Image forming device

Abstract

To effectively prevent a reduction in image quality due to separation electrical discharge.SOLUTION: An image forming apparatus is provided with a regulation part that extends between a transfer nip part and one end of an endless belt that conveys a sheet while opposing to an upper part of the endless belt. The regulation part includes a horizontal part that extends along a width direction orthogonal to a sheet conveyance direction, and a pair of inclined parts that extend in the width direction from both ends in the width direction of the horizontal part and are inclined in a direction approaching the endless belt as directed from one end closer to the horizontal part to the other end in the width direction. The regulation part comes into contact with both ends of a rear end of the sheet floating from the endless belt to prevent separation electrical discharge.SELECTED DRAWING: Figure 2

Description

[Technical field]

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

[0002] Conventionally, there is known an image forming apparatus that includes a process section having a photosensitive drum and a transfer roller, which transfers a developer image onto a sheet, and a fixing section having a heating roller and a pressure roller, which fixes the developer image onto the sheet. In such an image forming apparatus, when a sheet is discharged from the process section, the trailing end side of the sheet in the conveying direction may suddenly displace so as to float upward. In this case, the image forming surface of the sheet may collide with an internal structure of the apparatus, and the developer image before fixing may peel off, which may result in a deterioration in image quality.

[0003] In order to suppress such a deterioration in image quality, a configuration in which an inlet conveying guide is provided near the inlet of the fixing unit is described in Patent Document 1.

[0004] The invention described in Patent Document 1 relates to an inlet transport guide member that guides recording material to the fixing device. The inlet transport guide member is located near the fixing device and is formed of an upper member and a lower member having a predetermined gap. By making the gap narrower at both ends than at the central portion in the longitudinal direction, even if the trailing end of the recording material bounces, only the non-image areas at both ends of the recording material come into contact with the upper member, preventing rubbing of the image and suppressing deterioration in image quality. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-44230 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the image forming apparatus as described above, the surface of the endless belt is charged by applying a transfer bias between the photosensitive drum and the transfer roller, and the sheet is electrically attracted to this charged surface and conveyed. Therefore, if the sheet electrically attracted to the endless belt rises at a steep angle, a peeling discharge occurs between the sheet and the endless belt, and the resulting static electricity disturbs the developer before fixing, causing a deterioration in image quality.

[0007] Therefore, even if the collision of the image-forming surface of the sheet with internal structures of the device is prevented as described in Patent Document 1, the developer image before fixing is disturbed by this peeling discharge, resulting in a deterioration in image quality.

[0008] The present invention has been made to solve the above-mentioned problems, and has an object to provide an image forming apparatus that effectively suppresses degradation of image quality caused by peeling discharge. [Means for solving the problem]

[0009] In order to achieve this object, the image forming apparatus according to the present invention is an image forming apparatus that forms an image on a sheet by transferring a developer image onto the sheet, and includes a transfer unit (13) including a plurality of rollers (17, 18) and an endless belt (19) that is stretched between the plurality of rollers and transports the sheet in a transport direction with its upper surface as a transport surface, a process unit that includes a photosensitive drum (15) provided above the endless belt and forms an image on the sheet in a transfer nip portion between the photosensitive drum and the endless belt, and a transfer unit that transfers an image on the sheet in the transport direction between the transfer nip portion and the transport nip. a first regulating portion (31) facing the conveying surface above the conveying surface between the conveying surface and the downstream end of the conveying surface in the conveying direction, the first regulating portion being capable of abutting the sheet, the first regulating portion having a first horizontal portion (32) extending along a width direction perpendicular to the conveying direction, and a pair of first inclined portions (33) extending in the width direction from both ends of the first horizontal portion in the width direction and inclining in a direction approaching the endless belt as it moves from one end close to the horizontal portion in the width direction to the other end, the first inclined portions being capable of abutting both ends of the sheet in the width direction.

[0010] According to this configuration, when the trailing end of the sheet discharged from the transfer nip portion floats up, the first inclined portions come into contact with both widthwise ends of the trailing end of the sheet, thereby suppressing the sheet from floating up.

[0011] It is also preferable that the first inclined portion is provided at a position overlapping, in the transport direction, with a rotation axis center of a roller that is located furthest downstream in the transport direction among the plurality of rollers.

[0012] According to this configuration, even if the trailing end of the sheet lifts up when the sheet is separated from the endless belt, the first inclined portions abut against both widthwise ends of the trailing end of the sheet, thereby suppressing the sheet from lifting up.

[0013] The image forming apparatus according to the present invention may further include a process unit having a drum frame supporting the photosensitive drum, and the first regulating portion may be provided on the drum frame.

[0014] According to this configuration, the first regulating portion is accurately positioned with respect to the conveying surface of the endless belt, so that the first inclined portions accurately come into contact with both widthwise ends of the trailing end of the sheet when the trailing end of the sheet is lifted up.

[0015] The image forming apparatus according to the present invention may further include a transfer unit having a belt frame that rotatably supports the plurality of rollers, and the first regulating portion may be provided in the second housing.

[0016] According to this configuration, the first regulating portion is positioned with more precision with respect to the conveying surface of the endless belt, and the first inclined portion comes into contact with both widthwise ends of the trailing end of the sheet more accurately when the trailing end of the sheet is lifted up.

[0017] The image forming apparatus according to the present invention further includes a fixing unit for heat-fixing the image formed on the sheet, the fixing unit having a heating roller and a pressure roller that contacts the heating roller to form a fixing nip portion that nips the sheet. It is preferable that the other end of the first inclined portion is provided below a virtual straight line connecting the fixing nip portion and the transfer nip portion.

[0018] According to this configuration, the first inclined portion prevents the sheet in contact with the first inclined portion from bridging the gap between the transfer nip portion and the fixing nip portion in a straight line, and can bend the sheet.

[0019] The image forming apparatus according to the present invention is further capable of forming images on a sheet having a first width in the width direction and a sheet having a second width larger than the first width. It is preferable that the distance in the width direction between the other ends of the pair of first inclined portions is larger than the first width, and the distance in the width direction of the first horizontal portion is smaller than the first width.

[0020] According to this configuration, the first inclined portions come into contact with both widthwise ends of the sheet having the first width.

[0021] In addition, the image forming apparatus according to the present invention further includes a fixing device (50) that heats and fixes an image formed on the sheet, and a second regulating portion (41) provided in a transport path of the sheet between the first regulating portion and the fixing nip portion in the transport direction, the fixing device having a heating roller and a pressure roller that abuts against the heating roller at the fixing nip portion to nip the sheet, the second regulating portion having a second horizontal portion (42) extending along a width direction perpendicular to the transport direction, and a pair of second inclined portions (43) extending in the width direction from both ends of the second horizontal portion in the width direction and inclining downward from one end close to the second horizontal portion toward the other end in the width direction, the second inclined portions being capable of abutting against both ends of the sheet in the width direction, and it is preferable that the widthwise distance between the other ends of each of the pair of second inclined portions is greater than the second width, and the widthwise distance of the second horizontal portions is smaller than the second width.

[0022] According to this configuration, the second inclined portions come into contact with both widthwise ends of the sheet having a second width larger than the first width.

[0023] Moreover, it is preferable that a distance in the width direction of the second horizontal portion is greater than a distance in the width direction between the other ends of the first inclined portions.

[0024] According to this configuration, the second restricting portion restricts the image forming surface of the sheet that is in contact with the first inclined portion from contacting the second restricting portion.

[0025] It is also preferable that the other end of the second inclined portion is provided below a virtual straight line connecting the fixing nip portion and a lower end of the first inclined portion.

[0026] According to this configuration, the second restricting portion restricts the image forming surface of the sheet that is in contact with the second inclined portion from contacting the second restricting portion.

[0027] In addition, it is preferable that the angle that the second inclined portion makes with a horizontal plane is larger than the angle that the first inclined portion makes with the horizontal plane.

[0028] According to this configuration, the second regulating portion further regulates the image forming surface of the sheet abutting against the first inclined portion from contacting the second regulating portion. Also, the second regulating portion regulates the image forming surface of the sheet from contacting the second regulating portion even if the sheet is curved. Effect of the Invention

[0029] According to the present invention, deterioration of image quality caused by peeling discharge can be effectively suppressed. [Brief description of the drawings]

[0030] [Figure 1] 1 is a schematic side cross-sectional view showing a main part of an image forming apparatus 1 according to the present embodiment. [Diagram 2] 2 is a schematic side cross-sectional view of the drum unit 22, the fixing device 50, and the vicinity thereof. [Diagram 3] FIG. 2 is a perspective view of the drum unit 22. [Figure 4] FIG. [Diagram 5] FIG. 2 is a front view of the drum unit 22 as seen from the fixing device 50 side. [Figure 6] 1 is a front view of a sheet entrance of the fixing unit 50 as viewed from the downstream side of the sheet transport path. [Figure 7] 1 is a schematic side cross-sectional view showing a state in which thick paper S1 is conveyed from an image forming unit 11 to a fixing device 50. FIG. [Figure 8] 13 is a schematic side cross-sectional view showing a state in which thin paper S2 is conveyed from image forming unit 11 to fixing device 50. FIG. [Figure 9] FIG. 1 is an enlarged cross-sectional side view of the first restricting portion 31 and the second restricting portion 41 and their vicinity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0031] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0032] In the following description, the up-down direction is defined based on the state in Fig. 1 in which the image forming apparatus 1 is installed and ready for use, the front-rear direction is defined with the direction in which the driven roller 18 is located relative to the drive roller 17 in Fig. 1 being the front, and the left-right direction is defined when the image forming apparatus 1 is viewed from the front. The up-down direction, front-rear direction, and left-right direction are mutually perpendicular. In this embodiment, the up-down direction is the vertical direction, the front-rear direction and the left-right direction are horizontal directions, and the left-right direction is an example of the width direction.

[0033] The image forming device 1 is a color printer and comprises a housing 2 having an opening 5 located at the top, a top cover 6 for opening and closing the opening 5, an image forming section 11 for forming an image on a sheet, a feeder section 4, a transfer unit 13, and a fixing unit 50.

[0034] The top cover 6 is supported by the housing 2 so as to be able to swing about its rear end portion as a fulcrum. The paper discharge tray 3 is disposed on the upper surface of the top cover 6. The paper discharge tray 3 supports sheets that are discharged from a sheet discharge port 57 after printing.

[0035] The image forming unit 11 is housed inside the housing 2 and forms an image on a sheet. The feeder unit 4 is configured to supply a sheet to the image forming unit 11. The transfer unit 13 supplies the sheet supplied from the feeder unit 4 to the image forming unit 11. The fixing device 50 fixes the image formed on the sheet by the image forming unit 11 to the sheet.

[0036] In the image forming apparatus 1, the sheet on which the image has been formed is turned in a conveying direction by approximately 180° upward by intermediate conveying rollers 55 arranged downstream of the fixing unit 50 in the conveying direction and a discharge chute (not shown), and then discharged by discharge rollers 56 from the sheet discharge outlet 57 to the discharge tray 3.

[0037] <Feeder section 4> 1, the feeder unit 4 includes a paper feed tray 7, a pickup roller 8, a pair of paper feed rollers 9, and a pair of registration rollers 10. The feeder unit 4 conveys a sheet placed on the paper feed tray 7 to an image forming unit 11 located approximately in the center of the housing 2 in the front-rear direction, by making a U-turn at the front side of the housing 2.

[0038] The paper feed tray 7 is accommodated in the lowermost part of the housing 2. The paper feed tray 7 supports a plurality of sheets and is detachable from the housing 2. The pickup roller 8 is disposed above the front end of the paper feed tray 7 and sends out the sheets placed on the paper feed tray 7 toward the paper feed rollers 9. The pair of paper feed rollers 9 are located downstream of the pickup roller 8 in the conveying direction and feed the sheets sent out from the paper feed tray 7 by the pickup rollers 8 in the conveying direction. The pair of registration rollers 10 are located downstream of the paper feed rollers 9 in the conveying direction and convey the sheets fed by the paper feed rollers 9 toward the image forming unit 11. The leading edge of the sheet conveyed to the registration rollers 10 hits a nip portion of the pair of registration rollers 10, so that skew is corrected.

[0039] The image forming apparatus 1 can form images on a plurality of types of sheets having different thicknesses, rigidities, or sizes. The types of sheets are mainly divided into thin paper, which is thin, and thick paper, which is thicker than thin paper. Thick paper has higher rigidity than thin paper and is therefore stiffer. Generally, thick paper is shorter in the width direction than thin paper. Examples of thin paper include an A4 size sheet having a size of 210 mm x 297 mm, and a letter size sheet having a size of 216 mm x 279 mm. Examples of thick paper include a postcard size sheet having a size of 100 mm x 148 mm, and glossy paper whose image forming surface is coated with a glossy layer. In the following description, a sheet of thick paper is referred to as thick paper S1, and a sheet of thin paper is referred to as thin paper S2. The thick paper S1 is an example of a sheet having a first width in the present invention, and the thin paper S2 is an example of a sheet having a second width in the present invention.

[0040] <Image forming unit 11> 1, the image forming section 11 includes four process units 24 and four LED arrays 12. The process units 24 are of a so-called direct tandem type capable of color printing, and include a developing cartridge 25 and a drum unit 22.

[0041] <Developing Cartridge 25> 1, the four developer cartridges 25 are arranged corresponding to the four colors of developers (toners), black, yellow, magenta, and cyan, in order from the upstream side in the sheet transport direction. The four developer cartridges 25K, 25Y, 25M, and 25C are lined up at intervals along the sheet transport direction. The developer cartridges 25 supply developer images of each color to the photosensitive drum 15.

[0042] The developing cartridge 25 is detachably disposed inside the housing 2 below the LED array 12, and is replaceable by, for example, a user.

[0043] The developing cartridge 25C includes a developer storage chamber 27 in which developer is stored, an agitator 23, a supply roller 28, a developing roller 16, and a layer thickness regulating blade 29.

[0044] The agitator 23 is disposed in the developer storage chamber 27. The agitator 23 conveys the developer stored in the developer storage chamber 27 to the supply roller 28 by its rotation. The supply roller 28 supplies the developer conveyed by the agitator 23 to the developing roller 16 by its rotation. The developing roller 16 carries the developer supplied from the supply roller 28 on its surface. The surface of the developing roller 16 is in contact with the surface of the photosensitive drum 15, and the developing roller 16 supplies the developer carried on the surface of the developing roller 16 to the surface of the photosensitive drum 15 by rotating. The layer thickness regulating blade 29 adjusts the thickness of the developer carried on the surface of the developing roller 16 so that it is uniform and at a predetermined thickness. The layer thickness regulating blade 29 protrudes from diagonally above and behind the developing roller 16 toward the developing roller 16, and its tip abuts against the surface of the developing roller 16.

[0045] <Drum unit 22> The drum unit 22 includes a photosensitive drum 15 , a charger 26 , and a drum frame 30 that supports the photosensitive drum 15 .

[0046] The photosensitive drum 15 bears an image to be transferred to a sheet, and is a cylindrical photosensitive body whose outermost layer is formed of a positively charged photosensitive layer made of polycarbonate or the like, and transfers the electrostatic latent image formed on the surface to the sheet by contacting the sheet. The photosensitive drum 15 is disposed above the transfer unit 13, and its surface faces the conveying surface 19B of the endless belt 19.

[0047] The charger 26 charges the surface of the photosensitive drum 15, and faces the surface of the photosensitive drum 15 at a predetermined distance from the photosensitive drum 15 at an obliquely upper rear side thereof so as not to come into contact with the photosensitive drum 15.

[0048] The charger 26 is a scorotron charger that applies a substantially uniform positive charge to the surface of the photosensitive drum 15 by performing corona discharge from a charging wire made of tungsten or the like.

[0049] <LEDアレイ12> The LED array 12 has a plurality of LEDs at its tip. The LED array 12 is held by the top cover 6 so as to be suspended from the top cover 6. When the top cover 6 is closed, the LED array 12 is disposed above the photosensitive drum 15 and faces the surface of the photosensitive drum 15. Specifically, the LED array 12 moves between an exposure position where the photosensitive drum 15 is exposed and a retracted position located above the exposure position by opening and closing the top cover 6.

[0050] The LED array 12 exposes the surface of the corresponding photosensitive drum 15 by causing a plurality of LEDs to blink based on image data, thereby forming an electrostatic latent image on the surface.

[0051] <Transfer unit 13> As shown in FIGS. 1 and 2, the transfer unit 13 includes a drive roller 17, a driven roller 18, an endless belt 19, a transfer roller 20, and a belt frame 14.

[0052] The drive roller 17 rotates when a drive force is input from a motor (not shown). The driven roller 18 is rotatably disposed in a position separated from and forward of the drive roller 17. The endless belt 19 is stretched so as to span between the drive roller 17 and the driven roller 18. The endless belt 19 rotates together with the drive roller 17 and the driven roller 18 as the drive roller 17 rotates. The belt frame 14 supports the drive roller 17, the driven roller 18, the endless belt 19, and the transfer roller 20. The drive roller 17 and the driven roller 18 are an example of the multiple rollers in the present invention.

[0053] 2, the endless belt 19 has a conveying surface 19B. The conveying surface 19B is an upper surface that supports a sheet from below among the outer surfaces of the endless belt 19. The transfer unit 13 conveys the sheet conveyed from the feeder section 4 toward the fixing device 50 while placing the sheet on the conveying surface 19B of the endless belt 19.

[0054] The transfer roller 20 is disposed facing the photosensitive drum 15 in the vertical direction with the endless belt 19 sandwiched therebetween. As shown in Fig. 2, the transfer roller 20 sandwiches the endless belt 19 between itself and the photosensitive drum 15, thereby forming a transfer nip portion 21 at a position where the photosensitive drum 15 and the endless belt 19 come into contact with each other. The photosensitive drum 15 and the transfer roller 20 sandwich and press the sheet together in the transfer nip portion 21. The transfer roller 20 transfers the developer attached to the surface of the photosensitive drum 15 to the image forming surface of the sheet by applying a voltage of the opposite polarity to the charge on the photosensitive drum 15 in the transfer nip portion 21 to the sheet from the opposite side of the image forming surface.

[0055] The axial direction of the rotation shaft of the photosensitive drum 15 and the transfer roller 20 coincides with the sheet conveying direction and the thickness direction of the conveyed sheet, so that the photosensitive drum 15 and the transfer roller 20 are arranged along the direction perpendicular to the rotation shaft.

[0056] <Fixing unit 50> The fixing unit 50 heats and melts the developer transferred to the sheet discharged from the image forming unit 11, thereby fixing the developer to the sheet. The fixing unit 50 is disposed downstream of the drum unit 22 in the sheet transport direction. The fixing unit 50 is detachably attached to the housing 2.

[0057] The fixing device 50 includes a heating roller 51, a pressure roller 52, and a fixing frame 54. The heating roller 51 is disposed above the image forming surface of the sheet supported by the conveying surface 19B of the endless belt 19, and applies a conveying force to the sheet while heating the developer transferred to the sheet. The pressure roller 52 is disposed on the opposite side of the heating roller 51 with the sheet sandwiched therebetween in the vertical direction, and presses the sheet toward the heating roller 51. The heating roller 51 and the pressure roller 52 press against each other to form a fixing nip portion 53, and the sheet is sandwiched in the fixing nip portion 53. The fixing device 50 applies heat to the sheet in the fixing nip portion 53 to melt the developer, and fixes the developer to the sheet. The fixing frame 54 houses the heating roller 51 and the pressure roller 52.

[0058] <First restriction portion 31> FIG. 2 is a side cross-sectional view of the drum unit 22 and the vicinity of the fixing device 50. FIG. 9 is a side cross-sectional view further enlarging the vicinity of the first regulating portion 31 and the second regulating portion 41. As shown in FIG. 2 and FIG. 9, the drum frame 30 includes a first regulating portion 31 having a rib shape. The first regulating portion 31 is located between the transfer nip portion 21A located at the most downstream position in the sheet conveying direction and the one end portion 19A of the endless belt 19, and is located above the endless belt 19, and faces the conveying surface 19B of the endless belt 19 in the up-down direction. The one end portion 19A of the endless belt 19 is the rear end portion of the conveying surface 19B of the endless belt 19, and is located approximately directly above the center of the rotation shaft of the drive roller 17.

[0059] FIG. 3 is a perspective view of the drum unit 22. FIG. 5 is a front view of the drum unit 22 seen from the fixing device 50 side. As shown in FIG. 3 and FIG. 5, the first regulating portion 31 includes a first horizontal portion 32 and a pair of first inclined portions 33. The first horizontal portion 32 extends in the left-right direction. The pair of first inclined portions 33 extend in the left-right direction from both ends of the first horizontal portion 32 in the left-right direction. The pair of first inclined portions 33 are inclined in a direction approaching the endless belt 19 from the center toward both ends in the left-right direction. In detail, the first inclined portion 33R located on the right side of the pair of first inclined portions 33 has its left end connected to the right end of the first horizontal portion 32 and is inclined so as to gradually approach the endless belt 19 from the left end to the right end. The first inclined portion 33L located on the left side of the pair of first inclined portions 33 has its right end connected to the left end of the first horizontal portion 32, and is inclined from the right end to the left end so as to gradually approach the endless belt 19. Here, the lower end 34 of the first inclined portion 33 refers to the right end 34R of the first inclined portion 33R and the left end 34L of the first inclined portion 33L.

[0060] As shown in FIGS. 2 and 9, a portion of the pair of first inclined portions 33 is provided directly above one end portion 19A of the endless belt in the sheet conveying direction.

[0061] As shown in Figures 2 and 9, the lower end 34 of the first inclined portion 33 is located below the imaginary straight line L1 connecting the transfer nip portion 21A and the fixing nip portion 53, and is the position in the first regulating portion 31 closest to the endless belt 19 in the vertical direction.

[0062] 3 and 5, the left-right distance W1 between the left end 34L of the first inclined portion 33L and the right end 34R of the first inclined portion 33R is greater than the left-right width of the cardboard S1, and the left-right distance of the first horizontal portion 32 is smaller than the width of the cardboard S1. An example of the cardboard S1 is a postcard, and in this case, the width is 100 mm.

[0063] Here, the image forming apparatus 1 conveys the sheet by aligning the left-right center of the sheet conveying path with the left-right center of the sheet, so-called center reference. The first horizontal section 32 is disposed at a position where the left-right center of the sheet conveyed by the endless belt 19 and the left-right center of the first horizontal section 32 approximately coincide with each other.

[0064] <Second restriction portion 41> FIG. 4 is a perspective view of the fixing device 50. FIG. 6 is a front view of the sheet entrance of the fixing device 50 seen from the downstream side of the sheet transport path. As shown in FIG. 4 and FIG. 6, the fixing frame 54 includes a second regulating portion 41 having a rib shape. The second regulating portion 41 is disposed on the entrance side of the fixing device 50, that is, above the transport path of the sheet from the transfer nip portion 21A to the fixing device 50. The second regulating portion 41 includes a second horizontal portion 42 and a pair of second inclined portions 43. The second horizontal portion 42 extends along the left-right direction. The pair of second inclined portions 43 extend in the left-right direction from both ends of the second horizontal portion 42 in the left-right direction, respectively. The second inclined portion 43 is inclined downward from the center toward both ends in the left-right direction. In detail, the second inclined portion 43R located on the right side of the pair of second inclined portions 43 has one end connected to the right end of the second horizontal portion 42 and is inclined downward to the right from the left end to the right end. The second inclined portion 43L located on the left side of the pair of second inclined portions 43 has its right end connected to the left end of the second horizontal portion 42 and is inclined downward and left from the right to the left end. Here, the lower end 44 of the second inclined portion 43 refers to the right end 44R of the second inclined portion 43R and the left end 44L of the second inclined portion 43L.

[0065] 2 and 9, the lower end of the second inclined portion 43 is located below an imaginary straight line L2 that connects the lower end 34 of the first inclined portion 33 and the fixing nip portion 53. As shown in FIG.

[0066] 4 and 6, the distance W2 between the left end 44L of the second inclined portion 43L and the right end 44R of the second inclined portion 43R is greater than the width of the thin paper S2 in the left-right direction, and the distance of the second horizontal portion 42 in the left-right direction is smaller than the width of the thin paper S2. The distance of the second horizontal portion 42 in the left-right direction is greater than the width of the thick paper S1. The distance of the second horizontal portion 42 in the left-right direction is greater than the distance W1 between the left end 34L of the first inclined portion 33L and the right end 34R of the first inclined portion 33R.

[0067] As shown in FIG. 6, the angle θ 2 is the angle θ between the first inclined portion 33 and the horizontal plane 1 Greater than.

[0068] <Effects of this embodiment> The image forming apparatus 1 conveys a sheet on which an image has been formed in the transfer nip portion 21A toward the fixing device 50 by the endless belt 19. The sheet is in a stable position when the front end and rear end are sandwiched between the fixing nip portion 53 and the transfer nip portion 21A, respectively. When the rear end of the sheet is discharged from the transfer nip portion 21A, the sheet is in a state where only the front end is sandwiched in the fixing nip portion 53. At this time, the rear end of the sheet that is not sandwiched may be lifted up from the conveying surface 19B due to the impact on the sheet when the sheet is discharged or the force on the sheet in the fixing nip portion 53. When the rear end of the sheet is lifted up from the conveying surface 19B in this way, peeling discharge occurs between the conveying surface 19B and the lifted sheet, and the developer image before fixing may be disturbed by the generated static electricity and the impact, etc., which may lead to a deterioration in image quality.

[0069] A pair of first inclined portions 33 of the first regulating portion 31 are arranged between the transfer nip portion 21A, where the sheet floats up from the endless belt 19, and one end portion 19A of the endless belt 19, and face the conveying surface 19B above the conveying surface 19B of the endless belt 19.

[0070] According to this configuration, when the trailing end of the sheet rises up from the conveying surface 19B, the pair of first inclined portions 33 come into contact with both left and right ends of the raised trailing end of the sheet, and are able to directly press down on the trailing end of the sheet, thereby preventing the trailing end of the sheet from rising up and effectively suppressing peeling discharges.

[0071] When the sheet discharged from the transfer nip portion 21A is further conveyed, the rear end of the sheet separates from the conveying surface 19B at one end portion 19A of the endless belt 19. In this case as well, the rear end of the sheet, which is no longer supported by the endless belt 19, floats up, and there is a risk of peeling discharge occurring.

[0072] The pair of first inclined portions 33 of the first regulating portion 31 are disposed at positions where parts of the pair of first inclined portions 33 overlap substantially directly above one end portion 19A of the endless belt 19 in the sheet conveying direction.

[0073] According to this configuration, even when the trailing end of the sheet leaves the conveying surface 19B, the pair of first inclined portions 33 abut against both left and right ends of the trailing end of the sheet, and are able to directly press down on the trailing end of the sheet, thereby preventing the trailing end of the sheet from lifting up and effectively suppressing peeling discharges.

[0074] Further, the pair of first inclined portions 33 are inclined so as to gradually approach the conveying surface 19B of the endless belt 19 from the center toward both ends in the left-right direction.

[0075] According to this configuration, when the first inclined portion 33 abuts against both ends of the sheet in the left-right direction, it is possible to prevent the image forming surface at the center of the sheet in the left-right direction from contacting the first regulating portion 31, thereby suppressing deterioration in image quality due to image rubbing of the pre-fixed image.

[0076] Incidentally, when the fixing nip portion 53 is disposed above the conveying surface 19B of the endless belt 19, there is a high possibility that peeling discharge due to lifting of the sheet trailing edge occurs when forming an image on a stiff and resilient sheet such as thick paper. A stiff sheet bridges the gap between the transfer nip portion 21A and the fixing nip portion 53 in a substantially straight line without bending like thin paper, so that the sheet trailing edge is likely to be lifted up by being greatly inclined toward the conveying surface 19B of the endless belt 19. When the sheet trailing edge is largely lifted up in this manner, the impact due to peeling discharge becomes large, so that the peeling discharge is likely to significantly deteriorate the image quality, particularly in the case of a stiff sheet. In this embodiment, thick paper S1 is taken as an example of a stiff sheet.

[0077] In this embodiment, the left-right distance W1 between the left end 34L of the first inclined portion 33L and the right end 34R of the first inclined portion 33R is greater than the left-right width of the cardboard S1, and the left-right distance of the first horizontal portion 32 is smaller than the width of the cardboard S1.

[0078] According to this configuration, the first inclined portions 33 come into contact with both left and right ends of the thick sheet S1 and suppress lifting of the rear end of the thick sheet S1, thereby making it possible to effectively suppress peeling discharge.

[0079] As shown in FIG. 9, the lower end 34 of the first inclined portion 33 is disposed below the imaginary straight line L1 that connects the transfer nip portion 21A and the fixing nip portion 53. As shown in FIG.

[0080] Fig. 7 is a schematic side cross-sectional view showing how thick paper S1 is transported from image forming unit 11 to fixing device 50. With this configuration, as shown in Fig. 7, when first inclined portion 33 comes into contact with thick paper S1, first restricting portion 31 prevents thick paper S1 from bridging in a straight line between transfer nip portion 21A and fixing nip portion 53, and can bend thick paper S1. The bending of thick paper S1 reduces the impact when the rear end of thick paper S1 lifts up, further suppressing peeling discharge.

[0081] The first regulating portion 31 is disposed in the drum unit 22 which is in contact with the transfer unit 13 in the transfer nip portion 21A.

[0082] According to this configuration, the first regulating portion 31 is accurately positioned with respect to the conveying surface 19B of the endless belt 19. As a result, the first inclined portion 33 accurately contacts both ends of the sheet in the left-right direction when the trailing end of the sheet is lifted, and peeling discharge can be effectively suppressed.

[0083] However, when the sheet transported by the endless belt 19 is a thin paper S2 whose width in the left-right direction is greater than the left-right distance W1 between the right end 34R of the first inclined portion 33R and the left end 34L of the first inclined portion 33L, when the thin paper S2 floats up from the transport surface 19B of the endless belt 19, the first regulating portion 31 comes into contact with the image forming surface of the thin paper S2, and there is a risk that image rubbing will occur in the pre-fixed image.

[0084] Therefore, in this embodiment, the lower end 44 of the second inclined portion 43 is disposed below the imaginary straight line L2 connecting the lower end 34 of the first inclined portion 33 and the fixing nip portion 53.

[0085] Fig. 8 is a schematic side cross-sectional view showing how the thin paper S2 is transported from the image forming unit 11 to the fixing unit 50. With this configuration, as shown in Fig. 8, the second inclined portion 43 contacts the thin paper S2 before the image forming surface of the thin paper S2 contacts the first inclined portion 33. As a result, the second restricting portion 41 restricts the lifting of the thin paper S2 to suppress peeling discharge, and also restricts the image forming surface of the thin paper S2 from contacting the first restricting portion 31, simultaneously suppressing degradation of image quality due to image rubbing of the image on the thin paper S2 before fixing.

[0086] 9, the lower end 44 of the second inclined portion 43 is provided below the imaginary line L2 connecting the lower end 34 of the first inclined portion 33 and the fixing nip portion 53. In other words, the lower end 44 of the second inclined portion 43 is disposed below the imaginary line L1 connecting the transfer nip portion 21A and the fixing nip portion 53.

[0087] 8, when the thin paper S2 comes into contact with the second inclined portion 43, the second restricting portion 41 prevents the thin paper S2 from bridging the gap between the transfer nip portion 21A and the fixing nip portion 53 in a straight line, and can bend the thin paper S2. The bending of the thin paper S2 reduces the impact when the rear end of the thin paper S2 lifts up, further suppressing peeling discharge.

[0088] Further, the second inclined portion 43 is inclined downward from the center toward both ends in the left-right direction.

[0089] According to this configuration, when the second inclined portion 43 abuts both ends of the sheet in the left-right direction, it prevents the image forming surface at the center of the sheet in the left-right direction from contacting the second regulating portion 41, thereby suppressing deterioration in image quality due to image rubbing of the pre-fixed image.

[0090] As shown in FIG. 6, the angle θ 2is the angle θ between the first inclined portion 33 and the horizontal plane 1 It is larger than that.

[0091] According to this configuration, the pair of second inclined portions 43 widen the space between the left and right inclined portions 43L and 43R, thereby preventing the image forming surface of the thick paper S1 being transported through the space to the fixing device 50 from contacting the second regulating portion 41.

[0092] Incidentally, when the sheet is curved in an upward convex direction, even if both left-right ends of the sheet are in contact with the second inclined portion 43, the image forming surface at the center in the left-right direction of the sheet may come into contact with the second restricting portion 41. Also, thin paper S2 has weaker stiffness than thick paper S1 and tends to curve more easily.

[0093] The second inclined portion 43 forms an angle θ 2 is the angle θ 1 By making the thickness larger than the first limiting portion 41, even if the thin paper S2 is curved in an upward convex direction, the image forming surface of the thin paper S2 is further prevented from contacting the second limiting portion 41, thereby suppressing deterioration in image quality due to image rubbing of the image before fixing.

[0094] Although the embodiment has been described above, the present invention is not limited to the above-mentioned embodiment. The specific configuration can be appropriately changed as described below without departing from the spirit of the invention.

[0095] For example, in the above embodiment, the first regulating portion 31 is provided on the drum frame 30, but is not limited thereto. For example, the first regulating portion 31 may be provided on the belt frame 14 of the transfer unit 13. In this case, since the endless belt 19 that conveys the sheet and the first regulating portion 31 are both supported by the belt frame 14, the first regulating portion 31 is accurately positioned with respect to the conveying surface 19B. This allows the first inclined portions to more accurately abut against both widthwise ends of the rear end of the sheet when the rear end of the sheet is lifted up.

[0096] The first inclined portion 33 is not limited to the shape in the above embodiment, but may be inclined from the center toward both ends in the left-right direction toward the conveying surface 19B. The shapes of the left and right first inclined portions 33L and 33R do not have to be the same.

[0097] The second inclined portion 43 is not limited to the shape in the above embodiment, but may be inclined downward from the center toward both ends in the width direction. The shapes of the left and right second inclined portions 43L and 43R do not have to be the same.

[0098] In the above embodiment, an exposure unit using LEDs is exemplified as the LED array 12, but the present invention is not limited thereto. For example, the exposure unit may be an exposure unit including a laser light source, a polygon mirror, an fθ lens, and a reflecting mirror. In this case, a laser beam is emitted from the laser light source based on image data. The laser beam is deflected by the polygon mirror, passes through the fθ lens, and then the optical path is turned back by the reflecting mirror. The optical path is further bent downward by the reflecting mirror, so that the laser beam is irradiated onto the surface of the photosensitive drum 15, and an electrostatic latent image is formed on the photosensitive drum 15.

[0099] In the above embodiment, the fixing unit is exemplified as the fixing device 50 having the heating roller 51 and the pressure roller 52, but is not limited thereto. For example, the fixing unit may be a fixing device including a heating unit having an endless belt and a nip member disposed inside the endless belt and sandwiching the endless belt between the endless belt and the pressure roller 52.

[0100] In the above embodiment, the image forming apparatus 1 that forms a color image is exemplified, but the present invention is not limited to this and may be, for example, an image forming apparatus 1 that forms a monochrome image. The image forming apparatus 1 may be a laser printer, a copying machine or a multifunction machine that includes a document reading device such as a flatbed scanner, or the like.

[0101] Furthermore, the present invention is not limited to the above-described embodiment as long as it meets the spirit of the invention described in the claims. [Explanation of symbols]

[0102] 1. Image forming device 2. Chassis 13 Transcription Unit 15 Photosensitive drum 17 Drive roller 18 Driven roller 19 Endless Belt 19B Conveying surface 21 Transfer nip 24 Process Unit 31 First Regulatory Department 32 1st horizontal section 33 1st slope part 41 Second Regulatory Department 42 2nd horizontal section 43 2nd slope part 50 Fixing unit

Claims

1. An image forming apparatus for forming an image on a sheet by transferring a developer image onto the sheet, comprising: a transfer unit (13) including a plurality of rollers (17, 18) and an endless belt (19) that is stretched between the plurality of rollers and conveys the sheet in a conveying direction with an upper surface thereof as a conveying surface; a process unit including a photosensitive drum (15) provided above the endless belt, the process unit forming an image on the sheet at a transfer nip portion between the photosensitive drum and the endless belt; a fixing unit for heat-fixing the image formed on the sheet, the fixing unit having a heating roller and a pressure roller that contacts the heating roller at a fixing nip portion and nips the sheet; a first regulating portion (31) that faces the conveying surface above the conveying surface between the transfer nip portion in the conveying direction and a downstream end portion of the conveying surface in the conveying direction and is capable of contacting the sheet; a second restricting portion provided in a conveying path of the sheet between the first restricting portion and the fixing nip portion in the conveying direction; an image forming apparatus capable of forming an image on a sheet having a first width in a width direction perpendicular to the conveying direction and a sheet having a second width larger than the first width, The first restricting portion is A first horizontal portion (32) extending along the width direction; a pair of first inclined portions (33) extending in the width direction from both ends in the width direction of the first horizontal portion, inclined in a direction approaching the endless belt from one end close to the first horizontal portion in the width direction toward the other end, the first inclined portions being capable of abutting against both ends in the width direction of the sheet, a distance in the width direction between the other ends of the pair of first inclined portions is greater than the first width, The distance in the width direction of the first horizontal portion is smaller than the first width, The second restricting portion is A second horizontal portion (42) extending along a width direction perpendicular to the conveying direction; a pair of second inclined portions (43) extending in the width direction from both ends of the second horizontal portion in the width direction, inclined downward from one end close to the second horizontal portion in the width direction toward the other end, the second inclined portions being capable of abutting against both ends of the sheet in the width direction, a distance in the width direction between the other ends of the pair of second inclined portions is greater than the second width, an image forming apparatus, characterized in that the distance in the width direction of the second horizontal portion is smaller than the second width and is larger than the distance in the width direction between the other ends of the first inclined portions.

2. 2 . The image forming apparatus according to claim 1 , wherein the first inclined portion is provided at a position overlapping in the transport direction with a rotation axis center of a roller that is located most downstream in the transport direction among the plurality of rollers.

3. The process unit is The photosensitive drum further includes a drum frame for supporting the photosensitive drum.

3. The image forming apparatus according to claim 1, wherein the first regulating portion is provided on the drum frame.

4. The transfer unit further includes a belt frame that rotatably supports the rollers, 3. The image forming apparatus according to claim 1, wherein the first regulating portion is provided on the belt frame.

5. A fixing device that heats and fixes an image formed on the sheet, a fixing unit including a heating roller and a pressure roller that contacts the heating roller to form a fixing nip portion that nips the sheet; 5. The image forming apparatus according to claim 1, wherein the other end of the first inclined portion is provided below a virtual straight line connecting the fixing nip portion and the transfer nip portion.

6. 2 . The image forming apparatus according to claim 1 , wherein the other end of the second inclined portion is provided below a virtual straight line connecting the fixing nip portion and a lower end of the first inclined portion.

7. 2. The image forming apparatus according to claim 1, wherein an angle that the second inclined portion makes with a horizontal plane is larger than an angle that the first inclined portion makes with a horizontal plane.

Images