JP2006312543A - Sheet carrying device and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To carry a skew-corrected sheet in a stable state by a carrier roller and a carrier roller, in a sheet carrying device for correcting a skew of the sheet by a shutter member. <P>SOLUTION: The sheet P is carried from first carrier roller pairs 24, and is carried by second carrier roller pairs 28 composed of the carrier roller 26 and the carrier roller 27. The shutter member 30 is energized by first energizing force, and corrects the skew of the sheet by allowing the sheet tip to abut on an abutting surface 30a. The shutter member 30 retreats to a guide position energized by second energizing force by this abutment, and energizes the sheet P to the upper guide 31b side by guiding a lower side surface of the sheet by a guide surface 30d. Thus, the sheet P passed through the second carrier roller pairs 28 is stably carried. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a sheet conveying apparatus and an image forming apparatus that correct sheet skew using a shutter member.

  In an image forming apparatus such as a printer or a copying machine, there is a technique for correcting the skew of a sheet before image formation. As an example of this, a technique for correcting the skew of the sheet by causing the front end of the sheet to abut against the contact surface of the shutter member that is positioned substantially perpendicular to the sheet conveyance direction and causing the front end of the sheet to follow the contact surface. (For example, refer to Patent Document 1). This will be described with reference to FIG.

  The sheet P transported along the guide member 25 by the first transport roller pair 24 is then transported to the nip portion of the second transport roller pair 28 including the transport roller 26 and the transport roller 27. A shutter member 60 is rotatably attached to the transport roller 27 so as to cover the transport roller 27. The shutter member 60 is disposed such that its contact surface 60a is positioned on the transport path slightly upstream of the second transport roller pair 28. In addition, the shutter member 60 is given a biasing force F in the direction opposite to the sheet conveyance direction (counterclockwise in FIG. 9) by its own weight or a biasing member, and the contact surface is in a state where the sheet P is not conveyed. The configuration is such that 60 a is in contact with the downstream end of the conveyance guide 43.

  Accordingly, the sheet P sent from the first conveying roller pair 24 first comes into contact with the contact surface 60a of the shutter member 60, and the leading end is stopped to form a loop. When the restoring force F ′ of the loop exceeds the urging force F of the shutter member 60, the shutter member 60 rotates clockwise in the figure, and the sheet P can pass through the second conveying roller pair 28. . Here, when the loop is formed, the skew of the sheet P can be absorbed and the leading ends thereof can be aligned, and when the sheet P passes through the second conveying roller pair 28, the skew is corrected. .

  The sheet P that has passed through the second conveying roller pair 28 is guided between the lower guide 31 c and the upper guide 31 d constituting the pre-transfer guide 31, and is formed by the photosensitive drum 11 and the transfer roller 15. Guided to the nip T. The toner image formed on the photosensitive drum 11 is transferred to the sheet P by the transfer bias applied to the transfer roller 15 when the sheet P passes through the transfer nip T. The sheet P after the toner image is transferred is further conveyed to the downstream side, and is fixed to the sheet P by a fixing device (not shown).

  Since the sheet conveying apparatus having such a shutter member 60 can correct the skew of the sheet P with a relatively simple configuration, it is widely used in, for example, a small laser beam printer.

JP 2002-265100 A

  However, according to the above-described sheet conveying apparatus, there is a problem that the conveyance of the sheet after correcting the skew by the shutter member 60 is not stable.

  That is, in the above-described sheet conveying apparatus, after the leading edge of the sheet has passed through the second conveying roller pair 28, the shutter member 60 is rotated to the printing surface side (the side on which the toner image is transferred at the transfer nip T) to be conveyed. Therefore, the sheet is pressed from the printing surface side to the non-printing surface side (the side where the toner image is not transferred at the transfer nip T) by the shutter member 60.

  For this reason, the conveyance direction after passing through the second conveyance roller pair 28 differs depending on the type of sheet. For example, thick paper is not significantly affected by pressing by the shutter member 60, but in the case of thin paper or moisture-absorbed paper, the sheet leading edge may not follow the lower guide 31c due to pressing by the shutter member 60.

  As described above, when the conveyance of the sheet after skew correction is not stable, the following problems such as image blurring and deterioration of image quality occur.

  As shown in FIG. 8B, considering that the leading end of the sheet is conveyed along the lower guide 31c, the position where the leading end (downstream end) of the lower guide 31c is closer to the photosensitive drum 11 is on the photosensitive drum 11. The formed toner image can be faithfully transferred onto the sheet. However, when the leading end of the sheet does not follow the lower guide 31c as shown in FIG. The angle formed by the tangent line of the photosensitive drum 11 at the position: θ2) in FIG. 8B increases, and the vibration applied to the photosensitive drum 11 increases. For this reason, when the toner image on the photosensitive drum 11 is transferred to the sheet P, image blurring tends to occur.

  Therefore, conversely, as shown in FIG. 8A, in consideration of the fact that the leading edge of the sheet does not follow the lower guide 31c, if the position of the leading edge of the lower guide 31c is far from the photosensitive drum 11, it is formed on the photosensitive drum. The scattering of the toner image on the sheet P is deteriorated, and the image quality is deteriorated.

  Note that image blurring and degradation in image quality can be avoided by conveying the sheet P along the upper guide 31d and reducing the entry angle θ1 of the sheet P with respect to the photosensitive drum 11, but the above-described configuration can be avoided. In the conventional sheet conveying apparatus, since there is a pressure from the printing surface side by the shutter member 60, it is necessary to increase the distance between the transfer nip portion T and the second conveying roller pair 28, and the apparatus becomes large. It will be.

  SUMMARY An advantage of some aspects of the invention is that it provides a sheet conveying apparatus that can stably convey a sheet after correcting skew by a shutter member, and an image forming apparatus including the sheet conveying apparatus. If the sheet after skew correction can be stably conveyed, image blurring and image quality deterioration can be prevented without increasing the size of the apparatus.

  The present invention includes a first conveying unit disposed on the upstream side in the sheet conveying direction, a second conveying unit disposed on the downstream side, and a shutter member disposed in the vicinity of the second conveying unit. And the shutter member corrects the skew of the sheet by abutting the leading edge of the sheet that has been conveyed by the first conveying unit and has not reached the second conveying unit, and abuts the sheet. When the sheet is retracted and the skew of the sheet is corrected, the shutter member is biased by the first biasing means, and when the sheet is retracted, the shutter member is further biased by the second biasing means. By urging, the sheet abuts on the sheet after passing through the second conveying means to guide the sheet in a predetermined direction.

  According to the present invention, the biasing force at the time of guiding the back surface of the sheet after passing through the second transporting unit is increased compared with the case where the shutter member corrects the skew of the sheet, thereby affecting the thickness and moisture absorption state of the sheet. In other words, it is possible to guide a sheet with corrected skew in a predetermined direction.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In addition, what attached | subjected the same code | symbol in the same drawing or a different drawing performs the same structure or the same effect | action, The duplication description is abbreviate | omitted suitably about these.

<Embodiment 1>
FIG. 1 shows an image forming apparatus to which the present invention can be applied. The image forming apparatus shown in the figure is an electrophotographic laser beam printer, and the figure schematically shows a longitudinal sectional view of the laser beam printer as viewed from the front side, that is, from the side where the user is positioned during operation. FIG.

  An outline of the configuration and operation of a laser beam printer (hereinafter referred to as “image forming apparatus”) will be described with reference to FIG.

  The image forming apparatus 1 shown in FIG. 1 includes an image forming apparatus main body 2 constituting a frame, an image forming unit 3 for forming an image, a sheet storage unit 4 for storing sheets, and a sheet from the sheet storage unit 4 to the image forming unit 3. A sheet feeding / conveying unit 5 for feeding and conveying P, a fixing unit 6 for fixing a toner image on the sheet P, a sheet discharging unit 7 for discharging the sheet P after fixing the toner image, and a sheet after fixing the toner image during double-sided image formation. A sheet refeeding and conveying unit 8 that refeeds and conveys P to the image forming unit 3 is provided.

  In the image forming unit 3, the photosensitive drum 11 is rotationally driven in the direction of the arrow (clockwise) in FIG. 1, and after the surface is uniformly charged by the charger 12, the exposure of the laser scanner 13 based on the image information is performed. As a result, an electrostatic latent image is formed on the surface. This electrostatic latent image is developed as a toner image by the developing device 14. The toner image formed on the photosensitive drum 11 is transferred to a sheet P conveyed from a sheet feeding / conveying unit 5 (described later) at a transfer nip T formed between the photosensitive drum 11 and the transfer roller 15. 15 is electrostatically transferred. The sheet P after the toner image is transferred is discharged by the discharging needle 16 and peeled off from the surface of the photosensitive drum 11. Further, the toner remaining on the surface of the photosensitive drum 11 after the toner image transfer is removed by the cleaning device 17.

  The sheet storage unit 4 is provided with a paper feed cassette 21 that stores sheets P in a stacked state.

  The sheet feeding / conveying unit 5 includes a paper feeding roller 22, a conveyance guide 23, a first conveyance roller pair (first conveyance unit) 24, a conveyance guide 25, a second conveyance roller pair (second conveyance unit) 28, and a shutter. A member 30, a pre-transfer guide 31, and the like are disposed.

  The sheet P stored in the sheet feeding cassette 21 is fed by the sheet feeding roller 22 and is conveyed by the first conveying roller pair 24 along the conveying guides 23 and 25 to the second conveying roller pair 28. The second conveying roller pair 28 includes a conveying roller (rotating body) 26 and a conveying roller (rotating body) 27 in contact with the conveying roller (rotating body) 27, and the sheet P includes a conveying roller 26 and a conveying roller 27. It is conveyed to the nip portion N formed therebetween. Here, the actual nip portion N is formed in a strip shape having an appropriate width in the sheet conveyance direction. However, for the sake of convenience of explanation, the nip portion N is described as being formed in a linear shape having no width. To do. A manual feed guide 43 that guides the sheet P supplied manually is provided on the upstream side of the second conveyance roller pair 28 in addition to the above-described conveyance guide 25.

  The sheet P conveyed to the second conveyance roller pair 28 is corrected in skew by a shutter member 30 described later, and conveyed to the downstream pre-transfer guide 31 without being stopped. The pre-transfer guide 31 has a lower guide 31a (a guide on the non-printing surface side where an image on the sheet P is not formed) and an upper guide 31b (a guide on the printing surface side where an image on the sheet P is formed), A conveyance path 31e is formed between the two. A sheet detection sensor (not shown) is disposed immediately downstream of the second pair of conveyance rollers 28 in the conveyance path 31e. The above-described laser scanner 13 starts exposure on the surface of the photosensitive drum 11 based on the timing at which the sheet detection sensor detects the leading edge of the sheet P.

  After the toner image on the photosensitive drum 11 is transferred, the sheet P conveyed to the transfer nip T is separated from the surface of the photosensitive drum 11 by the curvature separation by the photosensitive drum 11 and the electrostatic separation by the static elimination needle 16, and before fixing. It is conveyed along the guide 32 to the fixing unit 6. The sheet P is heated and pressed here to fix the toner image on the surface. The sheet P after the toner image is fixed is discharged onto a discharge tray 36 by a sheet discharge unit 7 including a flapper 33, a discharge guide 34, a discharge roller 35, and the like. When image formation is performed on both sides of the sheet P, the sheet P having the toner image fixed on the surface thereof is guided to the sheet re-feeding / conveying unit 8 and is again fed and conveyed to the image forming unit 3 from here. . That is, the sheet P having the toner image fixed on the surface thereof is guided to the lower conveyance guide 37 by switching the flapper 33, and reversed by the reverse roller 38 and the reverse path 39, and then along the refeed guide 40. After that, the sheet is conveyed along the conveyance guide 42 by the re-feed roller 41, and is conveyed again to the image forming unit 3 by the first conveyance roller pair 24, the second conveyance roller pair 28, and the like to form an image. A toner image is formed on the back surface of the surface. The sheet P on which the toner image is formed on the back surface is discharged onto the discharge tray 36 by the sheet discharge unit 7.

Here, the transfer roller 15 described above is a roller configured by covering a core metal 15a with rubber such as urethane, EPDM, NBR, or a sponge-like elastic layer 15b obtained by firing them. As the transfer roller 15, it is preferable to use a roller having a roller hardness of 40 ° or less (Asker-C hardness, 500 g load) for the purpose of preventing missing characters in the transfer and scraping of the photosensitive drum 11. Further, even if the sheet P has a relatively high resistance, carbon or metal fine powder is uniformly dispersed in the elastic layer 15b to form a medium resistance roller having a volume resistivity of 10 ⁶ to 10 ⁹ Ω · cm. Good electrostatic transfer of an image can be performed. When the volume resistivity is smaller than 10 ⁶ Ω · cm, an excessive current flows to the photosensitive drum 11 to cause damage to the photosensitive drum 11, and conversely, when the volume resistivity is larger than 10 ⁹ Ω · cm. Causes a transfer failure due to insufficient current required for transfer.

  An appropriate voltage (transfer bias) of 1 to 6 kV is applied to the transfer roller 15 in accordance with the conveyance timing of the sheet P from the metal core 15a according to the resistance value. As a result, the toner image on the photosensitive drum 11 is electrostatically transferred to the surface of the sheet P.

  Next, a skew correction mechanism using the shutter member 30 will be described.

  FIG. 2 is an enlarged view of the vicinity of the second conveyance roller pair 28 in FIG. 1, and the sheet P conveyed by the first conveyance roller pair 24 is formed between the conveyance roller 26 and the conveyance roller 27 of the second conveyance roller pair 28. It is shown that the sheet passes through the nip portion N and is conveyed to the pre-transfer guide 31 constituted by the lower guide 31a and the upper guide 31b. 3 is a diagram illustrating a state before the sheet P is conveyed to the second conveying roller pair 28 in FIG. FIG. 4 is a perspective view of the transport roller 26 and the transport roller 27 having a skew correction mechanism. 2 and 3, a dotted line A indicates a tangent line at the nip portion N between the transport roller 26 and the transport roller 27.

  As shown in FIG. 4, the entire conveying roller 26 is constituted by a cored bar 26 a forming an axis and a plurality of cylindrical elastic layers 26 b provided around the cored bar 26 a. The elastic layer 26b is made of elastic rubber or elastomer, and is disposed in a comb-like shape at appropriate intervals in the axial direction of the cored bar 26a. On the other hand, the entire conveying roller 27 is constituted by a cored bar 27a that forms an axis and a plurality of cylindrical rollers 27b provided around the cored bar 27a. The rollers 27b are made of synthetic resin and are disposed at appropriate intervals in the axial direction of the cored bar 27a, that is, at positions corresponding to the above-described elastic layer 26b.

  A shutter member 30 made of synthetic resin (for example, PET (polyethylene terephthalate)) can be rotated between the guide position shown in FIG. 2 and the skew correction position shown in FIG. 3 on the cored bar 26a of the conveying roller 26. It is attached. As shown in FIGS. 2 to 4, the shutter member 30 has a cross-sectional shape in a direction orthogonal to the cored bar 26 a substantially formed in an arc shape, and a cored bar between the adjacent elastic layer 26 b and the adjacent roller 27 b. A convex portion 30c that can enter and exit from the downstream side (the pre-transfer guide 31 side) is formed in a comb-like shape between 26a and 27a. A contact surface 30a is formed on the end surface of the convex portion 30c. The contact surface 30a is located slightly upstream of the nip portion N on the sheet P conveyance surface when the shutter member 30 assumes the skew correction position shown in FIG. It is formed to be almost vertical. Further, an arcuate guide surface 30d (see FIG. 5) that is smoothly continuous with the contact surface 30a is formed on the tip side of the contact surface 30a (the side far from the rotation center of the shutter member 30). The abutting surface 30a is for abutting the leading end of the sheet P conveyed to the second conveying roller pair 28, while the guide surface 30d presses the surface of the sheet P on which the toner image is not transferred. To do.

  A coil spring (not shown) serving as a first biasing unit that biases the contact surface 30a toward the upstream side in the sheet conveying direction is disposed at the end of the shutter member 30 in the longitudinal direction. The shutter member 30 is urged clockwise by the coil spring with a first urging force F1 in FIGS. 2 and 3, and before the sheet P is conveyed, the contact surface 30a is manually guided. A stable posture in contact with the downstream end 43a of 43 is maintained. This posture is the skew correction position.

  On the other hand, when the shutter member 30 is disposed at the guide position shown in FIG. 2, the second spring is rotated clockwise in the figure by the above-described coil spring and a leaf spring (second biasing means) 29 described later. It is energized by force F2 (F2> F1).

  The sheet P conveyed by the first conveyance roller pair 24 is conveyed to the second conveyance roller pair 28 while being guided by the downstream portion of the conveyance guide 26 and the manual feed guide 43. First, the leading end of the sheet P is stopped by contacting the contact surface 30a of the shutter member 30, but the rear end side is continuously fed by the first conveying roller pair 24, so that a loop is formed on the leading end side. The Thereby, the skew of the sheet P is corrected. When the restoring force F ′ of the sheet P caused by the loop exceeds the first urging force F1 of the coil spring (F ′> F1), the shutter member 30 is centered around the cored bar 26a by the sheet P. 2 is rotated counterclockwise. As a result, the sheet P can pass through the nip portion N between the transport roller 26 and the transport roller 27 in a state where the skew is corrected. Here, the magnitude of the first urging force F <b> 1 by the above-described coil spring can reliably bring the shutter member 30 into contact with the downstream end 43 a of the manual feed guide 43, and the leading edge of the sheet P that has been conveyed is It is set in a range in which the shutter member 30 can be rotated counterclockwise without causing the sheet P to bend and generate a jam when contacting the contact surface 30a. In the present embodiment, the first urging force F1 is set to 0.098 to 0.294N.

  The shutter member 30 is rotated counterclockwise in FIG. 2 by the sheet P that has passed through the nip portion N, and is disposed at the guide position shown in FIG. The shutter member 30 arranged at the guide position abuts the base end side on the front end side of the leaf spring 29 fixed to the image forming apparatus main body 2, and conversely by the leaf spring 29, the second biasing force F <b> 2 is clockwise. Be energized. Here, the second urging force F2 is obtained by adding the urging force of the leaf spring 29 to the first urging force F1 by the above-described coil spring, and F2> F1.

  The sheet P that has passed through the second conveying roller pair 28 tends to advance in the direction of the tangent A of the nip portion N, but the second urging force F2 is applied by the shutter member 30 from the non-printing surface side where the toner image is not transferred. Since it is biased substantially upward, it is transported above the tangent line A. Accordingly, the sheet P that has passed through the second conveyance roller pair 28 is conveyed toward the upper guide 31b of the pre-transfer guide 31 located on the downstream side of the second conveyance roller pair 28. At this time, since the shutter member 30 urged by the leaf spring 29 acts as a jumping base, the sheet P is smoothly conveyed without bending the leading edge or suddenly increasing the conveyance resistance. .

  Hereinafter, the shutter member 30, the leaf spring 29, and the pre-transfer guide 31 will be described in more detail with reference to FIG. FIG. 5 is an enlarged cross-sectional view of the vicinity of the second conveying roller pair 28.

  As described above, the shutter member 30a disposed at the skew correction position has its contact surface 30a positioned slightly upstream from the nip portion N as indicated by the two-dot chain line in FIG. Yes. This is because the skew of the sheet P cannot be corrected after the leading end of the sheet P is nipped by the nip portion N. Therefore, before the leading end of the sheet P is nipped by the nip portion N, the contact surface 30a. This is because it is necessary to correct the skew of the sheet P.

  In the present embodiment, when the leading edge of the sheet P comes into contact with the contact surface 30a of the shutter member 30, the shutter member 30 rotates counterclockwise, and the guide surface 30d moves to the tangent line A1, that is, the guide. When the angle β formed by the tangent line A1 passing through the nip N and the tangent line A is 30 °, the fan angle α and the shutter member 30 so that the end face 30b contacts the leaf spring 29. The free length of the leaf spring 29 was set. Further, when the shutter member 30 further rotates and the guide surface 30d moves to the tangent line A2, that is, the angle γ formed by the tangent line A2 that is the tangent line of the guide surface 30d and passes through the nip portion N is 20 The leaf spring 29 was set so that the pressing force (second urging force F2) against the sheet P by the shutter member 30 would be 0.49 to 1.47N when the angle became.

The reason for this is that when the sheet P is thin paper having a basis weight of about 60 g / m ² , the sheet P can be conveyed toward the upper guide 31b only by the first urging force F1, but the sheet P When the basis weight is 75 g / m ² or more, the sheet P cannot be conveyed toward the upper guide 31b only by the first urging force F1, and therefore the second urging force F2 as described above is generated. Necessary. However, the above-mentioned value is an example and is not limited to this value. In place of the leaf spring 29, an elastic member such as a coil spring or rubber may be used.

  As shown in FIG. 2, the pre-transfer guide 31 has a lower guide 31a and an upper guide 31b, both of which are arranged so that the downstream side is narrowed. The lower guide 31a is disposed such that the intermediate portion intersects the tangent line A, and the downstream end a of the lower guide 31a is disposed downstream of the downstream end b of the upper guide 31b. Furthermore, the downstream end a of the lower guide 31a is disposed on the downstream extension of the upper guide 31b. In the present embodiment, the sheet P that has passed through the nip portion N is guided along the lower guide by the guide surface 30d of the shutter member 30 to change the transport direction, and is transported along the upper guide 31b. Accordingly, the sheet P is brought into contact with the extended line of the upper guide 31 b on the surface of the photosensitive drum 11. With such a configuration, the entry angle θ3 of the sheet P with respect to the photosensitive drum 11 can be reduced as compared with the conventional case, and the shock when the sheet P contacts the photosensitive drum 11 can be reduced. Image blurring during transfer can be prevented. Further, since the sheet P is conveyed along the upper guide 31b, the downstream end a of the lower guide 31a can be brought close to the transfer nip portion T. The toner can prevent the toner from being scattered during transfer. Furthermore, since the posture of the sheet P that has passed through the nip portion N can be stabilized at a short distance compared to the conventional case, the distance from the second conveying roller pair 28 to the transfer nip portion T can be shortened. Thus, the apparatus can be reduced in size.

  As described above, according to the present invention, the skew correction position at which the shutter member corrects the skew of the sheet P and the guide position at which the lower surface of the sheet P is guided after passing through the second conveying means. Therefore, the skew of the sheet can be corrected regardless of the thickness of the sheet P and the moisture absorption state, and the posture of the sheet P that has passed through the second conveying roller pair 28 can be stabilized.

<Embodiment 2>
6A, 6B, and 6C show different shutter members 51, 52, and 53, respectively. Instead of the shutter member 30 of the first embodiment described above, these shutter members 51, 52, and 53 can be used.

  In the shutter member 30 described above, the guide surface 30d acts as a jumping table and guides the lower surface of the sheet P. That is, the sheet P is strongly rubbed against the guide surface 30, and depending on the type of the sheet P, a large rubbing sound is generated or paper dust is likely to be generated.

  Therefore, in the present embodiment, the friction coefficient between the guide surfaces 51d, 52d, and 53d of the shutter members 51, 52, and 53 shown in FIGS. 6A, 6B, and 6C and the sheet P is small. A low friction member is used.

  In FIG. 6A, the shutter member 51 is formed of PET (polyethylene terephthalate), and the contact surface 51a with which the leading end of the sheet P abuts and the guide surface 51d that guides the lower surface of the sheet P are low friction members. As shown in FIG. A fluororesin sheet 54 having a thickness of 30 μm was used and adhered to a plurality of locations (for example, 6 locations) in the longitudinal direction of the shutter member 51. Thus, by providing the fluororesin sheet 54 on the contact surface 51a and the guide surface 51d, it is possible to reduce the rubbing resistance, reduce the rubbing noise, and reduce the generation of paper dust. The low-friction member is not limited to the above-described fluororesin sheet 54, and other low-friction members such as polyimide resin can be used. In this case, the same effect as the fluororesin sheet 54 can be used. Can give.

  In the shutter member 52 shown in FIG. 6B, ribs 55 are projected from a plurality of locations (for example, 6 locations) in the longitudinal direction, and the outer peripheral surface of the rib 55 is formed in an arc shape to form a guide surface 52d. . By providing such a rib 55, it is possible to reduce the contact area when guiding the lower surface side of the sheet P, and to suppress the frictional noise between the sheet P and the generation of paper dust. it can.

  The shutter member 53 shown in FIG. 6C is a low friction member in which rollers 56 made of synthetic resin are rotatably arranged at a plurality of locations (for example, 6 locations) in the longitudinal direction. Resin rollers 56 are arranged in the longitudinal direction as shown in the figure, and these rollers 56 have a guide surface 53d on the outer peripheral surface and are slid by being rotated by the sheet P during contact and conveyance. Generation of noise and paper dust can be suppressed. Since the roller 56 rotates during the conveyance of the sheet P, there is an effect that it is possible to prevent the sheet P from being charged due to rubbing.

<Embodiment 3>
FIG. 7 shows another image forming apparatus 1A that can be applied to the present invention. FIG. 1 is a diagram schematically showing a configuration of a small desktop image forming apparatus 1A viewed from the front side. In addition, about the thing of the structure similar to above-mentioned Embodiment 1, the same code | symbol is attached | subjected and the description is abbreviate | omitted suitably.

  In the image forming apparatus 1 </ b> A shown in FIG. 7, the conveyance path of the sheet P is substantially C-shaped, that is, the miracle until the sheet P in the state stored in the sheet feeding cassette 21 is conveyed and discharged onto the sheet discharge tray 36. Is substantially C-shaped.

  The image forming apparatus 1A shown in the figure has a shorter sheet conveyance distance from paper feeding to paper ejection than the image forming apparatus 1 having a substantially S-shaped conveyance path described in the first embodiment, and therefore the first print The time required for out can be shortened. Further, there is an advantage that the height of the image forming apparatus main body 2A can be reduced by shortening the distance between the paper feeding and the transfer and the distance between the transfer and the fixing.

  On the other hand, regarding the installation area of the image forming apparatus 1A, the position of the paper feed roller 22 is one factor that determines the left-right width (the distance from the left side wall 2a to the right side wall 2b of the printer main body 2A in FIG. 7). . That is, as the position of the paper feed roller 22 is closer to the left side wall 2a of the printer main body 2A, the left and right width of the image forming apparatus main body 2A can be the same as the width of the paper feed cassette 21. When placed close to the wall 2b, the paper feed roller 22 is positioned on the right side with respect to the position of the transfer nip T. Therefore, like the conventional shutter member (see FIG. 9), the sheet is retracted to the print surface side. Then, the sheet P is conveyed to the transfer nip T along the lower guide 31a (the left guide in FIG. 7), and the image quality is deteriorated. In order to avoid this, if the positions of the second conveying roller pair 28 and the lower guide 31a are arranged in the direction of the photosensitive drum 11 (on the right side in FIG. 7), the sheet P conveyed from the sheet feeding cassette 21 is fed to the sheet feeding roller 22. The sheet P cannot be smoothly conveyed because it is reversed and folded at the position. Therefore, there is a problem that the thickness (basis weight) of the sheet P that can be fed from the sheet feeding cassette 21 is also limited.

  In the present embodiment, as shown in FIG. 7, the shutter member 30 is rotatably attached to the shaft (not shown) of the transport roller 26 of the second transport roller pair 28, and the shutter member 30 is rotated, so that the second The sheet P is conveyed along the upper guide 31b when the shutter member 30 acts as a jump stand by a leaf spring (see FIG. 2) which is a biasing means. As a result, even when the paper feed roller 22, the second transport roller pair 28, and the transfer nip portion are arranged substantially on a straight line, the sheet P is smoothly transported to reduce image quality and toner scattering at the transfer nip portion T. Can be prevented.

  Therefore, the left and right width of the image forming apparatus main body 2A can be shortened as in the present embodiment, and the installation area can be reduced accordingly.

  As described above, the present invention is particularly effective for a desktop image forming apparatus having a C-shaped conveyance path as in the present embodiment.

  The present invention can be applied to, for example, an image forming apparatus in which the vertical relationship between the photosensitive drum 11 and the transfer roller 15 is opposite to that of the image forming apparatus 1 shown in FIG. In this case, the vertical relationship between the upper guide and the lower guide is reversed, and the shutter member is attached to a member disposed on the upper side of the second pair of conveying rollers.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment to which the present invention can be applied, as viewed from the front side. FIG. 4 is an enlarged view showing a configuration from a first conveyance roller pair to a transfer nip portion, and is a diagram showing a state in which a sheet is conveyed by a second conveyance roller pair. FIG. 4 is an enlarged view showing a configuration from a first conveyance roller pair to a transfer nip portion, and is a diagram showing a state where a sheet is not conveyed. It is a perspective view of a conveyance roller, a conveyance roller, and a shutter member. It is a figure explaining operation | movement of a shutter member. (A), (b), (c) is a figure which shows the shutter member of another structure, respectively. It is the figure which looked at schematic structure of the image forming apparatus of Embodiment 3 which can apply this invention from the front side. (A), (b) is a figure explaining the effect | action of the conventional shutter member and the guide before transfer. It is a figure explaining the state in which the sheet | seat front-end | tip contact | abutted the conventional shutter member.

Explanation of symbols

3 Image forming unit 5 Sheet feeding / conveying unit (sheet conveying device)
24 1st conveyance roller pair (1st conveyance means)
26 Conveying roller (rotating body)
26a Core (Rotating body shaft)
27 Conveyor roller (rotating body)
28 Second conveying roller pair (second conveying means, rotating body pair)
29 leaf spring (biasing means, first biasing means)
30, 51, 52, 53
Shutter members 30a, 51a, 52a, 53a
Contact surface 30d, 51d, 52d, 53d
Guide surface 31 Pre-transfer guide (guide member)
31a Lower guide 31b Upper guide 54 Fluororesin sheet (low friction member)
55 Rib (Low friction material)
56 Roller (low friction material)
N Nip part P Sheet T Transfer nip part

Claims (6)

A first conveying means disposed on the upstream side in the sheet conveying direction, a second conveying means disposed on the downstream side, and a shutter member disposed in the vicinity of the second conveying means,
The shutter member corrects the skew of the sheet by contacting the leading end of the sheet that has been conveyed by the first conveying unit and has not reached the second conveying unit. Evacuate,
When correcting the skew of the sheet, the shutter member is urged by the first urging means, and when retracted, the shutter member is further urged by the second urging means. In contact with the sheet after passing through the conveying means to guide the sheet in a predetermined direction,
A sheet conveying apparatus. The shutter member has a contact surface with which a front end of a sheet contacts when correcting the skew, and a guide surface that guides the sheet when retracted.
The sheet conveying apparatus according to claim 1. The shutter member is formed such that the contact surface and the guide surface are smoothly continuous.
The sheet conveying apparatus according to claim 2. The second conveying means includes a pair of rotating bodies that are in contact with each other to form a nip portion,
The shutter member is rotatably supported by an axis of one rotating body of the rotating body pair.
The sheet conveying apparatus according to claim 3. The guide surface of the shutter member is formed of a low friction member having a small coefficient of friction with the sheet.
The sheet conveying apparatus according to claim 2, wherein the sheet conveying apparatus is a sheet conveying apparatus. An image forming apparatus comprising: an image forming unit that forms an image on a sheet conveyed by the second conveying unit; and a sheet conveying device that conveys the sheet to the image forming unit.
A guide member that is disposed between the image forming unit and the sheet conveying device and guides the sheet so that the angle of the sheet that enters the image forming unit is appropriate;
The sheet conveying apparatus is the sheet conveying apparatus according to any one of claims 1 to 5,
The shutter member of the sheet conveying device guides the sheet toward the guide member when the sheet is retracted;
An image forming apparatus.

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