JP2000229759A - Sheet correction device and picture image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a paper correction device capable of correcting waving formed on an output paper of a picture image formation device so as to prevent giving damage such as paper wrinkle on the paper. SOLUTION: This sheet correction device is provided with a picture image formation means 1 forming a picture image on a sheet P based on input picture image information, a correction means 3 correcting waving of the sheet for the sheet P on which a picture image is formed by the picture image formation means 1, and a curl compensation means 8 applying curl compensation for the sheet P corrected by the correction means 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus used for a printer, a copying machine, a facsimile, and the like, and a sheet correcting apparatus connected to the image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus such as a laser printer or a color image copier using an electrophotographic system, generally, image data input from a personal computer or an image input device (IIT) is exposed to light by a laser or the like. An electrostatic latent image is formed on an image carrier such as a body drum, the toner is developed by a developing device, and then transferred to a sheet (mainly paper). A unit is used for fixing the image by fusing it and discharging the image. An apparatus for automating the operation by connecting an apparatus for performing post-processing such as stapling, punching, and sorting (collating) to such an image forming apparatus is also provided. When these post-processing devices are used, it has been known that the curl state of the paper is deeply related to the occurrence of a jam due to insufficient conveyance of the paper, the quality of the paper alignment in a sorter device, and the quality of the post-processing performance. Have been.

[0003] Japanese Patent Application Laid-Open No. Hei 4-2 discloses a method for removing the curl of a sheet by grasping the curl state of the sheet.
As disclosed in Japanese Patent Application Laid-Open No. 51067, there is a technique for adjusting the amount of curl correction by detecting the humidity, the water content of the paper, the type of paper, and the thickness of the paper. Further, when the transferred toner is fixed, the toner is heated when it is fixed, and contracts when the toner is discharged to the post-processing device with a decrease in temperature. This contraction greatly affects the curl of the sheet. Japanese Unexamined Patent Publication No. Hei 8-217313 discloses that the curl correction amount is adjusted according to the detection results of the image density and the toner amount, and that the transferred toner is fixed by a fixing device, that is, in the image forming apparatus in the sheet conveyance. On the downstream side of the fixing device, a curl correction device is mounted externally to the image forming apparatus. And
This curl correction device, for example, strongly sandwiches a sheet between an elastic roll and a hard roll, twists the sheet in a direction opposite to the curl of the sheet by deformation of the elastic roll, and removes the curl of the sheet.

Here, in an image forming apparatus without a curl correction device, generally, an outlet roll is provided at a paper discharge port on the downstream side of a fixing device, and a discharge tray is mounted. On the other hand, sheets on which images are formed are sequentially stacked. For the purpose of reliably discharging the paper to this discharge tray and improving the storage capacity, conventionally, the diameter of the exit roll is partially increased to forcibly form a corrugation (corrugation) in the paper transport direction, The paper is discharged to the discharge tray with the paper stiffened in the transport direction.

[0005]

However, if the curl correcting device is mounted as it is in place of the discharge tray, the paper is inserted into the curl correcting device in a state where the corrugation in the paper transport direction is formed. In this curl correction device, for example, in order to strongly sandwich the paper between the elastic roll and the hard roll, the corrugated paper is twisted by the nip portion of these rolls while being in a wavy state, and as a result, the paper escapes. It will cause folds and paper wrinkles. In particular, when a so-called single roll (having a uniform shape in a direction perpendicular to the transport direction) is used as the elastic roll and the hard roll, the paper breakage and the wrinkles are remarkably generated.

Further, in order to remove the paper damage such as paper breakage and paper wrinkling, it is conceivable to remove the exit roll or replace the exit roll when installing the curl correction device. Is not easy, and furthermore, when the curl correction device is subsequently removed, the storage capacity of the discharge tray cannot be maintained. Further, a method of separating the nip portions of these rolls in the curl correction device to a position where the corrugation completely disappears can be considered, but the curl correction device becomes extremely large.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned technical problems, and is intended to correct a wave formed on an output sheet of an image forming apparatus and to damage the sheet such as paper wrinkles. Paper correction device and an image forming apparatus using the same.

[0008]

That is, as shown in FIG. 1, a sheet straightening apparatus according to the present invention comprises an input section 2 for inputting a sheet P discharged from an image forming apparatus 1 on which an image is formed, and an input section 2 for inputting the sheet P. The image forming apparatus 1 provided near the input unit 2
Correction unit 3 that corrects the undulation of the sheet P discharged from the sheet P in the sheet conveying direction, and a discharge unit 4 that discharges the sheet P whose undulation has been corrected by the undulation correction unit 3 It is characterized by.

[0009] The wavy straightening section 3 is characterized in that it has a projecting ironing structure section 5 extending in a direction orthogonal to the sheet conveying direction.

Further, it is preferable that the ironing structure 5 be one in which a guide surface for guiding a sheet is bent in an arc shape.
Good shapeless performance can be obtained with a simple shape. The ironing structure 5 may be a sheet metal having an R-shape, and a material other than the sheet metal may be used.

In another aspect, the convex structure of the ironing structure 5 may be made of cardboard or OH if a roll is used.
This is more preferable in that the transportability for a sheet having strong stiffness such as P is also ensured.

Further, it is more preferable that the ironing structure 5 is located on the lower surface of the sheet conveying path, and the ironing performance is further improved.

Further, the waving correction section 3 is provided with a transport roll 6 for transporting the sheet downstream of the ironing structure section 5, and the transport roll 6 transports the sheet P discharged from the image forming apparatus 1. It is characterized in that the sheet is pushed and spread in a direction orthogonal to the sheet conveying direction.

The image forming apparatus according to the present invention includes an image forming unit 1 for forming an image on a sheet P based on input image information, and an image forming unit 1 for forming an image on the sheet P on which the image is formed by the image forming unit 1. On the other hand, a correcting means 3 for correcting the wavy of the sheet, and a sheet P corrected by the correcting means 3
And a curl correcting means 8 for performing curl correction on the image.

Further, the curl correcting means 8 includes a first curl correcting section 9 for applying a pressing force to the sheet P and performing a curl correction in a direction for lifting the edge of the sheet, and a pressing force for the sheet P. And a second curl correction unit 10 that performs curl correction in a direction to lower the end of the sheet.

Further, the correcting means 3 is provided with an ironing structure 5 having a convex shape extending in a direction perpendicular to the sheet conveying direction at a lower surface of the sheet conveying path. It is characterized in that curl correction is performed in the direction of lowering the portion.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 shows a schematic configuration of an image forming apparatus (a color electrophotographic copying machine in the present embodiment) to which the present invention is applied. In the figure, reference numeral 20 denotes a document reading device (IIT),
The reflected light of the document illuminated by the lamp is converged on the CCD using an exposure optical system. The CCD converts reflected light of the original image into an electric signal as each color component image of yellow (Y), magenta (M), cyan (C) and black (K), and the IIT 20 adjusts the gain of the analog electric signal. And performs a conversion to a digital signal and performs shading correction and the like. Reference numeral 21 denotes an image processing device (IPS) which performs data processing such as density correction, color conversion processing, enlargement / reduction, etc. on the image digital signal obtained from the IIT 20, and outputs color components of Y, M, C, and K. Each time it is output to the image writing device (ROS) 22. Where IPS
The input to the I / F 21 is not limited to the input from the IIT 20, and the same data processing is executed for image data from an externally connected device such as a personal computer.

Here, reference numeral 23 denotes a photosensitive drum (image carrier) which rotates in the direction of the arrow, for example, and reference numeral 24 denotes a charger such as a corotron which charges the photosensitive drum 23 in advance. Also, 22
Is an image writing device (ROS) such as a laser scanning device that writes a digital image input from the IPS 21 on the photosensitive drum 23 as an electrostatic latent image, and is modulated for each color component by a generated laser drive signal. The surface of the photosensitive drum 23 is irradiated with the laser beam. Reference numeral 25 denotes a rotary developing device on which developing devices corresponding to the respective colors of Y, M, C, and K are mounted.
The electrostatic latent image formed in No. 3 is developed by one of the developing units of each color to form a toner image of each color component.
A drum cleaner 26 removes residual toner on the photosensitive drum 23.

Reference numeral 27 denotes an intermediate transfer belt disposed so as to be in contact with the surface of the photosensitive drum 23;
It is stretched over a plurality of rolls (for example, five in the present embodiment) and is rotated in the arrow direction. Further, at a portion (primary transfer position) of the intermediate transfer belt 27 facing the photosensitive drum 23, a primary transfer device (transfer roll in the present embodiment) 28 is disposed on the back side of the intermediate transfer belt 27. By applying a voltage having a polarity opposite to the charge polarity of the toner to the transfer roll 28, the photosensitive drum 23
The upper toner image is electrostatically attracted to the intermediate transfer belt 27.

Further, a secondary transfer device 29 is provided at a secondary transfer position of the intermediate transfer belt 27 facing the conveyance path of the sheet P as a sheet. In the present embodiment, the intermediate transfer belt 27 is provided. A secondary transfer roll 30 that is disposed in pressure contact with the toner image bearing surface side and is grounded, and a counter roll (backup roll) 31 that is disposed on the back side of the intermediate transfer belt 27 and forms a counter electrode of the secondary transfer roll 30. ing. A bias having the same polarity as the charge polarity of the toner is stably applied to the opposing roll 31 via a power supply roll. Reference numeral 32 denotes a belt cleaner for removing residual toner on the intermediate transfer belt 27.

In the present embodiment, the fixing device 4
0 is a heating and fixing roll 41 having a built-in heater 42;
A pressure fixing roll 43 which is disposed in pressure contact with the heat fixing roll 41 in a predetermined nip area and rolls therein, and has a heater 44 built therein; Is provided with an exit sensor 48 for detecting that the paper P has passed. Here, reference numeral 49 denotes an exit roll, which is formed by a plurality of rolls having a partially increased roll diameter, and has a fixed upward angle (about 15 in this embodiment) with respect to the paper P fixed by the fixing device 40.
°) and undulate the paper P in the paper transport direction.
The paper is discharged out of the apparatus while sitting down in the transport direction.
The exit roll 49 rotates so that the transport speed is higher than that of the fixing device, but has a torque limiter (not shown) so as not to impair the fixing performance, and suppresses the transport speed until the sheet P exits from the fixing device 40. When the paper P comes out, the transport speed is increased.

Further, in the present embodiment, the paper transport system 50 transfers paper from a predetermined number (three in this embodiment) of paper trays 51 to 53 or a manual feed tray 55 via a predetermined paper path 56. After the paper is once positioned and stopped by a registration roll (registration roll) 57 in the paper path 56, the paper is transported to the secondary transfer position at a predetermined timing, and the paper after the secondary transfer is transported by the transport belt 58. To the fixing device 4
0. The paper path 56 is provided with an appropriate number of transport rolls 59. In particular, in the present embodiment, the sheet returning / conveying mechanism 60 is provided. When the duplex mode is selected, the sheet fixed on one side by the fixing device 40 is turned over and returned to the secondary transfer position, or the image is printed on only one side. In the case of forming
The sheet fixed by the fixing device 40 can be inverted and discharged out of the device.

The paper return / conveyance mechanism 60 includes a fixing device 4
A paper branch path 62 that branches downward from the paper discharge path 61 from 0 is provided. In the paper branch path 62, a paper reversing path 63 extends further downward, and
A paper return path 64 returning from the paper reversing path 63 to the paper path 56 just before the secondary transfer position is communicatively connected. An appropriate number of transport rolls 65 are provided in the paper branch path 62, the paper inversion path 63, and the paper return path 64. In particular, the transport rolls 65 provided in the paper inversion path 63 rotate forward and backward at appropriate timing. It has become. Further, a sheet switching gate (not shown) is provided between the sheet discharge path 61 and the sheet branch path 62 and between the sheet branch path 62, the sheet reversing path 63, and the sheet return path 64, respectively. The paper path is appropriately switched and selected according to the selected mode.

Here, when the paper P discharged from the fixing device 40 is directly discharged to the outside of the apparatus due to single-sided printing, an image is printed on the upper surface of the paper and discharged, that is, a so-called face-up discharge. In addition, the sheet P fixed by the fixing device 40 is discharged by the exit roll 49 to the outside of the device after being detected by the exit sensor 48. On the other hand, in the case of single-sided printing, when the sheet P discharged from the fixing device 40 is reversed from the sheet discharge path 61 via the sheet reversing path 63 and discharged outside the apparatus by the exit roll 49 from the sheet branch path 62. In this state, the image is printed and discharged on the lower surface of the sheet, that is, a so-called face-down discharge is performed.

Further, reference numeral 80 denotes a curl removing device for removing the curl of the paper P fixed by the fixing device 40 and discharged from the exit roll 49, and a substantially conical pin connecting portion 81 is provided on the image forming apparatus main body side. By fitting into the connection hole 35, the alignment with the image forming apparatus main body is performed, and after this alignment is performed, the image forming apparatus is fixed to the image forming apparatus main body by a magnet (not shown). Reference numeral 67 denotes a post-processing device that performs post-processing on the paper discharged from the curl removing device 80, and includes a sorter 68 for distributing a required number of papers, punching 69 for punching holes in the paper, and the like. I have. The post-processing device 67 has a substantially conical pin connecting portion 66 having the same shape as the pin connecting portion 81 of the curl removing device 80, and is fitted into the connection hole 82 of the curl removing device 80. The alignment with the curl removing device 80 is performed.

Here, reference numeral 70 denotes a control unit, which controls the paper conveyance and, in particular, recognizes that the curl removing device 80 and the post-processing device 67 have been connected to the image forming apparatus main body.
On the basis of the image output signal from the PS 21, the adjustment of the curl correction amount of the curl removing device 80 and the movement of the post-processing device 67 are controlled. Further, the control unit 70 recognizes the paper size of the paper P supplied from the paper trays 51 to 53 and the manual feed tray 55, and recognizes the humidity condition where the image forming apparatus is placed and the humidity in the paper trays 51 to 53. The curl amount in the curl removing device 80 is adjusted. The curl removing device 80 from the control unit 70
Is transmitted to the curl removing device 80 by the cable 73 via the curl removing device side connector 72 connected to the connector 71 provided on the image forming apparatus main body side,
On the other hand, the control signal from the control unit 70 to the post-processing device 67 is
The signal is transmitted to a post-processing device 67 via a cable 76 by a post-processing device-side connector 75 connected to a connector 74 of the image forming apparatus main body. Further, the curl removing device 80 includes:
It has a connector 77 that can be connected to the post-processing device connector 75, and a control signal from the control unit 70 to the post-processing device 67 can be transmitted via the connector 77.
At this time, the control signal to the post-processing device 67 is also transmitted to the connector 7.
1, transmitted through the curl removing device side connector 72 and the cable 73. It should be noted that it is also possible to provide a control unit independently for the curl removing device 80 or the post-processing device 67. In this case, the control unit receives various types of information from the image forming apparatus main body, and controls the curl correction amount. The adjustment and each operation are controlled.

Next, the configuration of the curl removing device 80 in the present embodiment will be described with reference to FIG. Code 8
Reference numeral 3 denotes a receiving port for receiving the sheet P fixed by the fixing device 40 of the image forming apparatus main body and discharged at a predetermined angle from the outlet roll 49. The receiving port has an inlet upper guide 84 for guiding the leading end of the sheet P discharged at an angle. Reference numeral 95 denotes an ironing guide, which will be described later. The ironing guide 95 removes ripples formed in the sheet transport direction of the sheet discharged from the outlet roll 49 by an ironing portion 96 having a convex end. In addition, 87
Denotes an entrance roll, which guides the sheet P discharged from the image forming apparatus main body into the inside of the curl removing device 80. Further, in the present embodiment, the entrance upper guide 84 is configured to jump up (in the direction of the arrow) via the fulcrum 94, and the sheet P, which has been delayed in conveyance by each decurler device described later, Raised to absorb. Reference numeral 85 denotes a first lower guide that guides the paper P that has entered the curl removing device 80, and guides the paper P together with the intermediate upper guide 86 to each decurler device.

Here, 100 is the first lower guide 85.
Is a first decurler device that presses paper from below to perform curl removal, and is a drive roll 1 that conveys paper.
01, and a pressing roll 102 that cuts into the drive roll 101 to execute curl correction. The first decurler device 100 is configured such that when the paper P enters, the pressing roll 102 bites into the drive roll 101, so that the drive roll 101 is sandwiched between the two.
Paper can be deformed by the arc. In the first decurler device 100, since the pressing roll 102 is bitten to form a downward convex, the downward convex direction
(In the direction in which the end rises). Also, 1
03 is a shaft at the center of the pressing roll 102,
It is movable by a first link, which will be described later, with an arc 105 drawn about the rotation shaft 104 as a trajectory. The movement of the shaft 103 changes the amount of biting of the pressing roll 102 into the drive roll 101.

Reference numeral 88 denotes a sensor for detecting the sheet passing through the first decurler 100, and reference numeral 110 denotes a second decurler for pressing the sheet from above the intermediate upper guide 86 to remove the curl. The second decurler 110 is provided with a drive roll 11 for conveying a sheet.
1 and a pressing roll 112 that cuts into the drive roll 111 to perform curl correction. When the paper P enters, the pressing roll 112 bites into the drive roll 111, so that the drive roll The paper is deformed by the arc of the roll 111 to form an upward convex, and is responsible for correction in the upward convex direction (the direction in which the end is lowered). Reference numeral 113 denotes a shaft at the center of the pressing roll 112, and a shaft 115 similar to the arc 105 in the first decurler device 100 is formed by a rotation shaft 114 having the same center as the rotation shaft 104 in the first decurler device 100. The trajectory is moved by a second link described later. The movement of the shaft 113 changes the amount of biting of the pressing roll 112 into the drive roll 111.

In the present embodiment, each drive row
SUS of Φ8 is used for
Of a uniform shape in the direction perpendicular to the
Roll. In addition, Φ
26 urethane materials (20lb / ft ^Three) With a certain elasticity
So that they can bite into the drive rolls 101 and 111
The drive roll is also
A so-called single roll with a uniform shape in the crossing direction
It is composed of Using such a single roll
By doing so, it is uniform in the direction orthogonal to the paper transport direction.
First, the curl can be removed.

On the other hand, reference numeral 89 denotes a second lower guide, 9
Reference numeral 0 denotes an exit upper guide, which guides the sheet P passing through each decurling device to a discharge roll 91, applies a conveying force by the discharge roll 91, and outputs the paper P from an exit 92 to the post-processing device 6.
7, the paper P is guided. As described above, 81
Reference numeral denotes a pin connection portion for positioning when connecting to the connection hole 35 of the image forming apparatus main body. Reference numeral denotes a post-processing device 6.
7 is a connection hole to be fitted with the pin connection portion of 7.

Next, a configuration for driving the first decurler 100 according to the embodiment of the present invention will be described with reference to FIG. In FIG. 4, reference numeral 106 denotes a first lever for moving the pressing roll 102 in the first decurler device 100, and the first roller 10 which comes into contact with the cam.
7 and rotates about the rotation shaft 104 as a fulcrum. Also,
120 is a cam for moving the first lever 106,
A cam surface 121 for actually moving the first lever 106 in contact with the first roller 107 is provided. The cam 120 receives a signal from the control unit 70 and determines a cam position by ON / OFF of a DC motor (not shown) and a cam clutch (not shown). With the determined cam position, the first lever 106 rotates about the rotation shaft 104 as a fulcrum via the first roller 107, and the shaft 103 is operated to cause the pressing roll 102 to bite into the drive roll 101. . The cam 120 also rotates a second lever of the second decurler 110, which will be described later. In the present embodiment, symmetrical mechanisms having the same dimensions as those in FIG. 4 are provided at both ends in the direction (front and back sides of the apparatus) orthogonal to the paper transport direction, and the pressing roll 102 is moved from the front and back sides. It is moving. As a result, it is possible to apply the pressing force uniformly to the pressing roll 102 from the near side and the back side in the direction orthogonal to the transport direction, and it is possible to perform stable curl correction.

Next, the configuration for driving the second decurler device 110 according to the embodiment of the present invention will be described with reference to FIG. In FIG. 5, reference numeral 116 denotes the second
It is a second lever for moving the pressing roll 112 in the decurler device 110, has a second roller 117 that comes into contact with a cam, and rotates around a rotation shaft 114 as a fulcrum.
Reference numeral 120 denotes a cam, which has a cam surface 122 for actually moving the second lever 116 in contact with the second roller 117. In the present embodiment, the rotation of the cam 120 causes the first decurler 100 and the second decurler 1 to rotate.
10 are simultaneously moved, and the cam surface 122 is formed on the same cam 120 as the cam surface 121 in a state of being out of phase with the cam surface 121 used in the first decurler device. As described above, the cam position of the cam 120 is determined by ON / OFF of a DC motor (not shown) and a cam clutch (not shown) in response to a signal from the control unit 70. Then, the second lever 1 is moved through the second roller 117.
16 is rotated, and the shaft 1 is
13, the drive roll 1 of the pressing roll 112
The bite amount for 11 is determined. In the present embodiment, similarly to the first decurler 100 described above, the pressing roll 112 is moved by a similar mechanism from the near side and the back side of the machine.

Here, in the present embodiment, the biting of the pressing rolls 102 and 112 into the drive rolls 101 and 111 is about 2 mm when the curl correction is ON.
It is designed to bite. This means that the image density is 150% (the theoretical maximum density of the four YMCK colors is 400%
This is because, for an image of about 150% of which, a biting amount of about 2 mm is required for curl correction. On the other hand, when the curl correction is OFF, in the present embodiment, the digging is not completely eliminated, but is digged by about 0.5 mm, so that the minimum conveyance force is secured. In the present embodiment, the pressing rolls 102, 1
12 slides, and the drive rolls 101 and 111 do not slide. This is the drive roll 101, 1
This takes into account the fact that when the user slides 11, the paper transport path changes, and the paper transport may not be performed properly.

Next, the structure of the ironing guide 95 in the present embodiment will be described with reference to FIG. Entrance 8
3, the ironing guide 95 has the ironing portion 96 having a convex end as described above. In the present embodiment, the ironing guide 95 has a radius of 6 mm in a direction perpendicular to the sheet conveying direction.
It is bent in the R shape. With such an R-shape, the stress on the paper can be reduced, and scratches and the like can be reduced. The interval d1 formed between the squeezed portion 96 and the vicinity of the squeezed portion of the entrance upper guide 84 is such that the leading end of the sheet P discharged at an angle (about 15 °) from the exit roll 49 on the image forming apparatus side can enter without difficulty. It is designed to be. Further, the lowermost end of the entrance upper guide 84 is at the same height as the intermediate upper guide 86. here,
The height and the distance d2 between the ironing portion 96 and the ironing portion 96 must not be too large to remove the wrinkles at the trailing edge of the sheet. On the other hand, if the dimension is set to 0 (zero), the OHP sheet is damaged during conveyance. Therefore, in the present embodiment, it is arranged with a slight gap. In addition, the leading end 97 of the sheet metal bending of the ironing guide 95 is configured so that the sheet pulled in the opposite direction when the paper jams (jam) does not enter the lower side of the ironing guide 95, and is preferable. It is suitable for paper jam removal to fully extend the sheet metal bending tip 97 to the first lower guide 85. It should be noted that the sheet metal of the ironing guide 95 used in the present embodiment has been subjected to a smooth post-processing as a coating so that the ironed sheet is not damaged.

The paper P that has entered the receiving opening 83 enters the ironing section 96 and the inlet upper guide 84 at an angle of about 15 ° while obtaining the conveying force of the outlet roll 49. The paper P whose leading end has entered the entrance upper guide 8
4 and comes into contact with the ironing section 96 and is conveyed to the entrance roll 87 while being ironed. The paper P transported to the entrance roll 87 is the entrance roll 8
7, the sheet P is conveyed while being squeezed by an especially squeezed portion 96 of the squeezing guide 95. Here, there is no member for pressing the sheet on the side opposite to the surface of the ironing portion 96 of the sheet P, and the sheet P is free in a direction orthogonal to the sheet conveying direction. In this state, the ironing part 9
6 and a gap d1 where the inlet upper guide 84 is formed
As a result, the paper P is pushed and spread in a direction orthogonal to the paper transport direction, and as a result, corrugations formed in the paper transport direction by the exit roll 49 are removed.

As described above, the waving (corrugation)
The paper P from which is removed is conveyed by the entrance roll 87 to the first decurler 100 on the downstream side.
Thus, the first decurler device 10 for performing the curl correction
By removing the corrugation before entering the zero and second decurler device 110, it is possible to prevent the paper P from folding or wrinkling. Furthermore, in the present embodiment, a so-called one roll is used for each decurler device. In particular, since there is no escape for the paper with one roll, the effect of eliminating the paper damage by corrugation removal is further increased. . Further, in the present embodiment, the ironing guide 95 is in contact with the lower surface of the paper, and performs corrugation removal from the lower surface of the paper. Since it has a constant angle upward when it is discharged from the outlet roll 49, it can be easily ironed by disposing it on the lower surface. Further, by arranging the lower surface of the sheet P on the lower surface, curling correction can be performed in a direction in which the end of the sheet is lowered by the ironing guide 95, and the specific gravity in the down-curl direction, which is a preferable direction for accommodating the sheet. Can be increased.

In this embodiment, the ironing guide 95 is used.
Is bent with a sheet metal having an R shape. However, similar results can be obtained by using a resin or the like other than the sheet metal shape. Also, the sheet may not necessarily have an R shape, and the sheet may be slid on one side or one side of the mylar sheet using a mylar sheet, for example. At this time, the mylar sheet may be in contact with the entrance upper guide 84 or may be separated with a gap. Even in the case of contact, a gap is created due to the elasticity of the mylar sheet, and the sheet is conveyed and ironing of the sheet becomes possible. In this case, the elasticity of the mylar sheet has the same effect as the R shape, and corrugation can be removed without damaging the paper. In short, the paper discharged with corrugation is transported through a predetermined gap, and the paper is transported on a predetermined surface on the curved transport path.
If the sheet can be slid, the corrugation generated on the sheet can be effectively removed.

Next, the control of the curl correction amount performed by the control unit 70 in this embodiment will be described with reference to FIGS. FIG. 7 is an explanatory diagram for detecting an image amount (toner amount) by designating an image area and predicting the occurrence of curl. Since the mode of curl changes depending on the difference in the amount of image transferred to the sheet, in the present embodiment, the IPS2
The curl amount is estimated by measuring the information from No. 1, for example, the image amount by reading the original by the IIT 20, or the image amount sent from the host. At this time, since the amount of image at the edge of the sheet greatly affects the occurrence of curling, in the present embodiment, for example, the length of the sheet in the conveyance direction L The image area of the leading end 1 / 3L in the transport direction is Zl, and the image area of the trailing end 1 / 3L is Zt. I have.

FIG. 8 illustrates the relationship between ON / OFF of the decurler device and the paper surface. For convenience of the following description, the first decurler 100 in the curl removing device 80 is a decurler and the second decurler 110 is a decurler.
The state of F is expressed as state “0”, the state of decurler ON is expressed as state “1”, and the state of decurler ON is expressed as state “−1”. Here, the side A of the sheet corresponds to the upper side of the curl removing device 80, and the side B corresponds to the lower side. In this embodiment, double-sided printing is possible. Alternatively, face-down output by paper inversion can be selected. Therefore, A side and B
Since it is difficult to define the plane, in the present embodiment, the plane A and plane B are defined as shown in FIG. Where Si
mp (Invet) is inverted on one side, Simp (Straight) is on one side as it is (not inverted), and Duplex is on both sides. In the image forming apparatus according to the present embodiment, since the transfer is performed on the upper surface of the sheet by the secondary transfer device 29, the front end Zl and the rear end Zt shown in FIG. ,
On the B side, since the image is inverted by the paper return transport mechanism 60, it is necessary to pay attention that the front end Zl and the rear end Zt are different from the paper transport direction. In addition, the front end is Zl2, the rear end is Zt2, and the front end is Zt1, and the rear end is Zt in the B surface.
l1.

FIG. 10 shows the A-plane /
ON of the decurler device based on the image amount for the B side
9 is a table showing how to determine / OFF and its conditions. Here, regarding the relationship between the image amount and the curl, when the sheet on which the toner is transferred is thermally fixed, the toner contracts greatly when the sheet is cooled, and the sheet curls with the transferred surface inside. Therefore, when the image amount is large, that is, when the amount of toner to be printed is large, the toner is contracted with the surface having the large amount inside. Therefore, in FIG. 10, the condition of the decurler is determined in consideration of the relationship between the image amount and the curl direction. The conditions of (a), (b), and (c) are determined by the environment where the image forming apparatus is placed or the “humidity” of the paper tray. In the present embodiment, the humidity M is 4
10 (a), 10 (b), and 10 (c), the first condition is less than 0%, the second condition is 40% or more and less than 70%, and the third condition is 70% or more. Is shown in In addition, each A
The numerical values in the table columns for the side and the side B indicate the ratio of the image amount when the maximum density is set to 100 (image amount ratio).

Here, for example, let us consider a case where the image amount ratio of the surface A is 8% and the surface B is 35% in a state where the humidity M is less than 40%. In this case, since the amount of toner on the side B is larger than that on the side A, the state is a curl downward. Next, the decurler condition in this case is examined from the table.
0 (a), side A, first column (~ 10%), side B, fourth row (~ 40%)
It can be seen that the decurler ON / OFF condition is “1”. This is because, as shown in FIG. 8, the decurler is in the ON state, that is, the sheet is bent upward (convex downward).
The correction is performed as follows. In the case of single-sided printing, the column of the first row or the first column of each table shown in FIG. ON / OFF may be determined. As described above, the decurler condition can be determined by (a), (b), and (c) of FIG.
That is, the decurler sets many ON states. This is because the down curl whose end is bent downward is in the direction in which the curl is corrected by its own weight, but the up curl whose end bounces upward cannot be corrected by itself. For reasons such as weakness, the specific gravity of the decurler for performing downward correction (correction for upcurl) is increased.

Based on these decurler conditions, the controller 70 controls the curl removing device 80 to perform the curl removal. More specifically, the control unit 70 controls the leading edge of the sheet (1/3 in the present embodiment) based on the image information from the IPS 21 and the recognized sheet size information and the like as described above.
Area) and the trailing edge of the sheet (1/3 area in the present embodiment). The ON / OFF condition of the decurler is determined from the image amount according to the above-described condition. next,
In the image apparatus shown in FIG. 2, the first decurling device 100 and the second decurling device 110 in the curl removing device 80 are checked while checking the sheet conveyance state by the exit sensor 48 and various sheet sensors in the device (not shown). Check the timing at which the paper passes. The ON / OFF of the DC motor (not shown) and the cam clutch (not shown) in the curl removing device 80 are synchronized with this timing.
By determining the cam position by turning OFF and rotating the cam 120, the curl correction is executed by switching ON / OFF of the first decurler 100 and the second decurler 110 for each sheet. In the present embodiment, such control enables fine curl correction according to the actual state of curl.

Second Embodiment In the first embodiment, the ironing portion 96 of the ironing guide 95 is formed by bending a sheet metal into an R shape in a direction perpendicular to the sheet conveying direction. A roll may be used instead of the shape, and the ironing portion 96 may be formed on the surface of the roll. Note that the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted here.

In FIG. 11, reference numeral 130 denotes an ironing guide, which guides the lower surface of the sheet P and rotates the roll 131 around the center of rotation 13 before and after the sheet P in a direction perpendicular to the sheet conveying direction.
Support from two. The roll 131 rotates around the roll rotation center 132, but has no drive source, and is configured to rotate with the conveyance of the sheet. The rotating roll 131 has a uniform shape in a direction orthogonal to the sheet conveying direction. The paper P enters the receiving port 83 at a fixed angle, enters between the roll 131 and the entrance upper guide 84, and is squeezed by the roll 131, but the roll 131 rotates with the paper P. When the leading end of the paper P reaches the entrance roll 87 and is conveyed by the entrance roll 87, the upstream side of the paper P is slid on the roll 131. At this time, since the sheet P is completely free in the direction orthogonal to the sheet conveyance direction, the sheet P is pushed and spread in the direction orthogonal to the sheet conveyance direction, and corrugation is removed.

As described above, by using the rotating roll, the stress on the sheet P can be reduced as compared with the first embodiment, and in particular, the scratches generated on a strong sheet such as an OHP sheet can be prevented. it can. In addition, if the roll 131 has a uniform shape in a direction perpendicular to the sheet conveying direction as in the present embodiment, it is more effective for removing corrugation, but is not necessarily limited to that form. There is no problem even if a plurality of narrow rolls are formed in a so-called dumpling shape. Further, in the present embodiment, the roll is rotated. However, the roll does not necessarily need to be rotated, and a function similar to that of the first embodiment may be applied. By using a roll, it is easier to obtain dimensional accuracy than by using a roll to bend a sheet metal to form an ironing portion 96.
The stress on the paper can be reduced as compared with the bending of the sheet metal.

In each embodiment of the present invention, the removal of corrugation before performing the curl correction by the curl correction means has been described. Although it is particularly effective to remove corrugation prior to curl correction, the present invention is not limited to this embodiment.For example, when applying any stress other than curl correction to discharged paper Also works effectively. Further, the present invention can be applied as a pre-process in a general post-processing apparatus that does not give a particularly large stress to a sheet.

[0048]

As described above, according to the present invention,
It is possible to easily remove the waviness of the sheet on which the image is formed, and it is possible to obtain an output sheet without paper damage.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing an outline of a curl correction device and an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram illustrating an outline of an image forming apparatus according to an embodiment.

FIG. 3 is an explanatory diagram illustrating a configuration of a curl removing device according to an embodiment.

FIG. 4 is an explanatory diagram for describing a drive system of a first decurler device according to the embodiment.

FIG. 5 is an explanatory diagram for describing a second decurler device driving system in the embodiment.

FIG. 6 is an explanatory diagram showing a structure of an ironing guide according to the embodiment.

FIG. 7 is an explanatory diagram of image amount detection according to the first embodiment.

FIG. 8 shows ON / OFF of the decurler device in the embodiment.
FIG. 4 is an explanatory diagram illustrating a relationship between OFF and a sheet surface.

FIG. 9 is an explanatory diagram of definitions of terms in the embodiment.

FIGS. 10A to 10C are tables illustrating patterns of decurler control on both sides in the embodiment.

FIG. 11 is an explanatory diagram illustrating another embodiment.

[Explanation of symbols]

P: sheet (paper), 1: image forming apparatus (image forming means),
Reference numeral 2 denotes an input unit, 3 denotes a waving correcting unit (correcting unit), 4 denotes a discharging unit, 5 denotes an ironing structure unit, 6 denotes a transport roll, 8 denotes a curl correcting unit, 9 denotes a first curl correcting unit, and 10 denotes a first curl correcting unit. Curl correction unit 2, 21: Image processing device (IPS), 22: Image writing device (ROS), 23: Photoconductor drum, 25: Rotary developing device, 27: Intermediate transfer belt, 29: Secondary transfer device , 40: fixing device, 49: exit roll, 51, 52, 5
3 paper tray, 60 paper return transport mechanism, 70 control unit, 67 post-processing device, 80 curl removing device, 83
Receiving entrance, 87 ... Entrance roll, 95 ... Ironing guide, 96 ... Ironing part, 100 ... First decurler device, 1
10 ... second decurler device, 130 ... ironing guide, 1
31 ... Roll

Claims (9)

[Claims] An input unit configured to input a sheet discharged from the image forming apparatus on which an image is formed, and a wave provided in the vicinity of the input unit and having a sheet discharged from the image forming apparatus in a sheet conveying direction. A sheet straightening device, comprising: a waving correcting unit for correcting the waving; and a discharge unit configured to discharge the sheet whose waving has been corrected by the waving correcting unit. 2. The sheet straightening apparatus according to claim 1, wherein the wavy straightening unit has a projecting ironing structure extending in a direction orthogonal to a sheet conveying direction. 3. The sheet straightening apparatus according to claim 2, wherein the ironing structure portion has a guide surface for guiding a sheet bent in an arc shape. 4. The sheet forcing device according to claim 2, wherein the convexity of the ironing structure portion uses a roll. 5. The sheet straightening apparatus according to claim 2, wherein the ironing structure is located on a lower surface of a sheet conveying path. 6. The waviness correction section includes a transport roll that transports a sheet downstream of the ironing structure section, and the transport roller transports a sheet discharged from the image forming apparatus by using the transport roll. The sheet straightening apparatus according to claim 1, wherein the sheet is spread in a direction orthogonal to the sheet. 7. An image forming means for forming an image on a sheet based on input image information, and a correcting means for correcting a wave of the sheet on the sheet on which the image is formed by the image forming means. An image forming apparatus comprising: a curl correction unit configured to perform a curl correction on a sheet corrected by the correction unit. 8. A curl correcting unit for applying a pressing force to a sheet to perform a curl correction in a direction to lift an end of the sheet, and applying a pressing force to the sheet. The image forming apparatus according to claim 7, further comprising a second curl correction unit configured to perform curl correction in a direction to lower an edge of the sheet. 9. The correcting means is provided with an ironing structure having a convex shape extending in a direction orthogonal to the sheet conveying direction at a lower surface of the sheet conveying path, and lowers an end of the sheet together with the curl correcting means. The image forming apparatus according to claim 7, wherein curl correction is performed in a direction.