JP2013097091A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing deterioration in image formation quality to a curled sheet.SOLUTION: A conveyance belt 50 absorbs and conveys a first surface 99A of a sheet 99 by a conveyance surface 50A in the middle of a conveyance path. A first conveyance guide 110 is provided on the upperstream side from the conveyance surface 50A in the conveyance path and can be contacted with the first surface 99A to guide the sheet 99 toward the conveyance surface 50A. A second conveyance guide 120 is provided facing the first conveyance guide 110 on the upperstream side from the conveyance surface 50A in the conveyance path and can be contacted with a second surface 99B of the sheet 99 to guide the sheet 99 toward the conveyance surface 50A. The first conveyance guide 110 has a shape in which both ends 110L and 110R in the width direction to a central part 110C in the width direction are protruded so as to approach in parallel to the conveyance surface 50A, and both ends 110L and 110R are protruded to the central part 110C so as to separate in a direction orthogonal to the conveyance surface 50A.

Description

  The present invention relates to an image forming apparatus.

  Patent Document 1 discloses an example of a conventional image forming apparatus. This image forming apparatus includes an apparatus main body provided with a conveyance path for conveying a sheet, and a conveyance belt that is provided in the middle of the conveyance path in the apparatus main body and is circulated around a plurality of rollers. The conveyance belt conveys the sheet while adsorbing the first surface of the sheet by the conveyance surface along the conveyance path.

  The image forming apparatus includes a plurality of photoconductors provided in the apparatus main body so as to face the conveyance surface, and in contact with a second surface opposite to the first surface of the sheet passing on the conveyance surface. And a plurality of developing means provided corresponding to the respective photoconductors in the apparatus main body.

  In the conventional image apparatus having the above-described configuration, when the conveying belt conveys the sheet while adsorbing the first surface of the sheet, the developing unit supplies the developer to the latent image formed on the photosensitive member, thereby developing the developer image. The photosensitive member transfers the developer image to the second surface of the sheet. Thereafter, the developer image transferred to the sheet is thermally fixed. Thus, the image forming apparatus forms an image on the second surface of the sheet.

JP 2006-96527 A

  By the way, in the conventional image forming apparatus, the discharged sheet tends to curl when the developer image transferred to the second surface is thermally fixed to the sheet. In particular, the phenomenon that both end edges in the width direction of the sheet curl easily occurs.

  For example, when an image is also formed on the first surface of the sheet on which the developer image is thermally fixed on the second surface, when the sheet is conveyed on the conveyance surface in a curled state, the curled state The sheet is easily attracted to the conveyance surface. Then, both end edges in the width direction of the sheet are attracted to the conveyance surface before the central region and cannot move, and there is a possibility that the sheet may float on the conveyance surface in the central region in the width direction of the sheet. As a result, it becomes difficult to transfer the developer image satisfactorily to the area floating with respect to the sheet conveyance surface, and there is a problem that the image forming quality for the curled sheet is likely to be lowered.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can suppress a reduction in image formation quality with respect to a curled sheet.

An image forming apparatus of the present invention includes an apparatus main body provided with a conveyance path for conveying a sheet,
It is provided in the middle of the conveyance path in the apparatus main body, is wound around a plurality of rollers and can circulate, extends in the width direction of the conveyed sheet, and is a plane along the conveyance path. A conveyor belt that conveys the sheet while adsorbing the first surface of the sheet;
The first surface of the sheet that is provided in the apparatus main body so as to face the conveyance surface, is parallel to the conveyance surface, is aligned in a longitudinal direction orthogonal to the width direction, and passes over the conveyance surface. A plurality of photoreceptors in contact with the second surface on the opposite side;
A plurality of developing means provided corresponding to each of the photoconductors in the apparatus main body, supplying a developer to a latent image formed on each of the photoconductors to form a developer image;
A first conveyance guide provided in the apparatus main body on the upstream side of the conveyance surface in the conveyance path, capable of contacting the first surface of the sheet, and guiding the sheet toward the conveyance surface;
In the apparatus main body, it is provided on the upstream side of the conveyance surface in the conveyance path so as to face the first conveyance guide, is capable of contacting the second surface of the sheet, and directs the sheet toward the conveyance surface. An image forming apparatus including a second conveyance guide for guiding
The first conveyance guide protrudes so that both ends in the width direction approach the parallel to the conveyance surface with respect to the central portion in the width direction, and the both ends are in the conveyance surface with respect to the central portion. It has a shape that protrudes so as to be separated in a direction orthogonal to.

  In the image forming apparatus of the present invention, when the sheet is conveyed on the conveying surface in a curled state, first, both end portions in the width direction of the curled sheet are lifted by both end portions in the width direction of the first conveyance guide. Then, the curl of the sheet is corrected to be flat so as to be sandwiched between the first conveyance guide and the second conveyance guide. At this time, the first conveyance guide allows the center region in the width direction of the sheet to escape to the center portion that is recessed from both ends. For this reason, the center area where the sheet escapes is first adsorbed to the conveyance surface, and then both end edges in the width direction of the sheet are adsorbed to the conveyance surface. Floating is unlikely to occur.

  Therefore, the image forming apparatus of the present invention can suppress a decrease in image forming quality with respect to the curled sheet.

  In the image forming apparatus of the present invention, it is desirable that the first transport guide gradually protrudes from the central portion toward both end portions. According to this configuration, it is easier to guide the sheet smoothly compared to the case where the first conveyance guide projects stepwise from the center in the width direction toward both ends.

  In the image forming apparatus of the present invention, the conveying surface extends substantially horizontally. Further, both ends of the first conveyance guide are at positions higher than the conveyance surface. According to this configuration, both end edges in the width direction of the sheet can be reliably lifted above the conveyance surface immediately before the conveyance surface. As a result, the central region in the width direction of the sheet is more easily adsorbed to the conveyance surface, and it is possible to reliably suppress a decrease in image formation quality with respect to the curled sheet.

  The image forming apparatus according to the present invention includes a first sheet placement section that is provided below the conveyance belt in the apparatus main body and on which a sheet is placed. The conveyance path has a U-turn path upstream of the conveyance surface and U-turns upward from the first sheet placement unit to convey the sheet to the conveyance surface. Further, the first transport guide is curved along the U-turn path so as to draw a substantially arc when viewed from the width direction. According to this configuration, since the first conveyance guide is curved, the sheet is less likely to be rubbed or unevenly fed than in the case where the first conveyance guide is bent, and moreover, the sheet is prevented from forming in the first conveyance guide. Since it becomes difficult to catch, it is easy to convey the sheet smoothly.

  The image forming apparatus of the present invention includes a second sheet placement section that is provided on a side surface of the apparatus main body and on which a sheet can be placed. Then, the sheet conveyed from the second sheet placement unit merges in the middle of the U-turn path in the conveyance path, and merges below the vertex of the second conveyance guide, whereby the first conveyance guide and the second sheet are conveyed. Guided by the transport guide. According to this configuration, since the sheet can be substantially straightly fed from the second sheet placing unit to the conveyance surface, it is easy to manually feed thick paper or the like. In addition, even when the sheet placed on the second sheet placement unit is curled, the first conveyance guide and the second conveyance guide can suppress a decrease in image formation quality with respect to the curled sheet.

  In the image forming apparatus of the present invention, the downstream end portion of the second transport guide extends from the downstream end portion of the first transport guide to the downstream side in the sheet transport direction. According to this configuration, the second conveyance guide can guide the sheet until the entire width direction of the sheet is attracted to the conveyance surface. As a result, it is possible to reliably suppress a decrease in image formation quality with respect to the curled sheet.

  In the image forming apparatus of the present invention, in the second conveyance guide, the guide surface that can contact the second surface is preferably a curved surface that is curved while maintaining a straight state in the width direction. According to this configuration, for example, even when an uncurled sheet is conveyed, the sheet is easily conveyed smoothly along the second conveyance guide.

  In the image forming apparatus of the present invention, it is preferable that the first conveyance guide is made of an elastic member that can absorb the thickness of the sheet. According to this configuration, the first conveyance guide is slightly crushed and slightly absorbs the thickness of the sheet, thereby making it difficult for the sheet to be caught by the first conveyance guide.

It is a schematic sectional drawing of the image forming apparatus of an Example. FIG. 5 is a schematic partial cross-sectional view illustrating a state in which a second placement unit is opened according to the image forming apparatus of the embodiment. FIG. 4 is an enlarged perspective view of a main part illustrating a conveyance surface of a conveyance belt and a first conveyance guide in the image forming apparatus according to the exemplary embodiment. FIG. 4 is an enlarged perspective view of a main part illustrating a conveyance surface of a conveyance belt and a first conveyance guide in the image forming apparatus according to the exemplary embodiment. FIG. 4 is an enlarged top view of a main part illustrating a conveyance surface of a conveyance belt, a first conveyance guide, and a second conveyance guide in the image forming apparatus according to the exemplary embodiment. FIG. 6 is an enlarged front view of a main part illustrating the conveyance surface of the conveyance belt, the first conveyance guide, and the second conveyance guide as seen from the direction of arrow A in FIG. 5 according to the image forming apparatus of the embodiment. FIG. 7 is an enlarged cross-sectional view of a main part showing the BB cross section of FIG. 6 according to the image forming apparatus of the embodiment. An image forming apparatus according to an embodiment includes (a) a conveying surface, a first conveying guide, and a second conveying guide as viewed from the direction of arrow A in FIG. 5, and a sheet of the first conveying guide and the second conveying guide. FIG. 5B is an explanatory diagram for explaining the behavior of a sheet in a comparative example in which the first conveyance guide is eliminated from FIG. FIG. 10 is an enlarged top view of a main part illustrating a conveyance surface of a conveyance belt, a first conveyance guide, and a second conveyance guide in an image forming apparatus according to Modification 1; FIG. 10 is an enlarged front view of a main part illustrating a conveyance surface of a conveyance belt, a first conveyance guide, and a second conveyance guide as seen from the direction of arrow C in FIG. FIG. 10 is an enlarged top view of a main part illustrating a conveyance surface of a conveyance belt, a first conveyance guide, and a second conveyance guide in an image forming apparatus according to Modification 2; FIG. 14 is an enlarged front view of a main part illustrating a conveyance surface of a conveyance belt, a first conveyance guide, and a second conveyance guide as seen from an arrow D direction in FIG. 11 according to an image forming apparatus of Modification 2;

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings.

(Example)
As shown in FIG. 1, the image forming apparatus 1 according to the embodiment is a color laser printer that forms a plurality of color images on a sheet 99 such as paper or an OHP sheet by an electrophotographic method. In FIG. 1, the right side of the page is defined as the front side of the apparatus, and the front side of the sheet, which is the side that comes to the left hand when the apparatus is viewed from the front side, is defined as the left side. 2 are displayed in correspondence with the directions shown in FIG. 1. Hereinafter, each component provided in the image forming apparatus 1 will be described with reference to FIG.

<Overall configuration>
As shown in FIG. 1, the image forming apparatus 1 includes a housing 90 that is a substantially box-shaped body, and a frame member (not shown) provided inside the housing 90. The housing 90 and the frame member constitute the apparatus main body of the present invention. A discharge tray 90A is formed on the upper surface of the housing 90 so as to be recessed downward. A first opening 90 </ b> B is formed on the lower side of the front surface of the housing 90. A second opening 90 </ b> C is formed on the upper side of the front surface of the housing 90. The front surface of the housing 90 is an example of the “side surface of the apparatus main body” of the present invention.

  The image forming apparatus 1 also includes a sheet cassette 21 and a multi-purpose tray (hereinafter referred to as “MP tray”) 81. The sheet cassette 21 is an example of the “first placement unit” in the present invention. The MP tray 81 is an example of the “second placement unit” in the present invention.

  The sheet cassette 21 is detachably provided below the housing 90. The sheet cassette 21 is a substantially box-shaped body that is open at the top and accommodates a plurality of sheets 99 in a stacked state. The sheet 99 is accommodated in the sheet cassette 21 with the first surface 99A facing upward and the second surface 99B opposite to the first surface 99A facing downward. The sheet cassette 21 is mounted in the housing 90 by being inserted substantially horizontally from the front side of the housing 90 through the first opening 90B, and removed from the housing 90 by the reverse operation.

  As shown in FIG. 1, the MP tray 81 is a substantially flat plate-like member, and closes the second opening 90 </ b> C while standing up and down. In this state, the MP tray 81 constitutes a part of the design surface on the front surface side of the housing 90. The lower end edge side of the MP tray 81 is swingably supported by the housing 90. Then, as shown in FIG. 2, the MP tray 81 changes from the housing 90 to a state extending substantially horizontally toward the front side by swinging the upper end side toward the front side. In this state, the sheet 99 is placed on the surface facing the upper side of the MP tray 81. The sheet 99 on the MP tray 81 is fed into the housing 90 by an MP sheet feeding unit 80 described later.

  As shown in FIGS. 1 and 2, the housing 90 is provided with a conveyance path including a U-turn path P1, a substantially horizontal path P2, a discharge path P3, and an MP path P4. As shown in FIG. 1, the U-turn path P <b> 1 is a path that changes from the front end portion of the sheet cassette 21 toward the front surface side of the housing 90, then U-turns upward and turns backward. The substantially horizontal path P <b> 2 is a path that is continuous with the U-turn path P <b> 1 and proceeds substantially horizontally toward the rear surface side of the housing 90. The discharge path P3 is a path that is continuous with the substantially horizontal path P2, proceeds toward the rear surface of the housing 90, then makes a U-turn upward, and further proceeds forward to reach the discharge tray 90A. As shown in FIG. 2, the MP path P4 is a path that advances while inclining backward from the open MP tray 81 and joins in the middle of the U-turn path P1. In the present embodiment, the width direction of the sheet 99 conveyed along the U-turn path P1, the substantially horizontal path P2, the discharge path P3, and the MP path P4 is the left-right direction.

  As shown in FIG. 1, in the housing 90, above the sheet cassette 21, there are a sheet feeding unit 20, an MP sheet feeding unit 80, a first conveyance guide 110, a second conveyance guide 120, an image forming unit 30, and a discharge roller. Pairs 29A, 29B, etc. are provided. These are assembled to a frame member (not shown).

  The sheet feeding unit 20 feeds the sheets 99 stored in the sheet cassette 21 one by one to the U-turn path P1 by the sheet feeding roller 22, the separation roller 23, and the separation pad 23A. Then, the sheet 99 is conveyed toward the image forming unit 30 by the conveying roller pair 24A, 24B and the registration roller pair 25A, 25B disposed in the middle of the U-turn path P1.

  As shown in FIG. 2, the MP paper feed unit 80 feeds the sheet 99 placed on the MP tray 81 with the second surface 99B facing upward, one by one by the paper feed roller 82 and the separation pad 82A. Transport along P4. Then, the MP sheet feeding unit 80 joins the sheet 99 in the middle of the U-turn path P1, and conveys the sheet 99 toward the image forming unit 30 by the registration roller pair 25A and 25B.

  The first conveyance guide 110 and the second conveyance guide 120 are provided in the housing 90 in the middle of the U-turn path P1.

  The first transport guide 110 is located at the uppermost end portion of the U-turn path P1. The first conveyance guide 110 is made contactable with the first surface 99A of the sheet 99 passing through the uppermost end portion of the U-turn path P1, and guides the sheet 99 toward the conveyance surface 50A described later. The second conveyance guide 120 is located at the uppermost end portion of the U-turn path P1 and faces the first conveyance guide 110. The second conveyance guide 120 is made contactable with the second surface 99B of the sheet 99 passing through the uppermost end portion of the U-turn path P1, and guides the sheet 99 toward the conveyance surface 50A described later. As shown in FIG. 2, the MP path P4 joins in the middle of the U-turn path P1 below the apex 120T of the second transport guide 120. Specific configurations of the first conveyance guide 110 and the second conveyance guide 120 will be described in detail later.

  As shown in FIG. 1, the image forming unit 30 is of a so-called direct tandem system. The image forming unit 30 includes a conveyance belt 50 provided below the substantially horizontal path P2, four sets of photosensitive drums 40 and process cartridges 31 positioned above the conveyance belt 50 with the substantially horizontal path P2 interposed therebetween, and each photosensitive element. The scanner unit 39 is located above the drum 40 and the process cartridge 31, and the fixing device 55 is located on the most upstream side of the discharge path P3. The photosensitive drum 40 is an example of the “photosensitive member” in the present invention. The process cartridge 31 is an example of the “developing unit” in the present invention.

  The conveyor belt 50 is wound around a driving roller 51 that rotates around a rotation axis that faces in the left-right direction in the rear of the housing 90 and a driven roller 52 that rotates around a rotation axis parallel to the driving roller 51 in the front of the housing 90. An endless belt that hangs and circulates. In the conveyance belt 50, a substantially horizontal plane extending in the left-right direction and the front-rear direction along the substantially horizontal path P2 between the driving roller 51 and the driven roller 52 is a conveyance surface 50A.

  The sheet 99 conveyed along the U-turn path P1 and entering the substantially horizontal path P2 is in a state where the first surface 99A is directed downward, and the first surface 99A is adsorbed to the conveyance surface 50A. Then, the sheet 99 is conveyed to the circulating conveyance belt 50, and thus passes below the four sets of the photosensitive drums 40 and the process cartridge 31 with the second surface 99B facing upward.

  The four sets of photosensitive drums 40 and process cartridges 31 respectively correspond to four color toners of black, yellow, magenta, and cyan. The toner is an example of the “developer” in the present invention.

  Each photosensitive drum 40 is a cylindrical body extending in the left-right direction, and is provided so as to face the conveyance surface 50A from above with the substantially horizontal path P2 interposed therebetween. The photosensitive drums 40 are arranged in the front-rear direction along a substantially horizontal path P2. In the present embodiment, the longitudinal direction parallel to the conveyance surface 50A and orthogonal to the width direction is the front-rear direction.

  The process cartridges 31 are positioned above the photosensitive drums 40 and are arranged in the front-rear direction along a substantially horizontal path P2. Each process cartridge 31 is a substantially box-shaped body extending in the left-right direction, and includes a developing roller 31A, a toner containing portion 31B, a charger 31C, and the like. Each process cartridge 31 is positioned forward and obliquely upward with respect to the corresponding photosensitive drum 40, and the developing roller 31 </ b> A is in contact with the photosensitive drum 40.

  The scanner unit 39 includes a laser light source, a polygon mirror, an fθ lens, a reflecting mirror, and the like, and irradiates each photosensitive drum 40 with a laser beam from above.

  The fixing device 55 includes a heating roller 55A and a pressure roller 55B that face each other across the discharge path P3.

  The discharge roller pair 29A, 29B is located on the most downstream side in the discharge path P3 and faces the discharge tray 90A.

  The image forming unit 30 forms an image on the second surface 99B of the sheet 99 conveyed along the substantially horizontal path P2 through the U-turn path P1 or the MP path P4 as follows. That is, the surface of each photosensitive drum 40 is uniformly charged positively by the charger 31C as it rotates, and then exposed by the laser beam emitted by the scanner unit 39. As a result, the scanner unit 39 forms an electrostatic latent image corresponding to the image to be formed on the surface of each photosensitive drum 40. Next, toner of a color corresponding to the electrostatic latent image on the surface of each photosensitive drum 40 is supplied from the toner storage portion 31B by the developing roller 31A of each process cartridge 31 to form a toner image. The toner image rotates while the photosensitive drum 40 is in contact with the second surface 99B of the sheet 99 conveyed along the substantially horizontal path P2, and a negative voltage applied to the conveyance surface 50A acts on the sheet. 99 is transferred to the second surface 99B.

  Then, the fixing unit 55 heats and presses the sheet 99 that passes under each process cartridge 31 and enters the discharge path P3 by the heating roller 55A and the pressing roller 55B, and transfers the sheet 99 to the second surface 99B of the sheet 99. The toner image is fixed. Thereafter, the sheet 99 is discharged to the discharge tray 90A by the discharge roller pair 29A and 29B. Thus, the image forming apparatus 1 ends the image forming operation on the sheet 99.

<Specific Configurations of First Transport Guide and Second Transport Guide>
As shown in FIGS. 3 to 7, the transport belt 50 includes a front frame portion 59 </ b> F, a rear frame portion (not shown), a left frame portion 59 </ b> L, and a right frame portion 59 </ b> R of a transport belt holding portion 59 that is a frame-shaped frame member. Thus, the conveying surface 50A is exposed upward in a state surrounded by front, rear, left and right. The driven roller 52 and the driving roller 51 around which the conveyance belt 50 is wound are held by a left frame portion 59L and a right frame portion 59R that are left and right frames.

  As shown in FIG. 3 and FIG. 7 and the like, an inclined surface 58 is formed on the front frame portion 59F of the transport belt holding portion 59 so as to be positioned forward with respect to the driven roller 52. The inclined surface 58 is inclined downward toward the front. As shown in FIG. 7, the height of the upper edge 58A of the inclined surface 58 is substantially equal to the height of the transport surface 50A.

  As shown in FIG. 7, the first conveyance guide 110 is continuous with the upper end edge 58 </ b> A of the inclined surface 58 in the front frame portion 59 </ b> F of the conveyance belt holding portion 59 and is against the conveyance belt 50 wound around the driven roller 52. This is a portion extending rearward so as to cover from above.

  When viewed from the left-right direction, the central portion 110C of the first transport guide 110 is gently curved so as to swell upward along the U-turn path P1. The rear end 111C of the central portion 110C extends to a position immediately before the conveyance surface 50A that is a substantially horizontal plane.

  As shown in FIGS. 3, 4, 7, etc., the degree of curvature that bulges upward of the first conveyance guide 110 gradually increases from the center portion 110 </ b> C in the left-right direction toward both end portions 110 </ b> L, 110 </ b> R in the left-right direction. It is getting bigger.

  As shown in FIG. 5, the rear ends 111L and 111R of both end portions 110L and 110R protrude from the rear end 111C of the central portion 110C so as to approach the conveyance surface 50A in parallel. When the first transport guide 110 is viewed from above, a line connecting the rear ends 111L, 111C, and 111R is a “V” -shaped broken line. As shown in FIG. 7, the rear ends 111L and 111R protrude rearward from the rear end 111C so as to cover the conveyance surface 50A from above.

  As shown in FIG. 6, the upper ends 112L and 112R of both end portions 110L and 110R protrude from the upper end 112C of the central portion 110C so as to be separated in the vertical direction perpendicular to the conveyance surface 50A. When the first conveyance guide 110 is viewed from the front, the line connecting the upper ends 112L, 112C, and 112R is also a “V” -shaped broken line. As shown in FIG. 7, the upper ends 112L and 112R are located obliquely behind the rear end 112C. The upper ends 112L and 112R are higher than the conveyance surface 50A.

  The front frame portion 59F of the transport belt holding portion 59 is a highly rigid resin molded product. However, for the portion where the first conveyance guide 110 is formed, an elastic material that is slightly recessed by the application of surface pressure is used. Specifically, the first conveyance guide 110 is made of an elastic material by attaching a rubber sheet or an elastomer sheet to a resin molded product or by insert molding rubber or an elastomer.

  As shown in FIGS. 6 and 7, the second conveyance guide 120 faces the first conveyance guide 110 from above. In the second transport guide 120, a guide surface 120A that can face downward and contact the second surface 99B is a curved surface that is curved while maintaining a straight state in the left-right direction. More specifically, it is straight in the left-right direction and curved in the front-rear direction. Further, the guide surface 120A is curved to be larger than the curvature of both end portions 110L and 110R of the first transport guide 110.

  As shown in FIGS. 5 and 7, the rear end edge 121 of the second conveyance guide 120 conveys more than the rear end 111C of the central portion 110C of the first conveyance guide 11 and the rear ends 111L and 111R of both end portions 110L and 110R. It extends so as to approach the surface 50A. Further, the rear end edge 121 of the second transport guide 120 is downstream in the transport direction D1 of the sheet 99 from the rear end 111C of the central portion 110C and the rear ends 111L and 111R of the both end portions 110L and 110R of the first transport guide 11. It extends to the length located on the side.

<Effect>
FIG. 8A shows a state in which the sheet 99 is conveyed onto the conveyance surface 50A in the image forming apparatus 1 of the embodiment in a curled state. In addition, the curl of the sheet 99 which is a problem in the embodiment is a curled curl such that the left and right end edges 99L and 99R of the sheet 99 are located below and the central region 99C is located above when viewed from the front-rear direction. It is. The sheet 99 having such a curl shape is conveyed as follows. First, the left and right end edges 99L and 99R of the curled sheet 99 are lifted by the left and right ends 110L and 110R of the first transport guide 110 and sandwiched between the first transport guide 110 and the second transport guide 120. Correct 99 curls to flatten. FIG. 8A shows the state of the sheet 99 after being corrected. At this time, the first conveyance guide 110 allows the central region 99C in the left-right direction of the sheet 99 to escape to the central portion 110C that is recessed from the both end portions 110L and 110R. For this reason, the central region 99C from which the sheet 99 has escaped is first adsorbed to the conveyance surface 50A, and then both left and right edges 99L and 99R of the sheet 99 are adsorbed to the conveyance surface 50A. In the central region 99C in the left-right direction, it is difficult for the transfer surface 50A to float.

  FIG. 8B shows a comparative example in which the first conveyance guide 110 having the above shape is eliminated. In this case, when the sheet 99 is conveyed on the conveyance surface 50A in a curled state, the first surface 99A of the sheet 99 is easily attracted to the conveyance surface 50A in the curled state. Then, both end edges 99L and 99R in the width direction of the sheet 99 are attracted to the conveyance surface before the central region 99C and cannot move, and the sheet 99 is lifted with respect to the conveyance surface 50A in the central region 99C in the width direction. End up. As a result, it becomes difficult to transfer the developer image satisfactorily to the area floating with respect to the conveyance surface 50A of the sheet 99.

  Therefore, the image forming apparatus 1 according to the embodiment can suppress a decrease in image formation quality with respect to the curled sheet 99.

  In the image forming apparatus 1, the first conveyance guide 110 gradually protrudes from the central portion 110C toward both end portions 110L and 110R. With this configuration, it is easier to guide the sheet 99 smoothly compared to the case where the first conveyance guide 110 projects stepwise from the central portion 110C in the left-right direction toward both end portions 110L and 110R.

  Further, in the image forming apparatus 1, the conveyance surface 50A extends substantially horizontally, and the first conveyance guide 110 has the upper ends 112L and 112R of both end portions 110L and 110R at a position higher than the conveyance surface 50A. With this configuration, the left and right end edges 99L and 99R of the sheet 99 can be reliably lifted above the conveyance surface 50A immediately before the conveyance surface 50A. As a result, the central region 99C in the width direction of the sheet 99 is more easily attracted to the conveyance surface 50A, and a decrease in image formation quality with respect to the curled sheet 99 can be reliably suppressed.

  Further, in this image forming apparatus 1, the first conveyance guide 110 that guides the sheet 99 conveyed from the sheet cassette 21 along the U-turn path P1 is curved, so that the first conveyance guide 110 is bent. Thus, the sheet 99 is less likely to be rubbed or unevenly fed, and the sheet 99 is less likely to be caught by the first conveyance guide 110, so that the sheet 99 can be easily conveyed smoothly.

  Further, as shown in FIG. 2, in the image forming apparatus 1, the sheet 99 conveyed along the MP path P <b> 4 from the MP tray 81 merges in the middle of the U-turn path P <b> 1 and the apex of the second conveyance guide 120. By merging below 120T, the first conveyance guide 110 and the second conveyance guide 120 are guided. With this configuration, the sheet 99 can be almost straightly fed from the MP tray 81 to the conveyance surface 50A, so that it is easy to manually feed thick paper or the like. Further, even when the sheet 99 placed on the MP tray 81 is curled, the first conveyance guide 110 and the second conveyance guide 120 can suppress a decrease in image formation quality with respect to the curled sheet 99.

  Further, in the image forming apparatus 1, the rear end 121 of the second conveyance guide 120 has a rear end 111C of the central portion 110C of the first conveyance guide 110 and both end portions 110L and 110R, as shown in FIGS. The rear ends 111L and 111R extend to the downstream side in the transport direction D1. With this configuration, the second conveyance guide 120 can guide the sheet 99 until all of the sheet 99 in the left-right direction is attracted to the conveyance surface 50A. As a result, it is possible to reliably suppress a decrease in image formation quality with respect to the curled sheet 99.

  Further, in the image forming apparatus 1, in the second conveyance guide 120, the guide surface 120A that can contact the second surface 99B is a curved surface that is curved while maintaining a straight state in the left-right direction. With this configuration, even when an uncurled sheet 99 is transported, the sheet 99 is easily transported smoothly along the second transport guide 120.

  In the image forming apparatus 1, the first conveyance guide 110 is made of an elastic member that can absorb the thickness of the sheet 99 slightly. With this configuration, the first conveyance guide 110 is slightly crushed and the thickness of the sheet 99 can be slightly absorbed, so that the sheet 99 is not easily caught by the first conveyance guide 110.

  While the present invention has been described with reference to the embodiments, it is needless to say that the present invention is not limited to the above-described embodiments and can be appropriately modified and applied without departing from the spirit thereof.

  For example, the first conveyance guide is not limited to the shape of the first conveyance guide 110 of the embodiment, and may be, for example, the shapes as in the following modifications 1 and 2.

(Modification 1)
In the first modification, as shown in FIG. 9, when the first transport guide 110 is viewed from above, the lines connecting the rear ends 111L, 111C, and 111R are curved so as to swell forward. Further, when the first conveyance guide 110 is viewed from the front, the line connecting the upper ends 112L, 112C, and 112R is curved so as to swell downward. Even if it is such a shape, there can exist an effect similar to an Example.

(Modification 2)
In the second modification, as shown in FIG. 11, when the first transport guide 110 is viewed from above, the lines connecting the rear ends 111L, 111C, and 111R are curved so that the central portion 110C side swells forward, and both ends The portions 110L and 110R are curved so as to swell rearward. Further, when the first transport guide 110 is viewed from the front, the line connecting the upper ends 112L, 112C, and 112R is curved so that the central portion 110C swells downward, and the both ends 110L and 110R are curved so as to bulge upward. doing. Even if it is such a shape, there can exist an effect similar to an Example.

  The present invention can be used for an image forming apparatus, a multifunction machine, and the like.

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 40 ... Photoconductor (photosensitive drum)
31. Developing means (process cartridge)
99 ... sheet, 99A ... first surface of sheet, 99B ... second surface of sheet P1, P2, P3, P4 ... conveying path (P1 ... U-turn path, P2 ... substantially horizontal path, P3 ... discharge path, P4 ... MP Route)
DESCRIPTION OF SYMBOLS 50 ... Conveyance belt, 50A ... Conveyance surface 51, 52 ... Roller (51 ... Drive roller, 52 ... Driven roller)
DESCRIPTION OF SYMBOLS 110 ... 1st conveyance guide, 120 ... 2nd conveyance guide 110C ... Center part of width direction of 1st conveyance guide 110L, 110R ... Both ends of width direction of 1st conveyance guide 21 ... 1st sheet mounting part (sheet cassette) )
81 ... Second sheet placement section (MP tray)
120A: Guide surface of second transport guide, 120T: Top of second transport guide 121 ... Downstream end (rear edge) of second transport guide
111C, 111L, 111R ... downstream end (rear end) of the first conveyance guide
D1 ... transport direction

Claims (8)

An apparatus main body provided with a conveyance path for conveying a sheet;
It is provided in the middle of the conveyance path in the apparatus main body, is wound around a plurality of rollers and can circulate, extends in the width direction of the conveyed sheet, and is a plane along the conveyance path. A conveyor belt that conveys the sheet while adsorbing the first surface of the sheet;
The first surface of the sheet that is provided in the apparatus main body so as to face the conveyance surface, is parallel to the conveyance surface, is aligned in a longitudinal direction orthogonal to the width direction, and passes over the conveyance surface. A plurality of photoreceptors in contact with the second surface on the opposite side;
A plurality of developing means provided corresponding to each of the photoconductors in the apparatus main body, supplying a developer to a latent image formed on each of the photoconductors to form a developer image;
A first conveyance guide provided in the apparatus main body on the upstream side of the conveyance surface in the conveyance path, capable of contacting the first surface of the sheet, and guiding the sheet toward the conveyance surface;
In the apparatus main body, it is provided on the upstream side of the conveyance surface in the conveyance path so as to face the first conveyance guide, is capable of contacting the second surface of the sheet, and directs the sheet toward the conveyance surface. An image forming apparatus including a second conveyance guide for guiding
The first conveyance guide protrudes so that both ends in the width direction approach the parallel to the conveyance surface with respect to the central portion in the width direction, and the both ends are in the conveyance surface with respect to the central portion. An image forming apparatus having a shape protruding so as to be separated in a direction perpendicular to the image forming apparatus.   The image forming apparatus according to claim 1, wherein the first conveyance guide gradually protrudes from the central portion toward the both end portions. The conveying surface extends substantially horizontally;
3. The image forming apparatus according to claim 1, wherein the first conveyance guide has the both end portions higher than the conveyance surface. In the apparatus main body, provided below the conveyor belt, and includes a first sheet placement portion on which the sheet is placed,
The transport path has a U-turn path on the upstream side of the transport surface, which U-turns upward from the first sheet placement unit and transports the sheet to the transport surface,
The image forming apparatus according to claim 3, wherein the first conveyance guide is curved along the U-turn path so as to draw a substantially arc when viewed from the width direction. A second sheet mounting portion provided on a side surface of the apparatus main body and capable of mounting the sheet;
The sheet conveyed from the second sheet stacking unit merges in the middle of the U-turn path in the conveyance path, and merges below the vertex of the second conveyance guide, whereby the first conveyance is performed. The image forming apparatus according to claim 4, wherein the image forming apparatus is guided by the guide and the second conveyance guide.   The image according to any one of claims 1 to 5, wherein a downstream end portion of the second conveyance guide extends to a downstream side in the conveyance direction of the sheet from a downstream end portion of the first conveyance guide. Forming equipment.   7. The image forming apparatus according to claim 1, wherein in the second transport guide, the guide surface that can contact the second surface is a curved surface that is curved while maintaining a straight state in the width direction. .   The image forming apparatus according to claim 1, wherein the first conveyance guide is made of an elastic member that can absorb the thickness of the sheet slightly.

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