Abstract:
A high resolution, high speed laser drilling system for operating on an advancing product operates to advances the product in a predetermined product advancement path at a product advancement speed. A laser-generating source provides a pulsed laser beam having a laser-on time and a laser-off time. The laser beam is reflected to direct a focal point of the laser beam onto the advancing product. The focal point of the laser beam is moved in a direction of the product advancement path during the laser-on time and is moved in a direction opposite to the direction of the product advancement path during the laser-off time. The system is therefore able to improve laser drilling resolution for a given product advancement speed.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a high speed laser drilling system, and more particularly to a method of operating a laser drilling system to achieve improved laser hole resolution without sacrificing product advancement speed.  
           [0002]    Laser systems are often employed to create uniformly spaced holes in a product material such as an advancing web, and such systems are advantageous because of the high product advancement speed and laser hole resolution that can be achieved. Similarly configured systems are used to create holes in continuously fed sheets and in products advanced on a conveyor. However, there are particular hole size and spacing configurations that limit the product advancement speed and/or laser hole resolution because of the constraint of laser turn-on and turn-off times. Specifically, where holes are spaced a relatively large distance apart in comparison to the size of the holes, laser turn-on and turn-off times can limit the speed of product advancement or the resolution of the laser holes. For example, if the product advances at too high of a speed, the laser may remain on for too long and therefore create too large of a hole. Therefore, a method of operating a laser drilling system that enables high laser hole resolution without sacrificing product advancement speed would be a significant improvement in the art.  
         BRIEF SUMMARY OF THE INVENTION  
         [0003]    The present invention is a method and apparatus for high resolution, high speed laser drilling of an advancing product. A product is advanced in a predetermined product advancement path at a web advancement speed. A laser-generating source provides a pulsed laser beam having a laser-on time and a laser-off time. The laser beam is reflected to direct a focal point of the laser beam onto the web. The focal point of the laser beam is moved in a direction of the product advancement path during the laser-on time and is moved in a direction opposite to the direction of the product advancement path during the laser-off time. The present invention is therefore able to improve laser drilling resolution for a given product advancement speed. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0004]    [0004]FIG. 1 is a diagram of a prior art laser drilling system for operating on a moving product such as a web.  
         [0005]    [0005]FIG. 2 is a diagram of a laser drilling system for operating on a moving web employing a rotating polygon scanner according to a first embodiment of the present invention.  
         [0006]    [0006]FIG. 3 is a diagram of a laser drilling system for operation on a moving web employing an angularly adjustable refracting material according to a second embodiment of the present invention.  
         [0007]    [0007]FIG. 4 is a diagram of a laser drilling system for operating on a moving web employing a linearly actuated lens according to a third embodiment of the present invention.  
         [0008]    [0008]FIG. 5 is a diagram of a laser drilling system for operating on a moving web employing a rotating disk having a plurality of lenses mounted thereon according to a fourth embodiment of the present invention.  
         [0009]    [0009]FIG. 6 is a top view of the rotating disk employed in the laser drilling system shown in FIG. 5.  
         [0010]    [0010]FIG. 7 is a diagram of a laser drilling system for operating on a moving web employing an optical deflector according to a fifth embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION  
       [0011]    [0011]FIG. 1 is a diagram of prior art laser drilling system  10 . Laser source  12  generates laser beam  14 , which is focused by lens  15  and reflected by properly positioned stationary mirror  16  in a target direction onto advancing web  18 . Lens  15  may alternatively be positioned between stationary mirror  16  and advancing web  18 , as shown in phantom by the position of lens  15 ′. Lens  15  focuses laser beam  14  so that it is a high resolution spot at the point where it impinges upon web  18 . Web  18  is carried by rollers  20  or a similar advancement mechanism known in the art, moving in the direction indicated by arrows  22 . In other embodiments, web  18  may be replaced by a conveyor carrying a series of products to be worked on by laser beam  14  or a series of sheets fed through the path of laser beam  14 , for example. The pulsing rate of laser source  12  and the speed of advancement of web  18  (or of other advancing product in other embodiments) on rollers  20  are controlled to match a set hole pattern  24 , which is represented in FIG. 1 as a group of drilled holes  24   a  (shown as darkened circles) and a group of yet-to-be-drilled holes  24   b  (shown as empty circles). As discussed above in the background of the invention, where hole pattern  24  comprises relatively small holes spaced a relatively large distance apart, the minimum “on-time” of laser source  12  can result in too large of a hole at high speeds of advancement of web  18 . Therefore, either the hole resolution or the web advancement speed must be sacrificed in operating the laser drilling system.  
         [0012]    The present invention addresses this problem associated with prior art laser drilling systems by providing a system for moving the focused laser beam spot at the point where it impinges on the advancing web/product in the same direction as the web/product is moving. The “effective speed” of the web/product in relation to the focused laser beam spot is therefore reduced by the speed of the spot. As a result, higher laser hole resolution may be achieved for a particular absolute web/product advancement speed, since the effective speed of the web/product with respect to the spot is reduced. Several exemplary embodiments are described below with respect to FIGS.  2 - 7  for providing systems to move the focused laser beam spot according to the general principles of the present invention, shown for use with an advancing web as an exemplary embodiment.  
         [0013]    [0013]FIG. 2 is a diagram of laser drilling system  30  according to a first embodiment of the present invention. Laser source  12  generates laser beam  14 , which is focused by lens  15  and reflected onto advancing web  18  by rotating polygon scanner  32 . Web  18  is carried by rollers  20  or a similar advancement mechanism known in the art, moving in the direction indicated by arrows  22 . Rotation of polygon scanner  32  around its axis in the direction indicated by arrow  34  results in linear movement of the focal point of laser beam  14  on web  18  in the direction of arrow  36  as a side of polygon scanner  32  rotates across the impingement position of laser beam  14  on polygon scanner  32 . When the adjacent side of polygon scanner  32  rotates to the impingement position of laser beam  14  on the scanner, the focal point of laser beam  14  on web  18  jumps back in the direction opposite of arrow  34  on web  18 , and then gradually moves in the direction of arrow  34  again as polygon scanner  32  continues to rotate. The speed of rotation of polygon scanner is synchronized with the speed of advancement of web  18  so that the difference between the speed of advancement of web  18  and the speed of movement of the focal point of laser  14  on web  18  is low, enabling a high resolution laser hole to be drilled while web  18  advances at a relatively high speed. In addition, the length of the sides and number of sides of polygon scanner  32 , as well as the pulsing rate of laser beam  14 , are coordinated with the spacing of laser hole pattern  24 , to achieve the proper spacing between holes.  
         [0014]    [0014]FIG. 3 is a diagram of laser drilling system  40  according to a second embodiment of the present invention. Laser source  12  generates laser beam  14 , which is reflected by stationary mirror  16  and focused by lens  15  onto advancing web  18 . Web  18  is carried by rollers  20  or a similar advancement mechanism known in the art, moving in the direction indicated by arrows  22 . Angularly adjustable refracting element  42  is located in the path of laser beam  14  between lens  15  and web  18 . The angular orientation of refracting element  42  is controlled to move in the direction indicated by arrow  44 , which adjusts the refracted angle of the laser beam within refracting element  42 , resulting in a parallel offset of laser beam  14  exiting refracting element  42  and moving the focused laser beam spot impinging upon web  18  in the direction indicated by arrow  36 . Thus, during the “on time” of the laser, refracting element  42  is gradually rotated from the position shown in solid lines to the position shown in phantom lines, to move the focused laser beam spot in the same direction as the advancement of web  18 . The effective speed of the focused laser beam spot is therefore equal to the difference between the speed of advancement of web  18  and the speed of movement of the focused laser beam spot. During the “off time” of the laser, refracting element  42  returns to the position shown in solid lines. The adjustment of the angular orientation of refracting element  42  is synchronized and coordinated with the advancement of web  18  to achieve the proper size and spacing of the holes drilled in web  18 . The embodiment shown in FIG. 3 thus achieves the same advantages discussed above with respect to FIG. 2.  
         [0015]    [0015]FIG. 4 is a diagram of laser drilling system  50  according to a third embodiment of the present invention. Laser source  12  generates laser beam  14 , which is reflected by stationary mirror  16  and focused by lens  15  onto advancing web  18 . Web  18  is carried by rollers  20  or a similar advancement mechanism known in the art, moving in the direction indicated by arrows  22 . The position of lens  15  is linearly adjustable by actuator  52  in the direction of arrow  54 , which causes the position of the focused laser beam spot impinging upon web  18  to move in the direction of arrow  36 . Thus, during the “on time” of the laser, lens  15  is gradually moved in the direction of arrow  54  by actuator  52 , from the position shown in solid lines to the position shown in phantom lines, to move the focused laser beam spot in the same direction as the advancement of web  18 . The effective speed of the focused laser beam spot is therefore equal to the difference between the speed of advancement of web  18  and the speed of movement of the focused laser beam spot. During the “off time” of the laser, lens  15  is returns to the position shown in solid lines. The movement of lens  15  by actuator  52  is synchronized and coordinated with the advancement of web  18  to achieve the proper size and spacing of the holes drilled in web  18 . The embodiment shown in FIG. 4 thus achieves the same advantages discussed above with respect to FIG. 2.  
         [0016]    [0016]FIG. 5 is a diagram of laser drilling system  60  according to a fourth embodiment of the present invention. Laser source  12  generates laser beam  14 , which is reflected by stationary mirror  16  and focused by a lens onto advancing web  18 . Web  18  is carried by rollers  20  or a similar advancement mechanism known in the art, moving in the direction indicated by arrows  22 . Rotating disk  62 , which is shown in a top view to illustrated greater detail in FIG. 6, carries a plurality of lenses  15   a ,  15   b  and  15   c . It should be understood that an exemplary configuration o disk  62  will include a plurality of lenses around the entire circumference of disk  62 , but only lenses  15   a ,  15   b  and  15   c  are shown for the purpose of simplicity and clarity. Disk  62  continually rotates around its axis in a plane generally parallel to the plane of web  18  as indicated by arrow  64 . The position of the lens that is aligned with laser beam  14  therefore moves roughly linearly, which causes the position o the focused laser beam spot impinging upon web  18  to move in the direction of arrow  36 . Thus, during the “on time” of the laser, the aligned lens (lens  15   a  in FIG. 5) is linearly moved in a manner that moves the focused beam spot in the same direction as the advancement of web  18 . The effective speed of the focused laser beam spot is therefore equal to the difference between the speed of advancement of web  18  and the speed of movement of the focused laser beam spot. During the “off time” of the laser, the next lens carried by disk  62  (lens  15   c  in FIG. 5) moves into the position aligned with laser beam  14 . The rotation of disk  62  (and the resultant positioning of lenses  15   a ,  15   b , and  15   c ) is synchronized and coordinated with the advancement of web  18  to achieve the proper size and spacing of the holes drilled in web  18 . The embodiment shown in FIGS. 5 and 6 thus achieves the same advantages discussed above with respect to FIG. 2.  
         [0017]    [0017]FIG. 7 is a diagram of laser drilling system  70  according to a fifth embodiment of the present invention. Laser source  12  generates laser beam  14 , which is reflected by stationary mirror  16  toward web  18 . Web  18  is carried by rollers  20  or a similar advancement mechanism known in the art, moving in the direction indicated by arrows  22 . Electro-optic modulator  72  and lens  15  are located in the path of laser beam  14 , with lens  15  focusing laser beam onto web  18 . Electro-optic modulator  72  is controlled by voltage signal V to gradually adjust an angle of refraction of laser beam  14  through electro-optic modulator  72  in the direction of arrow  74 , which moves the focused laser beam spot impinging upon web  18  in the direction of arrow  36 . Thus, during the “on time” of the laser, electro-optic modulator  72  is controlled to gradually adjust the angle of refraction of laser beam  14  from the position shown in solid lines to the position shown in phantom lines, to move the focused laser beam spot in the same direction as the advancement of web  18 . The effective speed of the focused laser beam spot is therefore equal to the difference between the speed of advancement of web  18  and the speed of movement of the focused laser beam spot. During the “off time” of the laser, the angle of refraction of electro-optic modulator  72  is controlled to return to the position shown in solid lines. The controlled angular refraction of electro-optic modulator  72  is synchronized and coordinated with the advancement of web  18  to achieve the proper size and spacing of the holes drilled in web  18 . The embodiment shown in FIG. 7 thus achieves the same advantages discussed above with respect to FIG. 2.  
         [0018]    As a result of the present invention, the advancement of a web material may be performed at quite high speeds without concern for low hole resolution due to a minimum laser-on time, since the “effective speed” of the web during laser-on time is the difference between the advancement speed of the web and the speed of movement of the focal point of the laser due to implementation of a mechanism for moving the focused laser beam spot in the same direction as movement of the web. For particularly widely spaced patterns of small laser holes, the present invention can improve web advancement speed by as much as twenty times, utilizing the full pulsing capability of the laser at maximum web speed. For example, in an exemplary embodiment the achievable laser hole resolution improved from sixty thousandths of an inch diameter holes to three thousandths of an inch laser holes. It should be understood from the above description of the present invention that configurations shown for moving the focused laser beam spot are merely examples of suitable mechanisms for performing the function of the invention. Other scanning devices such as a galvo scanner, a resonant scanner, a holographic scanner, or other mechanisms known in the art may also be used to implement the present invention.  
         [0019]    Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention.