Abstract:
A light sensor for an ultraviolet lamp system of the type having an electrodeless lamp excited by microwave energy includes a detector configured to detect light generated by the electrodeless lamp. An elongated channel is configured to be interposed between the detector and the electrodeless lamp. The elongated channel has a first aperture and a second aperture defined at opposing ends thereof. The first aperture is configured to receive light generated by the electrodeless lamp. The second aperture is positioned proximate the detector to transmit at least a portion of light received in the first aperture to the detector.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to ultraviolet lamp systems and, more particularly, to detection of light from ultraviolet lamp systems. 
       BACKGROUND OF THE INVENTION 
       [0002]    Ultraviolet (“UV”) lamp systems are commonly used for heating and curing materials such as adhesives, sealants, inks, and coatings. Certain ultraviolet lamp systems have electrodeless light sources and operate by exciting an electrodeless plasma lamp (“bulb”) with microwave energy. In an electrodeless ultraviolet lamp system that relies upon excitation with microwave energy, the bulb is mounted within a metallic microwave cavity or chamber. One or more microwave generators, such as magnetrons, are coupled via waveguides with the interior of the microwave chamber. The magnetrons supply microwave energy to initiate and sustain a plasma from a gas mixture enclosed in the bulb. The plasma emits a characteristic spectrum of electromagnetic radiation strongly weighted with spectral lines or photons having ultraviolet and infrared wavelengths. 
         [0003]    The bulb in an electrodeless UV lamp system lights when excited by microwave energy and has no direct electrical connections to the other portions of the lamp system. Therefore, a light sensor in the microwave cavity is used to determine if the bulb is lit. Without the light sensor, the UV lamp system has no indication of the status of the bulb (on or off). Conventional light sensors detect light intensity inside the lamp box but are not oriented directly at the bulb. However, in some applications, another lamp may be positioned such that it shines enough light into the cavity to activate the light sensor and cause it to falsely indicate that the bulb is lit. 
         [0004]    One method to reduce the false detections from stray light sources has been to place the light sensor in the microwave chamber and orient it such that it is directed toward the bulb. This method reduces the effects of incoming light from other sources; however, this method also exposes the light sensor to very intense UV light that must be reduced to a level compatible with the sensor&#39;s operating range. In some instances, colored glass filters have been used to reduce the intensity, though with extended exposure to the intense UV light, these filters often change or cloud over and this can adversely affect the calibration of the light sensors. Additionally, at sufficient intensities, incoming light from external sources can still activate the sensor. 
         [0005]    Another method used to avoid the challenges with filters is to direct the light sensor at a highly polished surface and detect the reflected light from the bulb. While this method may help in overcoming some of the challenges with the sensor oriented directly toward the bulb, it still can produce false detections if external light is also reflected from the highly polished surface. 
       SUMMARY OF THE INVENTION 
       [0006]    A light sensor is provided for an ultraviolet lamp system of the type having an electrodeless lamp excited by microwave energy. The light sensor includes an elongated channel having a first aperture and a second aperture. The first aperture is directed generally toward the electrodeless lamp. The second aperture is configured to receive at least a portion of light received in the first aperture and transmit it to a detector. The light received in the first aperture typically includes ultraviolet, visible, and infra-red components. In one embodiment of the light sensor, the elongated channel includes a first elongated channel portion and a second elongated channel portion. The first elongated channel portion is oriented generally transverse to the second elongated channel portion, such that the first elongated channel portion and the second elongated channel portion are not in a direct line of sight. The detector for this embodiment includes light detection circuitry that is configured to detect light reflected in the second elongated channel portion at the second aperture. 
         [0007]    In an alternate embodiment of the light sensor, a lens intersects the elongated channel and is positioned between the first aperture and the second aperture. The lens allows infrared radiation to pass through while substantially blocking visible light. In this embodiment, the detector includes infrared detection circuitry that is configured to detect infrared radiation in the elongated channel at the second aperture. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0008]    The accompanying drawings illustrate embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention. 
           [0009]      FIG. 1  is a block diagram of an ultraviolet lamp system incorporating a light sensor. 
           [0010]      FIG. 2  is a perspective view of the light sensor in  FIG. 1  illustrating an aperture facing the bulb and an aperture used to detect the light. 
           [0011]      FIG. 3  is a top plan view of the light sensor in  FIG. 2 . 
           [0012]      FIG. 4  is a cross sectional view of the light sensor in  FIG. 3  taken along line  4 - 4 . 
           [0013]      FIG. 5  is a cross sectional view of an alternative embodiment of the light sensor in  FIG. 1 . 
           [0014]      FIG. 6  is a cross sectional view of another alternative embodiment of the light sensor in  FIG. 1   
           [0015]      FIG. 7  is a detailed view of a portion of the ultraviolet lamp system in  FIG. 1 . 
           [0016]      FIG. 8  is a cross sectional view of another alternative embodiment of the light sensor in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION 
       [0017]    Referring now to the drawings where like numbers denote like components among the several views,  FIG. 1  is a block diagram of an ultraviolet lamp system  10  that relies upon excitation of an electrodeless lamp or bulb  12  with microwave energy. The bulb  12  is mounted within a metallic microwave chamber  14 . One or more magnetrons  16   a ,  16   b  are coupled via waveguides  18   a ,  18   b  with the interior of the microwave chamber  14 . The magnetrons  16   a ,  16   b  supply microwave energy to the bulb  12  in order to generate ultraviolet light  20 . The ultraviolet light  20  is directed from the microwave chamber  14  through a chamber outlet  22  to an external location through a fine-meshed metal screen  24  which covers the chamber outlet  22  and is capable of blocking emission of microwave energy, while allowing the ultraviolet light  20  to be transmitted outside the microwave chamber  14 . A light sensor  30  is positioned, at least in part, in the microwave chamber  14  in order to detect the ultraviolet light  20  produced by the bulb  12 . In some embodiments, the entire light sensor  30  is placed inside the microwave chamber  14 . In other embodiments, only a portion of the sensor  30  is in the chamber  14  or at least in communication with the chamber  14 . 
         [0018]    Referring now to  FIGS. 2-4 , an exemplary configuration of the light sensor  30  has a front face  32  defining a first aperture  34 , which faces the bulb  12 . The first aperture  34  begins an elongated channel  35 , which terminates at a second aperture  42 . In this embodiment, the elongated channel  35  includes a first elongated channel portion  36  that extends partially through the light sensor  30 . The first elongated channel portion  36  is generally transverse to and intersects with a second elongated channel portion  38 , which extends toward an external face  40  terminating at the second aperture  42 . The first elongated channel portion  36  and the second elongated channel portion  38  are oriented such that the first and second apertures are not in a direct line of sight with each other. In this embodiment, the first and second elongated channel portions  36 ,  38  are linear, though in other embodiments, channel portions may be linear, curvilinear, or combinations of both. Additionally, other orientations of the first and second channel portions  36 ,  38  in other embodiments may range from orientations where the first and second apertures  34 ,  42  are in a direct line of sight with each other to orientations where the first and second channel portions  36 ,  38  form an acute angle with respect to one another. In some embodiments, the first and second channel portions  36 ,  38  are substantially perpendicular. In other embodiments, the first and second channel portions  36 ,  38  are configured to form a U-shape, a V-shape, or other shapes. 
         [0019]    Additional channel portions may also be connected with channel portions  36 ,  38  as illustrated in the embodiments shown in  FIGS. 5 and 6 . With respect to  FIG. 5 , the sensor  50  contains three channel portions  52 ,  54 ,  56 . In this embodiment, the channel portions also do not form a direct line of sight between first and second apertures  58 ,  59 . The second channel portion  54  forms two doglegs with the first  52  and third  56  channel portions, thereby reducing the likelihood of transmitting stray light from external sources. An alternate configuration of the sensor  60  shown in  FIG. 6  is also composed of three channel portions  62 ,  64 ,  66 , where the second channel portion  64  is curvilinear in shape and positioned such that apertures  68 ,  69  are also not in a direct line of sight with each other. 
         [0020]    As illustrated in  FIG. 7  and referencing the embodiment shown in  FIGS. 2-4 , UV light  20  enters the first aperture  34  and travels down the first elongated channel portion  36 . The light  20  is reflected in the second elongated channel portion  38 . Detection circuitry  44  is positioned at the second aperture  42  and is configured to detect the reflected light in the second elongated channel portion  38 . The detection circuitry  44  communicates the status of the bulb (on or off) to the UV Lamp system  10 . By virtue of the fact that apertures  34 ,  42  are not in a direct line of sight with each other, detection circuitry  44  is similarly not in a direct line of sight with bulb  12 , and as such, the intensity of light to which circuitry  44  is subjected is attenuated to a level that is within the operation range of circuitry  44 . 
         [0021]    Sizes of the apertures and channels in some embodiments range, for example, from approximately 0.5 mils to approximately 10 mils. These sizes may be larger or smaller in other embodiments as appropriate for the channel lengths and light intensities of those embodiments. The sizes and configurations of the channel portions are dependent on the range of the detector circuitry  44 . For example, in the present embodiment the first and second channel portions  36 ,  38  may have different sized cross sections to accommodate the detection range of the detector circuitry  44 . The cross sections of the channel portions  36 ,  38  may be the same for other embodiments. Similarly, the first and second channel portions  36 ,  38 , in some embodiments, intersect each other at the ends opposite the first and second apertures  34 ,  42 , or as with this embodiment, the first channel portion  36  intersects the second channel portion  38  between the second aperture  42  and the end of the second channel portion  38  opposite the second aperture  42 . 
         [0022]    The light sensor  30  may be positioned anywhere in the microwave chamber  14  as long as it can be oriented generally toward the bulb. Positioning the light sensor  30  such that it is not directly in line with the chamber outlet  22  assists in reducing the number of false detections. In addition, while stray light  70  from an external light source  72  is able to enter the microwave chamber  14  through the chamber outlet  22 , elongated channel  35  in the light sensor  30  assists in attenuating the stray light  70  from the external light source  72 . This in turn also assists in reducing the number of false detections. 
         [0023]    Another embodiment of the light sensor  80 , illustrated in  FIG. 8 , uses a lens  82  composed of silicon or germanium. Infrared radiation is allowed to pass through the lens  82  but visible light is blocked. UV light and infrared radiation produced from the bulb  12  as well as stray light  70  from external light sources  72  enters the light sensor  80  through a first aperture  84  and travels down an elongated channel  86 . The UV light and stray visible light are blocked by the lens  82 , which allows only the infrared radiation to pass through as stated above. Detection circuitry (not shown), configured to detect infrared radiation, is positioned at a second aperture  88  and communicates the status of the bulb  12  (on or off) to a control of the UV lamp system  10 . While the first and second apertures  84 ,  88  are positioned in a direct line of sight with each other; other embodiments utilizing the lens may position the first and second apertures  84 ,  88  out of a direct line of sight with each other. 
         [0024]    The light sensor, in some embodiments, is machined from a block of aluminum. The walls of the channel (or channel portions) do not require a specific reflectivity; however, the wall properties should not degrade or change over time, as that would change the light input to the sensor, possibly causing the sensor output to be unreliable. The reflectivity of the channel walls may be a design parameter that is considered when the detection circuitry is selected. If a certain reflectivity is required, the walls can be treated by, for example, a gold plating or Teflon coating, though any type of reflective coating that would tolerate the harsh conditions of the environment could be used. 
         [0025]    While the present invention has been illustrated by a description of various embodiments and while these embodiments have been described in considerable detail, it is not the intention of the applicants to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative examples shown and described, for example, other embodiments of the light sensor may utilize combinations of the first and second elongated channel portions in the embodiment in  FIGS. 2-4 , the first, second and third elongated channel portions in the embodiments in  FIGS. 5 and 6 , and the lens in the embodiment in  FIG. 6 . The various features disclosed herein may be used alone or in any combination depending on the needs of the application. Accordingly, departures may be made from such details without departing from the spirit or scope of applicants&#39; general inventive concept.