Abstract:
A compact, energy-efficient extensible illumination source combines the reliability advantages of light emitting diodes (LEDs) with the brightness of conventional lighting. High reliability of the LEDs provides trouble-free operation over a long hour lifetime. This high-output light source can be used in direct lighting applications or for backlighting for translucent materials. The illumination source includes LED printed wire board segments that may be configured to form a light line of any length. The segments are mounted on a inner mounting base which also serves as a first stage heat sink for the LEDs. The illumination source includes a linear mirror for reflecting radiant energy away from the LEDs to produce a uniform linear illumination pattern. A window provides mechanical protection for the LEDs and may be used for diffusing or filtering light from the LEDs. An integral base in contact with the inner mounting base also serves as a heat sink and provides structural support for the illumination source. The integral base further includes channels and cavities for cooling the illumination source and for housing power cables.

Description:
RELATED APPLICATIONS  
       [0001]    This application claims the benefit of priority under 35 U.S.C. 119(e) to provisional U.S. Patent Application No. 60/366,066, filed Mar. 18, 2002 which is incorporated herein by reference in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    This invention relates generally to linear light sources, and more specifically to an assembly of high-intensity light emitting diodes in a linear, modular form such that the illumination line can be extended indefinitely.  
         BACKGROUND OF THE INVENTION  
         [0003]    Linear light arrays are desirable for use when an specific long, narrow target area must be illuminated. One such use is for illumination of a continuous web in a web manufacturing inspection system. A web is any material which is manufactured in a single continuous sheet, such as paper and cloth. The web typically passes through a web inspection station that analyzes the web for defects. Cameras are positioned along the width of a web, with each camera taking images of a specific portion of the width of the web. Defects in the web, including discolorations, holes and tears, are identified as inconsistences in the images. Thus, the analysis depends upon consistent lighting of the web. Although the analysis may correct for minor lighting variations, dark spots caused by defective or inconsistent lighting may result in a false identifications of defects.  
           [0004]    A number of companies manufacture modular LED linear arrays. However, these LED linear arrays often are of a fixed length that are not sufficiently long to illuminate a target width. Linear arrays that are extensible use modules that, when connected together, result in gaps between the modules so that the illumination is not uniform. In addition, the brightness of the existing illumination arrays are limited, and the focus of the light is not controllable. Some product offerings consist of LED circuit cards only, requiring the end user to construct a housing, structural mountings, and cooling provisions. Typical prior art illumination sources do not provide sufficient provisions for heat flow away from the illumination source. In addition, these products do not have power supply distribution provisions, and are not sealed for use in extreme environments.  
           [0005]    Therefore, a need exists for an illumination source which is compact, energy-efficient and indefinitely extensible, and which combines the reliability advantages of light emitting diodes (LEDs) with the brightness of conventional lighting for use in direct lighting applications or for backlighting for translucent materials. A need exists for an illumination source that includes LED printed wire board segments that are mountable on an inner mounting base, wherein the LED printed wire board segments are configured to form a uniform illumination line of any length. A further need exists of an illumination source that includes an integral base in contact with the inner mounting base which serves as a heat sink and provides structural support for the illumination source, and which includes channels and cavities for cooling the illumination source and for housing power cables.  
         SUMMARY OF THE INVENTION  
         [0006]    It is an advantage of the present invention to provide an illumination source that utilizes an illumination elements, e.g, light emitting diodes, to provide maximum brightness, long life, and diffuse or focused light of various wavelengths.  
           [0007]    It is a further advantage to provide an illumination source that is extensible to any length while providing uniformity of illumination.  
           [0008]    If is another advantage to provide an illumination source that individually groups LEDs to avoid catastrophic failure of the entire linear LED array.  
           [0009]    Another advantage of the present invention is to provide an illumination source that has a power distribution system that provides equal power to each LED of the linear LED array.  
           [0010]    Yet another advantage is to provide an environmentally sealed illumination source having structural supports which act as heat sinks, include cooling channels for forced air and other cooling means, and provide flexible mounting provisions.  
           [0011]    The exemplary embodiment of the present invention is a compact, energy-efficient extensible illumination source that utilizes light emitting diodes (LEDs) to provide the advantages of brightness and high reliability. The high reliability of the LEDs provides trouble-free operation over a long hour lifetime. The illumination source of the exemplary embodiment includes LED printed wire board segments that may be configured to form a light line of any length. The segments are mounted on a inner mounting base which also serves as a first stage heat sink for the LEDs. Linear mirrors are mounted on the inner mounting base with the LEDs running lengthwise between the mirrors. The mirrors reflect and focus the radiant energy from the LEDs onto the target to produce a uniform linear illumination pattern. A window is mounted in the illumination source above the LEDs and mirrors to provide mechanical protection for the LEDs. The window may be used for diffusing or filtering light from the LEDs.  
           [0012]    Many applications require continuous, high intensity linear light sources of indefinite length. The exemplary embodiment of the illumination source includes assembled segments of a length which can be practically manufactured, and which include provisions for joining individual assemblies together to make indefinitely extensible linear light sources. In one embodiment of the invention, the mounting base and printed wire boards form an assembled segment with the LEDs mounted in patterns such that when these segments are combined, end to end, the illumination remains uniform over the length of the combined assemblies. The assembled segments are mounted on a base and enclosed by brackets to provide an environmental seal as well as structural integrity for the illumination source unit. Each assembled segment of the exemplary embodiment is powered individually by cables so as to avoid power distribution problems.  
           [0013]    In the exemplary embodiment of the present invention, provisions are made to carry away the heat generated by the LEDs to surrounding structures. For example, the high intensity light emitting diodes (LEDs) are secured to the mounting base with heat conducting adhesives. The mounting base thus acts as a heat sink member. An integral base in contact with the inner mounting base also serves as a heat sink and provides structural support for the illumination source. The integral base further includes channels and cavities for cooling the illumination source and for housing power cables.  
           [0014]    In other embodiments of the invention, the high intensity linear light source may be shaped in other geometries other than a straight line, e.g., circular, by designing the printed circuit board accordingly. The light source of alternate embodiments can be lasers or incandescent lamps. In addition, the circuits controlling the light source can be designed to strobe the light source.  
           [0015]    The extensible linear light emitting diode illumination source of an exemplary embodiment is utilized in web inspection systems. The illumination source illuminates the continuously manufactured materials, i.e., “webs”, that are under inspection. The web inspection systems utilize cameras which optically inspect the webs for surface and other defects. Identified defect areas are analyzed by the cameras and/or by computers which receive the defect information from the cameras. Typical applications of the web inspection system includes defect detection of metals, non-woven materials, textiles, fabrics, film, paper, plastics and other materials that are manufactured as continuous web sheets. The illumination source of the exemplary embodiment provides uniform lighting of the web which enables the cameras and/or computers to accurately inspect the webs. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0016]    The present invention will be better understood from the accompanying drawings in which:  
         [0017]    [0017]FIG. 1 is an exploded top view of an assembly of an extensible linear light emitting diode illumination source of a preferred embodiment of the present invention;  
         [0018]    [0018]FIG. 2 an exploded bottom view of the assembly of FIG. 1;  
         [0019]    [0019]FIG. 3 is a isometric view of an assembled extensible linear light emitting diode illumination source;  
         [0020]    [0020]FIG. 4 is a isometric view of a mirrored window support of a preferred embodiment of the present invention;  
         [0021]    [0021]FIG. 5 is an side view of the mirrored window support illustrating an angle of the mirror surface;  
         [0022]    [0022]FIG. 6 is a isometric view of an inner Printed Wire Board (PWB) mounting base of an extensible linear light emitting diode illumination source of the present invention;  
         [0023]    [0023]FIG. 7 is a cross sectional view of the inner PWB mounting base of FIGS. 6 and 9;  
         [0024]    [0024]FIG. 8 is a drawing of a top layer of a left PWB of an embodiment of the present invention;  
         [0025]    [0025]FIG. 9 is a top view of an inner mounting base of a preferred embodiment;  
         [0026]    [0026]FIG. 10 is a drawing of a top layer of a right PWB of the present invention;  
         [0027]    [0027]FIG. 11 is a drawing of a web inspection system utilizing the extensible linear light emitting diode illumination source of a preferred embodiment; and  
         [0028]    [0028]FIG. 12 is a schematic diagram of the circuit of a preferred embodiment of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0029]    [0029]FIG. 1 illustrates an exploded view of an assembly of an extensible linear light emitting diode illumination source  2  of a preferred embodiment of the present invention. The illumination source  2  includes an inner printed wire board (PWB) mounting base  10  attached to a base  28 . Right and left mirrored window supports  18 ,  20  are mounted to a top surface  32  of the PWB mounting base  10 . A window  24  is mounted to top surfaces  34  of the window supports  18 ,  20 . The PWB mounting base  10 , the mirrored window supports  18 ,  20 , and the window  24  are enclosed by brackets  22  and end caps  26 . The brackets  22 , end caps  26 , base  28  and window  24  create an environmentally sealed assembly  2 . FIG. 3 illustrates an assembled extensible linear LED illumination source  2  of a preferred embodiment.  
         [0030]    Continuing with FIG. 1, the illumination source  2  includes light emitting diodes (LEDs)  16 , which are positioned along an entire length of the inner PWB mounting base  10 . As shown in FIGS. 6, 7, and  9 , the PWB mounting base  10  includes left and right troughs  60 ,  62  for accepting and securing the right and left PWB segments  12 ,  14 . One of the cathode or anode leads of each LED is mounted on a right LED printed wire board (PWB) segment  12 , and the other of the cathode or anode leads of each LED are mounted on a left LED PWB segment  14 . The illumination source  2  in alternate embodiments utilizes incandescent light, lasers, or other illumination sources in place of the LEDs  16 .  
         [0031]    Each PWB segment  12 ,  14  may be of a standardized size that has lead pads spaced evenly along the entire length of the segment. In other embodiments of the invention, the lead pads may be configured in other patterns to produce light patterns that are required by specific applications of the illumination source  2 . FIGS. 8 and 10 illustrate left and right PWB segments  12 ,  14  of a preferred embodiment with lead pads  70 ,  72 ,  74 ,  76 ,  78 . The distance “d” between each lead pad  70 ,  72  is constant. Further, a distance between the first lead pad  74  and the leading edge of the PWB  12 ,  14 , and the last lead pad  76  and the trailing edge of the PWB  12 ,  14  joined together equal the constant distance “d”. Thus, the illumination source  2  is extensible by joining right and left segments  12 ,  14  end to end. The resulting illumination source  2  produces a uniform illumination, i.e., without illumination gaps, along its entire length.  
         [0032]    All linear components, including the base  30 , the PWB mounting base  10 , the mirrored window supports  18 ,  20 , the window  24  and the brackets  22 , as shown in FIG. 1, can be manufactured to be of a particular length corresponding to the total number of end to end PWB segments  12 ,  14  required for a specific application of the illumination source  2 . In a preferred embodiment of the invention, only the printed wiring boards  12 ,  14  are manufactured and assembled in short 20 inch (50.8 cm) segments. Continuous length linear components, as described above, provide for mechanical integrity of the resulting illumination source assembly  2 . However, in alternate embodiments of the invention, a grouping of assembled components can create an assembled segment that is held together by brackets  24  and/or a base  30  of the required application length, as long as the grouping of assembled components maintain mechanical integrity and an environmental seal.  
         [0033]    Referring to FIGS. 6, 7, and  9 , the LED printed wire boards  12 ,  14  are securely fastened to the inner mounting base  10  which provides a heat sink path for dissipating heat generated by the LEDs  16 . The right and left PWB segments  12 ,  14  are positioned such that the LEDs  16  straddle a center ridge  64  of the mounting base  10 . The center ridge  64  of a preferred embodiment acts as a continuous structural support member and efficient heat sink for the LEDs  16 . The LEDs  16  are placed in intimate contact with the center ridge  64  of the inner mounting base  10 . In a preferred embodiment of the invention, the LEDs  16  are cemented to the center ridge  64  using conductive cement to increase rigidity of the LEDs as well as to provide maximum heat transfer of the heat generated by the individual LEDs to the inner mounting base  10 .  
         [0034]    As shown in FIGS. 1, 2, and  3 , the inner PWB mounting base  10  is in intimate contact with an outer support structure and base  28  which provides a further path for heat transfer. A base  28  of a preferred embodiment is extruded aluminum for maximum heat dissipation. Linear cavities  36  in the base  28  provide for the circulation of cooling fluid as necessary. Fans, filters and electrical junction boxes  130 ,  134 , as shown in FIG. 11, can be attached at each terminus of the base  28  to force cooling air through the linear cavities  36 , and/or the cable conduits  38  in the base  28 . Mounting channels  30  are utilized for mounting the entire assembly  2  to a supporting structure  102 , as illustrated in FIG. 11. The cable conduits  38  are used for running electrical and power supply cables to each of the PWB segments  12 ,  14 .  
         [0035]    [0035]FIG. 2 illustrates an exploded bottom view of the extensible linear light emitting diode illumination source  2  of FIG. 1. Although for discussion purposes FIG. 2 is referred to as a bottom view, it should be appreciated that the illumination source may be mounted above or in front of a target to provide top or front lighting, or may be mounted below or behind the target to provide backlighting. The lighting configuration and type of LED utilized depends upon the application of the illumination source. For example, in a web defect detection system  100 , as shown in FIG. 11, the material and type of defects to be detected dictates the lighting configuration, including the configurations of backlighting, front diffuse lighting, front specular lighting, dark field lighting, and oblique lighting.  
         [0036]    Continuing with FIG. 2, the bottom surface of the inner PWB mounting base  10  includes an electrical inset  40  that is aligned with a bore or hole  39  in the base  28 . A terminal block slot  42  is recessed within the electrical inset  40  for housing a terminal block  44 . The terminal block  44  connects power supply wiring to the PWB segment  12 ,  14  via feed thru slots  46 , as shown in FIGS. 7 and 9. In the preferred embodiment each LED illumination segment  12 ,  14  has is own power supply connection which allows the LED illumination source  2  to be extended indefinitely without undue power variations between LED illumination segments  12 ,  14 .  
         [0037]    The light emitting diodes of a preferred embodiment are red LEDs having a light output of 75,000 Lux. Red LEDs provide maximum illumination while providing a long lifetime, e.g., 100,000 hours. An illumination source of a preferred embodiment of the invention requires a 17V DC power source, at 3.5 amps per PWB segment  12 ,  14 . In alternate embodiments of the invention, other color wavelength LEDs, or other radiant sources of any wavelength colors, may be utilized if the application so requires. The use of LEDs in the illumination source provides illumination uniformity within 10% or better along the entire length of the illuminated target. In addition, the use of LEDs  16  in conjunction with the window  24  and mirror  50 , as described further below, provides a highly controllable and directed light output.  
         [0038]    The window  24  of a preferred embodiment, as shown in FIGS. 1 and 2, provides for mechanical protection for the LEDs  16 . The type of window  24  utilized in the illumination source  2  may vary according to the intended use of the illumination source  2 . For example, a translucent window  24  may be used as a diffuser in situations where diffused illumination is required. A clear window  24  may be used for non-diffuse applications. A specific color window  24  may be utilized when filtered emissions are appropriate. Other windows  24  may utilize lenslets, or continuous cylindrical or other shaped lenses, to focus the light from the illumination source, e.g., the LEDs  16 .  
         [0039]    [0039]FIGS. 1 and 4 illustrate mirrored window supports  18 ,  20  of a preferred embodiment. The mirror-finished surface  50  of the window support  18 ,  20  serves to reflect radiant energy from the individual LEDs  16  in such a manner that a maximum amount of radiant energy is directed away from the LED illumination source  2  and towards the intended target such as a web  108 , as shown in FIG. 11. The LEDs  16  are centered between the right mirrored window support  18  and the left mirrored window support  20 . The mirrors  50  span the entire length of the LED illumination source  2  to provide a continuous, uniform, linear illumination.  
         [0040]    [0040]FIG. 5 is an end view of the mirrored window support  18 ,  20 . As illustrated in FIG. 5, the mirrored surface  50  is angled with respect to the plane of the PWB segments  12 ,  14  on which the mirrored window supports  18 ,  20  are anchored. The mirrored surface  50  outwardly reflects the illumination produced by the LEDs  16 . In the preferred embodiment of the invention, the inside angle α of the bracket is approximately 80 degrees, to optimize the illumination intensity since LEDs typically emit a wide angle of illumination. In other embodiments, the angle is varied depending upon the lighting conditions necessary for the specific lighting requirements of the illumination source  2 .  
         [0041]    [0041]FIGS. 8 and 10 illustrate the top layers of the left and right printed wiring boards segments  14 ,  12  of an embodiment of the invention. The left and right printed wiring board segments  14 ,  12  are utilized to attach the anode and cathode wiring leads of the individual LEDs  16 . In the preferred embodiment, the printed wiring board circuitry/traces are arranged in a parallel series configuration so that the failure of a single component, e.g., an LED  16 , does not result in the loss of significant radiated illumination. In the example illustrated in FIGS. 8 and 9, the bottom layers of the PWB segments  12 ,  14 , not shown, include traces which connect groups of lead pads to create a series connection. For example, the cathodes of ten (10) LEDs of group A are connected in parallel on the right PWB  12 , the anodes of these LEDs are connected in series to group B on the left PWB  14 . The parallel series continues until the end of the PWD segments  12 ,  14 , when the anodes of the LEDs of group F are connected to a power return. This configuration results in ten (10) parallel LED paths of six (6) LEDs each. Thus, if an LED  16  of a series fails resulting in the failure of the other five LEDs of the series, then the surrounding LEDs of the other series will provide sufficiently uniform illumination along the length of the illumination line.  
         [0042]    [0042]FIG. 12 illustrates the circuit realized by the right and left PWB segments  12 ,  14  of FIGS. 8 and 10. Terminal block  44  includes a power line connected to the cathodes  150  of the ten LEDs of group A. Six LEDs are connected in ten (10) series branches  154 . The anodes of the final LEDs in the series  154  branches are connected to the power return of the terminal block  44 .  
         [0043]    The extensible linear light emitting diode illumination source  2  may be used for surface inspection applications. FIG. 11 illustrates a high performance, web inspection system  100 . The system  100  utilizes smart linescan cameras  110  which optically inspect continuous materials  108 , i.e., “webs”, for surface defects. Typical applications of the web inspection system  100  includes defect detection of metals, non-woven materials, textiles, fabrics, film, paper, plastics and other materials that are manufactured as continuous web sheets. The system  100  employs digital filter processing, adaptive background subtraction and advanced software algorithms to detect very small changes in surface properties.  
         [0044]    Continuing with FIG. 11, the web inspection system  100  includes an illumination source  2  of the preferred embodiment which directs light upward  106  towards the web  108 . Thus, FIG. 11 illustrates a backlit web  108 . In other embodiments of the web inspection system  100 , the illumination source  2  may be position above the web  108  for top lighting. The illumination source  2 , consisting of a number of PWB segments  12 ,  14 , is mounted on a structural support member  102  by means of the channels  30  of the base  28 , as described above. A structural support stand  104  supports both the bank of cameras  110  and the illumination source  102 . The cameras  110 , which are synchronized by an encoder  116  and synchronization signal  132 , output defect results to a computer  130  by means of an ethernet hub  112 . Power supplies  130  provide power to the cameras  110  and the illumination source  2 . Cooling equipment  134  provides cooling to the illumination source  2 . In a preferred embodiment of the invention, the computer  118  controls all elements of the inspection system  100 , including the cameras  110 , the illumination source  2 , the power supply  130 , and the cooling equipment  134 . The inspection system  100  is also connected via a network to additional equipment such as a remote monitor  124  and a modem  128  that connects to, e.g., the Internet.  
         [0045]    Although a preferred embodiment of the invention has been described above by way of example only, it will be understood by those skilled in the field that modifications may be made to the disclosed embodiment without departing from the scope of the invention, which is defined by the appended claims.