Patent Publication Number: US-11040528-B2

Title: Integration of a line-scan camera on a single pass inkjet printer

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is a continuation of U.S. patent application Ser. No. 15/603,304 filed on May 23, 2017, now U.S. Pat. No. 10,513,110, issued on Dec. 24, 2019, which is a continuation-in-part of U.S. patent application Ser. No. 14/304,824 filed on Jun. 13, 2014, now U.S. Pat. No. 9,914,309, issued on Mar. 13, 2018, and claims priority to U.S. Provisional Patent Application No. 62/340,984, filed May 24, 2016, each of which are incorporated herein in their entirety by this reference thereto. 
    
    
     TECHNICAL FIELD 
     Techniques disclosed concern single pass inkjet printers. More specifically, techniques disclosed pertain to imaging of the output of single pass inkjet printers and printer actions enabled by imaging techniques. 
     BACKGROUND 
     Inspection of printers and printer output, especially of industrial printers, is performed requiring notable manual labor. Likewise, cameras or scanners are used to assist in printer set up, but these operations typically do not occur inline during regular production. 
     Presently, line-scan cameras are used on web presses. Web presses operate on large rolls of paper that spool forward (out) and backward (in). The line-scan cameras record the paper roll as it spools out. Once complete, the paper roll is removed and taken to another apparatus known as a re-winder. The re-winder unwinds the paper roll in a play-back inspection to the location of a recorded defect and then enables a human operator to cut out the bad section, re-splice. This process is repeated for each recorded error in the roll. 
     SUMMARY 
     Embodiments of the invention incorporate an in-line camera on single-pass inkjet printing presses that inspects sheets for quality assurance purposes. The inspection results are tied back to a digital printer to take one or more of several possible actions without operator intervention. A first action could include coordination between system software and a stacker to divert printer output that fails a quality criterion into a reject stream. In this manner, a user requests a particular number of acceptable outputs, and the stacker sorts between acceptable and rejected sheets. Extras acceptable sheets are not printed and therefore wasted. The sorting occurs without stopping the printer or with human intervention. 
     A second action could include causing corrective action that reduces or eliminates defects without stopping. For example, corrective action includes nozzle adjustments. A third action, relating to severe defects, or repeating defects that occur on successive sheets, that require more intensive corrective action, could cause the printer to pause or stop, perform repairs (perhaps automatically) and then resume printing. 
     The above line-scan camera, and the correction actions the camera enables may additionally be integrated into a network, or web-based printer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       One or more embodiments of the present disclosure are illustrated by way of example and not limitation in the figures of the accompanying drawings, in which like references indicate similar elements. 
         FIG. 1  is a schematic diagram illustrating logical process blocks pertaining to a line-scan camera integrated into a single pass inkjet printer. 
         FIG. 2  is an illustration of a single-pass inkjet printer with an integrated line-scan camera. 
         FIG. 3  is a flowchart illustrating a process of operation for a single-pass inkjet printer with a line-scan camera. 
         FIG. 4  is an illustration of a line-scan module for an industrial single-pass inkjet printer. 
         FIG. 5  is a flowchart illustrating a process of a first applied correction for a single-pass inkjet printer with a line-scan camera. 
         FIG. 6  is a flowchart illustrating a process of a second applied correction for a single-pass inkjet printer with a line-scan camera. 
         FIG. 7  is a flowchart illustrating a process of a third applied correction for a single-pass inkjet printer with a line-scan camera. 
         FIG. 8  shows a print head mounting bar subassembly according to the invention. 
         FIG. 9  shows a diagrammatic representation of a machine in the example form of a computer system within which a set of instructions for causing the machine to perform one or more of the methodologies discussed herein may be executed. 
     
    
    
     Those skilled in the art will appreciate that the logic and process steps illustrated in the various flow diagrams discussed below may be altered in a variety of ways. For example, the order of the logic may be rearranged, sub-steps may be performed in parallel, illustrated logic may be omitted, other logic may be included, etc. One will recognize that certain steps may be consolidated into a single step and that actions represented by a single step may be alternatively represented as a collection of sub-steps. The figures are designed to make the disclosed concepts more comprehensible to a human reader. Those skilled in the art will appreciate that actual data structures used to store this information may differ from the figures and/or tables shown, in that they, for example, may be organized in a different manner; may contain more or less information than shown; may be compressed, scrambled and/or encrypted; etc. 
     DETAILED DESCRIPTION 
     Various example embodiments will now be described. The following description provides certain specific details for a thorough understanding and enabling description of these examples. One skilled in the relevant technology will understand, however, that some of the disclosed embodiments may be practiced without many of these details. 
     Likewise, one skilled in the relevant technology will also understand that some of the embodiments may include many other obvious features not described in detail herein. Additionally, some well-known structures or functions may not be shown or described in detail below, to avoid unnecessarily obscuring the relevant descriptions of the various examples. 
     The terminology used below is to be interpreted in its broadest reasonable manner, even though it is being used in conjunction with a detailed description of certain specific examples of the embodiments. Indeed, certain terms may even be emphasized below; however, any terminology intended to be interpreted in any restricted manner will be overtly and specifically defined as such in this Detailed Description section. 
       FIG. 1  is a schematic diagram illustrating logical process blocks pertaining to control of a line-scan camera integrated into a single pass inkjet printer. Central to the control process is the system software  102 . This system software may reside in one or more computing elements, including but not limited to a computer dedicated to the printing operation, a computer dedicated to the scanning operation, a programmable logic controller (PLC) for controlling the system, the image processor, or in a computing element that is shared across several of these functions. The line-scanner  104  provides input to the system software  102 . By incorporating a vision system into the printer, embodiments of the invention maximize productivity and uptime of the product and optimize the printed output in a largely-automated fashion. For example, in a printer with a 100 or more print heads, manually measuring and adjusting each print head would be very time consuming and arduous. Likewise, to maximize uptime, it is necessary to have a ready response to nozzle drop outs. It is also important to detect missing nozzles during the production and compensate without losing notable productivity. 
     The line-scan camera  104  receives input from scans of the production prints  106 , and likewise from the scans of diagnostic targets  108  that are not specifically part of a production order. Diagnostic targets  108  include specially designed targets that are printed in addition to or alongside of the production prints; these targets are designed in a way to highlight aspects of printer performance such as nozzle jetting performance, print head alignments, density uniformity, etc. After the line-scanner  104  transmits the scan results to the printer SW  102 , the system software is enabled to execute a number of actions. 
     System software  102  coordinates the disposition of printer sheets as each leaves the production line onto a stacker  110 . Equipped with the scan results, the print software  102  compares the scan to a reference of what the printer expects each print sheet to look like. The system software  102  makes a determination to accept or reject the print sheet. The determination is based off a threshold of errors. The stacker directs rejected print sheets to a rejected sheet repository, while accepted sheets are placed in a completed work repository. In this manner, a user does not have to sort reject print sheets out of the final printer output before initiating further use of the printer output. 
     System software  102  further coordinates with image processing  112  when comparing scan results to the reference specification/master image and can effect changes to the master image or processing of the image for printing. Coordinating with the printer electronics  114  and heads  116  enables nozzle and print head adjustments. Finally, coordinating with the production line  118  enables the printer to pause or shut down to effect repairs or make other adjustments during the production run. 
       FIG. 2  is an illustration of a single-pass inkjet printer with an integrated line-scan camera. The illustrated printer  200  is for industrial use. The printer  200  includes a production line  202  including a conveyor system (in this case, left to right) for propelling sheets along through the printer  200 . On the left side of the production line  202  is the sheet bay  204  from which the production line  202  draws sheets. On the far right side of the production line  202  is a stacker  206 . The stacker  206  directs printed sheets to reject or accept repositories. 
     In the center of the production line  202  is the single-pass inkjet  208 . The inkjet depicted includes 7 inks, though in various embodiments of a single-pass inkjet a number of ink colors may be selected. The particular inkjet  208  pictured includes a number of bays to insert various inks. As sheets pass below the inkjet  208  (a single time), the nozzles of the print head apply ink to the sheets. 
     To the right side of the inkjet  208 , is a line-scan camera  210 , mounted in an adjacent bay. A number of methods may be employed in order to mount the line-scan camera, though it is merely relevant that the line-scan camera  210  have coverage across an axis perpendicular to the major axis of the production line  202 . The line-scan camera  210  communicates scan results directly to a control processing device (not pictured). The control processing device directs the functions of all the printer hardware. 
     As an example of function of the line-scan camera, a user may request 1000 sheets printed of a given design. The end result, without additional human intervention, will be 1000 matching prints in an acceptable pile as directed by the stacker  206 . The stacker  206  places the prints containing errors in a reject pile, and the processor does not count those prints with respect to the  1000  requested prints. 
     This process differs from presently used methods where users often work in an average printer error rate to their requested print count. For example, the user would request 1100 prints, and hope that 1000 of those were acceptable. The user would partake in a time consuming process to sort the 1100 print by hand in order to remove the error prints. The user doesn&#39;t actually know if 1000 of those sheets include errors. It is possible that merely 10 of those would contain errors, then there are 90 extras. Use of a line-scan camera prevents this sort of waste. 
       FIG. 3  is a flowchart illustrating a process of operation for a single-pass inkjet printer with a line-scan camera. In step  302 , the production line draws a sheet on to the conveyor. In step  304 , the production line moves the sheet along the production line towards and through the single-pass inkjet. In step  306 , the printer applies ink to the sheet. In step  308 , the production line continues to propel the sheet through the line-scan camera. In step  310 , the line-scan camera scans the printed sheet. 
     In step  312 , the line-scan camera transmits the scan of the printed sheet to a control device. The control device may be a computer connected to the printer physically, or through a wireless connection. In step  314 , the control device evaluates the scan and issues a command to the printer hardware based upon the evaluation. 
       FIG. 4  is an illustration of a line-scan module  400  for an industrial single-pass inkjet printer. In some embodiments, the line-scan printer camera  402  is installed in a module that is mounted with the inkjet. The line-scan module  400  has similar mounting procedures as the inkjet print heads. The mechanical mounting interface  404  used to secure components being bonded is constructed so as to not impart preload forces that cause dimensional changes after being removed from the fixture. Ideally, the mounting mechanism  404  is common to both the fixture and the printer to eliminate, or reduce, the potential for additional position errors beyond the as-built accuracy of the fixture itself. 
     The mounting mechanism  404  provides a rigid and repeatable positioning of the connecting bodies that is also able to be disassembled. Exact constraint principles provide many possible solutions for designing a three dimensional connection mechanism between objects. One example of this is a kinematic coupling consisting of three rigidly mounted spheres that nest respectively against a rigidly mounted trihedral cup, vee cup, and a flat. This provides exact constraint between the two connecting bodies. That is to say, all six degrees of freedom are constrained with exactly six points of contact. 
     By mounting the integrated line-scan camera and print heads using the same mounting design, and including independent adjustment of both the print heads and integrated line-scan camera, allows for alignment to the varying media height throughout the entire length of the print area. 
     Further depicted in the figure is an umbilical chain  406 , that enables the line-scan camera  402  to easily slide away from the production line while maintaining electrical and communicative connections to the rest of the printer hardware. While the line-scan camera  402  is pulled away from the production line, a user may examine the hardware and perform adjustments or maintenance that may be necessary. 
       FIG. 5  is a flowchart illustrating a process of a first applied action for a single-pass inkjet printer with a line-scan camera. In step  502 , the control device compares received printed sheet scans to a reference. The reference may be a specification file or a model (ideal) image of a printed sheet. The comparison uses a threshold in or to evaluate the comparison for one or more attributes deemed to be important for this print job. At a predetermined number or magnitude of variances from the reference, the printed sheet will fail the comparison. Ensuring acceptable quality through 100% inspection ensures that there is good print quality throughout an entire production run. 
     In step  504 , the control device determines whether or not the threshold has been exceeded. Where the threshold is exceeded, in step  506 , the control device directs the stacker to sort the printed sheet into a rejected repository. Conversely, where the threshold is not exceeded, in step  508 , the control device directs the stacker to sort the printed sheet into an acceptable pile. In step  510 , the control device reduces the count of print copies remaining by one. Thus, the print count is only reduced when the error threshold is not exceeded. In step  512 , if the print request count contains more copies, the method repeats with the next printed sheet on the production line. 
       FIG. 6  is a flowchart illustrating a process of a second applied correction for a single-pass inkjet printer with a line-scan camera. The scanner can be used to read specially designed targets to optimize print quality. For example, the scanner can detect missing nozzles and effect nozzle compensation. The control device is able to measure color uniformity and effect compensations at the heads or in the raster image processor based on the sheet scans. The scanner can detect printer errors and the control device can affect automatic adjustments or report back to the operator what adjustments should be made. Importantly, these targets can be printed separately from the normal production run (on a dedicated sheet, for example) or can be imbedded (in the margins, for example) of the actual production run to get continuous feedback on these different performance attributes. 
     One of the actions is to identify nozzles that are not printing. In step  602 , the control device directs the printer to print diagnostic targets into unused margins of sheets. The line-scan camera scans the artwork from a print request and the margin where diagnostic target for a nozzle check are printed. 
     In step  604 , the control device analyzes the nozzle check samples. In some embodiments, an entire nozzle check does not fit into the margins of a single sheet, but over the course of multiple sheets (e.g., 5-10) the control device, through the line-scan camera is able to sample every nozzle of the inkjet. This step is performed with a comparison to a diagnostic target reference. The diagnostic target reference may be a model image or a specification file describing expected features of the diagnostic target. In step  606 , the control device evaluates the scans for printer performance issues. Such issues include identifying nozzle jetting issues from a malfunction or lack of ink, printer alignment, or uniformity of density produced by print heads. 
     In step  608 , the control device effects an operations change. An example of such an operations change would include applying a compensation algorithm. In real time, the printer can compensate for a nozzle that was detected missing, alter ink mixtures to compensate for missing inks, adjust to compensate for alignment, or to compensate for discrepancy in print head density all without shut-down or human intervention. 
       FIG. 7  is a flowchart illustrating a process of a third applied correction for a single-pass inkjet printer with a line-scan camera. In step  702 , the control device analyzes a first printed sheet scan for errors. This process occurs similarly as described in  FIG. 5  and the associated text. In step  704 , the control device compares the analysis of the prior step ( 702 ) to previous comparisons. This generates a recent history of errors. In step  706 , the control device evaluates for consistent issues. For example, if 10 sheets in a row include an inadvertent ink drip in the middle of the print, there is a consistent issue. It is unlikely that further printed sheets will suddenly no longer exhibit the issue and the printer can be directed by the system software to take some type of corrective action. 
     In step  708 , where a consistent issue is identified, the control device may trigger the printer press to stop in order to enable the operator to perform corrective action. Upon printer stoppage, the printer may send the operator an error message indicating the reason for the stoppage to better facilitate repairs. Alternatively, there may be actions the press can take automatically, for example, cleaning of one or more of the print heads. Otherwise, in step  710 , where there are no continuous errors and more sheets to print, the analysis continues unabated. 
       FIG. 8  shows a print head mounting bar subassembly according to the invention. The figure displays a mounting bar  802  including multiple parallel line-scan cameras  804 A,  804 B. It is unnecessary for a single line-scan camera to cover the width of the production line. Multiple scans of multiple line-scan cameras may be pasted together for analysis by the control device. 
     Computer System 
       FIG. 9  shows a diagrammatic representation of a machine in the example form of a computer system  900  within which a set of instructions for causing the machine to perform one or more of the methodologies discussed herein may be executed. 
     The computer system  900  may act as a control device in this disclosed and includes a processor  902 , a main memory  904 , and a static memory  906 , which communicate with each other via a bus  908 . The computer system  900  also includes an output interface  914 ; for example, a USB interface, a network interface, or electrical signal connections and/or contacts; 
     The disk drive unit  916  includes a machine-readable medium  918  upon which is stored a set of executable instructions, i.e., software  920 , embodying any one, or all, of the methodologies described herein. The software  920  is also shown to reside, completely or at least partially, within the main memory  904  and/or within the processor  902 . The software  920  may further be transmitted or received over a network by means of a network interface device  1214 . 
     In contrast to the system  900  discussed above, a different embodiment uses logic circuitry instead of computer-executed instructions to implement processing entities. Depending upon the particular requirements of the application in the areas of speed, expense, tooling costs, and the like, this logic may be implemented by constructing an application-specific integrated circuit (ASIC) having thousands of tiny integrated transistors. Such an ASIC may be implemented with CMOS (complementary metal oxide semiconductor), TTL (transistor-transistor logic), VLSI (very large systems integration), or another suitable construction. Other alternatives include a digital signal processing chip (DSP), discrete circuitry (such as resistors, capacitors, diodes, inductors, and transistors), field programmable gate array (FPGA), programmable logic array (PLA), programmable logic device (PLD), and the like. 
     It is to be understood that embodiments may be used as or to support software programs or software modules executed upon some form of processing core (such as the CPU of a computer) or otherwise implemented or realized upon or within a system or computer readable medium. A machine-readable medium includes any mechanism for storing or transmitting information in a form readable by a machine, e.g., a computer. For example, a machine-readable medium includes read-only memory (ROM); random access memory (RAM); magnetic disk storage media; optical storage media; flash memory devices; electrical, optical, acoustical or other form of propagated signals such as carrier waves, infrared signals, digital signals, etc.; or any other type of media suitable for storing or transmitting information. 
     Further, it is to be understood that embodiments may include performing operations and using storage with cloud computing. For the purposes of discussion herein, cloud computing may mean executing algorithms on any network that is accessible by internet-enabled or network-enabled devices, servers, or clients and that do not require complex hardware configurations (e.g., requiring cables and complex software configurations, or requiring a consultant to install). For example, embodiments may provide one or more cloud computing solutions that enable users, e.g., users on the go, to access real-time video delivery on such internet-enabled or other network-enabled devices, servers, or clients in accordance with embodiments herein. It further should be appreciated that one or more cloud computing embodiments include real-time video delivery using mobile devices, tablets, and the like, as such devices are becoming standard consumer devices. 
     The described embodiments are susceptible to various modifications and alternative forms, and specific examples thereof have been shown by way of example in the drawings and are herein described in detail. It should be understood, however, that the described embodiments are not to be limited to the particular forms or methods disclosed, but to the contrary, the present disclosure is to cover all modifications, equivalents, and alternatives.