Image formation device

Abstract

To provide an image formation device capable of achieving downsizing, inhibiting water vapor generated from a sheet passing through a nip part from flowing back into a fuser and inhibiting failure caused by water condensed and remained on a fixation frame.SOLUTION: An image formation device 1 comprises: an exhaust fan 89 that is located upstream from an upstream end N1U of a nip part N1 of a fuser 7 in a conveyance direction DT1 and above the upstream end N1U of the nip part N1; and a frame 50 that is located upstream from the upstream end N1U of the nip part N1 in the conveyance direction DT1 and below the upstream end N1U of the nip part N1. The frame 50 partitions a first space AS1 located upstream from the upstream end N1U of the nip part N1 in the conveyance direction DT1 and a second space AS2 located below the fixation frame 70. The frame 50 includes an opening 60 for communicating the first space AS1 and the second space AS2 at a downstream end 50D in the conveyance direction DT1.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Patent Document 1 discloses an example of a conventional image forming apparatus. As shown in Figures 1 and 2, in this image forming apparatus, the fixing unit has an upper roller and a lower roller that nip and heat the recording paper conveyed in the conveyance direction at a nip portion, and a fixing frame that covers the lower roller from below. The housing houses the fixing unit.

[0003] The suction fan is located upstream of the upstream end of the nip portion in the transport direction and below the upstream end of the nip portion, while the exhaust fan is located downstream of the downstream end of the nip portion in the transport direction and above the downstream end of the nip portion.

[0004] The suction fan draws air from a space located upstream of the upstream end of the nip in the transport direction into a duct and guides it to the exhaust fan below the fixing frame. The exhaust fan exhausts the air inside the housing, including the air guided by the duct and the air in a space located downstream of the downstream end of the nip in the transport direction, to the outside of the housing.

[0005] Here, water vapor generated from the sheet passing through the nip portion tends to stagnate in the space located downstream in the conveying direction from the downstream end of the nip portion, and there is a risk that this stagnant water vapor will flow back into the fixing portion and condense.

[0006] In this regard, this image forming apparatus uses a suction fan and an exhaust fan to prevent water vapor from flowing back into the fixing unit, thereby preventing the problem of condensed water accumulating on the fixing frame. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-115368 Summary of the Invention [Problem to be solved by the invention]

[0008] However, the placement of the suction fan and the exhaust fan in the conventional image forming apparatus is subject to many restrictions due to the space within the housing, making it difficult to reduce the size of the apparatus.

[0009] The present invention has been made in consideration of the above-mentioned conventional situation, and aims to provide an image forming device that can be made compact, can prevent water vapor generated from a sheet passing through the nip portion from flowing back into the fixing unit, and can prevent the problem of condensed water accumulating on the fixing frame. [Means for solving the problem]

[0010] The image forming apparatus of the present invention is a fixing device having a heating element and a pressure element that sandwich and heat a sheet conveyed in a conveyance direction at a nip portion, and that thermally fixes a toner image on the sheet passing through the nip portion, the fixing device having a fixing frame that covers from below one of the heating element and the pressure element that is located below the other; a housing that houses the fixing unit; an exhaust fan that exhausts air from within the housing to the outside of the housing, the exhaust fan being located upstream of an upstream end of the nip portion in the conveying direction and above the upstream end of the nip portion; a frame located upstream of the upstream end of the nip portion in the conveying direction and below the upstream end of the nip portion, the frame having a guide surface formed thereon to guide a sheet being conveyed; Equipped with the frame defines a first space located upstream of the upstream end of the nip portion in the transport direction and a second space located below the fixing frame, The frame has an opening at a downstream end in the conveying direction that connects the first space and the second space.

[0011] The image forming apparatus of the present invention does not have the suction fan of the conventional image forming apparatus, and the exhaust fan is located upstream of the nip portion of the fixing unit in the conveying direction, which allows the image forming apparatus to be made compact.

[0012] The opening in the frame connects the first space and the second space at the downstream end of the frame. This creates an exhaust path within the housing that runs from a space located downstream of the downstream end of the nip in the transport direction through the second space, the opening in the frame, the first space, and the exhaust fan to the outside of the housing. This exhaust path allows the image forming apparatus to reliably exhaust air containing water vapor from around the fixing unit to the outside of the housing.

[0013] Therefore, the image forming apparatus of the present invention can be made smaller and can prevent water vapor generated from a sheet passing through the nip portion from flowing back into the fixing unit, thereby preventing the problem of condensed water accumulating on the fixing frame. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a perspective view of an image forming apparatus according to a first embodiment. [Figure 2] FIG. 2 is a partial perspective view of the image forming apparatus according to the first embodiment. [Figure 3] FIG. 3 is a schematic cross-sectional view of the image forming apparatus according to the first embodiment. [Figure 4] FIG. 4 is a partial schematic cross-sectional view showing an enlarged essential part of FIG. [Figure 5] FIG. 5 is a schematic top view showing the re-feeding unit, the side frames, the connecting members, etc. [Figure 6] FIG. 6 is a partial perspective view showing the fixing unit, the exhaust duct, the exhaust fan, the frame, etc. [Figure 7]FIG. 7 is a partial perspective view showing the fixing unit, the exhaust duct, the exhaust fan, the frame, etc. [Figure 8] FIG. 8 is a perspective view showing the frame. [Figure 9] FIG. 9 is a partial bottom view showing the frame. [Figure 10] FIG. 10 is a partial perspective view showing a re-feeding unit and a frame of an image forming apparatus according to a second embodiment. [Figure 11] FIG. 11 is a partial perspective view showing the frame. [Figure 12] FIG. 12 is a partial bottom view showing the frame. [Figure 13] FIG. 13 is a partial cross-sectional view showing the cross section AA of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, first and second embodiments of the present invention will be described with reference to the drawings.

[0016] Example 1 As shown in FIG. 1, an image forming apparatus 1 according to the first embodiment is an example of a specific aspect of the image forming apparatus of the present invention.

[0017] In Fig. 1, the side of the operation panel 10P of the image forming apparatus 1 is the front. The side to the left when facing the operation panel 10P is the left side. The front-to-back, left-to-right, and up-to-down directions shown in Fig. 2 and subsequent figures are all shown corresponding to the directions shown in Fig. 1.

[0018] The width direction of the image forming apparatus 1 is a direction perpendicular to the front-rear direction and the up-down direction, and is a direction perpendicular to a conveying direction DT1 described later. In this embodiment, the left side is one of the width directions, and the right side is the other of the width directions. The width directions shown in Figure 2 and subsequent figures are all shown in accordance with Figure 1.

[0019] <General configuration of image forming apparatus> As shown in FIGS. 1 and 2, the image forming apparatus 1 is a so-called multifunction device, and includes a housing 9, a reading housing 10, an operation panel 10P, and a cover 11.

[0020] The housing 9 is substantially box-shaped. As shown in Figures 1 and 3, a discharge tray 9T is formed on the top surface of the housing 9.

[0021] The reading housing 10 is a flat, approximately box-shaped body, and is located above the housing 9. The reading housing 10 is supported by a pair of support parts that are located to the left and right of the discharge tray 9T on the top surface of the housing 9 and that protrude upward.

[0022] The reading housing 10 houses an image reading unit (not shown) that reads an image of a document placed on a document placement surface (not shown) located on the top surface of the reading housing 10.

[0023] 1, the operation panel 10P protrudes forward from the left portion of the front end of the reading housing 10. The operation panel 10P is a touch panel or the like, and receives operation inputs and displays various information related to the image forming apparatus 1.

[0024] The cover 11 is located above the reading housing 10. The rear end of the cover 11 is connected to the reading housing 10 via a hinge (not shown), so that the cover 11 can be opened and closed. When the cover 11 is closed, it covers the document placement surface. On the other hand, when the cover 11 is open, it exposes the document placement surface. In this state, the user can place a document on the document placement surface or remove a placed document.

[0025] As shown in Figures 3 and 4, the image forming apparatus 1 includes a sheet tray 9C housed in a housing 9, a feeding section 20, an image forming section 3, a scanner section 8, a fixing device 7, a post-fixing conveying roller pair 28, a discharge roller pair 29, and a re-conveying unit 30.

[0026] As shown in FIGS. 2 and 5, the image forming apparatus 1 includes a main board CB housed in the housing 9 along the left side surface of the housing 9.

[0027] The main board CB functions as the control unit C1 and has a calculation unit mainly consisting of a CPU, ROM, and RAM (not shown), and hardware for controlling the semiconductor laser, motors, etc. The ROM stores programs for the CPU to control various operations of the image forming apparatus 1 and programs for executing the recognition process. The RAM functions as a storage area for temporarily recording data and signals used when the CPU executes the programs, or as a work area for data processing.

[0028] The control unit C1 controls the entire image forming apparatus 1 including the feeding unit 20, the image forming unit 3, the scanner unit 8, the fixing unit 7, the post-fixing conveying roller pair 28, the discharge roller pair 29 and the re-conveying unit 30.

[0029] As shown in FIG. 3, the sheet tray 9C is located at the bottom of the housing 9. The sheet tray 9C accommodates stacked sheets SH before images are formed on them. The sheets SH are paper, overhead projector sheets, etc. The discharge tray 9T supports the sheets SH after image formation has been completed.

[0030] The feeding section 20, the image forming section 3, the scanner section 8, the fixing unit 7, the post-fixing conveying roller pair 28, and the discharge roller pair 29 are located above the sheet tray 9C in the housing 9. The re-conveying unit 30 is located below the image forming section 3 and the fixing unit 7 in the housing 9, and above the sheet tray 9C.

[0031] The image forming apparatus 1 includes a conveying path P1 and a re-conveying path P2.

[0032] The conveying path P1 is a path that guides the sheet SH from the sheet tray 9C toward the image forming unit 3, and then guides the sheet SH that has passed through the image forming unit 3 and the fixing device 7 and has a toner image thermally fixed to one side toward the discharge tray 9T.

[0033] More specifically, the conveying path P1 starts from the front end of the sheet tray 9C, makes an upward U-turn, passes through the feeding unit 20, then proceeds backward approximately horizontally, passes through the image forming unit 3 and the fixing unit 7, and then makes an upward U-turn, passes through the post-fixing conveying roller pair 28 and the discharge roller pair 29, and reaches the discharge tray 9T. The conveying direction of the sheet SH conveyed on the conveying path P1 is defined as DT1. The width direction is perpendicular to the conveying direction DT1.

[0034] The re-conveying path P2 is a path that turns over the sheet SH, one side of which has a toner image thermally fixed, and guides it in the re-conveying direction DT2, returning it to the image forming unit 3. The re-conveying path P2 guides the turned-over sheet SH to a junction position J1 that is located upstream of the image forming unit 3 in the conveying direction DT1 on the conveying path P1.

[0035] More specifically, the re-conveying path P2 travels along the back of the housing 9, making a downward U-turn from the discharge roller pair 29, changes direction to face forward at a position below the image forming unit 3 and the fixing device 7 and above the sheet tray 9C, travels approximately horizontally, passes through the re-conveying unit 30, and then joins the conveying path P1 at the joining position J1.

[0036] The feeding section 20 includes a feeding roller 21, a separation roller 22, a separation pad 22A, a conveying roller pair 23, and a registration roller pair 24.

[0037] The feed roller 21 is located at the upstream end of the conveying path P1 in the conveying direction DT1. The feed roller 21 sends out the sheets SH stored in the sheet tray 9C to the conveying path P1. When multiple sheets SH sent out by the feed roller 21 are stacked, the separation roller 22 and the separation pad 22A separate them one by one.

[0038] The conveying roller pair 23 is located downstream of the separation roller 22 in the conveying direction DT1 on the conveying path P1 and upstream of the joining position J1 in the conveying direction DT1. The conveying roller pair 23 conveys the sheet SH along the conveying path P1 toward the joining position J1.

[0039] The registration roller pair 24 is located downstream of the junction J1 on the conveying path P1 in the conveying direction DT1 and upstream of the image forming unit 3 in the conveying direction DT1. The registration roller pair 24 has registration rollers 24A and 24D. The registration roller 24A faces the registration roller 24D from above. The registration roller 24D is an example of the "conveying roller" in the present invention.

[0040] The pair of registration rollers 24 transports the sheet SH that has passed through the joining position J1 toward the image forming unit 3 and the fixing unit 7. At this time, the pair of registration rollers 24, while stopped, contacts the leading edge of the sheet SH that has passed through the joining position J1, and starts rotating after a predetermined time has elapsed, thereby suppressing skew of the sheet SH.

[0041] In this way, the sheet SH fed by the feeding section 20 toward the image forming section 3 passes through the image forming section 3 and the fixing device 7 in the portion of the conveying path P1 that extends substantially horizontally.

[0042] The image forming unit 3 is a direct transfer monochrome electrophotographic image forming unit, and is a process cartridge detachably supported in a housing 9.

[0043] The image forming unit 3 has a photosensitive drum 5 and a transfer roller 6. The photosensitive drum 5 rotates around a rotation axis X5 extending in the width direction. The transfer roller 6 is located below the photosensitive drum 5, sandwiching a substantially horizontally extending portion of the conveying path P1 therebetween. The transfer roller 6 rotates while sandwiching the conveyed sheet SH together with the photosensitive drum 5.

[0044] The image forming unit 3 also includes a developing roller 5A located around the photosensitive drum 5, a charger 5E, and a toner storage unit 5D.

[0045] The scanner unit 8 is located above the image forming unit 3. The scanner unit 8 has a laser light source, a polygon mirror, an fθ lens, a reflecting mirror, etc. The scanner unit 8 irradiates the photosensitive drum 5 with a laser beam from above.

[0046] In the image forming unit 3, the surface of the photosensitive drum 5 is uniformly positively charged by the charger 5E as it rotates, and then exposed to high-speed scanning of a laser beam emitted from the scanner unit 8. As a result, an electrostatic latent image corresponding to the image to be formed on the sheet SH is formed on the surface of the photosensitive drum 5.

[0047] Next, the developing roller 5A supplies the toner stored in the toner storage section 5D to the surface of the photosensitive drum 5 in accordance with the electrostatic latent image, thereby forming a toner image. Then, when the sheet SH, conveyed by the pair of registration rollers 24, passes between the photosensitive drum 5 and the transfer roller 6, the upward surface of the sheet SH faces the photosensitive drum 5. The toner image carried on the surface of the photosensitive drum 5 is transferred to the upward surface of the sheet SH.

[0048] The fixing unit 7 is located behind the image forming unit 3. In other words, the image forming unit 3 is provided upstream of the fixing unit 7 in the transport direction DT1. The fixing unit 7 has a heating element 7A and a pressure roller 7B. The pressure roller 7B is an example of the "pressure element" in the present invention.

[0049] 4, the heating element 7A includes an endless belt, a guide member that supports the endless belt from its inner periphery so that it can circulate, and a heater that heats the endless belt from its inner periphery. The pressure roller 7B is a drive roller made of a flexible and heat-resistant material and is located below the heating element 7A.

[0050] The heating element 7A is pressed against the pressure roller 7B. The endless belt of the heating element 7A is driven by the pressure roller 7B. The endless belt of the heating element 7A and the pressure roller 7B form a nip portion N1 that nips the sheet SH. The nip portion N1 is an area that extends slightly longer in the width direction than the width of the sheet SH and extends slightly shorter in the conveying direction DT1.

[0051] The heating element 7A and the pressure roller 7B sandwich the sheet SH conveyed in the conveying direction DT1 at the nip portion N1 and apply heat and pressure to the sheet SH. As a result, the fixing device 7 thermally fixes the toner image on the sheet SH passing through the nip portion N1.

[0052] The post-fixing conveying roller pair 28 nips the sheet SH that has passed through the fixing unit 7, and conveys it along the portion of the conveying path P1 that makes an upward U-turn on the rear side of the housing 9.

[0053] The pair of discharge rollers 29 is located at the most downstream side of the conveying path P1. The pair of discharge rollers 29 is controlled by the control unit C1 to rotate forward and backward.

[0054] When an image is formed on only one side of the sheet SH, the discharge roller pair 29 rotates forward while nipping the sheet SH being transported by the post-fixing transport roller pair 28, thereby discharging the sheet SH onto the discharge tray 9T.

[0055] When performing image formation on both sides of the sheet SH, while the pair of discharge rollers 29 is discharging the sheet SH toward the discharge tray 9T, the control unit C1 switches the pair of discharge rollers 29 from forward rotation to reverse rotation at the timing after the pair of post-fixing conveying rollers 28 no longer nip the sheet SH. As a result, the pair of discharge rollers 29 reverses the sheet SH and guides the sheet SH to the re-conveyance path P2.

[0056] As shown in FIGS. 3 and 5, the re-conveying unit 30 includes a re-conveying tray 33, a pair of skew rollers 31, and a pair of re-conveying rollers 32.

[0057] The re-conveying tray 33 extends in a generally flat plate shape in the front-rear and left-right directions. The upper surface of the re-conveying tray 33 is aligned with a portion of the re-conveying path P2 that extends generally horizontally forward at a position below the image forming unit 3 and the fixing unit 7 and above the sheet tray 9C.

[0058] 5, a biasing guide 33G is located on one edge side in the width direction of the upper surface of the re-feeding tray 33. The biasing guide 33G slides against one edge in the width direction of the sheet SH being re-feeded along the upper surface of the re-feeding tray 33, thereby positioning the sheet SH in the width direction.

[0059] The center in the width direction of the sheet SH positioned in the width direction by the shifting guide 33G is indicated by a straight line CL1.

[0060] The oblique roller pair 31 is located on the upstream end side of the re-conveying tray 33 in the re-conveying direction DT2. The oblique roller pair 31 is located on one side in the width direction from the center CL1 in the width direction. The oblique roller pair 31 has a drive roller 31D and an oblique roller 31A.

[0061] The drive roller 31D contacts the sheet SH from below as it is re-conveyed along the upper surface of the re-conveying tray 33, and conveys the sheet SH in the re-conveying direction DT2.

[0062] The oblique roller 31A faces the drive roller 31D from above. The rotation axis of the oblique roller 31A is inclined so as to shift downstream in the re-conveyance direction DT2 as it moves from one side in the width direction to the other.

[0063] The skew rollers 31A cause the sheet SH being re-conveyed along the upper surface of the re-conveyance tray 33 to travel obliquely in one direction in the width direction. As a result, one edge of the sheet SH in the width direction comes into sliding contact with the biasing guide 33G. The pair of skew rollers 31 is located on the front side of the paper in FIGS. 3 and 4.

[0064] 3 and 5, the re-conveying roller pair 32 is located on the downstream end side of the re-conveying tray 33 in the re-conveying direction DT2. The re-conveying roller pair 32 is located at the center CL1 in the width direction. The re-conveying roller pair 32 takes over the sheet SH, which is being re-conveyed along the upper surface of the re-conveying tray 33, from the oblique running roller pair 31, and conveys it toward the joining position J1.

[0065] 3, the re-conveyed sheet SH merges with the conveying path P1 at a merging position J1. Then, the image forming unit 3 transfers a toner image onto the other side of the re-conveyed sheet SH, and the fixing unit 7 thermally fixes the toner image onto the other side of the sheet SH. Thereafter, the post-fixing conveying roller pair 28 and the discharge roller pair 29 discharge the sheet SH, with the images formed on both sides, onto the discharge tray 9T.

[0066] <Side frames and connecting members> As shown in FIG. 5, the image forming apparatus 1 includes a pair of side frames 90L and 90R, and two connecting members 91F and 91B.

[0067] The side frame 90L extends in the front-rear and up-down directions along the left side surface of the housing 9. The side frame 90R extends in the front-rear and up-down directions along the right side surface of the housing 9.

[0068] The side frames 90L and 90R are positioned on one side and the other side in the width direction relative to the sheet tray 9C, the feeding section 20, the image forming section 3, the scanner section 8, the fixing unit 7, the post-fixing conveying roller pair 28, the discharge roller pair 29, and the re-conveying unit 30. The side frames 90L and 90R support the image forming section 3, the fixing unit 7, etc.

[0069] In this embodiment, both side frames 90L and 90R are resin members manufactured by injection molding of thermoplastic resin or the like.

[0070] As shown in FIG. 3, the connecting member 91F is located upstream of the pair of registration rollers 24 in the conveying direction DT1 and below the feed roller 21 and the sheet tray 9C.

[0071] The connecting member 91B is located downstream of the heating body 7A and the pressure roller 7B in the transport direction DT1, and below the fixing unit 7 and the sheet tray 9C.

[0072] 5, the connecting member 91F is located on the front end side of both side frames 90L, 90R and extends in the width direction. The connecting member 91F connects the lower end of the side frame 90L and the lower end of the side frame 90R.

[0073] The connecting member 91B is located on the rear end side of both side frames 90L, 90R and extends in the width direction. The connecting member 91B also connects the lower end of the side frame 90L and the lower end of the side frame 90R.

[0074] In this embodiment, the connecting members 91F, 91B are made of metal and are formed by bending a steel plate to increase its rigidity. The connecting members 91F, 91B can prevent the widthwise spacing between the side frames 90L, 90R from widening.

[0075] The side frame 90L supports the main circuit board CB. The side frame 90L also supports a drive motor M1 and a drive force transmission mechanism (not shown). The drive force transmission mechanism (not shown) transmits the drive force generated by the drive motor M1 to the feed unit 20, the image forming unit 3, the scanner unit 8, the fuser 7, the post-fixing transport roller pair 28, the discharge roller pair 29, and the re-transport unit 30.

[0076] The side frame 90R supports a low-voltage power supply circuit PS1. The low-voltage power supply circuit PS1 converts 100V AC supplied via a power outlet 9S located on the rear of the housing 9 into low-voltage DC and supplies power to the electrical components inside the housing 9. The low-voltage power supply circuit PS1 is housed in a metal housing.

[0077] <Fixing frame and fixing subframe of the fixing unit> As shown in FIGS. 4, 6 and 7, the fixing unit 7 includes a fixing frame 70 and a fixing sub-frame 76.

[0078] As shown in FIGS. 6 and 7, the fixing frame 70 extends longer in the width direction than the pressure roller 7B, and rotatably supports one end 7B1L and the other end 7B1R in the width direction of the rotation shaft 7B1 of the pressure roller 7B.

[0079] 4 and 7, the fixing frame 70 covers the pressure roller 7B from below. A second guide surface 70G is formed on a part of the lower surface of the fixing frame 70.

[0080] 4, the second guide surface 70G defines a part of the re-conveyance path P2 from above. The second guide surface 70G guides the sheet SH being re-conveyed along the upper surface of the re-conveyance tray 33 toward the pair of skew rollers 31.

[0081] A pre-nip guide 71 is attached to a portion of the fixing frame 70 located forward of the pressure roller 7B. The pre-nip guide 71 contacts the sheet SH that has passed through the image forming unit 3 from below and guides the sheet SH toward the nip portion N1.

[0082] 6 and 7, the fixing sub-frame 76 extends in the width direction with substantially the same length as the fixing frame 70. The fixing sub-frame 76 is assembled to the fixing frame 70 from above.

[0083] 4, the fixing subframe 76 covers the heating element 7A from above. Although not shown, the fixing subframe 76 supports both widthwise ends of the guide member and heater of the heating element 7A. This allows the endless belt of the heating element 7A to circulate while forming a nip N1 between it and the pressure roller 7B.

[0084] A portion of the fixing sub-frame 76 located forward of the heater 7A has a guide shape that contacts the sheet SH that has passed through the image forming unit 3 from above and guides the sheet SH toward the nip portion N1.

[0085] As shown in FIG. 7, the fixing sub-frame 76 rotatably supports at its rear end a driven roller that is positioned above the two rollers that make up the post-fixing conveying roller pair 28.

[0086] <Air intake, exhaust, exhaust fan and exhaust duct> 2, the image forming apparatus 1 is provided with an intake port 9H1. The intake port 9H1 is located near the front upper corner of the left side surface of the housing 9, and connects the outside and inside of the housing 9.

[0087] 1, the image forming apparatus 1 is provided with an intake port 9H2. The intake port 9H2 is located near the front lower corner on the right side surface of the housing 9, and connects the outside and inside of the housing 9.

[0088] Air from outside the housing 9 is introduced into the housing 9 through the air intakes 9H1 and 9H2.

[0089] The image forming apparatus 1 is provided with an exhaust port 9H3. The exhaust port 9H3 is located in the middle and upper part of the right side surface of the housing 9 in the front-rear direction, and allows the outside and inside of the housing 9 to communicate with each other.

[0090] 3 and 5, the image forming apparatus 1 is equipped with an exhaust fan 89. The exhaust fan 89 is located on the other side in the width direction of the housing 9, i.e., on the right side. The exhaust fan 89 is supported by the side frame 90R and faces the exhaust port 9H3 inside the housing 9.

[0091] 6 and 7, the exhaust fan 89 has a fan case 89C and a fan 89F. The fan 89F is driven to rotate by a fan motor (not shown) inside the fan case 89C, thereby discharging air inside the housing 9 to the outside of the housing 9 through the exhaust port 9H3.

[0092] As shown in FIG. 4, the exhaust fan 89 is located upstream of the upstream end N1U of the nip portion N1 in the transport direction DT1 and above the upstream end N1U of the nip portion N1.

[0093] The image forming apparatus 1 includes an exhaust duct 80. The exhaust duct 80 is located upstream of the upstream end N1U of the nip portion N1 in the transport direction DT1 and above the upstream end N1U of the nip portion N1.

[0094] 6, the exhaust duct 80 extends in the width direction and has substantially the same length as the fixing frame 70 and the fixing sub-frame 76. The right end of the exhaust duct 80 is connected to a fan case 89C of the exhaust fan 89.

[0095] 4, the upper end of the front wall of the exhaust duct 80 is adjacent to the upper wall of the housing 9, behind the scanner unit 8. The lower and upper sides of the exhaust duct 80 are open. The exhaust duct 80 takes in air from the lower and upper sides and guides it toward the exhaust fan 89.

[0096] <frame> As shown in Fig. 3, the image forming apparatus 1 includes a frame 50. The frame 50 is located between the image forming unit 3 and the re-conveying unit 30 in the up-down direction. As shown in Fig. 8, the frame 50 extends in the front-rear and width directions.

[0097] 7, the frame 50 extends in the width direction with substantially the same length as the fixing frame 70 and the fixing sub-frame 76. In this embodiment, the frame 50 is a resin member manufactured by injection molding of a thermoplastic resin or the like.

[0098] 8, a conveying guide surface 50F is formed on the upper surface of the front end side of the frame 50. The conveying guide surface 50F is an example of the "guide surface" in the present invention.

[0099] 3, the frame 50 rotatably supports the registration roller 24D at the front end side. The conveying guide surface 50F guides the sheet SH conveyed so as to pass through the pair of registration rollers 24 on the conveying path P1.

[0100] 4, the frame 50 is located upstream of the upstream end N1U of the nip N1 in the conveying direction DT1 and below the upstream end N1U of the nip N1. A downstream end 50D of the frame 50 in the conveying direction DT1 is the rear end of the frame 50 and is inclined downward toward the downstream in the re-conveying direction DT2.

[0101] 4 and 7, the downstream end 50D of the frame 50 is located below the pre-nip guide 71. The downstream end 50D of the frame 50 is located slightly away downstream from the second guide surface 70G in the re-conveyance direction DT2.

[0102] 3, a first guide surface 50G is formed on a part of the lower surface of the frame 50. The first guide surface 50G is also an example of the "guide surface" of the present invention. The upstream end of the first guide surface 50G in the re-conveying direction DT2 is the downstream end 50D of the frame 50. The downstream end of the first guide surface 50G in the re-conveying direction DT2 is located close to the re-conveying roller pair 32.

[0103] The first guide surface 50G defines a part of the re-conveying path P2 from above, downstream of the second guide surface 70G in the re-conveying direction DT2. The first guide surface 50G guides the sheet SH being re-conveyed along the upper surface of the re-conveying tray 33 from the pair of oblique rollers 31 toward the pair of re-conveying rollers 32.

[0104] As shown in FIG. 4, the frame 50 is partitioned into a first space AS1 and a second space AS2 by a portion located on the downstream end 50D side.

[0105] The first space AS1 is a space located upstream of the upstream end N1U of the nip portion N1 in the transport direction DT1. The first space AS1 is also a space located behind the photosensitive drum 5 and transfer roller 6 of the image forming unit 3. The first space AS1 extends in the width direction with approximately the same length as the fixing frame 70 and the fixing sub-frame 76.

[0106] A gap is formed between the front end of the pre-nip guide 71 and the upper end of the rib 50R located on the downstream end 50D side of the frame 50. The space located between the downstream end 50D of the frame 50 and the pre-nip guide 71 is also included in the first space AS1.

[0107] The lower surface of the exhaust duct 80 is located above the first space AS1. The exhaust duct 80 takes in air from the first space AS1 and guides it towards the exhaust fan 89.

[0108] The second space AS2 is a space located below the fixing frame 70. The second space AS2 also extends in the width direction with substantially the same length as the fixing frame 70 and the fixing sub-frame 76.

[0109] <Frame opening> 7 to 9, the frame 50 has a plurality of openings 60. Each opening 60 is a substantially rectangular hole that passes through the downstream end 50D of the frame 50 in the up-down direction. The openings 60 are formed side by side in the width direction from one end to the other end of the frame 50 in the width direction. Each opening 60, except for a right-end opening 61 described later, is formed by two peripheral edges along the re-conveyance direction DT2 and two peripheral edges along the width direction.

[0110] 4, each opening 60 connects the first space AS1 and the second space AS2 to each other. The obliquely traveling rollers 31A are located upstream of each opening 60 in the re-conveyance direction DT2.

[0111] As shown in FIG. 7, the opening 60 located farthest in the width direction is the right-end opening 61. The right-end opening 61 is an example of the "end opening" of the present invention. As shown in FIG. 9, the right-end opening 61 has a different shape from the other openings 60 and has an inclined inner peripheral edge 61E. The right-end opening 61 is located on the other side in the width direction, opposite to the one side where the biasing guide 33G and the obliquely traveling roller 31A are located. More specifically, it is located in the area where the right edge in the width direction of an A4-sized sheet passes.

[0112] The inclined inner peripheral edge 61E is a downstream inner peripheral edge that extends in the width direction downstream of the re-conveying direction DT2 among the peripheral edges that form the right-end opening 61. The inclined inner peripheral edge 61E is inclined so that the other end 61E2 in the width direction is located downstream of one end 61E1 in the re-conveying direction DT2.

[0113] <Earth wire> 8, the downstream end 50D of the frame 50 holds an earth wire 99 on the upper surface side of the frame 50. The earth wire 99 is made by bending both ends of a straight steel wire.

[0114] The portion of the earth wire 99 extending in the width direction is fitted into a plurality of grooves formed between the rib 50R on the upper surface side of the frame 50 and each opening 60. The earth wire 99 has one end 99L and the other end 99R in the width direction.

[0115] 5, a first conductive member 98A is connected to the main board CB. The first conductive member 98A is located on one side in the width direction from the fixing unit 7. Although not shown in the figure, one end 99L of the ground wire 99 is connected to the first conductive member 98A.

[0116] A second conductive member 98B is connected to the metal housing of the low-voltage power supply circuit PS1. The second conductive member 98B is located on the other side in the width direction from the fixing unit 7. Although not shown in the figure, the other end 99R of the ground wire 99 is connected to the second conductive member 98B.

[0117] As a result, electrical components such as the main board CB and drive motor M1 located on the side frame 90L are connected to earth via the first conductive member 98A, the earth wire 99, the second conductive member 98B, the metal housing of the low-voltage power supply circuit PS1, and the power outlet 9S.

[0118] <Action and effect> 3, the image forming apparatus 1 of the first embodiment does not have the suction fan of the conventional image forming apparatus, and the exhaust fan 89 is disposed upstream in the conveying direction DT1 from the nip portion N1 of the fixing device 7. This allows the image forming apparatus 1 to be made compact.

[0119] 4, the openings 60 of the frame 50 connect the first space AS1 and the second space AS2 at the downstream end 50D of the frame 50. As a result, when the exhaust fan 89 is activated, the air in the first space AS1 flows toward the exhaust fan 89 via the exhaust duct 80, the air in the second space AS2 passes through the openings 60 of the frame 50 and flows toward the first space AS1, which has become negatively pressured, and the air containing water vapor in a space located downstream of the downstream end N1D of the nip portion N1 in the transport direction DT1 flows toward the second space AS2, which has become negatively pressured.

[0120] That is, an exhaust path is formed within the housing 9, extending from a space located downstream of the downstream end N1D of the nip portion N1 in the transport direction DT1 through the second space AS2, the openings 60 of the frame 50, the first space AS1, the exhaust duct 80, and the exhaust fan 89 to the outside of the housing 9. The image forming apparatus 1 can reliably exhaust air containing water vapor from around the fixing unit 7 to the outside of the housing 9 via the exhaust path.

[0121] In addition, air moving into the gap between the upper surface of the fixing subframe 76 and the upper wall of the housing 9 is introduced into the exhaust duct 80 from the upper side of the exhaust duct 80, and reaches the outside of the housing 9 via the exhaust fan 89.

[0122] Therefore, the image forming apparatus 1 of Example 1 can be made compact and can prevent water vapor generated from the sheet SH passing through the nip portion N1 from flowing back into the fixing device 7, thereby preventing the problem of condensed water accumulating on the fixing frame 70.

[0123] In the image forming apparatus 1, a first guide surface 50G formed on a portion of the lower surface of the frame 50 defines a portion of the re-conveying path P2. A second guide surface 70G formed on a portion of the lower surface of the fixing frame 70 defines another portion of the re-conveying path P2. With this configuration, the openings 60 of the frame 50, in which the first guide surface 50G is formed, reliably connect the first space AS1 and the second space AS2 at the downstream end 50D of the frame 50. The second space AS2, located below the second guide surface 70G, provides a wide space through which the sheet SH transported along the re-conveying path P2 passes. As a result, air in the second space AS2 flows through the openings 60 of the frame 50 toward the negatively pressurized first space AS1 with high reliability, and air containing water vapor in a space located downstream of the downstream end N1D of the nip N1 in the conveying direction DT1 flows toward the negatively pressurized second space AS2 with high reliability. As a result, this image forming apparatus 1 can reliably prevent water vapor generated from the sheet SH passing through the nip portion N1 from flowing back into the fixing device 7, and can reliably prevent the problem of condensed water accumulating on the fixing frame 70.

[0124] Furthermore, in this image forming apparatus 1, as shown in FIG. 7, the openings 60 are aligned in the width direction. As shown in FIG. 5, the oblique roller 31A is located to one side of the width direction center CL1. As shown in FIG. 9, the right-end opening 61, which is the opening 60 located farthest in the width direction, has an inclined inner peripheral edge 61E. The inclined inner peripheral edge 61E is inclined so that the other width direction end 61E2 is located downstream of the one width direction end 61E1 in the re-conveyance direction DT2. With this configuration, each opening 60 in the frame 50 reliably connects the first space AS1 and the second space AS2 over a wide range in the width direction. As a result, this image forming apparatus 1 can more reliably prevent water vapor generated from the sheet SH passing through the nip portion N1 from flowing back into the fixing unit 7. Furthermore, the sheet SH transported along the re-conveyance path P2 is restricted on one side in the width direction by the oblique roller 31A, but not on the other side in the width direction. Therefore, even if the corner portion on the other end side in the width direction of the leading edge of the sheet SH moves wildly when the sheet SH is transported on the re-conveyance path P2, the corner portion is guided by the inclination of the inclined inner peripheral edge 61E of the right-end opening 61 located farthest on the other side in the width direction, and the wild corner portion does not get caught on the inclined inner peripheral edge 61E. Therefore, it is possible to prevent the sheet SH from getting jammed on the re-conveyance path P2.

[0125] As shown in FIG. 4 , in the image forming apparatus 1, the exhaust duct 80 extends in the width direction, located upstream of the upstream end N1U of the nip N1 in the conveying direction DT1 and above the upstream end N1U of the nip N1. The exhaust fan 89 is located on the other widthwise side of the housing 9, i.e., on the right side. The exhaust duct 80 introduces air from the first space AS1 and guides it toward the exhaust fan 89. In this embodiment, the oblique roller 31A is located to one side of the widthwise center CL1. The drive motor M1 and a drive force transmission mechanism (not shown) for driving the drive roller 31D paired with the oblique roller 31A are located on one widthwise side of the housing 9, i.e., on the left side. The drive motor M1 and the drive force transmission mechanism (not shown) are supported by a side frame 90L. This makes it difficult to secure space for the exhaust fan 89 on the left side of the housing 9. In this regard, the above configuration makes it easier to ensure a space for arranging the exhaust fan 89, and the exhaust duct 80 makes it easier to guide the air in the first space AS1 toward the exhaust fan 89.

[0126] 3, the frame 50 supports the registration roller 24D. With this configuration, the openings 60 communicate the first space AS1 with the second space AS2 at the downstream end 50D of the frame 50, which tends to have a large area, so that the advantageous effects of the present invention can be obtained with high reliability.

[0127] In addition, in this image forming apparatus 1, as shown in Fig. 8, the frame 50 holds a ground wire 99. Then, as shown in Fig. 5, the ground wire 99 electrically connects the first conductive member 98A and the second conductive member 98B. With this configuration, the downstream end 50D of the frame 50 serves multiple functions, thereby reducing the number of parts required.

[0128] 3, in the image forming apparatus 1, the connecting member 91B extends in the width direction, located downstream of the heating element 7A and the pressure roller 7B in the transport direction DT1 and below the fuser 7. As shown in FIG. 5, the connecting member 91B connects the lower ends of the side frames 90L and 90R. This configuration prevents the gap between the side frames 90L and 90R in the width direction from widening.

[0129] Example 2 As shown in FIG. 10, in the image forming apparatus of Example 2, the re-conveying unit 30 of the image forming apparatus 1 of Example 1 is modified to have a scooping protrusion 39, and as shown in FIGS. 10 to 13, the shape of each opening 60 of the frame 50 is modified in accordance with the scooping protrusion 39.

[0130] Other configurations of the second embodiment are the same as those of the first embodiment. Therefore, the same components as those of the first embodiment are denoted by the same reference numerals, and the description thereof will be omitted or simplified.

[0131] As shown in FIG. 10, the scooping protrusion 39 is located on the upper surface of the re-conveying tray 33 upstream of the skew roller 31A in the re-conveying direction DT2 and on the other side in the width direction, protruding upward and extending in the re-conveying direction DT2.

[0132] The upper edge of the scooping protrusion 39 slopes gently upward toward the downstream side in the re-conveying direction DT2, then extends approximately horizontally for a short distance toward the downstream side in the re-conveying direction DT2 at a position higher than the upper surface of the re-conveying tray 33, and finally slopes downward toward the downstream side in the re-conveying direction DT2.

[0133] The scooping protrusion 39 scoops up the sheet SH being guided by the upper surface of the re-conveying tray 33 and the second guide surface 70G and conveyed in the re-conveying direction DT2. This reduces the conveying resistance that the sheet SH receives from the upper surface of the re-conveying tray 33 when the skew roller 31A causes the re-conveyed sheet SH to travel obliquely in one direction in the width direction. As a result, one edge in the width direction of the obliquely traveling sheet SH is more likely to slide against the biasing guide 33G.

[0134] 11 and 12, the range in which the scooping projection 39 exists in the width direction is indicated by E1.

[0135] 10 to 12, each opening 60 is located at a distance on one side and the other side in the width direction from the scooping protrusion 39. In other words, each opening 60 is located at a position that does not overlap with the scooping protrusion 39 in the width direction. As a result, the leading edge of the sheet SH scooped up by the scooping protrusion 39 is unlikely to get caught on the frame 50 midway along the re-conveyance path P2, since there are no openings 60 in and around the range E1.

[0136] 11 and 12, each opening 60 except for the right end opening 61 has a downstream inner peripheral edge 60E. The downstream inner peripheral edge 60E extends in the width direction downstream in the re-conveyance direction DT2.

[0137] 13 indicates the position of the downstream inner peripheral edge of each opening 60 except for the right-end opening 61 according to Example 1. The downstream inner peripheral edge 60E according to Example 2 is located upstream and above the downstream inner peripheral edge according to Example 1 in the re-conveying direction DT2.

[0138] 11 and 13, the underside of the frame 50 has a scoop-shaped surface 69. The scoop-shaped surface 69 slopes downward from each downstream inner circumferential edge 60E toward the downstream side in the re-conveyance direction DT2. The scoop-shaped surface 69 is located higher than the underside of the downstream end 50D of the frame 50 at a portion where no openings 60 exist.

[0139] The leading edge of the sheet SH scooped up by the scooping projection 39 is guided to the scooping surface 69 of each opening 60 located away from the range E1 and its periphery, and is therefore less likely to get caught on the downstream inner peripheral edge 60E.

[0140] Like the image forming apparatus 1 of Example 1, the image forming apparatus of Example 2 having such a configuration can be made compact, and can prevent water vapor generated from the sheet SH passing through the nip portion N1 from flowing back into the fixing device 7, thereby preventing the problem of condensed water accumulating on the fixing frame 70.

[0141] The present invention has been described above in accordance with Examples 1 and 2, but it goes without saying that the present invention is not limited to the above Examples 1 and 2, and can be modified and applied as appropriate within the scope of the invention.

[0142] In the first and second embodiments, the image forming apparatus of the present invention is embodied as an image forming apparatus 1 having an image forming function and an image reading function, but the present invention is not limited to this configuration. For example, the configuration of the present invention may be applied to an image forming apparatus that does not have an image reading function.

[0143] In the first and second embodiments, the first guide surface 50G is formed on a part of the lower surface of the frame 50, but the present invention is not limited to this configuration, and the first guide surface may be formed on the entire lower surface of the frame.

[0144] In Examples 1 and 2, the second guide surface 70G is formed on a portion of the lower surface of the fixing frame 70, but the present invention is not limited to this configuration, and the second guide surface may be formed on the entire lower surface of the fixing frame.

[0145] The present invention also includes a configuration in which the frame 50 of Examples 1 and 2 is divided into two parts, one where the first guide surface 50G is formed and the other where the conveying guide surface 50F is formed, and the part where the first guide surface 50G is formed is the "frame" of the present invention.

[0146] The present invention also includes a configuration in which the heating element 7A in Examples 1 and 2 is replaced with a heating roller. The present invention also includes a configuration in which the heating element 7A and pressure roller 7B in Examples 1 and 2 are reversed in their up-down relationship. In Examples 1 and 2, the pressure roller 7B is a drive roller, and the endless belt of the heating element 7A is driven by the pressure roller 7B, but the present invention is not limited to this configuration. For example, the present invention also includes a configuration in which the heating element is driven and the pressure element is driven by the heating element.

[0147] In the frame 50 according to Examples 1 and 2, multiple openings 60 are arranged in the width direction, but as long as the configuration allows communication between the space AS1 and the space AS2, there may be only one opening, or the openings may be arranged in the conveying direction instead of the width direction, or the openings may be arranged diagonally or randomly relative to the width direction. [Explanation of symbols]

[0148] 1...image forming device, DT1...conveying direction, SH...sheet N1: Nip section, 7A: Heating element 7B...pressure body (pressure roller), 7...fixing unit 70...fixing frame, 9...casing N1U: Upstream end of nip in the transport direction 89...Exhaust fan, 50...Frame 50F, 50G...guide surface (50F...conveyor guide surface, 50G...first guide surface) AS1...first space, AS2...second space 50D...Downstream end of the frame in the conveying direction 60...opening, 3...image forming unit DT2: Re-transport direction, P2: Re-transport path 70G...Second guide surface, 31A...Slant roller 61...End opening (right end opening), 61E...Inclined inner peripheral edge 61E1...One end in the width direction of the inclined inner peripheral edge 61E2...the other end in the width direction of the inclined inner peripheral edge 80...Exhaust duct, 39...Scooping convex part 69...Scoop-shaped surface, 24D...Transport roller (registration roller) 99...Earth wire, 98A...First conductive member 98B... second conductive member, 90L, 90R... side frame 91F, 91B...Connecting members

Claims

1. a fixing device having a heating element and a pressure element that sandwich and heat a sheet conveyed in a conveyance direction at a nip portion, and that thermally fixes a toner image on the sheet passing through the nip portion, the fixing device having a fixing frame that covers one of the heating element and the pressure element located below from below; a housing that houses the fixing unit; an exhaust fan that exhausts air from within the housing to the outside of the housing, the exhaust fan being located upstream of an upstream end of the nip portion in the conveying direction and above the upstream end of the nip portion; a frame located upstream of the upstream end of the nip portion in the conveying direction and below the upstream end of the nip portion, the frame having a guide surface formed thereon to guide a sheet being conveyed; Equipped with the frame defines a first space located upstream of the upstream end of the nip portion in the transport direction and a second space located below the fixing frame, The image forming apparatus according to claim 1, wherein the frame has an opening at a downstream end in the transport direction that connects the first space and the second space.

2. an image forming unit that is provided upstream of the fixing unit in the conveying direction and that forms the toner image on the sheet; a re-conveyance path for inverting the sheet having the toner image thermally fixed on one side thereof, guiding it in a re-conveyance direction, and returning it to the image forming unit; Equipped with the guide surface includes a first guide surface formed on at least a portion of a lower surface of the frame and defining a portion of the re-transport path; 2. The image forming apparatus according to claim 1, wherein a second guide surface that defines another part of the re-feeding path is formed on at least a part of the lower surface of the fixing frame.

3. The plurality of openings are formed side by side in a width direction perpendicular to the conveying direction, a slanted roller positioned upstream of each of the openings in the re-conveying direction, the slanted roller causing the sheet being guided by the second guide surface and conveyed in the re-conveying direction to slant toward one side in the width direction; the obliquely traveling roller is located on the one side in the width direction rather than the center in the width direction, the end opening, which is the opening located furthest to the other in the width direction, has an inclined inner peripheral edge extending in the width direction downstream in the re-feeding direction, 3. The image forming apparatus according to claim 2, wherein the inclined inner peripheral edge is inclined so that the other end in the width direction is located downstream of the one end in the width direction in the re-conveying direction.

4. an exhaust duct extending in the width direction and located upstream of the upstream end of the nip portion in the conveying direction and above the upstream end of the nip portion; the exhaust fan is located on the other side surface of the housing in the width direction, 4. The image forming apparatus according to claim 3, wherein the exhaust duct takes in air from the first space and guides it toward the exhaust fan.

5. a scooping protrusion that is located upstream of the oblique running roller in the re-conveying direction and on the other side in the width direction, and that scoops up the sheet that is guided by the second guide surface and conveyed in the re-conveying direction, 4. The image forming apparatus according to claim 3, wherein the openings are located at positions spaced apart from the scooping convex portion on both sides in the width direction.

6. each of the openings except for the end openings has a downstream inner peripheral edge extending in the width direction downstream in the re-feeding direction; 6. The image forming apparatus according to claim 5, wherein the lower surface of the frame has a rake-shaped surface that slopes downward from each of the downstream inner peripheral edges toward the downstream side in the re-conveying direction.

7. 4. The image forming apparatus according to claim 1, wherein the frame supports a transport roller that transports a sheet toward the fixing unit.

8. An image forming apparatus according to any one of claims 1 to 3, wherein the frame holds an earth wire extending in a width direction perpendicular to the conveying direction, electrically connecting a first conductive member located on one side of the width direction relative to the fixing device and a second conductive member located on the other side of the width direction relative to the fixing device.

9. a pair of side frames positioned on one side and the other side of the fixing unit in a width direction perpendicular to the conveying direction and supporting the fixing unit; a connecting member located downstream of the heating body and the pressing body in the conveying direction and below the fixing unit, the connecting member extending in the width direction and connecting the side frames; 4. The image forming apparatus according to claim 1, further comprising:

Images