JP2008162744A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device capable of forming an image on both surfaces of a sheet without increasing the size of the device and lowering the throughput. <P>SOLUTION: A pair of normally and reversely rotatable sheet inverting and conveying rollers 16 are installed in a lead-in path R2 formed by branching from a sheet conveying path R1 between sheet conveying parts 13a, 13b for conveying sheets and a pair of sheet discharge rollers 14. After the sheet selectively conveyed into the lead-in path R2 by the sheet conveying parts 13a, 13b is temporarily led to the lead-in path side, it is inverted and conveyed into a re-conveying path 26. The sheet inverting and conveying roller 16 is installed at a position where the sheet conveying distance L2 between the branch point B between the sheet conveying path R1 and the lead-in path R2 and the sheet inverting and conveying roller 16 is shorter than the sheet conveying distance L1 between the branch point B and the pair of sheet discharge rollers 14. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an apparatus in which a sheet on which an image is formed on a first side is conveyed again to an image forming unit and an image is formed on a second side opposite to the sheet.

  In a conventional image forming apparatus, in addition to a mode in which an image is formed on one side (first side) of a sheet, a duplex mode in which an image is formed on the opposite side (second side) of the sheet on which an image is formed on one side. There is something to prepare.

  In such an image forming apparatus, in the duplex mode, the sheet is reversed so that an image is formed on the back side opposite to the sheet on which the image is formed on one side by the image forming unit, and then the image forming unit again It is made to convey (refer patent document 1).

  FIG. 10 is a diagram showing a schematic configuration of such a conventional image forming apparatus. In the image forming apparatus, when an image is formed, first, a sheet P stored in a sheet feeding cassette 701 provided at a lower portion of the apparatus main body 700 is fed to an electrostatic transfer conveyance unit 705 by a sheet feeding roller 702. To send.

  Next, the sheet P is electrostatically adsorbed by the transfer belt 705 a provided in the electrostatic transfer conveyance unit 705, and the sheet P is conveyed along the process cartridge 710. When the toner is conveyed along the process cartridge 710 in this way, the toner image formed in the process cartridge 710 is transferred to the sheet P.

  Next, the sheet P on which the toner image is transferred is conveyed to the fixing device 713, and the toner image is fixed by the fixing device 713. Thereafter, in the mode in which an image is formed on one side, the sheet P on which the toner image is fixed is discharged to a discharge tray 725 by a discharge roller pair 714.

  In the double-side mode in which images are formed on both sides of the sheet P, the sheet P is guided to the double-side reversing unit 715 located downstream of the paper discharge roller pair 714 and above the paper discharge tray 725. Here, the double-side reversing unit 715 is provided with a flapper 717 that switches between a path discharged toward the paper discharge tray 725 after passing through the paper discharge roller pair 714 and a path conveyed toward the double-side reversing unit 715. It has been. When images are formed on both surfaces of the sheet P, the flapper 717 is rotated clockwise around the shaft 717a to guide the sheet P to the reverse roller pair 716.

  Next, when the trailing edge of the sheet comes out of the discharge roller pair 714, the flapper 717 is rotated counterclockwise, and the sheet P is stopped at a position where the sheet P can be conveyed to the reconveying path 726. Thereafter, the reverse roller pair 716 is rotated in the reverse direction, and the sheet P is conveyed in the direction of the re-conveyance path 726 indicated by the arrow b.

  Next, the sheet P conveyed to the re-conveying path 726 by the reverse rotation of the reverse roller pair 716 is held by the electrostatic transfer conveying unit 705 in a state where one side (first surface) side on which an image is formed is adsorbed. It is conveyed along the process cartridge 710. As a result, an image is formed on the back surface (second surface) of the sheet P.

  Next, the sheet P on which the image is formed on the back side, that is, the image is formed on both sides as described above, is fixed with the toner image by the fixing unit 713 and conveyed to the paper discharge roller pair 714. Thereafter, as shown in FIG. 10, the sheet P passes through the lower surface of the flapper 717 stopped at a position where the sheet P can be conveyed to the re-conveyance path 726 without rotating, and then to the sheet discharge tray 725. And discharged.

Japanese Patent Laid-Open No. 2004-302182

  Incidentally, in such a conventional image forming apparatus, the reverse roller pair 716 of the double-side reversing unit 715 is positioned above the paper discharge roller pair 714 as shown in FIG. For this reason, not only the double-sided reversing portion 715 protrudes above the paper discharge tray 725, but also the height of the apparatus main body 700 is increased, and the apparatus main body 700 is increased in size and cost is increased.

  When the reverse roller pair 716 is positioned above the paper discharge roller pair 714, the distance from the fixing nip N of the heating roller 713a and the pressure roller 713b constituting the fixing device 713 to the reverse roller pair 716, that is, the sheet conveyance distance. Becomes longer.

  Here, when the sheet conveyance distance from the fixing nip N to the pair of reverse rollers 716 becomes longer in this way, after the sheet P is conveyed from the fixing nip N to the pair of reverse rollers 716, the sheet P is reversed and applied to both sides of the sheet P. The time required to form an image becomes longer. As a result, in particular, the time required to form images on both sides of the sheet becomes longer, and the throughput decreases.

  Accordingly, the present invention has been made in view of such a current situation, and provides an image forming apparatus capable of forming images on both sides of a sheet without increasing the size of the apparatus and reducing the throughput. It is for the purpose.

  The present invention provides an image forming apparatus in which a sheet is reversed so as to form an image on a second surface opposite to the sheet on which an image is formed on a first surface by an image forming unit, and the sheet is conveyed again to the image forming unit. A sheet conveying section that conveys the sheet, a sheet discharge roller that is disposed downstream of the sheet conveying section and that discharges the sheet conveyed by the sheet conveying section, and a sheet on which an image is formed on the first surface again. A re-conveying path for conveying to the image forming unit, a drawing path provided by branching from a sheet conveying path between the sheet conveying unit and the sheet discharge roller, provided in the drawing path, The sheet transport unit temporarily pulls the sheet transported to the pull-in path through a branch point between the sheet transport path and the pull-in path, and then reverses the sheet to the re-transport path. A sheet reversing and conveying roller capable of forward and reverse conveyance, and a switching member that selectively moves to a position that guides the sheet on which the image is formed on the first surface to the sheet reversing and conveying roller and a position that leads to the sheet discharge roller; The sheet is provided in the drawing path, and the sheet conveyed by the sheet conveying section through the branch point between the sheet conveying path and the drawing path is once drawn into the drawing path, and then reversed and reversed. A sheet reversing and conveying roller capable of normal and reversing conveyance to the passage, and the sheet reversing and conveying roller has a sheet conveying distance from the branching point to the sheet reversing and conveying roller from the branching point to the sheet discharging roller. It is characterized in that it is provided at a position that is shorter than the sheet conveying distance up to.

  As in the present invention, the sheet conveyance distance from the branch point is made shorter for the sheet reverse conveyance roller than for the sheet discharge roller, so that the apparatus is not enlarged and the throughput is not lowered. Images can be formed on both sides of the sheet.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a diagram illustrating a configuration of a full-color laser beam printer which is an example of an image forming apparatus according to a first embodiment of the present invention. Reference numeral 100 denotes a full color laser beam printer, 101 denotes a full color laser beam printer main body (hereinafter referred to as a printer main body), 102 denotes an image forming unit for forming an image on a sheet, 13 denotes a fixing unit, and the fixing unit 13 is a fixing roller pair 13a. , 13b.

  The image forming unit 102 includes the scanner unit 4 and four process cartridges 10 (10Y, 10M, 10M) that form toner images of four colors of yellow (Y), magenta (M), cyan (C), and black (Bk). 10C, 10Bk). Further, the image forming unit 102 includes an intermediate transfer unit 5 disposed above the process cartridge 10.

  Here, each process cartridge 10 includes a photosensitive drum 20 (20Y, 20M, 20C, 20Bk). Each photosensitive drum 20 is rotatably supported at both ends by a support member, and is driven to rotate clockwise when a driving force from a driving motor (not shown) is transmitted to one end. Is done. Each of the photosensitive drums 20 is configured by applying an organic photoconductive layer (OPC photosensitive member) to the outer peripheral surface of an aluminum cylinder having a diameter of 20 to 30 mm, for example.

  The intermediate transfer unit 5 includes an intermediate transfer belt 6 wound around a driving roller 8 and a tension roller 9. The intermediate transfer unit 5 includes a primary transfer roller 7 (7Y, 7M, 7C, 7Bk) that is provided inside the intermediate transfer belt 6 and contacts the intermediate transfer belt 6 at a position facing the photosensitive drum 20. ing. Reference numeral 11 denotes a cleaning unit that cleans the intermediate transfer belt 6.

  Here, the intermediate transfer belt 6 is composed of a film-like member and is disposed so as to be in contact with each photosensitive drum 20 and is rotated in the direction of arrow A by a driving roller 8 driven by a driving unit (not shown). It has become. Then, by applying a positive transfer bias to the intermediate transfer belt 6 by the primary transfer roller 7, each color toner image having a negative polarity on the photosensitive drum is sequentially transferred to the intermediate transfer belt 6 in a multiple transfer manner. As a result, a full-color image is formed on the intermediate transfer belt.

  A secondary transfer roller 12 constituting a secondary transfer portion T2 for transferring a full color image formed on the intermediate transfer belt to the sheet P is provided at a position facing the drive roller 8 of the intermediate transfer unit 5. Yes.

  Further, a fixing unit 13 is disposed above the secondary transfer roller 12, and a paper discharge roller pair 14 and a double-side reversing unit 15 are disposed at the upper left part of the fixing unit 13. The double-side reversing unit 15 includes a reversing roller pair 16 that is a sheet reversing and conveying roller capable of normal and reversing, and a flapper 17 that is a switching member.

  In FIG. 1, reference numeral 26 denotes a re-conveying path for reversing the front and back of the sheet and guiding it again to the image forming unit in order to form an image on the back side of the sheet on which the image is formed on one side by the image forming unit 102. is there. A reversing sensor 24 is provided on the downstream side of the fixing unit 13 and detects the passage of the rear end of the sheet P.

  Next, an image forming operation of the image forming apparatus 100 configured as described above will be described.

  When the image forming operation is started, first, the scanner unit 4 irradiates laser light (not shown) based on image information from a personal computer (not shown), and the surface is uniformly charged with a predetermined polarity and potential. The surface of the drum 20 is sequentially exposed to form an electrostatic latent image on the photosensitive drum. Thereafter, the electrostatic latent image is developed with toner and visualized.

  For example, first, the photosensitive drum 20Y is irradiated with laser light based on the image signal of the yellow component color from the scanner unit 4 to form a yellow electrostatic latent image on the photosensitive drum 20Y. The yellow electrostatic latent image is developed with yellow toner from a developing device and visualized as a yellow toner image.

  Next, when this toner image arrives at the primary transfer portion where the photosensitive drum 20Y and the intermediate transfer belt 6 come into contact with the rotation of the photosensitive drum 20Y, the primary transfer bias applied to the primary transfer roller 7Y causes a photosensitive transfer. The yellow toner image on the drum is transferred to the intermediate transfer belt 6.

  Next, when the portion of the intermediate transfer belt 6 carrying the yellow toner image moves, the magenta toner image formed on the photosensitive drum 20M by the same method as described above is transferred from the yellow toner image to the intermediate transfer belt. 6 is transferred. Similarly, as the intermediate transfer belt 6 moves, a cyan toner image and a black toner image are transferred onto the yellow toner image and the magenta toner image in a primary transfer portion. As a result, a full-color toner image is formed on the intermediate transfer belt 6.

  In parallel with this toner image forming operation, the sheet P stored in the paper feed cassette 1 is sent out by the pickup roller 21. Thereafter, the sheet P is separated one by one by a separation unit constituted by the feed roller 22 and the retard roller 23 and conveyed to the registration roller pair 2.

  Next, when the top sensor 3 positioned downstream of the registration roller pair 2 in the sheet conveying direction detects the leading edge of the sheet P, the secondary transfer unit T2 determines the positions of the full-color toner image and the sheet P on the intermediate transfer belt. The registration roller pair 2 is driven to match. As a result, the sheet P is conveyed to the secondary transfer portion T2, and the full-color toner image is collectively transferred onto the sheet P by the secondary transfer bias applied to the secondary transfer roller 12 at the secondary transfer portion T2. The

  Next, the sheet P on which the full-color toner image has been transferred in this manner is conveyed to the fixing unit 13, and the toner of each color is received by heat and pressure by the fixing roller pair 13 a and 13 b provided in the fixing unit 13. The melted and mixed colors are fixed on the sheet P as a full-color image. Thereafter, the sheet P on which the image is fixed in this manner is discharged to a discharge tray 25 by a discharge roller pair 14 provided downstream of the fixing unit 13.

  By the way, the full-color laser beam printer 100 according to the present embodiment can form images on both sides of a sheet. When images are formed on both sides of the sheet, the flapper 17 of the double-side reversing unit 15 is rotated clockwise by a drive mechanism such as a solenoid (not shown) to invert the sheet P on which the image is formed on one side. Guide to roller pair 16.

  Next, when the trailing edge of the sheet comes out of the discharge roller pair 14, the flapper 17 is rotated counterclockwise, and the sheet P shown in FIG. 1 is stopped at a position where it can be conveyed to the re-conveying path 26. Thereafter, the reverse roller pair 16 is rotated in the reverse direction, and the sheet P is conveyed in the direction of the re-conveyance path 26. Then, the sheet P conveyed to the reconveying path 26 by the reverse rotation of the reversing roller pair 16 is conveyed to the secondary transfer portion T2 in a reversed state. As a result, an image is formed on the back surface of the sheet P.

  Next, the toner image is fixed by the fixing device 13 on the sheet P on which the image is formed on the back surface, that is, the sheet P on which the image is formed on both sides. Here, the flapper 17 is rotated in the clockwise direction in order to convey the next sheet (not shown) of the sheet P to the re-conveying passage 26, but the sheet P on which images are formed reaches both sides. By the time, the sheet P has been returned to the position where it can be conveyed to the re-conveying passage 26 and stopped.

  Therefore, the sheet P passes through the lower surface of the flapper 17 stopped at a position where the sheet P can be conveyed to the re-conveyance path 26 without rotating, and is conveyed to the paper discharge roller pair 14. The sheet stacking unit 14 is disposed on the downstream side of the pair of fixing rollers 13a and 13b. The sheet stacking roller 14 is a sheet discharge roller that discharges the sheet conveyed by the pair of fixing rollers 13a and 13b. The paper is discharged to a paper discharge tray 25 as a part.

  Next, in order to form an image on the back side in this way, the configuration and operation of the double-side reversing unit 15 that reverses the sheet on which the image is formed on one side will be described.

  FIG. 2 is a diagram illustrating the configuration of the double-side reversing unit 15, and in FIG. 2, R <b> 1 is a sheet conveyance path between the fixing roller pair 13 a and 13 b and the paper discharge roller pair 14 (14 a and 14 b). Further, R2 is a drawing path provided by branching from the sheet conveying path R1, and a pair of reverse rollers 16 (16a, 16b) is provided in the drawing path R2.

  In FIG. 2, B indicates the switching of the conveyance direction of the sheet P by the flapper 17 in the operation range of the flapper 17 that selectively moves the sheet to the position to guide the sheet to the reverse roller pair side and the position to guide the sheet to the sheet discharge roller pair side. The position of the tip of the flapper that is possible is shown. Hereinafter, the point B at which the flapper 17 can switch the conveyance direction of the sheet P is referred to as a branch point B between the sheet conveyance path R1 and the drawing path R2.

  When the sheet is guided to the opposite side of the reverse roller, that is, the drawing path R2, the flapper 17 is rotated clockwise from the branch point B, and the sheet is guided to the opposite side of the sheet discharge roller, that is, the sheet conveying path R1. In this case, the flapper 17 is rotated counterclockwise from the branch point B.

  For example, when an image is formed on the back surface of the sheet P, the control unit (not shown), before the sheet P reaches the branch point B, the flapper 17 and the shaft 17a as shown in FIG. Turn counterclockwise as a fulcrum.

  As a result, the flapper 17 moves to a position where the sheet P can be guided to the reversing roller pair 16 (hereinafter referred to as a first position). The timing at which the flapper 17 is rotated in this way is after a predetermined time has elapsed since the top sensor 3 detected the leading edge of the sheet P sent out by the pickup roller 21.

  Here, by rotating the flapper 17 in this way, the sheet P that has passed through the secondary transfer portion T2 and the fixing portion 13 passes through the upper surface of the flapper 17 as shown in FIG. At this time, the reverse roller pair 16 has already been rotated in the sheet discharge direction indicated by the arrow c. Thereby, after passing through the upper surface of the flapper 17, the sheet P conveyed to the drawing path R <b> 2 through the branch point B between the sheet conveying path R <b> 1 and the drawing path R <b> 2 is drawn by the reversing roller pair 16 and a part thereof Is conveyed above the paper discharge tray 25.

  A guide 18 is disposed above the paper discharge tray 25, and the sheet P that has passed through the flapper 17 is conveyed above the paper discharge tray 25 along the guide 18 without hanging down to the paper discharge tray side. Is done.

  Next, the rotation of the pair of reversing rollers 16 causes the sheet P to pass through the fixing roller nip N of the fixing unit 13, and then the rear end of the sheet P is detected by the reversing sensor 24 positioned on the downstream side of the fixing unit 13. . Then, when the trailing edge is detected by the reversing sensor 24 in this way and then the sheet trailing edge reaches the flapper 17 after a predetermined time has elapsed, the pair of reversing rollers 16 is rotated by a signal from a control unit (not shown). Stop and stop the conveyance of the sheet P.

  Thereafter, as shown in FIG. 4A, the flapper 17 rotates counterclockwise and moves to a position where the sheet P can be conveyed to the re-conveying passage 26 (hereinafter referred to as a second position). Then, immediately after the flapper 17 rotates counterclockwise in this way, the reverse roller pair 16 starts to rotate in the reverse direction.

  As a result, the sheet P once drawn into the drawing path is reversed and conveyed in the direction of arrow D, and is conveyed to the re-conveying path 26 through the upper side of the fixing unit 13. Thereafter, the sheet P that has passed through the re-conveying passage 26 reaches the duplex conveying roller pair 30 and is conveyed by the duplex conveying roller pair 30 to the U-turn roller pair 32 via the duplex conveying sensor 31.

  Next, the sheet P is guided again to the registration roller pair 2 by the U-turn roller pair 32, and then the sheet P on which an image is formed on one side passes through the registration roller pair 2 and is conveyed to the secondary transfer portion T2. Is done. Then, the full color toner image is transferred to the back surface of the sheet P by the secondary transfer portion T2, and the full color toner image is fixed to the sheet P by the fixing portion 13.

  Next, after the full-color toner image is fixed in this way, when the sheet P passes through the fixing roller nip N, the flapper 17 is rotated to the already-described second position as shown in FIG. It is moving. Accordingly, the sheet P passes through the lower surface of the flapper 17, is guided to the paper discharge roller pair 14, and is discharged to the paper discharge tray 25 by the paper discharge roller pair 14.

  Note that when the sheet P on which an image is formed on only one side is discharged, the flapper 17 remains in the second position. As a result, the sheet P that has passed through the fixing unit 13 passes through the lower surface of the flapper 17, passes through the discharge roller pair 14 as it is, and is discharged to the discharge tray 25.

  By the way, in this embodiment, the reversing roller pair 16 has a sheet conveyance distance that is a distance from the branch point B to the reversing roller pair 16 rather than a sheet conveyance distance L1 that is a distance from the branch point B to the paper discharge roller pair 14. It is provided at a position where the distance L2 is shorter (see FIG. 2).

  With this configuration, the reversing roller pair 16 can be disposed downstream of the paper discharge roller pair 14, for example, between the fixing unit 13 and the paper discharge roller pair 14. Can be reduced in height.

  Further, with this configuration, the distance from the fixing roller nip N to the reversing roller pair 16 can be shortened, and thereby the distance necessary for reversing the sheet P can be shortened. As a result, the time required to form images on both sides of the sheet P is shortened, and a reduction in throughput can be prevented.

  Next, a second embodiment of the present invention will be described.

  FIG. 5 is a diagram showing a configuration of a full-color laser beam printer which is an example of an image forming apparatus according to the second embodiment of the present invention. In FIG. 5, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

  In FIG. 5, reference numeral 150 denotes a pre-reversing conveyance path for conveying a sheet having an image formed on one side and then reversing. The pre-reversing conveyance path 150 is located below the paper discharge tray 25, that is, inside the printer main body. Is provided.

  In FIG. 5, reference numeral 200 denotes a sheet discharge unit provided at the top of the printer main body 101, and the sheet discharge unit 200 is a plurality (two) of sheet stacking units provided above the discharge tray 25. Discharge bins 201 and 202 are provided.

  In this embodiment, the sheet is selectively discharged to the discharge bins 201 and 202 in addition to the discharge tray 25 via the discharge path 218. Here, by providing the paper discharge bins 201 and 202 in addition to the paper discharge tray 25 as the sheet stacking portion, the user needs can be satisfied.

  Reference numeral 115 denotes a double-sided reversing unit. The double-sided reversing unit 115 includes a reversing roller pair 116 that is a sheet reversing and conveying roller that can be rotated forward and backward, and a flapper 117 that is a switching member that can be rotated about a shaft 117a.

  FIG. 6 shows the configuration of such a double-sided reversing unit 115. In FIG. 6, B ′ represents the front end of the flapper that enables switching of the conveyance direction of the sheet P by the flapper 117 in the operation range of the flapper 117. Indicates the position. Hereinafter, this point B ′ is referred to as a branch point B ′.

  When forming an image on the back surface of the sheet, before the sheet P reaches the branch point B ′, the flapper 117 is rotated counterclockwise as shown in FIG. 7A with the shaft 117a as a fulcrum. Rotate. As a result, the flapper 117 moves to the first position where the sheet P can be guided to the pair of reverse rollers 116. The timing at which the flapper 117 is rotated in this way is after a predetermined time has elapsed since the top sensor 3 detected the leading edge of the sheet P sent out by the pickup roller 21.

  Here, by rotating the flapper 17 in this way, the sheet P that has passed through the secondary transfer portion T2 and the fixing portion 13 passes through the lower surface of the flapper 117 as shown in FIG. 7B. At this time, the reverse roller pair 116 has already been rotated in the sheet discharge direction indicated by the arrow d, whereby the sheet P that has passed through the lower surface of the flapper 117 is drawn into the pre-reverse transport path 150.

  Next, the rotation of the pair of reversing rollers 116 causes the sheet P to pass through the fixing roller nip N of the fixing unit 13 and is eventually detected by the reversing sensor 24 positioned at the downstream side of the fixing unit 13. . Then, when the trailing edge is detected by the reversing sensor 24 in this way and the trailing edge of the sheet reaches the flapper 117 after a predetermined time has elapsed, the pair of reversing rollers 116 stops rotating and stops conveying the sheet P. .

  Immediately after this, a control unit (not shown) rotates the reverse roller pair 116 in the reverse direction. When the reversing roller pair 116 rotates in the reverse direction in this way, the sheet P that is in a substantially parallel posture is reversed by being once drawn into the pre-reversing conveyance path 150, and due to its rigidity, as shown in FIG. It is conveyed in the direction of arrow F while maintaining a posture parallel to.

  As a result, the sheet P passes through the upper side of the fixing unit 13 and is conveyed to the re-conveying passage 26. Thereafter, the sheet P that has passed through the re-conveying passage 26 reaches the duplex conveying roller pair 30 and is conveyed by the duplex conveying roller pair 30 to the U-turn roller pair 32 via the duplex conveying sensor 31.

  Next, the sheet P is guided again to the registration roller pair 2 by the U-turn roller pair 32, and thereafter, the sheet P on which an image is formed on one side passes through the registration roller pair 2 to the secondary transfer portion T2. Be transported. Then, the full color toner image is transferred to the back surface of the sheet P by the secondary transfer portion T2, and the full color toner image is fixed to the sheet P by the fixing portion 13.

  In addition, after detecting the trailing edge of the sheet by the reversing sensor 24, the sheet P is reversed, and after a lapse of time until the trailing edge of the sheet leaves the rotation range of the leading edge of the flapper 117, the flapper 117 removes the sheet P from the discharge roller. It rotates counterclockwise to a position (third position) where it can be conveyed to the pair 114.

  Therefore, when the sheet P passes through the fixing roller nip after the full-color toner image is fixed as described above, the flapper 117 is rotated to the already-described third position as shown in FIG. 8B. ing. Accordingly, the sheet P passes through the upper surface of the flapper 117, is guided to the paper discharge roller pair 114, and is discharged to the paper discharge tray 25 by the paper discharge roller pair 114.

  When the sheet P is discharged to the discharge bins 201 and 202, the flappers 203 and 204 provided on the downstream side of the flapper 117 are rotated clockwise. For example, when discharging the sheet P to the discharge bin 201, the sheet P that has passed through the upper surface of the flapper 117 is guided to the discharge roller pair 205 by rotating the flapper 203 clockwise, and the discharge roller pair 205 is discharged. Is discharged to the paper discharge bin 201.

  When discharging the sheet P to the discharge bin 202, the flappers 203 and 204 are rotated clockwise to guide the sheet P that has passed through the upper surface of the flapper 117 to the discharge roller pair 206, thereby discharging the discharge roller. The paper is discharged to the paper discharge bin 202 by the pair 206.

  Further, when the sheet P on which an image is formed only on one side is discharged, the flapper 117 remains in the third position. As a result, the sheet P that has passed through the fixing unit 13 passes through the upper surface of the flapper 117, passes through the discharge roller pair 114 as it is, and is discharged to the discharge tray 25 or the discharge bins 201 and 202.

  Here, as in the present embodiment, when the pre-reversal conveyance path 150 is provided inside the printer main body and an image is formed on the back surface, the sheet with the image formed on one side is conveyed to the pre-reversal conveyance path 150. Thus, the sheet P can be prevented from touching the user's eyes.

  Accordingly, the user can be prevented from touching the sheet P that is reversed to form an image on the back surface, and the user can accidentally perform the reversing operation before the sheet P having the image formed on one side is reversed. It is possible to prevent the sheet P from being pulled out.

  Further, it is possible to prevent the reverse sheet P from coming into contact with the sheets that have already been discharged to the paper discharge tray 25, thereby preventing the alignment of the sheets on the paper discharge tray from being deteriorated, and while the paper is being reversed. The sheet P can be prevented from being damaged.

  Here, in the present embodiment, the reverse roller pair 116 has a sheet from the branch point B ′ to the reverse roller pair 116 rather than the sheet conveyance distance L1 ′, which is the distance from the branch point B ′ to the paper discharge roller pair 114. It is arranged at a position where the transport distance L2 ′ is shorter (see FIG. 6).

  With this configuration, the distance from the fixing roller nip N to the reversing roller pair 116 can be shortened, and thereby the distance necessary to reverse the sheet P can be shortened. As a result, the time required to form images on both sides of the sheet P is shortened, and a reduction in throughput can be prevented.

  Further, the discharge roller pair 114 is arranged such that the position of the nip N2 of the reverse roller pair 116 is lower than the position of the nip N1 of the discharge roller pair 114 (see FIG. 6). By disposing the reverse roller pair 116 below the discharge roller pair 114 in the apparatus height direction in this way, the printer main body 101 can be reduced in size.

  Next, a third embodiment of the present invention will be described.

  FIG. 9 is a diagram illustrating a configuration of a full-color laser beam printer which is an example of the image forming apparatus according to the present embodiment. In FIG. 9, the same reference numerals as those in FIG. 1 denote the same or corresponding parts.

  As shown in FIG. 9, the full-color laser beam printer according to the present embodiment has a scanner reader 600 attached to the upper part of the printer body. The image forming unit 102 forms an image based on the image information read by the scanner reader 600.

  By the way, when the scanner reader 600 is attached to the upper portion in this way, the sheet on which the image is formed is discharged to a discharge tray 504 provided on the side wall surface of the printer main body 101.

  Here, in order to discharge the sheet to the paper discharge tray 504 provided on the side surface of the printer main body 101 in this way, a sheet having an image formed on one side or both sides of the upper portion of the printer main body 101 is discharged. A paper discharge passage R3 is provided for transporting to the front. The paper discharge path R3 is provided below the pre-reversal conveyance path 150, and the first to third conveyance roller pairs 510 to 512 and the paper discharge roller pair 513 are provided in the paper discharge path R3. ing.

  When the sheet P on which an image is formed on one side or both sides passes through the fixing roller nip, the flapper 17 is rotated to the already-described first position. As a result, the sheet P passes through the lower surface of the flapper 17, is conveyed to the discharge roller pair 513 by the first to third conveyance roller pairs 510 to 512, and is discharged to the discharge tray 504 by the discharge roller pair 513.

  Thus, by providing at least one transport roller pair in addition to the paper discharge roller pair 513 in the paper discharge path R3, the position of the paper discharge roller pair 513 can be arbitrarily set. As a result, it is possible to take various measures such as attaching various paper discharge options such as the scanner reader 600 and making it multi-functional, thereby satisfying user needs. The number of transport roller pairs arranged in the paper discharge path R3 is not limited to two, but may be one or more, and the paper discharge path R3 may not be linear.

1 is a diagram illustrating a configuration of a full-color laser beam printer that is an example of an image forming apparatus according to a first embodiment of the present invention. The figure which shows the structure of the double-side inversion part provided in the said full color laser beam printer. FIG. 3 is a first diagram illustrating an operation for forming images on both sides of a sheet of the full-color laser beam printer. FIG. 6 is a second diagram illustrating an operation for forming images on both sides of a sheet of the full-color laser beam printer. FIG. 4 is a diagram illustrating a configuration of a full-color laser beam printer that is an example of an image forming apparatus according to a second embodiment of the present invention. The figure which shows the structure of the double-side inversion part provided in the said full color laser beam printer. FIG. 3 is a first diagram illustrating an operation for forming images on both sides of a sheet of the full-color laser beam printer. FIG. 6 is a second diagram illustrating an operation for forming images on both sides of a sheet of the full-color laser beam printer. FIG. 10 is a diagram illustrating a configuration of a full-color laser beam printer that is an example of an image forming apparatus according to a third embodiment of the present invention. 1 is a diagram illustrating a schematic configuration of a conventional image forming apparatus.

Explanation of symbols

13 fixing section 13a, 13b fixing roller pair 14 discharge roller pair 15 double-side reversing section 16 reverse roller pair 17 flapper 25 discharge tray 26 reconveying path 100 full color laser beam printer 101 full color laser beam printer main body (printer main body)
102 Image forming unit 115 Double-side reversing unit 116 Reversing roller pair 117 Flapper 150 Pre-reversing conveyance path 201, 202 Paper ejection bin 504 Paper ejection tray 510-512 First to third conveyance roller pair 600 Scanner leader B, B 'Branch point L1 , L1 ′ Sheet conveyance distance L2 from the branch point to the discharge roller pair L2, L2 ′ Sheet conveyance distance P from the branch point to the reverse roller pair P Sheet R1 Sheet conveyance path R2 Pull-in path R3 Paper discharge path

Claims (5)

In the image forming apparatus that inverts the sheet so as to form an image on the second surface on the opposite side of the sheet on which the image is formed on the first surface by the image forming unit, and transports the image to the image forming unit again.
A sheet conveying section for conveying the sheet;
A sheet discharge roller that is disposed on the downstream side of the sheet conveyance unit and discharges the sheet conveyed by the sheet conveyance unit;
A re-conveying passage for conveying the sheet on which the image is formed on the first surface to the image forming unit again;
A pull-in passage provided by branching from a sheet conveyance path between the sheet conveyance section and the sheet discharge roller;
The sheet is provided in the drawing path, and the sheet conveyed by the sheet conveying section through the branch point between the sheet conveying path and the drawing path is once drawn into the drawing path and then reversed and re-conveyed. A sheet reversing and conveying roller capable of forward / reverse conveyance to the passage;
A switching member that selectively moves to a position that guides the sheet on which the image is formed on the first surface to the sheet reverse conveyance roller and a position that guides the sheet to the sheet discharge roller;
The sheet is provided in the drawing path, and the sheet conveyed by the sheet conveying section through the branch point between the sheet conveying path and the drawing path is once drawn into the drawing path and then reversed and re-conveyed. A sheet reversing and conveying roller capable of normal and reverse conveyance conveyed in the passage,
The sheet reversal conveyance roller is provided at a position such that a sheet conveyance distance from the branch point to the sheet reverse conveyance roller is shorter than a sheet conveyance distance from the branch point to the sheet discharge roller. An image forming apparatus. Each of the sheet discharge rollers is provided, and includes a plurality of sheet stacking units on which sheets discharged by the sheet discharge rollers are stacked,
The sheet conveying distance from the branch point to the sheet reverse conveying roller is greater than the sheet conveying distance from the branch point to each sheet discharge roller provided in the plurality of sheet stacking units. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided at a position that is shortened.   3. The image forming apparatus according to claim 1, wherein the sheet discharge roller is disposed above the sheet reverse conveying roller. Provided on the downstream side of the drawing-in passage, and includes a pre-reversing conveyance path through which the sheet once drawn by the sheet reversing conveyance roller is conveyed,
The image forming apparatus according to claim 1, wherein the pre-reversing conveyance path is provided inside the apparatus main body. A sheet stacking unit provided on a side surface of the apparatus main body, on which sheets discharged by the sheet discharge roller are stacked;
A sheet discharge passage provided inside the apparatus main body and through which a sheet conveyed toward the sheet discharge roller by the sheet conveyance unit passes,
The image forming apparatus according to claim 1, further comprising: a pair of conveyance rollers configured to convey the sheet conveyed by the sheet conveyance unit toward the sheet discharge roller in the sheet discharge path.

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