Cleaning Inkjet Nozzles in Digital Printing Systems

Abstract

The system (10) has a printing position and a non-printing position, and the system (10) includes an imaging station (60) and a wiping assembly (200, 400). The imaging station (60) includes at least a nozzle plate (61) having one or more nozzles (166, 166a, 166b, 166c) configured to apply droplets of a printing fluid onto a surface of one or more substrates (44) to generate one or more images thereon. The wiping assembly (200, 400) is positioned at least partially within the gap (141) between the nozzle plate (61) and one or more substrates (44) and is configured to (i) physically contact the nozzle plate (61) and (ii) remove printing fluid residue from at least one of the nozzles (166, 166a, 166b, 166c) while the system (10) is in the printing position.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application claims the benefit of U.S. Provisional Patent Application No. 63 / 162,577, filed March 18, 2021, and U.S. Provisional Patent Application No. 63 / 214,286, filed June 24, 2021, the disclosures of which are incorporated herein by reference in their entireties.

[0002] The present invention relates generally to digital printing systems, and more particularly to a method and system for preventing clogging of inkjet nozzles in digital printing systems. [Background technology]

[0003] Various techniques have been disclosed for maintaining the cleanliness and functionality of nozzles in inkjet printing systems.

[0004] For example, Japanese Patent Application Publication No. 2000103086A describes an inkjet printer having an inkjet head and a transfer belt. The inkjet head includes a plurality of nozzles for ejecting ink onto the transfer belt, and the ink is further transferred to a recording paper. The maintenance unit is used in the maintenance process of the inkjet head, and includes a pull-out roller, a roller, and a maintenance sheet (wiping sheet). The maintenance sheet is pulled out of the maintenance unit by the pull-out roller, and the print head moves upward. The roller and the pull-out roller function as a pull-out member for pulling out the maintenance sheet in a horizontal direction. When the winding roller is driven to rotate, the maintenance sheet moves from the supply roller through the pull-out roller to the winding roller. When the maintenance sheet is moved, the nozzle surface is wiped by the maintenance sheet, and a wiping operation is performed.

[0005] U.S. Patent 10,449,767 describes a liquid ejection device that includes a liquid ejection head that ejects liquid from nozzles arranged on a nozzle face, a wiping member having a vertically elongated shape that can contact the nozzle face, a contact portion that can contact the side opposite to the side where the wiping member contacts the nozzle face, and a transport mechanism that transports the wiping member, the contact portion having a first contact portion that is separated from the wiping member when the wiping member is transported by the transport mechanism and that contacts the wiping member when the wiping member is driven to contact the nozzle face, and a second contact portion that contacts the wiping member when the wiping member is transported by the transport mechanism.

[0006] U.S. Patent No. 8,888,230 describes a fluid ejection device having a fluid ejection head including a nozzle array having a plurality of nozzles each and for ejecting fluid onto a medium, the fluid ejection device being capable of performing a flushing operation in which the fluid is ejected into an absorbing member which is used to absorb the fluid ejected from the nozzles, the absorbing member being a linear member which extends along the nozzle array and is capable of relative motion from the flight path of the fluid ejected from the nozzles to a retraction position.

[0007] US Patent 5,557,307 describes a cleaning thread for inkjet printing nozzles. An absorbent material is mounted on the nozzle plate of an inkjet printer to collect excess ink and particles that might otherwise clog the nozzle orifices of the printer. In an inkjet printer, ink droplets are propelled from an array of orifices in the nozzle plate of the printhead. During the ejection of the ink droplets, the ink is sprayed or accumulates around the orifices. The ink droplets accumulate on the paper web adjacent to the nozzles, and the mist from the droplets drifts back and coats the surface of the nozzle plate. This ink coating tends to attract particles and clog the nozzle orifices. By placing the absorbent material in close proximity to the nozzle orifice array, the material absorbs and removes the ink that coats the nozzle plate before it can clog the nozzle orifices. The thread is one example of an absorbent material. The thread slides in a groove across the surface of the nozzle plate, removing the ink coating and particles on the nozzle plate. A thread dispenser bobbin on one side of the printer head supplies clean thread to the printer head, and a rewind bobbin on the other side of the printer head pulls the thread from the dispenser bobbin across the nozzle plate.

[0008] China Patent Application Publication No. 100553982C describes an inkjet coating device that includes a shower nozzle with multiple nozzles through which a solution is sprayed onto a substrate using inkjet, and a cloth with an absorbent band shape. The cloth is discarded into a discharge gear release mechanism just in front of the nozzle face of the shower nozzle, and the cloth is pressed against a roller above the nozzle face. Summary of the Invention

[0009] Embodiments of the invention described herein provide a system having a printing position and a non-printing position, the system including an imaging station and a wiping assembly. The imaging station includes at least a nozzle plate having one or more nozzles configured to apply droplets of a printing fluid onto a surface of one or more substrates to generate one or more images thereon. The wiping assembly is positioned at least partially within a gap between the nozzle plate and the one or more substrates and is configured to (i) physically contact the nozzle plate while the system is in the printing position and (ii) remove residue of the printing fluid from at least one of the nozzles.

[0010] In some embodiments, the system includes (i) a transport assembly configured to move one or more substrates relative to the nozzle plate, and (ii) a processor configured to (a) control the transport assembly to move the one or more substrates and (b) control the wiping assembly to remove residue from at least one of the nozzles while the one or more substrates are moved by the transport assembly. In other embodiments, the processor is configured to maintain a constant throughput of producing one or more images at the print position, including while the wiping assembly is removing residue. In yet other embodiments, the one or more substrates include an intermediate transfer member (ITM) configured to receive droplets to generate one or more images and transfer the one or more images to a target substrate, and the transport assembly includes an ITM module configured to move the ITM relative to the imaging station to generate one or more images.

[0011] In one embodiment, the one or more substrates include one or more flat or continuous webs, and the transport assembly includes a substrate transport module configured to move the one or more flat or continuous webs relative to the imaging station to generate one or more images thereon. In another embodiment, the imaging station includes at least a first printbar having one or more first nozzles and a second printbar having one or more second nozzles, and in the printing position, the wiping assembly is configured to remove residue from at least one of the first nozzles while at least one of the second nozzles applies droplets. In yet another embodiment, in the printing position, a gap between the nozzle plate and the one or more substrates is maintained while (i) applying droplets and (ii) removing residue.

[0012] In some embodiments, the wiping assembly includes a wiping element configured to remove printing fluid residue by wiping it from at least an orifice of at least one of the nozzles. In other embodiments, the wiping element includes a ribbon configured to hold the cleaning fluid and physically contact the nozzle plate by self-adhering to the nozzle plate. In yet other embodiments, the ribbon includes (a) a residue removal layer configured to remove printing fluid residue from the nozzle plate, and (b) a compressible layer coupled to the residue removal layer and configured to (i) absorb and contain the cleaning fluid when placed in contact with the cleaning fluid, and (ii) release at least a portion of the cleaning fluid when a compressive force is applied to the ribbon.

[0013] In one embodiment, the wiping assembly is configured to position the ribbon over at least one of the nozzles when the imaging station is not applying droplets to the substrate. In another embodiment, the ribbon is configured to cap the nozzles, and the compressible layer is configured to retain humidity within the ribbon and prevent residue or another substance from solidifying on the nozzles. In yet another embodiment, the ribbon is configured to (i) retain a predetermined amount of cleaning fluid to wipe away residue that has built up on the nozzles, and (ii) absorb additional residue of the printing fluid that does not build up on the nozzles.

[0014] In some embodiments, the additional residue includes at least one of a printing-fluid vapor and aerosol, and the wiping element is configured to absorb at least one of the printing-fluid vapor and aerosol that has not accumulated on the nozzle. In other embodiments, the wiping assembly is configured to move the wiping element in the gap between the nozzle and the one or more substrates to at least one of (i) wipe the accumulated residue on at least one of the nozzles and (ii) absorb the additional residue of the printing fluid positioned between the nozzle and the one or more substrates. In yet other embodiments, the wiping assembly is configured to move the wiping element in a first direction during a first time interval and in a second direction during a second time interval.

[0015] In one embodiment, the nozzles are disposed along a first axis and across a second axis, and at least one of (i) the first direction is parallel to the first axis and (ii) the second direction is parallel to the second axis. In another embodiment, the one or more substrates move in a movement direction, the first direction being parallel to the movement direction and the second direction being perpendicular to the movement direction. In yet another embodiment, the processor is configured to control the wiping assembly to move the wiping element in at least one of the first direction and the second direction when at least one of the nozzles is ejecting printing fluid toward the one or more substrates.

[0016] In some embodiments, the first time interval is greater than the second time interval, in other embodiments the first time interval overlaps with one or more of the second time intervals, and in yet other embodiments the first direction is orthogonal to the second direction.

[0017] In one embodiment, the processor is configured to control the wiping assembly to move the wiping element (i) in a first direction at a first speed and (ii) in a second direction at a second speed different from the first speed. In another embodiment, the second speed is at least five times greater than the first speed. In yet another embodiment, the one or more substrates include a flexible substrate having a first section for receiving one or more printing fluids and a second section positioned between the first image and the second image, and the processor is configured to (i) control the flexible substrate to move in the movement direction and (ii) control the wiping assembly to move the wiping element in a second direction parallel to the movement direction of the flexible substrate when the second section passes next to the one or more nozzles.

[0018] In some embodiments, the processor is configured to control the wiping assembly to move the wiping element in a second direction parallel to the direction of movement of the flexible substrate when one or more nozzles are not applying droplets. In other embodiments, at least a portion of the wiping element is positioned in a gap between at least one of the nozzles and the second section during at least a portion of the second time interval. In yet other embodiments, the processor is configured to (i) control the imaging station to apply droplets when the first section passes next to one or more nozzles and not apply droplets when the second section is adjacent to one or more nozzles, and (ii) control the wiping assembly to move the wiping element to wipe residue from the nozzles when the processor controls one or more nozzles not to apply droplets.

[0019] In one embodiment, the flexible substrate includes an intermediate transfer member configured to receive droplets to form an image at the imaging station and transfer the image to a target substrate. In another embodiment, the second section is configured to connect between two ends of the first section to form an infinite loop including the first section and the second section. In yet another embodiment, the one or more substrates include a first flat configured to receive a first image and a second flat configured to receive a second image, and the processor is configured to control the wiping assembly to move the wiping element in a second direction while at least one of the first flat and the second flat is moving through the system after forming the first image and before forming the second image.

[0020] In some embodiments, the system includes a cleaning system configured to remove one or more of the residues from the wiping element. In other embodiments, the imaging station includes one or more printheads, each printhead including one or more of the nozzles, and a substrate transport module configured to move a substrate in a printing direction to form an image thereon, the one or more printheads having a first axis parallel to the printing direction and a second axis perpendicular to the printing direction, and the wiping assembly configured to remove residues from a nozzle of at least one of the printheads by moving a wiping element along the first axis of the one or more printheads. In yet other embodiments, the wiping assembly is configured to remove residues from at least one of the nozzles while moving a wiping element along the second axis of the printheads.

[0021] In one embodiment, the wiping assembly is configured to remove residue from at least one of the nozzles while the substrate transport module is moving the substrate in the printing direction. In another embodiment, the wiping assembly is configured to remove residue from at least one of the nozzles when the nozzle is not applying droplets to the substrate. In yet another embodiment, at least one of the one or more printheads includes a nozzle plate having a first section and a second section without a nozzle and a third section positioned between the first and second sections and including a nozzle, and the wiping assembly is configured to move a wiping element in at least a first axis from the first section, through the third section to the second section to remove residue.

[0022] In some embodiments, the wiping assembly is configured to move the wiping element in the second axis when the wiping element is positioned over the first section or the second section. In other embodiments, the wiping assembly is configured to continuously move the wiping element back and forth in the first axis between the first section and the second section at a predetermined frequency. In yet other embodiments, the substrate has a plurality of first sections and a plurality of second sections positioned alternately in a moving direction along the substrate, the imaging station is configured to form a plurality of images on each of the plurality of first sections when each of the plurality of first sections faces the imaging station, and the wiping assembly is configured to move the wiping element back and forth in the first axis when the second section faces the imaging station, and the predetermined frequency includes a discrete number of the second sections facing the imaging station.

[0023] In one embodiment, the predetermined frequency is defined by a time interval. In another embodiment, the substrate includes a flexible substrate having a first end and a second end joined by a seam section to form a loop, the flexible substrate moving in the print direction in cycles, each of the cycles being defined when the seam section faces the imaging station, and the predetermined frequency includes a discrete number of cycles. In yet another embodiment, the wiping assembly is configured to (i) move the wiping element along a first axis using a first motion profile and along a second axis using a different second motion profile.

[0024] In some embodiments, the first motion profile comprises a continuous motion profile and the second motion profile comprises a discrete motion profile.

[0025] According to an embodiment of the present invention, there is further provided a ribbon including: (a) a residue removal layer configured to remove printing-fluid residue from one or more nozzles of a printing system; and (b) a compressible layer coupled to the residue removal layer and configured to (i) absorb and contain the cleaning fluid when placed in contact with the cleaning fluid, and (ii) release at least a portion of the cleaning fluid when a compressive force is applied to the ribbon.

[0026] In some embodiments, the one or more nozzles are formed in the nozzle plate, and the residue removal layer is configured to receive at least a portion of the cleaning fluid from the compressible layer, self-adherent to the nozzle plate, and in physical contact with the one or more nozzles. In other embodiments, the ribbon includes a core layer, which is bonded to the compressible layer and configured to stiffen the ribbon in a given plane when tension is applied to the ribbon. In yet other embodiments, the core layer is mounted within the fluid containing layer such that the fluid containing layer has first and second outer surfaces facing one another, and the core layer is positioned between the first and second surfaces.

[0027] In one embodiment, the first outer surface is bonded to the residue removal layer and includes a polyethylene-based layer bonded to the second outer surface of the fluid-containing layer, the polyethylene-based layer configured to at least one of: (i) stiffen the ribbon in a given plane when tension is applied to the ribbon; and (ii) retain at least a portion of the cleaning fluid within the fluid-containing layer when no compression is applied to the ribbon. In another embodiment, the polyethylene-based layer includes polyethylene terephthalate (PET). In yet another embodiment, the ribbon moves in at least one of a first direction and a second direction parallel to the given plane, and the core layer and the polyethylene-based layer are configured to stiffen the ribbon in the first direction and the second direction.

[0028] In some embodiments, the printing system includes a first nozzle having a first printed residue and a second nozzle having a second printed residue, and at least one of the residue removal layer and the fluid containing layer is configured to compensate for topography differences between the first nozzle and the second nozzle and to adhere between (i) the residue removal layer and (ii) at least the first nozzle and the second nozzle to remove the first printed residue and the second printed residue.

[0029] According to one embodiment of the present invention, in a system having a printing position and a non-printing position, a method is further provided that includes applying droplets of a printing fluid onto a surface of one or more substrates using one or more nozzles of a nozzle plate to generate one or more images thereon. While the system is in the printing position, a wiping assembly is positioned at least partially within a gap between the nozzle plate and the one or more substrates and is (i) in physical contact with the nozzle plate and (ii) applied to remove printing fluid residue from at least one of the nozzles.

[0030] The present invention will be more fully understood from the following detailed description of the embodiments, taken in conjunction with the drawings, in which: [Brief description of the drawings]

[0031] [Figure 1]1 is a schematic side view of a digital printing system according to one embodiment of the present invention; [Diagram 2] 2 is a schematic side view of a wiping assembly and cleaning station according to one embodiment of the present invention; [Diagram 3] 1A, 1B, and 1C are schematic diagrams of a ribbon moving relative to a surface of a bottom section of a printbar in a digital printing system in accordance with one embodiment of the present invention. [Figure 4] 2 is a schematic diagram of a wiping assembly according to one embodiment of the present invention. [Diagram 5] 1 is a schematic cross-sectional view of a ribbon according to one embodiment of the present invention. [Figure 6] FIG. 2 is a schematic cross-sectional view of a ribbon compressed in a compressing assembly according to one embodiment of the present invention. [Figure 7] 1A and 1B are schematic diagrams of a wiping assembly according to one embodiment of the present invention. [Figure 8] 1 is a flow chart that generally illustrates a method for removing residue from nozzles of a digital printing system, in accordance with an embodiment of the present invention. [Figure 9] 1 is a flow chart that generally illustrates a method for imaging and removing residue from nozzles of a printbar in a digital printing system, in accordance with one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0032] overview Inkjet-based digital printing systems typically produce ink images by applying (eg, jetting or spraying) a printing fluid, such as ink, through nozzles onto a substrate.

[0033] One problem with this type of printing system is that ink residues may solidify and clog at least a portion of the nozzle, resulting in defective and / or distorted images in the subsequent print. For example, a partial blockage of the nozzle orifice may cause the next ink droplet to be deflected and land at a different location on the substrate than intended. As another example, a completely blocked nozzle may result in a lack of ink at the intended location(s) on the substrate.

[0034] In principle, it is possible to stop printing periodically to perform maintenance procedures to remove ink residues before clotting on the nozzles occurs, but such planned and unplanned maintenance reduces the availability and uptime of the printing system, thereby reducing system throughput.

[0035] Embodiments of the invention described herein below provide methods and systems for preventing distortions in a printed image on a substrate by removing ink residue without stopping the printing operation of an inkjet-based digital printing system, the disclosed techniques are also referred to herein as on-the-fly ink residue removal.

[0036] In some embodiments, a digital printing system includes an imaging station including a plurality of print bars, each print bar having a plurality of printheads arranged along a longitudinal axis of the print bar, each printhead including a nozzle plate having three sections: (i) a central section positioned at the center of the nozzle plate along the longitudinal axis and including an array of nozzles for ejecting ink droplets (or any other suitable printing fluid) onto a substrate, and (ii) two side sections, typically without nozzles, positioned to the sides of the central section along the longitudinal axis.

[0037] In some embodiments, the imaging station is configured to apply ink droplets to the substrate while the substrate is moving relative to the print head. The substrate has (i) first sections that are intended to receive ink droplets to form an image on the substrate, and (ii) second sections (also referred to herein as non-printable sections or areas) that are typically positioned alternately between the first sections. The second sections do not receive ink droplets and are not intended to form an image thereon. In some embodiments, one of the second sections may comprise a seam section, which is described in more detail below.

[0038] In some embodiments, the substrate moves in a direction of motion adjacent to the printbar of the imaging station to receive ink droplets on the first section, in this example perpendicular to the long axis of the printbar, In such embodiments, the first and second sections alternately face the printbar as the substrate moves.

[0039] In some embodiments, the processor of the digital printing system is configured to control the image forming station to (i) direct ink droplets through the nozzles toward the substrate when a first section of the substrate faces the print bar, and (ii) not direct ink droplets toward the substrate when a second section faces the print bar.

[0040] In some embodiments, the digital printing system comprises, for each printbar, a residue removal assembly, also referred to herein as a wiping assembly (WA), which is controlled by the processor and configured to wipe ink residue from the nozzles of the respective printhead. The WA comprises a ribbon and is configured to move the ribbon in two directions over a section of the nozzle plate. In this example, when the nozzles are ejecting ink droplets on the first section, the WA is configured to move the ribbon continuously along the major axis over one of the side sections of the nozzle plate such that the ribbon does not interfere with the ink droplet ejection process.

[0041] In some embodiments, when the substrate moves and at least one of the second sections faces the printbar, the processor is configured to control the WA to move the ribbon at least along the short axis of the printbar, which is generally parallel to the substrate movement direction. In these such embodiments, the ribbon moves along the short axis (i) from the first side section of the nozzle plate, (ii) over the nozzles in the central section to wipe ink residue from the nozzles, and (iii) to the second side section of the nozzle plate. Note that the ribbon moves along the short axis only when one of the second sections faces the printbar and the nozzles are not ejecting ink droplets. Furthermore, the WA is configured to move the ribbon along the short axis fast enough that the ribbon moves away from the central section of the printhead before the next first section of the substrate faces the printbar and the nozzles eject ink droplets toward the substrate.

[0042] In some embodiments, the processor is configured to schedule the frequency of the ribbon movement along the printbar's minor axis while continuously moving the ribbon along the printbar's major axis. In these such embodiments, when the processor controls the WA to perform a next wiping operation of ink residue, the WA is configured to move the ribbon in the opposite direction along the minor axis. In this example, the opposite direction is specified as the direction from the second side section of the nozzle plate, past the nozzles in the central section, toward the first side section of the nozzle plate. In other words, the processor is configured to control the WA to move the ribbon back and forth along the printbar's minor axis at any suitable frequency while continuously moving the ribbon along the printbar's major axis.

[0043] In some embodiments, the wiping frequency may include wiping any suitable discrete number of second sections, such as every 10th second section, or performing ink wiping at predetermined time intervals, such as every minute, or a combination thereof, or using any other suitable scheduling technique.

[0044] In some embodiments, the imaging station comprises multiple print bars for each of multiple colors of ink. For example, the system may comprise (i) a print bar (PB) for applying cyan ink (referred to herein as cyan PB), and (ii) a print bar (PB) for applying magenta ink (referred to herein as magenta PB). Each print bar comprises multiple (e.g., tens of thousands) nozzles configured to apply (e.g., by jetting or spraying) ink droplets of a respective color (e.g., cyan or magenta) to a first section of a substrate. It is noted that the digital printing system may be configured to apply any number of ink colors, e.g., four or seven different colors. This example of two ink colors is provided as an example for conceptual clarity.

[0045] In some embodiments, the substrate may include (i) a target substrate such as a flat or continuous web of paper configured to receive droplets to generate an image directly from an imaging station, or (ii) a flexible intermediate transfer member (ITM), also referred to herein as a blanket, configured to receive ink droplets to generate an image and then transfer the image to the target substrate. In this example, the blanket is designed in a loop shape, having two ends and a seam section for joining between the ends. In some embodiments, when the blanket moves in the moving direction and the aforementioned seam section (or any other second section) faces a given printbar, the processor controls the given printbar to temporarily stop applying ink to the blanket. After the seam section has passed the given printbar, the processor controls the given printbar to resume applying ink to the blanket.

[0046] In some embodiments, each printbar comprises a separate WA with a ribbon. For example, the ribbon of a given WA moves, among other things, on the nozzle plate below the given printbar, in the gap between the given printbar and the substrate, and in at least two directions as described above. The non-printable sections may include, for example, non-printable areas between images on a blanket or continuous web, or between flats in a direct printing system. It is noted that at the same time, the processor controls at least one of the other printbars of the system and is configured to apply ink droplets to the substrate while the ribbon wipes ink residue from the given printbar, as described in detail above.

[0047] For example, when the seam section of the blanket passes below (i.e., facing) the cyan PB, the processor is configured to control the first WA to remove ink residue from the nozzles of the cyan PB while the nozzles of the magenta PB apply ink droplets to another section of the substrate. Then, when the seam section of the blanket passes below the magenta PB, the processor is configured to control the second WA to remove ink residue from the nozzles of the magenta PB while the nozzles of the cyan PB apply ink droplets to the substrate. Note that the maintenance operation of removing ink residue from the nozzles is performed while the system is printing the image(s) on the blanket (i.e., on the fly).

[0048] In some embodiments, when the seam section passes under a given printbar, the processor is configured to control the wiping assembly to move the ribbon along the minor axis of the printbar to wipe the nozzles. As described above with respect to the second section, the wiping assembly is configured to move the ribbon along the minor axis of the printbar fast enough to complete wiping of the nozzles before the seam section passes under the printbar.

[0049] In some embodiments, the ribbon is configured to perform wiping within the confined space between the printbar and the blanket and has a self-supporting tensioning mechanism, also referred to herein as self-adhesion or self-adhesion, for adhering to the nozzles while the ribbon is moved by the wiping assembly, the self-adhesion being configured to, among other things, compensate for possible topography differences between nozzles of different printheads of a printbar, as described in the detailed description below.

[0050] In some embodiments, the ribbon includes a multi-layer stack including: (i) a residue removal layer positioned on the nozzle plate of the printhead while the ribbon is moving and configured to wipe residue from the nozzles; (ii) a compressible layer having an upper surface and a lower surface, the upper surface being coupled to the residue removal layer, the compressible layer being configured to contain water to improve adhesion between the ribbon and the nozzles (and for another purpose described below); (iii) a core layer mounted between the upper and lower surfaces of the compressible layer and configured to improve dimensional stability of the ribbon in the presence of tension applied to the ribbon by the wiping assembly; and (iv) a polyethylene terephthalate (PET) layer coupled to the lower surface of the compressible layer, the core layer being configured to improve dimensional stability of the ribbon, seal the compressible layer to prevent leakage of water toward the blanket, and improve flexibility of the ribbon to adhere to the nozzles of the print bar. These layers of the ribbon are described in more detail, for example, in FIG. 5 of this disclosure.

[0051] In some embodiments, the ribbon can be moved between (i) a supply drum configured to supply a clean ribbon for wiping off residue, and (ii) a receiving drum configured to receive the ribbon after wiping off ink residue from the nozzles. This configuration, also referred to herein as an inter-spool configuration, requires replacement of the supply drum once the entire clean ribbon has been used.

[0052] In other embodiments, the ribbon can move in a closed loop between the printbar and a cleaning station configured to remove ink residue from the ribbon using any suitable technique. In this example, the cleaning station includes a plurality of water containers, each containing water and coupled to a megasonic transducer configured to vibrate the water in the container to assist in removing ink residue from the ribbon. In some embodiments, the cleaning system can include a squeezing mechanism positioned between adjacent water containers to squeeze at least a portion of the water containing the residue and other contaminants contained in the ribbon out of the ribbon. The cleaning station is also described in more detail below.

[0053] In some embodiments, after megasonic cleaning, the ribbon is moved into a squeezing assembly to squeeze out some of the water contained within the ribbon, thereby removing ink residues (and other types of contaminants) that may remain in the ribbon after megasonic cleaning.

[0054] It should be noted that some of the water remains in the compressed layer after squeezing in order to maintain sufficient moisture in the ribbon to perform some of the operations described below. In the context of this disclosure and claims, the term "squeezing" refers to the act of applying a compressive force to the ribbon.

[0055] In some embodiments, the ribbon may be used to cap the orifices of the print nozzles when the print bars are idle and not applying ink to the substrate. The humidity of the ribbon prevents solidification of ink residue on the print nozzles. Additionally, in both the idle and printing positions of the system, the compressible layer is configured to absorb and capture ink vapors and aerosols and contaminants suspended between the print bars and the blanket to prevent solidification on the nozzles of those print bars.

[0056] In some embodiments, the moisture content of the ribbon is sufficient to perform wiping and to enable the ribbon to self-adhere using the adhesive forces between the water contained in the ribbon and the aforementioned nozzle plates of each printhead in the printbar.

[0057] The disclosed techniques improve print quality of inkjet printing systems by reducing the amount of defects and distortions caused by clogged nozzles in the printbars. Additionally, the disclosed techniques improve productivity of inkjet printing systems by cleaning nozzles on the fly, i.e., while the printing system is continuously printing images on a substrate.

[0058] System Description 1 is a schematic side view of a digital printing system 10 according to one embodiment of the present invention. In some embodiments, the system 10 includes a rotating flexible blanket 44 that cycles through an imaging station 60, a drying station 64, an impression station 84, and a blanket treatment station 52. In the context of the present invention and in the claims, the terms "blanket" and "intermediate transfer member (ITM)" are used interchangeably and refer to a flexible member including one or more layers that is used as an intermediate member, for example, formed in an infinite loop configured to receive an ink image from an imaging station 60 and transfer the ink image to a target substrate, as described in more detail below.

[0059] In an operational mode, imaging station 60 is configured to form a mirror ink image (also referred to herein as an "ink image" (not shown) or for simplicity as an "image") of digital image 42 on an upper run on the surface of blanket 44. The ink image is then transferred to a target substrate (e.g., paper, folding carton, multi-layer polymer, or any suitable flexible packaging in the form of a flat or continuous web) located beneath a lower run of blanket 44.

[0060] In the context of the present invention, the term "run" refers to the length or segment of blanket 44 between any two given rollers along which blanket 44 is guided.

[0061] In some embodiments, during installation, the blanket 44 can be attached edge-to-edge using seam section 45 to form a continuous blanket loop. One example of a seam installation method and system is described in detail in U.S. Patent Application Publication No. 2020 / 0171813, the disclosure of which is incorporated herein by reference.

[0062] In some embodiments, imaging station 60 generally comprises a plurality of printbars 62, each mounted on a frame (not shown) positioned at a fixed height above the surface of the upper run of blanket 44. In some embodiments, each printbar 62 comprises a strip of printheads as wide as the print area on blanket 44, with individually controllable print nozzles, such as those shown in Figures 3A and 3C below.

[0063] In some embodiments, imaging station 60 may include any suitable number of print bars 62 (also referred to herein for brevity as bars 62). Each bar 62 may include a printing fluid, such as a water-based ink of a different color. The inks typically have visible colors, such as, but not limited to, cyan, magenta, red, green, blue, yellow, black, and white. In the example of FIG. 1, imaging station 60 includes seven print bars 62, but may also include four print bars 62 having any selected color, such as, for example, cyan (C), magenta (M), yellow (Y), and black (K).

[0064] In some embodiments, the print heads are configured to eject ink droplets of different colors onto the surface of blanket 44 to form an ink image (not shown) on the surface of blanket 44. In this example, blanket 44 moves along the X-axis of an XYZ coordinate system of system 10, and the ink droplets are directed by the print heads generally parallel to the Z-axis of the coordinate system.

[0065] In some embodiments, the different print bars 62 are spaced apart from one another along an axis of movement, also referred to herein as (i) the direction of movement 94 of the blanket 44 or (ii) the printing direction. In this example, the direction of movement of the blanket 44 is parallel to the X-axis, and each print bar 62 extends along the Y-axis of the system 10. In this configuration, precise spacing between the bars 62 along the X-axis, and synchronization between the orientation of the ink droplets of each bar 62 and the movement of the blanket 44, is essential to enable precise placement of the image pattern.

[0066] In the context of this disclosure and in the claims, the terms “inter-color pattern placement,” “pattern placement accuracy,” “color-to-color registration,” “C2C registration,” “inter-color position difference,” “bar-to-bar registration,” and “color registration” are used interchangeably and refer to any placement accuracy of two or more colors relative to one another.

[0067] In some embodiments, system 10 includes a heater 66, such as an infrared-based heater with a hot air or air blowing device and / or a gas or air blowing device to flow gas or air at any suitable temperature. Heater 66 is positioned between print bars 62 and configured to partially dry ink droplets that have accumulated on the surface of blanket 44. This air flow between print bars can help, for example, (i) reduce condensation on the surface of the print head and / or deal with satellites (e.g., residue or small droplets distributed around a main drop of ink), and / or (ii) prevent clogging of inkjet nozzles of the print head, and / or (iii) prevent undesired mixing of different colored ink droplets into one another on blanket 44.

[0068] In some embodiments, system 10 includes a wiping assembly, also referred to herein as a wiper, that is configured to remove printing-fluid residue remaining on the nozzles of each printbar 62 after application of printing fluid to blanket 44. In such embodiments, each printbar 62 can have a separate wiping assembly for removing printing-fluid residue. Embodiments of wiping assemblies are shown and described in detail below in Figures 2-7B.

[0069] In some embodiments, system 10 includes a drying station 64 configured to direct infrared radiation and cooled air (or other gas) and / or blow hot air (or other gas) onto a surface of blanket 44. In some embodiments, drying station 64 may include an infrared-based lighting assembly (not shown) and / or an air blowing device 68 or any other suitable drying device.

[0070] In some embodiments, at drying station 64, the ink image formed on blanket 44 is exposed to radiation and / or hot air to more thoroughly dry the ink, heating it to a point where most or all of the liquid carrier evaporates, leaving only a layer of resin and colorant, resulting in a tacky ink film.

[0071] In some embodiments, system 10 includes a blanket module 70 (also referred to herein as an ITM module) that includes a rotating, flexible ITM, such as blanket 44. In some embodiments, blanket module 70 includes one or more rollers 78, at least one of which includes a motion encoder (not shown) configured to record the position of blanket 44 and control the position of sections of blanket 44 relative to their respective printbars 62. In some embodiments, the one or more motion encoders may be integrated with additional rollers and other moving parts of system 10.

[0072] In some embodiments, such motion encoders generally comprise at least one rotary encoder configured to generate rotation-based position signals indicative of the angular displacement of the respective roller. It should be noted that in the context of the present invention and in the claims, the terms "indicating" and "indicating" are used interchangeably.

[0073] Additionally or alternatively, blanket 44 may include an integrated encoder (not shown) to control the operation of various modules of system 10. One embodiment of an integrated motion encoder is described in detail, for example, in PCT International Publication No. WO 2020 / 003088, the disclosure of which is incorporated herein by reference.

[0074] In some embodiments, blanket 44 is guided over rollers 76, 78 and other rollers described herein, as well as a power tension roller, also referred to herein as dancer assembly 74. Dancer assembly 74 is configured to control the amount of slack in blanket 44, the movement of which is shown diagrammatically by a double-headed arrow in Figure 1. Furthermore, any stretching of blanket 44 due to aging does not affect the ink image placement performance of system 10, but simply requires more slack to be taken up by the tension of dancer assembly 74.

[0075] In some embodiments, dancer assembly 74 may be motor driven. The configuration and operation of rollers 76 and 78 are described in further detail, for example, in U.S. Patent Application Publication No. 2017 / 0008272 and the above-referenced PCT International Publication No. WO2013 / 132424, the disclosures of which are all incorporated herein by reference.

[0076] In some embodiments, the system 10 includes a blanket tension drive roller (BTD) 99 and a blanket control drive roller (BCD) 77, which are powered by first and second motors, typically electric motors (not shown), respectively, and configured to rotate about their own first and second axes, respectively.

[0077] In some embodiments, the system 10 may include one or more tension sensors (not shown) disposed at one or more locations along the blanket 44. The tension sensors may be integrated into the blanket 44 or may include sensors external to the blanket 44 using any other suitable technique for obtaining a signal indicative of the mechanical tension applied to the blanket 44. In some embodiments, the processor 20 and additional controllers of the system 10 are configured to receive signals generated by the tension sensors to monitor the tension applied to the blanket 44 and control the operation of the dancer assembly 74.

[0078] At the impression station 84, the blanket 44 passes between an impression cylinder 82 and a pressure cylinder 90 configured to convey a compressible blanket (not shown). In some embodiments, a motion encoder is integrated with at least one of the impression cylinder 82 and the pressure cylinder 90.

[0079] In some embodiments, the system 10 includes a control console 12 configured to control multiple modules of the system 10, such as a blanket module 70, an image forming station 60 located above the blanket module 70, and a substrate transport module 80 located below the blanket module 70 and including one or more impression stations as described below.

[0080] In some embodiments, console 12 includes processor 20, typically a general purpose processor, including suitable front end and interface circuitry for interfacing with and receiving signals from controller 54 and controller of dancer assembly 74 via cable 57. Additionally or alternatively, console 12 may include any suitable type of application specific integrated circuit (ASIC) and / or digital signal processor (DSP) and / or any other suitable type of processing unit configured to perform any type of processing on data processed in system 10.

[0081] In some embodiments, the controller 54, shown generally as a single device, may comprise one or more electronic modules mounted at predetermined locations in the system 10. At least one of the electronic modules of the controller 54 may comprise an electronic device, such as a control circuit or processor (not shown), configured to control the various modules and stations of the system 10. In some embodiments, the processor 20 and control circuitry may be programmed with software to perform functions used by the printing system and store software data in the memory 22. The software may be downloaded to the processor 20 and control circuitry in electronic form, for example over a network, or may be provided on a non-transitory tangible medium, such as an optical, magnetic or electronic memory medium.

[0082] In some embodiments, the console 12 includes a display 34 configured to display data and images received from the processor 20 or input inserted by a user (not shown) using an input device 40. In some embodiments, the console 12 may have any other suitable configuration, for example, alternative configurations of the console 12 and display 34 are described in detail in U.S. Patent 9,229,664, the disclosure of which is incorporated herein by reference.

[0083] In some embodiments, the processor 20 is configured to display on the display 34 a digital image 42 including one or more segments (not shown) of the image 42 and / or various types of test patterns that may be stored in the memory 22.

[0084] In some embodiments, the blanket treatment station 52, also referred to herein as a cooling station, is configured to treat the blanket, for example, by cooling the blanket and / or applying a treatment fluid to the exterior surface of the blanket 44 and / or cleaning the exterior surface of the blanket 44. The blanket treatment station 52 may reduce the temperature of the blanket 44 to a desired temperature level before the blanket 44 enters the imaging station 60. This treatment may be performed by passing the blanket 44 over one or more rollers or blades configured to apply a cooling fluid and / or a cleaning fluid and / or a treatment fluid to the exterior surface of the blanket.

[0085] In some embodiments, the blanket treatment station 52 may additionally or alternatively further comprise one or more bars (not shown) positioned adjacent to the print bar 62 so as to apply treatment fluid to the blanket 44 by spraying.

[0086] In some embodiments, processor 20 is configured to receive a signal indicative of the surface temperature of blanket 44, for example from a temperature sensor (not shown), to monitor the temperature of blanket 44 and control operation of blanket treatment station 52. Examples of such treatment stations are described, for example, in PCT International Publications WO2013 / 132424 and WO2017 / 208152, the disclosures of which are incorporated herein by reference in their entireties.

[0087] 1, station 52 is mounted between impression station 84 and imaging station 60, however, station 52 may be mounted adjacent blanket 44 at any other or additional suitable location or locations between impression station 84 and imaging station 60. As noted above, station 52 may additionally or alternatively be mounted on a bar adjacent imaging station 60.

[0088] 1, impression cylinder 82 and pressure cylinder 90 press an ink image onto a target flexible substrate, such as an individual flat sheet 50, which is transported by substrate transport module 80 from input stack 86 through impression station 84 to output stack 88. In this example, a rotary encoder (not shown) is integrated with impression cylinder 82.

[0089] In some embodiments, the lower run of blanket 44 selectively interacts with impression cylinder 82 at impression station 84 to press an image pattern onto a target flexible substrate compressed between blanket 44 and impression cylinder 82 under the action of pressure from pressure cylinder 90. For the single-sided printer shown in FIG. 1 (i.e., printing on one side of flat sheet 50), only one impression station 84 is required.

[0090] In other embodiments, the module 80 may include two or more impression cylinders (not shown) to allow for one or more double-sided printing. The two impression cylinder configuration also allows for single-sided printing to be performed twice as fast as double-sided printing. Additionally, mixed lots of single-sided and double-sided printing can be performed. In alternative embodiments, different configurations of the module 80 can be used to print onto a continuous web substrate. Detailed descriptions and various configurations of double-sided printing systems and systems for printing onto continuous web substrates are provided, for example, in U.S. Patents 9,914,316 and 9,186,884, PCT International Publication No. WO 2013 / 132424, U.S. Patent Application Publication No. 2015 / 0054865, and U.S. Provisional Application No. 62 / 596,926, the disclosures of which are all incorporated herein by reference.

[0091] As briefly described above, the flat 50 or a continuous web substrate (not shown) is conveyed by the module 80 from the feed stack 86 and passes through a nip (not shown) located between the impression cylinder 82 and the pressure cylinder 90. Within the nip, the ink image is pressed onto the surface of the flat 50 and appropriately separated from the surface of the blanket 44, for example by a compressible blanket of the pressure cylinder 90, firmly pressing the surface of the blanket 44 bearing the ink image against the flat 50 (or another suitable substrate). The flat 50 is then conveyed to the output stack 88.

[0092] 1, roller 78 is positioned on the upper run of blanket 44 and is configured to maintain tension on blanket 44 as it passes adjacent imaging station 60. Additionally, it is particularly important to control the speed of blanket 44 below imaging station 60 in order to obtain precise jetting and deposition of ink droplets to form an image on the surface of blanket 44 by imaging station 60.

[0093] In some embodiments, the impression cylinder 82 periodically engages and disengages from the blanket 44 to transfer an ink image from the moving blanket 44 to a target substrate passing between the blanket 44 and the impression cylinder 82. In some embodiments, the system 10 is configured to apply a torque to the blanket 44 using the roller and dancer assemblies described above to maintain tension on the upper run and to substantially isolate the upper run of the blanket 44 from the effects of mechanical vibrations generated in the lower run.

[0094] In some embodiments, system 10 includes an image quality control station 55 that functions as a closed-loop inspection system integrated into system 10, also referred to herein as an automated quality control (AQM) system. In some embodiments, image quality control station 55 may be positioned adjacent impression cylinder 82 as shown in FIG. 1, or at any other suitable location within system 10.

[0095] In some embodiments, image quality control station 55 includes a camera (not shown) configured to capture one or more digital images of the aforementioned ink images printed on format 50. In some embodiments, the camera may include any suitable image sensor, such as a contact image sensor (CIS) or a complementary metal oxide semiconductor (CMOS) image sensor, and a scanner including a slit having a width of about one meter or any other suitable width.

[0096] In the context of this disclosure and the claims, the term "about" or "approximately" in relation to any numerical value or range indicates an appropriate dimensional tolerance that enables a portion or collection of components to function for its intended purpose as described herein.

[0097] In some embodiments, station 55 may include a spectrophotometer (not shown) configured to monitor the quality of ink printed on the format 50 .

[0098] In some embodiments, the digital images acquired by station 55 are sent to a processor, such as processor 20 or any other processor of station 55, configured to evaluate the quality of each printed image. Based on the evaluation and signals received from controller 54, processor 20 is configured to control the operation of the modules and stations of system 10. In the context of the present invention and in the claims, the term "processor" refers to any processing unit, such as processor 20 or any other processor or controller connected to or integrated with station 55, configured to process signals received from the camera and / or spectrophotometer of station 55. It should be noted that the signal processing operations, control related instructions, and other computational operations described herein may be performed by a single processor or may be shared among multiple processors of one or more respective computers.

[0099] In some embodiments, station 55 is configured to inspect the quality of the printed images and test patterns to monitor various attributes such as, but not limited to, perfect image registration with flat 50, also referred to herein as image-to-substrate registration, color-to-color (C2C) registration, print geometry, image uniformity, color profile and linearity, and print nozzle functionality. In some embodiments, processor 20 is configured to automatically detect geometric distortions or other errors in one or more of the aforementioned attributes.

[0100] In some embodiments, the processor 20 is configured to analyze the detected distortion in order to apply corrective action to the malfunctioning module and / or provide instructions to another module or station of the system 10 to compensate for the detected distortion.

[0101] In some embodiments, the system 10 may print test marks (not shown) or other suitable features, for example, on the bevel or margin of the flat 50. By acquiring images of the test marks, the station 55 is configured to measure various types of distortions, such as C2C registration, image to substrate registration, different widths between colors, referred to herein as "bar-to-bar width delta" or "color-to-color width difference", various types of local distortions, and front to back misregistration (when duplexing). In some embodiments, the processor 20 is configured to (i) sort flats 50 having distortions that exceed a first predetermined threshold set, for example, to a waste tray (not shown), (ii) initiate corrective actions for flats 50 having distortions that exceed a lower second predetermined threshold set, and (iii) eject flats 50 having minor distortions, for example, below the second threshold set, to an ejection stack 88.

[0102] In some embodiments, processor 20 is configured to detect deviations in the profile and linearity of the printed colors based on signals received from the spectrophotometer of station 55 .

[0103] In some embodiments, the processor of station 55 is configured to determine whether to stop operation of system 10, for example, if the density of distortion exceeds a specified threshold. The processor of station 55 is further configured to initiate corrective actions in one or more of the modules and stations of system 10, as described above. In some embodiments, the corrective actions may be performed on-the-fly (while system 10 continues the printing process) by stopping printing operations and correcting the problem in the respective module and / or station of system 10, or may be performed offline. In other embodiments, any other processor or controller of system 10 (e.g., processor 20 or controller 54) is configured to initiate corrective actions or stop operation of system 10, if the density of distortion exceeds a specified threshold.

[0104] Additionally or alternatively, processor 20 is configured to receive signals, such as from station 55, indicative of additional types of distortions and problems during the printing process of system 10. Based on these signals, processor 20 is configured to automatically estimate the level of pattern placement accuracy and additional types of distortions and / or defects not described above. In other embodiments, any other suitable method may be used to examine the pattern printed on flat 50 (or any other substrate as described above), for example, an external (e.g., offline) inspection system, or any type of measurement fixture and / or scanner may be used. In these embodiments, processor 20 is configured to initiate any appropriate corrective action and / or stop operation of system 10 based on information received from the external inspection system.

[0105] The configuration of system 10 is simplified and provided merely as an example to clarify the present invention. The components, modules and stations described herein above in printing system 10, as well as additional components and configurations, are described in detail in, for example, U.S. Patents 9,327,496 and 9,186,884, PCT International Publication Nos. WO2013 / 132438, WO2013 / 132424 and WO2017 / 208152, and U.S. Patent Application Publication Nos. 2015 / 0118503 and 2017 / 0008272, the disclosures of which are all incorporated herein by reference.

[0106] The particular configuration of system 10 is shown as an example to illustrate the particular problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in improving the performance of such systems, however, embodiments of the present invention are in no way limited to this particular type of exemplary system, and the principles described herein may be applied to any other type of printing system as well.

[0107] Controlling the cleanliness of print nozzles using a wiping assembly and its cleaning station 2 is a schematic side view of a wiping assembly (WA) 200 and cleaning station (CS) 100, according to one embodiment of the present invention. In the context of this disclosure and in the claims, the terms "WA 200," "residue removal assembly," and "wiper 200" are used interchangeably to refer to an assembly for removing printing-fluid residue remaining on the nozzles of printbar 62 after printing-fluid has been applied to blanket 44 or any other substrate.

[0108] Please note that for clarity of presentation and concepts, WA200 and CS100 are not drawn to scale in Figure 2. For example, based on the coordinate system of X, Y and Z axes shown in Figure 2, the length of printbar 62 along the Y axis is about 1 meter, while the overall size of CS100 is between about 30 cm and 70 cm. CS100 is shown larger in Figure 2 for detailed explanation, and WA200 is explained in more detail in Figure 4 below.

[0109] In some embodiments, system 10 includes multiple WAs 200. In this example, system 10 includes a separate WA 200 for each printbar 62 shown in FIG. 1 above, but in other embodiments, system 10 may include any suitable number of wipers, each having any suitable configuration. For example, (i) a single wiping assembly may be used to clean the nozzles of all printbars 62 of system 10, or (ii) at least one printbar 62 may have multiple wipers.

[0110] In some embodiments, WA 200 includes a ribbon 111 that is configured to move in a direction 144 (described in more detail below) within a gap 141 between a printbar 62 and a blanket 44. Ribbon 111 moves in direction 144 to wipe ink residue and other types of residue from the nozzles of the printbar 62. It should be noted that each printbar 62 in system 10 has a separate ribbon 111 for wiping residue from the nozzles of its respective printbar 62.

[0111] In this example, the blanket 44 moves in a direction of movement 94 (shown in FIG. 1 above) parallel to the X-axis of the system 10. In some embodiments, the ribbon 111 moves in a direction 144 generally parallel to the Y-axis of the system 10, as well as in an additional direction parallel to the X-axis, as described in detail in FIGS. 3A, 3B, and 3C below. In other words, during a first time interval, the ribbon 111 moves along one axis (e.g., the Y-axis), and during a different second time interval, the ribbon 111 moves simultaneously along two axes (e.g., the X-axis and the Y-axis). Furthermore, the WA 200 is configured to move the ribbon 111 (i) along the Y-axis (which is also parallel to the major axis of the printbar 62 and perpendicular to the direction of movement 94 of the blanket 44) using a continuous motion profile, and (ii) along the X-axis (which is parallel to both the minor axis of the printbar 62 and the direction of movement 94 of the blanket 44) using a discrete motion profile. Embodiments relating to the aforementioned motion profiles are described in more detail below in Figures 3A-3C. In other embodiments, ribbon 111 may move in the first and second directions separately, or may move in the first and second directions simultaneously.

[0112] In some embodiments, after a given section of ribbon 111 has wiped residue from the nozzles, the given section of ribbon 111 is deflected by one or more reciprocating pulleys 230 (described in more detail in FIG. 4 below) to move in direction 150 and to be inserted into CS 100 for removing residue. The given section of ribbon 111 that has been cleaned of residue in CS 100 is then deflected by one or more reciprocating pulleys 210 (described in more detail in FIG. 4 below) to be inserted between blanket 44 and print bar 62. The WA 200 then repeats wiping residue from the nozzles by simultaneously moving in direction 144 (usually but not necessarily parallel to the Y-axis) and in parallel to the X-axis (usually but not necessarily parallel to the direction of movement of blanket 44) and then moves ribbon 111 for cleaning, as described above.

[0113] In some embodiments, the residue wiping and ribbon cleaning cycles described above may be repeated during a print cycle without stopping printing operations, i.e., on the fly. In some cases, after applying (e.g., ejecting) printing fluid from the nozzles of the printbar 62, printing fluid residue may remain on the surface of a given nozzle and solidify to produce undesirable clusters. The clusters may (i) partially clog the nozzle opening, resulting in C2C registration errors caused by interference with the steering angle of the subsequent printing fluid ejected from the given nozzle toward the blanket 44, or (ii) completely clog (i.e., completely block) the nozzle, which may result in, for example, missing ink at one or more locations on the image, or (iii) form undesirable defects, such as particles, when the clusters are ejected or dropped into the printed image.

[0114] In some embodiments, ribbon 111, described in detail below in FIG. 5, is configured to remove and collect residue from the nozzles of print bar 62 and release the collected residue into CS 100, as described herein.

[0115] In some embodiments, the cleaning station (CS) 100 includes multiple containers of suitable cleaning fluids, in this example five or more water containers (WC) 122 (referred to herein as WC 122a, 122b, 122c, 122d, 122e, and 122f) configured to contain any suitable type of water 120, such as, but not limited to, deionized water.

[0116] In some embodiments, the CS 100 is configured to perform acoustic-based removal of residues from the ribbon 111 (also referred to herein as acoustic cleaning). In this example, the CS 100 comprises five or more (e.g., six) megasonic transducers (MT) 106 each coupled to five or more (e.g., six) WCs 122a-122f and one or more generators (not shown). Each MT 106 is configured to generate an acoustic field having a suitable frequency, for example, between about 0.6 Hz and 5 MHz, in particular about 1.6 MHz, in the water 120 contained in the respective WC. In some embodiments, the MTs 106 of the CS 100 may comprise any suitable type of transducer. It is noted that the MTs 106, or any other type of ultrasonic or megasonic transducer, are configured to agitate the water 120 to aid in removing contaminants such as dyes or other residues from the ribbon 111. In other embodiments, CS 100 may include any other suitable type of agitator(s) instead of or in addition to the aforementioned transducers to remove wiped residue and other contaminants from ribbon 111. In alternative embodiments, residue and other contaminants may be removed from ribbon 111 by squeezing ribbon 111 as it passes between rollers 108, described below.

[0117] In some embodiments, the CS 100 comprises a water inlet tube 101 configured to fill the WCs 122f with cleaning water 120, and a drain tube 104 configured to receive the water 120, typically containing residue, away from the WCs 122a of the CS 100. In the context of this disclosure and in the claims, the term "clean" refers to a water container having a small amount of residue in the water 120, and the term "dirty" refers to a water container having a large amount of residue in the water 120.

[0118] 2, the WCs 122 are arranged in tiers such that water 120 flows from WC 122f through all of the WCs 122 to WC 122a, and then overflows into the drain 104. For example, when WC 122f is filled, the water 120 overflows into WC 122e at overflow point 102. Similarly, when the last water container, WC 122a, is filled, the water 120 overflows through overflow point 103 in direction 105 towards the drain 104.

[0119] In some embodiments, the CS 100 includes a conveyor 147 having a number of rollers 108 positioned within and outside the WC 122 and configured to transport the ribbon 111 through the WC 122 of the CS 100. Note that each pair of rollers 108 is also configured to be immersed within the ribbon 111 and to squeeze out the water 120 containing the residue and other contaminants described above. In this example, a given section of the ribbon 111 carrying the residue wiped from the nozzles moves in direction 107 to be inserted into WC 122a, which has more residue than any other WC 122 of the CS 100. After a first acoustic cleaning in WC 122a, the given section moves in direction 109, exits WC 122a, and moves again in direction 107 through a pair of rollers 108 into WC 122b. Note that the amount of residue in WC122b will typically be less than that in WC122a because (i) WC122a receives ribbon 111 containing residue wiped directly from the nozzles of printbar 62, and (ii) WC122b receives a flow of water from WC122c, which typically contains less residue than WC122b. Furthermore, upon entering WC122b, ribbon 111 has less residue compared to the amount of residue upon entering WC122a, because some of the residue has been removed by WC122a.

[0120] In some embodiments, processor 20 and / or controller 54 is configured to control the velocity of ribbon 111, for example, in direction 144 and directions 107 and 109. The velocity of ribbon 111 in directions 107 and 109 controls the amount of water 120 absorbed by ribbon 111, and the velocity of ribbon 111 in direction 144 (and other directions shown in Figures 3A and 3B below) controls the time a given section of ribbon 111 is in contact with a given nozzle during the wiping process.

[0121] In some embodiments, the ribbon 111 travels through CWs 122c, 122d, 122e, and 122f for further acoustic cleaning, and then is drawn from WC 122f in direction 116. Based on the above principles, WC 122f is the cleanest water container in CW 122 that receives clean water from water inlet 101, and WC 122a is the dirtiest water container in CW 122 whose water 120 spills into drain 104. Thus, CS 100 is configured to remove residues from ribbon 111 that are wiped from the nozzles.

[0122] In some embodiments, after ribbon 111 is drawn in direction 116, it exits WC 122f and is deflected by rollers 118, traveling into a squeeze assembly 110 configured to squeeze out a majority of the water 120 remaining in ribbon 111. In some embodiments, squeeze assembly 110 comprises rotatable drums 112 and 114 configured to rotate about their own axes for the squeezing operation, as briefly described above and in further detail in FIG. 6 below.

[0123] In some embodiments, the squeezing assembly 110 further comprises a controllable piston 117 and shaft 119 that are configured to control the amount of water 120 squeezed out of the ribbon 111 by controlling the distance between the drums 112 and 114. In such embodiments, the smaller the distance between the drums 112 and 114, the less amount of water 120 remaining in the ribbon 111 after the squeezing process.

[0124] In other embodiments, the CS 100 may include one or more cleaning fluids of any other suitable type instead of or in addition to the water 120.

[0125] In other embodiments, the squeeze assembly 110 may have, instead of the piston 117 and shaft 119, any other suitable technique for controlling the squeeze level.

[0126] In some embodiments, the cleaning station 100 comprises a tensioning assembly (TA) 130 configured to apply tension to the ribbon 111 to keep it taut during at least the squeezing process and when the ribbon 111 moves in the direction 140 towards the reciprocating pulley 210 as described above. In this example, the TA 130 comprises a controllable piston 132 and rollers 134, 136 and 138. The piston 132 is configured to move along the Z-axis to control the position of the roller 136 along the Z-axis to apply a specified tension to the ribbon 111. For example, if the ribbon 111 is not sufficiently taut, the piston 132 moves along the Z-axis to increase the distance between (i) the roller 136 and (ii) the rollers 134 and 138, thereby increasing the tension applied to the ribbon 111, so that the ribbon 111 is sufficiently taut.

[0127] In some embodiments, the TA 130 is configured to control the tension applied to the ribbon 111 during a full residue wiping (in the WA 200) and residue cleaning (in the CS 100) cycle.

[0128] In other embodiments, TA 130 may include, instead of or in addition to at least piston 132 and roller 136, a spring (not shown) or any other suitable mechanism for controlling the tension applied to ribbon 111. Additionally or alternatively, at least one of system 10, WA 200 and CS 100 may include one or more tensioning assemblies for controlling the tension level of ribbon 111 along the cycle described above.

[0129] In some embodiments, cleaning station 100 and assemblies 110 and 130 are controlled by processor 20 and / or controller 54 of system 10. In other embodiments, cleaning station 100 and one or more of assemblies 110 and 130 may be controlled by one or more controllers (not shown), such as CS 100, which are controlled by processor 20 and / or controller 54.

[0130] In an alternative embodiment, instead of using a closed loop to clean the ribbon 111 of residue as described above, the WA 200 may include two drums (not shown). A first drum supplies the clean ribbon 111 for wiping the residue from the printbar 62, and a second drum for receiving the ribbon 111 after wiping the residue from the printbar 62. This configuration is also referred to herein as inter-spool. Note that the clean ribbon may travel through a reservoir of cleaning fluid, such as water 120, and a squeeze assembly (e.g., squeeze assembly 110) to accommodate a predetermined amount of water 120 in the compressed layer 300 of the ribbon 111. As described above in Figures 2 and 5, the water contained in the compressed layer 300 may be used to stick the ribbon 111 to all the nozzles of the printbar 62 and to remove residue from the nozzles.

[0131] 3A, 3B, and 3C are schematic diagrams of ribbon 111 moving relative to a bottom surface of sections 170 and 172 of nozzle plate 61 of each printhead in printbar 62, according to one embodiment of the present invention. Each printhead in printbar 62 has nozzle plate 61 that includes sections 170 and 172, and an array of nozzles, which are described in detail below.

[0132] It should be noted that FIGS. 3A, 3B, and 3C show a bottom view of the printbar 62 and a sequence showing the position of the seam section 45 of the blanket 44 and ribbon 111 moving relative to the printbar 62.

[0133] In some embodiments, operation of the WA 200, and in particular the movement of the ribbon 111, is synchronized with the firing and non-firing time intervals of each printbar 62 in the system 10. In such embodiments, when a given printbar 62 is firing (through its nozzles) printing fluid (e.g., ink) onto the blanket 44, the ribbon is not wiping those nozzles. However, during the non-firing time intervals, a given WA 200 for a given printbar 62 is configured to move that given ribbon 111 to wipe the nozzles of the given printbar 62.

[0134] 3A-3C below, it will be described how the movement of the ribbon 111 is controlled based on the position of the seam section 45. In other words, wiping of the nozzles of the printbar 62 is performed during a non-firing time interval, for example when the seam section 45 of the blanket 44 passes next to (e.g., under) the printbar 62, so that the nozzles of the printbar are not ejecting printing fluid towards the blanket 44. Note that the same technique is applicable when other sections of the blanket 44 pass under the printbar 62. For example, if a section of the blanket 44 is located between two sections designated to receive ink droplets to generate an image thereon (e.g., between two flatbed images) and passes under the printbar 62, the nozzles do not eject printing fluid and at the same time, the ribbon 111 can be used to wipe these nozzles.

[0135] 3A-3C, snapshots of blanket 44 are shown with seam section 45, generally defined between solid lines 143 and 145, moving relative to printbar 62. As shown in FIG.

[0136] In FIG. 3A, seam section 45 has not yet reached printbar 62, in FIG. 3B, seam section 45 has reached printbar 62 and is facing nozzles 166, 166a and 166b, and in FIG. 3C, seam section 45 has already passed printbar 62 and is continuing toward another printbar 62 and / or drying station 64.

[0137] In some embodiments, printbar 62 comprises a plurality of printheads, shown as an array of nozzles 166, 166a, and 166b, and sections 170 and 172. In this example, sections 170 and 172 are typically made from a ceramic material and are positioned on the sides (e.g., edges) of nozzle 166 and are generally flush with nozzles 166, 166a, and 166b. Furthermore, sections 170 and 172 typically do not have nozzles and are therefore not configured to eject printing fluid.

[0138] 3A, nozzles 166, 166a, and 166b apply printing fluid (e.g., ink droplets) to blanket 44 in direction 171, which is generally perpendicular to the blanket's direction of motion and parallel to the Z-axis. At the same time, blanket 44, shown in dashed lines, moves in motion direction 94 (parallel to the X-axis), and ribbon 111 moves in direction 144, parallel to the Y-axis.

[0139] In some embodiments, printbar 62 has a width 180 that is between about 40 mm and 42 mm, and the array of nozzles 166, 166a, and 166b has a width 182 that is between about 12 mm and 14 mm. Based on widths 180 and 182, sections 170 and 172 each have a width between about 13 mm and 15 mm.

[0140] In some embodiments, ribbon 111 has a width 184 of between about 12 mm and 14 mm, which is similar to width 182 and slightly less than the width of sections 170 and 172. Note that in embodiments such as these, ribbon 111, as it moves in direction 144, is not positioned between (i) nozzles 166, 166a, and 166b and (ii) blanket 44, and therefore does not block printing fluid jetted in direction 171 from nozzles 166, 166a, and 166b toward the surface of blanket 44.

[0141] During operation of the system 10, e.g., during the printing process, the solid line 143 passes next to the print bar 62. The solid line 143 indicates a first edge of the seam section 45, which is an integral part of the blanket 44 and thus moves with the blanket 44 toward the print bar 62. In some embodiments, when the first edge of the seam section 45 is at a preassigned distance from the nozzles 166, 166a, and 166b, the processor 20 is configured to control the WA 200 to move the ribbon 111 in a direction 160 that is generally parallel to the X-axis. In the context of this disclosure and in the claims, the direction 160 parallel to the direction of movement of the blanket 44 is also referred to herein as the print direction, and the direction 144 perpendicular to the print direction is also referred to herein as the cross-print direction. Additionally, the print bar 62 has (i) a major axis that is parallel to the Y-axis and the direction 144, and (ii) a minor axis that is parallel to the X-axis and the direction 160. Thus, in some embodiments, the WA 200 is configured to move the ribbon 111 substantially parallel to the long axis of the print bar 62 (i.e., in direction 144) and also substantially parallel to the short axis of the print bar 62 (i.e., in direction 160).

[0142] In some embodiments, the pre-assigned distance is determined by processor 20 based on the speed of movement of blanket 44 and other parameters of system 10. Note that in such embodiments, WA 200 moves ribbon 111 in directions 144 and 160 simultaneously. In this example, the speed of movement of ribbon 111 in direction 144 is between about 1 mm / sec and 20 mm / sec, while the speed of movement of ribbon 111 in direction 160 may be substantially faster, e.g., any suitable speed greater than 750 mm / sec.

[0143] It should be noted that widths 180, 182, and 184, the configuration of printbar 62 and ribbon 111, and the speed of ribbon 111 in directions 144 and 160 are all provided as examples and may be varied. In other embodiments, at least one of printbar 62 and ribbon 111 may have any other suitable configuration and / or width, and WA 200 may move ribbon 111 at a different speed in at least one of directions 144 and 160. Additionally, while in this example, directions 144 and 160 are orthogonal to one another, in other embodiments, directions 144 and 160 may have any other suitable angle between them.

[0144] In alternative embodiments, system 10 may include, instead of or in addition to ribbon 111, any other suitable type of wiping element or residue removal assembly, such as a sprayer of a suitable cleaning fluid or any other contact or non-contact cleaning device, to remove printing-fluid residue from nozzles 166, 166a, and 166b.

[0145] 3A-3C, printbar 62 comprises multiple arrays of nozzles 166, 166a, and 166b arranged in multiple printheads across the X-axis along the Y-axis and sections 170 and 172. In other embodiments, nozzles 166, 166a, and 166b and sections 170 and 172 can be arranged using any suitable configuration other than in multiple printheads, for example, printbar 62 can comprise a single printhead having the length of printbar 62 (e.g., about 1 meter).

[0146] 3B, there is shown a time interval during which seam section 45 of blanket 44 is aligned in the Z axis with the array of nozzles 166, 166a, and 166b. In other words, seam section 45 passes next to and faces the array of nozzles 166, 166a, and 166b at a distance of gap 141 in this example (e.g., between about 1 mm and 2 mm).

[0147] In some cases, at least two of the printheads of printbar 62 may not be perfectly coplanar with one another, for example in the Z-axis. For example, the plate with the array of nozzles 166a may be positioned about 0.05 mm higher along the Z-axis than the plate with the array of nozzles 166b. In these cases, when a given ribbon (different from ribbon 111) moves in direction 144, a given ribbon that is sufficiently taut may remain in the air without touching nozzles 166b, such that printing-fluid residue may not be wiped from at least a portion of nozzles 166b by ribbon 111.

[0148] In some embodiments, ribbon 111 is configured to have self-adhesion, also referred to herein as a self-supporting tensioning mechanism, as described in detail below in FIG. 5, to make contact with all nozzles of all printheads of printbar 62.

[0149] In some embodiments, the ribbon 111 is configured to be sufficiently taut to sandwich in the limited space between the blanket 44 and the printhead of the printbar 62 when moving in the directions 144 and 160. Furthermore, based on self-adhesion, the ribbon 111 is configured to adhere to (i.e., make contact with) and wipe residue from all the nozzles of the printbar 62 (e.g., nozzles 166, 166a, and 166b). It is noted that when moving in at least one of the directions 144 and 160, one or more forces (e.g., tension) are applied to the ribbon 111 in the XY plane (e.g., along the X and Y axes). In some embodiments, based on self-adhesion, the ribbon 111 is configured to adhere to the surface of the nozzle plate 61 without applying any force to the ribbon 111 or the printbar 62 along the Z axis. In other words, the ribbon 111 is configured to adhere to the nozzle plate of the printbar 62 while lateral tension is applied to the ribbon along the X and / or Y axes, without applying any normal force to the ribbon and / or printbar. As mentioned above, the adhesion mechanism in the Z axis is also referred to herein as the self-adhesion or self-support of the ribbon to the nozzle plate of the printhead of the printbar 62. Additionally, the amount and type of fluid (e.g., water 120) contained within the compressible layer 300 may be used to improve the adhesion of the ribbon 111 to all the nozzles of the printbar 62 and to remove (also referred to herein as wiping) residue from the nozzles.

[0150] In some embodiments, based on self-adhesion, ribbon 111 is configured to compensate for topography differences between different nozzles of printbar 62 and adhere to and remove residue from each nozzle of printbar 62. In some embodiments, the adhesion mechanism is enabled by a multi-layer structure of ribbon 111, which is described in detail in FIG. 5 below.

[0151] In some embodiments, during a printing operation, the distance (e.g., gap 141) between blanket 44 (i.e., tensioned and moving in the direction of travel) and print bar 62 is typically between about 1 mm and 1.5 mm, although in other embodiments, gap 141 may be greater or less than the aforementioned range. Additionally, ribbon 111 has a thickness of about 0.1 mm and is typically in physical contact with (i) section 170 (as shown in FIG. 3A), or (ii) nozzles 166, 166a, and 166b (as shown in FIG. 3B), or (iii) section 172 (as shown in FIG. 3C), positioned between print bar 62 and blanket 44.

[0152] As described above in FIG. 2, ribbon 111 moves within gap 141 such that the thickness of ribbon 111 is substantially small (e.g., between about 5X and 15X) compared to gap 141. Additionally, as described above in FIG. 3A, width 184 of ribbon 111 is sized such that ribbon 111, or any section thereof, does not cover the nozzles when ribbon 111 moves only in direction 144. Additionally, as noted above, width 182 of the array of nozzles 166, 166a, and 166b is sufficiently small (e.g., about 12.9 mm) and the speed of movement of ribbon 111 in direction 160 is sufficiently fast (e.g., about 8 meters per second) to complete wiping of the nozzles within about 50 msec, which is typically less than the time interval for seam section 45 to pass under the nozzles of printbar 62.

[0153] In some embodiments, the WA 200 moves the ribbon 111 between sections 170 and 172, and when the seam section 45 faces the print bar 62, the nozzles 166 do not eject printing fluid toward the blanket 44 and the ribbon 111 wipes any printing fluid residue from the nozzles 166.

[0154] In some embodiments, ribbon 111 covers one or more nozzles 166 when at least one section of seam section 45 faces one or more of the nozzles 166 to remove printing fluid residue. As shown in FIG. 3B, when seam section 45 is completely opposite width 182, the entire width 182 of ribbon 111 is positioned above nozzles 166. Note that when seam section 45 is close to print bar 62 (as shown in FIG. 3A) and facing print bar 62 (as shown in FIG. 3B), WA 200 is configured to move ribbon 111 in both directions 144 and 160.

[0155] In some embodiments, processor 20 and / or controller 54 are configured to control the direction and speed of movement of ribbon 111, for example in directions 144 and 160. The speed of ribbon 111 in directions 144 and 160 controls the amount of time a given section of ribbon 111 is in contact with a given nozzle of printbar 62 for the wiping process.

[0156] 3C, the position of the ribbon 111 relative to the printbar 62 and seam section 45 is shown. In some embodiments, after the seam section 45 of the blanket 44 has passed the printbar 62 and continues to move toward the other printbars 62 and / or the drying station 64, the WA 200 completes wiping the nozzles 166 and moves the ribbon 111 to section 170 of the printbar 62. As shown in FIG. 3C, the solid line 145 indicating the second trailing end of the seam section 45 moves into the direction of movement and no longer faces the printbar 62. In some embodiments, the imaging station 60 resumes jetting printing fluid from the nozzles 166 in a direction 171 toward the blanket 44 to form the next image on the blanket 44.

[0157] 3A-3C, which is the time it takes for ribbon 111 to travel from section 170 through nozzle 166 to section 172, is between about 20 milliseconds (msec) and 300 msec. For example, if the blanket travels in travel direction 94 at a speed between about 2.5 and 4 meters / sec, the time interval for moving ribbon 111 between section 170 and section 172 is about 50 msec.

[0158] In some embodiments, the WA 200 is configured to move the ribbon 111 during the operation of the system 10 while the system 10 is jetting droplets of printing fluid to form images on the blanket 44 (i.e., on the fly). Additionally, the ribbon 111 is wiping residue from the nozzles 166 while the blanket 44 moves to receive an image from the imaging station 60. In such embodiments, the WA 200 of the system 10 is configured to clean residue while the system 10 continues printing operations.

[0159] In principle, it is possible to keep the system 10 printing and perform residue wiping during the maintenance mode. However, the maintenance mode reduces the productivity of the system 10 because the system 10 is not printing during maintenance. In some embodiments, in accordance with the disclosed techniques, maintenance operations (e.g., removing printing fluid residue from the nozzles 166) are performed on the fly while the system 10 is printing an image on the blanket 44.

[0160] In some embodiments, after the seam section 45 has passed the printbar 62, the WA200 continues to move the ribbon 111 only in the direction 144, and when the seam section 45 again approaches the printbar 62 (after completing a blanket 44 cycle as shown in FIG. 1 above), the WA200 is configured to move the ribbon 111 in a direction 161 opposite to the direction 160 to wipe the nozzles 166, 166a, and 166b of the printbar 62. In the example of FIG. 3C, the arrow indicating the direction 161 is shown in dashed lines to indicate that the ribbon 111 moves in the direction 161 only when the seam section 45 approaches the printbar 62, as described above. Note that in these and other such embodiments, the ribbon 111 moves in the reverse order, i.e., from FIG. 3C to FIG. 3A, so that the ribbon moves in the directions 144 and 161. In other words, the WA200 is configured to move the ribbon 111 in the directions 144 and 160. Direction 144 is parallel to the long axis of the printbar, and direction 160 is parallel to the short axis of the printbar 62. In this example, residue removal is scheduled each time the seam section 45 passes next to the printbar 62, also referred to herein as a cycle of the blanket 44. In this example, (i) when the seam section 45 is not adjacent to the printbar 62, the ribbon 111 moves only in direction 144, and (ii) when the seam section 45 passes next to the printbar 62, the ribbon 111 moves in both directions 144 and 160. Thus, the ribbon 111 moves back and forth between sections 170 and 172, completing one back and forth movement during two cycles of the blanket 44.

[0161] In some embodiments, WA 200 is configured to apply different motion profiles, e.g., a continuous motion profile and a discrete motion profile, when moving ribbon 111 in directions 144 and 160. In the context of this disclosure and in the claims, the term "continuous motion" refers to motion at a predefined speed that does not stop, and the term "discrete motion" refers to motion that occurs only for predefined time intervals, typically but not necessarily recurring with a predefined frequency.

[0162] In the continuous motion profile, WA 200 moves ribbon 111 in direction 144 at a relatively slow speed (e.g., slower than about 20 mm / sec). In the discrete motion profile, WA 200 moves ribbon 111 in direction 160 at a relatively fast speed (e.g., faster than about 750 mm / sec). As mentioned above, both motion profiles may be performed simultaneously or separately.

[0163] In some cases, the blanket 44 may have a temperature of about 80 degrees Celsius and the nozzles 166, 166a, and 166b may have a lower temperature, such as a temperature between about 30 degrees Celsius and 35 degrees Celsius. In such cases, printing fluid and other substances may evaporate from the blanket 44, condense on one or more of the nozzles 166, 166a, and 166b, and then solidify, potentially at least partially clogging the orifices of one or more of the nozzles 166, 166a, and 166b.

[0164] In some embodiments, ribbon 111 may be used to cap nozzles 166, 166a, and 166b when imaging station 60 is in its non-operational mode or undergoing maintenance, e.g., not applying droplets to blanket 44. In such embodiments, WA 200 is configured to position ribbon 111 over nozzles 166, 166a, and 166b, as shown in FIG. 3B, such that ribbon 111 prevents vapors and / or aerosols of printing fluid and other materials from depositing on nozzles 166, 166a, and 166b of print bar 62. In some embodiments, processor 20 and / or controller 54 are configured to control WA 200 to move (at any suitable speed) in direction 144 to continuously wipe the nozzles. In another embodiment, when the image forming station 60 is not applying droplets of printing fluid to the blanket 44, the processor 20 and / or controller 54 are configured to control the WA 200 to position the ribbon 111 in contact with the nozzles and hold the ribbon 111 from moving in the directions 144 and / or 160 to protect the nozzles from vapor or aerosol contamination.

[0165] It should be noted that the presence of water 120 in ribbon 111 prevents printing fluid residue on the nozzles from solidifying by increasing the humidity between ribbon 111 and nozzles 166, 166a, and 166b. This mechanism is effective both when: (i) ribbon 111 is moving (e.g., moving in directions 144 and / or 160 and contacting nozzles of printbar 62), and (ii) ribbon 111 is stationary and contacting nozzles of printbar 62. In other words, the humidity of ribbon 111 prevents printing fluid residue on the nozzles from solidifying.

[0166] In some embodiments, wiping the nozzles of each printbar 62 of the system 10 frequently, for example every 10 seconds, or every minute, or every two minutes, is useful for maintaining the designated functionality of the nozzles and reducing the frequency of maintenance operations during which the system 10 is not printing an image. The inventors have found that using the disclosed techniques, the amount of defects in printed images is substantially reduced. For example, when using the WA200 and applying the disclosed techniques, the number of missing nozzles and completely blocked nozzles (when the nozzle orifice is completely clogged) and the amount of nozzle deviation (when the nozzle orifice is partially clogged) can be reduced by one or two orders of magnitude over time.

[0167] In the context of this disclosure and in the claims, the terms "blocked" and "clogged" are used interchangeably, and the terms "nozzle orifice" and "nozzle" are used interchangeably.

[0168] In other embodiments, the techniques described in this disclosure may be applied mutatis mutandis to direct printing systems. For example, when jetting ink or other printing fluids directly onto a flat or any other suitable substrate, ribbon 111 may be used to clean residue from the print nozzles between (i) the printing of a first image on a first flat and (ii) the subsequent printing of a second image (similar or different) on a second flat.

[0169] In some embodiments, the wiping of the nozzles of the system 10 may be performed at any suitable frequency and may be scheduled after a predetermined number of images and / or plafonds, or based on a predetermined time interval (e.g., every predetermined number of minutes), or using any other suitable criteria to define the wiping frequency. That is, when printing images on multiple plafonds in succession, after printing an image on the first plafond, the printing system may use a short time interval to wipe the nozzles before starting to print an image on the second plafond following the first plafond. Furthermore, the same technique can be used when printing images sequentially on successive substrates, such as a web of paper. In processes such as these, cleaning of the nozzles (e.g., wiping of ink residues) may be performed when a portion or section of the web of paper between two successive images (one already printed and the next to be printed) is positioned in close proximity to the printing nozzles. For example, when a section of the successive substrate between two successive images passes under the nozzles.

[0170] As mentioned above, the cleaning frequency can be performed after every image or after every selected number of images. It should be noted that in both above direct printing cases (printing on separate flat or continuous substrates), wiping of the nozzles is performed during the printing process and does not require stopping the operation of the printing system and does not degrade the print output of the (direct) printing system. Furthermore, the same technique can also be used to wipe residues from the printhead in other types of indirect printing systems. For example, instead of or in addition to the blanket 44, the printing system may comprise a drum that transfers one or more images to the target substrate.

[0171] Figure 4 is a schematic diagram of a wiping assembly (WA) 200, according to one embodiment of the present invention. In some embodiments, the WA 200 comprises a mechanical assembly (MA) 222 configured to move the ribbon 111 in the direction 140 from the tension assembly (TA) 130, as shown in Figure 2 above. The MA 222 is further configured to deflect the ribbon 111 to wipe the nozzles 166, 166a, and 166b, and sections 170 and 172 of the printbar 62, as shown in Figures 3A-3C above.

[0172] In some embodiments, the WA 200 further comprises a mechanical assembly (MA) 255 which, together with the MA 222, is configured to move the ribbon 111 to wipe the surfaces of the nozzles and printbar 62 as previously described. The WA 255 is further configured to deflect the ribbon 111 in a direction 150 towards the cleaning station (CS) 100, as shown in Figure 2 above. The MAs 222 and 255 are described in more detail below in insets 201 and 251, respectively.

[0173] In some embodiments, WA 200 comprises a shaft 202 coupled between MA 222 and MA 255 and configured to rotate clockwise (CW) and counterclockwise (CCW) to move the ribbon back and forth in directions 160 and 161, as shown in Figures 3A-3C above. It should be noted that WA 200 is configured to move ribbon 111 (i) in direction 144 within a first time interval, which is typically performed at least while imaging assembly 60 is applying droplets of printing fluid to blanket 44 (when ribbon 111 is positioned over sections 170 and 172), and (ii) alternately in directions 160 and 161 within a shorter second time interval (e.g., about 50 msec in each of directions 160 and 161) to wipe printing fluid residue from nozzles 166, 166a, and 166b when ribbon 111 passes between sections 170 and 172. For example, the length of ribbon 111 may be between about 2 meters and 4 meters, and the speed of movement in direction 144 may be between about 10 mm / sec, as described above, or between about 1 mm / sec and 20 mm / sec. The second time interval is about 50 msec, and the speed of movement of ribbon 111 in direction 160 is between about 800 mm / sec and 900 mm / sec. Thus, the ratio between the first and second time intervals may vary and may depend, among other things, on the frequency of wiping (defined by the number of images), the length and speed of ribbon 111, as well as other parameters.

[0174] In some embodiments, the ratio between the speeds of movement of ribbon 111 in directions 160 and 144 (also referred to herein as a speed ratio) may be between about 8 (e.g., 800 / 100) and 900 (e.g., 900 / 1). In other embodiments, ribbon 111 may move using any other suitable speed ratio between about 5 and 10,000.

[0175] In one embodiment of the disclosed technology, nozzle wiping occurs only when the seam section is passing through imaging station 60. In this embodiment, ribbon 111 moves in direction 160 (as shown in FIG. 1 above) during one cycle of blanket 44, and then ribbon 111 moves in the opposite direction 161 during the next cycle of blanket 44, and this alternating cycle is repeated as long as imaging station 60 is operating (e.g., continues to apply droplets onto moving blanket 44). Further, in such embodiments, the first time interval overlaps with one or more, typically more than one, second time intervals.

[0176] Reference is now made to inset 201, which details the structure of MA 222. In some embodiments, MA 222 comprises a motor 204, typically a servo brushless motor or any other suitable motor, configured to rotate belt 209 between pulley 206 and pulley 208 to rotate shaft 202.

[0177] In some embodiments, MA 222 comprises gear 226 and track 224, both with respective sawtooth structures that intertwine with one another. Gear 226 is configured to rotate with shaft 202 to move track 224 back and forth in a linear motion in direction 220, which is generally parallel to direction 140, and in this example is also parallel to directions 160 and 161. Note that when shaft 202 and gear 226 rotate clockwise, track 224 is moving in direction 140, and when shaft 202 and gear 226 rotate CCW, track 224 is moving in the opposite direction to direction 140.

[0178] In some embodiments, MA 222 comprises a mechanical arm 216 configured to move with track 224. Reciprocating pulley 210, comprising rollers 211, 212, 213 and 214, is mounted on arm 216 by respective hinges and configured to deflect ribbon 111 from movement in direction 140 (before MA 222) to movement in direction 144 and directions 160 and 161 (after MA 222) as shown in Figures 3A-3C above.

[0179] In some embodiments, ribbon 111 travels in direction 140 and enters roller 211, and is deflected in direction 144 as it enters roller 212. Ribbon 111 then enters rollers 213 and 214 to maintain a specified tension on ribbon 111 while wiping printing-fluid residue from nozzles 166, 166a, and 166b.

[0180] Reference is now made to inset 251, which illustrates MA 255. In some embodiments, MA 255 comprises gear 246 and track 244, similar to gear 226 and track 224 of MA 222. Gear 246 is coupled to shaft 202 and rotates therewith, causing track 244 to move in direction 240, generally parallel to direction 220. Reciprocating pulley 230 is attached to mechanical arm 236, which moves back and forth in direction 240 by track 244, causing roller 111 to move alternately in directions 160 and 161. Note that because gears 226 and 246 are both coupled to shaft 202, when processor 20 and / or controller 54 controls motor 205 to rotate the belt (CW or CCW), tracks 224 and 244 move together, causing ribbon 111 to move in direction 160 or 161 as discussed above. Furthermore, if the seam section 45 is not immediately adjacent to the printbar 62 , the ribbon will move in direction 144 but not in directions 160 or 161 .

[0181] In some embodiments, reciprocating pulley 230 comprises multiple rollers, in this example rollers 232 and 233 configured to maintain a specified tension on ribbon 111 as it moves in direction 144, and roller 234 to deflect ribbon 111. Reciprocating pulley 230 may comprise additional rollers, such as roller 235 shown in full view in FIG. 4, that are configured to deflect ribbon 111 for movement in direction 150.

[0182] In some embodiments, MA 255 includes an arm 237 coupled between arm 236 and roller 234, which is configured to adjust the position of roller 234. In some embodiments, MA 222 can include an arm (almost completely hidden in inset 201) similar to arm 237 and configured to adjust the position of roller 212. Arms such as these may be used to replace ribbon 111 during maintenance operations of WA 200, or to adjust the tension applied to ribbon 111, or to adjust the direction of movement of ribbon 111, or any other suitable function.

[0183] In other embodiments, the motor 204 of the MA 222 may be directly coupled to the pulley 208 to rotate the gear 226 and shaft 202 .

[0184] The particular configuration of WA 200 is shown as an example to illustrate the particular problems addressed by embodiments of the invention and to demonstrate the application of these embodiments in improving the performance of such systems. However, embodiments of the invention are in no way limited to this particular type of example wiping assembly, and the principles described herein may be similarly applied to any other type of mechanism for controlling the removal of printing fluid residue from the nozzles of system 10, or from nozzles and / or other components of other types of printing systems.

[0185] 5 is a schematic cross-sectional view of ribbon 111, according to one embodiment of the present invention. In some embodiments, ribbon 111 comprises a core layer 303 made from a woven fabric, commercially known as a scrim, made from cotton or flax, configured to act as a backbone of ribbon 111 and improve its mechanical properties. For example, core layer 303 is configured to increase the tensile strength of ribbon 111 against tension applied by WA 200 and prevent plastic deformation and / or tearing of ribbon 111.

[0186] In some embodiments, the core layer 303 includes an array of woven fibers, which in this example are arranged in a crisscross configuration, or intertwined using any other suitable configuration. The core layer 303 is configured to provide dimensional stability to the ribbons 111 when the WA 200 applies tension to the ribbons 111.

[0187] In some embodiments, the fibers of the core layer 303 may comprise a mixture of polyester and water-based polyurethane.

[0188] In some embodiments, ribbon 111 comprises a compressed layer 300 configured to contain a fluid, such as water 120 and other fluids described herein. Compressed layer 300 has a total thickness of between about 300 μm and 900 μm, or any other suitable thickness, in this example about 600 μm. It is noted that when a force, such as a compressive force, is applied to ribbon 111, such as in squeeze assembly 110, particularly in the Z-axis, the thickness of compressed layer 300 decreases and at least a portion of the fluid is squeezed out of compressed layer 300. Embodiments such as these are described in more detail, for example, in FIG. 6 below.

[0189] In some embodiments, the packed bed 300 may include a top layer 302 and a bottom layer 304, both of which include three-dimensionally entangled polyester ultra-fine microfibers and are configured to absorb and contain the aforementioned fluids. In the context of this disclosure and claims, the term ultra-fine microfibers refers to fibers having a suitable diameter, for example, a diameter between about 2 μm and 6 μm.

[0190] In other embodiments, the compressible layer 300 may include any other suitable type of material, such as a polyethylene-based material.

[0191] In some embodiments, the ultra-fine microfibers of the compressible layer 300 can be impregnated with a water-based polyurethane in the spaces between the ultra-fine microfibers to impart a soft and highly flexible texture to both the front layer 302 and the back layer 304 of the compressible layer 300. In some embodiments, the microfibers are configured to reduce or prevent static charging, at least as the ribbon 111 moves relative to the print bar 62 and / or blanket 44.

[0192] In some embodiments, the core layer 303 may be integrated with the compressible layer 300 using any suitable technique, for example, by applying hydraulic pressure to bond between the compressible layer 300 and the core layer 303, or by bonding between the core layer 303 and the front and back layers using any suitable technique. In the example of Figure 5, the front layer 302 has a thickness of between about 400 μm and 500 μm, and the back layer 304 has a thickness of between about 200 μm and 100 μm, respectively, so that the combined thickness of layers 302 and 304 remains about 600 μm. Note that in this example, layers 302 and 304 constitute the compressible layer 300 with the core layer 303 positioned between them.

[0193] In some embodiments, ribbon 111 comprises a wiping layer 301 that is bonded to the surface of surface layer 302 using any suitable bonding technique. In this example, layer 301 is made from a suitable springy material, typically a polymer with very low density fibers. In other embodiments, layer 301 may comprise any other material suitable for wiping printing fluid residue from nozzles 166, 166a, and 166b. In some embodiments, layer 301 has a thickness between about 50 μm and 500 μm, and in this example, layer 301 has a thickness of about 200 μm.

[0194] In some embodiments, ribbon 111 includes a polyethylene-based layer, referred to herein as layer 305, having any suitable thickness between about 10 μm and 200 μm. In this example, layer 305 includes or is made from polyethylene terephthalate (PET), commercially referred to as polyester, and has a thickness of about 35 μm.

[0195] In some embodiments, layer 305 is bonded to back layer 304 of compressible layer 300 using any suitable technique, such as adhesion by applying thermal polyurethane (PTU) or any other suitable type of adhesive (not shown) between layer 304 and layer 305.

[0196] In some embodiments, the multi-layer structure described above provides ribbon 111 with sufficient tensile strength to prevent ribbon 111 from undesirably elongating by undergoing plastic deformation or creep of the material. It is noted that core layer 303 and PET layer 305 improve the mechanical strength of ribbon 111 to maintain tension and withstand the tension applied by WA 200. In other words, layers 303 and 305 stiffen ribbon 111 in the X and Y axes and improve ribbon 111's resistance to the tension applied by WA 200.

[0197] As described above in FIG. 3B, ribbon 111 is configured to compensate for topography differences between different nozzles (e.g., nozzles 166a and 166b) of printbar 62 and adhere to and remove residue from each nozzle of printbar 62. In some embodiments, the multi-layer structure described above provides ribbon 111 with the ability to compensate for the above-mentioned topography differences. In this example, the combination of (i) spring-like layer 301, (ii) compressible layer 300, which acts as a reservoir for water (e.g., water 120) received from CS 100, and (iii) layer 305 is configured to conform to and compensate for topography differences (e.g., in the Z-axis) between different printheads of printbar 62. The adhesive strength of water 120, the flexibility of layer 301, and the tensile strength and flexibility of layer 305 provide ribbon 111 with self-adhesive strength, allowing it to come into contact with nozzle plate 61 and wipe residue from all of the nozzles of print bar 62 (e.g., nozzles 166, 166a, and 166b).

[0198] In some embodiments, layer 305 is configured to seal ribbon 111 to prevent undesired leakage or dripping of water 120 from ribbon 111 toward surface blanket 44. Such dripping can cause, among other things, undesirable defects or other distortions in the image formed on blanket 44. Additionally, by retaining a desired amount of water 120 within compressible layer 300, layer 305 improves the self-adhesion of ribbon 111, as the adhesive forces of water 120 help layer 301 (when wet or damp) adhere to the nozzle plate of print bar 62, and more specifically, nozzles 166, 166a and 166b.

[0199] In some embodiments, as described above in FIG. 3C , layer 305 also seals ribbon 111 when capping the nozzles when printbar 62 is idle, e.g., not applying droplets of printing fluid to blanket 44. Note that a sufficient amount of water 120 in ribbon 111 is essential for the capping procedure and / or process, and to dissolve any residue formed on the nozzles of printbar 62.

[0200] The particular configuration and multi-layer structure of ribbon 111 are shown as examples to illustrate the particular problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in improving the performance of such systems. However, embodiments of the present invention are in no way limited to this particular type of multi-layer example, and the principles described herein may be similarly implemented using other types of materials, numbers of layers, thicknesses of each layer, and mechanical, physical, and chemical properties of each layer and stack. Additionally, the embodiments relating to ribbon 111 described above may be applied to any other type of printing system.

[0201] 6 is a schematic cross-sectional view of a ribbon 111 being pressed in a press assembly 110, according to one embodiment of the present invention. In some embodiments, the press assembly 110 includes drums 112 and 114 as described above in FIG. 2. In this example, rollers 114 rotate CW, as indicated by arrow 311, and drum 112 rotates CCW, as indicated by arrow 312.

[0202] In some embodiments, when the ribbon 111 is pulled from the WC 122f, at least the packed layer 300 is immersed in water 120 and has a thickness of about 600 μm or more depending on the volume of water 120 it picks up. In some embodiments, upon immersion, the packed layer 300 has a thickness of about 300 grams per square meter (about 300 g / m 2 ) to 950g / m 2 In this example, the compressed layer 300 is configured to contain water 120 between about 575 g / m 2 Includes.

[0203] In some embodiments, when the ribbon 111 is inserted between the drums 112 and 114, the thickness of the packed bed 300 is reduced to any suitable thickness between about 150 μm and 350 μm. In this example, the thickness of the packed bed 300 is reduced to a thickness 310 of about 250 μm, and the amount of water 120 contained within the packed bed 300 is about 225 g / m 2 decreases to.

[0204] In other words, in this example, approximately 60% of the water 120 is squeezed out of the ribbon 111. It should be noted that because the ribbon 111 is flexible, after the ribbon 111 exits the squeeze assembly 110, cavities in the condensed layer 300 (and other layers) of the ribbon 111 will typically fill with environmental fluid, such as, but not limited to, the air surrounding the squeeze assembly 110. Additionally, as the ribbon 111 moves between the blanket 44 and the imaging station 60, the condensed layer 300 (and other layers) of the ribbon 111 is configured to absorb printing fluid aerosols and vapors present between the blanket 44 and the print bar 62.

[0205] Based on the above-described embodiment, when the ribbon 111 moves along the bottom section of the nozzle plate into the gap between the blanket 44 and the imaging station 60 (e.g., gap 141 shown in FIG. 2 above), it: (i) moves in directions 144 and / or 160 to adhere to all the nozzles of the print bar 62 and wipe the printing fluid residue from the nozzles 166, 166a, and 166b; (ii) absorbs and contains various types of vapors and aerosols that may be undesirable to accumulate on one or more of the nozzles 166, 166a, and 166b; and (iii) removes the nozzles 166, 166a, and 166b from the nozzles 166, 166a, and 166b. 66b and on sections 170 and 172 of print bar 62 to prevent undesirable build-up and / or solidification of material around print bar 62; (iv) providing a buffer between nozzles 166, 166a and 166b and the aforementioned environment, particularly when print bar 62 is not applying droplets of printing fluid toward blanket 44 (e.g., when print bar 62 and possibly system 10 are both in an idle and / or waiting position); and (v) removing the aforementioned residue and other contaminants within water container 122 of cleaning station 100.

[0206] In some embodiments, the processor 20 and / or controller 54 is configured to control the amount of water 120 remaining in the ribbon 111 after squeezing by controlling the distance between the drums 112 and 114 (also referred to herein as rollers). For example, the distance between the drums 112 and 114 is controlled by applying a force in the direction 315, such as by the piston 117 and shaft 119 described in FIG. 2 above.

[0207] 7A is a schematic top view of a wiping assembly (WA) 400 according to another embodiment of the present invention. In some embodiments, the WA 400 can be used in the system 10 instead of or in addition to the WA 200 described in FIGS. 2-4 above.

[0208] In some embodiments, the WA 400 comprises a track 402, which may have a longitudinal axis parallel to the Y axis or in any other orientation. The WA 400 comprises a slider 404 configured to move in the Y axis and slide along the track 402.

[0209] In some embodiments, the WA 400 comprises a blade 406 made from a light, durable material, such as tungsten carbide, and is coupled to the slider 404, for example, using an adhesive.

[0210] In some embodiments, WA 400 comprises a wiper pad 408 coupled, for example by adhesive, to blade 406. Wiper pad 408 is made from any material suitable for removing printing-fluid residue from nozzles 166, 166a, and 166b of printbar 62.

[0211] In some embodiments, the blade 406 of the WA 400 is configured, as it moves along the print bar 62, to push the wiper pad 408 towards the nozzles 166, 166a, and 166b of the print bar 62 to compensate for topography differences (e.g., in the Z axis) between the different printheads of the print bar 62, as described above in Figures 3B and 5.

[0212] In some embodiments, after wiping the nozzles 166, 166a, and 166b of the printbar 62, the wiper pad 408 may be cleaned using any suitable technique to remove such residues.

[0213] FIG. 7B is a schematic bottom view of WA400 according to another embodiment of the present invention.

[0214] In some embodiments, blade 406 has a first edge coupled to slider 404 and a second edge coupled to wiper pad 408. This configuration allows movement of the second edge in the Z axis to match the topography of the printhead of printbar 62.

[0215] The particular configuration of the WA 400 is shown as an example to illustrate the particular problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in improving the performance of such systems, however, embodiments of the present invention are in no way limited to this particular type of example wiping assembly 400, and the principles described herein may be applied to any other type of residue removal device as well.

[0216] In other embodiments, the wiper pad may be attached to a cable (not shown), with or without a blade or any other suitable carrier. In such embodiments, the cable may be moved using rollers and / or pulleys and / or drums and / or any other suitable type of device.

[0217] FIG. 8 is a flow chart that generally illustrates a method for removing residue from nozzles 166, 166a, and 166b of one or more printbars 62 of system 10, in accordance with one embodiment of the present invention.

[0218] The method begins with a printing step 500 in which droplets of printing fluid are applied from one or more first and second nozzles to a moving substrate to produce an image thereon. In this example, the moving substrate comprises an intermediate transfer member, blanket 44. In other embodiments, the moving substrate may include a target substrate, such as one or more flat or continuous webs of paper, that receive an image directly from the nozzles of the printbar. Embodiments such as these may be implemented in a direct printing system.

[0219] In some embodiments, the first nozzles may be positioned in a first printbar 62 and the second nozzles may be positioned in a different, second printbar 62 of the system 10. It is noted that each printbar 62 has a separate WA 200 with a separate ribbon 111 for wiping residue from the nozzles of the respective printbar. In the context of the present description, the first WA 200 is configured to wipe the nozzles of the first printbar 62 and the second WA 200 is configured to wipe the nozzles of the second printbar 62.

[0220] In a first residue removal step 502, the processor 20 and / or controller 54 moves the ribbon 111 (or any other type of residue removal assembly) of the second WA 200 to remove residue from one or more second nozzles (e.g., nozzles 166, 166a and 166b of the second printbar) while the first nozzles (e.g., of the first printbar) are applying printing fluid and the substrate (e.g., the blanket 44) is moving.

[0221] It should be noted that steps 500 and 502 may be performed simultaneously. In some embodiments, when one or more first nozzles of a first printbar 62 of the system 10 are applying droplets of printing fluid to the blanket 44, the ribbon 111 of the second WA 200 is wiping printing fluid residue from one or more second nozzles of the second printbar 62 of the system 10. For example, the nozzles of a magenta printbar may apply magenta ink to the blanket 44, while at the same time the WA 200 of the cyan printbar may move the ribbon 111 in both directions 144 and 160 to wipe cyan ink residue from the nozzles of the cyan printbar. As described above in FIGS. 3A-3C, wiping the nozzles of the cyan printbar may be performed while the seam section 45 is positioned between the blanket 44 and the cyan printbar, e.g., shown as printbar 62 in FIGS. 3A-3C above.

[0222] In a residue cleaning step 504, the processor 20 and / or controller 54 are configured to move the ribbon 111, which transports residue removed from the nozzles of the cyan print bar while at least one of the magenta and cyan nozzles is applying droplets of printing fluid to the blanket 44, to a cleaning station (e.g., CS100) to remove the residue from the ribbon 111.

[0223] In another embodiment, instead of cleaning the residue from the ribbon 111, the WA 200 can include two drums (not shown). A first drum supplies the clean ribbon 111 for wiping the residue from the print bar 62, and a second drum is for receiving the ribbon 111 after wiping the residue from the print bar 62. It is noted that the clean ribbon can travel through a reservoir of cleaning fluid, such as water 120, and a squeeze assembly (e.g., squeeze assembly 110) to accommodate a predetermined amount of water 120 in the compressed layer 300 of the ribbon 111. As described in Figures 2 and 5, the water contained in the compressed layer 300 can be used to stick the ribbon 111 to all the nozzles of the print bar 62 and to remove the residue from the nozzles.

[0224] In a second residue removal step 506 that concludes the method, the processor 20 and / or controller 54 moves the ribbon 111 of the WA 200 (or any other type of residue removal assembly) to remove residue from one or more first nozzles (e.g., nozzles of a magenta printbar) while the second nozzles (e.g., nozzles of a cyan printbar) apply printing fluid (e.g., cyan ink) to the moving blanket 44 to create an ink image.

[0225] In the above-described embodiment, each print bar 62 has a separate WA 200, so that when the seam section 45 passes between the given print bars 62, the given WA 200 of the given print bar 62 is wiping printing fluid residue from the nozzles of the given print bar 62 while one or more nozzles (e.g., nozzles 166, 166a and 166b) of the other print bars 62 continue to apply printing fluid to the blanket 44 in accordance with the printing scheme of the particular image formed on the blanket 44.

[0226] 8 may be performed in multiple cycles. These cycles may be performed at least as long as imaging system 60 is applying any type of droplets (such as, but not limited to, ink) to blanket 44. Additionally, one or more of steps 500-506 may be performed simultaneously.

[0227] For example, in one embodiment, the residue wiping of step 502 may be performed within one section of the ribbon 111 while another section of the ribbon 111 is being cleaned as described in step 504. In another embodiment, the residue wiping may be performed on the first printbar 62 while one or more nozzles of one or more of the other printbars 62 of the system 10 are applying respective printing fluid to the blanket 44, as described in method steps 502 and 506.

[0228] In some embodiments, the techniques disclosed in the method of FIG. 8 and also described in detail in FIGS. 2-6 above, improve productivity of system 10 by performing maintenance on the fly, i.e., while system 10 is printing an image onto blanket 44 and / or transferring an image to a target substrate, such as, but not limited to, flat sheet 50.

[0229] FIG. 9 is a flow chart that generally illustrates a method for forming an image and cleaning residue from nozzles 166, 166a, and 166b of printbar 62, in accordance with one embodiment of the present invention.

[0230] The method begins with a substrate movement step 600, where a suitable intermediate or target substrate is moved along a movement direction 94. In this example, the substrate comprises a blanket 44 having one or more first sections, each intended to receive ink droplets and form the aforementioned image thereon, for example as described in detail in FIG. 1 above.

[0231] In some embodiments, blanket 44 further comprises one or more second sections positioned alternating between the first sections. The second sections do not receive droplets of ink or other printing fluid and are not intended to form an ink image thereon. In such embodiments, one of the second sections may include seam section 45.

[0232] It should be noted that because the first and second sections are interleaved, as blanket 44 moves in motion direction 94, the first and second sections alternately pass next to printbar 62. In other words, as blanket 44 moves in direction 94, the first section faces printbar 62 for a first time interval, and the second section faces printbar 62 for a second time interval following the first time interval. This sequence is repeated as blanket 44 moves in motion direction 94 (along the infinite loop of blanket 44), so that the next first section faces printbar 62, and then the next second section faces printbar 62.

[0233] In image formation step 602, when blanket 44 moves in movement direction 94 and one of the first sections of blanket 44 faces print bar 62, nozzles 166, 166a, and 166b apply (e.g., spray) printing fluid (in this example, ink droplets) onto the surface of the first section facing print bar 62.

[0234] In a residue removal step 604, while blanket 44 is moving in direction 94 with one of the second sections of blanket 44 facing nozzles 166, 166a, and 166b of printbar 62, processor 20 and / or controller 54 moves ribbon 111 at least in direction 160 (e.g., using a discrete motion profile as described in FIGS. 3A-3B above) and typically also in direction 144 (e.g., using a continuous motion profile as described in FIGS. 3A-3B above) to remove printing fluid residue from nozzles 166, 166a, and 166b of printbar 62. It is noted that step 604 may be performed using any suitable frequency, for example, blanket 44 may have eleven (11) first sections and eleven (11) second sections.

[0235] In a first embodiment, step 604 may be performed when each of the second sections faces the printbar 62 (i.e., after every image is formed and eleven times per blanket 44 cycle, defined as when the seam section 45 passes next to the printbar 62). In a second embodiment, step 604 may be performed when every fifth second section faces the printbar 62 (i.e., typically twice per blanket 44 cycle). In a third embodiment, step 604 may be performed only when the seam section 45 faces the printbar 62 (i.e., once per blanket 44 cycle).

[0236] Additionally or alternatively, step 604 may be performed using any other suitable schedule or frequency, such as every predetermined time interval. For example, about every 10 seconds, or about every 30 seconds, or about every 5 minutes, or about every hour, etc. It should be noted that the frequency may be constant or may be changed in conjunction with other operations, such as during preventive maintenance (PM) operations performed on system 10. For example, the frequency may be relatively low on the first day after a PM (e.g., every 10 minutes) and high on the last day before the next PM (e.g., every 5 minutes).

[0237] In other embodiments, when the print bar 62 is in an idle position (e.g., not applying ink to the blanket 44), the WA 200 is configured to position the ribbon 111 above the nozzles of the print bar 62 to prevent solidification of printing fluid residue or any other undesirable substance on the nozzles 166, 166a and 166b and / or on their orifice(s).

[0238] The method ends in ribbon removal step 606, where WA 200 moves ribbon 111 away from the nozzles of printbar 62. In some embodiments, step 606 is typically performed when blanket 44 is moving such that one of the first sections faces the nozzles of printbar 62 to receive ink droplets to form an image, for example, as described above in Figures 3A-3B.

[0239] Although the embodiments described herein are primarily directed to digital printing systems having an intermediate transfer member, the methods and systems described herein may also be used in other applications, such as any type of direct printing system that uses inkjet nozzles for two-dimensional and three-dimensional printing applications.

[0240] Therefore, it will be understood that the above-mentioned embodiments are cited by way of example, and the present invention is not limited to what has been particularly shown and described hereinabove. Rather, the scope of the present invention includes both combinations and subcombinations of the various features hereinabove, as well as variations and modifications thereof that would occur to a person skilled in the art upon reading the above description and that are not disclosed in the prior art. Documents incorporated by reference into this patent application shall be considered as integral parts of this application, except that if any term is defined in these incorporated documents in a manner that contradicts the definitions expressly or implicitly made herein, then only the definitions in this specification shall be considered.

Claims

1. 1. A system having a printing position and a non-printing position, an imaging station including at least a nozzle plate having one or more nozzles configured to apply droplets of a printing fluid onto a surface of one or more substrates to generate one or more images thereon; a wiping assembly positioned at least partially within a gap between the nozzle plate and the one or more substrates and configured to (i) physically contact the nozzle plate and (ii) remove residue of the printing fluid from at least one of the nozzles while the system is in the printing position; The system comprising:

2. 2. The system of claim 1 , comprising: (i) a transport assembly configured to move the one or more substrates relative to the nozzle plate; and (ii) a processor configured to (a) control the transport assembly to move the one or more substrates and (b) control the wiping assembly to remove the residue from at least one of the nozzles while the one or more substrates are moved by the transport assembly.

3. 2. The system of claim 1, wherein at the printing position, the gap between the nozzle plate and the one or more substrates is maintained while (i) applying the droplets and (ii) removing the residue.

4. The system of any one of claims 1 to 3, wherein the wiping assembly includes a wiping element configured to remove the residue of the printing fluid by wiping it from at least an orifice of at least one of the nozzles.

5. 5. The system of claim 4, wherein the wiping element comprises a ribbon, the ribbon configured to carry a cleaning fluid and to make physical contact with the nozzle plate by self-adhering to the nozzle plate.

6. 6. The system of claim 5, wherein the ribbon includes: (a) a residue removal layer configured to remove printing-fluid residue from the nozzle plate; and (b) a compressible layer coupled to the residue removal layer and configured to (i) absorb and contain a cleaning fluid when placed in contact with the cleaning fluid, and (ii) expel at least a portion of the cleaning fluid when a compressive force is applied to the ribbon.

7. The system of claim 4 , wherein the wiping assembly is configured to move the wiping element in a first direction during a first time interval and in a second direction during a second time interval.

8. 8. The system of claim 7, wherein the nozzle is disposed along a first axis and transverse to a second axis, and wherein at least one of: (i) the first direction is parallel to the first axis; and (ii) the second direction is parallel to the second axis.

9. 8. The system of claim 7, wherein the processor is configured to control the wiping assembly to move the wiping element in at least one of the first direction and the second direction when at least one of the nozzles is ejecting the printing fluid toward the one or more substrates.

10. The system of claim 7 , wherein the first time interval is greater than the second time interval.

11. The system of claim 7 , wherein the first time interval overlaps with one or more second time intervals.

12. 8. The system of claim 7, wherein the processor is configured to control the wiping assembly to move the wiping element (i) in the first direction at a first speed and (ii) in the second direction at a second speed different from the first speed.

13. A ribbon, a residue removal layer configured to remove printing fluid residue from one or more nozzles of the printing system; a compressible layer coupled to the residue removal layer and configured to (i) absorb and contain a cleaning fluid when placed in contact with the cleaning fluid, and (ii) release at least a portion of the cleaning fluid when a compressive force is applied to the ribbon; The ribbon.

14. 14. The ribbon of claim 13, wherein the one or more nozzles are formed in a nozzle plate, and the residue removal layer is configured to receive at least a portion of the cleaning fluid from the compressed layer, self-adhere to the nozzle plate, and in physical contact with the one or more nozzles.

15. 15. The ribbon of claim 13, further comprising a core layer coupled to said compressive layer and configured to stiffen said ribbon in a given plane when a tension force is applied to said ribbon.

Images