Conveyor

Abstract

To provide a conveyance device which prevents contact with respect to a processing part of a medium, while suppressing the number of media for correcting a curl.SOLUTION: A conveyance device includes: a suction conveyance part (below-head conveyance unit 16) including a conveyance member (conveyance belt 17) for conveying a medium (sheet P), and a suction part (suction fan 22) for allowing the conveyance member to suction the medium, and arranged so as to oppose to a processing part (printing part 13) for performing processing on the medium; a curl correction part 40 arranged on the upstream side of the processing part and the suction conveyance part in a conveyance direction (sub-scanning direction F2) of the medium, and for correcting a curl of the medium so that a tip of the medium does not come into contact with the processing part; and a control part 50 for controlling the curl correction part 40 in such a manner that, in the case where the media are conveyed continuously by the suction conveyance part, a curl is corrected on a first medium, and curl correction is omitted on at least some of the media after a second media.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to a transport device. [Background technology]

[0002] Conventionally, in image forming devices, when printing, it is required that media such as paper be transported to the printing section in an appropriate state. For example, in an inkjet image forming device, when paper is transported to the printing section in a curled state (with its leading end protruding toward the inkjet head from the center in the transport direction), the leading end of the paper may come into contact with the inkjet head. If the paper comes into contact with the inkjet head, there is a risk that the nozzle of the inkjet head may be damaged or ink may stain the paper.

[0003] Therefore, a method for straightening the curl of paper is known. For example, in order to straighten the curl of plain paper but not to straighten the curl of thick paper, a paper straightening device has been proposed that includes a curl straightening path with a curl straightening means, a path without a curl straightening means, a path switching means for guiding the paper to one of the above two paths, and a control means for switching the path switching means based on the settings for each paper feed means that feeds the paper (see, for example, Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2010-247526 A Summary of the Invention [Problem to be solved by the invention]

[0005] In a conveying device that conveys a medium such as paper, an adsorption conveying unit that adsorbs the medium may be disposed opposite a printing unit that prints on the medium. When the adsorption conveying unit has a suction unit that sucks air and a conveying member such as a conveying belt to which the medium is adsorbed by the suction of air from the suction unit, when the first medium of multiple media that are continuously conveyed is being conveyed by the conveying member, the suction holes of the conveying member are open and not blocked by the preceding medium, so that the adhesion force between the conveying member and the medium is small. Therefore, if the medium has the above-mentioned end-up shape, the printing unit may be damaged by the medium coming into contact with the printing unit, or ink stains may adhere to the medium. Note that even if a processing unit other than the printing unit, such as an inspection unit, is disposed opposite the adsorption conveying unit, there is a risk of damage to the processing unit other than the printing unit. In addition, the same problem may occur when the adsorption conveying unit adsorbs the medium to the conveying member by another adsorption method, such as electrostatic adsorption, rather than by suction adsorption using a suction unit that sucks air.

[0006] In contrast, when the second or subsequent medium is being transported by the transport member, the suction holes of the transport member are blocked by the preceding medium, so that the above-mentioned damage to the processing section is unlikely to occur.

[0007] The curl correction unit corrects the curl of the medium, for example, by sandwiching the medium between a pair of soft and hard rollers. However, when the curl of the medium is corrected with such a pair of rollers, wrinkles extending in the transport direction may occur on the medium, and image unevenness may occur due to fluctuations in the transport speed. In addition, the soft roller wears out at the portion that nips the width direction edge of the medium. When the soft roller wears out, the curl correction effect decreases. Furthermore, transporting the medium with a soft roller such as a soft roller has a large rotation resistance, which increases the power consumption of the device.

[0008] An object of the present invention is to provide a conveying device that can prevent the medium from coming into contact with a processing section while reducing the number of media to be straightened. [Means for solving the problem]

[0009] In one aspect, the conveying device has a conveying member that conveys a medium and an adsorption unit that adsorbs the medium to the conveying member, and is equipped with an adsorption conveying unit arranged to face a processing unit that processes the medium, a curl correction unit that is arranged upstream of the processing unit and the adsorption conveying unit in the conveying direction of the medium and corrects curls in the medium so that the leading edge of the medium does not contact the processing unit, and a control unit that controls the curl correction unit to correct curls in a first sheet of the medium and omit curl correction for at least some of the media from the second sheet onwards when the medium is continuously conveyed by the adsorption conveying unit. Effect of the Invention

[0010] According to the above aspect, it is possible to prevent the medium from coming into contact with the processing section while reducing the number of media to be straightened. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram showing a schematic configuration of an image forming apparatus including a conveying device according to an embodiment; [Diagram 2] 2 is an enlarged view showing a part of a curl straightening unit of the image forming apparatus according to the embodiment; FIG. [Diagram 3] FIG. 2 is a diagram illustrating a control configuration of the image forming apparatus according to an embodiment. [Figure 4] 5A and 5B are cross-sectional views showing the operation of a curl straightening unit according to an embodiment, in which (a) shows a pressed state and (b) shows a separated state. [Diagram 5] 5A and 5B are diagrams illustrating the operation of the curl straightening unit according to the embodiment, in which (a) shows a state in which the curl straightening unit is pressed against the first sheet of paper, and (b) shows a state in which the curl straightening unit is separated from the second and subsequent sheets of paper. [Figure 6] 11A and 11B are diagrams illustrating the operation of a curl straightening unit during double-sided printing of paper in an embodiment. [Figure 7] 11A and 11B are diagrams illustrating the operation of a curl straightening unit when the width of continuously transported paper becomes wider midway in an embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A conveying device according to an embodiment of the present invention will now be described with reference to the drawings.

[0013] FIG. 1 is a diagram showing a schematic configuration of an image forming apparatus 10 including a conveying device according to an embodiment of the present invention.

[0014] FIG. 2 is an enlarged view showing a part of the curl straightening unit 40 of the image forming apparatus 10. As shown in FIG.

[0015] FIG. 3 is a diagram showing a control configuration of the image forming apparatus 10. As shown in FIG.

[0016] The image forming apparatus 10 is an inkjet printing device that prints by ejecting ink from an inkjet head 14 of a printing unit 13 onto paper P, which is an example of a medium. The two-dot chain line in Fig. 1 represents the transport path of the paper P in the image forming apparatus 10, and a plurality of rollers and the like provided along the transport path transport the paper P. The image forming apparatus 10 includes a control unit 50 shown in Fig. 3, and the transport, curl correction, printing, and other operations of the paper P described below are performed under the control of the control unit 50.

[0017] As shown in Fig. 1, image forming apparatus 10 includes a paper feed section 11, and unprinted paper P is stacked in a paper feed tray (not shown) provided in paper feed section 11. When printing, paper P is sent from paper feed section 11 to circulating transport path T2 via feed-side transport path T1. Circulating transport path T2 is formed in a loop, and reversing section 12 can reverse paper P to transport it upside down.

[0018] Inside the image forming apparatus 10, there is provided a printing unit 13 which performs printing processing on the paper P sent to the circulating transport path T2. The printing unit 13 has a plurality of inkjet heads 14, and prints on the paper P transported on the circulating transport path T2 by ejecting ink from each inkjet head 14. By reversing the paper P by a reversing unit 12 located midway along the circulating transport path T2, it is possible to print on both sides of the paper P.

[0019] Below the inkjet head 14, an under-head transport unit 16 is disposed so as to face the inkjet head 14 (printing section 13). The paper P is transported at a predetermined speed while being adsorbed and held by the under-head transport unit 16, and ink is ejected from the inkjet head 14 to perform printing. The width direction of the paper P transported by the under-head transport unit 16 is defined as the main scanning direction F1 (see Figs. 6 and 7), and the transport direction of the paper P perpendicular to the main scanning direction F1 is defined as the sub-scanning direction F2. In the sub-scanning direction F2, the side where the paper feed side transport path T1 (paper feed section 11) is located is defined as the upstream side of the paper transport, and the side where the paper discharge side transport path T3 (paper discharge section 15) is located is defined as the downstream side of the paper transport. The printing section 13 is an example of a processing section that performs processing on the paper P. This processing section may be an inspection section that performs inspection on the paper P, or the like.

[0020] The under-head transport unit 16 includes a transport belt 17, a belt drive roller 18, and a plurality of driven rollers 19, 20, and .

[0021] The conveyor belt 17 is an endless (loop-shaped) strip stretched across a belt drive roller 18 and a number of driven rollers 19, 20, and 21, and forms a substantially horizontal conveying surface 17a between the belt drive roller 18 and the driven roller 19. The conveying surface 17a constitutes a part of the circulating conveying path T2, and the paper P conveyed from the paper feed-side conveying path T1 is placed on the conveying surface 17a.

[0022] The belt drive roller 18 is driven to rotate by a belt drive unit 51 shown in Fig. 3. The belt drive unit 51 is composed of a motor, which is an example of an actuator, and a transmission mechanism that transmits the driving force of the motor to the belt drive roller 18. When the belt drive roller 18 rotates, the driving force is transmitted to the conveyor belt 17, and the conveyor belt 17 moves in an orbit while being guided by the driven rollers 19, 20, and 21, and moves the paper P on the conveyor surface 17a from the upstream side to the downstream side in the sub-scanning direction F2. The driven rollers 19, 20, and 21 rotate following the belt drive roller 18 via the conveyor belt 17.

[0023] The conveyor belt 17 is formed with a plurality of suction holes (not shown) penetrating from the front to the back. The head under conveyor unit 16 is provided with a suction fan 22 below the conveyor surface 17a between the belt drive roller 18 and the driven roller 19. The suction fan 22 is driven to rotate by a fan drive unit 52 shown in FIG. 3, and the rotation of the suction fan 22 generates an air flow from above to below. When the suction fan 22 is rotated, a force (negative pressure) is generated that sucks air from the space above the conveyor surface 17a through the plurality of suction holes, and the paper P is adsorbed and held on the conveyor surface 17a by the negative pressure acting on the suction holes. By driving the suction fan 22 to rotate the belt drive roller 18, the paper P can be conveyed while being adsorbed and held on the conveyor surface 17a.

[0024] Here, the head transport lower unit 16 is an example of an adsorption transport section having a transport belt 17, which is an example of a transport member that transports the paper P, and a suction fan 22, which is an example of an adsorption section that adsorbs the paper P to the transport belt 17. This adsorption transport section is disposed so as to face a processing section (printing section 13) that processes the paper P. Note that the adsorption section is preferably a suction section such as the suction fan 22 that sucks in air, but may also use other adsorption methods such as electrostatic adsorption.

[0025] A flipper 23 provided downstream of the under-head transport unit 16 switches between circulating the paper P on the circulating transport path T2 and moving it to the paper discharge transport path T3. The paper P that has been printed in the printing unit 13 is sent to the paper discharge transport path T3 that continues to the circulating transport path T2. The paper discharge unit 15 is disposed at the exit of the paper discharge transport path T3, and a paper discharge tray (not shown) provided in the paper discharge unit 15 collects the printed paper P.

[0026] 1 shows only one feed-side transport path T1 and one discharge-side transport path T3, multiple feed-side transport paths and multiple discharge-side transport paths connected to the circulating transport path T2 may be provided. For example, multiple feed trays corresponding to multiple paper sizes may be provided, and the multiple feed-side transport paths corresponding to each feed tray may be configured to merge midway.

[0027] As shown in FIG. 2, the skew correction conveying device 30 located on the upstream side of the sub-scanning direction F2 constitutes the upstream conveying means, and the head under-conveying unit 16 (conveying belt 17) located on the downstream side constitutes the downstream conveying means. In addition, these upstream conveying means and downstream conveying means function as part of the conveying device. This conveying device may include at least a suction conveying section, an example of which is the head under-conveying unit 16, a curl correction section 40, and a control section 50. In addition, the conveying device is provided integrally with the image forming device 10 and includes a control section 50 that controls the overall operation of the image forming device 10, but may also include a control section that controls the operation of only the conveying device (at least the curl correction section 40). In addition, the conveying device does not have to be provided integrally with the image forming device 10, but may be disposed separately, or may be provided integrally with another processing section such as an inspection device.

[0028] As shown in Fig. 2, a skew correction conveying device 30 that corrects skew of the paper P before conveying the paper is disposed upstream of the under-head conveying unit 16. Paper guides 25A and 25B that guide the paper P to the skew correction conveying device 30 are disposed near the skew correction conveying device 30. The paper P sent from the paper feed unit 11 along the paper feed side conveying path T1 is guided to the skew correction conveying device 30 by passing between the paper guides 26A and 26B and between the paper guides 25A and 25B. The paper P that has circulated along the circulating conveying path T2 is guided to the skew correction conveying device 30 by passing between the paper guides 27A and 27B and between the paper guides 25A and 25B.

[0029] The skew correction conveyance device 30 is composed of roller pairs (registration rollers) arranged above and below the paper conveyance path (circulatory conveyance path T2). More specifically, the skew correction conveyance device 30 includes a first roller 31 located above and a second roller 32 located below. The first roller 31 has a paper contact portion 34, which is larger in diameter than the shaft portion 33, on the outer diameter side of the shaft portion 33 extending in the main scanning direction F1. Although not shown, a plurality of paper contact portions 34 are arranged at predetermined intervals in the main scanning direction F1.

[0030] The outer circumferential surface of the second roller 32 contacts the outer circumferential surface of the paper contact portion 34. The second roller 32 is formed of a harder material than the paper contact portion 34. The materials of the second roller 32 and the paper contact portion 34 can be selected arbitrarily. As an example, the paper contact portion 34 can be made of rubber, and the second roller 32 can be made of metal.

[0031] The first roller 31 and the second roller 32 are each supported rotatably about an axis oriented in the primary scanning direction F1, and are rotationally driven by a registration roller drive unit 53 shown in Fig. 3. The registration roller drive unit 53 is composed of a motor, which is an example of an actuator, a transmission mechanism that transmits the driving force of the motor, and the like, and rotates the first roller 31 and the second roller 32 at the same speed.

[0032] When the printing unit 13 performs printing, the control unit 50 controls the rotation and stopping of the first roller 31 and the second roller 32 through the registration roller drive unit 53. The rotation direction of the first roller 31 and the second roller 32 when driven is a forward feed direction that moves the paper P from the upstream side to the downstream side.

[0033] More specifically, when the paper P is guided to the skew correction conveyance device 30 along the paper guide parts 25A and 25B, the control part 50 stops the rotation of the first roller 31 and the second roller 32. The front end of the paper P abuts against the stopped first roller 31 (paper contact part 34) and second roller 32, and the paper P becomes loose. When the paper P in a state of being skewed with respect to the normal paper conveyance direction (sub-scanning direction F2) reaches the skew correction conveyance device 30, the paper P, whose progress is restricted by the stopped first roller 31 and second roller 32, is pushed from the rear, so that the front end of the paper P becomes parallel to the axial direction of the first roller 31 and the second roller 32. In other words, the skew of the paper P is corrected.

[0034] Next, at a predetermined timing when the skew correction is completed, the control unit 50 controls the registration roller driving unit 53 to rotate and drive the first roller 31 and the second roller 32. The paper P after the skew correction enters between the first roller 31 (paper contact unit 34) and the second roller 32, which are rotated and driven, and the paper P is sent downstream by the frictional force of the first roller 31 and the second roller 32. Immediately after the conveyance of the paper P to the downstream side is completed, the control unit 50 controls the registration roller driving unit 53 to stop the rotation of the first roller 31 and the second roller 32, and prepares for the skew correction of the paper P to be conveyed to the skew correction conveyance device 30 next. In this way, the skew correction conveyance device 30 corrects the skew of the paper P, and then conveys the paper P toward the under-head conveyance unit 16 located downstream of the skew correction conveyance device 30.

[0035] The control unit 50 has a processor (e.g., a CPU (Central Processing Unit)) that functions as an arithmetic processing device that controls the overall operation of the image forming apparatus 10, and controls each part of the image forming apparatus 10. As described above, the control unit 50 also functions as a control unit of the conveying device that controls at least the curl correction unit 40. The control unit 50 also determines the number of times the medium M circulates in the circulating conveying unit 30 and whether or not to circulate, and controls the flipper 23, etc.

[0036] The storage unit 55 has memories such as a ROM (Read Only Memory), which is a read-only semiconductor memory in which a specific control program is pre-recorded, and a RAM (Random Access Memory), which is a semiconductor memory that can be written to and read at any time and is used as a working memory area as needed when the processor executes various control programs.

[0037] The interface unit 56 transmits and receives various information to and from external devices. For example, the interface unit 56 receives a print job (print data) from a user terminal.

[0038] In addition, the image forming apparatus 10 may include a scanner for reading an image of a document, an input unit for accepting various operations by a user (for example, curl correction settings), and an operation panel that functions as an example of a display unit.

[0039] 2, a paper suction guide roller 36 that constitutes downstream transport means together with the head under transport unit 16 is provided near the driven roller 19 of the head under transport unit 16. The paper suction guide roller 36 is located directly above the transport surface 17a of the transport belt 17, and functions as a paper guide that presses the paper P toward the transport surface 17a to make it easier to suction and hold the paper P.

[0040] The paper P that has passed through the skew correction transport device 30 and reached the printing unit 13 is required to adhere closely to the transport surface 17a and be transported below the inkjet head 14 without floating upward. In particular, if the paper P has a curl with its leading end (front end) in the sub-scanning direction F2 protruding above the center (a downward convex shape when the paper P is viewed from the side), the leading end of the paper P that has floated above the transport surface 17a may come into contact with the inkjet head 14. In this case, the head surface of the inkjet head 14 that comes into contact with the paper P may be damaged, or ink may adhere to the paper P from the inkjet head 14, causing the paper P to become dirty.

[0041] As shown in FIG. 2, a paper float detection device 37 is disposed downstream of the paper suction guide roller 36 and upstream of the inkjet head 14. The paper float detection device 37 is composed of a known sensor located above the transport surface 17a and detects the lifting of the paper P from the transport surface 17a. A detection signal from the paper float detection device 37 is input to the control unit 50. When the paper float detection device 37 detects the lifting of the paper P from the transport surface 17a, the control unit 50 stops the transport of the paper P and performs a process to prevent the paper P from contacting the inkjet head 14 or clogging the paper P. However, when the paper transport speed increases, it becomes difficult to stop the paper P in a lifted state before it reaches the inkjet head 14. In addition, if the process of stopping printing is performed every time the lifting of the paper P is detected, the printing efficiency decreases.

[0042] In order to prevent the paper P from floating up from the transport surface 17a, the image forming apparatus 10 of this embodiment is provided with a curl straightening section 40 that straightens out curls such as raised end shapes in the paper P. This curl straightening section 40 is disposed upstream of the printing section 13 and the under-head transport unit 16 in the transport direction (sub-scanning direction F2) of the paper P, and straightens out curls in the paper P so that the leading edge of the paper P does not come into contact with the processing section.

[0043] The curl correction unit 40 shapes the paper P so that the ends in the sub-scanning direction F2 point downward relative to the center, thereby preventing upward curling that is likely to cause contact with the inkjet head 14.

[0044] The curl correction section 40 is composed of a pair of rollers (decurl rollers) arranged on either side of the paper transport path (circulatory transport path T2). More specifically, the curl correction section 40 includes a first roller 41 located above and a second roller 42 located below.

[0045] The first roller 41 has a paper contact portion 44, which is on the outer diameter side of the shaft portion 43 extending in the main scanning direction F1 and has a larger diameter than the shaft portion 43. Although not shown, a plurality of paper contact portions 44 are arranged at predetermined intervals in the main scanning direction F1. The paper contact portions 44 are made of a soft material (elastic body such as sponge) that can elastically deform. The second roller 42 is a cylindrical shaft member with a smaller diameter than the paper contact portion 44 of the first roller 41, and is made of a harder material (metal, etc.) than the paper contact portion 44. In other words, the paper contact portion 44 constitutes the soft portion of the curl correction unit 40, and the second roller 42 constitutes the hard portion of the curl correction unit 40.

[0046] The first roller 41 can perform an operation of changing the axial distance from the second roller 42 (moving closer to and away from the second roller 42). When the first roller 41 is brought closer to the second roller 42, due to the difference in hardness and diameter between the paper contact portion 44 and the second roller 42 (the second roller 42 is harder and has a smaller diameter), the second roller 42 enters inside the outer shape of the paper contact portion 44 in the free state (initial state), and the paper contact portion 44 is pressed toward the inner diameter side (the shaft portion 43 side) by the second roller 42, resulting in an elastically deformed pressed state (FIG. 4(a)). When the first roller 41 is separated from the second roller 42, the pressure on the paper contact portion 44 by the second roller 42 is released, and the deformation of the paper contact portion 44 is released, resulting in a separated state (FIG. 4(b)).

[0047] The first roller 41 and the second roller 42 are each supported rotatably about an axis oriented in the primary scanning direction F1, and are rotationally driven by a decurl roller drive unit 54 shown in Fig. 3. The decurl roller drive unit 54 is composed of a motor, which is an example of an actuator, a transmission mechanism that transmits the driving force of the motor, and the like, and rotates the first roller 41 and the second roller 42 at the same speed. In addition, the decurl roller drive unit 54 operates the curl correction unit 40 between a pressed state (Fig. 4(a)) and a separated state (Fig. 4(b)).

[0048] When the printing unit 13 performs printing, the control unit 50 controls the decurling roller drive unit 54 to bring the curl straightening unit 40 into a pressed state, and causes the decurling roller drive unit 54 to rotate the first roller 41 and the second roller 42. The rotation direction of the first roller 41 and the second roller 42 at this time is the forward feed direction that moves the paper P from the upstream side to the downstream side.

[0049] When the paper P passes between the first roller 41 (paper contact section 44) and the second roller 42, which are driven to rotate, the paper P is shaped to have an upward convex shape that conforms to the outer surface of the hard second roller 42 (see FIG. 4(a)). Therefore, the paper P transported from the curl correction section 40 to the printing section 13 advances with the front end in the sub-scanning direction F2 not pointing upward (not having an end-up shape) and with curl suppressed, and reaches the position of the head under-transport unit 16. The paper P that has reached the head under-transport unit 16 is pressed against the transport surface 17a of the transport belt 17 by the paper suction guide roller 36, and is transported downstream while being adsorbed to the transport belt 17. Then, the inkjet head 14 ejects ink toward the paper P held on the transport surface 17a to perform printing. When correcting the curl of paper P, it is sufficient to operate the curl correction section 40 in the pressed state (Figure 4(a)) at least when the leading edge of the paper P passes through the curl correction section 40. However, if the curl correction section 40 is operated from the pressed state (Figure 4(a)) to the separated state (Figure 4(b)) during the transport of a sheet of paper P, wrinkles may occur in the paper P.

[0050] The paper P with the curl at the end suppressed by the curl correction unit 40 is properly held on the transport surface 17a and transported by the transport belt 17 in a state where the front end in the sub-scanning direction F2 floats from the transport belt 17 and does not contact the inkjet head 14. Thereby, printing can be performed with excellent print quality without damaging the inkjet head 14 or causing ink smudging on the paper P.

[0051] When the paper transport speed by the skew correction transport device 30 is V1 and the paper transport speed by the under-head transport unit 16 is V2, the control unit 50 controls the driving of the registration roller drive unit 53 and the belt drive unit 51 during the printing operation so that V1 > V2.

[0052] Although it depends on the type of the paper P, the distance from the skew correction transport device 30 to the transport belt 17 in the sub-scanning direction F2 is smaller than the length of a general paper P used in the image forming apparatus 10. Therefore, the paper P reaches the transport surface 17a of the transport belt 17 while maintaining a state of being sandwiched between the first roller 31 (paper contact portion 34) and the second roller 32 of the skew correction transport device 30. Here, if V1 < V2, the paper P is suddenly pulled by the transport belt 17 and the transport accuracy of the paper P becomes unstable, and there is a possibility that print misregistration or print unevenness may occur. In contrast, by setting V1 > V2, the transport of the paper P from the skew correction transport device 30 to the under-head transport unit 16 is stabilized, and the behavior of the paper P that deteriorates the print quality can be prevented.

[0053] When V1>V2 is set, the amount of paper transported per unit time by the skew correction transport device 30 is greater than the amount of paper transported per unit time by the under-head transport unit 16. This difference in the amount of paper transport causes slack in the paper P between the skew correction transport device 30 and the under-head transport unit 16. In other words, it is necessary to appropriately slacken the paper P between the skew correction transport device 30 and the under-head transport unit 16. For example, if the structure is such that the slackness of the paper P transported from the skew correction transport device 30 is hindered, the paper P may not proceed smoothly toward the printing unit 13 or the paper P may be bent.

[0054] The image forming apparatus 10 includes a curl correction unit 40, which is a curl suppressing transport means, between the skew correction transport device 30, which is an upstream transport means, and the under-head transport unit 16 and the paper suction guide roller 36, which are downstream transport means. As shown in Fig. 2, the curl correction unit 40 is located immediately downstream of the skew correction transport device 30 in the sub-scanning direction F2, which is the paper transport direction. More specifically, the paper contact portion 34 of the skew correction transport device 30 and the paper contact portion 44 of the curl correction unit 40 are in a positional relationship in which they partially overlap each other in the sub-scanning direction F2, which is the paper transport direction.

[0055] When a large curl occurs at the end of the paper P in the main scanning direction F1 such that the amount of protrusion from the reference position of the paper surface exceeds 2 mm, the paper P is guided by the paper guide units 25A and 25B and is transported to the curl correction unit 40 with the amount of protrusion of 2 mm. In the curl correction unit 40, if the pressure contact area of ​​the first roller 41 and the second roller 42 against the paper P has a margin of 2 mm from the end of the paper width, the end of the paper width will not be pressed even if the paper P has a protrusion of 2 mm, so wear on the first roller 41 and the second roller 42 can be prevented. Therefore, by setting the pressure contact with a margin of 2 mm from the end of the paper width in the curl correction unit 40, it is possible to obtain a curl suppression effect that is sufficient for practical use while preventing wear on the rollers 41 and 42.

[0056] The operation of the image forming apparatus 10 will be described below while omitting points that overlap with the above description as appropriate.

[0057] First, when an instruction to execute a print job is input, the control unit 50 determines whether the curl straightening unit 40 is in a separated state. If the curl straightening unit 40 is in a separated state, the control unit 50 instructs the decurl roller drive unit 54 to move the first roller 41 closer to the second roller 42, thereby bringing the curl straightening unit 40 into a pressed state. On the other hand, if the curl straightening unit 40 is in a pressed state, the control unit 50 instructs the decurl roller drive unit 54 to drive the first roller 41 and the second roller 42 to rotate, thereby causing the curl straightening unit 40 to perform preliminary rotation.

[0058] The control unit 50 then controls the paper transport operation for transporting the paper P from the paper feed unit 11 to the printing unit 13, and the printing process in the printing unit 13.

[0059] The paper conveying operation is performed by the registration roller driving unit 53 rotating the first roller 31 and the second roller 32 (repeatly correcting skew while the rollers are stopped and driving the rollers after the skew correction), the decurling roller driving unit 54 rotating the first roller 41 and the second roller 42, and the belt driving unit 51 rotating the conveyor belt 17. The control unit 50 also drives the suction fan 22 by the fan driving unit 52 to convey the paper P while suctioning and holding it on the conveyor surface 17a of the conveyor belt 17. The printing process is performed by ejecting ink from the inkjet head 14 onto the paper P conveyed on the conveyor surface 17a based on the print job. After printing, the paper P is conveyed to the paper discharge unit 15 and collected.

[0060] Here, when multiple sheets of paper P are transported for a single print job, or when multiple print jobs are executed in succession, the paper P is continuously transported by the under-head transport unit 16. Note that when the paper P is continuously transported, this refers to, for example, when the under-head transport unit 16 simultaneously transports at least the rear end of the preceding paper P and at least the front end of the succeeding paper P.

[0061] When the paper sheets P are continuously transported by the under-head transport unit 16, as shown in Fig. 5(a), when the first sheet of paper P1 enters onto the transport surface 17a of the transport belt 17, the suction holes of the transport belt 17 are open and not blocked by the preceding sheet of paper P. Therefore, if the adhesion between the transport belt 17 and the first sheet of paper P1 is reduced and the first sheet of paper P1 has the above-mentioned edge-rising shape, the first sheet of paper P1 may come into contact with the inkjet head 14 (printing unit 13), damaging the inkjet head 14 or staining the first sheet of paper P1 with ink.

[0062] Therefore, when the first sheet of paper P1 passes through the curl correction section 40, the control section 50 instructs the decurling roller drive section 54 to move the first roller 41 closer to the second roller 42, as described above, thereby bringing the curl correction section 40 into a pressure contact state, i.e., controls the curl correction section 40 to correct the curl of the first sheet of paper P1.

[0063] 5(b), when the second (or subsequent) sheet of paper P2 enters onto the conveying surface 17a of the conveying belt 17, the suction holes of the conveying belt 17 are at least partially blocked by the preceding first sheet of paper P1. Therefore, even if the adhesion between the conveying belt 17 and the second sheet of paper P2 is strong and the curl is not corrected, there is little risk of the second sheet of paper P2 coming into contact with the inkjet head 14 (printing unit 13) causing damage to the inkjet head 14 or of ink stains adhering to the second sheet of paper P2.

[0064] Therefore, the control unit 50 may control the decurling roller drive unit 54 (curl straightening unit 40) to omit curl straightening for the second sheet of paper P2 and subsequent sheets of paper P. Note that when the sheets of paper P are continuously transported by the under-head transport unit 16, a mode in which curl straightening is omitted for the second sheet of paper P and subsequent sheets of paper P, a mode in which curl straightening is performed on all sheets of paper P, and a mode in which curl straightening is omitted for all sheets of paper P may be set, for example, via a print job or an operation panel of the image forming apparatus 10. In this case, the control unit 50 controls the curl straightening unit 40 based on the set mode.

[0065] As shown in FIG. 6, when double-sided printing is performed on the paper P, after the front side of the paper P is printed, the paper P may be transported in the circulating transport path T2 shown in FIG. 1 and inverted by the inversion unit 12, so that the paper P may be transported again to the printing unit 13 with an interval of, for example, four sheets of paper P. In such a case, an interval of one sheet of paper P or more may be left between the time when the front side of the first sheet of paper P (front side 1 in FIG. 6) is printed and the time when the front side of the second sheet of paper P (front side 2) is printed, or between the time when the front side of the second sheet of paper P (front side 2) is printed and the time when the front side of the third sheet of paper P (front side 3) is printed. Therefore, when the front side of the first sheet of paper P (front side 1) is printed and when the front side of the second sheet of paper P (front side 2) is printed, the paper P cannot be said to be continuously transported by the under-head transport unit 16. Therefore, when printing on the front sides of the first to third sheets of paper P (front sides 1, 2, and 3) is performed, the control unit 50 may control (ON) the curl straightening unit 40 so that the curl of the paper P is straightened.

[0066] In addition, the control unit 50 may not omit curl correction for all the sheets P from the second sheet onward that are continuously transported by the under-head transport unit 16. For example, the control unit 50 may determine which sheets P are to be curl corrected and which sheets P are to be omitted curl correction, based on the thickness, material, and other types of the sheets P. Alternatively, the last sheet P continuously transported by the under-head transport unit 16 is not transported by the succeeding sheets P, and therefore the adhesion between the transport belt 17 and the last sheet P is reduced by opening the suction holes of the transport belt 17 rather than blocking them, particularly when the leading edge of the sheet P leaves the transport surface 17a of the transport belt 17. Therefore, it is preferable to perform curl correction on the last sheet P continuously transported by the under-head transport unit 16. However, since the sheet P once adsorbed to the transport belt 17 is less likely to float up, the last sheet P is less likely to come into contact with the inkjet head 14 compared to the first sheet P. Furthermore, when the rear end of the last sheet P reaches approximately the middle position of the conveying surface 17a, the suction holes of the conveying belt 17 are not blocked but open, as described above, and the suction force weakens, but at this time the leading edge of the last sheet P is already about to leave the conveying surface 17a. Therefore, curl correction of the last sheet P may be omitted.

[0067] 7, when the width of the first to third sheets of paper P in the width direction (main scanning direction F1) perpendicular to the conveying direction (sub-scanning direction F2) is relatively narrow and the width of the fourth to sixth sheets of paper P is relatively wide, the fourth sheet of paper P (4 wide) is wider than the preceding sheet of paper P (3 narrow) even though it is the second or subsequent sheet of paper P conveyed continuously. Therefore, when the fourth sheet of paper P (4 wide) enters the conveying surface 17a of the conveying belt 17, the suction holes of the conveying belt 17 are opened, and the adhesion between the conveying belt 17 and the fourth sheet of paper P (4 wide) is likely to be smaller than when sheets of paper P of the same width are conveyed continuously. Therefore, in such a case, the control unit 50 may control (ON) the curl straightening unit 40 so that the curl of the fourth sheet of paper P (4 wide) is straightened.

[0068] When the print job is completed, the control unit 50 instructs the decurling roller driving unit 54 to move the first roller 41 away from the second roller 42, thereby putting the curl correction unit 40 in a separated state. By putting the curl correction unit 40 in a separated state in this way, the paper contact unit 44 is released from the pressure of the second roller 42 after printing is completed, and deformation (permanent deformation) of the paper contact unit 44 can be prevented. Note that printing may stop with the curl correction unit 40 in a pressed state due to a power outage or other cause during printing. In this case, the state in which the paper contact unit 44 is deformed by the pressure of the second roller 42 (FIG. 4(a)) continues. Here, if the curl correction unit 40 is pre-rotated as described above before the execution of the next print job, the deformation of the paper contact unit 44 is evened out and a restoration operation occurs to bring it closer to its original shape. If the paper is transported with a part of the paper contact unit 44 still having a concave permanent deformation, the paper P will not pass through the curl correction unit 40 smoothly, and the paper transport accuracy will decrease. In response to this, the shape of the paper contact portion 44 is restored by the preliminary rotation of the curl straightening portion 40, so that the deterioration of the paper transport accuracy can be prevented.

[0069] In the above description, the curl correction unit 40 is configured with a pair of rollers that sandwich the paper P from both sides, but the configuration of the curl correction unit 40 is not limited to this. For example, instead of the curl correction unit 40 configured with a pair of rollers, a combination of a conveyor belt and a roller that presses the paper against the conveyor belt may be used.

[0070] In the present embodiment described above, the conveying device includes the under-head conveying unit 16 (an example of an adsorption conveying unit), the curl straightening unit 40, and the control unit 50. The under-head conveying unit 16 has a conveying belt 17 (an example of a conveying member) that conveys the paper P (an example of a medium), and a suction fan 22 (an example of an adsorption unit) that adsorbs the paper P to the conveying belt 17, and is disposed to face the printing unit 13 (an example of a processing unit) that prints (an example of a process) on the paper P. The curl straightening unit 40 is disposed upstream of the printing unit 13 and the under-head conveying unit 16 in the conveying direction (sub-scanning direction F2) of the paper P, and straightens the curl of the paper P so that the leading edge of the paper P does not contact the printing unit 13. When the paper P is continuously conveyed by the under-head conveying unit 16, the control unit 50 controls the curl straightening unit 40 to straighten the curl of the first sheet of paper P and to omit curl straightening for at least some of the sheets of paper P from the second sheet onward.

[0071] Incidentally, when the first sheet P of multiple sheets P that are continuously conveyed is conveyed by the conveyor belt 17 (one example of a conveying member), for example, when the sheet P is adsorbed by suction of air, the suction holes of the conveyor belt 17 are open and not blocked by the preceding sheet P, so that the adhesive force between the conveyor belt 17 and the sheet P is small. Therefore, if the sheet P has curl (for example, an end rising shape), the sheet P may come into contact with the printing unit 13, causing damage to the printing unit 13 or ink stains to adhere to the sheet P. On the other hand, when the second and subsequent sheets P are conveyed by the conveyor belt 17, the suction holes of the conveyor belt 17 are blocked by the preceding sheet P, so that the above-mentioned damage to the printing unit 13 is unlikely to occur. Therefore, curl correction can be omitted for the second and subsequent sheets P. The same can be said when the adsorption unit is not a suction unit such as the suction fan 22 that sucks air, but is instead adsorbed to the conveyor belt 17 by other adsorption methods such as electrostatic adsorption. Therefore, according to this embodiment, it is possible to prevent the paper P from coming into contact with the printing unit 13 (an example of a processing unit) while reducing the number of sheets of paper P (an example of a medium) to be straightened.

[0072] Furthermore, if curl correction is performed on all sheets P, wrinkles extending in the conveying direction of the sheet P and image unevenness due to fluctuations in the conveying speed, which are likely to occur when curl correction is performed by pinching the sheet P between a pair of a soft roller (e.g., sheet contact portion 44 of first roller 41) and a hard roller (e.g., second roller 42), can occur on all sheets P, but the occurrence of these wrinkles and image unevenness can be suppressed. Also, when curl correction is performed using a soft roller such as a soft roller, the roller wears out, reducing the curl correction effect and increasing power consumption due to the large rotational resistance of the roller, but by omitting curl correction for at least some of the sheets P from the second sheet onwards, it is possible to prevent wear and save power.

[0073] Furthermore, in this embodiment, the control unit 50 controls the curl correction unit 40 to correct curls in the second or subsequent sheet of paper P when the sheet of paper P is continuously transported by the under-head transport unit 16 and which is wider in the width direction (main scanning direction F1) perpendicular to the transport direction (sub-scanning direction F2) of the sheet of paper P (e.g., 4-wide) than the previous sheet of paper P transported (e.g., 3-narrow in FIG. 7).

[0074] In this way, when a sheet of paper P that is wider than the previous sheet of paper P enters onto the conveying surface 17a of the conveying belt 17, the suction holes of the conveying belt 17 are more likely to open, and the adhesion force with the conveying belt 17 is more likely to be weaker, compared to when the previous sheet of paper P has the same width. Therefore, by correcting the curl of a sheet of paper P that is wider than the previous sheet of paper P, it is possible to more reliably prevent damage to the printing unit 13 and adhesion of ink stains to the sheet of paper P.

[0075] The present invention is not limited to the above-described embodiment as it is, and the components can be modified and embodied in the implementation stage without departing from the gist of the invention. In addition, various inventions can be formed by appropriate combinations of the multiple components disclosed in the above-described embodiment. For example, all the components shown in the above-described embodiment may be appropriately combined. Of course, various modifications and applications are possible without departing from the spirit of the invention. The invention described in the claims at the time of filing of this application is appended below.

[0076] [Appendix 1] a suction conveyance unit that has a conveyance member that conveys a medium and an adsorption unit that adsorbs the medium to the conveyance member, the suction conveyance unit being disposed opposite a processing unit that performs processing on the medium; a curl straightening unit that is disposed upstream of the processing unit and the suction transport unit in a transport direction of the medium and that straightens curls of the medium so that a leading edge of the medium does not contact the processing unit; a control unit that controls the curl straightening unit so that, when the medium is continuously conveyed by the suction conveying unit, curl is straightened for a first sheet of the medium and curl straightening is omitted for at least a portion of the second and subsequent sheets of the medium; A conveying device comprising:

[0077] [Appendix 2] The control unit controls the curl straightening unit to straighten curls of the second or subsequent medium when the medium is continuously conveyed by the suction conveying unit and has a wider width in a width direction perpendicular to a conveying direction of the medium than the previous medium conveyed. 2. The conveying device according to claim 1 . [Explanation of symbols]

[0078] 10: Image forming device 11:Paper feed section 13:Printing Department 14: Inkjet head 15: Paper ejection section 16: Head under transport unit (suction transport section) 17: Conveyor belt 17a: Transport surface 22: Suction fan (suction part) 30: Skew correction conveying device 31: First roller 32: Second roller 34:Paper contact part 35: Second roller 36: Paper suction guide roller 37:Detection device 40: Curl correction section 41: First roller 42: Second roller 44:Paper contact part 50: Control section P:Paper (medium) T1:Paper feed side transport path T2: Circulation conveying path T3: Paper ejection path

Claims

1. a suction conveyance unit that has a conveyance member that conveys a medium and an adsorption unit that adsorbs the medium to the conveyance member, the suction conveyance unit being disposed opposite a processing unit that processes the medium; a curl straightening unit that is disposed upstream of the processing unit and the suction transport unit in a transport direction of the medium and straightens curls of the medium so that a leading edge of the medium does not contact the processing unit; a control unit that controls the curl straightening unit so that, when the medium is continuously conveyed by the suction conveying unit, curl is straightened for a first sheet of the medium and curl straightening is omitted for at least a portion of the medium from the second sheet onward, The curl straightening unit straightens out curls in the medium by a pair of rollers that sandwich the medium. A conveying device characterized by the above.

2. The roller pair is a soft roller and a hard roller, The curl straightening unit straightens the curl of the medium when the hard roller presses the soft roller and elastically deforms the soft roller in a pressure-contact state, and omits the curl straightening when the soft roller and the hard roller are separated from each other.

2. The conveying device according to claim 1.

3. An adsorption conveying unit having a conveying member for conveying a medium and an adsorption unit for adsorbing the medium to the conveying member, the adsorption conveying unit being disposed opposite a processing unit for processing the medium; a curl straightening unit that is disposed upstream of the processing unit and the suction transport unit in a transport direction of the medium and straightens curls of the medium so that a leading edge of the medium does not contact the processing unit; a control unit that controls the curl straightening unit so that, when the medium is continuously conveyed by the suction conveying unit, curl is straightened for a first sheet of the medium and curl straightening is omitted for at least a portion of the medium from the second sheet onward, The control unit controls the curl straightening unit to straighten curls of the second or subsequent medium when the medium is continuously transported by the suction transport unit and has a wider width in a width direction perpendicular to a transport direction of the medium than the previously transported medium. A conveying device characterized by the above.

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