JP6958101B2 - Curl correction device and image forming device - Google Patents

Description

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

Patent Document 1 below discloses a curl correction device that divides sections in the length direction of paper and changes the amount of curl correction for paper according to the information of the image density divided for each section.

Japanese Unexamined Patent Publication No. 06-144678

For example, in a configuration in which a pressure roll that is pressurized at a constant pressure with respect to the facing roll is arranged and the paper is passed between the facing roll and the pressure roll to correct curl, the tip of the paper is broken. May be done.

The present invention obtains a curl correction device that suppresses curl of a recording medium and suppresses bending of the tip of a recording medium, as compared with a configuration in which the amount of bite of the second rotating body into the first rotating body is always the same. Is the purpose.

Curl straightening device according to the first embodiment includes a first rotary member, a second rotating body that rotates across the recording medium at the nip portion between the first rotary member while being positioned bite into the first rotary member And, when the straightening portion for correcting the curl generated in the recording medium and the tip portion of the recording medium in the transport direction pass through the nip portion, the rear end side of the recording medium in the transport direction is the nip. It has a changing means for making the amount of the second rotating body biting into the first rotating body smaller than when passing through the portion.

The curl correction device according to the second aspect is the curl correction device according to the first aspect , wherein the changing means is a tip of the recording medium that reduces the amount of the second rotating body biting into the first rotating body. The length of the portion is set to be longer than the width of the nip portion when the amount of the second rotating body biting into the first rotating body is large.

The image forming apparatus according to a third aspect, a conveying means for conveying the recording medium, an image forming unit for forming an image on said recording medium, and a fixing unit for fixing the image on said recording medium, said recording medium It is provided on the downstream side of the fixing portion in the transport direction, and has the curl correction device according to the first aspect or the second aspect.

The image forming apparatus according to the fourth aspect, the curl correction device according to the first aspect or the second aspect, an image forming unit for forming an image on said recording medium, and conveys the recording medium to the image forming section After that, the recording medium has a reversing mechanism that reverses the front and back sides of the recording medium and conveys the recording medium to the image forming unit, and the changing means of the recording medium at the time of forming an image on the back surface of the recording medium. When the tip portion in the transport direction passes through the nip portion, the amount of the second rotating body biting into the first rotating body is larger than that when the rear end side of the recording medium in the transport direction passes through the nip portion. Make it smaller.

The image forming apparatus according to the fifth aspect is the image forming apparatus according to the fourth aspect. When passing through the portion, the amount of the second rotating body biting into the first rotating body is smaller than that when the rear end side of the recording medium in the transport direction passes through the nip portion.

The image forming apparatus according to the sixth embodiment, chromatic conveying means for conveying the recording medium, wherein are arranged along the conveying direction of the recording medium, a plurality of correction unit for correcting the curl generated in the recording medium, the The straightening portion on the most upstream side in the transport direction of the recording medium is the curl straightening device according to the first aspect or the second aspect.

The image forming apparatus according to the seventh aspect is the image forming apparatus according to the sixth aspect , in which all of the plurality of correction portions are the curl correction devices.

The image forming apparatus according to an eighth aspect, a conveying means for conveying the recording medium, an image forming unit for forming an image on the recording medium, the nip between the heating member and the pressure member the image on the recording medium a fixing unit for fixing by passage through the nip of the fixing unit is a correction section to suppress the curl direction which is convex, and one correction unit is curl correction device according to the first aspect or second aspect, It has another straightening portion that suppresses curl on the side opposite to the direction in which the nip of the fixing portion becomes convex.

In the image forming apparatus according to the ninth aspect , in the image forming apparatus according to the eighth aspect , the one straightening portion is arranged on the upstream side in the transport direction of the recording medium.

According to the curl correction device according to the first aspect , curl of the recording medium and tip breakage of the recording medium are suppressed as compared with the configuration in which the amount of the second rotating body biting into the first rotating body is always the same. Are compatible.

According to the curl correction device according to the second aspect , the length of the tip portion of the recording medium that reduces the amount of the second rotating body biting into the first rotating body is set to the first rotating body of the second rotating body. Compared with the case where the bite amount is shorter than the width of the nip portion when the bite amount is large, the tip breakage of the recording medium is suppressed.

According to the image forming apparatus according to the third aspect , curling of the recording medium is suppressed and the tip of the recording medium is broken after fixing, as compared with the configuration in which the amount of the second rotating body biting into the first rotating body is always the same. It is compatible with suppression.

According to the image forming apparatus according to the fourth aspect , when the image forming on the back surface of the recording medium is performed, the image forming on the back surface of the recording medium is compared with the configuration in which the amount of the second rotating body biting into the first rotating body is always the same. Occasionally, both suppression of curl of the recording medium and suppression of tip bending of the recording medium are compatible.

According to the image forming apparatus according to the fifth aspect , when the surface of the recording medium is image-formed, the image of the surface of the recording medium is formed as compared with the configuration in which the amount of the second rotating body biting into the first rotating body is always the same. Occasionally, both suppression of curl of the recording medium and suppression of tip bending of the recording medium are compatible.

According to the image forming apparatus according to the sixth aspect , the curl of the recording medium is compared with the case where the curl correction device is provided on the most downstream side of the plurality of straightening portions arranged along the conveying direction of the recording medium. Both suppression and suppression of tip breakage of the recording medium are compatible.

According to the image forming apparatus according to the seventh aspect , the curl of the recording medium is compared with the case where the curl correction device is provided only in a part of the plurality of straightening portions arranged along the conveying direction of the recording medium. Both suppression and suppression of tip breakage of the recording medium are compatible.

According to the image forming apparatus according to the eighth aspect , the curl in the direction in which the curl in the fixing portion is more likely to occur is obtained as compared with the case where the bite amount of the nip portion is always the same in one straightening portion that suppresses the curl in the convex direction. On the other hand, curling of the recording medium is suppressed, and bending of the tip of the recording medium is suppressed.

According to the image forming apparatus according to the ninth aspect , the curl of the recording medium is different from the curl generated on the fixing portion side as compared with the one in which the upstream and downstream of one straightening portion and the other straightening portion are reversed. At the same time, the tip breakage of the recording medium is suppressed.

It is a schematic block diagram which shows an example of the image forming apparatus provided with the curl correction apparatus which concerns on one Embodiment. It is a front view which shows an example of the fixing apparatus used for the image forming apparatus shown in FIG. It is a front view which shows the state which the amount of biting into the 1st rotating body of a 2nd rotating body is small in the curl straightening apparatus which concerns on one Embodiment. It is a front view which shows the state which the amount of biting into the 1st rotating body of a 2nd rotating body is large in the curl straightening apparatus which concerns on one Embodiment. FIG. 5 is a front view showing a state in which paper is conveyed to the nip portion when the amount of bite of the second rotating body into the first rotating body is small in the curl correction device according to the embodiment. FIG. 5 is a front view showing a state in which paper is conveyed to a nip portion in which the amount of biting of the second rotating body into the first rotating body is large in the curl correction device of the comparative example.

Hereinafter, embodiments of the curl correction device and the image forming device of the present invention will be described with reference to the drawings. The arrow H shown in each figure is the vertical direction and indicates the vertical direction of the device, and the arrow W is the horizontal direction and indicates the width direction of the device.

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

Further, the image forming apparatus 10 has a control unit 70 that controls the operation of each unit, an operation unit 80 that the user performs various operations, and a fixing unit 34 that fixes the toner image on the paper P formed by the image forming unit 12. And an image inspection unit 24 for inspecting the image formed on the paper P. A correction mechanism 22 for correcting the curl of the paper P is provided between the fixing unit 34 and the image inspection unit 24 in the transport 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 (front side) and re-images. An inversion path 26 is provided as an example of an inversion mechanism that conveys the image to the forming portion 12.

In the image forming apparatus 10 having the above configuration, the image formed by the image forming unit 12 is formed on the surface (front side) of the paper P to be conveyed along the conveying path 16. Further, the paper 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 (front side) is conveyed along the inversion path 26, and this time, the image forming unit 12 conveys the back surface of the paper P. An image is formed in.

<Image forming part>
The image forming unit 12 includes a plurality of toner image forming units 30 for forming toner images of each color, and a transfer unit 32 for transferring the toner image formed by the toner image forming unit 30 onto the paper P. Further, the image forming unit 12 includes a fixing unit 34 for fixing the toner image transferred to the paper P by the transfer unit 32 to the paper P.

(Toner image forming part)
A plurality of toner image forming units 30 are provided so as to form a toner image for each color. In the present embodiment, the 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 above-mentioned colors.

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

The toner image forming unit 30 of each color is 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 photoconductor drum 40 and a charger 42 that charges the photoconductor drum 40. Further, the toner image forming unit 30 uses an exposure device 44 that irradiates the charged photoconductor 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. It is provided with a developing device 46 for developing.

Further, the photoconductor drum 40 of each color is 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 figure), the toner image forming portions 30 of yellow (Y), magenta (M), cyan (C), and black (K) are arranged in this order from the upstream side. They are arranged side by side in the horizontal direction. Then, the toner image forming unit 30 of each color forms a toner image of each color using the toner of each color.

(Transfer part)
The transfer unit 32 transfers the toner image formed on the above-mentioned transfer belt 50, which is wound around a plurality of rolls (reference numerals omitted) and orbits in the direction of the arrow in the drawing, and the photoconductor drum 40 of each color, onto the transfer belt 50. A primary transfer roll 52 for each color is provided.

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

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

A transfer bias voltage (voltage of the positive electrode) having a polarity opposite to that of the toner is applied to the secondary transfer roll 54 by a feeding portion (not shown). By applying this 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 passing through the transfer nip NT, so that the toner image is transferred to the paper P. A toner image is formed.

In the image forming apparatus 10, the toner image is superimposed on the transfer belt 50 by the primary transfer roll 52 and primary transferred in the order of yellow (Y), magenta (M), cyan (C), and black (K). NS. Further, 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 portion 34 includes a fixing module 60 including an endless fixing belt 62, and a pressure roll 66 that comes into contact with the fixing module 60 and pressurizes the fixing module 60. Further, a fixing nip NF in which the fixing belt 62 and the pressure roll 66 come into contact with each other 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, 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 contacts the outer peripheral surface of the fixing belt 62 between the roll 64B and the roll 64C to apply tension to the fixing belt 62. Further, the fixing module 60 is provided with a peeling pad 68 inside the fixing belt 62 for peeling the paper P from the fixing belt 62.

The roll 64A is arranged on the opposite side of the pressure roll 66 with the fixing belt 62 interposed therebetween. The roll 64C is arranged at the position farthest from the pressure roll 66 among the plurality of large and small rolls 64A, 64B, 64C, 64D, and 64E. The roll 64A and the roll 64C have a heat generating member (not shown) inside, and heat the fixing belt 62. Further, the roll 64A is adapted to rotate in the direction of the arrow in FIG. 2 by transmitting the rotational force. Here, the fixing belt 62 and the roll 64A are examples of heating members.

The pressure roll 66 is configured to press the fixing belt 62 against the roll 64A. The pressure roll 66 is adapted to rotate in the direction of the arrow in FIG. 2 at a peripheral speed similar to the peripheral speed of the fixing belt 62 by transmitting a rotational force. Here, the pressure roll 66 is an example of a pressure member. For example, the peripheral surface of the pressure roll 66 is provided with a rubber layer, and the roll 64A is made of metal. As a result, for example, the roll 64A bites into the peripheral surface portion of the pressure roll 66 via the fixing belt 62.

<Reversal path>
As shown in FIG. 1, the reversing path 26 is adapted to feed the paper P that has passed through the image inspection unit 24. The inversion path 26 has a branch inversion path 26P1, a transport path 26P2, an inversion path 26P3, and a branch inversion path 26P4.

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

The reverse path 26P3 reverses the front and back sides by folding back the paper P in the transport direction in the opposite direction (switchback transport), and feeds the paper P into the transport path 16 upstream of the transfer nip NT in the paper P transport direction. It has become.

The branch reversal path 26P4 is folded back at the transfer path 26P2 (by being switched back), so that the paper P whose front and back sides are reversed is discharged to the ejection unit 59.

Here, when an image is formed on the paper P, single-sided printing that forms an image on one side of the paper P and one side and the other side (front side (front side) and back side) of the paper P are used. 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 side (front side)) is conveyed along the inversion path 26, the front and back sides are inverted, and the paper P is directed to the image forming unit 12 again. And then the image is formed on the other side (back side).

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

However, the image forming apparatus 10 of the present embodiment has an inversion mode in which the surface of the paper P to be ejected can be selected. That is, in the case of single-sided printing, the side on which the image is formed on the paper P is ejected downward (downward), and in the case of double-sided printing, the side on which the image is formed on the paper P is downward (downward). It is possible to discharge with. Although not shown, the front and back sides are inverted by drawing the paper P having images formed on both the front and back surfaces into the branch path 26P1 of the inversion path 26, switching back, and discharging the paper P to the ejection unit 59 through the branch inversion path 26P4. ..

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

In the image forming apparatus 10 shown in FIG. 1, the control unit 70 that receives the image forming command operates each toner image forming unit 30 and the like. The photoconductor drum 40 of each color is 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 to expose each charged photoconductor drum 40. As a result, an electrostatic latent image is formed on the outer peripheral surface of each photoconductor drum 40. The electrostatic latent image formed on each photoconductor drum 40 is developed by the developing device 46, and the photoconductor drum 40 of each color has yellow (Y), magenta (M), cyan (C), and black (K). Toner image is formed.

The toner images of each color formed on the photoconductor drum 40 of each color are sequentially primary-transferred to the orbiting transfer belt 50 by the primary transfer roll 52 of each color at each primary transfer position. As a result, a superimposed toner image on which the toner images of four colors are superimposed is formed on the transfer belt 50. The superimposed toner image is conveyed to the transfer nip NT by the circulation of the transfer belt 50. Paper P is supplied to the transfer nip NT in time with the transfer of the superimposed toner image. Then, in this transfer nip NT, the superimposed toner image is transferred from the transfer belt 50 to the paper P.

The paper P on which the toner image is secondarily transferred is conveyed toward the fixing portion 34 by the conveying belt 58 while being sucked under negative pressure. The fixing unit 34 applies heat and pressing force to the paper P passing through the fixing nip NF. As a result, the toner image transferred to the paper P is fixed on the paper P.

The curl (curvature) of the paper P discharged from the fixing portion 34 is corrected by the straightening mechanism 22. Further, the image inspection unit 24 detects the presence or absence and degree of toner density defects, image defects, image position defects, etc. in the toner image (image) fixed on the paper P. Then, the paper P is discharged to the discharge unit 59.

In the case of double-sided printing, the control unit 70 switches the transport path of the paper P after passing through the image inspection unit 24 to the reversal path 26. As a result, the paper P is turned upside down and conveyed to the transfer nip NT. Then, the image is transferred and fixed on the back surface of the paper P in the same step as the image forming step on the front surface (Omotemen), and the same step as the post-processing step after forming the image on the front surface. Is discharged to the discharge unit 59.

<Main part composition>
Next, the configuration of the main parts of the present embodiment will be described.

As shown in FIGS. 3 and 4, the straightening mechanism 22 has a first straightening device 100 as an example of a curl straightening device that straightens the curl of the paper P, and a downstream of the first straightening device 100 in the transport direction of the paper P. It is provided with a second straightening device 102, which is arranged on the side and straightens the curl of the paper P.

The first straightening device 100 includes a straightening section 108 that straightens curls generated on the paper P. The straightening unit 108 includes a roll 104 as an example of the first rotating body and a roll 106 as an example of the second rotating body arranged so as to bite into the roll 104. Further, the first straightening device 100 includes a changing device 110 as an example of a changing means for changing the amount of the roll 106 biting into the roll 104.

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 an arrow in FIGS. 3 and 4. The roll 106 includes a rotating shaft 114, and the rotating shaft 114 is rotatably supported on one end side (upper side in the present embodiment) of the housing 116. The roll 106 is adapted to rotate in the direction of the arrow in FIGS. 3 and 4. In the first straightening device 100, the paper P is sandwiched between the nip portions N of the roll 104 and the roll 106 and conveyed. 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, which enables elastic deformation. Also, for example, the roll 106 is made of metal. As a result, when the roll 106 is pressed against the roll 104, the peripheral surface portion of the roll 104 is elastically deformed in a concave shape, and the roll 106 bites into the roll 104.

The changing device 110 is located on the cam 118 arranged on the opposite side of the roll 106 from the roll 104 (lower side in the vertical direction in the present embodiment) and on the other end side of the housing 116 (lower side in the present embodiment). It includes a cam driven member 120 that is rotatably supported and comes into contact with 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). Further, the cam 118 is pressed against the cam driven member 120 by a pressing mechanism (not shown). The cam driven member 120 is made of a circular roll and is rotatably arranged at a position away from the roll 106. The housing 116 moves in the direction of approaching or leaving the roll 104 (in the present embodiment, the vertical direction indicated by arrows A and B) along a guide (not shown).

In the changing device 110, when the cam 118 rotates, the cam driven member 120 is driven and rotated, and the housing 116 moves in the direction of approaching or leaving the roll 104 (vertical direction in the present embodiment) together with the cam driven member 120. As a result, the amount of the roll 106 biting into the roll 104 is changed. As shown in FIG. 3, when the portion 118A having the smallest radius of the cam 118 is in contact with the cam driven member 120, the amount of the roll 106 biting into the roll 104 is the smallest.

As shown in FIG. 4, when the portion 118B having the largest radius of the cam 118 is in contact with the cam driven member 120, the amount of the roll 106 biting into the roll 104 is the largest. That is, the position of the roll 106 that bites into the roll 104 moves within the range of the arrow C. Note that FIG. 4 exaggerates the bite of the roll 106 into the roll 104 in order to make the configuration easy to understand.

In the present embodiment, when the roll 106 bites into the roll 104, the curved portion of the nip portion N when viewed from the direction of the rotating shaft 112 is configured to be convex upward. In the first straightening device 100, as shown in FIG. 4, when the amount of the roll 106 biting 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 portion 34 shown in FIG. 2, although not shown, the roll 64A bites into the pressure roll 66 via the fixing belt 62, so that the fixing nip NF is curved when viewed from the axial direction of the pressure roll 66. The portion is configured to be convex downward. As a result, as shown in FIG. 2, the paper P tends to curl upward by passing through the fixing nip NF of the fixing portion 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 curl on the upper side because the paper P passes through the fixing nip NF of the fixing portion 34. Further, when the thin paper P passes through the fixing nip NF of the fixing portion 34, the upper curl is likely to occur on the paper P.

Further, as shown in FIG. 4, after fixing, the paper P passes through the nip portion N between the roll 106 and the roll 104 of the straightening portion 108, and the paper P is formed with a lower curl on the opposite side of the fixing portion 34. Therefore, the upper curl generated on the paper P is corrected. In the first straightening device 100, as shown in FIG. 4, when the amount of the roll 106 biting into the roll 104 is the largest, the curl of the paper P is most likely to be straightened.

The cam shaft 122 of the cam 118 is connected to a motor (not shown), and the drive of the motor is controlled by the control unit 70 (see FIG. 1). As shown in FIG. 5, in the changing device 110, when the tip portion P1 of the paper P enters the nip portion N of the roll 106 and the roll 104, the rear end P2 side of the paper P in the transport direction pushes the nip portion N. The amount of the roll 106 biting into the roll 104 is smaller than that when the roll 106 passes through. In other words, the width of the nip portion N between the roll 106 and the roll 104 in the transport 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 tip portion P1 of the paper P plunges into the nip portion N of the roll 106 and the roll 104, the width of the nip portion N is small.

Further, as shown in FIG. 4, in the changing device 110, when the rear end P2 side of the paper P in the transport direction passes through the nip portion N of the roll 106 and the roll 104, the tip portion P1 of the paper P is the nip portion. The amount of the roll 106 biting into the roll 104 is larger than that when passing through N. In other words, the changing device 110 is configured to increase the amount of the roll 106 biting into the roll 104 at a predetermined timing after the tip portion P1 of the paper P has entered the nip portion N between the roll 106 and the roll 104. It is said that. Note that in FIG. 4, paper P is omitted. More specifically, in the changing device 110, the nip portion N when the length of the tip portion P1 of the paper P for reducing the amount of the roll 106 biting into the roll 104 is large when the amount of the roll 106 biting into the roll 104 is large. The length is equal to or greater than the width of (the width of the nip portion N shown in FIG. 4).

Further, the length of the tip portion P1 of the paper P that reduces the amount of the roll 106 biting into the roll 104 is preferably 1/3 or less of the length of the paper P in the transport direction, and is preferably in the transport direction of the paper P. It is more preferably 1/4 or less of the length, and further preferably 1/5 or less of the length of the paper P in the transport direction.

Further, the length of the tip portion P1 of the paper P that reduces the amount of the roll 106 biting into the roll 104 is determined by, for example, providing a sensor for detecting the tip of the paper P on the inlet side of the nip portion N to convey the paper P. And time. Further, for example, when a sensor for detecting the tip of the paper P is provided on the outlet side of the nip portion N, the amount of the roll 106 biting into the roll 104 is kept small, and the tip of the paper P is directly detected by the sensor. The amount of the roll 106 biting into the roll 104 may be increased.

The second straightening device 102 has a straightening portion 138 that straightens the curl generated on the paper P. The straightening portion 138 includes two rolls 130 and 132 arranged apart from each other, an endless belt 134 wound around the rolls 130 and 132, and a pressing roll 136 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 the present embodiment, for example, by transmitting a rotational force to either one of the rolls 130 and 132, the belt 134 orbits in the direction of the arrow, 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 arranged on the upper side of the belt 134, and the curved portion of the contact portion between the belt 134 and the roll 136 when viewed from the axial direction of the roll 136 is configured to be convex downward. ing. As a result, after the paper P passes through the straightening portion 108 of the first straightening device 100, the paper P passes through the contact portion between the belt 134 and the roll 136, so that the paper P passes through the upper side opposite to the straightening portion 108. By making the curl, the lower curl generated on the paper P is corrected.

In the above image forming apparatus 10, as an example, in both the case of forming an image on the front surface of the paper P and the time of forming an image on the back surface of the paper P, the tip portion P1 of the paper P is a roll 106 and a roll 104. When plunging into the nip portion N, the amount of the roll 106 biting into the roll 104 is smaller than when the rear end P2 side of the paper P in the conveying direction passes through the nip portion N (see FIG. 5). ). When the rear end P2 side of the paper P in the transport direction passes through the nip portion N in both the time of forming an image on the front surface of the paper P and the time of forming an image on the back surface of the paper P, the tip of the paper P is formed. The amount of the roll 106 biting into the roll 104 is larger than that when the portion P1 passes through the nip portion N (see FIG. 4).

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

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

As shown in FIG. 1, the toner image transferred on the transfer belt 50 by the image forming unit 12 is transferred onto the paper P by the transfer nip NT. Further, the toner image on the paper P is fixed on the paper P by heating and pressurizing by passing through the fixing nip NF of the fixing portion 34 (see FIG. 2). Although not shown, in the fixing portion 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 is convex downward when viewed from the axial direction of the pressure roll 66. It is configured to be. As a result, the paper P tends to curl upward by passing through the fixing nip NF of the fixing portion 34.

After that, 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 straightening device 100, when the tip portion P1 of the paper P rushes into 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 the roll 106 biting into the roll 104 is smaller than that when the rear end P2 side of the paper P in the conveying direction passes through the nip portion N. Therefore, the tip portion P1 of the paper P easily enters the nip portion N between the roll 106 and the roll 104.

After that, as shown in FIG. 4, in the first straightening device 100, by controlling the rotation of the cam 118 of the changing device 110, when the rear end P2 side of the paper P in the conveying direction passes through the nip portion N, The amount of the roll 106 biting into the roll 104 is made larger than that when the tip portion P1 of the paper P passes through the nip portion N. At this time, the curved portion of the nip portion N of the roll 106 and the roll 104 when viewed from the direction of the rotation shaft 112 is configured to be convex upward, and passes through the nip portion N of the roll 106 and the roll 104. Paper P to be used is easy to make a lower curl. Therefore, when the rear end P2 side of the paper P in the transport direction passes through the nip portion N of the roll 106 and the roll 104, the paper P is formed with a lower curl on the opposite side of the fixing portion 34, so that the paper P is formed at the time of fixing. The upper curl generated on the paper P is corrected.

Further, the paper P passes through the contact portion between the belt 134 and the roll 136 of the second straightening device 102. At that time, the curved portion of the contact portion between the belt 134 and the roll 136 when viewed from the axial direction of the roll 136 is configured to be convex downward. As a result, the upper curl on the side opposite to the straightening portion 108 is formed on the paper P, so that the lower curl generated on the paper P when passing through the straightening portion 108 is corrected.

Here, the curl correction device 200 of the comparative example will be described with reference to FIG. As shown in FIG. 6, in the curl correction device 200 of the comparative example, the amount of the roll 202 biting into the roll 104 is not changed. More specifically, the amount of the roll 202 biting into the roll 104 is set as large as the amount of the roll 106 biting into the roll 104 shown in FIG. Therefore, when the tip portion P1 of the paper P rushes into the nip portion N between the roll 202 and the roll 104, the roll 106 goes into the roll 104 as compared with the amount of the roll 106 biting into the roll 104 shown in FIG. The amount of bite is large. Therefore, when the tip portion P1 of the paper P plunges into the nip portion N between the roll 202 and the roll 104, the tip of the paper P is likely to be broken. In addition, it may cause wrinkles on the paper P.

On the other hand, although not shown, if the amount of the roll 202 biting into the roll 104 is always smaller than the amount of the roll 202 biting into the roll 104 shown in FIG. 6, the curl of the paper P is not sufficiently corrected. There is.

On the other hand, in the present embodiment, as shown in FIG. 5, when the tip portion P1 of the paper P rushes into the nip portion N between the roll 106 and the roll 104, the amount of the roll 106 biting into the roll 104. Is small. Further, as shown in FIG. 4, when the rear end P2 side of the paper P passing through the nip portion N in the transport direction passes through the nip portion N, the tip portion P1 of the paper P passes through the nip portion N. Also increases the amount of the roll 106 biting into the roll 104. Therefore, in the first straightening device 100, the curl of the paper P and the tip breakage of the paper P are both suppressed as compared with the configuration in which the amount of the second rotating body biting into the first rotating body is always the same. NS. Especially in the case of thin paper P, curl of paper P and bending of the tip of paper P are both suppressed. Further, in the first straightening device 100, the occurrence of wrinkles on the paper P is suppressed as compared with the configuration in which the amount of the second rotating body biting into the first rotating body is always the same.

Further, in the first straightening device 100 described above, in the changing device 110, the length of the tip portion P1 of the paper P that reduces the amount of the roll 106 biting into the roll 104 is large, and the amount of the roll 106 biting into the roll 104 is large. The length is longer than the width of the nip portion N (the width of the nip portion N shown in FIG. 4). Therefore, after the tip portion P1 of the paper P has passed through the nip portion N, the amount of the roll 106 biting into the roll 104 becomes large. In the first straightening device 100, when the length of the tip portion of the recording medium that reduces the amount of the second rotating body biting into the first rotating body is large, the amount of the second rotating body biting into the first rotating body is large. Compared with the case where the width is shorter than the width of the nip portion, the tip bending of the paper P is suppressed.

Further, in the image forming apparatus 10, the changing apparatus 110 is on the rear end P2 side in the conveying direction of the paper P passing through the nip portion N between the roll 106 and the roll 104 when forming an image on the back surface of the paper P. The amount of the roll 106 biting into the roll 104 is made larger than that when the tip portion P1 of the paper P passes through the nip portion N (see FIG. 4). Therefore, in the above-mentioned image forming apparatus 10, when the image is formed on the back surface of the paper P, the image is formed on the back surface of the paper P as compared with the configuration in which the amount of the second rotating body biting into the first rotating body is always the same. Occasionally, curling of the paper P and bending of the tip of the paper P are both suppressed.

Further, in the image forming apparatus 10, the changing apparatus 110 is on the rear end P2 side in the conveying direction of the paper P passing through the nip portion N between the roll 106 and the roll 104 when forming an image on the surface of the paper P. The amount of the roll 106 biting into the roll 104 is made larger than that when the tip portion P1 of the paper P passes through the nip portion N (see FIG. 4). Therefore, in the above-mentioned image forming apparatus 10, when the image is formed on the surface of the paper P, the image is formed on the surface of the paper P as compared with the configuration in which the amount of the second rotating body biting into the first rotating body is always the same. Occasionally, curling of the paper P and bending of the tip of the paper P are both suppressed.

Further, the image forming apparatus 10 includes the first straightening device 100 and the second straightening device 102 in order from the upstream side in the transport direction of the paper P, and the first straightening device on the most upstream side in the transport direction of the paper P. In the device 100, the amount of the roll 106 biting into the roll 104 is changed. Therefore, in the image forming apparatus 10, the curl of the paper P is suppressed as compared with the case where the curl correction device is provided on the most downstream side of the plurality of straightening portions arranged along the conveying direction of the paper P. It is compatible with suppressing the tip bending of the paper P.

Further, in the image forming apparatus 10, the first straightening device 100 that suppresses curl (upper curl) in the direction in which the fixing nip NF of the fixing portion 34 becomes convex, and the direction in which the fixing nip NF of the fixing portion 34 becomes convex. A second straightening device 102 that suppresses curl on the opposite side (lower curl) is provided. Therefore, in the image forming apparatus 10, the direction in which the curl (upper curl) in the convex direction is suppressed is more likely to occur on the fixing portion 34 side than in the case where the bite amount of the nip portion is always the same in one straightening portion. The curl of the recording medium is suppressed with respect to the curl of the above, and the tip bending of the recording medium is suppressed.

Further, in the image forming apparatus 10, the first straightening apparatus 100 that suppresses curl (upper curl) in the direction in which the fixing nip NF of the fixing portion 34 becomes convex is arranged on the upstream side in the conveying direction of the paper P. .. Therefore, in the image forming apparatus 10, the curl of the paper P is suppressed against the curl generated on the fixing portion 34 side as compared with the one in which the upstream and downstream of the first straightening apparatus and the second straightening apparatus are reversed. At the same time, folding of the tip of the paper P is suppressed.

<Supplementary explanation>
The image forming apparatus 10 includes the first straightening apparatus 100 and the second straightening apparatus 102, but the present invention is not limited to this configuration and includes one straightening portion for correcting the curl of the paper P. It may be configured, or it may be configured to include three or more straightening portions for straightening the curl of the paper P.

Further, in the image forming apparatus 10, only the first straightening apparatus 100 out of the first straightening apparatus 100 and the second straightening apparatus 102 changes the amount of the roll 106 biting into the roll 104. Is not limited to this configuration. For example, a plurality of straightening portions for correcting the curl of the paper P are provided, and the amount of the second rotating body biting into the first rotating body can be changed in all the straightening portions or two or more straightening portions. When the tip 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 of the paper P in the conveying direction passes through the nip portion N. At that time, the plurality of straightening portions may be configured to alternately straighten the curls of the paper P on the opposite sides along the conveying direction of the paper P, for example.

Further, in the above embodiment, the changing device 110 is provided to change the amount of the roll 106 biting into the roll 104, but the components of the changing device 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. The shape of the cam 118 can also be changed.

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

Further, in the above embodiment, the range for reducing the amount of the roll 106 biting into the roll 104 when the tip portion P1 of the paper P passes through the nip portion N is, for example, switched by detecting the tip of the paper P with a sensor. You may.

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

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 obvious to the trader.

10 Image forming device 12 Image forming unit 18 Transfer roll pair (example of transfer means)
22 Correction mechanism 26 Inversion path 34 Fixing part 62 Fixing belt (an example of heating member)
64A roll (an example of heating member)
66 Pressurized roll (an example of pressurized member)
100 First orthodontic appliance (an example of curl orthodontic appliance)
104 rolls (an example of the first rotating body)
106 rolls (an example of the second rotating body)
108 Orthodontic unit 110 Changing device (example of changing means)
138 Orthodontic part N Nip part NF Fixing nip (Example of fixing part nip)
P paper (an example of recording medium)
P1 tip part P2 rear end

Claims (8)

A first rotating body and a second rotating body which is arranged so as to bite into the first rotating body and rotates with a recording medium sandwiched between nip portions of the first rotating body are provided, and the first rotating body is generated in the recording medium. A straightening part that corrects curls and
When the tip portion of the recording medium in the transport direction passes through the nip portion, the rear end side of the recording medium in the transport direction passes through the nip portion to the first rotating body of the second rotating body. As a means of changing to reduce the amount of bite in
Have a,
In the changing means, the length of the tip portion of the recording medium that reduces the amount of the second rotating body biting into the first rotating body is the amount of the second rotating body biting into the first rotating body. A curl correction device having a length equal to or longer than the width of the nip portion when it is large. A transport means for transporting a recording medium and
An image forming unit that forms an image on the recording medium,
A fixing portion for fixing an image on the recording medium and a fixing portion
The curl correction device according to claim 1, which is provided on the downstream side of the fixing portion in the transport direction of the recording medium.
An image forming apparatus having . The curl correction device according to claim 1 and
An image forming unit that forms an image on the recording medium,
After the recording medium is conveyed to the image forming unit, the front and back sides of the recording medium are inverted and the recording medium is conveyed to the image forming unit.
Have,
In the changing means, when an image is formed on the back surface of the recording medium, when the tip portion of the recording medium in the transport direction passes through the nip portion, the rear end side of the recording medium in the transport direction passes through the nip portion. An image forming apparatus in which the amount of biting of the second rotating body into the first rotating body is smaller than that of the case where the second rotating body is used. In the changing means, when an image is formed on the surface of the recording medium, when the tip portion of the recording medium in the transport direction passes through the nip portion, the rear end side of the recording medium in the transport direction passes through the nip portion. The image forming apparatus according to claim 3, wherein the amount of the second rotating body biting into the first rotating body is smaller than that of the second rotating body. A transport means for transporting a recording medium and
A plurality of straightening portions arranged along the transport direction of the recording medium and correcting curls generated in the recording medium, and a plurality of straightening portions.
Have,
The correction unit on the most upstream side in the transport direction of the recording medium is an image forming device which is the curl correction device according to claim 1. The image forming apparatus according to claim 5, wherein all of the plurality of straightening portions are the curl straightening devices. A transport means for transporting a recording medium and
An image forming unit that forms an image on the recording medium,
A fixing portion for fixing the image on the recording medium by passing through the nip of the heating member and the pressurizing member.
A straightening portion that suppresses curl in the direction in which the nip of the fixing portion is convex, and is a straightening portion that is the curl straightening device according to claim 1.
With other straightening parts that suppress curl on the side opposite to the direction in which the nip of the fixing part becomes convex,
An image forming apparatus having. The image forming apparatus according to claim 7, wherein the one straightening section is arranged on the upstream side in the transport direction of the recording medium.

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