Abstract:
A method for forming an image on a flexible media includes mounting said flexible media on an imaging device; scanning the flexible media to produce a digital representation of the flexible media; detecting defects in the digital representation to detect defective spots; and adjusting position of data for imaging according to the defects adapted to avoid imaging on the defective spots.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to commonly-assigned copending U.S. patent application Ser. No. ______ (Attorney Docket No. 96742/NAB), filed herewith, entitled MATCHING IMAGING DATA TO FLEXOGRAPHIC PLATE SURFACE, by Tauger et al.; and U.S. patent application Ser. No. 12/779,131, filed May 13, 2010, entitled WRITING AN IMAGE ON FLEXOGRAPHIC MEDIA, by Siman-Tov et al.; the disclosures of which are incorporated herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to methods and apparatus for matching the rendered image to be imaged on a flexographic plate to the structure of the flexographic plate. 
       BACKGROUND OF THE INVENTION 
       [0003]    Flexographic printing involves inking a raised image which then comes in contact with the print substrate, for instance paper or plastic, and the transfer of ink from the raised image onto the print substrate. The plate is made of a rubbery material which has a somewhat pliant nature, the extent of which depends on the smoothness and fragility of the substrate. In contrast to other print processes such as offset lithography and gravure where high pressure is used during ink transfer, it is generally desirable to have a minimum of pressure between the raised inked image on the plate and the substrate. Too little pressure and no ink transfer or very uneven ink transfer will occur. Too much pressure and the pliant surface of the plate will be squashed into the substrate causing blurring of the image edges resulting in poor print quality. 
         [0004]    Because of the requirement to work at minimal pressure for optimum quality, the distance between the plate surface and the substrate must be the same over the entire surface. This may depend on the uniformity of the press cylinder on which the plate is mounted and on the plate thickness uniformity. In the book Flexography Principles and Practices (Fourth Edition, page 109) accuracies of plus or minus 0.0005 inches are needed for the printing plates. 
         [0005]    For some years the dominant type of flexographic plates has been based on mixtures of elastomeric material, photosensitive monomers and photoinitiators. Such plates have been termed polymer plates and as such they are supplied to the customer as solid light-sensitive plate material. These plates are generally made to the above-mentioned tolerance. For instance, U.S. Pat. No. 4,272,608 (Proskow), describing the manufacture of such plates, states that they can be made by solvent casting or by extruding, calendaring, or pressing at an elevated temperature. A further development in plate technology was in the introduction of LAMS plates-laser ablated masks. A black layer is coated on the photopolymer plate and then ablated away in areas that will correspond to the print image. The plate is exposed to UV light and developed. However accurately the plate is made, there is some distortion due to solvent development. This problem was discussed in U.S. Pat. No. 5,252,432 (Bach et al.). Using suitable choice of photopolymers and developer liquids they were able to achieve a thickness tolerance after development of +/−less than 15 microns. 
         [0006]    An alternative way of preparing flexographic plates and sleeves is by engraving with a laser by ablation. Such a process does not require solvent development and therefore changes of thickness from such a cause are eliminated. For sleeves, the flexographic rubber has to be applied to a sleeve shell. U.S. Pat. No. 4,144,812 (Julian) describes such a process and grinding to obtain uniformity of thickness required. Such a method of grinding, however, was discussed in U.S. Pat. No. 5,798,202 (Cushner) as being time consuming and labour intensive. 
         [0007]    Flexographic printing has increased applications in high print quality products which had previously been dominated by gravure and litho printing. For instance, plate-making is much easier and quicker than gravure and the use of inks where the carrying media is evaporated for drying makes it more applicable to printing on polymer than offset litho. The roll-to-roll flexographic machine is simpler than any roll-to-roll offset press which would be needed to print for instance flexible packaging. 
         [0008]    For higher quality flexographic printing the plate thickness uniformity becomes an even more important issue. An additional part of obtaining high quality flexo printing is to use a soft under-cushion. During printing this cushion provided the give which would otherwise be provided by the plate image surface which would then slightly distort. However, generally the cushion has an even wider thickness tolerance than the plate itself. 
         [0009]    A challenge of all mass production is quality control. For instance, in the case of flexographic plate precursor sheets, mass production is done in a continuous manner and control of thickness must be monitored and adjusted to always be within the specification. There is always some possibility, however, that plate precursor material that will be outside the thickness specification, will escape notice, and reach the customer. Such defects may be visually undetectable and would only be seen once the plate is imaged during the printing process. While the manufacturer may accept responsibility for plate defects and replace any plates, they would be unlikely to recompense the customer for the cost of time, materials, and inconvenience involved. The only way the manufacturer could ensure that this does not happen would be to check each plate precursor in a way that would not be economically viable. 
         [0010]    The present invention solves a recognised need to ensure that the customer can optimise plate quality so that they are not wasting time and money in imaging and printing inferior plates. 
       SUMMARY OF THE INVENTION 
       [0011]    Briefly, according to one aspect of the present invention a method for forming an image on a flexible media includes mounting said flexible media on an imaging device; scanning the flexible media to produce a digital representation of the flexible media; detecting defects in the digital representation to detect defective spots; and adjusting position of data for imaging according to the defects adapted to avoid imaging on the defective spots. 
         [0012]    These and other objects, features, and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]      FIG. 1  represents in diagrammatic form of a digital front end driving an imaging device; 
           [0014]      FIG. 2  represents in diagrammatic form the optical displacement sensor (ODS) together with the laser imaging head situated on the imaging carriage imaging on a plate mounted on an imaging cylinder; 
           [0015]      FIG. 3  represents in diagrammatic form the ODS scanning process of a plate secured to the imaging cylinder; 
           [0016]      FIG. 4  represents in diagrammatic form an expanded flexographic plate; 
           [0017]      FIG. 5  represents in diagrammatic form a rendered image to be exposed on a flexographic plate; 
           [0018]      FIG. 6  represents in diagrammatic form a rendered image exposed on a flexographic plate; 
           [0019]      FIG. 7  represents in diagrammatic form an expanded flexographic plate showing defects found on plate; 
           [0020]      FIG. 8  represents in diagrammatic form a rendered image exposed on a flexographic plate wherein plate defects are shown in the exposed imaged areas; 
           [0021]      FIG. 9  represents in diagrammatic form a rendered image exposed on a flexographic plate wherein the image exposure parameters were adjusted to avoid the plate defects previously detected by the optical displacement scanner (ODS); 
           [0022]      FIG. 10  represents in diagrammatic form of a rendered image exposed on a flexographic plate where plate defects are shown in the exposed imaged areas; and 
           [0023]      FIG. 11  represents in diagrammatic form a rendered image exposed on a flexographic plate where the layout of the printing job was adjusted to avoid the plate defects previously detected by the optical displacement scanner (ODS). 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0024]    In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the disclosure. However, it will be understood by those skilled in the art that the teachings of the present disclosure may be practiced without these specific details. In other instances, well-known methods, procedures, components and circuits have not been described in detail so as not to obscure the teachings of the present disclosure. 
         [0025]    While the present invention is described in connection with one of the embodiments, it will be understood that it is not intended to limit the invention to this embodiment. On the contrary, it is intended to cover alternatives, modifications, and equivalents as covered by the appended claims. 
         [0026]      FIG. 1  shows a plate imaging device  108 . The imaging device is driven by a digital front end (DFE)  104 . The DFE receives printing jobs in a digital form from desktop publishing (DTP) systems (not shown), and renders the digital information for imaging. The rendered information and imaging device control data are communicated between DFE  104  and imaging device  108  over interface line  112 . 
         [0027]      FIG. 2  shows an imaging system  200 . The imaging system  200  includes an imaging carriage  232  on which an optical displacement sensor (ODS)  224  is mounted along with an imaging head  220 , the ODS  224  and imaging head  220  are controlled by controller  228 . The ODS  224  is positioned in such a manner that it precedes the imaging during scanning. The imaging head  220  is configured to image on a flexographic plate  208  mounted on a rotating cylinder  204 . The carriage  232  is adapted to move substantially in parallel to cylinder  204  guided by an advancement screw  216 . The flexographic plate  208  is imaged by imaging head  220  to form an imaged data on flexographic plate  212  on plate  208 . 
         [0028]      FIG. 3  shows an embodiment wherein the first stage of the imaging process is to scan the flexographic plate  208  with the ODS  224  in order to measure the structure of plate surface  304 . The ODS  224  is shown scanning the un-imaged flexographic plate  208  with the imaging head  220  inactive (imaging is not performed), producing scanned data  308  of the flexographic plate  208 . Scanned data  308  is communicated to DFE  104  for data analysis. 
         [0029]      FIG. 4  shows an expanded representation of a flexographic plate  400 , without any defects on the plate, such a case is obviously rare, it is presented just for illustration.  FIG. 5  shows a rendered image to be imaged on a plate  500 , rendered image  500  was prepared by DFE  104 , to be further imaged on the flexographic plate  208 .  FIG. 6  shows rendered image  500  imaged by imaging head  220  flexographic plate  208  to form an imaged plate  600 . 
         [0030]      FIG. 7  shows an expanded view of flexographic plate  208 , with marked defects types  704  and  708 . Defects type  704  represent removed plate spots, which will not print on the press. Defects of type  708  represent elevated spots on plate, which will show in printing. The defects were found by DFE  104  after analyzing the scanned data  308  obtained by ODS  224 . The scanned data  308  is received after scanning surface  304  of flexographic plate  208 . Defect  708   a  (from type  708 ) shows a spot on the plate where an image is planned to be printed. 
         [0031]      FIG. 8  depicts an imaged plate  600 , showing a rendered image  500  imaged on plate  400 . The imaging is done also on some of the previously detected defects, as is shown in  FIG. 7 . 
         [0032]      FIG. 9  shows a similar representation as is shown in  FIG. 8 , where by adjusting the exposure location of image  500  on plate  400 , defects of type  704  and  708  will not affect the print quality. The image  500  is adjusted downwards in the Y direction  904  and rightwards in the X direction  908 , thus not rejecting the usage of plate  400  for imaging; even thought defects were detected on the plate. Defect  708   a  (from type  708 ) shows a spot on the plate where an image is planned to be printed. Type  708  represents an elevated spot on plate  400 ; in this case  708   a  defect can be removed by polishing the spot where  708   a  is found with the imaging head  220 , as is suggested by commonly-assigned copending U.S. patent application Ser. No. 12/779,131. 
         [0033]      FIG. 10  shows a schematic representation of a rendered image  500  including plurality of image elements such as  1004 . The layout of the elements in  FIG. 10  when imaged on plate  400  will cause elements such as  1004 ,  1020 , and  1032  fall on defects of type  708 , and elements  1024 ,  1028 , and  1008  fall on defect type  704 . In this case the layout of the printing job can be changed to avoid imaging on areas where defects were found.  FIG. 11  shows the position of elements  1004 ,  1008 ,  1012 ,  1016 ,  1020 ,  1020 ,  1024 ,  1028 , and  1032  was rearranged by changing the layout of the printing job, thus avoiding from imaging on the defective spots ( 704 ,  708 , and  708   a ) of plate  400 . 
         [0034]    While the invention has been described with respect to a limited number of embodiments, these should not be construed as limitations on the scope of the invention, but rather as exemplifications of some of the preferred embodiments. Other possible variations, modifications, and applications are also within the scope of the invention. Accordingly, the scope of the invention should not be limited by what has thus far been described, but by the appended claims and their legal equivalents. 
       PARTS LIST 
       [0000]    
       
           104  digital front end (DFE) 
           108  imaging device 
           112  interface line 
           200  imaging system 
           204  rotating cylinder 
           208  flexographic plate 
           212  imaged data on flexographic plate 
           216  screw 
           220  imaging head 
           224  optical displacement sensor (ODS) 
           228  controller 
           232  carriage 
           304  plate surface 
           308  scanned data 
           400  expanded view of a flexographic plate  208   
           500  rendered image to be imaged on a plate 
           600  rendered image imaged on a plate 
           704  plate defect on a non image able area (removed) 
           708  plate defect on an image able area (elevated) 
           708   a    708  defect placed on an area to contain an imaged spot 
           904  Y axis offset adjustment 
           908  X axis offset adjustment 
           1004  image element 
           1008  image element 
           1012  image element 
           1016  image element 
           1020  image element 
           1024  image element 
           1028  image element 
           1032  image element