Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B41—PRINTING; LINING MACHINES; TYPEWRITERS; STAMPS
  • B41F—PRINTING MACHINES OR PRESSES
  • B41F33/00—Indicating, counting, warning, control or safety devices
  • B41F33/0036—Devices for scanning or checking the printed matter for quality control

Definitions

• the present invention relates to printing technology and, more particularly, but not exclusively to quality assessment of printed matter, and, even more particularly, but still not exclusively to the assessment of color quality of the printed image.
• the quality of the printed image is bound to change with time, during the printed job run, for various reasons:
• a continuous colorimetric measurement and a resulting modification of the printing calibration such as ink pressure, ink temperature, ink density, water to ink balance, press pressure and other parameters can enhance the color stability and the quality of the printed image.
• the common methods of acquiring colorimetric data for the sheet-fed printing comprise human inspection, Automatic Optical Inspection (AOI), and offline color measurement tables.
• AOI Automatic Optical Inspection
• Human inspection is performed by the operator of the printing machine.
• the operator randomly samples a printed sheet from the press delivery area, and checks the sampled sheet against a proofing sheet. If the operator detects a color change the operator manually manipulates a set of ink keys to correct the color in the designated area.
• Subjectivity the result is as good as the operator's capabilities at the time of printing and is therefore variable from person to person, from day to night, and prawn to errors •
• Delay the sampling is erratic, it takes the operator 2-3 minutes to pick up a sheet, analyze it and correct the printer settings while the printer is running. It therefore takes hundreds of sheets of low quality image until a problem is rectified.
• AOI Automatic Optical Inspection systems
• MAN Roland Druckmaschinen AG MAN Roland Druckmaschinen AG, Stadtbachstra ⁇ e 1, 86153 Augsburg, Germany
• Qualitronic II manufactured by Koenig & Bauer (Koenig & Bauer AG, W ⁇ rzburg Facility, Friedrich-Koenig-Str. 4, D-97080 Wurzburg, Germany).
• AOI systems employ a commercial CCD or CMOS line scan camera. The camera is typically mounted at an optical distance from the printed surface to capture the entire width of the printed image, while the illuminating fixture is positioned closely to the surface.
• Vibration the large optical distance between the camera and the printed image translates the small vibrations of the press frame into a significant movement of the camera, thus limiting the useful resolution of the camera.
• scanning apparatus for print control comprising: a plurality of contact image sensors, each having respective output connections, to obtain image quality data from a substrate, wherein said contact image sensors are arranged with their respective outputs connected in parallel for fast data readout; and a feedback unit for feeding back said image quality data for setting of parameters of a printer.
• an image quality measurement apparatus for measuring quality of an image printed on a surface, said apparatus comprising: at least one illumination element mounted in close proximity to said surface and operative to illuminate at least a portion of said surface; an array of image sensors mounted in close proximity to said surface and operative to produce measurements of light reflected from said illuminated portion of said surface; a controller operative to control said image sensors and said illumination elements and to receive said measurements of light; and an analyzer operative to analyze said measurements of light and produce a measure of quality of said image printed on said surface.
• said image quality measurement apparatus is capable of being integrated with a printing apparatus; and wherein said image quality measurement apparatus is operative to perform said measurements of light and to produce said measure of quality at printing speed.
• a method of measuring quality of a printed image comprising: illuminating said image at close proximity; measuring light reflected from said image at close proximity; and analyzing said measurement to form a quality analysis; wherein said steps of illuminating; measuring and analyzing are performed at printing speed.
• a printing apparatus for printing on a surface, said apparatus comprising: an surface moving apparatus for moving a surface to be printed under at least one printing head at printing speed; said at least one printing head for printing an image on said surface; at least one illumination element mounted in close proximity to said surface and operative to illuminate at least a portion of said image; an array of image sensors mounted in close proximity to said surface and operative to produce measurements of light reflected from said illuminated portion of said image; an analyzer operative to analyze said measurements of light and produce a measure of quality of said printed image; and a controller operative to control said image sensors, said illumination elements and said printing heads in accordance with said analysis of said measurement of light; wherein said array of image sensors, said analyzer and said controller are operative to perform said measurements of light and to produce said measure of quality at said printing speed.
• a printing method for printing on a surface comprising: moving a surface to be printed under at least one printing head at printing speed; printing an image on said surface; illuminating at least a portion of said surface at close proximity; measuring light reflected from said illuminated portion of said surface, said measuring performed at close proximity to said surface; analyzing said measurements of light and producing a measure of quality of said printed image; and controlling said image sensors, said illumination elements and said printing heads in accordance with said analysis of said measurement of light; wherein said steps of illuminating, measuring, analyzing and controlling are performed at said printing speed.
• scanning apparatus for print control comprising: a plurality of contact image sensors, each contact image sensor having respective output connections, and located in non-contact relation with a substrate to obtain image quality data from said substrate, wherein said contact image sensors are arranged with their respective outputs connected in parallel for fast data readout; and a feedback unit for feeding back said image quality data for setting of parameters of a printer. That is to say, the contact image sensors are not actually placed in contact with the substrate since they are optical devices and are able to scan without being in contact. The sensors are able to scan from distances in the order of magnitude of tens of centimeters and from further away if suitable optics are provided. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. The materials, methods, and examples provided herein are illustrative only and not intended to be limiting.
• Implementation of the method and system of the present invention involves performing or completing certain selected tasks or steps manually, automatically, or a combination thereof.
• several selected steps could be implemented by hardware or by software on any operating system of any firmware or a combination thereof.
• selected steps of the invention could be implemented as a chip or a circuit.
• selected steps of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system.
• selected steps of the method and system of the invention could be described as being performed by a data processor, such as a computing platform for executing a plurality of instructions.
• Fig. 1 is a simplified illustration of an image quality measurement apparatus 10 mounted within a sheet-fed printer system 11 according to a preferred embodiment of the present invention.
• Fig. 2 is a simplified drawing of the quality measurement apparatus of Fig. 1 according to a preferred embodiment of the present invention.
• Fig. 3 is a simplified drawing of another view of the quality measurement apparatus of Fig. 1 according to a preferred embodiment of the present invention.
• Fig. 4 and Fig. 5 are simplified illustrations of two configurations of the array of image sensors, according to a preferred embodiment of the present invention.
• Fig. 6 is a simplified block diagram of an image processing part of the quality measurement apparatus according to a preferred embodiment of the present invention.
• Fig. 7 is a simplified block diagram of a process executed by the quality measurement apparatus, according to a preferred embodiment of the present invention.
• Fig. 8 is a simplified block diagram of a program executed by the data processing module, according to a preferred embodiment of the present invention.
• the present embodiments enable high-speed, high-resolution imaging of a sheet within a sheet-fed offset press, and to use this imaging to assess the quality of the printed image.
• the present embodiments provide information about optical densities, color composition, color registration, etc.
• the present embodiments provide information regarding the image quality in real-time, to analyze this information and to produce feedback to the printing machine so as to correct drifts in image quality without stopping the printer or decreasing the printing speed.
• Sensors Preferably the sensors are connected in parallel so as to output information at high speed and allow real time processing, and the information is fed back to the printing machine to change settings as necessary.
• Automation a printed image quality control system that measures, analyses and controls the relevant settings of the printing machine without human intervention.
• the preferred embodiments use Contact Image Sensor (CIS) chips to provide colorimetric data.
• CIS Contact Image Sensor
• the preferred embodiments connect the CIS chips to the control circuitry in parallel, rather then serially.
• the parallel connection allows high speed data output and consequently enables sampling of the sheet at full printing speed in the highest possible resolution.
• the printed image quality control system as described hereinafter may be used for other than sheet-fed offset presses.
• Fig. 1 is a simplified illustration of an image quality measurement apparatus 10 mounted within a sheet-fed printer system 11.
• the printer 11 consists of a printing drum 12 and an impression drum 13.
• the printing drum 14 carries the ink bearing the image to be printed and transfers the ink onto a sheet 44, which is mounted on the impression drum 13.
• the printing drum 12 and the impression drum 13 are termed herein a drum system 15.
• the drum system 15 described and shown in Fig. 1 prints only one color.
• a multi-color sheet-fed printing system thus incorporates several drum systems 15 as shown in Fig. 1, each printing a single color, and the sheet is transferred sequentially between the drum systems 15.
• the drum system of Fig. 1 is typically the last drum system. It is appreciated that though the quality measurement apparatus 10 is preferably mounted within the last drum system 15, the quality measurement apparatus 10 can be mounted also within other drum systems 15 of the printer system 11.
• a third drum typically named an image drum, on which the image is first created by ink applying devices. The ink is then transferred onto a blanket covering the printing drum, and hence onto the sheet mounted on the impression drum.
• Some printing systems may print several colors within a single drum system.
• drum-based printing is merely given as an example, and the scanner of the present embodiments is 1 relevant for any kind of printing in which output quality measurements can be fed back to alter printer settings. This includes any kind of color printer.
• the quality measurement apparatus 10 preferably consists of illumination elements 16, image sensors 17, a data compression board 18 and a data processing unit 19.
• the illumination element 16 typically consists of a lamp 20 and an optical system such as a lens 21.
• the lamp 20 can be any type of lamp such as incandescent lamp, fluorescent lamp, light emitting diode (LED), Cold Cathode Fluorescent Lighting (CCFL), Metal Halide, etc.
• the optical system can be, for example, a lens or a light guide such as a fiber optic.
• the illumination element 16, the image sensors 17 and the data compression board 18 are preferably mounted within a frame 22 of the printing system 11.
• the illumination element 16 and the image sensors 17 are preferably mounted in close proximity to the printed sheet which is located on surface 45.
• the image sensors 17 are mounted 5 centimeters from the printed surface or closer.
• the data compression board 18 is preferably mounted in close proximity to the image sensors 17.
• the illumination element 16 and the data compression board 18 are connected to the data processing unit 19.
• the data processing unit 19 preferably comprises various communication facilities, such as control link 23 connected to the printer controller and display link 24 connected to various display units. It is appreciated that the quality measurement apparatus 10 is capable of providing a displayable scan of the printed image, to be displayed on a display unit, preferably via the display link 25. It is also appreciated that such display units can be co-located with the printing system 11 or located remotely from the printing system 11.
• Fig. 3 is a simplified drawing of another view of the quality measurement apparatus 10 of Fig. 1 according to a preferred embodiment of the present invention.
• the illumination elements 16 of Fig. 2 are two arrays 25 of illumination elements 16 and the image sensor 17 of Fig. 2 is an array 26 of image sensors 17.
• Fig. 4 and Fig. 5 are simplified illustrations of two configurations of the array 26 of image sensors 17, according to a preferred embodiment of the present invention.
• the array 26 consists of a single line of image sensors 17.
• the image sensors 17 of Fig. 3 are preferably arranged in a single row sequence of elements:
• the R image sensor element 27 senses red
• the G image sensor element 28 senses green
• the B image sensor element 29 senses blue.
• the image sensors 17 are equipped with R, G and B filters.
• the array 26 consists of a single line of image sensors 17.
• the image sensors 17 of Fig. 3 are preferably arrange in a dual row format (Bayer filters):
• each image sensor 17 senses a single picture element (pixel)
• Fig. 6 is a simplified block diagram of an image processing part of the quality measurement apparatus 10 according to a preferred embodiment of the present invention.
• the image processing part of the quality measurement apparatus 10 consists of the array 26 of image sensors 17, an array of analog-to-digital converters (ADC) 33, an array of the data reduction modules 18, and the data processing module 19.
• ADC analog-to-digital converters
• each image sensor 17 is preferably equipped with a color filter 34.
• the color filters are red, green and blue filters (RGB) as described above with reference to Figs. 4 and 5.
• each image sensor 17 is preferably connected to an ADC 33, which converts the analog measurement of the image sensors 17 into a digital signal.
• the ADC 33 is preferably connected to a data reduction module 18, which receives the digital signals, compresses and multiplexes them, and sends the signals in a continuous bit stream to the data processing module 19.
• the data reduction modules 18 are daisy-chained as shown in Fig. 7.
• the data processing module 19 typically and preferably comprises various communication facilities, such as control link 24 connected to the printer controller and display link 25 connected to various display units.
• Fig. 7 illustrates CIS chips with analog outputs.
• the front CIS chips can be single chips or a device comprising several CIS sensors.
• the digital connection between the CIS chips and the data compression board are preferably implemented using standard communication technologies such as camera link, USB2, RS485, Ethernet or similar high speed communication technologies.
• the data compression boards preferably implement binning and ROI (region of interest) functions to reduce the amount of data to be transferred to the processing unit. These functions are preferably implemented simultaneously for each frame, or separately, different from frame to frame.
• the digital connection between the data reduction board and the processing unit is preferably implemented in standard communication technologies such as camera link, USB2, RS485, Ethernet or any other high speed communication technologies.
• Fig. 7 is a simplified block diagram of a process executed by the quality measurement apparatus 10, according to a preferred embodiment of the present invention.
• step 37 the process starts with step 37, by setting the parameters of the illumination elements 16 and proceeds to step 38 to set the parameters of the image sensors 17, according to the characteristics of the printed image.
• step 39 the process than proceeds to step 39 to receive image data from the image sensors 17 and then to step 40 to process the image data, as will be explained below in further details.
• the results of the processing of step 40 are provided in step 41 as feedback, either manually or automatically, to the printing system 11.
• step 41 are also provided in step 42 as feedback to the illumination elements 16 and preferably also to the image sensors 17.
• Fig.8 is a simplified block diagram of a program executed by the data processing module 19, according to a preferred embodiment of the present invention.
• the program executed by the data processing module 19 preferably consists of 12 modules:
• the Receive Image module 51 receives the pixel bit stream from the reduction units or reduction boards 18, and performs the following functions: Identify a sheet image block; Identify image type;
• the Collate module 52 collects images from the same sheet and the same type and transfers the data, comprising the collection of sheet images, to the compensation module 53.
• the compensation module 53 process the sheet's collection of images to provide compensation for the following artifacts:
• the compensation module then transfers the compensated data to the Pad and Place module 54.
• the above operation is used to compensate for positioning errors that may have occurred during the physical butting of image sensors 18. More particularly, when a pixel is missing or moved due to sensor positioning errors, padding and placing algorithms are used to compensate for the missing pixel.
• the Pad and Place module 54 relocates the pixel information to create an image of equally spaced pixels.
• the Pad and Place module 54 then transfers the image data to the Display Manager 55, which reformats the image for the target display and transfer the reformatted image to the Display Communication module 56 to be transmitted to a local display, or to a remote display (or both).
• the Pad and Place module 54 also transfers the image data to the Locate Colors module 57.
• the Locate Colors module 57 identifies and locates color patches within the sheet image and transfers this information to the Registration Control module 59 and to the RGB to Density Conversion module 60.
• the Registration Control module 58 processes the image information, generates registration correction data, and transfers this data to the Printer Communication module 63.
• the RGB to Density Conversion module 60 converts the RGB signals into color density parameters and transfers these parameters to the Density Analysis module 61 and to the color control module 62.
• the Density Analysis module 61 analyses the changes in density values, preferably both the temporal and the spatial changes, generates density trend parameters and sends them to the color control module 62.
• the color control module 62 processes the density parameters received from the RGB to Density Conversion module 60 and the density trend parameters received from the Density Analysis module 61 and produces ink-key correction parameters, which it sends to the Printer Communication module 63.
• the Printer Communication module 63 transmits the registration correction parameters and the ink-key correction parameters to the printer system 11 to compensate for drifts in the image quality.
• the image quality is corrected in real ⁇ time and without affecting the printing speed.
• the printer system 11 is not equipped to receive feedback signals, the registration correction parameters and the ink-key correction parameters are provided to an operator of the printer system 11 so that he may carry out manual modification of the settings of the printer system 11.
• the present embodiments enable high-speed and high resolution imaging of a sheet inside a sheet-fed offset press and as an integral part of the printing process.
• the present embodiments further use this imaging data to provide: optical density measurements; color measurements; inspection of print quality; color registration analysis; and other optional information.
• the present invention uses Contact Image Sensor (CIS) chips for its image sensors 17.
• CIS Contact Image Sensor
• the use of CIS technology enables a faster scanner and a smaller scanner.
• the present embodiments can be mounted within a common sheet- fed offset press.
• the image sensors 17 preferably consist of Contact Image Sensor (CIS) chips that are preferably physically butted to each other to create a sensor of a preferred length.
• CIS Contact Image Sensor
• the image sensors 17 are operated simultaneously.
• the outputs of the CIS chips are preferably connected in parallel, rather than in daisy-chain configuration, to enable higher clock rates and to provide faster sampling rate, thus supporting imaging of the printed sheets at full printing speed and in the highest resolution required.
• Color filters 34 are preferably mounted on the image sensors 17 (preferably CIS devices), preferably in a single line or a dual line configurations as described with reference to Figs. 5 and 6. As described with reference to Fig. 7, the outputs of the CIS devices are preferably connected in parallel, rather than in daisy-chain configuration, to enable higher clock rates and to provide faster sampling rate, thus supporting imaging of the printed sheets at full printing speed and in the highest resolution required.
• the RGB information taken from each group of three CIS devices in single row format is converted to density information as described below.
• the RGB information is converted into XYZ values and then to LAB values to create Delta-E and LAB information readouts.
• the CIS devices are calibrated in the manufacturer's laboratory and all artifacts and differences between pixels and changes over time are rectified in real ⁇ time during operation, using the information created during the calibration procedure.
• the calibration procedure preferably includes the following steps:
• RGB outputs for a specific substrate are:
• R, G and B are the response functions of the image sensor
• the R, G and B functions are preferably integrals over the visible light, preferably estimated using 32 or 64 points, preferably every 5 or 10 nanometers.
• RGB functions are preferably written as a matrix equation as follows:
• A is the standard A illumination type (CGATS standards)
• c,m,y,k are the "ANSI status T (or A,E or I)" standard responses
• the above matrices are preferably solved to produce the CMYK value from the known response matrices of the light and the sensor, and the RGB values, as follows:
• CMYK values are predicted using the standard T (or A,E or I) functions and type A illumination parameters. Having multiple pairs of CMYK and RGB vectors from the same color sample, the following K matrix is solved:
• GMERR Generalized minimal error method
• the quality measurement apparatus 10 preferably enables the imaging of the entire sheet to provide the following functions (in addition to measurement of color density):
• Variable data verification comparing selected areas of the printed image with variable data retrieved from a database, checking for the correctness of the variable data, registration to the regular, fixed print, existence of all variable data elements, etc;
• Density reading enables continuous and automatic control of ink-keys, ink-to-water balance and other printer parameters that affect color reproduction. It is appreciated that the use of the quality measurement apparatus 10 enables approving of the print job without physically visiting the print shop to verify the printed image visually. Having a reliable and accurate reading of the colors from the printed material while in the press, and furthermore having a reliable and accurate verification and correction of text and variable images, enables the printing customer to rely on the digital data and approve the print job from a remote location.
• the use of the quality measurement apparatus 10 enables inspection for process control by comparing the printed image with a required standard image (proofing image, master image).
• the proofing images are preferably obtained from the pre-press design or by scanning an approved sheet.
• the quality measurement apparatus 10 preferably sends an alarm to an operator of the printing system, preferably indicating the detected defect.
• the differences are analyzed and compared against a pre-defined or user defined threshold to reduce false alarms.
• the detected defects are also analyzed for their type and origin, to assist the operator in resolving the problem. It is appreciated that such inspection can be performed by sampling sheets, since print defects tend to build up slowly.
• the quality measurement apparatus 10 can be processed using relatively low resolution, thus requiring lower processing power, and therefore can be performed continuously for each sheet. Hence defective sheets may be prevented from reaching the final customer. It is appreciated that this screening process can be performed on-line or off-line in a post-printing process.
• the contact image sensors may be located in non-contact relation with the sheet or other print substrate. That is to say the image sensors are removed a short distance away from the sheet.

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• Engineering & Computer Science (AREA)
• Quality & Reliability (AREA)
• Inking, Control Or Cleaning Of Printing Machines (AREA)

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• 2005
  • 2005-10-30 WO PCT/IL2005/001130 patent/WO2006046249A1/en active Application Filing
  • 2005-10-30 EP EP05800110A patent/EP1814737A1/de not_active Ceased

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