Heater, fixing device, image forming apparatus

Abstract

To avoid a situation where variations in a size or a conveyance position of a sheet makes a temperature of a part of a fixing member inappropriate.SOLUTION: An overcoating member 620 covers a plurality of resistor blocks 60 formed on a substrate 6x. The overcoating member 620 is formed to have a larger thickness in a specific area A2 than areas other than the specific area A2 on the substrate 6x. The specific area A2 is an area extending over a boundary area A1 between two adjacent blocks and two adjacent resistors 6a. The two adjacent blocks are adjacent two of the plurality of resistor blocks 60. The two adjacent resistors 6a are, of the plurality of resistors 6 in the two adjacent blocks, two adjacent to the boundary area A2.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a heater having a plurality of resistors, a fixing device including the heater, and an image forming apparatus including the fixing device. [Background technology]

[0002] An electrophotographic image forming apparatus includes a fixing device that heats and pressurizes a toner image transferred onto a sheet, and the fixing device may include a cylindrical fixing member that contains a heater and a pressure roller that forms a nip between the fixing member and the pressure roller, through which the sheet passes.

[0003] The heater heats the fixing member. In this case, a planar heater is employed in the fixing device. The planar heater has a plurality of resistors arranged in a main direction. The main direction is a direction intersecting the sheet conveying direction.

[0004] In the fixing device, the plurality of resistors of the planar heater may be divided into a plurality of resistor blocks aligned in the main direction, and each of the plurality of resistor blocks has a plurality of resistors aligned in the main direction.

[0005] Furthermore, the planar heater has a plurality of power supply electrodes capable of individually supplying power to the plurality of resistance blocks.

[0006] In general, the resistor blocks are arranged at intervals greater than the intervals between the resistors in each of the resistor blocks, thereby preventing current leakage at boundary regions between the resistor blocks.

[0007] On the other hand, the amount of heat applied to the portion of the fixing member corresponding to the boundary region may be insufficient, and the temperature required for fixing the toner image may not be maintained.

[0008] It is also known that in each of the plurality of resistor blocks, the resistor at the end in the main direction adjacent to the boundary region generates a larger amount of heat than the other resistors (see, for example, Patent Document 1). This prevents the portion of the fixing member corresponding to the boundary region from being heated to an insufficient amount. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2017-228525 Summary of the Invention [Problem to be solved by the invention]

[0010] In the planar heater of the fixing device, the length of each of the plurality of resistance blocks is set in accordance with a plurality of possible sizes of the sheet that passes through the fixing position.

[0011] The control unit of the image forming apparatus also executes block selection control, in which the control unit selects one or more operating blocks from the plurality of resistor blocks according to the sheet size, and further controls a heater power supply circuit so that power is supplied to the selected operating block.

[0012] However, there are cases where the sheet does not pass the end of the operating block in the main direction due to variations in the size of the sheet or the conveying position of the sheet, etc. If the heat value of a specific resistor located at the end of the operating block is large, the temperature of the part of the fixing member corresponding to the end of the operating block may exceed the allowable temperature.

[0013] An object of the present invention is to provide a heater, a fixing device, and an image forming apparatus that can prevent a part of the fixing member from reaching an inappropriate temperature due to variations in the size or conveying position of the sheet. [Means for solving the problem]

[0014] A heater according to one aspect of the present invention includes a substrate, a plurality of resistor blocks, a plurality of power supply electrodes, and an overcoating member. The plurality of resistor blocks each have a plurality of resistor elements formed on the substrate and arranged at a first interval in a main direction. The plurality of power supply electrodes are connected to one end of the plurality of resistor blocks in a sub-direction intersecting the main direction, and are capable of individually supplying power to each of the plurality of resistor blocks. The overcoating member is formed on the substrate and covers the plurality of resistor blocks. The plurality of resistor blocks are arranged at a second interval in the main direction, the second interval being larger than the first interval. The overcoating member is formed to a greater thickness in a specific region of the substrate than in regions other than the specific region. The specific region is a region spanning a boundary region between two adjacent blocks and two adjacent resistor elements. The two adjacent blocks are two of the plurality of resistor blocks adjacent to each other. The two adjacent resistor elements are two of the plurality of resistor elements in the two adjacent blocks that are adjacent to the boundary region.

[0015] A fixing device according to another aspect of the present invention fixes a toner image on a sheet by applying heat and pressure to the toner image on the sheet at a fixing position on a sheet transport path. The fixing device includes a support member, a fixing member, and the heater. The support member is arranged at the fixing position along a main direction intersecting the sheet transport direction. The fixing member is a cylindrical member rotatably supported by the support member. The heater is supported by the support member along the main direction and heats the fixing member.

[0016] An image forming apparatus according to another aspect of the present invention includes a transfer device that transfers a toner image onto a sheet, and the fixing device. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a heater, a fixing device, and an image forming apparatus that can prevent a part of the fixing member from reaching an inappropriate temperature due to variations in the size or conveying position of the sheet. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 1 is a diagram showing the configuration of an image forming apparatus equipped with a heater according to the first embodiment. [Figure 2] FIG. 2 is a diagram showing the configuration of a fixing device equipped with a heater according to the first embodiment. [Figure 3] FIG. 3 is a block diagram showing the configuration of a control device in the image forming apparatus. [Figure 4] FIG. 4 is a configuration diagram of the heater according to the first embodiment. [Figure 5] FIG. 5 is a configuration diagram of two adjacent resistor blocks in the heater according to the first embodiment. [Figure 6] FIG. 6 is a cross-sectional view of two adjacent resistor blocks in the heater according to the first embodiment. [Figure 7] FIG. 7 is a graph showing a first example of the fixing temperature distribution. [Figure 8] FIG. 8 is a graph showing a second example of the fixing temperature distribution. [Figure 9] FIG. 9 is a cross-sectional view of two adjacent resistor blocks in a heater according to the second embodiment. [Figure 10] FIG. 10 is a graph showing a third example of the fixing temperature distribution. [Figure 11] FIG. 11 is a graph showing a fourth example of the fixing temperature distribution. [Figure 12] FIG. 12 is a configuration diagram of two adjacent resistor blocks in a heater according to a reference example. [Figure 13] FIG. 13 is a graph showing a reference example of the fixing temperature distribution. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the following embodiment is an example of the present invention, and does not limit the technical scope of the present invention.

[0020] [First embodiment] The heater 53 according to the first embodiment is included in the fixing device 5 of the image forming apparatus 10 (see FIG. 1).

[0021] [Configuration of image forming apparatus 10] The image forming apparatus 10 includes a printing device 4 that performs a printing process to form an image on a sheet 9 .

[0022] The printing device 4 performs the printing process by electrophotography. The sheet 9 is an image forming medium such as paper or a sheet-like resin member.

[0023] As shown in FIG. 1, the image forming apparatus 10 includes a main body 1, a sheet conveying device 3, a printing device 4, and a control device 8. The main body 1 includes a sheet conveying device 3, a printing device 4, and a control device 8.

[0024] The printing device 4 includes one or more image forming devices 4x, an optical scanning device 40, a transfer device 44, and a fixing device 5. The image forming device 4x includes a drum-shaped photosensitive member 41, a charging device 42, a developing device 43, a drum cleaning device 45, and the like.

[0025] The sheet conveying device 3 includes a sheet sending device 30 and a plurality of pairs of conveying rollers 31. The sheet sending device 30 sends out the sheets 9 stored in the sheet storage unit 2 to a conveying path 300 in the main body 1. The conveying path 300 forms a passage along which the sheets 9 are conveyed.

[0026] The plurality of pairs of conveying rollers 31 are rotationally driven by a motor (not shown). The plurality of pairs of conveying rollers 31 rotate to convey the sheet 9 along the conveying path 300 and further discharge the sheet 9 onto the discharge tray 101.

[0027] The sheet 9 passes through a transfer position P1 and a fixing position P2 on the conveying path 300 and is discharged onto a discharge tray 101.

[0028] In the following description, the direction in which the sheet 9 is transported along the transport path 300 is referred to as a transport direction D01. The fixing position P2 is located downstream of the transfer position P1 in the transport direction D01.

[0029] Furthermore, a direction intersecting the conveying direction D01 in the conveying path 300 is referred to as a main direction D1. In this embodiment, the main direction D1 is a direction perpendicular to the conveying direction D01.

[0030] The printing device 4 forms a toner image on the sheet 9 conveyed along the conveying path 300. The toner image is a developer image using toner as a developer. The toner is an example of the granular developer.

[0031] 1 is a tandem color image forming apparatus, and therefore the printing device 4 includes four image forming devices 4x corresponding to the toners of the four colors, yellow, cyan, magenta, and black.

[0032] In the image forming device 4x, a photoconductor 41 rotates, and a charging device 42 charges the surface of the photoconductor 41. Furthermore, an optical scanning device 40 writes an electrostatic latent image on the surface of the photoconductor 41 by scanning with a laser beam.

[0033] Furthermore, the developing device 43 develops the electrostatic latent image into the toner image by supplying the toner to the surface of the photoreceptor 41. The photoreceptor 41 is an example of an image carrier that rotates while carrying the toner image.

[0034] The transfer device 44 transfers the toner image onto the sheet 9 at a transfer position P1 on the conveying path 300. The transfer device 44 includes an intermediate transfer belt 441, four primary transfer devices 442 corresponding to the four image forming devices 4x, a secondary transfer device 443, and a belt cleaning device 444.

[0035] In the transfer device 44, the primary transfer device 442 transfers the toner image on the surface of the photosensitive member 41 onto the surface of the intermediate transfer belt 441. As a result, the color toner image is formed on the surface of the intermediate transfer belt 441.

[0036] The secondary transfer device 443 transfers the toner image formed on the intermediate transfer belt 441 onto the sheet 9 in the conveying path 300 .

[0037] When the image forming apparatus 10 is a monochrome image forming apparatus, the secondary transfer device 443 transfers the toner image on the photosensitive member 41 onto the sheet 9 in the transport path 300 .

[0038] The drum cleaning device 45 removes the waste toner remaining on the surface of the photosensitive member 41. The belt cleaning device 444 removes the waste toner remaining on the intermediate transfer belt 441.

[0039] [Fixing device 5] The fixing device 5 applies heat and pressure to the toner image on the sheet 9 while conveying the sheet 9 at a fixing position P2 on the conveying path 300. In this way, the fixing device 5 fixes the toner image on the sheet 9.

[0040] 2, the fixing device 5 includes a pressure roller 50, a fixing member 51, a support member 52, a heater 53, a biasing mechanism 54, and a temperature sensor 55. The pressure roller 50, the fixing member 51, the support member 52, and the heater 53 are each arranged along the main direction D1 at a fixing position P2.

[0041] The fixing member 51 is a flexible cylindrical member. In other words, the fixing member 51 is an endless, belt-like flexible cylindrical body. For example, the fixing member 51 is a cylindrical film member. The fixing member 51 is rotatably supported by a support member 52.

[0042] The pressure roller 50 presses against the fixing member 51 to form a nip Np1 between the pressure roller 50 and the fixing member 51. The pressure roller 50 urges the sheet 9 against the fixing member 51 as it passes through the fixing position P2.

[0043] The support member 52 rotatably supports the fixing member 51. The support member 52 further supports the heater 53. The support member 52 has a facing portion 52a that faces the pressure roller 50 with the fixing member 51 interposed therebetween. The facing portion 52a contacts the inner surface of the fixing member 51.

[0044] The heater 53 is incorporated in the facing portion 52a. As a result, the heater 53 is supported by the support member 52 along the main direction D1. The pressure roller 50, the fixing member 51, and the support member 52 are formed to extend in the main direction D1. The heater 53 is in contact with the inner surface of the fixing member 51.

[0045] The urging mechanism 54 includes a pressing member 541 and a spring 542. The spring 542 elastically urges the opposing portion 52a toward the pressure roller 50 via the pressing member 541. That is, the urging mechanism 54 elastically urges the fixing member 51 toward the pressure roller 50 via the support member 52.

[0046] The pressure roller 50 is rotated by being driven by a motor (not shown). The pressure roller 50 rotates the fixing member 51. As the fixing member 51 rotates, the inner surface of the fixing member 51 slides against the heater 53 and the opposing portion 52a. A lubricant is applied to the inner surface of the fixing member 51.

[0047] The heater 53 heats the portion of the fixing member 51 that forms the nip Np1. The fixing member 51 is heated by the heater 53 while rotating around the support member 52.

[0048] The temperature sensor 55 measures the temperature of the heater 53. For example, the temperature sensor 55 is a thermistor.

[0049] The temperature detected by the temperature sensor 55 is used for fixing temperature control. The fixing temperature control is a feedback control that controls the power supplied to the heater 53 by comparing the temperature detected by the temperature sensor 55 with a preset target temperature.

[0050] The temperature sensor 55 measures a temperature that serves as an alternative index for the temperature of the portion that forms the nip Np1 in the fixing member 51. Therefore, the temperature sensor 55 may be disposed at a position where the temperature of the fixing member 51 can be measured.

[0051] [Control device 8] The control device 8 executes various data processing and controls devices such as the sheet conveying device 3 and the printing device 4. The control devices 8 control include the fixing device 5.

[0052] 3, the control device 8 includes a CPU (Central Processing Unit) 81 and peripheral devices, such as a RAM (Random Access Memory) 82, a secondary storage device 83, and a signal interface 84.

[0053] Furthermore, the control device 8 includes a communication device 85 and a heater power supply circuit 86 .

[0054] The CPU 81 is a processor that executes various data processing and control operations by executing computer programs.

[0055] The RAM 82 is a computer-readable volatile storage device that temporarily stores the computer programs executed by the CPU 81 and data that is output and referenced by the CPU 81 in the course of executing various processes.

[0056] The CPU 81 includes a plurality of processing modules that are realized by executing the computer programs, including a main control unit 8a, a heater control unit 8b, and a print control unit 8c.

[0057] The main control unit 8a executes start control for starting various processes in response to an operation on an operation device (not shown).

[0058] The heater control section 8b controls the amount of power supplied to the heater 53 by controlling the fixing temperature. The heater control section 8b controls the amount of power supplied to the heater 53 by controlling the heater power supply circuit 86.

[0059] The heater power supply circuit 86 supplies power to the heater 53 in accordance with a power supply command from the heater control unit 8b.

[0060] The print control unit 8c controls the sheet conveying device 3. Furthermore, in synchronization with the conveyance of the sheet 9 by the sheet conveying device 3, the print control unit 8c causes the printing device 4 to execute the print process.

[0061] The secondary storage device 83 is a computer-readable non-volatile storage device. For example, a flash memory or a hard disk drive, or both, may be used as the secondary storage device 83.

[0062] The signal interface 84 converts signals output by various sensors such as the temperature sensor 55 into digital data and transmits the digital data to the CPU 81. Furthermore, the signal interface 84 converts control commands output by the CPU 81 into control signals and transmits the control signals to the devices to be controlled.

[0063] The communication device 85 executes communication with other devices such as a host device that transmits a print job to the image forming apparatus 10. The CPU 81 communicates with the other devices through the communication device 85.

[0064] In this embodiment, the heater 53 is a planar heater having a plurality of resistors 6 (see FIG. 4).

[0065] The heater 53 includes a substrate 6x, a plurality of resistor blocks 60, a plurality of power supply electrodes 600, and a ground electrode 610 (see FIG. 4).

[0066] The substrate 6x is a non-conductive film, and a plurality of resistor blocks 60, a plurality of power electrodes 600, and a ground electrode 610 are formed on the substrate 6x.

[0067] Each of the plurality of resistor blocks 60 has a plurality of resistors 6 arranged at intervals in the main direction D1. Each of the resistors 6 is a heating element that generates heat when power is supplied thereto.

[0068] In the following description, the direction along the conveying direction D01 is referred to as the sub-direction D2. The sub-direction D2 is a direction that intersects with the main direction D1. The main direction D1 is the longitudinal direction of the heater 53. The sub-direction D2 is the lateral direction of the heater 53.

[0069] The plurality of power supply electrodes 600 are connected to one end in the secondary direction D2 of the plurality of resistor blocks 60, respectively. That is, each of the power supply electrodes 600 is connected to a first end in the secondary direction D2 of the plurality of resistors 6 of each of the corresponding resistor blocks 60.

[0070] The ground electrode 610 is connected to the other ends of the multiple resistor blocks 60 in the secondary direction D2. That is, the ground electrode 610 is connected to the second ends of all the resistors 6 of the heater 53 in the secondary direction D2.

[0071] The plurality of power supply electrodes 600 are formed corresponding to the plurality of resistor blocks 60. The plurality of power supply electrodes 600 can supply power to each of the plurality of resistor blocks 60 individually.

[0072] The resistors 6 in each resistor block 60 are spaced apart at a first interval L1 in the main direction D1 (see FIG. 5). The resistor blocks 60 are also spaced apart at a second interval L2 in the main direction D1. The second interval L2 is larger than the first interval L1.

[0073] The first interval L1 is a interval necessary to prevent current leakage in the region between the plurality of resistor elements 6. The second interval L2 is a interval necessary to prevent current leakage in the boundary region A1 between the plurality of resistor blocks 60 (see FIG. 5).

[0074] On the other hand, the amount of heat applied to the portion of the fixing member 51 corresponding to the boundary region may be insufficient, and the temperature required for fixing the toner image may not be maintained.

[0075] FIG. 12 shows the configuration of two adjacent resistor blocks 60 in a heater 53x according to a reference example.

[0076] In each of the resistor blocks 60 of the heater 53x, the resistor 6p at the end in the main direction D1 adjacent to the boundary area A1 generates more heat than the other resistors 6q (see FIG. 11). By employing the heater 53x, it is possible to prevent the amount of heat from being insufficient in the portion of the fixing member 51 that contacts the boundary area A1.

[0077] In the heater 53 of the fixing device 5, the length of each of the plurality of resistor blocks 60 in the main direction D1 is set in accordance with a plurality of possible sizes of the sheet 9 passing through the fixing position P2.

[0078] The heater control unit 8b also executes block selection control, in which the heater control unit 8b selects one or more working blocks from among the plurality of resistor blocks 60 in accordance with the size of the sheet 9. The heater control unit 8b further controls the heater power supply circuit 86 so that power is supplied to the selected working block.

[0079] For example, the heater control unit 8b acquires sheet size information when the print process is executed, and selects the operation block according to the sheet size information. For example, the sheet size information includes information on the standard size of the sheet 9 and information on the orientation of the sheet 9.

[0080] However, due to variations in the size or conveyance position of the sheet 9, the sheet 9 may not pass the end of the operating block in the main direction D1 (see FIG. 12). If the heat value of a specific resistor 6p located at the end of the operating block is large, the temperature of the part of the fixing member 51 corresponding to the end of the operating block may exceed the allowable temperature range TR1 (see FIG. 13).

[0081] Fig. 13 shows a reference example of the distribution of fixing temperature T1. Fixing temperature T1 is the temperature of fixing member 51. The reference example is an example in which fixing member 51 is heated by heater 53x. In Fig. 13, allowable temperature range TR1 is the allowable range of fixing temperature T1.

[0082] The lower limit temperature of the allowable temperature range TR1 is set based on the temperature required for fixing the toner image, and is set in accordance with the durability required for the fixing member 51.

[0083] The reference example is an example in which the width of the sheet 9 is slightly smaller than the original standard size. In this case, part or all of the resistor 6p located at the end of the operating block is outside the range through which the sheet 9 passes.

[0084] In the reference example, the end of the operating block is an area where the amount of heat dissipated from the fixing member 51 to the sheet 9 is small. Therefore, if the amount of heat generated by the resistor 6p at the end is large, the temperature of the part of the fixing member 51 corresponding to the end of the operating block may exceed the allowable temperature range TR1 (see FIG. 13).

[0085] On the other hand, the heater 53 has a configuration for preventing a part of the fixing member 51 from reaching an inappropriate temperature due to variations in the size or conveyance position of the sheet 9. The configuration will be described below.

[0086] In the heater 53, the length of each of the resistance blocks 60 in the main direction D1 is set in accordance with a plurality of possible sizes of the sheet 9 passing through the fixing position P2.

[0087] For example, the heater 53 includes one first resistor block 61, a pair of second resistor blocks 62, and a pair of third resistor blocks 63 (see FIG. 4). The pair of second resistor blocks 62 are arranged on both outer sides in the main direction D1 relative to the pair of second resistor blocks 62. The pair of third resistor blocks 63 are arranged on both outer sides in the main direction D1 relative to the pair of second resistor blocks 62.

[0088] The first resistor block 61 is formed to have a length corresponding to the size of the first sheet 9a in the main direction D1.

[0089] The combined length of the pair of second resistor blocks 62 and the first resistor block 61 corresponds to the size of the second sheet 9b in the main direction D1. The size of the second sheet 9b in the main direction D1 is larger than that of the first sheet 9a.

[0090] The combined length of the pair of third resistor blocks 63 and the pair of second resistor blocks 62 and the first resistor block 61 corresponds to the size of the third sheet 9c in the main direction D1. The size of the third sheet 9c in the main direction D1 is larger than that of the second sheet 9b.

[0091] The sizes of the first sheet 9a, the second sheet 9b, and the third sheet 9c are each an example of a predetermined standard size. That is, the multiple resistor blocks 60 of the heater 53 are formed with lengths corresponding to the multiple standard sizes of the sheet 9. The standard sizes corresponding to the first sheet 9a, the second sheet 9b, and the third sheet 9c are an example of multiple candidates for the size of the sheet 9 that passes through the fixing position P2.

[0092] When the size indicated by the sheet size information is equal to or smaller than the size of the first sheet 9a, the heater control section 8b selects the first resistance block 61 as the operating block.

[0093] In addition, when the size indicated by the sheet size information is equal to or larger than the size of the second sheet 9b and smaller than the size of the third sheet 9c, the heater control unit 8b selects the first resistance block 61 and a pair of second resistance blocks 62 as the active blocks.

[0094] In addition, when the size indicated by the sheet size information is larger than the size of the second sheet 9b, the heater control unit 8b selects the first resistance block 61, the pair of second resistance blocks 62, and the pair of third resistance blocks 63 as the operating blocks.

[0095] In the block selection control, the heater control unit 8b executes control to supply power to one or more selected operating blocks.

[0096] In the heater 53, each of the plurality of resistor blocks 60 includes one or two adjacent resistors 6a and a plurality of internal resistors 6b other than the adjacent resistors 6a (see FIGS. 5 and 6).

[0097] Each of the adjacent resistors 6a is formed adjacent to the boundary region A1 of the substrate 6x. On the other hand, the multiple internal resistors 6b are formed in positions not adjacent to the boundary region A1. The adjacent resistors 6a and the internal resistors 6b are some of the multiple resistors 6 in the two adjacent blocks.

[0098] In this embodiment, the first resistor block 61 includes two adjacent resistors 6a located at both ends in the main direction D1. Similarly, each of the pair of second resistor blocks 62 includes two adjacent resistors 6a located at both ends in the main direction D1. Furthermore, each of the pair of third resistor blocks 63 includes one adjacent resistor 6a located at one end in the main direction D1.

[0099] The heater 53 further includes an overcoating member 620 formed on the substrate 6x (see FIGS. 4 and 6). The overcoating member 620 covers the plurality of resistor blocks 60.

[0100] The overcoating member 620 is a non-conductive and wear-resistant member, for example, made of glass.

[0101] The overcoating member 620 is formed to a greater thickness in a specific region A2 of the substrate 6x than in other regions (see FIG. 6). The specific region A2 is a region that spans a boundary region A1 between two adjacent blocks and two adjacent resistors 6a on both sides of the boundary region A1 (see FIG. 6).

[0102] The two adjacent blocks are two adjacent ones of the plurality of resistor blocks 60. In Fig. 6, a first resistor block 61 and a second resistor block 62 are shown as an example of the two adjacent blocks.

[0103] The two adjacent resistors 6a corresponding to one specific area A2 are two of the resistors 6 in the two adjacent blocks that are adjacent to the boundary area A1.

[0104] The heat generated by each resistor 6 propagates radially from each resistor 6 within the overcoating member 620. Therefore, the heat generated by each adjacent resistor 6a propagates over a wider range than the heat generated by each internal resistor 6b, and then is radiated from the overcoating member 620.

[0105] That is, the temperature of the overcoating member 620 is more easily uniformed in the specific region A2 than in other regions. As a result, the temperature of the fixing member 51 is suppressed from increasing in the regions corresponding to the adjacent resistors 6a, but is suppressed from decreasing in the temperature of the fixing member 51 in the boundary region A1.

[0106] When power is supplied to the two adjacent blocks of the heater 53, the heat generation amount of each of the two adjacent resistors 6a adjacent to the boundary area A1 is the same as the heat generation amount of each of the multiple internal resistors 6b. That is, in each resistor block 60, the heat generation amount of each of the multiple resistors 6 when power is supplied is the same.

[0107] The configuration of the adjacent resistors 6a and the plurality of internal resistors 6b in the two adjacent blocks is the main configuration of this embodiment.

[0108] The main configuration of this embodiment is also employed in the region of the heater 53 where each of the pair of second resistance blocks 62 and each of the pair of third resistance blocks 63 are adjacent to each other.

[0109] 7 and 8 show an example of the distribution of the fixing temperature T1 in the fixing device 5 equipped with the heater 53. The fixing temperature T1 is the temperature of the fixing member 51. 7 and 8 show the distribution of the fixing temperature T1 in a region extending from a part of the first resistor block 61 to a part of one of the pair of second resistor blocks 62.

[0110] 7 and 8, the horizontal axis of the graph represents the position in the main direction D1 on the fixing member 51, and the vertical axis of the graph represents the fixing temperature T1.

[0111] In FIGS. 7 and 8, the first resistor block 61 and one of the pair of second resistor blocks 62 are an example of the two adjacent blocks.

[0112] 7 shows a first example of the distribution of the fixing temperature T1. The first example is an example in which the second sheet 9b or the third sheet 9c passes through the fixing position P2. In the first example, both of the two adjacent blocks are the operating blocks.

[0113] FIG. 7 shows that the rise in the fixing temperature T1 is suppressed in the areas corresponding to the adjacent resistors 6a, but the fall in the fixing temperature T1 is suppressed in the boundary area A1.

[0114] Therefore, in the first example, the fixing temperature T1 falls within the allowable temperature range TR1 in the two adjacent blocks and in the boundary area A1 between the two adjacent blocks.

[0115] 8 shows a second example of the distribution of the fixing temperature T1. The second example is an example in which a first sheet 9a having a relatively narrow width passes through the fixing position P2.

[0116] In the second example, the first sheet 9a passes through the area corresponding to the portion of the first resistor block 61 other than the adjacent resistor 6a.

[0117] That is, in the second example, the first sheet 9a does not pass through the area corresponding to the adjacent resistor 6a in the first resistor block 61. This is due to variations in the size of the first sheet 9a, which is a standard size.

[0118] In the second example, the first resistor block 61 is the active block and the second resistor block 62 is not powered.

[0119] The fixing temperature T1 in the second example exhibits a distribution that is generally similar to that of the fixing temperature T1 in the first example in the region corresponding to the portion of the first resistor block 61 other than the adjacent resistor 6a.

[0120] On the other hand, the fixing temperature T1 in the second example is slightly higher in the region corresponding to the adjacent resistor 6a in the first resistor block 61 than in other regions because the amount of heat dissipated from the fixing member 51 to the sheet 9 is small in the region corresponding to the adjacent resistor 6a in the first resistor block 61.

[0121] However, since the heat generation amount of the adjacent resistor 6a is not large, the fixing temperature T1 in the second example falls within the allowable temperature range TR1 in the region corresponding to the first resistor block 61.

[0122] By employing the heater 53 in the fixing device 5, it is possible to prevent a part of the fixing member 51 from reaching an inappropriate temperature due to variations in the size or conveyance position of the sheet 9, etc.

[0123] [Second embodiment] Next, a heater 53A according to a second embodiment will be described with reference to FIGS.

[0124] 9 to 11, the same components as those shown in Figures 4 to 8 are denoted by the same reference numerals. Heater 53A constitutes part of fixing device 5 in place of heater 53.

[0125] In the heater 53A, the overcoating member 620 is formed to a greater thickness in the specific region A2 of the substrate 6x than in the region other than the specific region A2 (see FIG. 9). This configuration is the same as that of the heater 53.

[0126] The differences between heater 53A and heater 53 will be described below.

[0127] When power is supplied to the two adjacent blocks of the heater 53A, the amount of heat generated by each of the two adjacent resistors 6a adjacent to the boundary area A1 is greater than the amount of heat generated by each of the multiple internal resistors 6b.

[0128] 9, the magnitude relationship between the widths of the multiple resistors 6 represents the magnitude relationship between the amounts of heat generated by the multiple resistors 6. However, in FIG. 9, the ratio between the widths of the multiple resistors 6 is unrelated to the ratio between the amounts of heat generated by the multiple resistors 6.

[0129] 10 and 11 show an example of the distribution of the fixing temperature T1 in the fixing device 5 equipped with the heater 53A. Figures 10 and 11 show the distribution of the fixing temperature T1 in a region spanning from a part of the first resistor block 61 to a part of one of the pair of second resistor blocks 62.

[0130] 10 and 11, the horizontal axis of the graph represents the position in the main direction D1 on the fixing member 51, and the vertical axis of the graph represents the fixing temperature T1.

[0131] In FIGS. 10 and 11, the first resistor block 61 and one of the pair of second resistor blocks 62 are an example of the two adjacent blocks.

[0132] 10 shows a third example of the distribution of the fixing temperature T1. The third example is an example in which the second sheet 9b or the third sheet 9c passes through the fixing position P2. In the third example, both of the two adjacent blocks are the active blocks.

[0133] 10 shows that the fixing temperature T1 is maintained at the same level in the specific area A2 and in areas other than the specific area A2 because the amount of heat generated by the adjacent resistor 6a is greater than the amount of heat generated by the internal resistor 6b.

[0134] Therefore, in the third example, the fixing temperature T1 falls within the allowable temperature range TR1 in the two adjacent blocks and in the boundary area A1 between the two adjacent blocks. Furthermore, the difference between the fixing temperature T1 in the specific area A2 and the fixing temperature T1 in areas other than the specific area A2 is small.

[0135] 11 shows a fourth example of the distribution of the fixing temperature T1. In the fourth example, a first sheet 9a having a relatively narrow width passes through the fixing position P2.

[0136] In the fourth example, the first sheet 9a passes through the area corresponding to the portion of the first resistor block 61 other than the adjacent resistor 6a.

[0137] That is, in the fourth example, the first sheet 9a does not pass through the area corresponding to the adjacent resistor 6a in the first resistor block 61. This is due to variations in the size of the first sheet 9a, which is a standard size.

[0138] In the fourth example, the first resistor block 61 is the active block and the second resistor block 62 is not powered.

[0139] The fixing temperature T1 in the fourth example exhibits a distribution that is generally similar to that of the fixing temperature T1 in the first example in the area other than the specific area A2 in the first resistor block 61.

[0140] On the other hand, the fixing temperature T1 in the fourth example is slightly higher in the area corresponding to the adjacent resistor 6a than in the area corresponding to the internal resistors 6b because the amount of heat generated by the adjacent resistor 6a is greater than the amount of heat generated by the internal resistors 6b.

[0141] However, the overcoating member 620 is formed with a large thickness in the specific area A2. Therefore, the heat generated by the adjacent resistor 6a is easily diffused throughout the specific area A2. As a result, the fixing temperature T1 in the fourth example falls within the allowable temperature range TR1 throughout the entire area corresponding to the first resistor block 61.

[0142] By employing the heater 53A in the fixing device 5, the same effects as when the heater 53 is employed can be obtained. [Explanation of symbols]

[0143] 5: Fixing device 6: Resistor 6a: Adjacent resistor 6b: Internal resistor 6x: Base material 10: Image forming device 50: Pressure roller 51: Fixing member 52: Support member 52a: Opposing part 53, 53A, 53x: heater 54: Biasing mechanism 55: Temperature sensor 60: Resistance block 61: First resistance block 62: Second resistance block 63: Third Resistance Block 600: Power supply electrode 610: Ground electrode 620: Overcoating material A1 : Boundary area A2:Specific area

Claims

1. A substrate; a plurality of resistor blocks each having a plurality of resistors formed on the substrate and arranged at first intervals in a main direction; a plurality of power supply electrodes connected to one end of each of the plurality of resistor blocks in a sub-direction intersecting the main direction, and capable of individually supplying power to each of the plurality of resistor blocks; an overcoating member formed on the substrate and covering the plurality of resistor blocks; the plurality of resistor blocks are arranged at second intervals in the main direction that are greater than the first intervals; the overcoating member is formed to a thickness greater in a specific region of the base material than in a region other than the specific region, the specific region is a region spanning a boundary region between two adjacent blocks and two adjacent resistors, the two adjacent blocks are two adjacent ones of the plurality of resistor blocks, The two adjacent resistors are two of the plurality of resistors in the two adjacent blocks that are adjacent to the boundary region.

2. 2. The heater according to claim 1, wherein when power is supplied to the two adjacent blocks, the amount of heat generated by each of the two adjacent resistors is the same as the amount of heat generated by each of a plurality of internal resistors that are not adjacent to the boundary region among the plurality of resistors in the two adjacent blocks.

3. 2. The heater according to claim 1, wherein when power is supplied to the two adjacent blocks, the amount of heat generated by each of the two adjacent resistors is greater than the amount of heat generated by each of a plurality of internal resistors that are not adjacent to the boundary region among the plurality of resistors in the two adjacent blocks.

4. A fixing device that fixes a toner image on a sheet by applying heat and pressure to the toner image on the sheet at a fixing position on a sheet conveyance path, a support member disposed at the fixing position along a main direction intersecting a sheet conveying direction; a cylindrical fixing member rotatably supported by the support member; The heater according to any one of claims 1 to 3, The heater is supported by the support member in a state along the main direction and heats the fixing member.

5. The fixing device according to claim 4 , wherein the plurality of resistance blocks of the heater are formed to have lengths corresponding to a plurality of standard sizes of the sheet.

6. a transfer device that transfers a toner image onto a sheet; An image forming apparatus comprising: the fixing device according to claim 4 or 5.

Images