Heater, fixing device, image forming apparatus

Abstract

The purpose of the present invention is to avoid the temperature of part of a fixing member becoming inappropriate, for example, due to variation in the size or conveyance position of a sheet. Multiple resistance blocks (60) include an object block and an adjacent block present adjacent to the object block. Multiple resistors (6) of the object block include one or multiple end resistors (6a) and an object resistor (6b). The end resistor (6a) is located at an end on the adjacent block side of the object block. The object resistor (6b) is located adjacent to the end resistor (6a). In a case where electric power is supplied to the object block, the heat generation amount of the object resistor (6b) is larger than the heat generation amount of the one end resistor (6a) or the heat generation amount of each of the multiple end resistors (6a).

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 plurality of resistor blocks and a plurality of power supply electrodes. Each of the plurality of resistor blocks has a plurality of resistors arranged at a first interval in a main direction. The plurality of power supply electrodes are connected to one end of each 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 plurality of resistor blocks are arranged at a second interval in the main direction that is larger than the first interval. The plurality of resistor blocks include a target block and an adjacent block adjacent to the target block. The plurality of resistors in the target block include one or more end resistors located at an end of the target block facing the adjacent block and a target resistor located adjacent to the one or more end resistors. When power is supplied to the target block, the amount of heat generated by the target resistor is greater than the amount of heat generated by one of the end resistors or the amount of heat generated by each of the plurality of end resistors.

[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 graph showing a first example of the fixing temperature distribution. [Figure 7] FIG. 7 is a graph showing a second example of the fixing temperature distribution. [Figure 8] FIG. 8 is a graph showing a third example of the fixing temperature distribution. [Figure 9] FIG. 9 is a configuration diagram of two adjacent resistor blocks in a heater according to the second embodiment. [Figure 10] FIG. 10 is a configuration diagram of two adjacent resistor blocks in a heater according to the third embodiment. [Figure 11] FIG. 11 is a configuration diagram of two adjacent resistor blocks in a heater according to a reference example. [Figure 12] FIG. 12 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 during the execution of 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. 11 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 conveying position of the sheet 9, the sheet 9 may not pass the end A2 of the operating block in the main direction D1 (see FIG. 11). If the amount of heat generated by a specific resistor 6p located at the end A2 of the operating block is large, the temperature of the part of the fixing member 51 corresponding to the end A2 of the operating block may exceed the allowable temperature range TR1 (see FIG. 12).

[0081] Fig. 12 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. 12, 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 A2 of the actuation block is outside the range through which the sheet 9 passes.

[0084] In the reference example, the end A2 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 A2 of the operating block may exceed the allowable temperature range TR1 (see FIG. 12).

[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, the plurality of resistance blocks 60 includes one or more target blocks and adjacent blocks located next to the target blocks.

[0097] In this embodiment, the first resistor block 61 and the pair of second resistor blocks 62 are the target blocks.

[0098] If the first resistor block 61 is the target block, each of the pair of second resistor blocks 62 is the adjacent block.

[0099] Furthermore, if one of the pair of second resistance blocks 62 is the target block, one of the pair of third resistance blocks 63 is the adjacent block.

[0100] In FIG. 5, a first resistor block 61 is shown as the target block, and one of a pair of second resistor blocks 62 is shown as the adjacent block.

[0101] The plurality of resistors 6 of the target block include a first end resistor 6a, a first target resistor 6b, and a plurality of first internal resistors 6c (see FIG. 5).

[0102] The first end resistor 6a is located at the end A2 of the target block on the adjacent block side, and the first target resistor 6b is located next to the first end resistor 6a.

[0103] The plurality of first internal resistors 6c are arranged on the opposite side of the end A2 side from the first target resistor 6b in the target block.

[0104] The width of the end A2 of the target block in the main direction D1 is determined according to the magnitude of the variation in size or the variation in conveyance position of the sheets 9 of the corresponding standard size.

[0105] In this embodiment, the end A2 of the target block in the main direction D1 includes one first end resistor 6a, and the first target resistor 6b is located second from the end of the target block on the adjacent block side among the multiple resistors 6.

[0106] When power is supplied to the target block, the heat generation amount of the first target resistor 6b is greater than that of one of the first end resistors 6a and is also greater than that of each of the first internal resistors 6c.

[0107] In this embodiment, the heat generation amount of the first end resistor 6a is the same as the heat generation amount of each of the first internal resistors 6c. Note that the heat generation amount of the first end resistor 6a may be smaller than the heat generation amount of each of the first internal resistors 6c.

[0108] 5 to 12, 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 FIGS. 5 to 12, 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.

[0109] In this embodiment, the plurality of resistors 6 in the adjacent block include a second end resistor 6d, a second target resistor 6e, and a plurality of second internal resistors 6f (see FIG. 5).

[0110] The second end resistor 6d is located at an end A3 of the adjacent block on the target block side. For example, the area of ​​the end A3 of the adjacent block is the same as the area of ​​the end A2 of the target block.

[0111] In this embodiment, the end A3 of the adjacent block in the main direction D1 includes one second end resistor 6d, and therefore the second target resistor 6e is located second from the end of the target block among the multiple resistors 6 of the adjacent block.

[0112] When power is supplied to the adjacent block, the second target resistor 6e generates more heat than the second end resistor 6d and each of the second internal resistors 6f.

[0113] In this embodiment, the heat generation amount of the second end resistor 6d is the same as the heat generation amount of each of the second internal resistors 6f. Note that the heat generation amount of the second end resistor 6d may be smaller than the heat generation amount of each of the second internal resistors 6f.

[0114] 6 to 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. 6 to 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.

[0115] 6 to 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.

[0116] 6 to 8, the target block is a first resistor block 61, and the adjacent block is one of a pair of second resistor blocks 62.

[0117] 6 shows a first example of the distribution of the fixing temperature T1, in which the second sheet 9b or the third sheet 9c passes through the fixing position P2.

[0118] In the first example, both the target block and the neighboring block are the working blocks.

[0119] The fixing temperature T1 in the first example falls within the allowable temperature range TR1 in the boundary area A1 between the target block and the adjacent block because the heat generated by the first target resistor 6b and the second target resistor 6e affects the boundary area A1.

[0120] Furthermore, the fixing temperature T1 in the first example is slightly higher in the areas corresponding to the first target resistor 6b and the second target resistor 6e than in the other areas.

[0121] However, the fixing temperature T1 in the first example falls within the allowable temperature range TR1 over the entire region spanning both the target block and the adjacent blocks.

[0122] 7 shows a second example of the distribution of the fixing temperature T1. In the second example, a first sheet 9a having a relatively wide width passes through the fixing position P2.

[0123] In the second example, the target block is the active block and the adjacent block is not powered. In the second example, the first sheet 9a passes through the entire area of ​​the target block.

[0124] 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 target block.

[0125] Therefore, the fixing temperature T1 in the second example falls within the allowable temperature range TR1 in the area corresponding to the target block.

[0126] 8 shows a third example of the distribution of the fixing temperature T1. In this example, a relatively narrow first sheet 9a passes through the fixing position P2. The difference between the second and third examples is due to variations in the size of the standard-sized first sheet 9a.

[0127] In the third example, the target block is the working block and the adjacent block is not powered. In the third example, the first sheet 9a passes through an area corresponding to a portion of the target block other than the end A2. That is, in the third example, the first sheet 9a does not pass through an area corresponding to the end A2 of the target block.

[0128] The fixing temperature T1 in the third example exhibits a distribution that is generally similar to the fixing temperature T1 in the first and second examples in the region corresponding to the portion of the target block other than the first end resistor 6a.

[0129] On the other hand, the fixing temperature T1 in the third example is slightly higher in the region corresponding to the first end resistor 6a of the target block 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 end A2 of the target block.

[0130] However, since the heat generation amount of the first end resistor 6a is not large, the fixing temperature T1 in the third example falls within the allowable temperature range TR1 in the region corresponding to the target block, which is different from the example in Figure 12 in which the heater 53x according to the reference example is used.

[0131] 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.

[0132] The configuration of the first end resistor 6a, the first target resistor 6b, and the plurality of first internal resistors 6c is a first main configuration in this embodiment, and the configuration of the second end resistor 6d, the second target resistor 6e, and the plurality of second internal resistors 6f is a second main configuration in this embodiment.

[0133] The first and second main configurations of this embodiment are also employed in the regions of the heater 53 where each of the pair of second resistor blocks 62 and each of the pair of third resistor blocks 63 are adjacent to each other.

[0134] [Second embodiment] Next, a heater 53A according to a second embodiment will be described with reference to FIG.

[0135] 9, the same components as those shown in FIGS. 4 to 8 are denoted by the same reference numerals. Heater 53A constitutes part of fixing device 5 in place of heater 53.

[0136] In this embodiment, the first resistor block 61 and the pair of second resistor blocks 62 are the target blocks.

[0137] If the first resistor block 61 is the target block, each of the pair of second resistor blocks 62 is the adjacent block.

[0138] Furthermore, if one of the pair of second resistance blocks 62 is the target block, one of the pair of third resistance blocks 63 is the adjacent block.

[0139] In FIG. 9, a first resistor block 61 is shown as the target block, and one of a pair of second resistor blocks 62 is shown as the adjacent block.

[0140] In the heater 53A, the plurality of resistors 6 of the target block include two first end resistors 6a, a first target resistor 6b, and a plurality of first internal resistors 6c (see FIG. 9). The first target resistor 6b is located adjacent to the two first end resistors 6a.

[0141] When power is supplied to the target block, the heat generation amount of the first target resistor 6b is greater than the heat generation amount of each of the two first end resistors 6a and the first internal resistors 6c.

[0142] In this embodiment, the end A2 of the target block in the main direction D1 includes two first end resistors 6a, and the first target resistor 6b is located third from the end of the target block on the adjacent block side among the multiple resistors 6.

[0143] Furthermore, in the heater 53A, the plurality of resistors 6 in the adjacent block include two second end resistors 6d, a second target resistor 6e, and a plurality of second internal resistors 6f (see FIG. 9).

[0144] For example, the heater 53A is used when there is greater variation in the size or transport position of the sheet 9 than when the heater 53 is used.

[0145] The heater 53A may be used when the size of the first target resistor 6b and the first internal resistors 6c in the main direction D1 is smaller than that of the heater 53.

[0146] When the heater 53A is employed, the same effect as when the heater 53 is employed can be obtained.

[0147] It is also conceivable that the end A2 in the main direction D1 of the target block includes three or more first end resistors 6a.

[0148] [Third embodiment] Next, a heater 53B according to a third embodiment will be described with reference to FIG.

[0149] 10, the same components as those shown in FIGS. 4 to 8 are denoted by the same reference numerals. Heater 53B constitutes part of fixing device 5 in place of heater 53.

[0150] In this embodiment, the first resistor block 61 and the pair of second resistor blocks 62 are the target blocks.

[0151] If the first resistor block 61 is the target block, each of the pair of second resistor blocks 62 is the adjacent block.

[0152] Furthermore, if one of the pair of second resistance blocks 62 is the target block, one of the pair of third resistance blocks 63 is the adjacent block.

[0153] In FIG. 10, a first resistor block 61 is shown as the target block, and one of a pair of second resistor blocks 62 is shown as the adjacent block.

[0154] In the heater 53B, the plurality of resistors 6 of the target block include two first end resistors 6a, a first target resistor 6b, and a plurality of first internal resistors 6c (see FIG. 10). This configuration is the same as that of the heater 53A.

[0155] Furthermore, in the heater 53B, the plurality of resistors 6 in the adjacent block include one third end resistor 6g and a plurality of third internal resistors 6h (see FIG. 10).

[0156] The third end resistor 6g is one of the resistors 6 in the adjacent block at the end closest to the target block. The third internal resistors 6h are formed in the adjacent block in a row, starting from a position next to the third end resistor 6g.

[0157] When power is supplied to the adjacent block, the amount of heat generated by the third end resistor 6g is greater than the amount of heat generated by each of the plurality of third internal resistors 6h.

[0158] When the block selection control is executed, if the sheet 9 does not pass through the area of ​​the adjacent block, power is not supplied to the adjacent block. Also, variations in the size or transport position of the second sheet 9b usually do not affect the presence or absence of the second sheet 9b in the area of ​​the third end resistor 6g.

[0159] Therefore, when the heater 53B is employed, the same effect as when the heater 53 is employed can be obtained.

[0160] The configuration of the adjacent block of the heater 53B may be adopted as the adjacent block of the heater 53.

Claims

1. a plurality of resistor blocks each having a plurality of resistors 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; the plurality of resistor blocks are arranged at second intervals in the main direction that are greater than the first intervals; The plurality of resistor blocks include: a first resistor block formed to a length corresponding to a first sheet size in the main direction; a pair of second resistor blocks adjacent to the first resistor block on both outer sides in the main direction, a combined length of the first resistor block and the pair of second resistor blocks in the main direction corresponds to a second sheet size that is larger than the first sheet size; The plurality of resistors of the first resistor block are one or more first end resistors located at both ends of the first resistor block in the main direction; a first target resistor located adjacent to the first end resistor; a plurality of first internal resistors other than the first end resistor and the first target resistor, A heater in which, when power is supplied to the first resistor block, the heat generation amount of the first target resistor is greater than the heat generation amount of one of the first end resistors or each of the plurality of first end resistors, and is greater than the heat generation amount of each of the plurality of first internal resistors.

2. The heater according to claim 1 , wherein the first target resistor is located second or third from an end of the plurality of resistors in the first resistor block in the main direction.

3. The plurality of resistors of the second resistor block are one or more second end resistors located at an end of the second resistor block on the first resistor block side; a second target resistor located adjacent to the second end resistor, 3. The heater according to claim 1, wherein when power is supplied to the second resistor block, the heat generation amount of the second target resistor is greater than the heat generation amount of one of the second end resistors or each of the plurality of second end resistors.

4. A heater as described in Claim 3, wherein the second target resistor is located second or third from the end of the first resistor block side of the plurality of resistors of the second resistor block.

5. 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 claim 1 or 2, The heater is supported by the support member in a state along the main direction and heats the fixing member.

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

Images