Image forming apparatus

Abstract

The purpose of the present invention is to provide an image forming apparatus that prevents excessive temperature rise of a portion of a plurality of heating blocks of a fixing device due to errors in size information of a sheet. The heater includes a main heating block disposed in a reference region corresponding to a sheet having a reference size, and a sub-heating block disposed in an outer region. The outer sheet sensor detects the sheet at a position within the outer region between the transfer device and the fixing device. The control device controls the power supply state to one of the first power supply state and the second power supply state on the basis of object size information indicating the size of the object sheet. When the object size information indicates a size exceeding the reference size, the control device determines whether the object sheet is detected by the outer sheet sensor according to whether or not the object sheet is detected by the outer sheet sensor. A conveyance interval between the target sheet and a next sheet following the target sheet is controlled to be one of a first interval and a second interval longer than the first interval.

Description

Technical Field

[0001] The present invention relates to an image forming apparatus provided with a fixing device including a plurality of heating blocks whose power supply states are switched according to the size of a sheet. Background Art

[0002] An electrophotographic image forming apparatus includes a transfer device and a fixing device. The transfer device transfers a toner image to a conveyed sheet. The fixing device fixes the toner image to the sheet by heating and pressurizing the toner image on the sheet.

[0003] In addition, it is known that the heater of the fixing device includes a plurality of electrodes divided in a width direction perpendicular to the sheet conveying direction, whereby the heater is divided into a plurality of heating blocks, and the power supply states of the plurality of heating blocks are switched according to the size of the sheet.

[0004] In the image forming apparatus, the control device acquires size information indicating the size of the sheet being conveyed, and switches the power supply state to the plurality of heating blocks according to the size indicated by the size information.

[0005] If the size information is erroneous information indicating a size larger than the actual size of the sheet, a situation occurs in which the amount of heat dissipated to the sheet is less than the expected amount of heat in some of the plurality of heating blocks.

[0006] In addition, the sheet may be conveyed in a state where the position of the sheet is offset from the expected position in the width direction. In this case, the amount of heat dissipated to the sheet may be less than the expected amount in some of the plurality of heating blocks.

[0007] When performing a continuous printing process of sequentially forming images on a plurality of sheets, if the size information is the error information, or if the plurality of sheets are conveyed in a state where the plurality of sheets are offset in the width direction, there is a possibility that the temperature of a portion of the plurality of heating blocks may rise higher than the assumed temperature. Summary of the invention

[0008] An object of the present invention is to provide an image forming apparatus capable of preventing an excessive temperature rise of a part of a plurality of heating blocks of a fixing device caused by an error in sheet size information or a deviation in a sheet conveyance position when executing a continuous printing process.

[0009] An image forming apparatus according to one aspect of the present invention includes a sheet conveying device, a transfer device, a fixing device, a sheet detection unit, and a control device. The sheet conveying device is capable of conveying a plurality of sheets in sequence. The transfer device transfers a toner image to the conveyed plurality of sheets respectively. The fixing device includes: a heater for heating the toner images on the plurality of sheets conveyed in sequence from the transfer device respectively; and a pressurizing unit for pressing the plurality of sheets against the heater respectively. The sheet detection unit is arranged on the upstream side of the sheet conveying direction relative to the fixing device, and detects the conveyed plurality of sheets respectively. The control device controls power supply to the heater and the sheet conveying device. The heater includes: a main heating block arranged in a reference area, the reference area corresponding to the sheet of a reference size in a main direction intersecting the sheet conveying direction; and a secondary heating block arranged in an outer area, the outer area being adjacent to the reference area in the main direction and corresponding to the sheet having a size larger than the reference size. The sheet detection unit includes an outer sheet sensor, which detects the sheet at a position in the outer region of the main direction between the transfer device and the fixing device. The control device obtains object size information, which indicates the size of the object sheet arriving at the fixing device. The control device also controls the power supply state of the heater to one of a first power supply state and a second power supply state, in which only the main heating block is powered, and in which the main heating block and the auxiliary heating block are powered, according to whether the object size information indicates a size within the reference size or a size exceeding the reference size. The control device also controls the conveying interval between the object sheet and the next sheet following the object sheet to one of a first interval and a second interval longer than the first interval, according to whether the outer sheet sensor detects the object sheet when the object size information indicates a size exceeding the reference size.

[0010] According to the present invention, an image forming apparatus can be provided that can prevent the temperature of some of the plurality of heating blocks of a fixing device from excessively rising due to errors in sheet size information or deviations in sheet conveyance positions when executing continuous printing processing.

[0011] This specification is presented in a simplified form, with appropriate reference to the accompanying drawings, to summarize the concepts described in the following detailed description. This specification is not intended to limit the important features and essential features of the subject matter described in the claims, nor is it intended to limit the scope of the subject matter described in the claims. In addition, the subject matter described in the claims is not limited to implementations that solve some or all of the disadvantages described in any part of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 It is a block diagram of an image forming apparatus according to an embodiment.

[0013] Figure 2 It is a structural diagram of a fixing device of the image forming apparatus according to the embodiment.

[0014] Figure 3 This is a block diagram showing a configuration of a control device of the image forming apparatus according to the embodiment.

[0015] Figure 4 It is a structural diagram of a heater and a sheet detection unit of the image forming apparatus according to the embodiment. DETAILED DESCRIPTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the following embodiment is an example of a specific embodiment of the present invention and does not limit the technical scope of the present invention.

[0017] [Structure of Image Forming Apparatus 10] like Figure 1 As shown, the image forming apparatus 10 includes a sheet conveying device 3 , a printing device 4 , and a control device 8 which are provided in a main body 1 .

[0018] The printing device 4 executes a printing process for forming an image on a sheet 9. The printing device 4 executes the printing process by an electrophotographic method. The sheet 9 is an image forming medium such as paper or a thin sheet of resin.

[0019] The sheet conveying device 3 includes a sheet feeding device 30 and a plurality of feeding roller pairs 31. The sheet feeding device 30 feeds the sheet 9 stored in the sheet storage unit 2 to a feeding path 300 in the main body 1. The feeding path 300 is a path for feeding the sheet 9.

[0020] The plurality of conveying roller pairs 31 are driven to rotate by a motor (not shown). The plurality of conveying roller pairs 31 convey the sheet 9 along the conveying path 300 by rotating, and discharge the sheet 9 to the discharge tray 1 x.

[0021] The sheet 9 passes through the transfer position P1 and the fixing position P2 in the conveyance path 300 and is discharged to the discharge tray 1 x.

[0022] In the following description, the sheet conveying direction along the conveying path 300 is referred to as a conveying direction D01. The fixing position P2 is located on the downstream side of the transfer position P1 in the conveying direction D01.

[0023] In addition, the direction intersecting the conveying direction D01 in the conveying path 300 is referred to as a main direction D1. In the present embodiment, the main direction D1 is a direction orthogonal to the conveying direction D01. The main direction D1 is a main scanning direction in the printing process.

[0024] 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 developer in a granular state.

[0025] The printing device 4 includes one or more image forming units 4x, an optical scanning device 40, a transfer device 44, and a fixing device 5. The image forming unit 4x includes a drum-shaped photoreceptor 41, a charging device 42, a developing device 43, a drum cleaning device 45, and the like.

[0026] Figure 1 The image forming apparatus 10 shown is a tandem color image forming apparatus. Therefore, the printing device 4 includes four image forming units 4x corresponding to the four color toners of yellow, cyan, magenta, and black.

[0027] In the image forming unit 4x, the photoconductor 41 rotates, and the charging device 42 charges the surface of the photoconductor 41. Furthermore, the optical scanning device 40 writes an electrostatic latent image on the surface of the photoconductor 41 by scanning with laser light.

[0028] 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.

[0029] The transfer device 44 transfers the toner image to the sheet 9 at the transfer position P1 of the conveyance path 300 . The transfer device 44 includes an intermediate transfer belt 441 , four primary transfer devices 442 corresponding to four image forming units 4 x , a secondary transfer device 443 , and a belt cleaning device 444 .

[0030] In the transfer device 44, the primary transfer device 442 transfers the toner image on the surface of the photoreceptor 41 to the surface of the intermediate transfer belt 441. Thus, the color toner image is formed on the surface of the intermediate transfer belt 441.

[0031] The secondary transfer device 443 transfers the toner image formed on the intermediate transfer belt 441 to the sheet 9 in the conveyance path 300 .

[0032] When the image forming apparatus 10 is a black-and-white image forming apparatus, the secondary transfer device 443 transfers the toner image on the photoreceptor 41 to the sheet 9 in the conveyance path 300 .

[0033] The drum cleaning device 45 removes the waste toner remaining on the surface of the photoreceptor 41 . The belt cleaning device 444 removes the waste toner remaining on the intermediate transfer belt 441 .

[0034] [Fixing device 5] The fixing device 5 heats and pressurizes the toner image on the sheet 9 while conveying the sheet 9 at the fixing position P2 of the conveyance path 300 . Thus, the fixing device 5 fixes the toner image on the sheet 9 to the sheet 9 .

[0035] like Figure 2 As shown, the fixing device 5 includes a pressure roller 50, a fixing member 51, a supporting member 52, a heater 53, a biasing mechanism 54, and a temperature detection unit 55. The pressure roller 50, the fixing member 51, the supporting member 52, and the heater 53 are arranged along the main direction D1 at the fixing position P2.

[0036] The fixing member 51 is a flexible cylindrical member. In other words, the fixing member 51 is an endless belt-shaped flexible cylindrical body. For example, the fixing member 51 is a cylindrical film member. The fixing member 51 is rotatably supported by the supporting member 52.

[0037] The pressure roller 50 is in pressure contact with the fixing member 51, thereby forming a nip Np1 (see FIG. 1 ) between the pressure roller 50 and the fixing member 51. Figure 2 ).

[0038] The pressure roller 50 presses the sheet 9 passing through the fixing position P2 toward the fixing member 51 . As a result, the sheet 9 is pressed toward the heater 53 . The pressure roller 50 is an example of a pressure section that presses the sheet 9 toward the heater 53 .

[0039] The supporting member 52 rotatably supports the fixing member 51. The supporting member 52 also supports the heater 53. The supporting member 52 has an opposing portion 52a that opposes the pressure roller 50 across the fixing member 51. The opposing portion 52a contacts the inner side surface of the fixing member 51.

[0040] The heater 53 is assembled to the facing portion 52 a. Thus, the heater 53 is supported by the support member 52 in the state 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 contacts the inner side surface of the fixing member 51 .

[0041] The urging mechanism 54 includes a pressing member 541 and a spring 542. The spring 542 elastically urges the facing 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 supporting member 52.

[0042] The pressure roller 50 is driven to rotate by a motor (not shown). The pressure roller 50 drives the fixing member 51 to rotate. By driving the fixing member 51 to rotate, the inner side surface of the fixing member 51 slides relative to the heater 53 and the facing portion 52a. A lubricant is applied to the inner side surface of the fixing member 51.

[0043] The heater 53 heats the toner image on the sheet 9 conveyed from the transfer device 44. Specifically, the heater 53 heats the sheet 9 via a portion of the fixing member 51 where the nip Np1 is formed.

[0044] The temperature detector 55 detects the temperature of the heater 53. The temperature detected by the temperature detector 55 is used for fixing temperature control, which is a feedback control for controlling the power supply to the heater 53 by comparing the temperature detected by the temperature detector 55 with a preset target temperature.

[0045] [Control device 8] The control device 8 performs various data processing and controls devices such as the sheet conveying device 3 and the printing device 4. The control device 8 controls the conveyance of the sheet 9 by the sheet conveying device 3 and the supply of power to the heater 53 of the fixing device 5.

[0046] like Figure 3 As shown, the control device 8 includes a CPU (Central Processing Unit) 81 and peripheral devices including a RAM (Random Access Memory) 82, a secondary storage device 83, a signal interface 84, and the like.

[0047] The control device 8 further includes a communication device 85 and a power supply circuit 86 .

[0048] The CPU 81 is a processor that performs various data processing and control by executing computer programs.

[0049] The RAM 82 is a computer-readable volatile storage device and temporarily stores the computer program executed by the CPU 81 and data output and referenced during the CPU 81 executing various processes.

[0050] The CPU 81 includes a plurality of processing modules realized by executing the computer program, including a main control unit 8a, a heater control unit 8b, and a print control unit 8c.

[0051] The main control unit 8a performs start control and the like for starting various processes in accordance with an operation performed on an operating device (not shown).

[0052] The heater control unit 8b controls the amount of power supplied to the heater 53 by the fixing temperature control. The heater control unit 8b adjusts the amount of power supplied to the heater 53 by controlling the power supply circuit 86.

[0053] The power supply circuit 86 supplies electric power to the heater 53 in accordance with a power supply instruction from the heater control unit 8 b.

[0054] The print control unit 8 c controls the sheet conveying device 3 . Furthermore, the print control unit 8 c causes the printing device 4 to execute the above-described printing process in synchronization with the conveyance of the sheet 9 by the sheet conveying device 3 .

[0055] The control device 8 controls the power supply to the heater 53 and the sheet conveying device 3 through the functions of the heater control unit 8 b and the print control unit 8 c , and also controls the image forming unit 4 x and the transfer device 44 .

[0056] The secondary storage device 83 is a computer-readable nonvolatile storage device, and for example, one or both of a flash memory and a hard disk drive are used as the secondary storage device 83 .

[0057] The signal interface 84 converts detection signals outputted by various sensors into digital data, and transmits the digital data to the CPU 81. The signal interface 84 also converts control instructions outputted by the CPU 81 into control signals, and transmits the control signals to the devices to be controlled.

[0058] The communication device 85 performs 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.

[0059] In this embodiment, the heater 53 is a sheet heater having a plurality of resistors 6 (see Figure 4 ).

[0060] The heater 53 includes a substrate 6x, a plurality of heating blocks 60, a plurality of power supply electrodes 600, and a ground electrode 610 (see Figure 4 ).

[0061] The substrate 6x is a non-conductive film. A plurality of heating blocks 60, a plurality of power supply electrodes 600, and a ground electrode 610 are formed on the substrate 6x.

[0062] Each of the plurality of heating blocks 60 includes a plurality of resistors 6 arranged in the main direction D1. Each of the resistors 6 is a heating element that generates heat when supplied with electricity.

[0063] In each figure, the secondary direction D2 is a direction along the conveying direction D01. The secondary direction D2 is a direction intersecting the main direction D1. The main direction D1 is the long side direction of the heater 53. The secondary direction D2 is the short side direction of the heater 53.

[0064] The plurality of power supply electrodes 600 are respectively connected to first ends of the plurality of heating blocks 60 in the sub-direction D2. The ground electrode 610 is connected to second ends of the plurality of heating blocks 60 in the sub-direction D2.

[0065] In the present embodiment, the sheet conveying device 3 conveys the sheet 9 with the center of the sheet 9 in the main direction D1 as a reference.

[0066] The heater 53 is divided into a main heating block 61 and a pair of auxiliary heating blocks 62 (see Figure 4 The main heating block 61 is disposed in a reference region in the main direction D1. The pair of auxiliary heating blocks 62 are respectively disposed in a pair of outer regions adjacent to the reference region in the main direction D1.

[0067] The reference area corresponds to a first-size sheet 9a, which is a sheet 9 of a predetermined reference size. The pair of outer areas corresponds to a second-size sheet 9b, which is a sheet 9 larger than the reference size.

[0068] exist Figure 4 In FIG. 1 , various sheets 9 including a first-size sheet 9a and a second-size sheet 9b are indicated by virtual lines (two-dot chain lines). Figure 4 In the embodiment, the center line L1 is a straight line passing through the center of the reference area in the main direction D1 and along the conveying direction D01.

[0069] The first size sheet 9 a passes through the reference area at the fixing position P2 , and the second size sheet 9 b passes through the reference area and the pair of outer areas at the fixing position P2 .

[0070] The plurality of power supply electrodes 600 include: a main electrode 601 connected to the first end of the main heating block 61; and a pair of secondary electrodes 602 connected to the first ends of a pair of secondary heating blocks 62 (see Figure 4 ).

[0071] The power supply circuit 86 can independently supply power to the main heating block 61 and the sub-heating block 62 through one or both of the main electrode 601 and the pair of sub-electrodes 602 .

[0072] In the image forming apparatus 10 , the control device acquires information indicating the size of the sheet 9 being conveyed, and switches the power supply state to the plurality of heating blocks 60 according to the size indicated by the acquired information.

[0073] In this embodiment, sheet size information indicating the size of the sheet 9 accommodated in the sheet accommodating section 2 is pre-stored in the secondary storage device 83. The print job also includes supply source information that specifies the sheet accommodating section 2 that is the supply source of the target sheet 9x.

[0074] The sheet size information corresponding to the supply source information included in the print job is target size information, and the target size information indicates the size of the target sheet 9 x .

[0075] When executing the printing process, the heater control section 8 b acquires the target size information corresponding to the target sheet 9 x from the secondary storage device 83 .

[0076] Furthermore, the heater control unit 8 b controls the power supply state to the heater 53 to one of the first power supply state and the second power supply state according to whether the target size information indicates a size within the reference size or a size exceeding the reference size.

[0077] The first power supply state is a state in which power is supplied only to the main heating block 61. The second power supply state is a state in which power is supplied to the main heating block 61 and a pair of auxiliary heating blocks 62.

[0078] When the target size information is erroneous information indicating a size larger than the actual size of the target sheet 9 x , a situation occurs in which the amount of heat dissipated to the target sheet 9 x is smaller than the expected amount of heat in the pair of sub-heat blocks 62 .

[0079] In addition, the target sheet 9x may be conveyed in a state where the position of the target sheet 9x is offset from the expected position in the main direction D1. In this case, the heat dissipated to the target sheet 9x at one of the pair of auxiliary heating blocks 62 is less than the expected amount of heat.

[0080] The image forming apparatus 10 may execute a continuous printing process. When the continuous printing process is executed, the sheet conveying device 3 sequentially conveys a plurality of sheets 9. The transfer device 44 transfers the toner image to each of the conveyed plurality of sheets 9.

[0081] Furthermore, in the fixing device 5 , the heater 53 heats the toner images on the plurality of sheets 9 sequentially conveyed from the transfer device 44 , respectively, and the pressure roller 50 presses the plurality of sheets 9 against the heater 53 , respectively.

[0082] When executing the continuous printing process, if the object size information is the error information, or if the multiple sheets 9 are conveyed in a state where they are offset along the main direction D1, there is a possibility that the temperature of one or both of the pair of auxiliary heating blocks 62 may rise higher than the assumed temperature.

[0083] That is, when the continuous printing process is executed, there is a possibility that the temperature of a part of the plurality of heating blocks 60 may excessively rise due to an error in the target size information or a deviation in the conveyance position of the target sheet 9 x .

[0084] The image forming apparatus 10 includes a structure for preventing the temperature of a part of the plurality of heating blocks 60 from excessively rising when the continuous printing process is executed. This structure will be described below.

[0085] In the fixing device 5, the temperature detection unit 55 includes a main temperature sensor 55a and a sub-temperature sensor 55b (see Figure 4 ). For example, the main temperature sensor 55a and the subsidiary temperature sensor 55b are thermistors, respectively.

[0086] The main temperature sensor 55a detects the temperature of the main heat block 61. The sub-temperature sensor 55b detects the temperature of one of the pair of sub-heat blocks 62.

[0087] The pair of auxiliary heating blocks 62 includes a first auxiliary heating block 62a and a second auxiliary heating block 62b (see Figure 4 The first auxiliary heating block 62a is disposed adjacent to the main heating block 61 on the first side SD1 of the main direction D1. The second auxiliary heating block 62b is disposed adjacent to the main heating block 61 on the second side SD2 of the main direction D1.

[0088] The pair of outer regions include: a first outer region adjacent to the reference region at a first side SD1 of the main direction D1 ; and a second outer region adjacent to the reference region at a second side SD2 of the main direction D1 .

[0089] The first sub-heating block 62a is disposed in the first outer region in the main direction D1, and the second sub-heating block 62b is disposed in the second outer region in the main direction D1. The sub-temperature sensor 55b detects the temperature of the first sub-heating block 62a.

[0090] In the present embodiment, the heater control unit 8 b controls the amount of power supplied to the main heating block 61 by the feedback control of the temperature detected by the main temperature sensor 55 a in the first power supply state.

[0091] Similarly, the heater control unit 8 b controls the amount of power supplied to the main heating block 61 and the pair of sub-heating blocks 62 by the feedback control of the temperature detected by the main temperature sensor 55 a in the second power supply state.

[0092] Furthermore, the heater control unit 8b stops supplying power to the main heating block 61 when the temperature detected by the main temperature sensor 55a exceeds a preset upper limit temperature. Similarly, the heater control unit 8b stops supplying power to the sub-heating block 62 when the temperature detected by the sub-temperature sensor 55b exceeds the upper limit temperature.

[0093] In addition, the heater control unit 8b may stop supplying power to the main heating block 61 and the sub-heating block 62 when the detected temperature of at least one of the main temperature sensor 55a and the sub-temperature sensor 55b exceeds the upper limit temperature.

[0094] The fixing device 5 further includes two thermal protectors 56 (see Figure 4 ). The thermal protectors 56 are bimetallic thermostats.

[0095] The two thermal protectors 56 include a first thermal protector 56a and a second thermal protector 56b (see Figure 4 The first thermal protector 56a is disposed on the main heating block 61 of the heater 53. The second thermal protector 56b is disposed on the second auxiliary heating block 62b of the heater 53.

[0096] The first thermal protector 56a electrically cuts off the power supply line to the main heating block 61 when the temperature of the main heating block 61 exceeds the allowable temperature. The second thermal protector 56b electrically cuts off the power supply line to the pair of auxiliary heating blocks 62 when the temperature of the second auxiliary heating block 62b exceeds the allowable temperature.

[0097] exist Figure 3 In the example shown, the control device 8 further includes a first cutoff circuit 87 a electrically connected to the first thermal protector 56 a , and a second cutoff circuit 87 b electrically connected to the second thermal protector 56 b .

[0098] The first thermal protector 56a operates when the temperature of the main heating block 61 exceeds the allowable temperature, and the first cutoff circuit 87a electrically cuts off the power supply line supplying power to the main heating block 61 through the operation of the first thermal protector 56a.

[0099] The second thermal protector 56b is activated when the temperature of the second auxiliary heating block 62b exceeds the allowable temperature, and the second cutoff circuit 87b electrically cuts off the power supply line to the pair of auxiliary heating blocks 62 through the activation of the second thermal protector 56b.

[0100] The second thermal protector 56 b is disposed at a position in the second sub-heat block 62 b that is line-symmetrical with respect to the position of the sub-temperature sensor 55 b with reference to the center line L1 .

[0101] In the above case, when the target sheet 9x is conveyed in a state where the target sheet 9x is offset to the first side SD1 of the main direction D1, the target sheet 9x is likely to deviate from the position of the second thermal protector 56b. In this case, the second thermal protector 56b can reliably detect that the temperature of the second auxiliary heating block 62b exceeds the allowable temperature.

[0102] On the other hand, when the target sheet 9x is conveyed in a state where it is offset to the second side SD2 of the main direction D1, the target sheet 9x is likely to deviate from the position of the auxiliary temperature sensor 55b. In this case, the auxiliary temperature sensor 55b can easily reliably detect that the temperature of the first auxiliary heating block 62a exceeds the upper limit temperature.

[0103] Therefore, when the target sheet 9 x is displaced in the main direction D1, power supply to the pair of sub-heat blocks 62 can be reliably cut off before the temperature of the first sub-heat block 62 a or the second sub-heat block 62 b rises excessively.

[0104] In the present embodiment, the first thermal protector 56 a is disposed at a position in the main heating block 61 that is line-symmetrical with respect to the position of the main temperature sensor 55 a with respect to the center line L1 .

[0105] For example, the main temperature sensor 55 a and the first thermal protector 56 a are arranged at positions corresponding to both ends of the sheet 9 of the smallest size assumed in the main direction D1 .

[0106] The image forming apparatus 10 further includes a sheet detection unit 7 disposed on the upstream side of the fixing device 5 in the conveying direction D01 (see FIG. 1 ). Figure 1 , Figure 4 ) When the continuous printing process is executed, the sheet detection unit 7 detects each of the plurality of sheets 9 being conveyed.

[0107] In this embodiment, the sheet detection unit 7 includes a main sheet sensor 71 and a pair of outer sheet sensors 72 (see Figure 4 ).

[0108] For example, each of the main sheet sensor 71 and the pair of outer sheet sensors 72 includes a swing member and a photoelectric sensor. The swing member is supported to be swingable and swings by contacting each of the conveyed sheets 9. The photoelectric sensor detects the swing of the swing member.

[0109] The main sheet sensor 71 detects each sheet 9 at a position within the reference area in the main direction D1 between the transfer device 44 and the fixing device 5. The pair of outer sheet sensors 72 detect each sheet 9 at a position within the pair of outer areas in the main direction D1 between the transfer device 44 and the fixing device 5.

[0110] The pair of outer sheet sensors 72 includes a first outer sheet sensor 72a and a second outer sheet sensor 72b (see Figure 4 The first outer sheet sensor 72a detects the sheet 9 in the first outer region in the main direction D1. The second outer sheet sensor 72b detects the sheet 9 in the second outer region in the main direction D1.

[0111] When the continuous printing process is executed, the print control unit 8 c executes conveyance interval control when the object size information indicates a size exceeding the reference size.

[0112] When the target sheet 9 x of the reference size is conveyed at the original position in the main direction D1 , both ends of the target sheet 9 x in the main direction D1 pass through the positions of the pair of outer sheet sensors 72 .

[0113] The conveyance interval control is a control to make the conveyance interval between the target sheet 9x and the next sheet 9y become one of a first interval and a second interval, depending on whether the pair of outer sheet sensors 72 detects the target sheet 9x. The second interval is longer than the first interval.

[0114] The next sheet 9y is a sheet 9 conveyed immediately following the target sheet 9x in the continuous printing process (see Figure 4 ).

[0115] In the conveyance interval control, when both the first outside sheet sensor 72a and the second outside sheet sensor 72b detect the target sheet 9x, the print control unit 8c controls the conveyance interval between the target sheet 9x and the next sheet 9y to the first interval.

[0116] In the conveyance interval control, when at least one of the first outer sheet sensor 72a and the second outer sheet sensor 72b does not detect the target sheet 9x, the print control unit 8c controls the conveyance interval between the target sheet 9x and the next sheet 9y to the second interval.

[0117] When the target sheet 9x is conveyed at a position offset along the main direction D1, one of the pair of outer sheet sensors 72 may fail to detect the target sheet 9x. In addition, when the target size information is erroneous information indicating a size larger than the actual size of the target sheet 9x, one or both of the pair of outer sheet sensors 72 may fail to detect the target sheet 9x.

[0118] On the other hand, by increasing the conveyance interval between the target sheet 9 x and the next sheet 9 y , the amount of power supplied to the heater 53 from the time when the target sheet 9 x passes through the fixing position P2 to the time when the next sheet 9 y reaches the fixing position P2 is reduced.

[0119] By executing the conveyance interval control, it is possible to avoid an excessive increase in temperature of one or both of the pair of sub-heating blocks 62 due to a positional deviation of the target sheet 9 x or an error in the target size information.

[0120] In the present embodiment, the subsidiary temperature sensor 55b is arranged at a position overlapping with the position of the first outer sheet sensor 72a in the main direction D1. Figure 4 In the example shown, the subsidiary temperature sensor 55b is arranged at the same position as the first outer sheet sensor 72a in the main direction D1. Therefore, the temperature detected by the subsidiary temperature sensor 55b indicates a temperature reflecting whether the target sheet 9x passes the position of the first outer sheet sensor 72a.

[0121] In the present embodiment, the second thermal protector 56b is arranged at a position that overlaps with the position of the second outer sheet sensor 72b in the main direction D1. Figure 4 In the example shown, the second thermal protector 56b is arranged at the same position as the second outer sheet sensor 72b in the main direction D1. Thus, the second thermal protector 56b operates according to the temperature reflecting whether the target sheet 9x passes the position of the second outer sheet sensor 72b.

[0122] [First application example] Next, a first application example of the image forming apparatus 10 will be described. Hereinafter, differences from the image forming apparatus 10 in this application example will be described.

[0123] In this application example, the heater control unit 8 b controls the amount of power supplied to the main heating block 61 by the feedback control of the temperature detected by the main temperature sensor 55 a in the first power supply state. This control is the same as that in the image forming apparatus 10 .

[0124] On the other hand, the heater control unit 8b controls the amount of power supplied to the main heating block 61 by the feedback control of the temperature detected by the main temperature sensor 55a in the second power supply state, but performs different control on the amount of power supplied to the pair of auxiliary heating blocks 62.

[0125] The heater control unit 8 b of this application example controls the amount of power supplied to the pair of sub-heating blocks 62 by the feedback control of the temperature detected by the sub-temperature sensor 55 b in the second power supply state.

[0126] When this application example is used, the same effects as those when the image forming apparatus 10 is used can be obtained.

[0127] [Second application example] Next, a second application example of the image forming apparatus 10 will be described. Hereinafter, differences from the image forming apparatus 10 in this application example will be described.

[0128] In this application example, the sheet conveying device 3 conveys the sheet 9 with one end of the main direction D1 of the sheet 9 as a reference. Therefore, in this application example, the heater 53 is divided into one main heating block 61 and one auxiliary heating block 62 .

[0129] In this application example, the subsidiary temperature sensor 55 b and the second thermal protector 56 b are arranged at different positions in one subsidiary heating block 62 .

[0130] In this application example, the second outer sheet sensor 72 b of the pair of outer sheet sensors 72 of the image forming apparatus 10 is not provided.

[0131] When this application example is used, the same effects as those when the image forming apparatus 10 is used can be obtained.

[0132] The scope of the present invention is not limited to the above content, but is defined by the description of the claims, so it can be considered that the embodiments described in this specification are only illustrative, not limiting. Therefore, all changes that do not depart from the scope and limits of the claims, as well as contents that are equivalent to the scope and limits of the claims, are included in the scope of the claims.

Claims

1. An image forming device, characterized in that: include: A sheet conveying device capable of conveying a plurality of sheets in sequence; A transfer device for transferring the toner images to the plurality of sheets being conveyed; The fixing device comprises: a heater for heating the toner images on the plurality of sheets sequentially conveyed from the transfer device; and a pressurizing unit for pressing the plurality of sheets against the heater; a sheet detecting section arranged on an upstream side of the fixing device in a sheet conveying direction and detecting the plurality of sheets being conveyed respectively; as well as a control device for controlling power supply to the heater and the sheet conveying device, The heater comprises: a main heating block arranged in a reference area corresponding to the sheet of a reference size in a main direction intersecting the sheet conveying direction; and a secondary heating block disposed in an outer region, the outer region being adjacent to the reference region in the main direction and corresponding to the sheet body having a size larger than the reference size, The sheet detection unit includes an outer sheet sensor configured to detect the sheet at a position in the outer region in the main direction between the transfer device and the fixing device. The control device acquires target size information indicating the size of a target sheet arriving at the fixing device. The control device also controls the power supply state of the heater to one of a first power supply state and a second power supply state according to whether the object size information indicates a size within the reference size or a size exceeding the reference size, wherein in the first power supply state, power is supplied only to the main heating block, and in the second power supply state, power is supplied to the main heating block and the auxiliary heating block. The control device also controls the conveying interval between the target sheet and the next sheet following the target sheet to one of a first interval and a second interval longer than the first interval, depending on whether the outer sheet sensor detects the target sheet, when the target size information indicates a size exceeding the reference size.

2. The image forming apparatus according to claim 1, wherein: comprising a main temperature sensor, the main temperature sensor detecting the temperature of the main heating block, The control device controls the amount of power supplied to the main heating block and the sub-heating block through feedback control of the temperature detected by the main temperature sensor.

3. The image forming apparatus according to claim 1, wherein: include: A main temperature sensor, detecting the temperature of the main heating block; as well as A secondary temperature sensor, detecting the temperature of the secondary heating block, The control device controls the amount of power supplied to the main heating block by feedback control of the temperature detected by the main temperature sensor, and controls the amount of power supplied to the auxiliary heating block by feedback control of the temperature detected by the auxiliary temperature sensor.

4. The image forming apparatus according to claim 1, wherein: include: A main temperature sensor, detecting the temperature of the main heating block; A secondary temperature sensor, detecting the temperature of the secondary heating block; A first thermal protector is disposed on the main heating block, and electrically cuts off a power supply line supplying power to the main heating block when the temperature of the main heating block exceeds an allowable temperature; as well as The second thermal protector is disposed on the auxiliary heating block, and electrically cuts off the power supply line to the auxiliary heating block when the temperature of the auxiliary heating block exceeds the allowable temperature. When the detected temperature of one or both of the main temperature sensor and the sub-temperature sensor exceeds a preset upper limit temperature, the control device stops the power supply to one or both of the main heat block and the sub-heat block.

5. The image forming apparatus according to claim 4, wherein: The outer region includes a first outer region and a second outer region adjacent to both sides of the reference region, The auxiliary heating block includes a first auxiliary heating block disposed in the first outer region and a second auxiliary heating block disposed in the second outer region. The subsidiary temperature sensor detects the temperature of the first subsidiary heating block, The second thermal protector is configured on the second auxiliary heating block.

6. The image forming apparatus according to claim 5, wherein: The second thermal protector is arranged at a position line-symmetrical with respect to the position of the sub-temperature sensor with reference to a center line passing through the center of the reference area in the main direction and along the sheet conveying direction.

Images