Patent Application
20240239115
This disclosure is directed to printers that print documents containing security features and, more particularly, to the printing of the security features so they are not humanly perceptible.
Inkjet imaging devices eject liquid ink from printheads to form images on an image receiving surface. The printheads include a plurality of inkjets that are arranged in some type of array. Each inkjet has a thermal or piezoelectric actuator that is coupled to a printhead driver. The printhead controller generates firing signals that correspond to digital data for images. Actuators in the printheads respond to the firing signals by expanding into an ink chamber to eject ink drops onto an image receiving member and form an ink image that corresponds to the digital image used to generate the firing signals.
Security features are elements printed in a document that are not part of the ink image content data for a document. As used in this document, the term “ink image content data” means digital data that identifies a color and a volume of each ejected ink drop that forms pixels in a humanly perceptible ink image to be printed on a media sheet. A security feature typically appears in the original of a printed when viewed under certain predetermined lighting conditions but they do not appear in a copy under those same lighting conditions. These security features permit a holder of a printed document to determine whether they possess an original document or a copy Printing documents with security features is a popular anti-counterfeiting and anti-forging method that protects valuable documents, such as prescriptions and concert tickets.
Typically, security features are added to the ink image content data for a document to be printed and are formed with drops of ink that are different than the inks used to form the ink image of the document produced using the ink image content data. The inks used for the security features usually have glosses or infrared properties that differ from the inks used to print the humanly perceptible content of a document. Thus, these types of security features require additional reservoirs and printheads for the special inks used to form the security features. Being able to form security features with the inks typically used to form humanly perceptible content of a document without making the security features discernible in the original would be beneficial.
A new method of operating an inkjet printer forms security marks with the inks typically used to form humanly perceptible content of a document without making the security features discernible. The method includes printing a line target in an ink image of the original document on media with at least one printhead that has been rotated so rows of inkjets in the at least one printhead are not aligned in a direction of movement during printing of the line target; generating an expected frequency response of the line target; generating image data of a document; generating a frequency response of the line target in the image data of the document; and identifying the document as the original document when the frequency response of the line target in the image data of the document equals the expected frequency response of the line target.
A new inkjet printer forms security marks with the inks typically used to form humanly perceptible content of a document without making the security features discernible. The inkjet printer includes a media transport configured to carry media sheets through the inkjet printer; at least one printhead that has been rotated so rows of inkjets in the at least one printhead are not aligned in a direction of movement during printing of the line target and the at least one printhead is configured to eject ink drops onto the media sheets; a controller operatively connected to the at least one printhead. The controller is configured to: print a line target in an ink image of an original document on media with the at least one printhead; generate an expected frequency response of the line target; generate image data of a document; generate a frequency response of the line target in the image data of the document; and identify the document as the original document when the frequency response of the line target in the image data of the document equals the expected frequency response of the line target.
Another new method of operating an inkjet printer forms security marks with the inks typically used to form humanly perceptible content of a document without making the security features discernible. The method includes generating a sneeze pattern having a plurality of color separations; modifying a portion of the sneeze pattern by altering positions of pixels within the generated sneeze pattern; printing the original document with the sneeze pattern having the modified portion in the background of the original document; generating image data of a document; and identifying the document as the original document when the modified portion of the generated sneeze pattern is detected in the background of the document.
Another new inkjet printer forms security marks with the inks typically used to form humanly perceptible content of a document without making the security features discernible. The inkjet printer includes a media transport configured to carry media sheets through the inkjet printer; at least one printhead configured to eject ink drops onto the media sheets as the media sheets pass the at least one printhead; a controller operatively connected to the at least one printhead. The controller is configured to: generate a sneeze pattern having a plurality of color separations; modify a portion of the sneeze pattern by altering positions of pixels within the generated sneeze pattern; print an original document with the sneeze pattern having the modified portion in a background of the original document; generate image data of a document; and identify the document as the original document when the modified portion of the generated sneeze pattern is detected in the background of the document.
The foregoing aspects and other features of an inkjet printer and its method of operation to form security marks with the inks typically used to form humanly perceptible content of a document without making the security features discernible are explained in the following description, taken in connection with the accompanying drawings.
For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, reference is made to the drawings. In the drawings, like reference numerals have been used throughout to designate like elements. As used herein, the word “inkjet printer” encompasses any apparatus that produces ink images on media by operating inkjets in printheads to eject drops of ink toward the media. As used herein, the term “process direction” refers to a direction of travel of an image receiving surface, such as an imaging drum or print media, and the term “cross-process direction” is a direction that is substantially perpendicular to the process direction along the surface of the image receiving surface. Also, a reader of the description presented below that is directed to a system for operating inkjets in an inkjet printer should appreciate that the principles set forth in this description are applicable to similar imaging devices that generate images with pixels of other types of marking material.
The printer and method described below form security marks with the inks typically used to form humanly perceptible content of a document without making the security features discernible. By rotating the printheads about an axis perpendicular to the faceplate of the printhead by a small amount and printing a line target in the image content of the document, a security feature is formed that is detectable from a Fourier transform of the document. The reason that the security feature is not reproduced in a copy of the document is that the copying device quantizes the positions of the pixels in the copy so the security feature does not produce the same frequency response. The only way that the copier can reproduce the security feature is to replicate the rotation of the printheads that produced the original security feature in the copying device. Thus, a very small risk exists that a security feature so produced can be reproduced in a copy.
As shown in
A duplex path 72 is provided to receive a sheet from the transport system 42 after a substrate has been printed and move it by the rotation of rollers in an opposite direction to the direction of movement past the printheads. At position 76 in the duplex path 72, the substrate can be turned over so it can merge into the job stream being carried by the media transport system 42. The controller 80 is configured to flip the sheet selectively. That is, the controller 80 can operate actuators to turn the sheet over so the reverse side of the sheet can be printed or it can operate actuators so the sheet is returned to the transport path without turning over the sheet so the printed side of the sheet can be printed again. Movement of pivoting member 88 provides access to the duplex path 72. Rotation of pivoting member 88 is controlled by controller 80 selectively operating an actuator 40 operatively connected to the pivoting member 88. When pivoting member 88 is rotated counterclockwise, a substrate from media transport 42 is diverted to the duplex path 72. Rotating the pivoting member 88 in the clockwise direction from the diverting position closes access to the duplex path 72 so substrates on the media transport move to the receptacle 56. Another pivoting member 86 is positioned between position 76 in the duplex path 72 and the media transport 42. When controller 80 operates an actuator to rotate pivoting member 86 in the counterclockwise direction, a substrate from the duplex path 72 merges into the job stream on media transport 42. Rotating the pivoting member 86 in the clockwise direction closes the duplex path access to the media transport 42.
As further shown in
Operation and control of the various subsystems, components and functions of the machine or printer 10 are performed with the aid of a controller or electronic subsystem (ESS) 80. The ESS or controller 80 is operatively connected to the components of the printhead modules 34A-34D (and thus the printheads), the actuators 40, and the dryer 30. The ESS or controller 80, for example, is a self-contained computer having a central processor unit (CPU) with electronic data storage, and a display or user interface (UI) 50. The ESS or controller 80, for example, includes a sensor input and control circuit as well as a pixel placement and control circuit. In addition, the CPU reads, captures, prepares, and manages the image data flow between image input sources, such as a scanning system or an online or a work station connection (not shown), and the printhead modules 34A-34D. As such, the ESS or controller 80 is the main multi-tasking processor for operating and controlling all of the other machine subsystems and functions, including the printing process.
The controller 80 can be implemented with general or specialized programmable processors that execute programmed instructions. The instructions and data required to perform the programmed functions can be stored in memory associated with the processors or controllers. The processors, their memories, and interface circuitry configure the controllers to perform the operations described below. These components can be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits can be implemented with a separate processor or multiple circuits can be implemented on the same processor. Alternatively, the circuits can be implemented with discrete components or circuits provided in very large scale integrated (VLSI) circuits. Also, the circuits described herein can be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits.
In operation, image content data for an image to be produced are sent to the controller 80 from either a scanning system or an online or work station connection for processing and generation of the printhead control signals output to the printhead modules 34A-34D. Additionally, a previously known process generates a uniform sneeze pattern that is also printed in the image area of the media sheet. Along with the image content data, the controller receives print job parameters that identify the media weight, media dimensions, print speed, media type, ink area coverage to be produced on each side of each sheet, location of the image to be produced on each side of each sheet, media color, media fiber orientation for fibrous media, print zone temperature and humidity, media moisture content, and media manufacturer. As used in this document, the term “print job parameters” means non-image content data for a print job and the term “image content data” means digital data that identifies an ink image containing the image content and the sneeze pattern to be printed on a media sheet.
The print zone PZ in the printer 10 of
Printheads in inkjet printers are formed with multiple rows that span at least several millimeters. In order to have equal 1200 dot per inch (dpi) spacing between adjacent pixels in a cross-process line, the printheads must be properly set about the axis through the printhead and perpendicular to the faceplate of the printhead as noted above. Methods that operate the motors connected to the printheads, such as motors 412 in
In a printer that has had the printheads of each printhead module intentionally rotated by the same amount, the location of the pixels vary from the positions where they would have landed if the printheads had been rotated to eject the pixels in a straight line across the cross-process direction. Since the printheads are formed with multiple rows of inkjets that extend in the cross-process when aligned in the cross-process direction, the signature of the pixels formed by the printheads intentionally rotated out of cross-process direction alignment provides a known frequency response of the signature. Deviations from a best fit line of the pixel positions can be used to identify a residual error. These deviations can be determined from an image scan of a printed document. Even though the scans are generated using a 600 or 1200 dpi grid, the location of the pixels can be inferred from the gray edges of the lines in the scan.
Production of the security features using this method includes two steps. First, a line target, such as the one shown in
To determine whether a printed document is an original produced by the inkjet printer 10 or a copy produced by a copier, the printed document is scanned using an inline or flatbed scanner. The resulting image is analyzed with knowledge that the positional deviations of the line locations from a best line fit are different for the original and the copy. As used in this document, the term “best line fit” means a straight line that minimizes the distance between the straight line and the image content data used to form the line.
Using FFT analysis on a scanned copy of a document can verify that the copy did not occur from a non-gridded set of lines. This analysis cannot be done in the printer of the original document via digital image manipulation, but only by changing the output grid locations to be non-equally spaced by rotation. Digital manipulation means adding pixels of one or more colors to form a security feature or changing the halftone stochastic pattern used to identify pixels for an ink image. Thus, producing the original from a copy of the original that has been digitally manipulated, even if the original digital image is known, is impossible because the end user does not know the configuration of the printer that produced the original.
The example discussed above shows how an embedded line target can be introduced into a document print by carefully choosing the line spacing and the amount of printhead rotation. The only requirement is to make the printhead rotation large compared to the amount of deviation from a best line fit. In the example shown above, 500 μradians, was used since it is an order of magnitude larger than the rotation placement accuracy of the printhead with reference to the motion of the media past stationary printheads or with reference to the motion of the printhead in printers where the printheads traverse the width of the media to print a line of an image. This target line in the original image data leaves no residual signature in the printed image since the lines are evenly spaced on the printed media.
Given that different versions of line targets can be easily detected by the method described above, three or more line targets can be chosen that are well spaced in their FFT responses so they can be easily distinguished. Since yellow pixels are more difficult to detect in document images because yellow does not contrast well with light media, which is the more common media color, (3)3 or 27 unique combinations of printhead rotations in three printhead modules ejecting the three more easily detected colors can be effectively used to print documents with security features. If more easily separable combinations can be found the number of possible combinations grows cubically since three different colors of pixels are used in this example.
An alternative embodiment of the printer 10 calibrates the printheads in the printhead modules so the inkjets in each row of the printheads are aligned in the cross-process direction. To form a security feature in a printed document, a digital manipulation technique is used in the formation of a sneeze pattern used to maintain the operational status of the inkjets in the printer. A sneeze pattern is printed in the ink image of a document to maintain the operational status of the inkjets. To form sneeze patterns in documents, each inkjet in each printhead is periodically operated to eject single drops from each nozzle in some prescribed pattern onto a printed page. This pattern is designed to be below the visibility threshold of the viewer. If the pattern is too dense, the customer finds the print objectionable, if the pattern is not dense enough, the firing frequency of the inkjets may be insufficient to maintain the operational status of the inkjets. This method of maintaining inkjet operational status during printing is typically referred to as “sneezing” or “background jetting.” As used in this document, the term “sneeze drop” or “sneeze drop ejection” refers to non-image ink drops ejected by identified inkjets to maintain the operational status of the inkjets in the printer. As used in this document, the term “sneeze pattern” means an arrangement of sneeze drops printed in the background of an ink image and the term “background” means areas of a printed document containing pixels that were not generated from the ink image content data. A method of printing sneeze pattern is disclosed in co-pending U.S. patent application Ser. No. 16/704,370, which is entitled “Methods For Operating Printhead Inkjets To Attenuate Ink Drying In The Inkjets During Printing Operations,” which was filed on Dec. 5, 2019, the entirety of which is hereby expressly incorporated in this application by reference. Such a sneeze pattern is shown in
In the alternative embodiment of an inkjet printer that prints security features, a sneeze pattern is altered to encode a security feature that is identifiable via current scanner technology by inserting a permutation of the sneeze pattern with respect to the distance from the intended locations of the sneeze pattern prior to its printing. Moving the pixels of the sneeze pattern by a predetermined distance within certain areas of the ink image produces a known, scannable pattern in the background of the document that can be used as a security feature.
Sneeze patterns currently generated place sparse drops across the printed image such that specific colors are separated by a distance sufficient to prevent them from being observable by a human observer. The generation of the sneeze pattern also manages the separation between different ink colors, which in a typical inkjet printer are cyan, magenta, yellow, and black (CMYK), so a human observer does not notice the image background having a perceptible hue. Finally, the sneeze pattern is generated so the amount of ink each nozzle fires meets the requirements for keeping each inkjet operational. The generated sneeze pattern is repeated down the length of a page in the process direction.
This known method of generating a sneeze pattern can be altered so that a specific, identifiable pattern exists on each page that can be used for security purposes. Each background drop or pixel is moved a predetermined distance from the location it occupies in the generated sneeze pattern. For example, a given set of pixels in a sneeze pattern generated by a known method are offset in the cross-process direction by the distance between adjacent nozzles, which is the minimum resolution of distance units in a printhead. This altered pattern is repeated across the complete image or it is repeated over an area having a predetermined size and then this area is repeated throughout regions of the printed image.
One implementation of this method leaves the positions of the pixels for one of the four color planes in a sneeze pattern, black for example, in their expected locations, as shown in
A process 1100 for generating a rotated signature within a printed document in an inkjet printer is shown in
The process 1100 begins with the controller operating the actuators operatively connected to the printheads in the printhead modules to rotate the printheads by a predetermined amount (block 1104). Digital data corresponding to a line target is then added to the ink image content data for a document (block 1108) and an expected shifted frequency response of the line target in the document printed with the rotated printheads is generated (block 1110). The document is then printed (block 1112). A scan of the printed document is conducted to generate image data of the (block 1116) and a frequency response of the line target in the image data generated by the scanner is generated (block 1120). The frequency response of the line target in the image data is compared to the expected shifted frequency response of the line target printed with an inkjet printer having the rotated printheads (block 1124). If the responses match (block 1128), then the printed document is the original (block 1132). Otherwise, the printed document is a copy (block 1136).
A process 1200 for printed an altered sneeze pattern as a security feature within a printed document in an inkjet printer is shown in
The process 1200 begins with the generation of a sneeze pattern for a media sheet (block 1204). The sneeze pattern can be generated by one of the methods in the application expressly incorporated in this application by reference above or another known method. This sneeze pattern is altered by permutating the sneeze pattern using the one of the permutations discussed previously (block 1208). The altered sneeze pattern and the ink image content data for a media sheet are used to operate the inkjets to form an ink image and the altered sneeze pattern on the media sheet (block 1212). The printed sheet can then be scanned (block 1216) and, if the digital data corresponding to the scanned document contains the altered sneeze pattern (block 1220), the printed document is the original (block 1224). Otherwise, it is a copy (block 1228).
It will be appreciated that variants of the above-disclosed and other features, and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art, which are also intended to be encompassed by the following claims.
