JP6332004B2 - RECORDING MEDIUM CONVEYING DEVICE AND INK JET IMAGE FORMING DEVICE - Google Patents

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 the recording liquid is finished is constrained 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.

  By the way, in the image forming apparatus, a suction suction belt having a plurality of suction holes is provided below the inkjet head, and the sheet on the suction suction belt is sucked and sucked through the suction holes by the decompression chamber. Some of them are equipped with a suction-and-adsorption conveyance system that rotates the paper to convey the paper. In this suction suction conveyance system, the suction force is constantly changing during paper feeding because the negative pressure in the decompression chamber changes by closing or opening the suction hole when transporting the paper. Since the opening and closing of the suction holes depends on the size of the paper and the distance between the transported papers, there is a problem that the suction force changes depending on the type of paper and the paper feed route (cassette, manual feed tray, etc.).

  On the other hand, for example, the conveyance device described in Patent Document 3 has a plurality of belt holes for adsorbing the sheet material, adsorbs and holds the sheet material supplied onto the conveyance surface, and moves endlessly. An annular conveying belt that conveys the material, a fan that sucks air through the belt hole and sucks the sheet material onto the conveying surface of the conveying belt, and a sheet that is supplied to the conveying belt at a predetermined position on the conveying surface Detection unit for detecting the material, movement amount acquisition unit for acquiring movement amount information indicating the movement amount of the conveyor belt, detection output of the detection unit, movement amount information, size of the sheet material, sheet material supplied continuously A control unit that calculates an area ratio that is a ratio of an area occupied by the sheet material that is sucked and held on the conveyance surface by using the distance between them and controls the air volume of the fan according to a change in the area ratio; , Be prepared To have.

JP 2002-020015 A JP 2006-082546 A JP 2012-201503 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 In the curl removing means described in Document 1 and Patent Document 2, there is a possibility that the curl correction (removal) is 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.

  Further, in the ink jet image forming apparatus provided with the suction suction conveyance system as described in Patent Document 3, the suction force of the sheet to the conveyance belt can be increased by increasing the fan air volume. If it is raised, paper dust may fly up and clog the inkjet nozzles, or vibration may increase and the conveyance accuracy may be reduced. For this reason, it is not possible to increase the air volume of the fan in order to correct (remove) the curl generated on the paper. Therefore, in Patent Document 3, when the suction force changes due to the difference in the type of paper and the paper feed route (cassette, manual feed tray, etc.), the curl of the paper cannot be properly corrected. A problem occurs when the second side of the paper is printed.

  In view of the above-described circumstances, an object of the present invention is to control the curl correction force in accordance with the change in the suction force due to the type of recording medium and the difference in the paper feed route.

  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, and a third transport that is provided by branching from the second transport path and reverses the recording medium that has passed through the first transport path for double-sided printing and transports the recording medium again to the first transport path. A curl correction unit that performs a curl correction process before re-transporting the recording medium that has passed through the first transport path to the first transport path, and a control unit that adjusts a curl correction force by the curl correction unit And the image forming unit includes a recording unit provided with a plurality of nozzle holes for ejecting ink to the recording medium passing through the first conveyance path, and the first conveyance path across the first conveyance path. Carrying with a plurality of through holes arranged opposite to the recording unit A negative pressure generation source that sucks air through the through-hole and generates a suction force through the through-hole with respect to the recording medium passing through the first conveyance path, and the control unit includes: The curl correction force is adjusted according to the distance between the sheets of the recording medium in the first transport path.

  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 control the curl correction force in accordance with the change in the adsorption force due to the type of recording medium and the feeding route.

1 is a cross-sectional view illustrating a printer according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating an image forming unit of a printer according to an embodiment of the invention. FIG. 3 is a plan view showing a first belt conveyance unit in an image forming unit of a printer according to an embodiment of the present disclosure. FIG. 4 is a bottom view illustrating a recording unit in an image forming unit of a printer according to an embodiment of the invention. It is sectional drawing which shows the pressurization type curl correction part in the printer which concerns on one Embodiment of this invention. 6 is a graph showing the relationship between the sheet position on the platen of the suction case and the coverage of the suction hole of the platen in the printer according to the embodiment of the present invention. 6 is a graph showing the relationship between the coverage rate of the suction holes of the platen and the negative pressure in the suction case in the printer according to the embodiment of the present invention. 4 is a graph showing a relationship between time and a coverage of an intake hole of a platen when a sheet is continuously passed through a printer according to an embodiment of the present invention. It is sectional drawing which shows the pressurization type curl correction part of the printer which concerns on other embodiment of this invention. It is sectional drawing which shows the pressurization type curl correction part of the printer which concerns on other embodiment of this invention. In the printer which concerns on other embodiment of this invention, it is sectional drawing which shows what was provided with the curl correction part which has a flap. FIG. 6 is a cross-sectional view schematically showing a distance measuring sensor that measures a primary curl amount in a printer according to another embodiment of the present invention. FIG. 6 is a cross-sectional view schematically showing an actuator for measuring a primary curl amount in a printer according to another embodiment of the present 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. 1 is the front side (front side) of the printer 1, and in FIGS. 3 and 4, the front side of the printer 1 is indicated by an arrow Fr. 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. Inside the printer main body 2, a control unit 3 that performs overall control of the operation of the printer 1 is provided. The control unit 3 includes, for example, a CPU (Central Processing Unit), a memory, and the like. In the present embodiment, the control unit 3 has a function of adjusting the curl correction force (curl correction amount) of each of the curl correction units 38, 40, 45, and 60 described later. Will be described later.

  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, below the first conveyance path 14, a first belt conveyance unit 15 that conveys the paper sent from the registration roller 8 along the first conveyance path 14 is disposed. 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 case 20 is disposed between the plurality of rollers 17 so as to be surrounded by the conveyance belt 18. As shown in FIG. 2, the upper surface of the suction case 20 is configured as a platen 21, and many intake holes 22 are formed in the platen 21 in the vertical direction. As shown in FIG. 3, the suction case 20 is connected to a suction device 23 (negative pressure generation source) disposed behind the suction case 20 and outside the conveyor belt 18.

  The conveying belt 18 has a plurality of through holes 24 that penetrate in the thickness direction (vertical direction). The suction device 23 is configured by, for example, a vacuum pump, a fan, and the like, and generates a negative pressure inside the suction case 20 by operating. Through the through hole 24 of the transport belt 18 and the suction hole 22 of the platen 21, Air can be sucked into the suction case 20 from the first conveying path 14 side of the conveying belt 18.

  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 conveyance direction of the paper in the conveyance path 14. Hereinafter, the symbols “K”, “C”, “M”, and “Y” are omitted except for the case of specifying the color. As shown in FIG. 4, the lower surface of each recording head 25 is an ink ejection surface 26, and a plurality of nozzle holes 27 are opened on the ink ejection surface 26 so as to face the upper surface of the conveyance belt 18. These nozzle holes 27 constitute an ink discharge port. In addition, 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 each recording head 25, and ink stored in each ink container is supplied to each recording head 25. It is comprised so that it may 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 fed from the first conveyance path 14 by the first belt conveyance unit 15 is second conveyed. It is configured to transport along the path 28. A plurality of transport rollers 31 are provided in the second transport path 28, and a discharge roller 32 that discharges paper 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. Further, for example, a heat drying type curl correction unit 38 is provided above the second belt conveyance unit 30 across the second conveyance path 28, and the second belt conveyance unit in the paper conveyance direction of the second conveyance path 28. A humidified curl correction unit 40 is provided below the second conveyance path 28 on the downstream side (left side) of 30.

  The heat-drying type curl correction unit 38 heats the printing surface of the paper conveyed on the second belt conveyance unit 30 and dries the ink ejected on the paper by the recording unit 16, so that 1 Next, it prevents curling, and is composed of, for example, a heating and drying device such as a dryer. The humidifying curl correction unit 40 humidifies the surface opposite to the printing surface of the paper conveyed on the second belt conveyance unit 30 to adjust the moisture content of the front and back of the paper, thereby adjusting the primary of the paper. It prevents curling, and is composed of a humidifier such as a spray or a steam generator.

  When performing double-sided printing (double-sided printing), the third transport path 35 forms an image on one side of the paper (first side printing) by the image forming unit 13 and then forms an image on the other side of the paper ( This is a double-sided circulation conveyance path that reverses the sheet and re-conveys it to the image forming unit 13 in order to perform (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 41 are provided in the third transport path 35, and a reversing unit 42 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 42 includes a reversing path 43 branched from the third transport path 35, and a switchback roller 44 is provided in the reversing path 43. The switchback roller 44 reverses the sheet fed from the upstream side of the third transport path 35 to the reverse path 43 and returns it to the downstream side of the third transport path 35. The reversing path 43 is provided with a pressure-type curl correction unit 45 on the third transport path 35 side of the switchback roller 44. For this reason, in the reverse path 43, the paper passes through the pressure-type curl correction unit 45 twice when it goes to the switchback roller 44 and when it returns from the switchback roller 44, and one curl correction is performed. Two portions can be obtained at the portion 45.

  The reversing unit 42 temporarily stops when the paper in the reversing path 43 is reversed by the switchback roller 44, and holds the rear end of the paper (the front end after the reversal) by the pressure-type curl correction unit 45. Composed. Since the trailing edge of the sheet is distorted during the temporary stop time, a larger curl correction effect (curl removal effect) can be obtained at the trailing edge of the sheet. The curl correction effect applied to the trailing edge of the sheet can be adjusted by adjusting the timing at which the trailing edge of the sheet is held by the pressure-type curl correcting unit 45 and the pause time. As described above, when the curl of the paper is corrected by using a large 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, the rear end of the paper is As a result, the leading edge can enter the recording unit 16 more smoothly when printing on the second side, and paper jams are less likely to occur.

  As shown in FIG. 5, the pressure-type curl correction unit 45 includes a pair of small-diameter hard rollers 46 and a large-diameter elastic roller 47, and the hard rollers 46 and the elastic rollers 47 are sent to the reverse path 43. The sheet is sandwiched by a predetermined nip amount (nip width), and the sheet is wound around the hard roller 46 while being pressed, so that the sheet is distorted and plastically deformed to correct the primary curl. The hard roller 46 is provided so as to be movable with respect to the elastic roller 47, and the nip amount can be adjusted according to the amount of movement. The amount of nip, that is, the nip width indicates a width that contacts the paper conveyance direction when the hard roller 46 and the elastic roller 47 are in pressure contact, and is preferably 2.5 mm or more on average, and preferably 5 mm or more. Is more desirable.

  The smaller the outer shape of the hard roller 46, the higher the effect of sandwiching the paper. However, it is preferable that the hard roller 46 be formed with an outer diameter that does not affect the deflection of the nip width. For example, the hard roller 46 is specifically formed with an outer diameter of Φ5 to 30 mm, and more preferably with an outer diameter of Φ6 to 10 mm. The larger the outer diameter, the larger the outer diameter of the elastic roller 47, so that the effect of sandwiching the paper becomes higher. However, if the outer diameter is too large, the sensitivity is almost lost, so the outer diameter is sufficient to maintain sufficient sensitivity. It is formed. For example, the elastic roller 47 is preferably formed with an outer diameter of Φ15 to 40 mm, and more preferably with an outer diameter of Φ20 to 30 mm. Further, the lower the hardness of the elastic roller 47, the larger the nip width and the higher the effect of sandwiching the paper. However, if the hardness is too low, the elastic roller 47 loses the waist of the paper and strains the paper to cause plastic deformation. It becomes impossible, that is, the paper cannot be brazed. For example, the elastic roller 47 is specifically preferably formed at 5 to 40 degrees by asker-C, more preferably at 15 to 25 degrees.

  Next, an image forming operation of the printer 1 having such a configuration, particularly an operation of continuously printing a plurality of sheets 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 23 is operated, and from the first conveyance path 14 side of the conveyance belt 18 into the suction case 21 through the through hole 24 of the conveyance belt 18 and the suction hole 22 of the platen 21 of the suction case 20. Air is aspirated. Then, the sheet P sent out onto the conveyor belt 18 is adsorbed onto the conveyor belt 18 by the suction force of the suction device 23.

  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.

  At this time, in the second conveyance path 28, the paper after the first side printing is subjected to the curl correction processing by the heat-drying type curl correction unit 38 and / or the humidified curl correction unit 40. Thereafter, the sheet is conveyed from the midstream portion of the second conveyance path 28 to the third conveyance path 35.

  In the third conveyance path 35, the sheet is first conveyed to the reversing path 43 of the reversing unit 42. In the reversing path 43, when the paper reaches the switchback roller 44 through the pressure-type curl correction unit 45, the sheet temporarily stops for a predetermined time and the rear end is held by the pressure-type curl correction unit 45. Then, after the predetermined time has passed, the sheet is returned by the switchback roller 44, passes through the pressure-type curl correction unit 45 again, and is reversely reversed from the state before entering the reversing unit 42. 35 to the downstream side.

  The paper is then transported from the third transport path 35 to the downstream end of the first paper feed path 5, sent out to the first transport path 14 by the registration rollers 8, and the first surface with the second face up. It is sent out onto the conveyor belt 18 of the belt conveyor 15.

  Next, the paper is sucked onto the transport belt 18 by the suction device 23 in the same manner as the first side printing described above, and a color ink image is formed on the back surface (second side) of the paper P by each recording head 25. Is done. 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.

  At this time, in the second conveyance path 28, as with the first-side printing described above, the paper after the first-side printing is curled by the heat-drying type curl correcting unit 38 and / or the humidifying curl correcting unit 40. Correction processing is performed. Thereafter, the sheet is transported to the downstream portion of the second transport path 28, and is discharged onto the discharge tray 34 via the discharge port 33 by the discharge roller 32.

  Next, a function of adjusting the curl correction force of each of the curl correction units 38, 40, and 45 by the control unit 3 in double-sided printing of the printer 1 will be described.

  In the double-sided printing, if the primary curl is lifted on the paper by the first-side printing, the image cannot be properly recorded (printed) on the paper at the second-side printing. Needs to be properly adsorbed onto the conveyor belt 18 of the first belt conveyor 15. The suction force of the sheet by the suction device 23 is such that the distance between the sheets passing through the first conveyance path 14 and the sheet size, the maximum of the through hole 24 of the conveyance belt 18 (the suction hole 22 of the platen 21 of the suction case 20). It changes according to the aperture ratio or the minimum suction pressure in the suction case 20.

  FIG. 6 shows a change in the coverage ratio of the sheet covering the intake holes 22 of the platen 21 when a sheet of paper passes over the conveying belt 18 above the platen 21. The coverage increases as the leading edge of the sheet advances with respect to the platen 21, and becomes maximum when all of the intake holes 22 are covered, and changes so that the trailing edge of the sheet passes through the platen 21 and decreases. Depends on the paper size.

  FIG. 7 shows the relationship between the coverage and the suction negative pressure in the suction case 20. The higher the coverage, the greater the pressure loss in the suction case 20, so the negative pressure increases due to the PQ characteristics of the suction device 23. FIG. 8 shows a change in the coverage of the platen 21 when the paper continuously passes on the transport belt 18. When the sheet is conveyed between sheets shorter than the width of the platen 21 in the conveyance direction, the coverage is not 0% between the sheets, and a certain value P is the lowest value. The suction pressure of the paper changes in the same manner, and becomes the minimum value between the papers. When the maximum opening ratio of the through hole 24 of the conveying belt 18 is defined as (100−P)%, the minimum suction pressure in the suction case 20 during the sheet passing is inversely proportional to the maximum opening ratio. Accordingly, the minimum suction pressure during the sheet passing depends on the sheet size and the distance between the sheets. The smaller the sheet size and the greater the distance between the sheets, the smaller the minimum suction pressure. When the primary curl is lifted on the paper on the 15 conveying belts 18, the force of attracting the paper onto the conveying belt 18 by the suction device 23 is weakened.

  Therefore, the control unit 3 determines the distance between the sheets passing through the first conveyance path 14 and the sheet size, the maximum opening ratio of the through hole 24 of the conveyance belt 18 (the suction hole 22 of the platen 21 of the suction case 20), Alternatively, the curl correction force by each of the curl correction units 38, 40 and 45 is adjusted according to the minimum suction pressure by the suction device 23. For example, the control unit 3 specifically corrects the curl when at least one of a case where the distance between sheets is large, the sheet size is small, the maximum aperture ratio is large, or the minimum suction pressure is small is applicable. Adjust the force greatly. For example, the control unit 3 increases the amount of heat supplied to the heat-drying type curl correction unit 38 or adjusts the amount of water supplied to the humidified curl correction unit 40 according to the amount of ink used for the paper. The curl correction force is largely adjusted by making the moisture content of the front and back surfaces uniform, or increasing the nip amount between the hard roller 46 and the elastic roller 47 of the pressure type curl correction unit 45.

  In the present embodiment, as described above, the printer 1 uses the first conveyance path 14 that conveys the sheet in the image forming unit 13 that forms an image on the sheet (recording medium), and the sheet that has passed through the first conveyance path 14 to the outside. A second conveyance path 28 that conveys to the first and second conveyance paths 28, and the paper that has passed through the first conveyance path 14 is reversed for double-sided printing and re-conveyed to the first conveyance path 14. The third conveyance path 35, the curl correction units 38, 40, and 45 that perform curl correction processing before the paper that has passed through the first conveyance path 14 is re-conveyed to the first conveyance path 14, and the curl correction unit 38. , 40, and 45, the control unit 3 for adjusting the curl correction force is provided in the recording medium conveyance device. Then, the image forming unit 13 passes through each recording head 25 (recording unit 16) provided with a plurality of nozzle holes 27 for ejecting ink to the paper passing through the first conveying path 14 and the first conveying path 14. A conveying belt 18 having a plurality of through holes 24 disposed so as to be opposed to the respective recording heads 25 and air is sucked through the through holes 24, and the sheet passing through the first conveying path 14 is passed through the through holes 24. A suction device 23 (negative pressure generation source) that generates a suction force, and the control unit 3 adjusts the curl correction force according to the distance between the sheets of the paper in the first transport path 14.

  Thus, the curl correction force is controlled in accordance with the change in the suction force in the suction device 23 and the suction case 20 due to the difference in paper type (size) and paper feed route (paper feed cassette 4, manual feed tray, etc.). Is possible. Therefore, when double-sided printing of a plurality of sheets is performed, primary curl that occurs on the front surface (first surface) during front surface printing (first surface printing) is suppressed, and the paper is printed during back surface printing (second surface printing). It can be appropriately adsorbed onto the conveying belt 18 of the one-belt conveying unit 15 and an image can be appropriately recorded (printed).

  In addition, the control unit 3 determines the size of the sheet passing through the first conveyance path 14 (area of the sheet), the maximum opening ratio of the through hole 24 of the conveyance belt 18, and the minimum suction pressure in the suction case 20 by the suction device 23. The curl correction force is adjusted according to at least one. As a result, the curl correction force can be adjusted more appropriately.

  The pressure-type curl correction unit 45 includes a hard roller 46 and an elastic roller 47 (nip pair) that correct the curl of the paper by sandwiching the conveyed paper with a predetermined nip amount. The curl correction force is adjusted by adjusting the nip amount between the roller 46 and the elastic roller 47. Thereby, the curl correction force can be appropriately adjusted by a simple method of adjusting the nip amount.

  The heat drying type curl correction unit 38 is configured to correct the curl of the paper by heating and drying the conveyed paper, and the control unit 3 supplies heat to the heat drying type curl correction unit 38. Adjust the curl correction force by adjusting the amount. Thereby, the curl correction force can be appropriately adjusted by a simple method of adjusting the heat supply amount.

  The humidifying curl correcting unit 40 includes a humidifying unit that corrects the curling of the paper by humidifying the conveyed paper, and the control unit 3 adjusts the amount of water supplied to the humidifying curl correcting unit 40. Adjust the curl correction force by adjusting the moisture content on the front and back of the paper. Thereby, the curl correction force can be appropriately adjusted by a simple method of adjusting the water supply amount.

  In the present embodiment, the configuration of the pressure-type curl correction unit 45 including the pair of hard rollers 46 and the elastic roller 47 has been described. However, the pressure-type curl correction unit 45 wraps paper around a small-diameter curved surface and plastically deforms it. If it can be made, it will not be limited to this structure. In another embodiment, the pressure-type curl correction unit 50 may be configured by a combination of a belt 52 and a hard roller 53 wound between a plurality of rollers 51 as shown in FIG. 9, for example. In this case, since the outer diameter of the hard roller 53 is smaller than the length of the belt 52 between the rollers 51, the paper conveyed between the belt 52 and the hard roller 53 is wound around a small-diameter curved surface and plastically deformed. The primary curl is corrected. Alternatively, in another embodiment, as shown in FIG. 10, the pressure-type curl correction unit 54 includes a first belt 56 wound between a plurality of rollers 55 and a first belt 56 wound between a plurality of rollers 57. A combination with two belts 58 may be used. In this case, a small-diameter roller 55 is disposed in the first belt 56 so that the first belt 56 bites into the tensioned second belt 58, and the second belt 58 against the tensioned first belt 56. By placing the small-diameter roller 57 in the second belt 58 so as to bite the paper, the paper conveyed between the first belt 56 and the second belt 58 is wound around the small-diameter curved surface and plastically deformed. The primary curl will be corrected.

  In the present embodiment, the configuration in which the pressurization-type curl correction unit 45 is provided in the reversing unit 42 has been described, but the curl correction unit provided in the reversal unit 42 is not limited to the pressurization type. For example, in other embodiments, the reversing unit 42 may include a heat-drying type curl correcting unit 38 or a humidifying curl correcting unit 40.

  Alternatively, in another embodiment, the reversing unit 42 includes a curl correcting unit that mechanically distorts the paper conveyed through the reversing path 43, for example, a curl correcting unit 60 having a flap 61 as shown in FIG. You may prepare. In this case, the reversing unit 42 includes a switchback roller 44 on the upstream side in the reversing path 43 and a flap 61 on the downstream side. The flap 61 is arranged so as to be movable. For example, the flap 61 is arranged so that the angle with respect to the reversing path 43 (paper conveyance direction) can be adjusted. The curl correction unit 60 is configured to correct the curl by plastically deforming the sheet by conveying the sheet along the flap 61 and curving it. At this time, the curl correction unit 60 can use the weight of the sheet and increase the curl correction force when the sheet is curved in the direction of gravity. The angle of the flap 61 can be adjusted by the control unit 3. As a result, the curl correction process can be realized with a simple configuration that eliminates the need for power required for heating and moisture necessary for humidification.

  Furthermore, in another embodiment, the control unit 3 may be configured to adjust the curl correction force by adjusting the sheet conveyance speed in the curl correction units 38, 40, 45, and 60. Thereby, since the distortion time, heating time, and humidification time of the paper become longer, the correction force can be increased.

  Furthermore, in another embodiment, the curl correction units 38, 40, 60 are larger at the rear end (back side in the transport direction) than the front end (front side in the transport direction) of the paper, like the pressure type curl correction unit 45. The curl of the paper may be corrected using the curl correction force. As a result, the trailing edge of the paper becomes the leading edge of the paper after the reversal, and the leading edge can enter the recording unit 16 more smoothly during printing on the second side, so paper jamming is less likely to occur.

  In other embodiments, the control unit 3 preferably takes into account environmental information such as the primary curl amount and type of paper, the image pattern during printing, the printing rate and image quality, the temperature and humidity of the printer 1, and the like. Then, the curl correction power should be adjusted. The primary curl amount may be predicted by a predetermined calculation based on the above-described paper type, image pattern, printing rate, image quality, temperature, humidity, and printing speed, or may be detected by a sensor described later. Further, it is desirable that the control unit 3 controls the curl correction force according to the primary curl amount of the paper so that the curl correction is not excessive. When a high density solid portion exists in the image pattern, the primary curl amount of the paper becomes large. Therefore, the control unit 3 grasps the density of the image pattern, and when there is a high density solid portion, the curl. It is better to increase the correction power. Also, depending on the paper type, there are papers that are easy to correct curl and papers that are difficult to correct. Therefore, the control unit 3 should grasp the paper type and reduce the curl correction force when the paper is easy to correct curl. .

  The primary curl amount can be measured with a displacement sensor. The displacement sensor is composed of, for example, a distance measuring sensor, an actuator (pressure sensor) or the like, and the second conveyance path 28, the third conveyance path 35, or the like between the recording unit 16 and the curl correction units 38, 40, 45, 60, or the like. It is installed on the reverse path 43.

  When the distance measuring sensor 62 as shown in FIG. 12 is used as the displacement sensor, the distance measuring sensor 62 includes a light emitting unit 63, a light receiving unit 64, and a signal processing unit 65, emits detection light L from the light emitting unit 63, and uses paper. The reflected detection light L is detected by the light receiving unit 64, and the signal processing unit 65 measures the distance between the sheet and the distance measuring sensor 62 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. 12, the position of the detection light L in the light receiving unit 64 differs depending on the magnitude of the primary curl amount.

  When an actuator 66 as shown in FIGS. 13A and 13B is used as the displacement sensor, the actuator 66 includes a sheet contact piece 67 and a contact piece sensor 68, and the sheet contact piece 67 responds to contact with the sheet. The contact piece sensor 68 detects the amount of movement (rotation amount) of the paper contact piece 67 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. 13A, when the primary curl amount is small, the movement amount of the paper contact piece 67 is small. As shown in FIG. 13B, when the primary curl amount is large, the paper contact piece 67 is small. The amount of movement of the piece 67 increases.

  In the above-described embodiment, the heat drying type curl correction unit 38 and the humidified curl correction unit 40 are provided, and the reversing unit 42 includes the pressure type curl correction unit 45 or the curl correction unit 60 having the flap 61. As described above, if the curl correction processing can be performed before the paper on which the first side printing is performed in the double-sided printing is re-transported to the image forming unit 13 for the second side printing, It is sufficient that at least one curl correction unit is provided.

  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 16 Recording part 18 Conveyance belt 20 Suction case 21 Platen 22 Intake hole 23 Suction device 24 Through-hole 25 Recording head 27 Nozzle hole 28 2nd conveyance path 35 3rd conveyance path 38 Heat drying type curl correction part 40 Wetting curl correction part 42 Inversion part 43 Inversion path 44 Switchback roller 45, 50, 54 Pressure type curl correction part 46 Hard roller 47 Elastic roller 60 Curl correction part 61 flaps

Claims (10)

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 conveyance path that is branched from the second conveyance path and reverses the recording medium that has passed through the first conveyance path for double-sided printing and re-conveyed to the first conveyance path;
A curl correction unit that performs a curl correction process before re-transporting the recording medium that has passed through the first transport path to the first transport path;
A control unit for adjusting the curl correction force by the curl correction unit,
The image forming unit includes a recording unit provided with a plurality of nozzle holes for discharging ink to the recording medium passing through the first conveyance path;
A conveying belt having a plurality of through holes disposed opposite to the recording unit across the first conveying path;
A negative pressure generation source that sucks air through the through-hole and generates a suction force through the through-hole with respect to the recording medium passing through the first conveyance path,
The control unit adjusts the curl correction force according to a distance between sheets of the recording medium in the first transport path. 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 conveyance path that is branched from the second conveyance path and reverses the recording medium that has passed through the first conveyance path for double-sided printing and re-conveyed to the first conveyance path;
A curl correction unit that performs a curl correction process before re-transporting the recording medium that has passed through the first transport path to the first transport path;
A control unit for adjusting the curl correction force by the curl correction unit,
The image forming unit includes a recording unit provided with a plurality of nozzle holes for discharging ink to the recording medium passing through the first conveyance path;
A conveying belt having a plurality of through holes disposed opposite to the recording unit across the first conveying path;
A negative pressure generation source that sucks air through the through-hole and generates a suction force through the through-hole with respect to the recording medium passing through the first conveyance path,
Wherein the control unit, and adjusting the curl correcting force according to the area of the recording medium records the medium conveying device. The recording medium conveying apparatus according to claim 1, wherein the control unit adjusts the curl correction force according to a minimum suction pressure of the negative pressure generation source that decreases as the inter-paper distance increases . The curl correction unit includes a nip pair that corrects curl of the recording medium by sandwiching the conveyed recording medium with a predetermined nip amount,
The recording medium conveying apparatus according to claim 1, wherein the control unit adjusts the curl correction force by adjusting the nip amount between the nip pairs. The curl correction unit is configured to correct curl of the recording medium by heating and drying the recording medium being conveyed,
The recording medium conveying apparatus according to claim 1, wherein the control unit adjusts the curl correction force by adjusting a heat supply amount to the curl correction unit. The curl correction unit is configured to correct the curl of the recording medium by humidifying the recording medium being conveyed,
The recording medium conveying apparatus according to claim 1, wherein the control unit adjusts the curl correction force by adjusting a water supply amount to the curl correction unit. The curl correction unit includes a flap that is arranged so that an angle with respect to a conveyance direction of the recording medium can be adjusted, and is configured to correct the curl of the recording medium by conveying the recording medium along the flap. And
2. The recording according to claim 1, wherein the control unit adjusts the curl correction force by adjusting an angle of the flap with respect to an inversion path when the recording medium is inverted in the third transport path. Medium transport device. Wherein the control unit, the recording medium according to any one of claims 4 to 7, characterized in that adjusting the curl correcting force by adjusting the conveying speed of the recording medium in the curl straightening unit Conveying device. The curl correcting section, claim 1, characterized in that correcting the curl of the recording medium with large the curl straightening force in the transport direction rear side of the front reversal than the transport direction front side of the front reversal of the recording medium 2. A recording medium conveying apparatus according to 1. Inkjet image forming apparatus characterized by comprising a recording medium conveying apparatus according to any one of claims 1-9.

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