IMAGE FORMING APPARATUS

An image forming apparatus includes a photosensitive drum and a fuser. The fuser includes an upper frame. The upper frame includes an upper first rib downstream of a heating rotating member in a sheet conveying direction, an upper second rib adjacent to the upper first rib in a width direction perpendicular to the sheet conveying direction, and first and second conveying rollers. The upper first rib includes a first guide surface, and a separation surface. The upper second rib includes a second guide surface. The second guide surface is located downstream of the first guide surface in the sheet conveying direction. A distance between a nip point between the first and second conveying rollers and the second guide surface in a direction perpendicular to the sheet conveying direction and the width direction is smaller than a distance between the nip point and the separation surface.

REFERENCE TO RELATED APPLICATIONS

This application claims priority from Japanese Patent Application No. 2022-152960 filed on Sep. 26, 2022. The entire content of the priority application is incorporated herein by reference.

BACKGROUND ART

Aspects of the present disclosure relate to an image forming apparatus.

Conventionally, there has been known an image forming apparatus including a fuser configured to thermally fix a toner image transferred from a photosensitive drum to a sheet.

The fuser includes a frame to which ribs for guiding a sheet to be conveyed are formed. When the toner image transferred to the sheet is thermally fixed with the fuser, water vapor is generated from the heated sheet, and water droplets adhere to the ribs of the frame due to the water vapor.

DESCRIPTION

When executing duplex printing on a sheet with the image forming apparatus, the sheet passing through the fuser during printing on one side of the sheet wipes off water droplets adhered to the ribs, and when the sheet after the printing on one side is re-conveyed to the photosensitive drum, the water droplets wiped by the sheet may transfer to the photosensitive drum.

When the water droplets adhere to the photosensitive drum, surface potential of the photosensitive drum decreases. Therefore, toner may adhere even to portions of the photosensitive drum that are not exposed and stain may occur on the sheet.

At least one aspect of the present disclosure is advantageous to provide an image forming apparatus capable of reducing the amount of water adhering to a sheet and suppressing the occurrence of stain on the sheet.

According to aspects of the present disclosure, there is provided an image forming apparatus including a photosensitive drum on which a toner image is to be formed, and a fuser configured to fix the toner image transferred from the photosensitive drum onto a conveyed sheet. The fuser includes a heating rotating member, a pressing rotating member configured to nip the sheet together with the heating rotating member, and an upper frame covering the heating rotating member. The upper frame includes an upper first rib extending in the sheet conveying direction downstream of the heating rotating member in the sheet conveying direction, an upper second rib adjacent to the upper first rib in a width direction perpendicular to the sheet conveying direction and extending in the sheet conveying direction, a first conveying roller configured to convey the sheet, and a second conveying roller configured to face the first conveying roller, the first conveying roller and the second conveying roller configured to nip the sheet at a nip point therebetween. The upper first rib includes a first guide surface configured to guide an upper surface of the conveyed sheet, and a separation surface located downstream of the first guide surface in the sheet conveying direction and at a position farther from the nip point than the first guide surface in a direction perpendicular to the sheet conveying direction and the width direction. The upper second rib includes a second guide surface configured to guide the upper surface of the conveyed sheet. The second guide surface is located downstream of the first guide surface in the sheet conveying direction. A distance between the nip point and the second guide surface in the direction perpendicular to the sheet conveying direction and the width direction is smaller than a distance between the nip point and the separation surface.

Hereinafter, embodiments according to aspects of the present disclosure will be described with reference to the accompanying drawings.

Image Forming Apparatus

An image forming apparatus1shown inFIG.1is an illustrative embodiment of an image forming apparatus including a sheet conveyer according to aspects of the present disclosure. The image forming apparatus1is a laser printer configured to form an image on a sheet S by an electrophotographic method.

In the following description, the right side inFIG.1is defined as the front side of the image forming apparatus1, the left side inFIG.1is defined as the rear side of the image forming apparatus1, the near side inFIG.1is defined as the left side of the image forming apparatus1, the far side inFIG.1is defined as the right side of the image forming apparatus1, the upper side inFIG.1is defined as the top side of the image forming apparatus1, and the lower side inFIG.1is defined as the bottom side of the image forming apparatus1.

The image forming apparatus1includes a first housing2and a second housing3.

The first housing2is formed in a substantially rectangular parallelepiped shape with an opening2A on a front surface thereof. The first housing2includes a front cover21configured to open and close the opening2A. The front cover21is configured to pivot about a pivot axis21aat a lower end portion thereof, and is movable between a closed position for closing the opening2A and an open position for opening the opening2A by pivoting about the pivot axis21a. An upper surface22of the first housing2is formed with a sheet discharge tray22athat is inclined downward from the front side toward the rear side.

The first housing2accommodates a sheet feed tray10configured to support one or more sheets S, a sheet conveyer11configured to convey the sheet S, an image forming engine5configured to form a toner image on the sheet S conveyed by the sheet conveyer11, a fuser6configured to fix the toner image on the conveyed sheet S, and a sheet discharge unit7configured to discharge the sheet S.

The sheet feed tray10and the sheet conveyer11constitute a sheet feeder4. The sheet feed tray10is located in a lower portion of the first housing2, and the sheet conveyer11conveys the sheet S supported by the sheet feed tray10to the image forming engine5. The sheet feed tray10is configured to slide in the front-rear direction to move between an accommodated position where the sheet feed tray10is accommodated in the first housing2and a separated position where the sheet feed tray10is drawn forward from the accommodated position.

The sheet conveyer11includes a sheet feed roller12, a separation roller13, a separation pad13a, a conveying roller pair14, and a registration roller pair15. In the first housing2, a conveyance path P for the sheet S from the sheet feed tray10to the sheet discharge tray22avia the image forming engine5is formed.

The sheets S supported by the sheet feed tray10are separated one by one and sent to the conveyance path P by the sheet feed roller12, the separation roller13, and the separation pad13a. The sheet feed roller12is a roller configured to convey the sheets S from the sheet feed tray10toward the image forming engine5. The separation roller13and the separation pad13aconstitute a separator configured to separate the sheets S supported by the sheet feed tray10one by one.

The sheet S fed to the conveyance path P is conveyed toward the image forming engine5by the conveying roller pair14and the registration roller pair15. The registration roller pair15regulates the movement of the leading end of the conveyed sheet S to temporarily stop the sheet S, and then conveys the sheet S toward the image forming engine5at a predetermined timing.

The image forming engine5is located downstream of the sheet conveyer11in a sheet conveying direction, and forms an image on the sheet S conveyed by the sheet conveyer11. The image forming engine5includes a process cartridge50configured to transfer an image onto a surface of the sheet S conveyed from the sheet feeder4, a transfer roller55that faces a photosensitive drum54of the process cartridge50, and an exposure unit56that exposes a surface of the photosensitive drum54.

The process cartridge50is located in the first housing2above the sheet feed tray10, and includes a developer accommodating chamber51, a supply roller52, a developing roller53, the photosensitive drum54, and the like.

The process cartridge50includes a drum cartridge having the photosensitive drum54and a developing cartridge attached to the drum cartridge and having the developing roller53, and is detachably attached to the first housing2. The process cartridge50can be attached to and detached from the first housing2when the front cover21is at the open position.

In a state where the process cartridge50is attached to the first housing2, the photosensitive drum54is disposed such that an axial center X extends in a left-right direction. The photosensitive drum54includes a drum shaft54athat is made of metal and that extends in a direction along the axial center X.

The exposure unit56includes a laser diode, a polygon mirror, a lens, a reflection mirror and the like, and exposes the surface of the photosensitive drum54by irradiating the photosensitive drum54with a laser beam based on image data input to the image forming apparatus1.

The developer accommodating chamber51accommodates toner to be used as developer. The toner accommodated in the developer accommodating chamber51is fed to the supply roller52while being stirred by a conventionally-known stirring member, and the supply roller52further supplies the toner fed from the developer accommodating chamber51to the developing roller53.

The developing roller53is disposed in close contact with the supply roller52and carries toner that is supplied from the supply roller52and positively charged by a conventionally-known sliding contact member. A developing bias is applied to the developing roller53by a conventionally-known bias applying unit.

The photosensitive drum54is adjacent to the developing roller53. The surface of the photosensitive drum54is uniformly charged by a conventionally-known charger and is then exposed to light by the exposure unit56. A potential of the exposed portion of the photosensitive drum54becomes lower than that of the other portion, and an electrostatic latent image based on the image data is formed on the photosensitive drum54. Then, positively charged toner is supplied from the developing roller53to the surface of the photosensitive drum54on which the electrostatic latent image is formed, and the electrostatic latent image is developed into a toner image.

The transfer roller55faces the photosensitive drum54, and a transfer bias is applied to the transfer roller55by a conventionally-known bias applying unit. The toner image formed on the surface of the photosensitive drum54is transferred onto a surface of a sheet S as the sheet S is nipped and conveyed between the photosensitive drum54on which the toner image is formed and the transfer roller55in a state where the transfer bias is applied to a surface of the transfer roller55. The sheet S onto which the toner image has been transferred is conveyed to the fuser6.

The fuser6includes a heating rotating member61and a pressing rotating member62, and fixes the toner image transferred from the photosensitive drum54of the process cartridge50to the sheet S. The heating rotating member61is heated by electric power supplied from a conventionally-known power source. The pressing rotating member62and the heating rotating member61oppose to each other, and the heating rotating member61is biased toward the pressing rotating member. The pressing rotating member62nips the sheet S together with the heating rotating member61.

When the sheet S to which the toner image has been transferred is conveyed to the fuser6, the sheet S is conveyed and heated while being nipped between the heating rotating member61and the pressing rotating member62to fix the toner image to the sheet S. In this manner, the fuser6fixes the toner image transferred from the photosensitive drum54to the conveyed sheet S.

The sheet discharge unit7is located downstream of the image forming engine5in the sheet conveying direction, and discharges the sheet S on which an image has been formed by the image forming engine5to the outside of the image forming apparatus1. The sheet discharge unit7includes an intermediate sheet discharge roller pair71, and a sheet discharge roller pair72located downstream of the intermediate sheet discharge roller pair71in the sheet conveying direction. The sheet S conveyed from the fuser6along the conveyance path P is discharged to the outside of the first housing2by the intermediate sheet discharge roller pair71and the sheet discharge roller pair72. The sheet S discharged to the outside of the first housing2is supported by the sheet discharge tray22aformed on the upper surface22of the first housing2.

The second housing3is located above the first housing2. The second housing3includes a document platen31, a document presser32, and an operation panel33. The document platen31is supported by a support column23extending upward from the upper surface22of the first housing2. The document platen31accommodates an image reading sensor312. The image reading sensor312reads an image of a document placed on an upper surface311of the document platen31.

The document presser32is located above the document platen31. The document presser32is configured to swing about a rotation shaft321which is at a rear end portion of the document presser32, and is movable between a pressing position at which the document presser32covers the upper surface311of the document platen31and an open position at which the document presser32exposes the upper surface311of the document platen31. The document presser32presses a document placed on the upper surface311of the document platen31when the document presser32is at the pressing position.

The operation panel33is connected to the document platen31of the second housing3and is projecting forward from the document platen31. The operation panel33includes a display tool such as a liquid crystal panel and an operation tool such as a touch panel or operation buttons for operating the image forming apparatus1.

As shown inFIGS.2and3, the heating rotating member61of the fuser6includes a heater611, a holder612, a stay613, and a belt614. The heater611is a flat plate-shaped heater extending in the left-right direction. The heater611includes a first surface611A, and a second surface611B opposite to the first surface611A. The first surface611A is supported by the holder612.

The holder612is made for example of a plastic member, and includes guide surfaces612aand a support wall612b. The guide surfaces612aare in contact with an inner circumferential surface614aof the belt614to guide the belt614. The support wall612bincludes a support surface612A that supports the heater611. The support surface612A of the support wall612bis in contact with the first surface611A of the heater611. The stay613is a member that supports the holder612, and is formed by bending a plate material having a higher rigidity than the holder612, such as a steel plate, into a substantially U-shape in a cross-sectional view.

The belt614is an endless belt having heat resistance and flexibility, and includes a metal tube made of stainless steel or the like, and a fluorine resin layer covering the metal tube. The heater611, the holder612, and the stay613are located inside the belt614. The belt614is configured to rotate around the heater611, the holder612, and the stay613. The inner circumferential surface614aof the belt614is in contact with the heater611.

The pressing rotating member62includes a shaft62A made of metal, and a roller62B made of an elastic body and covering the shaft62A. The pressing rotating member62is pressed against the heater611across the belt614. The pressing rotating member62nips the belt614with the heater611to form a nip point NP1for nipping, heating, and pressing the sheet S. That is, the pressing rotating member62heats and presses the sheet S together with the heater611at the nip point NP1.

The pressing rotating member62is configured to be rotationally driven by a driving force transmitted from a driving source included in the image forming apparatus1. As the pressing rotating member62is rotationally driven, the belt614is rotated by a friction force between the belt614and the pressing rotating member62or between the belt614and the sheet S nipped at the nip point NP1. The toner image transferred onto the sheet S is fixed to the sheet S as the sheet S is conveyed between the pressing rotating member62and the heated belt614.

As shown inFIG.4, an exhaust port24that communicates the inside and the outside of the first housing2is formed on a right surface of the first housing2. Inside the first housing2, a fan25is disposed adjacent to the exhaust port24. Inside the first housing2, an air duct8that guides air inside the first housing2toward the fan25is disposed in front of the fuser6.

In the image forming apparatus1, air and the like heated by the heating rotating member61of the fuser6is exhausted from the exhaust port24to the outside of the first housing2by the fan25. In this case, the air and the like heated by the heating rotating member61is guided toward the fan25by the air duct8.

As shown inFIGS.1and5to8, the fuser6includes a lower frame63that supports the heating rotating member61and the pressing rotating member62, and an upper frame64that is located above the lower frame63and covers the heating rotating member61.

The upper frame64includes an upper sheet guide64A that is located downstream of the heating rotating member61and the pressing rotating member62in the sheet conveying direction and guides an upper surface of the sheet S conveyed along the conveyance path P. The lower frame63includes a lower sheet guide63A that is located downstream of the heating rotating member61and the pressing rotating member62in the sheet conveying direction and guides a lower surface of the sheet S conveyed along the conveyance path P.

The conveyance path P in the fuser6extends in a direction substantially along the front-rear direction, and is inclined upward from the front toward the rear. That is, the sheet conveying direction in the fuser6is substantially in the front-rear direction.

A static electricity remover65configured to remove static electricity generated in the fuser6is attached to an upper surface of the upper frame64. The static electricity remover65is located at a right half portion of the upper frame64.

In the present embodiment, the heating rotating member61includes the heater611and the belt614. However, for example, the heating rotating member61may be a heating roller with a built-in heater. In the present embodiment, the pressing rotating member62includes the shaft62A and the roller62B. However, the pressing rotating member62may include a pressing belt pressed against the heating rotating member61by an elastic member.

Upper Sheet Guide of Upper Frame

As shown inFIGS.9to11, the upper sheet guide64A of the upper frame64includes upper first ribs641, upper second ribs642, and rollers643. The upper first ribs641, the upper second ribs642, and the rollers643are located downstream of the heating rotating member61and the pressing rotating member62in the sheet conveying direction.

The upper first ribs641extend in the sheet conveying direction. A plurality of upper first ribs641are arranged in the left-right direction The left-right direction in the fuser6is a widthwise direction orthogonal to the sheet conveying direction.

Each upper first rib641includes a first guide surface641aconfigured to guide the upper surface of the sheet S conveyed along the conveyance path P, and a separation surface641blocated downstream of the first guide surface641ain the sheet conveying direction. The separation surface641bis located farther from a later-described nip point NP2between a later-described driving roller66and a later-described roller643than the first guide surface641ain a direction orthogonal to the sheet conveying direction and the widthwise direction. The direction orthogonal to the sheet conveying direction and the widthwise direction is a direction substantially along the up-down direction.

The upper second ribs642are located adjacent to the upper first ribs641in the left-right direction, and extends along the sheet conveying direction. Each upper second rib642includes a second guide surface642alocated closer to the conveyed sheet S than the separation surface641bof the upper first rib641in the direction orthogonal to the sheet conveying direction and the widthwise direction. The second guide surface642ais configured to guide the upper surface of the sheet S conveyed along the conveyance path P.

The image forming apparatus1includes driving rollers66facing the rollers643, respectively. The driving rollers66nip the sheet S together with the rollers643(seeFIG.8). The rollers643nip the sheet S together with the driving rollers66to convey the sheet S. In the direction orthogonal to the sheet conveying direction and the widthwise direction, a distance d1between the second guide surface642aand a nip point NP2between the roller643and the driving roller66is smaller than a distance d2between the separation surface641band the nip point NP2.

That is, the distance d1between the second guide surface642aand the nip point NP2is smaller than the distance d2between the separation surface641band the nip point NP2, and the second guide surface642ais closer to the conveyed sheet S than the separation surface641b. Therefore, when the sheet S passes through a position, in the sheet conveying direction, where the second guide surface642aand the separation surface641bare, the sheet S is guided by the second guide surface642a.

When the sheet S conveyed along the conveyance path P passes through the fuser6, the sheet S is heated by the heating rotating member61, and moisture contained in the sheet S evaporates to generate water vapor. When the generated water vapor adheres to the upper first ribs641and the upper second ribs642, the water vapor may condense into water droplets, and the water droplets adhered to the upper first ribs641and the upper second ribs642may be wiped off by the sheet S guided by the upper first ribs641and the upper second ribs642.

For example, when executing duplex printing on the sheet S with the image forming apparatus1, if the sheet S passing through the fuser6during printing of one side thereof wipes off water droplets adhered to the upper first ribs641and the upper second ribs642, the water droplets wiped off by the sheet S may be transferred to the photosensitive drum54when the sheet S after the printing of one side thereof is re-conveyed to the photosensitive drum54.

On the other hand, when the sheet S conveyed along the conveyance path P passes through the upper sheet guide64A of the upper frame64, the sheet S is guided by the first guide surfaces641aof the upper first ribs641, and then guided by the second guide surfaces642aof the upper second ribs642adjacent to the upper first ribs641in the left-right direction.

As described above, in the upper frame64, ribs that guide the conveyed sheet S can be taken over from the upper first ribs641to the upper second ribs642. Therefore, as illustrated inFIGS.12A and12B, provided that a guiding length of the sheet S by one or more ribs in the sheet conveying direction is the same, for example, a length L2in the sheet conveying direction of a portion of the sheet S that contacts the first guide surface641aof the upper first rib641(seeFIG.12B) and a length L3in the sheet conveying direction of a portion of the sheet S that contact the second guide surface642aof the upper second rib642(seeFIG.12B) can be made shorter than a length L1in the sheet conveying direction of a portion of the sheet S guided by one rib that is not divided in the sheet conveying direction (seeFIG.12A).

Therefore, it is possible to reduce the amount of moisture adhering to the sheet S from one upper first rib641and the amount of moisture adhering to the sheet S from one upper second rib642. That is, the amount of moisture adhering to the sheet S from one rib can be reduced. Accordingly, if the number of ribs arranged in the left-right direction is the same, it is possible to reduce the amount of moisture to be transferred from the sheet S to the photosensitive drum54and thereby suppress the occurrence of stain on the sheet S. Additionally, the occurrence of stain on the sheet S can also be reduced due to the reduction of the length in the sheet conveying direction of areas to which moisture adheres.

The upper second ribs642are disposed on both sides in the left-right direction of each roller643, and each roller643is supported by the upper second ribs642disposed on both sides in the left-right direction. The upper first ribs641are disposed on both sides in the left-right direction of the two upper second ribs642supporting one roller643.

By configuring the upper second ribs642to support the roller643as described above, the upper second ribs642can be used both as guide ribs and as members for supporting the rollers643. Therefore, it is possible to reduce area of the upper frame64that contacts the sheet S.

Lower Sheet Guide of Lower Frame

As shown inFIGS.13to16, the lower sheet guide63A of the lower frame63includes lower guide surfaces630, lower first ribs631, and lower second ribs632. The lower guide surfaces630, the lower first ribs631, and the lower second ribs632are located downstream of the heating rotating member61and the pressing rotating member62in the sheet conveying direction. The lower guide surfaces630extend in the left-right direction and are facing substantially up.

The lower first ribs631project upward from the lower guide surfaces630and extend in the sheet conveying direction. A plurality of lower first ribs631are arranged in the left-right direction and guide the lower surface of the conveyed sheet S.

Each lower first rib631includes a first portion631awhich is a downstream end portion of the lower first rib631in the sheet conveying direction, and a second portion631bextending from the first portion631atoward the upstream side in the sheet conveying direction. In the sheet conveying direction, the first portion631aand a downstream end portion of the second portion631bare located on the lower guide surface630. The other portion of the second portion631bis located upstream of the lower guide surface630in the sheet conveying direction.

A projection height of the first portion631afrom the lower guide surface630is h1, and a projection height of the downstream end portion of the second portion631bin the sheet conveying direction from the lower guide surface630is h1which is the same as the projection height of the first portion631a. The second portion631bis inclined upward from the downstream end portion toward the upstream side in the sheet conveying direction, and a projection height of the upstream end portion of the second portion631bfrom the lower guide surface630is h2. The projection height h2of the upstream end portion of the second portion631bis greater than the projection height h1of the first portion631a. That is, an upper end of the second portion631bis higher than an upper end of the first portion631a.

Each lower second rib632projects upward from the lower guide surface630and extends in the sheet conveying direction. Each lower second rib632is located between two lower first ribs631in the left-right direction, and a plurality of lower second ribs632are arranged in the left-right direction. The lower second ribs632guides the lower surface of the conveyed sheet S.

A projection height of the lower second rib632from the lower guide surface630is h3. The projection height h3of the lower second rib632is the same as the projection height h1of the first portion631aof the lower first rib631. That is, an upper end of the lower second rib632and the upper end of the first portion631aof the lower first rib631are at the same height.

The lower second ribs632are formed over a range, in the sheet conveying direction, where the lower guide surfaces630are present, and a length L4of the lower second ribs632in the sheet conveying direction is shorter than a length L5of the lower first ribs631in the sheet conveying direction.

Positions of downstream ends of the lower second ribs632coincide with positions of downstream ends of the first portions631aof the lower first ribs631, and the lower second ribs632are located at positions overlapping the downstream end portion of the lower first ribs631in the sheet conveying direction. That is, the lower second ribs632are located at positions overlapping the downstream end portion of the second portions631band the first portions631aof the lower first ribs631when viewed in the left-right direction which is the direction along the axial center X of the drum shaft54a.

In the lower sheet guide63A of the lower frame63, water droplets caused by moisture evaporated from the sheet S easily accumulate on the lower guide surfaces630which are portions where the downstream end portions of the lower first ribs631in the sheet conveying direction are located. Therefore, if only the lower first ribs631are provided on the lower guide surfaces630, water droplets accumulated on the lower guide surfaces630easily adhere to the sheet S when the sheet S guided by the lower first ribs631deflects between two lower first ribs631in the left-right direction, the water droplets accumulated on the lower guide surface are likely to adhere to the sheet S.

However, in the lower frame63, since each lower second rib632is provided between the downstream end portions of two lower first ribs631, even if the sheet S guided by the lower first ribs631deflects in the left-right direction between the lower first ribs631, the deflected portion of the sheet S can be supported by the lower second ribs632. Therefore, the amount of moisture adhering to the sheet S can be reduced and thus occurrence of stain on the sheet S can be suppressed.

As shown inFIG.16, in the lower frame63, upper ends of the lower first ribs631and upper ends of the lower second ribs632are formed in an arcuate shape. Therefore, when the conveyed sheet S contacts the lower first ribs631and the lower second ribs632, a contact area between the sheet S and the lower first ribs631and a contact area between the sheet S and the lower second ribs632can be reduced, and the amount of moisture contacting the sheet S can be further reduced.

In the lower frame63, the upper ends of the second portions631bof the lower first ribs631are higher than the upper ends of the first portions631aof the lower first ribs631. Therefore, when a finger is inserted into a clearance between the lower sheet guide63A of the lower frame63and the upper sheet guide64A of the upper frame64from the downstream side in the sheet conveying direction, the inserted finger contacts the second portions631bof the lower first ribs631and thus it is possible to prevent the finger from entering into an upstream side of the first portion631aof the lower first rib631in the sheet conveying direction.

The lower second ribs632are located at positions overlapping the upper first ribs641in the left-right direction. That is, positions of the lower second ribs632and the upper first ribs641in the left-right direction coincide with each other when viewed in the sheet conveying direction.

Therefore, gaps in the fuser6between the lower frame63and the upper frame64at portions where the lower second ribs632and the upper first ribs641are formed can be reduced, and thus it is possible to suppress a finger from entering between the lower frame63and the upper frame64.

Furthermore, each lower first rib631is located between two upper first ribs641in the left-right direction. Therefore, the gap between the lower frame63and the upper frame64at positions between the upper first ribs641can be reduced by the lower first ribs631, and thus it is possible to suppress a finger from entering between the lower frame63and the upper frame64.

Modification of Lower Sheet Guide

The lower sheet guide63A of the lower frame63may also be configured like a lower sheet guide163A of a lower frame163shown inFIGS.17to19. The lower sheet guide163A differs from the lower sheet guide63A in that the lower sheet guide163A includes lower guide surfaces1630, lower first ribs1631, and lower second ribs1632instead of the lower guide surfaces630, the lower first ribs631, and the lower second ribs632.

The lower guide surfaces1630, the lower first ribs1631, and the lower second ribs1632are located downstream of the heating rotating member61and the pressing rotating member62in the sheet conveying direction. The lower guide surfaces1630are surfaces extending in the left-right direction and facing substantially up.

The lower first ribs1631project upward from the lower guide surfaces1630and extend in the sheet conveying direction. A plurality of lower first ribs1631are arranged in the left-right direction and guide the lower surface of the conveyed sheet S.

A downstream end of each lower first rib1631in the sheet conveying direction is at an intermediate portion of the lower guide surface1630in the sheet conveying direction. A projection height of the lower first ribs1631from the lower guide surfaces1630is h4.

Each lower second rib1632projects upward from the lower guide surface1630and extends in the sheet conveying direction. Each lower second rib1632is located between two lower first ribs1631in the left-right direction, and a plurality of lower second ribs1632are arranged in the left-right direction. The lower second ribs1632guide the lower surface of the conveyed sheet S.

A downstream end of each lower second rib1632in the sheet conveying direction is located at a downstream end of the lower guide surface1630in the sheet conveying direction. That is, the downstream ends of the lower first ribs1631are located upstream of the downstream ends of the lower second ribs1632in the sheet conveying direction.

Therefore, when the sheet S conveyed along the conveyance path P passes through the lower sheet guide163A of the lower frame163, the sheet S is guided by the lower first ribs1631and then guided by the lower second ribs1632adjacent to the lower first ribs1631in the left-right direction. As described above, in the lower frame163, ribs for guiding the conveyed sheet S can be taken over from the lower first ribs1631to the lower second ribs1632.

Accordingly, similarly to the case of the upper first ribs641and the upper second ribs642of the upper frame64, it is possible to reduce the amount of moisture adhering to the sheet S from one lower first rib1631and the amount of moisture adhering to the sheet S from one lower second rib1632.

Furthermore, a projection height of each lower second rib1632from the lower guide surface1630is h5, and the projection height h5of the lower second rib1632is greater than the projection height h4of the lower first rib1631. That is, upper ends of the lower second ribs1632are higher than upper ends of the lower first rib1631.

Therefore, when the lower second ribs1632take over the guiding of the conveyed sheet S, it is possible to effectively suppress the adhesion of the moisture accumulated on the lower guide surfaces1630of the lower frame163between the lower first ribs1631to the sheet S.

Furthermore, similarly to the lower second ribs632, the lower second ribs1632are located at positions overlapping the upper first ribs641in the left-right direction. That is, the positions of the lower second ribs1632and the upper first ribs641in the left-right direction coincide with each other. Additionally, similarly to the case of the lower first ribs631, each lower first rib1631is located between two upper first ribs641in the left-right direction.

Air Duct

As shown inFIGS.5to7and20to22, the air duct8extends in the left-right direction. The air duct8includes a first wall81and a second wall82that are located in front of the fuser6, that is, upstream of the fuser6in the sheet conveying direction, and face the fuser6with a gap therebetween.

The first wall81and the second wall82face in the front-rear direction, and the first wall81is located on the right side of the second wall82. The first wall81faces the right half of the fuser6, and the second wall82faces the left half of the fuser6.

The second wall82is located closer to the fuser6than the first wall81in the sheet conveying direction. The second wall82is adjacent to the fuser in the sheet conveying direction, and there is a clearance G1between the first wall81and the fuser6in the sheet conveying direction. The clearance G1is covered from above by the static electricity remover65attached to the upper surface of the upper frame64.

The air duct8includes a third wall83located in front of the first wall81and the second wall82. The third wall83faces the first wall81and the second wall82across a gap in the sheet conveying direction, and there is a clearance G2between the third wall83and the first and second walls81and82.

The fan25is located on the right side of the air duct8. The air duct8includes an exhaust guide84located between right ends of the first and third walls81and83and the fan25. The exhaust guide84is integrally connected to a right end portion of the third wall83, and guides air flowing through the clearance G2between the first and second walls81and82and the third wall83to the fan25(see an air flow F1shown inFIG.6).

The air duct8includes a side frame85that projects from a right end portion of the first wall81toward the rear side, that is, toward the downstream side in the sheet conveying direction. The side frame85is located between the first wall81and the fuser6at a right end portion of the air duct8. The side frame85includes an opening85athat is open in the left-right direction.

Airflow formed by the fan25can easily flow through the clearance G1between the first wall81and the fuser6. On the other hand, since the second wall82is adjacent to the fuser6, it is difficult for the airflow formed by the fan25to flow through between the second wall82and the fuser6.

Therefore, in the image forming apparatus1, an airflow causing air on the left side of the fuser6to flow between the second wall82and the fuser toward the fan25is less likely to occur, and thus the air on the left side of the fuser6flows rightward on the rear side of the fuser6, then goes around the fuser6from the rear side to the front side, and flows into the fan25through the clearance G1between the first wall81and the fuser6(see air flows F2shown inFIG.6).

That is, on the front side of the fuser6, the airflow generated by the fan25can be suppressed from flowing from the left side to the right side of the fuser6by the second wall82, and on the rear side of the fuser6, the airflow generated by the fan25can be promoted to flow from the left side to the right side of the fuser6by the first wall81.

Accordingly, it is possible to increase a flow amount of the air flowing, by the fan25, adjacent to the lower sheet guide63A of the lower frame63and the upper sheet guide64A of the upper frame64located at the rear end portion of the fuser6, and thus it is possible to promote drying of the moisture adhered to the lower sheet guide63A and the upper sheet guide64A.

In this case, since the clearance G1between the first wall81and the fuser6is covered with the static electricity remover65from above, air on the left side of the fuser6can be suppressed from flowing around the front side of the fuser6to the clearance G1by the static electricity remover65. Therefore, it is possible to further increase the flow amount of air flowing on the rear side of the fuser6.

Since the side frame85formed at the right end portion of the first wall81has the opening85athat is open in the left-right direction, the air flowing through the clearance G1easily flows toward the fan25, and thus it is possible to further increase the flow amount of air flowing on the rear side of the fuser6.

The first wall81and the second wall82for promoting the airflow of air flowing on the rear side of the fuser6are provided to the air duct8, that is, the air duct8also serves as a wall member constituting the first wall81and the second wall82. Therefore, the number of components can be reduced.

The rollers643are examples of a first conveying roller, and the driving rollers66are examples of a second conveying roller. The left side of the fuser6is an example of the other side of the fuser in the width direction, and the right side of the fuser6is an example of one side of the fuser in the width direction.