JP2019034810A - Curl correction device and image forming apparatus - Google Patents

Abstract

To provide a curl correction device that achieves both suppression of curling of a recording medium and suppression of tip breakage of the recording medium, as compared to a configuration in which an amount of biting into a first rotary body of a second rotary body is always the same.SOLUTION: A first correction device 100 includes: a roll 104; and a roll 106 which is disposed to bite into the roll 104 and rotates while nipping a sheet P at a nip portion N with the roll 104. The first correction device has a correction unit 108 that corrects a curl generated on the sheet P and a change device 110 configured to make an amount of biting in of the roll 106 into the roll 104 smaller than when a rear end P2 side in a transport direction of the sheet P passes through the nip portion N when a leading end portion P1 in the transport direction of the sheet P passes through the nip portion N.SELECTED DRAWING: Figure 5

Description

  The present invention relates to a curl correction apparatus and an image forming apparatus.

  Patent Document 1 below discloses a curl correction apparatus that divides a section in the length direction of a sheet and changes a curl correction amount for the sheet in accordance with image density information divided for each section.

Japanese Patent Laid-Open No. 06-144678

  For example, in a configuration in which a pressure roll that is pressurized with a constant pressure is placed on the opposite roll and the paper is passed between the opposite roll and the pressure roll to correct the curl, the leading edge of the paper is broken. There is a case.

  The present invention provides a curl correcting device that achieves both curling of a recording medium and curling of the leading edge of the recording medium as compared with a configuration in which the amount of biting of the second rotating body into the first rotating body is always the same. Is the purpose.

  According to a first aspect of the present invention, there is provided a curl straightening device that is arranged so as to bite into the first rotating body and the first rotating body, and rotates while sandwiching a recording medium at a nip portion between the first rotating body and the first rotating body. A rotating portion that corrects curl generated in the recording medium, and a trailing end of the recording medium in the transport direction when a leading end portion in the transport direction of the recording medium passes through the nip portion. Changing means for making the amount of biting of the second rotating body into the first rotating body smaller than when the side passes through the nip portion.

  According to a second aspect of the present invention, in the curl straightening device according to the first aspect, the changing means may reduce a biting amount of the second rotating body into the first rotating body. The length is equal to or longer than the width of the nip portion when the amount of biting of the second rotating body into the first rotating body is large.

  According to a third aspect of the present invention, there is provided an image forming apparatus comprising: a conveying unit that conveys a recording medium; an image forming unit that forms an image on the recording medium; a fixing unit that fixes an image on the recording medium; The curl correction apparatus according to claim 1, further provided on a downstream side of the fixing unit in a conveyance direction of the recording medium.

  According to a fourth aspect of the present invention, there is provided an image forming apparatus according to the first or second aspect, an image forming unit that forms an image on the recording medium, and the recording medium that is the image forming unit. And a reversing mechanism that reverses the front and back of the recording medium and conveys the recording medium to the image forming unit. When the leading end portion of the recording medium in the conveyance direction passes through the nip portion, the second rotation body moves toward the first rotation body more than when the rear end side in the recording medium conveyance direction passes through the nip portion. Reduce the amount of bite.

  According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the changing unit is configured such that, when an image is formed on the surface of the recording medium, a leading end portion in the conveyance direction of the recording medium has the nip portion. When passing, the amount of biting of the second rotating body into the first rotating body is made smaller than when the rear end side in the conveyance direction of the recording medium passes through the nip portion.

  According to a sixth aspect of the present invention, there is provided an image forming apparatus comprising: a conveying unit that conveys a recording medium; and a plurality of correcting units that are arranged along a conveying direction of the recording medium and correct curl generated on the recording medium. The curling correction device according to claim 1, wherein the correction unit on the most upstream side in the conveyance direction of the recording medium is the curl correction device according to claim 1.

  According to a seventh aspect of the present invention, in the image forming apparatus according to the sixth aspect, all of the plurality of correction portions are the curl correction device.

  According to an eighth aspect of the present invention, there is provided an image forming apparatus comprising: a conveying unit that conveys a recording medium; an image forming unit that forms an image on the recording medium; an image on the recording medium; A fixing unit that passes through a nip of the fixing unit and a correction unit that suppresses curling in a direction in which the nip of the fixing unit protrudes, wherein the correction is the curl correction device according to claim 1 or 2. And another correction part that suppresses curling on the opposite side to the direction in which the nip of the fixing part becomes convex.

  According to a ninth aspect of the present invention, in the image forming apparatus according to the eighth aspect, the one correction portion is disposed on the upstream side in the conveyance direction of the recording medium.

  According to the first aspect of the present invention, both curling of the recording medium and curling of the leading edge of the recording medium are compatible as compared with a configuration in which the amount of biting of the second rotating body into the first rotating body is always the same. Is done.

  According to the second aspect of the present invention, the length of the tip portion of the recording medium that reduces the amount of biting of the second rotating body into the first rotating body is the amount of biting of the second rotating body into the first rotating body. As compared with the case where the width of the nip portion is shorter than the width of the nip portion, the leading edge of the recording medium is suppressed.

  According to the third aspect of the present invention, compared to the configuration in which the amount of biting of the second rotating body into the first rotating body is always the same, the curling of the recording medium after the fixing and the bending of the leading edge of the recording medium are suppressed. Are compatible.

  According to the fourth aspect of the present invention, when the image on the back surface of the recording medium is formed, the amount of biting into the first rotating body of the second rotating body is always the same as that of the configuration when the image is formed on the back surface of the recording medium. It is possible to achieve both curling of the medium and curling of the leading edge of the recording medium.

  According to the fifth aspect of the present invention, when the image of the surface of the recording medium is formed, the amount of biting of the second rotating body into the first rotating body is always the same as in the configuration, and the recording is performed when the image of the surface of the recording medium is formed. It is possible to achieve both curling of the medium and curling of the leading edge of the recording medium.

  According to the sixth aspect of the present invention, the curling of the recording medium can be suppressed as compared with the case where the curl correcting device is provided on the most downstream side of the plurality of correcting portions arranged along the conveyance direction of the recording medium. It is compatible with the suppression of the bending of the tip of the recording medium.

  According to the seventh aspect of the present invention, the curling of the recording medium can be suppressed as compared with the case where the curl correcting device is provided only in a part of the plurality of correcting portions arranged along the conveyance direction of the recording medium. It is compatible with the suppression of the bending of the tip of the recording medium.

  According to the eighth aspect of the present invention, compared with the case where the amount of biting of the nip portion is always the same in one correction portion that suppresses curling in the convex direction, the curling in the direction that tends to occur on the fixing portion side. Curling of the recording medium is suppressed, and bending of the tip of the recording medium is suppressed.

  According to the ninth aspect of the present invention, the curling of the recording medium is suppressed against the curl generated on the fixing unit side as compared with the one in which the upstream and the downstream of the other correcting unit are opposite to each other. In addition, bending of the recording medium at the tip is suppressed.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus including a curl correction apparatus according to an embodiment. FIG. 2 is a front view illustrating an example of a fixing device used in the image forming apparatus illustrated in FIG. 1. In the curl correction apparatus according to an embodiment, it is a front view showing a state in which the amount of biting of the second rotating body into the first rotating body is small. In the curl correction apparatus according to an embodiment, it is a front view showing a state where the amount of biting into the first rotating body of the second rotating body is large. In the curl correction apparatus according to the embodiment, when the amount of biting of the second rotating body into the first rotating body is small, the sheet is transported to the nip portion. In the curl correction apparatus of the comparative example, it is a front view showing a state in which a sheet is conveyed to a nip portion where the amount of biting of the second rotating body into the first rotating body is large.

  Embodiments of a curl correction apparatus and an image forming apparatus according to the present invention will be described below with reference to the drawings. In addition, the arrow H shown in each figure is the vertical direction and indicates the apparatus vertical direction, and the arrow W is the horizontal direction and indicates the apparatus width direction.

<Overall configuration of image forming apparatus>
FIG. 1 shows an example of an image forming apparatus 10 provided with a curl correction apparatus according to an embodiment. As shown in FIG. 1, the image forming apparatus 10 includes an image forming unit 12 that forms an image by electrophotography on a sheet P as an example of a recording medium conveyed along a conveyance path 16. The transport path 16 is provided with a plurality of transport roll pairs 18 as an example of transport means for transporting the paper P.

  In addition, the image forming apparatus 10 includes a control unit 70 that controls the operation of each unit, an operation unit 80 that a user performs various operations, and a fixing unit 34 that fixes a toner image on the paper P formed by the image forming unit 12. And an image inspection unit 24 for inspecting an image formed on the paper P. A correction mechanism 22 that corrects curl (curvature) of the paper P is provided between the fixing unit 34 and the image inspection unit 24 in the conveyance direction of the paper P. The correction mechanism 22 will be described in detail later.

  Further, in order to form an image on both sides of the paper P (for double-sided printing), the image forming apparatus 10 reverses the front and back of the paper P on which the image is formed on the front surface. A reversing path 26 is provided as an example of a reversing mechanism that conveys toward the forming unit 12.

  In the image forming apparatus 10 having the above-described configuration, the image formed by the image forming unit 12 is formed on the surface of the paper P that is transported along the transport path 16. Further, the sheet P on which the image is formed passes through the fixing unit 34, the correction mechanism 22, and the image inspection unit 24 in this order and is discharged to the outside of the apparatus.

  On the other hand, when an image is formed on the back surface of the paper P, the paper P on which the image is formed on the front surface is conveyed along the reverse path 26, and this time, the back surface of the paper P is formed by the image forming unit 12. An image is formed.

<Image forming unit>
The image forming unit 12 includes a plurality of toner image forming units 30 that respectively form toner images of respective colors, and a transfer unit 32 that transfers the toner images formed by the toner image forming unit 30 onto the paper P. Further, the image forming unit 12 includes a fixing unit 34 that fixes the toner image transferred onto the paper P by the transfer unit 32 onto the paper P.

(Toner image forming unit)
A plurality of toner image forming units 30 are provided so as to form a toner image for each color. In the present exemplary embodiment, a toner image forming unit 30 of a total of four colors of yellow (Y), magenta (M), cyan (C), and black (K) is provided. (Y), (M), (C), and (K) shown in FIG. 1 indicate the colors described above.

  In the following description, when it is not necessary to distinguish yellow (Y), magenta (M), cyan (C), and black (K), Y, M, C, and K attached to the reference numerals are omitted. To do.

  The toner image forming units 30 for the respective colors are basically configured in the same manner except for the toner to be used. More specifically, the toner image forming unit 30 includes a rotating cylindrical photosensitive drum 40 and a charger 42 that charges the photosensitive drum 40. Further, the toner image forming unit 30 irradiates the charged photosensitive drum 40 with the exposure light L to form an electrostatic latent image, and a developer containing toner to convert the electrostatic latent image into a toner image. And a developing device 46 for developing.

  The photosensitive drums 40 of the respective colors are in contact with the transfer belt 50 that moves around. Then, in the circumferential direction of the transfer belt 50 (see the arrow in the drawing), the yellow (Y), magenta (M), cyan (C), and black (K) toner image forming units 30 are arranged in this order from the upstream side. They are arranged side by side in the horizontal direction. Each color toner image forming unit 30 forms each color toner image using each color toner.

(Transfer part)
The transfer unit 32 transfers to the transfer belt 50 the above-described transfer belt 50 that is wound around a plurality of rolls (reference numerals omitted) and circulates in the direction of the arrow in the figure, and the toner image formed on the photosensitive drum 40 of each color. A primary transfer roll 52 for each color.

  The primary transfer roll 52 is disposed on the opposite side of the photosensitive drum 40 with the transfer belt 50 interposed therebetween. The primary transfer roll 52 is applied with a transfer bias voltage (positive voltage) having a polarity opposite to the toner polarity (negative polarity in the present embodiment as an example) by a power supply unit (not shown). By applying this transfer bias voltage, a transfer current flows between the primary transfer roll 52 and the photosensitive drum 40, and the toner image formed on the photosensitive drum 40 is transferred to the transfer belt 50.

  Further, the transfer unit 32 is disposed on the opposite side of the roll 56 from the roll 56 around which the transfer belt 50 is wound, and transfers the toner image transferred to the transfer belt 50 onto the paper P. And a next transfer roll 54. As a result, a transfer nip NT for transferring the toner image onto the paper P is formed between the secondary transfer roll 54 and the transfer belt 50.

  The secondary transfer roll 54 is applied with a transfer bias voltage (positive voltage) having a polarity opposite to the toner polarity by a power supply unit (not shown). By applying the transfer bias voltage, a transfer current flows between the secondary transfer roll 54 and the roll 56, and the toner image is transferred from the transfer belt 50 to the paper P that passes through the transfer nip NT. A toner image is formed.

  In the image forming apparatus 10 described above, the toner images are primarily transferred onto the transfer belt 50 by the primary transfer roll 52 in the order of yellow (Y), magenta (M), cyan (C), and black (K). The The superimposed toner image is secondarily transferred by the secondary transfer roll 54 to the paper P passing through the transfer nip NT.

<Fixing part>
As shown in FIG. 2, the fixing unit 34 includes a fixing module 60 including an endless fixing belt 62 and a pressure roll 66 that presses the fixing module 60 in contact with the fixing module 60. Further, a fixing nip NF in which the fixing belt 62 and the pressure roll 66 are in contact is formed between the fixing belt 62 and the pressure roll 66.

  The fixing module 60 includes a plurality of large and small rolls 64A, 64B, 64C, 64D, and 64E around which the fixing belt 62 is wound. The rolls 64A, 64B, 64C, and 64D are in contact with the inner peripheral surface of the fixing belt 62 and support the fixing belt 62 from the inside. The roll 64E is in contact with the outer peripheral surface of the fixing belt 62 between the roll 64B and the roll 64C, and applies tension to the fixing belt 62. Further, the fixing module 60 is provided with a peeling pad 68 for peeling the paper P from the fixing belt 62 inside the fixing belt 62.

  The roll 64 </ b> A is disposed on the opposite side of the pressure roll 66 with the fixing belt 62 interposed therebetween. The roll 64C is disposed at a position farthest from the pressure roll 66 among the large and small rolls 64A, 64B, 64C, 64D, and 64E. The rolls 64 </ b> A and 64 </ b> C have heating members (not shown) inside to heat the fixing belt 62. Further, the roll 64A is rotated in the direction of the arrow in FIG. Here, the fixing belt 62 and the roll 64A are examples of a heating member.

  The pressure roll 66 is configured to press the fixing belt 62 against the roll 64A. The pressure roll 66 is rotated in the direction of the arrow in FIG. 2 at a peripheral speed similar to the peripheral speed of the fixing belt 62 when the rotational force is transmitted. Here, the pressure roll 66 is an example of a pressure member. For example, the peripheral surface portion of the pressure roll 66 includes a rubber layer, and the roll 64A is made of metal. Thereby, for example, the roll 64 </ b> A bites into the peripheral surface portion of the pressure roll 66 via the fixing belt 62.

<Reversal path>
As shown in FIG. 1, the paper P that has passed through the image inspection unit 24 is fed into the inversion path 26. The reverse path 26 includes a branch path 26P1, a transport path 26P2, a reverse path 26P3, and a branch reverse path 26P4.

  The branch path 26P1 is branched from the transport route 16. The transport path 26P2 transports the paper P received from the branch path 26P1 to the reversal path 26P3 or the folded back (switched back) to the branch reversal path 26P4.

  The reverse path 26P3 reverses the conveyance direction of the paper P in the opposite direction (switchback conveyance) and reverses the front and back so as to feed the conveyance path 16 upstream of the transfer nip NT in the conveyance direction of the paper P. It has become.

  The branch reversal path 26P4 is configured to discharge the paper P whose front and back are reversed to the discharge unit 59 by being turned back (switched back) in the transport path 26P2.

  Here, when an image is formed on the paper P, single-sided printing for forming an image on one surface of the paper P, and one surface and the other surface (front surface and back surface) of the paper P. There is double-sided printing that forms an image. In the case of double-sided printing, the paper P on which an image is formed on one side (front surface) is conveyed along the reverse path 26, the front and back sides are reversed, and again directed to the image forming unit 12. Then, an image is formed on the other side (back side).

  In the case of single-sided printing, the surface of the paper P on which the image is formed is discharged on the upper side (upward). In the case of duplex printing, the side on which the image is formed on the paper P is discharged on the upper side (upward).

  However, the image forming apparatus 10 of the present embodiment has a reversal mode in which the surface of the paper P to be discharged can be selected. That is, in the case of single-sided printing, the surface on which the image is formed on the paper P is discharged on the lower side (downward). In the case of double-sided printing, the side on which the image is formed on the paper P later is on the lower side (downward). It is possible to discharge with. Although not shown, the sheet P on which images are formed on both the front and back sides is pulled back into the branch path 26P1 of the reversing path 26, switched back, and discharged to the discharge unit 59 through the branch reversing path 26P4, so that the front and back are reversed. .

<Image forming operation>
Next, an outline of an image forming process on the paper P and a post-processing process by the image forming apparatus 10 will be described.

  In the image forming apparatus 10 shown in FIG. 1, the control unit 70 that has received an image formation command operates each toner image forming unit 30 and the like. The photosensitive drums 40 of the respective colors are charged by the charger 42 while being rotated. Further, the control unit 70 sends the image data subjected to the image processing by the image signal processing unit to each exposure device 44. Each exposure device 44 emits each exposure light L according to the image data, and exposes each charged photosensitive drum 40. Thereby, an electrostatic latent image is formed on the outer peripheral surface of each photosensitive drum 40. The electrostatic latent image formed on each photoconductor drum 40 is developed by the developing device 46, and each color photoconductor drum 40 has yellow (Y), magenta (M), cyan (C), and black (K). The toner image is formed.

  The toner images of the respective colors formed on the photosensitive drums 40 of the respective colors are sequentially primary-transferred sequentially to the rotating transfer belt 50 by the primary transfer rolls 52 of the respective colors at the respective primary transfer positions. As a result, a superimposed toner image in which toner images for four colors are superimposed is formed on the transfer belt 50. The superimposed toner image is conveyed to the transfer nip NT by the rotation of the transfer belt 50. A sheet P is supplied to the transfer nip NT in synchronization with the conveyance of the superimposed toner image. Then, the superimposed toner image is transferred from the transfer belt 50 onto the paper P at the transfer nip NT.

  The sheet P onto which the toner image has been secondarily transferred is transported toward the fixing unit 34 by the transport belt 58 while being sucked with negative pressure. The fixing unit 34 applies heat and pressure to the paper P that passes through the fixing nip NF. As a result, the toner image transferred to the paper P is fixed on the paper P.

  The paper P discharged from the fixing unit 34 is curled (curved) by the correction mechanism 22. Furthermore, the toner image (image) fixed on the paper P is detected by the image inspection unit 24 for the presence and extent of toner density defects, image defects, image position defects, and the like. Then, the paper P is discharged to the discharge unit 59.

  In the case of duplex printing, the control unit 70 switches the conveyance path of the paper P after passing through the image inspection unit 24 to the reverse path 26. As a result, the sheet P is reversed and conveyed to the transfer nip NT. Then, on the back surface of the paper P, an image is transferred and fixed in the same process as the image forming process on the front surface, and the same process as the post-processing process after the image is formed on the front surface. It is discharged to the discharge part 59 via

<Main part configuration>
Next, the configuration of the main part of this embodiment will be described.

  As shown in FIGS. 3 and 4, the correction mechanism 22 includes a first correction device 100 as an example of a curl correction device that corrects the curl of the paper P, and the conveyance direction of the paper P downstream of the first correction device 100. And a second correction device 102 that is disposed on the side and corrects the curl of the paper P.

  The first correction device 100 includes a correction unit 108 that corrects curl generated on the paper P. The correction unit 108 includes a roll 104 as an example of a first rotating body, and a roll 106 as an example of a second rotating body that is arranged to bite into the roll 104. Moreover, the 1st correction apparatus 100 is provided with the change apparatus 110 as an example of the change means which changes the amount of biting of the roll 106 to the roll 104. FIG.

  The roll 104 includes a rotating shaft 112, and a rotational force is transmitted to the rotating shaft 112 so that the roll 104 rotates in the direction of the arrow in FIGS. 3 and 4. The roll 106 includes a rotation shaft 114, and the rotation shaft 114 is rotatably supported on one end side (upper side in the present embodiment) of the housing 116. The roll 106 rotates in the direction of the arrow in FIGS. In the first straightening device 100, the paper P is sandwiched and conveyed by the nip portion N between the roll 104 and the roll 106. In the first straightening device 100, as an example, the roll 104 is driven by a drive unit (not shown), and the roll 106 is driven to rotate. Instead of this configuration, the roll 106 may be driven and the roll 104 may be driven to rotate.

  For example, the peripheral surface portion of the roll 104 is a rubber layer and can be elastically deformed. For example, the roll 106 is made of metal. Thus, when the roll 106 is pressed against the roll 104, the peripheral surface portion of the roll 104 is elastically deformed into a concave shape, and the roll 106 bites into the roll 104.

  The changing device 110 is arranged on the cam 118 disposed on the opposite side to the roll 104 (the lower side in the vertical direction in the present embodiment) with respect to the roll 106 and on the other end side (the lower side in the present embodiment) of the housing 116. And a cam follower member 120 that is rotatably supported and contacts the cam 118. The cam 118 includes a cam shaft 122, and the cam shaft 122 is rotatably supported by a support portion (not shown). The cam 118 is pressed against the cam driven member 120 by a pressing mechanism (not shown). The cam follower member 120 is formed of a circular roll and is rotatably disposed at a position away from the roll 106. The casing 116 moves along a guide (not shown) in a direction approaching or leaving the roll 104 (in this embodiment, the vertical direction indicated by arrows A and B).

  In the changing device 110, when the cam 118 rotates, the cam driven member 120 is driven to rotate, and the casing 116 moves together with the cam driven member 120 in a direction approaching or leaving the roll 104 (vertical direction in this embodiment). Thereby, the amount of biting of the roll 106 into the roll 104 is changed. As shown in FIG. 3, when the portion 118 </ b> A having the smallest radius of the cam 118 is in contact with the cam follower 120, the amount of biting of the roll 106 into the roll 104 is the smallest.

  As shown in FIG. 4, when the portion 118 </ b> B having the largest radius of the cam 118 is in contact with the cam driven member 120, the amount of biting of the roll 106 into the roll 104 is the largest. That is, the roll 106 moves in a range indicated by an arrow C with respect to the roll 104. In FIG. 4, the biting of the roll 106 into the roll 104 is exaggerated for easy understanding of the configuration.

  In the present embodiment, when the roll 106 bites into the roll 104, the curved portion of the nip portion N is configured to be convex upward when viewed from the direction of the rotation shaft 112. In the first straightening device 100, as shown in FIG. 4, when the amount of biting of the roll 106 into the roll 104 is the largest, the lower side in the direction of curling downward with respect to the paper P passing through the nip portion N It is designed to make curls.

  On the other hand, in the fixing unit 34 shown in FIG. 2, the roll 64A bites into the pressure roll 66 via the fixing belt 62, so that the fixing nip NF is curved as viewed from the axial direction of the pressure roll 66. The part is configured to be convex downward. As a result, as shown in FIG. 2, the sheet P is likely to curl upward as it passes through the fixing nip NF of the fixing unit 34. In particular, when printing on the back side of the paper P in the case of double-sided printing, the paper P tends to cause an upper curl because the paper P passes through the fixing nip NF of the fixing unit 34. Further, when the thin paper P passes through the fixing nip NF of the fixing unit 34, the upper curl is likely to occur on the paper P.

  Further, as shown in FIG. 4, after fixing, the sheet P passes through the nip portion N between the roll 106 and the roll 104 of the correction unit 108, and forms a lower curl on the sheet P opposite to the fixing unit 34. Thus, the upper curl generated on the paper P is corrected. In the first correction device 100, as shown in FIG. 4, when the amount of biting of the roll 106 into the roll 104 is the largest, the curl of the paper P is most easily corrected.

  The cam shaft 122 of the cam 118 is connected to a motor (not shown), and the driving of the motor is controlled by the control unit 70 (see FIG. 1). As shown in FIG. 5, when the leading end portion P1 of the paper P enters the nip portion N between the roll 106 and the roll 104, the changing device 110 has the rear end P2 side in the transport direction of the paper P at the nip portion N. The amount of biting of the roll 106 into the roll 104 is made smaller than when passing. In other words, the width of the nip portion N between the roll 106 and the roll 104 in the conveyance direction of the paper P can be changed, and the path shape of the nip portion N through which the paper P passes can be changed. That is, when the leading end portion P1 of the paper P enters the nip portion N between the roll 106 and the roll 104, the width of the nip portion N is small.

  As shown in FIG. 4, when the rear end P2 side in the conveyance direction of the sheet P passes through the nip portion N between the roll 106 and the roll 104, the changing device 110 causes the leading end portion P1 of the sheet P to move to the nip portion. The amount of biting of the roll 106 into the roll 104 is larger than when passing through N. In other words, the changing device 110 increases the amount of biting of the roll 106 into the roll 104 at a predetermined timing after the leading end portion P1 of the paper P has entered the nip portion N between the roll 106 and the roll 104. It is said that. In FIG. 4, the paper P is omitted. More specifically, the changing device 110 has a nip portion N when the length of the leading end portion P1 of the sheet P that reduces the amount of biting of the roll 106 into the roll 104 is large. The width is equal to or longer than the width (the width of the nip portion N shown in FIG. 4).

  Further, the length of the leading end portion P1 of the paper P that reduces the amount of biting of the roll 106 into the roll 104 is preferably 1/3 or less of the length of the paper P in the transport direction. The length is more preferably ¼ or less of the length, and further preferably さ ら に or less of the length of the paper P in the transport direction.

  The length of the leading end portion P1 of the paper P that reduces the amount of biting of the roll 106 into the roll 104 is, for example, a sensor that detects the leading end of the paper P on the entrance side of the nip portion N, and the transport speed of the paper P And calculate by time etc. For example, when a sensor for detecting the leading edge of the paper P is provided on the exit side of the nip portion N, the amount of biting of the roll 106 into the roll 104 is reduced, and the leading edge of the paper P is directly detected by the sensor. The amount of biting of the roll 106 into the roll 104 may be increased.

  The second straightening device 102 has a straightening unit 138 that straightens the curl generated on the paper P. The correction unit 138 includes two rolls 130 and 132 that are spaced apart from each other, an endless belt 134 that is wound around the rolls 130 and 132, and a pressing roll 136 that is pressed against the outer peripheral surface of the belt 134. . By pressing the pressing roll 136 against the belt 134, the belt 134 is curved in a concave shape. In this embodiment, for example, when a rotational force is transmitted to one of the rolls 130 and 132, the belt 134 rotates in the direction of the arrow and the other of the rolls 130 and 132 rotates, and the pressing roll 136 is driven. It is designed to rotate.

  In the present embodiment, the pressing roll 136 is disposed on the upper side of the belt 134, and the curved portion of the contact portion between the belt 134 and the roll 136 is configured to protrude downward when viewed from the axial direction of the roll 136. ing. Thereby, after the paper P passes through the correction unit 108 of the first correction device 100, the paper P passes through the contact portion between the belt 134 and the roll 136, so that the upper side of the paper P opposite to the correction unit 108. By making the curl, the lower curl generated in the paper P is corrected.

  In the image forming apparatus 10 described above, as an example, the leading end portion P1 of the paper P is formed between the roll 106 and the roll 104 in both cases of image formation on the front surface of the paper P and image formation on the back surface of the paper P. When entering the nip portion N, the amount of biting of the roll 106 into the roll 104 is made smaller than when the rear end P2 side in the transport direction of the paper P passes through the nip portion N (see FIG. 5). ). In both cases of image formation on the front surface of the paper P and image formation on the back surface of the paper P, when the rear end P2 side in the transport direction of the paper P passes through the nip portion N, the front end of the paper P The amount of biting of the roll 106 into the roll 104 is larger than when the portion P1 passes through the nip portion N (see FIG. 4).

  Further, the image forming apparatus 10 includes the first correction device 100 and the second correction device 102 in order from the upstream side in the transport direction of the paper P, and the first correction on the most upstream side in the transport direction of the paper P. The amount of biting of the roll 106 into the roll 104 is changed by the apparatus 100.

<Action and effect>
Next, the operation and effect of this embodiment will be described.

  As shown in FIG. 1, the toner image transferred onto the transfer belt 50 by the image forming unit 12 is transferred onto the paper P at the transfer nip NT. Further, the toner image on the paper P passes through the fixing nip NF of the fixing unit 34 and is fixed on the paper P by heating and pressing (see FIG. 2). Although not shown, in the fixing unit 34, the roll 64A bites into the pressure roll 66 via the fixing belt 62, so that the curved portion of the fixing nip NF protrudes downward as viewed from the axial direction of the pressure roll 66. It is comprised so that. As a result, the paper P tends to curl upward as it passes through the fixing nip NF of the fixing unit 34.

  Thereafter, the paper P passes through the nip portion N between the roll 106 and the roll 104 of the first straightening device 100. As shown in FIG. 5, in the first correction device 100, when the leading end portion P <b> 1 of the paper P enters the nip portion N between the roll 106 and the roll 104 by controlling the rotation of the cam 118 of the changing device 110. The amount of biting of the roll 106 into the roll 104 is smaller than when the rear end P2 side in the conveyance direction of the paper P passes through the nip portion N. For this reason, the leading end portion P 1 of the paper P is likely to enter the nip portion N between the roll 106 and the roll 104.

  Thereafter, as shown in FIG. 4, in the first correction device 100, when the rear end P <b> 2 side in the conveyance direction of the paper P passes the nip portion N by controlling the rotation of the cam 118 of the changing device 110, The amount of biting of the roll 106 into the roll 104 is made larger than when the leading end portion P1 of the paper P passes through the nip portion N. At this time, the curved portion of the nip portion N between the roll 106 and the roll 104 as viewed from the direction of the rotating shaft 112 is configured to be convex upward, and passes through the nip portion N between the roll 106 and the roll 104. The sheet P to be printed is easy to make a lower curl. For this reason, when the rear end P2 side in the conveyance direction of the paper P passes through the nip portion N between the roll 106 and the roll 104, a lower curl opposite to the fixing portion 34 is formed on the paper P, so The upper curl generated on the paper P is corrected.

  Further, the paper P passes through a contact portion between the belt 134 and the roll 136 of the second correction device 102. In that case, the curved part of the contact part of the belt 134 and the roll 136 is comprised so that it may protrude below seeing from the axial direction of the roll 136. FIG. As a result, an upper curl on the side opposite to the correction unit 108 is formed on the paper P, whereby the lower curl generated on the paper P when passing through the correction unit 108 is corrected.

  Here, a curl correction apparatus 200 of a comparative example will be described with reference to FIG. As shown in FIG. 6, in the curl correction apparatus 200 of the comparative example, the amount of biting of the roll 202 into the roll 104 is not changed. More specifically, the amount of biting of the roll 202 into the roll 104 is set to be large in the same way as the amount of biting of the roll 106 into the roll 104 shown in FIG. For this reason, when the leading end portion P1 of the sheet P enters the nip portion N between the roll 202 and the roll 104, the amount of biting of the roll 106 into the roll 104 shown in FIG. The amount of bite is large. Therefore, when the leading end portion P1 of the sheet P enters the nip portion N between the roll 202 and the roll 104, the leading end of the sheet P is likely to be broken. In addition, the paper P may become wrinkled.

  On the other hand, although illustration is omitted, when the amount of biting of the roll 202 into the roll 104 is always made smaller than the amount of biting of the roll 202 into the roll 104 shown in FIG. There is.

  In contrast, in the present embodiment, as shown in FIG. 5, when the leading end portion P1 of the paper P enters the nip portion N between the roll 106 and the roll 104, the amount of biting of the roll 106 into the roll 104 is increased. Is small. Further, as shown in FIG. 4, when the rear end P2 side in the transport direction of the paper P passing through the nip N passes through the nip N, the leading end portion P1 of the paper P passes through the nip N. Also, the amount of biting of the roll 106 into the roll 104 is increased. For this reason, in the 1st correction apparatus 100, compared with the structure where the amount of biting into the 1st rotary body of the 2nd rotary body is always the same, suppression of the curl of the paper P and suppression of the front end bending of the paper P are compatible. The Particularly in the case of a thin paper P, both curling of the paper P and curling of the leading edge of the paper P are compatible. Furthermore, in the first correction device 100, the occurrence of wrinkles on the paper P is also suppressed as compared with a configuration in which the amount of biting of the second rotating body into the first rotating body is always the same.

  In the first straightening device 100 described above, the changing device 110 is such that the length of the leading end portion P1 of the paper P that reduces the amount of biting of the roll 106 into the roll 104 is large. The length of the nip portion N is greater than the width of the nip portion N (the width of the nip portion N shown in FIG. 4). For this reason, after the leading end portion P1 of the paper P passes through the nip portion N, the amount of biting of the roll 106 into the roll 104 increases. In the first correction device 100, the length of the leading end portion of the recording medium that reduces the amount of biting of the second rotating body into the first rotating body is large when the amount of biting of the second rotating body into the first rotating body is large. Compared to a case where the width of the nip portion is shorter than that of the nip portion, the leading edge of the paper P is suppressed.

  Further, in the image forming apparatus 10 described above, the changing device 110 is arranged on the rear end P2 side in the transport direction of the paper P that passes through the nip N between the roll 106 and the roll 104 when the image is formed on the back surface of the paper P. The amount of biting of the roll 106 into the roll 104 is made larger than when the leading end portion P1 of the paper P passes through the nip portion N (see FIG. 4). For this reason, in the image forming apparatus 10 described above, when the image is formed on the back surface of the paper P, the amount of biting of the second rotating body into the first rotating body is always the same as in the configuration, and the image is formed on the back surface of the paper P. Sometimes, curling of the paper P and curling of the leading edge of the paper P are compatible.

  Further, in the image forming apparatus 10 described above, the changing device 110 is arranged on the rear end P2 side in the transport direction of the paper P that passes through the nip portion N between the roll 106 and the roll 104 when the image is formed on the surface of the paper P. The amount of biting of the roll 106 into the roll 104 is made larger than when the leading end portion P1 of the paper P passes through the nip portion N (see FIG. 4). For this reason, in the image forming apparatus 10 described above, when the image is formed on the surface of the paper P, the amount of biting of the second rotating body into the first rotating body is always compared with the configuration in which the image is formed on the surface of the paper P. Sometimes, curling of the paper P and curling of the leading edge of the paper P are compatible.

  Further, the image forming apparatus 10 includes the first correction device 100 and the second correction device 102 in order from the upstream side in the transport direction of the paper P, and the first correction on the most upstream side in the transport direction of the paper P. In the apparatus 100, the amount of biting of the roll 106 into the roll 104 is changed. For this reason, in the image forming apparatus 10 described above, curling of the paper P can be suppressed as compared with the case where the curling correction device is provided on the most downstream side of the plurality of correction units arranged along the conveyance direction of the paper P. It is possible to achieve both suppression of the leading edge of the paper P.

  Further, in the image forming apparatus 10 described above, the first correction device 100 that suppresses curling (upper curl) in the direction in which the fixing nip NF of the fixing unit 34 becomes convex, and the direction in which the fixing nip NF of the fixing unit 34 becomes convex. And a second straightening device 102 that suppresses curling on the opposite side (lower curl). For this reason, in the image forming apparatus 10 described above, the direction that tends to occur on the fixing unit 34 side as compared with the case where the amount of biting in the nip portion is always the same in one correction unit that suppresses curling in the convex direction (upper curl). In addition to curling of the recording medium, curling of the recording medium is suppressed, and bending of the leading end of the recording medium is suppressed.

  Further, in the image forming apparatus 10 described above, the first correction device 100 that suppresses curling in the direction in which the fixing nip NF of the fixing unit 34 becomes convex (upper curl) is arranged on the upstream side in the conveyance direction of the paper P. . For this reason, in the image forming apparatus 10 described above, curling of the paper P is suppressed with respect to curling occurring on the fixing unit 34 side as compared with the upstream and downstream of the first correcting device and the second correcting device reversed. At the same time, bending of the leading edge of the paper P is suppressed.

<Supplementary explanation>
The image forming apparatus 10 includes the first correction device 100 and the second correction device 102. However, the present invention is not limited to this configuration, and includes one correction unit that corrects the curl of the paper P. The structure may be sufficient, and the structure provided with three or more correction | amendment parts which correct the curl of the paper P may be sufficient.

  In the image forming apparatus 10 described above, only the first correction device 100 of the first correction device 100 and the second correction device 102 is configured to change the amount of biting of the roll 106 into the roll 104. Is not limited to this configuration. For example, a plurality of correction units that correct the curl of the paper P are provided, and the amount of biting of the second rotary body into the first rotary body can be changed in all of the correction sections or two or more correction sections. When the leading end portion passes through the nip portion N, the amount of biting of the second rotating body into the first rotating body may be smaller than when the rear end side in the transport direction of the paper P passes through the nip portion N. At this time, the plurality of correction units may be configured to alternately correct the curl of the paper P to the opposite side along the conveyance direction of the paper P, for example.

  Moreover, in the said embodiment, although the change apparatus 110 is provided in order to change the amount of biting of the roll 106 to the roll 104, the component of the change apparatus 110 can be changed. For example, the arrangement of the cam driven member 120 may be changed, or the cam driven member 120 may not be provided. Also, the shape of the cam 118 can be changed.

  Moreover, in the said embodiment, in order to change the amount of biting of the roll 106 to the roll 104, the change apparatus 110 provided with the cam 118 is provided, However, This invention is not limited to this. For example, the amount of biting of the second rotating body into the first rotating body may be changed by changing means such as a solenoid, a rack and pinion, and a cylinder.

  In the above embodiment, the range in which the amount of biting of the roll 106 into the roll 104 when the leading end portion P1 of the paper P passes through the nip portion N is switched by detecting the leading edge of the paper P with a sensor, for example. May be.

  Further, instead of the image forming apparatus 10 of the above-described embodiment, a configuration in which a curl correction apparatus independent of the image forming apparatus is provided as an optional post-processing apparatus may be employed.

  Although the present invention has been described in detail with respect to specific embodiments, the present invention is not limited to such embodiments, and various other embodiments are possible within the scope of the present invention. It is clear to the contractor.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Image forming part 18 Conveyance roll pair (an example of a conveyance means)
22 Correction mechanism 26 Reverse path 34 Fixing unit 62 Fixing belt (an example of a heating member)
64A roll (an example of a heating member)
66 Pressure roll (an example of a pressure member)
100 First straightening device (an example of a curl straightening device)
104 roll (an example of a first rotating body)
106 roll (an example of a second rotating body)
108 Correction unit 110 Changing device (an example of changing means)
138 Correction part N Nip part NF Fixing nip (an example of a nip of the fixing part)
P paper (an example of a recording medium)
P1 Front end portion P2 Rear end

Claims (9)

A first rotator and a second rotator which is arranged so as to bite into the first rotator and which sandwiches the recording medium at a nip portion with the first rotator, and is generated in the recording medium. A correction section for correcting curl;
When the leading end portion of the recording medium in the conveyance direction passes through the nip portion, the rear end side of the recording medium in the conveyance direction moves to the first rotation body of the second rotator than when passing through the nip portion. Changing means to reduce the amount of bite,
A curl straightening device.   The changing means is configured such that the length of the leading end portion of the recording medium that reduces the amount of biting of the second rotating body into the first rotating body is the amount of biting into the first rotating body of the second rotating body. The curl correction apparatus according to claim 1, wherein the curl correction apparatus has a length equal to or greater than a width of the nip portion when it is large. Conveying means for conveying the recording medium;
An image forming unit for forming an image on the recording medium;
A fixing unit for fixing an image on the recording medium;
The curl correction apparatus according to claim 1 or 2, provided on the downstream side of the fixing unit in the conveyance direction of the recording medium,
An image forming apparatus. The curl correction apparatus according to claim 1 or 2,
An image forming unit for forming an image on the recording medium;
A reversing mechanism for reversing the front and back of the recording medium and conveying the recording medium to the image forming unit after conveying the recording medium to the image forming unit;
Have
The changing means is configured such that, at the time of forming an image on the back surface of the recording medium, when the leading end portion in the transport direction of the recording medium passes through the nip portion, the rear end side in the transport direction of the recording medium passes through the nip portion. An image forming apparatus that reduces the amount of biting of the second rotating body into the first rotating body than when performing the above.   The changing means is configured such that, when an image is formed on the surface of the recording medium, a rear end side of the recording medium in the conveyance direction passes through the nip portion when a leading end portion in the conveyance direction of the recording medium passes through the nip portion. The image forming apparatus according to claim 4, wherein an amount of biting of the second rotating body into the first rotating body is smaller than when the second rotating body is engaged. Conveying means for conveying the recording medium;
A plurality of correction units arranged along the conveyance direction of the recording medium and correcting the curl generated in the recording medium;
Have
The image forming apparatus according to claim 1, wherein the correction unit on the most upstream side in the conveyance direction of the recording medium is the curl correction apparatus according to claim 1.   The image forming apparatus according to claim 6, wherein all of the plurality of correction units are the curl correction apparatus. Conveying means for conveying the recording medium;
An image forming unit for forming an image on the recording medium;
A fixing unit for fixing the image on the recording medium through a nip between a heating member and a pressure member;
A correction unit that suppresses curling in a direction in which the nip of the fixing unit becomes convex, and one correction unit that is the curl correction device according to claim 1 or 2,
Other correction parts for suppressing curling on the opposite side to the direction in which the nip of the fixing part is convex,
An image forming apparatus.   The image forming apparatus according to claim 8, wherein the one correction unit is arranged on the upstream side in the conveyance direction of the recording medium.