JP2016117561A - Recording medium conveyance device and inkjet type image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To properly correct a curl generated in a recording medium when conveying the recording medium with front and rear surfaces reversed.SOLUTION: A printer 1 comprises: a first conveyance path 14 for conveying a sheet P in an image formation part 13; a second conveyance path 28 for conveying the sheet P having passed through the first conveyance path 14 to the outside; a third conveyance path 35 provided branching from the second conveyance path 28 for re-conveying the sheet P having passed through the first conveyance path 14 to the first conveyance path 14 by reversing the sheet P for double-sided printing; and a reversing unit 40 which reverses the front and rear surfaces of the sheet P in the third conveyance path 35. The reversing unit 40 includes a curl correction part 42 performing curl correction processing before the sheet P is re-conveyed to the first conveyance path 14. The curl correction part 42 includes a nip formation section 43 which holds the rear end of the sheet P at the time of entering the third conveyance path 35, and a flap 44 which curves the second surface opposite to the first surface on which an image is formed in the image formation part 13 on the rear end of the sheet P into a protrusion shape with a prescribed curl correction force.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a recording medium conveyance device capable of reversing and conveying a recording medium for duplex printing, and an ink jet image forming apparatus including the recording medium conveyance device.

  Conventionally, in an inkjet image forming apparatus, for example, water-based ink is ejected onto a sheet to form an image. However, the ink may be distorted, that is, curled (see Non-Patent Document 1). ). Here, the distortion caused by ink wetting is called primary curl, and the distortion caused by ink drying is called secondary curl. The primary curl and the secondary curl have opposite curl directions, and the primary curl occurs and disappears within a few seconds immediately after printing, whereas the secondary curl occurs slowly over several seconds to several days after printing. . Therefore, an image forming apparatus that removes these curls has been proposed.

  For example, in the image forming apparatus described in Patent Document 1, a curling unit that curls a sheet in a predetermined direction, for example, in a direction opposite to the primary curl, is arranged upstream of the sheet conveyance direction in an inkjet image forming unit. Thus, unnecessary ink does not adhere to the leading edge of the sheet. The curling means is configured to take two states, that is, a pressure contact state where the two rotating bodies curl the sheet, and a separated state where the two rotating members are separated from each other.

  Further, in the image forming apparatus described in Patent Document 2, the liquid droplets are applied to the recording medium in a state where at least a part of the recording medium on which the image formation by the recording head that discharges the liquid droplets of recording liquid is completed is restrained from above and below. The recording medium is provided with a means for performing a paper discharge operation after waiting for the recording medium for a curling suppression waiting time until it becomes difficult for the recording medium to curl due to the landing of the recording medium, and configured to reduce curling. Has been.

JP 2002-020015 A JP 2006-082546 A

Water-based inkjet ink suitable for plain paper printing (KONICA MINOLTA TECHNOLOGY REPORT VOL.4 (2007)) http://www.konicaminolta.jp/about/research/technology_report/2007/pdf/treatise_003.pdf

  In the image forming apparatus, the image forming unit forms an image on one side of the sheet (recording medium) (printing the first side), and then reverses the sheet and transports it again to the image forming unit. Double-sided printing (double-sided printing) for forming an image on the side (second-side printing) is possible. In the ink jet type image forming apparatus, when double-sided printing is performed, the floating of the sheet caused by the primary curl as described above becomes a problem. The primary curl in which the printing surface of the paper extends after the first printing is curled in the direction of the ink jet head when the second printing is performed. For this reason, the primary curl portion of the paper easily collides with the ink jet head, and the paper may become dirty or paper jam may occur.

  In the above Patent Document 1 and Patent Document 2, the curl removing means is described. However, the primary curl of the water-based ink is very large. In particular, when a large amount of ink is ejected onto a sheet in order to increase the print density, the patent With the curl removing means described in Document 1 and Patent Document 2, curl removal may be insufficient. Further, when a standby time is provided as in Patent Document 2, there is a problem that the printing processing speed is remarkably reduced.

  In view of the above circumstances, an object of the present invention is to appropriately correct a curl generated on a recording medium when the recording medium is conveyed with its front and back reversed.

  The recording medium transport apparatus of the present invention includes a first transport path for transporting the recording medium in an image forming unit that forms an image on the recording medium, and a first transport path for transporting the recording medium that has passed through the first transport path to the outside. A second transport path, a third transport path that is branched from the second transport path and re-transports the recording medium that has passed through the first transport path to the first transport path for duplex printing; A reversing unit that reverses the recording medium in the third transport path, and the reversing unit curls before re-transporting the recording medium that has passed through the first transport path to the first transport path. A curl correction unit for performing a correction process, wherein the curl correction unit holds a rear end when the recording medium enters the third conveyance path, and forms the image at the rear end of the recording medium. The surface opposite the surface on which the image is formed, Characterized in that it comprises a curved portion curving convexly at a constant curl correcting power.

  The recording medium conveying device described above may be provided in an ink jet image forming apparatus.

  According to the present invention, it is possible to appropriately correct curl generated on a recording medium when the recording medium is conveyed with its front and back reversed.

1 is a cross-sectional view illustrating a printer according to an embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating a distance measuring sensor that measures a primary curl amount in the printer according to the embodiment of the present invention. FIG. 3 is a cross-sectional view illustrating an actuator that measures a primary curl amount in a printer according to an embodiment of the present invention. 6 is a graph showing time changes in braking time and acceleration time and curl correction force when paper conveyance in a nip forming unit is performed at a constant acceleration / deceleration in a printer according to another embodiment of the present invention. In the printer according to another embodiment of the present invention, a graph showing the braking time and acceleration time and the time change of the curl correction force when the paper conveyance in the nip forming portion is performed with a long conveyance time at the minimum speed. is there. It is sectional drawing which shows the printer which concerns on other embodiment of this invention.

  First, the overall configuration of an inkjet color printer 1 (hereinafter referred to as “printer 1”) as an inkjet image forming apparatus will be described with reference to FIG. Hereinafter, the front side in FIG. 1 is defined as the front side (front side) of the printer 1. The printer 1 is equipped with a suction suction belt paper transport system.

  The printer 1 includes a box-shaped printer main body 2 as an apparatus main body. A paper feed cassette 4 for containing paper P (recording medium) is housed in the lower part of the printer main body 2. A first paper feed path 5 for paper P is provided at the lower right of the printer main body 2. A paper feed roller 6 is provided in the vicinity of the paper feed cassette 4 at the upstream end of the first paper feed path 5, and a plurality of transports are provided downstream of the paper feed roller 6 in the paper feed direction in the first paper feed path 5. A roller 7 is provided, and a registration roller 8 is provided at the downstream end of the first paper feed path 5.

  Further, a manual feed tray (not shown) is provided outside the right side surface of the printer main body 2, and a second paper feed path 10 is provided near the right center portion of the printer main body 2 on the left side of the manual feed tray. . A paper feed roller 11 is provided in the vicinity of the manual feed tray at the upstream end of the second paper feed path 10, and a transport roller 12 is provided downstream of the paper feed roller 11 in the paper feed direction in the second paper feed path 10. The downstream end portion of the second paper feed path 10 joins the downstream portion of the first paper feed path 5 immediately before the registration roller 8.

  An image forming unit 13 is provided on the left side of the registration roller 8 at the center of the printer main body 2, and a first conveyance path 14 with the horizontal direction as the conveyance direction is provided on the left side of the registration roller 8. Is provided continuously. In the present embodiment, the conveyance direction of the first conveyance path 14 is a direction from the left side (the sheet feeding side including the first sheet feeding path 5 and the second sheet feeding path 10) to the right side (the side opposite to the sheet feeding side). It is. In the image forming unit 13, a first belt conveyance unit 15 that conveys the paper P sent from the registration roller 8 along the first conveyance path 14 is disposed below the first conveyance path 14. Further, the recording unit 16 is disposed above the first conveyance path 14 so as to face the first belt conveyance unit 15, that is, the recording unit 16 faces the first belt conveyance unit 15 across the first conveyance path 14. Be placed.

  The first belt conveyance unit 15 includes a plurality of rollers 17 that are spaced apart in the left-right direction, and an endless conveyance belt 18 that is wound around these rollers 17. A suction device 20 is disposed between the plurality of rollers 17 so as to be surrounded by the conveyance belt 18.

  The transport belt 18 has a plurality of through holes (not shown) penetrating in the thickness direction (up and down direction), and the suction device 20 passes through the through holes from the first transport path 14 side of the transport belt 18. The air can be sucked.

  In the recording unit 16, four recording heads 25 (25K, 25C, 25M, and 25Y) corresponding to ink colors (black (K), cyan (C), magenta (M), and yellow (Y)) are the first. They are arranged in this order in the transport direction of the paper P in the transport path 14. Hereinafter, the symbols “K”, “C”, “M”, and “Y” are omitted except for the case of specifying the color. A plurality of nozzle holes (not shown) are opened on the lower surface of each recording head 25 so as to face the upper surface of the conveyance belt 18. An ink container (not shown) corresponding to each color of ink is provided on the upper portion of the printer main body 2 and connected to the recording head 25, and the ink stored in each ink container is supplied to each recording head 25. It is configured to supply.

  Furthermore, a second conveyance path 28 is provided continuously from the left side of the image forming unit 13 toward the upper left side of the printer main body 2 on the left side of the first conveyance path 14 at the center of the printer main body 2. Below the second conveyance path 28, a second belt conveyance unit 30 is disposed on the left side of the first belt conveyance unit 15, and the sheet P sent out from the first conveyance path 14 by the first belt conveyance unit 15 is second. It is configured to transport along the transport path 28. A plurality of transport rollers 31 are provided in the second transport path 28, and a discharge roller 32 that discharges the paper P is provided in the downstream portion of the second transport path 28. The downstream end of the second transport path 28 is continuous with a paper discharge port 33 that is opened at the upper left surface of the printer body 2, and a paper discharge tray 34 is provided outside the paper discharge port 33. The midstream portion of the second transport path 28 branches to the third transport path 35.

  Similar to the first belt conveyance unit 15, the second belt conveyance unit 30 includes a plurality of rollers 36 that are spaced apart from each other, and an endless conveyance belt 37 that is wound around these rollers 36. Note that a drying device (not shown) may be provided in the vicinity of the second belt conveyance unit 30 in order to dry the ink on the printing surface of the paper P conveyed through the second conveyance path 28.

  The third transport path 35 forms an image on one side of the paper P by the image forming unit 13 when performing double-sided printing (double-sided printing), and then prints an image on the other side of the paper P. This is a double-sided circulation conveyance path that reverses the paper P and re-conveys it to the image forming unit 13 for formation (second-side printing). The third conveyance path 35 extends from the midstream portion of the second conveyance path 28 to the right side through the upper portion of the printer main body 2, and further extends to the right center portion of the printer main body 2. A plurality of transport rollers 38 are provided in the third transport path 35, and a reversing unit 40 is provided in the middle part of the third transport path 35. The downstream end portion of the third conveyance path 35 joins the downstream portion of the first paper feed path 5 immediately before the registration roller 8.

  The reversing unit 40 includes a reversing path 41 branched from the third transport path 35, and a curl correcting unit 42 is provided in the reversing path 41. The curl correction unit 42 includes a nip forming portion 43 disposed on the upstream side of the reversing path 41 and a flap 44 (curved portion) disposed on the downstream side of the nip forming portion 43.

  The curl correction unit 42 corrects the primary curl of the paper P with a predetermined curl correction force (curl correction amount), and the curl correction force of the curl correction unit 42 can be adjusted by the control unit 3 including a CPU or the like. Thus, the control unit 3 determines the amount of primary curl generated on the paper P by the image formation, the type of the paper P at the time of image formation, the image pattern formed on the paper P, the printing rate of the image to be formed, and the image formation The curl correction force is adjusted for each printing according to the image quality at the time and the temperature and humidity (or water vapor amount) in the vicinity of the paper feed cassette 4 inside the printer main body 2.

  The primary curl amount may be predicted by the control unit 3 by a predetermined calculation based on the above-described paper type, image pattern, printing rate, image quality, temperature, humidity, and printing speed, or a distance measuring sensor or actuator You may detect with displacement sensors, such as (pressure sensor). Thereby, while detecting the primary curl amount with a simple configuration, the control unit 3 can increase the curl correction force of the curl correction unit 42 as the predicted or detected primary curl amount increases. It is desirable that the control unit 3 controls the curl correction force according to the primary curl amount of the paper P so that the curl correction is not excessive. The prediction of the primary curl amount will be described later. The displacement sensor is installed on the second conveyance path 28 or the third conveyance path 35 between the recording unit 16 and the curl correction unit 42.

  When the distance sensor 50 as shown in FIG. 2 is used as the displacement sensor, the distance sensor 50 includes a light emitting unit 51, a light receiving unit 52, and a signal processing unit 53. Is detected by the light receiving unit 52, the signal processing unit 53 measures the distance between the paper P and the distance measuring sensor 50 according to the detection result, and sends the measurement result to the control unit 3. . The controller 3 determines the primary curl amount according to the measurement result. As shown in FIG. 2, the position of the detection light L in the light receiving unit 52 varies depending on the magnitude of the primary curl amount.

  When the actuator 54 as shown in FIGS. 3A and 3B is used as the displacement sensor, the actuator 54 includes a sheet contact piece 55 and a contact piece sensor 56, and the sheet contact piece 55 is in contact with the sheet P. Accordingly, the contact piece sensor 56 detects the movement amount (rotation amount) of the paper contact piece 55 and sends the detection result to the control unit 3. The control unit 3 determines the primary curl amount according to the detection result. As shown in FIG. 3A, when the primary curl amount is small, the movement amount of the paper contact piece 55 is small. As shown in FIG. 3B, when the primary curl amount is large, the paper contact piece 55 is small. The amount of movement of the piece 55 increases.

  The type and image quality of the paper P described above can be determined by the control unit 3 based on print settings by the user. As the type of the paper P, the composition, thickness, basis weight, and the like of the paper P may be determined, and a sensor that detects the thickness of the paper P may be provided. Further, since the primary curl amount can be predicted to increase when the basis weight is small, the curl correction force of the curl correction unit 42 is increased. On the other hand, when the basis weight is large, the primary curl amount can be predicted to be small. Decrease the curl correction power. In addition, depending on the paper type, there are papers that are easy to correct curl and papers that are difficult to correct. In the case of paper (when the paper P is thin, etc.), the curl correction force is increased.

  The image pattern formed on the paper P and the printing rate of the image can be determined by the control unit 3 analyzing the image data input to the printer 1. For example, the control unit 3 can determine the amount of ink used based on the image density by obtaining the image density from the image pattern and the printing rate, and when the image density is high (when there is a high density solid portion, etc.) ), The amount of ink used is large, and it can be predicted that the amount of primary curl will increase. Therefore, the curl correction force of the curl correction unit 42 increases as the image density increases. In double-sided printing, the rear end of the paper P printed on the first side enters the recording unit 16 at the head for printing on the second side after switchback at a nip forming unit 43 described later. Since the recording head 25 is at a height of about 1 to 3 mm from the surface of the second surface of the paper P, if the leading edge of the paper P is curled, it will easily catch on the recording head 25 at the time of entry, and jamming is likely to occur. Therefore, it is necessary to correct as much as possible the curl at the beginning of the paper P in the second side printing, that is, the rear end of the paper P in the first side printing, and the curls tend to be particularly high at the four corners of the paper P. . Therefore, especially when the image density is high in the area corresponding to the rear end and the four corners of the paper P printed on the first side, the curl correction force is increased.

  Further, since the primary curl amount can be predicted to increase when the temperature and humidity are low, the control unit 3 increases the curl correction force of the curl correction unit 42 as the humidity and temperature decrease.

  The nip forming unit 43 includes a pair of rollers that sandwich the paper P conveyed through the reversing path 41 with a predetermined nip amount. The nip forming unit 43 receives the paper P sent from the upstream side of the third conveying path 35 to the reversing path 41. It functions as a switchback roller that reverses over and returns to the downstream side of the third transport path 35. For example, the nip forming unit 43 can adjust the nip amount according to the amount of movement by providing one roller so as to be movable with respect to the other roller. Particularly in the present embodiment, the nip forming unit 43 temporarily stops when the paper P that has entered the reversing path 41 is reversed, and the rear end when the paper P enters the third transport path 35 (the front end after the reverse) ) At a predetermined nip amount for a predetermined stop time. Since the trailing edge of the paper P is distorted during the stop time, the trailing edge of the paper P can obtain a larger curl correction effect (curl removal effect). By adjusting the timing at which the rear end of the paper P is held by the nip forming unit 43 and the stop time of the paper P by the control unit 3, the curl correction effect applied to the rear end of the paper P can be adjusted. As described above, when the curl of the paper P is corrected using a larger curl correcting force at the rear end (back side in the transport direction) than the front end (front side in the transport direction) of the paper P, the rear end of the paper P is the paper after the reverse. Since it becomes the leading edge of P, the leading edge can enter the recording unit 16 more smoothly when printing on the second side, and therefore paper jams are less likely to occur.

  The flap 44 is configured so that the surface of the paper P opposite to the surface on which the image is formed by the image forming unit 13, that is, the second surface of the paper P in double-sided printing is curved in a convex shape with a predetermined curl correction force. Composed. Then, the curl correcting unit 42 conveys the paper P along the flap 44 and curves it, thereby plastically deforming the paper P and correcting the curl. The flap 44 is provided so as to be movable. For example, the flap 44 is provided so that the angle with respect to the reversing path 41 (the conveyance direction of the paper P) can be adjusted, and is controlled so that the curl correction force adjusted by the control unit 3 can be obtained. The drive of movement (angle adjustment) is controlled by the unit 3. In other words, the angle of the flap 44 is the curl amount generated on the paper P by the image formation, the type of the paper P, the image pattern formed on the paper P, the printing rate at the time of image formation, the image quality, temperature, and humidity. The curl correction force of the curl correction unit 42 is adjusted by adjusting for each printing according to any of the above. Further, when the paper 44 is bent in the direction of gravity, the flap 44 can use the weight of the paper P and can increase the curl correction force.

  Next, an image forming operation of the printer 1 having such a configuration, particularly an operation of continuously printing a plurality of sheets P on both sides will be described.

  When the printer 1 receives image data from an external computer or the like, the paper P stored in the paper feed cassette 4 is sent out to the first paper feed path 5 by the paper feed roller 6. The paper P sent out to the first paper feed path 5 is transported to the downstream side of the first paper feed path 5 by the transport roller 7, and from the first paper feed path 5 to the first transport path 14 by the registration roller 8. It is sent out onto the conveyor belt 18 of the first belt conveyor 15 with the first side up. At this time, the suction device 20 is operated, and air is sucked from the first conveyance path 14 side of the conveyance belt 18 to the suction device 20 through the through hole of the conveyance belt 18 and is sent out onto the conveyance belt 18. The sheet P is sucked onto the transport belt 18 by the suction force of the suction device 20.

  On the other hand, each recording head 25 ejects ink supplied from each ink container to the paper P adsorbed on the conveyance belt 18 based on information of image data received from an external computer or the like. As a result, a color ink image is formed on the front surface (first surface) of the paper P. The paper P on which the color ink image is formed is sent out from the first transport path 14 to the second transport path 28 by the first belt transport section 15 and transported by the second belt transport section 30. Further, the sheet P conveyed through the second conveyance path 28 is conveyed to the third conveyance path 35 branched at the midstream portion.

  In the third transport path 35, the paper P is first transported to the reversing path 41 of the reversing unit 40. In the reversing path 41, the paper P is conveyed along the flap 44 through the nip forming portion 43, so that the second side of the paper P in double-sided printing is bent into a convex shape with a predetermined curl correction force. The curl is corrected. For example, as shown by a broken line in FIG. 1, by setting the flap 44a at an angle inclined more in the direction of gravity, the inversion path 41a can be set more inclined in the direction of gravity, thereby increasing the curl correction force. Can do. Further, when the conveyance of the paper P is reversed by the reversing unit 40, the nip forming unit 43 temporarily stops the paper P for a predetermined stop time and holds the trailing edge of the paper P. Then, after the predetermined stop time has elapsed, the paper P is returned by the nip forming portion 43 that functions as a switchback roller, and is downstream of the third conveyance path 35 in a state where the paper P is reversed from the state before entering the reversing portion 40. It is conveyed to.

  Then, the paper P is transported from the third transport path 35 to the downstream end portion of the first paper feed path 5, sent out to the first transport path 14 by the registration roller 8, and the second surface is faced up. 1 belt is fed onto the conveyor belt 18 of the conveyor unit 15.

  Next, the paper P is sucked onto the transport belt 18 by the suction device 20 in the same manner as the first-side printing described above, and the color ink image is applied to the back surface (second side) of the paper P by each recording head 25. It is formed. The paper P on which the color ink image is formed is sent out from the first transport path 14 to the second transport path 28 by the first belt transport section 15 and transported by the second belt transport section 30. Thereafter, the paper P is transported to the downstream portion of the second transport path 28 and is discharged onto the paper discharge tray 34 via the paper discharge port 33 by the paper discharge roller 32.

  In the present embodiment, as described above, the printer 1 includes the first conveyance path 14 that conveys the paper P in the image forming unit 13 that forms an image on the paper P (recording medium), and the paper that has passed through the first conveyance path 14. A second conveyance path 28 that conveys P to the outside and a branching path provided from the second conveyance path 28, and the sheet P that has passed through the first conveyance path 14 is reversed for double-sided printing so that the first conveyance path 14 And a reversing unit 40 for reversing the sheet P in the third conveying path 35. The reversing unit 40 includes a curl correction unit 42 that performs a curl correction process before the paper P that has passed through the first transport path 14 is transported again to the first transport path 14. The curl correction unit 42 includes a nip forming unit 43 that holds the rear end of the paper P when entering the third conveyance path 35, and a surface on which an image is formed by the image forming unit 13 at the rear end of the paper P (printing surface). A flap 44 (curved portion) that bends the surface opposite to the first surface (second surface) in a convex shape with a predetermined curl correction force.

  Accordingly, when the paper P is conveyed with the front and back reversed, the curl generated on the paper P can be appropriately corrected.

  Further, the flap 44 can be any of the curl amount generated on the paper P by the image formation, the type of the paper P, the image pattern formed on the paper P, the printing rate at the time of image formation, the image quality, temperature, and humidity. Adjust curl correction power accordingly. This makes it possible to correct the primary curl of the paper P more appropriately according to the printing situation.

  In addition, the curl correction unit 42 includes a flap 44 that can move (adjustable angle) as a curved portion for correcting the curl of the paper P. Therefore, the primary curl of the paper P can be corrected with a simple configuration. .

  Further, the flap 44 is configured to bend with the conveyance direction of the paper P being the gravity direction. Thereby, the curl correction force can be increased using the weight of the paper P.

  In another embodiment, the control unit 3 determines the position of the paper P that is held when the conveyance of the paper P is temporarily stopped by the nip forming unit 43 of the curl correction unit 42, that is, the stop position, using the curl amount, This is determined for each printing based on the paper type, image pattern, printing rate, image quality, temperature and humidity. Since the paper P is locally strongly curled at the stop position in the nip forming unit 43, the curl correcting unit 42 sets the stop position at a position where the rear end of the paper P or other primary curl becomes large. Thereby, it becomes possible to correct the primary curl of the paper P even more appropriately according to the printing situation.

  For example, the stop position of the paper P is preferably set in a range of 20 mm from the rear end of the first surface toward the front end, and is particularly set in a range of ± 5 mm near the boundary of the maximum print area on the rear end side. Good. Further, the present invention is not limited to the rear end of the paper P, and if it can be estimated or detected that the curl curvature is locally increased in the image by analyzing the image pattern, the position may be set as the stop position. Good. If it is determined that the curl correction will be excessive based on the curl amount, the paper type, the image pattern, the printing rate, the image quality, the temperature, and the humidity, the nip forming unit 43 may be used to reverse the paper P. The stop position may be appropriately shifted.

  Further, in another embodiment, the control unit 3 uses the above-described curl amount, the paper when the nip forming unit 43 of the curl correcting unit 42 temporarily stops the conveyance of the paper P and the acceleration time after the temporary stop. This is determined for each printing based on the type, image pattern, printing rate, image quality, temperature and humidity. In the curl correction process, the slower the conveyance speed of the paper P, the higher the effect of the curl correction, and the longer the braking time and acceleration time, the more the curl can be corrected over a wider range of the paper P. Since the unnatural curl correction is eliminated, the curl correction unit 42 can appropriately set the curl correction force by setting the braking time and the acceleration time in the nip forming unit 43 to be long. Furthermore, the primary curl of the paper P can be corrected more appropriately.

  For example, the braking time and the acceleration time are preferably set in the range of 10 to 8000 msec, and in particular, set within 100 msec or more and the time until the trailing edge of the paper P passes through the nip forming portion 43. Is more desirable. The braking pattern and the acceleration pattern are not particularly limited. However, rather than making the acceleration / deceleration constant (see FIG. 4), the time for transporting at the minimum speed of the driving unit such as a motor driving the nip forming unit 43 is lengthened. It is desirable to adjust (see FIG. 5). However, if the braking time and acceleration time are made longer than necessary, the printing speed is also lowered. Therefore, it is desirable to set the acceleration / deceleration at the minimum necessary limit according to the primary curl amount. If it is determined that the curl correction is excessive based on the curl amount, paper type, image pattern, printing rate, image quality, temperature and humidity, the braking time and acceleration time in the nip forming unit 43 are set. It is better not to set long.

  In another embodiment, the control unit 3 sets the stop time when the conveyance of the paper P is temporarily stopped by the nip forming unit 43 of the curl correction unit 42 as the curl amount, the paper type, the image pattern, and the printing rate. Determine for each print based on image quality, temperature and humidity. When the conveyance of the paper P is temporarily stopped by the nip forming unit 43, strong curl correction is locally performed at the position, so the curl correction unit 42 can increase the curl correction force by extending the stop time. . Thereby, it becomes possible to correct the primary curl of the paper P even more appropriately according to the printing situation.

  For example, the stop time is preferably set in the range of 10 to 8000 msec, and more preferably set in the range of 100 to 2000 msec. The stop time is desirably set so that the curl correction does not become unnatural locally. However, if the stop time is made longer than necessary, excessive curl correction will be performed locally and the output will be corrected unnaturally, and the printing speed will also decrease. It is desirable to set the minimum required stop time. If it is determined that curl correction will be excessive based on the curl amount, paper type, image pattern, printing rate, image quality, temperature and humidity, the stop time at the nip forming unit 43 may be shortened. .

  In another embodiment, the control unit 3 sets the conveyance speed of the paper P passing through the nip forming unit 43 of the curl correction unit 42 to the curl amount, the paper type, the image pattern, the printing rate, the image quality, and the temperature. It is determined for each printing based on humidity and humidity. In the curl correction process, the curl correction effect becomes higher as the conveyance speed of the paper P is slower. Therefore, the curl correction unit 42 sets a lower conveyance speed when the primary curl amount is predicted to be larger or larger. By doing so, the curl correction force can be strengthened. Thereby, it becomes possible to correct the primary curl of the paper P even more appropriately according to the printing situation. However, if the conveyance speed is made slower than necessary, the printing speed also decreases, so it is desirable to set the conveyance speed to the minimum necessary limit according to the primary curl amount. If it is determined that curl correction will be excessive based on the curl amount, paper type, image pattern, printing rate, image quality, temperature and humidity, it is better not to slow the conveyance speed.

  Furthermore, in the above-described embodiment, the curl correcting unit 42 has been described as a configuration that functions as a switchback roller that reverses the paper P in the nip forming unit 43 and returns the paper P to the third transport path 35, but the configuration is limited to this configuration. Not. For example, in another embodiment, as illustrated in FIG. 6, the curl correction unit 42 includes a nip forming unit 43 disposed on the upstream side of the inversion path 41 and a flap disposed on the downstream side of the nip forming unit 43. 44 (curved portion) and a reversing member 60 disposed on the downstream side of the flap 44. Since the nip forming portion 43 and the flap 44 have the same configuration as that of the above-described embodiment, the description thereof is omitted.

  The reversing member 60 functions as a switchback roller that reverses the paper P sent from the upstream side of the third conveying path 35 to the reversing path 41 and returns it to the downstream side of the third conveying path 35. That is, the reversing member 60 has a function as a switchback roller of the nip forming portion 43 of the above-described embodiment. The reversing member 60 preferably does not have a curl correction function.

  When the paper P is temporarily stopped at the nip forming portion 43, strong curl correction is locally applied to the paper P. Therefore, if the curl correction is excessively performed, the output product may be unnaturally corrected. However, according to this embodiment, since the reversing member 60 is provided on the upstream side of the reversing path 41, for example, when the primary curl amount of the paper P is small and there is no problem in the conveyance for the second side printing. Since the paper P is allowed to pass through the nip forming portion 43 without being temporarily stopped and then reversed by the reversing member 60, it can be returned to the third transport path 35 without excessive curl correction. That is, the curl correction unit 42 can shift the stop position when the paper P is reversed. As described above, the stop position of the paper P can be determined for each printing based on the curl amount, paper type, image pattern, printing rate, image quality, temperature and humidity. When the primary curl amount of the paper P is large, the nip forming unit 43 temporarily stops the conveyance of the paper P and reverses the front and back to the third conveyance path 35 in the same manner as in the above-described embodiment. Will return.

  In this embodiment, the case where the configuration of the present invention is applied to the printer 1 as an ink jet image forming apparatus has been described. However, in other different embodiments, other different ink jet images such as a copying machine, a facsimile machine, and a multifunction machine are used. It is also possible to apply the configuration of the present invention to the forming apparatus.

1 Color printer (image forming device)
DESCRIPTION OF SYMBOLS 3 Control part 13 Image formation part 14 1st conveyance path 15 1st belt conveyance part 28 2nd conveyance path 35 3rd conveyance path 40 Inversion part 41 Inversion path 42 Curl correction part 43 Nip formation part 44 Flap

Claims (11)

A first transport path for transporting the recording medium in an image forming unit that forms an image on the recording medium;
A second transport path for transporting the recording medium that has passed through the first transport path to the outside;
A third transport path that is branched from the second transport path and re-transports the recording medium that has passed through the first transport path to the first transport path for duplex printing;
A reversing unit for turning the recording medium upside down in the third transport path,
The reversing unit includes a curl correction unit that performs a curl correction process on the recording medium before re-transporting the recording medium that has passed through the first conveyance path to the first conveyance path,
The curl correction unit includes a nip forming unit that holds a rear end when the recording medium enters the third conveyance path;
A recording medium comprising: a bending portion that curves a surface opposite to a surface on which an image is formed by the image forming unit at a rear end of the recording medium into a convex shape with a predetermined curl correction force. Conveying device. A control unit;
The control unit includes any one of a curl amount generated on the recording medium by image formation, a type of the recording medium, an image pattern formed on the recording medium, a printing rate at the time of image formation, image quality, temperature, and humidity. 2. The recording medium conveying apparatus according to claim 1, wherein the curl correction force of the curved portion is adjusted accordingly.   The recording medium conveying apparatus according to claim 1, wherein the bending portion is a flap that is movably provided.   The recording medium conveyance device according to claim 1, wherein the bending portion is bent with the conveyance direction of the recording medium being a gravity direction. A control unit;
The control unit controls the conveyance of the recording medium accompanied by reversal in the reversing unit to be held and stopped by the nip forming unit for a predetermined stop time, and the stop position of the recording medium is controlled. , Curl amount generated on the recording medium by the image forming unit, type of the recording medium, image pattern formed by the image forming unit, print rate at the time of image formation by the image forming unit, image quality, temperature and humidity The recording medium conveying apparatus according to claim 1, wherein the recording medium conveying apparatus is adjusted according to any one of the parameters. A control unit;
The control unit controls the conveyance of the recording medium accompanied by the reversal in the reversing unit to be held and stopped by the nip forming unit for a predetermined stop time, and until the recording medium is stopped. Braking time of the image forming unit, the amount of curl generated on the recording medium by the image forming unit, the type of the recording medium, the image pattern formed by the image forming unit, the printing rate at the time of image formation by the image forming unit, and the image quality The recording medium conveying apparatus according to claim 1, wherein the recording medium conveying apparatus is adjusted according to any one of temperature and humidity. A control unit;
The control unit controls the conveyance of the recording medium accompanied by reversal in the reversing unit to be held and stopped by the nip forming unit for a predetermined stop time, and after the stop of the recording medium Acceleration time, the amount of curl generated on the recording medium by the image forming unit, the type of the recording medium, the image pattern formed by the image forming unit, the printing rate at the time of image formation by the image forming unit, the image quality, The recording medium conveying apparatus according to claim 1, wherein the recording medium conveying apparatus is adjusted according to any one of temperature and humidity. A control unit;
The control unit controls the conveyance of the recording medium accompanied by the reversal in the reversing unit to be held and stopped by the nip forming unit for a predetermined stop time, and the stop time is set to the image. The amount of curl generated on the recording medium by the forming unit, the type of the recording medium, the image pattern formed by the image forming unit, the printing rate at the time of image formation by the image forming unit, image quality, temperature and humidity, The recording medium conveying apparatus according to claim 1, wherein the recording medium conveying apparatus is adjusted according to any one of them. A control unit;
The control unit controls the conveyance of the recording medium accompanied by reversal in the reversing unit to be held and stopped by the nip forming unit for a predetermined stop time, and passes through the nip forming unit. The conveyance speed of the recording medium, the curl amount generated on the recording medium by the image forming unit, the type of the recording medium, the image pattern formed by the image forming unit, and the printing rate at the time of image formation by the image forming unit The recording medium conveying apparatus according to claim 1, wherein the recording medium conveying apparatus is adjusted according to any of image quality, temperature, and humidity.   The recording medium conveying apparatus according to claim 1, further comprising a displacement sensor that measures a curl amount generated in the recording medium by the image forming unit.  An ink jet image forming apparatus comprising the recording medium conveyance device according to claim 1.

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