Abstract:
An imaging head ( 404 ) for writing an image on a substrate ( 108 ) includes an array of emitters ( 104 ) comprised of groups of emitters ( 120, 116, 112 ); imaging lens ( 408 ) that focuses light from each group onto the substrate; and wherein light from each group is focused at a different depth relative to a surface of the substrate.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    Reference is made to commonly-assigned co-pending U.S. patent application Ser. No. 11/615,025, filed Dec. 22, 2006, now U.S. Publication No. 2008/0153038, entitled HYBRID OPTICAL HEAD FOR DIRECT ENGRAVING OF FLEXOGRAPHIC PRINTING PLATES, by Siman-Tov et al.; and U.S. patent application Ser. No. 11/424,919, filed Jun. 19, 2006, now U.S. Publication No. 2008/0018943, entitled DIRECT ENGRAVING OF FLEXOGRAPHIC PRINTING PLATES, by Eyal et al.; the disclosures of which are incorporated herein. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to 3D imaging of a flexographic plate by using multiple emitters. The multiple emitters are configured to engrave on the same region of the flexographic plate during different time periods. 
       BACKGROUND OF THE INVENTION 
       [0003]    Prior to setting forth the background of the invention in detail, it may be helpful to set forth definitions of certain terms that will be used hereinafter. The term computer-to-plate (CTP) as used herein relates to an imaging technology used in modern printing processes. In this technology, an image created in a desktop publishing application is output directly to a printing plate. CTP as used hereinafter relates also to the imaging device carrying out the process of outputting the computer-stored image to printing plates. 
         [0004]    There are different types of printing plates used by CTP imaging devices. Most plates require post processing steps to produce two or three-dimensional features. The present invention refers to the type of plate known as flexographic printing plates. More specifically it refers to a CTP imaging device that is used for direct engraving of a flexography plates utilizing a light source configured from multiple emitters. 
         [0005]    Direct engraving of a flexography plates means three-dimensional (3D) carving on the plate material by applied light source energy such as a laser. The concept of direct engraving is remarkably different from two-dimensional imaging techniques which require post processing steps in order to produce three-dimensional features on a plate to be applicable for the flexography market. 
         [0006]      FIG. 1  shows a prior art CTP machine for direct engraving of a flexographic plate; multiple emitters array  104  is aligned parallel to the flexographic plate surface  108 . The flexographic plate is attached to a rotating drum. For simplicity of the discussion the array of multiple emitters  104  comprises nine emitters. The array of multiple emitters  104  is composed from three groups of emitters  112 ,  116 , and  120 , each containing three emitters. 
         [0007]    Group  112  emits light  136  on plate surface  108  during first drum revolution  124 , group  116  emits light  140  during the second drum revolution  128 , and group  120  emits light  144  during the third drum revolution  132 . Each of the three groups  112 ,  116 , and  120  in the previous example emit light on the same region of plate surface  108 , i.e. pixels p 1 , p 2 , and p 3  of pixels array  160  are affected by the three groups. 
         [0008]    Additionally, during the second drum revolution  128  the first group of emitters  112  emits light  148  on pixels p 4 -p 6 . During the third drum revolution  132  pixels p 4 -p 6  are affected by the second group of emitters  116  emitting light  152 , while the first group of emitters  112  emit light  156  on pixels p 7 -p 9 . The emitters described by the prior art are all imaged just on the surface plane of the flexographic printing plate. 
         [0009]    The present invention propose new embodiments concepts for CTP machines, wherein a light source, configured from multiple emitters, is adjusted in a slant or stair configuration relative to the surface plane of the flexographic plate. The slant or stair configuration enables simultaneously imaging different emitters on both the surface plane and at various depths within the printing plate. The multiple emitters are then activated in a way that enhances the direct engraving and ablating effect. 
       SUMMARY OF THE INVENTION 
       [0010]    Briefly, according to one aspect of the present invention an imaging head writes an image on a substrate. The head includes an array of emitters comprised of groups of emitters; imaging lens that focuses light from each group onto the substrate; and wherein light from each group is focused at a different depth relative to a surface of the substrate. 
         [0011]    The invention and its objects and advantages will become more apparent in the detailed description of the preferred embodiment presented below. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    The subject matter regarded as the invention will become more clearly understood in light of the ensuing description of embodiments herein, given by way of example and for purposes of illustrative discussion of the present invention only, with reference to the accompanying drawings wherein: 
           [0013]      FIG. 1  is schematic illustration of a prior art emitter array configured in parallel with respect to a plate imaging system; 
           [0014]      FIG. 2  is a schematic illustration of an emitter array divided into groups with each group offset with respect to other groups (stairs configuration); 
           [0015]      FIG. 3  is a schematic illustration of an emitter array slanted with respect to the plate imaging system; 
           [0016]      FIG. 4  is a schematic illustration of an emitter array as part of an imaging head configured to image a printing plate, mounted on a rotating drum; and 
           [0017]      FIG. 5  is a schematic describing a preferred embodiment based on the concept of a tilted optical head configured from fiber coupled diodes. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    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. 
         [0019]      FIG. 4  describes the general concept of a CTP printing machine that uses an array of multiple emitters. 
         [0020]    Multiple emitters array  104  is shown as part of an imaging head  404 , which includes at least the array of multiple emitters  104  and an imaging lens  408  such as a telecentric lens. The array of emitters emits light, which is focused by the imaging lens  408  on pixels  160  of printing plate  416 . The printing plate  416  is wrapped around, the imaging drum  412 , and is imaged by imaging head  404  as the drum rotates. 
         [0021]    The configuration in  FIG. 1  shows multiple emitters array  104  positioned substantially in parallel to the plate surface  108 , or perpendicular to the optical axis, created for example by emitted light  136 . The array of emitters may include fiber coupled emitters or may be constructed from fiber lasers. Due to this geometric configuration, emitted light e.g.  136 ,  140 , and  144  is applied on pixels p 1 -p 3  at different drum revolutions, and is focused on the same focal plane. This results in a marginal incremental engraving on the surface of plate  108 , between subsequent drum revolutions. 
         [0022]    In order to achieve more efficient engraving on plate surface  108 , the focal plane of the emitted light applied on the same region should be substantially different for each subsequent drum revolution.  FIG. 2  shows an array of emitters  204 , wherein each group of emitters  112 ,  116 , and  120  is positioned in incremental offset with respect to the other. Multiple emitter array  204 , similar to multiple emitter array  104  shown in  FIG. 1 , is positioned parallel to plate surface  108 . The suggested configuration of multiple emitter array  204  enables deeper engraving between subsequent drum revolutions during imaging. For example, first group  112  emits light  236  during first drum revolution  124  on pixels p 1 -p 3 . Subsequently, second group  116  emits light  240  in second drum revolution  128 , and subsequently third group  120  emit light  244  in third drum revolution  132  on same pixels p 1 -p 3 . Each of the emitted lights  236 ,  240 , and  244  is focused by imaging lens  408  on a deeper focal plane per subsequent drum revolution, thus yielding a deeper engraving into plate surface  108 . 
         [0023]    Similarly  FIG. 2  shows that the first group of emitters  112  emits light  248  in a second drum revolution on pixels p 4 -p 6 . The second group of emitters  116  emits light  252  in a third drum revolution on pixels p 4 -p 6 , and the first group of emitters  112  emits light  256  in a third drum revolution on pixels p 7 -p 9 . 
         [0024]    An array  204 , with multiple group of emitters offset to each other, is difficult to manufacture.  FIG. 3  shows array  104  tilted at an oblique angle relative to the optical axis. Such a configuration will cause a deeper engraving between subsequent drum revolutions. For example, groups  112 ,  116 , and  120  will emit lights  336 ,  340 , and  344  on pixels p 1 -p 3  during subsequent drum revolutions. Due to the tilted configuration of multiple emitter array  104  with respect to plate surface  108 , each of lights  336 ,  340 , and  344  are focused by imaging lens  408  on a deeper plane for each subsequent drum revolution, and as such will result in deeper engraving on pixels p 1 -p 3  during imaging. 
         [0025]    Similarly  FIG. 3  shows that the first group of emitters  112  emits light  348  in a second drum revolution on pixels p 4 -p 6 . The second group of emitters  116  emits light  352  in a third drum revolution on pixels p 4 -p 6 , and the first group of emitters  112  emits light  356  in a third drum revolution on pixels p 7 -p 9 . While  FIG. 2  and  FIG. 3  show the concept of the patent application,  FIG. 5  describes an enabling embodiment for a CTP machine based on the concept shown by  FIG. 3 . 
         [0026]      FIG. 5  describes an optical head with array of emitters  104  configured from fiber coupled laser diodes that move in the Y direction in parallel and relative to a printing plate  416 . A predefined inclination angle  504  and pitch  508  enables to focus a laser source; the distal tip of the fiber, underneath the upper surface of the printing plate  416 , on a spot that was already irradiated and ablated by at least one of the previous laser sources. The optical head can be adjusted within the CTP machine at a desired inclination angle  504  and distance relative to the plate  416  by using an adequate mechanical assembly. Such a configuration improves the engraving of different types of flexographic plates. 
         [0027]    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. For example, even though one imaging lens has been shown, multiple lenses may be used. 
       PARTS LIST 
       [0000]    
       
           104  array of multiple emitters 
           108  plate surface (substrate) 
           112  first group of emitters 
           116  second group of emitters 
           120  third group of emitters 
           124  first drum revolution 
           128  second drum revolution 
           132  third drum revolution 
           136  first group of emitters emitting in first drum revolution 
           140  second group of emitters emitting in second drum revolution 
           144  third group of emitters emitting in third drum revolution 
           148  first group of emitters emitting in second drum revolution 
           152  second group of emitters emitting in third drum revolution 
           156  first group of emitters emitting in third drum revolution 
           160  pixels on plate created by multiple imaging 
           204  array of multiple emitters arranged in a staircase configuration 
           236  first group of emitters emitting in first drum revolution 
           240  second group of emitters emitting in second drum revolution 
           244  third group of emitters emitting in third drum revolution 
           248  first group of emitters emitting in second drum revolution 
           252  second group of emitters emitting in third drum revolution 
           256  first group of emitters emitting in third drum revolution 
           336  first group of emitters emitting in first drum revolution 
           340  second group of emitters emitting in second drum revolution 
           344  third group of emitters emitting in third drum revolution 
           348  first group of emitters emitting in second drum revolution 
           352  second group of emitters emitting in third drum revolution 
           356  first group of emitters emitting in third drum revolution 
           404  imaging head 
           408  imaging lens 
           412  imaging drum 
           416  printing plate 
           504  inclination angle 
           508  pitch