Device for controlling the tension applied to a flexible member

Abstract

A digital printing system (10) includes a flexible intermediate transfer member (ITM) (44) and a floating roller assembly (100). The ITM (44) is configured to receive ink drops from an ink supply system to form an image on the ITM and transfer the image to a target substrate (50). The floating roller assembly (100) includes a fluid chamber (103) and a rotatable element (111) mounted in the fluid chamber (103), the fluid chamber (103) including an inlet (107) configured to receive a pressurized fluid (130) into the fluid chamber (103), and the pressurized fluid (130) causes the rotatable element (111) to move relative to the fluid chamber (103) and apply tension to the ITM (44) when rotated by the ITM (44).

Description

Technical Field

[0001] The present invention relates generally to digital printing systems, and more particularly to methods and systems for applying tension to a flexible intermediate transfer member of a digital printing system. Background Art

[0002] Various techniques have been developed to guide flexible substrates in printing systems.

[0003] For example, US Patent 5,246,155 describes a web guide roller assembly for a printer that utilizes a cylindrical roller support body and a concentric hollow roller body. Summary of the Invention

[0004] Embodiments of the invention described herein provide a digital printing system comprising a flexible intermediate transfer member (ITM) and a dancer roller assembly. The ITM is configured to receive ink droplets from an ink supply system to form an image on the ITM and transfer the image to a target substrate. The dancer roller assembly comprises a fluid chamber and a rotatable element mounted within the fluid chamber. The fluid chamber includes an inlet configured to receive pressurized fluid into the fluid chamber. The pressurized fluid causes the rotatable element to move relative to the fluid chamber and apply tension to the ITM when rotated by the ITM.

[0005] In some embodiments, the system includes a processor configured to control movement of the rotatable element, including: (i) selecting between at least a first position and a second position of the dancer roller assembly, (ii) in the first position, moving at least the fluid chamber relative to the ITM, and (iii) in the second position, moving at least the rotatable element relative to the fluid chamber. In other embodiments, the system includes a fluid compressor configured to supply pressurized fluid into the fluid chamber through the inlet. In yet other embodiments, the system includes a processor configured to: (a) calculate a target pressure based on an indication of tension applied to the ITM, the target pressure causing the rotatable element to apply tension to the ITM when applied to the pressurized fluid, and (b) control the fluid compressor to supply pressurized fluid at the target pressure into the fluid chamber.

[0006] In one embodiment, the system includes a pressure sensor configured to generate a pressure signal indicating a current pressure of the pressurized fluid in the fluid chamber, and the processor is configured to control the fluid compressor based on the pressure signal to match the current pressure to a target pressure. In another embodiment, the pressurized fluid includes pressurized air, and the fluid compressor includes an air blower configured to supply the pressurized air. In yet another embodiment, the system includes a position sensing assembly configured to generate a position signal indicating a position of the rotatable element relative to a predetermined reference point.

[0007] In some embodiments, the processor is configured to control a motor based on the position signal to at least move the fluid chamber relative to the ITM. In other embodiments, based on the position signal, the processor is configured to control a fluid compressor to at least move the rotatable element along the axis of the fluid chamber by controlling the pressure of the pressurized fluid. In still other embodiments, the rotatable element comprises a roller.

[0008] In one embodiment, the roller has a circular cross-section. In another embodiment, the rotatable element comprises at least one material selected from the list of materials consisting of (a) carbon, (b) polymethacrylimide (PMI), and (c) perfluoroalkoxyalkane (PFA). In yet another embodiment, the PMI is formed into a rigid foam.

[0009] In some embodiments, the PFA is formed into a tube. In other embodiments, the system includes a motor configured to move at least the fluid chamber relative to the ITM, and in at least a first position, the processor is configured to control the motor to move at least the fluid chamber relative to the ITM. In other embodiments, the system includes an opening sized and shaped to fit snugly over the rotatable element, and the pressurized fluid causes the rotatable element to extend from the fluid chamber through the opening. In yet other embodiments, the system includes a seal coupled to the opening and configured to retain the pressurized fluid within the fluid chamber when the pressure of the pressurized fluid is less than or equal to a predefined pressure, and to release at least a portion of the pressurized fluid from the fluid chamber when the pressure exceeds the predefined pressure.

[0010] In one embodiment, the seal is configured to reduce friction between the rotatable element and the wall of the opening. In another embodiment, the seal comprises at least an element selected from the list consisting of a sponge and a strip. In yet another embodiment, the strip is bonded to the surface of the sponge.

[0011] In some embodiments, the sponge comprises polyester. In other embodiments, the strip comprises ultra-high molecular weight (UHMW) polyethylene. In still other embodiments, the seal comprises a leaf spring having a first section coupled to a wall of the opening and a second section configured to release at least a portion of the pressurized fluid from the fluid chamber by moving relative to the rotatable element.

[0012] In one embodiment, the second section is configured to move in response to a change in the position of the rotatable element. In another embodiment, the leaf spring comprises stainless steel, and the second section is configured to flex relative to the first section in response to a change in the position of the rotatable element. In yet another embodiment, the second section comprises one or more elements selected from the group consisting of a sponge and a ribbon.

[0013] In some embodiments, the tape is bonded to the surface of the sponge. In other embodiments, the sponge comprises polyurethane foam. In yet other embodiments, the tape comprises ultra-high molecular weight (UHMW) polyethylene or polytetrafluoroethylene (PTFE).

[0014] In some embodiments, the sponge is coupled to the second segment and the ribbon is coupled to the sponge, and in response to a change in the position of the rotatable element, the second segment is configured to move relative to the rotatable element so as to maintain a distance between the ribbon and the outer surface of the rotatable element. In other embodiments, the pressurized fluid causes the rotatable element to move along an axis of the fluid chamber, and at the point of contact between the ITM and the rotatable element, the axis of the fluid chamber is orthogonal to the axis of movement of the ITM.

[0015] According to an embodiment of the present invention, a method is also provided, which includes a digital printing system comprising (a) a flexible intermediate transfer member (ITM) and (b) a dancer roller assembly, the dancer roller assembly including a fluid chamber and a rotatable element mounted in the fluid chamber, the fluid chamber including an inlet for receiving pressurized fluid into the fluid chamber, wherein the rotatable element applies tension to the ITM by supplying pressurized fluid into the fluid chamber and causing the rotatable element to move relative to the fluid chamber. An image is formed on the ITM by receiving ink droplets from an ink supply system, and the image is transferred to a target substrate.

[0016] According to an embodiment of the present invention, a method is also provided, which includes a method in a digital printing system comprising (a) a flexible target substrate and (b) a floating roller assembly, the floating roller assembly including a fluid chamber and a rotatable element mounted in the fluid chamber, the fluid chamber including an inlet for receiving a pressurized fluid into the fluid chamber, wherein a predefined tension is applied to the flexible target substrate by the rotatable element by supplying the pressurized fluid into the fluid chamber and causing the rotatable element to move relative to the fluid chamber, and an image is formed on the flexible target substrate by receiving ink droplets from an ink supply system.

[0017] According to an embodiment of the present invention, an apparatus for controlling tension applied to a flexible member is further provided. The apparatus includes a substrate and a floating roller assembly. The substrate includes the flexible member. The floating roller assembly includes a fluid chamber and a rotatable element mounted within the fluid chamber. The fluid chamber includes an inlet configured to receive pressurized fluid into the fluid chamber. The pressurized fluid causes the rotatable element to move relative to the fluid chamber and apply tension to the substrate when rotated by the substrate.

[0018] The present invention will be more fully understood through the following detailed description of embodiments of the present invention in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 is a schematic side view of a digital printing system according to an embodiment of the present invention;

[0020] Figure 2 is a block diagram schematically illustrating a dancer roller assembly of a digital printing system according to an embodiment of the present invention;

[0021] Figure 3 is a schematic pictorial illustration of a dancer roller assembly of a digital printing system according to an embodiment of the present invention;

[0022] Figure 4A is a cross-sectional view of a dancer roller assembly in a blanket mounted position according to an embodiment of the present invention;

[0023] Figure 4B is a cross-sectional view of a dancer roller assembly in an operational position according to an embodiment of the present invention; and

[0024] Figure 5 is a cross-sectional view of a dancer roller assembly having a spring-based seal according to an embodiment of the present invention. DETAILED DESCRIPTION

[0025] Overview

[0026] Embodiments of the present invention described below provide a device for applying controlled tension to a flexible member of a digital printing system to maintain the member taut. In some embodiments, the digital printing system includes a flexible intermediate transfer member (ITM), also referred to herein as a blanket, which is typically made of multiple layers of fabric. The ITM is configured to receive ink droplets from an image forming station for image formation thereon and to transfer the image to a target substrate (such as paper or a continuous web) at an imprinting station. Maintaining the ITM taut is important to prevent distortion during both image formation (on the ITM) and transfer (to the target substrate). In principle, a motorized dancer roller can be used to apply tension to the ITM. Such a dancer roller must be: (a) sufficiently stiff to maintain uniform tension across the ITM without deflection that would cause image distortion, and therefore such dancer rollers are typically heavyweight; and (b) sufficiently lightweight to compensate for high-frequency tension variations caused by vibrations that may occur in the ITM during the printing process. This trade-off can limit the performance envelope of printing processes performed on any type of flexible member.

[0027] In some embodiments, the digital printing system includes a device referred to herein as a floating roller assembly, which includes an air chamber and a lightweight roller mounted in the air chamber. The air chamber includes an inlet and an opening, the inlet and opening being sized and shaped to fit tightly onto the roller. The air floating roller includes a controllable air blower configured to supply pressurized air into the air chamber via the inlet. The pressurized air applies uniform pressure to the roller and causes the roller to move along the longitudinal axis of the air chamber. Thus, the roller can extend from the air chamber through the opening and apply tension to the ITM when rotated by the ITM. It is noted that applying a uniform force allows the use of a lightweight roller that provides (a) sufficiently high stiffness and (b) responsiveness to high-frequency vibrations.

[0028] In some embodiments, the dancer roller assembly includes a controller configured to receive a signal indicating a target tension to be applied to the ITM and, based on the signal, control the rotational speed of the air blower (typically measured in revolutions per minute (RPM)) to supply pressurized air at a controllable pressure. In such embodiments, the controller controls the air blower to cause the roller to supply pressurized air at a pressure that applies the target tension to the ITM.

[0029] In some embodiments, the air chamber further includes a seal coupled to the wall of the opening. In one embodiment, the seal contacts the roller; in another embodiment, the design of the floating roller assembly can incorporate an air gap between the seal and the roller. The seal is configured to maintain the pressurized air within the air chamber at a specified pressure. The seal is also configured to reduce or eliminate friction between the opening and the roller rotated by the ITM, for example, by providing the aforementioned air gap between the seal and the roller.

[0030] In some embodiments, the dancer roller assembly includes a pressure sensor configured to generate a pressure signal indicative of the air pressure within the air chamber. The processor can use the air pressure measurement to control the pressure applied to the pressurized air, for example, by sending a tension command including the aforementioned target tension to a controller. Additionally or alternatively, the dancer roller assembly can include a position sensor configured to generate a position signal indicative of the position of the roller relative to a predetermined reference point, such as an opening of the air chamber. The processor can use the position measurement to control the position of the air chamber, for example, by sending a target position signal to the controller.

[0031] In some embodiments, the pressurized air dancer roller assembly is configured to substantially isolate the ITM from mechanical vibrations occurring in the printing system. Furthermore, by controlling the air pressure, the dancer roller assembly is configured to maintain the ITM taut and help the ITM move at a specified speed as it passes adjacent to an image forming station and as it enters an imprinting station of the digital printing system.

[0032] In some cases, the ITM may experience high acceleration or deceleration, for example, due to stopping immediately while moving (e.g., at 1.7 m / s). In such cases, a heavy (e.g., 20 kg) floating roller assembly may apply excessive force to the ITM, potentially causing mechanical damage to the ITM. In some embodiments, the lightweight rollers may have a total weight of less than 500 grams, or any other suitable weight, and thus apply less than one-tenth the force applied by the heavy floating roller assembly.

[0033] The disclosed technology improves the image quality of digitally printed images, for example, by reducing image distortion caused by color-to-color and image-to-substrate registration errors. Improved registration is achieved by increasing the stability and uniformity of the tension applied to the ITM during the printing process.

[0034] System Description

[0035] Figure 1is a schematic side view of a digital printing system 10 according to an embodiment of the present invention. In some embodiments, the system 10 includes a rolling flexible blanket 44 that can be cycled between an image forming station 60, a drying station 64, an imprinting station 84, and a blanket handling 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 serves as an intermediate member configured to receive an ink image and transfer the ink image to a target substrate, as will be described in detail below.

[0036] In an operational mode, image forming station 60 is configured to form a mirror image of digital image 42 (also referred to herein as an "ink image" (not shown) or simply as an "image") on the upper run of 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 sheets or a continuous web) positioned beneath the lower run of blanket 44.

[0037] In the context of the present invention, the term "run" refers to the length or segment of blanket 44 between any two given rollers over which blanket 44 is guided.

[0038] In some embodiments, during installation, the blanket 44 may be adhered edge to edge to form a continuous blanket loop (not shown). Examples of methods and systems for installing seams are described in detail in U.S. Provisional Application 62 / 532,400, the disclosure of which is incorporated herein by reference.

[0039] In some embodiments, image forming station 60 generally includes a plurality of print bars 62, each of which is mounted (e.g., using slides) on a frame (not shown) that is positioned at a fixed height above the surface of the upper run of blanket 44. In some embodiments, each print bar 62 includes a printhead strip as wide as the print area on blanket 44 and includes individually controllable print nozzles.

[0040] In some embodiments, the image forming station 60 may include any suitable number of rods 62, each of which may contain a printing fluid, such as a different colored aqueous ink. The inks typically have visible colors such as, but not limited to, cyan, magenta, red, green, blue, yellow, black, and white. Figure 1 In the example of FIG. 5 , the image forming station 60 includes seven print bars 62 , but may include, for example, four print bars 62 of any selected color, such as cyan, magenta, yellow, and black.

[0041] In some embodiments, the printheads 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 .

[0042] In some embodiments, the various print bars 62 are spaced apart from one another along the axis of movement of the blanket 44, indicated by arrow 94. In this configuration, accurate spacing between the bars 62 and synchronization between the ink droplets directed from each bar 62 and the moving blanket 44 are critical to achieving proper placement of the image pattern.

[0043] In some embodiments, the system 10 includes a heater, such as a hot air or air blower 66 and / or an infrared (IR) heater and / or other suitable type of heater suitable for printing applications. Figure 1 In the example of FIG, air blower 66 is positioned between print bars 62 and is configured to partially dry ink droplets deposited on the surface of blanket 44. This flow of hot air between the print bars can, for example, help reduce condensation on the surface of the print head and / or deal with satellites (e.g., residue or small droplets distributed around the main ink droplets) and / or prevent clogging of the inkjet nozzles of the print head and / or prevent different color ink droplets on blanket 44 from undesirably merging with each other. In some embodiments, system 10 includes a drying station 64 that is configured to blow hot air (or another gas) onto the surface of blanket 44. In some embodiments, the drying station includes an air blower 68 or any other suitable drying device.

[0044] In the drying station 64, the ink image formed on the blanket 44 is exposed to radiation and / or hot air to more thoroughly dry the ink, causing most or all of the liquid vehicle to evaporate and leaving only a layer of resin and colorant that is heated to the point of becoming a viscous ink film.

[0045] In some embodiments, system 10 includes a blanket module 70 that includes a rolling ITM, such as blanket 44. In some embodiments, blanket module 70 includes one or more rollers 78, wherein at least one of rollers 78 includes an encoder (not shown) configured to record the position of blanket 44 in order to control the position of a segment of blanket 44 relative to a corresponding print bar 62. In some embodiments, the encoder of roller 78 typically includes a rotary encoder configured to generate a rotation-based position signal indicative of the angular displacement of the corresponding roller. It is noted that in the context of the present invention and in the claims, the terms "indicative of" and "indication" are used interchangeably.

[0046] Additionally or alternatively, blanket 44 may include an integrated encoder (not shown) for controlling the operation of the various modules of system 10. One embodiment of an integrated encoder is described in detail in U.S. Provisional Application No. 62 / 689,852, the disclosure of which is incorporated herein by reference.

[0047] In some embodiments, blanket 44 is guided over rollers 76 and 78 and a powered tensioning roller (also referred to herein as dancer assembly 74). Dancer assembly 74 is configured to control the length of slack in blanket 44, and its movement is schematically represented by a double-sided arrow. Furthermore, any stretching of blanket 44 with aging will not affect the ink image placement performance of system 10, and will simply require taking up more slack by tensioning dancer assembly 74.

[0048] In some embodiments, the floating roller assembly 74 may be motorized. The configuration and operation of rollers 76 and 78 are described in more detail, for example, in U.S. Patent Application Publication No. 2017 / 0008272 and PCT International Publication No. WO 2013 / 132424 mentioned above, the disclosures of which are incorporated herein by reference in their entireties. Figure 2-3 、 Figure 4A and Figure 4B Described in detail in.

[0049] In some embodiments, system 10 may include one or more tension sensors (not shown) disposed at one or more locations along blanket 44. The tension sensors may be integrated into blanket 44 or may include sensors external to blanket 44 that use any other suitable technique to acquire a signal indicative of the mechanical tension applied to blanket 44. In some embodiments, processor 20 of system 10 and an additional controller (e.g., in the following example) may be configured to control the tension of the blanket 44. Figure 2 and Figure 3 ) is configured to receive a signal generated by the tension sensor to monitor the tension applied to the blanket 44 and control the operation of the dancer roller assembly 74.

[0050] In the embossing station 84 , the blanket 44 passes between the impression cylinder 82 and a pressure cylinder 90 , which is configured to carry a compressible blanket.

[0051] In some embodiments, the system 10 includes a 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 imprinting stations, as will be described below.

[0052] In some embodiments, console 12 includes a processor 20 (typically a general-purpose computer) having a suitable front end and interface circuitry for interfacing with and receiving signals from a controller of dancer assembly 74 and controller 54 via cable 57. In some embodiments, controller 54, schematically shown as a single device, may include one or more electronic modules mounted at predefined locations on system 10. At least one of the electronic modules of controller 54 may include an electronic device, such as a control circuit or processor (not shown), configured to control the various modules and stations of system 10. In some embodiments, processor 20 and control circuitry may be programmed in software to perform functions used by the printing system, and data for the software may be stored in memory 22. The software may be downloaded to processor 20 and control circuitry in electronic form, for example, over a network, or it may be provided on non-transitory tangible media, such as optical, magnetic, or electronic storage media.

[0053] In some embodiments, console 12 includes a display 34 configured to display data and images received from processor 20, or input inserted by a user (not shown) using input device 40. In some embodiments, console 12 may have any other suitable configuration, for example, alternative configurations of 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.

[0054] In some embodiments, processor 20 is configured to display a digital image 42 on display 34 that includes one or more sections (not shown) of image 42 and / or various types of test patterns that may be stored in memory 22 .

[0055] In some embodiments, a blanket treatment station 52 (also referred to herein as a cooling station) is configured to treat the blanket by, for example, cooling the blanket and / or applying a treatment fluid to the outer surface of the blanket 44 and / or cleaning the outer surface of the blanket 44. At the blanket treatment station 52, the temperature of the blanket 44 may be reduced to a desired value before the blanket 44 enters the image forming station 60. The treatment may be performed by passing the blanket 44 over one or more rollers or blades configured to apply cooling and / or cleaning and / or treatment fluids to the outer surface of the blanket.

[0056] In some embodiments, in addition to Figure 1 In addition to or in lieu of the blanket handling station 52 shown in Figure 1, the blanket processing station 52 can be positioned adjacent to the image forming station 60. In such an embodiment, the blanket processing station can include one or more bars adjacent to the print bar 62, and the processing fluid is applied to the blanket 44 by spraying.

[0057] 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), in order to monitor the temperature of blanket 44 and control the operation of blanket processing station 52. Examples of such processing stations are described, for example, in PCT International Publications WO 2013 / 132424 and WO 2017 / 208152, the disclosures of which are incorporated herein by reference in their entireties.

[0058] Additionally or alternatively, the processing fluid may be applied to the blanket 44 by jetting prior to inkjetting at the image forming station.

[0059] exist Figure 1 In the example shown, station 52 is mounted between stamping station 84 and image forming station 60; however, station 52 may be mounted adjacent to blanket 44 at any other or additional suitable location(s) between stamping station 84 and image forming station 60. As described above, station 52 may additionally or alternatively include a bar adjacent to image forming station 60.

[0060] exist Figure 1 In the example of , the impression cylinder 82 impresses the ink image onto a target flexible substrate, such as a single sheet of paper 50 , which is transported by the substrate transport module 80 from an input stack 86 to an output stack 88 via the impression cylinder 82 .

[0061] In some embodiments, the lower run of the blanket 44 selectively interacts with the impression cylinder 82 at the impression station 84 to emboss the image pattern onto the target flexible substrate compressed between the blanket 44 and the impression cylinder 82 by the pressure of the pressure cylinder 90. Figure 1 In the case of a simplex printer (ie printing on one side of the sheet 50) as shown in FIG, only one embossing station 84 is required.

[0062] In other embodiments, module 80 may include two or more impression rollers to allow one or more duplex printings. The configuration of the two impression rollers also enables single-sided printing at twice the speed of printing duplex prints. In addition, mixed batches of single-sided and duplex prints can also be printed. In alternative embodiments, different configurations of module 80 can be used to print on a continuous web substrate. For example, detailed descriptions and various configurations of duplex printing systems and systems for printing on a continuous web substrate are provided in U.S. Patents 9,914,316 and 9,186,884, PCT International Publication WO 2013 / 132424, U.S. Patent Application Publication 2015 / 0054865, and U.S. Provisional Application 62 / 596,926, the disclosures of which are incorporated herein by reference in their entirety.

[0063] As briefly described above, paper 50 or a continuous web substrate (not shown) is carried by module 80 from an input stack 86 and passed through a nip (not shown) located between impression cylinder 82 and pressure cylinder 90. Within the nip, the surface of blanket 44 carrying the ink image is firmly pressed against the paper 50 (or other suitable substrate), for example, by a compressible blanket (not shown) of pressure cylinder 90, so that the ink image is impressed onto the surface of the paper 50 and neatly separated from the surface of blanket 44. The paper 50 is then transported to an output stack 88.

[0064] exist Figure 1 In the example shown, roller 78 is positioned at the upper run of blanket 44 and is configured to maintain tension on blanket 44 as it passes adjacent to image forming station 60. Furthermore, it is particularly important to control the velocity of blanket 44 beneath image forming station 60 in order to achieve accurate ink drop ejection and deposition to place an ink image on the surface of blanket 44 by image forming station 60.

[0065] In some embodiments, the impression cylinder 82 periodically engages and disengages the blanket 44 to transfer the 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 torque to the blanket 44 using the aforementioned roller and dancer roller assembly in order to keep the upper run taut and substantially isolate the upper run of the blanket 44 from mechanical vibrations occurring in the lower run.

[0066] In some embodiments, the system 10 includes an image quality control station 55 (also referred to herein as an automatic quality management (AQM) system) that serves as a closed-loop inspection system integrated into the system 10. In some embodiments, such as Figure 1 As shown, station 55 may be positioned adjacent to impression cylinder 82 , or at any other suitable location in system 10 .

[0067] In some embodiments, station 55 includes a camera (not shown) configured to capture one or more digital images of the aforementioned ink image printed on paper 50. In some embodiments, the camera can 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.

[0068] In some embodiments, station 55 may include a spectrophotometer (not shown) configured to monitor the quality of ink printed on paper 50 .

[0069] In some embodiments, the digital images captured by the station 55 are transmitted to a processor (such as processor 20 or any other processor of the station 55), which is configured to evaluate the quality of the corresponding printed image. Based on the evaluation and the signals received from the controller 54, the processor 20 is configured to control the operation of the modules and stations of the 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 the station 55) that is configured to process signals received from the camera and / or spectrophotometer of the station 55. It is noted that the signal processing operations, control-related instructions, and other computing operations described herein can be performed by a single processor or shared among multiple processors of one or more corresponding computers.

[0070] In some embodiments, the station 55 is configured to check the quality of the printed image and test pattern to monitor various attributes, such as, but not limited to, full image registration with the paper 50, color-to-color (C2C) registration, print geometry, image uniformity, color contours and linearity, and print nozzle functionality. In some embodiments, the processor 20 is configured to automatically detect geometric distortion or other errors in one or more of the aforementioned attributes. For example, the processor 20 is configured to compare a design version of a given digital image (also referred to herein as a "master" or "source image") with a digital image of a printed version of the given image acquired by a camera.

[0071] In other embodiments, processor 20 may apply any suitable type of image processing software to, for example, a test pattern to detect distortions indicative of the aforementioned errors. In some embodiments, processor 20 is configured to analyze the detected distortions to apply corrective action to the faulty module and / or to feed instructions to another module or station of system 10 to compensate for the detected distortions.

[0072] In some embodiments, processor 20 is configured to detect deviations from profile and linearity of printed colors based on signals received from the spectrophotometer of station 55 .

[0073] In some embodiments, the processor 20 is configured to detect the following types of defects based on the signals obtained by the station 55: (i) defects in the substrate (e.g., the blanket 44 and / or the paper 50), such as scratches, pinholes, and chipped edges; and (ii) printing-related defects, such as irregular color spots, satellites, and bright blocks.

[0074] In some embodiments, the processor 20 is configured to detect these defects by comparing the printed sections with corresponding reference sections of the original design (also referred to herein as a master). The processor 20 is also configured to classify the defects and, based on the classification and predefined criteria, reject paper 50 having defects that are not within the specified predefined criteria.

[0075] In some embodiments, the processor of station 55 is configured to, for example, decide whether to stop operation of system 10 if the defect density is above a specified threshold. The processor of station 55 is also configured to initiate corrective action in one or more of the modules and stations of system 10, as described above. The corrective action can be performed in real time or offline (while system 10 continues the printing process) by stopping printing operations and resolving the problem in the corresponding module and / or station of system 10. In other embodiments, any other processor or controller of system 10 (e.g., processor 20 or controller 54) is configured to initiate corrective action or stop operation of system 10 if the defect density is above a specified threshold.

[0076] Additionally or alternatively, the processor 20 is configured to receive signals, for example from the station 55, indicating additional types of defects and problems in the printing process of the system 10. Based on these signals, the processor 20 is configured to automatically estimate the level of pattern placement accuracy and additional types of defects not mentioned above. In other embodiments, any other suitable method for inspecting the pattern printed on the paper 50 (or any other substrate described above) may also be used, such as using an external (e.g., offline) inspection system or any type of measurement fixture and / or scanner. In these embodiments, based on the information received from the external inspection system, the processor 20 is configured to initiate any suitable corrective action and / or cease operation of the system 10.

[0077] To illustrate the present invention, the configuration of system 10 is simplified and provided purely by way of example. For example, the components, modules, and stations described in the printing system 10 above, as well as additional components and configurations, are described in detail in U.S. Patents 9,327,496 and 9,186,884, PCT International Publications WO 2013 / 132438, WO 2013 / 132424, and WO 2017 / 208152, and U.S. Patent Application Publications 2015 / 0118503 and 2017 / 0008272, the disclosures of which are incorporated herein by reference in their entirety.

[0078] The specific configuration of system 10 is shown by way of example in order to illustrate certain problems solved by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such systems. However, embodiments of the present invention are by no means limited to this particular type of exemplary system, and the principles described herein may be similarly applied to any other type of printing system.

[0079] Uses a fluid-based dancer assembly to apply tension to the blanket

[0080] Figure 2 1 is a block diagram schematically illustrating a floating roller assembly 100 according to an embodiment of the present invention. The floating roller assembly 100 may be used to implement, for example, the above Figure 1 The floating roller assembly 74. Figure 2 In the example of FIG. 1 , dancer assembly 100 is shown in two different positions: (a) a blanket mounted position, also referred to herein as a first position or home position, and (b) an operating position, also referred to herein as a second position. Note that system 10 may have additional positions such as a standby position, which are not shown in FIG. Figure 2 , but described below.

[0081] In some embodiments, dancer roller assembly 100 includes a fluid chamber, referred to herein as chamber 103, having a longitudinal axis, referred to herein as axis 115. In some embodiments, chamber 103 includes a housing 102 and an inlet 107 configured to receive a pressurized fluid (in this example, pressurized air 130) into fluid chamber 103 via an inlet tube 132. In other embodiments, the pressurized fluid can include any suitable gas, or any suitable liquid, or any suitable combination thereof.

[0082] In some embodiments, dancer roller assembly 100 includes a rotatable element, in this example a roller 111 having a circular cross-section, which fits within fluid chamber 103. In other embodiments, the rotatable element may include one or more balls, rollers having any cross-section other than circular, or any other suitable element adapted to be rotated by blanket 44, as will be described below.

[0083] In some embodiments, the rotatable element (e.g., roller 111) is made of any suitable lightweight material, such as, but not limited to, carbon (e.g., carbon fiber) and rigid foam including polymethacrylimide (PMI), commercially known as PTFE provided by Evonik industries (Essen, Germany). In some embodiments, the rigid foam can be formed into roller 111 using a lightweight shrinkable sleeve comprising perfluoroalkoxyalkane (PFA) or any other suitable material formed into a tube to contain the rigid foam and protect the foam surface from wear, moisture, and reduce friction.

[0084] As will be described in detail below, roller 111 is moved by pressurized air, which applies a linear force that is evenly distributed along the surface of roller 111. Accordingly, roller 111 may comprise a lightweight material having low friction, allowing dancer roller assembly 100 to be configured to apply a stable tension (e.g., 700 N + / - 5 N) to blanket 44, as will be described below. As will be described in detail below, the tension applied to blanket 44 by roller 111 depends on the dimensions of roller 111, such as its length and diameter, and the pressure applied to roller 111 by the pressurized air.

[0085] In some embodiments, chamber 103 includes an opening 105 that is sized and shaped to fit snugly over roller 111. In an operating position, which will be described in detail below, pressurized air 130 causes roller 111 to extend from chamber 103 through opening 105 and apply a predefined and controllable tension to blanket 44 as it is rotated.

[0086] In some embodiments, dancer roller assembly 100 includes a position sensing assembly 112 configured to sense and generate electrical signals (also referred to herein as position signals) indicating the position of roller 111 relative to any suitable reference point such as, but not limited to, opening 105 or any type of motion limiter (hereinafter referred to as a position signal). Figure 3 The position sensing assembly 112 may include an optically based position sensor having an optical fiber (shown in the following Figure 3 ) or any other suitable type of position sensor.

[0087] In other embodiments, position sensing assembly 112 may be mounted at any other location on dancer roller assembly 100 suitable for sensing the position of roller 111 .

[0088] In some embodiments, the dancer roller assembly 100 includes a fluid compressor, in this example an air blower (also referred to herein as blower 104), configured to supply pressurized air 130 into the chamber 103 via the inlet 107. In other embodiments, the dancer roller assembly 100 can include any other suitable type of fluid compressor configured to apply pressure to any of the aforementioned types of fluids.

[0089] In some embodiments, dancer roller assembly 100 includes a pressure sensor 114 configured to sense the pressure of pressurized air 130 in chamber 103 and send an electrical signal (also referred to herein as a pressure signal) to processor 20 indicative of the sensed pressure.

[0090] In some embodiments, dancer assembly 100 includes a controller 106 configured to receive a tension command 110, for example, from processor 20. Tension command 110 includes an electrical signal indicating a predefined tension (also referred to herein as a target tension) to be applied to blanket 44. Controller 106 is further configured to receive a pressure signal generated by pressure sensor 114 via cable 113. In some embodiments, controller 106 can include a proportional-integral-derivative (PID) controller having a control loop feedback mechanism and a driver (not shown) configured to drive blower 104.

[0091] Reference is now made to the operating position. In some embodiments, roller 111 is in physical contact with blanket 44 (as described in detail below), and pressurized air 130 applies a force to roller 111. In response, roller 111 moves through opening 105 toward blanket 44 in the direction indicated by double-headed arrow 166.

[0092] exist Figure 2 In the exemplary embodiment shown in the operational position of FIG, chamber 103 is designed such that, in response to the force applied by pressurized air 130, roller 111 moves along double-headed arrow 166 parallel to axis 115. In one embodiment, when in physical contact with blanket 44, roller 111 applies tension, referred to herein as "roller tension," to blanket 44.

[0093] In some embodiments, at a point of contact (POC) 117 between blanket 44 and roller 111, the direction of movement of roller 111 along axis 115 is generally orthogonal to the axis of movement of blanket 44, indicated by arrow 94. Note that blanket 44 and roller 111 may have a contact surface greater than a single point, such as POC 117 (as indicated below). Figure 4BThus, POC 117 can be defined as the center of the segment of blanket 44 that is in physical contact with roller 111, or in other words, the center of the wrap angle. In other embodiments, the direction of movement of roller 111 at POC 117 can be at any other suitable angle relative to blanket 44.

[0094] For conceptual clarity, the illustrated shape of chamber 103 is simplified and shown by way of example. In alternative embodiments, chamber 103 may have any other suitable design such that roller 111 or any other suitable type of rotatable element may move in any suitable linear or nonlinear trajectory in response to the force applied by pressurized air 130.

[0095] In some embodiments, dancer roller assembly 100 includes closed-loop control of roller tension using controller 106, blower 104, and pressure sensor 114, also referred to herein as a "pressure loop," as will be described herein.

[0096] In some embodiments, controller 106 is configured to calculate the roller tension applied to blanket 44 based on the pressure signal received from pressure sensor 114. Controller 106 is further configured to compare the roller tension with a target tension, which is received from processor 20 in tension command 110. Based on the comparison, controller 106 is configured to adjust the roller tension by controlling the rotational speed of the shaft and blades of blower 104. In other words, controller 106 is configured to determine a target pressure to be applied to roller 111 by pressurized air 130 based on the target tension.

[0097] For example, when the target tension is greater than the roller tension, controller 106 sends a control signal to blower 104 to increase the rotational speed of the blower's shaft and blades, thereby increasing the air pressure, resulting in an increase in the roller tension applied by the movement of roller 111 toward blanket 44. When the roller tension matches the target tension, controller 106 commands blower 104 to maintain the rotational speed in order to keep the target tension and roller tension matched. In this position, roller 111 does not move along arrow 166, but rather, the blanket 44 rotates about its own axis, causing the blanket to move along the aforementioned blanket movement axis, indicated by arrow 94.

[0098] In other embodiments, processor 20 is configured to control blower 114 based on the pressure signal received from pressure sensor 114 to match the current pressure of pressurized air 130 in chamber 103 to a target pressure.

[0099] In some embodiments, dancer roller assembly 100 is configured to absorb shock caused by any non-linear motion along blanket 44 and to keep blanket 44 taut as it passes adjacent image forming station 60 and upon entering impression station 84 .

[0100] Note that when system 10 is in the aforementioned standby position (eg, between print jobs), blanket 44 does not move, but dancer assembly 100 generally remains in the operative position to keep blanket 44 taut.

[0101] In some cases, it may be necessary to replace blanket 44 and / or install a new blanket 44 in system 10. In some embodiments, controller 106 instructs blower 104 to reduce the pressure of pressurized air 130 in order to reduce the roller tension to a value less than the target tension. In response to the reduced pressure of pressurized air 130, roller 111 retracts into fluid chamber 103 and has a significantly smaller extension from chamber 103 via opening 105. In other embodiments, roller 111 may be completely contained within chamber 103 and not extend through opening 105.

[0102] In some embodiments, the dancer assembly 100 includes a motor 120, such as a stepper motor coupled to a gear having, for example, an 80:1 ratio or any other suitable ratio. Alternatively, the dancer assembly 100 can include any other suitable type of motor or motion assembly with or without gears. The motion assembly can include control-enabling features such as, but not limited to, an encoder.

[0103] In some embodiments, dancer assembly 100 further includes a motor controller, referred to herein as controller 122, that is configured to receive the position signal generated by position sensing assembly 112 via cable 109. Controller 122 may include a PID controller having any suitable type of control loop feedback mechanism, and a driver (not shown) configured to drive motor 120.

[0104] In some cases, movement of the blanket 44 (e.g., during the printing process) may cause vibrations that may affect the target tension applied to the blanket in the operating position. Figure 1 As described in , the impression station 84 periodically engages and disengages between the blanket 44 and the impression cylinder 82, which may contribute to the aforementioned vibrations.

[0105] In some embodiments, controller 106 is configured to maintain pressure to position roller 111 at a given position that applies a desired tension to blanket 44. In response to changes in the tension applied to blanket 44 by any component of system 10 (except dancer roller assembly 100), roller 111 moves relative to the given position to compensate for the change in tension. For example, in response to vibrations in system 10, roller 111 may move with an amplitude of approximately 0.8 mm every 20 milliseconds to compensate for the vibrations.

[0106] In other embodiments, the controller 106 is configured to oscillate the roller 111 within a predefined interval (e.g., 0.3 mm-0.8 mm) at an exemplary frequency of 40 Hz (or any other suitable frequency) to maintain a constant tension applied to the blanket 44, thereby compensating for any vibrations occurring in the blanket 44. This vibration compensation mechanism can reduce the need to move the entire structure of the chamber 103 at a relatively high frequency. In such embodiments, the controller 122 also includes (or is electrically coupled to) a circuit (not shown) that can act as a low-pass (LP) filter for the target position signal 128 received from the processor 20.

[0107] In some embodiments, dancer roller assembly 100 includes closed-loop control of the position of chamber 103 using controller 122 and motor 120, also referred to herein as a "position loop," as will be described herein.

[0108] Reference is now made to the blanket mounting position. In some embodiments, motor 120 is physically coupled to chamber 103 via arm 108 and is configured to move chamber 103 in the direction indicated by double-headed arrow 133. Figure 2 In the example of FIG, motor 120 is configured to move chamber 103 in an arc motion as indicated by arrow 133. The speed of the arc motion can be controlled by controller 122 using any suitable speed (such as in the range of 3 cm / s-5 cm / s) and depends on the arc radius determined by the length of arm 108 (e.g., 63 cm). The speed of motion along arrow 133 can be constant or can vary with distance from blanket 44.

[0109] In other embodiments, chamber 103 can be moved by any suitable motion assembly using any other suitable motion profile (eg, linear).

[0110] exist Figure 2In the example shown, the blower 104 and controller 106 move along with the chamber 103, the position sensing assembly 112, and the sensor 114. In an alternative embodiment, the motor 120 may move only the chamber 103, the position sensing assembly 112, and the sensor 114, while at least one of the inlet tube 132 and the cable 113 is sufficiently long and flexible to maintain the other parts, such as the blower 104 and the controller 106, in their schematically shown respective positions in the blanket mounted position.

[0111] Note that by having the position loop and pressure loop described above, processor 20 is configured to separately control the coarse and fine movements of roller 111 relative to blanket 44. In other words, the position loop moves chamber 103 and roller 111 as rigid bodies relative to blanket 44, and the pressure loop only adjusts the position of roller 111 relative to blanket 44.

[0112] As described above, roller 111 is made of a lightweight material, such as a rigid PMI-based foam contained in a PFA-based tube. The lightweight nature of roller 111 can prevent mechanical damage to blanket 44 in the event of high acceleration or deceleration of blanket 44. For example, in the event of an emergency stop of blanket 44 moving at an exemplary speed of 1.7 m / s, or at any other speed suitable for digital printing.

[0113] In some embodiments, the light weight of roller 111 results in low inertia, so dancer roller assembly 100 can apply stable tension to blanket 44 even when blanket 44 experiences high acceleration or deceleration, such as when rubber portion 44 has an unexpected, immediate stop.

[0114] In such embodiments, the mass of roller 111 is proportional to the force applied to blanket 44. In the aforementioned immediate stop scenario, a sufficiently large mass of roller 111 (e.g., several kilograms) can apply a sufficiently large force to blanket 44 that can cause mechanical damage, such as deformation and / or tearing thereof.

[0115] Typically, at least one of the controllers 106 and 122 comprises a general purpose controller that is programmed with software to perform the functions described herein. For example, the software may be downloaded to the controller electronically over a network, or additionally or alternatively, the software may be provided and / or stored on non-transitory tangible media such as magnetic, optical, or electronic memory.

[0116] For conceptual clarity, Figure 2The detailed block diagram of dancer roller assembly 100 shown in FIG is simplified. Furthermore, this configuration is depicted by way of example only, in order to illustrate certain issues addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such digital printing systems having ITMs. However, embodiments of the present invention are by no means limited to this particular type of exemplary configuration, and in alternative embodiments, dancer roller assembly may include any additional or alternative suitable elements to apply a specific tension to blanket 44.

[0117] In alternative embodiments, processor 20 may include or replace at least one of controllers 106 and 122. In such embodiments, processor 20 is configured to: (a) receive a pressure signal generated by pressure sensor 114 and drive blower 104 to achieve a target pressure, such as described in the operating position, and / or (b) receive a position signal generated by position sensing assembly 112 and drive motor 120 to move chamber 103 to any suitable position described above. Note that in these embodiments, processor 20 may maintain a threshold value indicative of a target tension, or may receive an electrical signal indicative of a target tension.

[0118] Figure 3 is a schematic illustration of a floating roller assembly 100 according to an embodiment of the present invention. In some embodiments, the floating roller assembly 100 includes the above Figure 2 The blower 104, inlet pipe 132, chamber 103, roller 111 and motor 120 are depicted in detail.

[0119] exist Figure 3 In the example of FIG. 1 , the inlet duct 132 is configured to flow pressurized air 130 between the blower 104 and the chamber 103 at an exemplary temperature of 25° C., or at any other suitable temperature, such as the temperature of the blanket 44 at the stamping station 84. The temperature can be controlled, for example, by measuring and heating or cooling the pressurized air, or the air can flow at room temperature without heating or cooling the air. In addition, the inlet duct 132 may include a rigid structure such that the blower 104, the inlet duct 132, and the chamber 103 are moved as a single rigid body by the motor 120, as described above. Figure 2 As described in.

[0120] Reference is now made to illustration 150. In some embodiments, the position sensing assembly 112 and the pressure sensor 114 are coupled to the chamber 103. The position sensing assembly 112 includes any suitable number of optical fibers 127 configured to transmit an optical signal from a light source (not shown) to impinge on the surface of the roller 111 and subsequently be sensed by the position sensor (not shown), as described above. Figure 2 As described in.

[0121] Reference is now made to illustration 125. In some embodiments, the floating roller assembly 100 includes a motion limiter 126 having a groove around a bearing 124 coupled to a shaft (not shown) of the roller 111. The motion limiter 126 is configured to limit lateral movement of the roller 111 along an axis 129. Figure 3 In an example, roller 111 is retracted into fluid chamber 103, such as when dancer roller assembly 100 is in the blanket mounted position.

[0122] In some embodiments, before moving to the Figure 2 , processor 20 activates the pressure circuit by sending a tension command 110 to controller 106 to increase the pressure of air 130. The increased pressure of air 130 causes roller 111 to move laterally along axis 129 in the direction indicated by arrow 131 until bearing 124 enters edge 134 of the groove of motion limiter 126 and stops lateral movement in the direction of arrow 131.

[0123] In some embodiments, position sensing assembly 112 sends a position signal to controller 106 indicating that bearing 124 is in physical contact (or close proximity) with edge 134, and controller 106 sends a signal to processor 20 indicating the position of bearing 124. In response to receiving the signal from controller 106, processor 20 activates the position loop by sending a target position signal 128 to controller 122, which commands motor 120 to move at least chamber 103 to the operating position. When roller 111 is in physical contact with blanket 44, roller 111 typically retracts into chamber 103, causing bearing 124 to move in a direction opposite to arrow 131.

[0124] In some embodiments, the position sensing assembly 112 sends a position signal to the controller 106 indicating that the roller 111 has retracted, and in response, the controller 106 operates the pressure circuit until the target tension and the roller tension match. At this point, the blanket 44 is ready to begin the above Figure 1 The digital printing process described in .

[0125] In alternative embodiments, the position sensing component 112 may be based on any other suitable sensing technology, such as, but not limited to, ultrasound, confocal wavelength, triangulation surface, mechanical probing, magnetic, and reflected power.

[0126] This particular configuration of dancer roller assembly 100 is shown by way of example to illustrate certain issues addressed by embodiments of the present invention and to demonstrate the application of these embodiments to enhance the performance of such systems. However, embodiments of the present invention are by no means limited to this particular type of exemplary dancer roller assembly, and the principles described herein can similarly be applied to other types of devices for stretching any type of media and / or for maintaining such media taut. The disclosed technology can be applied to any suitable type of printing system or flexible conveyor for use in a material transfer system.

[0127] Figure 4A is a cross-sectional view of dancer roller assembly 100 in a blanket mounted position according to an embodiment of the present invention. In some embodiments, chamber 103 is moved away from blanket 44 by motor 120 and arm 108 so that roller 111 is not in physical contact with blanket 44.

[0128] Reference is now made to illustration 180. In some embodiments, chamber 103 includes an inlet 107 configured to allow pressurized air 130 to flow into chamber 103 at any suitable temperature (e.g., 25°, 40°), as described above. Figure 2 The chamber 103 also includes an inner wall 163 of the housing 102 .

[0129] In some embodiments, when dancer roller assembly 100 is in the blanket mounted position, blower 104 does not blow pressurized air 130 into chamber 103. Thus, the surface of roller 111 is in contact with inner wall 163, or within a distance 161 from the inner wall.

[0130] In some embodiments, the floating roller assembly 100 includes one or more sealing elements, referred to herein as seals 170, coupled to the inner wall 163 at the opening 105 or disposed between the opening 105 and the roller 111 using any suitable technique. In some embodiments, the seal 170 can include any suitable material, such as, but not limited to, a sponge made of polyester and an ultra-high molecular weight (UHMW) polyethylene tape bonded to the surface of the sponge. In some embodiments, the seal 170 is configured to retain the pressurized air 130 within the chamber 103 and to reduce or eliminate friction between the roller 111 and the housing 102, as will be described below. Figure 4B Described in .

[0131] Figure 4B is a cross-sectional view of chamber 103 and roller 111 in an operating position according to an embodiment of the present invention. Figure 2 As described in , when the pressure circuit is activated, the blower 104 increases the pressure of the air 130 flowing into the chamber 103 so as to match between the target tension and the roller tension.

[0132] In some embodiments, pressurized air 103 applies a force to roller 111, which is represented by arrow 162. Note that pressurized air 130, or any other suitable fluid, is used to apply a uniform force across the surface of roller 111. The uniform force prevents warping or any other deformation of roller 111 and maintains uniform tension on blanket 44. In such embodiments, roller 111 (which may have an exemplary diameter of approximately 62 mm, or any other suitable diameter) may have an exemplary weight between 250 grams and 450 grams, or any other suitable weight.

[0133] As described above, the lower mass of roller 111, or any rotatable element, allows for higher relative accelerations or decelerations of roller 111 without causing mechanical damage to blanket 44. Furthermore, by having a lower mass of roller 111, dancer assembly 100 can achieve higher accelerations of roller 111 under a constant pressure or force applied thereto. A motorized dancer roller with gears can weigh approximately 25 kg, which can maintain the same tension as a heavy roller to prevent significant deflection. Thus, based on the exemplary weights of the present invention, dancer assembly 100 can accelerate roller 111 at approximately 78 times higher accelerations without causing any deflection of roller 111.

[0134] In some embodiments, pressurized air 130 moves roller 111 in the direction of arrow 166 to extend further from opening 105. Figure 4B As shown, in response to the increased pressure of the air 130, the distance 161 between the outer surface of the roller 111 and the inner wall 163 increases and is greater than Figure 4A The distance 161 in the blanket mounted position is shown.

[0135] In some embodiments, seal 170 is configured to maintain pressurized air 130 at a predefined pressure within chamber 103, the predefined pressure having an exemplary pressure range between about 10 kPa and about 15 kPa. In one embodiment, when the predefined pressure is relatively low within the range (e.g., about 11 kPa or 12 kPa), seal 170 is correspondingly separated from roller 111, and some pressurized air 130 leaks between roller 111 and seal 170, so as to prevent friction between seal 170 and rotating roller 111 and still maintain the predefined pressure of pressurized air 130 within chamber 103. In another embodiment, when the predefined pressure is relatively high (e.g., about 14KPa or 14.5KPa), the seal 170 is still separated from the roller 111 (i.e., there is an air gap), and a larger amount of pressurized air 130 leaks between the roller 111 and the seal 170 so as to maintain (i) zero friction between the seal 170 and the rotating roller 111, and (ii) the predefined pressure. It should be noted that the aforementioned pressure values ​​are provided by way of example, and in other embodiments, any other suitable pressure or pressure range may be used. In addition, the maximum pressure that can be generated in the event of higher leakage depends on the specifications of the blower 104 (e.g., the flow-pressure curve). Therefore, when the blower 104 is running at full power, the maximum pressure of the pressurized air 130 in the chamber 103 is generally obtained, and this maximum pressure depends on the type and configuration of the seal 170.

[0136] In some embodiments, seal 170 is further configured to reduce or eliminate friction between roller 111 and inner wall 163 of opening 105 when blanket 44 rotates roller 111 in the operating position. In one embodiment, seal 170 contacts roller 111, and in another embodiment, the design of dancer roller assembly 100 can incorporate an air gap between seal 170 and roller 111 to reduce or eliminate friction between roller 111 and inner wall 163 of opening 105.

[0137] In the configuration of dancer roller assembly 100, the force applied to blanket 44 is determined by multiplying the length and diameter of roller 111 by the pressure in the fluid chamber. In the exemplary embodiment, a 62 mm diameter and 1177 mm length of roller 111 and air 130 at a pressure of approximately 10 kPa apply an exemplary prescribed force of 700 N to blanket 44. The resulting tension applied to blanket 44 is determined by the contact surface between roller 111 and blanket 44, which corresponds to a predefined wrap angle 165 (e.g., 70°).

[0138] As above Figure 2As described in detail in the accompanying drawings, the dancer roller assembly 100, which is based on pressurized air 130 or any other suitable fluid, is configured to absorb shock caused by any nonlinear motion along the blanket 44. In some embodiments, the fluid-based dancer roller assembly is configured to substantially isolate the upper run of the blanket 44 from mechanical vibrations occurring in the lower run of the blanket 44. In other words, the dancer roller assembly 100 is configured to dampen at least some of the undesirable mechanical vibrations generated during operation of the system 10. Thus, the dancer roller assembly 100 is configured to keep the blanket 44 taut and help the blanket 44 move at a specified speed as it passes near the image forming station 60 and when entering the impression station 84.

[0139] Furthermore, the light weight of the roller 111 can prevent mechanical damage to the blanket 44 in the event of high acceleration or deceleration of the blanket 44, as described above. Figure 2 Described in detail in .

[0140] Figure 5 is a cross-sectional view of a dancer roller assembly 100 having a spring based seal (SBS) 177 according to an embodiment of the present invention.

[0141] In some embodiments, the floating roller assembly 100 includes an SBS 177 that is coupled to the inner wall 163 rather than the above Figure 4A and Figure 4B The seal 170 shown in FIG. Figure 5 In the example of FIG. 1 , the SBS 177 is disposed between the inner wall 163 of the housing 102 and the roller 111 .

[0142] Reference is now made to illustration 182 showing the detailed structure of SBS 177. In some embodiments, SBS 177 includes a leaf spring (LS) 188, which is typically made of stainless steel (SS) such as SS 301 alloy or any other suitable material and has a thickness of about 0.2 mm or any other suitable thickness.

[0143] In the context of the present disclosure and claims, the term "about" or "substantially" as used with respect to any numerical value or range of numerical values ​​indicates that suitable dimensional tolerances are allowed for a part or assembly of components, or a physical parameter such as thickness, to function for its intended purpose as described herein. More specifically, the term "about" or "approximately" may refer to a range of values ​​of ±20% of the stated value, for example, "about 90%" may refer to a range of values ​​of 71% to 99%.

[0144] In some embodiments, LS 188 includes sections 189 and 190, wherein section 189 is coupled to inner wall 163 of housing 102 (at Figure 51 and 163, and segment 190 is bent at a bend angle α relative to a dashed line 185, which extends from segment 189 and indicates a plane defined by segment 189 and inner wall 163. In this example, angle α has a nominal value of approximately 15 degrees with a tolerance of approximately ±0.5 degrees, but in other embodiments, angle α may have any other suitable angle with any other suitable tolerance.

[0145] In some embodiments, the SBS 177 includes a layer 184 coupled to a section 190 of the LS 188 and configured to retain the pressurized air 130 within the chamber 103 and reduce or eliminate friction between the roller 111 and the housing 102 .

[0146] In some embodiments, layer 184 comprises a polyurethane foam such as 4701-30, also referred to herein as a sponge, has a thickness of about 1 mm or any other suitable thickness. In other embodiments, layer 184 can include one or more sub-layers made of any other material suitable for retaining pressurized air 130 within chamber 103 and for reducing friction between roller 111 and layer 184.

[0147] In some embodiments, SBS 177 includes a tape 186 that is bonded to layer 184 and comprises a UHMW polyethylene tape or polytetrafluoroethylene (PTFE), also known as Teflon. TM , or any other material suitable for retaining pressurized air 130 within chamber 103 and for reducing friction between roller 111 and housing 102 .

[0148] In some embodiments, during operation of the floating roller assembly 100, in response to the application of increased pressurized air 130, the roller 111 moves in a direction 191 toward a distal end 198 of the SBS 177 and the segment 190 bends in a direction 192 that decreases the angle α. Similarly, when the pressure of the pressurized air 130 is decreased, the roller 111 moves in a direction 193 toward a proximal end 196 of the SBS 177 and the segment 190 bends in a direction 194 that increases the angle α.

[0149] In some embodiments, when dancer roller assembly 100 operates at a predefined (i.e., constant) pressure of pressurized air 130 within chamber 103, and the tension applied to blanket 44 fluctuates or changes to a different constant tension during operation of system 10, roller 111 is configured to move in direction 191 or 193 in response to the change in tension. For example, when roller 111 moves in direction 191, a larger portion of segment 190 is exposed to pressurized air 130, causing segment 190 to bend in direction 192 and thereby reduce angle α, and vice versa, when roller 111 moves in direction 193 in response to a change in tension applied to blanket 44, causing segment 190 to bend in direction 194 and thereby increase angle α. It is noted that, based on the above-described mechanism, when roller 111 moves in direction 191 or 193, floating roller assembly 100 is configured to maintain: (i) a predefined pressure of pressurized air 130 within chamber 103, and (ii) the aforementioned air gap between seal 170 and roller 111 so as to eliminate any friction between seal 170 and rotating roller 111.

[0150] In some embodiments, a point 195 indicating the closest proximity between roller 111 and strip 186 of SBS 177 moves with the movement of roller 111. Note that when pressurized air 130 is applied, roller 111 and strip 186 are not in physical contact with each other at point 195 and typically maintain a distance of approximately 0.2 mm from each other, which allows the aforementioned specified pressure of pressurized air to be maintained within chamber 103 and prevents or reduces friction between roller 111 and layer 184. In other words, in response to changes in the pressure of pressurized air 130, segment 190 moves relative to roller 111 such that strip 186 is positioned at the aforementioned distance from the outer surface of roller 111 (or at any other suitable settable distance). By preventing friction, the disclosed technology prevents corrosion of at least one of strip 186 and roller 111 while roller 111 is rotating. In the absence of pressurized air 130 or a pressure less than or equal to a predefined pressure level, roller 111 generally does not rotate about its axis, in which case roller 111 and strip 186 may be in physical contact with each other at point 195 .

[0151] In some embodiments, based on the flexibility of the LS 188, the SBS 177 is configured to operate under a wide range of pressurized air 130, such that the rollers 111 or the strip 186 do not corrode when low pressure is applied, and a specified air leakage and pressure are maintained even at increased pressures of the air 130. Furthermore, the disclosed technology enables continuous operation and working conditions at different levels of pressurized air 130 by moving the rollers 111 and the segments 190 relative to each other.

[0152] The above configurations and specific dimensions and pressures are depicted by way of example only. In alternative embodiments, dancer assembly 100 and chamber 103 may have any other suitable configurations and dimensions and may operate using any other suitable specified conditions.

[0153] Although the embodiments described herein primarily relate to digital printing using flexible ITMs, the methods and systems described herein may also be used in other applications, such as for digital printing by applying ink directly to a flexible target substrate (e.g., by jetting), for controlling tension applied to any type of flexible member, and for any system that includes a conveyor with a flexible media, such as for use in the machinery and / or food industries.

[0154] It will therefore be understood that the embodiments described above are cited by way of example, and the present invention is not limited to what has been specifically shown and described above. On the contrary, the scope of the present invention includes both the combination and sub-combination of the various features described above, as well as variations and modifications thereof that occur to those skilled in the art after reading the foregoing description and that are not disclosed in the prior art. The documents incorporated by reference into this patent application are considered to be an integral part of this application, except that with respect to any definition of any term in these incorporated documents that conflicts with the definition explicitly or implicitly in this specification, only the definition in this specification should be considered.

Claims

1. A digital printing system, comprising: a flexible intermediate transfer member configured to receive ink droplets from an ink supply system to form an image on the flexible intermediate transfer member and transfer the image to a target substrate; as well as A floating roller assembly, the floating roller assembly comprising a fluid chamber and a rotatable element mounted in the fluid chamber, the fluid chamber including an inlet configured to receive a pressurized fluid into the fluid chamber, wherein the pressurized fluid causes the rotatable element to move relative to the fluid chamber and apply tension to the flexible intermediate transfer member when rotated by the flexible intermediate transfer member; an opening sized and shaped to fit over the rotatable element, wherein the pressurized fluid causes the rotatable element to extend from the fluid chamber through the opening; as well as A seal is coupled to the opening and is configured to retain the pressurized fluid within the fluid chamber when the pressure of the pressurized fluid is less than or equal to a predefined pressure, and to release at least a portion of the pressurized fluid out of the fluid chamber when the pressure exceeds the predefined pressure.

2. A digital printing system according to claim 1, and comprising a processor configured to control the movement of the rotatable element, comprising: selecting between at least a first position and a second position of the dancer roller assembly; in said first position, moving at least said fluid chamber relative to said flexible intermediate transfer member; as well as In the second position, at least the rotatable element is moved relative to the fluid chamber.

3. A digital printing system according to claim 1 or claim 2, and comprising a fluid compressor configured to supply the pressurized fluid into the fluid chamber through the inlet.

4. A digital printing system according to claim 3, and comprising a processor configured to: (a) calculate a target pressure based on an indication of the tension applied to the flexible intermediate transfer member, the target pressure causing the rotatable element to apply the tension to the flexible intermediate transfer member when applied to the pressurized fluid, and (b) control the fluid compressor to supply the pressurized fluid at the target pressure into the fluid chamber.

5. A digital printing system according to claim 4, and comprising a pressure sensor configured to generate a pressure signal indicative of a current pressure of the pressurized fluid in the fluid chamber, wherein the processor is configured to control the fluid compressor based on the pressure signal to match the current pressure with the target pressure.

6. The digital printing system of claim 4, wherein the pressurized fluid comprises pressurized air, and wherein the fluid compressor comprises an air blower configured to supply the pressurized air.

7. The digital printing system of claim 1, further comprising a position sensing assembly configured to generate a position signal indicative of a position of the rotatable element relative to a predetermined reference point.

8. A digital printing system according to claim 7, and comprising a processor, wherein the processor is configured to perform at least one of the following items based on the position signal: (a) control a motor to move at least the fluid chamber relative to the flexible intermediate transfer member, and (b) control a fluid compressor to move at least the rotatable element along the axis of the fluid chamber by controlling the pressure of the pressurized fluid.

9. A digital printing system according to claim 1 or claim 2, wherein the rotatable element comprises a roller.

10. The digital printing system of claim 2, further comprising a motor configured to move at least the fluid chamber relative to the flexible intermediate transfer member, and wherein at least in the first position, the processor is configured to control the motor to move at least the fluid chamber relative to the flexible intermediate transfer member.

11. The digital printing system of claim 1 , wherein the seal is configured to reduce friction between the rotatable element and a wall of the opening.

12. A digital printing system according to claim 11, wherein the seal comprises a leaf spring having a first section and a second section, wherein the first section is connected to a wall of the opening, and wherein the second section is configured to release at least a portion of the pressurized fluid out of the fluid chamber by moving relative to the rotatable element.

13. The digital printing system of claim 12, wherein the second segment is configured to move in response to a change in position of the rotatable element.

14. The digital printing system of claim 12, wherein the leaf spring comprises stainless steel, and wherein the second section is configured to flex relative to the first section in response to a change in the position of the rotatable element.

15. A digital printing method, comprising: In a digital printing system, the digital printing system includes (a) a flexible intermediate transfer member and (b) a floating roller assembly, the floating roller assembly including: (i) a fluid chamber and a rotatable element mounted in the fluid chamber, the fluid chamber including an inlet for receiving a pressurized fluid into the fluid chamber, (ii) an opening sized and shaped to be mounted on the rotatable element, wherein the pressurized fluid causes the rotatable element to extend from the fluid chamber through the opening, and (iii) a seal coupled to the opening and configured to retain the pressurized fluid in the fluid chamber when a pressure of the pressurized fluid is less than or equal to a predefined pressure and release at least a portion of the pressurized fluid out of the fluid chamber when the pressure exceeds the predefined pressure, the rotatable element applying tension to the flexible intermediate transfer member by supplying the pressurized fluid into the fluid chamber and causing the rotatable element to move relative to the fluid chamber; and An image is formed on the flexible intermediate transfer member by receiving ink droplets from an ink supply system, and the image is transferred to a target substrate.

16. A digital printing method, comprising: In a digital printing system, the digital printing system includes (a) a flexible target substrate and (b) a floating roller assembly, the floating roller assembly including: (i) a fluid chamber and a rotatable element mounted in the fluid chamber, the fluid chamber including an inlet for receiving a pressurized fluid into the fluid chamber, (ii) an opening sized and shaped to fit over the rotatable element, wherein the pressurized fluid causes the rotatable element to extend from the fluid chamber through the opening, and (iii) a seal coupled to the opening and configured to retain the pressurized fluid within the fluid chamber when a pressure of the pressurized fluid is less than or equal to a predefined pressure and release at least a portion of the pressurized fluid out of the fluid chamber when the pressure exceeds the predefined pressure, wherein a predefined tension is applied to the flexible target substrate by the rotatable element by supplying the pressurized fluid into the fluid chamber and causing the rotatable element to move relative to the fluid chamber; and An image is formed on the flexible target substrate by receiving ink drops from an ink supply system.

17. An apparatus for controlling tension applied to a flexible member, the apparatus comprising: a substrate, the substrate comprising the flexible member; as well as A floating roller assembly comprising: (i) a fluid chamber and a rotatable element mounted in the fluid chamber, the fluid chamber comprising an inlet configured to receive a pressurized fluid into the fluid chamber, wherein the pressurized fluid causes the rotatable element to move relative to the fluid chamber and apply tension to the substrate when rotated by the substrate, (ii) an opening sized and shaped to fit over the rotatable element, wherein the pressurized fluid causes the rotatable element to extend from the fluid chamber via the opening, and (iii) a seal coupled to the opening and configured to retain the pressurized fluid within the fluid chamber when a pressure of the pressurized fluid is less than or equal to a predefined pressure, and to release at least a portion of the pressurized fluid out of the fluid chamber when the pressure exceeds the predefined pressure.

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