JP7521985B2 - Conveyor - Google Patents

Description

The present invention relates to a conveying device for conveying paper.

Printing devices are known that have a printing section that ejects ink from an inkjet head while transporting paper to print on the paper. In addition, a mechanism is known for such printing devices that uses a pair of registration rollers to correct the skew of the paper and transport the paper to the printing section.

In this type of mechanism, the paper is pushed against the stopped registration roller pair and stopped temporarily, creating slack in the paper and correcting any skew in the paper. The registration roller pair is then driven to send the paper to the printing section. When the paper passes through the registration roller pair, the registration roller pair stops.

In addition, in printing devices such as those described above, it is known to provide a pair of de-curling rollers that convey the paper while curling it in an upward convex direction in order to reduce contact of the paper with the inkjet head (see Patent Document 1).

Here, in order to reduce the size of the device, it is preferable to provide one de-curling roller pair at a position where all the sheets that enter the registration roller pair from multiple transport paths, such as the path for feeding paper from the paper feed tray and the path for double-sided printing, pass through. In other words, it is preferable that the de-curling roller pair be located between the registration roller pair and the printing unit.

In a configuration in which a de-curling roller pair is disposed between the registration roller pair and the printing unit, if slack occurs in the paper between the registration roller pair and the de-curling roller pair, it can cause the paper to wrinkle. For this reason, it is preferable to drive the de-curling roller pair so as to maintain a transport speed slightly faster than that of the registration roller pair while being synchronized with the registration roller pair. To achieve this, it is preferable to drive the de-curling roller pair with the same drive source as the registration roller pair.

Patent No. 4345873

However, in a configuration in which the de-curling roller pair is driven by the same drive source as the registration roller pair, the registration roller pair cannot be stopped until the paper has passed the de-curling roller pair. As a result, the registration roller pair cannot accept the next sheet of paper until the paper has passed the de-curling roller pair, and so it is necessary to increase the gap (paper spacing) between successively transported sheets of paper. This results in reduced productivity.

Therefore, there was a demand for technology that could curl the paper while minimizing the increase in the gap between continuously transported sheets of paper.

The present invention has been made in consideration of the above, and aims to provide a conveying device that can curl paper while suppressing the increase in the gap between continuously conveyed sheets of paper.

To achieve the above object, the conveying device of the present invention is characterized by comprising: a first roller pair that conveys paper for each sheet; a second roller pair that is disposed downstream of the first roller pair in the paper conveying direction and is driven together with the first roller pair by the same drive source as the drive source of the first roller pair, and nip and convey the paper while curling it; a switching unit that switches the second roller pair between a nipping state in which the paper can be nipped and a nipping release state in which the paper is not nipped; and a control unit that controls the switching unit to set the second roller pair to the nipping state before the leading edge of the paper reaches the second roller pair and to set the second roller pair to the nipping release state before the trailing edge of the paper leaves the first roller pair.

The conveying device of the present invention can curl the paper while preventing the gap between successively conveyed sheets from increasing.

1 is a schematic configuration diagram of a printing device according to an embodiment. FIG. 2 is a control block diagram of the printing apparatus shown in FIG. 1 . 2 is a perspective view showing a schematic configuration of a pair of registration rollers, a pair of de-curling rollers, and a switching unit of the printing apparatus shown in FIG. 1 . 2 is a plan view showing the vicinity of a registration motor of the printing apparatus shown in FIG. 1. 2 is a front view showing the vicinity of the de-curling roller pair of the printing device shown in FIG. 1 when the de-curling roller pair is in a nipping state. 2 is a front view showing the vicinity of the de-curling roller pair of the printing device shown in FIG. 1 when the de-curling roller pair is in a nip release state. 13A and 13B are diagrams showing the transition of the conveying speed of the registration roller pair and the de-curling roller pair, the switching timing between the nipping possible state and the nipping released state of the de-curling roller pair, and the presence or absence of paper P in the registration roller pair and the de-curling roller pair.

The following describes an embodiment of the present invention with reference to the drawings. The same or equivalent parts and components are denoted by the same or equivalent reference numerals throughout the drawings.

The embodiments shown below are examples of devices that embody the technical idea of this invention, and the technical idea of this invention does not specify the materials, shapes, structures, arrangements, etc. of each component part to those described below. The technical idea of this invention can be modified in various ways within the scope of the claims.

Figure 1 is a schematic diagram of a printing device equipped with a conveying device according to an embodiment of the present invention. Figure 2 is a control block diagram of the printing device shown in Figure 1. Figure 3 is a perspective view showing the schematic configuration of the registration roller pair, de-curling roller pair, and switching unit of the printing device shown in Figure 1. Figure 4 is a plan view showing the vicinity of the registration motor of the printing device shown in Figure 1. Figure 5 is a front view showing the vicinity of the de-curling roller pair when the de-curling roller pair of the printing device shown in Figure 1 is in a nip-enabled state. Figure 6 is a front view showing the vicinity of the de-curling roller pair when the de-curling roller pair of the printing device shown in Figure 1 is in a nip-released state. In the following description, the direction perpendicular to the paper surface of Figure 1 is the front-rear direction, and the front direction of the paper surface is the forward direction. Also, the up-down-left-right directions of the paper surface in Figure 1 are the up-down-left-right directions.

In FIG. 1, the path indicated by the thick line is the transport path along which paper P, which is the print medium, is transported. Of the transport paths, the path indicated by the solid line is the normal path RC, the path indicated by the dashed line is the reversal path RR, the path indicated by the dashed line is the paper discharge path RD, and the path indicated by the two-dot chain line is the paper feed path RS. In the following explanation, upstream and downstream refer to upstream and downstream in the transport path.

As shown in Figures 1 and 2, the printing device 1 according to this embodiment includes a paper feed section 2, a printing section 3, an upper transport section 4, a paper discharge section 5, an inversion section 6, an operation panel 7, a control section 8, and a housing 9 that houses or holds each section. The paper feed section 2 and the control section 8 form a transport device.

The paper feed unit 2 feeds paper P to the printing unit 3. The paper feed unit 2 includes an external paper feed unit 11, an internal paper feed unit 12, a pair of registration rollers (corresponding to a first pair of rollers) 13, a pair of de-curling rollers (corresponding to a second pair of rollers) 14, a registration motor (corresponding to a drive source) 15, and a switching unit 16.

The external paper feed unit 11 includes an external paper feed tray 21 and an external paper feed transport unit 22.

The external paper feed tray 21 is installed with a portion exposed to the outside of the housing 9, and is where paper P is loaded.

The external paper feed conveying unit 22 takes out the paper P stacked on the external paper feed tray 21 one sheet at a time and conveys the paper P along the paper feed path RS toward the registration roller pair 13.

The internal paper feed unit 12 includes multiple internal paper feed trays 26 and an internal paper feed transport unit 27.

The internal paper feed tray 26 is installed inside the housing 9 and is where the paper P is loaded.

The internal paper feed conveying unit 27 takes out paper P one sheet at a time from the internal paper feed tray 26 and conveys the paper P along the paper feed path RS toward the registration roller pair 13.

The registration roller pair 13 temporarily stops the paper P conveyed from either the external paper feed unit 11, the internal paper feed unit 12, or the inversion unit 6, and then nips the paper P while conveying it toward the printing unit 3. The registration roller pair 13 intermittently conveys the paper P for each sheet P fed to the printing unit 3. The registration roller pair 13 is disposed on the normal path RC near the junction of the paper feed path RS and the inversion path RR. The registration roller pair 13 includes multiple registration drive rollers 13a and multiple registration driven rollers 13b.

As shown in FIG. 3, the registration drive rollers 13a are attached to a drive shaft 13c extending in the front-rear direction at intervals in the front-rear direction. The registration drive rollers 13a are rotated by the driving force generated by the registration motor 15.

The registration driven rollers 13b are attached to a rotating shaft 13d (see FIG. 5) that extends in the front-rear direction, spaced apart in the front-rear direction. The same number of registration driven rollers 13b as the registration drive rollers 13a are installed below each registration drive roller 13a so that each one is in contact with each registration drive roller 13a. The registration driven rollers 13b rotate in response to the registration drive rollers 13a.

The de-curling roller pair 14 nips and transports the paper P while curling it in a direction that does not contact the inkjet head 48 described below. Specifically, the de-curling roller pair 14 nips and transports the paper P while curling it in a direction that makes the paper convex upward. The de-curling roller pair 14 is disposed downstream of the registration roller pair 13 on the normal path RC, between the registration roller pair 13 and the printing unit 3. The de-curling roller pair 14 includes a plurality of de-curling driven rollers 14a and a de-curling drive roller 14b.

As shown in FIG. 3, the multiple decurler driven rollers 14a are attached to a rotating shaft 14c extending along the front-rear direction with a gap between them. The decurler driven rollers 14a are arranged in a position in the front-rear direction where there is no registration drive roller 13a. This allows the gap between the registration roller pair 13 and the decurler roller pair 14 on the normal path RC to be kept small, thereby preventing the printing device 1 from becoming larger. The decurler driven rollers 14a are made of an elastically deformable material. The decurler driven rollers 14a can be moved toward and away from the decurler drive roller 14b by the switching unit 16.

The decurler drive roller 14b is a single roller that is elongated in the front-rear direction. The decurler drive roller 14b is attached to a drive shaft 14d (see FIG. 4) that extends along the front-rear direction. The decurler drive roller 14b is provided below the decurler driven roller 14a. The decurler drive roller 14b is formed of a rigid body such as metal. The decurler drive roller 14b is driven to rotate by the driving force generated by the registration motor 15. In other words, the drive source of the decurler roller pair 14 is the same as the drive source (registration motor 15) of the registration roller pair 13.

The registration motor 15 drives the registration roller pair 13 and the de-curling roller pair 14. As shown in FIG. 4, a gear 31 is attached to the output shaft 15a of the registration motor 15. The gear 31 meshes with a gear 32 attached to the drive shaft 13c of the registration drive roller 13a, and the gear 32 meshes with a gear 33 attached to the drive shaft 14d of the de-curling drive roller 14b. As a result, the registration roller pair 13 and the de-curling roller pair 14 are driven by the rotation of the output shaft 15a of the registration motor 15.

Here, the gear ratio between gear 32 and gear 33 is set so that the conveying speed of the de-curling roller pair 14 is slightly faster than the conveying speed of the registration roller pair 13. This prevents sagging of the paper P between the registration roller pair 13 and the de-curling roller pair 14, which causes wrinkles in the paper P.

The switching unit 16 switches the decurling roller pair 14 between a nipping state and a nipping release state.

The nipping state is a state in which the decurler roller pair 14 can nip the paper P, and as shown in FIG. 5, the decurler drive roller 14b is pressed against the decurler driven roller 14a. In the nipping state, the decurler driven roller 14a is pressed by the decurler drive roller 14b and deforms, forming an upwardly convex nip portion between the decurler driven roller 14a and the decurler drive roller 14b. As a result, in the nipping state, the decurler roller pair 14 can curl the paper P in an upwardly convex direction while nipping and transporting the paper P.

The nip release state is a state in which the decurler roller pair 14 does not nip the paper P, and the decurler driven roller 14a and the decurler drive roller 14b are separated from each other, as shown in FIG. 6.

The switching unit 16 includes a cam 41, a cam follower 42, and a cam motor 43.

The cam 41 is a member for changing the height position of the decurler driven roller 14a in order to switch the decurler roller pair 14 between a nip-enabled state and a nip-disengaged state. The cam 41 is attached to a cam shaft 41a that extends in the front-rear direction.

The cam follower 42 is a member that abuts against the outer periphery of the cam 41. The cam follower 42 is attached to the rotating shaft 14c of the decurler driven roller 14a. The rotating shaft 14c of the decurler driven roller 14a is biased toward the cam 41 by a spring (not shown). This keeps the cam follower 42 in contact with the cam 41, and allows the height position of the rotating shaft 14c to be adjusted in response to the rotation of the cam 41.

The cam motor 43 rotates the cam 41 by rotating the cam shaft 41a.

The printing unit 3 ejects ink onto the paper P while transporting the paper P to print. The printing unit 3 includes a belt platen unit 46, two pressure rollers 47, and multiple inkjet heads (corresponding to image forming units) 48.

The belt platen unit 46 transports the paper P transported by the paper feed unit 2 or the inversion unit 6 while holding the paper P by air suction. The belt platen unit 46 includes a transport belt 51 and a fan 52.

The conveyor belt 51 adsorbs and holds the paper P and transports it. The conveyor belt 51 has many belt holes formed therein, which are through holes for suctioning air. The conveyor belt 51 adsorbs and holds the paper P by the suction force generated in the belt holes by the drive of the fan 52. The conveyor belt 51 rotates (moves endlessly) in the clockwise direction in FIG. 1, thereby transporting the adsorbed and held paper P from left to right.

The fan 52 draws air through the belt holes of the conveyor belt 51 to generate negative pressure in the belt holes, thereby adsorbing and holding the paper P onto the conveyor belt 51.

The pressure roller 47 is a roller for pressing the paper P against the conveyor belt 51. The pressure roller 47 rotates in response to the rotation of the conveyor belt 51. One pressure roller 47 is disposed at each of the upstream and downstream ends of the belt platen portion.

The inkjet head 48 has multiple nozzles arranged along the front-to-rear direction, and prints (forms an image) by ejecting ink from the nozzles onto the upper surface of the paper P transported by the belt platen unit 46. Each of the multiple inkjet heads 48 ejects ink of a different color (e.g., black, cyan, magenta, yellow). The multiple inkjet heads 48 are arranged in parallel above the paper P transported by the belt platen unit 46 along the transport direction (left-right direction) of the paper P.

The upper conveying unit 4 conveys the paper P conveyed by the belt platen unit 46 along the normal path RC to the paper discharge unit 5 or the inversion unit 6.

The paper discharge unit 5 has a paper discharge tray 56, and discharges the printed paper P transported by the upper transport unit 4 onto the paper discharge tray 56.

When double-sided printing is performed, the reversing unit 6 reverses the paper P that has been printed on one side and transports it to the pair of registration rollers 13.

The operation panel 7 displays various input screens and accepts input operations by the user. The operation panel 7 includes a display unit (not shown) having a liquid crystal display panel or the like, and an input unit (not shown) having various operation keys, a touch panel, etc.

The control unit 8 controls the operation of each part of the printing device 1. The control unit 8 is configured with a CPU, RAM, ROM, hard disk, etc.

During printing operation, the control unit 8 controls the switching unit 16 to put the de-curling roller pair 14 into a nipping state before the leading edge of the paper reaches the de-curling roller pair 14, and to put the de-curling roller pair 14 into a nipping release state before the trailing edge of the paper passes through the registration roller pair 13.

Next, we will explain the operation of the printing device 1.

When a print job is input, the control unit 8 executes the printing operation. Here, the control unit 8 acquires the print setting information contained in the print job, and executes single-sided or double-sided printing according to the contents.

In the case of single-sided printing, the control unit 8 controls the paper feed unit 2 to sequentially take out unprinted paper P from either the external paper feed tray 21 or one of the multiple internal paper feed trays 26 and feed it to the printing unit 3.

Here, the control unit 8 controls the pair of registration rollers 13 to send out each sheet P so that it is transported at a predetermined interval on the belt platen unit 46. The control unit 8 also controls the switching unit 16 to set the pair of de-curling rollers 14 to a nipping state before the leading edge of the sheet reaches the pair of de-curling rollers 14, and to set the pair of de-curling rollers 14 to a released nip state before the trailing edge of the sheet passes through the pair of registration rollers 13. The operation of the pair of registration rollers 13, the pair of de-curling rollers 14, and the switching unit 16 will be described in detail later.

The paper P fed to the printing unit 3 is printed with ink ejected from the inkjet head 48 while being transported by the belt platen unit 46. The printed paper P is transported from the belt platen unit 46 to the upper surface transport unit 4, and then transported by the upper surface transport unit 4 to the paper discharge unit 5. The paper P is then discharged to the paper discharge tray 56 in the paper discharge unit 5.

In the case of double-sided printing, the control unit 8 controls the paper feed unit 2 to sequentially feed unprinted paper P to the printing unit 3 at a timing that doubles the time between the paper feed timings of each paper P compared to the paper feed timing during single-sided printing. At this time, the control unit 8 controls the switching unit 16 in the same way as in the single-sided printing described above.

As in single-sided printing, the paper P fed to the printing unit 3 is printed on with ink ejected from the inkjet head 48 while being transported by the belt platen unit 46. After single-sided printing, the paper P is transported from the belt platen unit 46 to the upper surface transport unit 4, and after being transported by the upper surface transport unit 4, is guided to the inversion unit 6. The paper P guided to the inversion unit 6 is inverted in the inversion unit 6, and then refed to the printing unit 3 by the pair of registration rollers 13. Even during this re-feed, the control unit 8 controls the switching unit 16 in the same way as in single-sided printing described above.

Here, the paper P after single-sided printing is refed at a timing such that it is sent to the belt platen unit 46 alternately with the unprinted paper P that is fed in sequence. As described above, in double-sided printing, the time between the feeding timing of each paper P is twice as long as in single-sided printing. For this reason, it is possible to insert the paper P after single-sided printing between the unprinted paper P, and refed the paper P after single-sided printing alternately with the feeding of the unprinted paper P.

After printing on one side, the paper P is inverted by the inversion unit 6 and sent to the belt platen unit 46 with the unprinted side facing up. Then, while the paper P is transported by the belt platen unit 46, the unprinted side is printed with ink ejected from the inkjet head 48. The paper P that has been printed on both sides is transported by the upper transport unit 4 to the paper discharge unit 5, where it is discharged onto the paper discharge tray 56.

Next, we will explain the operation of the registration roller pair 13, the decurling roller pair 14, and the switching unit 16 during the above-mentioned printing operation.

Figure 7 shows the transition of the conveying speed of the registration roller pair 13 and the de-curling roller pair 14, the switching timing between the nipping possible state and the nipping released state of the de-curling roller pair 14, and the presence or absence of paper P in the registration roller pair 13 and the de-curling roller pair 14.

Here, the period from when the leading edge of the paper reaches the pair of registration rollers 13 until the trailing edge of the paper leaves is the period when the paper is present at the pair of registration rollers 13, and the other period is the period when the paper is not present at the pair of registration rollers 13. The same applies to the presence or absence of the paper P at the pair of de-curling rollers 14.

At time t1 in FIG. 7, the leading edge of the paper reaches the pair of registration rollers 13. At this time t1, the pair of registration rollers 13 and the pair of de-curling rollers 14 are stopped. The paper P is pushed against the stopped pair of registration rollers 13, causing slack in the paper P and correcting the skew of the paper P. Also, at time t1, the pair of de-curling rollers 14 is in a released nip state.

After this, the control unit 8 starts driving the registration motor 15, thereby starting to drive the registration roller pair 13. As a result, the paper P starts to be transported by the registration roller pair 13. When the registration motor 15 starts to be driven, the registration roller pair 13 starts to be driven and the decurling roller pair 14 also starts to be driven at the same time.

After the registration roller pair 13 and the de-curling roller pair 14 start to be driven, the control unit 8 controls the switching unit 16 to switch the de-curling roller pair 14 to a nipping-enabled state before time t2 when the paper P reaches the de-curling roller pair 14. Here, the timing when the paper P reaches the de-curling roller pair 14 (time t2) is determined by the distance on the conveying path between the registration roller pair 13 and the de-curling roller pair 14, and a predetermined acceleration from when the registration roller pair 13 starts to be driven until it reaches the top speed Vt described below.

When the paper P reaches the de-curling roller pair 14, the paper P is nipped between the registration roller pair 13 and the de-curling roller pair 14 and transported to the belt platen section 46.

At this time, the paper P curls in an upward convex direction by passing through the upward convex nip formed between the decurler driven roller 14a and the decurler drive roller 14b of the decurler roller pair 14, as shown in FIG. 5. This prevents the leading edge of the paper P from lifting off the belt platen portion 46 in the printing unit 3 and coming into contact with the inkjet head 48.

Here, after the registration roller pair 13 and the decurling roller pair 14 start to be driven, when the conveying speed of the registration roller pair 13 reaches a predetermined top speed Vt, the control unit 8 causes the conveying speed of the registration roller pair 13 to be maintained at the top speed Vt for a predetermined period of time. After this, the control unit 8 causes the conveying speed of the registration roller pair 13 to be decelerated to a predetermined registration conveying speed Vr, and transitions to constant speed conveying at the registration conveying speed Vr.

The registration conveying speed Vr is the conveying speed when the registration roller pair 13 delivers the paper P to the belt platen unit 46, and is set to a speed slightly faster than the conveying speed of the paper P by the belt platen unit 46. The top speed Vt is set as the maximum conveying speed of the registration roller pair 13 for sequentially conveying the paper P at a specified paper interval. The registration roller pair 13 temporarily accelerates to the top speed Vt in order to shorten the paper interval and improve productivity.

When the registration roller pair 13 is being driven, as shown in FIG. 7, the de-curling roller pair 14 is also driven in synchronization with the registration roller pair 13, and the conveying speed of the de-curling roller pair 14 is slightly faster than the conveying speed of the registration roller pair 13. As described above, this is because the gear ratio between gear 32 and gear 33 is set so that the conveying speed of the de-curling roller pair 14 is slightly faster than the conveying speed of the registration roller pair 13. This prevents sagging of the paper P between the registration roller pair 13 and the de-curling roller pair 14, which would otherwise cause wrinkles in the paper P.

After switching the de-curling roller pair 14 to a nipping-enabled state before time t2, the control unit 8 controls the switching unit 16 to switch the de-curling roller pair 14 to a nipping-disengagement state at a predetermined timing before time t3 when the trailing edge of the paper leaves the registration roller pair 13. Here, the timing (time t3) when the trailing edge of the paper leaves the registration roller pair 13 is predetermined according to the length of the paper.

Immediately after time t3 when the trailing edge of the paper leaves the pair of registration rollers 13, the control unit 8 stops the registration motor 15, thereby stopping the pair of registration rollers 13 and the pair of de-curling rollers 14. Because the pair of de-curling rollers 14 is in a released nip state when the trailing edge of the paper leaves the pair of registration rollers 13 (time t3), the registration motor 15 can be stopped immediately after time t3 without waiting for the timing when the trailing edge of the paper leaves the pair of de-curling rollers 14 (time t4).

When the registration roller pair 13 and the de-curling roller pair 14 stop, the operation of transporting one sheet of paper by the registration roller pair 13 and the de-curling roller pair 14 is completed. The control unit 8 controls the registration roller pair 13 and the de-curling roller pair 14 to perform this operation intermittently for each sheet of paper P that they transport toward the printing unit 3. In addition, the control unit 8 accordingly controls the de-curling roller pair 14 to perform an operation of switching between a nip-enabled state and a nip-released state as described above by the switching unit 16 for each sheet of paper P.

As described above, in the printing device 1, the control unit 8 controls the switching unit 16 during printing operation to put the de-curling roller pair 14 into a nipping state before the leading edge of the paper reaches the de-curling roller pair 14, and to put the de-curling roller pair 14 into a nipping release state before the trailing edge of the paper passes through the registration roller pair 13.

As a result, the de-curling roller pair 14 is in a released nip state when the trailing edge of the paper passes through the registration roller pair 13, so the registration motor 15 can be stopped without waiting for the trailing edge of the paper to pass through the de-curling roller pair 14. This prevents the gap between the sheets of paper P being continuously fed to the printing unit 3 from widening.

Therefore, according to the printing device 1, the paper P can be curled by the de-curling roller pair 14 while suppressing the increase in the gap between the continuously transported sheets of paper P. Here, because the increase in the gap between the continuously transported sheets of paper P is suppressed, the decrease in productivity is suppressed.

In addition, the de-curling roller pair 14 curls the paper P convexly upward, reducing contact of the paper P with the inkjet head 48.

Therefore, the printing device 1 can reduce contact of the paper P with the inkjet head 48 while minimizing any decline in productivity.

In addition, the timing at which the de-curling roller pair 14 is put into the nip release state by the switching unit 16 may be adjustable between the time when the leading edge of the paper reaches the de-curling roller pair 14 and the time when the trailing edge of the paper leaves the registration roller pair 13.

For example, the user may specify the timing for putting the de-curling roller pair 14 into the nip release state by inputting an input operation on the operation panel 7, and the control unit 8 may control the switching unit 16 so that the de-curling roller pair 14 is put into the nip release state at the specified timing. The timing for putting the de-curling roller pair 14 into the nip release state may be specified, for example, by the ratio of the length of the portion of the paper P that has passed through the de-curling roller pair 14 to the total length of the paper P.

This allows the user to specify that the de-curling roller pair 14 be put into a nip release state at an early stage if, for example, they wish to reduce wrinkles caused by the nip of the de-curling roller pair 14. As a result, it becomes possible to reduce wrinkles in the paper P.

Here, factors that affect the likelihood of wrinkles occurring in the paper P due to the nip of the de-curling roller pair 14 include the paper type and humidity. With regard to the paper type, for example, the thinner the paper, the more likely it is to wrinkle. Also, the higher the humidity, the weaker the stiffness of the paper P becomes, making it more likely to wrinkle. The control unit 8 may determine and adjust the timing for releasing the nip of the de-curling roller pair 14 based on at least one of the factors that affect the likelihood of wrinkles occurring in the paper P, such as those described above.

In addition, in the above-described embodiment, the conveying speed of the de-curling roller pair 14 is set to be slightly faster than the conveying speed of the registration roller pair 13, but the conveying speed of the de-curling roller pair 14 may be the same as the conveying speed of the registration roller pair 13.

In addition, in the above-described embodiment, an image is formed on paper using an inkjet head, but the mechanism for forming an image is not limited to an inkjet head.

In addition, in the above-mentioned embodiment, an inkjet printing device has been described, but the present invention is not limited to this, and can be applied to a conveying device that includes a first roller pair that conveys paper for each sheet of paper, and a second roller pair that is arranged downstream of the first roller pair, is driven together with the first roller pair by the same drive source as the drive source of the first roller pair, and nips and conveys the paper while curling it.

The present invention is not limited to the above-described embodiment as it is, and in the implementation stage, the components can be modified and embodied without departing from the gist of the invention. In addition, various inventions can be formed by appropriately combining multiple components disclosed in the above-described embodiment. For example, some components may be deleted from all the components shown in the embodiment.

[Additional Notes]
This application discloses the following inventions.

(Appendix 1)
a first roller pair that conveys the paper for each sheet;
a second roller pair that is disposed downstream of the first roller pair in a paper conveying direction, and is driven together with the first roller pair by the same drive source as the drive source of the first roller pair, and curls the paper while nipping and conveying the paper;
a switching unit that switches the second roller pair between a nipping state in which the second roller pair can nip a sheet and a nipping release state in which the second roller pair does not nip the sheet;
a control unit that controls the switching unit so as to put the second roller pair into the nipping state before the leading edge of the paper reaches the second roller pair, and to put the second roller pair into the nipping release state before the trailing edge of the paper leaves the first roller pair.

(Appendix 2)
The conveying device described in Appendix 1, characterized in that the control unit is capable of adjusting the timing of the switching unit putting the second roller pair into the nip release state between the time when the leading edge of the paper reaches the second roller pair and the time when the trailing edge of the paper passes through the first roller pair.

(Appendix 3)
the first roller pair is disposed above the paper and transports the paper to an image forming section that forms an image on the upper surface of the paper;
The conveying device described in Appendix 1 or 2, characterized in that the second roller pair is arranged between the first roller pair and the image forming unit in the paper conveying direction, and curls the paper in an upward convex direction.

(Appendix 4)
a first roller pair for transporting paper;
a second roller pair disposed downstream of the first roller pair in a paper conveying direction, the second roller pair nipping and conveying the paper while curling the paper;
a switching unit that switches the second roller pair between a nipping state in which the second roller pair can nip a sheet and a nipping release state in which the second roller pair does not nip the sheet;
a control unit that controls the switching unit so as to put the second roller pair into the nipping state before the leading edge of the paper reaches the second roller pair, and to put the second roller pair into the nipping release state before the trailing edge of the paper leaves the first roller pair.

REFERENCE SIGNS LIST 1 Printing device 2 Paper feed section 3 Printing section 4 Upper transport section 5 Paper discharge section 6 Reversing section 7 Operation panel 8 Control section 9 Housing 11 External paper feed section 12 Internal paper feed section 13 Registration roller pair 14 De-curling roller pair 15 Registration motor 16 Switching section 41 Cam 42 Cam follower 43 Cam motor 46 Belt platen section 48 Inkjet head

Claims (4)

a first roller pair that conveys the paper for each sheet;
a second roller pair that is disposed downstream of the first roller pair in a paper conveying direction, and is driven together with the first roller pair by the same drive source as the drive source of the first roller pair, and curls the paper while nipping and conveying the paper;
a switching unit that switches the second roller pair between a nipping state in which the second roller pair can nip a sheet and a nipping release state in which the second roller pair does not nip the sheet;
a control unit that controls the switching unit so as to put the second roller pair into the nipping state before the leading edge of the paper reaches the second roller pair, and to put the second roller pair into the nipping release state before the trailing edge of the paper leaves the first roller pair. The conveying device according to claim 1, characterized in that the control unit is capable of adjusting the timing at which the switching unit brings the second roller pair into the nip release state between the time when the leading edge of the paper reaches the second roller pair and the time when the trailing edge of the paper leaves the first roller pair. the first roller pair is disposed above the paper and transports the paper to an image forming section that forms an image on the upper surface of the paper;
3. The conveying device according to claim 1, wherein the second roller pair is disposed between the first roller pair and the image forming unit in the conveying direction of the paper, and curls the paper in an upward convex direction. a first roller pair for transporting paper;
a second roller pair disposed downstream of the first roller pair in a paper conveying direction, the second roller pair nipping and conveying the paper while curling the paper;
a switching unit that switches the second roller pair between a nipping state in which the second roller pair can nip a sheet and a nipping release state in which the second roller pair does not nip the sheet;
a control unit that controls the switching unit so as to put the second roller pair into the nipping state before the leading edge of the paper reaches the second roller pair, and to put the second roller pair into the nipping release state before the trailing edge of the paper leaves the first roller pair.