JP2006168890A - Sheet conveying apparatus and image forming apparatus provided with the apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the trace left on an image forming surface of a sheet when the sheet is carried. <P>SOLUTION: A sheet carrying device has a sucking/carrying belt 41 including a circulating belt 44 for sucking the sheet on which the image is fixed by heat-fixing by means of a fixing unit 30, and carrying the sheet. Since the sheet on which the image is fixed by heat-fixing by means of the fixing unit 30 is sucked to the circulating carrying belt 44 of the sucking/carrying belt 41 and then the sheet is carried, the image forming surface of the sheet is not susceptible to occurrence of image defect such as uneven gloss. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention provides a sheet conveying apparatus that conveys a sheet without making a mark when conveying the sheet to the image forming surface of the sheet on which an image is formed, and causes the sheet conveying apparatus to convey the sheet immediately after the image is formed. The present invention relates to an image forming apparatus.

  Conventionally, there is an image forming apparatus that forms an image on a sheet. Examples of the image forming apparatus include a copying machine, a printer, a facsimile, and a complex machine of these. In order to form an image on a sheet by conveying the sheet, the image forming apparatus includes a plurality of sheet conveying apparatuses that convey the sheet (see Patent Document 1). Among them, there is a sheet conveying device disposed on the downstream side of the fixing device. The fixing device is a device that heats and presses the sheet on which the toner image is transferred in the image forming unit to fix the toner image on the sheet.

  The sheet conveying device disposed downstream of the fixing device is discharged to the outside of the sheet post-processing device such as a sorter or finisher that performs post-processing on the sheet, a refeed conveyance path for duplex printing, and an image forming apparatus. Sheets are selectively conveyed to a sheet discharge tray or the like on which stacked sheets are stacked.

  FIG. 9 is a cross-sectional view along the sheet conveying direction of a full-color laser printer as a conventional image forming apparatus provided with a sheet conveying device on the downstream side of the fixing device. A full-color laser printer (hereinafter simply referred to as “printer”) 211 includes a sheet discharge tray 260 at the top of the apparatus main body 210, and a sorter 270 that is a sheet post-processing apparatus on one side of the apparatus main body 210. Is provided with a refeed conveyance path 280 on the other side.

  In the printer 211, the sheet S stored in the sheet supply cassette 221 in the apparatus main body 210 is sent out from the sheet supply cassette 221 by the sheet supply roller 222, and the four color toner images are transferred by the image forming unit 208. Thereafter, the printer 211 heats and presses the sheet with the fixing device 212 to fix the color toner image on the sheet.

  When the sheet is discharged to the sheet discharge tray 260, the printer 211 conveys the sheet while being nipped between the roller pair 231 by the sheet discharge unit 230 including the plurality of roller pairs 231 and rotating (niping) the sheet discharge tray 260. Drain onto 260.

  The printer 211 includes a relay transport path 240 that feeds a sheet to the sorter 270 and the refeed transport path 280 at the top of the apparatus main body 210. The relay conveyance path 240 is a conveyance path that extends from the paper discharge port 220 provided in the upper part of the apparatus main body 210 toward the sorter 270.

  When the sheet S is guided to the sorter 270, the relay conveyance path 240 conveys the sheet S from the sheet discharge outlet 220 to the sorter 270 as it is by a plurality of roller pairs 241. Further, when the sheet S is guided to the refeed conveyance path 280, the relay conveyance path 240 once pulls the sheet into the relay conveyance path 240 and reverses the roller pair 214 to the refeed conveyance path 280. And transport the sheet. During this time, the relay conveyance path 240 is the reverse of the sheet. The re-feed conveyance path 280 feeds the sheet to the image forming unit 208. The image forming unit 208 forms an image on the other side of the sheet. As a result, the sheet has images formed on both sides.

  In the above configuration, the paper discharge unit 230 and the relay conveyance path 240 constitute a sheet conveyance device 290.

  Incidentally, the image forming apparatus generally does not include the relay conveyance path 240. Therefore, an image forming apparatus in which the image forming unit 208 is vertical cannot receive a sheet from the fixing device 212 unless an optional apparatus such as a sorter or a finisher is provided on the upper part of the apparatus main body 210. . For this reason, the conventional image forming apparatus is expensive because the optional apparatus is provided on the upper part of the apparatus main body 210, and it may be difficult to use.

  Therefore, the printer 211 shown in FIG. 9 includes a relay conveyance path 240 in the upper part of the apparatus main body 210 so that a sorter 270 as an optional apparatus can be provided on the side of the apparatus main body 210 without increasing the height. Easy to use.

Japanese Patent Laid-Open No. 09-309655 (FIG. 1)

  However, the conventional sheet conveying device 290 conveys the sheet immediately after the toner image is fixed by the fixing device 212 by being nipped between the roller pairs 231 and 241 (nipped). The part which 241 contacts and the part which does not contact arise. As a result, the gloss level of the toner image may differ between the portion where the roller pairs 231 and 241 are in contact with the portion where the roller pair 231 and 241 are not in contact.

  The gloss difference of the toner image means the following. When the sheet is heated and pressurized by the fixing device 212, the toner image heated together becomes slow to cool down depending on the ambient temperature and humidity at that time, or the toner amount of the toner image. The rollers and rollers of the roller pairs 231 and 241 may come into contact with the surface on which the toner image is formed or on the back side of the surface on which the toner image is formed. The portions of the roller pair 231 and 241 where the rollers and the rollers are in contact with each other are deprived of heat earlier than other portions, and the color appearance of the toner image changes, and when viewed with the eyes, it may appear as glossy spots. Such glossy spots are called gloss differences. That is, it refers to a phenomenon in which the rollers of rollers 231 and 241 and the marks of the rollers remain on the toner image. This phenomenon is noticeable depending on how light strikes, and does not disturb the toner image.

  This glossy spot is less noticeable on plain paper sheets. However, glossy spots are particularly noticeable when the toner image has a high glossiness, such as a sheet of glossy paper or glossy film.

  In addition, when the relay conveyance path 240 having a plurality of roller pairs 241 is provided as in the printer 211, the number of roller pairs that come into contact with the toner image before cooling immediately after fixing increases, resulting in more glossy spots. It may appear even more prominently. It should be noted that the above-mentioned phenomenon of occurrence of gloss spots may occur not only in the printer described above but also in a monochrome copying machine.

  Although the printer described above has been described with respect to the occurrence of glossy spots on the toner image formed on the sheet, an inkjet image forming apparatus that forms an image by injecting ink onto the sheet also includes the ambient temperature at that time. Depending on the humidity or the amount of ink, the drying of the ink is slow, and before the ink is completely dried, the sheet is conveyed by a pair of rollers, and the marks of the rollers and the rollers may be made on the image forming surface.

  In addition, the conventional sheet conveying device is arranged at a position where the temperature of the toner image is lowered or the ink is dried in any situation so that the image of the roller pair is not left on the image formed on the sheet. Therefore, the downsizing of the image forming apparatus is hindered.

  SUMMARY OF THE INVENTION An object of the present invention is to provide a sheet conveying apparatus that conveys a sheet without making a mark when conveying the sheet to the image forming surface of the sheet on which an image is formed.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus that includes a sheet conveying device that does not leave a mark when conveying a sheet on the image forming surface of the sheet and that can be downsized.

  In order to achieve the above object, the sheet conveying apparatus of the present invention includes an adsorption conveying unit that adsorbs and conveys a sheet on which an image is thermally fixed by a fixing device that thermally fixes the image formed on the sheet to a circulating belt. I have.

  In order to achieve the above object, an image forming apparatus according to the present invention includes an image forming unit that forms an image on a sheet, a fixing unit that fixes an image formed by the image forming unit to the sheet, and an image formed by the fixing unit. And a sheet conveying apparatus that conveys the heat-fixed sheet, and the sheet conveying apparatus is the sheet conveying apparatus described above.

  In the sheet conveying apparatus of the present invention, the sheet on which the image is thermally fixed by the fixing device is conveyed by being adsorbed to the circulating belt of the adsorption conveying means, so that an image defect such as glossy spots on the image surface of the sheet Can be reduced.

  The image forming apparatus according to the present invention includes a sheet conveying device that does not leave a mark when conveying a sheet to the image forming surface of the sheet, so that there is almost no need to redo image formation and the image forming efficiency can be improved. .

  Hereinafter, a sheet conveying apparatus according to an embodiment of the present invention and a full-color laser printer as an image forming apparatus including the sheet conveying apparatus in an apparatus main body will be described with reference to the drawings. The sheet conveying apparatus according to the embodiment of the present invention can be provided not only in a full-color laser printer but also in various forms of printers and copiers. Moreover, the numerical value taken up by this embodiment is a numerical value for making an invention easy to understand, Comprising: It is a reference numerical value and does not limit this invention.

(Full-color laser printer and sheet conveying apparatus of the first embodiment)
FIG. 1 is a schematic diagram of a full color laser printer as an image forming apparatus according to a first embodiment of the present invention and a sheet conveying apparatus according to the first embodiment provided in the full color laser printer. FIG. The full-color laser printer 101 is hereinafter simply referred to as “printer”.

  A sheet supply device 20 provided in the lower portion of the apparatus main body 100 of the printer 101 is configured to supply the sheet S to the image forming unit 8 from a sheet supply cassette 21 that stores a plurality of sheets S. The apparatus main body 100 of the printer 101 has four photosensitive drums 1a, 1b, 1c, and 1d corresponding to the respective colors of yellow, cyan, magenta, and black in the vertical direction (hereinafter referred to as “1” when generically referring to photosensitive drums). Use). The photosensitive drum 1 is rotated in a direction opposite to the clockwise direction in the figure by driving means (not shown).

  Around the photosensitive drum 1, charging devices 2a, 2b, 2c, and 2d for charging the surface of the photosensitive drum 1 uniformly in order in accordance with the rotation direction (hereinafter, the symbol “2” is used to collectively refer to the charging devices). Scanner units 3a, 3b, 3c, 3d (hereinafter referred to as “3” when generically referred to as scanner units) for forming an electrostatic latent image on the photosensitive drum 1 by irradiating a laser beam based on the image information of each color. Developing devices 4a, 4b, 4c, and 4d (hereinafter referred to as developing devices collectively) that develop toner images by attaching toners of yellow, cyan, magenta, and black colors to the electrostatic latent image. 4 ”), and cleaning devices 6a, 6b, 6c and 6d for removing toner remaining on the surface of the photosensitive drum 1 after transfer (hereinafter, the cleaning devices are collectively referred to as“ 6 ”). The use) and the like are disposed. The photosensitive drum 1, the charging device 2, the developing device 4, and the like constitute an image forming unit 8 as an image forming unit.

  Here, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaning device 6 are integrally formed into a cartridge, and the process cartridges 7 a, 7 b, 7 c, and 7 d (hereinafter, the process cartridge is collectively referred to as “7”). Use).

  The electrostatic transfer belt device 10 is opposed to and in contact with the photosensitive drums 1a, 1b, 1c, and 1d. The electrostatic transfer belt 11 is formed of a film-like member having a predetermined volume specific resistance and a thickness of about 150 μm. The electrostatic transfer belt 11 is stretched around four rollers, that is, a driving roller 12 and driven rollers 13, 14, and 15, and rotates clockwise in the drawing.

  On the most upstream side in the sheet conveyance direction of the electrostatic transfer belt device 10, an electrostatic adsorption roller 17 that sandwiches the electrostatic transfer belt 11 with the driven roller 13 is provided. The electrostatic attraction roller 17 presses the sheet S to the outer periphery of the electrostatic transfer belt 11 and applies a voltage to the electrostatic transfer belt 11 so that the sheet S is electrostatically attracted to the electrostatic transfer belt 11 and conveyed. I try to do it. Inside the electrostatic transfer belt 11, transfer rollers 18a, 18b, 18c, and 18d (hereinafter collectively referred to as transfer rollers) sandwiching the electrostatic transfer belt 11 between the four photosensitive drums 1a, 1b, 1c, and 1d. , The code “18” is used).

  The fixing device 30 includes a fixing roller 31 and a pressure roller 32 pressed against the fixing roller 31. The fixing device 30 also includes a fixing inlet guide 33 that guides the sheet S conveyed from the electrostatic transfer belt device 10 to the nip N between the fixing roller 31 and the pressure roller 32. The fixing device 30 is configured to fix the toner image on the sheet by heating and pressing while rotating and conveying the sheet between the fixing roller 31 and the pressure roller 32.

  On the downstream side of the fixing device 30, the image-formed sheet S is fed to a sheet discharge tray 60 as a sheet stacking unit installed on the upper portion of the apparatus main body 100 or to a sorter 70 installed on the side surface of the apparatus main body 100. The sheet conveying apparatus 40 of 1st Embodiment which conveys is provided.

  A sheet conveying apparatus 40 according to the first embodiment will be described with reference to FIGS. 1 to 5. FIG. 2 is a schematic diagram of the sheet conveying apparatus according to the first embodiment, and is a cross-sectional view taken along the sheet conveying direction. FIG. 3 is a perspective view of the first suction conveyance belt of the first embodiment.

  The sheet conveyance device 40 includes a first adsorption conveyance belt 41 as an adsorption conveyance unit that receives the sheet S from the fixing device 30, and a first adsorption conveyance unit that receives the sheet S from the adsorption conveyance belt 41 and conveys the sheet S to the sorter 70. 2 suction conveyance belts 51. The first and second suction conveyance belts 41 and 51 have the same shape.

  The first suction conveyance belt 41 includes a belt driving roller 42, a driven roller 43, a conveyance belt 44 stretched over both rollers 42, 43, a suction duct 45 installed inside the conveyance belt 44, and a suction duct. 45, a suction fan 46 connected to 45, a drive motor M1 for rotating the belt drive roller 42, and the like. The conveyor belt 44 is a thin film endless belt made of rubber, resin, or the like. A plurality of holes 44a having a diameter of about 5 mm are formed in the transport belt 44 over the entire circumference. When the suction fan 46 is operated, the first suction conveyance belt 41 sucks air from the hole 44a through the suction duct 45 and sucks the sheet S to the lower surface (lower surface) of the conveyance belt 44. .

  Similarly to the first suction transport belt 41, the second suction transport belt 51 also includes a transport belt 54, a plurality of holes 54a, a belt driving roller 52, a driven roller 53, a suction duct 55, a suction fan (not shown), and a drive. A motor M2 is provided. The second suction conveyance belt 51 also sucks air from the hole 54 a through the suction duct 55 when a suction fan (not shown) is operated, and adsorbs the sheet S to the lower surface of the conveyance belt 54.

  The sorter 70 is an example of a sheet post-processing apparatus provided with a plurality of paper discharge trays 72, and the user selects a system according to the application and increases the added value of the operation of the apparatus main body 100. The sheet S taking-in port 71 to the sorter 70 is provided on an extension line on the downstream side in the conveyance direction of the second suction conveyance belt 51. The intake port 7 guides the sheet S sucked and conveyed by the second sucking and conveying belt 51 into the sorter 70 as it is.

  The operation of the printer 101 will be described. The sheet supply roller 22 of the printer 101 is driven and rotated in accordance with an image forming operation during printing. The sheet supply roller 22 separates the sheets S in the sheet supply cassette 21 one by one and sends them out from the sheet supply cassette 21. The leading edge of the sheet S abuts against the pair of registration rollers 23 whose rotation has stopped, temporarily stops and forms a loop, and the skew is corrected.

  On the other hand, the process cartridges 7a, 7b, 7c, and 7d are sequentially driven in accordance with the print timing, and the photosensitive drums 1a, 1b, 1c, and 1d are rotated in the counterclockwise direction in accordance with the drive. Then, the scanner units 3 corresponding to the respective process cartridges 7 are sequentially driven. By this driving, the charging roller 2 applies a uniform charge to the peripheral surface of the photosensitive drum 1. The scanner unit 3 exposes the peripheral surface of the photosensitive drum 1 in accordance with an image signal to form an electrostatic latent image on the peripheral surface of the photosensitive drum 1. A developing roller in the developing device 4 transfers toner to a low potential portion of the electrostatic latent image to form a toner image on the peripheral surface of the photosensitive drum 1.

  At the timing when the leading edge of the toner image formed on the peripheral surface of the most upstream photoreceptor drum 1a is rotated and conveyed to the point facing the electrostatic transfer belt 11, the print start position of the sheet S is at the point facing the toner image. The registration roller pair 23 starts to rotate so that the sheets S are fed to the electrostatic transfer belt device 10 so as to coincide with each other.

  The sheet S charged by the electrostatic attraction roller 17 and adsorbed on the electrostatic transfer belt 11 is subjected to an electric field formed between the respective photosensitive drums 1 and the transfer roller 18 so that the color toner image on each photosensitive drum 1 is obtained. Are sequentially transferred. When the leading edge of the sheet S to which the four color toner images are transferred is conveyed to the belt driving roller 12, the sheet S is separated from the electrostatic transfer belt 11 by the curvature of the belt driving roller 12 (peeled) and fixed. It is guided to the entrance guide 33 and carried into the fixing device 30.

  When the sheet S passes through the nip between the fixing roller 31 and the pressure roller 32, the fixing device 30 applies heat and pressure to the sheet S to fix the toner image transferred on the sheet onto the sheet S. Thereafter, the sheet conveying device 40 conveys the sheet.

  Here, the operation of the sheet conveying apparatus 40 will be described with reference to FIGS. FIG. 4 is a diagram for explaining the operation when the sheet conveying apparatus 40 discharges a sheet to the sheet discharge tray 60. FIG. 5 is a diagram for explaining the operation when the sheet conveying device 40 feeds a sheet into the take-in port 71 of the sorter 70.

  The fixing device 30 conveys the sheet S along the guide 34 while heating and pressing, and sends the sheet S to the first suction conveyance belt 41. The conveyor belt 44 is rotated in the clockwise direction by the motor M1. When the sheet S advances to a position where air is sucked by the suction duct 45 on the transport belt 44, the back surface of the image forming surface on which the toner image is formed (the surface on which the toner image is not formed) is transported on the transport belt. It is attracted to 44 and is transported together with the transport belt 44. When the sheet S passes through the suction area of the suction duct 45, the suction is released and transferred to the second suction conveyance belt 51. Similarly to the first suction transport belt 41, the second suction transport belt 51 sucks the sheet and transports it in the direction of arrow A.

  When the sheet conveying device 40 discharges and stacks the sheet S on the sheet discharge tray 60, at least the rear end of the sheet S is completely transferred from the first suction conveyance belt 41 to the second suction conveyance belt 51. After that, the circulation of the conveyor belt 54 is stopped, and the suction fan (not shown) is also stopped. The suction duct 55 of the second suction conveyance belt 51 is disposed directly above the sheet discharge tray 60. For this reason, when the suction duct 55 stops the suction operation of the sheet, the sheet is dropped onto the sheet discharge tray 60 in the direction of arrow B by its own weight and stacked. It is not always necessary to stop the circulation of the conveyor belt 54.

  When the sheet conveying apparatus 40 conveys the sheet S to the sorter 70 without discharging the sheet S onto the sheet discharge tray 60, the circulation operation of the conveying belt 54 is performed even if the sheet S is completely delivered to the second suction conveying belt 51. Without stopping the suction operation of the suction fan (not shown), the sheet continues to be conveyed in the direction of arrow C while adsorbing the sheet to the conveying belt 54, and the leading edge of the sheet S is conveyed to the intake port 71 of the sorter 70. . When the sheet S passes the suction area of the suction duct 55, the suction is released, and the sheet S is sent to the intake port 71 and subjected to post-processing by the sorter 70. Finally, the sheet S is discharged to the paper discharge tray 72.

  As described above, the sheet conveying apparatus 40 of the present embodiment is configured to adsorb and convey the sheet S immediately after the toner image is fixed to the conveying belt 44 without conveying the sheet S at the nip of the roller pair unlike the conventional case. Therefore, no glossy spots occur on the toner image. That is, the toner image does not have a roller mark, and the image quality of the toner image is not deteriorated.

  As in the sheet conveying apparatus 40 of the present embodiment, when the sheet is conveyed by adsorbing the back surface of the image forming surface on which the toner image is formed to the conveying belts 44 and 54, the toner image is touched. The sheet can be conveyed without any damage to the toner image. In addition, even if the toner image is not cooled by being heated by the fixing device 30, the toner image is not damaged.

  Since the sheet conveying apparatus 40 adsorbs and conveys the sheet to the conveying belts 44 and 45 by the air suction of the suction ducts 45 and 55, the toner image heated by the fixing device 30 and not completely cooled is quickly cooled by the suction air. And the toner image can be made less likely to be scratched.

  In the sheet conveying apparatus 40, the suction duct 55 of the second suction conveyance belt 51 is disposed directly above the sheet discharge tray 60. Therefore, when the air suction operation of the suction duct 55 is stopped, the sheet is transferred to the sheet discharge tray. The sheet can be stacked in a state in which the sheet is dropped from directly above the sheet 60 and is aligned with the sheet discharge tray 60.

  Since the conventional sheet conveying apparatus conveys the sheet with the roller pair, the sheet is conveyed by the driving rotation of the driving roller, so that there is a possibility that the sheet slips. If it slips, the toner image will be damaged. For this reason, it is necessary to increase the pressure contact force between the rollers of the roller pair so that slip does not occur. However, if the pressure contact force between the rollers is too strong, the toner image is likely to be marked with a roller. For this reason, the conventional sheet conveying device requires time and effort to adjust the pressure contact force between the rollers to a pressure contact force that does not cause slippage and does not leave a mark on the toner image. Was low. In contrast, the sheet conveying apparatus of the present invention is configured to convey a sheet without using a roller pair, so that it is possible to save time and labor for adjusting the pressure contact pressure, and to improve manufacturing productivity. Can be increased.

  In addition, the sheet conveying apparatus 40 may provide the conventional relay conveyance path 240 instead of providing the second suction conveyance belt 51. In other words, a structure in which the first suction conveyance belt 41 is provided instead of the two pairs of rollers 231 immediately downstream of the conventional fixing device 212 shown in FIG. Even in this case, the sheet can be conveyed by the first suction conveyance belt 41 without causing the toner image to have a roller mark or scratch.

(Full Color Laser Printer and Sheet Conveying Device of Second Embodiment)
FIG. 6 is a schematic diagram of a full color laser printer as an image forming apparatus according to the second embodiment of the present invention and a sheet conveying apparatus according to the second embodiment provided in the full color laser printer. FIG. FIG. 7 is a schematic view of the sheet conveying apparatus according to the second embodiment, and is a cross-sectional view along the sheet conveying direction. The full-color laser printer 102 is hereinafter simply referred to as “printer”. In the printer 102 of the present embodiment, the same parts as those of the printer 101 of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The printer 102 includes a refeed conveyance path 80 serving as a resupply guide unit on the opposite side of the apparatus main body 103 from the sorter 70. The re-feed conveyance path 80 includes roller pairs 82, 83, 84, and the like, conveys a sheet on which a toner image is formed on one side to the image forming unit 8 again, and places the toner image on the other side. It can be formed.

  The sheet conveying apparatus 90 according to the second embodiment is provided to convey a sheet to any one of the sheet discharge tray 60, the sorter 70, and the refeed conveyance path 80. The sheet conveyance device 90 includes a first adsorption conveyance belt 41 serving as an adsorption conveyance unit that receives the sheet S from the fixing device 30, and a second adsorption conveyance belt 61 serving as an adsorption continuous conveyance unit that conveys the sheet S in the horizontal direction. It has. The first and second suction conveyance belts 41 and 61 have the same shape.

  Similarly to the first suction conveyance belt 41, the second suction conveyance belt 61 also has a conveyance belt 64, a plurality of holes 64 a formed in the conveyance belt 64, a belt driving roller 62, a driven roller 63, a suction duct 65, A suction fan (not shown) and a drive motor M3 are provided. The second suction conveyance belt 61 also sucks air from the hole 64a through the suction duct 65 when a suction fan (not shown) is operated, and sucks the sheet S onto the lower surface (lower surface) of the conveyance belt 64. ing.

  Note that the suction conveyance belt 61 of the present embodiment is configured such that the drive motor M3 rotates in both forward and reverse directions. For this reason, the conveyor belt 64 also circulates in both forward and reverse directions. Further, a gap is formed between the first suction conveyance belt 41 and the second suction conveyance belt 61. This gap serves as an intake port 81 for the sheet S to the refeed conveyance path 80. The intake port 81 is formed on an extension line on the upstream side in the conveyance direction of the second suction conveyance belt 61. The second suction conveyance belt 61 is reversely circulated to feed the sheet S into the refeed conveyance path 80.

  The operation of the sheet conveying apparatus 90 will be described. The sheet conveying device 90 can also convey the sheet to the sheet discharge tray 60 and the sorter 70. Since the operation is the same as that of the sheet conveying apparatus 40 of the first embodiment, the description thereof is omitted.

  When the sheet conveying apparatus 90 conveys the sheet to the refeed conveyance path 80, after the rear end (right end in FIG. 7) of the sheet S is completely transferred to the suction conveyance belt 61, the circulation direction of the conveyance belt 64 is determined. Is reversed from the arrow A direction to the arrow D direction, and the sheet is conveyed in the arrow E direction without releasing the suction of the sheet. In FIG. 7, the right end of the sheet is conveyed to the right end of the conveyance belt 64 and is not sucked by the suction duct 65, so that the sheet is separated from the conveyance belt 64 and enters the intake port 81, and passes through the refeed conveyance path 80. It will be transported.

  The sheet conveying device 90 of the second embodiment also has the same effect as the sheet conveying device 40 of the first embodiment.

  Further, the sheet conveying apparatus 90 of the present embodiment reverses the conveying belt 64 while the conventional sheet conveying apparatus performs reverse rotation of the roller pair in order to cause the sheet to enter the refeed conveyance path 80. Therefore, it is possible to eliminate the possibility of scratching the toner image generated during the reverse rotation of the roller pair, which has occurred in the past.

  Further, when the sheet conveying apparatus 90 according to the second embodiment conveys a sheet to the refeed conveyance path, the conventional sheet conveying apparatus does not reverse a plurality of roller pairs at the same time. Although the sheet cannot be reliably conveyed due to the slack, the conveyance belt 64 is circulated in the opposite direction, so that the sheet is fed to the refeed conveyance path 80 without being pulled or loosened. It can be reliably conveyed.

(Sheet Conveying Device of Third Embodiment)
FIG. 8 is a schematic view of the sheet conveying apparatus according to the third embodiment, and is a cross-sectional view taken along the sheet conveying direction. The sheet conveying apparatus 95 of the present embodiment has a structure in which a part of the second suction conveying belt 51 in the sheet conveying apparatus 40 of the first embodiment shown in FIGS. 1 to 5 is changed. In the sheet conveying apparatus of the present embodiment, the same parts as those of the sheet conveying apparatus of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

  The sheet conveying device 95 includes first and second suction conveying belts 41 and 96. The second suction conveyance belt 96 as the suction continuous conveyance means includes two divided suction ducts 97 and 98. A suction fan (not shown) is connected to each of the two suction ducts 97 and 98.

  When the sheet conveying device 95 discharges a short sheet whose length is approximately equal to or less than the length of the suction duct 97 to the sheet discharge tray 60, the downstream suction duct 98 is not operated. Only the upstream suction duct 97 is activated. Further, the sheet conveying device 95 operates both the suction ducts 97 and 98 when discharging a long sheet to the sheet discharge tray 60 or conveying it to the sorter 70. As described above, the sheet conveying apparatus 95 according to the present embodiment can efficiently operate the suction fan by selectively using the two suction ducts 97 and 98 according to the sheet size and the conveyance mode. Note that the number of suction ducts is not limited to two and may be three or more.

  Further, the suction duct 65 of the sheet conveying apparatus 90 of the second embodiment may be divided into a plurality of parts. Even in this case, the suction fan can be used efficiently.

  In the above description, the sheet conveying apparatuses 40, 90, and 95 of each embodiment use the suction ducts 45, 55, 65, 97, and 98 to adsorb the sheet to the conveying belts 44, 54, and 64. However, in the image forming unit 8, the sheet may be attracted and conveyed by the same structure as the electrostatic transfer belt 11 that attracts and conveys the sheet by static electricity. In this case, the sheet is separated by the curvature of the conveying belts 44, 54, 64 when the leading edge is conveyed to the end of the conveying belts 44, 54, 64. However, in order to allow the second suction conveyance belts 51 and 96 to drop the sheet onto the sheet discharge tray 60 from directly above, an electrostatic eraser that erases static electricity is provided at a position corresponding to the suction ducts 55, 97, and 98. There is a need. Therefore, the apparatus for adsorbing the sheet to the belt is not limited to the suction duct.

  The above-described sheet conveying apparatus has been described when incorporated in a printer that forms a toner image on a sheet. However, even when incorporated in an inkjet printer that ejects ink onto a sheet to form an image, Depending on the temperature and humidity of the ink, or the amount of ink, the ink will dry slowly, and even if the ink does not dry completely, there will be no marks of rollers or rollers on the image forming surface or scratches on the image forming surface. The sheet can be conveyed.

  In addition, unlike the conventional sheet conveying device, the sheet conveying device can be disposed downstream of the position where the temperature of the toner image is lowered or the ink is dry, without the trace of the conventional roller pair. Thus, the image forming apparatus can be reduced in size.

1 is a schematic view of a full-color laser printer as an image forming apparatus according to a first embodiment of the present invention and a sheet conveying apparatus according to the first embodiment provided in the full-color laser printer, and a cross-sectional view along the sheet conveying direction. It is. FIG. 2 is a schematic view of the sheet conveying apparatus according to the first embodiment, and is a cross-sectional view along the sheet conveying direction. It is a perspective view of the 1st adsorption conveyance belt of a 1st embodiment. FIG. 6 is a diagram for explaining an operation when the sheet conveying apparatus of the first embodiment discharges a sheet to a sheet discharge tray. FIG. 5 is a diagram for explaining an operation when the sheet conveying apparatus according to the first embodiment feeds a sheet into a sorter take-in port. FIG. 4 is a schematic view of a full-color laser printer as an image forming apparatus according to a second embodiment of the present invention and a sheet conveying device according to a second embodiment provided in the full-color laser printer, and a cross-sectional view along the sheet conveying direction. It is. It is the schematic of the sheet conveying apparatus of 2nd Embodiment, and is sectional drawing along the conveyance direction of a sheet | seat. It is the schematic of the sheet conveying apparatus of 3rd Embodiment, and is sectional drawing along the conveyance direction of a sheet | seat. FIG. 6 is a cross-sectional view taken along the sheet conveying direction of a full-color laser printer as a conventional image forming apparatus provided with a sheet conveying device on the downstream side of the fixing device.

Explanation of symbols

S sheet M1, M2, M3 Motor 1 (1a, 1b, 1c, 1d) Photosensitive drum 8 Image forming section (image forming means)
DESCRIPTION OF SYMBOLS 10 Electrostatic transfer belt apparatus 20 Sheet supply apparatus 30 Fixing device 31 Fixing roller 32 Pressure roller 40 Sheet conveyance apparatus 41 of 1st Embodiment 41 1st adsorption conveyance belt (adsorption conveyance means)
44 (first) transport belt 45 (first) suction duct 46 suction fan 51 second suction transport belt (suction continuous transport means)
54 (second) conveying belt 55 (second) suction duct 60 sheet discharge tray (sheet stacking means)
61 2nd adsorption conveyance belt (adsorption continuous conveyance means)
64 (Second) Conveying Belt 65 (Second) Suction Duct 70 Sorter 80 Refeeding Conveying Path (Refeeding Guiding Unit)
81 Sheet intake port (between the suction conveyance means and the continuous suction conveyance means)
90 Sheet Conveying Device of Second Embodiment 95 Sheet Conveying Device of Third Embodiment 96 (Second) Adsorption Conveying Belt (Continuous Adsorption Conveying Means)
97, 98 Suction duct 101, 102 Full color laser printer (image forming device)

Claims (8)

  A sheet conveying apparatus comprising: an adsorption conveying unit that adsorbs and conveys a sheet, on which an image is thermally fixed by a fixing device that thermally fixes an image formed on the sheet, to a circulating belt. A suction continuation transporting means for sucking and continuously transporting the sheet that has been transported by the suction transporting means to the lower surface of the circulating belt;
The sheet conveying apparatus according to claim 1, wherein the suction continuous conveying unit is disposed above the sheet stacking unit on which the sheets are stacked, and can release the sucked sheet. An adsorption continuation conveying means for adsorbing and continuously conveying the sheet that has been conveyed by the adsorption conveyance means to the lower surface of the belt that circulates;
The re-feeding guide unit that guides the sheet to the image forming unit that forms an image on the sheet from between the suction transport unit and the suction continuous transport unit by reversely feeding the sucked sheet. The sheet conveying apparatus according to claim 1, wherein the sheet conveying apparatus is capable of conveying the sheet. An adsorption continuation conveying means for adsorbing and continuously conveying the sheet that has been conveyed by the adsorption conveyance means to the lower surface of the belt that circulates;
The suction continuous conveyance means is disposed above the sheet stacking means on which the sheets are stacked, and performs a release operation to release the sucked sheets, and reversely feeds the sucked sheets to the suction conveyance means and the 2. A sheet feeding operation to selectively supply a sheet to a re-feeding guide unit that guides the sheet to an image forming unit that forms an image on the sheet from between the continuous suction conveyance unit and the image forming unit. 4. The sheet conveying apparatus according to claim 1.   5. The suction continuous conveyance unit includes a plurality of belts in a sheet conveyance direction, and each belt can perform adsorption and adsorption release of the sheet. The sheet conveying apparatus according to claim 1.   The sheet conveying apparatus according to claim 1, wherein the suction conveying unit conveys the sheet while adsorbing a surface on the back side of the surface on which the image of the sheet is formed.   6. The sheet conveying apparatus according to claim 2, wherein the suction continuous conveying unit conveys the sheet while adsorbing a surface on the back side of the surface on which the image of the sheet is formed. . Image forming means for forming an image on a sheet;
A fixing device for fixing the image formed by the image forming means to the sheet;
A sheet conveying device that conveys a sheet on which an image is thermally fixed by the fixing device,
The image forming apparatus, wherein the sheet conveying apparatus is the sheet conveying apparatus according to claim 1.

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