Digital printing system

Abstract

To provide methods and devices for digital printing on continuous substrates.SOLUTION: A digital printing system (10) includes: an intermediate transfer member (ITM) (44) which is configured to receive a printing fluid in order to form an image; a continuous target substrate (50); and a processor (20). The continuous target substrate (50) is configured to engage with the ITM (44) at an engagement point for receiving the image from the ITM (44); at the engagement point, the ITM (44) is configured to move at a first velocity and the continuous target substrate (50) is configured to move at a second velocity. The processor (20) is configured to match the first velocity and the second velocity at the engagement point.SELECTED DRAWING: Figure 1A

Description

Technical Field

[0001] Cross - Reference to Related Applications This application claims the benefit of U.S. Provisional Patent Application No. 62 / 784,576, filed on December 24, 2018, and U.S. Provisional Patent Application No. 62 / 784,579, filed on December 24, 2018, the disclosures of which are hereby incorporated by reference in their entirety.

[0002] The present invention generally relates to digital printing, and more particularly to methods and systems for digital printing onto a continuous substrate.

Background Art

[0003] In various applications, such as the manufacture of labels and plastic bags, printing of images onto a suitable continuous medium is required. Further, in digital printing, various methods have been developed for monitoring and reducing distortion, especially geometric distortion.

[0004] For example, U.S. Patent Application Publication No. 2002 / 0149771 describes an inspection apparatus that includes an inspection light projector and an auxiliary light emitter that project inspection light and auxiliary light, respectively, onto the position of a film strip. After the film strip is fed out, the inspection light is received by a defect detector. When receiving the inspection light, the defect detector generates a data signal and transmits it to a controller. In the controller, a threshold value of the level of the data signal is stored, and the level of the data signal is compared with the threshold value. When the level of the data signal is less than the threshold value, the controller determines that there is a coloring defect in the film strip.

[0005] U.S. Patent Application Publication No. 2010 / 0165333 describes a method and an apparatus for inspecting a laminate film. The method includes a first inspection process of inspecting for the presence of defects on the front side of the film body with the protective film separated from the film body. The method further includes a second inspection process of vertically inspecting for the presence of defects in the film body while introducing the film body with the separator separated and removed from the film body into a vertically oriented film movement path and storing the detection data.

[0006] U.S. Patent No. 5,969,372 describes a method and an apparatus for detecting surface defects and artifacts on a transmission image in an optical image scanner and correcting the resulting scanned image. In one scan, the image is scanned normally. Surface defects and artifacts such as dust, scratches, and fingerprints are detected by providing a separate scan using infrared rays or by measuring light (white or infrared) scattered or diffracted by the defects and artifacts.

SUMMARY OF THE INVENTION

PROBLEMS TO BE SOLVED BY THE INVENTION

[0007] One embodiment of the invention described herein provides a digital printing system including an intermediate transfer member (ITM), a continuous target substrate, and a processor configured to receive a printing fluid to form an image. The continuous target substrate is configured to engage the ITM at an engagement point to receive an image from the ITM, at which engagement point the ITM is configured to move at a first speed and the continuous target substrate is configured to move at a second speed. The processor is configured to match the first speed and the second speed at the engagement point.

MEANS FOR SOLVING THE PROBLEMS

[0008] In some embodiments, the printing fluid includes ink droplets received from an ink supply system to form an image on its surface. In other embodiments, the system includes a first and a second drum, the first drum being configured to rotate in a first direction and at a first rotational speed to move the ITM at a first speed, and the second drum being configured to rotate in a second direction and at a second rotational speed to move a continuous target substrate at a second speed, and the processor is configured to engage and disengage between the ITM and the continuous target substrate at an engagement point by moving one or both of the first drum and the second drum. In yet other embodiments, the processor is configured to receive an electrical signal indicative of a difference between the first speed and the second speed and, based on the electrical signal, to match the first and second speeds.

[0009] In one embodiment, the processor is configured to set at least one operation selected from the list consisting of (a) the timing of engagement and disengagement between the first drum and the second drum, (b) the movement profile of at least one of the first and second drums, and (c) the size of the gap between the released first drum and the second drum. In another embodiment, the system includes an electric motor configured to move one or both of the ITM and the target substrate, and the processor is configured to receive a signal indicative of a temporal change in the current flowing through the electric motor and, in response to the signal, to match the first and second speeds. In yet another embodiment, the processor is configured to match the first and second speeds by reducing the temporal change in the current.

[0010] In some embodiments, the temporal change includes the gradient of the current as a function of time over a predetermined time interval. In another embodiment, the processor is configured to correct for thermal expansion of at least one of the first drum and the second drum by reducing the temporal change in the current. In yet another embodiment, the continuous target substrate includes a first substrate having a first thickness or a second substrate having a second thickness different from the first thickness, and the processor is configured to correct for the difference between the first thickness and the second thickness by reducing the temporal change in the current.

[0011] In one embodiment, the ITM is in the form of a loop closed by a seam, and the processor prevents physical contact between the seam and the continuous target substrate from (a) causing a temporary release between the ITM and the continuous target substrate during the time interval when the seam passes through the engagement point, and (b) backtracking the continuous target substrate during that time interval to correct for the temporary release. In another embodiment, the system includes a backtracking mechanism configured to backtrack the continuous target substrate and including at least first and second movable rollers configured to physically contact the continuous target substrate and backtrack the continuous target substrate by moving the rollers relative to each other. In yet another embodiment, the ITM includes a multi-layer stack having one or more markers etched within at least one of the layers at respective marking positions along the ITM.

[0012] In some embodiments, the system includes one or more sensing assemblies disposed at one or more predefined positions relative to the ITM, and the sensing assemblies are configured to generate signals indicating the respective positions of the markers. In other embodiments, the processor is configured to receive the signals and, based on the signals, control the deposition of ink droplets onto the ITM. In still other embodiments, the system includes at least one station or assembly, and the processor is configured to control the operation of at least one station or assembly of the system based on the signals.

[0013] In one embodiment, the at least one station or assembly is selected from the list consisting of (a) an image forming station, (b) a printing station, (c) an ITM guiding system, (d) one or more drying assemblies, (e) an ITM processing station, and (f) an image quality management station. In another embodiment, the system includes an image forming module, which is configured to apply a substance to the ITM.

[0014] In some embodiments, the substance includes at least a portion of a printing fluid. In other embodiments, the image forming module includes a gravure printing apparatus.

[0015] In accordance with an embodiment of the present invention, a method is additionally provided that includes receiving a printing fluid on an intermediate transfer member (ITM) to form an image. A continuous target substrate engages the ITM at an engagement point to receive the image from the ITM, at which engagement point the ITM moves at a first speed and the continuous target substrate moves at a second speed. The first speed and the second speed match at the engagement point.

[0016] According to an embodiment of the present invention, a digital printing system is further provided that includes an intermediate transfer member (ITM), a light source, an image sensor assembly, and a processor. The ITM is configured to receive a printing fluid to form an image and engage with a target substrate having opposing first and second surfaces to transfer the image to the target substrate. The light source is configured to irradiate the first surface of the target substrate with light. The image sensor assembly is configured to image at least a portion of the light transmitted through the target substrate to the second surface and generate an electrical signal in response to the imaged light. The processor is configured to generate a digital image based on the electrical signal and estimate at least distortion in the printed image based on the digital image.

[0017] In some embodiments, the target substrate includes a continuous target substrate. In other embodiments, the distortion includes geometric distortion. In still other embodiments, the processor is configured to estimate the distortion by analyzing one or more marks on the target substrate.

[0018] In one embodiment, at least one of the marks includes a barcode. In another embodiment, the light source includes a light diffuser. In another embodiment, the light source includes at least a light emitting diode (LED). In still another embodiment, the system includes one or more motion assemblies configured to move at least one of the target substrate and the image sensor assembly relative to each other, and the processor is configured to generate a digital image by controlling the one or more motion assemblies.

[0019] In some embodiments, the processor is configured to use at least one of the one or more movement assemblies to position a mark formed on the target substrate between a light source and an image sensor assembly. In other embodiments, the movement assembly includes first and second movement assemblies, and the processor is configured to (i) move only one of the first and second movement assemblies at a time and (ii) move the first and second movement assemblies simultaneously. In still other embodiments, the processor is configured to estimate at least distortion in an image during the production of a printed image.

[0020] In one embodiment, the processor is configured to estimate at least the density of the printing fluid by analyzing the intensity of light transmitted through the target substrate to a second surface. In another embodiment, the printing fluid includes white ink. In still another embodiment, the electrical signal indicates intensity, and the processor is configured to generate a density indicating the intensity in a digital image.

[0021] In accordance with an embodiment of the present invention, a method is additionally provided in a digital printing system that includes receiving a printing fluid by an intermediate transfer member (ITM) to form an image and engaging a target substrate having opposing first and second surfaces to transfer the image to the target substrate. A light source is used to irradiate the first surface of the target substrate with light. An image sensor assembly is used to image at least a portion of the light transmitted through the target substrate onto the second surface, and an electrical signal is generated in response to the imaged light. A digital image is generated based on the electrical signal, and at least distortion in a printed image is estimated based on the digital image.

Advantages of the Invention

[0022] The present invention will be more fully understood from the following detailed description of its embodiments when interpreted in conjunction with the drawings.

Brief Description of the Drawings

[0023]

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DETAILED DESCRIPTION OF THE INVENTION

[0024] Overview Embodiments of the present invention described below provide a method and apparatus for digital printing onto a continuous substrate. In some embodiments, the digital printing system includes a flexible intermediate transfer member (ITM) configured to receive an image formed by placing a printing fluid, such as aqueous ink, onto the ITM, and a target substrate configured to engage the ITM at an engagement point to receive the image from the ITM. At the engagement point, the ITM and the substrate are moved at first and second speeds, respectively.

[0025] In some embodiments, the digital printing system further includes an impression cylinder configured to move the target substrate at a first speed, and a printing station including a pressure cylinder configured to move the ITM at a second speed.

[0026] In some embodiments, the digital printing system further includes a processor, the processor being configured to effect engagement and disengagement between the ITM and the substrate at the engagement point by moving at least the impression cylinder, and to match the first and second speeds at the engagement point for transferring ink from the ITM to the substrate.

[0027] In some embodiments, the ITM is in the form of a loop closed by a seam, and the processor is configured to prevent an unwanted physical contact between the seam and the substrate by (a) causing a temporary disengagement between the ITM and the continuous target substrate during a time interval when the seam passes through the engagement point, and (b) backtracking the continuous target substrate during these time intervals to correct for the temporary disengagement.

[0028] In some embodiments, the digital printing system includes an electric motor configured to move one or both of the ITM and the target substrate. In these embodiments, the processor is configured to receive a signal indicative of a temporal change in the current flowing through the electric motor and, based on the signal, match the first and second speeds, for example, by reducing the temporal change in the current.

[0029] In some cases, the printing system and / or the printing process may have variations caused, for example, by thermal expansion of one or more cylinders of the printing station or by a change in the thickness of the substrate. In some embodiments, based on the aforementioned received signal, the processor is configured to correct such (and other) variations by reducing the temporal change in the current flowing through the electric motor.

[0030] The disclosed technology improves the accuracy, quality, and productivity of digital printing onto a continuous substrate by correcting for variations in various systems and processes. Additionally, the disclosed technology reduces potential waste of substrate physical property by preventing physical contact between seams and the substrate and by backtracking the continuous substrate to minimize the margin between adjacent printed images.

[0031] Polymeric substrates in the form of continuous webs are used in various applications of flexible packaging, such as in food packaging, plastic bags, and tubes. In some cases, the process of printing an image onto such a substrate can result in distortions, such as geometric distortions and other defects in the printed image. In principle, such distortions can be detected using, for example, optical inspection methods based on reflection. However, the high reflectivity of the substrate to which it is applied and other sources of noise, such as wrinkles in the substrate, can interfere with the inspection signal indicating the inherent distortion, reducing the detection rate and accuracy. For example, the high reflectivity of the substrate can cause non-uniform contrast and local saturation across the field of view (FOV) of the image acquired by the optical inspection equipment, which can reduce the detection rate of the defect of interest.

[0032] Other embodiments of the present invention provide methods and systems for detecting defects, such as geometric distortions, in digital printing onto a continuous substrate. In some of these embodiments, the digital printing system includes an ITM configured to receive an image formed by placing a printing fluid, such as the aqueous ink described above, onto the ITM. The digital printing system prints an image onto a continuous target substrate having opposing upper and lower surfaces. The target substrate is configured to engage with the ITM to receive the image from the ITM. The image printed on the target substrate typically includes a base layer created from white ink and a pattern printed on the base layer using ink of one or more other colors.

[0033] In some embodiments, the image printed on the target is subjected to an inspection for detecting defects. To perform defect detection, the digital printing system further includes a light source configured to irradiate one surface (e.g., the lower surface) of the target substrate with appropriate light rays. The digital printing system further includes an image sensor assembly configured to detect the light rays transmitted through the target substrate to the opposite surface (e.g., the upper surface) and generate an electrical signal in response to the detected light. In some embodiments, the image sensor assembly is configured to detect the intensity of the transmitted light that has passed through the target substrate, the base layer, and the ink pattern. For example, since white ink is partially transmissive to the emitted light, the intensity of the detected light, and thus the electrical signal generated by the image sensor assembly, is also determined by the density and / or thickness of the white ink layer.

[0034] In some embodiments, the processor of the digital printing system is configured to generate a digital image based on the electrical signal received from the image sensor assembly. For example, the processor is configured to generate a digital color image having the same or different color tones at different positions of the digital image for each color.

[0035] In some embodiments, the image sensor assembly includes a color camera having red, green, and blue (RGB) channels. In the context and claims of the present disclosure, the term "gray level" in a color image refers to a scale indicating the luminance level of the color of the digital image. In a camera having RGB channels, each channel has a scale of gray levels. For example, in a green channel image including two regions having gray levels of 100 and 200 respectively, the region with a gray level of 200 has a brighter green color than the region with a gray level of 100.

[0036] In an alternative embodiment, the image sensor assembly may include a monochrome camera having only black, white, and gray. In these embodiments, the term "density" represents a scale indicating luminance levels only between black and white. The actual density in a digital image is determined by the density of the ink applied to each position of the target substrate. In some embodiments, the processor is further configured to process the digital image to detect geometric distortion and other defects in the printed image.

[0037] In some embodiments, the target substrate may include various types of test features, also referred to herein as test targets printed on the top surface, and each test target can be used to check the state of components of the digital system. For example, a given test target can be used to monitor a specific nozzle within a print bar of a digital printing system to check whether the nozzle is functioning or clogged. The processor is configured to position the test target between a light source and the image sensor assembly, acquire one or more digital images of the test target, and analyze the acquired images to determine the state of the nozzle in question. The processor is further configured to correct at least some types of malfunctions detected using the test target, for example, by reconfiguring the printing process.

[0038] The disclosed technology improves the quality of printing onto flexible packaging due to various types of defects that cannot be detected or have a low detection rate using other (e.g., reflection-based) optical inspection methods. The use of the disclosed test targets and test methods helps to identify and correct malfunctions occurring within the digital printing process that cause these defects. Further, the disclosed technology reduces the amount of plastic waste generated by scrapped substrates and ink.

[0039] System Description Figure 1A is a schematic side view of a digital printing system 10 according to an embodiment of the present invention. In some embodiments, system 10 includes a rotating flexible ITM 44 that circulates through an image forming station 60, a drying station 64, a printing station 84, and a blanket processing station 52 (also referred to herein as an ITM processing station). In the context and claims of the present invention, the terms "blanket" and "intermediate transfer member (ITM)" are used interchangeably and refer to a flexible member that includes one or more layers configured to receive an ink image and transfer that ink image to a continuous target substrate 50, as described in detail below.

[0040] ITM 44 is described in more detail, for example, in PCT patent applications PCT / IB2017 / 053167, PCT / IB2019 / 055288, and PCT / IB2019 / 055288, the disclosures of which are hereby incorporated by reference in their entirety.

[0041] Figure 1B is a schematic side view of a substrate transport module 100 of system 10 according to an embodiment of the present invention.

[0042] In the operating mode, the image forming station 60 is configured to form a mirror ink image of the digital image 42, also referred to herein as an "ink image" (not shown), on the upper run of the surface of the ITM 44, such as on the blanket release layer or any other suitable layer of the ITM 44. The ink image is then transferred to a continuous target substrate 50 disposed under the lower run of the ITM 44. In some embodiments, the continuous target substrate 50 includes one or more layers of any suitable material, such as aluminum foil, paper, polyester, polyethylene terephthalate (PET), biaxially oriented polypropylene (BOPP), biaxially oriented polyamide (BOPA), other types of oriented polypropylene (OPP), a shrink film, also referred to herein as a polymeric plastic film, or any other material suitable for flexible packaging in the form of a continuous web, or a continuous ("web") substrate made from any suitable combination thereof, such as in a multi-layer structure. The continuous target substrate 50 can be used in a variety of applications, including, but not limited to, food packaging, plastic bags and tubes, labels, decorations, and floor coverings.

[0043] In the context of the present invention, the term "run" refers to the length or segment of the ITM 44 between any two given rollers over which the ITM 44 is guided.

[0044] In some embodiments, during installation, the ITM 44 can form a continuous blanket loop with edges attached to each other, referred to herein as a seam (not shown). An example of a method and system for forming a seam is described in detail in PCT Patent Publication No. WO 2016 / 166690 and PCT Patent Publication No. WO 2019 / 012456, the disclosures of which are hereby incorporated by reference in their entirety.

[0045] In some embodiments, system 10 is configured to be synchronized between ITM 44 and imaging station 60 so that the ink image is not printed on the seam. In other embodiments, processor 20 of system 10 is configured to prevent physical contact between the seam portion and continuous target substrate 50, as will be described in detail in FIG. 2 below.

[0046] In an alternative embodiment, ITM 44 may include any other configuration using a connection for connecting the ends of a blanket (not shown), such as the aforementioned seam, or any other technique for connecting the ends of ITM 44. In these embodiments, at least a portion of the ink image and / or at least a portion of any type of test feature may be printed on the connection.

[0047] In some embodiments, imaging station 60 typically includes a plurality of print bars 62, each of which is mounted (e.g., using a slider) on a frame (not shown) positioned at a fixed height above the surface of the upper run of ITM 44. In some embodiments, each print bar 62 includes a plurality of print heads arranged to cover the width of the printing area on ITM 44 and includes individually controllable print nozzles.

[0048] In some embodiments, imaging station 60 may include any suitable number of print bars 62, and each print bar 62 may contain a printing fluid, such as aqueous ink of different colors. The ink typically has visible colors such as, but not limited to, cyan, magenta, red, green, blue, yellow, black, and white. In the example of FIG. 1A, imaging station 60 includes seven print bars 62, but may include four print bars 62 having any selected colors, such as cyan, magenta, yellow, and black.

[0049] In some embodiments, the print head is configured to eject ink droplets of different colors onto the surface of the ITM44 to form an ink image (not shown) on the surface of the ITM44. In some embodiments, the system 10 may include an image forming module (not shown) in addition to the aforementioned image forming station. The image forming module is configured to apply at least one color (e.g., white) to the surface of the ITM44 using any suitable technique. For example, the image forming module may include a gravure printing device (not shown), and the gravure printing device is configured to apply a printing fluid (e.g., ink), or a primer or any other type of substance, to the surface of the ITM44, and includes a set of engraved rollers, such as an anilox roll and / or one or more rollers of any other suitable type. In some embodiments, the gravure printing device may be coupled to the system 10 as described below. In other embodiments, any other type of printing device may be coupled to the system 10 to apply one or more substances to the continuous target substrate 50.

[0050] In some embodiments, the different print bars 62 are spaced apart from each other along the axis of movement of the ITM44, represented by the arrow 94. In this configuration, the exact spacing between the bars 62 and the synchronization between the direction of the ink droplets of each bar 62 and the movement of the ITM44 are essential to enable the accurate placement of the image pattern.

[0051] In some embodiments, the system 10 includes an infrared-based dryer (shown in detail in FIG. 5 below) configured to emit infrared radiation, and / or a dryer such as, but not limited to, a hot gas or air blower 66. It should be noted that the image forming station 60 may include any suitable combination of ink dryers, such as the print bars 62, and the blower 66 and the aforementioned infrared-based dryer. These dryers are arranged between the print bars 62 and are configured to partially dry the ink droplets placed on the surface of the ITM44.

[0052] In some embodiments, the station 60 may include one or more blowers 66 and / or one or more infrared-based dryers (or any other type of dryer) between at least two adjacent printing bars 62, and a configuration example of these embodiments is shown in FIG. 5 below. However, in other embodiments, the station 60 may include any other suitable configuration. This hot air flow and / or infrared radiation between the printing bars can, for example, reduce condensation on the surface of the print head and / or process satellites (e.g., residues or small droplets dispersed around the main ink droplets) and / or prevent clogging of the inkjet nozzles of the print head and / or prevent unnecessary mixing of droplets of different color inks on the ITM 44.

[0053] In some embodiments, the drying station 64 is configured to dry the ink image applied to the surface of the ITM 44, for example, from a solvent and / or water, by blowing hot air (or another gas) onto the surface and / or irradiating the surface of the ITM 44 with infrared or any other suitable radiation. The use of these or any other suitable drying techniques makes the ink image tacky, thereby enabling a complete and proper transfer of the ink image from the ITM 44 to the continuous target substrate 50.

[0054] In an example embodiment, the drying station 64 may include a blower 68 configured to blow hot air and / or gas, and / or any other suitable drying device. In the example of FIG. 1A, the drying station 64 further includes one or more infrared dryers (IRD) 67 configured to emit infrared radiation onto the surface of the ITM 44. In the drying station 64, the ink image formed on the ITM 44 is exposed to radiation and / or hot air to more completely dry the ink, heating it to a point where most or all of the liquid carrier evaporates, leaving only the layer of resin and colorant that becomes a tacky ink film.

[0055] Additionally or alternatively, system 10 includes a drying station 75 configured to emit infrared light or light of any other suitable frequency, or range of frequencies, to dry the ink image formed on ITM 44 using the aforementioned techniques.

[0056] Note that system 10 may include one or more suitable drying stations of a single type, e.g., a blower-based or radiation-based drying station, or a combination of multiple drying techniques integrated with each other, such as that shown at station 64. Each dryer at stations 64 and 75 can be selectively operated based on the type and order of the colors applied to the surface of ITM 44 and based on the types of ITM 44 and continuous target substrate 50.

[0057] In some embodiments, system 10 includes a blanket module 70, also referred to herein as an ITM induction system, that includes a rotating ITM such as ITM 44. In some embodiments, blanket module 70 includes one or more rollers 78, at least one of which includes an encoder (not shown) configured to record the position of ITM 44 to control the position of sections of ITM 44 relative to respective print bars 62. In some embodiments, the encoder of roller 78 typically includes a rotary encoder configured to generate a rotary-based position signal indicative of the angular displacement of each roller.

[0058] Additionally or alternatively, ITM 44 may include an embedded encoder (not shown) that includes one or more markers embedded within one or more layers of ITM 44. In some embodiments, the embedded encoder can be used to control the operation of various modules of system 10.

[0059] In some embodiments, system 10 may include one or more sensing assemblies (not shown) disposed at one or more respective pre-defined positions adjacent to ITM 44. The sensing assemblies are configured to generate an electrical signal, such as a position signal indicating the respective position of the marker, in response to detection of the marker.

[0060] In some embodiments, the signal received from the sensing assembly may be used to control the process of printing station 84, for example, to control the engagement and release timing of cylinders 90 and 102 and their respective motion profiles, to control the size of the gap between cylinders 90 and 102, to synchronize the operation of printing station 84 with respect to the blanket seam position, and to control any other appropriate operation of station 84.

[0061] In some embodiments, the signal received from the sensing assembly may be used to control the operation of blanket processing station 52, for example, to control the cleaning process and / or the application of the processing fluid to ITM 44, and to control all other aspects of the blanket processing process.

[0062] Further, the signal received from the sensing assembly may be used to control the operation of all the rollers and dancers of system 10, and each roller is individually and mutually synchronized to control the temperature aspect of the operation of system 10 and any subsystem of system 10 that controls the heat exchange aspect. In some embodiments, the signal received from the sensing assembly may be used to control the blanket imaging operation of system 10. For example, based on data obtained from an image quality control station (shown in FIG. 6 below) configured to acquire a digital image of an image printed on a target substrate, to control the operation of any other component of system 10.

[0063] The built-in encoder is described in detail, for example, in the aforementioned U.S. Provisional Application No. 62 / 689,852, the disclosure of which is incorporated herein by reference.

[0064] In some embodiments, the ITM 44 is guided over rollers 76 and 78 and a powered tension roller, also referred to herein as dancer 74. The dancer 74 is configured to control the length of slack in the ITM 44, and its movement is schematically represented by the double-headed arrow. Further, any elongation of the ITM 44 due to the printing process and / or aging will not affect the ink image placement performance of the system 10 and will only require further slack to be taken up by the tension dancer 74.

[0065] In some embodiments, the dancer 74 can be powered. The construction and operation of rollers 76 and 78, and dancer 74 are described in further detail, for example, in U.S. Application Publication No. 2017 / 0008272 and the aforementioned PCT International Publication No. WO 2013 / 132424, the disclosures of which are hereby incorporated by reference in their entirety.

[0066] At the printing station 84, the ITM 44 passes between the impression cylinder 102 and the pressure cylinder 90, which is configured to convey a compressible blanket wrapped around its periphery. In the context and claims of the present invention, the terms "cylinder" and "drum" are used interchangeably to refer to the impression cylinder 102 and the pressure cylinder 90 of the printing station 84.

[0067] In some embodiments, the system 10 includes a control console 12, which is configured to control a plurality of modules of the system 10, such as the blanket module 70, the image forming station 60 disposed on the blanket module 70, and the substrate transport module 100 disposed under the blanket module 70.

[0068] In some embodiments, console 12 includes a processor 20, typically a general-purpose computer, with appropriate front-end and interface circuitry for interfacing with and receiving signals from 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 predetermined 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 a processor (not shown), which is configured to control the various modules and stations of system 10. In some embodiments, processor 20 and the control circuit may be programmed with software to perform the functions used by the printing system and may store data for the software in memory 22. The software may be downloaded in electronic form to processor 20 and the control circuit via, for example, a network, or may be provided on a persistent tangible medium, such as an optical, magnetic, or electronic memory medium.

[0069] 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, for example, U.S. Patent No. 9,229,664, the disclosure of which is incorporated herein by reference.

[0070] In some embodiments, processor 20 is configured to display on display 34 a digital image 42 that includes one or more segments (not shown) of image 42 and various types of test patterns stored in memory 22.

[0071] In some embodiments, the blanket processing station 52, also referred to as a cooling station, is configured to process the blanket, for example, by cooling it and / or applying a processing fluid to the outer surface of the ITM 44 and / or cleaning the outer surface of the ITM 44. In the blanket processing station 52, the temperature of the ITM 44 can be lowered to a desired value before the ITM 44 enters the imaging station 60. The processing can be performed by passing the ITM 44 over one or more rollers and / or blades configured to cool and / or clean and / or apply a processing fluid onto the outer surface of the blanket. In some embodiments, the processor 20 is configured to receive a signal indicative of the surface temperature of the ITM 44 from, for example, a temperature sensor (not shown) to monitor the temperature of the ITM 44 and control the operation of the 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 hereby incorporated by reference in their entirety. Additionally or alternatively, the processing fluid can be applied by spraying prior to inkjetting at the imaging station.

[0072] In the example of FIG. 1A, the blanket processing station 52 is attached between roller 78 and roller 76, but the blanket processing station 52 can be attached adjacent to the ITM 44 at any other suitable location between the printing station 84 and the imaging station 60.

[0073] Referring now to FIG. 1B. In some embodiments, the impression cylinder 102 presses an ink image onto a target flexible web continuous target substrate 50 that has been conveyed by the substrate conveyance module 100 from the pre-print buffer unit 86 to the post-print buffer unit 88 via the impression cylinder 102. As shown in module 100 of FIG. 1B, the continuous target substrate 50 moves through the module 100 in a direction represented by an arrow, also referred to herein as the moving direction 99, but as will be described below, it can also move in a direction opposite to the moving direction 99.

[0074] In some embodiments, the lower run of the ITM 44 selectively interacts with the impression cylinder 102 at the printing station 84 to press an image pattern onto a target flexible substrate that is compressed between the ITM 44 and the impression cylinder 102 by the action of the pressure of the pressure cylinder 90. In the case of the simplex printer shown in FIG. 1A (i.e., printing on one side of the continuous target substrate 50), only one printing station 84 is required.

[0075]

[0074] Referring again to FIG. 1A. In some embodiments, the roller 78 is positioned on the upper run of the ITM 44 and is configured to keep the ITM 44 taut as it passes adjacent to the image forming station 60. Further, it is particularly important for the image forming station 60 to control the speed of the ITM 44 under the image forming station 60 in order to obtain accurate ejection and deposition of ink droplets onto the surface of the ITM 44, and thereby the placement of the ink image.

[0076] Referring now to FIG. 1B. In some embodiments, the impression cylinder 102 is periodically engaged with and released from the ITM 44 to transfer the ink image from the moving ITM 44 to the continuous target substrate 50 passing between the ITM 44 and the impression cylinder 102. Note that if the continuous target substrate 50 is permanently engaged with the ITM 44 at the printing station 84, a large amount of the continuous target substrate 50 located between the printed ink images needs to be discarded. The embodiments described in FIGS. 1B and 2 below reduce the amount of physical property of the continuous target substrate 50 that is discarded between the printed ink images.

[0077] In the context and claims of the present invention, the terms "engagement position" and "engagement" refer to the close proximity between cylinder 90 and 102 such that ITM44 and the continuous target substrate 50 are in physical contact with each other, for example, at engagement point 150. At the engagement position, the ink image is transferred from ITM44 to the continuous target substrate 50. Similarly, the terms "disengagement position" and "disengagement" refer to the distance between cylinder 90 and 102 such that ITM44 and the continuous target substrate 50 are not in physical contact with each other and can move relative to each other.

[0078] In some embodiments, system 10 is configured to apply torque to ITM44 using the aforementioned rollers and dancer to maintain the upper run of ITM44 pinned and substantially isolate it from being affected by any mechanical vibrations occurring in the lower run.

[0079] Referring now to FIG. 1B. In some embodiments, system 10 includes an image quality management station 55, also referred to herein as an automatic quality management (AQM) system, which functions as a closed-loop inspection system integrated within system 10. In some embodiments, station 55 can be disposed adjacent to impression cylinder 102 or at any other suitable location within system 10, as shown in FIG. 1A.

[0080] In some embodiments, station 55 includes a camera (shown in FIG. 6 below) configured to acquire one or more digital images of the aforementioned ink images printed on the continuous target substrate 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.

[0081] In some embodiments, station 55 may include a spectrophotometer (not shown) configured to monitor the quality of the ink printed on the continuous target substrate 50.

[0082] In some embodiments, the digital images acquired by station 55 are transmitted to a processor, such as processor 20 or any other processor of station 55, which is configured to evaluate the quality of each printed image. Based on that evaluation and the signals received from controller 54, processor 20 is configured to control the operation of the modules and stations of system 10. In the context and claims of the present invention, the term "processor" refers to any processing device, such as processor 20 or any other processor connected to or integrated with station 55, which is 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 executed by a single processor or distributed among multiple processors of one or more respective computers.

[0083] In some embodiments, station 55 is configured to inspect the quality of printed images and test patterns to monitor various attributes, such as, but not limited to, complete image registration, color-to-color registration, printed geometries, image uniformity, color profiles and linearity, and the functionality of the print nozzles, on the continuous target substrate 50. In some embodiments, processor 20 is configured to automatically detect geometric distortions or other defects and / or errors in one or more of the aforementioned attributes. For example, processor 20 is configured to compare a design version of a given digital image with a digital image of the printed version of the given image acquired by the camera.

[0084] In other embodiments, the processor 20 may apply any suitable type of image processing software, for example, to a test pattern, to detect distortions indicating the aforementioned errors. In some embodiments, the processor 20 is configured to analyze the detected distortions in order to apply corrective measures to the malfunctioning module and / or to supply instructions to another module or station of the system 10 to correct the detected distortions.

[0085] In some embodiments, the processor 20 is configured to analyze signals acquired by the station 55 to monitor the nozzles of the image forming station 60. By printing test patterns of each color of the station 60, the processor 20 is configured to identify various types of defects indicating malfunctions in the operation of each nozzle.

[0086] In some embodiments, the processor of the station 55 is configured to determine, for example, whether to stop the operation of the system 10 if the defect density exceeds a specified threshold. The processor of the station 55 is further configured to initiate corrective measures in one or more of the modules and stations of the system 10. The corrective measures may be performed on-the-fly (while the system 10 continues the printing process) or offline, by stopping the printing operation and correcting problems within each module and / or station of the system 10. In other embodiments, any other processor or controller of the system 10 (e.g., the processor 20 or the controller 54) is configured to initiate corrective measures or stop the operation of the system 10 if the defect density exceeds a specified threshold.

[0087] Additionally or alternatively, the processor 20 is configured to receive, for example, from the station 55, signals 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 pattern placement accuracy and the level of additional types of defects not described above. In other embodiments, any other suitable method for inspecting the pattern printed on the continuous target substrate 50 can also be used, for example, an external (e.g., offline) inspection system, or any type of measuring jig 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 stop the operation of the system 10.

[0088] Referring now to FIG. 1A. In some embodiments, the substrate conveyance module 100 is configured to receive (e.g., pull) the continuous target substrate 50 from a pre-print roller, also referred to herein as the pre-print winder 180, which is disposed outside the pre-print buffer unit 86.

[0089] In some embodiments, the substrate conveyance module 100 is configured to convey the web continuous target substrate 50 from the pre-print buffer unit 86, through the printing station 84 for receiving the ink image from the ITM 44, to the post-print buffer unit 88.

[0090] In some embodiments, the buffer units 86 and 88 each include one or more buffer idlers 104, also referred to herein as buffer rollers. Each buffer idler 104 has a fixed axis and is configured to rotate around the fixed axis to guide the continuous target substrate 50 along the substrate conveyance module 100 and maintain a constant tension in the continuous target substrate 50.

[0091] In the example of FIG. 1B, buffer unit 86 includes six buffer idlers 104, and buffer unit 88 includes seven buffer idlers 104. However, in other configurations, each buffer unit may have any other suitable number of buffer idlers 104. In other embodiments, at least one of the buffer idlers 104 may have a movable shaft to control the level of mechanical tension in the continuous target substrate 50.

[0092] In some embodiments, the substrate conveyance module 100 includes a web guiding unit 110, which includes one or more rollers 108, sensors, and motors (not shown), and is configured to maintain a specified (typically constant) tension in the continuous target substrate 50 and align it between the substrate 100 and the rollers and idlers of the substrate conveyance module 100.

[0093] In some embodiments, the substrate conveyance module 100 includes an idler 106 attached adjacent to the unit 110. Each idler 106 has a fixed shaft and is configured to rotate around the fixed shaft to guide the continuous target substrate 50 along the substrate conveyance module 100 and maintain the tension applied to the continuous target substrate 50 by the web guiding unit 110. In other embodiments, at least one of the idlers 106 may have a movable shaft.

[0094] In some embodiments, the substrate conveyance module 100 includes one or more tension control units, such as tension control units 112 and 128. Each of these tension control units is configured to detect the tension in the continuous target substrate 50 and adjust the level of tension based on the detection to keep the continuous target substrate 50 taut as it passes between buffer units 86 and 88. In the example of FIG. 1B, module 100 includes unit 112 attached between buffer unit 86 and printing station 84, and unit 128 attached between printing station 84 and buffer unit 88.

[0095] In some embodiments, each of these tension control units includes a tension sensing roller 114, which is configured to detect the level of tension in the continuous target substrate 50 by applying a predetermined weight to the continuous target substrate 50 or by using any other suitable sensing mechanism. The tension control unit is configured to transmit an electrical signal indicative of the level of tension detected by the roller 114 to the controller 54 and / or the processor 20.

[0096] In some embodiments, each of the units 112 and 128 further includes a gear, also referred to herein as a pulley 116, which is coupled to a motor (not shown) configured to adjust the tension in the continuous target substrate 50 based on the level of tension detected by the roller 114. The motor can be driven by the controller 54 and / or by the processor 20 and / or by any suitable type of driver.

[0097] In some embodiments, each of the units 112 and 128 further includes a backing nip roller 118 and a tension roller 122, which is powered by the pulley 116 using a belt 124 or any other suitable mechanism. The backing nip roller 118 includes a movable shaft and a pneumatic piston configured to move the movable shaft to connect between the continuous target substrate 50 and the tension roller 122.

[0098] In some embodiments, the substrate conveyance module 100 includes a plurality of idlers 106 disposed between the tension control unit 128 and the post-print buffer unit 88 and configured to maintain the tension applied to the continuous target substrate 50 by the tension control unit 128. After receiving the ink image at the printing station 84, the continuous target substrate 50 is moved from the unit 128 to the post-print buffer unit 88 and then to a post-print roller, also referred to herein as a rewinder 190, where it is wound onto the post-print roller.

[0099] In some embodiments, the foregoing gravure printing apparatus (and any other optional printing module for applying white ink) can be coupled to the system 10 at any suitable location, such as between the pre-print winder 180 and the pre-print buffer unit 86. Additionally or alternatively, the gravure printing apparatus can be coupled to the system 10 between the post-print buffer unit 88 and the rewinder 190.

[0100] In some embodiments, the system 10 includes a pressure roller block 140 coupled to the substrate conveyance module 100. The block 140 is configured to fix the pressure cylinder 90 to the substrate conveyance module 100. The block 140 is further configured to fix a blanket idler 142 mounted thereon. The idler 142 is configured to maintain the tension in the ITM44.

[0101] In some embodiments, the substrate conveyance module 100 includes a backtracking mechanism, also referred to herein as the backtracking module 166, which is configured to backtrack the continuous target substrate 50 relative to the moving direction 99. In other words, the module 166 is configured to move the continuous target substrate 50 in a direction opposite to the direction 99.

[0102] In some embodiments, the backtracking module 166 includes two or more movable rollers, dancer 120 and 130 in the example of FIG. 1B, each of these dancers being configured to physically contact the continuous target substrate 50 and move relative to each other to backtrack the continuous target substrate 50. The operation of the backtracking module 166 is described in detail in FIG. 2 below.

[0103] As described above, the impression cylinder 102 is periodically engaged with and released from the ITM44 in order to transfer the ink image from the moving ITM44 to the continuous target substrate 50 passing between the ITM44 and the impression cylinder 102. As shown in FIG. 1B, the pressure cylinder 90 and the impression cylinder 102 are engaged with each other at the engagement point 150 in order to transfer the ink image from the ITM44 to the continuous target substrate 50.

[0104] In some embodiments, the pressure cylinder 90 has a fixed axis, while the impression cylinder 102 has a movable axis that allows for the aforementioned engagement and release.

[0105] In an alternative embodiment, the system 10 may have any other suitable configuration to support the engagement and release operations. For example, both cylinders 90 and 102 may each have a movable axis, or the cylinder 102 may have a fixed axis and the other cylinder 90 may have a movable axis.

[0106] In some embodiments, the pressure cylinder 90 is configured to rotate about its axis at a first predetermined speed using a rotation motor (not shown). Similarly, the impression cylinder 102 is configured to rotate about its axis at a second predetermined speed using another rotation motor (not shown). These rotation motors may include any suitable type of electric motor that is driven and controlled by any suitable driver and / or by the controller 54 and / or by the processor 20.

[0107] It should be noted that it is important to match the linear speeds of the cylinders 90 and 102 at the engagement point 150 in order to accurately transfer the ink image from the ITM44 to the continuous target substrate 50. In some embodiments, the processor 20, or any other processor or controller of the system, is configured to match the first speed of the cylinder 90 and the second speed of the cylinder 102 at the engagement point 150.

[0108] In other embodiments, both the pressure cylinder 90 and the impression cylinder 102 can be powered to perform rotational movement using any other suitable type of motion mechanism that allows the aforementioned first and second speeds to match at the engagement point 150.

[0109] The configuration of the system 10 is provided simplified as an example purely for clarity of the present invention. The components, modules and stations described in the printing system 10 above, as well as additional components and configurations, are described in detail, for example, in U.S. Pat. Nos. 9,327,496 and 9,186,884, PCT International Publications WO 2013 / 132438, WO 2013 / 132424 and WO 2017 / 208152, U.S. Patent Application Publications 2015 / 0118503 and 2017 / 0008272, the disclosures of all of which are hereby incorporated by reference.

[0110] FIG. 1A shows a digital printing system 10 having only a single printing station 84 for printing on only one side of a continuous target substrate 50. For double-sided printing, a tandem system with two printing stations can be provided, and a web substrate inverter mechanism can be provided between the printing stations to allow the web substrate to be turned over for double-sided printing. Alternatively, if the width of the ITM44 exceeds twice the width of the continuous target substrate 50, it is possible to use both halves of the same blanket and impression cylinder to print on both sides of different sections of the web substrate simultaneously.

[0111] The specific configuration of the system 10 is shown as an example to illustrate the specific problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such a system. However, embodiments of the present invention are in no way limited to this specific type of system example, and the principles described herein can be equally applied to any other type of printing system.

[0112] Prevention of physical contact between the joint portion and the continuous web substrate Figure 2 is a schematic side view of the backtracking module 166 according to an embodiment of the present invention. In some embodiments, the dancers 120 and 130 are powered, and the processor 20 is configured to synchronize the dancers 120 and 130 with each other and move them up and down in opposite directions.

[0113] In some embodiments, the processor 20 is configured to prevent physical contact between the continuous target substrate 50 and the joint portion of the ITM 44 by performing a sequence including the release between the cylinders 90 and 102, the temporary backtracking of a given section of the continuous target substrate 50, and the re-engagement of the cylinders 90 and 102. The sequence is described in detail herein. The length of a given section is determined by various parameters such as the transition time between the release position and the engagement position and the specified speed of the continuous target substrate 50, but is not limited thereto.

[0114] After the ink image is transferred from the ITM 44 to the continuous target substrate 50 at the engagement point 150, the processor 20 releases the impression cylinder 102 from the pressure cylinder 90 by moving the cylinder 102 in the direction 170, also referred to herein as "downward", to allow the continuous target substrate 50 and the ITM 44 to move relative to each other.

[0115] In one embodiment, in response to the release, at least one of the tension sensing rollers 114 detects a change in the tension level in the continuous target substrate 50. In some embodiments, the processor 20 receives an electrical signal indicative of the detected tension and moves the dancer 120 in direction 180, also referred to herein as "downward", and simultaneously moves the dancer 130 in direction 192, also referred to herein as "upward". In this embodiment, a given section of the continuous target substrate 50 located between the dancers 120 and 130 is backtracked, while another section of the continuous target substrate 50 continues to move forward at a specified speed, which may be the same as or substantially the same as the speed of the continuous target substrate 50 when the cylinders 90 and 102 are engaged with each other.

[0116] In some embodiments, the processor 20 is configured to perform backtracking by taking the slack out of a run of the continuous target substrate 50 behind the impression cylinder 102 and transferring that slack to a run in front of the pressure cylinder 90. The processor 20 then reverses the movement of the dancers 120 and 130 to return them to the positions shown in FIG. 2, as a result of which a given section of the continuous target substrate 50 is again accelerated to the specified speed of the ITM 44. In some embodiments, the processor 20 also moves the impression cylinder 102 towards the pressure cylinder 90 (i.e., in the direction opposite to 170) to re-engage them and resume ink image transfer from the ITM 44 to the continuous target substrate 50. It should be noted that the above-described sequence of release, backtracking and re-engagement enables the system 10 to prevent physical contact between the continuous target substrate 50 and the seam between the continuous target substrate 50 and the ITM 44 without leaving a large blank area between the images printed on the continuous target substrate 50.

[0117] In some embodiments, the impression cylinder 102 is mounted on any suitable mechanism, which is controlled by the processor 20 to move the cylinder 102 downward (e.g., in direction 170) to the release position and upward (e.g., opposite to direction 170) to the engagement position. In an example embodiment, the cylinder 102 is mounted on an eccentric 172 that is rotatable using any suitable motor or actuator (not shown).

[0118] In some embodiments, to cause the rotational movement of the cylinder 102, the eccentric 172 can be connected, for example, by a belt, to an idler 106 and an electric gear (not shown). In one embodiment, when the eccentric 172 is rotated by the aforementioned motor or actuator to an upper position within the support frame 98 of the module 100, the cylinder 102 is moved to the engagement position. This position is shown in FIG. 2. In another embodiment, when the eccentric 172 is rotated downward to a lower position in direction 170, the cylinder 102 is moved to the release position. The engagement and release mechanisms based on the aforementioned eccentric enable a fast and reliable transition between the engagement position and the release position of the cylinder 102.

[0119] In other embodiments, the processor 20 is configured to prevent physical contact between any predefined section of the ITM 44 other than the connection part with the continuous target substrate 50, and in particular, between the aforementioned joint part. In these embodiments, the processor 20 is configured to perform a plurality of releases between the cylinders 90 and 102 within one cycle of the ITM 44. For example, one release to prevent physical contact between the joint part and the continuous target substrate 50, and at least one or more releases to prevent physical contact between any other predefined section of the ITM 44 and the continuous target substrate 50.

[0120] In other embodiments, the engagement and release mechanisms can be implemented using any other suitable technique, such as, but not limited to, piston-type, spring-type, or magnetic-type mechanisms.

[0121] The specific configurations and operations of the engagement and release mechanism and the backtracking module 166 are shown simplified as examples in order to illustrate the specific problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of the system 10. However, embodiments of the present invention are in no way limited to this specific type of module example and mechanism, and the principles described herein may equally apply to any other type of printing system.

[0122] Control of the Substrate Conveying Module FIG. 3 shows the motor current over time and is a schematic representation of a graph 300 that can be used to control the substrate conveying module 100 in accordance with an embodiment of the present invention.

[0123] As described above, at the engagement position, the pressure cylinder 90 and the impression cylinder 102 engage with each other, and the processor 20 is configured to match the linear velocities of the cylinders 90 and 102 at the engagement point 150. The system 10 further includes one or more electric motors configured to move one or both of the cylinders 90 and 102 to move the ITM 44 and the continuous target substrate 50, respectively.

[0124] In some embodiments, line 302 in graph 300 includes a plurality of points representing respective measurements of the current flowing through the electric motor that moves cylinder 90 as a function of time. In some embodiments, the temporal change in the current flowing through the electric motor indicates a mismatch between the linear velocities of cylinders 90 and 102. Note that any undesirable or unspecified force applied to at least one of cylinders 90 and 102, ITM 44, and continuous target substrate 50 can cause a temporal change in the current flowing through the electric motor. For example, a mismatch between the linear velocities of cylinders 90 and 102 can cause an unspecified torque to be applied to cylinder 90 by the ITM 44.

[0125] In some embodiments, system 10 may include additional measurement functionality that is configured to measure at least a portion of the torque and other forces applied to the aforementioned elements of buffer units 86 and 88.

[0126] For example, point 304 of graph 300 indicates the current flowing through the electric motor when the engagement between cylinders 90 and 102 begins. As shown in graph 300, the slope of line 302 between point 304 where the engagement begins and point 306 where the engagement ends indicates a decrease in current during that time interval. It should be noted that when evaluating the slope, we ignore the rapid low-amplitude variations in current shown as a sawtooth wave in graph 300.

[0127] Temporal variations, such as the slope between points 304 and 306 and any other changes, indicate undesirable interactions due to the speed of that misalignment between cylinders 90 and 102. In the example of FIG. 3, the motor rotating cylinder 90 moves cylinder 90 at a speed higher than the speed of cylinder 102. As a result, the motor of cylinder 90 reduces its speed to match the linear speed between cylinders 90 and 102. Accordingly, the current flowing through the motor gradually decreases during the time interval between points 304 and 306.

[0128] Similarly, when the motor moves cylinder 90 at a linear speed lower than the linear speed of cylinder 102, cylinder 102 should pull cylinder 0 (e.g., due to the frictional force between the continuous target substrate 50 and ITM 44), and as a result, the current flowing through the motor of cylinder 90 should increase.

[0129] In some embodiments, the processor 20 is configured to receive current measurements (using any suitable sampling frequency, such as 500 Hz but not limited thereto) shown in the graph 300 from at least one of the electric motors, and to evaluate a trend, for example, over consecutive or overlapping time intervals or over a predefined gradient value. Based on the temporal trend, the processor 20 is configured to adjust the speed of at least one of the electric motors to match the linear speeds of the cylinders 90 and 102 by reducing the temporal change in the current.

[0130] For example, the time interval of the line 302 between the points 308 and 310 indicates the current flowing through the motor of the cylinder 90 during an additional cycle of engagement and transfer of the ink image from the ITM44 to the continuous target substrate 50. As shown in FIG. 3, the gradient of this time interval is significantly smaller than the gradient of the line 302 between the points 304 and 306, indicating that the basic speeds are approximately the same.

[0131] In a further example of the graph 300, the points 312 and 314 of the line 302 represent the start and end of another engagement cycle between the cylinders 90 and 102. In some embodiments, the processor 20 matches the linear speeds of the cylinders 90 and 102 such that the line 302 has a zero (or near zero) gradient during the time interval between the points 312 and 314.

[0132] Note that the linear speeds of the cylinders 90 and 102 can be different from each other for various reasons, such as different thermal expansions between the cylinders 90 and 102 and other reasons described herein.

[0133] FIG. 4 is a schematic side view of a printing station 400 of a digital printing system, such as the system 10, according to an embodiment of the present invention. The printing station 400 can replace, for example, the printing station 84 shown in FIG. 1B above.

[0134] In some embodiments, the station 400 includes a pressure cylinder 402 and a pressure cylinder 404 that are rotated at rotational speeds ω1 and ω2, respectively, by first and second motors, respectively.

[0135] In some embodiments, the ITM 44 and the continuous target substrate 50 are moved through the station 400 to transfer the ink image from the ITM 44 to the continuous target substrate 50. During the setup of the station 400, a predetermined distance 406 is set between the cylinders 402 and 404. In some embodiments, at least one of the cylinders 402 and 404 includes an encoder (not shown), and the encoder is configured to record the positions of the ITM 44 and the continuous target substrate 50, respectively.

[0136] In some embodiments, the processor 20 is configured to receive a plurality of position signals from the encoder of the cylinder 402 that indicate the positions of respective sections of the ITM 44. Based on the position signals, the processor 20 is configured to calculate the linear velocity of the ITM 44 and the rotational speed ω1 of the cylinder 402.

[0137] In some embodiments, the processor 20 is configured to adjust the rotational speed ω2 of the cylinder 404 to match the linear velocities of the ITM 44 and the continuous target substrate 50 at the engagement point 150. In the context and claims of the present disclosure, the terms "rotational velocity" and "rotary velocity" are used interchangeably to refer to the speeds of various drums, cylinders, and rollers of the system 10.

[0138] In some cases, different substrates may have different thicknesses, for example, due to different requirements for mechanical strength or due to regulatory requirements. In principle, it is possible to adjust the distance 406 for all substrates, however, this adjustment can reduce the productivity of the system 10, for example, the production output per hour, and also make its operation complex.

[0139] In some embodiments, the processor 20 is configured to receive a digital signal based on a converted analog signal indicative of the current flowing through at least one of the first and second motors of the station 400, and to compensate for different thicknesses of the continuous target substrate 50 by changing at least one of the rotational speeds ω1 and ω2. By applying an adjusted drive voltage and / or current to at least one of the first and second motors, the system 10 can switch between different types of substrates having different thicknesses without making hardware or structural changes, such as changing the value of the distance 406. It should be noted that the distance 406 can initially be set according to the expected typical thickness of the target substrate. For example, PET and OPP are thinner than paper. If the difference in thickness between different substrates is large (e.g., more than twice the thickness), the processor 20 is configured to, for example, set two values of the distance 406 and adjust the corresponding rotational speeds for each set.

[0140] In other embodiments, the processor 20 is configured to apply the same technique to correct for changes in the diameter of at least one of the cylinders 402 and 404 (e.g., due to thermal expansion), or changes in the thickness of the ITM 44, or other undesirable effects that may affect the operation of the station 400.

[0141] In some embodiments, the processor 20 is configured to improve the printing process by enhancing the control of the station 400 and continuously adjusting and matching the linear speeds of the ITM 44 and the continuous target substrate 50. By improving the printing process, the processor 20 can improve the quality of the ink image printed on the continuous target substrate 50.

[0142] FIG. 5 is a schematic side view of an image forming station 500 and drying stations 502 and 504, which are part of a digital printing system 10, in accordance with an embodiment of the present invention. The image forming station 500 and the drying station 502 may replace, for example, respective stations 60 and 64 of FIG. 1A described above, and the drying station 504 may replace, for example, the station 75 of FIG. 1A described above or may be added to a different configuration described herein.

[0143] In some embodiments, the image forming station 500 includes a plurality of printing bars, such as, for example, a white printing bar 510, a black printing bar 530, a cyan printing bar 540, a magenta printing bar 550, and a yellow printing bar 560.

[0144] In some embodiments, the station 500 includes a plurality of infrared-based dryers (IRDs) 520A - 520E. Each IRD is configured to direct infrared (IR) radiation onto the surface of the ITM44 facing the station 500. The IR radiation is configured to dry the ink previously applied to the surface of the ITM44. In some embodiments, at least one of the IRDs may include only an IR dryer or a combination of an IR-based dryer and a hot air-based dryer.

[0145] In some embodiments, the station 500 includes a plurality of blowers 511A - 511E having a configuration similar to the blower 66 of FIG. 1A described above.

[0146] In some embodiments, the station 500 includes three IRDs 520A - 520C and two blowers 511A and 511B arranged in the illustrated sequence example of FIG. 5 to dry the white ink applied to the ITM44 using the printing bar 510.

[0147] In some embodiments, a single blower, such as any of blowers 511C, 511D, 511E, and 511F, is attached after each of print bars 530, 540, 550, and 560, respectively, and two IRDs 520D and 520E are attached between the yellow print bar 560 and the dryer 502.

[0148] In some embodiments, the drying station 502 includes eight sections of blowers (not shown), each blower being similar to the blower 68 of FIG. 1A described above. In other embodiments, the blowers can be arranged in four sections, each section including two blowers. In alternative embodiments, the drying station 502 can include any suitable type and number of dryers arranged in any suitable configuration.

[0149] In some embodiments, the drying station 504 includes a single IRD, or an array of multiple IRDs (not shown), configured to apply a final amount of IR to the ITM 44 before each ink image enters the printing station.

[0150] The configuration of the image forming station 500 is simplified for clarity and is described by way of example. In other embodiments, the image forming station of the digital printing system can include any other suitable configuration.

[0151] The embodiments described herein mainly address digital printing onto a continuous web substrate, and the methods and systems described herein can also be used in other applications.

[0152] Transmission-based imaging of patterns printed on a continuous web substrate FIG. 6 is a schematic side view of an inspection station 200 integrated into a digital printing system 10 according to an embodiment of the present invention. In one embodiment, the inspection station 200 is integrated into the rewinder 190 of the digital printing system 10 before the continuous target substrate 50 on which the image is printed is wound onto the roller 214.

[0153] In another embodiment, inspection station 200 can be mounted or integrated onto any other suitable station or assembly of digital printing system 10 using any suitable configuration.

[0154] As described above, continuous target substrate 50 is made from one or more layers of any suitable material such as polyester, polyethylene terephthalate (PET), or oriented polypropylene (OPP), or any other material suitable for flexible packaging in the form of a continuous web. Such materials are partially transmissive to visible light, but still typically reflect at least a portion of the visible light. Reflection from continuous target substrate 50 can reduce the ability of the integrated inspection system to generate an image of continuous target substrate 50 and / or detect various types of process problems and defects formed during the digital printing process described above.

[0155] Note that several types of process problems and defects can occur in continuous target substrate 50. For example, random defects such as particles or scratches on the surface or between layers of continuous target substrate 50, and systematic defects such as missing or clogged nozzles in one or more of print bars 62.

[0156] In some embodiments, inspection station 200 includes a light source, also referred to herein as backlight module 210, which is configured to irradiate lower surface 202 of continuous target substrate 50 with one or more light beams 208.

[0157] In some embodiments, the backlight module 210 can include any suitable type of light source (not shown), such as one or more light emitting diodes (LEDs), a fluorescence-based light source, a neon-based light source, and one or more incandescent bulbs. The light source can include a light diffuser or can be coupled to a light diffusing device (not shown). In some embodiments, the light diffusing device, also referred to herein as a light diffuser, is configured to supply diffused light having a uniform irradiation profile that improves the performance of the image processing algorithm to the inspection station 200.

[0158] In some embodiments, the backlight module 210 is configured to emit light of any spectrum, such as white light, any selected range within visible light, or invisible light (e.g., infrared or ultraviolet) of any frequency or range of frequencies.

[0159] In some embodiments, the backlight module 210 is configured to emit light using any irradiation mode, such as continuous irradiation, pulses having symmetric or asymmetric shapes, or any other type of irradiation mode.

[0160] In some embodiments, the backlight module 210 is electrically connected to any suitable power supply unit (not shown) configured to supply a suitable voltage current or any other suitable power to the backlight module 210.

[0161] In some embodiments, the inspection station 200 includes an image sensor assembly 220, which is configured to acquire an image based on at least a portion of the light beam 208 transmitted through the continuous target substrate 50.

[0162] In some embodiments, the image sensor assembly 220 is electrically connected to the control console 12 to generate an electrical signal in response to the imaged light and transmit the electrical signal to the processor 20 of the control console 12 via, for example, the cable 57.

[0163] In some embodiments, the image sensor assembly 220 faces the upper surface 204 of the continuous target substrate 50 and the backlight module 210. In the example of FIG. 6, the illumination axis 212 extending between the image sensor assembly 220 and the backlight module 210 is substantially perpendicular to the continuous target substrate 50. In this configuration, the inspection station 200 is configured to generate a bright-field image of the ink image applied to the continuous target substrate 50 and can also acquire images of defects that may be present on the surfaces 202 and 204 or within the continuous target substrate 50. The types and geometric distortions of the defects are described in detail in FIG. 7 below.

[0164] In other embodiments, the image sensor assembly 220 and / or the backlight module 210 can be mounted on the digital printing system 10 using any other suitable configuration. For example, the image sensor assembly 220 can include one or more imaging sub-assemblies (not shown) arranged at an angle to the illumination axis 212 to generate a dark-field image of the continuous target substrate 50.

[0165] As described in FIG. 1B above, the substrate transport module 100 is configured to move the continuous target substrate 50 in direction 99. In some embodiments, the image sensor assembly 220 is mounted on a stage, for example, a scanning device (not shown), which is configured to move the image sensor assembly 220 in direction 206, typically perpendicular to direction 99.

[0166] In some embodiments, the processor 20 is configured to control the motion profiles in directions 99 and 206 to acquire an image from a selected position by positioning the selected position of the continuous target substrate 50 between the backlight module 210 and the image sensor assembly 220.

[0167] In some embodiments, the image sensor assembly 220 includes any suitable camera (not shown), such as a Surface camera including a 12 megapixel (MP) image sensor coupled to any suitable lens, for example.

[0168] In some embodiments, the camera of the image sensor assembly 220 can have any suitable field of view (FOV), such as 8 cm to 15 cm by 4 cm to 8 cm, but not limited thereto, and is configured to provide any suitable resolution, such as 1000 dots per inch (dpi), which is converted to a pixel size of 25 μm. The camera is configured to have different resolutions and FOVs that are subject to a trade-off with the FOV. For example, the camera can have a resolution of 2000 dpi using a smaller FOV.

[0169] In some embodiments, the processor 20 is configured to receive a set of FOVs from the camera and stitch a plurality of FOVs to display an image of a selected region of interest (ROI) of the continuous target substrate 50.

[0170] In some embodiments, the system 10 applies a base layer of white ink to the surface of the continuous target substrate 50 as described in FIG. 1A above. Although the substrate and the white ink are highly reflective, by using the configuration of the inspection station 200, the image sensor assembly 220 is configured to image at least a portion of the light beam 208 transmitted through the continuous target substrate 50 and the white ink.

[0171] In some embodiments, the image sensor assembly 220 is further configured to detect light of different intensities transmitted through a stack including the continuous target substrate 50, the base layer, and the ink pattern. For example, the white ink is partially transmissive to the light beam 208, and thus, different densities and / or thicknesses of the white ink result in different intensities of the transmitted beam 208, and thus, different electrical signals generated by the image sensor assembly 220. In some embodiments, the system 10 is configured to apply white ink and inks of other colors of different densities and / or thicknesses to the continuous target substrate 50 by controlling the amount of each ink droplet placed on a predefined area on the surface 204 of the continuous target substrate 50.

[0172] In some embodiments, the processor 20 is configured to generate different concentrations in a digital image indicative of, for example, the density and / or thickness of the white ink applied to the surface 204 of the continuous target substrate 50.

[0173] In some embodiments, the continuous target substrate 50 may include various types of printed and / or integrated marks (not shown), such as alignment marks, stitch marks for the aforementioned stitch operation, and barcode marks, but is not limited thereto. In some embodiments, the system 10 may include a sensor configured to read the marks of the continuous target substrate 50 to monitor the printing process as described in detail in FIG. 7 below.

[0174] In some embodiments, system 10 is configured to scan an entire area of continuous target substrate 50 in direction 206 using high-speed scanning when substrate transport module 100 moves continuous target substrate 50 in direction 99. Additionally or alternatively, system 10 may include a plurality of inspection stations 200 arranged in direction 206 across the width of continuous target substrate 50, for example, to cover the entire area of continuous target substrate 50. In yet other embodiments, system 10 may include any other suitable configuration, such as a plurality of cameras, each having a predefined movement path along direction 206, such that at least some of these cameras cover the entire area of continuous target substrate 50.

[0175] In other embodiments, inspection station 200 may include a plurality of image sensor assemblies 220 arranged in direction 206 across the width of continuous target substrate 50, for example, to cover the entire area of continuous target substrate 50 using the single backlight module 210 described above.

[0176] In the example of FIG. 6, backlight module 210 is fixed and image sensor assembly 220 moves. In alternative embodiments, inspection station 200 may have any other suitable configuration. For example, both backlight module 210 and image sensor assembly 220 may be movable by processor 20, or backlight module 210 may be movable and one or more image sensor assemblies 220 may be fixed.

[0177] This particular configuration of inspection station 200 is shown as an example in order to illustrate the particular problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such inspection station 200 and system 10. However, embodiments of the present invention are in no way limited to these particular kinds of example inspection stations and digital image systems, and the principles described herein may be equally applicable to other kinds of inspection station printing systems. For example, system 10 may include a blanket inspection station (not shown) having any suitable configuration for detecting defects and / or distortions on ITM 44 prior to transferring an ink image onto a continuous target substrate 50. The blanket inspection station may be integrated into system 10 at any suitable location and may operate in addition to, or instead of, inspection station 200.

[0178] In other embodiments, control console 12 may be electrically connected to an external inspection system (not shown), also referred to herein as a stand-alone inspection system, having any suitable configuration, such as the configuration of inspection station 200. The stand-alone inspection system is configured to image at least a portion of the light transmitted through continuous target substrate 50 and generate an electrical signal in response to the imaged light. Note that a stand-alone inspection system that inspects continuous target substrate 50 after the aforementioned printing process may operate instead of, or in addition to, inspection station 200.

[0179] In some embodiments, processor 20 is configured to generate a digital image based on electrical signals received from inspection station 200 and / or from a stand-alone inspection system, each of which may inspect a different section of continuous target substrate 50 and / or apply different inspection techniques (hardware and software) to inspect different features of concern, such as marks and ink patterns on continuous target substrate 50.

[0180] In other embodiments, the stand-alone inspection system may include one or more processors, interface circuits, memory devices, and other suitable devices to perform the imaging and detection described below, and may send output files to the processor 20 to improve the controlled operation of the system 10.

[0181] Detection of Defects and Distortions in Patterns Printed on a Continuous Web Substrate FIG. 7 is a flowchart schematically showing a method for detecting defects occurring in digital printing onto a continuous target substrate 50 according to an embodiment of the present invention. As described in FIG. 6 above, several types of process problems and defects can occur in the continuous target substrate 50. For example, random defects such as particles or scratches on the surface or between layers of the continuous target substrate 50, and systematic defects such as missing or clogged nozzles in one or more of the printing bars 62, misalignment between printing heads, non-uniformity, and other types of systematic defects. The term "systematic defect" refers to a defect that can occur due to problems in the system 10 and / or its operation. Thus, a systematic defect can be repeated in each printed image at a specific position and / or can have a specific geometric size and / or shape.

[0182] In some embodiments, the method of FIG. 7 is aimed at detecting systematic process problems and defects using the various test structures and marks described in FIG. 6 above. The method begins at a web homing step 702 by positioning a given mark placed on a selected section of the continuous target substrate 50 between the backlight module 210 and the image sensor assembly 220. In some embodiments, a given mark defines the origin of the coordinate system of the inspection station 200 on the continuous target substrate 50.

[0183] In calibration step 704, the processor 34 moves the continuous target substrate 50 and the image sensor assembly 220 so that the camera of the image sensor assembly 220 detects the beam 208 from a section of the continuous target substrate 50 without a pattern. In some embodiments, the processor 20 applies white balance techniques to calibrate various parameters of the inspection station 200, such as exposure time, RGB channels, etc. In some embodiments, the section without a pattern is also used to correct optical defects such as lens aperture correction.

[0184] As described in FIG. 6 above, the processor 20 is configured to generate different intensities (e.g., luminance) in the digital image that indicate, for example, the density and / or thickness of the ink of each color applied to the surface 204 of the continuous target substrate 50. For example, the different densities indicate the density of the white ink applied to the surface 204 of the continuous target substrate 50. Similarly, regions having a high density and / or thick layer of cyan ink, or any other color, appear with low luminance (e.g., dark color) in the digital image.

[0185] In the focus verification step 706, the processor 20 measures the focus of the inspection station 200 by testing the response of the inspection station 200 to obtain a focus calibration target or any other suitable pattern of the continuous target substrate 50 and focuses. Focus calibration can also be performed in lenses and camera models that support such operations.

[0186] In the substrate rotation step 708, the processor 20 rotates the continuous target substrate 50 in the direction 99 to a target section, also referred to herein as a target line, which includes one or more targets for testing process problems and systematic defects in the continuous target substrate 50. For example, the target line may include an array of targets for detecting defective nozzles in one or more printed bars 62 of a black printed bar. Another target line may include an array of targets for detecting defective nozzles in one or more printed bars 62 of a cyan printed bar.

[0187] In the camera movement step 710, the processor 20 moves the camera of the image sensor assembly 220 in direction 206 to position the camera in alignment with the test target of the test method. For example, it is a target for testing whether there is a defective nozzle in print head No. 9 of the black printed bar.

[0188] In some embodiments, steps 308 and 310 can be executed in a sequential mode. In these embodiments, the processor 20 rotates the continuous target substrate 50 in direction 99 to the target section or array. Then, the processor 20 stops the rotation of the continuous target substrate 50 and starts moving the camera of the image sensor assembly 220 in direction 206 to align the camera with the desired test target. These embodiments are also applicable to the calibration step 704.

[0189] In other embodiments, steps 308 and 310 can be executed in a simultaneous processing mode. In these embodiments, the processor 20 rotates the continuous target substrate 50 in direction 99 to the target section and simultaneously moves the camera of the image sensor assembly 220 in direction 206 to align the camera with the test target. These embodiments are also applicable to the calibration step 704.

[0190] In one embodiment, the simultaneous processing mode can also be executed during manufacturing when the system 10 prints an image on a product substrate rather than on a test substrate. In this embodiment, the image forming station 60 creates a test target placed between the product images or at any other suitable position on the continuous target substrate 50. During the printing of the printed image on the product substrate, the processor 20 moves the camera of the image sensor assembly 220 to the desired test target while rotating the continuous target substrate 50.

[0191] In the image acquisition step 712, the processor 20 applies the camera to the aforementioned target to acquire its image.

[0192] As described in FIG. 6 above, each object may have a mark, such as a barcode, which refers to a registry in a lookup table (or any other type of file). In barcode detection and reading step 714, the processor 20 detects and reads the barcode.

[0193] In some embodiments, the barcode may describe the feature being tested (e.g., the black nozzles of printhead 9), the type of test (detection of clogged nozzles), and the algorithm applied to the acquired image.

[0194] In other embodiments, the method may exclude the barcode detection and reading step 714 by replacing the barcode with any other suitable technique. For example, the information associated with a given feature being tested may be set based on the position of a given object in the coordinate system of inspection station 200.

[0195] In image analysis step 716, the processor 20 applies one or more algorithms corresponding to the test features shown in the image to the image acquired by the image sensor assembly 220. The algorithms analyze the image, and the processor 20 saves the results, for example, an indication of whether the black nozzles of print bar 9 are functioning within the specifications of system 10, or an alert if this nozzle is partially or completely clogged.

[0196] In target line determination step 718, the processor 20 checks whether the target line has additional targets that are part of the test method and have not yet been visited. If there are additional targets to be tested in the same target line (e.g., the black nozzles of print bar 8), the method loops back to camera movement step 710, and the processor 20 moves the camera of the image sensor assembly 220 along direction 206 to position the camera over the next test target in the same target line and test method.

[0197] After analyzing the last target within the target line, the processor checks, at scan completion step 720, whether there are additional target lines within the test regime. If there are additional target lines, the method loops back to substrate rotation step 708 and the processor 20 rotates the substrate to the next target line. For example, a target line including targets for testing the cyan color nozzles of print bar 62, and a similar (or different) target line for testing the nozzles of all other colors (e.g., yellow, magenta, and white) of print bar 62.

[0198] After completion of the last target line, at reporting step 722, the processor 20 outputs a status report for each of the nozzles tested. The report summarizes the nozzles within the specification range of the system 10 and the nozzles with malfunctions, and also generates a correction file.

[0199] At implementation step 724 to complete the method, the processor 20 applies corrective actions to the image forming station 60 as well as other stations and assemblies of the system 10.

[0200] In other embodiments, the method of FIG. 7 may be applicable to the monitoring and analysis of any other malfunctions of one or more stations, modules, and assemblies of the system 10.

[0201] For example, the same method may be applied to monitor other problems and defects such as print bar calibration, such as mechanical alignment of the print head, as well as print non-uniformities and color registration errors, but not limited thereto.

[0202] The embodiments described herein mainly address digital printing onto a continuous web substrate, and the methods and systems described herein can also be used in other applications such as in sheet-fed printing inspection.

[0203] Therefore, it will be understood that the foregoing embodiments are mentioned by way of example and that the present invention is not limited to what has been specifically shown and described above. Rather, the scope of the present invention includes both combinations and sub-combinations of the various features described above, as well as variations and modifications that will occur to those skilled in the art upon reading the foregoing description and that are not disclosed in the prior art. Documents incorporated by reference into this patent application are to be considered an integral part of this application, except that only the definitions in this specification are to be considered to the extent that any term is defined in these incorporated documents in a manner that conflicts with the definitions made explicitly or implicitly in this specification.

Claims

1. A digital printing system, comprising: An intermediate transfer member (ITM) configured to receive a printing fluid for forming an image and to engage with a continuous target substrate to transfer the image to the continuous target substrate having a first surface and a second surface, wherein the first surface and the second surface face each other; the ITM; A light source configured to irradiate the first surface of the continuous target substrate with light; An image sensor assembly configured to image at least a part of the light transmitted through the continuous target substrate to the second surface and to generate an electrical signal in response to the imaged light; A processor configured to generate a digital image based on the electrical signal and to estimate at least distortion in a printed image based on the digital image; A system comprising: The processor is further configured to cause a temporary release between the ITM and the continuous target substrate during a time interval when a joint portion of the ITM passes through an engagement point, and to backtrack the continuous target substrate during the time interval to correct the temporary release, so as to prevent physical contact between the joint portion of the ITM and the continuous target substrate. A digital printing system.

2. The system according to claim 1, wherein the distortion comprises geometric distortion.

3. The system according to claim 1 or 2, wherein the processor is configured to estimate the distortion by analyzing one or more marks on the continuous target substrate.

4. The system according to claim 3, wherein at least one of the one or more marks comprises a barcode.

5. The system according to claim 1 or 2, wherein the light source comprises a light diffuser.

6. The system according to claim 1 or 2, wherein the light source comprises at least a light emitting diode (LED).

7. The system according to claim 1 or 2, comprising one or more movement assemblies configured to move at least one of the continuous target substrate and the image sensor assembly relative to each other, and the processor is configured to generate the digital image by controlling the one or more movement assemblies.

8. The system according to claim 7, wherein the processor is configured to use at least one of the one or more movement assemblies to position a mark formed on the continuous target substrate between the light source and the image sensor assembly.

9. The system according to claim 8, wherein the one or more movement assemblies comprise a first movement assembly and a second movement assembly, and the processor is configured to (i) move only one of the first movement assembly and the second movement assembly at a time, and (ii) move the first movement assembly and the second movement assembly simultaneously.

10. The system according to claim 1 or 2, wherein the processor is configured to estimate at least distortion within the image during manufacture of the printed image.

11. The system according to claim 1 or 2, wherein the processor is configured to estimate at least the density of the printing fluid by analyzing the intensity of light transmitted through the continuous target substrate to the second surface.

12. The system according to claim 11, wherein the printing fluid comprises white ink.

13. The system according to claim 11, wherein the electrical signal indicates the intensity, and the processor is configured to generate a density indicating the intensity within the digital image.

14. A method comprising: receiving, within a digital printing system, a printing fluid by an intermediate transfer member (ITM) to form an image, and engaging the continuous target substrate to transfer the image to the continuous target substrate having a first surface and a second surface, the first surface and the second surface facing each other; irradiating the first surface of the continuous target substrate with light using a light source; using an image sensor assembly to image at least a portion of the light transmitted through the continuous target substrate to the second surface, and generating an electrical signal in response to the imaged light; generating a digital image based on the electrical signal, and estimating at least distortion within the printed image based on the digital image; During the time interval in which the joint portion of the ITM passes through the engagement point, causing a temporary release between the ITM and the continuous target substrate, and by backtracking the continuous target substrate during the time interval to correct the temporary release, preventing physical contact between the joint portion of the ITM and the continuous target substrate, A method comprising.

15. The method according to claim 14, wherein the distortion comprises geometric distortion.

16. The method according to claim 14 or 15, wherein estimating the distortion comprises analyzing one or more marks on the continuous target substrate.

17. The method according to claim 16, wherein at least one of the one or more marks comprises a barcode.

18. The method according to claim 14 or 15, wherein irradiating the first surface comprises irradiating the first surface using diffused light.

19. The method according to claim 14 or 15, wherein irradiating the first surface comprises irradiating the first surface using at least a light emitting diode (LED).

20. The method comprises moving at least one of the continuous target substrate and the image sensor assembly relative to each other using one or more motion assemblies, and generating the digital image comprises generating the digital image by controlling the one or more motion assemblies. The method according to claim 14 or 15.

21. The method according to claim 20, wherein moving at least one of the continuous target substrate and the image sensor assembly comprises positioning a mark formed on the continuous target substrate between the light source and the image sensor assembly.

22. The one or more motion assemblies comprise a first motion assembly and a second motion assembly, and moving at least one of the continuous target substrate and the image sensor assembly comprises (i) moving only one of the first motion assembly and the second motion assembly at a time, and (ii) The method according to claim 20, comprising at least one of moving the first motion assembly and the second motion assembly simultaneously.

23. The method according to claim 14 or 15, wherein estimating the distortion comprises estimating the distortion during manufacture of the printed image.

24. The method according to claim 14 or 15, comprising estimating at least the density of the printing fluid by analyzing the intensity of light transmitted through the continuous target substrate to the second surface.

25. The method according to claim 24, wherein the printing fluid comprises white ink.

26. The method according to claim 24, wherein the electrical signal indicates the intensity, and analyzing the intensity comprises generating a density indicating the intensity within the digital image.

Images