JP7380049B2 - Sheet straightening device, printing device, printing system - Google Patents

Description

The present invention relates to a sheet straightening device, a printing device, and a printing system.

2. Description of the Related Art When printing by applying liquid to a sheet such as paper, it is known to include a sheet straightening device that suppresses cockling caused by applying liquid to the sheet.

Conventionally, a sheet straightening device includes a pair of belts that sandwich and convey a sheet to which a liquid has been applied, a plurality of curved members that give curvature to the pair of belts, and a heating means that heats the sheet via at least one of the pair of belts. A device is known that includes a steering control roller that corrects meandering of each belt of a belt pair (Patent Document 1).

Japanese Patent Application Publication No. 2019-119607

By the way, when straightening a sheet while heating the sheet by sandwiching the sheet between a pair of belts, there is a problem in that unfixed liquid is rubbed by the belts due to meandering of the belts, causing image scratches.

The present invention has been made in view of the above problems, and an object of the present invention is to suppress the occurrence of image scratches.

In order to solve the above problems, the seat straightening device according to the present invention includes:
a pair of belts that sandwich and convey a sheet to which liquid has been applied;
a plurality of curved members giving curvature to the pair of belts;
heating means for heating the sheet via at least one of the pair of belts;
Belt position detection means for detecting the widthwise position of each belt of the pair of belts;
Meandering correction means for correcting meandering of each of the belts based on the detection results of the belt position detection means;
means for controlling the meandering correction means,
The pair of belts are movable in the width direction of the belts along the curved surface of the curved member while in contact with the curved member,
At least one of the belts that comes into contact with the surface of the sheet to which the liquid is applied has a fluororesin layer on the surface,
The controlling means performs control to correct the meandering of each of the belts so that the sum of the movement amounts in the width direction of each belt falls within a predetermined value,
The specified value when conveying the thin sheet is smaller than the specified value when conveying the thick sheet.
The structure is as follows.

According to the present invention, it is possible to suppress the occurrence of image scratches.

1 is a schematic explanatory diagram of a printing apparatus according to a first embodiment of the present invention. It is a side explanatory view of an example of the drying device which constitutes a drying part. FIG. 2 is an explanatory side view of an example of a sheet straightening device that constitutes a sheet straightening section. It is an enlarged side explanatory view of the exit side of the sheet straightening device. FIG. 3 is a perspective explanatory view of an example of a meandering correction mechanism for the upper belt. It is an explanatory view provided for explanation of a belt position detection means. FIG. 2 is a block diagram illustrating a portion related to meandering correction control of the sheet straightening device and heating control of the drying device. FIG. 6 is an explanatory diagram of an example of the relationship between the inclination angle of the steering control roller and the moving speed of the belt in the width direction, which is used to explain the meandering correction control of the belt by the meandering correction control means. FIG. 7 is an explanatory diagram illustrating the sum of belt movement amounts in the width direction in meandering correction. FIG. 3 is an explanatory diagram illustrating an example of the relationship between the amount of residual solvent in a sheet and the correction effect on deformation of the sheet. FIG. 6 is an explanatory diagram illustrating an example of the relationship between belt coating of a belt pair and image scratches. FIG. 6 is an explanatory diagram illustrating an example of the relationship between the coating of a pair of belts, the amount of rubbing (amount of rubbing), and image scratches; FIG. 2 is a flow diagram illustrating an example of heating control of the drying device. FIG. 3 is a flowchart for explaining meandering correction control in the sheet straightening device. It is a side explanatory view of the sheet|seat correction apparatus based on 2nd Embodiment of this invention. It is a flowchart provided for explanation of meandering correction control in the same 2nd embodiment. It is a flowchart provided for explanation of meandering correction control in a 3rd embodiment of the present invention. It is a flowchart provided for explanation of meandering correction control in a 4th embodiment of the present invention. It is a side explanatory view of the sheet|seat correction apparatus based on 5th Embodiment of this invention. It is a side explanatory view of the sheet|seat correction apparatus based on 6th Embodiment of this invention. It is a side explanatory view of the sheet|seat correction apparatus based on 7th Embodiment of this invention. It is a side explanatory view of the sheet|seat correction apparatus based on 8th Embodiment of this invention.

Embodiments of the present invention will be described below with reference to the accompanying drawings. First, an overview of a printing apparatus according to a first embodiment of the present invention will be explained with reference to FIG. FIG. 1 is a schematic explanatory diagram of the printing apparatus.

The printing apparatus 1 includes a carry-in section 100, a printing section 200, a drying section 300, a sheet straightening section 600, and a carry-out section 400. In the printing apparatus 1, a printing section 200 applies liquid to a sheet P carried in from a carrying section 100 to perform required printing, and a drying section 300 dries the liquid attached to the sheet P, and then straightens the sheet. In the section 600, waving deformation such as cockling occurring in the sheet P is corrected, and the sheet P is discharged to the unloading section 400.

The carry-in unit 100 includes a carry-in tray 110 on which a plurality of sheets P are stacked, a feeding device 120 that separates and feeds the sheets P one by one from the carry-in tray 110, and a pair of registration rollers that feed the sheets P to the printing unit 200. 130.

As the feeding device 120, any feeding device can be used, such as a device using rollers or a device using air suction. After the leading edge of the sheet P sent out from the carry-in tray 110 by the feeding device 120 reaches the registration roller pair 130, the sheet P is sent to the printing unit 200 by driving the registration roller pair 130 at a predetermined timing.

The printing unit 200 includes a carrying drum 210 that supports and conveys the sheet P on its outer peripheral surface, and a liquid ejecting unit 220 that is a means for applying liquid to eject liquid toward the sheet P supported on the carrying drum 210. We are prepared. The printing section 200 also includes a transfer cylinder 201 that receives the fed sheet P and transfers it to the carrying drum 210, and a transfer cylinder 202 that transfers the sheet P conveyed by the carrying drum 210 to the drying section 300.

The leading end of the sheet P conveyed from the carry-in section 100 to the printing section 200 is gripped by a sheet gripper provided on the surface of the transfer cylinder 201, and is conveyed as the transfer cylinder 201 rotates. The sheet P conveyed by the transfer drum 201 is transferred to the carrier drum 210 at a position facing the carrier drum 210.

A sheet gripper is also provided on the surface of the carrying drum 210, and the leading end of the sheet P is gripped by the sheet gripper. A plurality of suction holes are formed in a distributed manner on the surface of the support drum 210, and a suction airflow directed toward the inside of the support drum 210 is generated in each suction hole by the suction device 211.

Then, the sheet P transferred from the transfer drum 201 to the carrier drum 210 is gripped by the sheet gripper at the leading end, is attracted to the surface of the carrier drum 210 by the suction air current, and is conveyed as the carrier drum 210 rotates. Ru.

The liquid ejection unit 220 is a liquid ejection means that prints images by ejecting liquids (inks) in four colors: C (cyan), M (magenta), Y (yellow), and K (black). , liquid ejection heads 220C, 220M, 220Y, and 220K are provided as means for applying individual liquids for each color of liquid. Note that, if necessary, a liquid ejection head that ejects a special liquid such as white, gold, or silver, or a liquid ejection head that ejects a processing liquid such as a surface coating liquid may be provided.

The liquid ejection heads 220C, 220M, 220Y, and 220K of the liquid ejection unit 220 have their ejection operations controlled by drive signals according to print information. When the sheet P carried by the carrying drum 210 passes through the area facing the liquid ejecting section 220, liquid of each color is ejected from the liquid ejecting heads 220C, 220M, 220Y, and 220K, and an image corresponding to the printing information is produced. printed.

The drying section 300 includes a suction conveyance mechanism section 320 that sucks and conveys the sheet P conveyed from the printing section 200, a drying mechanism section 310 that dries the sheet P conveyed by the suction conveyance mechanism section 320, and the like. ing.

The sheet P conveyed from the printing section 200 is received by the suction conveyance mechanism section 320, then conveyed to pass through the drying mechanism section 310, delivered to the sheet straightening section 600, and carried out from the sheet straightening section 600. The information is transferred to the department 400.

When passing through the drying mechanism section 310, the liquid on the sheet P is subjected to a drying process. As a result, liquid components such as water in the liquid evaporate, and the colorant contained in the liquid is fixed onto the sheet P.

As the sheet P after the drying process passes through the sheet correction section 600, deformations such as cockling of the sheet P are corrected.

The carry-out section 400 includes a discharge tray 410 on which a plurality of sheets P are stacked. The sheets P conveyed from the sheet correction section 600 are sequentially stacked and held on the discharge tray 410.

Note that the printing apparatus 1 may include, for example, a pre-processing section that performs pre-processing on the sheet P disposed upstream of the printing section 200, or a post-processing section that performs post-processing on the sheet P to which liquid has adhered. may also be placed between the sheet straightening section 600 and the carrying out section 400.

Examples of the pre-treatment section include one that performs a pre-coating process in which a treatment liquid is applied to the sheet P to suppress bleeding by reacting with the liquid. The post-processing section also performs, for example, sheet reversal conveyance processing for inverting the sheet printed in the printing section 200 and sending it again to the printing section 200 to print on both sides of the sheet P, and binding a plurality of sheets. Examples include those that perform processing.

Note that the printing apparatus 1 may include, for example, a pre-processing unit that performs pre-processing on the sheet material P disposed upstream of the printing unit 200, or a post-processing unit that performs post-processing on the sheet material P to which liquid has adhered. The processing section may also be placed between the drying section 300 and the unloading section 400.

Examples of the pre-treatment section include one that performs a pre-coating process in which the sheet material P is coated with a treatment liquid that reacts with the liquid and suppresses bleeding. In addition, the post-processing section includes, for example, a sheet reversing conveyance process for inverting the sheet printed in the printing section 200 and sending it again to the printing section 200 to print on both sides of the sheet material P, and for processing a plurality of sheets. Examples include those that perform binding processing.

Furthermore, the term "printing device" in this application is not limited to an inkjet recording device, but also includes a device that is equipped with a liquid ejection head that ejects liquid toward a sheet, and that allows significant images such as characters and figures to be visualized by the ejected liquid. It is not limited to this, and includes, for example, patterns that form a pattern that has no meaning in itself.

Furthermore, the term "printing device" can include means for feeding, transporting, and discharging devices to which liquid can adhere, as well as pre-processing devices, post-processing devices, and the like.

Furthermore, the "liquid" is not particularly limited as long as it has a viscosity and surface tension that allows it to be discharged from the head, but it must be one that has a viscosity of 30 mPa・s or less at room temperature and normal pressure, or when heated or cooled. It is preferable that there be. More specifically, solvents such as water and organic solvents, coloring agents such as dyes and pigments, functional materials such as polymerizable compounds, resins, and surfactants, and biocompatible materials such as DNA, amino acids, proteins, and calcium. and edible materials such as natural pigments, etc., and these can be used, for example, in inkjet inks, surface treatment liquids, and the like.

Further, the "printing device" includes a device in which a liquid ejection head and a sheet material move relatively, but is not limited to this. Specific examples include a serial type device that moves a liquid ejection head, a line type device that does not move a liquid ejection head, and the like.

Furthermore, a "liquid ejection head" is a functional component that ejects and jets liquid from an ejection hole (nozzle). As an energy generation source for discharging liquid, piezoelectric actuators (laminated piezoelectric elements or thin film piezoelectric elements), thermal actuators using electrothermal conversion elements such as heating resistors, and electrostatic actuators consisting of a diaphragm and opposing electrodes are used for discharging liquid. Although energy generating means can be used, the discharge energy generating means to be used is not limited.

Next, an example of a drying device constituting the drying section will be described with reference to FIG. 2. FIG. 2 is an explanatory side view of the drying device.

The drying device 301 is a drying means and includes a drying mechanism section 310 that includes a heating means, and a suction conveyance mechanism section 320 that is a conveyance means.

The drying mechanism section 310 includes, in an internal space 311a of a chamber 311, a blowing unit 312 as a blowing means, and a radiant heater 313 such as an IR heater as a heating means. The air blowing unit 312 blows air toward the sheet P conveyed by the suction conveyance mechanism section 320. The radiant heater 313 emits radiant heat (for example, infrared rays) toward the sheet P conveyed by the suction conveyance mechanism section 320.

In the drying mechanism section 310, radiant heat is applied to the sheet material P conveyed to the internal space 311a of the chamber 311 by radiant heat from the radiant heater 313 and air blowing (air blowing) from the blower unit 312. Dry the liquid.

In addition, although the several ventilation unit 312 is set as the structure arrange|positioned along with the conveyance direction of the sheet material P here, the number and arrangement|positioning of the ventilation unit 312 are not limited to this. Further, although the configuration is such that a plurality of radiant heaters 313 are arranged side by side in the conveyance direction of the sheet material P, the number and arrangement of the radiant heaters 313 are not limited to this.

The suction conveyance mechanism section 320 has a conveyance belt 321 that is stretched between a drive roller 322 and a driven roller 323, and moves the sheet P carried on the surface of the conveyance belt 321 in the conveyance direction by the rotation movement of the conveyance belt 321. Convey in Y (arrow direction).

The conveyance belt 321 has a plurality of minute through holes (suction holes), and the sheet P is attracted to the conveyance belt 321 by a suction mechanism 324 and conveyed. The conveyance belt 321 is arranged such that the upstream portion in the conveyance direction faces the delivery cylinder 25 of the printing section 20 . The sheet P conveyed by the transfer cylinder 25 is transferred to the conveyor belt 321 and supported on the surface of the conveyor belt 321.

In the internal space 311a of the chamber 311 of the drying mechanism section 310, a guard member 316 is disposed between the conveyor belt 321 forming the conveyor surface, the blower unit 312, and the radiant heater 313. The guard member 316 prevents the sheet P from coming into contact with the radiant heater 313 or the like when the sheet P is lifted off the conveyor belt 321 or the like.

Next, an example of a sheet straightening device constituting the sheet straightening section will be described with reference to FIGS. 3 and 4. FIG. 3 is a side view of the sheet straightening device, and FIG. 4 is an enlarged view of the vicinity of the conveyance roller.

The sheet straightening device 601 is arranged downstream of the drying device 301 in the sheet conveyance direction.

The sheet straightening device 601 includes a belt pair 602. The belt pair 602 is composed of a pair of belts 611 (upper belt 611A, lower belt 611B) that convey the sheet P with it sandwiched therebetween. The belt pair 602 constitutes means for applying tension to the sheet P.

In this embodiment, belts having a fluororesin layer on their surfaces are used as the upper belt 611A and the lower belt 611B. Here, a fluororesin layer is formed by coating PFA (perfluoroalkoxyalkane). The fluororesin layer may also be a film containing both PFA and PTFE (polytetrafluoroethylene). Durability can be improved by including PTFE.

The upper belt 611A is wound around a conveyance roller 621A, a steering control roller 622A, and driven rollers 624A and 625A, and is given tension by a tension roller 623A.

The lower belt 611B is wound around a conveyance roller 621B, a steering control roller 622B, and driven rollers 624B and 625B, and is given tension by a tension roller 623B.

These upper belt 611A and lower belt 611B move around in the direction of the arrow by rotationally driving the conveyance rollers 621A and 621B, and sandwich the sheet P in the conveyance direction (arrow Y direction, hereinafter referred to as the "conveyance direction"). (referred to as "Y"). In this embodiment, rotational driving force is transmitted from a drive motor to the conveying roller 621B, and driving force is transmitted from the conveying roller 621B to the conveying roller 621A via a gear.

Moreover, as shown in FIG. 4, the conveyance roller 621A and the conveyance roller 621B are arranged apart from each other with a gap G10 between them.

The region T where the upper belt 611A and the lower belt 611B sandwich and convey the sheet P is the region T where the sheet P is sandwiched and conveyed only by the upper belt 611A and the lower belt 611B, and the region where the roller 603 carries the belt pair 602. It is composed of a region where the sheet P is held between by the holding force generated by pressing.

At this time, no rotating body or the like is arranged on the opposite side of the roller 603 across the belt pair 602, and the upper belt 611A or the lower belt 611B on the side that is not in contact with the roller 603 is placed on the opposite side of the roller 603. It is not in contact with any other parts. Therefore, each belt 611 is in contact with the roller 603, which is a curved member, along the circumferential surface of the roller 603 (the curved surface of the curved member) in the belt width direction (the width direction of the upper belt 611A and the lower belt 611B). It is possible to move to

Here, the tension rollers 623A and 623B apply tension to each belt 611A and 612 of the belt pair 602 in a direction in which the belt surfaces holding the sheet P are pulled in the upstream and downstream sides of the conveyance direction Y. It becomes a means to do so.

Then, each belt surface of the upper belt 611A and the lower belt 611B of the belt pair 602 is in contact with the inner surface of the upper belt 611A or the lower belt 611B of the belt pair 602 in a region T where they face each other and sandwich the sheet P, It includes a plurality (six in this case) of rollers 603 (603A, 603B) that are curved members arranged along the conveyance direction Y. The roller 603 deforms a portion of the belt pair 602 into a curved shape (curved deformation).

The roller 603 is a heating roller that has a built-in heater 604 as a heat generating means and also serves as a heating means for heating a region of the sheet P that is pressed against the roller 603 via the belt pair 602 and is curved and deformed. .

Here, in a region where the respective belt surfaces of the upper belt 611A and the lower belt 611B face each other (facing each other), the rollers 603A and the rollers 603B are arranged alternately, with the roller 603B being the most upstream side.

The roller 603A has its peripheral surface pressed against the upper belt 611A side of the belt pair 602, thereby bending and deforming the belt pair 602 into a downwardly convex shape. The roller 603B has its peripheral surface pressed against the lower belt 611B side of the belt pair 602, thereby bending and deforming the belt pair 602 into an upwardly convex shape.

That is, in the conveyance direction of the sheet P, rollers 603A that curve and deform the sheet P in a direction in which one surface side becomes convex and rollers 603B that curve and deform the sheet P in a direction that the other surface side becomes convex are arranged alternately. ing. Note that the rollers 603A and 603B may be arranged alternately, with the roller 603A on the most upstream side.

The cockling (deformation) correcting action by the seat correction device 601 in the seat correction unit 600 will be explained.

When cockling (undulation) remains on the sheet P, if the sheet P is wound around a curved surface such as the peripheral surface of the roller 603 while applying tension, the undulation disappears while the sheet P is wound. This is because the lengths of the swollen portion of the sheet P to which the liquid has been applied and the portion of the sheet P to which no liquid has been applied can be forced to be the same length.

However, if the curved surface is simply wrapped while applying tension, the waving will return to its original state and will not be corrected when the tension is removed.

Therefore, by heating the sheet P with a heating means and squeezing it while evaporating the moisture inside the sheet P, the length of the part to which the liquid is applied and the part to which no liquid is applied can be made the same, and the cock ring of the sheet P can be made. It is possible to correct wavy deformities such as

That is, as shown in FIG. 3, the sheet P is held between two upper belts 611A and lower belts 611B, and in this state, the belt pair 602 is pressed against the circumferential surface of the roller 603, which is a heating roller. The belt pair 602 is deformed into a curved shape while holding the sheet P therebetween.

As a result, the sheet P is heated by the roller 603, and by following the circumferential surface of the roller 603, the length of the part to which the liquid is applied and the part to which the liquid is not applied become the same, and cockling of the sheet P, etc. Corrects the wavy deformity of

In this way, by applying tension to the sheet P in a heated state and pressing it against a curved member (here, a roller) to cause it to curve and deform, it is possible to efficiently correct the deformation of the sheet.

As shown in FIG. 3, heating rollers as a plurality of curved members are brought into contact with an area where the upper belt 611A and the lower belt 611B face each other (area T where the sheet P is sandwiched) and are moved along the conveying direction P. Rollers 603 (603A, 603B) are arranged.

In other words, as mentioned above, by heating the sheet P with a heating means and squeezing it while removing the moisture in the sheet P, the length of the part to which the liquid is applied and the part to which no liquid is applied can be made the same, Waving deformation such as cockling of the sheet P can be corrected.

In this case, the correction effect is greater by wrapping the tape around multiple curved members (rollers) multiple times at a small wrapping angle than by wrapping it around the peripheral surface of one curved member (roller) at a large wrapping angle.

For example, when wrapping the sheet P around a φ80 roller three times at a wrapping angle θ of 30 degrees than when wrapping the sheet P once at a wrapping angle θ of 90 degrees, the deformation of the sheet P is better. The correction effect will be greater.

In this way, by arranging a plurality of curved members side by side in the conveyance direction, deformation of the sheet can be corrected more efficiently.

Further, in this embodiment, the tension of the lower belt 611B is set to be equal to or lower than the tension of the upper belt 611A.

In other words, the sheet P is conveyed while being sandwiched between the upper belt 611A and the lower belt 611B. Since the sheet P is sandwiched between the upper belt 611A and the lower belt 611B, it is the lower belt 611B that applies the force to press the sheet P against the roller 603A. It is the upper belt 611A that presses P.

Here, by weakening the tension of the lower belt 611B, the force with which the surface to which the liquid is applied (the image surface) contacts the roller 603A is weakened, and the occurrence of image scratches can be reduced.

On the other hand, by maintaining the necessary tension and reliably pressing the upper belt 611A against the roller 603B, the correction ability can be prevented from decreasing.

In addition, in the present embodiment, in the conveying direction of the sheet P, the length of the circumferential region where the sheet P follows the circumferential surface of the roller 603B (603Ba) on the most upstream side is the length in the circumferential direction where the sheet follows the other rollers 603. The configuration is shorter than the length of the area. In other words, the winding angle around the most upstream roller 603B (603Ba) is made the smallest.

This reduces the contact area at the most upstream roller 603B (603Ba) with which the sheet P contacts immediately after passing through the drying section 300, reducing the amount of rubbing and suppressing the occurrence of image scratches. be able to.

Further, in the transport direction of the sheet P, the roller 603B (603Ba) on the most upstream side contacts the lower belt 611B, which is in contact with the surface of the belt pair 602 that is opposite to the liquid application surface of the sheet P.

As the temperature is higher, image scratches are more likely to occur, so the most upstream side, where image scratches are most likely to occur, is heated from the back side, which has the effect of not increasing the liquid temperature more than necessary and suppressing the occurrence of image scratches. can.

Further, by using the roller 603 as a driven roller, meandering is less likely to occur and the correction effect is improved.

Next, an example of belt meandering correction means will be described with reference to FIGS. 5 and 6. FIG. 5 is a perspective explanatory view of an example of the meandering correction mechanism for the upper belt, and FIG. 6 is an explanatory view for explaining the belt position detection means.

The meandering correction mechanism 660 constitutes meandering correction means, and adjusts the positions of the steering control roller 622A, the motor 661, the arm 662 rotated by the motor 661, and the upper belt 611A in the width direction (direction perpendicular to the moving direction). belt position detection means 670 for detecting the belt position.

The steering control roller 622A is rotatably held at both ends by a roller holding member 666 that is held so as to be tiltable in the direction of arrow A via a support portion 665 that is a rotation center of the stay 664. One end of the steering control roller 622A is connected to one end of an arm 662, and the other end of the arm 662 is connected to a motor 661.

Thereby, by rotationally driving the motor 661, the arm 662 can rotate in the direction of arrow B around the rotation center 662a, and the steering control roller 622A can be tilted in the direction of arrow A around the support part 665. Therefore, by controlling the rotation angle of the motor 661, the steering angle of the steering control roller 622A can be set to an arbitrary value.

As shown in FIG. 6, the belt position detection means 670 includes a light receiving section 671 in which two light receiving elements 671A and 671B are arranged, and a shielding plate 672 arranged to block the two light receiving elements 671A and 671B. ing.

The shielding plate 672 is arranged to be rotatable in the direction of arrow C around a rotating shaft 672a, and is provided with a pin member 674 on one end side that abuts the widthwise end of the upper belt 611A. A slit 673 is provided on the end side.

In the meandering correction means configured as described above, when the upper belt 611A meanders, the pin member 674 is pushed at the end of the upper belt 611A, and the shielding plate 672 rotates in the direction of arrow C around the rotation axis 672a. . As a result, the positional relationship between the slit 673 of the shielding plate 672 and the light receiving elements 671A and 671B of the light receiving section 671 changes.

At this time, the positional relationship between the slit 673 of the shielding plate 672 and the light receiving elements 671A and 671B is as shown in FIG. 6, for example. FIG. 6A shows a case where the slit 673 is in a linear range facing across the light receiving elements 671A and 671B. FIG. 6B shows a case where the slit 673 is in a saturated region facing only one side (here, the light receiving element 671B). FIG. 6C shows a case where the slit 673 is in an error region facing only a part of one side (here, the light receiving element 671B).

The light receiving elements 671A and 671B output a voltage according to the opening area (the area facing the slit 673). Therefore, the current position of the upper belt 611A can be determined by looking at the outputs of the light receiving elements 671A and 671B.

Therefore, if it is determined that the upper belt 611A is deviated from the median value based on the result detected by the belt position detection means 670, the meandering can be corrected by steering the steering control roller 622A in the direction of movement in the opposite direction. .

The same applies to the meandering correction mechanism of the lower belt 611B.

Next, parts related to meandering correction control of the sheet straightening device and heating control of the drying device will be described with reference to the block diagram of FIG. 7.

The meandering correction control means 801 controls the drive of the motor 661 of the meandering correction mechanism 660 based on the detection result of the belt position detecting means 670 to correct the meandering of the upper belt 611A and the lower belt 611B. At this time, the meandering correction control means 801 determines that the moving speed of the upper belt 611A and the lower belt 611B in the width direction (the sum of deviation amounts when the belts are conveyed per unit length (total movement amount L3)) is within a specified value. control so that it fits.

Information correlated to the thickness of the sheet P is input to the meandering correction control means 801 from the operation unit 802. Here, information indicating the type of sheet P is input.

The storage unit 803 stores the relationship between the type and thickness of the sheet P, a specified value for meandering correction for the thickness of the sheet P, and the like.

Then, the meandering correction control means 801 determines the thickness of the sheet P from the type information of the sheet P input from the operation unit 802, reads out a specified value corresponding to the thickness of the sheet P, and keeps the belt within the specified value. The rotation angle of the motor 661 is controlled so that the movement speed in the width direction is controlled.

The drying control means 811 is a means for controlling ON/OFF and heat generation temperature (heating temperature) of the radiant heater 313 of the drying device 301, which is a drying means.

Information correlated to the thickness of the sheet P is input to the drying control means 811 from the operation unit 802. Here, information indicating the type of sheet P is input.

The storage unit 803 stores information such as the relationship between the type and thickness of the sheet P, and the relationship between the thickness of the sheet P and the heating temperature of the drying device 301.

Then, the drying control unit 811 determines the thickness of the sheet P from the type information of the sheet P input from the operation unit 802, and controls the heat generation temperature (heating temperature) of the radiant heater 313 based on the thickness of the sheet P. , the degree of drying of the sheet P is changed.

Next, meandering correction control of the belt 611 by the meandering correction control means will be described with reference to FIGS. 8 and 9 as well. FIG. 8 is an explanatory diagram of an example of the relationship between the inclination angle of the steering control roller and the movement speed of the belt in the width direction, and FIG. 9 is an explanatory diagram for explaining the sum of the belt movement amounts in the width direction in meandering correction.

The meandering correction control means 801 performs a homing operation for the roller position of the steering control roller 622. In this homing operation, the motor 661 of the meandering correction mechanism 660 is rotated in one direction to detect the home position, thereby constantly moving the steering control roller 622 to the home position.

Next, the meandering correction control means 801 initializes the position of the belt 611. In this initialization operation, the belts 611 are driven for a specified time (short time), and the total deviation amount (L1 + L2) of each belt 611 from the target median value is within a specified value (for example, within 0 ± 100 μm: the deviation shown in FIG. 9). If the total amount is L3), the state is set as ready.

Thereafter, the meandering correction control means 801 starts driving the belt 611 and starts meandering correction control at the same time as printing starts.

In this meandering correction control, the current position of the belt 611 is acquired from the output value of each light receiving element 671A, 671B of the light receiving section 671 of the belt position detecting means 670. For example, the average of one circumference of the belt 611 is acquired as the current position, and as shown in FIG. 8, from the relationship between the roller angle and the movement speed in the width direction (denoted as "belt deviation speed" in FIG. 8) acquired in advance, Control is performed to tilt the steering control roller 622 so as to suppress the movement speed in the width direction within a specified value.

Here, in this embodiment, with reference to FIG. 9, control is performed so that the sum of relative belt movement amounts in the width direction of the upper belt 611A and the lower belt 611B is within a specified value. The sum L3 of belt movement amounts in the width direction is the movement amount when the upper belt 611A and the lower belt 611B move in opposite directions with respect to the reference positions of the upper belt 611A and the lower belt 611B (FIG. 9(a)). (L3=L1+L2), which is an amount that does not cause image scratches.

If the movement amount (deviation amount) L1 and the movement amount (deviation amount) L2 are the same amount, the movement speed of the upper belt 611A and the lower belt 611B in the width direction with respect to the sheet P will be the same, so the front and back sides of the sheet P will be The amount of rubbing can be made uniform.

Further, the movement amount L1 and the movement amount L2 may be different amounts. For example, if the shift amount L2 of the lower belt 611B that contacts the surface opposite to the image surface (liquid application surface) of the sheet P is made larger than the shift amount L1 of the upper belt 611A, the surface of the sheet P which is the image surface Since the amount of rubbing can be made smaller than that on the back side, the influence on image scratches can be reduced.

In this way, control is performed to correct the meandering of each belt 611 so that the sum L3 of the movement amounts L1 and L2 of each belt 611 in the width direction falls within a predetermined value. This suppresses the occurrence of image scratches.

Furthermore, if the moving speed of the belt 611 in the width direction differs greatly between the upper and lower sides, the sheet P (liquid applying surface) will rub against the belt 611 and image scratches will easily occur. The movement of the belt 611B in the belt width direction is assumed to be the same.

Note that the upper belt 611A and the lower belt 611B do not need to move in the belt width direction exactly the same; for example, the lower belt 611B may move faster than the upper belt 611A. However, at this time, it is preferable to set the vertical speed difference to such an extent that the sheet P is not pulled by the movement of the lower belt 611B.

On the other hand, meandering correction is performed by controlling the upper and lower belts 611 separately. In other words, when each belt reaches its meandering amount upper limit value, it moves to the opposite side, and when it reaches the meandering amount upper limit value on the other side, it moves to the opposite side. If control is performed in which the liquid application surface of the sheet P is repeatedly moved, image scratches are likely to occur due to rubbing of the liquid application surface of the sheet P.

Next, an example of the relationship between the amount of residual solvent in the sheet P sent to the sheet straightening device 601 and the straightening effect on deformation of the sheet P will be described with reference to FIG. FIG. 10 is an explanatory diagram for explaining the same.

In FIG. 10, the horizontal axis represents the amount of residual solvent, and the vertical axis represents the degree of deformation of the sheet P, ranked from rank 0 to rank 5. Rank 0 is the largest deformation, and rank 5 is the least deformed.

In this example, the amount of residual solvent immediately after drying in the drying section 300 is less than 500 [mg/m ² ] for sheet P1, 1600 [mg/m ² ] for sheet P2, and 2100 [mg/m 2 ] for sheet P3. ² ].

At this time, the deformation rank a1 of the sheet P1 is "0", the deformation rank a2 of the sheet P2 is "1", and the deformation rank a3 of the sheet P3 is "2.5".

By passing such sheets P1 to P3 through the sheet correction unit 600 in high speed mode (relatively high conveyance speed), the sheets transition to deformation ranks b1, b2, and b3, respectively, and the deformation ranks become high in all cases. (less deformation).

Furthermore, by passing the sheet P2 through the sheet straightening unit 600 in a low speed mode (lower transport speed than the high speed mode), the deformation rank changes to c, and the deformation rank becomes higher than that in the high speed mode (the deformation is ).

Furthermore, by passing the sheet P2 through the sheet straightening section 600 in a low speed mode and increasing the heating temperature of the heater 604, the deformation rank changes to d, and the deformation rank becomes higher than that in the constant speed mode. (less deformation).

From this result, the larger the amount of residual solvent in the sheet P, the less deformation of the sheet P immediately after drying. Furthermore, when the amount of residual solvent is greater than when it is less than 500 [mg/m ² ], the straightening effect (the amount by which deformation is reduced by straightening) is improved. Furthermore, the higher the heating temperature of the sheet straightening section 600 is, and the lower the speed mode is (the larger the amount of heat input), the better the straightening effect is. Therefore, it is preferable that the amount of residual solvent is 500 [mg/m ² ] or more.

In other words, by increasing the amount of residual solvent for the sheet P that undergoes deformation such as cockling, the correction effect in the sheet correction section 600 can be enhanced. In order to increase the amount of residual solvent, the degree of drying (degree of drying) in the drying section 300 may be lowered, that is, it may be in a semi-dry state that is not completely dry.

Next, an example of the relationship between the belt coating of the belt pair and image scratches will be described with reference to FIG. 11. FIG. 11 is an explanatory diagram for explaining the same.

In this embodiment, as described above, the upper belt 611A and the lower belt 611B of the belt pair 602 are coated with PFA (perfluoroalkoxyalkane) to form a fluororesin layer (film).

In FIG. 11, the horizontal axis represents the amount of remaining solvent, and the vertical axis represents the area ratio of the portion destroyed when the image was rubbed (rubbed) (destroyed area ratio). FIG. 11(a) shows the case of a belt having a PFA fluororesin layer, and FIG. 11(b) shows the case of a PI (polyimide) belt. Further, the belt temperature (probe temperature) is 130°C and 150°C as examples.

From FIG. 7, it can be seen that by using a belt having a fluororesin layer, image scratches can be suppressed more than a belt not having a fluororesin layer.

Next, an example of the relationship between the coating of the belt pair, the amount of rubbing (amount of rubbing), and image scratches will be described with reference to FIG. FIG. 12 is an explanatory diagram for explaining the same.

The horizontal axis of FIG. 12 represents the amount of rubbing, and the vertical axis represents the area ratio of white spots (damaged area ratio) when the image is rubbed (scrubbed). In this case, the amount of residual solvent is 1261 mg/m ² ).

It can be seen from FIG. 12 that when the amount of rubbing is reduced, image scratches are less likely to occur.

In relation to the amount of rubbing, it is preferable that the amount of residual solvent is 1300 mg/m ² or less.

Next, an example of heating control of the drying device will be described with reference to the flowchart of FIG. 13.

First, the type information of the sheet P is acquired (step S1, hereinafter simply referred to as "S1"), and based on the acquired type information of the sheet P, the sheet P stored in the storage unit 803 is It is determined whether the sheet is thin (hereinafter referred to as "thin paper") or not (S2). "Thin paper" is, for example, 158 gsm or less.

Then, when the sheet P is thin paper, the radiant heater 313 is turned on and the output is lowered (S3). On the other hand, when the sheet P is not thin paper, that is, when the sheet P is thick (hereinafter referred to as "cardboard"), the radiant heater 313 is turned on and the output is increased (S4 ). The "cardboard" is, for example, 158 gsm to 450 gsm.

Here, by lowering the output of the radiant heater 313 (lowering the heat generation temperature), the heating temperature for the sheet P is lowered, so the degree (degree) of drying of the sheet P is lowered, and the sheet P is in a semi-dry state ( The above-mentioned state in which the amount of residual solvent is large is reached.

On the other hand, by increasing the output of the radiant heater 313 (higher heat generation temperature), the heating temperature for the sheet P becomes higher, so the degree of drying of the sheet P increases, and the sheet P reaches a predetermined dry state. Become.

Thereafter, it is determined whether the sheet P has passed through the drying section 300 (S5), and when the sheet P has passed through the drying section 300, it is determined whether printing has ended (S6). If the printing has not been completed, the process returns to step S2, and when the printing has been completed, the radiant heater 313 is turned off (S7), and the process ends.

In this manner, when the sheet P is thin paper, the degree of dryness is set to a semi-dry state, and the sheet P is sent to the sheet straightening device 601 of the sheet straightening section 600 at the subsequent stage.

As a result, in the case of thin paper that is prone to cockling, the effect of straightening the sheet P by the sheet straightening unit 600 is enhanced, and the sheet P can be reliably straightened.

Note that when the sheet P is made of cardboard, cockling is less likely to occur, so that no inconvenience occurs even if the sheet P is dried to a required dry state.

Next, meandering correction control in the sheet straightening device 601 will be explained with reference to the flowchart of FIG. 14.

First, type information of the sheet P is acquired (S11), and based on the acquired type information of the sheet P, whether the sheet P stored in the storage unit 803 is a thin sheet (hereinafter referred to as "thin paper") or not. It is determined whether or not (S12).

Then, when the sheet P is thin paper, meandering correction is performed so that the moving speed in the belt width direction falls within the specified value V1 (S13). The specified value V1 is set based on the permissible value of the amount by which the sheet P is rubbed by the belts of the belt pair 602 when straightening thin paper.

For example, if the total amount of movement in the width direction of each belt is L3 with respect to the time t for the sheet P (thin paper) to pass through the area T where the sheet P is conveyed while holding it, the specified value V1 is L3/t. Desired.

On the other hand, when the sheet P is not thin paper, that is, when the sheet P is thick (hereinafter referred to as "cardboard"), the moving speed in the belt width direction is the specified value V2 (V2>V1 ) The meandering correction is performed so as to fall within the range (S14).

For example, if the total amount of movement in the width direction of each belt is L4 (>L3) with respect to the time t for the sheet P (thin paper) to pass through the area T where the sheet P is conveyed while holding it, the specified value V2 is It is determined by L4/t. The reason why the sum L3 of the movement amount of each belt in the width direction when the sheet P is thin paper is smaller than the sum L4 when the sheet P is thick paper is because in the case of thin paper, the sheet P is kept in a semi-dry state where the amount of residual solvent increases. This is because images are more easily destroyed than cardboard because they are fed into the correction device 601.

Thereafter, the above process is repeated until the meandering correction is completed (S15), and when the meandering correction is completed, this process is ended.

That is, as described above, when the sheet P is thin paper, the drying device 301 converts the sheet P into a semi-dry state in which the amount of residual solvent increases and sends it to the sheet straightening device 601, thereby increasing the sheet straightening effect. .

Therefore, when the sheet P is thin paper, when correcting meandering of the belt pair 602 in the sheet straightening device 601, the sliding between the liquid application surface of the sheet P and the upper belt 611A (including the lower belt 611B in the case of both sides) When the amount of rubbing increases, image scratches are more likely to occur.

Therefore, when the sheet P is thin paper, the upper belt 611A is moved slowly by making the specified value that defines the movement in the width direction (movement amount or movement speed) smaller than when the sheet P is thick paper. Correct the meandering by returning at a faster speed to reduce the amount of friction.

This makes it possible to suppress the occurrence of image scratches even in the case of a thin sheet P where image scratches are likely to occur.

On the other hand, when the sheet P is made of cardboard, it is dried to a sufficiently dry state in the drying device 301 as described above, so the occurrence of image scratches due to friction with the belt pair 602 is suppressed, and the sheet P is quickly dried. No problem will occur even if the upper belt 611A is returned.

Next, a second embodiment of the present invention will be described with reference to FIG. 15. FIG. 15 is an explanatory side view of the sheet straightening device according to the same embodiment.

In this embodiment, an entrance sensor 618 is arranged on the entrance side of the sheet straightening device 601 to detect the leading edge of the sheet P based on the presence or absence of the sheet P, and an entrance sensor 618 is arranged on the exit side to detect the leading edge of the sheet P depending on the presence or absence of the sheet P. An exit sensor 619 is arranged for this purpose.

Then, based on the detection results of the entrance sensor 618 and the exit sensor 619, only while the sheet P is passing through the sheet straightening device 601, the meandering is performed so that the moving speed in the belt width direction is within a predetermined value. It is being corrected.

Next, meandering correction control in this second embodiment will be explained with reference to the flowchart of FIG. 16.

First, when rotational driving of the conveyance rollers 621A and 621B is started (S21), the meandering correction control means 801 starts meandering correction of the belt 611 using the correction amount A (S22).

The correction amount A at this time is set to a large amount of movement in the belt width direction. This is to control the upper belt 611A and the lower belt 611B to positions closer to proper values when the sheet P is received into the sheet straightening device 601. Further, even if the amount of movement in the width direction is set to be large, the problem of image scratches does not occur because the sheet P is not held between the upper belt 611A and the lower belt 611B.

Thereafter, it is determined whether the entrance sensor 618 has detected the leading edge of the sheet P (S23), and when the entrance sensor 618 has detected the leading edge of the sheet P, it is determined whether the sheet P is thin paper (S24).

Then, when the sheet P is thin paper, meandering correction is performed so that the moving speed in the belt width direction falls within a specified value V1 (A>V1) (S25). Thereafter, it is determined whether the exit sensor 619 has detected the rear end of the sheet P (S26), and meandering correction within the specified value V1 is continued until the exit sensor 619 detects the rear end of the sheet P.

On the other hand, when the sheet P is not thin paper, that is, when the sheet P is thick paper, meandering correction is performed so that the moving speed in the belt width direction falls within the specified value V2 (A>V2>V1). S27). Thereafter, it is determined whether the exit sensor 619 has detected the rear end of the sheet P (S28), and meandering correction within the specified value V1 is continued until the exit sensor 619 detects the rear end of the sheet P.

Then, when the exit sensor 619 detects the rear end of the sheet P, it is determined whether the rotational drive of the conveyance roller 621 has stopped (S29).

At this time, if the rotational drive of the conveyance roller 621 has not stopped, the process returns to step S22, and the meandering correction is performed once returning to the correction amount A.

On the other hand, when the rotational drive of the conveyance roller 621 is stopped, this process ends.

Note that when the exit sensor 619 detects the rear end of the sheet P, it may be determined whether the entrance sensor 618 has detected the leading edge of the next sheet P, and the correction amount for the meandering correction control may be set. At this time, if the next sheet P does not continue, it is determined whether the rotational drive of the transport rollers 621A, 621B has stopped, the correction amount is changed to A, and meandering correction control is executed.

Next, a third embodiment of the present invention will be described with reference to FIG. 17. FIG. 17 is a flowchart for explaining meandering correction control in the same embodiment.

In this embodiment, when two sheets P pass through the sheet straightening device 601, meandering is corrected so that the movement speed in the belt width direction falls within a predetermined value.

First, when rotational driving of the conveyance rollers 621A and 621B is started (S31), the meandering correction control means 801 starts meandering correction of the belt 611 with the correction amount A (S32).

After that, it is determined whether the entrance sensor 618 has detected the leading edge of the sheet P (S33), and when the entrance sensor 618 has detected the leading edge of the sheet P, the thickness of the leading sheet P and the trailing sheet P are It is determined whether or not they are different (S34).

Here, when the thickness of the preceding sheet P and the following sheet P are different, the moving speed in the belt width direction is within the specified value V1 (A>V1) until the exit sensor 619 detects the rear end of the sheet P. The meandering correction is performed so that it fits within (S35, S36).

Further, when the thickness of the preceding sheet P and the following sheet P are not different, it is determined whether the sheet P is thin paper or not (S37).

Then, when the sheet P is thin paper, the process moves to step S35.

On the other hand, when the sheet P is not thin paper, that is, when the sheet P is thick paper, the moving speed in the belt width direction is set to the specified value V2 (A> Meandering correction is performed so that the value falls within (V2>V1) (S38, S39).

Then, when the exit sensor 619 detects the rear end of the sheet P, it is determined whether the rotational drive of the conveying roller 621 has stopped (S30).

At this time, if the rotational drive of the conveyance roller 621 has not stopped, the process returns to step S32, and the meandering correction is performed once returning to the correction amount A.

On the other hand, when the rotational drive of the conveyance roller 621 is stopped, this process ends.

That is, in order to increase printing productivity, it is conceivable to shorten the sheet interval between the preceding sheet P and the subsequent sheet P.

In this case, each condition for the plurality of sheets P to be sent out by the feeding device 120 is acquired. When the entrance sensor 618 detects the leading edge of the preceding sheet P, if the thickness of the preceding sheet and the next succeeding sheet P are different, the meandering correction control means 801 performs meandering correction control within the specified value V1. Execute. Even if the preceding sheet P (thick paper) and the next sheet P (thin paper) are mixed in the sheet correction device 601, the images of both sheets P can be corrected by adjusting the correction conditions for thin paper, which is more likely to cause image scratches. It can prevent injuries.

Next, a fourth embodiment of the present invention will be described with reference to FIG. 18. FIG. 18 is a flowchart for explaining meandering correction control in the same embodiment.

In this embodiment, regardless of the thickness of the sheet P, meandering is corrected only while the sheet P passes through the sheet straightening device 601 so that the moving speed in the belt width direction falls within a predetermined value. ing.

First, when rotational driving of the conveyance rollers 621A and 621B is started (S41), the meandering correction control means 801 starts meandering correction of the belt 611 with the correction amount A (S42).

Thereafter, it is determined whether the entrance sensor 618 has detected the leading edge of the sheet P (S43), and when the entrance sensor 618 has detected the leading edge of the sheet P, the process continues until the exit sensor 619 detects the trailing edge of the sheet P. Meandering correction is performed so that the moving speed in the belt width direction falls within a specified value (S44, S45).

Then, when the exit sensor 619 detects the rear end of the sheet P, it is determined whether the rotational drive of the conveying roller 621 has stopped (S46).

At this time, if the rotational drive of the conveyance roller 621 has not stopped, the process returns to step S42, and the meandering correction is performed once returning to the correction amount A.

On the other hand, when the rotational drive of the conveyance roller 621 is stopped, this process ends.

Next, a fifth embodiment of the present invention will be described with reference to FIG. 19. FIG. 19 is an explanatory side view of the sheet straightening device according to the same embodiment.

In this embodiment, in place of the driven rollers 624A and 624B in the first embodiment, a heating roller 634A that heats the upper belt 611A and a heating roller 634B that heats the lower belt 611B are provided, respectively.

With this configuration, the upper belt 611A and the lower belt 611B can be heated before the upper belt 611A and the lower belt 611B come into contact with the sheet P, and the upper belt 611A and the lower belt 611B can be heated to a constant temperature. It can be brought into contact with the sheet P in a heated state.

Thereby, the heat from the roller 603, which is the heating roller on the most upstream side in the conveyance direction of the sheet P, is used to heat the sheet P, and the sheet P can be efficiently straightened.

Next, a sixth embodiment of the present invention will be described with reference to FIG. 20. FIG. 20 is an explanatory side view of the sheet straightening device according to the same embodiment.

In this embodiment, the upper roller 603A is arranged to be movable (in this case, vertically movable) as shown by the arrow. Note that the lower roller 603B may be movably arranged in place of the upper roller 603A or in conjunction with the upper roller 603A.

Thereby, the wrapping angle of the sheet P around the roller 603 can be changed. For example, when the sheet P is thick, the conveyance load can be reduced by reducing the wrapping angle. Further, since the tension on the sheet P at the portion wrapped around the roller 603 can be weakened, it is possible to suppress image damage caused by meandering correction of the upper belt 611A and the lower belt 611B.

Next, a seventh embodiment of the present invention will be described with reference to FIG. 21. FIG. 21 is an explanatory side view of the sheet straightening device according to the same embodiment.

In this embodiment, a temperature sensor 641 that detects the temperature of each roller 603, and a belt temperature sensor 642 that detects the temperature of the upper belt 611A and the lower belt 611B are arranged.

Since the purpose of the belt heating roller 634 is to raise the temperature of the belt, it monitors the temperatures of the upper belt 611A and the lower belt 611B (belt temperature), and controls the heater built in the belt heating roller 634 by feeding back the temperatures.

Note that the belt temperature can also be controlled by measuring the relationship between the belt temperature and the surface temperature of the belt heating roller 634 in advance and measuring the surface temperature of the belt heating roller 634.

Further, the surface temperature of the roller 603 is detected by a temperature sensor 641 and the heat generation temperature of the heater 604 is controlled to keep the surface temperature of the roller 603 constant.

Note that the temperature sensor 641 is placed at the center of the roller because the sheet P is conveyed at the center, but if the temperature relationship in the width direction is known in advance, It is not limited to the center.

Next, an eighth embodiment of the present invention will be described with reference to FIG. 22. FIG. 22 is an explanatory side view of the sheet straightening device according to the same embodiment.

In this embodiment, the lower belt 611B uses a belt 611Ba that does not have a fluororesin layer.

In single-sided printing, the lower belt 611B contacts the surface of the sheet P opposite to the liquid application surface, and therefore does not contribute to the occurrence of image scratches. In addition, in double-sided printing, the lower belt 611B passes through the drying section 300 twice and comes into contact with the first side where the amount of residual solvent is reduced, so even if there is no fluororesin layer, the occurrence of image scratches is suppressed. There is.

Thereby, costs can be reduced.

In the above embodiment, the printing device 1 includes the printing section 200 and the drying device 301 according to the present invention, or the device 500 for drying and straightening a sheet. A printing system can also be configured by the drying device 301 according to the present invention or the device 500 for drying and straightening a sheet.

In each of the above embodiments, the sheet straightening device is described as an example in which the sheet is conveyed in the horizontal direction (lateral direction), but it may also be configured to convey the sheet in the vertical direction or diagonally. can.

1 Printing device 100 Loading section 200 Printing section 300 Drying section 301 Drying device 310 Drying mechanism section 313 Radiant heater 320 Suction conveyance mechanism section 400 Discharge section 600 Sheet straightening section 601 Sheet straightening device 602 Belt pair 603 Roller 604 Heater 611A Upper belt 611B Lower Belt 660 Meandering correction mechanism 670 Belt position detection means 801 Meandering correction control means 811 Drying control means

Claims (12)

a pair of belts that sandwich and convey a sheet to which liquid has been applied;
a plurality of curved members giving curvature to the pair of belts;
heating means for heating the sheet via at least one of the pair of belts;
Belt position detection means for detecting the widthwise position of each belt of the pair of belts;
Meandering correction means for correcting meandering of each of the belts based on the detection results of the belt position detection means;
means for controlling the meandering correction means,
The pair of belts are movable in the width direction of the belts along the curved surface of the curved member while in contact with the curved member,
At least one of the belts that comes into contact with the surface of the sheet to which the liquid is applied has a fluororesin layer on the surface,
The controlling means performs control to correct the meandering of each of the belts so that the sum of the movement amounts in the width direction of each belt falls within a predetermined value,
The specified value when conveying the thin sheet is smaller than the specified value when conveying the thick sheet.
A seat straightening device characterized by: The sheet straightening apparatus according to claim 1, wherein the controlling means performs control to correct meandering of each of the belts so that the movement amount of each of the belts in the width direction is the same. 3. The sheet straightening apparatus according to claim 1, wherein the controlling means performs control to correct meandering of each of the belts so that the moving speeds of each of the belts in the width direction are the same. Among the plurality of curved members, in the sheet conveyance direction, the length of the circumferential region where the sheet follows the most upstream curved member is longer than the length of the circumferential region where the sheet follows the other curved members. The sheet straightening device according to any one of claims 1 to 3, characterized in that the sheet straightening device is short. Among the plurality of curved members, in the sheet conveyance direction, the most upstream curved member is in contact with the belt that is in contact with the surface of the pair of belts that is opposite to the surface to which the liquid is applied. The sheet straightening device according to any one of claims 1 to 4, wherein the sheet straightening device is in contact with the sheet straightening device. The sheet straightening device according to any one of claims 1 to 5, wherein the fluororesin layer contains PFA and PTFE. 6. The prescribed value is set based on an allowable amount of rubbing of the sheet by each belt of the pair of belts when straightening the thin sheet. The sheet straightening device according to any one of the above. 8. The control means performs control to correct the meandering of each belt so that it falls within the specified value only while the sheet is passing. seat straightening device. The pair of belts is composed of an upper belt and a lower belt in the height direction,
9. The sheet straightening device according to claim 1, wherein the tension of the lower belt is less than or equal to the tension of the upper belt. A printing apparatus comprising the sheet straightening device according to any one of claims 1 to 9 . means for applying a liquid to the sheet;
drying means for drying the sheet to which the liquid has been applied,
11. The printing apparatus according to claim 10 , wherein the sheet straightening device is arranged downstream of the drying means. a printing device that prints on the sheet;
A printing system comprising: the sheet straightening device according to any one of claims 1 to 9 .

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