Fixing device and image forming apparatus incorporating same

Abstract

A fixing device (20) includes a fixing rotator (21), a heater inside the fixing rotator, an opposed rotator (22) contacting the fixing rotator to form a nip and convey a sheet along a sheet conveyance path in a conveyance direction, a roller pair downstream from the nip in the conveyance direction to convey the sheet from the nip along the sheet conveyance path in the conveyance direction, and a separator (207, 208). The roller pair includes a first roller (204) adjacent to the opposed rotator and a second roller (203) contacting the first roller and adjacent to the fixing rotator. The separator is adjacent to the first roller and downstream from the first roller along the sheet conveyance path in the conveyance direction. The separator includes a projecting portion (207a, 208a) having a part along a circumferential surface of the first roller in a cross-section orthogonal to the conveyance direction and an axial direction of the first roller.

Description

[DESCRIPTION][Title of Invention]FIXING DEVICE AND IMAGE FORMING APPARATUS INCORPORATING SAME [Technical Field]

[0001] The present disclosure relates to a fixing device and an image forming apparatus incorporating the fixing device.[Background Art]

[0002] A fixing device known in the background art applies heat and pressure to a toner image on a sheet to fix the toner image onto the sheet. The fixing device known in the background art includes an auxiliary roller pair conveying the sheet downstream in a conveyance direction and a guide guiding the sheet to a sheet ejection path to eject the sheet to the outside of the image forming apparatus. In this technique, the guide reduces the curl of the sheet. The fixing device known in the background art further includes another guide disposed downstream from the guide in the conveyance direction.

[0003] Japanese Unexamined Patent Application Publication No. 2017-026811 discloses an image forming apparatus including the fixing device, the auxiliary roller pair to convey the sheet, the guide, the sheet ejection path, and a bifurcating member to switch one of sheet conveyance paths. The auxiliary roller pair is disposed between the fixing device and the bifurcating member and conveys the sheet fed from the fixing device downstream in the conveyance direction. The guide is disposed between the auxiliary roller pair and the bifurcating member to face a surface of the sheet that is opposite the latest image fixed surface of the sheet and guides the sheet fed from the auxiliary roller pair to the sheet ejection path. The abovedescribed configuration, for example, can effectively reduce a back curl of the sheet caused by heat in the fixing device.[Citation List][Patent Literature]

[0004] [PTL 1]Japanese Unexamined Patent Application Publication No. 2017-026811 [Summary of Invention] [Technical Problem]

[0005] The toner of a toner image on the sheet may adhere to one roller of the auxiliary roller pair. The toner may cause the sheet to stick to the one roller. In such a case, the guide having the shape disclosed in Japanese Unexamined Patent Application Publication No. 2017-026811 cannot separate the sheet from the one roller and may cause sheet jam, sheet folding, and wrinkles of the sheet. An object of the present disclosure is to provide a fixing device thatcan separate the sheet adhering the one roller of the auxiliary conveyance roller pair without damaging the sheet and can prevent the occurrence of the sheet jam, the sheet folding, and the wrinkles of the sheet.[Solution to Problem]

[0006] In order to achieve the above object, the present disclosure discloses a fixing device. The fixing device includes a fixing rotator, a heater, an opposed rotator, an auxiliary roller pair, and a separator. The heater is inside the fixing rotator. The opposed rotator contacts the fixing rotator to form a fixing nip to fix an image on a sheet and convey the sheet along a sheet conveyance path in a conveyance direction. The auxiliary roller pair is downstream from the fixing nip in the conveyance direction to convey the sheet from the fixing nip along the sheet conveyance path in the conveyance direction. The auxiliary roller pair includes a first roller and a second roller. The first roller is adjacent to the opposed rotator. The second roller contacts the first roller and is adjacent to the fixing rotator. The separator is adjacent to the first roller and downstream from the first roller along the sheet conveyance path in the conveyance direction. The separator includes a projecting portion having a part along a circumferential surface of the first roller in a cross-section orthogonal to the conveyance direction and an axial direction of the first roller.[Advantageous Effects of Invention]

[0007] According to one aspect of the present disclosure, the fixing device can separate the sheet adhering the one roller of the auxiliary roller pair without damaging the sheet and can prevent the occurrence of the sheet jam, the sheet folding, and the wrinkles of the sheet.[Brief Description of Drawings]

[0008] A more complete appreciation of embodiments of the present disclosure and many of the attendant advantages and features thereof can be readily obtained and understood from the following detailed description with reference to the accompanying drawings.[FIG. 1]FIG. 1 is a schematic diagram illustrating a configuration of an image forming apparatus. [FIGS. 2 A and 2B]FIGS. 2A and 2B are partial schematic side views of fixing devices known in the background art.[FIGS. 3 A to 3C]FIGS. 3 A to 3C are partial schematic side views each illustrating a part of the fixing device of FIG. 2A.[FIGS. 4 A to 4C]FIGS. 4A to 4C are partial schematic side views each illustrating a part of the fixing device of FIG. 2A.[FIGS. 5 A and 5B]FIGS. 5 A and 5B are partial schematic side views each illustrating a part of the fixing device of FIG. 2B.[FIGS. 6 A and 6B]FIGS. 6A and 6B are partial schematic side views of a fixing device according to an embodiment of the present disclosure.[FIG. 7]FIG. 7 is a partial schematic side view of a fixing device according to another embodiment of the present disclosure.[FIG. 8A]FIG. 8A is a partial schematic side view of a fixing device known in the background art including a guide forming an angle 9 with a tangent of a cross-sectional circle of a driving roller.[FIG. 8B]FIG. 8B is a partial schematic side view of a fixing device according to an embodiment including a separator that includes a projecting portion forming an angle 9 with a tangent of a cross-sectional circle of a driving roller.[FIGS. 9 A and 9B]FIGS. 9A and 9B are schematic perspective views of arrangements of separators.[FIGS. lOA to 10D]FIGS. 10A to 10D are schematic perspective views of arrangements of separators different from the arrangements of FIGS. 9 A and 9B.The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views. [Description of Embodiments]

[0009] In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

[0010] With reference to the drawings, a description is given below of an image forming apparatus. As illustrated in FIG. 1, the image forming apparatus 1 is a color laser printer and includes an image forming section A, a sheet feeding section B, a fixing device 20, an output roller pair 13, an output tray 14, a reverse roller pair 16, and a duplex unit 17.

[0011] The image forming section A includes four image forming devices 4Y, 4M, 4C, and 4K, an exposure device 9, and a transfer device 3.

[0012] The image forming apparatus 1 includes four image forming devices 4Y, 4M, 4C, and 4K disposed at a center portion of the body of the image forming apparatus 1. The image forming devices 4Y, 4M, 4C, and 4K have substantially the same configuration except for containing different color developers (e.g., toners) of yellow (Y), magenta (M), cyan (C), and black (K), respectively, corresponding to color separation components of color images.

[0013] Each of the image forming devices 4Y, 4M, 4C, and 4K includes, e.g., a drum-shaped photoconductor 5 serving as a latent image bearer, a charger 6 that charges the surface of the photoconductor 5, a developing device 7 that supplies toner to the surface of the photoconductor 5, and a cleaner 8 that cleans the surface of the photoconductor 5.

[0014] In FIG. 1, reference numerals are assigned to the photoconductor 5, the charger 6, the developing device 7, and the cleaner 8 of the image forming device 4K that forms a black toner image, whereas reference numerals for the image forming devices 4Y, 4M, and 4C that form yellow, magenta, and cyan toner images, respectively, are omitted because the image forming devices 4Y, 4M, and 4C have substantially the same configuration as the image forming device 4K.

[0015] The image forming apparatus 1 includes the exposure device 9 disposed below the image forming devices 4Y, 4M, 4C, and 4K, and the exposure device 9 exposes the outer circumferential surfaces of the respective photoconductors 5 with laser beams. The exposure device 9 includes a laser light source, a polygon mirror 51a, an f-9 lens 51b, and multiple reflection mirrors 51c to irradiate the surface of the photoconductor 5 with a laser beam according to image data and form an electrostatic latent image on the surface of the photoconductor 5.

[0016] In the image forming apparatus 1, the transfer device 3 is disposed above the image forming devices 4Y, 4M, 4C, and 4K. The transfer device 3 includes an intermediate transfer belt 30 as an intermediate transferor, four primary transfer rollers 31 as primary transferors, a secondary transfer roller 36 as a secondary transferor, and a secondary transfer backup roller 32. In addition, the transfer device 3 includes a cleaning backup roller 33, a tension roller 34, and a belt cleaner 35.

[0017] The intermediate transfer belt 30 is an endless belt stretched taut across the secondary transfer backup roller 32, the cleaning backup roller 33, and the tension roller 34. As a driver drivesand rotates the secondary transfer backup roller 32 counterclockwise, the intermediate transfer belt 30 rotates in a direction indicated by an arrow in FIG. 1.

[0018] The four primary transfer rollers 31 sandwich the intermediate transfer belt 30 together with the four photoconductors 5, forming four primary transfer nips between the intermediate transfer belt 30 and the photoconductors 5. Each primary transfer roller 31 is connected to a power supply that applies a predetermined direct current (DC) voltage or a predetermined alternating current (AC) voltage to each primary transfer roller 31.

[0019] The intermediate transfer belt 30 is interposed between the secondary transfer roller 36 and the secondary transfer backup roller 32 to form a secondary transfer nip. Similar to the primary transfer rollers 31, the secondary transfer roller 36 is connected to a power supply that applies a predetermined direct current (DC) voltage or alternating current (AC) voltage to the secondary transfer roller 36.

[0020] The belt cleaner 35 includes a cleaning brush and a cleaning blade that are disposed to contact an outer circumferential surface of the intermediate transfer belt 30. Waste toner collected by the belt cleaner 35 is conveyed through a waste toner conveyance tube and stored in a waste toner container.

[0021] A bottle holder 2 is disposed in an upper portion of the image forming apparatus 1 and accommodates four toner bottles 2Y, 2M, 2C, and 2K detachably attached to the bottle holder 2. The toner bottles 2Y, 2M, 2C, and 2K contain fresh yellow, cyan, magenta, and black toners to be supplied to the developing devices 7 of the image forming devices 4Y, 4M, 4C, and 4K, respectively. The fresh toner is supplied from the toner bottles 2Y, 2M, 2C, and 2K to the respective developing devices 7 through toner supply tubes connected between the toner bottles 2Y, 2M, 2C, and 2K and the respective developing devices 7.

[0022] The image forming apparatus 1 includes the sheet feeding section B in a lower portion of the body of the image forming apparatus 1. The sheet feeding section B includes a sheet feeding tray 10 that stores sheets P as recording media, and a feed roller 11 that feeds the sheet P from the sheet feeding tray 10.

[0023] Examples of the recording medium include, but are not limited to, plain paper, thick paper, thin paper, coated paper such as art paper, tracing paper, overhead projector (OHP) transparency, a postcard, and an envelope. The image forming apparatus 1 may include a bypass feeder. In the present embodiment, the thick paper indicates paper having a basis weight of 160 g I m2or more.

[0024] The image forming apparatus 1 includes a conveyance path R to convey the sheet P from the sheet feeding tray 10 to the output roller pair 13 via the secondary transfer nip. The output roller pair 13 ejects the sheet P outside the body of the image forming apparatus 1. In the conveyance path R, a registration roller pair 12 as a timing roller pair is disposed upstream from the position of the secondary transfer roller 36 in a direction in which the sheet P is conveyed (hereinafter referred to simply as a sheet conveyance direction). The registration roller pair 12 sends out the sheet P fed from the feed roller 11 toward the secondary transfer nip at a proper timing.

[0025] The image forming apparatus 1 includes the fixing device 20 disposed downstream from the position of the secondary transfer roller 36 in the sheet conveyance direction inside the body of the image forming apparatus 1. The fixing device applies heat and pressure to the sheet bearing an unfixed toner image to fix the toner image onto the sheet P.

[0026] The image forming apparatus 1 includes the output roller pair 13 on the conveyance path R downstream from the fixing device 20 inside the body of the image forming apparatus 1 in the sheet conveyance direction to eject the sheet P outside the body of the image forming apparatus 1. The image forming apparatus 1 includes the output tray 14 disposed on a top surface of the body of the image forming apparatus 1 to stack the sheet P ejected outside the body of the image forming apparatus 1.

[0027] The image forming apparatus 1 includes a branching member 15 between the output roller pair 13 and the fixing device 20. The branching member 15 is rotatably disposed in the body of the image forming apparatus 1. The image forming apparatus 1 can perform a single-sided printing mode and a double-sided printing mode. In the single-sided printing mode, the image forming apparatus 1 forms the toner image on one face of the sheet P that is referred to as a first face of the sheet P. In the double-sided printing mode, the image forming apparatus 1 forms the toner image on the other face of the sheet that is referred to as a second face of the sheet P in addition to forming the toner image on the first face. The branching member 15 is in a first state illustrated in FIG. 1 in the single-sided printing mode to open a sheet ejection path guiding the sheet P having the toner image fixed on the first face to the outside of the image forming apparatus 1. In the double-sided printing mode, the branching member 15 rotates in a direction indicated by an arrow in FIG. 1 to be in a second state to close the sheet ejection path and guide the sheet P to a reverse path 40 for forming the toner image on the second face.

[0028] In other words, the branching member 15 is configured to guide the sheet P conveyed to the downstream side of the fixing device 20 to either one of the reverse path for the double- sided printing mode and the sheet ejection path to eject the sheet P to the output tray 14 outside the body of the image forming apparatus. The sheet P passes through the output roller pair 13 viathe sheet ejection path. In the reverse path 40, the sheet P passes through the duplex unit 17 that is described below.

[0029] A reverse roller pair 16 that switches back the sheet P is downstream from the branching member 15 in the sheet conveyance direction and is in the reverse path 40. The duplex unit 17 is between the reverse roller pair 16 and the registration roller pair 12 in the reverse path 40. The duplex unit 17 includes conveyance roller pairs 42, 43, and 44 that form a part of the reverse path 40 for the double-sided printing mode. The reverse roller pair 16 switches back the sheet P after the image is fixed on the first face of the sheet P. The conveyance roller pairs 42, 43, and 44 convey the sheet P to the registration roller pair 12.

[0030] A basic operation of the image forming apparatus 1 is described below.

[0031] When the image forming apparatus 1 starts an image forming operation, the driver drives and rotates the photoconductor 5 in each of the image forming devices 4Y, 4M, 4C, and 4K clockwise in FIG. 1, and the charger 6 uniformly charges the surface of the photoconductor 5 in a predetermined polarity. The exposure device 9 emits laser beams onto the charged surfaces of the photoconductors 5, respectively, thus forming electrostatic latent images on the photoconductors 5.

[0032] The image data used to expose the respective photoconductors 5 is monochrome image data produced by decomposing a desired full-color image into yellow, cyan, magenta, and black image data. The developing devices 7 supply yellow, cyan, magenta, and black toners to the electrostatic latent images formed on the photoconductors 5, visualizing the electrostatic latent images as yellow, cyan, magenta, and black images, respectively.

[0033] When the image forming apparatus 1 starts the image forming operation, the secondary transfer backup roller 32 is driven and rotated counterclockwise in FIG. 1, rotating the intermediate transfer belt 30 in the direction indicated by the arrow in FIG. 1 by friction therebetween.

[0034] The power supply in the image forming apparatus 1 applies a constant voltage or a constantcurrent control voltage having a polarity opposite the polarity of the toner to the primary transfer roller 31, creating a transfer electric field at each primary transfer nip formed between the photoconductor 5 and the primary transfer roller 31.

[0035] When the yellow, magenta, cyan, and black images formed on the photoconductors 5 in the image forming apparatus 1 reach the primary transfer nips, respectively, in accordance with rotation of the photoconductors 5, the transfer electric fields generated at the primary transfer nips transfer the yellow, magenta, cyan, and black toner images from the photoconductors 5onto the intermediate transfer belt 30, respectively, such that the yellow, magenta, cyan, and black toner images are superimposed successively on the intermediate transfer belt 30.

[0036] Thus, a full-color toner image is formed on the surface of the intermediate transfer belt 30 in the image forming apparatus 1. After the primary transfer of the yellow, cyan, magenta, and black toner images from the photoconductors 5 onto the intermediate transfer belt 30, the cleaners 8 remove residual toner failed to be transferred onto the intermediate transfer belt 30 and therefore remaining on the photoconductors 5 therefrom, respectively. Subsequently, a discharger removes the charge on the surface of the photoconductor 5 to initialize the surface potential of the photoconductor 5.

[0037] A controller in the image forming apparatus 1 controls the driver to starts driving and rotating the feed roller 11, and the feed roller 11 feeds the sheet P from the sheet feeding tray 10 toward the registration roller pair 12 through the conveyance path R. Subsequently, the controller controls the driver to temporarily stop rotating the registration roller pair 12 and stop conveying the sheet P in the conveyance path R.

[0038] After the controller temporarily stops conveying the sheet P, the controller controls the driver to start driving and rotating the registration roller pair 12 at a predetermined timing to convey the sheet P to the secondary transfer nip in synchronization with the arrival of the full-color toner image formed on the intermediate transfer belt 30 to the secondary transfer nip.

[0039] At this time, the power supply applies a transfer voltage to the secondary transfer roller 36. The transfer voltage has the polarity opposite the polarity of the charged toner contained in the full-color toner image formed on the intermediate transfer belt 30. As a result, a transfer electric field is generated at the secondary transfer nip. The transfer electric field transfers the full-color toner image from the intermediate transfer belt 30 to the sheet P at a time. After the full-color toner image is transferred to the sheet P, residual toner that is not transferred to the sheet P remains on the intermediate transfer belt 30. The belt cleaner 35 removes the residual toner from the intermediate transfer belt 30. The removed toner is conveyed to a waste toner container.

[0040] After the full-color toner image is transferred to the sheet P, the sheet P is conveyed to the fixing device 20. The fixing device 20 fixes the full-color toner image onto the sheet P. The sheet P conveyed from the fixing device 20 is guided to a sheet ejection direction or a sheet re-feeding direction via the branching member 15. The branching member 15 switches a conveyance path to either one of the reverse path 40 and the sheet ejection path ejecting the sheet P to the outside of the body of the image forming apparatus.

[0041] In the single- sided printing mode, the branching member 15 is in the first state to open the sheet ejection path. As a result, the output roller pair 13 ejects the sheet P to the output tray 14 outside the body of the image forming apparatus 1.

[0042] In the double-sided printing mode, the branching member 15 is in the second state to close the sheet ejection path. As a result, the sheet P after the image is fixed on the first face is guided to the reverse path 40. The reverse roller pair 16 switches back the sheet P guided to the reverse path 40, and the sheet P is conveyed to the duplex unit 17 and conveyed again to the registration roller pair 12 to be re-fed.

[0043] Thus, the sheet P is conveyed to the fixing device 20. The fixing device 20 fixes the fullcolor toner image onto the second face of the sheet P in the same manner as the first face. Subsequently, the output roller pair 13 ejects the sheet P to the output tray 14 outside the body of the image forming apparatus 1.

[0044] In the above description, the image forming operation forms the full-color toner image on the sheet P. The image forming apparatus 1 can form a single color toner image by using any one of the four image forming devices 4Y, 4M, 4C, and 4K. The image forming apparatus 1 can also form a composite color toner image of two or three colors by using two or three of the image forming devices 4Y, 4M, 4C, and 4K.

[0045] With reference to FIG. 1, the fixing device 20 is described below. The fixing device 20 is used to cause the transferred toner image T borne on the sheet P to melt and permeate under heat and pressure to fix the toner image T onto the sheet P. The fixing device 20 includes a flexible fixing belt 21 as a fixing rotator that can perform endless travel while being heated.

[0046] The fixing device 20 includes a fixing section. In the fixing section, a fixing nip is formed. The sheet P to which the toner image is transferred in the image forming section A is conveyed in a conveyance direction F (see FIGS. 2A and 2B) and passes through the fixing nip. In the fixing nip, heat and pressure are applied to the toner image on the sheet P to fix the toner image onto the sheet P.

[0047] The fixing device 20 includes, in addition to the endless fixing belt 21, a pressure roller 22 as an opposed rotator that contacts the fixing belt 21 and applies pressure to the fixing belt 21 to form the fixing nip between the pressure roller 22 and the fixing belt 21. The pressure roller 22 rotates together with the fixing belt 21 to convey the sheet P along a sheet conveyance path in the conveyance direction.

[0048] A heater (a heat source) is disposed inside the loop of the fixing belt 21. The heater includes multiple halogen lamps to heat the inner surface of the fixing belt 21 at a portion other than the fixing nip.

[0049] The fixing device 20 includes a driving roller 204, a driven roller 203, and a separator 207 that are located downstream of the fixing belt 21 and the pressure roller 22 in the conveyance direction F. The driving roller 204 and the driven roller 203 form an auxiliary roller pair to convey the sheet P downstream from the fixing nip along the sheet conveyance path in the conveyance direction.

[0050] The driving roller 204 as a first roller is disposed on the sheet conveyance path between the fixing nip and the branching member 15 and is adjacent to the pressure roller 22.

[0051] The driven roller 203 as a second roller contacts the driving roller 204, is disposed on the sheet conveyance path between the fixing nip and the branching member 15, and is adjacent to the fixing belt 21 that is the fixing rotator heating the sheet P in the fixing nip.

[0052] The driving roller 204 and the driven roller 203 contact each other to form an auxiliary nip and assist the conveyance of the sheet P. The distance between the fixing nip and the auxiliary nip is set to be shorter than the length of the sheet P.

[0053] The driving roller 204 has at least the outer circumferential face made of rubber. The driven roller 203 is formed so that at least the outer circumferential face has a releasability and is harder than the outer circumferential face of the driving roller 204.

[0054] The driving roller 204 includes a roller shaft 204a and a cylinder 204b fitted and fixed to the roller shaft 204a. The cylinder 204b is made of elastic material such as silicone, ethylene - propylene-diene monomer (EPDM), urethane, or fluororubber, which gives a high friction coefficient to obtain a sheet conveying force.

[0055] The driven roller 203 includes a hollow metal pipe and a tube covering the outer circumferential face of the hollow metal pipe. The tube has a thickness from 30 p to 300 p and is made of perfluoroalkoxy alkane (PFA), ethylene tetrafluoroethylene (ETFE), or fluorinated ethylene propylene (FEP) to obtain a low friction coefficient.

[0056] The driven roller 203 includes the hollow metal pipe to reduce the thermal capacity of the driven roller 203. The driven roller 203 having a low thermal capacity is quickly heated by the heat generated while the fixing device fixes the image. Quickly heating the driven roller 203 prevents the water vapor evaporated from the sheet P from condensing on the driven roller 203.

[0057] The tube having the low friction coefficient and covering the outer circumferential face of the metal pipe makes it difficult for a small amount of toner that has not been completely melted while the image is fixed to adhere to the surface of the driven roller 203 after the image is fixed and to prevent the toner from accumulating on the driven roller 203. Since the driven roller 203 conveys the sheet P while always contacting the face of the sheet on which the image is formed, the driven roller 203 is configured as described above.

[0058] Both ends of the driven roller 203 are held by the body of the image forming apparatus 1 via holders and tension springs. The tension springs press the holders to press the driven roller203 against the driving roller 204. As a result, the driven roller 203 contacts the driving roller204 to form the auxiliary nip, which enables performing auxiliary conveyance of the sheet P.

[0059] FIGS. 2A and 2B are partial schematic side views of fixing devices known in the background art. FIG. 2A schematically illustrates a part of the fixing device 20 known in the background art, a guide 205 integrally formed with the fixing device 20, and a second guide 206.The fixing device 20 includes the driving roller 204, the driven roller 203, the guide 205, and the second guide 206. The driving roller 204 and the driven roller 203 convey the sheet P downstream in the conveyance direction, and the guide 205 and the second guide 206 guide the sheet P to the sheet ejection path.

[0060] FIG. 2B schematically illustrates a part of the fixing device that includes the second guide having a guide function. The fixing device 20 does not include the guide 205 but includes the second guide 206 having the guide function. In this example, the second guide 206 is not integrally formed with the fixing device 20.

[0061] FIGS. 3 A to 4C are partial schematic side views each illustrating a part of the fixing device of FIG. 2A. FIG. 3A illustrates the sheet P typically conveyed. As illustrated in FIG. 3A, the sheet P having passed through the fixing nip passes through the auxiliary nip formed by the driving roller 204 and the driven roller 203 and is then guided by the guide 205 to be ejected to the output tray 14. In contrast, FIG. 3B illustrates a case in which toner T adheres to one of the driving roller 204 and the driven roller 203 that form the auxiliary roller pair to convey the sheet P (in FIG. 3B, the driving roller 204). The toner T functions like glue and may cause the sheet P, which is conveyed after the toner T adheres to the driving roller 204, to stick to the driving roller 204. In this case, the guide 205 having a shape known in the background art cannot separate the sheet P from the toner T sticking the sheet P to the one of the driving roller 204 and the driven roller 203. As a result, the sheet P is wound around one of the driving roller 204 and the driven roller 203, causing the sheet jam, sheet folding, and wrinkle formation to occur (see FIG. 3C).

[0062] The rotational position of the guide 205 in each of FIGS. 4A to 4C is different from that in each of FIGS. 3A to 3C, but the same situation occurs. FIG. 4A illustrates the sheet P typically conveyed. In contrast, FIG. 4B illustrates a case in which the toner T adheres to one of the driving roller 204 and the driven roller 203 (in FIG. 4B, the driving roller 204). The toner T functions like glue and may cause the sheet P conveyed after the toner T adheres to the driving roller 204 to stick to the driving roller 203. In this case, the guide 205 having a shape known in the background art cannot separate the sheet P from the toner T sticking the sheet P to the one of the driving roller 204 and the driven roller 203. As a result, the sheet P is wound around one of the driving roller 204 and the driven roller 203, causing the sheet jam, sheet folding, and wrinkle formation to occur (see FIG. 4C).

[0063] FIGS. 5 A and 5B are partial schematic side views each illustrating a part of the fixing device of FIG. 2B. FIG. 5A illustrates the sheet P typically conveyed. In contrast, FIG. 5B illustrates a case in which the toner T adheres to one of the driving roller 204 and the driven roller 203 (in FIG. 5B, the driving roller 204). The toner T functions like glue and may cause the sheet P conveyed after the toner T adheres to the driving roller 204 to stick to the driving roller 203. As a result, the sheet P is wound around the one of the driving roller 204 and the driven roller 203, causing the sheet jam.

[0064] FIGS. 6A and 6B are partial schematic side views of the fixing device according to the embodiment of the present disclosure. Instead of the guide in the fixing device known in the background art illustrated in FIGS. 2A to 5B, the fixing device according to the embodiment of the present disclosure includes the separator having a separating performance and a guiding performance.

[0065] In the fixing device 20 illustrated in FIGS. 6A and 6B, the separator 207 is disposed close to the driven roller 203 and the driving roller 204 that form the auxiliary roller pair to convey the sheet P. A separator moving unit disposed in the fixing device 20 can move the position of the separator 207 between a first position illustrated in FIG. 6A and a second position illustrated in FIG. 6B.

[0066] As illustrated in FIGS. 6A and 6B, the separator 207 according to the embodiment of the present disclosure has a characteristic shape. In a cross section orthogonal to the conveyance direction of the sheet P and orthogonal to the front-back direction of the image forming apparatus, the separator 207 includes a projecting portion 207a continuously extending from a body of the separator 207. The projecting portion 207a has a shape along the outer shape of the driving roller 204. The driving roller 204 is an example of one roller of the auxiliary roller pair and the one roller opposite to the latest image face of the sheet P. The abovedescried latest image face means the first face of the sheet P in the single-sided printing mode and the second face of the sheet P switched back by the reverse roller pair 16 in the double-sided printing mode. The driving roller 204 has a groove facing the separator 207. The upstream end of the projecting portion 207a of the separator 207 in the conveyance direction enters the groove. Alternatively, the upstream end of the projecting portion 207a is disposed at the axial end of the driving roller 204. The outer face of the projecting portion 207a of the separator 207 extends along the outer circumferential surface of the driving roller 204 at one of both sides of the groove. The projecting portion 207a of the separator 207 extends along a tangent of the outer circumferential surface of the driving roller 204. In other words, the separator 207 is adjacent to the driving roller 204 as the first roller and downstream from the driving roller 204 along the sheet conveyance path in the conveyance direction. In addition, the separator 207 includes the projecting portion 207a, and the shape of the projecting portion 207a in a cross section orthogonal to the conveyance direction and an axial direction of the driving roller 204 has a part along a circle in a cross section of the driving roller 204 that is orthogonal to the conveyance direction and the axial direction. The cross section of the driving roller does not include the grooves described above but includes the auxiliary nip. The cross section defining the cross-sectional circle of the driving roller is different from the cross section defining the cross-sectional shape of the projecting portion. In other words, the separator 207 includes the projecting portion 207a having a part along the circumferential surface of the driving roller 204 as the first roller in the cross-section of the driving roller 204. Thus, even when the toner T functions like glue and sticks the sheet P to the driving roller 204, the projecting portion 207a of the separator 207 separates the sheet P rotating together with the driving roller 204 from the driving roller 204. As a result, the separator 207 can separate the sheet P from the driving roller 204, and the auxiliary roller pair can convey the sheet without folding the sheet P or forming the wrinkles. Therefore, the above-described configuration can prevent the occurrence of the sheet folding, the wrinkles of the sheet, and the sheet jam.

[0067] In addition, the shape of the projecting portion 207a of the separator 207 in the cross section orthogonal to the conveyance direction of the sheet P and the axial direction of the driving roller 204 has an upstream end in the conveyance direction of the sheet P. The upstream end of the projecting portion 207a is inside the circumferential surface of the driving roller 204 in the cross-section. In other words, assuming that the cross section of the projecting portion 207a is superimposed on the cross section of the driving roller, the upstream end of the projecting portion 207a is inside the circle in the cross section of the driving roller.Additionally, the shape of the projecting portion has a curve extending from the upstream end, and the curve is along the circle in the cross section of the driving roller. As a result, the separator 207 can separate the sheet P from the driving roller 204 without damaging the sheet P.

[0068] The projecting portion 207a of the separator 207 is located in a black hatching region in FIGS. 6A and 6B between a vertical line passing through the center of the driven roller 203and a vertical line passing through the center of the driving roller 204, and the black hatching region is perpendicular to a line connecting the centers of the driven roller 203 and the driving roller 204.

[0069] FIG. 7 is a partial schematic side view of the fixing device according to another embodiment of the present disclosure. The fixing device 20 in FIG. 7 does not include the separator 207 in the embodiment of FIG. 6 that is an independently rotatable component. Alternatively, the fixing device in FIG. 7 includes a separator 208 fixed to a part of the fixing device housing. The driving roller 204 has a groove facing the separator 208. The upstream end of a projecting portion 208a of the separator 208 in the conveyance direction enters the groove. Alternatively, the upstream end of the projecting portion 208a in the conveyance direction is disposed at the axial end of the driving roller 204. The shape of the projecting portion 208a of the separator 208 in the cross section orthogonal to the conveyance direction of the sheet P and the axial direction of the driving roller 204 has a part along the circle in the cross section of the driving roller 204 orthogonal to the conveyance direction of the sheet P and the axial direction of the driving roller 204. Assuming that the cross section of the projecting portion 208a is superimposed on the cross section of the driving roller, the upstream end of the projecting portion 208a in the conveyance direction is inside the circle in the cross section of the driving roller, and the shape of the projecting portion 208a has a portion extending from the upstream end and along the circle in the cross section of the driving roller. In other words, the outer face of the projecting portion 208a has a shape overlapping a tangent of the circle in the cross section of the driving roller. Thus, even when the toner T functions like glue and sticks the sheet P to the driving roller 204, the projecting portion 208a of the separator 208 separates the sheet P rotating together with the driving roller 204 from the driving roller 204. As a result, the separator 207 can separate the sheet P from the driving roller 204, and the auxiliary roller pair can convey the sheet without folding the sheet P or forming the wrinkles.

[0070] In this embodiment, the projecting portion 208a of the separator 208 is located in a black hatching region in FIG. 7 between the vertical line passing through the center of the driven roller 203 and the vertical line passing through the center of the driving roller 204, and the black hatching region is perpendicular to the line connecting the centers of the driven roller 203 and the driving roller 204.

[0071] FIGS. 8A and 8B are partial schematic side views of the fixing devices. FIG. 8A illustrates an angle 9 formed by one side face 205b of the guide 205 and the tangent of the circle in the cross section of the driving roller 204 in the fixing device known in the background art. FIG. 8B illustrates an angle 9 formed by the projecting portion 207a of the separator 207 and the tangent of the circle in the cross section of the driving roller 204 in the fixing device according to the present embodiment.

[0072] In the configuration known in the background art illustrated in FIG. 8A, since the angle 9 is equal to or larger than 90°, the guide cannot separate the sheet P stuck to the driving roller from the driving roller, which causes the sheet folding and the wrinkles of the sheet.

[0073] The projecting portion 207a of the separator 207 according to the present embodiment illustrated in FIG. 8B forms an acute angle 9 with respect to the tangent of the circle in the cross section of the driving roller 204 (in other words, the tangent of the circumferential surface in the cross section of the driving roller 204) that is the example of one roller of the auxiliary roller pair and the one roller opposite to the latest image face of the sheet P. As described above, since the angle 9 is smaller than 90°, the projecting portion 207a separates a part of the sheet stuck to the driving roller 204 immediately after the part of the sheet sticks to the driving roller 204. As a result, the projecting portion 207a can separate the sheet from the driving roller 204 without damaging the sheet P.

[0074] The fixing device includes multiple separators 207 arranged in the front-back direction, and the multiple separators 207 have angles 9, each of which is as illustrated in FIG. 8B. The angles 9 may not be the same angle. The angle 9 formed by the projecting portion 207a adjacent to an end region of the driving roller 204 in the axial direction of the driving roller may be designed to be smaller than the angle 9 formed by the projecting portion 207a adjacent to the center region of the driving roller 204 in the axial direction. Specifically, an angle formed by a part of the shape of the projecting portion 207a of the separator 207 adjacent to the end region of the driving roller 204 in the axial direction and the tangent of the circle in the cross section of the driving roller 204 may be designed to be smaller than an angle formed by a part of the shape of the projecting portion 207a of the separator 207 adjacent to the center region of the driving roller 204 in the axial direction and the tangent of the circle in the cross section of the driving roller 204. The toner is easily adhered to the end region of the driving roller 204 in the axial direction due to the temperature rise in end regions of the fixing device. In such a case, the above-described configuration can easily separate the sheet P stuck to the end region in the axial direction from the driving roller 204.

[0075] FIGS. 9A and 9B are schematic perspective views of the arrangements of the separators 207. FIG. 9A illustrates the arrangement of the separators 207 illustrated in FIGS. 6A and 6B to illustrate positions of the projecting portions 207a. As illustrated in FIG. 9A, the driving roller 204 has multiple grooves arranged in the axial direction. The groove is formed over the entire outer circumference of the driving roller 204. In other words, the cross-sectional shape of the driving roller at the position at which the driving roller has the groove is a circle smaller than the circle in the cross section of the driving roller without the groove. The separators 207 are arranged corresponding to the grooves. A part of the separator enters the groove. In addition, the separators 207 are arranged at both ends of the driving roller 204. The above-described structure enables placing the tip of the projecting portion 207a of theseparator 207 between the bottom of the groove and the imaginary outer circumferential surface of the driving roller 204. The imaginary outer circumferential surface means the outer circumferential surface of the driving roller 204 assumed that the driving roller 204 has no groove. Additionally, the above-described structure enables forming the tip of the projecting portion 207a to be along the tangent of the imaginary outer circumferential surface and forming the entire projecting portion 207a so as to draw a smooth curve from the tip. Increasing the number of the projecting portions 207a having the separation function enables easily separating the sheet P from the driving roller 204.

[0076] FIG. 9B illustrates the arrangement of the separators 208 illustrated in FIG. 7 to illustrate the positions of the projecting portions 208a. Similarly, the driving roller 204 has multiple grooves arranged in the axial direction as illustrated in FIG. 9B. The projecting portions 208a of the separators 208 are arranged corresponding to the grooves. A part of the projecting portion 208a enters the groove.

[0077] FIGS. 10A to 10D are schematic perspective views of the separators 207 arranged differently from the above embodiments. In the example of FIG. 10A, the driving roller 204 has no groove arranged in the axial direction. In this case, the separators 207 including the projecting portions 207a are disposed at positions outside both ends of the driving roller 204 in the axial direction. Thus, the sheet P and the toner can be separated well.

[0078] In the example of FIG. 10B, the driving roller 204 has grooves arranged at intervals in the axial direction. The projecting portions 207a of the separators 207 are arranged corresponding to the grooves in both end regions of the driving roller 204 in the axial direction. Additionally, the projecting portions 207a of the separators 207 are disposed at the positions outside both ends of the driving roller 204 in the axial direction. The guides 205 are disposed adjacent to a center region of the driving roller 204 in the axial direction, and the separator including the projection portion is not disposed adjacent to the center region. The reason why the projecting portions 207a of the separators 207 are arranged adjacent to both end regions of the driving roller 204 is as follows. The temperature rise in both end regions in the fixing device is likely to cause the toner to adhere to both end regions of the driving roller 204. In this case, arranging the separators 207 including the projecting portions 207a adjacent to both end regions of the driving roller 204 in the axial direction satisfactorily separates the sheet P from the driving roller 204.

[0079] In the example of FIG. 10C, the driving roller 204 has grooves arranged at intervals in the axial direction. The projecting portions 207a of the separators 207 are arranged corresponding to the grooves in both end regions of the driving roller 204 in the axial direction. Additionally, the projecting portions 207a of the separators 207 are disposed at the positions outside both ends of the driving roller 204 in the axial direction. In FIG. 10C, oneseparator 207 includes multiple projecting portions 207a. For the same reason as in the above examples, the above-described structure can enhance a separation performance separating the sheet P from both end regions of the driving roller 204 in the axial direction.

[0080] In the example of FIG. 10D, the driving roller 204 has grooves arranged at intervals in the axial direction. The projecting portions 207a of the separators 207 are arranged corresponding to the grooves in the center and both end regions of the driving roller 204 in the axial direction. Additionally, the projecting portions 207a of the separators 207 are disposed at the positions outside both ends of the driving roller 204 in the axial direction. In particular, the number of the projecting portions 207a on the separator 207 disposed adjacent to both end regions of the driving roller 204 in the axial direction is larger than the number of the projecting portions 207a on the separator 207 disposed adjacent to the center region of the driving roller 204 in the axial direction in FIG. 10D. In the example of FIG. 10D, the separator 207 disposed adjacent to each of both end regions of the driving roller 204 in the axial direction, as an end separator, includes two projecting portions 207a. The separator 207 disposed adjacent to the center region of the driving roller 204 in the axial direction, as a center separator, includes one projecting portion 207a. The above-described structure can enhance the separation performance separating the sheet P from both end regions of the driving roller 204 in the axial direction. Even when the temperature rise in both end regions in the fixing device causes the sheet P to easily stick to the end region of the driving roller 204 in the axial direction, the above-described structure easily separates the sheet P from the driving roller 204.

[0081] Aspects of the present disclosure are, for example, as follows.(First Aspect)In a first aspect, a fixing device includes a fixing section, a conveyance auxiliary roller pair, and a separator. The fixing section includes a fixing member and an opposed rotator that form a fixing nip. The fixing section fixes an image onto a sheet. The sheet is conveyed from the fixing section, and the conveyance auxiliary roller pair conveys the sheet downstream in a conveyance direction. The separator is located downstream of the conveyance auxiliary roller pair. The separator separates the sheet from one roller of the conveyance auxiliary roller pair. The one roller is opposite to the latest image face of the sheet P. The separator includes a projecting portion. Viewed in a direction orthogonal to the conveyance direction of the sheet, the projecting portion continuously extends from an outer shape of the one roller of the conveyance auxiliary roller pair, the one roller opposite to the latest image face of the sheet. (Second Aspect)In a second aspect, the projecting portion in the fixing device according to the first aspect extends inward from the outer shape of the one roller of the conveyance auxiliary roller pair, the one roller opposite to the latest image face of the sheet.(Third Aspect)In a third aspect, an angle 9 of the projecting portion in the fixing device according to the first aspect or the second aspect with respect to a tangent line of the outer shape of the one roller of the conveyance auxiliary roller pair, the one roller opposite to the latest image face of the sheet is an acute angle.(Fourth Aspect)In a fourth aspect, the fixing device according to the third aspect includes separators including the separator. One separator is in an end region in the axial direction, and the other separator is in a center region in the axial direction. An angle 9 of a projecting portion of the one separator with respect to the tangent line is smaller than an angle 9 of a projecting portion of the other separator with respect to the tangent line.(Fifth Aspect)In a fifth aspect, the fixing device according to any one of the first to fourth aspects includes separators including the separator, and the separators are disposed outside both ends of the one roller of the conveyance auxiliary roller pair in the axial direction. The one roller is opposite to the latest image face of the sheet. The one roller is continuously disposed in the axial direction.(Sixth Aspect)The fixing device according to any one of the first to fourth aspects includes the one roller of the conveyance auxiliary roller pair, and the one roller opposite to the latest image face of the sheet. The roller is intermittently disposed in the axial direction, and the separator is disposed between the roller and the roller.(Seventh Aspect)In the seventh aspect, the fixing device according to any one of the first to sixth aspects includes a greater number of separators in an end region in the axial direction than separators in a center region in the axial direction.(Eighth Aspect)In an eighth aspect, an image forming apparatus includes the fixing device according to any one of the first to seventh aspects.

[0082] The above-described embodiments are illustrative and do not limit the present invention. Thus, numerous additional modifications and variations are possible in light of the above teachings. For example, elements and / or features of different illustrative embodiments may be combined with each other and / or substituted for each other within the scope of the present invention.

[0083] This patent application is based on and claims priority to Japanese Patent Application No. 2024-035686, filed on March 8, 2024, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.[Reference Signs List]

[0084] 1: image forming apparatus20: fixing device21: fixing belt (fixing rotator)22: pressure roller (opposed rotator)203: driven roller (conveyance auxiliary roller pair)204: driving roller (conveyance auxiliary roller pair)205: separator205a: projecting portionP: sheet

Claims

[CLAIMS]

1. A fixing device comprising: a fixing rotator; a heater inside the fixing rotator; an opposed rotator contacting the fixing rotator to form a fixing nip to fix an image on a sheet and convey the sheet along a sheet conveyance path in a conveyance direction; an auxiliary roller pair downstream from the fixing nip in the conveyance direction to convey the sheet from the fixing nip along the sheet conveyance path in the conveyance direction, the auxiliary roller pair including: a first roller adjacent to the opposed rotator; and a second roller contacting the first roller and adjacent to the fixing rotator; and a separator adjacent to the first roller and downstream from the first roller along the sheet conveyance path in the conveyance direction, the separator including a projecting portion having a part along a circumferential surface of the first roller in a cross-section orthogonal to the conveyance direction and an axial direction of the first roller.

2. The fixing device according to claim 1, wherein the projecting portion further has a part inside the circumferential surface of the first roller in the cross-section.

3. The fixing device according to claim 1 or 2, wherein the projecting portion further has a part forming an acute angle with a tangent to the circumferential surface of the first roller in the cross- section.

4. The fixing device according to claim 3, further comprising multiple separators including the separator, the multiple separators arranged in the axial direction of the first roller, wherein the multiple separators respectively include projecting portions, the part of the projecting portion forms a first angle with the tangent to the circumferential surface of the first roller in the cross-section at each end region of the first roller in the axial direction, the part of the projecting portion forms a second angle with the tangent to the circumferential surface of the first roller in the cross-section at a center region of the first roller in the axial direction, and the first angle is smaller than the second angle.

5. The fixing device according to any one of claims 1 to 4,wherein the separator is disposed outside at least one end of the first roller in the axial direction.

6. The fixing device according to any one of claims 1 to 5, wherein the first roller has a groove into which the part of the projecting portion of the separator enters.

7. The fixing device according to any one of claims 1 to 6, further comprising multiple separators including the separator, wherein the multiple separators include: an end separator at an end region of the first roller in the axial direction; and a center separator at a center region of the first roller in the axial direction, the end separator includes a first number of projecting portions, and the center separator includes a second number smaller than the first number of projecting portions.

8. An image forming apparatus comprising the fixing device according to any one of claims 1 to 7.

Images