Controlling the movement of a flexible intermediate transfer member

Abstract

The system (11) includes: (a) actuators (23, 25, 27) configured to tilt rollers (99, 77, 76) while an intermediate transfer member (ITM) (44) of the printing system (11) moves thereover; and a controller (54, 20) configured to (i) identify distortion in the ITM (44) and (ii) control the actuators (23, 25, 27) to tilt the rollers (99, 77, 76) to reduce the distortion during movement of the ITM (44).

Description

[Technical Field]

[0001] FIELD OF THE INVENTION The present invention relates generally to digital printing, and more particularly to a method and system for controlling the movement of a flexible intermediate transfer member during the printing process. [Background technology]

[0002] Some printing systems include one or more intermediate transfer members that receive an image and typically move to transfer the image to a target substrate. Various techniques have been disclosed for moving such intermediate transfer members. Summary of the Invention [Problem to be solved by the invention]

[0003] One embodiment of the present invention described herein provides a system that includes an actuator and a controller, where the actuator is configured to tilt an intermediate transfer member (ITM) of a printing system while the ITM moves over the roller, and the controller is configured to: (i) identify a distortion in the ITM, and (ii) control the actuator to tilt the roller to mitigate the distortion while the ITM is moving. [Means for solving the problem]

[0004] In some embodiments, the ITM moves along a continuous path in a first direction, and the controller is configured to reduce distortion while the ITM moves in the first direction by: (i) determining a first movement speed of the ITM in a second direction different from the first direction, and (ii) controlling the actuator to tilt the roller to move the ITM at a second movement speed that is smaller than the first movement speed.

[0005] In another embodiment, the controller is configured to receive a signal indicative of the first rate of movement and to control the actuator in response to receiving the signal. In yet another embodiment, the system includes: (i) a first edge sensor disposed in a first section of the continuous path and configured to generate a first signal indicative of the first rate of movement in the first section, and (ii) a second edge sensor disposed in a second section of the continuous path different from the first section and configured to generate a second signal indicative of the first rate of movement in the second section.

[0006] In some embodiments, the controller is configured to determine a first distortion in the first interval and a second distortion in the second interval in response to receiving the first and second signals.

[0007] In other embodiments, the system includes a first actuator configured to tilt the first roller and a second actuator configured to tilt the second roller, and in response to identifying the first and second strains, the controller is configured to control at least one of the first and second actuators to tilt the first and second rollers, respectively.

[0008] In yet another embodiment, the controller is configured to control: (i) a first actuator to tilt the first roller to a first tilt angle, and (ii) a second actuator to tilt the second roller to a second tilt angle different from the first tilt angle.

[0009] In some embodiments, the controller is configured to control the first and second actuators to apply the first and second tilts simultaneously. In other embodiments, the ITM is configured to receive ink droplets to form an ink image thereon and to transfer the ink image to a target substrate. In yet other embodiments, the controller is configured to: (i) maintain a lookup table (LUT) that includes one or more known distortions, respectively, caused by one or more operations performed in the printing system, and (ii) control the actuator to tilt the roller according to the LUT to reduce the one or more known distortions.

[0010] In some embodiments, the one or more known distortions include a first known distortion in a first section on the ITM and a second known distortion in a second section of the ITM, and the printing system includes a first actuator configured to tilt a first roller of the printing system and a second actuator configured to tilt a second roller of the printing system, and in response to identifying the first and second known distortions, the controller is configured to control at least one of the first and second actuators to tilt the first and second rollers, respectively.

[0011] In other embodiments, the controller is configured to control: (i) a first actuator to tilt the first roller to a first tilt angle, and (ii) a second actuator to tilt the second roller to a second tilt angle different from the first tilt angle. In yet other embodiments, the controller is configured to control the first and second actuators to apply the first and second tilts simultaneously.

[0012] In some embodiments, the controller is configured to: (i) maintain a neural network (NN) configured to identify one or more known distortions each caused by one or more operations performed in the printing system, and (ii) control the actuator to tilt the roller according to the output of the NN in response to a given operation in the printing system to reduce the one or more known distortions.

[0013] In other embodiments, the controller is configured to receive one or more signals indicative of the one or more additional distortions, respectively, and the controller is configured to apply the NN to determine whether at least one of the one or more known distortions includes at least one of the one or more additional distortions. In yet other embodiments, the controller is configured to apply the NN to control the actuator in response to receiving the signals.

[0014] In some embodiments, the printing system includes at least first and second rollers, and the controller is configured to control the actuator to tilt the first roller so that at least the first roller and the second roller are not parallel to one another. In other embodiments, distortion of the ITM causes deflection of the roller, where the roller is moved by a driver and includes an encoder configured to generate a deflection signal indicative of a deflection angle of the roller, and the controller is configured to determine the distortion of the ITM based on the deflection signal.

[0015] In yet another embodiment, a system comprises: (i) a housing and at least first and second print bars, wherein the first and second print bars are coupled to the housing and configured to apply ink droplets of first and second colors to the ITM to generate first and second patterns of an image, respectively, on the ITM; and (ii) at least a given edge sensor, wherein the edge sensor is coupled to the housing and configured to generate (a) a first edge signal indicative of a first position of the housing, and (b) a second edge signal indicative of a second position of an edge portion of the ITM moved relative to the at least first and second print bars.

[0016] In some embodiments, distortion in the housing causes a color-to-color (C2C) registration error between the first pattern and the second pattern of the image, and the controller is configured to do the following based on the first edge signal and the second edge signal: (i) identify the distortion in the housing, (ii) estimate the C2C registration error, and (iii) control the actuator to tilt the roller to reduce the C2C registration error by compensating for the distortion in the housing while (a) the ITM moves and (b) the first and second print bars apply ink drops of the first and second colors.

[0017] In some embodiments, the controller is configured to control at least the first and second print bars to adjust at least one of the first and second timings for applying ink drops of the first and second colors, respectively, to reduce C2C registration errors in the image.

[0018] In another embodiment, the ITM has a plurality of marks formed at a predetermined distance from each other along at least an edge of the ITM, and includes one or more sensors configured to generate a plurality of signals indicating a plurality of positions of the plurality of marks, respectively, and the controller is configured to control at least one of: (i) a first movement speed, and (ii) an actuator based on the plurality of signals.

[0019] In yet another embodiment, at least one of the marks includes a plurality of trapezoids, and the controller is configured to estimate at least one of: (i) a movement speed in a first direction, and (ii) a first movement speed, based on a plurality of signals indicating a plurality of positions of the plurality of trapezoids, respectively.

[0020] In some embodiments, the plurality of trapezoids each have (i) a plurality of orthogonal edges perpendicular to the first direction, and (ii) a plurality of diagonal edges extending at a predetermined angle relative to the first direction, and the controller is configured to estimate the movement speed in at least the first direction based on a plurality of signals respectively indicating a plurality of positions of each of the orthogonal edges.

[0021] In another embodiment, the plurality of marks includes: (i) a first mark having a first orthogonal side and a first diagonal side, and (ii) a second mark having a second orthogonal side and a second diagonal side, and the controller is configured to receive a given signal indicative of the orthogonal side and the diagonal side, and identify distortion of the ITM by estimating, based on the signal: (a) a first distance between the first orthogonal side and the first diagonal side, and (b) a second distance between the second orthogonal side and the second diagonal side.

[0022] In yet another embodiment, in response to movement of the ITM in the second direction, the controller is configured to: (i) determine a difference between the first distance and the second distance, and (ii) estimate a magnitude of movement of the ITM in the second direction based on (a) the estimated difference between the first distance and the second distance, and (b) a predetermined angle.

[0023] In some embodiments, the plurality of trapezoids include a plurality of isosceles trapezoids each having (i) a plurality of third diagonal sides extending at a first angle with respect to the first direction and (ii) a plurality of fourth diagonal sides extending at a second angle with respect to the first direction, and the controller is configured to receive a third signal and a fourth signal indicating a third position and a fourth position of the third diagonal side and the fourth diagonal side, respectively, the plurality of isosceles trapezoids include first and second isosceles trapezoids located at a given distance, and based on the third signal and the fourth signal, the controller is configured to identify distortion of the ITM by estimating: (a) a third distance between the third diagonal side and the fourth diagonal side of the first isosceles trapezoid, and (b) a fourth distance between the third diagonal side and the fourth diagonal side of the second isosceles trapezoid.

[0024] In another embodiment, the controller is configured to estimate the magnitude of movement of the ITM in the second direction based on: (a) an estimated difference between the third distance and the fourth distance, and (b) the first angle and the second angle.

[0025] In some embodiments, at least one of the marks includes one or more polygons having pairs of sides perpendicular to the first direction, and the controller is configured to estimate the speed of movement in at least the first direction based on given signals that respectively indicate one or more given positions of the pairs of sides.

[0026] In another embodiment, the ITM has a first axis and a second axis perpendicular to the first axis, the marks include a third mark formed along one or more first edge portions of the first axis and a fourth mark formed along one or more second edge portions of the second axis, and the controller is configured to: (i) identify at least one of (a) a third distortion of the ITM based on the third mark, (b) a fourth distortion of the ITM based on the fourth mark, and (c) a fifth distortion of the ITM based on the third and fourth marks, and (ii) control the actuator to tilt the roller to reduce at least one of the third, fourth, and fifth distortions while the ITM is moving.

[0027] In some embodiments, based on at least one of the plurality of signals, the controller is configured to control the operation of at least one station or assembly of the system. In other embodiments, the at least one station or assembly is selected from the list consisting of: (a) an imaging station configured to apply ink drops to the ITM and generate an image on the ITM, (b) an impression station configured to transfer the image to a target substrate, (c) at least a roller configured to move the ITM, (d) one or more drying assemblies configured to at least partially dry the ink drops on the ITM, and (e) an ITM processing station.

[0028] In some embodiments, the impression station includes a rotatable impression cylinder and a rotatable pressure cylinder configured to transfer an image to the target substrate, and based on at least one of the plurality of signals, the controller is configured to control at least one operation selected from the list consisting of: (a) timing of engagement and disengagement between the impression cylinder and the pressure cylinder; (b) a motion profile of at least one of the impression cylinder and the pressure cylinder; and (c) a size of a gap between a disengaged impression cylinder and the pressure cylinder.

[0029] Further, in accordance with one embodiment of the present invention, there is provided a method that includes identifying distortion of an intermediate transfer member (ITM) moving over a roller in a printing system, wherein an actuator is controlled to tilt the roller to reduce the distortion during movement of the ITM.

[0030] 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 explanation of the drawings]

[0031] [Figure 1] FIG. 1 is a schematic side view of a digital printing system according to one embodiment of the present invention. [Figure 2A] FIG. 2A is a schematic top view illustrating sensors configured to detect unwanted movement of a blanket of a digital printing system and the position of an edge of the blanket during a printing process, according to one embodiment of the present invention. [Figure 2B] FIG. 2B is a schematic top view illustrating compensation for unwanted blanket movement during the printing process, according to one embodiment of the present invention. [Figure 3] FIG. 3 is a schematic diagram illustrating the control of blanket movement in the Y-axis direction, according to one embodiment of the present invention. [Figure 4] FIG. 4 is a schematic side view of a blanket and a graph illustrating a method for distinguishing between blanket cutting errors and undesired blanket movement according to one embodiment of the present invention. [Figure 5] FIG. 5 is a flow chart that schematically illustrates a method for reducing distortion of a blanket that experiences undesired movement along the Y-axis during a printing process, in accordance with one embodiment of the present invention. [Figure 6A] FIG. 6A is a schematic top view illustrating the alignment between the movement of the blanket and the printing of the pattern by the print bar of the system of FIG. 1, in accordance with one embodiment of the present invention. [Figure 6B]FIG. 6B is a schematic top view illustrating the detection of undesired distortions in a blanket of a digital printing system during the printing process, according to one embodiment of the present invention. [Figure 7] FIG. 7 is a schematic top view illustrating detection of distortions in the sidewalls of a housing of a digital printing system that result in color-to-color (C2C) registration errors during the printing process, according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0032] Detailed Description of the Embodiments overview Some printing systems have a movable intermediate member configured to receive an image and transfer the image to a target substrate. In some cases, the intermediate member is flexible and can distort as it moves, which can result in distortion of the printed image and reduced print output from the printing system.

[0033] In principle, the edge of the flexible intermediate member could be coupled to a transport subsystem configured to control the movement of the intermediate member. One implementation of a transport subsystem is a zipper configured to couple between the transport subsystem and the intermediate member. However, such coupling mechanisms (e.g., zippers) can introduce non-uniform flexibility into the flexible member, which can cause distortions in the printed image and various issues with the operation of the printing system.

[0034] The embodiments of the present invention described below provide improved techniques for controlling the movement of a flexible intermediate member (ITM) to reduce or prevent distortion as the ITM moves to print an image.

[0035] In some embodiments, a digital printing system, also referred to herein simply as a system, includes an imaging system configured to apply one or more droplets of printing fluid to an ITM, also referred to herein as a blanket, to generate an image thereon, and an impression station configured to transfer the image from the blanket to a target substrate, such as a sheet or continuous web, for example, by alternately engaging and disengaging the blanket from the target substrate.

[0036] In some embodiments, the blanket is formed into an endless loop (e.g., using a seam between the ends of the blanket), and the system includes a plurality of rollers for moving and guiding the blanket along an endless continuous path, such as shown in the examples below in Figures 1 and 3. Some rollers are motorized and controlled by the system's controller to move and guide the blanket, while other rollers are not motorized and are primarily used to guide the moving blanket.

[0037] In some embodiments, the system includes one or more actuators configured to tilt one or more respective rollers of the system while the blanket moves thereover.

[0038] In some embodiments, the controller of the system is configured to identify and reduce distortion in the blanket, which can be performed in a proactive mode (i.e., beforehand), a reactive mode (i.e., afterward), or a combination of both modes, as described herein.

[0039] In some embodiments, the system includes one or more sensors disposed in one or more respective sections of the system. As the blanket moves in a first direction, e.g., along the X-axis of the system to perform printing, the one or more sensors are configured to generate one or more respective signals indicative of the position of one or both edges of the blanket in a second direction different from the first direction. In this example, the second direction is parallel to the Y-axis of the system, which is orthogonal to the X-axis. Embodiments relating to the sensors and respective signals are described in more detail, for example, in Figures 2A, 3, and 4 below.

[0040] In some embodiments, in reactive mode, the controller is configured to receive signals from the sensors, and based on the signals, the controller is configured to calculate or estimate the speed of blanket movement along the y-axis in each section of the system. For example, in a first section where a print bar positioned along the x-axis is used to apply droplets to the blanket, movement of the blanket in the y-axis can cause color-to-color (C2C) registration errors, which are described in detail below in Figures 1 and 2A. Similarly, in a second section positioned in the system prior to transferring the image to the target substrate, movement of the blanket in the y-axis can cause registration errors in the position of the image on the target substrate (also referred to herein as image-to-substrate (I2S) registration errors), which are described in detail below in Figures 1 and 2A.

[0041] In some embodiments, the controller is configured to maintain one or more thresholds indicating the allowed speed of blanket movement in the Y-axis. Note that because C2C registration error specifications are tighter than I2S registration error specifications, the respective thresholds for the maximum allowed speeds may differ from each other.

[0042] In some embodiments, in the reactive mode, if the controller determines that the estimated blanket movement speed in a given section is greater than a respective threshold, the controller is configured to control one or more actuators to tilt one or more respective rollers at a selected angle to reduce the blanket movement speed in the Y-axis during blanket movement. Note that tilting the roller(s) reduces blanket distortion in a given section of the system and improves the quality of the printed image. Embodiments related to the reactive mode are described in more detail, for example, in Figures 2A, 3, and 4 below.

[0043] In some embodiments, the controller is configured to maintain a look-up table (LUT) that includes one or more known distortions, each caused by one or more operations performed in the system. For example, changing a blade in a blanket processing (e.g., cleaning) station, described in detail below in FIG. 3, may change the force(s) applied to the moving blanket, causing a known movement of the blanket along the Y-axis (and thus a distortion of the blanket). An embodiment relating to the LUT is described in more detail, for example, in FIG. 3 below.

[0044] In some embodiments, in proactive mode, the controller is configured to control one or more of the actuators to tilt the respective rollers before starting a print job, thereby proactively preventing blanket distortion that may be caused by uncontrolled movement of the blanket along the Y axis, as described above.

[0045] In other embodiments, instead of or in addition to the LUT, the controller is configured to maintain a neural network (NN) trained to identify one or more distortions of the blanket caused by uncontrolled movement of the blanket along the Y axis. An embodiment relating to a NN is described in more detail, for example, in FIG. 3 below.

[0046] The disclosed techniques improve the quality of images printed in systems and increase the productivity of such printing systems. Embodiments relating to further improvements, such as, but not limited to, reducing the appearance of memory effects, are described in the detailed description below.

[0047] System Description 1 is a schematic side view of a digital printing system 10 according to one embodiment of the present invention. In some embodiments, system 10 includes a rolling flexible blanket 44 that circulates 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 the claims, the terms "blanket" and "intermediate transfer member (ITM)" are used interchangeably and refer to a flexible member comprising one or more layers used as an intermediate member, for example, formed into an endless loop configured to receive an ink image from imaging station 60 and transfer the ink image to a target substrate, as described in more detail below.

[0048] In an operational mode, imaging station 60 is configured to form a mirror ink image of digital image 42, also referred to herein as an "ink image" (not shown) or simply "image," on an upper run of the surface of blanket 44. The ink image is then transferred to a target substrate (e.g., paper, folding carton, multi-layer polymer, or any suitable flexible packaging in the form of a sheet or continuous web) disposed below the lower run of blanket 44.

[0049] In the present invention, the term "run" refers to the length or section of blanket 44 between any two given rollers along which blanket 44 is guided.

[0050] In some embodiments, during attachment, blanket 44 may be bonded edge-to-edge using a seam, also referred to herein as seam 45, to form a continuous blanket loop, also referred to herein as a closed loop. Example methods and systems for seam attachment are described in detail in U.S. Patent Application Publication No. 2020 / 0171813, the disclosure of which is incorporated herein by reference.

[0051] In some embodiments, imaging station 60 typically includes a plurality of print bars 62, each mounted to 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 heads approximately as wide as the print area on blanket 44, with individually controllable print nozzles configured to eject ink and other types of printing fluids onto blanket 44, as described in more detail below.

[0052] In some embodiments, imaging station 60 may include any suitable number of print bars 62 (also referred to herein simply as bars 62). Each bar 62 may contain 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 also include four print bars 62 having any selected color, such as cyan (C), magenta (M), yellow (Y), and black (K).

[0053] In some embodiments, the print head is configured to eject ink droplets of different colors onto the surface of blanket 44 so as to form an ink image (not shown) on the surface of blanket 44. In this example, blanket 44 is moved along the X-axis of an XYZ coordinate system of system 10, and the ink droplets are directed by the print head, typically parallel to the Z-axis of the coordinate system.

[0054] In some embodiments, the different print bars 62 are spaced apart from one another along a movement axis, also referred to herein as (i) the direction of blanket 44 movement 94 or (ii) the printing direction. In this example, the blanket 44 movement direction is parallel to the X axis, and each print bar 62 extends along the Y axis of the XYZ coordinate system 10. In this configuration, precise spacing between the bars 62 along the X axis and synchronization between the direction of the ink droplets of each bar 62 and the movement of the blanket 44 is essential to achieve correct placement of the image pattern.

[0055] In this disclosure and claims, the terms “inter-color pattern,” “pattern placement accuracy,” “color-to-color registration,” “C2C registration,” “color-to-color position difference,” “bar-to-bar registration,” and “color registration” are used interchangeably and refer to any placement accuracy of two or more colors relative to each other.

[0056] In some embodiments, system 10 includes a heater 66, such as a gas or air blower for blowing gas or air at any suitable temperature, a hot gas or air blower, and / or an infrared-based heater. Heater 66 is disposed between print bars 62 and configured to partially dry ink droplets deposited on the surface of blanket 44. This air flow between print bars can help, for example, (i) reduce condensation on the surface of the print head and / or treat satellites (e.g., residue or small droplets distributed around the main ink droplet), and / or (ii) prevent clogging of the inkjet nozzle openings of the print head, and / or (iii) prevent droplets of different colors of ink on blanket 44 from undesirably coalescing with one another.

[0057] In some embodiments, system 10 includes a drying station 64 configured to direct infrared radiation and cooled air (or another gas) and / or blow hot air (or another gas) onto the surface of blanket 44. In some embodiments, drying station 64 may include an infrared-based lighting assembly (not shown) and / or a blower 68, or any other suitable drying device.

[0058] In some embodiments, at drying station 64, the ink image formed on blanket 44 is exposed to radiation and / or hot air to more thoroughly dry the ink, evaporating most or all of the liquid carrier and leaving only a layer of resin and colorant that has been heated to a tacky ink film.

[0059] In some embodiments, system 10 includes a blanket module 70, also referred to herein as an ITM module, that includes a rolling 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 so as to control the position of segments of blanket 44 relative to their respective print bars 62. In some embodiments, one or more motion encoders may be integrated with additional rollers and other moving parts of system 10.

[0060] In some embodiments, such motion encoders typically comprise at least one rotary encoder configured to generate rotation-based position signals indicative of the angular displacement of the respective roller. It should be noted that in the context of the present invention and the claims, the terms "indicative of" and "indication" are used interchangeably.

[0061] Additionally or alternatively, blanket 44 may include an integrated encoder (not shown) for controlling the operation of various modules of system 10. One implementation of an integrated motion encoder is described in detail, for example, in PCT International Publication (WO) No. 2020 / 003088, the disclosure of which is incorporated herein by reference.

[0062] In some embodiments, blanket 44 may comprise a fabric (not shown) and any suitable type of additional layer. Detailed embodiments relating to the stacked layer structure of any suitable blanket, such as blanket 44, are provided, for example, in PCT International Publication (WO) No. 2017 / 208144 and PCT Patent Application No. PCT / IB2019 / 055288, the disclosures of which are incorporated herein by reference in their entirety.

[0063] In some embodiments, the fabric is comprised of two or more sets of alternating fibers (not shown). In this example, the two sets of fibers are substantially perpendicular to one another, and the fibers in one set of fibers are laid out parallel to one another and to the direction of travel 94. Additionally, the fabric of blanket 44 has an opacity that varies according to the periodic pattern of the fibers.

[0064] In some embodiments, the fabric of blanket 44 may be comprised of any suitable number of fibers, for example, 20,000 to 30,000 fibers. In a set of fibers arranged parallel to the direction of travel 94, each fiber and / or the distance between adjacent fibers may be used as a position reference along the axis of travel of blanket 44.

[0065] In some embodiments, a processor 20 (described below) of the system 10 can use the position of one or more fibers of the blanket 44 to control parameters of the position and movement of the blanket 44. Detailed embodiments relating to controlling the movement of the blanket 44 are provided, for example, in PCT International Publication (WO) No. 2021 / 044303, the disclosure of which is incorporated herein by reference.

[0066] In some embodiments, blanket 44 is guided over rollers 78, idlers 76, and other rollers described herein, as well as a powered tensioning roller, also referred to herein as a dancer assembly 74. Dancer assembly 74 is configured to control the amount of slack in blanket 44, the movement of which is represented diagrammatically by a double-headed arrow in FIG. 1. Furthermore, stretching of blanket 44 due to aging will not affect the ink image placement performance of system 10, but will simply result in more slack being required to be removed by tensioning dancer assembly 74.

[0067] In some embodiments, both the idler 76 and the dancer assembly 74 may be electrically powered, with the idler 76 being described in more detail below in Figure 3. Additionally, the construction and operation of the roller 78 are described in more detail, for example, in U.S. Patent Application Publication No. 2017 / 0008272 and the aforementioned PCT International Publication (WO) No. 2013 / 132424, the disclosures of which are incorporated herein by reference in their entirety.

[0068] In some embodiments, system 10 includes a blanket tension drive roller (BTD) 99 and a blanket control drive roller (BCD) 77, which are powered by respective first and second motors, typically electric motors (not shown), and configured to rotate about their respective first and second axes. For example, BTD 99 is coupled to a rotor of the electric motor, and the stator of the electric motor is coupled to (the housing of) system 10. The same arrangement applies to BCD 77.

[0069] In some embodiments, each of the idlers 76, BCD 77, and BTD 99 is configured to rotate about a respective axis, also referred to herein as the axis of rotation. The axis of rotation of each of the idlers 76, BCD 77, and BTD 99 may comprise a rotatable roller, as shown in FIG. 2 below. In some embodiments, at least one, and typically each, of the rotatable rollers of the idlers 76, BCD 77, and BTD 99 has a first end that is fixed and configured to function as a pivot, and a second end that is configured to move relative to the pivot through one or more controlled angles, as described in more detail in FIG. 2 below.

[0070] In some embodiments, system 10 includes one or more edge sensors (shown in FIGS. 2A, 2B, 3, and 4 below) positioned at one or more locations along blanket 44. Each edge sensor is configured to generate a signal indicative of the position of an edge of blanket 44 (shown in FIGS. 2A, 2B, 3, and 4 below) along a Y-axis perpendicular to the direction of travel 94 of blanket 44.

[0071] 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 into blanket 44 or may include sensors external to blanket 44 using any other suitable technique to obtain 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, thereby monitoring the tension applied to blanket 44 and controlling the operation of dancer assembly 74 and other components such as, but not limited to, idler 76, BCD 77, and BTD 99.

[0072] In some embodiments, at impression station 84, blanket 44 passes between impression cylinder 82 and pressure cylinder 90, which are configured to hold the compressible blanket. In some embodiments, a motion encoder is integrated with at least one of impression cylinder 82 and pressure cylinder 90.

[0073] In some embodiments, the system 10 includes a control console 12 configured to control multiple modules of the system 10, such as a blanket module 70, an image forming station 60 located above the blanket module 70, and a substrate transport module 80 located below the blanket module 70 and including one or more impression stations, as described below.

[0074] In some embodiments, console 12 includes processor 20, typically a general-purpose processor, with appropriate front-end and interface circuitry for interfacing with and receiving signals from controller 54 and the controller of dancer assembly 74 via cable 57. Additionally or alternatively, console 12 may include an application specific integrated circuit (ASIC) and / or a digital signal processor (DSP) and / or any other suitable type of processing unit configured to perform any type of processing on data processed in system 10.

[0075] In some embodiments, controller 54, which is shown schematically as a single device, may include one or more electronic modules mounted at predetermined locations on system 10. At least one of the electronic modules of controller 54 may include electronic devices, such as control circuitry or a 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 that performs functions used by the printing system, and data for the software may be stored in memory 22. The software may be downloaded to processor 20 and control circuitry in electronic form, for example, over a network, or may be provided on a non-transitory, tangible medium, such as an optical, magnetic, or electronic memory medium.

[0076] 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 other suitable configurations, for example, alternative configurations of 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.

[0077] In some embodiments, the processor 20 is configured to display on the display 34 a digital image 42 including one or more sections (not shown) of the image 42 and / or various types of test patterns that may be stored in the memory 22.

[0078] In some embodiments, the blanket treatment station 52, also referred to herein as a cooling station, is configured to treat the blanket, for example, by cooling the blanket and / or applying a treatment liquid to the exterior surface of the blanket 44 and / or cleaning the exterior surface of the blanket 44. The blanket treatment station 52 can reduce the temperature of the blanket 44 to a desired temperature level before the blanket 44 enters the imaging station 60. This treatment may be performed by passing the blanket 44 over one or more rollers or blades configured to apply cooling and / or cleaning and / or treatment liquid to the exterior surface of the blanket.

[0079] 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 liquid can also or alternatively be applied to the blanket 44 by jetting.

[0080] In some embodiments, processor 20 is configured to receive a signal indicative of the surface temperature of blanket 44, for example, from a temperature sensor (not shown), to monitor the temperature of blanket 44 and control the operation of blanket treatment station 52. Examples of such treatment stations are described, for example, in PCT International Publication Nos. (WO) 2013 / 132424 and (WO) 2017 / 208152, the disclosures of which are incorporated herein by reference in their entireties.

[0081] 1, station 52 is mounted between impression station 84 and imaging station 60, however, station 52 may be mounted adjacent blanket 44 at any other or additional suitable location(s) between impression station 84 and imaging station 60. As noted above, station 52 may also or instead be mounted on a bar adjacent imaging station 60.

[0082] 1, impression cylinder 82 and pressure cylinder 90 impress ink images onto target flexible substrates, such as individual sheets 50, which are transported by substrate transport module 80 from input stack 86 through impression station 84 to output stack 88. In this embodiment, a rotary encoder (not shown) is integrated with impression cylinder 82.

[0083] 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 that is compressed between blanket 44 and impression cylinder 82 under the pressure of pressure cylinder 90. For single-sided printing (i.e., printing on one side of sheet 50) as shown in FIG. 1, only one impression station 84 is required.

[0084] In other embodiments, module 80 may include two or more impression cylinders (not shown) to enable one or more duplex printing operations. A configuration with two impression cylinders may also enable simplex printing at twice the speed of duplex printing. It may also be possible to print mixed lots of simplex and duplex printing. In another embodiment, a different configuration of module 80 may be used for printing on continuous web substrates. Detailed descriptions and various configurations of duplex printing systems and systems for printing on continuous web substrates are provided, for example, in U.S. Pat. Nos. 9,914,316 and 9,186,884, PCT International Publication (WO) No. 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.

[0085] As briefly mentioned above, a sheet 50 or continuous web substrate (not shown) is transported by module 80 from an input stack 86 and passes through a nip (not shown) located between impression cylinder 82 and pressure cylinder 90. Within the nip, the surface of blanket 44 bearing the ink image is pressed firmly against the sheet 50 (or other suitable substrate) by, for example, the compressible blanket of pressure cylinder 90, thereby pressing the ink image onto the surface of sheet 50 and properly separating it from the surface of blanket 44. The sheet 50 is then transported to an output stack 88.

[0086] 1, rollers 78 are positioned on the upper run of blanket 44 and are configured to maintain taut blanket 44 as it passes adjacent imaging station 60. Additionally, it is particularly important to control the speed of blanket 44 below imaging station 60 so as to achieve precise jetting and deposition of ink droplets by imaging station 60 to form an image on the surface of blanket 44.

[0087] In some embodiments, the impression cylinder 82 periodically engages and disengages from the moving blanket 44 to transfer an ink image from the blanket 44 to a target substrate passing between the blanket 44 and the impression cylinder 82. In some embodiments, the system 10 is configured to apply torque to the blanket 44 using the roller and dancer assembly described above to maintain the upper run in tension and to substantially isolate the upper run of the blanket 44 from the effects of mechanical vibrations generated in the lower run.

[0088] In some embodiments, system 10 includes a 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 system 10. In some embodiments, quality control station 55 can be located adjacent impression cylinder 82 as shown in FIG. 1 or at another suitable location within system 10.

[0089] In some embodiments, image quality control station 55 comprises a camera (not shown) configured to acquire one or more digital images of the aforementioned ink images printed on sheet 50. In some embodiments, the camera may comprise any suitable image sensor, such as a contact image sensor (CIS) or a complementary metal oxide semiconductor (CMOS) image sensor, and a scanner comprising a slit having a width of about 1 meter or any other suitable width.

[0090] In this disclosure and claims, the term "about" or "approximately" in connection with any numerical value or range indicates an appropriate dimensional tolerance that enables a collection of parts or components to function for its intended purpose as described herein.

[0091] In some embodiments, station 55 may include a spectrophotometer (not shown) configured to monitor the quality of the ink printed on sheet 50 .

[0092] In some embodiments, digital images acquired by station 55 are transmitted to a processor, such as processor 20 or any other processor in station 55, configured to evaluate the quality of each printed image. Based on the evaluation and signals received from controller 54, processor 20 is configured to control the operation of the modules and stations of system 10. For purposes of this specification and the claims, the term "processor" refers to any processing device, such as processor 20 or another processor or controller connected to or integrated with station 55, configured to process signals received from the camera and / or spectrophotometer in station 55. It should be noted that the signal processing operations, control-related instructions, and other computational operations described herein may be performed by a single processor or may be shared among multiple processors in one or more respective computers.

[0093] 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 (also referred to herein as image-to-substrate registration, color-to-color (C2C) registration), print geometry, image uniformity, color profile and linearity, and print nozzle functionality. In some embodiments, processor 20 is configured to automatically detect geometric distortions or other errors in one or more of the foregoing attributes.

[0094] In some embodiments, processor 20 is configured to analyze the detected distortion to apply corrective action to the malfunctioning module and / or provide instructions to another module or station of system 10 to compensate for the detected distortion.

[0095] In some embodiments, system 10 can print test marks (not shown) or other suitable features, for example, on the bevel or margin of sheets 50. By acquiring images of the test marks, station 55 is configured to measure various types of distortions, such as C2C registration, image-to-substrate registration, color-to-color width differences, 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) sort sheets 50 having distortions that exceed a first set of predetermined thresholds, for example, to a reject tray (not shown); (ii) initiate corrective action for sheets 50 having distortions that exceed a second, lower set of predetermined thresholds; and (iii) output sheets 50 having minor distortions, for example, below the second set of thresholds, to output stack 88.

[0096] 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 spectrophotometers of station 55 .

[0097] In some embodiments, the processor of station 55 is configured to determine whether to stop operation of system 10, for example, if the density of distortion exceeds a certain 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. In some embodiments, the corrective action can be performed in-situ (while 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 exceeds a certain threshold.

[0098] Additionally or alternatively, processor 20 may be configured to receive signals, for example, from station 55, indicative of additional distortions and types of problems in the printing process of system 10. Based on these signals, processor 20 may be configured to automatically estimate the level of pattern placement accuracy and additional distortions and / or types of defects not described above. In other embodiments, any other suitable method for inspecting patterns printed on sheet 50 (or any other substrate described above) may also be used, for example, 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 may be configured to initiate any appropriate corrective action and / or cease operation of system 10.

[0099] The configuration of system 10 is simplified for clarity of the present invention and is provided merely as an example. The components, modules, and stations described in 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. (WO) 2013 / 132438, (WO) 2013 / 132424, and (WO) 2017 / 208152, and U.S. Patent Application Publication Nos. 2015 / 0118503 and 2017 / 0008272, the disclosures of which are incorporated herein by reference in their entirety.

[0100] The particular configuration of system 10 is presented as an example to illustrate the particular problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in improving the performance of such systems. However, embodiments of the present invention are by no means limited to this particular type of exemplary system, and the principles described herein may be applied to any other type of printing system as well.

[0101] Detecting unwanted blanket movement during the printing process FIG. 2A is a schematic top view illustrating a sensor 11 configured to detect unwanted movement of a blanket 44 and the position of an edge of the blanket 44 during the printing process, according to an embodiment of the present invention.

[0102] In some cases, when moving blanket 44 in movement direction 94 (as described above in FIG. 1), various operations associated with the printing process may cause undesired movement of blanket 44, for example, in the Y axis perpendicular to movement direction 94.

[0103] In principle, it is possible to move the blanket within system 10 using a zipper integrated with the blanket and configured to reduce movement of the blanket along the Y-axis. Such blankets are described, for example, in U.S. Patent Application Publication Nos. 2022 / 0357699, 2022 / 0250376, 2018 / 0126726, and 2021 / 0260869, the disclosures of which are all incorporated herein by reference. However, zippers can increase friction between the blanket and the transport system, potentially causing various defects and / or registration errors during the printing process performed in system 10.

[0104] In some embodiments, blanket 44 is zipperless, i.e., does not have an integrated zipper. In this example, blanket 44 is moved using powered rollers, such as, but not limited to, BTD99 and BCD77, previously described in FIG. 1.

[0105] In the example of Figure 2A, blanket 44 slides in direction 31 along BTD 99 having axis 33, also referred to herein as the longitudinal axis or axis of rotation of BTD 99. Note that, as shown in Figure 2A, blanket 44 is distorted due to movement in direction 31. As blanket 44 moves in movement direction 94 and passes under imaging station 60, print bars 62a and 62b are configured to apply a first color and a second color, respectively, to print zone 18 of blanket 44. In this example, print bars 62a and 62b are configured to apply droplets of blue and magenta ink, respectively, to the same location on the surface of blanket 44.

[0106] In the design of the image to be printed, a blue pattern is intended to be printed on blanket 44 at location 15. In some cases, undesired movement of blanket 44 in direction 31 may cause the blue pattern to be printed at location 15a, which is offset in the Y-axis direction from the intended location 15. As print zone 18 of blanket 44 passes under print bar 62b, a magenta pattern is printed at location 16, which is intended to overlap the intended location 15 of the blue pattern. Thus, the undesired movement of blanket 44 in direction 31 causes a C2C registration error 17 between the blue and magenta patterns.

[0107] In some embodiments, system 10 includes one or more edge detection devices, referred to herein as sensors 11, configured to detect the position of each edge of blanket 44. In this example, system 10 includes sensors 11a and 11c disposed on a first side of blanket 44, and sensors 11b and 11d disposed on a second side of blanket 44 opposite the first side.

[0108] In some embodiments, sensors 11a-11d may comprise any suitable type of edge sensor, such as a laser-based PosCon OXE7 sensor manufactured by Baumer Electric AG (Hummelstrasse 17, 8500 Frauenfeld, Switzerland), or a suitable ultrasonic-based sensor, or any other suitable type of sensor based on any suitable technology.

[0109] In some embodiments, sensors 11a-11d are each configured to transmit one or more signals to controller 54 (and / or to processor 20) indicative of the position of a respective edge of blanket 44. In some embodiments, controller 54 is configured to determine a strain experienced by blanket 44 based on the signals received from sensors 11a-11d.

[0110] In other embodiments, system 10 may include one or more sensors 11 a-11 d arranged in any suitable combination. In a first implementation, system 10 includes only sensor 11 a for detecting the position of each edge of blanket 44. In a second implementation, system 10 includes sensors 11 a and 11 b, and controller 54 is configured to calculate the actual size of blanket 44 in proximity to BTD 99. Note that this calculated size of blanket 44 indicates the level of stretch of blanket 44 (e.g., whether blanket 44 is sufficiently taut) and / or distortion of blanket 44 that may be caused by undesired movement of blanket 44 in at least direction 31. In a third implementation example, the system 10 includes sensors 11a and 11c, and the controller 54 is configured to calculate, among other things: (i) the actual size of the section of the blanket 44 between the sensors 11a and 11c, (ii) uneven blanket cutting during the blanket 44 manufacturing process (which is described in Figure 4 below among other ways of doing this), (iii) undesired movement of the blanket 44 in direction 31, and other parameters related to the components of the system 10 and characteristics associated with the blanket 44, and the attachment of the blanket 44 to the system 10.

[0111] In another embodiment, the number of sensors 11 and the location of each sensor 11 are determined to detect any type of non-uniformity associated with the blanket 44 and its movement, such as insufficient parallelism between the rollers, variations in the movement of the blanket 44 in the direction of movement 94, the shape of the blanket 44, and any other non-uniformity in the system 10 that may affect the blanket movement and / or the quality of the imaging and image transfer, as described in more detail below in FIG.

[0112] Compensating for unwanted blanket movement due to roller tilt in a printing system FIG. 2B is a schematic top view illustrating compensation for unwanted movement of blanket 44 during the printing process implemented in system 10, according to an embodiment of the present invention.

[0113] As described above, controller 54 is configured to identify distortions induced in blanket 44. In some embodiments, in response to detecting distortions induced by undesired movement of blanket 44 in direction 31 based on signals received from one or more sensors 11a-11d (as described above in FIG. 2A ), controller 54 (and / or processor 20) is configured to control the tilt of BTD 99 to reduce the distortions, e.g., by compensating for the undesired movement and / or by reducing the rate of the undesired movement.

[0114] In some embodiments, a first end of the BTD 99 is fixed (e.g., to the housing of the system 10) and acts as a pivot 14, and a second end of the BTD is movable relative to the pivot 14. In the example of FIG. 2B, the controller 54 is configured to control an actuator (shown in FIG. 3 below) that is configured to move the second end of the BTD 99 in a pre-assigned vector 19 such that the axis 33 rotates at a given angle relative to the position of the axis 33 shown in FIG. 2A above.

[0115] In some embodiments, when blanket 44 moves in movement direction 94, tilting of BTD 99 causes movement of blanket 44 in direction 32 to compensate for movement in direction 31 shown in FIG. 2A above. Note that tilting of BTD 99 is performed when the speed of movement of blanket 44 in direction 31 is greater than a predetermined threshold. For example, if blanket 44 moves about 10 μm in direction 31 when blanket 44 moves about 2 meters in movement direction 94, tilting of BTD 99 is not necessary. However, if blanket 44 moves about 1 mm in direction 31 when blanket 44 moves about 1 meter, tilting of BTD 99 is necessary.

[0116] In some embodiments, the controller 54 (and / or processor 20) is configured to control the tilt amount (e.g., tilt angle) and tilt rate of the BTD 99 to reduce the movement rate of the blanket 44 in the Y-axis (e.g., direction 31 in FIG. 2A above). In this disclosure and claims, the term "reducing the movement speed" (or "reducing the movement rate") in a given direction refers to reducing the movement rate in this direction or reversing at least one component of the vector indicating the direction of the movement rate. For example, in FIG. 2A, the blanket 44 is distorted by moving in direction 31 at a given rate. In this example, the controller 54 is configured to reduce the movement rate of the blanket in direction 31 or reverse the movement direction to direction 32 as shown in FIG. 2B above. When moving in the reverse direction (i.e., direction 32), the velocity of the blanket 44 in direction 31 is negative and therefore reduced relative to the movement rate of the blanket 44 in direction 31 as shown in FIG. 2A above.

[0117] In some embodiments, when a desired blanket 44 travel speed along the Y-axis is achieved (e.g., below a predetermined threshold), the controller 54 is configured to maintain the tilt angle of the BTD 99. In this example, when a sufficiently low blanket Y-axis travel speed is achieved, the blue and magenta patterns are printed at positions 15 and 16, respectively, such that the C2C registration error (e.g., C2C registration error 17 in FIG. 2A above) is less than a predetermined threshold. For example, the C2C registration error 17 in FIG. 2A is approximately 0.1 mm, whereas in FIG. 2B, the C2C registration error between the blue and magenta patterns is less than approximately 10 μm.

[0118] In some embodiments, in response to detecting distortion caused by undesired movement of blanket 44 in direction 31 based on signals received from one or more sensors 11a-11d, controller 54 (and / or processor 20) is configured to control both: (i) the tilt angle of BTD 99 and / or any other roller or rollers involved in rotating blanket 44 (to compensate for mechanical distortion of blanket 44), and (ii) the timing of droplets of printing fluid applied to blanket 44 by one or more print bars 62 of the image forming station (to compensate for C2C registration errors caused by mechanical distortion of blanket 44).

[0119] In some embodiments, (a) in addition to machine-based corrections by tilting one or more rollers (as described above), the processor 20 and / or controller 54 are configured to compensate for C2C registration errors and scale distortions in the printed image (as described in more detail below) by applying software-based corrections, such as, but not limited to, (i) adjusting the speed of the blanket 44 along the direction of movement 94, and (ii) adjusting the timing at which each of the print bars 62 applies ink color droplets to the blanket 44.

[0120] Additionally, and possibly based on signals received from one or more of sensors 11a-11d and / or from other sensors of system 11 (e.g., station 55, described above in FIG. 1 ), processor 20 and / or controller 54 are configured to control impression station 84 to adjust the operation of impression cylinder 82 and pressure cylinder 90 (described above in FIG. 1 ) to compensate for or eliminate various distortions occurring in the image printed on blanket 44. In one implementation, based on the signals, processor 20 and / or controller 54 are configured to estimate an image-to-substrate registration error (described above in FIG. 1 ) and control at least one operation selected from the list of operations consisting of: (a) a timing of engagement between impression cylinder 82 and pressure cylinder 90 of impression station 84 to compensate for the image-to-substrate registration error; (b) a motion profile of at least one of impression cylinder 82 and pressure cylinder 90; and (c) a gap size between disengaged impression cylinder 82 and impression cylinder 90.

[0121] In another implementation, based on the aforementioned signals, the processor 20 and / or controller 54 is configured to estimate that one or more of the aforementioned distortions and / or errors occurring in the blanket 44 exceed the specifications for the printed image. As such, the processor 20 and / or controller 54 is configured to stop operation of one or more stations of the system 11, such as, but not limited to, (a) the image-forming station 60, (b) the impression station 84, (c) one or more rollers configured to guide the blanket 44, (d) one or more drying assemblies, such as the drying station 64, and (e) the blanket handling station 52. For example, the processor 20 and / or controller 54 is configured to prevent engagement between the impression cylinder 82 and the impression cylinder 90 of the impression station 84 and / or to stop the application of ink drops by one or more print bars 62 of the image-forming station 60.

[0122] Additionally or alternatively, corrective action may be taken proactively rather than in response to the detection of distortion. Proactive corrective action may be taken based on a preliminary characterization of the system before the print job begins, for example, by running a test job under the same conditions as the intended print job. Furthermore, some of the distortion is caused by heating of the blanket 44 and other components of the system 10. Heating may be caused by infrared radiation applied to the blanket 44 by the heater 66 and / or drying station 64, as described above.

[0123] In other embodiments, the controller 54 is configured to apply tilt to one or more selected rollers of the system 10, for example, to simultaneously tilt both the BTD 99 and the BCD 77, as described in detail in FIG. 3 below.

[0124] In this disclosure and claims, embodiments relating to any computational and / or control operations may be implemented using the controller 54 or the processor 20, or any suitable combination of the controller 54 and the processor 20.

[0125] It should be noted that the configuration shown in FIG. 2B is simplified for conceptual clarity and is provided as an example to illustrate embodiments of the present invention.

[0126] 3 is a schematic diagram illustrating control of the speed of travel of blanket 44 along the Y-axis, in accordance with an embodiment of the present invention. FIG. 3 describes an embodiment relating to applying the technique shown in FIG. 2B above to one or more selected components of system 10 to reduce errors in images printed by system 10.

[0127] In some embodiments, system 10 comprises a BTD driver 199 controlled by controller 54 and configured to drive BTD 99 (e.g., based on signals received from one or more position encoders described above in FIG. 1 ). System 10 further comprises a suitable actuator, referred to herein as actuator 23, controlled by controller 54 or a BTD guide (e.g., a slave of controller 54). In this example, actuator 23 comprises a linear actuator made from a powered screw configured to move the non-fixed end (also referred to as the second end in above-described FIG. 2B ) of BTD 99 in a controlled direction 24. Note that direction 24 is indicated using a double-headed arrow because actuator 23 is configured to be moved back and forth (e.g., along the X-axis).

[0128] In the example of FIG. 3, each of the BTD 99, BCD 77 and idler 76 has one fixed end, also referred to herein as a first end, and one non-fixed end, also referred to herein as a second end, which is configured to be moved by a suitable actuator, such as actuator 23, as described in detail herein.

[0129] In some embodiments, system 10 includes a BCD driver 177, which is controlled by controller 54 and configured to drive BCD 77 based on signals received from one or more position encoders described above in Figure 1. System 10 also includes an electric actuator 25, which has similar characteristics to actuator 23 and is controlled using controller 54 or a BCD guide (a slave of controller 54).

[0130] In some embodiments, the actuator 25 is configured to move the non-fixed end (i.e., the second end) of the BCD 77 in a controlled direction 26. Note that the direction 26 is indicated with a double arrow because the actuator 25 is configured to be moved back and forth (e.g., along the X axis).

[0131] In some embodiments, the idler 76 is not motorized, but is configured to be rotated about its longitudinal axis by the blanket 44 as the blanket moves. The system 10 further includes a motorized actuator 27, which has similar characteristics to the actuator 23, and is controlled by the controller 54 or by means of an idler guide 176 (e.g., a slave to the controller 54).

[0132] In some embodiments, actuator 27 is configured to move the non-fixed end (i.e., second end) of idler 76 in a controlled direction 28. Note that direction 28 is indicated with a double arrow because actuator 27 is configured to be moved back and forth (e.g., along the X axis).

[0133] In this example, the first ends of the idler 76, BCD 77, and BTD 99 are all fixed adjacent to the edge 30 of the blanket 44, and the actuators 23, 25, and 27 are positioned adjacent to the second ends of the idler 76, BCD 77, and BTD 99, respectively, which are positioned adjacent to the edge 29 of the blanket 44. In other embodiments, the end of at least one of the idler 76, BCD 77, and BTD 99 may be switched, and the position of each actuator may be changed. For example, the free end of the idler 76 and the actuator 27 may both be positioned adjacent to the edge 30 of the blanket 44.

[0134] In some embodiments, the system 10 includes additional components, such as (but not limited to) a dancer driver 174 (configured to drive the dancer 74) and an idler 76a, which may be associated with the movement of the blanket 44 but are not described in embodiments of the present invention.

[0135] In some embodiments, blanket 44 is moved along an endless, continuous path as shown in FIGS. 1 and 3, and system 10 includes multiple edge sensors, such as sensors 11a-11d shown in FIGS. 2A and 2B above. System 10 includes additional sensors (described below) distributed at different sections of system 10 along the continuous path of blanket 44. In the example of FIG. 3, sensors 11a and 11b are positioned proximate BTD 99, sensors 11c and 11d are positioned proximate BCD 77, sensor 11e is positioned between idler 76a and impression station 84, sensor 11f is positioned between impression station 84 and blanket handling station 52, and sensor 11g is positioned between blanket handling station 52 and idler 76. Sensors 11a and 11c are configured to detect the position of edge 30, and sensors 11b and 11d are configured to detect the position of edge 29.

[0136] In one embodiment, sensors 11e, 11f, and 11g may each comprise one sensor positioned proximate either edge 29 or 30 to detect the position of the respective edge. In another embodiment, one or more of sensors 11e, 11f, and 11g comprise two sensors positioned proximate edges 29 and 30, respectively.

[0137] In principle, any interaction between blanket 44 and other elements or components can affect the speed of movement of blanket 44 along the Y axis. For example, undesired movement along the Y axis can be caused by: (i) undesired tilting of one or more rollers (e.g., BTD 99, BCD 77, idlers 76 and 76a, roller 78), one or more rollers of blanket handling station 52 (described in more detail below), or one or both of pressure cylinder 90 and impression cylinder 82, or another element positioned in contact with both edges 29 and 30; (ii) at least two rollers (typically in close proximity, e.g., BTD 99 and idler 76) that are not parallel to one another; (iii) the blanket 44 is not moving in the Y direction; (iv) deviations in the contact force between the blanket 44 and elements placed in contact therewith, for example, replacement of a revolver (i.e., scraping blade (not shown)) in the blanket processing station 52, which may change the force applied to the blanket 44 and result in movement of the blanket 44 along the Y-axis; (iv) uneven thermal expansion of elements placed in contact with the blanket 44 along the Y-axis, for example, the first end of a roller expanding more than the second end; and (v) other causes that may affect the force applied to the blanket 44.

[0138] In some embodiments, based on signals received from one or both of sensors 11 a and 11 b, controller 54 is configured to estimate C2C registration errors that may be caused by movement of blanket 44 along the Y axis, as described above with reference to FIG. 2A. For example, blanket 44 may be moved along the Y axis if: (i) BTD 99 is unintentionally tilted (e.g., when mounted to system 10), (ii) BTD 99 and BCD 77 are not parallel to each other, (iii) BTD 99 and idler 76 are not parallel to each other, (iv) uneven thermal expansion of the ends of BTD 99, or other causes.

[0139] In some embodiments, based on signals received from one or more of sensors 11c, 11d, and 11e, controller 54 is configured to estimate image-to-substrate (12S) registration errors that may be caused by Y-axis movement of blanket 44. For example, the blanket may move if: (i) at least one of BCD 77, dancer 74, and idler 76a is unintentionally tilted (e.g., when mounted in system 10), (ii) two or more of BCD 77, dancer 74, and idler 76a are not parallel to one another, (iii) due to uneven thermal expansion of the ends of at least one of BCD 77, dancer 74, and idler 76a, and (iv) due to improper mounting or misoperation of one or both of impression cylinder 90 and impression cylinder 82 when engaged when an ink image is impressed onto the surface of sheet 50, particularly as described above in FIG.

[0140] As noted above, changing blades on a revolver (not shown) of blanket processing station 52 can change the force applied to blanket 44, potentially resulting in movement of blanket 44 along the Y-axis. Note that because C2C registration specifications are typically tighter than I2S specifications, controller 54 is configured to control actuators 23 and 25 to apply different tilt angles and different tilt rates to BTD 99 and BCD 77, respectively, to control movement of blanket 44 along the Y-axis and / or reduce distortion of blanket 44.

[0141] In some embodiments, the controller 54 is configured to apply tilt (using respective actuators) to one or more selected rollers of the system 10. For example, the controller 54 may apply tilt to both the BTD 99 and the BCD 77 simultaneously. Alternatively, the controller 54 may be configured to apply tilt to the BCD 77 without applying tilt to the BTD 99, or the controller 54 may use any other suitable tilt scheme applied to one or more selected rollers of the system 10. It should be noted that the tilt scheme may be determined based on a known force applied to the blanket 44 or in response to detecting a respective movement profile in the Y-axis.

[0142] In some embodiments, the controller 54 is configured to maintain a look-up table (LUT) (not shown) that includes one or more known distortions, each caused by one or more operations performed by the system 10. For example, a blade change in the blanket handling station 52 may change the force applied to the blanket 44 in a known manner. In such an embodiment, the LUT can be used to feed forward proactive corrections; for example, the controller 54 can control the actuator 27 to tilt the idler 76 immediately after a blade change to proactively reduce or eliminate movement of the blanket 44 along the Y-axis due to the blade change.

[0143] In other embodiments, if the BTD 99 is not properly assembled in the system 10, the BTD 99 may tilt and may not be parallel with at least one of the idler 76 and the BCD 77. In such embodiments, the LUT may include a C2C registration error associated with improper assembly of the BTD 99, and the controller 54 is configured to: (i) display a message on the display 34 indicating the improper assembly, and (ii) suspend operation of the system 10 if the C2C error is greater than a predetermined threshold, or control the actuator 23 to tilt the BTD 99 in accordance with the LUT to reduce the known distortion, e.g., C2C registration.

[0144] In some embodiments, the controller 54 is configured to control the actuator 23 to tilt the BTD 99 based on the LUT and signals received from one or more of the sensors 11a-11g. In this manner, the controller 54 is configured to compensate for C2C registration errors caused by distortion of the blanket 44, for example, by tilting at least one of the BCD 77, the BTD 99, and the idler 76 of the system 10. The compensation can be performed proactively (based on a prior characterization of the system 10 while executing the intended print job) and / or reactively (in response to a signal received from at least one of the sensors 11a-11g). Furthermore, by controlling the tilt levels of the BCD 77, the BTD 99, the idler 76, and optionally other rollers of the system 10, the controller 54 is configured to control the guiding of the blanket 44 and compensate for distortions of the blanket 44 and / or components used to guide the blanket 44.

[0145] In some embodiments, controlling the movement of the blanket 44 along the Y-axis can be used to reduce the appearance of memory effects in the printing process. The term memory effect refers to the imprint of an image that is repeatedly printed at the same location or locations on the surface of the blanket 44. Memory effects can cause a silhouette of an image to appear in other subsequently printed images. Embodiments for reducing memory effects and their appearance are described, for example, in U.S. Provisional Patent Application No. 63 / 210,507 and PCT International Publication No. WO 2022 / 263989, the disclosures of which are incorporated herein by reference. In some embodiments, the disclosed techniques can be used to change the position of an image formed on the blanket 44, thereby reducing the memory effect as described above.

[0146] In other embodiments, instead of or in addition to the LUT, controller 54 is configured to maintain a neural network (NN) (not shown), which is trained to identify one or more distortions in blanket 44, such as the distortions shown in Figures 2A and 2B above.

[0147] In some embodiments, the NN may include any suitable type of NN, such as, but not limited to, a convolutional neural network (CNN), a recurrent neural network (RNN), or a combination thereof, which may be trained using supervised or unsupervised training techniques. For example, the NN may be trained based on known events to identify known distortions. Based on the trained NN and one or more signals received from one or more of sensors 11a-11g, controller 54 is configured to control one or more of the actuators of system 10 (e.g., one or more of actuators 23, 25, and 27) to apply a tilt to a respective roller (e.g., BTD 99, BCD 77, and idler 76) to reduce one or more identified known or unknown distortions.

[0148] Additionally or alternatively, the processor 20 may include at least one of a LUT and a NN and is configured to control one or more of the actuators of the system 10 to apply tilt to the respective rollers to reduce one or more identified known or unknown distortions, as described above for the controller 54.

[0149] The particular configuration of Figure 3 is simplified for conceptual clarity and is presented as an example to explain the particular problems addressed by embodiments of the present invention and to demonstrate the application of these embodiments in improving the performance of system 10. However, embodiments of the present invention are in no way limited to this particular type of exemplary system, and the principles described herein may be applied to any other type of printing system that uses flexible ITMs, or to other types of ITMs as well. Furthermore, the techniques of Figures 2B and 3 may be applied mutatis mutandis in any other system that moves a member, particularly a flexible member, using rollers or other suitable techniques, to which the disclosed embodiments may be applied.

[0150] Distinguishing between blanket cutting errors and unwanted blanket movement 4 is a schematic side view of section 47 of blanket 44 and graphs 71 and 72 for illustrating a method for distinguishing between blanket cutting errors and undesired blanket movement, in accordance with an embodiment of the present invention. In this disclosure and claims, the term "blanket cutting error" refers to cutting an edge of blanket 44 (e.g., edge 29) that is not parallel to the X-axis.

[0151] In the example of FIG. 4 , when blanket 44 moves in direction 94 (e.g., parallel to the X-axis), a given edge sensor 11 (e.g., sensor 11b or 11d) can detect movement of edge portion 29 of section 47 along the Y-axis. In some cases, movement of edge portion 29 of section 47 along the Y-axis can be caused by roughness of edge portion 29 introduced during the manufacturing process of blanket 44. For example, insufficient precision in cutting the fabric of blanket 44, at least in section 47, can cause one or more sections of edge portion 29 to be non-parallel to the X-axis. In other cases, the signal received from sensor 11 can indicate movement of blanket 44 along the Y-axis, such as shown in the example of FIG. 2A above.

[0152] It should be noted that to correct for distortion caused by movement along the Y-axis, the controller 54 needs to filter out and remove the contribution of blanket cutting error in order to quantify the Y-axis movement rate based on the signal received from the sensor 11, as described above in Figures 2B and 3.

[0153] Please refer to graphs 71 and 72. Graph axis 73 indicates the detected position (e.g., shift) of edge 29 along the Y axis relative to a reference point, and graph axis 75 indicates the time that blanket 44 moves in direction 94. In other words, graphs 71 and 72 show the detected movement of edge 29 over time during the printing process. In this disclosure, the term "detected movement" refers to movement of edge 29 detected based on signals received from sensor 11. It should be noted that the detected movement may indicate physical movement of blanket 44 along the Y axis (e.g., as shown in FIG. 2A above), or blanket cutting error as described above, or any combination thereof.

[0154] Referring now to graph 71, during a first rotation of blanket 44, designated by numeral 81, the detected position of edge 29 of section 47 is depicted using line 85a. Similarly, during a second rotation of blanket 44 (following the first rotation and designated by numeral 83), the detected position of edge 29 of section 47 is depicted using line 85b. The terms first rotation and second rotation refer to "n rotations" and "n+1 rotations," respectively, of blanket 44. Note that the second rotation may refer to "n+10 rotations" of blanket 44 in system 10 if the step size of the blanket 44's movement velocity in the Y-axis is less than a given threshold (e.g., less than about 0.1 mm for each rotation).

[0155] In the example of Figure 4, dashed line 87 on axis 73 indicates the detected translation of point 91. In graph 71, point 91 has the same value of detected translation in both rotations, so both lines 85a and 85b touch dashed line 87.

[0156] Referring now to graph 72, lines 85c and 85d, as described above, indicate the detected positions of edge 29 of section 47 during the first and second rotations of blanket 44. Note that because lines 85a and 85c are identical, point 91 on line 85c is tangent to dashed line 87, while point 91 on line 85d is tangent to dashed line 89, which is a distance 93 from dashed line 87. Furthermore, point 95 on edge 29 is located a distance 97 from point 91.

[0157] In some embodiments, by comparing the detected positions of blanket 44 at the same point on edge 29, controller 54 is configured to detect movement of blanket 44 along the Y-axis. In the example of graph 72, distance 97 indicates a blanket cutting error at edge 29, and distance 93 indicates movement of the blanket along the Y-axis. In such an embodiment, based on distance 93, controller 54 is configured to control one or more actuators of system 10 to tilt respective rollers of system 10 to reduce distortion in blanket 44 due to movement along the Y-axis.

[0158] 4, controller 54 is configured to determine that distance 97 indicates a blanket cutting error at edge 29. Accordingly, controller 54 does not control any actuators of system 10 to tilt their respective rollers because distance 97 does not indicate any movement of edge 29 along the Y axis.

[0159] In other embodiments, system 10 may include at least first and second edge sensors 11 positioned at first and second respective locations along edge portion 29 of section 47. In such embodiments, controller 54 is configured to calculate the blanket cutting error by comparing the first and second signals received from first and second edge sensors 11, respectively.

[0160] FIG. 5 is a flow chart that schematically illustrates a method for reducing distortion of blanket 44 that undergoes undesired movement along the Y-axis during the printing process, in accordance with an embodiment of the present invention.

[0161] In some embodiments, the method begins with a blanket moving step 100, in which blanket 44 is moved along direction 94 (typically parallel to the X-axis of system 10) using first and second rollers, such as, but not limited to, BTD 99 and BCD 77, respectively, as described above in FIG. 1.

[0162] In some embodiments, the controller 54 receives first and second signals from two or more sensors 11 indicative of the speed of movement of the blanket 44 along the Y-axis in the first and second sections of the printing system 10. For example, the controller 54 receives: (i) a first signal from a sensor 11a located proximate to the BTD 99, and (ii) a second signal from a sensor 11c located proximate to the BCD 77, as described above in FIGS. 2B and 3 .

[0163] In some embodiments, in a first determination step 102, the controller 54 checks, for example, based on a signal received from the sensor 11a, whether the edge portion 30 of the blanket 44 moves along the Y-axis at a movement speed greater than a pre-assigned threshold (e.g., approximately 1 mm per rotation of the blanket 44).

[0164] Similarly, in a second decision step 104, the controller 54 checks, for example, based on a signal received from the sensor 11c, whether the edge portion 30 of the blanket 44 moves along the Y-axis at a movement speed greater than a preassigned threshold (e.g., approximately 5 mm per rotation of the blanket 44).

[0165] In some embodiments, the thresholds in step 104 are related to a particular I2S registration of system 10, and the thresholds in step 102 are related to a particular C2C registration of system 10, which is typically stricter than the I2S specification. In other embodiments, the thresholds in steps 102 and 104 may be similar.

[0166] In some embodiments, if the movement speed in step 102 is less than the threshold, controller 54 and processor 20 control system 10 to continue the printing process described in FIG. 1 above.

[0167] In another embodiment, if the movement rate in step 102 is greater than the threshold, the method proceeds to BTD tilt step 106, in which controller 54 controls actuator 23 to tilt BTD 99 while moving blanket 44 along the X-axis to reduce the blanket movement rate in the Y-axis, as described above in FIG. 3.

[0168] In some embodiments, the controller 54 receives a signal, referred to herein as a third signal, for example from the sensor 11a, which signal indicates a reduction in the blanket movement rate along the Y-axis proximate the BTD 99 (in response to applying a tilt to the BTD 99), as detailed in FIG. 3 above.

[0169] In a third decision step 108, the controller 54 checks, for example based on a third signal received from the sensor 11c, whether the edge portion 30 of the blanket 44 moves along the Y-axis at a movement speed greater than the pre-assigned threshold value of step 102 above.

[0170] In some embodiments, if the rate of movement of the blanket 44 along the Y-axis is greater than the threshold value, the method loops back to step 106, and the controller 54 controls the actuator 23 to adjust the tilt of the BTD 99 to achieve a further reduction in the rate of movement of the blanket 44 along the Y-axis proximate the BTD 99.

[0171] In another embodiment, if the rate of movement of the blanket 44 along the Y-axis is less than the threshold value, the method proceeds to a first tilt holding step 110, in which the controller 54 controls the actuator 23 to hold the tilt of the BTD 99 so that the movement of the blanket 44 along the Y-axis is stabilized, e.g., with minor amplitude fluctuations around a given value.

[0172] In some embodiments, steps 102, 106, 108, and 110 may be applied mutatis mutandis to one or more additional rollers in system 10. In the example of Figure 5, steps 112, 114, and 116 correspond to steps 106, 108, and 110, respectively, and are applied to BCD 77 and actuator 25 as described in detail herein. Note that the same techniques may be applied to idler 76, sensor 11g, and actuator 27, or other suitable components of system 10.

[0173] In some embodiments, if the movement speed in step 104 is less than the threshold, the controller 54 and processor 20 control the system 10 to continue the printing process described in FIG. 1 above.

[0174] In another embodiment, if the movement rate in step 104 is greater than the threshold, the method proceeds to BCD tilt step 112, in which controller 54 controls actuator 25 to tilt BCD 77 while moving blanket 44 along the X-axis to reduce the blanket movement rate in the Y-axis, as described above with respect to FIG. 3.

[0175] In some embodiments, the controller 54 receives a signal, referred to herein as a fourth signal, from, for example, the sensor 11c, which signal indicates a reduction in the blanket movement speed along the Y-axis proximate the BCD 77 (in response to applying a tilt to the BCD 77), as detailed in FIG. 3 above.

[0176] In a fourth decision step 114, the controller 54 checks, for example based on the third signal received from the sensor 11c, whether the edge portion 30 of the blanket 44 moves along the Y-axis at a movement speed greater than the pre-assigned threshold value of step 102 above.

[0177] In some embodiments, if the rate of movement of the blanket 44 along the Y-axis is greater than the threshold value in step 104, the method loops back to step 112, and the controller 54 controls the actuator 25 to adjust the tilt of the BCD 77 to achieve a further reduction in the rate of movement of the blanket 44 along the Y-axis proximate the BCD 77.

[0178] In other embodiments, if the speed of movement of the blanket 44 along the Y-axis is less than the threshold value, the method proceeds to a second tilt hold step 116, in which the controller 54 controls the actuator 25 to hold the tilt of the BCD 77 so that the movement of the blanket 44 along the Y-axis is stabilized, for example, with a small amplitude fluctuation around a given value, which is typically different from the given value of step 110 above.

[0179] In some embodiments, if the blanket movement speed along the Y-axis at steps 102 and 108 is less than the threshold at step 102, and if the blanket movement speed along the Y-axis at steps 104 and 114 is less than the threshold at step 104, controller 54 and processor 20 control system 10 to continue the printing process as described above for steps 102 and 104. Further during the printing process, the method proceeds to a fifth decision step 118, where processor 20 or controller 54 checks whether the print job is complete.

[0180] In some embodiments, if the print job is not completed, the method loops back to step 100, and if the print job is completed, the method proceeds to end step 120, which ends the method and performs various standard operations to terminate the printing process of system 10.

[0181] FIG. 6A is a schematic top view illustrating the alignment between the movement of blanket 44 and the printing of patterns at locations 15 and 16 by print bar 62 of system 10, in accordance with an embodiment of the present invention.

[0182] In some embodiments, when blanket 44 is aligned with the guide rollers of system 10 to achieve sufficiently small (e.g., substantially no) blanket movement along the Y axis, the blue and magenta patterns are printed at positions 15 and 16, respectively, such that the C2C registration error is less than a predefined threshold. In the example of Figure 6A, BCD 77 and BTD 99 appear to be parallel to each other and to the Y axis, and edges 29 and 30 of blanket 44 (i) appear to be parallel to each other and to the X axis, and therefore (ii) appear to be orthogonal to BCD 77, BTD 99, and the Y axis.

[0183] In some cases, the BCD 77 and the BTD 99 may not be positioned parallel to one another, and / or one or both of the edges 29 and 30 of the blanket 44 may not be positioned orthogonal to one or both of the BCD 77 and the BTD 99. In some embodiments, based on signals received from the sensors 11 (e.g., sensors 11b and 11d), the controller 54 is configured to control the actuators 23 and 25 to compensate for deviations from the parallelism and / or orthogonality, thereby achieving a C2C registration error less than a predefined threshold. In other words, even in the event of deviations from the parallelism and / or orthogonality, the controller 54 is configured to achieve a required level of C2C registration, for example, by controlling the timing of application of printing fluid to the surface of the blanket 44 or by using any other suitable compensation technique.

[0184] FIG. 6B is a schematic top view illustrating detection of undesired distortions in blanket 44 and / or patterns printed by system 10, in accordance with an embodiment of the present invention.

[0185] In the example of Figure 6B, overheating of blanket 44 (and its guide components) causes thermal expansion of blanket 44, resulting in BTD 99 tilting at angle 35 relative to BTD driver 199. This tilting causes C2C registration error 17, as described above in Figure 2A.

[0186] In some embodiments, driver 119 comprises a rotary encoder configured to generate a signal indicative of the angle 35 of BTD 99. Based on the signal received from driver 119, controller 54 and / or processor 20 are configured to: (i) estimate the distortion and C2C registration error 17 of blanket 44, and (ii) control corrective actions such as, but not limited to, the corrective actions described in Figures 2A-5 above.

[0187] Furthermore, in some cases, the BTD 99 may also be distorted (e.g., having an arc shape). In some embodiments, based on the signal received from the driver 119, the controller 54 and / or the processor 20 is configured to estimate the level of distortion of the BTD 99 and determine corrective action, such as replacing the BTD 99.

[0188] Additionally or alternatively, the processor 20 is configured to receive a signal indicative of the C2C registration error 17, for example from the station 55, and based on the C2C registration error 17 estimated thereby, the processor 20 and / or the controller 54 is configured to determine a corrective action, such as any of the corrective actions described above.

[0189] 7 is a schematic top view illustrating detection of strain on a sidewall 36 of the housing of system 10, according to an embodiment of the present invention. The term sidewall refers to any type of bar or other portion of the housing of system 10, which other portions of the housing have been removed from FIG. 7 for conceptual clarity.

[0190] In some embodiments, print bars 62a and 62b coupled to sidewall 36 are configured to apply droplets of blue ink and magenta ink, respectively, to the same location on the surface of blanket 44.

[0191] In this example, sidewall 36 is distorted relative to axis 41, which represents the longitudinal axis of sidewall 36's original (undistorted) shape. Due to the distortion of sidewall 36, at least print bars 62a and 62b are shifted, potentially directing blue and magenta ink droplets to positions 15a and 16a, respectively. Note that positions 15a and 16a are offset from the intended positions 15 and 16 (shown in FIGS. 2A and 2B above) of the droplets (and the patterns formed by the droplets). Thus, the offset between positions 15 and 15a and between positions 16 and 16a results in C2C registration error 39.

[0192] In some embodiments, in addition to or instead of sensors 11a-11g, system 11 includes at least edge sensors 37 and 38 coupled to sidewall 36 and sufficiently long to generate a first signal indicative of the position of edge portion 29 and a second signal indicative of the position of sidewall 36.

[0193] In some embodiments, based on the first and second signals received from each of the edge sensors 37 and 38, the processor 20 and / or the controller 54 are configured to: (i) estimate the distortion of the sidewall 36, and (ii) control at least the print bars 62a and 62b to direct these droplets to either positions 15 and 16, respectively, or any other position that compensates for the C2C registration 39, thereby reducing the level of the C2C registration below a predetermined threshold.

[0194] Additionally or alternatively, processor 20 and / or controller 54 are configured to receive further signals from sensors 11a-11g indicative of distortions in blanket 44 (and / or at least BCD 77 and / or BTD 99), as described above with reference to Figures 2A-5. Based on the signals from sensors 11a-11g and the signals from sensors 37 and 38, processor 20 and / or controller 54 are configured to control at least print bars 62a and 62b to direct droplets to either positions 15 and 16, respectively, or any other positions that compensate for C2C registration 39, thereby reducing the level of C2C registration below the aforementioned predetermined threshold.

[0195] In some embodiments, blanket 44 includes marks that indicate respective locations on blanket 44, and more particularly, the locations of these marks indicate the location of a starting page on the surface of blanket 44. In this disclosure and in the claims, the term starting page refers to the location on blanket 44 where printing of an image begins (e.g., a corner of the image intended to be printed).

[0196] In some embodiments, marks are formed on one or both of edges 29 and 30. In this example, the marks are formed at predetermined (typically equidistant) locations along one or both of edges 29 and 30 and serve as graduations for a position encoder along the X-axis of blanket 44, as described in more detail below. These marks will generally be similar along edges 29 and 30, although in this example, for purposes of illustration, marks 122a, 122b, 124a, 124b, and 126 shown on edge 30 differ from one another as described below.

[0197] In some embodiments, these marks are formed on or within both edge portions 29 and 30 and are positioned on both edge portions, and based on signals received from sensors (such as sensors 11a-11d and / or sensors 37 and 38) that detect these marks, processor 20 and / or controller 54 are configured to detect and correct further distortions of blanket 44, such as (but not limited to) torsional distortions, based on signals received from sensors on both sides of blanket 44.

[0198] In some embodiments, marks 122a, 122b, 124a, 124b, and 126 may be formed as stickers, labels, or tags disposed on one or both edges 29 and 30. In other embodiments, marks 122a, 122b, 124a, 124b, and 126 may be comprised of openings formed in blanket 44 by mechanical stitching, laser ablation, or chemical etching. In another embodiment, marks 122a, 122b, 124a, 124b, and 126 may be printed by system 11 or using any other suitable printing system. For stickers, labels, tags and printing, marks 122a, 122b, 124a, 124b and 126 can be formed on (i) the outer surface of blanket 44 (which receives droplets of printing fluid), (ii) the inner surface of blanket 44 (which faces the outer surface and does not receive droplets of printing fluid), or (iii) a suitable combination on the outer and inner surfaces.

[0199] Reference is now made to inset 51 of mark 122a, which shows right-angled trapezoids 56a and 56b of similar size and shape. Trapezoids 56a and 56b are aligned along the X-axis and have edges 59a and 59b, respectively, that are perpendicular to bases 46 and 48. Trapezoids 56a and 56b further include edges 61a and 61b, respectively (also referred to herein as diagonal edges that are disposed at an angle relative to the X-axis).

[0200] In some embodiments, the aforementioned sensors, such as sensors 37 and 38, are configured to detect edges 59a and 59b and edges 61a and 61b as blanket 44 moves along the X-axis. In some embodiments, before commencing the printing process, blanket 44 is moved through several rotations to learn the positions of marks 122a, 122b, 124a, 124b, and 126 on blanket 44 (and optionally with respect to a predetermined position on blanket 44 and / or within system 11). In such embodiments, processor 20 and / or controller 54 are configured to receive signals from sensors 37 and 38 indicative of the positions of edges 69a and 59b and edges 61a and 61b. Then, during the printing process, based on the aforementioned learning, processor 20 and / or controller 54 are configured to estimate the velocity of blanket 44 along the X-axis and the distortion of blanket 44 along the Y-axis, as described herein. Note that the same structures are formed along edge 30, for example, in mark 122b.

[0201] In some embodiments, based on the known distance (along the X-axis) between sides 59 a and 59 b, processor 20 and / or controller 54 are configured to estimate the velocity of blanket 44 along the X-axis. In such embodiments, sides 59 a and 59 b function as position encoders at one or both edges 29 and 30 of blanket 44, which can be used to control the position and velocity of blanket 44 along the X-axis. Thus, the distance between marks is determined by the position and velocity control requirements of blanket 44. As such, the marks can be formed every few millimeters, every tens of micrometers, or any other suitable spacing between adjacent marks.

[0202] In some embodiments, based on signals received from sensors 37 and 38, processor 20 and / or controller 54 is configured to control the firing times of all pixels and all colors within an image printed by each print bar 62. Based on the estimated position and velocity of blanket 44, processor 20 and / or controller 54 is configured to control the appropriate position for each printed color image and the appropriate (typically similar) scale for all printed color images, respectively.

[0203] In some embodiments, in addition to or instead of the marks formed along the X-axis, the structures and functions of which are described in detail above, blanket 44 may also include suitable marks formed along the Y-axis. Such marks may have the same size and / or shape as marks 122, 124, and 126 (described above), but may also have any other suitable size and / or shape, such as (i) marks similar to mark 122a formed by rotating trapezoids 56a and 56b by 90 degrees, (ii) marks similar to mark 124b formed by rotating trapezoids 58a and 58b by 90 degrees, and (iii) any other suitable marks, such as bars (not shown) having any suitable size along the X-axis and Y-axis, and typically (a) parallel to the X-axis and (b) positioned along the Y-axis using any pitch size suitable for detecting additional distortions, such as, but not limited to, scale distortions along the Y-axis. In such an embodiment, based on these marks, processor 20 and / or controller 54 is configured to detect and correct scale distortion along the Y axis (as well as other types of distortion) in at least one, and typically all, of the images, and color images, printed by system 11. For example, the correction may be performed by controlling at least one of actuators 23, 25, and 27, as detailed above in FIG.

[0204] Additionally or alternatively, the encoder can be implemented using marks 126 having polygonal shapes, such as rectangles or squares, with the encoder's sensitivity determined by the distance between sides of mark 126 parallel to the Y-axis (e.g., parallel to sides 59 of mark 122). It should be noted that, in some cases, the strength of the signals received from sensors 37 and 38 may contain undesirable noise, caused by, for example, printing fluid and other types of material residue. In some embodiments, based on the signals received from sensors 37 and 38, processor 20 and / or controller 54 are configured to estimate a centerline between adjacent sides parallel to the Y-axis (e.g., an average position along the X-axis). Signal averaging reduces position reading errors due to such noise.

[0205] In some embodiments, processor 20 and / or controller 54 is configured to estimate the distortion of blanket 44 along the Y-axis based on an estimate (along the X-axis) of (i) reconstruction 63a of edge 30 passing between sides 59a and 61a, and (ii) reconstruction 63b of edge 30 passing between sides 59b and 61b. Due to the (same) tilt of sides 61a and 61b, respectively, reconstructions 63a and 63b along the X-axis are different in size.

[0206] Note that distortion of blanket 44 is a physical phenomenon and therefore typically occurs between structures that are not adjacent to one another. In this example, distortion along the Y-axis causes movement of edge 30 between (i) reconstruction 63a in mark 122a and (ii) reconstruction 63b in mark 122b. In other words, based on detection of sides 59 and 61 of mark 122 (by sensors 37 and 38), processor 20 and / or controller 54 are configured to estimate: (i) the size of reconstructions 63a and 63b along the X-axis, and thereby (ii) the distortion of blanket 44 along the Y-axis.

[0207] See inset 53 of mark 124b, which shows isosceles trapezoids 58a and 58b of similar size and shape. Isoosceles trapezoids 58a and 58b are aligned along the X-axis and have (i) sides 67a and 69a, and (ii) sides 67b and 69b, respectively. In this disclosure and claims, sides 67a, 67b, 69a, and 69b are also referred to herein as oblique sides, which are disposed at a predetermined angle (typically different from the predetermined angle of sides 61a and 61b) with respect to the X-axis.

[0208] In some embodiments, when blanket 44 moves along the X-axis, distortion along the Y-axis causes reconstructions 65a and 65b (of blanket edge 30) to be detected in isosceles trapezoids 58a and 58b of marks 124a and 124b, respectively. The size of reconstructions 65a and 65b along the X-axis is determined by: (i) the position of blanket edge 30 along the Y-axis, and (ii) the slope of sides 67 and 69. Based on the known slope of sides 67 and 69 and the estimated size of reconstructions 65a and 65b, processor 20 and / or controller 54 are configured to estimate the distortion of blanket 44 along the Y-axis.

[0209] In some embodiments, based on signals received from sensors 37 and 38 and indicative of the positions of the sides (e.g., sides 67a and 69a of isosceles trapezoid 58a), processor 20 and / or controller 54 are configured to calculate an average of the positions of these signals and output a center point, e.g., along the X-axis of the line representing reconstruction portion 65a. As noted above, averaging reduces noise in the intensity of the signals received from sensors 37 and 38, thereby improving the accuracy of position detection and the calculated position and velocity of blanket 44 along the X-axis.

[0210] Although the embodiments described herein primarily address digital printing using flexible intermediate transfer members, the methods and systems described herein can be used in other applications, such as with any type of printing system and process having any suitable type of intermediate device (e.g., member) for receiving an image and transferring the image to a target substrate.

[0211] Therefore, it will be understood that the above embodiments are cited by way of example, and that the present invention is not limited to what has been particularly shown and described herein. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described herein, as well as variations and modifications thereof which would occur to one skilled in the art upon reading the foregoing description and which are not disclosed in the prior art. Documents incorporated by reference in this patent application are considered to be an integral part of this application, except that, in the event that any term is defined in these incorporated documents in a manner that contradicts a definition expressly or implicitly given herein, only the definition in this specification shall be considered.

Claims

1. 1. A system comprising: an actuator configured to tilt the roller while an intermediate transfer member (ITM) of the printing system moves over the roller; and a controller configured to: (i) identify a distortion in the ITM; and (ii) control an actuator to tilt a roller to reduce the distortion while the ITM is moving. The system comprising:

2. 2. The system of claim 1, wherein the ITM moves along a continuous path in a first direction, and the controller is configured to reduce distortion by: while the ITM moves in the first direction, (i) specifying a first movement speed of the ITM in a second direction different from the first direction, and (ii) controlling the actuator to tilt the rollers to move the ITM at a second movement speed less than the first movement speed.

3. The system of claim 2 , wherein the controller is configured to receive a signal indicative of the first rate of movement and to control the actuator in response to receiving the signal.

4. 4. The system of claim 3, comprising: (i) a first edge sensor disposed in a first section of the continuous path and configured to generate a first signal indicative of a first speed of movement in the first section; and (ii) a second edge sensor disposed in a second section of the continuous path different from the first section and configured to generate a second signal indicative of the first speed of movement in the second section.

5. The system of claim 4 , wherein in response to receiving the first and second signals, the controller is configured to identify a first distortion in the first interval and a second distortion in the second interval.

6. 6. The system of claim 5, wherein the system comprises a first actuator configured to tilt the first roller and a second actuator configured to tilt the second roller, and wherein in response to identifying the first and second strains, the controller is configured to control at least one of the first and second actuators to tilt the first and second rollers, respectively.

7. 7. The system of claim 6, wherein the controller is configured to control: (i) a first actuator to tilt the first roller at a first tilt angle; and (ii) a second actuator to tilt the second roller at a second tilt angle different from the first tilt angle.

8. The system of claim 6 , wherein the controller is configured to control the first and second actuators to simultaneously apply the first and second tilts.

9. The system of any one of claims 1 to 8, wherein the ITM is configured to receive ink droplets to form an image thereon and to transfer the image to a target substrate.

10. 9. The system of claim 1, wherein the controller is configured to: (i) maintain a look-up table (LUT) containing one or more known distortions respectively caused by one or more operations performed in the printing system; and (ii) control the actuator to tilt the roller according to the LUT to reduce the one or more known distortions.

11. 11. The system of claim 10, wherein the one or more known distortions include a first known distortion in a first section on the ITM and a second known distortion in a second section of the ITM, and the system comprises a first actuator configured to tilt a first roller of the printing system and a second actuator configured to tilt a second roller of the printing system, and wherein in response to identifying the first and second known distortions, the controller is configured to control at least one of the first and second actuators to tilt the first and second rollers, respectively.

12. 12. The system of claim 11, wherein the controller is configured to control: (i) a first actuator to tilt the first roller at a first tilt angle; and (ii) a second actuator to tilt the second roller at a second tilt angle different from the first tilt angle.

13. The system of claim 12 , wherein the controller is configured to control the first and second actuators to simultaneously apply the first and second tilts.

14. 9. The system of claim 1, wherein the controller is configured to: (i) maintain a neural network (NN) configured to identify one or more known distortions caused by one or more operations performed in the printing system, respectively; and (ii) control the actuator to tilt the roller according to an output of the NN in response to a given operation in the printing system to reduce the one or more known distortions.

15. 15. The system of claim 14, wherein the controller is configured to receive one or more signals each indicative of the one or more further distortions, and wherein the controller is configured to apply the neural network to identify whether at least one of the one or more known distortions includes at least one of the one or more further distortions.

16. The system of claim 14 , wherein the controller is configured to apply the NN to control the actuator in response to receiving the signal.

17. 9. The system of claim 1, wherein the printing system comprises at least first and second rollers, and wherein the controller is configured to control the actuator to tilt the first roller, thereby causing at least the first roller and the second roller to be non-parallel to each other.

18. 10. The system of claim 1, wherein distortion of the ITM causes deflection of the roller, wherein the roller is moved by a driver and comprises an encoder configured to generate a deflection signal indicative of a deflection angle of the roller, and wherein the controller is configured to determine the distortion of the ITM based on the deflection signal.

19. 9. The system of claim 1, comprising: (i) a housing and at least first and second print bars, the first and second print bars coupled to the housing and configured to apply ink droplets of first and second colors to the ITM to generate first and second patterns of an image, respectively, on the ITM; and (ii) at least a given edge sensor, the edge sensor coupled to the housing and configured to generate (a) a first edge signal indicative of a first position of the housing, and (b) a second edge signal indicative of a second position of an edge portion of the ITM moved relative to the at least first and second print bars.

20. 20. The system of claim 19, wherein the distortion of the housing causes a color-to-color (C2C) registration error between the first pattern and the second pattern of the image, and wherein based on the first edge signal and the second edge signal, the controller is configured to: (i) identify the distortion of the housing, (ii) estimate the C2C registration error, and (iii) control the actuator to (a) move the ITM, and (b) tilt the roller to reduce the C2C registration error by compensating for the distortion of the housing while the first and second print bars apply ink drops of the first and second colors.

21. 21. The system of claim 19, wherein the controller is configured to control at least the first and second print bars to adjust at least one of first and second timings for applying ink drops of the first and second colors, respectively, to reduce C2C registration errors in the image.

22. 5. The system of claim 3 or 4, wherein the ITM has a plurality of marks formed at a predetermined distance from each other along at least an edge portion of the ITM, and the system comprises one or more sensors configured to generate a plurality of signals respectively indicating a plurality of positions of the plurality of marks, and wherein the controller is configured to control at least one of (i) the first movement speed and (ii) the actuator based on the plurality of signals.

23. 23. The system of claim 22, wherein at least one of the marks includes a plurality of trapezoids, and wherein the controller is configured to: estimate at least one of (i) a movement speed in a first direction, and (ii) a first movement speed based on a plurality of signals indicating a plurality of positions of the plurality of trapezoids, respectively.

24. 24. The system of claim 23, wherein the plurality of trapezoids each have (i) a plurality of orthogonal sides perpendicular to the first direction, and (ii) a plurality of diagonal sides extending at a predetermined angle relative to the first direction, and wherein the controller is configured to estimate a speed of movement in at least the first direction based on a plurality of signals respectively indicative of a plurality of positions of each of the orthogonal sides.

25. 25. The system of claim 24, wherein the plurality of marks include: (i) a first mark having a first orthogonal side and a first diagonal side, and (ii) a second mark having a second orthogonal side and a second diagonal side, and wherein the controller is configured to receive a given signal indicative of the orthogonal side and the diagonal side, and to identify distortion of the ITM by estimating, based on the signal: (a) a first distance between the first orthogonal side and the first diagonal side, and (b) a second distance between the second orthogonal side and the second diagonal side.

26. 26. The system of claim 25, wherein in response to movement of the ITM in the second direction, the controller is configured to: (i) determine a difference between the first distance and the second distance, and (ii) estimate a magnitude of movement of the ITM in the second direction based on (a) the estimated difference between the first distance and the second distance, and (b) the predetermined angle.

27. 24. The system of claim 23, wherein the plurality of trapezoids includes a plurality of isosceles trapezoids each having (i) a plurality of third diagonal sides extending at a first angle with respect to the first direction and (ii) a plurality of fourth diagonal sides extending at a second angle with respect to the first direction, wherein the controller is configured to receive third and fourth signals indicating third and fourth positions of the third and fourth diagonal sides, respectively, the plurality of isosceles trapezoids include first and second isosceles trapezoids positioned at a given distance, and wherein based on the third and fourth signals, the controller is configured to identify distortion of the ITM by estimating: (a) a third distance between the third diagonal side and the fourth diagonal side of the first isosceles trapezoid, and (b) a fourth distance between the third diagonal side and the fourth diagonal side of the second isosceles trapezoid.

28. 28. The system of claim 27, wherein the controller is configured to estimate a magnitude of movement of the ITM in the second direction based on: (a) an estimated difference between the third distance and the fourth distance, and (b) the first angle and the second angle.

29. 23. The system of claim 22, wherein at least one of the marks includes one or more polygons having pairs of sides perpendicular to the first direction, and wherein the controller is configured to estimate a rate of movement in at least the first direction based on given signals that respectively indicate given positions of the one or more pairs of sides.

30. 30. The system of claim 29, wherein the one or more polygons include one or more rectangles, each rectangle having a pair of sides that are orthogonal to the first direction.

31. 31. The system of claim 22, wherein the ITM has a first axis and a second axis orthogonal to the first axis, and the marks include a third mark formed along one or more first edge portions of the first axis and a fourth mark formed along one or more second edge portions of the second axis, and wherein the controller is configured to: (i) determine at least one of (a) a third distortion of the ITM based on the third mark, (b) a fourth distortion of the ITM based on the fourth mark, and (c) a fifth distortion of the ITM based on the third and fourth marks, and (ii) control the actuator to tilt the roller to reduce at least one of the third, fourth, and fifth distortions while the ITM moves.

32. A system according to any one of claims 22 to 31, wherein the controller is configured to control the operation of at least one station or assembly of the system based on at least one of the plurality of signals.

33. 33. The system of claim 32, wherein the at least one station or assembly is selected from the list consisting of: (a) an image forming station configured to apply ink droplets to the ITM and generate an image on the ITM; (b) an impression station configured to transfer the image to a target substrate; (c) at least a roller configured to move the ITM; (d) one or more drying assemblies configured to at least partially dry the ink droplets on the ITM; and (e) an ITM processing station.

34. 33. The system of claim 32, wherein the impression station comprises a rotatable impression cylinder and a rotatable pressure cylinder configured to transfer an image to the target substrate, and wherein based on at least one of the plurality of signals, the controller is configured to control at least one operation selected from the list consisting of: (a) timing of engagement and disengagement between the impression cylinder and the pressure cylinder; (b) a motion profile of at least one of the impression cylinder and the pressure cylinder; and (c) a gap size between a disengaged impression cylinder and the pressure cylinder.

35. Identifying distortions in an intermediate transfer member (ITM) moving over rollers in a printing system; and controlling an actuator to tilt a roller to reduce distortion during movement of the ITM.

36. 36. The method of claim 35, wherein the ITM moves along a continuous path in a first direction, and wherein reducing distortion comprises: while the ITM moves in the first direction, (i) specifying a first movement speed of the ITM in a second direction different from the first direction, and (ii) tilting the rollers to move the ITM at a second movement speed less than the first movement speed.

37. 37. The method of claim 36, comprising receiving a signal indicative of the first rate of movement, and controlling an actuator in response to the received signal.

38. 38. The method of claim 37, comprising: (i) a first edge sensor positioned in a first section of the continuous path to generate a first signal indicative of the first speed of movement in the first section; and (ii) a second edge sensor positioned in a second section of the continuous path, different from the first section, to generate a second signal indicative of the first speed of movement in the second section.

39. 39. The method of claim 38, comprising determining a first distortion in the first interval and a second distortion in the second interval in response to receiving the first and second signals.

40. 40. The method of claim 39, comprising a first actuator for tilting the first roller and a second actuator for tilting the second roller, and controlling at least one of the first and second actuators to tilt the first and second rollers, respectively, in response to identifying the first and second strains.

41. 41. The method of claim 40, wherein controlling the first and second actuators comprises controlling: (i) a first actuator to tilt the first roller at a first tilt angle, and (ii) a second actuator to tilt the second roller at a second tilt angle different from the first tilt angle.

42. 41. The method of claim 40, wherein controlling the first and second actuators comprises controlling the first and second actuators to simultaneously apply the first and second tilts.

43. The method of any one of claims 35 to 42, comprising receiving ink droplets applied to the ITM to form an ink image on the ITM, and transferring the ink image from the ITM to a target substrate.

44. 43. The method of any one of claims 35 to 42, wherein controlling the actuator to tilt the roller comprises: (i) maintaining a look-up table (LUT) including one or more known distortions respectively caused by one or more operations performed in the printing system; and (ii) controlling the actuator to tilt the roller according to the LUT to reduce the one or more known distortions.

45. 45. The method of claim 44, wherein the one or more known distortions include a first known distortion in a first section on the ITM and a second known distortion in a second section of the ITM, and the method includes first and second actuators for tilting a first roller of the printing system and a second roller of the printing system, respectively, and controlling at least one of the first and second actuators to tilt the first and second rollers, respectively, in response to identifying the first and second known distortions.

46. 46. ​​The method of claim 45, wherein controlling at least one of the first and second actuators comprises controlling: (i) a first actuator to tilt the first roller at a first tilt angle, and (ii) a second actuator to tilt the second roller at a second tilt angle different from the first tilt angle.

47. 47. The method of claim 46, wherein controlling at least one of the first and second actuators comprises controlling the first and second actuators to simultaneously apply the first and second tilts.

48. 43. The method of any one of claims 35-42, wherein controlling the actuator to tilt the roller comprises: (i) maintaining a neural network (NN) to identify one or more known distortions caused by one or more operations performed in the printing system, respectively; and (ii) controlling the actuator to tilt the roller according to an output of the NN in response to a given operation in the printing system, to reduce the one or more known distortions.

49. 49. The method of claim 48, wherein controlling the actuator to tilt the roller comprises receiving one or more signals each indicative of the one or more additional distortions, and applying the neural network to identify whether at least one of the one or more known distortions includes at least one of the one or more additional distortions.

50. 49. The method of claim 48, wherein controlling the actuator to tilt the roller comprises applying a neural network to control the actuator in response to receiving the signal.

51. 43. The method of any one of claims 35 to 42, wherein the printing system comprises at least first and second rollers, and wherein controlling the actuator to tilt the rollers comprises controlling the actuator to tilt the first roller, thereby causing the at least first and second rollers to be non-parallel to one another.

52. 43. The method of any one of claims 35-42, wherein distortion of the ITM causes deflection of the roller, and the method includes moving the ITM and generating a deflection signal indicative of a deflection angle of the roller, and wherein controlling the actuator to tilt the roller includes determining the distortion of the ITM based on the deflection signal.

53. 43. The method of any one of claims 35-42, comprising: (i) a housing and at least first and second print bars, wherein the first and second print bars are coupled to the housing and for applying ink droplets of first and second colors to the ITM to generate first and second patterns of an image, respectively, on the ITM; and (ii) at least a given edge sensor, wherein the edge sensor is coupled to the housing and for generating (a) a first edge signal indicative of a first position of the housing, and (b) a second edge signal indicative of a second position of an edge of the ITM moving relative to the at least first and second print bars.

54. 44. The method of claim 43, wherein the distortion of the housing causes a color-to-color (C2C) registration error between the first pattern and the second pattern of the image, and wherein controlling the actuator to tilt the roller based on the first and second edge signals comprises: (i) identifying the distortion of the housing; (ii) estimating the C2C registration error; and (iii) controlling the actuator to tilt the roller to reduce the C2C registration error by compensating for the distortion of the housing while (a) the ITM moves; and (b) the first and second print bars apply ink drops of the first and second colors.

55. 55. The method of claim 53, further comprising controlling at least the first and second print bars to adjust at least one of the first and second timings for applying ink drops of the first and second colors, respectively, to reduce C2C registration errors in the image.

56. 39. The method of claim 37 or 38, wherein the ITM has a plurality of marks formed at a predetermined distance from each other along at least an edge portion of the ITM, wherein receiving signals includes receiving a plurality of signals indicating a plurality of positions of the plurality of marks, respectively, and controlling the actuator includes: controlling at least one of (i) a first moving speed, and (ii) an inclination of the roller based on the plurality of signals.

57. 57. The method of claim 56, wherein at least one of the marks includes a plurality of trapezoids, and wherein controlling the actuator includes: estimating at least one of (i) a movement velocity in a first direction, and (ii) a first movement velocity, based on a plurality of signals indicating a plurality of positions of the plurality of trapezoids, respectively.

58. 58. The method of claim 57, wherein the plurality of trapezoids comprises a plurality of right-angled trapezoids each having (i) a plurality of orthogonal sides perpendicular to the first direction, and (ii) a plurality of oblique sides extending at a predetermined angle relative to the first direction, and wherein the method comprises estimating a speed of movement in at least the first direction based on a plurality of signals respectively indicative of a plurality of positions of each of the orthogonal sides.

59. 59. The method of claim 58, wherein the plurality of marks include: (i) a first mark having a first orthogonal side and a first diagonal side, and (ii) a second mark having a second orthogonal side and a second diagonal side, and wherein estimating the rate of movement in at least the first direction includes receiving a given signal indicative of the orthogonal side and the diagonal side, and determining distortion of the ITM by estimating, based on the signal: (a) a first distance between the first orthogonal side and the first diagonal side, and (b) a second distance between the second orthogonal side and the second diagonal side.

60. 60. The method of claim 59, wherein determining the distortion comprises, in response to movement of the ITM in the second direction: (i) determining a difference between the first distance and the second distance, and (ii) estimating a magnitude of the movement of the ITM in the second direction based on (a) the estimated difference between the first distance and the second distance, and (b) a predetermined angle.

61. 58. The method of claim 57, wherein the plurality of trapezoids comprises a plurality of isosceles trapezoids each having (i) a plurality of third diagonal sides extending at a first angle with respect to the first direction and (ii) a plurality of fourth diagonal sides extending at a second angle with respect to the first direction, wherein determining the distortion comprises receiving a third signal and a fourth signal indicating a third position and a fourth position of the third and fourth diagonal sides, respectively, the plurality of isosceles trapezoids comprise first and second isosceles trapezoids disposed at a given distance, and determining the distortion comprises determining the distortion of the ITM by estimating, based on the third and fourth signals: (a) a third distance between the third diagonal side and the fourth diagonal side of the first isosceles trapezoid, and (b) a fourth distance between the third diagonal side and the fourth diagonal side of the second isosceles trapezoid.

62. 62. The method of claim 61 , wherein determining the distortion includes estimating a magnitude of movement of the ITM in the second direction based on: (a) an estimated difference between the third distance and the fourth distance, and (b) the first angle and the second angle.

63. 56. The method of claim 55, wherein at least one of the marks includes one or more polygons having pairs of sides perpendicular to the first direction, and the method includes estimating a rate of movement in at least the first direction based on given signals that respectively indicate given positions of the one or more pairs of sides.

64. 64. The method of claim 63, wherein the one or more polygons include one or more rectangles, each of the rectangles having a pair of sides that are orthogonal to the first direction.

65. 65. The method of claim 55, wherein the ITM has a first axis and a second axis orthogonal to the first axis, the marks include a third mark formed along one or more first edge portions of the first axis and a fourth mark formed along one or more second edge portions of the second axis, and (i) determining the distortion includes determining at least one of: (a) a third distortion of the ITM based on the third mark, (b) a fourth distortion of the ITM based on the fourth mark, and (c) a fifth distortion of the ITM based on the third and fourth marks, and (ii) controlling the actuator includes controlling the actuator to tilt the roller to reduce at least one of the third, fourth, and fifth distortions while the ITM is moving.

66. 66. The method of any one of claims 56 to 65, comprising controlling operation of at least one station or assembly of a printing system based on at least one of the plurality of signals.

67. 67. The method of claim 66, wherein controlling the operation of at least one station or assembly includes controlling the operation of a station or assembly selected from the list consisting of: (a) an image forming station for applying ink droplets to the ITM and creating an image on the ITM; (b) an impression station for transferring the image to a target substrate; (c) at least rollers for moving the ITM; (d) one or more drying assemblies for at least partially drying the ink droplets on the ITM; and (e) an ITM processing station.

68. 67. The method of claim 66, wherein the impression station comprises a rotatable impression cylinder and a rotatable pressure cylinder for transferring an ink image to the target substrate, and wherein controlling the operations comprises controlling at least one operation selected from the list consisting of: (a) timing of engagement and disengagement between the impression cylinder and the pressure cylinder; (b) a motion profile of at least one of the impression cylinder and the pressure cylinder; and (c) a gap size between a disengaged impression cylinder and the pressure cylinder based on at least one of a plurality of signals.

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