JP2006117365A - Sheet conveying apparatus and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To remove a curl without substantially forming a trace of a roller on a sheet by curling. <P>SOLUTION: This sheet carrying device 51 carries the image-formed sheet by a pair of carrier rollers. The pair of carrier rollers have a whole width curved surface roller 16 for alternately forming a thick diameter part 16a and a thin diameter part 16b, forming the part between the thick diameter part and the thin diameter part into an inclined face 16c and contacting with an image formed on the sheet, and a driving roller 13 contacting with this whole width curved surface roller 16. The length of the whole width curvred surface roller 16 is set longer than an area width of the image formed on the sheet. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a sheet conveying apparatus that conveys a sheet, and more particularly to a sheet conveying apparatus that removes curl and conveys the sheet, and an image forming apparatus that includes the sheet conveying apparatus.

  Conventional image forming apparatuses such as copiers, printers, facsimiles, and multi-functional machines that form images on sheets have adopted electrostatic recording methods, electrophotographic recording methods, and the like. After the formation, the toner image is fixed on the sheet by heating and pressing the sheet with a fixing device. The sheet on which the toner image has been fixed is conveyed by a sheet conveying device and sent to a discharge tray, a sheet post-processing device, or the like.

  However, the sheet is often a heat roller type fixing device, and may be heated to curl (warp). When the curled sheets are stacked on the discharge tray, the end portions are not stacked together. For this reason, the user who has taken out the bundled sheet has to realign the sheet bundle again. Further, the curled sheet may be clogged when sent to the sheet post-processing apparatus.

  Therefore, there is a sheet conveying device provided on the downstream side of the fixing device, which has a function of removing curls somewhat (see Patent Documents 1 and 2).

  FIG. 5 shows a pair of conveying rollers of a conventional sheet conveying apparatus. The conveying roller pair is composed of a driving roller 113 and driven rollers 114a to 114d. The driving roller 113 and the driven rollers 114a to 114d are pressed against each other with a predetermined pressure, so that the curling of the sheet (transfer material) generated by thermal fixing is nipped and conveyed while being flattened.

  Such a sheet conveying apparatus can reduce the curl amount by correcting the curl of the sheet with a compact structure, and can improve the quality of the image formed on the sheet. When the curl is removed, the stackability is improved when the sheet is discharged to the discharge tray, and the user can easily handle the sheet bundle. Further, when the sheet is fed into the sheet post-processing apparatus, the sheet is jammed. The sheet post-processing apparatus can be smoothly moved without any trouble.

  Furthermore, as a pair of conveying rollers of the sheet conveying apparatus that more reliably removes curl, a discharge roller in which a large diameter portion and a small diameter portion are alternately formed, and a plurality of discharge rollers press-contacted to the small diameter portion of the discharge roller Some of them are configured by (Patent Document 3).

Japanese Patent Laid-Open No. 13-22615 JP-A-9-249345 Japanese Patent Laid-Open No. 2000-238003

  However, when the sheet S is nipped and conveyed between the driving roller 113 and the driven rollers 114a to 114d, the pair of conveying rollers of the conventional sheet conveying apparatus has the driven rollers 114a to 14d of the sheet S as shown in FIG. Since it is in local contact with the image surface Sa, the traces of the driven rollers 114a to 114d remain, causing image defects.

  The phenomenon that the trace of the driven roller remains on the image surface Sa tends to appear more prominently in the OHT sheet, gloss paper, and the like.

  In recent image forming apparatuses, the conveyance path tends to be shortened in order to reduce the size of the apparatus main body, increase the printing speed, and improve productivity. For this reason, the distance from the fixing device to the sheet discharge port becomes extremely short, and the toner image of the sheet S on which the toner image is heat-fixed at the nip of the heating and pressure roller pair of the fixing device is not sufficiently cooled down. Since the sheet is sandwiched between the sheet conveying rollers of the sheet conveying apparatus in the state, the above problem is more likely to occur.

  Further, in order to stably convey the sheet S, the holding force between the driving roller 113 and the driven rollers 114a to 114d has to be increased to some extent. When the clamping force is increased, a crease (hereinafter referred to as a “drum line”) is formed in the sheet conveyance direction at the edge of the driving roller 113 and the edge of the driven rollers 114a to 114d, which causes a decrease in print quality. . This is also the case with the conveying roller pair in the last conventional sheet conveying apparatus.

  Therefore, it is conceivable to provide a curl removal device for removing curl or the like on the downstream side of the fixing device. However, if the image forming apparatus is equipped with the decurling device, the structure of the image forming apparatus itself is complicated, and not only the cost is increased, but another problem that it is difficult to secure an installation space arises. become.

  The above-described sheet processing apparatus has been described with respect to a problem when it is provided in an image forming apparatus that forms a toner image on a sheet. However, some image forming apparatuses form an image on a sheet by an inkjet method. Even in an inkjet image forming apparatus, a sheet may be curled by ink. For this reason, when a conventional sheet processing apparatus is installed in an inkjet image forming apparatus, the same problem as described above occurs when the curl of the sheet is removed.

  Further, the image forming apparatus provided with the conventional sheet processing apparatus has a problem in that the sheet processing apparatus has a low rate of removing curl, and thus jamming may occur in the sheet, and the image forming efficiency is poor.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet conveying apparatus that removes curl while curling and hardly leaving a roller mark on the sheet.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus provided with a sheet conveying device capable of removing curl and having an increased image forming efficiency by reducing the occurrence rate of jam.

  In order to achieve the above object, the sheet conveying apparatus of the present invention is configured to convey a sheet on which an image is formed by a pair of conveying rollers, and the conveying roller pair has alternating large diameter portions and small diameter portions. And a second roller in contact with the first roller, and a first roller and a first roller formed on the inclined surface between the large diameter portion and the small diameter portion. Among the two rollers, the length of the roller that contacts the image formed on the sheet is set longer than the region width of the image formed on the sheet.

  In order to achieve the above object, an image forming apparatus of the present invention includes an image forming unit that forms an image on a sheet, and a sheet conveying device that is disposed downstream of the image forming unit in the sheet conveying direction and conveys the sheet. The sheet conveying apparatus is the sheet conveying apparatus.

  In the sheet conveying apparatus of the present invention, a pair of conveying rollers for conveying a sheet on which an image is formed has a large diameter portion and a small diameter portion alternately formed, and a gap between the large diameter portion and the small diameter portion is inclined. The length of the roller which has the formed 1st roller and the 2nd roller which contacts the 1st roller, and contacts the image formed in the sheet among the 1st roller and the 2nd roller Is set to be longer than the area width of the image formed on the sheet, so that it is possible to prevent the occurrence of a jam or the like due to curling, and also to prevent image unevenness and image failure due to roller marks on the sheet. it can.

  Hereinafter, a sheet conveying apparatus according to an embodiment of the present invention and an image forming apparatus equipped with the sheet conveying apparatus will be described with reference to the drawings.

  FIG. 1 is a schematic front sectional view of a color printer as an image forming apparatus that forms an image on a sheet with four color toners.

  Note that the image forming apparatus includes a copying machine, a printer, a facsimile, and a complex machine of these, and is not limited to a color printer.

  The color printer 50 includes four photosensitive drums 1 (1a, 1b, 1c, 1d). The surface of the photosensitive drum 1 is sequentially arranged around each photosensitive drum 1 in accordance with the rotation direction. Charger 2 (2a, 2b, 2c, 2d) for uniformly charging, and exposure unit 3 (3a, 3b, 3c, 3a, 3c, 2c) for forming an electrostatic latent image on photosensitive drum 1 by irradiating a laser beam based on image information 3d), a developing device 4 (4a, 4b, 4c, 4d) for attaching toner to the electrostatic latent image to visualize the toner image, and a transfer device for transferring the toner image on the photosensitive drum 1 to the sheet (transfer) Roller) 5 (5a, 5b, 5c, 5d), a cleaner 6 (6a, 6b, 6c, 6d) for removing the toner after transfer remaining on the surface of the photosensitive drum 1 after transfer, and the like are disposed. An image forming unit as a means is configured

  Here, the photosensitive drum 1, the charger 2, the developing device 4, and the cleaner 6 for removing the toner are integrally formed into a cartridge to form a process cartridge 7 (7a, 7b, 7c, 7d).

  The sheet S fed from the sheet feeding unit 8 is transported to the image forming unit 22 by the transport belt 21 of the transport unit 9, and the color toner images are sequentially transferred to record the color image, and then the fixing unit. The color image is fixed at 10, and is discharged to the discharge unit 15 by the conveyance roller pairs 11, 12 and 13, 16.

  In the case of double-sided printing, the sheet S is fixed on the double-sided conveyance path 54 (in the direction of arrow A) by reverse rotation of the conveyance rollers 13 and 16 before the toner image is fixed by the fixing unit 10 and discharged by the conveyance roller pairs 13 and 16. It is designed to be conveyed. The sheet S conveyed to the double-sided conveyance path 54 passes through the oblique feeding roller 52 on the front surface of the apparatus main body and is conveyed vertically downward to the U-turn roller 53, and image formation is performed by the U-turn roller 53 and the registration roller pair 8d. It is conveyed to the part 22.

  The fixing device 10 includes a heating roller 10a and a pressure roller 10b, and a driving roller 11 and a driven roller 12 provided on the downstream side in the conveyance direction of the sheet S that is nipped and conveyed by the rollers 10a and 10b.

  The sheet S immediately after the toner image is heat-fixed at the fixing nip formed by the heating roller 10a and the pressure roller 10b is not sufficiently cooled and has a weak strain. When the sheet S is conveyed while sliding along the conveyance path after the fixing nip, the sliding image of the roller is attached to an uncooled toner image, and the image quality is remarkably deteriorated.

  For this reason, the printer 50 sandwiches and conveys the sheet by the driven roller 12 and the driving roller 11 whose roller width is longer than the image area width, and conveys the image surface side of the sheet S with the driven roller 12 being in uniform contact. By doing so, the degradation of image quality is suppressed. In this way, the sheet S passes through the first-stage conveyance roller pair 11, 12 and is sequentially nipped and conveyed by the second-stage conveyance roller pair composed of the driving roller 13 and the full-width curved roller 16.

  The full-width curved roller 16 as the first roller has a length equal to or greater than the width of the region of the toner image formed on the sheet by the printer, and is formed in a wavy shape with a smooth curve in the longitudinal direction as a whole. . That is, as shown in FIG. 2, the full-width curved surface roller 16 has a large-diameter portion 16a and a small-diameter portion 16b that are alternately formed, and a slope having a convex arc shape between the large-diameter portion 16a and the small-diameter portion 16b. It is formed in 16c and has a wave shape. The slope 16c may be a straight line. In this case, it is preferable that the large diameter portion 16a is a convex arc surface and the small diameter portion 16b is a concave arc surface. In the sheet conveying apparatus 51 of the present embodiment, the length of the full width curved surface roller 16 is longer than the largest sheet width for conveying.

  A difference in outer diameter between the large diameter portion 16a and the small diameter portion 16b will be described. FIG. 4 is a diagram in which several full-width curved rollers having different outer diameter differences are prepared, and the relationship between the outer diameter difference and the curl reduction amount is obtained experimentally. Note that the data in the figure is compared relative to the average curl amount when the roller outer diameter difference is 0 mm. Each plot shows the average curl reduction amount of the sheet S when passing through the roller pairs 13 and 16 N times (N = 10 or more), and the maximum and minimum curl amounts are the maximum (most curl reduction). The value of the one with the smallest amount) and the minimum value (the one with the largest curl reduction amount) are shown.

  As shown in FIG. 4, the curl amount is reduced by about 5 mm to about 8 mm by making the outer diameter difference of the roller 16, and the effect can be confirmed from the viewpoint of curling reduction.

  If the difference between the roller outer diameters is extremely small, the sheet S will be weakened and the curl correcting effect will be reduced. On the other hand, if the difference between the roller outer diameters is too large, the sheet S will be stiffened more than necessary, and undulations (waveness) will remain in the sheet S. The sheet conveyance quality deteriorates.

  In FIG. 4, when the roller outer diameter difference is 4 mm, the amount of waveness is about 5 mm or more by visual observation, and although the amount of curl reduction is large, it is considered that the wayness cannot be ignored.

  Considering comprehensively considering the suppression of image quality degradation, the roller outer diameter difference is particularly effective in the range of about 1 mm to about 3 mm. In the sheet conveying apparatus 51 of the present embodiment, the difference in roller outer diameter is set to 1.575 mm from the viewpoint of trade-off, so that the sheet curling can be performed appropriately and sheet curling can be reduced. Thereby, the stackability of sheets on the discharge unit 15 is improved.

  The conveyance roller pairs 13 and 16 are formed of a silicon rubber elastic member. The pair of transport rollers 13 and 16 is assumed to be used at about 150 ° C., and the hardness change of the rubber roller is heated for about 100 hours in a constant temperature bath of about 100 ° C. and then left for about 4 hours in an environment of about 20 ° C. ± 5 ° C. Then, the measured change in hardness is about 1.5 degrees or less. The outer circumference of the full-width curved roller 16 on the image surface side is covered with a heat-shrinkable PFA tube having a thickness of about 50 μm. As a result, the toner transferred to the sheet S is prevented from adhering to the full width curved surface roller 16.

  The surface elastic hardness of the driving roller 13 facing the full-width curved roller 16 is lower than the elastic hardness of the full-width curved roller 16 surface. That is, the surface of the drive roller 13 is made softer than the surface of the full-width curved roller 16. For this reason, the drive roller 13 is configured to follow and deform the roller surface shape of the full-width curved roller 16 that abuts.

  If the difference in elastic hardness between the conveying roller pairs 13 and 16 is small, it becomes difficult to bring the rollers 13 and 16 into contact with each other without a gap, and the surface of the driving roller 13 facing the full-width curved roller 16 is the full-width curved roller surface 16. Will not follow and deform. In such a case, the sheet S conveyed while being sandwiched between the conveying roller pairs 13 and 16 is not sufficiently rubbed by the full width curved surface roller 16.

  On the contrary, if the elastic hardness difference is large, the surface of the driving roller 13 facing the full width curved roller 16 is deformed following the surface of the full width curved roller, but the nipping and conveying force of the conveying roller pairs 13 and 16 tends to vary. The pair of conveying rollers 13 and 16 skews the sheet S, damages the toner image, and further, the durability of the surfaces of the rollers 13 and 16 is lowered, and the conveying property is lowered.

  In the sheet conveying apparatus 51 of the present embodiment, the difference in elastic hardness between the conveying roller pairs 13 and 16 is about 20 ° ± 5 °. The sheet S that is nipped and conveyed by the conveyance roller pairs 13 and 16 is uniformly brought into contact with the full-width curved surface roller 16, and is nipped and conveyed while being rubbed. Thereby, the conveyance roller pairs 13 and 16 can correct the curl of the sheet S.

  Each of the above values is often determined by various conditions such as the printing speed of the printer main body, and by selecting an appropriate value according to each situation, the image unevenness is corrected while correcting the curl of the sheet S as described above. The effect which suppresses is acquired.

  Therefore, the sheet conveying apparatus 51 of the present embodiment is in contact with the full width curved surface roller 16 as the first roller formed between the large diameter portion 16a and the small diameter portion 16b on the inclined surface 16c, and the full width curved surface roller 16. And the driving roller 13 is more elastic (elastic hardness difference of about 20 degrees) than the full width curved surface roller 16, so that the curling of the sheet S is corrected. Image unevenness can be suppressed.

  That is, the sheet processing apparatus 51 of the present embodiment is effective in correcting the curl of the sheet S, and at the same time, the contact of the roller with the image surface side is almost uniform with no gaps, so that it is formed on the sheet. Image defects can be prevented with almost no image unevenness, roller marks, or tramlines in the toner image.

  In place of the driving roller 13 shown in FIG. 2, a cylindrical roller 17 having a cylindrical shape or a non-cylindrical round shaft shape may be used as the second roller, as shown in FIG. 3A.

  Further, instead of the driving roller 13 shown in FIG. 2, a driving roller 18 having an undulating shape as shown in FIG. 3B is used, and instead of the full-width curved roller 16 shown in FIG. 2, FIG. A cylindrical roller 19 having a cylindrical shape or a non-cylindrical round shaft may be used as the second roller having a length equal to or longer than the image area shown in FIG. The driving roller 18 as the first roller has a full-width curved surface formed by a large-diameter portion 18a, a thin-diameter portion 18b, and a slope 18c formed between the large-diameter portion 18a and the small-diameter portion 18b. Laura. The cylindrical roller 19 is covered with a heat-shrinkable PFA tube having a thickness of about 50 μm, and the silicon rubber elastic hardness is lower than that of the opposing drive roller 18. The cylindrical roller 19 is set to have a length longer than the width of the toner image forming area because it contacts the image forming surface of the sheet.

  Furthermore, instead of the drive roller 13 shown in FIG. 2, as shown in FIG. 3C, a full-width curved roller 20 may be used as the second roller. The full width curved surface roller 20 is also formed by a large diameter portion 20a, a small diameter portion 20b, and an inclined surface 20c formed between the large diameter portion 20a and the small diameter portion 20b. In this case, the large-diameter portion 20a and the small-diameter portion 20b of the full-width curved roller 20 are in contact with the narrow-diameter portion 16b and the large-diameter portion 16a of the full-width curved roller 16, and the full-width curved roller 20 and the full-width curved roller 16 There are few gaps between them. The difference between the large diameter portion 20a and the small diameter portion 20b of the full-width curved roller 20 is also preferably about 1 mm to about 3 mm, and most preferably 1.575 mm.

  In the conveyance roller pairs (16, 17), (19, 18), (16, 20) shown in FIGS. 3A, 3B, and 3C, similarly to the roller pairs 13 and 16 shown in FIG. The effect of correcting the curl of the sheet S is obtained, and at the same time, the contact of the roller to the image surface side is almost uniform with no gap, so that the image unevenness of the toner image formed on the sheet, the roller trace and the tramline Image defects can be prevented with almost no occurrence.

  The above-described sheet processing apparatus has been described as being provided in an image forming apparatus that forms a toner image on a sheet. However, the sheet processing apparatus may also be provided in an image forming apparatus that forms an image on a sheet using an inkjet method. The curl of the sheet curled by the ink ejected from the ink head can be corrected. In this case, the sheet processing apparatus is disposed on the downstream side in the sheet conveying direction of the ink head which is an image forming unit.

  The sheet conveying device 51 of the present embodiment has the following effects.

  The length of the roller in contact with the image formed on the sheet is set to be longer than the area width of the image formed on the sheet, and the roller surface is brought into contact with the sheet substantially uniformly without gaps. It is possible to eliminate image unevenness that occurs at the time.

  A first roller having a large diameter portion and a small diameter portion alternately formed, and a portion between the large diameter portion and the small diameter portion formed on the inclined surface, that is, a wavy shape in the longitudinal direction; Since the roller surface is generally in contact with the sheet with almost no gap by nipping and conveying with the second roller in contact with the first roller, the sheet is curled locally, and the sheet is conveyed in other areas. Only power can be gained.

  Of the first roller and the second roller, the hardness of the roller that does not contact the image formed on the sheet is lower than the hardness of the roller that contacts the image formed on the sheet. The sheet can be uniformly contacted with no gap, and the curl of the sheet is locally corrected. In other areas, only the conveying force of the sheet S can be obtained.

  Further, in the image forming apparatus provided with the sheet processing apparatus of the present embodiment, the curl of the sheet is removed by the sheet processing apparatus, so that jamming hardly occurs on the sheet, and the image forming efficiency is improved.

1 is a schematic front sectional view of a color printer as an image forming apparatus that forms an image on a sheet with four color toners, including a sheet conveying device according to an embodiment of the present invention. FIG. 5 is a diagram of a conveyance roller pair as viewed from the sheet conveyance direction in the sheet conveyance apparatus of the present embodiment. It is a perspective view of the conveyance roller pair of other embodiment in the sheet conveyance apparatus of this embodiment. (A) is a conveyance roller pair when the drive roller is cylindrical. (B) is a pair of conveying rollers when the shape of the roller pair in (a) is reversed. (C) is a pair of conveying rollers in the case where both rollers are formed with a large diameter portion and a small diameter portion. It is a figure of the experimental data of the relationship between the external shape difference with the large diameter part of a roller, and a thin diameter part, and a curl amount. It is a perspective view of the conventional conveyance roller pair. FIG. 10 is a view of a conventional conveyance roller pair as viewed from a sheet conveyance direction.

Explanation of symbols

S sheet 1 photosensitive drum 10 fixing device 10a heating roller 10b pressure roller 11 driving roller 12 driven roller 13 driving roller (second roller)
14 driven roller 15 paper discharge unit 16 full width curved surface roller (first roller)
16a Large diameter portion 16b Small diameter portion 16c Slope 17 Cylindrical roller (second roller)
18 Driving roller (first roller)
18a Large diameter portion 18b Small diameter portion 18c Slope 19 Cylindrical roller (second roller)
20 Full-width curved roller (second roller)
20a Large diameter portion 20b Small diameter portion 20c Slope 22 Image forming portion (image forming means)
50 Printer (image forming device)
51 Sheet conveying device

Claims (10)

In a sheet conveying apparatus that conveys a sheet on which an image is formed with a pair of conveying rollers,
The conveying roller pair is in contact with the first roller, and a first roller in which a large diameter portion and a small diameter portion are alternately formed and a slope is formed between the large diameter portion and the small diameter portion. A length of a roller in contact with the image formed on the sheet, of the first roller and the second roller, based on a region width of the image formed on the sheet. The sheet conveying apparatus is characterized in that it is set longer.   Of the first roller and the second roller, the length of the roller that does not contact the image formed on the sheet is set to be longer than the region width of the image formed on the sheet. The sheet conveying apparatus according to claim 1.   The sheet conveying apparatus according to claim 1 or 2, wherein a difference between the large diameter portion and the small diameter portion of the first roller is about 1 mm to about 3 mm.   The sheet conveying apparatus according to claim 1, wherein the second roller is a roller having a uniform diameter.   3. The second roller according to claim 1 or 2, wherein the second roller is formed such that a large diameter portion and a small diameter portion are alternately formed, and a slope is formed between the large diameter portion and the small diameter portion. The sheet conveying apparatus according to the description.   6. The sheet conveying apparatus according to claim 5, wherein a difference between the large diameter portion and the small diameter portion of the second roller is about 1 mm to about 3 mm.   The hardness of a roller that does not contact the image formed on the sheet among the first roller and the second roller is lower than the hardness of the roller that contacts the image formed on the sheet. Item 7. The sheet conveying apparatus according to any one of Items 1 to 6.   8. The sheet according to claim 1, wherein the sheet is brought into contact with the surface of the first roller with almost no gap by nipping and conveying between the first roller and the second roller. 9. Sheet transport device. Image forming means for forming an image on a sheet;
A sheet conveying device disposed on the downstream side in the sheet conveying direction of the image forming unit and conveying the sheet,
The image forming apparatus, wherein the sheet conveying apparatus is the sheet conveying apparatus according to claim 1. Fixing means for fixing the toner image transferred to the sheet to the sheet by heating and pressing the sheet;
A sheet conveying device disposed on the downstream side in the sheet conveying direction of the fixing unit and conveying the sheet,
The image forming apparatus, wherein the sheet conveying apparatus is the sheet conveying apparatus according to claim 1.

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