals. In the following description, the letters Y, M, C, and K at the end of reference numerals indicate that the corresponding components are related to the formation of toner images of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In the following description, when it is not necessary to distinguish between colors, reference numerals without the letters Y, M, C, and K at the end may be used.

[0012] The image forming station 3 has a photosensitive drum 4 as an image carrier and a charging roller 5 as a charging means. The image forming station 3 also has an exposure device 6 as an exposure means, a developing device 7 as a developing means, and a cleaning device 8 as a cleaning means.

[0013] Based on information received from an external device (not shown) such as a host computer, the video controller 30 performs processes such as bitmapping character codes and halftoning using dithering of halftone images, and transmits a print signal and image information to the engine control unit 31. When the engine control unit 31 receives the image information from the video controller 30, it forms an image according to the image information.

[0014] It is rotated in the direction of the arrow. The outer peripheral surface (surface) of the photosensitive drum 4 is uniformly charged by a charging roller 5. An exposure device 6 irradiates the charged photosensitive drum 4 with laser light corresponding to image information, thereby forming an electrostatic latent image on the photosensitive drum 4. A developing device 7 develops the electrostatic latent image with toner to form a toner image (hereinafter also referred to as an image).

[0015] An endless intermediate transfer belt 9 is provided along the direction in which the image forming stations 3 are arranged, and is stretched around a drive roller 9a, a driven roller 9b, and a driven roller 9c. The drive roller 9a rotates in the direction of the arrow. This causes the intermediate transfer belt 9 to rotate along the image forming stations 3 at a speed of 100 mm / sec.

[0016] The toner images formed at each image forming station 3 are sequentially transferred onto the intermediate transfer belt 9 by a primary transfer roller 10 to which a primary transfer bias is applied. Residual toner remaining on the photosensitive drum 4 after the primary transfer is removed by a cleaning blade (not shown) provided in the cleaning device 8.

[0017] For example, a sheet S, which is paper, is loaded in a paper feed cassette 11 and fed by a paper feed roller 12. The fed sheet S is transported to a pair of registration rollers 13. The pair of registration rollers 13 transports the sheet S to a secondary transfer nip portion between the intermediate transfer belt 9 and a secondary transfer roller 14.

[0018] The secondary transfer roller 14 is disposed so as to face the driven roller 9b across the intermediate transfer belt 9. A secondary transfer bias is applied to the secondary transfer roller 14, thereby performing a second transfer of the image on the intermediate transfer belt 9 onto the sheet S passing through the secondary transfer nip. Any residual toner remaining on the surface of the intermediate transfer belt 9 after the secondary transfer is removed by an intermediate transfer belt cleaning device 16.

[0019] The sheet S onto which the image has been secondarily transferred is heated and pressed by a fixing device F1, which serves as a heating device, to fix the image. The detailed configuration of the fixing device F1 will be described later. The sheet S onto which the image has been fixed is discharged onto a paper discharge tray 15.

[0020] [Fusing device] FIG. 2 is a cross-sectional view of the fixing device F1. The fixing device F1 has a fixing film 22 and a pressure roller 21. The fixing film 22 and the pressure roller 21 form a nip. The fixing device F1 is a tensionless device that uses a film heating method and a pressure roller driving method, in which the pressure roller 21 is driven to rotate and the fixing film 22 is rotated by the conveying force of the pressure roller 21. The fixing device F1 also has a heater 23, a heater holder 24, a rigid stay 25, etc. The detailed configuration of the heater 23 will be described later in FIG. 3 and other figures. The direction of the long side of the elongated heater 23 is referred to as the longitudinal direction (the left-right direction in FIG. 3), the direction of the short side of the heater 23 perpendicular to the longitudinal direction is referred to as the lateral direction (the up-down direction in FIG. 3), and the thickness direction of the heater 23 perpendicular to the longitudinal and lateral directions is referred to as the thickness direction (the up-down direction in FIG. 4).

[0021] The fixing film 22 is cylindrically formed from a flexible heat-resistant resin material. The peripheral length of the fixing film 22 is 57 mm. The fixing film 22 has a cylindrical base layer 221 made of a polyimide layer having a thickness of 50 microns, and an elastic layer 222 made of silicone rubber having a thickness of 200 microns on the outer periphery of the base layer 221. The elastic layer 222 has a release layer 223 made of fluororesin having a thickness of 15 microns on the outer periphery of the elastic layer 222.

[0022] The inner peripheral length of the fixing film 22 is 3 mm longer than the outer peripheral length of the heater holder 24 that holds the heater 23, and the fixing film 22 is loosely fitted around the heater holder 24 with some leeway in the peripheral length. The heater 23 is disposed in the internal space of the fixing film 22 while being held by the heater holder. The rigid stay 25 is a rigid member with a downward U-shaped cross section. The rigid stay 25 is disposed in the center of the short side of the upper surface of the heater holder 24.

[0023] The pressure roller 21 has a round shaft-shaped core 211, an elastic layer 212 made of silicone rubber formed concentrically around the outer periphery of the core 211, and a release layer 213 made of conductive fluororesin around the elastic layer 212. The outer periphery of the pressure roller 21 is 63 mm. The elastic layer 212 may be made of heat-resistant rubber such as fluororubber or foamed silicone rubber. The release layer 213 may be made of insulating fluororesin.

[0024] The pressure roller 21 is disposed below and parallel to the fixing film 22. The pressure roller 21 is rotatably supported at both ends of a core metal 211 in the longitudinal direction via bearing members. The core metal 211 of the pressure roller 21 and the rigid stay 25 are pressurized at both longitudinal ends by a pressure spring (not shown) so that the outer circumferential surface of the pressure roller 21 and the outer circumferential surface of the fixing film 22 come into contact. The pressure of the pressure spring brings the pressure roller 21 and the fixing film 22 into contact with each other, forming a nip portion NF between the pressure roller 21 and the fixing film 22. The sheet S is transported through the nip portion NF. The total pressure applied to the pressure roller 21 and the rigid stay 25 is 20 kgf.

[0025] In response to a print command, the engine control unit 31 rotates the pressure roller 21 in the direction of the arrow at a predetermined peripheral speed (process speed). At this time, a rotational force acts on the fixing film 22 due to the frictional force between the surface of the pressure roller 21 and the surface of the fixing film 22 at the nip portion NF. The rotational force causes the fixing film 22 to rotate in the direction of the arrow around the outer periphery of the heater holder 24 while the inner periphery of the fixing film 22 slides in close contact with the heater 23. The rotation of the fixing film 22 is guided by the outer periphery of the heater holder 24, which is formed to fit the inner periphery of the fixing film 22. This stabilizes the rotation of the fixing film 22, allowing the fixing film 22 to rotate while tracing the same rotational trajectory.

[0026] In response to a print command, the engine control unit 31 energizes the heating element of the heater 23. When the heater 23 is energized and power is supplied, the heater 23 increases in temperature and heats the fixing film 22. Details of the heater 23 will be described later.

[0027] When the rotation of the pressure roller 21 and the fixing film 22 stabilizes and the temperature of the heater 23 reaches the target temperature, the sheet S carrying the unfixed image t is conveyed to the nip portion NF through the entrance guide 27. The sheet S is sandwiched and conveyed between the pressure roller 21 and the fixing film 22 at the nip portion NF. Heat and pressure are applied to the sheet S at the nip portion NF, and the unfixed image t is fixed to the sheet S. The sheet S with the fixed image t separates from the surface of the fixing film 22 due to its curvature and is discharged from the nip portion NF.

[0028] [heater] The configuration of heater 23 will be described using Figures 3 and 4. Figure 3 is a schematic diagram of heater 23 in the longitudinal direction. Figure 3(a) shows a first surface side (also referred to as the front surface side) of a substrate on which a heating element is arranged, and Figure 3(b) shows a second surface side (also referred to as the back surface side) of the substrate. Figure 4 is a schematic diagram showing a cross section of heater 23 taken along line U in Figure 3.

[0029] Heater 23 includes ceramic substrate 231 that is elongated in the longitudinal direction and has heat resistance, insulation properties, and good thermal conductivity, heating elements 232a, 232b, 232c, and 232d made of a conductive material mainly composed of silver and palladium, conductors 233a and 233b mainly composed of silver, contacts 234a, 234b, and 234c, and heat-resistant surface protection layer 235 made of glass or the like.

[0030] Heating elements 232a, 232b, 232c, and 232d, conductors 233a and 233b, and contacts 234a, 234b, and 234c are formed on the surface of substrate 231. Furthermore, a surface protection layer 235 is formed thereon to ensure insulation between heating elements 232a, 234b, 234c, and 232d, conductors 233a, and 233b, and film 22. In this example, substrate 231 has a length of 250 mm in the longitudinal direction, a length of 7 mm in the lateral direction, and a thickness of 1 mm. Heating elements 232a, 232b, 232c, and 232d and conductor 233 are 10 μm thick, contacts 234a, 234b, and 234c are 20 μm thick, and surface protection layer 235 is 50 μm thick.

[0031] Heating elements 232c and 232d are connected in series via conductor 233b. Heating elements 232a and 232b are connected in series via conductor 233a. Heating elements 232c and 232d and heating elements 232a and 232b have different longitudinal lengths. Specifically, the longitudinal length of heating elements 232c and 232d is L1, and the longitudinal length of heating elements 232a and 232b is L2. The relationship between length L1 and length L2 is L1 > L2. Here, as an example, length L1 = 222 mm, and length L2 = 216 mm.

[0032] Heating elements 232a and 232b are arranged line-symmetrically with respect to the center of the substrate 231 in the short-side direction. Heating elements 232c and 232d are arranged line-symmetrically with respect to the center of the substrate 231 in the short-side direction. Heating elements 232c and 232d are arranged outward in the short-side direction of the substrate 231 than heating elements 232a and 232b. Here, as an example, the width of each of heating elements 232a, 232b, 232c, and 232d is 0.7 mm. Furthermore, the heating elements are arranged with a predetermined distance or more between them for insulation. Here, as an example, the distance between the heating elements is 0.6 mm. That is, heating elements 232a and 232b are arranged in an area 0.3 mm to 1.0 mm from the center in the short-side direction of the substrate 231. The heating elements 232c and 232d are arranged in an area 1.6 mm to 2.3 mm away from the center in the short direction of the substrate 231.

[0033] Here, as an example, the total resistance value of heating elements 232a and 232b is 18Ω. The total resistance value of heating elements 232a and 232b is 20Ω. Heating elements 232a and 232b are electrically connected to contacts 234a and 234c via conductor 233a. Heating elements 232c and 232d are electrically connected to contacts 234b and 234c via conductor 233b. Contact 234c is a contact that is commonly connected to each of the heating elements.

[0034] The length L1 of the heating elements 232c and 232d is set to a length that allows fixing of the sheet S having the largest width (hereinafter also referred to as the maximum paper passing width) among the sheets S that can be printed (or conveyed) by the image forming apparatus. Here, as an example, the heating elements 232a and 232b, and the heating elements 232c and 232d are configured so that either one generates heat exclusively depending on the width of the sheet S to be printed. For example, the heating elements 232c and 232d are used when fixing an LTR size sheet S with a width of 216 mm, and the heating elements 232a and 232b are used when fixing an A4 size sheet S with a width of 210 mm.

[0035] Temperature detection element 26, which is, for example, a thermistor, is disposed on the surface of substrate 231 opposite to the surface on which heating element 232 is disposed. Temperature detection element 26 is disposed at approximately the center of heating elements 232a, 232b, 232c, and 232d in the longitudinal and lateral directions of substrate 231. Temperature detection element 26 is also bonded to substrate 231.

[0036] Furthermore, conductive conductors 236a and 236b are formed on the same surface as the surface on which the temperature detection element 26 is disposed. The temperature detection element 26 is in contact with and electrically connected to the conductors 236a and 236b. Conductive wires 237a and 237b are electrically connected to the conductors 236a and 236b by welding or the like, and are connected to the engine control unit 31. The temperature detection element 26 outputs the temperature detection result to the engine control unit 31 via the conductors 236a and 236b. The engine control unit 31 controls the supply of electricity to the heating element based on the temperature detected by the temperature detection element 26 so that the temperature of the heater 23 becomes the target temperature T.

[0037] 5 is a schematic diagram of a power control unit 97, which is a control circuit of the fixing device F1. The power control unit 97 is composed of a bidirectional thyristor 56 (hereinafter also referred to as a triac), a switch 57 that exclusively selects a heating element to which power is supplied, and the like. In this example, the switch 57 is a C-contact relay. The power control unit 97 selects a heating element 232 to which power is supplied and determines the amount of power to supply.

[0038] The triac 56 is turned on and conductive when power is supplied from the AC power supply 55 to the heating elements 232a, 232b or the heating elements 232c, 232d. On the other hand, the triac 56 is turned off and non-conductive when power is not supplied to the heating elements 232a, 232b or the heating elements 232c, 232d. The engine control unit 31 calculates the power required to control the temperature to a target temperature (for example, the above-mentioned 180°C) based on the temperature detected by the temperature detection element 26, and controls the triac 56 to be conductive or non-conductive.

[0039] The switch 57 has a contact 57c connected to the AC power supply 55, a contact 57a connected to the contact 234a, and a contact 57b connected to the contact 234b. The switch 57 is in one of two states: a state in which the contact 57c is connected to the contact 57a, and a state in which the contact 57c is connected to the contact 57b. By switching the contacts with the switch 57, it is possible to exclusively switch between a state in which power is supplied to the heating elements 232a and 232b and a state in which power is supplied to the heating elements 232c and 232d. The switch 57 performs switching in response to a signal from the engine control unit 31. To prevent the contacts of the switch 57, which is a C-contact relay, from welding, the triac 56 is made non-conductive when switching.

[0040] Power is simultaneously applied to heating elements 232a and 232b, causing them to generate heat. Power is also simultaneously applied to heating elements 232c and 232d. In this way, the heating elements that generate heat simultaneously are arranged so as to be line-symmetrical about the center in the short-side direction of substrate 231. By arranging the heating elements so as to be line-symmetrical about the center in the short-side direction of substrate 231, thermal expansion when the heating elements are heated is also symmetrical, making it less likely that cracks will occur in substrate 231.

[0041] The heating elements 232c and 232d are disposed closer to the end of the substrate 231 in the short-side direction of the substrate 231 than the heating elements 232a and 232b. In the short-side direction of the substrate 231, the distance from the temperature detection element 26 to the heating elements 232c and 232d is longer than that to the heating elements 232a and 232b. The longer the distance from the temperature detection element 26 to the heating element 232, the longer the time it takes for the heat generated by the heating element 232 to be transmitted to the temperature detection element 26. In other words, the time it takes for the temperature detection element 26 to detect a temperature change due to the heating element 232 generating heat becomes longer. In other words, the temperature responsiveness of the temperature detection element 26 varies depending on which heating element 232 generates heat. As a result, the time it takes for the temperature of the heater 23 to reach the desired temperature also changes, and if the distance is long, the temperature of the heater 23 is slow to follow. Furthermore, when the distance between the heating element 232 and the temperature detection element 26 varies, the heat transfer to the temperature detection element 26 varies depending on the heating element 232. Even if the temperature of the temperature detection element 26 is the same, the temperature of the heater 23 may vary depending on the heating element 232 used.

[0042] In consideration of this situation, the temperature detection element 26 and the heating element 232 of the heater 23 are arranged as follows. That is, the conductors 236a and 236b connected to the temperature detection element 26 are arranged so that they overlap the heating elements 232a, 232b, 232c, and 232d in the thickness direction of the substrate 231. Note that the overlapping area may be only a portion of the conductors 236a and 236b, but the larger the overlapping area, the better. In FIGS. 3 and 4, as an example, the widths of the conductors 236a and 236b in the short direction of the substrate 231 are W1 = 2.0 mm and W2 = 5.0 mm. Furthermore, the lengths of the conductors 236a and 236b in the long direction of the substrate 231 are L3 = 2.0 mm and L4 = 6.0 mm.

[0043] Conductors 236a and 236b are formed of a material that is electrically conductive and has good thermal conductivity. Here, as an example, they are a metal paste of silver, copper, or the like formed on substrate 231 by screen printing or the like, and have a thickness of 20 μm. In addition to metal paste, a paste containing a material with good thermal conductivity, such as graphite, carbon, or ceramic, may be formed on substrate 231. The paste may also be formed into a sheet and adhered to or in contact with substrate 231. Note that the paste may have any configuration as long as it is a thin-film or sheet-like member that is in close contact with substrate 231, has conductivity that allows it to function as an electrical circuit by electrically connecting to temperature detection element 26, and has good thermal conductivity equal to or greater than that of substrate 231.

[0044] The conductors 236a and 236b are in physical contact with and electrically connected to the temperature detection element 26. The conductors 236a and 236b are capable of conducting electricity to the temperature detection element 26 and also conducting heat to the temperature detection element 26. The conductors 236a and 236b are electric circuits that electrically transmit the temperature detected by the temperature detection element 26 to the engine control unit 31, and also function as heat collecting members for the temperature detection element 26.

[0045] The heat generated from heating element 232 is transferred to conductors 236a and 236b via substrate 231, and then transferred to temperature detection element 26 via conductors 236a and 236b. This reduces the delay before the heat generated from the heating element is transferred to temperature detection element 26 as a predetermined temperature change, and reduces the delay in controlling the flow of electricity to heating element 232.

[0046] The conductors 236a and 236b are arranged so as to overlap all of the heating elements 232a, 232b, 232c, and 232d in the thickness direction of the substrate 231. As a result, regardless of whether the heating elements 232a and 232b or the heating elements 232c and 232d are heated, heat can be transferred to the temperature detection element 26 via the conductors 236a and 236b. In the short-side direction of the substrate 231, the heating elements 232a and 232b are at different distances from the temperature detection element 26 than the heating elements 232c and 232d. In this way, whether the heating elements 232a and 232b are heated or the heating elements 232c and 232d are heated, fluctuations in the temperature responsiveness of the temperature detection element 26 can be suppressed due to the heat transfer effect of the conductors 236a and 236b. Heat generated from a heating element 232 located a long distance from the temperature detection element 26 may be delayed in transmission or may be thermally diffused by surrounding components. This may result in the temperature detection element 26 detecting a relatively low temperature. The power supplied to the heating element 232 is controlled based on the temperature detected by the temperature detection element 26. Therefore, if the temperature response of the temperature detection element 26 varies depending on the heating element 232 used, there is a risk of overshoot, in which the temperature of the heater 23 greatly exceeds the target temperature, or undershoot, in which the temperature drops too far below the target temperature, or temperature fluctuations (ripples) occurring. Such risks can be reduced by arranging the conductors 236a and 236b as shown in Figures 3 and 4.

[0047] (Experiment 1) An experiment was conducted to confirm the effect using the fixing device F1 of the present embodiment described above. The process speed of the image forming apparatus used in the experiment was 100 mm / s, and the interval (paper interval) between the preceding sheet S and the succeeding sheet S was 30 mm. 2 ,The sheet S of LTR size (216mm width, 279mm length) and the sheet S of A4 size (210mm width, 297mm length) were used.

[0048] When fixing an LTR size sheet S, the engine control unit 31 controls the switch 57 to perform fixing using the heating elements 232c and 232d. When fixing an A4 size sheet S, the engine control unit 31 controls the switch 57 to perform fixing using the heating elements 232a and 232b.

[0049] The experiment was conducted with an image forming apparatus placed in an environment with an ambient temperature of 23°C and humidity of 50%. Printing was performed using an image forming apparatus equipped with the fixing device F1 of this embodiment and an image forming apparatus equipped with a fixing device as a comparative example. As described above, the heater 23 of the fixing device F1 of this embodiment is arranged so that the conductors 236a and 236b and the heating elements 232a, 232b, 232c, and 232d overlap in the thickness direction of the substrate 231. The conductors 236a and 236b have widths W1 = 2.0 mm and W2 = 5.0 mm. Furthermore, the lengths L3 = 2.0 mm and L4 = 6.0 mm.

[0050] The fixing device of the comparative example has a different shape of the conductor disposed in the heater 23. FIG. 6 shows a schematic diagram of the heater 23 of the comparative example in the longitudinal direction. The heating element 232 of the heater 23 and the engine control unit 31 are the same as those of this embodiment. In the comparative example, the shapes of the conductors 236a and 236b disposed on the back side of the heating element 232 in the thickness direction of the substrate 231 are different. The conductors 236a and 236b in the comparative example have a width W of 2.0 mm and a length L of 8.0 mm. The conductors 236a and 236b in the comparative example overlap with the heating elements 232a and 232b in the thickness direction of the substrate 231, but do not overlap with the heating elements 232c and 232d.

[0051] In an image forming apparatus using each fixing device, the fixing device is driven and power is supplied to the heater 23 when the temperature detected by the temperature detection element 26 is 23°C. Then, a ramp-up operation is performed until the temperature detected by the temperature detection element 26 reaches the target temperature of 180°C, and the engine control unit 31 controls power supply to the heater 23 so that the target temperature of 180°C is maintained. Both the fixing device of this embodiment and the fixing device of the comparative example use PID control for temperature control. The engine control unit 31 controls power supply to the heater 23 based on the difference or proportionality between the temperature detected by the temperature detection element 26 and the target temperature.

[0052] The temperature detected by temperature detection element 26 was measured during the period from when the start of the fixing device began until the temperature detected by temperature detection element 26 was maintained at the target temperature. In the fixing device of this embodiment and the fixing device of the comparative example, the temperatures detected by temperature detection element 26 were measured in the cases where heating elements 232a and 232b were made to generate heat and where heating elements 232c and 232d were made to generate heat.

[0053] FIG. 7 shows the transition of the temperature detected by the temperature detection element 26 when the heating elements 232a and 232b are heated in the fixing device of this embodiment. The horizontal axis represents the elapsed time from when power is first applied to the heater 23, and the vertical axis represents the temperature detected by the temperature detection element 26. The detected temperature rose to the target temperature of 180°C in approximately 5 seconds, overshot the target temperature, and then fluctuated slightly above and below the target temperature (ripple), while being controlled to maintain a value close to the target temperature of 180°C. The temperature at which the temperature rose above the target temperature of 180°C and overshot was defined as ΔTth1. Furthermore, the maximum value of the difference between the detected temperature and the target temperature after rising to the target temperature, overshooting, and then dropping back to the target temperature was defined as ΔTth2.

[0054] FIG. 8 is a table showing the temperatures detected by the temperature detection element 26 in the fixing device of this embodiment and the fixing device of the comparative example. In the fixing device of this embodiment, the values ​​of ΔTth1 and ΔTth2 were the same when heating elements 232a and 232b were heated and when heating elements 232c and 232d were heated. ΔTth1 = 5°C, and ΔTth2 = 2°C. In the short direction of the substrate 231, the distance between the temperature detection element 26 and heating elements 232a and 232b is shorter than the distance between the temperature detection element 26 and heating elements 232c and 232d. The reason why the values ​​of ΔTth1 and ΔTth2 remained the same is because the heating elements and conductors 236a and 236b are arranged so as to overlap with each other in the thickness direction of the substrate 231. In the fixing device of the comparative example, when heating elements 232a and 232b were heated, ΔTth1=5°C and ΔTth2=2°C. On the other hand, when heating elements 232c and 232d were heated, ΔTth1=8°C and ΔTth2=5°C.

[0055] As described above, in the fixing device of this embodiment, the overshoot and temperature deviation were smaller when heating elements 232a and 232b were heated and when heating elements 232c and 232d were heated, compared to the fixing device of the comparative example. In the fixing device of this embodiment, the difference in the amount of temperature overshoot between heating elements 232a and 232b and heating elements 232c and 232d was smaller than in the fixing device of the comparative example. In the fixing device of the comparative example, when heating elements 232c and 232d were heated, the overshoot from the target temperature was large and the deviation from the target temperature was also large. Furthermore, the difference in the amount of temperature overshoot between heating elements 232a and 232b and heating elements 232c and 232d was large.

[0056] In the fixing device of the comparative example, the distance between temperature detection element 26 and heating elements 232a and 232b in the short direction of substrate 231 is relatively shorter than the distance between temperature detection element 26 and heating elements 232c and 232d. Also, conductors 236a and 236b are arranged so as not to overlap heating elements 232c and 232d in the thickness direction of substrate 231. This is because, when the temperature detected by temperature detection element 26 reaches the target temperature of 180°C and then the power supply to heater 23 is turned on and off to maintain the target temperature, the temperature response is slowed down, resulting in a large difference from the target temperature.

[0057] If the difference between the temperature of the heater 23 and the target temperature becomes large, the toner may be overheated or heated insufficiently when heat-fixing the toner on the sheet S. If the toner is heated excessively, the toner melts too much, causing the viscosity to drop too much and adhering to the fixing film 22. The toner that has adhered to the fixing film 22 is transferred onto the sheet S after one revolution of the fixing film 22, resulting in a defective image. This is known as hot offset. Furthermore, if the amount of heat applied to the toner is insufficient, the toner cannot be sufficiently fixed to the sheet S, resulting in poor fixing.

[0058] If the temperature response of the temperature detection element 26 to the current flow through the heating element 232 is constant, it is possible to improve temperature overshoot and ripple to some extent by optimizing PID control. However, if the temperature response of the temperature detection element 26 differs depending on the heating element 232 used and heating elements with high and low temperature response are mixed, it becomes difficult to address the issue by adjusting the control. If control is performed based on the heat generation of one heating element 232, the control of the other heating element 232 will overreact or there will be a delay in control.

[0059] In the fixing device of this embodiment, heating elements 232a, 232b, 232c, and 232d are arranged so as to overlap conductors 236a and 236b in the thickness direction of substrate 231. As a result, regardless of which heating element is activated, heat generated from heating element 232 is transferred to temperature detection element 26 connected to conductors 236a and 236b via conductors 236a and 236b, which are good thermal conductors. Compared to a case in which conductors 236a and 236b do not overlap in the thickness direction of substrate 231, heat generated from heating element 232 can be transferred to temperature detection element 26 more efficiently.

[0060] (Variation) 3 and 4 illustrate conductors 236a and 236b that overlap all of the heating elements 232, but the present invention is not limited to this. The shape and material of conductor 236 are not limited as long as it overlaps at least those heating elements 232 that are relatively far from temperature detection element 26 in the short direction of substrate 231. Although the greater the overlapping area between conductor 236 and heating element 232, the greater the expected effect, even partial overlap can suppress fluctuations in temperature responsiveness of temperature detection element 26 compared to when there is no overlap.

[0061] 9, conductor 236a is arranged to overlap heating elements 232a, 232b, 232c, and 232d in the thickness direction of substrate 231. Conductor 236b is arranged to overlap heating elements 232a and 232b. Even with this shape of conductor 236, fluctuations in the temperature responsiveness of temperature detection element 26 can be suppressed.

[0062] 10 and 11, conductors 236a and 236b are arranged to overlap heating elements 232a, 232b, and 232c in the thickness direction of substrate 231. Even with this shape of conductor 236, fluctuations in the temperature responsiveness of temperature detection element 26 can be suppressed.

[0063] (Second embodiment) The configuration of the heater 23 in this embodiment will be described. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted here.

[0064] FIG. 12 is a schematic diagram of a power control unit 97, which is a control circuit of the fixing device F1. In this embodiment, triacs 56a and 56b are used to switch the heating elements to which power is supplied, rather than the switch 57 used in the first embodiment. The power control unit 97 turns on triac 56a to supply power from the AC power supply 55 to heating elements 232a and 232b, and turns off triac 56a to cut off the power. Also, turning on triac 56b to supply power from the AC power supply 55 to heating elements 232c and 232d, and turns off triac 56b to cut off the power. Because the power supply to heating element 232 is controlled using triac 56, turning on both triacs 56a and 56b can simultaneously generate heat for heating elements 232a, 232b, 232c, and 232d. In this way, the switching of power supply to multiple heating elements 232 with different longitudinal lengths does not necessarily have to be exclusive; there may be periods when the heating elements simultaneously generate heat.

[0065] As in the first embodiment, the conductors 236a and 236b connected to the temperature detection element 26 are arranged so as to overlap with the heating elements 232a, 232b, 232c, and 232d in the thickness direction of the substrate 231. As a result, regardless of which heating element 232 is made to generate heat, the heat generated from the heating element 232 is transferred to the temperature detection element 26 connected to the conductors 236a and 236b via the conductors 236a and 236b, which are good thermal conductors. Compared to a case in which the conductors 236a and 236b do not overlap in the thickness direction of the substrate 231, the heat generated from the heating element 232 can be transferred to the temperature detection element 26 more efficiently.

[0066] (Third embodiment) The configuration of the heater 23 in this embodiment will be described. Note that the same components as those in the first and second embodiments are denoted by the same reference numerals, and detailed description thereof will be omitted here.

[0067] Fig. 13 is a schematic diagram of the heater 23 in the longitudinal direction. Fig. 13(a) shows the first surface side (also referred to as the front surface side) of the substrate on which the heating element is arranged, and Fig. 13(b) shows the second surface side (also referred to as the back surface side) of the substrate. Fig. 14 is a schematic diagram showing a cross section of the heater 23 taken along line U in Fig. 13.

[0068] Heating elements 232c and 232d are arranged at the endmost positions in the lateral direction of substrate 231. Here, as an example, length L1 is 222 mm, width is 0.7 mm, and thickness is 10 μm. Heating elements 232a and 232b are arranged closer to the center of heating elements 232c and 232d in the lateral direction of substrate 231. Here, as an example, length L2 is 180 mm, width is 0.7 mm, and thickness is 10 μm. Heating element 232e is arranged closer to the center of heating elements 232a and 232b in the lateral direction of substrate 231. Here, as an example, length L3 is 150 mm, width is 0.7 mm, and thickness is 10 μm. The spacing between each heating element 232 is 0.6 mm. The width of substrate 231 in the lateral direction is 8.0 mm. Also, as an example here, the total resistance value of the heating elements 232c and 232d is 20Ω, the total resistance value of the heating elements 232a and 232b is 18Ω, and the total resistance value of the heating element 232e is 18Ω.

[0069] Temperature detection element 26 is disposed on the surface of substrate 231 opposite to the surface on which heating element 232 is disposed. Conductors 236a and 236b are connected to temperature detection element 26. Conductors 236a and 236b are disposed so as to overlap heating elements 232a, 232b, 232c, 232d, and 232e in the thickness direction of substrate 231. Here, as an example, conductors 236a and 236b have widths W1=2.0 mm and widths W2=7.0 mm. Furthermore, lengths L3=2.0 mm and length L4=6.0 mm.

[0070] The length L1 of the heating elements 232c and 232d is a length that allows fixing of the sheet S having the largest width (hereinafter also referred to as the maximum paper passing width) among the sheets S that can be printed (or transported) by the image forming device.

[0071] For example, heating elements 232c and 232d are used when fixing an LTR size sheet S with a width of 216 mm. Heating elements 232a and 232b are used when fixing a sheet S with a width of 182 mm or less than B5 size but wider than A5 size with a width of 148 mm. Heating element 232e is used when fixing a sheet S with a paper width equal to or less than A5 size.

[0072] 15 is a schematic diagram of the power control unit 97, which is a control circuit of the fixing device F1. The energization circuits and switching operations for the heating elements 232c and 232d and the heating elements 232a and 232b are the same as those in the first embodiment, and therefore will not be described in detail here. The heating element 232e is connected to electrodes 234e and 234c, and is connected to an AC power supply 55 via a triac 56b. The connections of the heating elements 232c and 232d and the heating elements 232a and 232b are switched by a switch 57, and the energization state is controlled by the triac 56a. The energization state of the heating element 232e is controlled by the triac 56b.

[0073] Conductors 236a and 236b connected to temperature detection element 26 are arranged so as to overlap heating elements 232a, 232b, 232c, 232d, and 232e in the thickness direction of substrate 231. As a result, regardless of which heating element 232 is made to generate heat, the heat generated from heating element 232 is transferred to temperature detection element 26 connected to conductors 236a and 236b via conductors 236a and 236b, which are good thermal conductors. Compared to a case in which conductors 236a and 236b do not overlap in the thickness direction of substrate 231, heat generated from heating element 232 can be transferred to temperature detection element 26 more efficiently.

[0074] (Variation) 13 and 14 illustrate conductors 236a and 236b that overlap all of the heating elements 232, but the present invention is not limited to this. The shape and material of conductor 236 are not limited as long as it overlaps at least those heating elements 232 that are relatively far from temperature detection element 26 in the short direction of substrate 231. Although the greater the overlapping area between conductor 236 and heating element 232, the greater the expected effect, even partial overlap can suppress fluctuations in temperature responsiveness of temperature detection element 26 compared to when there is no overlap.

[0075] 16 is a schematic diagram showing a cross section of heater 23. In the thickness direction of substrate 231, conductors 236a and 236b are arranged so as to overlap heating elements 232a, 232b, and 232e. Here, as an example, conductors 236a and 236b have widths W1=2.0 mm and widths W2=5.0 mm. Also, lengths L3=2.0 mm and length L4=6.0 mm.

[0076] Heating elements 232a, 232b, and 232e are used when fixing small-sized sheets S. The width of small-sized sheets S varies widely, taking into account envelopes and other sizes, and sheets S of widths other than B5 and A5 may also be fixed. In particular, when fixing a sheet S of a size between B5 and A5, heating elements 232a and 232b, which have a length L2 optimal for B5 size, and heating element 232e, which has a length L3 optimal for A5 size, are alternately heated at a constant ratio. Conductors 236a and 236b are arranged to overlap heating elements 232a, 232b, and 232e in the thickness direction of substrate 231. Therefore, even if heating elements 232 are frequently switched depending on the width of sheet S, fluctuations in the temperature response of temperature detection element 26 can be suppressed.

[0077] Fig. 17 is a schematic diagram of heater 23 in the longitudinal direction. Fig. 17(a) shows the first surface side (also referred to as the front surface side) of the substrate on which the heating element is arranged, and Fig. 17(b) shows the second surface side (also referred to as the back surface side) of the substrate. Fig. 18 is a schematic diagram showing a cross section of heater 23 taken along line U in Fig. 17.

[0078] Conductors 236a and 236b connected to temperature detection element 26 are arranged so as to overlap with heating elements 232a, 232b, 232c, and 232d in the thickness direction of substrate 231. In the short-side direction of substrate 231, heating elements 232a, 232b, 232c, and 232d are arranged at a relatively greater distance from temperature detection element 26 than heating element 232e. Even in this configuration, heat generated from heating elements 232a, 232b, 232c, and 232d is transferred to temperature detection element 26 connected to conductors 236a and 236b via conductors 236a and 236b, which are good thermal conductors. Compared to a case where conductors 236a and 236b do not overlap in the thickness direction of substrate 231, heat generated from heating element 232 can be transferred to temperature detection element 26 more efficiently.

[0079] (Fourth embodiment) The configuration of the heater 23 in this embodiment will be described. Note that the same components as those in the first to third embodiments are given the same reference numerals, and detailed description thereof will be omitted here.

[0080] FIG. 19 is a schematic diagram of the heater 23 in the longitudinal direction. FIG. 19(a) shows the first surface side (also referred to as the front side) of the substrate on which the heating element is arranged, and FIG. 19(b) shows the second surface side (also referred to as the back side) of the substrate. FIG. 20 is a schematic diagram showing a cross section of the heater 23 taken along line U in FIG. 19. The heating element 232h is arranged at the center in the lateral direction of the substrate 231. This heating element pattern generates more heat at the ends than at the center in the longitudinal direction of the substrate 231. Here, as an example, the resistance value is 18Ω. The heating elements 232f and 232g are arranged on the end sides in the lateral direction of the substrate 231. This heating element pattern generates less heat at the ends than at the center in the longitudinal direction of the substrate 231. They are connected in series via the conductor 233a. Here, as an example, the total resistance is 20Ω.

[0081] The heating elements 232f, 232g, and 232h have a shape in which the width changes continuously in the longitudinal direction of the substrate 231. Here, as an example, the widths of the heating elements 232f and 232g at the center in the longitudinal direction of the substrate 231 are Wfc = Wgc = 0.7 mm, and the width of the heating element 232h is Wfc = 3.2 mm. The widths of the heating elements 232f and 232g at the ends in the longitudinal direction of the substrate 231 are Wfs = Wgs = 1.6 mm, and the width of the heating element 232h is Whs = 0.7 mm.

[0082] The length L of the heating elements 232f, 232g, and 232h in the longitudinal direction of the substrate 231 is 222 mm. The interval between each heating element in the lateral direction of the substrate 231 is 0.6 mm. The width of the substrate 231 is 7.0 mm.

[0083] Temperature detection element 26 is disposed on the surface of substrate 231 opposite to the surface on which heating element 232 is disposed. Conductors 236a and 236b are connected to temperature detection element 26. Conductors 236a and 236b are disposed so as to overlap heating elements 232f, 232g, and 232h in the thickness direction of substrate 231. Here, as an example, conductors 236a and 236b have widths W1=2.0 mm and widths W2=6.0 mm. Furthermore, lengths L3=2.0 mm and length L4=6.0 mm.

[0084] 21 is a schematic diagram of the power control unit 97, which is a control circuit of the fixing device F1. The heating element 232h is connected to the electrodes 234e and 234c, and is connected to the AC power supply 55 via the triac 56b. The heating elements 232f and 232g are connected to the electrodes 234a and 234c, and are connected to the AC power supply 55 via the triac 56a. The power supply to the heating element 232h is controlled by the triac 56a. The power supply to the heating elements 232f and 232g is controlled by the triac 56b.

[0085] Heat generating element 232h is patterned such that the amount of heat generated increases toward the longitudinal end of substrate 231. Heat generating elements 232f and 232g are patterned such that the amount of heat generated decreases toward the longitudinal end of substrate 231. By controlling the power distribution ratio of each heat generating element, the amount of heat generated in the longitudinal direction can be controlled. The power distribution ratio of each heat generating element is determined according to the size of the sheet S to be used, etc.

[0086] Conductors 236a and 236b connected to temperature detection element 26 are arranged so as to overlap heating elements 232f, 232g, and 232h in the thickness direction of substrate 231. As a result, regardless of which heating element 232 is made to generate heat, the heat generated from heating element 232 is transferred to temperature detection element 26 connected to conductors 236a and 236b via conductors 236a and 236b, which are good thermal conductors. Compared to a case in which conductors 236a and 236b do not overlap in the thickness direction of substrate 231, heat generated from heating element 232 can be transferred to temperature detection element 26 more efficiently.

[0087] (Fifth embodiment) The configuration of the heater 23 in this embodiment will be described. Note that the same components as those in the first to fourth embodiments are given the same reference numerals, and detailed description thereof will be omitted here.

[0088] FIG. 22 is a schematic diagram of the heater 23 in the longitudinal direction. FIG. 22(a) shows the first surface side (also referred to as the front side) of the substrate on which the heating element is arranged, and FIG. 22(b) shows the second surface side (also referred to as the back side) of the substrate. FIG. 23 is a schematic diagram showing a cross section of the heater 23 taken along line U in FIG. 22. The heating elements 232i and 232j have different lengths in the longitudinal direction of the substrate 231. In other words, the heater 23 has an asymmetric shape in the lateral direction. The heating element 232i is disposed on the upstream side in the conveying direction A of the sheet S, and the heating element 232j is disposed on the downstream side. Here, as an example, the length L1 of the heating element 232i is 222 mm, the width is 0.7 mm, and the thickness is 10 μm. The length L2 of the heating element 232j is 180 mm, the width is 0.7 mm, and the thickness is 10 μm.

[0089] The length L1 of the heating element 232i is set to a length that allows fixing of the sheet S having the largest width (hereinafter also referred to as the maximum paper passing width) among the sheets S that can be printed (or conveyed) by the image forming apparatus. The heating element 232j is used when fixing of the sheet S having a paper width of 182 mm, which is equal to or smaller than the B5 size.

[0090] 24 is a schematic diagram of the power control unit 97, which is a control circuit of the fixing device F1. As with the power control unit 97 of the first embodiment, by switching the switch 57 depending on the width of the sheet S, it is possible to switch between heating element 232i and heating element 232j to generate heat.

[0091] Temperature detection element 26 is arranged on the surface of substrate 231 opposite to the surface on which heating element 232 is arranged. Temperature detection element 26 is arranged at approximately the center in the longitudinal and lateral directions of substrate 231, and is connected to conductors 236a and 236b. Conductors 236a and 236b are arranged so as to overlap heating elements 232i and 232j in the thickness direction of substrate 231.

[0092] The heating elements 232i and 232j are disposed at positions where they are the same distance from the temperature detection element 26 in the short-side direction of the substrate 231. The heating element 232i is disposed on the upstream side in the conveyance direction, and the heating element 232j is disposed on the downstream side. The fixing film 22 is heated by the heater 23 while moving in the conveyance direction A in the fixing nip Nf. Heat from the heating element 232i disposed on the upstream side of the fixing nip Nf is easily transferred to the temperature detection element 26 as the fixing film 22 rotates, while heat from the heating element 232j disposed on the downstream side of the fixing nip Nf is less easily transferred to the temperature detection element 26. There was a risk that the temperature responsiveness of the temperature detection element 26 would vary depending on whether the heating element 232i or the heating element 232j is heated while the fixing film 22 is rotating.

[0093] Conductors 236a and 236b connected to temperature detection element 26 are arranged so as to overlap heating elements 232i and 232f in the thickness direction of substrate 231. As a result, regardless of which heating element 232 is made to generate heat, the heat generated from heating element 232 is transferred to temperature detection element 26 connected to conductors 236a and 236b via conductors 236a and 236b, which are good thermal conductors. Compared to a case in which conductors 236a and 236b do not overlap in the thickness direction of substrate 231, heat generated from heating element 232 can be transferred to temperature detection element 26 more efficiently. [Explanation of symbols]

[0094] 23 Heater 26 Temperature detection element

Claims

1. A heater used in a device body having a control unit, the heater being configured so that the supplied power is controlled by the control unit, A thin board and a first heating element, a second heating element, and a third heating element disposed on a first surface of the substrate and configured to generate heat when the power is supplied thereto; a temperature sensing element disposed on a second surface of the substrate opposite the first surface; a conductor disposed on the second surface of the substrate and in contact with the temperature sensing element, the conductor being configured to electrically connect to the controller; Equipped with the second heating element, the first heating element, and the third heating element are arranged in this order in a short-side direction of the substrate, In the short-side direction of the substrate, a distance from the temperature detection element to the second heating element and a distance from the temperature detection element to the third heating element are both longer than a distance from the temperature detection element to the first heating element; A heater characterized in that, when viewed in the thickness direction of the substrate, the conductor overlaps the first heating element, the second heating element, and the third heating element.

2. A heater as described in Claim 1, characterized in that the conductor has a conductor portion that overlaps the first heating element, the second heating element, and the third heating element at a position different from the temperature detection element in the longitudinal direction of the substrate.

3. The heater described in Claim 1, characterized in that the conductor includes a first conductor portion located on one end side of the temperature detection element and a second conductor portion located on the other end side of the temperature detection element in the longitudinal direction of the substrate, and the first conductor portion and the second conductor portion overlap the first heating element, the second heating element, and the third heating element, respectively.

4. a fourth heating element disposed on the first surface of the substrate; the second heating element, the first heating element, the fourth heating element, and the third heating element are arranged in this order in the short-side direction of the substrate; 2. The heater according to claim 1, wherein in the short direction of the substrate, the distance from the temperature detection element to the second heating element and the distance from the temperature detection element to the third heating element are both longer than the distance from the temperature detection element to the fourth heating element.

5. the conductors include a first conductor and a second conductor; 5. The heater according to claim 4, wherein, when viewed in the thickness direction, the first conductor overlaps with the first heating element, the second heating element, the third heating element, and the fourth heating element, and the second conductor overlaps with the first heating element and the fourth heating element.

6. the conductors include a first conductor and a second conductor; 5. The heater according to claim 4, wherein, when viewed in the thickness direction, the first conductor overlaps with the first heating element, the second heating element, the third heating element, and the fourth heating element, and the second conductor overlaps with the first heating element, the second heating element, the third heating element, and the fourth heating element.

7. 2. The heater according to claim 1, wherein the second heating element and the third heating element are both longer than the first heating element in the longitudinal direction of the substrate.

8. 5. The heater according to claim 4, wherein the second heating element and the third heating element are both longer than the first heating element and longer than the fourth heating element in the longitudinal direction of the substrate.

9. A heater as described in Claim 7, characterized in that the first heating element, the second heating element, and the third heating element have uniform widths in the longitudinal direction of the substrate.

10. a width in the short-side direction of an end portion of the first heating element in the longitudinal direction of the substrate is narrower than a width in the short-side direction of a central portion of the first heating element in the longitudinal direction of the substrate, a width in the short-side direction of an end portion of the second heating element in the longitudinal direction is wider than a width in the short-side direction of a central portion of the second heating element in the longitudinal direction, a width in the short side direction of an end portion of the third heating element in the longitudinal direction is wider than a width in the short side direction of a central portion of the third heating element in the longitudinal direction; 2. The heater according to claim 1.

11. 11. The heater according to claim 10, wherein the second heating element and the third heating element have the same length as the first heating element in the longitudinal direction of the substrate.

12. a cylindrical film heated by the heater according to any one of claims 1 to 11; a pressure roller that forms a nip portion with the film, A heating device characterized in that the heater is arranged in the internal space of the film, the film is clamped between the heater and the pressure roller, and the image formed on the sheet is heated through the film at the nip portion.

Images