Abstract:
A fiber optic light source having an improved cooling scheme for preventing heat damage to the fiber optic cable input ends. The housing for the light source is divided into two sections, with a separate cooling air supply for each section. The first section is provided with a high volume cooling air flow for general area cooling of the lamp assembly, power supply and other exothermic components. The second section is provided with a high velocity cooling air flow directed at the fiber ends. The second cooling air flow is isolated from the heat generated by the lamp assembly and is provided to the fiber ends at essentially ambient temperature.

Description:
[0001]    This application claims the benefit of the Mar. 17, 2000, filing date of U.S. provisional patent application No. 60/190,432. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    Fiber optic lighting systems are used in a variety of applications to provide a cool, flexible, safe source of light. The assignee of the present invention provides fiber optic light systems for use in signs, displays, swimming pools, landscapes and general area lighting. One such fiber optic light system for providing multi-color light effects is described in U.S. Pat. No. 5,528,714 issued Jun. 18, 1996, to Kingstone et al., assigned to the assignee of the present invention and incorporated by reference herein. A fiber optic lighting system may typically include a light source having a fiber optic cable bundle for transmitting light from the light source to a location remote from the light source. The light source may include an enclosure containing a light bulb, a means for securing the end of a fiber optic cable bundle near the light bulb, a power supply or other electronic equipment, and a fan for providing cooling air to the enclosure.  
           [0003]    One of the limiting characteristics of a fiber optic light system is the amount of light that can be delivered from the fiber optic cable. The output of the system depends upon numerous variables, such as the intensity of the light produced by the bulb, the effectiveness of the delivery of the light into the fiber end, and the efficiency of the transmission of the light by the fiber optic cable.  
           [0004]    Numerous advances have been made to improve the optical performance of the fiber optic cables themselves. For example, U.S. Pat. No. 5,333,228 issued Jul. 26, 1994, to Kingstone, assigned to the assignee of the present invention and incorporated by reference herein, describes a fiber optic cable having a reflective center core for reflecting inwardly directed emissions back toward the outside surface of the cable.  
           [0005]    It is known to increase the amount of light introduced at the inlet end of the fiber optic cable bundle in order to increase the amount of light produced by the system. However, light bulbs used to produce such light, for example incandescent and halogen lamps, produce a significant amount of heat energy along with the visible light energy. As the power of the light bulb is increased, the bulb is placed closer to the ends of the fiber optic cables, and the light is focused onto the fiber ends, it becomes increasingly difficult to provide cooling for the cable ends. It is known that plastic cable fibers will melt at approximately 125 degrees Centigrade. Even local melting of the cable will cause a depression in the cable end, thus causing the cooling air to become stagnant and intensifying the local heating effect. In this manner, even a small local hot spot will quickly destroy the functionality of a cable fiber. Therefore, in order to improve the performance of a fiber optic light source, it is necessary to provide an additional margin of safety against melting of the cable ends. U.S. Pat. No. 5,838,860 issued Nov. 17, 1998, to Kingstone et al., assigned to the assignee of the present invention and incorporated by reference herein, describes the use of a plate of heat absorbing material as part of a temperature control scheme within the enclosure of a fiber optic illumination system. In most designs of fiber optic lighting systems the factor limiting the brightness that can be achieved in the cable is the cooling of the cable ends.  
           [0006]    In a light source for a fiber optic system it is necessary to provide both local cooling to the ends of the cable bundle fibers and general cooling for the bulb and other components included in the light source enclosure. The large amount of heat generated by the bulb and other electronics within the enclosure mandates the supply of a high volume of cooling air. However, for cooling the cable end, the volume of air is not as critical as is the velocity of the air, due to the geometry of the cable end and the relatively poor thermal conductivity of the air. In order to provide the required velocity for cooling the fiber end, prior art systems have used fans that are much larger than necessary for the general cooling requirements. As a result, such fans have proven to be noisy and have consumed more electrical power than is necessary for the overall application requirements. Furthermore, prior art fiber optic cable systems incorporating the higher light output of metal halide lamps have been limited. Although these lamps produce more visible light than incandescent and halogen lamps, they also produce more infrared and ultraviolet energy, thereby making it more difficult to provide the necessary cooling to the fiber ends in order to take advantage of these higher output lamps.  
           [0007]    Prior art fiber optic light sources generally include an apparatus for positioning a bulb and an associated reflector along an optical axis to direct a beam of light through a lens to the fiber ends. Such an apparatus can be seen in FIG. 2 of the aforementioned U.S. Pat. No. 5,838,860. The reflector design described in that patent is a one piece glass reflector having a generally truncated ellipsoid reflecting portion formed to be integral with a rearward rectangular or rounded base portion. The bulb is typically affixed within the base portion of the reflector with a high temperature adhesive. Therefore, when a bulb fails, it is necessary to replace not only the bulb but also the reflector assembly. The cable ends are held in position by a ferrule assembly that is attached to the light source housing, and the ferrule and reflector are positioned relative to each other by an optical bench.  
           [0008]    What is desired is an improved fiber optic lighting system capable of providing a higher level of light intensity. It is an object of this invention to provide an improved fiber optic light source capable of providing high intensity light into the fiber ends without causing damage to the fibers.  
           [0009]    It is a further object of this invention to provide such an apparatus with an improved cooling arrangement.  
           [0010]    It is a further object of this invention to provide a light source wherein the fiber optic cable can be replaced quickly and without the need for disassembly of the light source housing, while ensuring that the location of the cable ends is held in tight tolerance to a preferred position.  
           [0011]    It is a further object of this invention to provide a lower cost apparatus for replacing failed bulbs in a fiber optic light source.  
           [0012]    It is a further object of this invention to provide a fiber optic light source that incorporates a metal halide light bulb without the danger of melting of the fiber optic cable bundle ends.  
           [0013]    It is yet another object of this invention to provide an efficient and quiet cooling arrangement for a fiber optic cable light source.  
         SUMMARY OF THE INVENTION  
         [0014]    These and other objects, features and advantages of the present invention are provided by an improved light source apparatus and methods that are described in greater detail below. The lighting apparatus described herein includes a housing; a wall disposed within the housing and defining a first interior volume and a second interior volume; a lamp assembly disposed within the first interior volume and adapted to produce a beam of light; a fiber optic cable having an input end disposed within the second interior volume and extending through the housing; a lens forming a portion of the wall and positioned to focus the beam of light onto the fiber optic cable input end; a first fan in fluid communication with the first interior volume for moving a first flow of cooling air from exterior of the housing through the first interior volume; and a second fan in fluid communication with the second interior volume and adapted to move a second flow of cooling air from exterior of the housing through the second interior volume across the fiber optic cable input end, the first flow of cooling air and the second flow of cooling air being isolated from each other within the housing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    For a better understanding of the present invention, the following detailed description may be taken in conjunction with the accompanying drawings in which:  
         [0016]    [0016]FIG. 1 is a plan view of a fiber optic light source.  
         [0017]    [0017]FIG. 2 is an exploded view of the lamp assembly used in the fiber optic light source of FIG. 1.  
         [0018]    [0018]FIG. 3 is an exploded view of the fiber cable connector assembly used in the fiber optic light source of FIG. 1.  
         [0019]    [0019]FIG. 4 is a cross sectional view of a collar adapted for quick connecting and disconnecting with the connector of FIG. 3.  
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]    The fiber optic light source  10  illustrated in FIG. 1 has a housing  12  including a generally horizontal base  14  mounted on a plurality of feet (not shown), four vertical side walls  16  attached to the base  14  along respective edges, and a top (not shown) generally parallel to the base  14  and removably connected along edges of the side walls  16  opposed the base  14 . The housing  12  defines an interior space for the assembly of various other components of the light source  10 . A generally vertical interior wall  18  is attached at its respective edges to the base  14 , two of the side walls  16 , and the top to divide the interior space into a first interior volume  20  and a second interior volume  22  within the housing  12 . The housing  12  may be fabricated from sheet metal or other known materials by processes known in the art. Joints between the various portions of the housing  12  are preferably formed to be air tight, such as by soldering, welding, gluing, the use of gaskets, or by forming adjoining portions from a single piece of material. An optical member  24  forms a portion of the interior wall  18  for the purpose of allowing a beam of light to pass from the first interior volume  20  to the second interior volume  22 , as will be discussed more fully below.  
         [0021]    A lamp assembly  26  is disposed within the first interior volume  20  and may be removably affixed to the base  14  at a predetermined position in alignment with the optical member  24 . The lamp assembly  26  receives electrical power from a power supply  28  through a wire  30 , also disposed within the first interior volume  20 . Lamp assembly  26  produces a beam of light that is directed through optical member  24  toward an input end  32  of a fiber optic cable  34 . The input end  32  of fiber optic cable  34  is disposed within the second interior volume  22  and is held at a predetermined position by a connector  36  which supports the fiber optic cable  34  as it extends through one side wall  16  of housing  12 .  
         [0022]    The heat energy produced by lamp assembly  26 , power supply  28  and any other exothermic components that may be located within the first interior volume  20  is removed from the housing  12  by a first flow of cooling air  38 . A first fan  40  in fluid communication with the first interior volume  20  produces the first flow of cooling air  38 . The first fan  40  may be mounted directly over an opening (not shown) located in the base  14  for drawing air into the first interior volume  20  and across the lamp assembly  26  and other exothermic components. The heated first flow of cooling air  38  is then directed out of the first interior volume  20  through one or more ventilation openings  42  formed in one of the walls  16 . One may appreciate that the cooling air inlet and outlet may be located at any convenient locations on housing  12 , preferably in locations wherein the heated air is not directly drawn back into the interior of the housing.  
         [0023]    Input end  32  of fiber optic cable end  34  is isolated from the first flow of cooling air  38  by interior wall  18 , however it will receive a significant amount of thermal energy from the lamp assembly  26  in the form of radiant energy. Optical member  24  may be a lens that focuses the beam of light produced by the lamp assembly  26  onto the input end  32 , thereby concentrating the heating effect of the radiant energy. Optical member  24  may be formed to be an infrared filter to lessen the heating effect on the input end  32  of the fiber optic cable  34 , however, supplemental cooling is necessary to prevent the overheating of the cable ends. Such cooling is provided by a second flow of cooling air  44 , isolated from the first flow of cooling air  38 , and produced by a second fan  46  in fluid communication with the second interior volume  22 . The second flow of cooling air  44  may be directed into and out of the second interior volume  22  through respective inlet and outlet openings  48 , 50  formed in the walls  16  or base of the housing  12 . In one embodiment, the base  14  may have dividers located along its bottom surface to divide the air space under the housing  12  into four volumes, one each for the respective inlets and outlets of first and second interior volumes  20 , 22 . The position of the various cooling air openings  42 , 48 , 50  are formed to minimize the mixing of the first  38  and second  48  flows of cooling air outside of the housing  12 . The second flow of cooling air  44  need not be a high volume flow, but is preferably a very high velocity flow directed toward and concentrated at the input end  32  of the fiber optic cable  34 . A baffle plate or tube  52  may be used to concentrate and direct the second flow of cooling air  44  from the second fan  46  onto the fiber ends. Importantly, because the first and second flows of cooling air  38 , 48  are isolated from each other within the housing  12 , the temperature of the second flow of cooling air  48  as it impacts the input end  32  is essentially at ambient temperature. Prior art devices that utilize a single flow of cooling air for cooling both the lamp and the cable ends have an air temperature directed onto the cable ends that is higher than ambient as a result of mixing of the air within the housing volume. The present invention isolates the second flow of cooling air  48  from the cooling air  38  used to cool the lamp assembly  26 . Therefore, a cooler temperature flow of air can be provided at the cable ends than is possible with prior art devices, thereby significantly improving the efficiency of the cooling of the input end  32  of the fiber optic cable  34 .  
         [0024]    [0024]FIG. 2 illustrates an exploded view of the lamp assembly  26  of the fiber optic light source  10  of FIG. 1. The lamp assembly  26  includes a bulb  60 , which may be any commercially available high intensity gas discharge lamp, such as a Thorn ArcStream 4000 metal halide lamp. Unlike prior art designs that utilize a one-piece glass reflector assembly, the reflector assembly of the present invention includes a separate metal base portion  62  and a glass reflector portion  64 . The base  62  may be machined from metal bar stock, with aluminum being preferred due to its heat transfer properties. Base  62  may have a generally round or rectangular external cross-sectional shape, and includes a central bore opening  66  adapted to receive bulb  60 . One or more fins  68  may be formed on the outside diameter surface of the base  62  to improve heat transfer from the base to the first flow of cooling air  38 . Reflector  64  is formed of glass and may have a hollow generally truncated ellipsoidal shape with a reflective coating  68  disposed thereon. Reflector  64  may be made thicker than prior art one piece designs which were purposefully made thin to simplify the manufacturing of an integral base and reflector. Reflector  64  includes a bulb opening  70  adapted to align with the bore opening  66  of base  62 . Bulb  60  is inserted into base  62  and positioned so that its light emitting electrode discharge will be centered at a focal point of the ellipsoidal reflection surface of reflector  64 . Bulb  60  may be attached to base  62  by an ultra high temperature ceramic adhesive such as  904  Zirconia available from Caltronics Corporation in Brooklyn, N.Y. The base  62  may be attached to the reflector  64  with a flexible epoxy such as Duralxo 538 available from Caltronics Corporation. The entire lamp assembly  26  may be provided as a pre-assembled unit, or only the bulb  60  and base  62  may be pre-assembled, with the joint between the base  62  and reflector  64  remaining unglued in order to lower the cost of bulb replacement. For such an embodiment, a mounting fixture must be provided within the housing  12  that is capable of holding the base  62  and reflector  64  together in a predetermined position during operation of the light source  10 .  
         [0025]    The output of lamp assembly  26  is sensitive to the relative positioning of the light-emitting portion of the bulb  60  and the focal point of the reflector  64 . Because the location of the light-emitting portion may vary from bulb to bulb, assembly of lamp assembly  26  may be accomplished in a fixture which allows the output of light to be measured as the bulb  60  is adjusted to various positions within the bore opening  66 . The bulb  60  is moved to a position providing at least a predetermined amount of light output, or to the position of maximum light output, and the assembly is held in this position until the glue adjoining the pieces has hardened. The inventors have found that such a two-piece reflector assembly design is less expensive to manufacture than prior art one-piece base/reflector designs.  
         [0026]    [0026]FIG. 3 illustrates an exploded view of a connector  80  adapted for attachment to the input end  32  of fiber optic cable  34 . The fiber optic cable  34  is not illustrated in FIG. 3, but one may envision the cable  34  inserted through the center openings of the various pieces of connector  80 , as will be described in more detail below. Connector  80  includes an internal clamp assembly  82  comprising a hollow double-ended connector  84  having a first threaded end  86  and a second end  88  threaded over a partial extent and having a distal portion containing a plurality of flexible longitudinal fingers  90 . A connector cap  92  has internal threads  94  sized for engagement with the threads on the second end  88  of the clamp assembly  82 . Connector cap  92  also contains an internal taper (not shown) that compresses the longitudinal fingers  90  onto an inserted fiber optic cable  34  as the connector cap  92  is threaded onto the clamp assembly  82 . Elastomeric washer  96  fits within fingers  90  to protect the cable and to distribute the force exerted by the fingers  90 . A cover  98  fits over the clamp assembly  82  by a friction fit to protect the various components. A bayonet portion  100  includes internal threads on a first end  101  sized for engagement with the external threads on the first threaded end  86  of the internal clamp assembly  82 . The inside diameter of the opposed end portion  102  of bayonet  100  is selected to provide a friction fit with the outside diameter of the inserted fiber optic cable  34 .  
         [0027]    Assembly of connector  80  onto fiber optic cable  34  is accomplished by sliding each of the respective pieces  98 ,  92 ,  96 ,  84 ,  100  over an end of the cable  34 . Connector cap  92  is threaded onto double-ended connector  84  to provide a compression attachment to the cable  34 . Bayonet portion is then threaded onto first threaded end  86  of double-ended connector  84 . Cover  98  is slide over double-ended connector  84  to abut the first end  101  of bayonet portion  100 . The end of the fiber optic cable  34  which is now protruding out of end portion  102  of bayonet  100  is then cut flush with the end of the end portion  102  to form the input end  32  of cable  34 . For plastic cable  34  this cutting step may be accomplished by using a hot knife, as is known in the art.  
         [0028]    [0028]FIG. 4 illustrates a collar  110  adapted for installation into an opening in the wall  16  of housing  12  of fiber optic light source  10  and to receive bayonet  100 . Collar  110  includes a body  112  having a central opening  114  for receiving the end portion  102  of bayonet  100 . The body  112  may be secured into an opening in a side wall  16  of housing  12  by any known mechanism, such as with screws threaded into holes (not shown) formed in the body  112 . A spring-loaded pin  116  is retained in an opening formed perpendicular to the central opening  114 . Pin  116  is spring biased to protrude into the central opening  114 . The pin is sized to fit into a groove  104  formed in the outside surface of bayonet  100  (as seen in FIG. 3) when the bayonet  100  is inserted to a desired position within collar  110 . A taper  106  formed on the surface of the bayonet  100  facilitates the retraction of pin  116  as the bayonet  100  is inserted into the collar  110 . The diameter of pin  116  is selected to be only slightly smaller than the width of groove  104 , for example 0.010 inch smaller, in order to hold the input end  32  of fiber optic cable close to a predetermined position. Similarly, the outside diameter of end portion  102  of bayonet  100  is selected to be only about 0.010 inch smaller than the inside diameter of the central opening  114  of collar  110 . In this manner, fiber optic cable  34  can be quickly and accurately inserted into housing  12  to position input end  32  at a desired position with respect to optical member  24  and lamp assembly  26 . The fiber optic cable  34  may be withdrawn by simply lifting pin  116  away from bayonet  100  and pulling the bayonet  100  out of collar  110 .  
         [0029]    Thus, the device described herein provides the capability for higher light output than prior art devices by incorporating a low cost, high intensity metal halide lamp assembly without risk of cable melting, and by ensuring precise alignment of the fiber ends with regard to the lamp assembly while permitting a quick-disconnect fiber cable attachment.  
         [0030]    While the invention has been described in what is presently considered to be a preferred embodiment, many variations and modifications will become apparent to those skilled in the art. Accordingly, it is intended that the invention not be limited to the specific illustrated embodiment, but that it be interpreted within the full scope and spirit of the appended claims.