Printing apparatus

A printing apparatus includes a print section to perform printing on a medium, a supply path to supply the medium to the print section, a correction roller pair to enable the medium transported on the supply path to strike the correction roller pair to correct skewing of the medium, an adjusting mechanism for adjusting a nip load applied to the correction roller pair, and a controller to control the adjusting mechanism based on print job information.

BACKGROUND

1. Technical Field

The present invention relates to a printing apparatus for performing printing on a medium.

2. Related Art

A color printer, which is an example printing apparatus, including a transfer unit (printing unit) for transferring a toner image onto a sheet of paper, which is an example medium, is known (see, for example, JP-A-2014-38201). Such a color printer includes a registration roller pair (correction roller pair) that enables the leading edge of a sheet of paper to strike the registration roller pair to correct skewing of the sheet and transports the sheet toward the transfer unit.

If the pressing force of the registration roller pair is too weak (the pinching load is small, i.e., the nip load applied to the registration roller pair is small), the sheet can pass through the registration roller pair and the skewing is not corrected. On the other hand, if the pressing force of the registration roller pair is too strong, when the trailing edge of the sheet passes through the registration roller pair, the sheet transport speed changes undesirably. To address the problem, in the color printer, the pressing force of the registration roller pair is reduced after skewing of the sheet has been corrected.

In such a color printer (laser printer), the pressing force of the registration roller pair is reduced after the leading edge of the sheet has passed through the registration roller pair and before the trailing edge of the sheet passes through the registration roller pair.

Compared with the laser printer, an ink jet printer needs be more carefully designed to prevent transfer of ink onto a transport path, especially, transfer of ink onto a registration roller pair. Accordingly, it is preferable that the pressing force of the registration roller pair be changed at an appropriate time in consideration of skew correction and transfer prevention.

SUMMARY

An advantage of some aspect of the invention is that there is provided a printing apparatus capable of adjusting contact between a registration roller pair and paper and thereby reducing print quality degradation.

Hereinafter, an apparatus for solving the above-mentioned problem and its operational advantages will be described. A printing apparatus for solving the above problems includes a print section configured to perform printing on a medium, a supply path configured to supply the medium to the print section, a correction roller pair configured to enable the medium transported on the supply path to strike the correction roller pair to correct skewing of the medium, an adjusting mechanism for adjusting a nip load applied to the correction roller pair, and a controller configured to control the adjusting mechanism based on print job information.

With this structure, the controller controls the adjusting mechanism based on print job information to adjust the nip load applied to the correction roller pair. That is, for example, the nip load can be adjusted based on the type of medium, the size of a margin of the medium, or the like included in the print job information, and print quality degradation can be reduced accordingly.

It is preferable that the printing apparatus further include a switchback mechanism for switching back the medium having a first side and a second side on which printing has been performed on the first side and for transporting the medium to the supply path. In the printing apparatus, between a first transport operation in which the first side is on the print section side and a second transport operation in which the medium is switched back by the switchback mechanism and the second side is on the print section side, the controller reduces the nip load in the second transport operation compared to the nip load in the first transport.

With this structure, after printing has been performed on the first side in the first transport, the medium is switched back by the switchback mechanism and printing is performed on the second side in the second transport. As a result, when the second transport operation is performed, printing has already been performed on the first side. The controller reduces the nip load in the second transport operation compared with the nip load in the first transport, and this small nip load enables a reduction in print quality degradation on the previously printed first side.

In this printing apparatus, it is preferable that the controller reduce the nip load in the second transport operation before the correction roller pair pinches the print area on the first side. With this structure, the controller reduces the nip load before the correction roller pair pinches the print area on the first side, and accordingly, the print area on the first side is pinched under the small nip load. Consequently, when printing is performed on both the first side and the second side, this small nip load enables a reduction in print quality degradation on the previously printed first side.

In this printing apparatus, it is preferable that, when the grammage of the medium is smaller than a threshold value, before the correction roller pair pinches the medium in the second transport, the controller switch the nip load to a second nip load that is smaller than the nip load in the first transport.

The smaller the grammage of the medium, the lower the firmness of the medium. Accordingly, when a medium having a small grammage strikes the correction roller pair to which the small nip load has been applied, the medium cannot easily pass through the correction roller pair. Consequently, when the grammage of the medium is smaller than the threshold value, the nip load can be reduced in advance before the correction roller pair pinches the medium. By this operation, the time necessary to adjust the nip loads can be reduced.

In the printing apparatus, it is preferable that the controller switch the nip load to a third nip load, which is smaller than the second nip load, in the second transport operation while the correction roller pair is pinching a margin area, which extends from a leading edge of the medium to a print area on the first side.

For example, reducing the nip load when the leading edge of the medium is striking the correction roller pair may enable the medium to pass through the correction roller pair and this may cause skewing. To address this problem, in this structure, the controller reduces the nip load while the correction roller pair is pinching the medium, and this small nip load can reduce the occurrence of the medium skewing.

In the printing apparatus, it is preferable that the controller adjust the nip load in accordance with the type of medium to next be printed after a trailing edge of the medium has passed through the correction roller pair in the second transport.

With this structure, after the trailing edge of the medium has passed through the correction roller pair, the nip load is changed in accordance with the type of medium to next be printed. This change can prevent the medium to next be printed from passing through the correction roller pair when the medium strikes the correction roller pair.

In this printing apparatus, it is preferable that the correction roller pair include a driving roller that includes at least one toothed roller and a driven roller that is driven by the driving roller, and that when the print section performs printing onto the one side of the medium, the driven roller come into contact with one side of the medium and the driving roller come into contact with the other side of the medium to pinch and transport the medium.

With this structure, after printing has been performed on the first side of the medium and printing is to next be performed on the second side of the medium, the printed first side of the medium comes into contact with the toothed roller and the medium is transported when printing is performed on the second side of the medium. Consequently, this structure can reduce transfer of an image (for example, ink) printed on the first side of the medium onto the driving roller because the contact area of the driving roller with the first side of the medium is small when the toothed roller comes into contact with the first side of the medium compared with the case where the flat surface comes into contact with the first side of the medium. Furthermore, the nip load applied to the correction roller pair is reduced in advance before the correction roller pair nips the print area on the first side of the medium. This small nip load further reduces transfer of the image printed on the first side of the medium onto the driving roller.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, an embodiment of a printing apparatus will be described with reference to the attached drawings. The printing apparatus according to the embodiment is a printer that performs printing (recording) by discharging an ink, which is an example liquid, onto a medium such as paper to print (record) characters, images, and the like.

As illustrated inFIG. 1, a printing apparatus11according to the embodiment includes a substantially rectangular parallelepiped housing12and a transport section15that transports a medium14along a transport path13denoted by the alternate long and short dashed line inFIG. 1. The printing apparatus11further includes, along the transport path13, a transport belt16that transports the medium14while supporting the medium14against gravity and a printing unit17that is disposed opposite the transport belt16with the transport path13therebetween.

The transport belt16is an endless belt and is looped around a drive pulley18, which is driven by a drive source to rotate, and a driven pulley19, which is freely rotatable around a shaft that is parallel to a shaft of the drive pulley18. The transport belt16travels around the pulleys and transports the medium14, which is supported by electrostatic adsorption on the outer peripheral surface of the transport belt16. In other words, the outer peripheral surface of the transport belt16is a part of the transport path13.

The printing unit17is a line head that can simultaneously discharge a liquid such as an ink in the width direction X of the medium14. The width direction X intersects (for example, is orthogonal to) a transport direction Y in which the medium14is transported. The printing unit17performs printing onto the medium14by discharging a liquid onto the medium14that is transported by the transport belt16.

The transport path13includes a first supply path21, a second supply path22, and a third supply path23, which are on the upstream side of the transport belt16in the transport direction Y, and a branch path24and a discharge path25, which are on the downstream side of the transport belt16in the transport direction Y. The first supply path21, the second supply path22, and the third supply path23serve as a supply path26along which the medium14is supplied toward the printing unit17.

The first supply path21connects a medium cassette28, which is detachably attached to a bottom section on the lower side in the direction of gravity, and the transport belt16. In the first supply path21, a pickup roller29for feeding the top medium14of the media14stacked in the medium cassette28and separation rollers30for separating the media14fed by the pickup roller29one by one, are provided. The first supply path21further includes a first supply roller pair31disposed on the downstream side of the separation rollers30in the transport direction Y.

The second supply path22connects an insertion slot12b, which is exposed when a cover12aprovided on one side surface of the housing12is opened, and the transport belt16. In the second supply path22, a second supply roller pair32that pinches and transports the medium14that has been inserted from the insertion slot12bis provided. At a position where the first supply path21, the second supply path22, and the third supply path23merge, a correction roller pair33is provided. The medium14transported on the supply path26strikes the correction roller pair33, and thereby skewing of the medium14is corrected.

The correction roller pair33includes a driving roller34that is provided on the transport belt16side opposite the printing unit17with respect to the supply path26and a driven roller35that is provided on the printing unit17side with respect to the supply path26. The driving roller34is rotated by a drive source such as a motor (not illustrated) in a counterclockwise direction. The correction roller pair33pinches the medium14by using the driving roller34and the driven roller35, which is driven by the driving roller34, and correction roller pair33rotates to transport the medium14toward the printing unit17.

The third supply path23is disposed above the printing unit17to partially encompass the printing unit17. The third supply path23returns again the medium14that has passed through the transport belt16and the printing unit17to the upstream side of the transport belt16. On the downstream side of the transport belt16, a branching mechanism36that is capable of guiding the medium14to the branch path24is provided. The branching mechanism36includes, for example, a flap. The branching mechanism36guides the medium14, which has been guided toward the branch path24, to the third supply path23. In the branch path24, a branch roller pair37that is rotatable in both forward and reverse directions is provided. In this embodiment, the branch path24, the branching mechanism36, and the branch roller pair37serve as a switchback mechanism38. That is, the switchback mechanism38switches back the medium14, which has a front side14athat is an example first side and a back side14bthat is an example second side of the medium14, on which printing has been performed on the front side14a, to transport the medium14to the third supply path23(seeFIG. 12).

The discharge path25connects a discharge port39, from which the printed medium14is discharged, and the transport belt16. The medium14discharged from the discharge port39is placed onto a mounting table40. In the discharge path25, at least one transport roller pair is provided. In this embodiment, five transport roller pairs, that is, a first transport roller pair41to a fifth transport roller pair45, are provided. In the third supply path23, at least one transport roller pair is provided. In this embodiment, three transport roller pairs, that is, a sixth transport roller pair46to an eighth transport roller pair48, are provided.

The transport section15according to the embodiment includes the transport belt16, the drive pulley18, the driven pulley19, the pickup roller29, the first supply roller pair31, the second supply roller pair32, the correction roller pair33, and the first transport roller pair41to the eighth transport roller pair48.

As illustrated inFIG. 2andFIG. 3, the driving roller34of the correction roller pair33includes a drive shaft50that extends in the width direction X and at least one (in this embodiment, ten) toothed roller52having a plurality of convex portions (seeFIG. 3)51on its peripheral surface. The drive shaft50is inserted into the toothed roller52, and the toothed roller52is fixed to the drive shaft50. The toothed roller52rotates together with the drive shaft50. The toothed roller52includes a plurality of ring-shaped members (in this embodiment, six) each having a plurality of convex portions51, and the ring-shaped member are combined together. Viewed in the X direction, each toothed roller52includes the six ring-shaped members that are combined together such that the alignment of the convex portions51of the ring-shaped members is shifted with respect to each other. This structure enables the respective convex portions51of the ring-shaped members of the toothed roller52to be arranged at different positions. Accordingly, the spaces between the adjacent convex portions51in a single ring-shaped member can be substantially reduced. This structure enables the leading edge of a medium to strike the correction roller pair33, and thereby skewing of the medium can be appropriately corrected. If the spaces between the adjacent convex portions51are wide, relative spaces between the convex portions51corresponding to a portion of the leading edge of the skewed medium that first strikes the correction roller pair33and a portion of the leading edge that subsequently strikes the correction roller pair33are also wide. In such a case, due to the shape of the convex portions51, the respective portions are caught on the convex portions51in the state where the space between the portion that strikes first the correction roller pair33and the portion that subsequently strikes the correction roller pair33is wide. As a result, skew correction is not sufficiently performed.

The driven roller35includes a driven shaft53that extends in the width direction X and at least one (the number of the cylindrical rollers54is the same as the number of the toothed rollers52) cylindrical roller54that has no projections and depressions on its peripheral surface. The driven shaft53is movable in a direction (for example, the vertical direction) which intersects the width direction X and the transport direction Y. The cylindrical roller54is rotatably supported by the driven shaft53and disposed to face the toothed roller52in the width direction X.

The printing apparatus11includes a switching mechanism56that switches pinching loads applied to the correction roller pair33to pinch the medium14. The switching mechanism56includes a round-bar shaped driver section58that is rotated by the driving force of a switching motor57(seeFIG. 4) and at least one (in this embodiment, two) cam section59that rotates together with the driver section58. The switching mechanism56further includes a round-bar shaped driven section60that adjoins the cam section59and at least one (in this embodiment, eight) biasing member61that is provided between the driven section60and the driven shaft53such as a coil spring. The pinching load applied to the correction roller pair33to pinch the medium14corresponds to a nip load applied to the correction roller pair33. Accordingly, the term “pinching load” in this specification can be read as “nip load”.

The cam section59has a substantially disc shape and is an eccentric cam into which the driver section58is inserted at a position different from the center. The driven section60extends in the width direction X and is movable in a direction (for example, the vertical direction) that intersects the width direction X and the transport direction Y similarly to the driven shaft53.

Now, an electrical configuration of the printing apparatus11will be described. As illustrated inFIG. 4, the printing apparatus11includes a controller63that controls the switching mechanism56based on print job information input from an external device (not illustrated) or the like. The controller63performs overall drive control of the mechanisms such as the transport section15, the printing unit17, and other mechanisms in the printing apparatus11. The print job information according to the embodiment includes which one of one-sided printing and two-sided printing is to be performed, the size of the margin, the number of sheets, the type of the medium14, the grammage, and the like.

Hereinafter, a load switching process routine to be performed by the controller63will be described with reference to the flowchart inFIG. 5. The load switching process routine is executed when a print job is started by a user.

As illustrated inFIG. 5, in step S101, the controller63determines based on print job information which one of one-sided printing and two-sided printing is to be performed. If one-sided printing is to be performed (YES in step S101), in step S102, the controller63causes the switching mechanism56to set a pinching load to be applied when the correction roller pair33pinches the medium14to a large load.

In step S103, the controller63performs skew correction for correcting skewing of the medium14by enabling the medium14to strike the stationary driving roller34at a leading edge of the medium14. In step S104, the controller63causes the driving roller34to rotate.

In step S105, the controller63determines whether the trailing edge of the medium14has passed through the correction roller pair33. If the trailing edge of the medium14has not passed through the correction roller pair33(NO in step S105), the controller63enables the driving roller34to keep rotating and stand by until the medium14passes through the correction roller pair33. If the trailing edge of the medium14has passed through the correction roller pair33(YES in step S105), in step S106, the controller63causes the driving roller34to stop.

In step S107, the controller63determines based on the print job information whether a subsequent medium14to pass through the correction roller pair33exists. If no subsequent medium14exists (NO in step S107), the controller63ends the process. If a subsequent medium14exists (YES in step S107), the process goes to step S101.

In step S101, if two-sided printing is to be performed (NO in step S101), in step S108, the controller63determines whether printing is to be performed on the front side14aor the back side14b. In this embodiment, a side to be printed first is defined as the front side14aand a side to be printed after the printing of the front side14ahas been performed is defined as the back side14b. If the front side printing is to be performed (YES in step S108), the controller63moves the process to step S102. If the back side printing is to be performed (NO in step S108), in step S109, the controller63determines based on the print job information whether the grammage of the medium14is greater than or equal to a threshold value (for example, 90 g/m2).

If the grammage of the medium14is greater than or equal to the threshold value (YES in step S109), in step S110, the controller63sets the pinching load to the large load. If the grammage of the medium14is smaller than the threshold value (NO in step S109), in step S111, the controller63sets the pinching load to a medium load. The medium load is smaller than the large load.

In step S112, the controller63performs skew correction to the medium14similarly to step S103. In step S113, the controller63causes the driving roller34to rotate, and in step S114, the controller63causes the driving roller34to stop while the correction roller pair33is pinching a margin area B (seeFIG. 13) of the medium14. In step S115, the controller63sets the pinching load to the small load. The small load is smaller than the large load and the middle load. Then, the controller63moves the process to step S104.

Now, operations of the printing apparatus11for performing printing onto the medium14will be described. First, an operation to be performed when print job information for performing one-sided printing on two (two sheets of) media14supplied from the medium cassette28is described.

As illustrated inFIG. 6, the controller63causes the pickup roller29to drive to feed a first medium14A, which is the first sheet, from the medium cassette28. Then, the first medium14A is transported on the first supply path21with the front side14abeing placed on the printing unit17side, and the leading edge strikes the stationary correction roller pair33.

As illustrated inFIG. 7, the controller63sets the pinching load to be applied to the correction roller pair33to the large load before the leading edge of the first medium14A reaches the correction roller pair33. That is, the controller63causes the switching motor57to drive to rotate the cam section59such that the length from the rotation center of the cam section59to its peripheral surface becomes long. When the leading edge of the first medium14A strikes the correction roller pair33, the first medium14A bends and skewing of the first medium14A is corrected (hereinafter, may also be referred to as “skew correction”).

As illustrated inFIG. 8, after skewing of the first medium14A has been corrected, the controller63causes the driving roller34to rotate while maintaining the pinching load at the large load to transport the first medium14A toward the printing unit17. The printing unit17discharges a liquid such as an ink to perform printing onto the front side14aof the first medium14A when the first medium14A passes through the printing unit17.

As illustrated inFIG. 9, the printed first medium14A is transported on the discharge path25. The controller63causes the pickup roller29to drive to feed a second medium14B, which is the second sheet, subsequently to the first medium14A from the medium cassette28. The second medium14B is transported on the first supply path21with the front side14abeing placed on the printing unit17side, and the leading edge strikes the stationary correction roller pair33, which is maintaining the large load, and skew correction is performed similarly to the first medium14A accordingly (seeFIG. 7). After skew correction has been performed, the second medium14B is transported by the correction roller pair33, which is maintaining the large load, toward the printing unit17(seeFIG. 8). That is, when the printing is performed only on one side (the front side14a) of the medium14, the pinching load is maintained at the large load.

Next, an operation to be performed in response to an input of print job information for two-sided printing on two (two sheets of) media14supplied from the medium cassette28is described. The first medium14A, which is the first sheet, is thick paper having a grammage of a threshold value or greater, and the second medium14B, which is the second sheet, is thin paper having a grammage smaller than the threshold value. The operation for performing printing onto the front side14aof the first medium14A, which is the first sheet, is similar to that in the one-sided printing, and its description is omitted.

As illustrated inFIG. 10, the first medium14A, on which printing has been performed on the front side14aby the printing unit17, is guided to the branch path24by the branching mechanism36. In the first transport operation with the front side14aof the medium14A being located on the printing unit17side, the pinching load being applied to the correction roller pair33is maintained at the large load during skew correction and pinching and transporting of the first medium14A.

The next medium14that passes through the correction roller pair33is the second medium14B whose front side14ais located on the printing unit17side. Consequently, after the trailing edge of the first medium14A has passed through the correction roller pair33, the pinching load applied to the correction roller pair33is maintained at the large load suitable for the first transport operation of the second medium14B.

As illustrated inFIG. 11, the controller63causes the pickup roller29to drive to feed the second medium14B, which is the second sheet, subsequently to the first medium14A from the medium cassette28. The second medium14B is transported on the first supply path21, and the leading edge strikes the correction roller pair33, which is maintaining the large load, and skew correction is performed accordingly similarly to the first medium14A (seeFIG. 7).

In other words, during the first transport operation with the front side14abeing located on the printing unit17side, the printing apparatus11performs skew correction by using the correction roller pair33under the large load regardless of the grammage of the medium14. Then, the controller63causes the driving roller34to rotate after skew correction to transport the second medium14B toward the printing unit17while maintaining the large load (seeFIG. 8).

As illustrated inFIG. 12, the branch roller pair37is reversely driven to reversely transport the first medium14A, which has been held on the branch path24, on the branch path24, and the first medium14A is further guided by the branching mechanism36to the third supply path23. The second medium14B, on which printing has been performed on the front side14a, is guided to the branch path24by the branching mechanism36. Consequently, the next medium14that passes through the correction roller pair33is the first medium14A whose back side14bis located on the printing unit17side. After the trailing edge of the second medium14B has passed through the correction roller pair33, the pinching load of the correction roller pair33is maintained at the large load, which is suitable for the second transport operation of the first medium14A.

In other words, during the second transport in which the first medium14A is switched back by the switchback mechanism38and the back side14bis located on the printing unit17side, the leading edge strikes the stationary correction roller pair33that is maintaining the large load, and skew correction is performed accordingly. After the skew correction has been performed, the controller63causes the driving roller34to rotate to transport the first medium14A toward the printing unit17.

As illustrated inFIG. 13, the controller63stops the rotation of the driving roller34while the correction roller pair33is pinching the margin area B. Then, the controller63causes the switching motor57to drive to rotate the cam section59by 180 degrees such that the length from the rotation center of the cam section59to its peripheral surface becomes short to switch the pinching load applied to the correction roller pair33to the small load. That is, during the second transport operation of the first medium14A, the controller63reduces the pinching load while the correction roller pair33is pinching the margin area B, which is from the leading edge of the first medium14A to a print area A on the front side14a.

In other words, in the first transport operation and the second transport operation, the pinching load in the second transport operation is reduced compared with the pinching load in the first transport. During the second transport, the controller63reduces the pinching load before the correction roller pair33pinches the print area A on the front side14a. Then, the controller63causes the driving roller34, which is maintaining the small load, to rotate to transport the first medium14A toward the printing unit17. Then, the printing unit17performs printing on the back side14bof the first medium14A.

As illustrated inFIG. 14, the first medium14A, on which printing has been performed on both front side14aand back side14b, is transported on the discharge path25. After the trailing edge of the first medium14A has passed through the correction roller pair33in the second transport, the controller63changes the pinching load in accordance with the type of the medium14to next be printed. That is, the next medium14that passes through the correction roller pair33is the second medium14B whose back side14bis located on the printing unit17side. Consequently, the pinching load applied to the correction roller pair33is switched to the medium load, which is suitable for the second transport operation of the second medium14B having the grammage smaller than the threshold value.

Specifically, as illustrated inFIG. 15, the controller63causes the driving roller34to stop, and drives the switching motor57to rotate the cam section59by 90 degrees to switch the pinching load applied to the correction roller pair33from the small load to the middle load. That is, when the grammage of the medium14is smaller than the threshold value, the controller63reduces the pinching load to the pinching load smaller than the large load, which is suitable for the first transport, before the correction roller pair33pinches the medium14in the second transport. Then, the second medium14B is switched back by the switchback mechanism38and transported on the third supply path23, and the leading edge of the second medium14B strikes the correction roller pair33and skew correction is performed accordingly.

After the skew correction, the controller63causes the driving roller34to rotate to transport the second medium14B toward the printing unit17, and reduces the pinching load in the margin area B of the second medium14B similarly to the second transport operation of the first medium14A.

That is, as illustrated inFIG. 13, during the second transport operation of the second medium14B, the controller63reduces the pinching load while the correction roller pair33is pinching the margin area B, which is from the leading edge of the second medium14B to the print area A on the front side14a. Specifically, the controller63stops the drive of the driving roller34while the correction roller pair33is pinching the margin area B, and switches the pinching load applied to the correction roller pair33from the middle load to the small load. To switch the pinching load from the middle load to the small load, the controller63causes the cam to rotate by 90 degrees. Consequently, compared with the case where the cam section is rotated by 180 degrees to switch the pinching load applied to the correction roller pair33from the large load to the small load, the pinching load can be switched to the small load in a short time. Then, the controller63transports the second medium14B toward the printing unit17. On the back side14bof the second medium14B, printing is performed and the second medium14B is discharged.

According to the above-described embodiment, the following advantages can be achieved.

(1) The controller63controls the switching mechanism56based on print job information such that the pinching load applied to the correction roller pair33to pinch the medium14can be switched. That is, for example, the pinching load can be switched based on the type of the medium14, the size of the margin, or the like included in the print job information, and print quality degradation can be reduced accordingly.

(2) After printing has been performed on the front side14ain the first transport, the medium14is switched back by the switchback mechanism38and printing is performed on the back side14bin the second transport. As a result, when the second transport operation is performed, printing has already been performed on the front side14a. Consequently, the controller63reduces the pinching load in the second transport operation compared with the pinching load in the first transport operation, and this small pinching load can prevent print quality degradation on the previously printed front side14a.

(3) The controller63reduces the pinching load before the correction roller pair33pinches the print area A on the front side14a, and accordingly, the print area A on the front side14ais pinched under the small pinching load. Consequently, when printing is performed on the front side14aand the back side14b, this small pinching load can reduce print quality degradation on the previously printed front side14a.

(4) For example, reducing the pinching load when the leading edge of the medium14is striking the correction roller pair33may enable the medium14to pass through the correction roller pair33and this may cause skewing. To address the problem, in this structure, the controller63reduces the pinching load while the correction roller pair33is pinching the medium14, and this small pinching load can reduce the occurrence of the skewing of the medium14.

(5) The smaller the grammage is, the lower the firmness of the medium14is. Accordingly, when the medium14having a small grammage strikes the correction roller pair33to which the reduced pinching load has been applied, the medium14cannot easily pass through the correction roller pair33. Consequently, when the grammage of the medium14is smaller than the threshold value, the pinching load can be reduced before the correction roller pair33pinches the medium14. By this operation, the time necessary to switch the pinching loads can be reduced.

(6) After the trailing edge of the medium14has passed through the correction roller pair33, the pinching load is changed in accordance with the type of the medium14to next be printed. This change can prevent the medium14to next be printed from passing through the correction roller pair33when the medium14strikes the correction roller pair33.

The above-described embodiment may be modified as described below.

In the above-described embodiment, the controller63may change the pinching load while the driving roller34is being driven.In the above-described embodiment, the printing apparatus11may feed a next medium14after printing has been made on the front side14aand the back side14bof the medium14. For example, after the printing apparatus11has performed printing on the front side14aand the back side14bof the first medium14A, the printing apparatus11may perform printing on the second medium14B.In the above-described embodiment, the switching mechanism56may be an electromagnetic clutch that can press the driven roller35. Furthermore, for example, the switching mechanism56may include a plurality of electromagnetic clutches, and the number of the electromagnetic clutches for pressing the driven roller35may be changed to change the magnitude of the pinching load.In the above-described embodiment, after the feeding of the medium14, the controller63may change the pinching load applied to the correction roller pair33in accordance with the type of the fed medium14.In the above-described embodiment, after the print area A of the medium14has passed through the correction roller pair33, the controller63may change the pinching load applied to the correction roller pair33in accordance with the type of the medium14to next be printed.In the above-described embodiment, the controller63may control the switching mechanism56regardless of the grammage of the medium14.In the above-described embodiment, when the medium14having a grammage smaller than the threshold value is transported in the second transport, the controller63may perform skew correction under the medium load and transport the medium14while maintaining the middle load. That is, the medium14may be transported under the middle load, which is smaller than the large load.In the above-described embodiment, the levels of the switchable pinching loads may be two. For example, the pinching load may be switched between the large load and the small load. When the grammage of the medium14is smaller than the threshold value, the pinching load may be switched to the small load before the correction roller pair33pinches the medium14in the second transport. That is, the skew correction may be performed under the small load. Furthermore, the levels of the switchable pinching loads may be four or more. For example, the pinching load adjustment may be stepless adjustment. In such a case, the pinching load may be adjusted in accordance with the rotational angle of the cam section59.In the above-described embodiment, in the second transport operation of the medium14, the controller63may reduce the pinching load after the skew correction has been made and before the driving roller34is driven. That is, the pinching load may be reduced while the correction roller pair33is not pinching the medium14. Furthermore, the controller63may control the switching mechanism56based on the print job information about whether the margin area B exists or not. That is, for example, if the margin area B exists, the controller63may reduce the pinching load while the correction roller pair33is pinching the margin area B, whereas if the margin area B does not exist, the controller63may reduce the pinching load before the correction roller pair33pinches the medium14. Furthermore, for example, if the grammage is greater than or equal to the threshold value, the controller63may reduce the pinching load while the correction roller pair33is pinching the margin area B, whereas if the grammage is smaller than the threshold, the controller63may reduce the pinching load before the correction roller pair33pinches the medium14.In the above-described embodiment, the controller63may control the switching mechanism56in accordance with a print duty (an amount of liquid to be applied per unit area) that is included in print job information. For example, the higher the print duty is, the more an image scraped by the correction roller pair33is retransferred and adheres to a subsequent medium14. On the other hand, the lower the print duty is, the less the image is retransferred. Consequently, for example, when the print duty is low, in the second transport operation of the medium14, the correction roller pair33may pinch the print area A on the front side14a, and then the controller63may reduce the pinching load. If the pinching load being applied to the correction roller pair33is changed during printing, the print color may change before and after the pinching load change, and this change may cause image quality degradation. To address the problem, to change the pinching load in the print area A, it is preferable that the pinching load be changed before the printing unit17starts printing.In the above-described embodiment, the printing apparatus11may omit the switchback mechanism38. Furthermore, the printing apparatus11may include at least one of the first supply path21to the third supply path23. The printing apparatus11that omits the switchback mechanism38and the third supply path23may perform printing on the front side14aof the medium14and feed the medium14again to perform printing on both sides. That is, the controller63may control the switching mechanism56depending on whether printing has been performed on the front side14aof the medium14, which is transported based on the print job information. Specifically, to transport the medium14on which printing has not been performed on the front side14a, the printing apparatus11may increase the pinching load. On the other hand, to transport the medium14on which printing has been performed on the front side14aand then to perform printing on the back side14b, the pinching load may be reduced.In the above-described embodiment, the printing apparatus11may be a fluid ejection apparatus that ejects or discharges a fluid (for example, a liquid, a liquid material containing particles of a functional material dispersed or mixed in a liquid, a fluid material such as a gel, and a solid that can be ejected as a fluid) other than inks for recording. For example, the printing apparatus11may be a liquid material ejecting apparatus that ejects a liquid material containing a dispersed or dissolved material such as an electrode material or a color material (pixel material) used for manufacturing liquid crystal displays, electroluminescence (EL) displays, or field emission displays (FEDs) for recording. The printing apparatus11may be a fluid material ejecting apparatus that ejects a fluid material such as a gel (for example, a physical gel), or a powder and granular material ejecting apparatus (for example, a toner jet type recording apparatus) that ejects a solid, for example a powder (powder and granular material) such as a toner. The present invention can be applied to any one of the fluid ejecting apparatuses. In this specification, “fluid” implies a concept that does not include fluids that consist of only gas, and the fluid includes, for example, liquids (including inorganic solvents, organic solvents, solutions, liquid resins, liquid metals (metallic melts), and the like), liquid materials, fluid materials, and powder and granular materials (including grains and powders).

The entire disclosure of Japanese Patent Application No. 2016-045578, filed Mar. 9, 2016 is expressly incorporated by reference herein.