Printing marks on the edge of the substrate

Abstract

The system (10) includes a printing assembly (13) and a stacking assembly (59). The printing assembly (13) is configured to (i) print a plurality of images on each of a plurality of substrates (50) and (ii) print a plurality of marks on one or more edges of each of the plurality of substrates. The stacking assembly (59) is configured to stack the plurality of substrates on one another to form a stack (88) having a top surface (32) parallel to one or more of the substrates and side surfaces (21, 31, 41, 51) created from the stacked edges of the substrates. One or more of the marks are visible in a side view of at least a given one of the sides (21), and at least the location of the one or more marks in the side view of the given side indicates a problem that occurred while printing one or more of the plurality of images.

Description

[Technical field]

[0001] (CROSS REFERENCE TO RELATED APPLICATIONS) This application claims the benefit of U.S. Provisional Patent Application No. 63 / 307,126, filed February 6, 2022, the disclosure of which is incorporated herein by reference.

[0002] The present invention relates generally to digital printing, and more particularly to a method and system for controlling the printing process using marks printed on the edge of a substrate. [Background technology]

[0003] Various techniques have been published for printing on the edge of a substrate and for controlling the printing process.

[0004] For example, US Patent 5,243,394 describes an electrophotographic device that records a linear mark on at least one side edge of a sheet according to a job. Designating the job makes it easy to sort the recorded sheets stacked in a stacker. The sheets are conveyed sequentially by a conveying device, and then the edge of the sheet is detected by a paper leading edge detection device or a paper side edge detection device. Based on the position of the detected paper edge, a linear mark K corresponding to the position designated by the control device is recorded on the sheet.

[0005] US Patent Application Publication 2008 / 0053327 describes a method for identifying sheets in a stack of printed sheets for sorting or further evaluation. In one embodiment, the method includes printing (one or more) non-test production print jobs on sheets of media and outputting the printed sheets in a stack of sheets. The method monitors the printing of the non-test production print jobs and, when a "predetermined event" occurs during the monitoring, creates an identifier sheet from one of the sheets of the non-test production print job by adding a unique marking to an edge area of ​​the printed sheet (of the non-test production print job) being printed. The unique marking is visible from the side of the stack of sheets. The identifier sheet is then output to the stack of sheets together with other sheets of the non-test production print job. The method continues printing and monitoring sheets during the printing of the remainder of the non-test production print job. After printing is completed, the identifier sheet can be subject to a specific inspection or can be used to indicate a specific sheet count in the stack of sheets. The stack of sheets is then subjected to subsequent processes such as trimming and binding, the trimming process removing edge areas from the printed sheets.

[0006] US Patent Application Publication 2010 / 0141985 describes a method for separating multiple print jobs sent by one or more computers to a document printer, the method including printing a first banner on an edge of an upper sheet of a first print job and printing a second banner on an edge of an upper sheet of a second print job. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] U.S. Pat. No. 5,243,394 [Patent Document 2] US Patent Application Publication No. 2008 / 0053327 [Patent Document 3] US Patent Application Publication No. 2010 / 0141985 [Patent Document 4] US Patent Application Publication No. 2020 / 0171813 [Patent Document 5] International Publication No. 2020 / 003088 Brochure [Patent Document 6] US Patent Application Publication No. 2017 / 0008272 [Patent Document 7] International Publication No. 2013 / 132424 Brochure [Patent Document 8] U.S. Pat. No. 9,229,664 [Patent Document 9] International Publication No. 2017 / 208152 Brochure [Patent Document 10] U.S. Pat. No. 9,914,316 [Patent Document 11] U.S. Pat. No. 9,186,884 [Patent Document 12] US Patent Application Publication No. 2015 / 0054865 [Patent Document 13] U.S. Provisional Patent Application No. 62 / 596,926 [Patent Document 14] U.S. Pat. No. 9,327,496 [Patent Document 15] International Publication No. 2013 / 132438 Brochure [Patent Document 16] US Patent Application Publication No. 2015 / 0118503

[0008] (Summary of the invention) An embodiment of the invention described herein provides a system including a printing assembly and a stacking assembly. The printing assembly is configured to (i) print a plurality of images on each of a plurality of substrates, and (ii) print a plurality of marks on one or more edges of each of the plurality of substrates. The stacking assembly is configured to stack the plurality of substrates on one another to form a stack having a top surface parallel to one or more of the substrates and a side surface created from the stacked edges of the substrates. One or more of the marks are visible in a side view of at least a given one of the sides, and at least a position of the one or more marks in the side view of the given side is indicative of a problem that occurred during printing one or more of the plurality of images.

[0009] In some embodiments, the image includes a first image and a second image, the mark includes a first mark and a second mark, the substrate includes a first substrate and a second substrate, respectively, and (i) on the first substrate, the first image is printed at an intended position and the first mark is printed at a first edge position on a given one of the edges, and (ii) on the second substrate, the second image is printed at an actual position and the second mark is printed on the given edge at a second edge position. In other embodiments, the problem includes an offset between the intended and actual positions, and in the side view image, a difference between the first edge position and the second edge position indicates an offset between the actual and intended positions. In yet another embodiment, the first image includes a first color image in a first color and a second color image in a second color different from the first color, and the first mark includes (i) a first color mark associated with the first color image and located at a first color location, and (ii) a second color mark associated with the second color image and located at a second color location different from the first color location. The problem includes a registration error between the first and second color images, and in the side view image, a distance between the first and second color locations indicates the registration error between the first and second color images.

[0010] In some embodiments, the problem includes a movement of the second substrate relative to the second image, where a difference between the first and second edge positions in the side view image indicates the movement. In other embodiments, the movement includes a rotation of the second substrate about an axis perpendicular to the top surface. In yet other embodiments, the first image is printed on the first substrate using a first print job and the second image is intended to be printed on the second substrate using a second print job that is different from the first print job, and the problem includes a motion error using the first print job to print the second substrate on the second substrate, where a difference between the first and second edge positions indicates the motion error.

[0011] In some embodiments, the system includes a processor configured to receive a side view image of the side view and identify a problem based on at least a position of the one or more marks in the side view image. In other embodiments, prior to printing the plurality of marks, the processor is configured to define one or more characteristics of the plurality of marks intended to be printed on the one or more edges. In yet other embodiments, the one or more characteristics include at least one of: (i) a position of the one or more marks in the side view, (ii) a size of the one or more marks in the side view, and (iii) a color of the one or more marks in the side view.

[0012] In some embodiments, at least one of the marks comprises a machine readable label (MRL), the MRL configured to include information about at least one of: (i) one or more characteristics of at least one of the substrates, (ii) one or more characteristics of at least one of the images, (iii) one or more characteristics of at least one of the marks, (iv) one or more characteristics of interest, and (v) one or more control characteristics of at least a portion of the stack. In other embodiments, the MRL comprises at least one of: (i) a machine readable optical label, and (ii) a machine readable magnetic label.

[0013] In some embodiments, the system includes a processor configured to receive a signal indicative of the information contained in the MRL and display the information to a user. In other embodiments, the information contained in the MRL includes at least a control limit indicative of a level of concern based on one or more characteristics of the mark. In yet other embodiments, the one or more control characteristics include at least one characteristic of (i) print jobs of the portion of the stack, and (ii) clients of the portion of the stack.

[0014] According to one embodiment of the present invention, there is further provided a method comprising the steps of: (i) printing a plurality of images on a plurality of respective substrates; and (ii) printing a plurality of marks on one or more edges of the plurality of respective substrates. The plurality of respective substrates are stacked on top of one another to form a stack having a top surface parallel to one or more of the substrates and a side surface created from the stacked edges of the substrates, where one or more of the marks are visible in a side view of at least a given one of the sides. A problem occurring during printing one or more of the plurality of images is identified based on a position of at least one of the one or more marks in a side view of the given side, the position being indicative of the problem.

[0015] The present invention will be more fully understood from the following detailed description of the embodiments thereof, taken in conjunction with the drawings, in which: [Brief description of the drawings]

[0016] [Figure 1] 1 is a schematic side view of a digital printing system according to one embodiment of the present invention; [Figure 2A] 2 is a schematic side view of an output stack of printed sheets having a pattern of marks printed on an edge of one or more of the printed sheets, in accordance with one embodiment of the present invention; [Figure 2B] 2 is a schematic side view of an output stack of printed sheets having a pattern of marks printed on an edge of one or more of the printed sheets, in accordance with one embodiment of the present invention; [Diagram 3]4 is a flow chart that generally illustrates a method for generating and using marks to identify process problems and distortions in an image printed on a sheet, in accordance with one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] (overview) A printing process, such as digital printing, in which droplets of ink are applied to a substrate to produce an image on the substrate may include multiple print jobs with different print settings, and optionally different images printed in at least two of the print jobs. The printed sheets are typically stacked as an output stack of the printing system.

[0018] In principle, it is possible to insert mechanical tabs between print jobs in the output stack, for example using a suitable tab insertion assembly of the printing system or using a dedicated system for tab insertion. Furthermore, digital printing processes can have problems such as process issues and equipment failures that can cause distortions in the printed image. Some of the process issues and / or distortions may not be detectable during the printing process or may require inspection of each sheet immediately after it is printed.

[0019] The embodiments of the invention described below provide methods and systems for replacing mechanical tabbing with a digital tabulating process by printing marks on one or more edges of a sheet. In some embodiments, the edge printing marks may be designed to detect certain problems in the printing process and equipment malfunctions as well as distortions that may occur during the printing process.

[0020] In some embodiments, a digital printing system, also referred to herein as a blanket, includes a print assembly having an imaging station configured to apply droplets of a printing fluid (e.g., jet ink droplets) onto a movable closed-loop surface of a flexible intermediate transfer member (ITM) for producing an image thereon. The blanket is described in more detail in FIG.

[0021] In some embodiments, the digital printing system further includes (i) an impression station configured to transfer an image from the blanket to a target substrate (e.g., a sheet); (ii) a blanket module configured to generate an image on the blanket and move the blanket to transfer the image to the sheet; (iii) input and output stacks of sheets before and after receiving an image, respectively; (iv) a stacking assembly configured to stack the sheets that have received each image into an output stack; and (v) a substrate transport module configured to move the sheets from the input stack through the impression station to the output stack.

[0022] In some embodiments, when the printed sheets are stacked on top of each other in an output stack, the output stack typically has a top surface that is parallel to the surface of the sheet on which the image is printed. The edges of the stacked sheets form a number of sides in the output stack. For example, a sheet may have a rectangular shape with four edges, and the output stack of sheets may have four sides corresponding to the four edges.

[0023] In some embodiments, the digital printing system further comprises a processor configured to receive a plurality of images, such as a product image, intended to be printed on each of the plurality of sheets, and a plurality of marks intended to be printed on an edge of the sheet. In some embodiments, after simultaneously printing the images on the sheets and the marks on one or more edges of the sheets, the marks are visible in a side view of the output stack of sheets. Further, the marks printed on the edges of the sheets collectively form a pattern having a graphical representation on each respective side of the output stack.

[0024] In some embodiments, the graphical representation indicates one or more problems that may have occurred in the printing process. For example, the distance between two of the marks may indicate a distortion in one or more of the printed image(s).

[0025] In some embodiments, the processor is configured to control the printing assembly, the imprinting station, the blanket module, the stacking assembly, the substrate transport module, and other elements of the system to perform the printing process and to stack sheets having printed images into an output stack.

[0026] In some embodiments, the printed marks can collectively form a graphic representation on one or more sides of the output stack of the position and orientation of the sheets relative to their intended position and orientation. In other words, the pattern formed on the side by the printed marks can be indicative of a misalignment between at least two of the sheets in the output stack. For example, when the printed sheets are stacked, the marks create a graphic representation indicative of a registration error in the printed image (as described in the Detailed Description) and / or an unintended movement (e.g., rotation and / or translation) of one or more of the sheets.

[0027] In some embodiments, based on the graphical representation of the marks in the output stack, (i) an operator of the system can identify process issues and image distortions, and / or (ii) a processor can receive a side view image of the edge(s) of the output stack and identify process issues and / or image distortions by analyzing the side view image.

[0028] In some embodiments, this identification may be performed while the system is printing images and marks on the sheet (also referred to herein as on-the-fly (OTF)) or after printing has completed. In response to identifying process issues and / or distortions, an operator and / or processor may take corrective actions to improve the quality of the images printed by the system. Exemplary embodiments of process issues, distortions, and corrective actions are described in detail in FIGS. 2A, 2B, and 3.

[0029] The disclosed techniques improve the quality of images printed by digital printing systems by early identification of process problems and the occurrence of image distortions. Additionally, the disclosed techniques increase the productivity of the system by reducing the number of distorted images and increasing the availability of the system to print qualified images. Additionally, by reducing the number of distorted images and unqualified sheets, the disclosed techniques reduce the amount of waste (e.g., sheets and fluids associated with the printing process) consumed and generated by the system.

[0030] (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 cycles through an imaging station 60, a drying station 64, an imprint station 84, and a blanket treatment station 52. In the context of the present invention and in the claims, the terms "blanket" and "intermediate transfer member (ITM)" are used interchangeably and refer to a flexible member including 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.

[0031] During an operational mode, imaging station 60 is configured to form a mirror ink image (herein also referred to as an "ink image" (not shown), or for simplicity, an "image") of digital image 42 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 a sheet or continuous web) located beneath the lower run of blanket 44.

[0032] In the context of the present invention, the term "run" refers to the length or section of blanket 44 between any two given rollers that guide blanket 44.

[0033] In some embodiments, during installation, the blanket 44 may be bonded end-to-end using a seam section (also referred to herein as seam 45) to form a continuous blanket loop (also referred to herein as a closed loop). Examples of methods and systems for seam installation are described in detail in U.S. Patent Application Publication No. 2020 / 0171813, the disclosure of which is incorporated herein by reference.

[0034] 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 printhead that is the same width as the print area on blanket 44, and includes individually controllable print nozzles that are configured to eject ink and other types of printing fluids onto blanket 44, as described in more detail below.

[0035] In some embodiments, imaging station 60 may include any suitable number of print bars 62 (also referred to herein as bars 62 for brevity). Each bar 62 may include a printing fluid, such as a water-based ink of a different color. Typically, the inks have visible colors, such as, but not limited to, cyan, magenta, red, green, blue, yellow, black, and white. In the example of FIG. 1, imaging station 60 includes seven print bars 62, but may include four print bars 62 having any selected color, such as, for example, cyan (C), magenta (M), yellow (Y), and black (K).

[0036] In some embodiments, the print heads are 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 heads, typically parallel to the Z-axis of the coordinate system.

[0037] In some embodiments, the different print bars 62 are spaced apart from one another along an axis of movement, also referred to herein as (i) the direction of blanket 44 movement 94 or (ii) the printing direction. In this example, the direction of blanket 44 movement is parallel to the X-axis, and each print bar 62 extends along the Y-axis of the XYZ coordinate system of system 10. In this configuration, precise spacing between the bars 62 along the X-axis and synchronization between the directing of the ink droplets of each bar 62 and the moving blanket 44 is essential to enable precise placement of the image pattern.

[0038] In the context of this disclosure and the claims, the terms “inter-color pattern placement,” “pattern placement accuracy,” “inter-color registration,” “C2C registration,” and “color registration” are used interchangeably and refer to any placement accuracy of two or more colors relative to one another.

[0039] In some embodiments, the system 10 includes a heater 66, such as a hot gas or air blower having a gas or air blower for flowing gas or air at any suitable temperature and / or an infrared heater. The heater 66 is disposed between the print bars 62 and configured to partially dry the ink droplets deposited on the surface of the blanket 44. This air flow between the print bars can contribute, for example, to (i) reducing condensation on the surface of the print head and / or to treating satellites (e.g., residue or small droplets that are dispersed around the main ink droplets), and / or (ii) preventing clogging of the orifices of the inkjet nozzles of the print head, and / or (iii) preventing droplets of different colors of ink from undesirably merging with one another on the blanket 44.

[0040] In some embodiments, system 10 includes a drying station 64 configured to direct infrared radiation and cooling air (or other gas) and / or blow hot air (or other gas) onto a surface of blanket 44. In some embodiments, drying station 64 may include an infrared radiation assembly (not shown) and / or a blower 68, or any other suitable drying device.

[0041] In some embodiments, in a drying station 64, the ink image formed on the blanket 44 is exposed to radiation and / or hot air to more completely dry the ink, leaving behind only a layer of resin and colorant that has been heated to the point where most or all of the liquid carrier has evaporated and become a viscous ink film.

[0042] 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, thereby controlling the position of a section of blanket 44 relative to each print bar 62. In some embodiments, one or more motion encoders may be integrated with additional rollers and other motion components of system 10.

[0043] In some embodiments, such motion encoders typically comprise at least one rotary encoder configured to generate rotary position signals indicative of the angular displacement of each roller. It should be noted that in the context of the present invention and in the claims, the terms "indicative of" and "indication" are used interchangeably.

[0044] Additionally or alternatively, blanket 44 may include an integrated encoder (not shown) for controlling the operation of various modules of system 10. One embodiment of an integrated motion encoder is described in detail, for example, in WO 2020 / 003088, the disclosure of which is incorporated herein by reference.

[0045] In some embodiments, blanket 44 is guided within blanket module 70 over rollers 76, 78 and other rollers described herein, as well as over a motorized tension roller (also referred to herein as dancer assembly 74). Dancer assembly 74 is configured to control the length of slack in blanket 44, and its movement is represented diagrammatically in FIG. 1 by a double-headed arrow. Furthermore, any stretching of blanket 44 with age does not affect the ink image placement performance of system 10, and only requires more slack to be taken up by tension dancer assembly 74.

[0046] In some embodiments, dancer assembly 74 may be motorized. The configuration and operation of rollers 76 and 78 are described in further detail, for example, in U.S. Patent Application Publication No. 2017 / 0008272 and the above-referenced U.S. Patent Application Publication No. WO 2013 / 132424, the disclosures of which are incorporated herein by reference in their entireties.

[0047] In some embodiments, the 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 respective first and second axes.

[0048] 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 with blanket 44 or may include sensors external to blanket 44 using any other suitable technique for obtaining a signal indicative of the mechanical tension applied to blanket 44. In some embodiments, processor 20 and additional controllers of system 10 are configured to receive the signals generated by the tension sensors to monitor the tension applied to blanket 44 and to control the operation of dancer assembly 74.

[0049] At the impression station 84, the blanket 44 passes between the impression cylinder 82 and a pressure cylinder 90 configured to transport the compressible blanket. In some embodiments, a motion encoder is integrated into at least one of the impression cylinder 82 and the pressure cylinder 90.

[0050] In some embodiments, the system 10 includes a control console 12 configured to control multiple modules of the system 10, such as a blanket module 70, an image forming station 60 disposed above the blanket module 70, and a substrate transport module 80 disposed below the blanket module 70 and including one or more imprint stations, as described below.

[0051] In some embodiments, console 12 includes a processor 20 (typically a general purpose processor) with suitable front end and interface circuitry for interfacing with and receiving signals from the controllers 54 and the controls for dancer assembly 74 via cable 57. Additionally or alternatively, console 12 may include any suitable type of application specific integrated circuit (ASIC) and / or digital signal processor (DSP), and / or any other suitable type of processing unit configured to perform any type of processing on data processed in system 10.

[0052] In some embodiments, the controller 54, while shown generally as a single unit, may comprise one or more electronic modules implemented at predetermined locations in the system 10. At least one of the electronic modules of the controller 54 may comprise electronics, such as control circuitry or a processor (not shown), configured to control the various modules and stations of the system 10. In some embodiments, the processor 20 and control circuitry may be programmed with software to perform functions used by the printing system and to store data for the software in the memory 22. The software may be downloaded, for example, over a network, into the processor 20 and electronic control circuitry, or may be provided on a non-transitory, tangible medium, such as an optical, magnetic, or electronic memory medium.

[0053] In some embodiments, the console 12 includes a display 34 configured to display data and images received from the processor 20 or input inserted by a user (not shown) using an input device 40. In some embodiments, the console 12 can have any other suitable configuration, for example, alternative configurations of the console 12 and display device 34 are described in detail in U.S. Pat. No. 9,229,664, the disclosure of which is incorporated herein by reference.

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

[0055] 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 fluid to the exterior of the blanket 44 and / or cleaning the exterior of the blanket 44. The blanket treatment station 52 may reduce the temperature of the blanket 44 to a desired temperature level before the blanket 44 enters (e.g., is located proximate to) the imaging station 60. Treatment may be performed by passing the blanket 44 over one or more rolls or blades configured to cool and / or clean and / or apply a treatment fluid to the exterior surface of the blanket.

[0056] In some embodiments, additionally or alternatively, blanket treatment station 52 may further include one or more bars (not shown) positioned adjacent print bar 62 so as to apply treatment fluid to blanket 44 by spraying.

[0057] In some embodiments, the processor 20 is configured to receive a signal indicative of the surface temperature of the blanket 44, for example from a temperature sensor (not shown), to monitor the temperature of the blanket 44 and control operation of the blanket treatment station 52. Examples of such treatment stations are described, for example, in WO 2013 / 132424 and WO 2017 / 208152, the disclosures of which are incorporated herein by reference in their entireties.

[0058] 1, station 52 is mounted between imprint station 84 and imaging station 60, however, station 52 may be mounted adjacent blanket 44 at any other or additional suitable location or locations between imprint station 84 and imaging station 60. As noted above, station 52 may additionally or alternatively be mounted on a bar adjacent imaging station 60.

[0059] 1, impression cylinder 82 and pressure cylinder 90 impress an ink image onto a target flexible substrate, 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.

[0060] In some embodiments, the lower run of blanket 44 selectively interacts with impression cylinder 82 at impression station 84 to impress an image pattern onto a target flexible substrate compressed between blanket 44 and impression cylinder 82 under the action of pressure from pressure cylinder 90. For the single-sided printer shown in FIG. 1 (i.e., printing on one side of sheet 50), only one impression station 84 is required.

[0061] In other embodiments, the module 80 may include two or more impression cylinders (not shown) to allow one or more double-sided printing. The two impression cylinder configuration also allows single-sided printing to be performed twice as fast as double-sided printing. Additionally, mixed lots of single-sided and double-sided prints can also be printed. In alternative embodiments, a different configuration of the module 80 may be used to print on a continuous web substrate. Detailed descriptions and various configurations of double-sided printing systems and systems for printing on continuous web substrates are provided, for example, in U.S. Pat. No. 9,914,316 and U.S. Pat. No. 9,186,884, WO 2013 / 132424, U.S. 2015 / 0054865, and U.S. Provisional Patent Application No. 62 / 596,926, the disclosures of which are all incorporated herein by reference.

[0062] In some embodiments, a sheet 50 or continuous web substrate (not shown) is transported by module 80 from 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 carrying the ink image is pressed firmly against sheet 50 (or against another suitable substrate), for example by a compressible blanket of pressure cylinder 90, such that the ink image is impressed onto the surface of sheet 50 and cleanly separated from the surface of blanket 44.

[0063] In some embodiments, system 10 includes a stacking assembly 59 configured to receive sheets 50 transported by modules 80 and arrange the sheets 50 into an output stack 88. In some embodiments, stacking assembly 59 is configured to stack sheets 50 on top of one another to form an output stack 88 having a top surface 32 that is typically parallel to the sheets 50. Output stack 88 has sides (shown and described in detail in FIGS. 2A and 2B ) that are created from the stacked edges of sheets 50 and that are typically (but not necessarily) perpendicular to top surface 32.

[0064] In other embodiments, system 10 may include any other suitable type of stacking assembly configured to stack the aforementioned continuous web substrates (or any other suitable type of substrate) using any suitable stack configuration.

[0065] 1, rollers 78 are disposed on the upper run of blanket 44 and are configured to maintain blanket 44 taut as it passes adjacent imaging station 60. Furthermore, for imaging on the surface of blanket 44 by imaging station 60, it is particularly important to control the speed of blanket 44 below imaging station 60 to obtain accurate jetting and deposition of ink droplets.

[0066] In some embodiments, the impression cylinder 82 is periodically engaged and disengaged from the blanket 44 to transfer an ink image to a target substrate from the moving blanket 44 passing between the blanket 44 and the impression cylinder 82. In some embodiments, the system 10 is configured to apply a torque to the blanket 44 using the roller and dancer assemblies described above to maintain the upper run taut and to substantially prevent the upper run of the blanket 44 from being subjected to mechanical vibrations experienced by the lower run.

[0067] In some embodiments, system 10 includes a quality control station 55 (also referred to herein as an automated quality control (AQM) system) that functions as a closed-loop inspection system integrated into system 10. In some embodiments, quality control station 55 may be adjacent to impression cylinder 82, as shown in FIG. 1, or may be located in any other suitable location in system 10.

[0068] In some embodiments, image quality control station 55 includes a camera (not shown) configured to capture one or more digital images of the ink images printed on sheet 50. In some embodiments, the camera may include any suitable image sensor, such as a contact image sensor (CIS) or a complementary metal oxide semiconductor (CMOS) image sensor, and a scanner including a slit having a width of about one meter or any other suitable width.

[0069] In the context of this disclosure and the claims, the terms "about" or "substantially" in relation to any numerical value or range indicate appropriate dimensional tolerances that enable a collection of parts or components to function for its intended purpose as described herein.

[0070] In some embodiments, the digital images acquired by station 55 are sent to a processor, such as processor 20 or any other processor of 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. In the context of the present invention and in the claims, the term "processor" refers to any processing unit, such as processor 20 or any other processor or controller connected to or integrated with station 55, configured to process signals received from the camera and / or spectrophotometer of station 55. It should be noted that the signal processing operations, control related instructions, and other computational operations described herein may be performed by a single processor or may be shared among multiple processors in one or more respective computers.

[0071] 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, printed geometry, image uniformity, color profile and linearity, and print nozzle functionality. In some embodiments, processor 20 is configured to automatically detect geometric distortions or other errors in one or more of the aforementioned attributes. In the context of this disclosure and in the claims, the terms "detect" and "identify" are used interchangeably and refer to finding defects and / or distortions in the printed image and / or to finding process problems occurring in a digital printing system.

[0072] In some embodiments, the processor 20 is configured to analyze the detected distortion and / or provide instructions to another module or station of the system 10 to compensate for the detected distortion in order to apply corrective action to the malfunctioning module.

[0073] In some embodiments, system 10 is configured to print test marks (shown in detail in FIGS. 2A and 2B ) or other suitable features, for example, on the bevel or margin of sheet 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 differential widths (referred to herein as “bar-to-bar width Δ” or “color-to-color width delta”), 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, for example, a first predetermined threshold set, into a reject tray (not shown), (ii) initiate corrective actions for sheets 50 having distortions that exceed a second, lower, predetermined threshold set, and (iii) output sheets 50 having slight distortions, for example below the second threshold set, into output stack 88.

[0074] In the context of this disclosure and in the claims, the term "image-to-substrate registration error" refers to an offset between the intended and actual position of a printed image on a sheet. The offset may be caused, among other things, by unintended movement of the image relative to its intended position on the sheet 50. The unintended movement may result from one or both of the following: (i) a movement of the image relative to its intended position on the sheet 50, e.g., in the XY plane of the XYZ coordinate system, prior to printing the image on the sheet 50 (this movement is also referred to herein as "translation"), and (ii) an unintended rotation of the sheet 50, e.g., about the Z axis of the XYZ coordinate system, which is orthogonal to the XY plane, prior to printing the image on the sheet 50.

[0075] In some embodiments, processor 20 is configured to detect deviations in the profile and linearity of the printed colors based on signals received from the spectrophotometer of station 55 .

[0076] 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 specified threshold. The processor of station 55 is further configured to initiate corrective action in one or more of the modules and stations of system 10, as described above. In some embodiments, the corrective action may be performed on-the-fly (while system 10 continues the printing process) or may be performed offline by stopping printing operations and correcting the problem in each 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 specified threshold.

[0077] Additionally or alternatively, processor 20 may be configured to receive signals, e.g., from station 55, indicative of additional types of distortions and 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 types of distortions and / or defects not described above. In other embodiments, any other suitable method for inspecting the patterns printed on sheet 50 (or on any other substrate as described above) may be used, e.g., using an external (e.g., offline) inspection system or any type of measurement fixture and / or scanner. In these embodiments, based on the information received from the external inspection system, processor 20 may be configured to initiate any appropriate corrective action and / or to stop operation of system 10.

[0078] In some embodiments, the combination of the image forming station 60, drying station 64, blanket module 70, substrate transport module 80 and one or more imprint stations 84 is also referred to herein as a printing assembly 13, which is configured to print images onto sheets 50 and print the above-mentioned marks on one or more edges of each sheet 50, as described in detail in Figures 2A and 2B.

[0079] In order to clarify the present invention, the configuration of the system 10 is simplified and provided as a mere example. The components, modules and stations described hereinabove for the above printing system 10, as well as additional components and configurations, are described in detail in, for example, U.S. Pat. No. 9,327,496 and U.S. Pat. No. 9,186,884, WO 2013 / 132438, WO 2013 / 132424, WO 2017 / 208152, U.S. Pat. No. 2015 / 0118503 and U.S. Pat. No. 2017 / 0008272, all of which are incorporated herein by reference.

[0080] The particular configuration of system 10 is provided as an example to illustrate the particular problem solved by embodiments of the present invention and to demonstrate the application of these embodiments in improving the performance of such systems, however, the present embodiments 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 as well.

[0081] (A mark is printed on the edge of the sheet to indicate that a problem occurred while printing the image) FIG. 2A is a schematic side view of an output stack 88 having several marks printed on a side 21 of one or more sheets 50, according to one embodiment of the present invention.

[0082] In some embodiments, each sheet 50 has a surface configured to receive an image from the blanket 44, which surface is typically parallel to the top surface 32 of the output stack 88. As also illustrated in FIG. 1, during printing with the system 10, a section of the blanket 44 and a sheet 50 are simultaneously positioned between an impression cylinder 82 and a pressure cylinder 90 that are engaged with each other to transfer an ink image from the blanket 44 onto the surface of the sheet 50. In this embodiment, each sheet 50 has a rectangular shape and includes four edges that are typically orthogonal to the surface that receives the image from the blanket 44. In the XYZ coordinate system of FIGS. 2A and 2B, the surface that receives the image is typically parallel to the XY plane, and the edges of each sheet 50 indicate the sheet thickness along the Z axis of the XYZ coordinate system.

[0083] In some embodiments, after transferring the image to each surface, the sheets 50 are stacked together along the Z axis in an output stack 88. In this example, the output stack 88 has four sides 21, 31, 41, and 51 created by stacking the four edges of each of the stacked sheets 50. Sides 21, 31, 41, and 51 are visible in a side view of the output stack 88, and the thicknesses of sides 21, 31, 41, and 51 are measured along the Z axis and are typically equal to the sum of the thicknesses of all sheets 50 stacked in the output stack 88.

[0084] In the context of this disclosure and in the claims, the term "side view" is obtained when the line of sight of an operator and / or a camera (not shown) of the system 10 is directed toward one or more of the sides 21, 31, 41, and 51. The camera is configured to acquire a sidewall image of each side (e.g., side 21) of the output stack 88. In this example, the marks described in detail herein are shown only on side 21, which is typically parallel to the XZ plane of the XYZ coordinate system. In some cases, one or more of the sheets 50 may not be in registration with other sheets of the output stack 88. In other words, there may be a misalignment between at least two sheets 50 of the output stack 88. Thus, although corresponding edges of each sheet 50 may not be in the same XZ plane, in the side view, the edges can be seen along the Z axis of the XYZ coordinate system. In some embodiments, based on the sidewall image, the processor 20 is configured to detect a misalignment between at least two sheets 50 stacked on top of each other in the output stack 88. Additionally or alternatively, any suitable combination of marks may be printed on one or more edges of sheet 50 and visible in a side view of one or more of sides 31, 41, and 51 of output stack 88. For example, marks may be printed on another edge of sheet 50 that is perpendicular to the edge corresponding to side 21. In this example, the printed marks are visible in a side view of side 31, which is typically parallel to the YZ plane of an XYZ coordinate system.

[0085] In some embodiments, processor 20 receives an image from a user of system 10 or from a client that has a product image for printing. The image may be in the form of (i) a page description in a high-level page description language (PDL) such as PostScript (PS), Portable Document Format (PDF), or any other suitable format of a high-level PDL, or (ii) a vector image, or any other suitable format of an image intended to be printed using system 10.

[0086] In some embodiments, based on the received image, the processor 20 is configured to generate a digital image, such as image 42 shown in FIG. 1 , which has an appropriate format and is intended to be printed using the features of the system 10 described in FIG. 1 . Essentially, (i) the image forming station 60 applies droplets of ink to the surface of a moving blanket 44 to form an ink image on the blanket 44, (ii) the image is transferred to a sheet 50 received from an input stack 86, and (iii) after transferring the image to the sheet 50, the substrate transport module 80 transports the sheet 50 with the image printed on it to an output stack 88.

[0087] In some embodiments, processor 20 is configured to determine various types of marks intended to be printed on the edges of one or more sheets 50. In this example, marks visible in side view of side 21 may indicate one or more problems that occurred during printing of one or more images on each sheet 50 stacked in output stack 88.

[0088] In some embodiments, markings visible on side 21 may indicate one or more faults that may have occurred in system 10 while processing sheet 50 .

[0089] It should be noted that in this embodiment, the disclosed technology typically relates to printing marks on one or more edges of a sheet 50 using, among other things, a blanket 44 or any other suitable type of ITM. However, the disclosed technology may be utilized, mutatis mutandis, for other applications, such as, but not limited to, (i) printing marks on the edge of a continuous web (instead of a sheet 50), and (ii) printing directly onto a target substrate, such as a sheet 50, using an imaging station or any other suitable type of inkjet technology. The term "directly printing" refers to jetting printing fluid (e.g., droplets of ink) directly onto a sheet 50, without the use of a blanket 44 or any other type of ITM.

[0090] Additionally or alternatively, system 10 may include an edge printing device (not shown) configured to print marks on side 21 of one or more sheets 50 while they are being processed by system 10.

[0091] In some embodiments, system 10 is configured to print marks on side 21 while printing image 42 , such that the marks printed on side 21 are visible in a side view of output stack 88 .

[0092] In some embodiments, when sheets 50 are stacked on top of each other in output stack 88, corresponding side view visible marks collectively form a pattern having a graphical representation of a problem that occurred while printing the image. The problem may cause distortions that are manifested as a function of the position of each stacked sheet 50 in output stack 88.

[0093] In some embodiments, the marks printed on the edges of sheets 50 and visible in a side view of side 21 may be used by an operator (not shown) of system 10 to monitor the health of the printing process by viewing the marks shown on side 21 (and other sides) of output stack 88. Additionally or alternatively, processor 20 is configured to receive side view images of the marks visible in a side view of side 21 of output stack 88, and processor 20 is configured to analyze the printed marks based on the side view images to detect (i) one or more distortions in one or more of the printed images, and / or (ii) a malfunction of one or more modules of system 10, and / or (iii) an operational problem, such as selection of an incorrect print job as shown in FIG. 2B .

[0094] In other embodiments, processor 20 is configured to analyze all marks appearing in the side view image, or some of the marks shown in one or more sections of the side view image of side 21. In yet other embodiments, the side view image may be only a portion of side 21, and processor 20 may analyze all marks within that portion, or only a predetermined set of marks shown in the side view image.

[0095] In this embodiment, image 42 includes four color images, such as cyan (C), magenta (M), yellow (Y), and black (K) (CMYK) images, which are combined into a printed version of image 42. In other embodiments, image 42 may include any other suitable number of color images, such as seven or eight color images (e.g., cyan, magenta, red, green, blue, yellow, black, and white) that are combined into image 42. Although the techniques described below relate to CMYK images, the same techniques may be applied to images that include any suitable number of color images. In the context of this disclosure and the claims, the terms "color" and "colour" are used interchangeably.

[0096] In some embodiments, the processor 20 is configured to determine marks 35, 36, 37, and 38 intended to be printed by the system 10 on the edge of the sheet 50 corresponding to the side 21. In this example, the marks 35, 36, 37, and 38 are associated with the C, M, Y, and K color images, respectively. The marks 35-38 indicate the location of each color image (also referred to herein as "color location") and are typically printed during printing of each color image. The shape of the graphic representation of the marks in a side view of the side 21 indicates whether each color image is distorted. For example, the mark 35 is printed on the edge of the sheet 50 (as shown in the side view of the side 21), while the cyan image of the image 42 is printed on the sheet 50, and the graphic representation of the mark 35 in a side view indicates whether the printed cyan image is distorted.

[0097] In one embodiment, at least one, and typically all, of marks 35, 36, 37 and 38 may individually or collectively form one or more graphical representations of distortion as a function of the position of the respective one or more color images in each of the images printed on sheets 50 stacked in output stack 88.

[0098] In some embodiments, the shapes and positions of the marks 35-38, as well as the distances between the marks 35-38, are selected to monitor various types of problems that may have occurred during printing of the images on the sheet 50. The positions of the marks 35-38 may indicate one or more registration errors caused by these problems, such as image-to-substrate registration errors and C2C registration errors. In the example of FIG. 2A, none of the images printed on the sheet 50 have any indication of distortions or problems, such as problems in the printing process and / or system malfunctions that have occurred during the printing process. In such an embodiment, the marks 35 and 36 are determined at a distance 71 from each other, similarly, the marks 36 and 37 are determined at a distance 72 from each other, and the marks 37 and 38 are determined at a distance 73 from each other. In an embodiment, the distances 71-73 may be similar (i.e., the distance 71 is equal to the distance 72 and the distance 73), or one or more of the distances 71-73 may be different from one or more of the other distances.

[0099] In some embodiments, in the absence of image-to-substrate and C2C registration errors, marks 35-38 appear as straight lines in a side view of side surface 21. The appearance of marks 35-38 in the presence of distortions and / or registration errors, such as image-to-substrate and C2C registration errors, is shown in Figure 2B.

[0100] In some embodiments, after determining the marks, system 10 is configured to simultaneously print the image and the marks on at least one of the sheets 50. As described above, since the image is printed on a substrate, system 10 is configured to simultaneously print marks (such as marks 35-38 and additional marks described below) on a given sheet 50 while printing the image on the given sheet 50. In this example, the simultaneous printing of images and marks is applied to all sheets 50, and more particularly, to the sheets 50 that are intended to receive the product image.

[0101] In some cases, one or more non-product sheets, such as service sheets 50, are printed on the system 10, for example, for testing, calibration, and other maintenance operations. In some embodiments, the processor 20 is configured to determine one or more marks, such as mark 79, indicative of such non-product printed sheets 50. Such non-product sheets 50 are sorted from a stack of product sheets 50 having printed product images 42, for example. In some embodiments, the mark 79 may have a color different from the color of the sheets 50 having product images. For example, the edges of the sheets 50 having product images 42 may have a black or white color, while the mark 79 may have a magenta color.

[0102] In some embodiments, the processor 20 is configured to determine the marks 46 and 48 intended to be printed on the sheet 50 and the marks 47 and 49 intended to be printed by the system 10 at the edge of the sheet 50 such that the marks 47 and 49 are visible in a side view of the side 21. The marks 46 and 48 each have a triangular shape such that the marks 47 and 49 are printed at a predetermined size (e.g., width) along the X-axis of the XYZ coordinate system. For example, when printing the mark 46, the apex end of the triangle forms a thin mark 47 at the edge of the sheet 50, shown in a side view of the side 21, and similarly, when printing the mark 48 at the edge of the sheet 50, the base end of the triangle forms a mark 49 that appears wider along the X-axis than the mark 47 in a side view of the side 21. Furthermore, the different positions between the marks 47 and 49 along the X-axis of the edge of the sheet 50 may indicate the orientation of the sheet 50.

[0103] In some embodiments, the marks 47 and 49 having a triangular shape may indicate an orientation of the sheets 50 in the output stack 88, and thus a side view image of the graphic representation of the marks 47 and 49 is also referred to herein as an orientation graphic representation, which indicates the printed image and the orientation of each sheet 50 having the marks 47 and / or 49 in the output stack 88. For example, when duplexing both sides of the sheets 50, one or more sheets 50 may be erroneously printed on only one side, and at least some of the misprocessed sheets 50 may be positioned in an inverted position in the output stack 88.

[0104] In some embodiments, the processor 20 receives a first image intended to be printed on a first side of each sheet 50 and a second image intended to be printed on a second side opposite the first side of each sheet 50. The processor 20 is configured to determine (i) marks 46 and 47 on the sheet 50 and on the edge of the sheet 50 corresponding to the side 21, respectively, and (ii) marks 48 and 49 on the sheet 50 and on the edge of the sheet 50 corresponding to the side 21, respectively. In such embodiments, any inversion or distortion of one or more sheets 50 is immediately identifiable by a user of the system 10 and / or by the processor 20 receiving the side view image of the side 21. Thus, the marks 47 and 49 indicate any undesired distortion or inversion in one or more sheets 50. An example of such a malfunction is shown in FIG. 2B.

[0105] In some embodiments, the processor 20 is configured to determine marks 23a, 23b, 23c, and 23d that are intended to be printed by the system 10 on an edge of the sheet 50 that corresponds to the side 21 of the output stack 88. In this example, the marks 23a, 23b, 23c, and 23d represent print jobs 33a, 33b, 33c, and 33d, respectively, that are executed by the system 10. It should be noted that the marks 23a, 23b, 23c, and 23d may indicate a process problem, such as a distortion in the image printed on the sheet 50 and / or a process fault associated with one or more sheets 50 in the output stack 88. An example of an indication of such a process problem is shown in FIG. 2B.

[0106] In some embodiments, the processor 20 is configured to determine one or more marks, each of which comprises one or more machine-readable labels (MRLs). The MRLs may be any suitable type of readable label, including, but not limited to, (i) one or more machine-readable optical labels, and (ii) one or more machine-readable magnetic labels. The MRLs may include suitable information, as described in more detail below.

[0107] In one embodiment, a user of system 10 may use a smartphone to read the information and / or any suitable type of optical or magnetic reader or scanner to read the information stored on the MRL. Additionally or alternatively, system 10 may include one or more suitable optical or magnetic readers or scanners configured to generate a signal indicative of the information stored on the MRL. Based on this signal, processor 20 is configured to display the information to the user (e.g., on display 34) and, if necessary, to control system 10 to take corrective action, as described below.

[0108] In some embodiments, the MRL may have (i) a two-dimensional (2D) shape, such as, but not limited to, a Quick Response (QR) Code or an AZTEC Code, or (ii) a one-dimensional (1D) shape, such as, but not limited to, a barcode.

[0109] In some embodiments, the MRL may include information regarding at least one of: (i) one or more characteristics of at least one of the substrates (e.g., size, thickness, and material); (ii) one or more characteristics of at least one of the images (e.g., number and color of inks used to generate the image, image resolution and size); and (iii) one or more management characteristics of at least a portion of the output stack 88. The management information may include at least one of the intended number of sheets 50 and clients of each portion of the stack 88. In this example, the processor 20 is configured to determine marks 81, 83, 85, and 87, which are MRLs that include one or more characteristics of the substrates and / or images, and / or management of the stacks of print jobs 33d, 33c, 33b, and 33a, respectively.

[0110] In some embodiments, the information stored in the MRL may include one or more characteristics of at least one of the marks and the problem that each mark is intended to detect. In one exemplary implementation, the processor 20 is configured to determine marks 91, which are associated with marks 35-38 and distances 71-73. In one embodiment, the marks 91 may include control limits indicative of a specified level at each of the distances 71-73. For example, the control limit for distance 71 is about 1 cm to 1.1 cm, such that in response to receiving a measured distance 71 of about 1.05 cm, the information stored in the marks 91 provides an indication to the user that the C2C registration between the colors cyan and magenta is within specifications. If the measured distance 71 is greater than about 1.1 cm or less than about 1 cm, the user may immediately receive an alarm indicating a problem in the C2C registration between the colors cyan and magenta. Examples of C2C and image-to-substrate registration errors are shown in FIG. 2B and described in detail.

[0111] In some embodiments, processor 20 is configured to determine mark 89, which is an MRL located proximate mark 79, and to provide a user with information regarding testing, calibration, or other maintenance operations to be performed during printing of one or more non-product images on each of one or more sheets 50 having mark 79. In some embodiments, processor 20 is configured to determine marks 26 and 27 intended to be printed by system 10 on an edge of sheet 50 corresponding to side 21. In this example, marks 26 and 27 and the relative position (e.g., vector distance) therebetween are indicative of a C2C registration error between two or more color images in a printed version of image 42. For example, in response to a misalignment or offset between the two color images or between selected sections of the color images, the position of at least one of marks 26 and 27 may change (as shown in FIG. 2B ), indicating a C2C registration error.

[0112] In another exemplary implementation, processor 20 is configured to determine mark 93, which is an MRL located in close proximity to marks 26 and 27. In this embodiment, mark 93 indicates a control limit for a C2C registration error between two or more color images in a printed version of image 42. As described in the example of mark 91, by reading the information stored in mark 93, a user can compare the calculated C2C registration error to the control limit for the C2C registration error and infer whether the measured C2C registration error is within specifications for print job 33d.

[0113] In some embodiments, the processor 20 is configured to determine marks 25a, 25b, 25c, and 25d that are intended to be printed by the system 10 on the edge of the sheet 50 corresponding to the side 21. In this example, the marks 25a, 25b, 25c, and 25d indicate different types of problems that have occurred during printing of the image on one or more sheets 50. Exemplary indications are shown in FIG. 2B. Furthermore, the marks 25a, 25b, 25c, and 25d may be used for other applications, such as distinguishing between clients of the system 10, or printing products such as dictionaries.

[0114] The above-mentioned marks are presented as an example for conceptual clarity. In other embodiments, one or more of these marks may have a different size, shape, position, color, or any other suitable attribute that indicates process issues and / or distortions in one or more images printed on one or more sheets 50. Furthermore, at least one of these marks may be determined and applied to other edges of output stack 88 in addition to or instead of the marks shown on side 21.

[0115] FIG. 2B is a schematic side view of an output stack 88 of sheets 50 having several marks printed on the edges of sheets 50 corresponding to side 21, according to one embodiment of the present invention.

[0116] In some embodiments, the intended positions (in the absence of distortion as shown in FIG. 2A above) of marks 35, 36, 37, and 38 are shown by dashed lines, and their actual appearances are shown by marks 95, 96, 97, and 98, respectively. In this example, distance 71a between marks 95 and 96 is approximately the same as distance 71 between marks 35 and 36. In such embodiments, (i) the difference between the positions of the marks of each color (e.g., marks 35 and 95) and (ii) the approximately identical distances between the marks of a pair of colors (e.g., distances 71 and 71a) indicate (i) that some of the images printed on each sheet 50 have image-to-substrate registration errors, and (ii) that there are no C2C registration errors between the color images that comprise each printed image 42.

[0117] In the example of marks 97 and 98, distance 73a between marks 97 and 98 is approximately the same as distance 73 between marks 37 and 38, while in section 75, distance 73b is different (e.g., larger) than distance 73. In such an embodiment, in print jobs 33b, 33c, and 33d, (i) the difference between the positions of the marks of each color (e.g., marks 38 and 98) and (ii) the approximately identical distances between the marks of a pair of colors (e.g., distances 73 and 73a) indicate (i) that some of the images printed on each sheet 50 have image-to-substrate registration errors, and (ii) that there are no C2C registration errors between the color images that comprise each printed image 42. However, in section 75 of print job 33a, (i) the positions of marks 37 and 97 are different, and (ii) distance 73b is different (e.g., larger) than distance 73. Thus, marks 97 and 98 indicate both image-to-substrate registration error and C2C registration error in the printed version of image 42 on sheet 50 in section 75 of output stack 88 .

[0118] In the example of FIG. 2B, during the process of print job 33a, a C2C registration error begins to occur while printing sheet 50 in section 75. In some embodiments, based on the difference between distances 73b and 73, processor 20 and / or an operator of system 10 detects a C2C registration error that may exceed the process specifications of print job 33a in system 10. In response to detecting the suspected C2C registration error, the operator stops print job 33a and controls system 10 to perform one or more test and calibration prints on a non-production sheet having mark 79 described in FIG. 2A above. In some embodiments, system 10 is calibrated to correct the registration problem in the yellow image of image 42, which is indicated by mark 97. The operator then controls system 10 to resume print job 33a. In print job 33a, the position of mark 97 and the distances between marks 97 and 96 and between marks 97 and 98 are within the specifications for print job 33a, as shown by the graphical representation of marks 95-98 printed on the edge of sheet 50 corresponding to side 21.

[0119] In some embodiments, in section 47a of print job 33a, mark 47 indicates the inversion of one or more sheets 50 during duplex printing, such as that described above in Figures 1 and 2A. Similarly, in section 49a of print job 33a, mark 49, which may be printed (additionally or alternatively) on an edge of sheet 50 corresponding to side 41, indicates the inversion of one or more sheets 50.

[0120] In some embodiments, in response to detecting an inversion, processor 20 and / or an operator halts operation of system 10, corrects the problem causing the inversion, and resumes print job 33a. As shown in sections 47b and 49b of print jobs 33a and 33b, after resuming the process, inverted pages have not been transferred to output stack 88 in print jobs 33a and 33b. Furthermore, as shown in sections 49b and 49d, as well as sections 47b and 47d, marks 47 and 49 indicate that sheets 50 are in the correct orientation in output stack 88 and have not been inverted.

[0121] In some embodiments, in sections 47c and 49c of print job 33c, marks 47 and 49 indicate distortion errors in the printed image caused by some rotation of sheet 50 about the Z axis of the XYZ coordinate system. In the example of Figure 2B, the sheet rotation and image distortion errors are graphically represented by sloping lines indicating the offset and drift in the positions of marks 47 and 49.

[0122] In some embodiments, processor 20 is configured to control system 10 to print mixed single-sided (i.e., single-sided) and double-sided (i.e., duplex) lots and / or print jobs as described above in FIG. 1. In some embodiments, processor 20 is configured to determine the location, shape, and size of marks 46-49 to indicate whether a process issue has occurred in such a mixed lot. For example, a configuration of sections 47a and / or 49a may indicate duplex printing, and a configuration of sections 47d and / or 49d may indicate single-sided printing.

[0123] In some embodiments, marks 23c and 25c are skewed, and sections 24d of marks 26 and 27 are also skewed, all of these graphic representations of misaligned marks and / or skewed patterns illustrating the distortion of the position of printed image 42 with respect to each sheet 50, which distortion is caused by the rotation of sheets 50 about the Z axis as described above. Note that in the example of mark 25c, the graphic representation of text (e.g., the letters ABCD) appears skewed in side view of side surface 21.

[0124] In some embodiments, mark 23d indicates an error in the operation of system 10. In this example, during print job 33c, an operator stopped production and performed test and / or calibration prints on some non-production sheets 50, which is indicated by the appearance of mark 79a. The operator then mistakenly selected the recipe to apply print job 33a to paper 50 instead of print job 33d.

[0125] In some embodiments, mark 23e (corresponding to print job 33a) is printed on an edge of sheet 50 corresponding to side 21, also causing a gap 23e in the graphical representation of mark 23d shown on side 21. In response to detecting an operational error, processor 20 and / or an operator stops operation of system 10, performs additional calibration operations as indicated by marks 79b printed on one or more sheets 50, selects the correct recipe, and resumes print job 33d.

[0126] In such an embodiment, a sheet 50 having mark 23f may be added to the stack of print job 33a, and if necessary, the recipe for print job 33d may be applied to the additional sheet 50 to fill the missing sheet 50 indicated by gap 23e in the graphical representation of mark 23d on side 21. Note that in this embodiment, marks 23d, 23f are utilized to conserve waste of sheet 50 and printing fluid that might otherwise be discarded.

[0127] In some embodiments, marks 26 and 27 determined by processor 20 as described in FIG. 2A may be indicative of C2C registration. In this example, section 24b of print job 33a shows a registration error of the yellow image in printed sheet 50 in section 24b. Note that the graphical representation of the distance between marks 26 and 27 shows C2C registration and is independent of other distortions and printing process issues, such as image-to-substrate registration and / or image distortions, as discussed above. For example, in sections 24a, 24c, 24d, and 24e, the C2C registration is within the process specifications of each print job, and the other distortions discussed above do not affect the position of marks 26 and 27 relative to each other.

[0128] In some embodiments, the shape of the letter "C" of mark 25a also indicates a C2C registration error caused by a registration error in the yellow image of image 42 printed on stacked sheets 50 in section 24b.

[0129] In alternative embodiments, characters that graphically represent the positions of marks 25a-25d may be used to indicate other problems in the printing process carried out by system 10. For example, processor 20 may determine the positions of these marks such that local deviations in the graphical representation of one or more characters (or sections thereof) indicate image-to-substrate registration errors (e.g., resulting in blurred or distorted characters or sections thereof) and distortions that appear as slanted words formed by the characters of the marks, as shown, for example, in the position of the character of mark 25c.

[0130] These particular configurations of marks shown in Figures 2A and 2B are shown and described as examples to illustrate particular problems addressed by embodiments of the present invention, such as detection of process problems, image distortions, equipment failures and operational errors, and to demonstrate the application of these embodiments in improving the performance of such digital printing systems. However, embodiments of the present invention are in no way limited to this particular type of exemplary problem and mark, and the principles described herein may be similarly applied to other types of problems and distortions in printing images using system 10, or in other printing systems utilizing one or more intermediate transfer components of any suitable type for direct printing or printing applications in printing systems of various configurations known in the art. Additionally, the size, shape, position, color, and other attributes of the marks may be determined to indicate any particular type(s) of process problem(s) and / or defects and / or distortions that may occur during any suitable type of printing process.

[0131] 2A and 2B may be used in conjunction with additional tools to detect distortions in images printed by system 10. For example, processor 20 and / or an operator may be configured to use information received from image quality control station 55 in conjunction with an analysis of the graphical representations of the marks shown in FIGS.

[0132] FIG. 3 is a flow chart that generally illustrates a method for identifying printing and distortion problems in an image 42 printed on a sheet 50 using the marks of FIGS. 2A and 2B, in accordance with one embodiment of the present invention.

[0133] The method begins with an image receiving step 100 in which processor 20 receives (i) a plurality of product images, such as image 42, intended to be printed on each of a plurality of sheets 50, and (ii) one or more marks intended to be printed on an edge of sheet 50 (e.g., an edge corresponding to side 21), as described in Figures 1 and 2 above.

[0134] In a printing step 102, processor 20 controls one or more printing assemblies of system 10 to (i) print product images 42 on a predetermined number of sheets 50 and (ii) print indicia on the edges of one or more of the sheets, as described in detail in FIGS. 1, 2A, and 2B.

[0135] In a stacking step 104, the processor 20 controls the stacking assembly 59 to stack the printed sheets 50 into an output stack 88 having sides 21, 31, 41, and 51. In some embodiments, marks printed on the edges of the sheets 50 are visible in a side view of one or more sides (e.g., side 21) of the output stack 88.

[0136] In some embodiments, when multiple sheets 50 are stacked on top of each other in output stack 88, the marks may collectively form a pattern having a graphical representation of a problem that occurred while printing image 42. In some cases, the problem may be caused by selecting an incorrect print job such that the printed image, while not distorted, is positioned in the wrong position in output stack 88, as shown, for example, by mark 23f in FIG.

[0137] Additionally or alternatively, the marks may indicate one or more distortions in one or more images 42 printed on each sheet 50, as described in detail in FIG. 2B.

[0138] In a review step 106, an operator of the system 10 reviews at least a portion of one or more sides (e.g., side 21) of the output stack 88 in a side view as depicted in Figures 2A and 2B. The sheets 50 in the output stack 88 have (i) a plurality of images 42 printed on each of the plurality of sheets 50, and (ii) marks printed on at least an edge of (at least some, typically all) of the sheets 50. The edge of each sheet 50 corresponds to a side 21, and the marks visible on the side 21 collectively form a graphical representation, as depicted in step 104 and in Figures 2A and 2B. Additionally or alternatively, the processor 20 may receive (e.g., from a suitable camera or inspection system) a side view image of the side 21 of the output stack 88 as depicted in Figure 2A.

[0139] In a side view image analysis step 108, the operator and / or processor 20 may check, based on the marks shown on side 21, whether the graphical representation indicates one or more problems that occurred during printing of one or more images 42 on each of one or more sheets 50. In some cases, the graphical representation on side 21 of output stack 88 indicates distortions in one or more images 42 printed on each sheet 50, as described in detail in Figures 2A and 2B.

[0140] In some embodiments, steps 106 and 108 may be performed after all print jobs shown in FIGS. 2A and 2B (eg, print jobs 33a-33d) have been completed.

[0141] In other embodiments, steps 106 and 108 may be performed while printing marks on image 42 on sheet 50 and on an edge of sheet 50 that corresponds to side 21 (and optionally other sides) of output stack 88, as illustrated in Figures 2A and 2B.

[0142] If step 108 identifies one or more problems, the method proceeds to corrective action step 110, where corrective action is applied to system 10 to eliminate or reduce the identified problem(s), as described in FIG. 2B.

[0143] In some embodiments, if steps 106 and 108 have been performed after finishing all print jobs (eg, print jobs 33a, 33b, 33c, and 33d), step 110 ends the method.

[0144] In other embodiments, if steps 106, 108 and 110 are performed while printing the image 42 on the sheet 50 and printing the mark on the edge of the sheet 50 corresponding to the side 21 of the output stack 88, the method loops back to step 102 according to the following embodiment. In some embodiments, if no distortion and / or process problem is identified in step 108, the method loops back to step 102 to resume the printing process of the product image 42 on each sheet 50 according to the process recipe of each print job (e.g., print job 33d). Furthermore, after applying the corrective action of step 110, the method loops back to step 102 to resume each print job as described in FIG. 2B. Thus, the loopback arrow between steps 110 and 102 is optional and depends on whether the operating mode of identifying the problem is performed during the printing process as described in FIGS. 2A and 2B or after the printing process of print jobs 33a-33d is finished.

[0145] In an alternative embodiment, prior to step 102 (e.g., during or before step 100), processor 20 is configured to define one or more characteristics of one or more of the marks intended to be printed on the edge(s) of sheet 50. The one or more characteristics may depend on one or more variables, such as, but not limited to, (i) the image intended to be printed, (ii) the configuration of system 10, (iii) the type of substrate (e.g., sheet or continuous web), (iv) the printing fluid intended to be applied to blanket 44, and (v) parameters of the intended printing process.

[0146] In such embodiments, the characteristics may include at least one of: (i) a position of the one or more marks in a side view (e.g., of side 21); (ii) a size of the one or more marks in a side view (e.g., along the X-axis and / or Y-axis of side 21, as shown in Figures 2A and 2B); and (iii) a color of the one or more marks shown in a side view (e.g., of side 21).

[0147] Although the embodiments described herein primarily address digital printing using flexible intermediate transfer members, the methods and systems described herein may be used in other applications, such as any type of printing system and process that applies droplets of ink directly or indirectly to any suitable type of target substrate, including, but not limited to, (i) paper sheets, (ii) folding cartons, (iii) multi-layer polymers, and (iv) continuous webs.

[0148] Thus, the above embodiments are cited by way of example, and it will be understood that the present invention is not limited to what has been particularly shown and described above. Rather, the scope of the present invention includes both combinations and subcombinations of the various features described above, as well as variations and modifications thereof not disclosed in the prior art that would occur to one skilled in the art upon reading the foregoing description. Documents incorporated by reference into this patent application are to be considered an integral part of this application, except that to the extent that any term is defined in these incorporated documents in a manner that is inconsistent with a definition made expressly or impliedly within this specification, only the definition in this specification shall be considered.

Claims

1. 1. A system comprising: a printing assembly configured to (i) print a plurality of images on each of a plurality of substrates, and (ii) print a plurality of marks on one or more edges of each of the plurality of substrates; a stacking assembly configured to stack each of the plurality of substrates on top of one another to form a stack having a top surface parallel to one or more of the substrates and a side surface formed from the stacked edges of the substrates; Equipped with one or more of the marks are visible in a side view of at least a given one of the sides; At least the location of one or more of the marks in a side view of the given side indicates a problem that occurred during printing of one or more of the plurality of images.

2. 2. The system of claim 1, wherein the image includes a first image and a second image, the mark includes a first mark and a second mark, and the substrate includes a first substrate and a second substrate, respectively; (i) on the first substrate, the first image is printed in an intended position and the first mark is printed at a first edge position of a given one of the edges; and (ii) on the second substrate, the second image is printed at an actual position and the second mark is printed on the given edge at a second edge position.

3. 3. The system of claim 2, wherein the problem includes an offset between the intended position and the actual position, and wherein in a side view image, a difference between the first edge position and the second edge position indicates the offset between the actual position and the intended position.

4. 3. The system of claim 2, wherein the first image includes a first color image of a first color and a second color image of a second color different from the first color, the first marks include (i) a first color mark associated with the first color image and located at a first color location, and (ii) a second color mark associated with the second color image and located at a second color location different from the first color location, the problem includes a registration error between the first color image and the second color image, and in a side view image, a distance between the first color location and the second color location indicates the registration error between the first color image and the second color image.

5. 3. The system of claim 2, wherein the problem includes movement of the second substrate relative to the second image, and a difference between the first edge position and the second edge position in a side view image indicates the movement.

6. 6. The system of claim 5, wherein said moving comprises rotating said second substrate about an axis perpendicular to said top surface.

7. 3. The system of claim 2, wherein the first image is printed on the first substrate using a first print job and the second image is intended to be printed on the second substrate using a second print job different from the first print job, and the problem includes a motion error using the first print job to print the second image on the second substrate, and a difference between the first edge position and the second edge position indicates the motion error.

8. 8. The system of claim 1, comprising a processor configured to receive a side view image of the side view and to identify the problem based on at least a position of the one or more marks in the side view image.

9. 9. The system of claim 8, wherein prior to printing the plurality of marks, the processor is configured to define one or more characteristics of the plurality of marks intended to be printed on the one or more edges.

10. 10. The system of claim 9, wherein the one or more characteristics include at least one of: (i) a position of the one or more marks in the side view; (ii) a size of the one or more marks in the side view; and (iii) a color of the one or more marks in the side view.

11. 8. The system of claim 1, wherein at least one of the marks comprises a machine-readable label (MRL), the MRL configured to include information about at least one of: (i) one or more characteristics of at least one of the substrates; (ii) one or more characteristics of at least one of the images; (iii) one or more characteristics of at least one of the marks; (iv) the one or more characteristics of the problem; and (v) one or more control characteristics of at least a portion of the stack.

12. 1. A method comprising: (i) printing a plurality of images onto each of a plurality of substrates; and (ii) printing a plurality of marks on one or more edges of each of the plurality of substrates; a stacking step of stacking each of the plurality of substrates on top of one another to form a stack having a top surface parallel to one or more of the substrates and side surfaces formed from the stacked edges of the substrates, wherein one or more of the marks are visible in a side view of at least a given one of the side surfaces; and identifying a problem that occurred while printing one or more of the plurality of images based on at least a position of the one or more marks in a side view of the given side, the position being indicative of the problem; A method comprising:

13. 13. The method of claim 12, wherein the image includes a first image and a second image, the mark includes a first mark and a second mark, and the substrates include a first substrate and a second substrate, respectively; and wherein (i) on the first substrate, the first image is printed in an intended position and the first mark is printed at a first edge position of a given one of the edges, and (ii) on the second substrate, the second image is printed at an actual position and the second mark is printed at the given edge at a second edge position.

14. 14. The method of claim 13, wherein the step of identifying the problem comprises: (i) identifying an offset between the intended position and the actual position, wherein a difference between the first edge position and the second edge position in a side view image indicates the offset between the actual position and the intended position; and (ii) identifying a movement of the second substrate relative to the second image, wherein a difference between the first edge position and the second edge position in a side view image indicates the movement; A method selected from the following.

15. 14. The method of claim 13, wherein printing the first image includes printing a first color image in a first color and a second color image in a second color different from the first color; printing the first mark includes printing (i) a first color mark associated with the first color image and located at a first color position, and (ii) a second color mark associated with the second color image and located at a second color position different from the first color position; and identifying the problem includes identifying a registration error between the first color image and the second color image, wherein a distance between the first color position and the second color image in a side view image indicates a registration error between the first color image and the second color image.

Images