Reducing distortion in printed images

Abstract

The method includes receiving a first signal indicative of a first current measured with respect to a first motion assembly (77) for moving a flexible substrate (44) that receives droplets of printing fluid from an image forming station (60) to form an image thereon. A second signal indicative of a second current measured with respect to a second motion assembly (99) for moving the flexible substrate (44) is received, a section of the flexible substrate (44) being moved between the first motion assembly (77) and the second motion assembly (99). A parameter indicative of a distortion in the image is calculated based on the first and second signals. Based on the parameter, and in response to detecting an increase in the distortion, corrective action is applied to reduce the distortion.

Description

[Technical field]

[0001] The present invention relates generally to digital printing systems, and more particularly to a method and system for reducing distortion in digitally printed images. [Background technology]

[0002] Flexible substrates are sometimes used in reading and / or applying media to a flexible substrate, such as in digital printing. Various techniques have been disclosed for controlling the tension applied to a flexible substrate during reading and / or application of media.

[0003] For example, U.S. Patent Application Publication No. 2009 / 0196670 describes a tape drive for use in a transfer printing device to drive a print ribbon. The print ribbon is mounted on two spools, each driven by a respective stepper motor. A controller controls energization of the motors such that the ribbon is transported in at least one direction between spools mounted on a spool support. The controller operates to energize both motors to drive the spools of ribbon in the direction of ribbon transport to achieve a push-pull action. Ribbon tension is monitored to enable precise control of ribbon supply and ribbon take-up, for example by monitoring power supply to the two stepper motors.

[0004] U.S. Patent Application Publication No. 2013 / 0033554 describes a print station system having a chassis for housing modular print stations, a power supply in communication with the print stations, a controller circuit card assembly in communication with the print stations, a display panel in communication with the print stations, a media rewind hub, a pair of adjustable media guides coupled around a base of the print stations, and at least one sensor secured to the print station base and operable to detect the presence and position of media passing through a media feed path of the print station system. Summary of the Invention [Means for solving the problem]

[0005] One embodiment of the present invention described herein provides a method that includes receiving a first signal indicative of a first current measured on a first motion assembly for moving a flexible substrate that receives droplets of printing fluid from an image forming station to form an image thereon. A second signal indicative of a second current measured on a second motion assembly for moving the flexible substrate, a section of the flexible substrate being moved between the first and second motion assemblies. A parameter indicative of a distortion in the image is calculated based on the first and second signals. In response to detecting an increase in the distortion based on the parameter, corrective action is applied to reduce the distortion.

[0006] In some embodiments, the image has a first and a second axis, the distortion includes a displacement of the pattern along the first axis that varies with position along the second axis within at least one section of the image, and applying the corrective action includes reducing an increase in the displacement along the first axis. In other embodiments, the first axis is orthogonal to the second axis, and the first axis is parallel to the axis of movement of the flexible substrate. In yet other embodiments, the first axis is orthogonal to the second axis, and the first axis is orthogonal to the axis of movement of the flexible substrate.

[0007] In one embodiment, the image includes a first color having a first pattern and a second color having a second pattern, the distortion includes a difference in displacement between the first pattern and the second pattern, and applying the corrective action includes reducing an increase in the difference in the displacement. In another embodiment, the distortion includes a difference in inter-color positional difference between the first and second colors of the image, and applying the corrective action includes reducing an increase in the difference in the inter-color positional difference in the image. In yet another embodiment, the distortion includes a difference between an intended position of the image on the flexible substrate and a measured position of the image on the flexible substrate, and applying the corrective action includes reducing a difference between the intended position and the measured position.

[0008] In some embodiments, at least one of the first and second motion assemblies includes a roller for moving the flexible substrate and an electric motor for rotating the roller, and a first current is measured for the electric motor. In other embodiments, calculating the parameter includes calculating a difference between the first and second currents, such that the calculated difference is indicative of the tension applied to the section of the flexible substrate. In yet other embodiments, applying the corrective action includes maintaining the tension applied to the section by adjusting a speed in at least one of the first and second motion assemblies.

[0009] In one embodiment, the flexible substrate includes an intermediate transfer member (ITM) for transferring the image to a target substrate in the printing station, and the method includes receiving a third signal indicative of a velocity of the ITM at the printing station, and applying corrective action includes adjusting a velocity of at least one of the first and second motion assemblies based on the third signal and in response to detecting that the velocity is changing beyond a predefined velocity range. In another embodiment, the printing station includes an impression cylinder, and the third signal is indicative of a velocity of the impression cylinder.

[0010] In some embodiments, the method includes (a) receiving (i) a first input signal indicative of one or more first variables of a first motion assembly, and (ii) a second input signal indicative of one or more second variables of a second motion assembly, and (b) defining virtual axes for determining a first velocity of an ITM in the first motion assembly and a second velocity of an ITM in the second motion assembly based on (i) the third signal, and (ii) the first and second input signals.

[0011] In another embodiment, the first motion assembly includes a first roller, a first motor, and a first gear for rotating the first roller. The second motion assembly includes a second roller, a second motor, and a second gear for rotating the second roller, and applying the corrective action includes adjusting at least one of the first and second gears in response to detecting that at least one of the first and second variables is above a predefined threshold. In yet another embodiment, at least one of the first and second variables is selected from the list consisting of: (i) a diameter of the roller, (ii) a temperature of the roller, and (iii) a nominal speed of the roller.

[0012] According to an embodiment of the present invention, there is additionally provided a system including an interface and a processor. The interface is configured to (i) receive a first signal indicative of a first current measured on a first motion assembly for moving a flexible substrate receiving droplets of printing fluid from an image forming station to form an image thereon, and (ii) receive a second signal indicative of a second current measured on a second motion assembly for moving the flexible substrate, a section of the flexible substrate being moved between the first and second motion assemblies. The processor is configured to (i) calculate a parameter indicative of a distortion in the image based on the first and second signals, and (ii) based on the parameter, in response to detecting an increase in the distortion, the processor is configured to apply a corrective action to reduce the distortion.

[0013] The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken in conjunction with the drawings in which: [Brief description of the drawings]

[0014] [Figure 1] 1 is a schematic side view of a digital printing system in accordance with one embodiment of the present invention; [Diagram 2] FIG. 2 is a block diagram that illustrates a schematic workflow for synchronizing gear ratios of motion assemblies in a digital printing system, in accordance with one embodiment of the present invention. [Diagram 3] 1 is a graph that illustrates a schematic representation of the distortion measured at different times on two similar images formed on a flexible substrate in accordance with an embodiment of the present invention. [Figure 4] 2 is a flow chart that generally illustrates a method for reducing distortions induced in a digitally printed image, in accordance with an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] overview Although printing on flexible substrates offers many benefits, under certain circumstances images printed on flexible substrates may contain distortions related, inter alia, to the flexibility of the substrate.

[0016] Embodiments of the invention described below provide methods and systems for reducing distortions in printed images. In some embodiments, a system for digital printing includes a flexible intermediate transfer member (ITM) configured to receive droplets of printing fluid to form an image thereon and move along an axis, referred to herein as the X-axis, to a printing station to transfer the image to a target substrate, such as a sheet of paper.

[0017] The printed image may have a geometric distortion along the X-axis that varies with position on the Y-axis (orthogonal to the X-axis), referred to herein as waveform X(Y), and / or a distortion along the Y-axis that varies with position on the X-axis, referred to herein as waveform Y(X).

[0018] At least one of the wave form X(Y) and wave form Y(X) distortions may be caused by a number of sources, including, but not limited to, flexure and stretching of the ITM and deviations from specified velocities when (i) receiving droplets of printing fluid from the image-forming station and (ii) transferring the image at the press station.

[0019] In some embodiments, the system includes first and second motion assemblies configured to move the ITM to receive and transfer an image, as described above, and each motion assembly includes a roller and an electric motor configured to rotate the roller about its axis of rotation.

[0020] In some embodiments, the system includes a processing unit, also referred to herein as a controller, that is configured to control the speed of the rollers (by controlling various components of the motion assemblies, such as motors and gears) to move the ITM at a specified speed. Note that each motion assembly is configured to move the ITM at a different speed to keep the moving ITM taut.

[0021] In some embodiments, when moving the ITM, the controller interface is configured to receive (i) a first signal indicative of a first current measured for a motor of a first motion assembly, and (ii) a second signal indicative of a second current measured for a motor of a second motion assembly.

[0022] In some embodiments, based on the first and second signals, the controller is configured to calculate a parameter indicative of a distortion in the image. The parameter may include a difference or ratio between the first and second currents, or any other suitable parameter.

[0023] In some embodiments, based on the parameter, and in response to detecting an increase in the distortion, the controller is configured to apply corrective action to reduce the distortion. For example, if the difference between the first and second currents exceeds a predefined upper or lower threshold, the controller is configured to control at least one of the motion assemblies to adjust the speed of the respective roller(s) to (i) reduce said distortion and / or (ii) prevent the formation of new distortion.

[0024] In some embodiments, the controller is configured to receive a third signal indicative of a speed of the ITM at the printing station. The speed may be measured using a motion encoder integrated with the printing station, and the measured speed may be filtered to smooth the third signal. Based on the speed of the third signal, the controller is configured to determine a gear ratio between gears of the first and second motion assemblies. Moreover, in response to detecting a variation in the ITM speed at the printing station, the controller is configured to adjust a speed of a roller in at least one of the first and second motion assemblies.

[0025] In other embodiments, in addition to the aforementioned signals, the controller is configured to receive one or more signals indicative of the speed of the ITM using one or more encoders of any type disposed at any suitable location(s) along the path of the ITM. Moreover, the ITM may have an encoder on, within, or integrated therewith, and one or more suitable sensor(s) disposed along the path of the ITM and configured to generate respective signal(s) indicative of the positions of sections of the ITM. Based on the respective signals, the controller is configured to estimate the speed of the ITM along the path.

[0026] The disclosed technology mitigates various types of distortions in images printed on flexible substrates. Moreover, the disclosed technology improves the productivity of a printing system by automatically calibrating the ITM speed during the printing process (without stopping system operation). Such calibration may be necessary, for example, when the diameter of one or more of (i) the roller(s) of the motion assembly and / or (ii) the cylinder(s) of the printing station changes in response to their changing temperature.

[0027] The embodiments and principles described above are applicable to (i) printing systems that use an intermediate transfer member to transfer an image to a target substrate (as described above), and (ii) printing systems for printing directly onto a flexible target substrate.

[0028] Moreover, the disclosed techniques may be used, mutatis mutandis, to improve the quality and reliability of systems for reading content from flexible media.

[0029] System Description 1 is a schematic side view of a digital printing system 10 in accordance with one embodiment of the present invention. In some embodiments, system 10 includes a rotating flexible blanket 44 that cycles through an imaging station 60, a drying station 64, an impression station 84, and a blanket treatment station 52. In the context of the present invention and in the claims, the terms "blanket" and "intermediate transfer member (ITM)" are used interchangeably to refer to a flexible member including one or more layers that is used as an intermediate member configured to receive an ink image and transfer the ink image to a target substrate, as described in more detail below.

[0030] In an operational mode, imaging station 60 is configured to form a mirror ink image, also referred to herein as an “ink image” (not shown) or simply “image,” of digital image 42 on an upper run of the surface of blanket 44. Thereafter, upon reaching impression station 84, the ink image is transferred to a target substrate (e.g., paper, folding carton, multi-layer polymer, or any suitable flexible packaging in the form of a sheet or continuous web) that is disposed beneath the lower run of blanket 44.

[0031] In the context of the present invention, the term "run" refers to the length or segment of blanket 44 between any two given rollers over which blanket 44 is guided.

[0032] In some embodiments, during installation, the blanket 44 may be bonded to form a continuous blanket loop (not shown). One example of a method and system for splice installation is described in detail in U.S. Provisional Application No. 62 / 532,400, the disclosure of which is incorporated herein by reference.

[0033] In some embodiments, imaging station 60 typically includes a plurality of print bars 62, each mounted (e.g., using a slider) on a frame (not shown) that is positioned at a fixed height above the surface of the upper run of blanket 44. In some embodiments, each print bar 62 includes a strip of print head substantially the same width as the print area on blanket 44 and includes individually controllable print nozzles.

[0034] In some embodiments, imaging station 60 may include any suitable number of bars 62, and each bar 62 may include a printing fluid, such as a different colored water-based ink. The inks typically have visible colors, such as, but not limited to, cyan, magenta, red, green, blue, yellow, black, and white. In the example of FIG. 1, imaging station 60 includes seven print bars 62, but may include four print bars 62 having any selected color, such as, for example, cyan (C), magenta (M), yellow (Y), and black (K).

[0035] In some embodiments, the print heads are configured to eject ink droplets of different colors onto the surface of blanket 44 to form an ink image (not shown) on the surface of blanket 44 .

[0036] In some embodiments, the different print bars 62 are spaced from one another along an axis of movement, also referred to herein as the direction of movement of the blanket 44, represented by arrow 94. In this configuration, precise spacing between the bars 62 and synchronization between the direction of the ink droplets of each bar 62 and the moving blanket 44 is essential to enable precise placement of the image pattern.

[0037] In the context of this disclosure and in the claims, the terms “inter-color pattern placement”, “pattern placement accuracy”, “inter-color registration”, “C2C registration”, “inter-color registration difference”, “bar-to-bar registration” and “color registration” are used interchangeably to refer to any placement accuracy of two or more colors relative to one another.

[0038] In some embodiments, the system 10 includes a heater 66, such as a hot gas or air blower and / or an infrared heater with a gas or air blower for flowing gas or air at any suitable temperature. The heater 66 is positioned between the print bars 62 and configured to partially dry the ink droplets deposited on the surface of the blanket 44. This air flow between the print bars can help, for example, (i) to reduce condensation on the surface of the print head and / or to deal with satellites (e.g., residue or small droplets dispersed around the main ink droplets), and / or (ii) to prevent clogging of the inkjet nozzles of the print head, and / or (iii) to prevent droplets of different color inks on the blanket 44 from unnecessarily intermixing with each other. In some embodiments, the system 10 includes a drying station 64 configured to direct infrared radiation at the surface of the blanket 44 and / or blow hot air (or another gas) onto the surface of the blanket 44. In some embodiments, the drying station 64 may include an infrared-based lighting assembly (not shown) and / or a blower 68 or any other suitable drying device.

[0039] At drying station 64, the ink image formed on blanket 44 is exposed to radiation and / or hot air to more thoroughly dry the ink, evaporating most or all of the liquid carrier and leaving only a layer of resin and colorant that is heated to the point where it becomes a tacky ink film.

[0040] In some embodiments, system 10 includes a blanket module 70 that includes a rotating flexible ITM, such as blanket 44. In some embodiments, blanket module 70 includes one or more rollers 78, at least one of which includes a motion encoder (not shown) configured to record the position of blanket 44 in order to control the position of sections of blanket 44 relative to respective print bars 62. It should be noted that one or more motion encoders may be integrated with additional rollers and other moving components of system 10, as described in more detail below in FIGS. 2-4.

[0041] In some embodiments, such motion encoders typically include at least one rotary encoder configured to generate rotary-based position signals indicative of the angular displacement of the respective rollers. It should be noted that in the context of the present invention and claims, the terms "indicative of" and "indication" are used interchangeably.

[0042] Additionally or alternatively, blanket 44 may include built-in encoders (not shown) for controlling the operation of various modules of system 10. One embodiment of a built-in motion encoder is described in detail, for example, in U.S. Provisional Application No. 62 / 689,852, the disclosure of which is incorporated herein by reference.

[0043] In some embodiments, blanket 44 is guided over rollers 76, 78 and other rollers described herein, as well as over a powered tensioning roller, also referred to herein as dancer assembly 74. Dancer assembly 74 is configured to control the amount of slack in blanket 44, and its movement is represented diagrammatically by a double-headed arrow. Furthermore, any stretching of blanket 44 with aging will not affect the ink image placement performance of system 10 and will only require further slack to be taken up by tensioning dancer assembly 74.

[0044] In some embodiments, dancer assembly 74 may be motorized. The configuration and operation of rollers 76 and 78 are described in further detail, for example, in U.S. Patent Application Publication No. 2017 / 0008272 and the aforementioned PCT International Publication No. WO2013 / 132424, the disclosures of which are incorporated herein by reference in their entireties.

[0045] In some embodiments, the system 10 includes a blanket tension drive roller (BTD) 99 and a blanket control drive roller (BCD) 77, which are configured to rotate about their own first and second axes, respectively, powered by first and second motors, typically electric motors (not shown).

[0046] In some embodiments, the BTD 99 is configured to rotate at a first speed and the BCD 77 is configured to rotate at a second speed, typically greater than the first speed, to keep the top run of the blanket 44 taut as it passes adjacent the imaging station 60. In some embodiments, the first and second speeds are monitored and controlled to prevent the formation of distortions, for example, along the axis of travel of the blanket 44, as described in more detail below in FIGS.

[0047] In some embodiments, system 10 may include one or more tension sensors (not shown) positioned at one or more locations along blanket 44. The tension sensors may be integrated within blanket 44 or may include sensors external to blanket 44 using any other suitable technique for obtaining signals indicative of the mechanical tension applied to blanket 44. In some embodiments, processor 20 and additional controllers of system 10 are configured to receive signals generated by the tension sensors to monitor the tension applied to blanket 44 and to control the operation of dancer assembly 74.

[0048] At the impression station 84, the blanket 44 passes between an impression cylinder 82 and a pressure cylinder 90, which are configured to transport a compressible blanket. In some embodiments, a motion encoder is integrated with at least one of the impression cylinder 82 and the pressure cylinder 90.

[0049] 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 disposed above the blanket module 70, and a substrate transport module 80 disposed below the blanket module 70, including one or more printing stations, as described below.

[0050] In some embodiments, the console 12 includes a processor 20, typically a general purpose processor, with suitable front end and interface circuitry for interfacing with and receiving signals from the controllers of the dancer assemblies 74 and the controllers 54 via cables 57. Additionally or alternatively, the console 12 may include any suitable type of application specific integrated circuit (ASIC) and / or digital signal processor (DSP) and / or any other suitable type of processing device configured to perform any type of processing on data processed in the system 10.

[0051] In some embodiments, the controller 54, shown diagrammatically as a single device, may include one or more electronic modules mounted at predetermined locations on the system 10. At least one of the electronic modules of the controller 54 may include an electronic device, such as a control circuit or processor (not shown), that is configured to control the various modules and stations of the system 10. In some embodiments, the processor 20 and control circuitry may be programmed with software to perform functions used by the printing system, and data for the software may be stored in memory 22. The software may be downloaded in electronic form to the processor 20 and control circuitry, for example, via a network, or may be provided on a non-transitory, tangible medium, such as an optical, magnetic, or electronic memory medium.

[0052] In some embodiments, the console 12 includes a display 34 configured to display data and images received from the processor 20 or input inserted by a user (not shown) using an input device 40. In some embodiments, the console 12 may have any other suitable configuration, for example, alternative configurations of the console 12 and display 34 are described in detail in U.S. Pat. No. 9,229,664, the disclosure of which is incorporated herein by reference.

[0053] In some embodiments, the processor 20 is configured to display on the display 34 a digital image 42 including one or more segments (not shown) of the image 42 and / or various types of test patterns that may be stored in the memory 22.

[0054] In some embodiments, the blanket treatment station 52, also referred to herein as a cooling station, is configured to treat the blanket, for example, by cooling it and / or applying a treatment fluid to the outer surface of the blanket 44 and / or cleaning the outer surface of the blanket 44. At the blanket treatment station 52, the temperature of the blanket 44 can be reduced to a desired temperature level before the blanket 44 enters the imaging station 60. Treatment can be performed by passing the blanket 44 over one or more rollers or blades configured for cooling and / or cleaning and / or applying a treatment fluid onto the outer surface of the blanket.

[0055] In some embodiments, the blanket treatment station 52 may further include one or more bars (not shown) positioned adjacent to the print bar 62 so that treatment fluid may additionally or alternatively be applied to the blanket 44 by jetting.

[0056] 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), to monitor the temperature of blanket 44 and control operation of blanket treatment station 52. Examples of such treatment stations are described, e.g., in PCT International Publication Nos. WO 2013 / 132424 and WO 2017 / 208152, the disclosures of which are incorporated herein by reference in their entireties.

[0057] 1, station 52 is mounted between impression station 84 and imaging station 60, however, station 52 may be mounted adjacent blanket 44 in any other or additional suitable location or locations between impression station 84 and imaging station 60. As previously mentioned, station 52 may additionally or alternatively be mounted on a bar adjacent imaging station 60.

[0058] 1, impression cylinder 82 presses an ink image onto a target flexible substrate, such as an individual sheet 50, that has been conveyed by substrate transport module 80 via impression cylinder 82 from an input stack 86 to an output stack 88. In this example, a rotary encoder (not shown) is integrated with impression cylinder 82, as described in more detail below.

[0059] In some embodiments, the lower run of blanket 44 selectively interacts with impression cylinder 82 at impression station 84 to impress an image pattern onto a target flexible substrate compressed between blanket 44 and impression cylinder 82 under the action of pressure from pressure cylinder 90. For the simplex printer shown in FIG. 1 (i.e., printing on one side of sheet 50), only one impression station 84 is required.

[0060] In other embodiments, the module 80 may include two or more impression cylinders (not shown) to enable one or more double-sided printing. The two impression cylinder configuration also allows single-sided printing to be performed at twice the speed of double-sided printing. In addition, mixed lots of single-sided and double-sided prints can also be printed. In alternative embodiments, a different configuration of the module 80 may be used for printing on a continuous web substrate. Detailed descriptions and various configurations of double-sided printing systems and systems for printing on a continuous web substrate are provided, for example, in U.S. Pat. Nos. 9,914,316 and 9,186,884, PCT International Publication No. WO 2013 / 132424, U.S. Patent Application Publication No. 2015 / 0054865, and U.S. Provisional Application No. 62 / 596,926, the disclosures of which are all incorporated herein by reference.

[0061] As briefly described above, a sheet 50 or continuous web substrate (not shown) is conveyed by module 80 from an input stack 86 and passed through a nip (not shown) located between impression cylinder 82 and pressure cylinder 90. Within the nip, the surface of blanket 44 carrying the ink image is pressed firmly against sheet 50 (or other suitable substrate) by, for example, a compressible blanket (not shown) of pressure cylinder 90, thereby imprinting the ink image onto the surface of sheet 50 and cleanly separating it from the surface of blanket 44. Sheet 50 is then conveyed to output stack 88.

[0062] 1, rollers 78 are positioned on the upper run of blanket 44 and are configured to keep blanket 44 taut as it passes adjacent to imaging station 60. Additionally, it is particularly important to control the speed of blanket 44 under imaging station 60 to obtain precise jetting and deposition of ink droplets onto the surface of blanket 44 by imaging station 60, thereby achieving placement of the ink image.

[0063] In some embodiments, the impression cylinder 82 is periodically engaged and disengaged from the blanket 44 in order to transfer the ink image from the moving blanket 44 to a target substrate passing between the blanket 44 and the impression cylinder 82. In some embodiments, the system 10 is configured to apply a torque to the blanket 44 using the roller and dancer assemblies described above in order to maintain the upper run taut and substantially isolate the upper run of the blanket 44 from being affected by mechanical vibrations occurring in the lower run.

[0064] In some embodiments, system 10 includes an image quality control station 55, also referred to herein as an automated quality control (AQM) system, which functions as a closed-loop inspection system integrated within system 10. In some embodiments, image quality control station 55 may be located adjacent impression cylinder 82, as shown in FIG. 1, or at any other suitable location within system 10.

[0065] In some embodiments, image quality control station 55 includes a camera (not shown) that is configured to capture one or more digital images of the aforementioned ink images printed on sheet 50. In some embodiments, the camera may include any suitable image sensor, such as a contact image sensor (CIS) or a complementary metal oxide semiconductor (CMOS) image sensor, and a scanner that includes a slit having a width of about one meter or any other suitable width.

[0066] In the context of this disclosure and in the claims, the term "about" or "approximately" in relation to any numerical value or range indicates an appropriate tolerance that enables a part or collection of components to function for its intended purpose as described herein.

[0067] In some embodiments, station 55 may include a spectrophotometer (not shown) configured to monitor the quality of the ink printed on sheet 50 .

[0068] In some embodiments, the digital images acquired by station 55 are transmitted to a processor, such as processor 20 or any other processor of station 55, that is configured to evaluate the quality of each printed image. Based on that 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 claims, the term "processor" refers to any processing device, such as processor 20 or any other processor or controller connected to or integrated with station 55, that is configured to process signals received from the camera and / or spectrophotometer of station 55. It should be noted that the signal processing operations, control-related instructions, and other computational operations described herein may be performed by a single processor or distributed among multiple processors of one or more respective computers.

[0069] In some embodiments, station 55 is configured to inspect the quality of the printed images and test patterns to monitor various attributes such as, but not limited to, perfect image registration with sheet 50, color-to-color (CTC) registration, printed geometry, image uniformity, color profile and linearity, and print nozzle functionality. In some embodiments, processor 20 is configured to automatically detect geometric distortions or other errors in one or more of the aforementioned attributes. For example, processor 20 is configured to compare between a design version of a given digital image (also referred to herein as a "master" or "source image") and a digital image of a printed version of the given image, captured by a camera.

[0070] In other embodiments, processor 20 may apply any suitable type of image processing software, for example to a test pattern, to detect distortions indicative of the aforementioned errors. In some embodiments, processor 20 is configured to analyze the detected distortions to apply corrective action to the malfunctioning module and / or provide instructions to another module or station of system 10 to correct the detected distortions.

[0071] In some embodiments, system 10 may print inspection marks (not shown) or other suitable features, for example, on the bevel or margin of sheets 50. By acquiring images of the inspection marks, station 55 is configured to measure various types of distortions, such as C2C registration, image-to-substrate registration, color-to-color differentials, referred to herein as "bar-to-bar width delta" or "color-to-color width difference," various types of local distortions, and front-to-back registration errors (in duplex printing). In some embodiments, processor 20 is configured to (i) select sheets 50 having distortions above a first predefined set of thresholds, for example, to a reject tray, (ii) initiate corrective action on sheets 50 having distortions above a second, lower, predefined set of thresholds, and (iii) output sheets 50 having small distortions, for example, below the second set of thresholds, to output stack 88.

[0072] In some embodiments, the processor 20 is further configured to detect additional geometric distortions, such as expansion or contraction, skew, or wave distortion, occurring in at least one of (i) an axis parallel to the axis of movement of the blanket 44, and (ii) an axis perpendicular to the axis of movement of the blanket 44, for example, by analyzing the pattern of appropriately printed features.

[0073] In some embodiments, processor 20 is configured to detect deviations in the profile and linearity of the printed colors based on signals received from the spectrophotometer of station 55 .

[0074] In some embodiments, the processor of station 55 is configured to determine whether to stop operation of system 10, for example, if the density of distortion is above a specified threshold. The processor of station 55 is further configured to initiate corrective action in one or more of the modules and stations of system 10, as described above. As described below, corrective action can be performed on-the-fly (during which system 10 continues the printing process) or offline by stopping the printing operation and correcting the problem in the respective module and / or station of system 10. In other embodiments, any other processor or controller of system 10 (e.g., processor 20 or controller 54) is configured to initiate corrective action or stop operation of system 10, if the density of distortion is above a specified threshold.

[0075] Additionally or alternatively, processor 20 is configured to receive signals, for example from station 55, indicative of additional types of distortions and problems in the printing process of system 10. Based on these signals, processor 20 is configured to automatically estimate the level of pattern placement accuracy and additional types of distortions and / or defects not previously described. In other embodiments, any other suitable method for inspecting the patterns printed on sheet 50 (or on any other substrate previously described) can also be used, for example using an external (e.g., offline) inspection system, or any type of measurement fixture and / or scanner. In these embodiments, based on information received from the external inspection system, processor 20 is configured to initiate any suitable corrective action and / or stop operation of system 10.

[0076] The configuration of system 10 is provided in a simplified manner purely as an example to clarify the present invention. The components, modules and stations described in the printing system 10 described above, as well as additional components and configurations, are described in detail in, for example, U.S. Patent Nos. 9,327,496 and 9,186,884, PCT International Publication Nos. WO2013 / 132438, WO2013 / 132424 and WO2017 / 208152, U.S. Patent Application Publication Nos. 2015 / 0118503 and 2017 / 0008272, the disclosures of which are all incorporated herein by reference.

[0077] The particular configuration of system 10 is shown by way of example to illustrate the particular problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in enhancing the performance of such systems, but embodiments of the present invention are in no way limited to this particular type of example system, and the principles described herein may be applied to any other type of printing system as well.

[0078] Use of a virtual axis to synchronize the gear ratio of the BCD and BTD rollers with the impression cylinder speed

[0079] 2 is a block diagram that generally illustrates a workflow for synchronizing the gear ratios of the BCD 77 and BTD 99 with the speed of the impression cylinder 82 using a virtual axis 111, in accordance with one embodiment of the present invention. In some embodiments, this workflow may be implemented to keep the blanket 44 taut while moving at least between the BTD 99 and the impression station 84 at a predefined speed (or within a range of speeds).

[0080] In some embodiments, the system 10 includes a rotary encoder 102 integrated with the impression cylinder 81 (FIG. 1). The encoder 102 is configured to generate a rotary-based position signal indicative of the angular displacement of the impression cylinder 82. In some embodiments, the encoder 102 is configured to generate the position signal at a predefined frequency, in this example, at a frequency of about 1 KHz.

[0081] In some embodiments, system 10 includes a smoothing filter 104, in this example a low-pass filter, that is applied to the position signal received from encoder 102 to remove frequencies greater than a predefined cutoff threshold, e.g., about 50 Hz. Smoothing filter 104 may be implemented in any suitable device of system 10, such as in processor 20 and / or controller 54, and may apply a moving average or any other suitable technique to smooth the position signal received from encoder 102.

[0082] In some embodiments, the system 10 includes a virtual axis 111, which may be implemented as a software module within the controller 54 or any other suitable device. The virtual axis 111 is configured to receive the position signal from the smoothing filter 104 and generate a signal indicative of the angular position and velocity of the impression cylinder 82.

[0083] In some embodiments, the controller 54 is configured to receive an input 106 including parameters associated with the BCD 77 and an input 108 including parameters associated with the BTD 99. The input 106 may include any suitable parameters, such as, but not limited to, (i) a nominal diameter of the BCD 77, (ii) a correction for changes in the diameter of the BCD 77, for example, based on an estimated or measured temperature of the BCD 77, and (iii) a target speed (typically a rotational speed, but can also be an estimate of a linear speed) of the BCD 77. Similarly, the input 108 may include a nominal diameter of the BTD 99 as well as other parameters, such as an estimated or measured temperature for the BTD 99, and a target speed (typically a rotational speed, but can also be an estimate of a linear speed) of the BTD 99.

[0084] In some embodiments, in addition to compensating for changes in the diameter of the BCD 77, the controller 54 is configured to compensate for additional variations, such as, but not limited to, variations in the effective thickness of the blanket 44, the effective spring constant of the blanket 44 resisting tension applied to the blanket 44, etc.

[0085] In some embodiments, based on (i) the position and rotational speed of the impression cylinder 82, and (ii) the inputs 106 and 108, the controller 54 is configured to determine a BCD gear ratio (BCDGR) 107 and a BTD gear ratio (BTDGR) 109, which are the physical axes of the BCG 77 and BTG 99, respectively. For example, to keep the blanket 44 taut between the BTD 99 and the impression station 84, the controller 54 may determine a ratio of 1.1, or 1.01, or 1.001, or any other suitable ratio between the BCDGR 107 and the BTDGR 109.

[0086] In such an embodiment, the BCD 77 rotates about its fixed axis at a first angular velocity (e.g., the nominal rotational speed of the BCD 77 is between about 5 revolutions / second and about 6 revolutions / second), in this example, about 5.42 revolutions / second. Note that based on the aforementioned gear ratio, the BTD 99 rotates about its fixed axis at a second angular velocity for the same time interval that the BCD 77 rotates, but at a different rotational speed. For example, if the BCD 77 rotates at a nominal rotational speed of about 5.42 revolutions / second, the BTD 99 rotates at a nominal rotational speed of about 5.414 revolutions / second, which is calculated by dividing the aforementioned nominal rotational speed of the BCD 77 (5.42 revolutions / second) by the gear ratio of 1.001 (5.42 / 1.001).

[0087] In the context of this disclosure and claims, signal reception, signal processing and process control operations may be performed by or divided between controller 54 and / or processor 20. For example, where an embodiment is described as being performed by controller 54, the same embodiment may be performed by processor 20.

[0088] 2, the controller 54 is configured to synchronize the linear velocity of the blanket 44 passing through the BTD 99, the BCD 77, and the impression cylinder 82 to keep the blanket 44 taut (i) when passing between the BTD 99 and the BCD 77 along the top run of the blanket 44 in the direction of travel of the blanket 44 to form an image on the blanket 44, and (ii) when passing through the impression station 84 to transfer the image from the blanket 44 to the sheet 50. In such an embodiment, the controller 54 is configured to perform the aforementioned synchronization by defining the velocity of the blanket 44 such that with each revolution of the blanket 44, the image formed on the blanket 44 is located on the same section of the impression cylinder 82 to be transferred to the sheet 50. It should be noted that this synchronization improves the match between images printed by the system 10.

[0089] In some embodiments, the controller 54 is further configured to apply the operation of the dancer assembly 74 to the calculation of the rotational speeds of the BTD 99, the BCD 77 and the impression cylinder 82.

[0090] In some embodiments, dancer assembly 74 includes one or more load cells (not shown), each typically including a piezoelectric element that is configured to measure a pressure applied to blanket 44 by dancer assembly 74. The load cells may function similarly to a gravimetric measuring device that is configured to output a signal indicative of a given pressure in response to a given pressure applied to the load cell. The given pressure is also indicative of the tension applied to blanket 44.

[0091] In this example, the dancer assembly includes two load cells attached to two respective ends of the dancer assembly 74. Note that because the blanket 44 is flexible, the pressure and tension applied by the dancer assembly 74 may change the length of the blanket 44 (e.g., due to elastic deformation).

[0092] In some embodiments, the controller 54 controls the dancer assembly 74 to maintain a preassigned (e.g., constant) tension on the blanket 44. Moreover, based on signals received from two load cells mounted on the dancer assembly 74, the controller 54 is configured to estimate a length of the blanket 44 and adjust the rotational speed of the BCD 77 and the BTD 99 based on the estimated length. Moreover, the controller 54 is configured to control the position of one or more elements of the dancer assembly 74 to obtain the preassigned tension on the blanket 44 and synchronize the movement of the blanket 44 such that an image printed on the blanket 44 is transferred to the sheet 50 at an intended section of the impression cylinder 82.

[0093] In some embodiments, as the system 10 moves the blanket 44, the controller 54 is configured to receive a first signal indicative of a first current measured for the motor of the BTD 99. The controller 54 is further configured to receive a second signal indicative of a second current measured for the motor of the BCD 77. The second current may be different, e.g., greater, than the first current. In some embodiments, the first and second currents typically represent first and second respective torque forces applied to the blanket 44 via the BTD 99 and BCD 77, respectively.

[0094] In other embodiments, at least one of the first and second signals may be received from one or more other devices configured to measure the tension applied to the blanket 44. For example, the flexibility of the blanket 44 may be converted to a spring constant, which may be calculated based on a distance measured between two predefined features of the blanket 44. For example, the blanket 44 may include a woven fabric having fibers disposed along the direction of travel of the blanket 44. In such an embodiment, the system 10 may include one or more sensors configured to output a signal indicative of the position of a given fiber of the blanket 44. Based on that signal, the controller 54 and / or the processor 20 may be configured to estimate the length of the blanket 44 and adjust the tension applied to the blanket 44 (e.g., tension applied to the top run between the BTD 99 and the BCD 77) and / or the speed of the blanket 44 in the direction of travel, as described above.

[0095] In some embodiments, the controller 54 is configured to calculate a parameter based on the first and second signals, the parameter being indicative of a distortion including, but not limited to, (i) waveform X(Y) distortion, (ii) waveform Y(X) distortion, (i) C2C positioning error between two or more colors of the image formed on the blanket 44, (iv) a deviation in pattern placement accuracy (PPA) of at least one section of the image formed on the blanket 44 and transferred to the sheet 50, referred to herein as substrate positioning error, or (v) any combination of the foregoing.

[0096] In some embodiments, the parameter may include the difference between the aforementioned first and second currents, which indicates the torque, and therefore the tension, applied to the blanket 44 as the blanket is moved in the direction of movement between BTD 99 and BCD 77. Note that in this example, the currents are determined based on the printing application, and therefore the maximum current is normalized to 100%, and the difference between the first and second currents is measured by a percentage normalized to the maximum current. For example, the second current measured for the BCD 77 motor may be normalized to about 75% of the maximum current, and the first current measured for the BTD 99 motor may be normalized to about 42% of the maximum current. In this example, the difference between the first and second currents is about 33%.

[0097] In some embodiments, the controller 54 is configured to maintain control of a threshold for the difference between the first and second currents. For example, the blanket 44 may detect a degradation in X(Y) waveform distortion because it is not sufficiently taut when the difference between the first and second currents is less than a certain threshold (e.g., about 29%) or greater than a certain threshold (e.g., about 33%). In such an embodiment, the processor 20 may apply corrective action, such as adjusting the speed of at least one of the BCD 77 and BTD 99 motors, to have a required difference between the first and second currents (e.g., between about 29% and 33%). It should be noted that the aforementioned monitoring and corrective action may be performed at any predefined time during the print cycle, preferably prior to application of an image to the blanket 44 by the imaging station. Thus, processor 20 is configured to control imaging station 60 to apply an image to blanket 44 only after achieving a stable predefined difference (e.g., between about 29% and 33%) between the first and second currents.

[0098] Reducing waveform distortion by measuring current in BCD and BTD motors

[0099] FIG. 3 is a graph 120 that generally illustrates polychromatic waveform distortion measured on two similar images formed on blanket 44 with a time difference of about four days, in accordance with one embodiment of the present invention.

[0100] In some embodiments, the waveform distortion was measured and calculated using any suitable inspection technique, such as using image quality control station 55 described above in Figure 1. The vertical axis of graph 120 represents distortion error, in this example, waveform distortion error.

[0101] Waveform distortion errors may occur along the direction of travel of blanket 44, referred to herein as the X-axis, which varies with position on the Y-axis (orthogonal to the X-axis), shown in graph 120, referred to herein as waveform X (Y). Note that waveform distortion is calculated based on the measured distance between the intended and measured positions of a given pattern of each color in the printed image. In the context of this disclosure, the term "intended position" refers to the position of a given pattern of each color within the design of the image intended to be printed by system 10.

[0102] In the example graph 120, distance is measured relative to a dashed horizontal line that extends from number "0" on the waveform distortion axis to represent zero distortion. Curves above and below the dashed line indicate the direction of deviation of the measured position of the pattern relative to its intended position.

[0103] In other embodiments, a different graph (not shown in FIG. 3) may show distortion along the Y-axis, referred to herein as waveform Y(X), which varies with position on the X-axis.

[0104] Waveform distortion may be caused by a variety of errors, such as, but not limited to, (i) deviations from a specified motion profile of the blanket 44, (ii) deviations from a specified relative velocity between the blanket 44 and the sheet 50 at the printing station 84, (iii) deviations in the profile (e.g., position, shape and orientation) of the print bar 62 relative to the blanket 44, and (iv) other deviations caused by temperature changes in one or more components and / or modules and / or stations of the system 10.

[0105] In the example of FIG. 3, graph 120 includes graphs 122 and 124 of two respective similar images with seven different color inks (in this example, black, blue, cyan, green, magenta, orange and yellow).

[0106] In some embodiments, two similar images are generated, for example, about four days apart during continuous operation of system 10. Respective graphs 122 and 124 are shown superimposed on graph 120 and show the measured waveform X(Y) distortion for each color in each of the two images.

[0107] The aforementioned errors, and additional errors, can result in a wavy pattern of printed features, as shown in graph 120. Note that typically the wavy pattern has two components: (i) a common waviness of all colors, for example, due to the aforementioned deviations at printing station 84, and (ii) a different waviness formed in each color image, caused, for example, by temporary changes in the speed of and tension applied to blanket 44, for example, as the top run passes between print bars of different colors.

[0108] In some embodiments, controller 54 is configured to control the motors of BCD 77 and BTD 99 to maintain a difference (e.g., about 32%) between the measured first and second currents, as previously described in Figure 2. In this example, said difference is maintained for at least four days in order to keep blanket 44 taut as system 10 prints images during this period.

[0109] As shown in graph 120, the waveform distortion profile is maintained for each color in both images. For example, at location 123A on blanket 44, the measured waveform distortion of blue ink, shown by points 122A and 124A on graphs 122 and 124, respectively, has a slight difference (e.g., between a few microns and about 10 μm). Similarly, at a different location 123B on blanket 44, the waveform distortion of blue ink is the same in both images, as shown by points 122B and 124B on graphs 122 and 124, respectively.

[0110] In some embodiments, the controller 54 is configured to maintain the waveform distortion profile of each color ink constant over time. In this example, the waveform profile is maintained by controlling the difference between the measured currents of the BCD 77 and BTD 99 motors within an appropriate specified range, such as the range described in FIG. 2 above.

[0111] In some embodiments, the processor 20 may apply various techniques to correct waveform distortion in the printed image. Some implementations of waveform distortion correction are described in detail, for example, in U.S. Patent Application Publication No. 2019 / 0152218 and U.S. Provisional Application No. 62 / 717,957, the disclosures of which are incorporated herein by reference. In some embodiments, after correcting the waveform distortion, the disclosed techniques may be applied to keep the correction stable over the operation time of the system 10. Moreover, the disclosed techniques may maintain the stability of the correction for both the waveform X(Y) and waveform Y(X) described above.

[0112] 4 is a flow diagram that generally illustrates a method for improving waveform distortion stability over time, in accordance with an embodiment of the present invention. The method begins with a first signal receiving step 200, in which a first signal is received (e.g., by the controller 54) indicative of a first current measured for a motor of the BCD 77 that moves the blanket 44 to print an image thereon. In a second signal receiving step 202, the controller 54 receives a second signal indicative of a second current measured for a motor of the BTD 99 that moves the blanket 44 together with the BCD 77. In some embodiments, the controller 54 and / or the processor 20 may maintain a predefined process window having, among other things, a threshold value of the difference between the first and second measured currents. In such an embodiment, the controller 54 and / or the processor 20 is configured to suspend operation of the system 10 if the difference between the first and second measured currents is greater than the threshold value.

[0113] At a parameter calculation step 204, the controller 54 calculates a parameter indicative of an estimated waveform distortion in the image intended to be printed on the blanket 44 based on the first and second signals. In some embodiments, the controller 54 is configured to calculate one or more indicators of the estimated waveform distortion based on a difference between the first and second currents. Such waveform distortion may be related to an error in pattern placement accuracy (PPA) during the printing process of the image in the system 10.

[0114] In some embodiments, when monitoring the difference between the first and second currents, the controller 54 is configured to maintain a threshold value (e.g., about 29% and 33% of the maximum current as described above in FIG. 2) that indicates whether the estimated waveform distortion is within the specifications of the imaging process or whether the estimated waveform distortion exceeds the specifications. In a first decision step 206, the controller 54 compares (i) the calculated difference between the first and second currents with (ii) the aforementioned threshold value to check whether the estimated waveform distortion is within the specifications of the imaging process.

[0115] In some embodiments, if the estimated waveform distortion is above the imaging process specifications, the method proceeds to a current adjustment step 208. In some embodiments, in step 208, the controller 54 adjusts the speed of at least one of the BCD 77 and the BTD 99 to obtain a difference between the first and second currents within a specified range, e.g., between about 29% and 33%, as described above in FIG.

[0116] In some embodiments, after step 208, the method loops back to step 200 to receive the first and second signals and check (e.g., in step 206) whether the estimated distortion is within the specifications for the printing process.

[0117] In another embodiment, if the estimated waveform distortion is within the specifications of the image formation process, the method proceeds to an image printing step 210, which controls stations of the system 10 to apply ink droplets to the blanket 44 to form an image thereon.

[0118] In a second decision step 212, the processor 20 checks whether or not to print additional images on the blanket 44 based on the print plan of the system 10. If the print plan calls for printing additional images on the blanket 44, the method loops back to step 200 to receive a signal, estimate whether the estimated waveform distortion is within the specifications of the printing process, and adjust the speed of at least one of the BCD 77 and the BTD 99, if necessary.

[0119] In another embodiment, if at step 212 the printing plan does not call for printing additional images, the method proceeds to a termination step 214 where the method ends.

[0120] Although the embodiments described herein primarily address distortions associated with digital printing of images onto flexible substrates, the methods and systems described herein may also be used in other applications, such as systems including moving flexible substrates / blankets / belts and their control means.

[0121] It will be understood that the foregoing embodiments are cited as examples, and that the present invention is not limited to what has been specifically shown and described herein 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 thereof not disclosed in the prior art, which would occur to one skilled in the art upon reading the foregoing description. Documents incorporated by reference in this patent application are to be considered as integral parts of this application, except that to the extent that any term is defined in these incorporated documents in a manner that is inconsistent with the definition expressly or implicitly made herein, only the definition in this specification shall be considered.

Claims

1. receiving a first signal indicative of a first current measured on a first motion assembly for moving a flexible substrate that receives droplets of printing fluid from an imaging station to form an image thereon; receiving a second signal indicative of a second current measured on a second motion assembly for moving the flexible substrate, the section of the flexible substrate being moved between the first and second motion assemblies; calculating a parameter indicative of a distortion in the image based on the first and second signals; applying corrective action to reduce the distortion in response to detecting an increase in the distortion based on the parameters; A method comprising:

2. 2. The method of claim 1 , wherein the image has first and second axes, the distortion comprises a displacement of a pattern along the first axis that varies with position along the second axis within at least one section of the image, and applying the corrective action comprises reducing an increase in the displacement along the first axis.

3. The method of claim 2 , wherein the first axis is orthogonal to the second axis, and the first axis is parallel to an axis of movement of the flexible substrate.

4. The method of claim 2 , wherein the first axis is orthogonal to the second axis, and the first axis is orthogonal to an axis of movement of the flexible substrate.

5. 3. The method of claim 2, wherein the image includes a first color having a first pattern and a second color having a second pattern, the distortion includes a difference in the displacement between the first pattern and the second pattern, and applying the corrective action includes reducing an increase in the difference in the displacement.

6. 6. The method of claim 1, wherein the distortion comprises a difference in inter-color positional difference between a first and a second color of the image, and applying the corrective action comprises reducing an increase in the difference in the inter-color positional difference within the image.

7. The method of any one of claims 1 to 5, wherein the flexible substrate includes an intermediate transfer member (ITM) for transferring the image to a target substrate at a printing station, and the method further includes receiving a third signal indicative of a speed of the ITM at the printing station, and the applying corrective action includes adjusting a speed of at least one of the first and second motion assemblies based on the third signal and in response to detecting that the speed is changing beyond a predefined speed range.

8. (i) receiving a first input signal indicative of one or more first variables of the first motion assembly, and (ii) a second input signal indicative of one or more second variables of the second motion assembly; (i) defining a virtual axis for determining a first velocity of the ITM in the first motion assembly and a second velocity of the ITM in the second motion assembly based on the third signal and the first and second input signals; The method of claim 7, comprising:

9. 9. The method of claim 8, wherein the first motion assembly includes a first roller, a first motor, and a first gear for rotating the first roller, and the second motion assembly includes a second roller, a second motor, and a second gear for rotating the second roller, and applying the corrective action includes adjusting at least one of the first and second gears in response to detecting that at least one of the first and second variables is above a predefined threshold.

10. 9. The method of claim 8, wherein at least one of the first and second variables is selected from the list consisting of: (i) a diameter of the roller, (ii) a temperature of the roller, and (iii) a nominal speed of the roller.

11. an interface configured to (i) receive a first signal indicative of a first current measured on a first motion assembly for moving a flexible substrate receiving droplets of printing fluid from an imaging station to form an image thereon, and (ii) receive a second signal indicative of a second current measured on a second motion assembly for moving the flexible substrate, a section of the flexible substrate being moved between the first and second motion assemblies; a processor configured to (i) calculate a parameter indicative of a distortion in the image based on the first and second signals, and (ii) apply a corrective action to reduce the distortion based on the parameter and in response to detecting an increase in the distortion; A system comprising:

12. 12. The system of claim 11, wherein the image has first and second axes, the distortion comprises a displacement of a pattern along the first axis that varies with position along the second axis within at least one section of the image, and the processor is configured to apply the corrective action by reducing increases in the displacement along the first axis.

13. The system of claim 12 , wherein the first axis is orthogonal to the second axis, and the first axis is parallel to an axis of movement of the flexible substrate.

14. The system of claim 12 , wherein the first axis is orthogonal to the second axis, and the first axis is orthogonal to an axis of movement of the flexible substrate.

15. 13. The system of claim 12, wherein the image includes a first color having a first pattern and a second color having a second pattern, the distortion includes a difference in the displacement between the first pattern and the second pattern, and the processor is configured to apply the corrective action by reducing an increase in the difference in the displacement.

16. The system of any one of claims 11 to 15, wherein the distortion comprises a difference in inter-color positional difference between a first and a second color of the image, and the processor is configured to apply the corrective action by reducing an increase in the difference in the inter-color positional difference within the image.

17. The system of any one of claims 11 to 15, wherein the flexible substrate includes an intermediate transfer member (ITM) for transferring the image to a target substrate at a printing station, the interface is configured to receive a third signal indicative of a speed of the ITM at the printing station, and based on the third signal, in response to detecting that the speed is changing beyond a predefined speed range, the processor is configured to adjust a speed of at least one of the first and second motion assemblies.

18. 18. The system of claim 17, wherein the interface is configured to receive (i) a first input signal indicative of one or more first variables of the first motion assembly and (ii) a second input signal indicative of one or more second variables of the second motion assembly, and the processor is configured to define virtual axes for determining a first velocity of the ITM in the first motion assembly and a second velocity of the ITM in the second motion assembly based on (i) the third signal and (ii) the first and second input signals.

19. 20. The system of claim 18, wherein the first motion assembly includes a first roller, a first motor, and a first gear for rotating the first roller, and the second motion assembly includes a second roller, a second motor, and a second gear for rotating the second roller, and the processor is configured to apply the corrective action by adjusting at least one of the first and second gears in response to detecting that at least one of the first and second variables is above a predefined threshold.

20. 20. The system of claim 18, wherein at least one of the first and second variables is selected from the list consisting of: (i) a diameter of the roller, (ii) a temperature of the roller, and (iii) a nominal speed of the roller.

Images