JP2005330084A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct skewing due to the deformation of paper at a fixing part during one-side printing in a both-side printing process while preventing a trouble such as paper jamming during reverse printing or dislocation in reverse printing. <P>SOLUTION: A carrying roller pressure control means is provided for correcting the skewing of paper, whereby the pressure balance of a carrying roller arranged in a re-carriage passage connected between the downstream side of the fixing part through which the paper passes during the reverse printing of the both-side printing and an image forming part is changed in the cross direction of the paper to give a difference to the feeding amount of the paper in the cross direction of the paper. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as an electrophotographic printer or a copier having a double-sided printing function.

  In a conventional image forming apparatus such as a printer or a copying machine, an image is printed obliquely on a sheet when the sheet arrives at an image forming unit that forms an image on the sheet in a skewed manner (skew). So that the registration roller is placed in the paper conveyance path near the upstream side of the image forming unit and the leading edge of the paper conveyed to the registration roller is abutted against the nip portion of the registration roller temporarily stopped, and then the registration roller upstream The paper is transported excessively by a predetermined amount by using the paper transport means on the side, thereby causing the paper to sag, and thus correcting skew using the stiffness of the paper (see, for example, Patent Document 1).

  However, in an image forming apparatus having a double-sided printing function in which paper passes through the image forming unit a plurality of times, fixing is performed on the downstream side of the image forming unit after the image is formed by the image forming unit during the first side printing of double-sided printing. The sheet that has passed through the section is deformed by the heat and pressure of the fixing section, and may skew in the conveyance path from the fixing section that passes through to the image forming section in order to print the back surface of double-sided printing.

  In addition, the skew amount varies depending on the paper quality, thickness, size, and paper deformation shape at the fixing unit. When the skew amount is large, even if the paper reaching the image forming unit for back side printing reaches the registration roller near the upstream side of the image forming unit and performs the conventional skew correction, the skew amount is too large to correct the skew. As a result, there may occur a failure such that the image on the back side is formed obliquely with respect to the paper, or a paper skew error or the device stops due to paper jam.

JP 2003-72982 A

  The present invention corrects a skew in a re-conveying path through which paper skewed due to deformation of the paper in a fixing unit at the time of first-side printing of double-sided printing is used for back-side printing of double-sided printing, and backside due to paper skew An object of the present invention is to provide a highly reliable image forming apparatus having a duplex printing function that prevents troubles such as paper jam and printing position deviation on the back side during printing.

  By changing the pressure balance in the paper width direction of the conveyance roller arranged in the conveyance path connected between the downstream side of the fixing unit provided for duplex printing and the image forming unit, the paper width is changed to the paper feed amount. This is achieved by including a conveyance roller pressure adjusting means for correcting the skew of the sheet by making a difference in the direction.

  According to the present invention, a paper jam at the time of reverse side printing due to paper skew is corrected by correcting the skew in a re-conveying path that passes through the paper skewed due to paper deformation at the fixing unit at the time of first side printing in double-sided printing. And troubles such as misalignment of the printing position on the back side can be prevented.

  Embodiments of the present invention will be described below with reference to the drawings.

  FIG. 1 is a schematic diagram showing the overall structure of an image forming apparatus according to the present invention. As shown in FIG. 1, in this image forming apparatus, a sheet tray 1 which is a sheet storage unit in which sheets are stacked and held, a sheet fed from the sheet tray 1 or a first surface is again formed after image formation is performed. An image forming unit 2 that forms an image on the back side of the first surface of the conveyed paper, a fixing unit 3 that fixes an image formed on the paper, and a paper discharge unit that discharges the paper fixed by the fixing unit 3 4 etc. are provided.

  Further, a portion of the paper path from the paper tray 1 to the image forming unit 2 is a paper conveyance path 5, and a conveyance roller 15, a registration roller 14, and the like are arranged on the paper conveyance path 5.

  A direct paper discharge path 19 is provided between the paper discharge side of the fixing unit 3 and the paper discharge unit 4, and the back side after the first surface printing is performed between the paper discharge side of the fixing unit 3 and the paper transport path 5 during double-sided printing. In order to form an image, a re-conveying path 20 for conveying the paper to the image forming unit 2 again is provided. A switching claw 16 for switching the conveyance direction of the sheet that has passed through the fixing unit 3 to the direct discharge path 19 or the reconveyance path 20 is provided at a branch point between the direct discharge path 19 and the reconveyance path 20. On the reconveying path 20, there is a reversing unit 6 for switching back the paper. The reversing unit 6 includes a switchback roller 17, a pressure roller 18 of the switchback roller 17, and the like.

  Here, the flow of paper when performing duplex printing on the paper according to the present invention will be described. The paper fed from the paper tray 1 is sent to the paper transport path 5. In this sheet conveyance path 5, the sheet conveyed to the registration roller 14 is excessively fed by a predetermined amount by the conveyance roller 15 while abutting the nip portion of the registration roller 14 whose tip is temporarily stopped, so that the sheet is slackened. And the leading edge of the sheet is corrected so as to be parallel to the axial direction of the registration roller 14 by the slack and the stiffness of the sheet, thereby correcting the skew of the sheet. The sheet that has passed through the sheet conveyance path 5 is sent to the image forming unit 2 and an image on the first surface is formed on the sheet. The sheet that has passed through the image forming unit 2 passes through the fixing unit 3 and is guided to the reconveying path 20 by the switching claw 16. The paper that has reached the reversing unit 6 on the re-conveying path 20 is switched back and sent to the paper conveying path 5 again in order to form an image on the back surface of the first surface by the image forming unit 2. The paper sent again to the paper transport path 5 is again skew-corrected by the registration rollers 14, and the image on the back side is formed on the paper by the image forming unit 2. The paper that has passed through the image forming unit 2 passes through the fixing unit 3, is directly guided to the paper discharge path 19 by the switching claw 16, and is discharged to the paper discharge unit 4.

  FIG. 2 is an explanatory view of the roller pressure adjusting means according to the present invention. At the time of double-sided printing, the shaft of the pressure roller 18 is arranged at one axial end of the pressure roller 18 in the reversing unit 6 on the re-conveying path 20 through which the paper passes in order to form an image on the back side after the first side printing. A bearing (right) 10 that holds the spring, a spring 12 that is a tension coil spring, and a spring tension member 11 are disposed. Both ends of the spring 12 are attached to a main body frame (right) 7 of the image forming apparatus and a spring tension member 11 fixed to the main body frame (right) 7, and a central portion of the spring 12 is a bearing (right) 10. The pressure roller 18 presses the switchback roller 17 because the spring 12 is attached to the outer periphery of the switchback roller and the bearing (right) 10 is movable toward the center of the switchback roller 17. Is done.

  Here, the spring tension member 11 can be rotated to the state A around the screw 13, and by tightening the screw 13, the spring tension member 11 can be moved to the main body frame (at any rotational position within the rotatable range). (Right) 7 can be fixed, and the amount of extension of the spring 12 stretched on the spring tension member 11 changes with the fixing position of the spring tension member 11, thereby switching back the pressure roller 18. The pressure applied to the roller 17 can be adjusted.

FIG. 3 is an explanatory diagram of skew correction according to the present invention. The pressure F ₁ applied to the bearing (right) 10 on the body frame (right) 7 side of the pressure roller 18 is adjustable, and the body frame (left) 8 side on the opposite side of the body frame (right) 7 is adjustable. The pressure F ₂ applied to the bearing (left) 9 is constant. Adjust the pressure F _1, by attaching a difference in pressure of the axial ends of the pressure roller 18, a difference is generated in accordance pressure roller (right) 18a and the roller (left) 18b of the pressure roller 18 Therefore, the sheet skew can be corrected by making a difference in the sheet feed amount between the roller (right) 18a and the roller (left) 18b when the sheet passes between the pressure roller 18 and the switchback roller 17. It becomes.

1 is a schematic diagram illustrating an overall structure of an image forming apparatus according to the present invention. It is explanatory drawing of the roller pressure adjustment means which concerns on this invention. It is explanatory drawing of the skew correction which concerns on this invention.

Explanation of symbols

1 is a paper tray, 2 is an image forming unit, 3 is a fixing unit, 4 is a paper discharge unit, 5 is a paper conveyance path, 6 is a reversing unit, 7 is a main body frame (right), 8 is a main body frame (left), 9 Is a bearing (left), 10 is a bearing (right), 11 is a spring tension member, 12 is a spring, 13 is a screw, 14 is a registration roller, 15 is a transport roller, 16 is a switching claw, 17 is a switchback roller, 18 Is a pressure roller, 19 is a direct discharge path, and 20 is a re-conveyance path.

Claims (1)

A paper feed unit for stacking and holding paper;
An image forming unit that forms an image on the fed paper;
A fixing unit that is located downstream of the image forming unit and applies heat and pressure to fix the image on the paper;
A paper conveyance path from the paper feeding unit to the image forming unit;
An image forming apparatus having a re-conveying path connected between a downstream side of the fixing unit and the sheet conveying path;
The re-conveying path has a conveying roller that is rotationally driven in the direction of conveying the paper,
A roller pressure adjusting unit for the conveying roller that corrects skew of the sheet by changing a pressure balance in the sheet width direction with respect to the sheet of the conveying roller to make a difference in a sheet feeding amount of the conveying roller in the sheet width direction; An image forming apparatus.

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