JP2006168940A - Curl correcting device for paper sheet, image forming device and curl correcting device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To automatically cancel correction work for a paper sheet less prone to the development of a curl such as thick paper, to surely correct the curl in humid and thin paper having the high curl, and to highly maintain carrying efficiency of the paper sheet in any cases. <P>SOLUTION: In the curl correcting method for correcting the curl of the paper sheet with the usage of a nip part formed by a rigid roller 71 and an elastic roller 72 confronting the rigid roller 71 and a carrying guide member 77 for guiding the paper sheet on the downstream side of the nip part, the curl is corrected by making a delivery angle from the nip part to a tilt guide part 77a of the carrying guide member 77 steep and twisting the paper sheet to the direction opposite from the curl when the thin paper easily developing the curl is carried, and the carrying resistance of the paper sheet is reduced by making the delivery angle from the nip part to the tilt guide part 77a gentle when the thick paper hard to develop the curl is carried. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a curl correction device for correcting a curl formed on a sheet, for example, used in an image forming apparatus such as a copying machine or a printer.

  For example, in an image forming apparatus such as a printer or a copier using an electrophotographic method, an electrostatic latent image is formed on the surface of an image carrier made of a drum or belt-shaped organic photoreceptor by a known electrophotographic process. Thereafter, the electrostatic latent image is developed with toner to form a toner image. Next, the toner image is transferred to a sheet directly or via an intermediate transfer member, and then the toner image is fixed on the sheet by, for example, a heat fixing mechanism, thereby forming an image. As the heat fixing mechanism, for example, a roller pair composed of a heating roller heated by a heater and a pressure roller covered with an elastic body is provided, and a sheet on which a toner image is transferred passes between the roller pair. By doing so, the unfixed toner image is fixed on the paper.

  The sheet after fixing that has passed through such a heat fixing mechanism tends to bend (curl) in one direction orthogonal to the sheet conveying direction. The curled paper deteriorates the stacking performance of the paper discharge and may greatly reduce the post-processing performance when an additional post-processing device is added. In addition, when images are formed on both sides of a sheet, the curl of the sheet deteriorates the reversing performance and conveyance performance of the sheet, and may adversely affect image formation on the second side. Therefore, a curl correction (correction) apparatus for removing the generated paper curl has been conventionally used.

  As a conventional technique described in the publication, for example, a curling correction device having a metal roller and an elastic roller and an elastic paper guide for guiding is provided on the downstream side of the fixing device, and discharging from a nip portion between the metal roller and the elastic roller. The applicant has proposed a technique for correcting paper curl at an angle (see, for example, Patent Document 1). In addition, there is a technique in which a curl correcting device includes a plurality of driven rollers and changes the hardness of the driven rollers to increase the paper winding angle around the paper discharge roller (see, for example, Patent Document 2). Furthermore, in order to cancel the correction action automatically for paper with little curling, such as thick paper, and to correct the high-humidity thin paper with large curl, etc., a drive such as a torque limiter or one-way clutch is used. A technique is disclosed in which force limiting means is provided and a sheet having high rigidity causes slippage in the drive path by its own rigidity (see, for example, Patent Document 3).

Japanese Patent No. 3049345 (page 3-5, FIG. 1) Japanese Unexamined Patent Publication No. 2001-2226015 (page 4, FIG. 2) JP 2000-272803 A (page 4, FIG. 2)

  FIGS. 7A to 7C are diagrams for explaining a conventional curl correction (correction) apparatus. The curl correcting apparatus shown in FIG. 7A includes a rigid roller 201 for winding the curled paper, and an elastic roller 202 for driving the paper in contact with the rigid roller 201, and the paper curled on the paper guide 203. , The curling of the paper fixed by a fixing device (not shown) is corrected. In the configuration shown in FIG. 7A, the rigid roller 201 is urged toward the elastic roller 202 using the spring member 204. By providing this spring member 204, it is intended to automatically cancel the correction action for paper with less curling, such as thick paper, and to reliably correct thin paper with high humidity and high humidity. Yes. That is, as shown in FIG. 7B, when the thick paper is transported, the rigid roller 201 is lifted by the stiffness of the paper, and the curl correcting device prevents the reverse curling with respect to the thick paper. can do.

  However, as shown in FIG. 7B, when the thick paper is conveyed in the direction of the arrow in the figure, the rigid roller 201 is pushed upward by the stiffness of the thick paper, and the thick paper and the elastic roller 202 are separated. As a result, when only the elastic roller 202 has a driving force and the rigid roller 201 does not have a driving force, the cardboard transport capability is lost, and the sheet transport performance deteriorates. In order to solve such a problem, it is conceivable to increase the spring coefficient of the spring member 204 to make it a strong spring. However, the curling force in the curl correction direction is strengthened, and curling occurring in the reverse direction can be suppressed. become unable. Further, in the structure in which the driving force is given to the rigid roller 201 side, it is necessary to give the driving force to the displacing side, and the mechanism becomes complicated, resulting in an increase in cost. In addition, even with the technique described in Patent Document 3 described above, it is impossible to avoid a decrease in conveying force due to the driving force limiting means.

  In order to solve such a problem, as shown in FIG. 7C, a belt member 205 is provided instead of the elastic roller 202, and the rigid roller 201 is urged in the direction of the belt member 205 by the spring member 204. A method is also conceivable. According to the configuration of FIG. 7C, even when the rigid roller 201 is largely lifted by the strength of the thick paper during the conveyance of the thick paper, the rigid roller 201 and the belt can follow the elastic force of the belt member 205. Contact of the member 205 is maintained. As a result, it is possible to maintain the conveying force even for thick paper with strong stiffness. However, in the belt member 205 shown in FIG. 7C, the belt expands and contracts due to temperature changes, and this belt expansion and contraction is a factor that does not stabilize the curl correction function. In particular, the curl correction device is often provided in the vicinity of the fixing device, and is greatly affected by the heat of the fixing device and conveys a sheet having a relatively high temperature, thereby avoiding deterioration of the function due to the expansion and contraction of the belt. difficult.

  The present invention has been made in order to solve the technical problems as described above, and its purpose is to automatically cancel the curl correction action for a paper with little curling such as a thick paper. However, high-humidity thin paper having a large curl is surely corrected, and in any case, the paper conveyance performance is kept high.

  For this purpose, the present invention provides a curl correction device that is provided in a paper conveyance path and corrects the curl of the paper to be conveyed, and a first conveyance unit that rotates in contact with the paper, and the first conveyance unit. A portion having a lower hardness than the conveyance unit is disposed in pressure contact with the first conveyance unit, and includes a second conveyance unit that rotates in contact with the paper, and either the first conveyance unit or the second conveyance unit One is characterized in that it can move around the other rotation center.

Here, a guide member that is provided on the downstream side of the press-contact portion between the first transport portion and the second transport portion and that transports the paper discharged from the press-contact portion while guiding the paper in the curl correction direction is further provided. It can be characterized by including.
In addition, any one of the rotatable members is arranged on the guide member side by its own weight, and can be moved by utilizing the rigidity force of the paper abutting against the guide member.

Further, the first transport unit and the second transport unit are configured by roller members, and the roller members configuring the first transport unit are rod-shaped members that are continuous in a direction orthogonal to the transport direction of the paper. Can be a feature.
Still further, if an elastic sheet guide is provided for guiding the sheet that has passed through the nip portion between the first conveyance unit and the second conveyance unit toward the first conveyance unit, Even if any one of the second transport unit and the second transport unit moves, it is preferable in that the paper transport performance can be maintained high.

  On the other hand, according to the present invention, in an image forming apparatus having a curl correcting function for correcting curl of a sheet to be conveyed, a first conveying unit that rotates in contact with the conveyed sheet, and the first conveying unit. A portion having a low hardness is disposed in pressure contact with the first transport unit, and rotates in contact with the transported paper, and a nip between the first transport unit and the second transport unit. And a guide member for guiding the curled paper in the curl correction direction, and the position of the nip portion in the paper conveyance direction can be changed. More specifically, the position of the nip portion in the sheet conveyance direction can be configured to be changeable by the rigidity of the sheet conveyed and abutting against the guide member.

Here, any one of the first conveyance unit and the second conveyance unit is configured to be movable with the other rotation center as an axis center, so that the nip portion can be changed. Further, it may be characterized by further comprising a spring member that pulls one of the first transport unit and the second transport unit toward the guide member. According to these configurations, for example, even if any one of the transport units moves, the contact pressure with the other can be maintained within a certain range.
Further, if one side portion is fixed to the guide member and an elastic paper guide is further provided for guiding the paper that has passed through the nip portion toward the first conveyance portion, one of the conveyances is provided. Even when the section is moved, it is preferable in that the sheet can be favorably conveyed toward the guide member.
Furthermore, a carrier for carrying the toner image, a transfer unit for transferring the toner image carried on the carrier to a sheet, and a fixing device for heating and fixing the sheet onto which the toner image has been transferred by the transfer unit are further provided. The nip portion is provided on the downstream side of the fixing device in the paper conveyance direction, and the first conveyance portion is disposed so as to contact the paper from the curl convex portion side of the paper via the fixing device. It can be.

  From another point of view, the present invention relates to a nip portion formed by a rigid member and an elastic member facing the rigid member in the paper conveyance path, and a paper guide for guiding the paper downstream of the nip portion. Is a curl correction method that corrects paper curl, and when thin paper that is easily curled is transported, the discharge angle from the nip to the paper guide is tight and the paper is the opposite of curl. The curling is corrected by twisting in the direction, and when thick paper that is difficult to curl is transported, the discharge angle from the nip to the paper guide is relaxed to reduce the transport resistance by the paper guide. Can do.

  Here, when the thick paper is conveyed, the discharge angle can be made gentle by moving the nip portion away from the paper guide. More specifically, the nip portion can be moved away from the paper guide using the rigidity of cardboard.

  According to the curl correcting device and the image forming apparatus of the present invention, the curl correcting (correcting) action is automatically canceled for the paper with little curling such as thick paper, and the thin paper having a large curl is surely corrected. can do. Even when such a function is realized, it is possible to maintain high sheet conveyance performance.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
[Embodiment 1]
FIG. 1 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. The image forming apparatus shown in FIG. 1 is a so-called tandem type image forming apparatus, for example, a plurality of image forming units 10 (10Y, 10M, 10C, 10K) on which toner images of respective color components are formed by electrophotography. The intermediate transfer belt 15 for sequentially transferring (primary transfer) and holding each color component toner image formed by each image forming unit 10, and the superimposed image transferred on the intermediate transfer belt 15 on a sheet as a transfer material A secondary transfer device 20 that performs batch transfer (secondary transfer) and a fixing device 40 that fixes the secondary transferred image on a sheet are provided. Further, a curl correcting device 70 which is a characteristic configuration in the present embodiment is provided on the downstream side of the fixing device 40 in the sheet conveyance direction.

  Each image forming unit 10 (10Y, 10M, 10C, 10K) has a charger 12 for charging the photosensitive drums 11 around the photosensitive drums 11 rotating in the direction of arrow A, and the photosensitive drums 11 on the photosensitive drums 11. A laser exposure device 13 for writing an electrostatic latent image on the photosensitive drum (exposure beam is indicated by a symbol Bm in the figure), each color component toner is accommodated, and the electrostatic latent image on the photosensitive drum 11 is visualized with toner. For electrophotography, such as a developing device 14, a primary transfer roller 16 for transferring each color component toner image formed on the photosensitive drum 11 to the intermediate transfer belt 15, and a drum cleaner 17 for removing residual toner on the photosensitive drum 11. A device is provided. Each image forming unit 10 is arranged in order of yellow (Y color), magenta (M color), cyan (C color), and black (K color) from the upstream side of the intermediate transfer belt 15.

Further, the intermediate transfer belt 15 is configured to be rotatable in the B direction shown in the drawing by various rollers. As these various rollers, a driving roller 31 that is driven by a motor (not shown) to rotate the intermediate transfer belt 15 and has a function of giving a constant tension to the intermediate transfer belt 15 and preventing meandering of the intermediate transfer belt 15. A tension roller 32 and an idle roller 33 that supports the intermediate transfer belt 15 are provided. A belt cleaner 35 for cleaning the surface of the intermediate transfer belt 15 after the secondary transfer is provided on the downstream side of the secondary transfer device 20.
The secondary transfer device 20 includes a secondary transfer roller 21 disposed in pressure contact with the toner image carrying surface side of the intermediate transfer belt 15 and a counter electrode of the secondary transfer roller 21 disposed on the back surface side of the intermediate transfer belt 15. A backup roller 22 is provided, and a metal power supply roller 23 to which a secondary transfer bias is stably applied is disposed in contact with the backup roller 22.

  The fixing device 40 includes a heat roller 41 provided with a heater therein and heated, and a pressure roller 42 provided to face the heat roller 41. Furthermore, in the present embodiment, as a paper transport system, a paper tray 50 that stores paper, a pickup roller 51 that picks up and transports the paper stacked in the paper tray 50 at a predetermined timing, and a pickup roller 51 And a transport roller 52 for transporting the fed paper. Further, a transport chute 53 that feeds the paper transported by the transport roller 52 to a secondary transfer position by the secondary transfer device 20 and a transport belt 54 that transports the paper after the secondary transfer to the fixing device 40 are provided. . Further, a discharge path 55 for discharging the paper on which the image is formed, a reversing mechanism unit 56 for inverting the paper after fixing, and a double-sided transport path for transporting the paper on which the image is formed on one side for duplex printing. 57.

Next, the curl correction device 70 to which this exemplary embodiment is applied will be described in detail.
FIG. 2 is a diagram for explaining a schematic configuration of the curl correcting device 70. The curl correcting device 70 is provided on the downstream side of the fixing device 40 in the sheet conveyance direction, and is positioned below the reversing gate 58 that forms the discharge path 55 in the overall configuration of the image forming apparatus. A reversing mechanism 56 shown in FIG. 1 is provided on the downstream side of the curl correcting device 70 in the paper conveyance direction.

  The curl correcting device 70 includes a rigid roller 71 formed of a long metal rod-like member, and an elastic roller 72 that contacts the rigid roller 71 so as to face the rigid roller 71. The elastic roller 72 rotates around a drive shaft 72a, and a plurality of elastic roller members (72b described later) are provided in a skewered manner with a predetermined gap on the drive shaft 72a. The rigid roller 71 is configured to rotate following the rotational drive of the elastic roller 72 and to be rotatable (movable) about the rotation center of the elastic roller 72 (the center of the drive shaft 72a). . That is, the elastic roller 72 operates so as to revolve around the axis of rotation. This revolution operation is performed in the range of α to 6 ° at an angle α from the horizontal shown in FIG. In addition, the curl correcting device 70 is provided with a conveyance guide member 77 on the downstream side of the contact portion between the rigid roller 71 and the elastic roller 72. The transport guide member 77 includes an inclined guide portion 77 a for determining the discharge angle of the sheet from the contact portion in the vicinity of the downstream side of the contact portion between the rigid roller 71 and the elastic roller 72.

  The paper pressed and heat-fixed by the heat roller 41 and the pressure roller 42 of the fixing device 40 is curled to the opposite side of the image surface (the low pressure roller 42 side), particularly in the case of thin paper or high-humidity paper, At the time of discharging from the fixing device 40, as shown in FIG. The curled paper is conveyed to the curl correcting device 70 and passes through the contact portion between the rigid roller 71 and the elastic roller 72. At this time, the convex upper surface of the curled paper is conveyed along the metal roller surface of the rigid roller 71 having a small curvature in the direction opposite to the curling direction of the paper, and is curved in the direction opposite to the initial curling direction. Be energized by. Further, the sheet that has passed through the contact portion and is urged in the direction opposite to the curl direction by the rigid roller 71 is further strongly urged in the direction opposite to the curl direction by the inclined guide portion 77a. By these actions, the curled sheet discharged from the fixing device 40 is subjected to curl correction.

  On the other hand, in the case of thick paper and low-humidity paper, unlike the above-described thin paper and high-humidity paper, the curl of the paper discharged from the fixing device 40 is small. For this reason, there is little need for curl correction for cardboard and low-humidity paper. On the other hand, forced curl correction results in curling in the reverse direction, which adversely affects paper conveyance performance. End up. Therefore, in the curl correcting device 70 to which this exemplary embodiment is applied, as described above, the rigid roller 71 is configured to be movable about the rotation center of the elastic roller 72 as an axis center, so that the stiffness of the paper ( The degree of curl correction can be naturally reduced according to the degree of rigidity).

  FIGS. 3A and 3B are diagrams showing a configuration of a curl correcting device 70 for allowing the rigid roller 71 to move about the rotation center of the elastic roller 72 as an axis center. The elastic roller 72 is provided with a plurality of elastic roller members 72b in a skewered manner with a predetermined gap with respect to the drive shaft 72a. Further, as shown in FIGS. 3A and 3B, the rigid roller 71 is supported by a bending portion of a rigid roller support member 73 formed of a U-shaped sheet metal bending member or the like via a bearing 74. ing. Both end portions on the distal end side of the bent portion of the rigid roller support member 73 are connected to the drive shaft 72a via bearings 75. By connecting the rigid roller support member 73 to the drive shaft 72a via the bearing 75, the rigid roller support member 73 can rotate about the drive shaft 72a. As a result, the rigid roller 71 in contact with the elastic roller member 72b of the elastic roller 72 can move around the rotation center of the elastic roller 72, that is, can rotate around the elastic roller member 72b.

  The curl correcting device 70 is provided with a lower positioning member 76 of the rigid roller support member 73 at a position below the portion where the rigid roller support member 73 moves. When no force is applied from the outside, the rigid roller support member 73 is lowered by its own weight. However, the rigid roller support member 73 comes into contact with the lower positioning member 76, and the position when the rigid roller support member 73 is lowered is determined. Can be determined. Further, an upper positioning member (not shown) is provided above the portion where the rigid roller support member 73 moves and contacts. With the lower positioning member 76 and the upper positioning member (not shown), the angle α from the horizontal shown in FIG. 2 can be determined.

  4A and 4B are views for explaining the state of the sheet when the sheet is conveyed to the curl correcting device 70. FIG. 4A shows a case where thin paper having curls is conveyed, and FIG. 4B shows a case where thick paper which is hardly affected by curls is conveyed. As shown in FIG. 4A, when the paper to be transported is a thin paper, the paper that has reached the inclined guide portion 77a of the transport guide member 77 through the nip portion between the rigid roller 71 and the elastic roller 72 is The stiffness roller 71 cannot be lifted because the stiffness of the paper is weak (the stiffness is low). In other words, due to the weight of the rotating member including the rigid roller support member 73, the downward force overcomes the rigidity of the sheet, and the rigid roller 71 remains maintained downward. Therefore, the conveyed paper abuts on the inclined guide portion 77a from the nip portion with a large entry angle (discharge angle) and moves as it is along the inclined guide portion 77a. As a result, the sheet is twisted in the direction opposite to the direction of curl generated by the fixing device 40, and the curl correction function works. For example, when thin paper having a weight of about 50 gsm to 120 gsm is transported on a basis weight, the weights of the rigid roller 71 and the rigid roller support member 73 can be determined so as to remain below the figure.

  On the other hand, as shown in FIG. 4B, when the sheet to be conveyed is a thick sheet, the sheet reaches the inclined guide portion 77a of the conveyance guide member 77 through the nip portion between the rigid roller 71 and the elastic roller 72. Has a function of lifting the rigid roller 71 in accordance with the stiffness (rigidity) of the paper. That is, the rigid roller 71 is moved in the direction in which the conveyance resistance is small. When the rigid roller 71 is lifted, the conveyed paper comes into contact with the inclined guide portion 77a at a small (gradual) entry angle (discharge angle), and the entry of the paper becomes smooth. Here, as described above, generally, cardboard has little curl, and if curl correction is performed as it is, curl is generated in the curl correction direction. However, according to the present embodiment, it is possible to reduce the curl correction function according to the stiffness of the paper, and prevent (lower) the conveyance resistance from increasing with respect to the curl strength of the paper. Therefore, it is possible to reduce the trouble of curling paper (particularly thick paper) in the reverse direction. Further, in this embodiment, since the rigid roller 71 is allowed to move up and down (revolution operation) with the rotation center of the elastic roller 72 as a central axis, the curl correction function is provided according to the strength of the paper. Even if it is lowered, the contact between the elastic roller 72 on the driving side and the paper can be maintained. As a result, it is possible to maintain the paper conveyance performance even if the curl correction function is lowered. The moving operation of the rigid roller 71 can be configured to move upward when, for example, thick paper of about 300 gsm is transported on a basis weight.

In this embodiment, the curl correcting device 70 is provided with a paper guide having elasticity in order to maintain high conveyance performance even when the rigid roller 71 moves up and down.
5A and 5B show an example in which a paper guide 78 having elasticity is provided in the curl correcting device 70. FIG. As shown in FIG. 5A, the paper guide 78 is formed by cutting out a mylar film, for example. Further, as shown in FIG. 5B, the paper guide 78 has one side portion on the downstream side in the paper conveyance direction adhered to the conveyance guide member 77 with a double-sided tape or the like, for example. The leading end (notch leading end) of the sheet guide 78 on the upstream side in the sheet conveying direction is positioned so as to be inside the outer periphery of the elastic roller 72 that does not move. The paper guide 78 guides the paper that has passed through the nip portion between the rigid roller 71 and the elastic roller 72 toward the rigid roller. The sheet that has passed through the nip portion between the rigid roller 71 and the elastic roller 72 moves along the sheet guide 78 having elasticity, and is further conveyed to the downstream side. Even when the rigid roller 71 moves, the sheet does not deviate from the sheet guide 78, and the sheet conveyance performance can be maintained high.

[Embodiment 2]
In the first embodiment, the structure in which the rigid roller 71 is moved up and down by the own weight of the rigid roller 71 and the rigid roller support member 73 and the strength of the paper in the conveyance path that moves from the upper side to the lower side has been described. In the second embodiment, a biasing member is separately provided on the rigid roller 71, and a structure that does not depend on its own weight is employed. In addition, the same code | symbol is used about the function similar to Embodiment 1, and the detailed description is abbreviate | omitted here.

  FIG. 6 is a diagram for explaining the curl correcting apparatus 100 according to the second embodiment. The curl correcting device 100 shown in FIG. 6 includes a rigid roller 101, an elastic roller 102, an upstream guide 103, and a downstream guide 104. In addition, a spring member 105 that pulls the rigid roller 101 downstream in the paper conveyance direction (S direction) is provided. The elastic roller 102 is driven with the drive shaft 107 as a central axis, and the rigid roller 101 is configured to be driven and rotated by the elastic roller 102. In order to correct the curl of the paper curled downward (upstream side guide 103 side) so that the downstream guide 104 is convex upward, the downstream guide 104 extends from the nip portion between the rigid roller 101 and the elastic roller 102 in the curl correction direction. In order to bend the paper, it is configured to tilt toward the rigid roller 101. In FIG. 6, the downstream guide 104 is formed so that the sheet is directed upward. The spring constant of the spring member 105 is pulled in the S direction in the figure when, for example, 50 gsm to 120 gsm of thin paper is transported in US tsubo, and moves most in the P direction when, for example, a thick paper of about 300 gsm is transported in US tsubo A value with a value that can be used is selected. Further, the movable restriction range by the spring member 105 is determined so that the rigid roller 101 can be positioned with respect to the elastic roller 102 in a state where a predetermined range of pressing force is always maintained. In the example shown in FIG. 6, a tensile force is acting in the substantially tangential direction of the elastic roller 102.

  If the sheet to be conveyed is a thin sheet such as a thin sheet, the tensile force of the spring member 105 cannot be pushed back by the rigidity of the sheet. Therefore, the rigid roller 101 is pulled in the S direction in the figure, and the sheet discharged from the nip portion between the rigid roller 101 and the elastic roller 102 contacts the downstream guide 104 at a large abutting angle. . When the abutting angle is large, the sheet conveyed from the nip portion is pushed in a downward convex direction and is largely twisted to sufficiently correct the curl after fixing. On the other hand, when the conveyed sheet is a stiff sheet such as a thick sheet, the rigidity force (reaction force) of the sheet contacting the downstream guide 104 appropriately cancels the tensile force of the spring member 105, and the rigidity The roller 101 is pushed back in the P direction. As a result, the paper discharged from the nip portion between the rigid roller 101 and the elastic roller 102 moves away from the downstream guide 104, and the discharge angle after the nip becomes gentle. Therefore, curling in the reverse direction can be suppressed without increasing the conveyance resistance.

  According to the second embodiment, even when the paper conveyance direction in the curl correction apparatus is not adjusted by its own weight as in the first embodiment, such as in the substantially horizontal direction, the strength (reaction force) of the paper is low. It is possible to control the curl correction function according to the above. Further, even when the correction function is controlled, the contact between the elastic roller 102 on the driving side and the paper can be maintained. As a result, it is possible to maintain the paper conveyance performance even if the curl correction function is lowered.

  As described above in detail, according to the first and second embodiments, high-humidity thin paper with large curl is surely corrected (corrected), and paper with less curling such as thick paper is used. Can automatically cancel the curl correction (correction) action. Further, even when this canceling action is performed, it is possible to maintain high sheet conveyance performance. Furthermore, whether or not the curl correction (correction) action is canceled uses the rigidity of the paper, so it is possible to easily configure the curl correction device and reduce the product cost of the image forming apparatus. It becomes.

  In the first and second embodiments, the elastic rollers 72 and 102 are driven, and the rigid rollers 71 and 101 on the driven side are configured to be swingable or movable. However, by changing these configurations, it is also possible to determine a transport unit that can be moved. That is, it is possible to configure the rigid roller to be the driving side by reversing the driving side and the driven side, and to move the elastic roller that is the driven side that is reversed. Even in such a configuration, when thin paper that is likely to curl is conveyed, curling is performed by twisting the paper in the opposite direction to the curl by tightening the discharge angle from the nip portion to the paper guide. When thick paper that is difficult to curl is transported, the discharge angle from the nip to the paper guide can be relaxed to reduce the transport resistance by the paper guide, and the same effect as described above can be obtained. Can do.

1 is a diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. It is a figure for demonstrating schematic structure of a curl correction apparatus. (a), (b) is the figure which showed the structure of the curl correction apparatus for enabling a rigid roller to move centering | focusing on the rotation center of an elastic roller. (a), (b) is a figure for demonstrating the state of a paper when a paper is conveyed by the curl correction apparatus. (a), (b) is the figure which showed the example which provided the paper guide which has elasticity in the curl correction apparatus. FIG. 6 is a diagram for explaining a curl correction apparatus according to a second embodiment. (a)-(c) is a figure for demonstrating the conventional curl correction (correction) apparatus.

Explanation of symbols

DESCRIPTION OF SYMBOLS 40 ... Fixing device, 41 ... Heat roller, 42 ... Pressure roller, 70 ... Curl correction device, 71 ... Rigid roller, 72 ... Elastic roller, 72a ... Drive shaft, 72b ... Elastic roller member, 73 ... Rigid roller support member, 76 DESCRIPTION OF SYMBOLS Lower positioning member, 77 ... Conveyance guide member, 77a ... Inclination guide part, 78 ... Paper guide, 100 ... Curl correction device, 101 ... Rigid roller, 102 ... Elastic roller, 104 ... Downstream guide, 105 ... Spring member, 107 ... Drive shaft

Claims (14)

In a curl correction device that is provided in a paper conveyance path and corrects curl of a conveyed paper,
A first transport unit that rotates in contact with the paper;
A portion having a lower hardness than the first transport unit is disposed in pressure contact with the first transport unit and includes a second transport unit that rotates in contact with the paper;
Either one of the first transport unit and the second transport unit can move around the other rotation center as an axis center.   And a guide member that is provided on a downstream side of the press contact portion between the first transport portion and the second transport portion and transports the paper discharged from the press contact portion in a curl correction direction. Item 4. The curl correcting apparatus according to item 1.   3. The curl correcting device according to claim 2, wherein one of the rotatable members is disposed on the guide member side by its own weight and moves by utilizing a rigidity force of a sheet abutting on the guide member. .   The first conveyance unit and the second conveyance unit are configured by roller members, and the roller member configuring the first conveyance unit is a rod-like member that is continuous in a direction orthogonal to the sheet conveyance direction. The curl correcting apparatus according to claim 1, wherein   The elastic paper guide for guiding the paper that has passed through the nip portion between the first transport unit and the second transport unit toward the first transport unit. Curl correction device. In an image forming apparatus provided with a curl correcting function for correcting curl of conveyed paper,
A first transport unit that rotates in contact with the transported paper;
A second conveyance unit that is disposed in pressure contact with the first conveyance unit and has a lower hardness than the first conveyance unit, and rotates in contact with the conveyed paper;
A guide member that is provided on the downstream side in the paper conveyance direction of the nip portion where the first conveyance unit and the second conveyance unit abut, and guides the curled paper in the curl correction direction;
An image forming apparatus, wherein the position of the nip portion in the sheet conveyance direction is changeable.   The image forming apparatus according to claim 6, wherein the position of the nip portion in the sheet conveyance direction is configured to be changed by a rigidity force of the sheet conveyed and abutting against the guide member.   One of the first transport unit and the second transport unit is configured to be movable about the other rotation center as an axis center so that the nip portion can be changed. Item 7. The image forming apparatus according to Item 6.   The image forming apparatus according to claim 6, further comprising a spring member that pulls one of the first transport unit and the second transport unit toward the guide member.   The image forming apparatus according to claim 6, further comprising: an elastic paper guide having one side fixed to the guide member and guiding the paper that has passed through the nip portion toward the first transport unit. apparatus. A carrier carrying a toner image;
A transfer unit for transferring the toner image carried on the carrier to a sheet;
A fixing device that heat-fixes the paper on which the toner image has been transferred by the transfer unit;
The nip portion is provided on the downstream side of the fixing device in the sheet conveying direction,
The image forming apparatus according to claim 6, wherein the first transport unit is disposed so as to contact the paper from a curl convex portion side of the paper passing through the fixing device. Using a nip portion formed by a rigid member and an elastic member facing the rigid member in the paper conveyance path, and a paper guide for guiding the paper downstream of the nip portion, the paper curl is corrected. A curl correction method,
When thin paper that is likely to curl is conveyed, the curl is corrected by twisting the paper in the opposite direction to the curl by tightly adjusting the discharge angle from the nip portion to the paper guide,
A curl correcting method, wherein when thick paper that is not easily curled is transported, a discharge angle from the nip portion to the paper guide is relaxed to reduce transport resistance by the paper guide.   13. The curl correction method according to claim 12, wherein when the thick paper is conveyed, the discharge angle is relaxed by moving the nip portion in a direction away from the paper guide.   The curl correcting method according to claim 13, wherein the nip portion is moved away from the paper guide by using the rigidity of the thick paper.

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