Control and monitoring of digital printing systems by inspecting periodic patterns on flexible substrates

Abstract

A digital printing system (10) includes a flexible substrate (44), an optical assembly (200, 301), and a processor (20). The flexible substrate (44) has a periodic pattern and is configured to move and receive ink droplets during a printing process that forms an image on the flexible substrate. The optical assembly (200, 301) is configured to illuminate the flexible substrate (44) with light (215, 315), detect the light (215, 315) from the flexible substrate (44), and derive a signal from the detected light (215, 315) indicating the periodic pattern. The processor (20) is configured to receive the signal and monitor or control the digital printing system (10) based on the periodic pattern as indicated by the signal.

Description

Technical Field

[0001] The present invention relates generally to digital printing, and in particular to methods and systems for controlling and monitoring the operation and calibration of digital printing systems. Background Art

[0002] Various methods and apparatus for controlling a digital printing process are known in the art.

[0003] For example, PCT patent application PCT / IB2013 / 051727 describes control devices and methods for a printing system, for example, including an intermediate transfer member (ITM). Some embodiments relate to adjusting the speed, tension, and / or length of the ITM. Some embodiments relate to adjusting ink deposition on a moving ITM. Some embodiments regulate a device configured to alert a user to one or more events related to the operation of the ITM.

[0004] PCT patent application PCT / IB2019 / 055288 describes an intermediate transfer member (ITM) configured to receive ink droplets to form an ink image thereon and transfer the ink image to a target substrate, the ITM comprising one or more layers and one or more markings integrated with at least one of the one or more layers at one or more corresponding marking positions along the ITM. Summary of the Invention

[0005] Embodiments of the invention described herein provide a digital printing system comprising a flexible substrate, an optical assembly, and a processor. The flexible substrate has a periodic pattern and is configured to move and receive ink droplets during a printing process that forms an image on the flexible substrate. The optical assembly is configured to illuminate the flexible substrate with light, detect the light from the flexible substrate, and derive a signal from the detected light that indicates the periodic pattern. The processor is configured to receive the signal and monitor or control the digital printing system based on the periodic pattern as indicated by the signal.

[0006] In some embodiments, the flexible substrate comprises a flexible intermediate transfer member (ITM) configured to receive the ink droplets and transfer the image to a target substrate. In other embodiments, the flexible substrate comprises a fabric. In other embodiments, the fabric comprises a first set of fibers and a second set of fibers interwoven with each other according to the periodic pattern, and the optical assembly is configured to derive the signal indicative of the periodic pattern from the interwoven first and second sets of fibers.

[0007] In an embodiment, the first group of fibers and the second group of fibers are arranged orthogonally to each other according to the periodic pattern, and the optical assembly is configured to derive the signal indicative of the periodic pattern from the orthogonal arrangement of the first group of fibers and the second group of fibers. In another embodiment, the first group of fibers is arranged orthogonally to the axis of movement of the flexible substrate according to the periodic pattern, and the optical assembly is configured to derive the signal indicative of the periodic pattern from the first group of fibers. In yet another embodiment, the fabric includes the periodic pattern, the optical assembly is configured to detect a plurality of position reference points in the periodic pattern of the fabric, and the processor is configured to calculate the position of the flexible substrate based on at least one of the position reference points.

[0008] In some embodiments, the signal indicates the position of at least one of the position reference points, and the processor is configured to control the digital printing system based on one or more of the position reference points. In other embodiments, the system includes an image forming station configured to direct a first ink droplet to a first ink location on the flexible substrate and a second ink droplet to a second ink location on the flexible substrate, the signal includes a first signal indicating the first ink location and a second signal indicating the second ink location, and the processor is configured to control registration between the first ink location and the second ink location based on the first signal and the second signal. In other embodiments, the first ink droplet includes a first color and the second ink droplet includes a second color different from the first color, and the processor is configured to control color-to-color registration based on the first signal and the second signal.

[0009] In one embodiment, the signal comprises a first signal derived at a first time and a second signal derived at a second time, the second time being different from the first time, and the processor is configured to monitor one or more parameters of the flexible substrate based on the first signal and the second signal. In another embodiment, the processor is configured to schedule replacement of the flexible substrate based on the first signal and the second signal. In yet another embodiment, the processor is configured to monitor stretching of the flexible substrate based on at least one of the first signal and the second signal.

[0010] In some embodiments, the processor is configured to adjust the speed of movement of the flexible substrate based on at least one of the first signal and the second signal. In other embodiments, the processor is configured to adjust the tension applied to the flexible substrate based on at least one of the first signal and the second signal. In other embodiments, the flexible substrate has an opacity that varies according to the periodic pattern.

[0011] In an embodiment, the processor is configured to control the printing process based on the periodic pattern as indicated by the signal. In another embodiment, the flexible substrate includes a flexible intermediate transfer member (ITM) configured to transfer the image to a target substrate after receiving the image, and the processor is configured to adjust or terminate the transfer of the image based on the signal. In another embodiment, the processor is configured to calibrate at least one component of the digital printing system based on the signal.

[0012] In some embodiments, wherein the flexible substrate comprises: (i) the fabric having the periodic pattern and a first elongation obtained when a given tension is applied to the moving flexible substrate; and (ii) a seam for connecting between edges of the fabric, the seam having a structure other than the periodic pattern such that when the given tension is applied to the moving flexible substrate, the seam has a second elongation different from the first elongation, and the processor is configured to calculate a ratio between the first elongation and the second elongation based on the signal. In other embodiments, the processor is configured to control the digital printing system based on the calculated ratio between the first elongation and the second elongation. In other embodiments, the flexible substrate includes a continuous loop that is configured to move within the digital printing system in at least a first rotation and a second rotation, and the processor is configured to calculate at least: (i) a first ratio between the first elongation and the second elongation for each of the first rotation; and (ii) a second ratio between the first elongation and the second elongation for each of the second rotation, and the processor is configured to monitor or control the digital printing system based at least on the first ratio and the second ratio.

[0013] In an embodiment, the optical assembly includes at least a first sensing component configured to derive a first periodic signal and a second position sensing component configured to derive a second periodic signal, the first position component and the second position component being arranged at first and second corresponding positions across the flexible substrate, and the processor being configured to detect deformation occurring in the flexible substrate based on the first and second periodic signals. In another embodiment, the first position component and the second position component are arranged along an axis orthogonal to a direction of movement of the flexible substrate. In yet another embodiment, at least one of the first position component and the second position component is arranged adjacent to an edge of the flexible substrate.

[0014] In some embodiments, the periodic pattern of the flexible substrate serves as an encoder scale of a motion encoder. In other embodiments, the flexible substrate and the optical assembly together serve as the motion encoder.

[0015] According to an embodiment of the present invention, a method for controlling a digital printing system is further provided. The method includes: illuminating a movable flexible substrate having a periodic pattern with light, wherein the flexible substrate receives ink droplets during a printing process, wherein the printing process forms an image on the flexible substrate; detecting the light from the flexible substrate and deriving a signal indicative of the periodic pattern from the detected light; and monitoring or controlling the digital printing system based on the periodic pattern indicated by the signal.

[0016] According to an embodiment of the present invention, a system for producing a flexible substrate having a periodic pattern is also provided, the system comprising a motion assembly, an optical assembly, a cutting subsystem, and a processor. The motion assembly is configured to move the flexible substrate along a movement direction. The optical assembly is configured to illuminate the flexible substrate with light, detect the light from the flexible substrate, and derive a signal indicative of the periodic pattern from the detected light. The cutting subsystem is configured to cut the flexible substrate. The processor is configured to receive the signal from the optical assembly, determine a cutting position for cutting the flexible substrate based on the signal, and control the cutting subsystem to cut the flexible substrate at the position.

[0017] In some embodiments, the periodic pattern includes a plurality of repeating pattern units, the signal includes a plurality of pulses indicative of corresponding pattern units detected by the optical assembly, and the processor is configured to count the number of pulses in the signal and determine the cutting position in response to detecting that the number of pulses exceeds a pre-assigned value. In other embodiments, the processor is configured to control the motion assembly to move the flexible substrate at a first speed during a first time interval in which the processor counts the pulses, and to move the flexible substrate at a second speed during a second time interval in which the processor controls the cutting subsystem to cut the flexible substrate. In other embodiments, the flexible substrate includes a fabric having a first set of fibers and a second set of fibers interwoven with each other according to the periodic pattern, and the optical assembly is configured to derive the signal indicative of the periodic pattern from light detected from the interwoven first and second sets of fibers.

[0018] In an embodiment, the first group of fibers and the second group of fibers are arranged orthogonally to each other according to the periodic pattern, and the optical assembly is configured to derive the signal indicative of the periodic pattern from light detected from the orthogonal arrangement of the first group of fibers and the second group of fibers. In another embodiment, the first group of fibers is arranged orthogonally to the direction of movement of the flexible substrate according to the periodic pattern, and the optical assembly is configured to derive the signal indicative of the periodic pattern from light detected from the first group of fibers.

[0019] According to an embodiment of the present invention, there is also provided a method for producing a flexible substrate having a periodic pattern, the method comprising moving the flexible substrate along a movement direction on a production surface. The flexible substrate is illuminated with light, the light from the flexible substrate is detected, and a signal indicative of the periodic pattern is derived from the detected light. Based on the signal, a cutting position for cutting the flexible substrate is determined, and the flexible substrate is cut at the cutting position.

[0020] The present invention will be more fully understood from the following detailed description of embodiments of the present invention when taken in conjunction with the accompanying drawings, in which: BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is a schematic side view of a digital printing system according to an embodiment of the present invention;

[0022] Figure 2A is a schematic diagrammatic illustration of a blanket fabric of a digital printing system according to an embodiment of the present invention;

[0023] Figure 2Bis a schematic cross-sectional view of a blanket fabric of a digital printing system according to an embodiment of the present invention;

[0024] Figure 3 is a schematic cross-sectional view of a position sensing assembly according to an embodiment of the present invention;

[0025] Figure 4 is a schematic cross-sectional view of a process control assembly according to an embodiment of the present invention;

[0026] Figure 5 is a block diagram schematically illustrating a method for synchronizing a distance measured on a blanket with a pitch size between two nozzles of different print heads according to an embodiment of the present invention;

[0027] Figure 6 is a block diagram schematically illustrating a method for estimating relative elongation between a seam and a fabric section of a blanket using fiber events received from a position sensing assembly according to an embodiment of the present invention;

[0028] Figure 7 is a schematic illustration of a system for cutting blanket fabric during production of a blanket according to an embodiment of the present invention; and

[0029] Figure 8 is a schematic, pictorial illustration of a subsystem for monitoring the position and alignment of a moving blanket, according to an embodiment of the present invention. DETAILED DESCRIPTION

[0030] Overview

[0031] The embodiments of the present invention described below provide methods and systems for controlling a printing process implemented in a digital printing system. In some embodiments, the printing process includes moving a flexible intermediate transfer member (ITM), also referred to herein as a blanket, configured to receive ink droplets to form an image thereon. The image is then transferred from the blanket to a target substrate (such as a sheet or continuous substrate).

[0032] In order to control the printing process, a processor of the system (also referred to herein as a print controller) receives control data, such as the position of the blanket relative to a reference point. In principle, marks can be provided on the blanket and a signal acquisition device can be installed on the printing system, the signal acquisition device being configured to provide a signal indicative of the position of one of the marks passing through the signal acquisition device. However, at least some of the marks (a) may differ from one another, for example due to variations in the mark formation process, and / or (b) may be obscured by defects formed in the blanket. Furthermore, the number of marks provided on the blanket is limited by various parameters (such as the mark size and the distance between adjacent marks), which can affect the frequency and / or quality of mark measurements.

[0033] In some embodiments, the blanket comprises a fabric made of two or more groups of fibers interwoven with each other. The fabric has an opacity that varies according to a periodic pattern of the interwoven fibers.

[0034] In some embodiments, a digital printing system includes an optical assembly having a light source on one side of a blanket and a light detector on the other side of the blanket. The optical assembly is configured to illuminate the blanket with light, detect the light that passes through the fabric, and derive one or more position signals from the detected light, the one or more position signals indicating one or more corresponding position reference points (e.g., fibers) in a periodic pattern of the fabric.

[0035] In some embodiments, based on the signals, the processor of the digital printing system is configured to control the printing process and monitor the condition of various components of the system, such as a replaceable blanket. For example, based on the signals, the processor can adjust the speed of movement of the blanket and / or the timing / sequence of ink droplet ejection during the printing process to compensate for deformation of the blanket, for example, to improve registration between different ink images produced by different colored inks. Furthermore, based on the signals, the processor can detect over- or under-stretching of the blanket and, in response, adjust the tension applied to the blanket by the printing system. In some embodiments, the processor can maintain a threshold value and can schedule a blanket replacement if over-stretching exceeds the threshold value.

[0036] The disclosed technology improves the quality of digitally printed images by reducing image distortion caused, for example, by registration errors during the printing process. Furthermore, the disclosed technology reduces manufacturing costs by eliminating the need to produce position marks on the ITM or any flexible continuous substrate configured to receive ink droplets to form an image thereon and / or by increasing system reliability by enabling close monitoring of blanket movement and condition.

[0037] System Description

[0038] Figure 1 is a schematic side view of a digital printing system 10 according to an embodiment of the present invention. In some embodiments, the system 10 includes a rolling flexible blanket 44 that circulates through an image forming station 60, a drying station 64, an imprinting station 84, and a blanket handling station 52. In the context of the present invention and in the claims, the terms "blanket" and "intermediate transfer member (ITM)" are used interchangeably and refer to a flexible member including one or more layers that serves as an intermediate member configured to receive an ink image and transfer the ink image to a target substrate, as described in detail below.

[0039] In one mode of operation, image forming station 60 is configured to form a mirror image of digital image 42, also referred to herein as an "ink image" (not shown) or, for brevity, an "image," on the upper run of the surface of blanket 44. The ink image is then transferred to a target substrate (e.g., paper, folding box, multilayer polymer, or any suitable flexible packaging in sheet or continuous web form) located beneath the lower run of blanket 44.

[0040] In the context of the present invention, the term “run” refers to the length or segment of blanket 44 between any two given rollers that guide blanket 44 .

[0041] In some embodiments, during installation, blanket 44 may be adhered edge to edge in an area referred to herein as seam 59 to form a continuous blanket loop (not shown). In some embodiments, seam 59 may have a different structure, and therefore different mechanical properties, than the fabric of blanket 44. Figure 2A and Figure 2B The structural differences are described in and below in Figure 6 Embodiments related to the differences in mechanical properties are described in detail in . Examples of methods and systems for installing seams are described in detail in PCT International Publication WO 2019 / 012456, the disclosure of which is incorporated herein by reference.

[0042] In some embodiments, image forming station 60 generally includes a plurality of print bars 62, each of which is mounted (e.g., using slides) on a frame (not shown) at a fixed height above the surface of the upper run of blanket 44. In some embodiments, each print bar 62 includes a bank of print heads as wide as the print area on blanket 44 and includes individually controllable print nozzles.

[0043] In some embodiments, the image forming station 60 may include any suitable number of rods 62, each of which may contain a printing fluid, such as a different colored aqueous ink. The inks typically have visible colors such as, but not limited to, cyan, magenta, red, green, blue, yellow, black, and white. Figure 1 In the example of FIG. 5 , image forming station 60 includes seven printbars 62 , but could include, for example, four printbars 62 of any selected color, such as cyan, magenta, yellow, and black.

[0044] In some embodiments, the printheads are configured to eject ink drops of different colors onto the surface of blanket 44 to form an ink image (not shown) on the surface of blanket 44 .

[0045] In some embodiments, the various print bars 62 are spaced apart from one another along an axis of movement, also referred to herein as the direction of movement of the blanket 44, indicated by arrow 94. In this configuration, accurate spacing between the bars 62 and synchronization between the ink droplets directed at each bar 62 and the moving blanket 44 are critical to achieving proper placement of the image pattern.

[0046] In some embodiments, the system 10 includes a heater, such as a hot gas or air blower 66 and / or an infrared (IR) heater or other suitable type of heater suitable for printing applications. Figure 1 In the example of FIG, air blower 66 is positioned between print bars 62 and is configured to partially dry ink droplets deposited on the surface of blanket 44. This flow of hot air between the print bars can help, for example, reduce condensation on the surface of the print head and / or deal with splatter (e.g., residue or droplets distributed around a main ink drop), and / or prevent clogging of the inkjet nozzles of the print head, and / or prevent ink droplets of different colors on blanket 44 from undesirably merging with each other. In some embodiments, system 10 includes a drying station 64 configured to blow hot air (or another gas) onto the surface of blanket 44. In some embodiments, the drying station includes air blower 68 or any other suitable drying equipment.

[0047] In the drying station 64, the ink image formed on the blanket 44 is exposed to radiation and / or hot air to more thoroughly dry the ink, thereby evaporating most or all of the liquid vehicle and leaving only the resin layer and the dye, which is heated to the point of becoming a tacky ink film.

[0048] In some embodiments, system 10 includes a blanket module 70 that includes a rolling ITM, such as blanket 44. In some embodiments, blanket module 70 includes one or more rollers 78, wherein at least one of rollers 78 includes an encoder (not shown) configured to record the position of blanket 44 in order to control the position of a segment of blanket 44 relative to a corresponding print bar 62. In some embodiments, the encoder of roller 78 typically includes a rotary encoder configured to generate a rotation-based position signal indicative of the angular displacement of the corresponding roller. Note that in the context of the present invention and in the claims, the terms "indicative of" and "indication" are used interchangeably.

[0049] Additionally or alternatively, blanket 44 may include an integrated encoder (not shown) for controlling the operation of the various modules of system 10. One embodiment of an integrated encoder is described in detail, for example, in U.S. Provisional Application 62 / 689,852, the disclosure of which is incorporated herein by reference.

[0050] In some embodiments, blanket 44 is guided over rollers 76 and 78 and a powered tensioning roller, also referred to herein as dancer assembly 74. Dancer assembly 74 is configured to control the slack length of blanket 44, and its movement is schematically represented by a double-headed arrow. Furthermore, any stretching of blanket 44 due to aging will not affect the ink image placement performance of system 10, and will simply require taking up more slack by tensioning dancer assembly 74.

[0051] In some embodiments, the floating roller assembly 74 can be motorized. The configuration and operation of rollers 76 and 78 are described in more detail, for example, in U.S. Patent Application Publication No. 2017 / 0008272 and the aforementioned PCT International Publication No. WO 2013 / 132424, the disclosures of which are incorporated herein by reference in their entirety.

[0052] In some embodiments, system 10 may include one or more tension sensors (not shown) disposed at one or more locations along blanket 44. The tension sensors may be integrated into blanket 44 or may include sensors external to blanket 44 that use any other suitable technology to acquire a signal indicative of the mechanical tension applied to blanket 44. In some embodiments, processor 20 of system 10 and additional controllers (e.g., as described below in FIG. 2 and FIG. 3 ) may be configured to control the tension of the blanket 44. Figure 3 ) is configured to receive a signal generated by the tension sensor to monitor the tension applied to the blanket 44 and control the operation of the dancer roller assembly 74.

[0053] In the embossing station 84 , the blanket 44 passes between the impression cylinder 82 and a pressure cylinder 90 , which is configured to carry a compressible blanket.

[0054] In some embodiments, the system 10 includes a control console 12 configured to control multiple modules of the system 10, such as a blanket module 70, an image forming station 60 located above the blanket module 70, and a substrate transport module 80 located below the blanket module 70, and the system includes one or more imprinting stations, as will be described below.

[0055] In some embodiments, console 12 includes a processor 20 (typically a general-purpose computer) having a suitable front end and interface circuitry for interfacing with a controller of dancer assembly 74 and controller 54 via cable 57, and for receiving signals from the controller. In some embodiments, controller 54, schematically shown as a single device, may include one or more electronic modules mounted on system 10 at predefined locations. At least one of the electronic modules of controller 54 may include an electronic device, such as a control circuit or processor (not shown), configured to control the various modules and stations of system 10. In some embodiments, processor 20 and control circuitry may be programmed with software to implement functions used by the printing system and store data for the software in memory 22. For example, the software may be downloaded electronically to processor 20 and control circuitry via a network, or the software may be provided on a non-transitory tangible medium, such as an optical storage medium, a magnetic storage medium, or an electronic storage medium.

[0056] 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, such as the alternative configurations of console 12 and display 34 described in detail in U.S. Patent 9,229,664, the disclosure of which is incorporated herein by reference.

[0057] In some embodiments, processor 20 is configured to display a digital image 42 on display 34 that includes one or more segments (not shown) of image 42 and / or various types of test patterns that may be stored in memory 22 .

[0058] In some embodiments, a blanket treatment station 52 (also referred to herein as a cooling station) is configured to treat the blanket by, for example, cooling the blanket and / or applying a treatment fluid to the outer surface of the blanket 44 and / or washing the outer surface of the blanket 44. At the blanket treatment station 52, the temperature of the blanket 44 may be reduced to a desired value before the blanket 44 enters the image forming station 60. Treatment may be performed by passing the blanket 44 over one or more rollers or blades configured to apply cooling and / or washing and / or treatment fluids to the outer surface of the blanket.

[0059] In some embodiments, in addition to or instead of Figure 1 , the blanket processing station 52 can be positioned adjacent to the image forming station 60. In such an embodiment, the blanket processing station can include one or more bars adjacent to the print bar 62 and apply the processing fluid to the blanket 44 by spraying.

[0060] In some embodiments, processor 20 is configured to receive a signal indicative of the surface temperature of blanket 44, e.g., from a temperature sensor (not shown), in order to monitor the temperature of blanket 44 and control the operation of blanket processing station 52. Examples of such processing stations are described, for example, in PCT International Publications WO 2013 / 132424 and WO 2017 / 208152, the disclosures of which are incorporated herein by reference in their entireties.

[0061] Additionally or alternatively, a treatment fluid may be applied to the blanket 44 by jetting prior to inkjet printing at the image forming station.

[0062] exist Figure 1 In the example shown, station 52 is mounted between stamping station 84 and image forming station 60, but station 52 may be mounted adjacent to blanket 44 at any other or additional suitable location or locations between stamping station 84 and image forming station 60. As described above, station 52 may additionally or alternatively include a bar adjacent to image forming station 60.

[0063] exist Figure 1 In the example of , the impression cylinder 82 impresses the ink image onto a target flexible substrate, such as each sheet 50 , which is transported by the substrate transport module 80 from an input stack 86 via the impression cylinder 82 to an output stack 88 .

[0064] In some embodiments, the lower run of the blanket 44 selectively interacts with the impression cylinder 82 at the impression station 84 to emboss the image pattern onto the target flexible substrate compressed between the blanket 44 and the impression cylinder 82 by the pressure of the pressure cylinder 90. Figure 1 In the case of a simplex printer (ie printing on one side of the sheet 50) as shown in FIG, only one embossing station 84 is required.

[0065] In other embodiments, module 80 may include two or more impression cylinders to allow for one or more duplex printing operations. The configuration of two impression cylinders also enables single-sided printing at twice the speed of double-sided printing. Additionally, a large number of mixed single-sided and double-sided prints can be printed. In alternative embodiments, different configurations of module 80 can be used to print on continuous substrates. Detailed descriptions and various configurations of duplex printing systems and systems for printing on continuous substrates are provided, for example, in U.S. Patents 9,914,316 and 9,186,884, PCT International Publication WO 2013 / 132424, U.S. Patent Application Publication 2015 / 0054865, and U.S. Provisional Application 62 / 596,926, the disclosures of which are incorporated herein by reference.

[0066] As briefly described above, the sheet 50 or continuous base material substrate (not shown) is carried by the module 80 from the input stack 86 through the nip (not shown) located between the impression cylinder 82 and the pressure cylinder 90. Within the nip, the surface of the blanket 44 carrying the ink image is firmly pressed against the sheet 50 (or other suitable substrate) by the pressure cylinder 90, for example, by a compressible blanket (not shown), so that the ink image is impressed onto the surface of the sheet 50 and is cleanly separated from the surface of the blanket 44. The sheet 50 is then transported to the output stack 88.

[0067] exist Figure 1 In the example shown, roller 78 is positioned at the upper run of blanket 44 and is configured to keep blanket 44 taut as it passes adjacent to image forming station 60. Furthermore, it is particularly important to control the speed of blanket 44 beneath image forming station 60 in order to achieve accurate ejection and deposition of ink droplets to place an ink image on the surface of blanket 44 by image forming station 60.

[0068] In some embodiments, impression cylinder 82 periodically engages and disengages blanket 44 to transfer the ink image from moving blanket 44 to a target substrate passing between blanket 44 and impression cylinder 82. In some embodiments, system 10 is configured to apply torque to blanket 44 using the aforementioned roller and dancer roller assembly in order to keep the upper run taut and substantially isolate the upper run of blanket 44 from mechanical vibrations occurring in the lower run.

[0069] In some embodiments, the system 10 includes an image quality control station 55 (also referred to herein as an automatic quality management (AQM) system) that functions as a closed-loop inspection system integrated into the system 10. In some embodiments, the station 55 can be positioned adjacent to the impression cylinder 82 (e.g., Figure 1 ) or positioned at any other suitable location in system 10.

[0070] In some embodiments, station 55 includes a camera (not shown) configured to capture one or more digital images of the aforementioned ink image printed on sheet 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.

[0071] In the context of this disclosure and in the claims, the term "about" or "approximately" used for any numerical values ​​or ranges indicates a suitable dimensional tolerance that allows a part or collection of components to function for its intended purpose, as described herein. For example, "about" or "approximately" may refer to a range of ±20% of the value of the stated value, for example, "about 90%" may refer to a range of 72% to 100% of the value.

[0072] In some embodiments, station 55 may include a spectrophotometer (not shown) configured to monitor the quality of the ink printed on sheet 50 .

[0073] In some embodiments, the digital images acquired by station 55 are transmitted to a processor, such as processor 20 of station 55 or any other processor, which is configured to evaluate the quality of the corresponding printed image. Based on the evaluation and signals received from controller 54, processor 20 is configured to control the operation of the modules and stations of system 10. In the context of the present invention and in the claims, the term "processor" refers to any processing unit configured to process signals received from the camera and / or spectrophotometer of station 55, such as processor 20 or any other processor or controller connected to or integrated with station 55. Note that the signal processing operations, control-related instructions, and other computing operations described herein can be implemented by a single processor or shared among multiple processors of one or more corresponding computers.

[0074] 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, full image registration with sheet 50, color-to-color (C2C) registration, printed geometry, image uniformity, color contours and linearity, and print nozzle functionality. In some embodiments, processor 20 is configured to automatically detect geometric distortion or other 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 (also referred to herein as a "master" or "source image") with a camera-acquired digital image of a printed version of the given image.

[0075] In other embodiments, the processor 20 may apply any suitable type of image processing software to the test pattern, for example, to detect distortions indicative of the aforementioned errors. In some embodiments, the processor 20 is configured to analyze the detected distortions to apply corrective action to the faulty module and / or feed instructions to another module or station of the system 10 to compensate for the detected distortions.

[0076] In some embodiments, processor 20 is configured to detect deviations in profile and linearity of printed colors based on signals received from the spectrophotometer of station 55 .

[0077] In some embodiments, the processor 20 is configured to detect various types of defects based on the signals acquired by the station 55: (i) in the substrate (e.g., the blanket 44 and / or the sheet 50), such as scratches, pinholes, and broken edges; and (ii) printing-related defects, such as irregular color spots, spatters, and smudges.

[0078] In some embodiments, the processor 20 is configured to detect these defects by comparing the printed sections with corresponding reference sections of the original design (also referred to herein as a master). The processor 20 is further configured to classify the defects and, based on the classification and predefined criteria, reject sheets 50 having defects that are not within the specified predefined criteria.

[0079] In some embodiments, the processor of station 55 is configured to decide whether to stop the operation of system 10, for example, if the defect density is above a specified threshold. The processor of station 55 is further configured to initiate corrective actions in one or more of the modules and stations of system 10, as described above. The corrective actions can be implemented immediately (while system 10 continues the printing process) or offline by stopping the printing operation and resolving the problem in the corresponding module and / or station of system 10. In other embodiments, any other processor or controller of system 10 (e.g., processor 20 or controller 54) is configured to initiate corrective actions or stop the operation of system 10 if the defect density is above a specified threshold.

[0080] Additionally or alternatively, the processor 20 is configured to receive signals, for example from the station 55, indicating additional types of defects and problems in the printing process of the system 10. Based on these signals, the processor 20 is configured to automatically estimate the accuracy of pattern placement and additional types of defects not mentioned above. In other embodiments, any other suitable method for inspecting the pattern printed on the sheet 50 (or on any other substrate described above) may also be used, such as using an external (e.g., offline) inspection system or any type of measuring device 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 halt the operation of the system 10.

[0081] For the purpose of illustrating the present invention, the configuration of system 10 is simplified and provided by way of example only. The components, modules, and stations described above in printing system 10, as well as additional components and configurations, are described in detail, for example, in U.S. Patents 9,327,496 and 9,186,884, PCT International Publications WO 2013 / 132438, WO 2013 / 132424, and WO 2017 / 208152, and U.S. Patent Application Publications 2015 / 0118503 and 2017 / 0008272, the disclosures of which are incorporated herein by reference in their entirety.

[0082] The specific configuration of system 10 is shown by way of example in order to illustrate certain problems solved by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such systems. However, embodiments of the present invention are in no way limited to this particular class of example systems, and the principles described herein may be similarly applied to any other class of printing systems.

[0083] Figure 2A is a schematic illustration of blanket fabric 100 of blanket 44 according to an embodiment of the present invention. For simplicity, blanket fabric 100 is also referred to herein as "fabric 100."

[0084] In some embodiments, blanket 44 may include fabric 100 and any suitable type of additional layers. Detailed embodiments related to the construction of stacked layers of any suitable blanket, such as blanket 44, are provided, for example, in PCT International Publication No. WO 2017 / 208144 and PCT Patent Application No. PCT / IB2019 / 055288, the disclosures of which are incorporated herein by reference in their entireties.

[0085] In some embodiments, fabric 100 includes two or more groups of fibers interwoven with one another. In this embodiment, fibers 102 and 104 constitute a first group of fibers and a second group of fibers that are substantially orthogonal to one another. In this configuration, each fiber 102 is interwoven with all fibers 104, and each fiber 104 is interwoven with all fibers 102.

[0086] In some embodiments, the fabric 100 of the blanket 44 has an opacity that varies according to its periodic pattern. In the present example, the periodic pattern of opacity is caused by fibers 102 and 104, while the openings 106 between the fibers 102 and 104 are not opaque (e.g., transparent or translucent), as will be described below. Figure 3 Described in detail in.

[0087] In some embodiments, blanket 44 is configured to be moved by substrate transport module 80 (e.g., in the direction of movement indicated by arrow 94) and to receive ink droplets during a printing process performed by system 10 that forms an image on blanket 44. Note that in the example of fabric 100, fibers 102 are arranged parallel to each other and to the direction of movement indicated by arrow 94, and fibers 104 are arranged parallel to each other but orthogonal to arrow 94.

[0088] In some embodiments, the fabric 100 of the blanket 44 may include any suitable number of fibers, such as between 20,000 and 30,000 fibers 104. Figure 3As described in , each fiber 104 and / or the distance between adjacent fibers 104 and / or the openings 106 may be used as a position reference along the axis of movement of the blanket 44 .

[0089] In other embodiments, the fibers of fabric 100 may have any other suitable configuration. For example, the longitudinal axes of two or more groups of fibers may have any suitable angle relative to each other (e.g., other than orthogonal) and may be oriented at any other suitable angle relative to the axis of movement of blanket 44, represented by arrow 94. Figure 2A In the example of FIG, opening 106 has a rectangular shape determined by the orthogonality between fibers 102 and fibers 104. In other embodiments, fibers 102 and 104 may be arranged at another angle relative to each other, such that opening 106 may have a diamond shape or any other shape, such as a non-rectangular shape.

[0090] Figure 2B According to the embodiment of the present invention, Figure 2A A schematic cross-sectional view of the fabric 100 is shown in FIG. Figure 2B In the example of FIG, the cross-sectional view is orthogonal to arrow 94, so that the single fiber 102 is interwoven with the plurality of fibers 104, as described above in Figure 2A As described in.

[0091] In some embodiments, the size and periodic pattern of the openings 106 are determined by the width of the fibers and the distance between any pair of adjacent fibers, which is generally uniform along the blanket 44. Figure 2B In the example of FIG. 1 , the width 110 of each fiber 104 determines the aforementioned opacity and the distance 112 between the edges of adjacent fibers 104 determines the aforementioned periodic pattern, which is substantially similar to the size of the openings 106 along arrows 94 .

[0092] As mentioned above Figure 2A As stated in Figure 2B Another cross-sectional view (not shown) orthogonal to the cross-sectional view will show a single fiber 104 interwoven with multiple fibers 102. Note that in the so-called orthogonal cross-sectional view (not shown), the width of each fiber 102 may determine the aforementioned opacity and the distance between the edges of adjacent fibers 102 may determine the aforementioned periodic pattern, which is similar to the size of the openings 106 in a direction orthogonal to arrow 94.

[0093] In some embodiments, seam 59 may be formed using, inter alia, a thermal process that may deform or even melt fibers 102 and 104 (described above in Figure 1 ). Thus, seam 59 may not have any fibers, or at least may not have the ordered structure of fibers 102 and 104 of blanket fabric 100.

[0094] Detecting light passing through the fabric to produce a signal indicating a periodic pattern

[0095] Figure 3 is a schematic cross-sectional view of a position sensing assembly 200 according to an embodiment of the present invention. In the context of this disclosure and in the claims, the terms "position sensing assembly" and "optical assembly" are used interchangeably and refer to an optical subsystem that is configured to (a) illuminate the blanket 44 with light, (b) detect the light passing through the fabric 100 of the blanket 44, and (c) derive an indication from the detected light as described above in Figure 2A and Figure 2B As described above, blanket 44 may include fabric 100 and any suitable type of additional layers.

[0096] In some embodiments, at least one of the aforementioned additional layers may be transparent or translucent to light of a suitable wavelength or wavelengths. As will be described in detail below, suitable light irradiating the blanket 44 may pass through Figure 2A and Figure 2B The opening 106 of the fabric 100 is shown in FIG. 1 and is detected by the sensor.

[0097] In some embodiments, system 10 is configured to move blanket 44 at a predefined and controlled speed in the direction of movement represented by arrow 94 .

[0098] exist Figure 3 In the exemplary embodiment shown in FIG, the fabric 100 of the blanket 44 includes three openings 106A, 106B, and 106C that are located between corresponding pairs of adjacent fibers 104 of the fabric 100. Note that the openings 106A, 106B, and 106C are also located between adjacent fibers 102, as shown in FIG. Figure 2A As shown in the top view of the opening 106. Figure 3 The cross-sectional view of FIG. 1 cannot show the dimension orthogonal to arrow 94, and therefore the openings 106A, 106B and 106C are shown as dashed boxes to illustrate that they are also located between two adjacent fibers 102, as described above in Figure 2A shown in the top view.

[0099] In some embodiments, the position sensing assembly 200 is configured to detect the positions of the openings 106A, 106B, and 106C in the blanket 44 and derive signals indicative of the aforementioned periodic pattern from the detected positions. As will be described in detail below, the disclosed techniques can obtain, for a given opening, one or more signals indicative of one or more corresponding positions of the given opening (e.g., by using multiple position sensing assemblies 200 mounted on the system 10 along the blanket 44). These techniques can also be applied to multiple openings or other features of the fabric 100 to estimate the actual position of a selected point of the blanket 44 and control the printing process of the system 10 based on these signals. In some embodiments, the openings 106A, 106B, and 106C and the fibers 104 can be used as a scale to encode one or more predefined positions on or within the blanket 44. In such embodiments, the blanket 44 can be used as an encoder scale for the position sensing assembly 200 to sense the positions of predefined fibers 104 and / or openings (such as openings 106A, 106B, and 106C). In other words, blanket 44 has integrated encoder scale features, such as, but not limited to, fibers 104 and openings 106A, 106B, and 106C. Furthermore, the combination of blanket 44 and position sensing assembly 200 (or any other suitable position sensing device configured to detect fibers 104 and one or both of openings 106A, 106B, and 106C) can function as a linear encoder for controlling the movement of blanket 44 and controlling the printing process of system 10. In other words, blanket 44 has integrated encoder scales for controlling the movement of blanket 44 relative to the various stations and modules of system 10.

[0100] In some embodiments, position sensing assembly 200 includes a light source 216, such as one or more light emitting diodes (LEDs), one or more lasers, or any other suitable type of light source configured to emit any suitable range of wavelengths or monochromatic wavelengths with sufficiently high luminous intensity (e.g., about 4500 to 9000 mcd). For example, the Power SMD LED PLCC-2Plus product supplied by Vishay (Malvern, Pennsylvania). Light source 216 is configured to emit and direct one or more collimated light beams (such as light beam 215) that can pass through openings 106A, 106B, and 106C of fabric 100.

[0101] In some embodiments, position sensing assembly 200 may include one or more channels, where each channel may include a light source and a corresponding sensor as described below.

[0102] In other embodiments, blanket 44 may not have openings (such as openings 106A-106C) or may include at least one layer that is not transparent or translucent to white light. In such embodiments, position sensing component 200 may emit light including wavelengths that can pass through fabric 100 but are affected by the periodic pattern. For example, position sensing component 200 may emit infrared (IR) radiation that is configured to pass through the layers of blanket 44 but has a varying intensity that is indicative of the periodic pattern.

[0103] In some embodiments, position sensing assembly 200 includes a slit assembly 208 having one or more slits, such as slit 210 having opening 204. Slit 210 is configured to pass light beam 215 that has passed through openings 106A, 106B, and 106C as described above.

[0104] In some embodiments, where the slit assembly 208 includes two or more slits located at a predefined distance from each other, the slit assembly 208 may include a shield (not shown) that is configured to block stray light or scattered light, for example, between adjacent slits of the slit assembly 208.

[0105] In some embodiments, the position sensing assembly 200 includes a fiber optic assembly 218 having a bundle of multiple optical fibers 220 arranged between a lower surface 221 and an upper surface 223 of the fiber optic assembly 218. In some embodiments, the surfaces 221 and 223 are transparent to the light beam 215, and the optical fibers 220 are configured to transmit the light beam 215 through the fiber optic assembly 218. In the case of multiple light beams and / or multiple slits, the optical fibers 220 are adapted to prevent interference between different light beams.

[0106] like Figure 3 , position sensing assembly 200 may include a single light beam 215 and a single slit 210. In alternative embodiments, fiber optic assembly 218 may include a single optical fiber or any other suitable type of optical channel configured to transmit light beam 215 therethrough as described above with respect to fiber optic assembly 218.

[0107] In some embodiments, position sensing assembly 200 includes sensor 222, which may include a suitable type of photodiode, such as the silicon PIN photodiode SFH 206K product supplied by OSRAM Opto Semiconductors GmbH (Regensburg, Germany), or any other suitable sensing device.

[0108] In some embodiments, sensor 222 of position sensing assembly 200 is configured to sense light beam 215 passing through the aforementioned opening of fabric 100 and derive from the sensed light a signal indicative of the periodic pattern described above, such as current intensity as a function of time.

[0109] Reference is now made to inset 207, which illustrates a top view of a section of fabric 100 moving with blanket 44 in the direction of arrow 94. In some embodiments, slit 210 of position sensing assembly 200 is generally stationary but is illustrated in inset 207 as three dashed rectangles at three locations relative to fabric 100 due to the movement of blanket 44.

[0110] In some embodiments, the slits 210 can be sized along the Y-axis of the blanket 44 to cover a predefined section or the entire width of the blanket 44. In the example embodiment shown in graph 209 of inset 207, in response to a light beam 215 passing through openings 106 and 106C and through slit 210, the sensor 222 is configured to generate a current signal 217 indicative of the light intensity sensed between two adjacent fibers 104. As shown in graph 209, each current signal 217 is aligned with a corresponding opening (e.g., opening 106 or 106C). Note that the current signals 217 of graph 209 indicate a periodic pattern of the corresponding section of the fabric 100.

[0111] Reference is now made to graph 205, which illustrates the current intensity (I) of the signal generated by sensor 222 as a function of time. In some embodiments, sensor 222 is configured to derive from the sensed light signals 206A, 206B, and 206C that are indicative of the current signals sensed at the respective locations of openings 106A, 106B, and 106C. Note that signals 206A, 206B, and 206C also indicate the current intensity (I) of the signal generated by sensor 222 as a function of time. Figure 2A and Figure 2B In other words, each of openings 106A, 106B, and 106C is a pattern unit of the periodic pattern of blanket 44, and each of light signals from light signals 206A, 206B, and 206C (also referred to herein as pulses) indicates a corresponding pattern unit detected by sensor 222 of position sensing assembly 200 (e.g., from openings 106A, 106B, and 106C).

[0112] In some embodiments, sensor 222 may include a controller (not shown) configured to calculate signals 206A, 206B, and 206C based on a statistical analysis of the respective current signals acquired by sensor 222. For example, the intensity of signal 206C of graph 205 may be calculated based on an average or median value of the intensity of current signal 217 shown in graph 209.

[0113] In other embodiments, processor 20 is configured to calculate signals 206A, 206B, and 206C based on the aforementioned statistical analysis of the corresponding current signals acquired by sensor 222 .

[0114] As shown in the cross-sectional and top views of fabric 100, a virtual box 202 may be used to describe the signal acquisition and processing flow. Note that box 202 is shown only for conceptual clarity of the description and is not part of blanket 44 or assembly 200.

[0115] In some embodiments, system 10 moves blanket 44 at a predefined speed in the direction of movement indicated by arrow 94, and light source 216 emits light beam 215. When opening 106A is aligned with opening 204 of slit 210, light beam 215 passes through opening 106A of fabric 100 and fiber optic assembly 218 and is sensed by sensor 222.

[0116] In some embodiments, sensor 222 outputs a signal 206A indicating the sensed intensity of light beam 215 and the position of opening 106A. Meanwhile, system 10 maintains moving blanket 44 in the direction of arrow 94 at a predefined speed. When opening 106B is aligned with slit 210, light beam 215 passes through it and passes through slit 210 and fiber optic assembly 218. Light beam 215 passing through opening 106B is then sensed by sensor 222, which outputs a signal 206B indicating the position of opening 106B. The same signal acquisition process is then repeated for opening 106C while system 10 moves blanket 44, such that when opening 106C is aligned with slit 210, light beam 215 passes through it and passes through slit 210 and fiber optic assembly 218. Light beam 215 passing through opening 106C is then sensed by sensor 222, which outputs a signal 206C indicating the position of opening 106C.

[0117] Note that in Figure 3 In the example configuration of FIG. 1 , the position sensing assembly 200 is configured to generate three different signals 206A, 206B, and 206C that are indicative of the positions of the openings 106A, 106B, and 106C, respectively.

[0118] In some embodiments, processor 20 is configured to receive at least one of signals 206A, 206B, and 206C and control the printing process of system 10 based on the received signal. As described above, blanket 44 is configured to function as a scale that encodes the position of predefined features (such as openings 106A, 106B, and 106C) over time. In other words, the combination of blanket 44 and position sensing assembly 200 constitutes a motion control encoder for system 10. Note that: (i) when position sensing assembly 200 faces, for example, dancer roller assembly 74, the combination of blanket 44 and position sensing assembly 200 constitutes a rotary encoder, and (ii) when position sensing assembly 200 faces, for example, a linear segment along an upper run or lower run of blanket 44, the combination of blanket 44 and position sensing assembly 200 constitutes a linear encoder.

[0119] In an embodiment, processor 20 may control the timing of ink ejection from the nozzles of one or more print heads based on the speed of blanket 44 and the aforementioned signals 206A, 206B, and 206C. For example, processor 20 may receive more than 20,000 signals from position sensing assembly 200 indicating corresponding position reference points of more than 20,000 openings 106 of fabric 100 and improve C2C registration of an image printed on blanket 44 based on the received signals. Note that by having more than 20,000 position reference points along blanket 44, processor 20 may apply a position-based approach rather than a speed-based approach to control the printing process of system 10.

[0120] like Figure 1 As described in

[0045] , one or more encoders can be used, for example, to measure the motion (e.g., velocity) of the blanket 44. However, such measurements are indirect and therefore prone to error. For example, insufficient component rigidity, mounting errors, and thermal expansion of the rotary scale can cause errors in the encoder's measurement accuracy. Note that during the printing process and when monitoring and calibrating various components and / or stations of the system 10, measurement accuracy errors typically accumulate with each cycle of the rotary encoder and can cause various registration errors (e.g., C2C and image-to-substrate registration errors).

[0121] In some embodiments, position sensing assembly 200 is configured to directly measure the position of a reference point on blanket 44, for example, by generating signals 206A, 206B, and 206C indicating the positions of openings 106A, 106B, and 106C, respectively. In other embodiments, processor 20 may count the number of fibers 104 in blanket 44 and thus have a direct position measurement of any feature on blanket 44 based on the signals received from position sensing assembly 200 as blanket 44 moves in the direction of arrow 94.

[0122] In such embodiments, the processor 20 may adjust various types of process parameters, such as the local velocity of the blanket 44 and / or the jetting times of different color inks jetted from particular nozzles, in order to improve C2C registration of the printing process implemented by the system 10. Additionally or alternatively, based on signals received from the position sensing assembly 200, the processor 20 is configured to improve the placement accuracy of one or more ink drops jetted onto the surface of the blanket 44, which may improve the image-to-substrate registration of the system 10.

[0123] In some embodiments, in a duplex printing system, improved drop placement accuracy can help improve registration between images printed on the front and back sides of a target substrate (e.g., a sheet or base material). It will be appreciated that accurately printing an image on blanket 44 may not guarantee improved image-to-substrate registration, for example, where undesirable registration errors may occur at other stations of system 10 (e.g., at imprint station 84). In some embodiments, processor 20 can use the aforementioned signals to improve C2C registration by compensating for known issues in system 10, such as known misalignment between two or more printbars 62.

[0124] In some embodiments, by receiving signals indicating a large number (e.g., more than 20,000) of position reference points along the blanket 44, the processor 20 can control the printing process of the system 10 without being affected by local damage or contamination that may occur on the blanket 44 and may obscure or cover one or more position reference points located along the blanket 44.

[0125] In some embodiments, based on the signals (e.g., signals 206A, 206B, and 206C), the processor 20 is configured to identify errors and / or failures of the system 10. For example, the processor 20 may set or calculate the movement speed of the blanket 44 and may receive the aforementioned signals for two or more specific openings located along the fabric 100 of the blanket 44. In such embodiments, the processor 20 is configured to estimate the distance between the corresponding specific openings and estimate whether the blanket 44 has been deformed, for example, due to overstretching, overheating, or aging of the blanket. Figure 5 These embodiments are described in further detail in .

[0126] In some embodiments, blanket 44 may be replaced as part of a preventative maintenance process. In such embodiments, processor 20 is configured to monitor various parameters over the life cycle of blanket 44. For example, based on signals received from position sensing assembly 200, processor 20 is configured to generate a “fingerprint” of each blanket 44 installed on system 10.

[0127] In some embodiments, the fingerprint may include parameters or variables having specific values ​​for each blanket 44. For example, based on the signals received from the position sensing assembly 200, the processor 20 is configured to: (a) count the number of fibers 102 and 104 comprising the fabric 100, (b) estimate the average width of a group of fibers, (c) estimate the distance between adjacent fibers, and (d) estimate the size and location of defects in the blanket 44.

[0128] In some embodiments, processor 20 is configured to monitor the fingerprint of a given blanket 44 over time, and based on predefined criteria, processor 20 may manage at least a portion of preventative maintenance activities for system 10, and in particular, blanket 44. For example, by monitoring the distance between adjacent fibers, processor 20 may detect overstretching of blanket 44, and in response, may schedule preventative replacement of the overstretched blanket 44.

[0129] In such embodiments, processor 20 may maintain one or more thresholds for controlling and compensating for stretching of blanket 44. For example, when the distance between adjacent fibers is greater than a predefined threshold, processor 20 may display a warning about a stretched blanket on display 34. In addition, processor 20 may adjust the movement speed of blanket 44 or other process parameters of system 10 to compensate for excessive blanket stretching.

[0130] exist Figure 3 In the example configuration shown in , light source 216 and sensor 222 are positioned on different sides of blanket 44 and the detected light passes through the periodic pattern of fabric 100. In alternative embodiments, blanket 44 may include a reflective periodic pattern and a light source. In such embodiments, the sensor and light source of the position sensing assembly may be mounted on the same side of the blanket using any suitable configuration to acquire position signals using bright field and / or dark field imaging and detection techniques.

[0131] In other embodiments, the blanket may include a periodic pattern that can be detected using any suitable non-optical technique. For example, the blanket 44 may include magnetic elements arranged in a periodic pattern, and the sensor 222 may include a magnetic sensor configured to detect a magnetic-based position reference point on the blanket.

[0132] Some of the alternative position sensing techniques described above may affect the configuration of the position sensing component. For example, the light source and slit may be removed from a magnetic-based position sensing component configuration, and the slit may be removed from a dark-field-based position sensing component configuration.

[0133] This particular configuration of position sensing assembly 200 and fabric 100 of blanket 44 is shown by way of example to illustrate certain issues addressed by embodiments of the present invention (such as C2C registration and blanket stretch) and to demonstrate the application of these embodiments to enhancing the performance of digital printing systems, such as system 10. However, embodiments of the present invention are in no way limited to this particular class of example systems, and the principles described herein may be similarly applied to other classes of position sensing assemblies and / or blankets and / or printing systems.

[0134] Controlling the printing process based on a signal indicative of a periodic pattern

[0135] Figure 4 is a schematic cross-sectional view of a process control assembly (PCA) 300 according to an embodiment of the present invention. In some embodiments, PCA 300 includes position sensing assembly 200 aligned with printbar 62A and position sensing assembly 301 aligned with printbar 62B.

[0136] In some embodiments, position sensing assemblies 200 and 301 may be mounted on print bars 62A and 62B, respectively. Note that print bars 62A and 62B may be implemented in system 10 and / or may replace the position sensing assemblies described above. Figure 1 Any of the print bars 62 shown in .

[0137] In some embodiments, printbars 62A and 62B may be similar, but typically eject different colors of ink. For example, printbar 62A may eject one or more drops of black ink 303A, and printbar 62B may eject one or more drops of magenta ink 303B.

[0138] In some embodiments, position sensing assemblies 200 and 301 can have similar configurations, such that light sources 216 and 316 are similar to each other, fiber optic assemblies 218 and 318 are similar to each other, and sensors 222 and 322 are similar to each other. Note that system 10 may include additional position sensing assemblies having the same configuration as position sensing assembly 200, each of which may be mounted on a different print bar (such as described above in FIG. Figure 1 The plurality of print bars 62 shown in FIG. 5 are positioned on and / or aligned with different print bars.

[0139] In the context of this disclosure and in the claims, the term "alignment" between a given position sensing assembly and a corresponding print bar refers to directing light and ink to the same location or to a predefined offset from each other on the surface of blanket 44. In an example embodiment, light source 216 may direct light beam 215 to a location on blanket 44 where print bar 62A ejects one or more drops of ink 303A.

[0140] In another embodiment, the processor 20 may store the offset between the position of the light beam 215 and the predefined ink 303A falling on the blanket 44, and take the predefined offset into account when calculating relevant printing control parameters (such as, but not limited to, inkjet time and blanket movement speed).

[0141] In some embodiments, when the PCA 300 faces a linear segment (such as Figure 4 The combination of blanket 44 and PCA 300 constitutes a linear motion encoder to control the motion of blanket 44 relative to print bars 62A and 62B of image forming station 60, for example, when the linear section between adjacent rollers 78 is shown in FIG.

[0142] As mentioned above Figure 3 As described above, for example, each of the position sensing components 200 and 301 is configured to send the acquired signals (such as signals 206A, 206B and 206C) to the processor 20 and / or any suitable printing controller of the system 10 via one or more cables 302 to control the above-mentioned printing process. Figure 3 The printing process described in .

[0143] In other embodiments, the configuration of at least one position sensing assembly (e.g., position sensing assembly 301) can differ in at least one element from the configuration of position sensing assembly 200. For example, light source 316 can emit one or more light beams (such as light beam 315) that can have a different wavelength spectrum or different power than light beam 215.

[0144] In alternative embodiments, all position sensing assemblies mounted on and / or aligned with respective print bars may have the same configuration. In these embodiments, system 10 may include at least one additional position sensing assembly having a different configuration. The additional position sensing assembly is configured to sense different signals indicating different information that can be used by processor 20 to perform measurements and / or detect specific types of defects that may be present on blanket 44. In such embodiments, processor 20 may use the different signals as supplemental information in addition to the signals received from position sensing assemblies having the same configuration as position sensing assembly 200.

[0145] In some embodiments, one or more additional position sensing components may be mounted on printbar 62 of image forming station 60 that is not used in a printing application. Additionally or alternatively, one or more additional position sensing components may be mounted at any other suitable mounting location on system 10.

[0146] Improving print registration based on signals acquired by multiple position sensing components

[0147] Figure 5 is a block diagram 400 illustrating a method for synchronizing a distance measured on a blanket 44 with a pitch size between two nozzles of different print heads, according to an embodiment of the present invention.

[0148] In some embodiments, block diagram 400 includes printbars 62A and 62B having respective nozzles 63A and 63B of a printhead configured to eject one or more drops of black ink 303A and magenta ink 303B, respectively. In some embodiments, nozzles 63A and 63B are positioned a distance 440 from each other and are configured to direct respective drops of ink 303A and 303B to land on blanket 44 at locations 406 and 408, respectively.

[0149] As described above, the blanket 44 moves along the axis of movement indicated by arrow 94, and the position sensing assemblies 200 and 301 (described above in Figure 4 408 ) derives one or more signals indicative of a periodic pattern formed by the fibers of blanket 44. In some embodiments, as the blanket moves in the direction of arrow 94, processor 20 counts the number of signals indicative of the positions of the respective fibers that pass through position sensing assemblies 200 and 301. In some embodiments, processor 20 is configured to calculate the velocity of blanket 44 based on distance 440, the signals received from position sensing assemblies 200 and 301, and a time interval 442 taken for a position reference point to pass between positions 406 and 408. In some embodiments, time interval 442 includes the duration between jetting black ink 303A and magenta ink 303B, which achieves a specified C2C registration between the black image and the magenta image.

[0150] In some embodiments, fibers 410, 411, 412, 413, 414, and 415 of diagram 400 represent the aforementioned fibers of blanket 44, such as described above in Figure 2A 、 Figure 2B and Figure 3 104 is shown in FIG. 4 . For conceptual clarity, in the present example, four of the fibers (i.e., fibers 411 to 414) are located within a distance 440, but it will be understood that a real blanket 44 typically includes hundreds or thousands of fibers within the distance 440. In the present example, a pair of adjacent fibers (such as fibers 412 and 413) has a nominal distance 444 between the fibers that is designed to be substantially the same between any pair of adjacent fibers among fibers 410 to 415 (e.g., a distance of approximately 470 μm ± 10 μm between fibers 411 and 412, between fibers 412 and 413, and between fibers 413 and 414).

[0151] In some embodiments, processor 20 maintains a threshold value indicating a maximum specified distance 444 of blanket 44. Based on signals received from position sensing assemblies 200 and 301, processor 20 is configured to measure the actual value of distance 444 using the following sequence: At step 1, processor 20 controls printbar 62A to direct one or more drops of ink 303A via nozzle 63A to land at position 406 on blanket 44, which is located at a distance 421 from fiber 411.

[0152] At step 2, processor 20 controls blanket module 70 to move blanket 44 at a constant speed and measures time interval 442 taken for ink 303A ejected at step 1 to be positioned at position 408 on blanket 44. Additionally or alternatively, processor 20 may receive signals from position sensing assemblies 200 and 301 indicating any other position reference points (e.g., fiber 410 or 411) passing between positions 406 and 408 and measure the corresponding duration, i.e., time interval 442.

[0153] At step 3, which may be performed simultaneously with step 2, processor 20 counts the number of fibers that pass between positions 406 and 408 during time interval 442 (using signals received from position sensing assemblies 200 and 301), and adds distances 421 and 422 as fractions of distance 444. Figure 5 In the example of , the distance 440 is equal to the sum of the four distances 444 and the four widths of the fibers 411 to 414 and the distances 421 and 422 .

[0154] At step 4, based on distance 440, time interval 442, and the signals received from position sensing assemblies 200 and 301, processor 20 calculates an average value of the actual speed of blanket 44 during time interval 442 and the actual magnitude of distance 444 based on the distance measured between fibers 411 and 414. Processor 20 then compares the calculated actual magnitude of distance 444 with a threshold value indicating a specified magnitude of distance 444 and determines whether blanket 44 is overstretched, for example, by module 80 of system 10.

[0155] In some embodiments, processor 20 is further configured to issue a warning in response to detecting excessive stretching of blanket 44 and / or reduce the tension applied to blanket 44 , for example, by dancer roller assembly 74 .

[0156] In an embodiment, based on the signals received from position sensing assemblies 200 and 301, processor 20 is configured to adjust the tension applied to blanket 44, for example, by dancer assembly 74. For example, processor 20 may control dancer assembly 74 to adjust the applied tension to compensate for overheating of blanket 44 (as described above in Figure 1 ) or overstretch (measured by a change in the distance between adjacent fibers). Similarly, processor 20 may control dancer assembly 74 to increase the applied tension to compensate for understretching of blanket 44.

[0157] In some embodiments, based on signals received from position sensing assembly 200 and / or 301, processor 20 is configured to improve placement accuracy of one or more ink drops ejected onto the surface of blanket 44. As described above, improving placement accuracy can also improve image-to-substrate registration of system 10 and registration between images on different sides of a print target substrate in a duplex printing system.

[0158] In some embodiments, processor 20 may maintain one or more threshold values ​​indicating specified registration errors (e.g., C2C and image-to-substrate registration errors) for system 10. Based on signals received from position sensing components 200 and / or 301, processor 20 is configured to detect whether an image printed on blanket 44 has one or more registration errors that exceed the specified registration errors indicated by the aforementioned threshold values.

[0159] In such embodiments, the processor 20 is configured to adjust the image transfer process from the blanket 44 to the sheet 50 to compensate for the registration error, for example, by adjusting parameters of the impression station 84. If the registration error cannot be adjusted, the processor 20 may terminate the image transfer (e.g., by disengaging the impression cylinder 82 from the pressure cylinder 90) and remove the corresponding image from the blanket 44.

[0160] In other embodiments, processor 20 may save an image printed on blanket 44 , for example, in response to detecting severe overstretching of blanket 44 .

[0161] Estimate the relative elongation between the seam and the blanket fabric

[0162] Figure 6 is a block diagram schematically illustrating a method for estimating the relative elongation between the seam 59 and the fabric section 61 of the blanket 44 according to an embodiment of the present invention. In some embodiments, the method uses fiber events 504 received from the position sensing assembly 200. In the context of this disclosure and in the claims, the term "fiber event" refers to an indication of the relative elongation of the seam 59 and the fabric section 61 of the blanket 44. Figure 2A and Figure 2B The signal has a periodic pattern as described in .

[0163] In some embodiments, after blanket 44 is mounted on system 10, processor 20 is configured to control: (i) dancer roller assembly 74 to apply a predefined tension T1 to blanket 44, and (ii) blanket module 70 to move blanket 44 along a movement direction indicated by arrow 94. In the present example, seam 59 is defined as the distance between fibers 104A and 104B and has a length 501 (e.g., between approximately 10 cm and 15 cm).

[0164] In some embodiments, processor 20 may select a fabric segment 61 along blanket 44 while applying T1 and moving blanket 44, the fabric segment being defined between fibers 104C and 104D and having a length 502 similar to length 501. Note that selected fabric segment 61 may be located at any suitable distance from seam 59. For example, at a distance of approximately five or ten meters from seam 59, but may also be located immediately adjacent to seam 59 (e.g., approximately 20 cm). Further, note that blanket 44 moves in a repeating cycle, also referred to herein as a revolution, such that lengths 501 and 502 are measured several times (e.g., during each revolution) as blanket 44 moves at speed V (e.g., a constant movement speed for any suitable printing process).

[0165] In some embodiments, the position sensing assembly 200 is configured to send a fiber event 504 to the processor 20 in response to detecting each fiber 104. In the present example, at a first point in time (POT), the processor 20 is configured to receive the fiber event 504A generated when the position sensing assembly 200 senses the position of the fiber 104A moving with the blanket 44. Similarly, the processor 20 is configured to receive the fiber events 504B, 504C, and 504D generated at the second, third, and fourth POTs when the position sensing assembly 200 senses the positions of the fibers 104B, 104C, and 104D, respectively.

[0166] As mentioned above Figure 1 As described in , seam 59 does not have the ordered structure of fibers 102 and 104 of blanket fabric 100 and, therefore: (i) may have different mechanical properties, such as elastic modulus, than blanket fabric 100, and (ii) position sensing assembly 200 may be unable to generate fiber events 504 within section 502 of seam 59.

[0167] In some embodiments, processor 20 is configured to store the POTs of five events sensed by position sensing assembly 200 for each revolution of blanket 44. In the present example, based on the POTs received for fiber events 504A through 504D in revolution n, processor 20 can calculate the magnitudes of lengths 501 and 502 in revolution n, which are described herein using equations (1) and (2), respectively:

[0168] (1)

[0169] (2)

[0170] in and denote the lengths 501 and 502 measured during the blanket revolution n,

[0171] and denote the magnitudes of the lengths 501 and 502 measured during the first measured revolution, respectively,

[0172] and represents the absolute elongation of the lengths 501 and 502 between revolution n and the first measured revolution.

[0173] In this paper, equations (3) and (4) are used to describe the absolute elongation of lengths 501 and 502, respectively:

[0174] (3)

[0175] (4)

[0176] Based on the basic laws of physics that state that a given length (x) is obtained by multiplying velocity (v) and time (t), equation (5) is used to describe the relative elongation between the length 501 of the seam 59 and the length 502 of the fabric section 61 between the first and nth revolutions:

[0177] (5)

[0178] where V represents the moving speed of the blanket 44 during the period between the first revolution and the nth revolution,

[0179] and respectively represent the POTs of the magnitudes of the indicated lengths 501 and 502 received from the position sensing assembly 200 at the nth revolution,

[0180] and The POTs respectively represent the magnitudes of the indicated lengths 501 and 502 received from the position sensing assembly 200 during the first revolution.

[0181] In some embodiments, based on equation (5), processor 20 is configured to estimate the relative elongation between length 501 of seam 59 and length 502 of fabric section 61. Note that the movement velocity V can be reduced from both the numerator and denominator of equation (5), and thus based on the POTs of fiber events 504A-504D received in the first and nth revolutions, processor 20 is configured to estimate the relative elongation between length 501 of seam 59 and length 502 of fabric section 61.

[0182] As described above, relative elongation may occur due to different elastic moduli (also known as Young's moduli) between blanket fabric 100 and seam 61 and depends on the tension applied to blanket 44 moved in the movement direction by blanket module 70. In some embodiments, processor 20 is configured to store a table of relative elongations caused when corresponding tensions are applied to blanket 44.

[0183] In some embodiments, generating the table can be performed during the printing process of the system 10 without allocating any resources other than process management and processing time of the processor 20. Thus, the table can be generated for each blanket 44 installed on each system 10 and can be monitored over the life of a given blanket 44 to monitor the condition (e.g., mechanical properties) of both the blanket fabric 100 and the seam 59.

[0184] In some embodiments, processor 20 is configured to monitor or control system 10 based on the ratio shown in equation (5) and calculated over one or more revolutions of blanket 44 .

[0185] In other embodiments, the processor may use the techniques described above to define a plurality of fabric sections 61 along the blanket 44 , wherein the plurality of fabric sections have one or more predefined distances from the seam 59 and from each other.

[0186] Figure 7 is a schematic illustration of a system 600 for cutting blanket fabric 100 during the production of blanket 44 according to an embodiment of the present invention. In some embodiments, system 600 includes a position sensing assembly 200 having a light source 216 configured to direct a light beam 215 that passes through blanket fabric 100 and fiber optic assembly 218 and is detected by sensor 222, as described above in Figure 3 Described in detail in.

[0187] In some embodiments, system 600 includes a computer 610 configured to send control signals to a subsystem 602 via a cable 618, the subsystem having a motion assembly 620 and a production surface (in the present example, a table 622). The motion assembly 620 is configured to transport the blanket fabric 100 on the table 622 along an axis parallel to the direction of movement 616 of the fabric 100. The computer 610 is further configured to receive the optical signal 206 from the position sensing assembly 200 via the cable 614, the optical signal indicating the position of the corresponding opening 106 of the blanket fabric 100, as described above. Figure 3 As described in.

[0188] In some embodiments, system 600 includes a fabric cutting subsystem 604 having a blade 606 configured to move in a direction 608 to cut blanket fabric 100. In other embodiments, cutting subsystem 604 may have any other configuration suitable for cutting blanket fabric 100.

[0189] In some embodiments, the computer 610 is configured to store a number (e.g., between about 20,000 and 30,000) indicating the number of light signals 206 that indicate a specified number of fibers 104 in the blanket 44, as described above in Figure 2A Based on the light signals 206, the computer 610 is configured to count the number of light signals 206 (indicating the corresponding fibers 104) and determine a cutting position for cutting the blanket fabric 100. The computer 610 is further configured to send a control signal to the fabric cutting subsystem 604 via the cable 612 to cut the fabric 100 when the aforementioned specified number of fibers is reached.

[0190] exist Figure 7 In the example of FIG. 5 , blanket web 100A has been cut by fabric cutting subsystem 604 , and computer 610 counts the number of fibers 104 in blanket web 100B based on signals 206 received from position sensing assembly 200 , as described above.

[0191] In some embodiments, the computer 610 is configured to control the motion assembly 620 to adjust the speed of movement of the blanket fabric 100 during the process of cutting the blanket fabric 100. For example, the process may include: (i) a first time interval during which the computer 610 counts the light signals 206 and determines a cut position for cutting the blanket fabric 100; and (ii) a second time interval during which the computer 610 controls the cutting subsystem 604 to cut the blanket fabric 100. In such embodiments, the computer 610 is configured to control the motion assembly 620 to move the blanket fabric 100 at a first speed (e.g., approximately 5 m / s) during the first time interval and to move the blanket fabric at a second, lower speed or even to a complete stop (zero speed) during the second time interval in order to obtain an accurate cut of the blanket fabric 100.

[0192] In other embodiments, the techniques described above can be used mutatis mutandis to cut any type of flexible substrate (or rigid substrate) having a periodic pattern.

[0193] The disclosed technology enables improved accuracy (i.e., the exact size of the blanket fabric 100) and repeatability (i.e., all blanket fabrics 100 cut by the system 600 have the same length) when cutting the blanket fabric 100 during the production of the blanket 44. Note that by counting the number of fibers 104, the system 600 is unaffected by changes in parameters such as the temperature and elasticity of the blanket fabric 100, and therefore, the system 600 can achieve improved accuracy and repeatability of the length of the blanket fabric 100.

[0194] Typically, computer 610 comprises a general-purpose computer that is programmed with software to implement the functions described herein. For example, the software may be downloaded to the computer electronically via a network, or alternatively or additionally, the software may be provided and / or stored on a non-transitory tangible medium (such as magnetic, optical, or electronic storage). In the context of this disclosure and in the claims, computer 610 is also referred to as a processor, which is configured to implement all of the functions of computer 610 described above.

[0195] This particular configuration of system 600 is shown by way of example in order to illustrate certain problems solved by embodiments of the present invention and to demonstrate the application of these embodiments to enhance the performance of this system. However, embodiments of the present invention are by no means limited to this particular class of example systems, and the principles described herein can be similarly applied to other classes of systems for producing blankets 44 and for producing other types of fabrics (e.g., cotton) that are generally flexible and have an ordered structure.

[0196] Figure 8 is a schematic illustration of a subsystem 700 for monitoring the position and alignment of a moving blanket 44, according to an embodiment of the present invention. The subsystem 700 is configured to monitor the movement and alignment of the blanket 44 during a printing process, a test run, blanket handling, or during any other movement of the blanket 44.

[0197] In some embodiments, the subsystem 700 may include the Figure 3 Two or more position sensing components 200 described in detail in Figure 4 In the present example, subsystem 700 includes position sensing assemblies 200A and 200B adjacent respective edges of blanket 44 extending along the X-axis (e.g., between approximately 5 mm and 100 mm from the respective nearest edges of blanket 44, noting that this range may include the ordered structure of blanket fabric 100 and does not include other features of blanket 44 (such as a zipper) or printing fluid that may obstruct the ordered structure of blanket fabric 100) and mounted on subsystem 700 between rollers 78A and 78B.

[0198] like Figure 8 As shown in , subsystem 700 may include one or more additional position sensing assemblies, such as position sensing assembly 200C located proximate the center of blanket 44, but position sensing assemblies 200A and 200B are sufficient.

[0199] In some embodiments, position sensing assemblies 200A, 200B, and 200C are all positioned along an imaginary line (referred to herein as axis 726) that is orthogonal to the direction of movement of blanket 44, as indicated by arrow 94, and parallel to, for example, the axis 726 described above. Figure 2A and Figure 2B Fiber 104 is shown in FIG.

[0200] In other embodiments, at least one of position sensing assemblies 200A and 200B is positioned adjacent to an edge of blanket 44 (e.g., within the aforementioned range), and the other position sensing assembly may be disposed at any suitable location along axis 726 that is not within the aforementioned range from the nearest edge of blanket 44. For example, subsystem 700 may include position sensing assemblies 200A and 200C, with position sensing assembly 200A disposed within 50 cm from the nearest edge of blanket 44.

[0201] In some embodiments, subsystem 700 further includes processor 20 configured to receive signals indicative of the periodic pattern of blanket 44 from position sensing assemblies 200A, 200B, and 200C via cables 302, such as described above in Figure 3 As described in.

[0202] In principle, when the blanket 44 intersects the axis 726, the fibers 104 should be aligned with the axis 726. Figure 8 As shown in FIG, when blanket 44 moves a predefined distance ΔX along the X-axis of system 10 (e.g., in the direction of movement indicated by arrow 94), points 702 and 704 positioned on another imaginary line (referred to herein as axis 706 of blanket 44) should move to points 712 and 714, respectively, positioned on a different imaginary line (referred to herein as axis 716 of blanket 44). In other words, axes 706 and 716 are parallel to each other. Therefore, a rotary encoder (not shown) may be coupled to, for example, roller 78A to detect the position of blanket 44 that varies according to the rotation angle of the encoder.

[0203] However, due to one or more possible faults in system 10 (such as different friction between blanket 44 and blanket module 70 at points 702 and 704, or non-linear or irregular rotational motion of rollers 78A and 78B), or any other reason, distance ΔX may not be equal on the Y-axis. For example, axis 716A of blanket 44 shows that point 702 moves slower than point 704.

[0204] In this example, point 712A, indicating the position of shift point 702, has moved a shorter distance along the X-axis than point 714A, indicating the position of shift point 704. Similarly, axis 716C of blanket 44, which includes points 712C and 714A, is not parallel to axis 706 because point 712A, indicating the position of shift point 702, has moved a greater distance along the X-axis than point 714A. As a reference to demonstrate the technical problem described above, if points 702 and 704 were moved equal distances along the X-axis, both would be located at points 712B and 714A on axis 716B of blanket 44, which is parallel to axis 706.

[0205] The different movement speeds of point 702 and point 704, as well as other points along axis 706, can cause image distortion, such as wave distortion, to be applied to blanket 44. Wave distortion can be caused by various errors, such as deviations from a specified motion profile for blanket 44, as described above, and by other causes, such as, but not limited to, (i) incorrect positioning of one or more print bars 62 in image forming station 60 and (ii) deviations from a specified relative speed between blanket 44 and sheet 50 at impression station 84.

[0206] The distortions and additional errors described above may result in a wavy pattern in the printed features. Note that generally the wavy pattern has two components: (i) a common waveform for all colors, e.g., due to the aforementioned deviations at the impression station 84; and (ii) a different waveform in each color image, e.g., due to mispositioning of one or more print bars 62 and / or due to temporary changes in the speed of the blanket 44. Figure 8 As shown and described above. Generally, waveform distortion has two components: distortion along the X-axis that varies with position on the Y-axis (referred to herein as waveform X(Y)), and distortion along the Y-axis that varies with position on the X-axis (referred to herein as waveform Y(X)). Waveform distortion and methods for correcting waveform distortion are described in detail, for example, in PCT patent application PCT / IB2019 / 056746 and U.S. patent application publication 2019 / 0152218, the disclosures of which are incorporated herein by reference in their entirety.

[0207] In some embodiments, processor 20 is configured to receive signals from at least two position sensing assemblies 200 mounted proximate to blanket 44 (such as along axis 726 or in any other suitable configuration). In this example, processor 20 may receive signals from position sensing assemblies 200A and 200B and, optionally, from additional position sensing assemblies, such as position sensing assembly 200C.

[0208] In some embodiments, the processor 20 is configured to: (i) identify and map potential distortions, such as, but not limited to, distortions occurring along the axis 716A, as described above; and (ii) apply any suitable method to correct the distortions. For example, one or more of the techniques described in the aforementioned PCT patent application PCT / IB2019 / 056746 and U.S. Patent Application Publication 2019 / 0152218 may be used. Additionally or alternatively, the processor 20 may use any other suitable technique to compensate for the mapped distortions.

[0209] This particular configuration of subsystem 700 is shown by way of example in order to illustrate certain problems solved by embodiments of the present invention and to demonstrate the application of these embodiments to enhancing the performance of system 10. However, embodiments of the present invention are by no means limited to this particular class of example subsystems, and the principles described herein may be similarly applied to other classes of distortion detection, mapping, and correction used in any class of other suitable digital printing systems.

[0210] Although the embodiments described herein primarily address the control, monitoring, and calibration of digital printing systems and monitoring the condition of flexible ITMs and detecting and correcting distortions in images applied to the ITMs, the methods and systems described herein may also be used in other applications, such as for controlling direct printing on flexible target substrates and monitoring various parameters related to the functionality of flexible substrates.

[0211] It will therefore be understood that the embodiments described above are illustrated by way of example, and the present invention is not limited to what has been particularly shown and described above. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described above, as well as variations and modifications that will occur to those skilled in the art after reading the foregoing description and that are not disclosed in the prior art. The documents incorporated by reference into this patent application should be considered an integral part of this application, but in the event that any term defined in these incorporated documents conflicts with a definition explicitly or implicitly made in this specification, only the definition in this specification should be considered.

Claims

1. A digital printing system, comprising: a flexible substrate comprising an intermediate transfer member (ITM) and comprising a continuous loop configured to move in at least a first revolution and a second revolution to receive ink droplets during a printing process for forming an image on the flexible substrate and to transfer the image to a target substrate, the flexible substrate comprising a fabric having a first set of fibers and a second set of fibers interwoven with each other according to a periodic pattern; an optical assembly configured to illuminate the flexible substrate with light, detect the light from the flexible substrate, and derive from the detected light a signal indicative of the periodic pattern from the interwoven first and second sets of fibers; as well as A processor is configured to receive the signal and monitor or control the digital printing system based on the periodic pattern indicated by the signal.

2. The system of claim 1 , wherein the first group of fibers and the second group of fibers are arranged orthogonally to each other according to the periodic pattern, and wherein the optical component is configured to derive the signal indicative of the periodic pattern from the orthogonal arrangement of the first group of fibers and the second group of fibers.

3. The system of claim 1 , wherein the first set of fibers is arranged orthogonal to the axis of movement of the flexible substrate according to the periodic pattern, and wherein the optical component is configured to derive the signal indicative of the periodic pattern from the first set of fibers.

4. The system according to claim 1 or 2, wherein: Based on the first set of fibers and the second set of fibers, the optical assembly is configured to detect a plurality of position reference points in the periodic pattern of the fabric, and wherein the processor is configured to calculate a position of the flexible substrate based on at least one of the position reference points.

5. The system of claim 4, wherein the signal indicates a position of at least one of the position reference points, and wherein the processor is configured to control the digital printing system based on one or more of the position reference points.

6. The system of claim 1 , further comprising an image forming station configured to direct a first ink drop to a first ink location on the flexible substrate and a second ink drop to a second ink location on the flexible substrate, wherein the signal comprises a first signal indicative of the first ink location and a second signal indicative of the second ink location, and wherein the processor is configured to control registration between the first ink location and the second ink location based on the first signal and the second signal.

7. The system of claim 1 or 2, wherein the flexible substrate comprises: (i) the fabric having the periodic pattern and a first elongation obtained when a given tension is applied to the moving flexible substrate; and (ii) a seam for joining edges of the fabric, wherein the seam has a structure other than the periodic pattern, wherein when the given tension is applied to the moving flexible substrate, the seam has a second elongation different from the first elongation, and wherein the processor is configured to calculate a ratio between the first elongation and the second elongation based on the signal. 8 . The system of claim 7 , wherein the processor is configured to control the digital printing system based on the calculated ratio between the first elongation and the second elongation.

9. A system according to claim 8, wherein the processor is configured to calculate at least: (i) a first ratio between the first elongation and the second elongation for each of the first rotation; and (ii) a second ratio between the first elongation and the second elongation for each of the second rotation, and wherein the processor is configured to monitor or control the digital printing system based at least on the first ratio and the second ratio.

10. A method for controlling a digital printing system, the method comprising: illuminating a movable flexible substrate with light, the flexible substrate comprising a fabric having a first set of fibers and a second set of fibers interwoven with each other according to a periodic pattern; detecting the light from the flexible substrate and deriving a signal from the detected light indicative of the periodic pattern from the interwoven first and second groups of fibers; as well as monitoring or controlling the digital printing system based on the periodic pattern indicated by the signal; The movable flexible substrate includes an intermediate transfer member (ITM) and a continuous loop configured to move in at least a first revolution and a second revolution to receive ink drops during a printing process to form an image on the movable flexible substrate and transfer the image to a target substrate.

11. The method of claim 10, wherein the first group of fibers and the second group of fibers are arranged orthogonally to each other according to the periodic pattern, and wherein deriving the signal indicative of the periodic pattern is based on the orthogonal arrangement of the first group of fibers and the second group of fibers.

12. The method of claim 11, wherein the first set of fibers is arranged orthogonally to an axis of movement of the flexible substrate according to the periodic pattern, and wherein deriving the signal indicative of the periodic pattern comprises deriving the signal from the arrangement of the first set of fibers.

13. The method of claim 12 , wherein detecting the light comprises detecting a plurality of position reference points in the periodic pattern of the fabric based on the first group of fibers and the second group of fibers, and the method comprises calculating the position of the flexible substrate based on at least one of the position reference points.

14. The method of claim 13 , further comprising directing a first ink drop to a first ink location on the flexible substrate and directing a second ink drop to a second ink location on the flexible substrate, wherein deriving the signal comprises deriving a first signal indicative of the first ink location and deriving a second signal indicative of the second ink location, and wherein the method comprises controlling registration between the first ink location and the second ink location based on the first signal and the second signal.

15. The method of claim 13, wherein the signal indicates a position of at least one of the position reference points, and wherein the digital printing system is controlled based on one or more of the position reference points.

16. The method according to any one of claims 10 to 15, wherein the flexible substrate comprises: (i) the fabric having the periodic pattern and a first elongation obtained when a given tension is applied to the moving flexible substrate; and (ii) a seam for joining edges of the fabric, wherein the seam has a structure other than the periodic pattern, wherein when the given tension is applied to the moving flexible substrate, the seam has a second elongation different from the first elongation, and wherein monitoring or controlling the digital printing system includes calculating a ratio between the first elongation and the second elongation based on the signal.

17. The method of claim 16, wherein controlling the digital printing system is based on the calculated ratio between the first elongation and the second elongation.

18. A method according to claim 17, wherein calculating the ratio includes calculating at least: (i) a first ratio between the first elongation and the second elongation per the first rotation; and (ii) a second ratio between the first elongation and the second elongation per the second rotation, and wherein monitoring or controlling the digital printing system is based at least on the first ratio and the second ratio.

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