Tension control system for a digital printing system

Abstract

A digital printing system comprising: a web media transport system configured to transport a continuous web media having a width, one or more printhead mounts positioned above the web media and extending across the width of the web media in a transverse direction X, a tensioning shoe comprising a number of support rollers (N2), where the number of support rollers (N2) exceeds the number of printhead mounts (N1) by at least one additional support roller (N2=N1+Nx).

Description

TENSION CONTROL SYSTEM FOR A DIGITAL PRINTING SYSTEM

[0001] The present invention relates to the field of digital printers, and more particularly to a web media-fed digital printing system for continuous web media printing. An aspect of the invention relates to a digital printing system, more specifically to a tensioning shoe that ensures that the web media is properly aligned and stabilized across its entire width as it moves beneath each printhead module and help reduce variations in tension.BACKGROUND

[0002] In a continuous web media fed printing system, a web media is fed through the printer as a continuous web media. The term "web media" refers to the continuous roll of print media, such as fabric, film, or other materials, that is fed from large reels through one or more printing systems that create images by applying one or more colorants to the surface of the web. This system allows for high-speed, high-volume printing, making it efficient for large- scale production.

[0003] When a web media (such as paper, plastic, or fabric) is processed in a continuous web media-fed printing system, maintaining the right amount of tension is crucial. Proper tension control is essential because even slight variations can have significant impacts on the quality of the final product, potentially resulting in blurred or misaligned prints.

[0004] One of the problems that affects the tension of the web media is the slippage of the web media. Slippage occurs when the web material does not maintain its grip on the roller as it moves through the printing system. If the web media slips, it can lead to misalignment, inconsistent tension, and defects in the printed material. When the web media slips on the roller, the tension across the web is not uniform. Some areas may become too tight, while others become too loose. This uneven tension is a primary cause of wrinkles. Wrinkles form when parts of the web are under lower tension than others. For example, if the edges of the web media are slack while the centre is tight, the loose areas can buckle, leading to wrinkles or creases.

[0005] Additionally, this uneven tension or compressive stress can cause buckling, which deforms the web media out of its plane, creating waves or folds. These deformations severely impact print quality by distorting the printed image and can even pose a risk of damaging the printhead if the web media comes into contact with it. Furthermore, when tension becomes too high, the web media can overstretch, resulting in permanent deformation, thinning, oreven tearing of the material. These issues complicate the printing process by reducing efficiency, increasing waste, and lowering overall print quality.

[0006] In the printing process, it is crucial that the printhead remains perfectly aligned with the web media to ensure accurate and high-quality printing. Typically, the printhead is mounted perpendicular to the web media, meaning it is aligned at a right angle to the surface of the web media as it moves through the printer. This perpendicular alignment is essential because it ensures that the ink or other printing materials are applied evenly and precisely. However, problems arise when the web media passes over surfaces that are curved or angled, such as improperly aligned rollers or misconfigured machine parts. When the web media is forced to travel over these uneven surfaces, its path can deviate from being flat and straight. This deviation can cause the printhead to become misaligned relative to the web media's surface, particularly in the vertical direction (Z-axis).

[0007] It is an aim of the present invention to at least partly mitigate one or more of the aforementioned issues, such as preventing wrinkles, avoiding overstretching, providing stability to the web media and maintaining consistent print quality.BRIEF SUMMARY

[0008] The present invention aims to address at least in part the issue of slippage, wrinkling or overstretching of the web media during printing by implementing a tensioning shoe in a digital printing system. This tensioning shoe is designed to ensure stability and consistent and optimal tension across the entire web media, thereby preventing slippage on the rollers, reducing the risk of buckling and wrinkles, and avoiding the overstretching of the material. By maintaining precise control over the web media tension, the invention aims to enhance print quality, minimize defects, and improve the overall efficiency of the printing process.

[0009] In an aspect of the present invention, there is provided a digital printing system comprising: a web media transport system configured to transport a continuous web media having a width, one or more printhead mounts positioned above the web media and extending across the width of the web media in a transverse direction X, a plurality of printheads being connected to each printhead mount; and a tensioning shoe comprising a number of support rollers (N2), each support roller being provided with a drive motor, wherein the number of support rollers (N2) exceeds the number of printhead mounts (Ni) by at least one additional support roller.

[0010] This can also be expressed as N2=NI +NX, where Nxis a variable number representing the additional support roller added to Ni and where Nxs 1 . Thus, N2 is greater than N1 by atleast one additional support roller. Further, for example, Nxcan be up to 11 . This variable number Nxcould depend on the spacing between printhead mounts, desired tension level.Also, the thickness, elasticity, and weight of the web media might require different numbers of support rollers to ensure consistent tension and avoid slippage. Thus, the number of support rollers is at least one more than the number of printhead mounts, due to the inclusion of at least one additional support roller.

[0011] Further, the additional support roller can be similar or essentially the same, or identical as the other support rollers. The additional support roller may have a drive motor. In an alternative embodiment, the additional support roller may differ from the other support rollers.

[0012] In an embodiment, the tensioning shoe comprises a number of support rollers (N2), wherein the number of support rollers (N2) exceeds the number of printhead mounts (N1) by one additional support roller (N2=NI + Nx, where Nx=1 ). The additional support roller can be the same as the other support rollers.

[0013] In an embodiment, the tensioning shoe comprises a number of support rollers, wherein the number of support rollers exceeds the number of printhead mounts by at least one additional roller, which additional support roller is identical (or similar) to the other support rollers.

[0014] In some embodiments, the tensioning shoe comprises a number of support rollers (N2), wherein the number of support rollers (N2) exceeds the number of printhead mounts (N1) by one additional support roller (N2=NI + Nx, where Nx=1 ), wherein the support rollers are arranged such that an angle defined between three successive roller centres lies within a predetermined range.

[0015] The support rollers of the tensioning shoe may be mounted at their ends in a common rigid block on each side of the web path. The blocks may be formed of steel or another rigid material and serve to hold all roller shafts in precise angular positions relative to one another.

[0016] The support rollers can preferably be arranged in a sequence along the substrate (web media) path such that an angle defined by lines connecting the centres of three successive support rollers is between 90° and 180°.

[0017] In some embodiment, the tensioning shoe comprises a number of support rollers as defined above, wherein each of the support rollers is provided with a drive motor configured to independently control a rotational speed and torque of the support roller.

[0018] Thus, the number of support rollers N2is equal to the number of printhead mounts Ni plus at least one. By having at least one extra support roller in relation to the number of printhead mounts, the digital printing system ensures that the web media is properly aligned and stabilized across its entire width as it moves beneath each printhead mount and helps to evenly distribute the tension and prevent sagging or misalignment, which could otherwise lead to printing defects or variations in print quality.

[0019] The number of printhead mounts (Ni) can be in the range between 1 and 40, preferably between 1 and 20, more preferably between 2 and 10.

[0020] In an embodiment, the number of printhead mounts (Ni) is in the range between 1 and 20, preferably between 2 and 10, more preferably between 3 and 8, even more preferably between 4 and 6. In case where Ni is between 1 and 20 and Nx=1 , the number (N2) of the support rollers forming the tensioning shoe will between 2 and 21 depending on the number (Ni) of printhead mounts, where N2=NI +NX, where Nx=1 .

[0021] In an embodiment, the tensioning shoe is positioned beneath the one or more printhead mounts and configured to provide tension control and stability across the width of web media as it passes under the printhead mounts.

[0022] Each support roller may have a cylindrical cross-section with diameter in the range of from 20 mm to 1000 mm, preferably in the range of from 100 mm and 500 mm. In an exemplary embodiment, each support roller has a cylindrical cross-section with diameter in the range of from 200 mm to 400 mm.

[0023] In an embodiment, each support roller has a length equal to or greater than 40 mm, preferably equal to or greater than 1 m, more preferably equal to or greater than 2 m, even more preferably equal to or greater than 3 m in the transverse direction X across the width of the web media.

[0024] In a further embodiment, each support roller has a length equal to or greater than 4m, even more preferably equal to or greater than 5 m, extending in the transverse direction X across the width of the web media. In an embodiment, the wrapping angle around the support rollers is in the range of from 0.5 degrees to 6 degrees, preferably of from 0.5 degrees to 3 degrees.

[0025] In an embodiment, each printhead mount has a width along the longitudinal direction Y (Y-axis) in the range between 40 mm and 1000 mm, or 40 mm and 500 mm, preferably in the range between 100 mm and 500 mm, more preferably between 200 mm and 300 mm. Further, each printhead mount may have an elongated body with a length equal to or greater than 40mm, or equal to or greater than 600 mm, or equal to or greater than 1 m, more preferably equal to or greater than 2 m, more preferably equal to or greater than 3 m, even more preferably equal to or greater than 4m, or even equal to or greater than 5 m, spanning the width of the web media in the transverse direction X (X-axis). In an embodiment, the elongated body comprises metal or fibre-reinforced polymeric material, or a combination thereof.

[0026] In an embodiment, the digital printing system comprises one or more printhead mounts are positioned along a curved surface that curves outward, such that a first angular interval defined between a centreline (A) of each printhead mount, which extends in vertical direction (Z-axis) and a centreline (B) of the corresponding support roller, which also extends in vertical direction (Z-axis), is in the range between 0.5 degrees and 4 degrees, preferably between 0.5 degrees and 3 degrees, more preferably between 0.5 degrees and 2 degrees, and further wherein a second angular interval defined between the centrelines (A) both in the vertical direction (Z-axis) of two subsequent printhead mounts is in the range of from 0.5 degrees to 4 degrees, preferably of from 0.5 degrees to 3 degrees.

[0027] In an embodiment, one or more printhead mounts are positioned along a circumference of a curved surface that curves outward, such that the first angular interval between the centreline (A) in the Z-axis (the vertical direction) of each printhead mount and the centreline (B) of the corresponding support roller along the Z-axis (the vertical direction) is in the range of from 0.5 degrees to 4 degrees, preferably of from 0.5 degrees to 3 degrees, more preferably between 0.5 degrees and 2 degrees.

[0028] In an embodiment, the second angular interval between the centrelines (A) along the Z-axis (the vertical direction) of two subsequent printhead mounts is in the range of from 0.5 degrees to 4 degrees, preferably in the range of from 0.5 degrees to 3 degrees, more preferably in the range of from 0.5 to 2 degrees.

[0029] In an embodiment, the angle of inclination of the printhead mount to the web media's surface can be in the range between 0° and 6°, preferably in the range of from 0° and 4°, more preferably in the range of from 0° and 2°.

[0030] The digital printing system may further comprise at least one printhead module supported by the printhead mount. Preferably, the digital printing system comprises at least one printhead mount, each printhead mount being configured to receive and support at least one printhead module. The printhead mount is preferably mechanically attachable to and detachable from the printhead module, thereby providing a stable structural interface while allowing the module to be removed or replaced as a unit.

[0031] In certain embodiments, the printhead modules, including the printheads contained therein, are stationary while the web media moves continuously beneath them.

[0032] In an embodiment, the digital printing system further comprises a tension control system configured to control the tension of a web media, the tension control system comprising a tensioning shoe.

[0033] Advantageously, the tension control system of the present invention can actively adjust the web media's tension in real-time as it is transported on a roll-fed system. The tension control system may further comprise a feedback control system.

[0034] In an embodiment, the tension control system further comprises a dancer roller and / or at least one tensioning roller.

[0035] Advantageously , the digital printing system can be a single -pass digital printing system.

[0036] Within the scope of this application, it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and / or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination.

[0037] That is, all embodiments and / or features of any embodiment can be combined in any way and / or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim, accordingly, including the right to amend any originally filed claim to depend on and / or incorporate any feature of any other claim although not originally claimed in that manner.TERMS AND DEFINITIONS

[0038] The term "digital printing" refers to methods of printing from a digital-based image directly to a variety of substrates. Examples of digital printing techniques include inkjet printing and laser printing.

[0039] The term “printhead” specifically refers to a component that includes the nozzle plate comprising a nozzle (s) and ink chamber, among other integral parts, designed for dispensing ink onto a substrate.

[0040] The term “angular interval” refers to the angle between two points measured along the circumference of a circle or curved surface In the context of the present invention, the angular interval refers to an angle measured between the centrelines of two adjacent components, such as printhead mounts or support rollers, where the measurement is taken from the centre of one mount to the centre of the next along the curved surface.

[0041] The term “wrap angle” (also called wrapping angle) refers to the angle formed between the tangent points of a web as it wraps around a roller, or for example to the portion of the support roller's circumference that is in contact with the web media.

[0042] The terms “web”, “web media” or “web material” or “print media” are used herein interchangeably.

[0043] The term “curved surface” refers to a surface in convex form, in which every point is located at a distance from a central axis or point, with the surface extending outward from the centre. The curved surface may include an arc or segment of a circle, or it may represent more general outwardly curved geometries. The term curvature refers to the geometric property of a curved surface, describing the extent to which the surface bends or deviates from a flat plane.

[0044] The term “central axis” refers to refers to an imaginary line running along the lengthwise centre, parallel to the longitudinal direction, which corresponds to the X-axis.

[0045] The term “centre point” of the curved surface refers to the geometric centre of the curvature or geometric point from which the curvature of the surface extends outward. In the case of a circular or arc-shaped surface, this would be the central point of the circle, from which all points on the curved surface are equidistant. For more complex curved surfaces, the center point represents the focal point or axis that defines the curvature and serves as a reference for positioning elements, such as the printhead mount.

[0046] The term printhead mount refers to a beam-like support structure that extends across the substrate (web media) path and carries one or more printheads together with their associated equipment.

[0047] As used herein, the term “printhead module” refers to a unit comprising a plurality of printheads with their nozzle arrays, together with additional components required for their operation.

[0048] In the description and claims of the present disclosure, each of the verbs, “comprise”, “include” and “have”, and conjugates thereof, are used to indicate that the object or objects of the verb are not necessarily a complete listing of members, components, elements or parts of the subject or subjects of the verb. As used herein, the singular form “a”, “an” and “the” include plural references unless the context clearly dictates otherwise.BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0049] To easily identify the discussion of any particular element or act, the most significant digit or digits in a reference number refer to the figure number in which that element is first introduced.

[0050] FIG. 1 provides a schematic view of the digital printing system in accordance with one embodiment.

[0051] FIG. 2 illustrates a digital printing system comprising a tensioning shoe with support rollers and a number of printhead mounts in accordance with one embodiment.

[0052] FIG. 3 illustrates a schematic drawing of the tensioning shoe 20 in the digital printing system in accordance with one embodiment.

[0053] FIG. 4 illustrates an aspect of the subject matter in accordance with one embodiment.

[0054] FIG. 5 illustrates a schematic drawing of the side view of the digital printing system, in particular the tensioning shoe in accordance with an embodiment.DETAILED DESCRIPTION

[0055] Digital printing systems are tools for generating printed images across a diverse array of print media. They are capable of printing on various receivers, herein also referred to as web material or web media. The digital printing system is a web media-fed digital printing system designed to apply precise, high-quality prints onto the web media as it moves through the system. For example, the web media can receive a decoration layer. Further, the web media may receive one or more layers on the decorated web media to form a decorative panel. The decorative panel can be a kitchen panel, a flooring panel, furniture panel, celling panel, or a wall panel.

[0056] Further, the digital printing system comprises a web media transport system, preferably a roll-fed web transport system. In a (roll-fed) web media transport system a continuous roll of material, known as the web media, is unwound and fed through a series of processing stations, such as printing units, cutting machines, or coating stations. The web media can be a continuous, flat material like paper, fabric, woven and non-woven materials, plastic material (e.g. polyvinyl chloride, polyethylene terephthalate, polyethylene, polypropylene, and polyolefin), or metal foils.

[0057] Further, the digital printing system can be a large-scale digital printing system. An example of such a digital printing system is a single-pass digital printing system, in which the print media moves continuously beneath a fixed array of printhead modules, where each module is attached to a printhead mount, which support a plurality of printheads. In such systems, each printhead module comprises a plurality of printheads, and each printhead in turn contains many nozzles that eject ink in fixed positions across the printing width. Because all of these nozzles contribute directly to the printed image in a single-pass process, any irregular movement of the substrate beneath the modules can lead to visible defects. In particular, if the substrate slips while passing under the printheads, the nozzles will deposit ink at the wrong positions, producing misaligned or distorted images. If the substrate wrinkles, some areas of the web surface may lift while others sag away, leading to uneven ink coverage or unprinted gaps. By providing a tensioning shoe with a plurality of support rollers incombination with a plurality of printhead mounts, the invention holds the substrate / web media under controlled tension. Ensuring that the number of support rollers exceeds the number of printhead mounts means that the substrate is supported between successive mounts, thereby reducing the risk of slippage and wrinkling during high-speed operation.

[0058] Single-pass digital printing system is particularly well-suited for industrial applications that require large quantities of prints and high throughput.

[0059] Thus, in an embodiment, the digital printing system of the present invention is a single-pass digital printing system, comprising a web media transport system configured to transport a continuous web media having a width, one or more printhead mounts positioned above the web media and extending across the width of the web media in a transverse direction X, and a plurality of printheads being connected to each printhead mount, a tensioning shoe comprising a number of support rollers (N2), each support roller being provided with a drive motor, wherein the number of support rollers (N2) exceeds the number of printhead mounts (Ni) by at least one additional support roller.

[0060] While the present invention may exemplify a single pass digital printing system, it is not limited thereto and can also be integrated into diverse printing setups.

[0061] Additionally, the digital printing system can be a well-suited for wide-format printing, where maintaining consistent tension and alignment across the width of the media is crucial for high-quality results. For example, wide-format printing systems are commonly used for producing large banners, large signs, posters, ceiling, floor and wall coverings, laminate flooring, wall graphics, tarpaulins, flooring graphics, and various decorative materials. These systems can print on a wide range of substrates, such as vinyl, paper, fabric, and other flexible or rigid materials, with web media widths often exceeding 45 cm. For example, web media width can be in the range between 45 cm and5 m, or 45 cm and 4m. For example, the web media width can be in the range between 50 cm and 3 m, or in the range between 50 cm and 2.5 m, or in the range between 50 cm and 2 m, or in the range between 50 cm and 1 .5 m, or in the range between 50 cm and 1 m. The wider the web, the more likely tension differences will appear across its width, increasing the risk of slippage, wrinkling, or stretching unless controlled support is provided.

[0062] In and embodiment, the web media width is in the range between 1 m and 3 m.

[0063] In an embodiment, the web media width is in the range between 50 cm and 3 m.

[0064] The digital printing system comprises at least one printhead mount. The term “printhead mount” as used herein refers to a structural support element for one or more printhead modules. A plurality of printheads can be directly or indirectly connected to a printhead mount. For example, the printheads may be secured to the printhead mount via an intermediate component,such as a casing or housing, which is itself attached to the printhead mount (indirect connection), or, alternatively, the printheads may be physically fastened to the printhead mount without any intermediate component (direct connection). Further, the printhead mount supports the plurality of printheads. The digital printing system may comprise one or more printhead modules. Each printhead module may accommodate a plurality of printheads in a single structural unit. Thus, one printhead mount may be associated with a plurality of print heads.

[0065] In an embodiment, the digital printing system as described above comprises at least one printhead module supported by the printhead mount, wherein each printhead module comprises a plurality of printheads adapted to carry out printing and having a plurality of nozzles, and wherein the printhead module can be configured to be detachably secured to the printhead mount.

[0066] The digital printing system may comprise a frame structure for supporting the printhead mounts. The frame structure may extend along opposite sides of the web path. For example, a rigid metal frame (steel or aluminium) may span along both sides of the web path. The printhead mounts are preferably suspended or hung from this frame above the web media path, so that the printhead modules attached to the printhead mounts are held in fixed alignment relative to the moving web media.

[0067] The printhead mount is a beam-like or elongated body that extends across the substrate path (web media path) and supports the printing equipment. In some embodiments, the printhead mount comprises a rigid body that provides the necessary structural stiffness to span the substrate path without excessive deflection. In particular, the printhead mount is a structural support configured to carry a plurality of printheads and / or printhead modules.

[0068] The printhead module may comprise a plurality of printheads, and the nozzle arrays of the respective printheads and associated components, all components located within the housing of the printhead module to cover a wider print zone.

[0069] The printhead module may further comprise additional components required for operation of the printheads. For example, the printhead module can include a nozzle array and associated ink supply components. Ink supply tanks may be arranged above the printhead modules to provide ink to the printheads and to function as backflow tanks for returning excess ink. In some embodiments, the printhead module may also comprise one or more solution boards or driver boards for controlling the printhead operation, as well as intermediate inlet and outlet tanks for managing ink flow. Colour-specific inlet and outlet connectors may be provided for each ink channel, together with tubing that fluidically connects the tanks to the printheads. These additional components allow the printheadmodule to operate as a self-contained unit that can be attached to and detached from the corresponding printhead mount.

[0070] The printhead mount may also carry or being attached to at least one printhead module or plurality of printheads. The printhead module may comprise the associated driver boards, electronic circuitry, and ink tubing, plurality of printheads. The arrangement of these components can vary depending on the system configuration, but in all cases the printhead mount serves as the principal beam-like support structure that spans the substrate path and integrates the printing equipment.

[0071] In a printing mode, the printhead mounts are positioned such that the nozzle plates of the printheads are parallel to the web media passing underneath, thereby ensuring accurate ink deposition. In a maintenance mode, the printhead mounts can be contracted or detached from the tensioning shoe, with the nozzle plates repositioned to be parallel to the floor rather than the substrate / web media. This facilitates cleaning, calibration, and servicing operations without disturbing the alignment of the printing system.

[0072] Each printhead mount can be attached to the frame of the tensioning shoe via a flexible attachment mechanism that allows adjustment of the printhead mount in the X, Y, and Z directions. This enables precise positioning of the printheads relative to the substrate path.

[0073] Preferably, the printhead mounts are arranged along a curved path corresponding to the arc defined by the support rollers in the tensioning shoe. The curvature of the support roller arrangement provides constant substrate tension across the transverse width of the web media.

[0074] Further, the digital printing system comprises a tensioning shoe which is configured to provide tension control and stability across the width of web media as it passes under the printhead mounts. The tensioning shoe is arranged beneath the substrate path, while the plurality of printhead mounts is suspended above. As used herein, the term tensioning shoe refers to a support roller assembly that engages the substrate to be printed and acts as an integrated unit.

[0075] The tensioning shoe comprises a plurality of support rollers. The number of support rollers of the tensioning shoe is defined in relation to the printhead mount. Preferably, the tensioning shoes comprises a number of support rollers (N2), each support roller being operationally connected to drive motor, wherein the number of support rollers (N2) exceeds the number of printhead mounts (N 1 ) by at least one additional support roller (N2=NI +NX, where Nx=1 ).

[0076] Each support roller forming the tensioning shoe is operatively connected to a drive motor. Accordingly, the support rollers are actively driven and are not passive idlers that merely rotate under the movement of the web media. All of the support rollers of the tensioning shoe may be mounted on a common rigid block, for example a steel block located on each side of the web path, thereby providing precise mechanical stability across the printing width.

[0077] The drive motors are controlled to coordinate the rotational speeds of the support rollers so as to maintain constant substrate tension and reduce flutter across the width of the web media. The coordinated arrangement and driving of the support rollers maintain stable substrate (web media) tension and reduces wrinkling across the width of the web media. In some embodiments, the drive motors are operated by a controller, optionally in combination with sensors that monitor substrate position or tension.

[0078] The relative positioning of the tensioning shoe and the printhead mount is selected such that the distance of unsupported substrate between these elements is minimized. By maintaining a short span length, the elastic stretching of the printing support (substrate) under tension is reduced. A reduced degree of stretching correspondingly lowers the likelihood of substrate slippage relative to the printhead during transport. This provides a more stable web path through the print zone and enhances registration accuracy across multiple printheads.

[0079] Unlike conventional guide rollers, the tensioning shoe is configured not merely to redirect or support a substrate but to actively regulate substrate tension across the print zone. Each support roller, including the additional support roller, of the tensioning shoe can be provided with its own independent drive motor, enabling individual adjustment of roller speed and torque.

[0080] In the digital printing system of the present invention, the support rollers forming the tensioning shoe are arranged such that an angle defined between three successive roller centres lies within a predetermined range.

[0081] For example, the support rollers within the tensioning shoe can be arranged with respect to one another such that the angle defined between three successive support roller centres lies between 90° and 180°, thereby ensuring ensure stability and consistent tension across the entire width of the web media,

[0082] Referring to the configuration and use of the digital printing system as illustrated in the Figs 1 to 5; three orthogonal directions are further defined: a first direction or vertical direction Z (designated as the Z-axis). The Z-axis represents the vertical direction; a second direction or longitudinal direction, or horizontal direction Y (designated as the Y-axis); a thirddirection or transverse direction X (designated as the X-axis) that is orthogonal to the first two directions.

[0083] In the digital printing system of the present invention, a continuous roll of web material may be fed through the printing unit, where the printheads apply printing composition, preferably in a single pass. As illustrated in FIG. 1 , the digital printing system 1 of the present invention includes a web media transport system, such as a roll-fed web media transport system, which facilitates the continuous feeding of the web material through the printing unit. The digital printing system has a reel 3 at the start of the system, which feeds the web material 19 having a width into the printing machine. The web media 19 is gradually unwound from the reel 3 and fed into the digital printing system. A splicing station 5 allows operators to join a new roll of material to the tail end of the expiring roll while the printing unit 4 is still running, and in combination with a buffer, ensuring uninterrupted printing. As the web media unwinds from the reel 3the infeed roller 16 positioned in the proximity of the dancer roller 12 helps to guide the web material into the machine, ensuring that it enters the printing unit 4 in a controlled and aligned manner. By changing the speed of the infeed roller 16, based on the position of the dancer roller 12 which may be monitored by sensors that provide feedback to the reel’s drive system, the tension is kept constant. The digital printing system 1 further comprises a printing unit 4, where colorants (e.g., inks) or other coating liquids are applied to the surface of the web media through the nozzles of the printheads. The printing unit 4 comprises one or more printhead mounts 7 that are print bars each mounted on a frame positioned at a fixed height above the surface of the web media. The printheads mounts 7 comprise one or more printhead modules 10 that comprise the print heads with nozzles, thus each printhead mount support a plurality of printheads. The printing unit 4 can have any number of printhead mounts 7. In an embodiment, the number of printhead mounts that are print bars is between 4 and 6. Further, a tensioning shoe 20 comprising support rollers 2 is positioned beneath the printhead mounts 7. The tensioning shoe 20 is exemplified in greater detail in Figures 2-5. Further, each support roller 2 has a drive motor (not shown). The roller 8 determines the linear speed of the web media. A tension roller 15 measures the tension in the web media and provides input to the infeed roller 9. Flange load cells are used as tension sensors, replacing the traditional bearings of the tension rollers. Each tension roller is equipped with two flange load cells, which function as bearings while simultaneously measuring the tension applied to the web media. The actual tension of each tension roller is calculated by a programmable logic controller (PLC), which processes the combined load data from both flange load cells. Optionally, the digital printing system may also include additional processing units or components integrated within the system to further process theweb media. Other examples of digital printing system components include web cleaners, web tension sensors, or quality control sensors.

[0084] A web media guide 6 ensures the proper alignment and tracking of the web media as it moves through the print unit 4. At least one cleaning unit 14 is integrated within the print unit 4, ensuring that the web media is thoroughly cleaned before printing. This helps to remove any dust, debris, or contaminants from the web media's surface.

[0085] The tensioning shoe 20, shown in FIG. 3, has a number (N2) of support rollers 2, with the exact number depending on the number (Ni) of printhead mounts 7 in the system. It has been determined that the relationship between the number (N2) of support rollers 2 and the number (Ni) of printhead mounts 7 provides more uniform tension distribution of the incoming and outgoing web media within the printing unit 4. The number of support rollers is always at least one greater than the number of printhead mounts, due to the inclusion of at least one additional support roller. Further, the additional support roller can be the same as the other support rollers 2. All of the support rollers, including the additional support roller(s) are structurally identical and are designated with the same reference numeral (2) in Figures 1-5. The support rollers 2, including the additional support roller 2, have a drive motor. The support rollers 2 are arranged in contact with the surface of the web media to regulate and maintain consistent tension across the web media as it is fed through the print heads during the printing process. Each support roller 2 may feature a cylindrical cross-section, preferably a cylindrical cross-section. Further, each support roller 2 may have an elongated body, with the length of the elongated body being equal to or greater than 40 mm, or equal to or greater than 600 mm, or equal to or greater than 1 m, or equal to or greater than 2 m (2000 mm (52 m)), or equal to or greater than 3m, or equal to or greater than 3 m (a3m), or equal to or greater than 4m (54m), or equal to or greater than 5 m (a5m)along the transverse X-axis,). The diameter of the cross-section of the support rollers 2 can be in the range of from 20 mm to 1000 mm. For example, the diameter of the cross-section of the support rollers 2 can be in the range of from or from 50 mm to 1000 mm, or from 70 mm to 800 mm, or from 100 mm to 700 mm, or from 100 mm to 600 mm, or from 100 mm to 500 mm, or from 150 mm to 450mm, or of from 200 mm to 400 mm.

[0086] In an embodiment, each support roller has a cylindrical cross-section with diameter in the range of from in the range of from 200 to 400 mm. For example, the diameter of the cross-section of each support roller may be equal to or greater than 200 mm, equal to or greater than 225 mm, equal to or greater than 250 mm, equal to or greater than 300 mm. A support roller with a length exceeding 2 meters along the transverse direction X (X-axis) and a diameter below 180 mm may lack the structural strength needed to adequately support theweb media, potentially leading to deformation (bending) of the roller which would cause uneven jetting distance. On the other hand, a support roller with a diameter exceeding 700 mm would likely interfere with adjacent rollers, causing operational issues, he number (N2) of support rollers 2 depends on the number (Ni) of printhead mounts 7, where the number (N2) of support rollers 2 is equal to the number of printhead mounts 7 plus at least one additional support roller (N2=NI +NX, where Nxis a variable number, and where Nx£1 ).

[0087] Further, the additional support roller(s) can be identical to the other support rollers.

[0088] For example, the number of support rollers can be equal to the number of printhead mounts plus a variable number Nx, where Nxmay be 1 , 2, 3, 4, or 5, representing the additional support roller(s). Nxcan also be as high as 11 .

[0089] In an embodiment, the number (N2) of support rollers 2 depends on the number (Ni) of printhead mounts 7, where the number (N2) of support rollers 2 is equal to the number of printhead mounts 7 plus one additional support roller (N2=NI +NX, where Nx=1 ). Further, the additional support roller can be identical to the other support rollers.

[0090] For example, with reference to FIG. 1 , the number (Ni) of printhead mounts 7 is four (Ni=4), and the number (N2) of support rollers 2 is five (N2=NI +NX=5, where Ni=4; Nx=1 ). Thus, the problem of maintaining optimal tension and preventing slippage of the web media is addressed by implementing a specific number of tension rollers beneath the web media, with the number of support rollers equalling the number of printhead mounts plus one (where Nx=1 ). The present invention is not limited to this particular configuration, and variations in the number and arrangement of tension and support rollers may be used depending on the specific application or design requirements.

[0091] Without being bound by any specific theories, the inventors have surprisingly found that, to prevent the web media from slipping around the support rollers of the tensioning shoe in a digital printing system with one or more printhead mounts, and to maintain a low wrapping angle, the number of support rollers should be equal to the number of printhead mounts plus at least one additional support roller ( N2=NI +NX, where NX£1 ). For Example, Nxcan be up to 11 . In another example Nxcan be up to 10, or up to 9, or up to 8, or up to 7 or up to 6, or up to 5, or 4, or up to 3, or up to 2. In an exemplary embodiment, the number of support rollers (N2) is equal to the number of printhead mounts (N1 ) plus one, where Nx=1 .

[0092] The wrapping angle (wrap angle) refers to the angle formed between the web media and the support roller as the web media wraps around the support roller's surface. Thewrapping angle can be greater than 0° and lower than 20°. For example, the wrapping angle around the support rollers can be in the range or from 0.5 degrees to 6 degrees, or of from 0.5 degrees to 4 degrees, preferably of from 0.5 degrees to 3 degree, more preferably of from 0.5 degrees to 2 degrees, allowing to maintain more consistent tension across the web media, reducing the likelihood of defects like wrinkles or buckling and also helps prevent slippage, ensuring that the web media maintains its grip on the roller surface, which leads to smoother, more controlled transport.

[0093] The following formula Tout=Tin-eMeis used to calculate the maximum tension difference of a web media as it passes over a support roller in a web-fed digital printing system without slipping. This is a fundamental formula in web media tension control and is derived from the Capstan equation, which is the relationship between the tensions on either side of a surface (like a roller) when friction is present. Tout is the maximum tension in the web media on the outgoing side (exit side) of the roller (after it has passed over the roller); Tin is the tension in the web media on the incoming side (entry side) of the roller (before it passes over the roller); e is Euler's number; p is the coefficient of friction between the web material and the surface of the roller. This coefficient p represents how much frictional force is present between the two surfaces; 6 is the wrapping angle (in radians), which is the angle through which the web media contacts the roller. It represents the extent to which the web media wraps around the support roller. When the web media wraps around the support roller, the contact between the web and the roller generates friction. This friction is essential for managing and isolating tension, as it enables the support roller to control the web media without the need for physical gripping. The degree to which the tension can be controlled or isolated by the support roller depends on both the wrapping angle 6 (angle of contact) and the coefficient of friction p between the web media and the support roller. Additionally, this friction can introduce tension into the web media, influencing the overall tension distribution.

[0094] The tension range of the web media can be between 60 N / m and 1600 N / m. For example, the tension range can be between 60N / m and 900 N / m, 80 M / m and 900 N / m, or between 112 N / m and 900 N / m, or between 180 N / m and 500 N / m, or between 200 N / m and 400 N / m, or between 200 N / m and 300 N / m.

[0095] In an embodiment, the E-modulus (elastic modulus) of the web media can be in the range between 40 N / mm2and 1000 N / mm2.

[0096] The digital printing system has one or more printhead mounts 7 which are structural components, configured to support the printhead modules 10 comprising the print heads and their respective nozzles, as shown in FIG. 2. The print heads 10 can comprise nozzles fordispensing ink onto the web media (print substrate) like paper, plastic, metal or other materials.

[0097] The number of the printhead mounts can be in the range between 1 and 40. For example, the digital printing system can be equipped with 2 to 20 printhead mounts each holding multiple printhead modules, where the number of support rollers forming the tensioning shoe can be in the range between 3 and 21 , when Nx=1 depending on the number of printhead mounts. In an embodiment, the digital printing system may have 4 to 6 printhead mounts, as shown in FIG. 1 and FIG. 2. Further, the printhead mounts 7 can be in the form of print bars and may have an elongated body with a length equal to or greater than 40 mm, or equal to or greater than 600 mm, or equal to or greater than 1 m, or equal or greater than 2 m, or equal to or greater than 3 m, or equal to or greater than 4 m, spanning the width of the web media along the X-axis (transverse X direction) that allows for a wider coverage area, which is essential for printing on large-area objects efficiently. In an embodiment, the length of the elongated body of the printhead mount 7 is equal to or greater than 2 m. In a further preferred embodiment, the length of the elongated body of the printhead mount 7 is equal to or greater than 3 m. In yet another embodiment, the length of the elongated body of the printhead mount 7 is equal to or greater than 4 m. This elongated body of the printhead mount 7 may comprise metal or a fibre- reinforced polymeric material or combinations thereof. For example, the fibre-reinforced material may be a natural fibre- reinforced polymeric material, or a carbon- fibre reinforced polymeric material, or a glass-fibre reinforced polymeric material.Alternatively, the elongated body of the printhead mount may comprise metal that is selected from the group consisting of aluminium, aluminium alloy, steel, steel alloy, titanium, or titanium alloy.

[0098] In a digital printing system, printing is typically done with the printhead mounted perpendicular to the web media (along the Z-axis) to ensure accurate and even application of ink or other printing materials. However, if the web media runs over a curved surface (rollers) or a series of angled surfaces, the printhead is no longer perfectly perpendicular to the web media. This is solved by angling the printhead mounts along with their corresponding printheads so that they are perpendicular to the web. The one or more printhead mounts (along with the printheads) may be positioned along a curved surface that curves outward. Each printhead mount has a centreline (A), defined as the line extending vertically along the Z- axis and that symmetrically divides the printhead mount. This centreline (A) can either be substantially parallel to the Z-axis or can be slightly inclined relative to the Z-axis, meaning it is not perfectly parallel, as it is directed towards the centre point of the curvature. The centreline (A) in the vertical direction (Z) passes through the central axis (X direction) of theprinthead mount and extends through the centre of a curvature such as circle or arc segment, that defines the curved surface.

[0099] The central axis of the printhead mount refers to an imaginary line running along the midpoint of the printhead mount in its longitudinal direction, which is the X-axis.

[0100] The centre point of the curved surface refers to the geometric point from which the curvature of the surface extends outward. In an embodiment, the centreline (A) is slightly inclined relative to the Z-axis. In another embodiment, the centreline (A) substantially parallel to the Z-axis.

[0101] Also, each support roller may be positioned along a curved surface that curves outward. Each support roller has a centreline (B), defined as the line extending vertically along the Z-axis. The centreline (B) in the vertical direction (Z) passes through the central axis (X axis) of the support roller and extends through the centre of a curvature such as circle or arc segment, that defines the curved surface.

[0102] The central axis of the support roller is an imaginary line that runs along the length of the roller in the X direction, through the geometric centre of its circular cross-section.

[0103] The centreline (B) and the central axis of the support roller intersect at the midpoint of the support roller's length. This intersection point is where the centreline (B) is perpendicular to the central axis and may establish a reference for alignment towards the centre point of the curvature. Also, the centreline (A) and the central axis of the printhead mount may intersect at the midpoint of the printhead mount, where the centreline (A) is perpendicular to the central axis.

[0104] The centreline (B) can either be substantially parallel to the Z-axis or can be slightly inclined relative to the Z-axis, meaning it is not perfectly parallel, as it is directed towards the centre point of the curvature. In another embodiment, the centreline (B) substantially parallel to the Z-axis. In an embodiment, the centreline (B) is slightly inclined relative to the Z-axis.

[0105] In case when the printheads and their printhead mounts are angled, which means forming an angle of inclination between the surface of the web media and the centreline in the vertical direction (Z) of the printhead mount, an additional force Fy is introduced due to the angling (see FIG. 4). This force along the Y axis (Fy), emerges as a component of the overall force acting on the printhead mount. Specifically, this force can be calculated as Fy=Fzsin(angle), where Fzis the force in the z-direction (Z-axis), and the angle is the degree to which the printhead is tilted from the vertical axis, as shown in FIG. 4. The inventors have found that the optimal angle of inclination of the printhead mount to the web media's surface can be in the range between 0° and 6°, preferably between 0° and 4°, more preferably between 0° and 2°or between 0.5° and 2°. If the angle is greater than 6°, this would require a re-design of the printhead mount as the force Fybecomes significant.

[0106] The printhead mounts are positioned along a curved surface that curves outward, with a radius in the range of from 10 m to 20 m, preferably of from 11 m to 17 m, even more preferably of from 12 m to 16 m. Each printhead mount can be spaced at an angular interval (also referred to as a second angular interval) along this curved surface, where an angular interval between the centrelines (A) in the vertical direction Z or centres of two subsequent printhead mounts is in the range of from 0.5 degrees to 4 degrees, preferably of from 0.5 degrees to 3 degrees, more preferably of from 0.5 degrees to 2.5 degrees. Thus, this second angular interval is measured from the centreline (A) in the vertical direction Z or centre of one printhead mount to the centreline (A) or centre of the next printhead mount along the curved surface, where the centre refers to a point where the Z-axis crosses the X-axis and the Y-axis, representing the geometric centre of the printhead mount. Additionally, one or more printhead mounts can be positioned along the circumference of the curved surface that curves outward, so that the angular interval, also referred to as a first angular interval, between the centreline(A) in the vertical direction Z or centre of each printhead mount and the centreline (B) in the vertical direction Z or centre of the support roller is between 0.5 and 3 degrees, preferably between 0.5 and 2 degrees. For example, this first angular interval can be in the range of from 0.5 degrees and 3 degrees, or of from 0. 5 degrees and 2 degrees, or of from 0. 5 degrees and1 .5 degrees, or of from 0. 5 degrees and 1 degree. The centre of the support roller refers to the point at the geometric centre of the circular cross-section of the support roller, in case of cylindrical roller. Thus, this first angular interval is measured from the centreline (A) in the vertical direction (Z) or centre of one printhead mount to the centreline (B) in the vertical direction (Z) or centre of the support roller.

[0107] FIG. 5 shows an example of the digital printing system having a tensioning shoe. In this example, with reference to FIG. 5, the digital printing system comprises a number of printhead mounts 7, a number of support roller 2 and a moving web media W. The number Ni of printhead mounts is five (Ni=5), while the number of support rollers is six, as shown in FIG. 5. Each printhead mount 7 is 250 mm wide. The diameter of the support roller is 300 mm. The centreline (A) in the vertical direction (Z) of a printhead mount 7 refers to an imaginary line that extends vertically (Z-direction) and passes through the central axis (X-axis) of the printhead mount, extending perpendicularly from the printhead's surface toward the web media w, as shown in Fig 5. Due to the curvature of the surface, this centreline (A) may be slightly inclined relative to the Z-axis but generally follows a vertical direction. The centreline(B) refers to an imaginary line that extends vertically along the Z direction (vertical direction),passing through the central axis (the X axis that runs along the longitudinal direction of the support roller) of the support roller 2 and being directed towards the centre point of the curvature, which may be a circle or arc shape. For example, in the case of a circular curvature, this means it is directed towards the geometric centre of that circle. Furthermore, the printhead mounts are arranged along a curved surface that curves outward, such that the angular interval (also referred to as a first angular interval) between the centreline (A) in the vertical direction Z of each printhead mount and the centreline (B) in the vertical direction Z of its corresponding support roller is within the range of 0.5° to 3°. The printhead mounts 7 are positioned at 2° intervals along a circle with a radius of 15000 mm. The wrapping angle (0) around the support rollers is 2° (or approximately 0.0349 radians). The friction coefficient is p=0.7. If the incoming web media has a tension Tinof 200 N / m width, the maximum outgoing tension Tout after six support rollers 2 is: Tout =200. e (°-7x6 0x0349) = 866 N / m. This means that maximum 866 N / m - 200 N / m = 666 N / m tension difference can be created over the print shoe without risk of slipping. This maximum tension difference allows for sufficiently strong pulling on the web to prevent wrinkles, floppy edges, and other issues.

[0108] In another example (not shown), the printhead mount 7 has a width of 250 mm along the longitudinal Y-axis. These printhead mounts 7 are arranged at 1° intervals along a circle with a radius of 15000 mm. The number of printhead mounts is five (Ni =5). The number of support rollers (N2=NI +1 ) is six. The support rollers 2 have a diameter of 250 mm, with a web media wrapping angle 0 of 1 ° (approximately 0.0175 radians) around each support roller. The friction coefficient is =0.7. The tension of the incoming web media (Tin) is 200 N / m, while the outgoing tension (Tout) is 215 N / m. The web media travels a total distance of 1309 mm between the apex of the first support roller 2 and the last support roller 2 along the Y-axis, with a printhead mount-to-printhead mount spacing of approximately 261 .8 mm. This configuration ensures that the 1° interval spacing generates a negligible force (Fy) on the printhead mount, thus avoiding any additional costs for re-design. The present invention is not limited to the examples described above.

[0109] The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the presentinvention comprising different combinations of features noted in the described embodiments will occur to persons skilled in the art to which the invention pertains.

Claims

22CLAIMS1 . A digital printing system comprising: a web media transport system configured to transport a continuous web media having a width, one or more printhead mounts positioned above the web media and extending across the width of the web media in a transverse direction X, and a plurality of printheads being connected to each printhead mount, a tensioning shoe comprising a number of support rollers (N2), each support roller being provided with a drive motor, wherein the number of support rollers (N2) exceeds the number of printhead mounts (N1) by at least one additional support roller.

2. The digital printing system according to claim 1 , wherein the number of support rollers (N2) exceeds the number of printhead mounts (N1) by one additional support roller (N2 = N1 + 1 ).

3. The digital printing system according to any one of claims 1 or 2, wherein the support rollers forming the tensioning shoe are arranged such that an angle defined between three successive roller centres lies within a predetermined range.

4. The digital printing system according to any one of claims 1 to 3, further comprising at least one printhead module supported by the printhead mount, wherein each printhead module comprises a plurality of printheads adapted to carry out printing and having a plurality of nozzles, and wherein the printhead module is configured to be detachably secured to the printhead mount.

5. The digital printing system according to any one of the preceding claims, wherein each support roller has a cylindrical cross-section with diameter in the range of from 20 mm to 1000 mm.

6. The digital printing system according to any one of the preceding claims, wherein each support roller, has a length equal to or greater than 40 mm, preferably equal to or greater than 1 m, more preferably equal to or greater than 2 m, even more preferably equal to or greater than 3m in the transverse direction X across the width of the web media.

7. The digital printing system according to any one of the preceding claims, wherein each printhead mount has a width along a longitudinal direction Y in the range between 40 mm and 1000 mm.

8. The digital printing system according to any one of the preceding claims, wherein the one or more printhead mounts are positioned along a curved surface that curves outward, such that a first angular interval defined between a centreline (A) of each printhead mount, which extends in vertical direction (Z-axis) and a centreline (B) of the corresponding support roller, which also extends in vertical direction (Z-axis), is in the range between 0.5 degrees and 4 degrees, , and wherein a second angular interval defined between the centrelines (A) both in the vertical direction (Z-axis) of two subsequent printhead mounts is in the range of from 0.5 degrees to 4 degrees.

9. The digital printing system according to any one of the preceding claims, wherein the at least one printhead mount has an elongated body spanning the width of the web media in the transverse direction X with a length equal to or greater than 40 mm, preferably equal to or greater than 1 m, more preferably equal to or greater than 2 m, more preferably equal to or greater than 3 m, even more preferably equal to or greater than 4 m.

10. The digital printing system according to claim 9, wherein the elongated body of each printhead mount comprises metal or fibre-reinforced polymeric material, or a combination thereof.11 . The digital printing system according to any one of the preceding claims, wherein a wrapping angle around the support rollers is in the range of from 0.5 degrees to 6 degrees.

12. The digital printing system according to any one of the preceding claims, wherein an angle of inclination of the printhead mount to a web media's surface is in the range between 0° and 6°.

13. The digital printing system according to any one of the preceding claims, wherein the number of printhead mounts (Ni) is in the range between 1 and 40, preferably between 1 and 20, more preferably between 2 and 10.

14. The digital printing system according to any one of claims 1 to 13, further comprising a tension control system configured to control the tension of the web media.

15. The digital printing system according to claim to 14, wherein the tension control system further comprises a feedback control system configured to adjust the wrapping angle.

16. The digital printing system according to claims 14 or 15, wherein the tension control system further comprises a dancer roller.

17. The digital printing system according to any one of claims 14 to 16, wherein the tension control system further comprising at least one tensioning roller.

18. The digital printing system according to any one of claims 1 to 17, wherein the digital printing system is a single-pass digital printing system.

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