Abstract:
A thermal imaging apparatus comprises a housing defining an entrance pupil for ingress of imaging radiation. At least one light sensor is positioned forward of the entrance pupil. An electronic imaging device such as a focal plane array is located in the housing rearward of the entrance pupil for converting imaging radiation to electrical signals for further processing. The apparatus further includes a shutter having an open position and a closed position. In the closed position, the shutter is located between the entrance pupil and the electronic imaging device so as to inhibit exposure of the electronic imaging device to incident radiation. Circuitry is provided for selectively operating the shutter to be in the closed position based on signals produced at the light sensor.

Description:
BACKGROUND OF THE INVENTION 
     The present invention relates generally to thermal imagers. More particularly, the invention relates to a thermal imager having a mechanism for protecting internal components from damage due to sunlight and other high energy radiation sources. 
     Thermal imaging cameras are widely used in a variety of applications, such as predictive maintenance in industrial facilities. While past imagers often utilized a scanning technique, modern imagers generally incorporate an infrared (IR) focal plane array (FPA) for producing the thermal image. Focal plane arrays have many advantages, such as the speed at which successive images can be produced for display. 
     One drawback of current focal plane arrays is their susceptibility to damage when exposed to high radiation sources such as sunlight. For example, a user may inadvertently damage the focal plane array (and thus the overall imager) by waving the imager&#39;s lens in a direction toward the sun. Thus, a need exists to provide methods of protecting the focal plane array from sunlight exposure. 
     SUMMARY OF THE INVENTION 
     According to one aspect, the present invention provides a thermal imaging apparatus comprising a housing defining an entrance pupil for ingress of imaging radiation. At least one light sensor is positioned forward of the entrance pupil. An electronic imaging device is located in the housing rearward of the entrance pupil for converting imaging radiation to electrical signals for further processing. 
     The apparatus further includes a shutter having an open position and a closed position. In the closed position, the shutter is located between the entrance pupil and the electronic imaging device so as to inhibit exposure of the electronic imaging device to incident radiation. Circuitry is provided for selectively operating the shutter to be in the closed position based on signals produced at the light sensor. In presently preferred embodiments, the electronic imaging device is a focal plane array (such as an alpha-silicon or vanadium oxide infrared focal plane array). 
     The light sensor may be located in a portion of the housing forward of the entrance pupil which forms a hood. For example, the light sensor may be situated at a position in the hood below the entrance pupil. In such a position, the light sensor will detect sun exposure before imaging thereof by the electronic imaging device. Often, a silicon phototransistor may be utilized as the light sensor. In some exemplary embodiments, the light sensor may comprise a pair of light sensors located at respective left and right positions below the entrance pupil. 
     Preferably, the thermal imaging apparatus may comprise a lens cap adapted to cover the entrance pupil when the apparatus is not in use. The apparatus may be advantageously adapted to be in a powered off state when the lens cap is in position to cover the entrance pupil. 
     Other aspects of the present invention are achieved by an imaging apparatus comprising structure defining an entrance pupil for ingress of imaging radiation. A focal plane array is located rearward of a lens at the entrance pupil. A shutter is provided having an open position and a closed position. In the closed position, the shutter is located between the lens and the focal plane array so as to inhibit exposure of the focal plane array to incident radiation. Circuitry is provided for selectively operating the shutter to be in the closed position when radiation that would otherwise impinge the focal plane array exceeds a predetermined threshold. 
     Additional aspects of the present invention are achieved by an imaging apparatus comprising structure defining an entrance pupil for ingress of imaging radiation. A focal plane array is located rearward of a lens at the entrance pupil. A shutter is provided having an open position and a closed position. In the closed position, the shutter is located between the lens and the focal plane array so as to inhibit exposure of the focal plane array to incident radiation. 
     The apparatus also includes circuitry for selectively operating the shutter to be in the closed position when radiation that would otherwise impinge the focal plane array exceeds a predetermined threshold. At least one light sensor is located forward of the lens, the circuitry being operative to control the shutter based on signals produced at the light sensor. A lens cap adapted to cover the entrance pupil when the apparatus is not in use is also provided. The apparatus is adapted to be in a powered off state when the lens cap is in position to cover the entrance pupil. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A full and enabling disclosure of the present invention, including the best mode thereof, to one of ordinary skill in the art, is set forth more particularly in the remainder of the specification, including reference to the accompanying drawings, in which: 
         FIG. 1  is a rear perspective view of a thermal imager constructed in accordance with an embodiment of the present invention; 
         FIG. 2  is a front perspective view of the thermal imager of  FIG. 1 ; 
         FIG. 3  is an enlarged front elevation showing the lens of the thermal imager of  FIG. 1 ; 
         FIG. 4  is an enlarged rear elevation showing the display of the thermal imager of  FIG. 1  in the sun protection mode; and 
         FIG. 5  is a schematic diagram of a sun protection mechanism constructed in accordance with the present invention. 
     
    
    
     Repeat use of reference characters in the present specification and drawings is intended to represent same or analogous features or elements of the invention. 
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     It is to be understood by one of ordinary skill in the art that the present discussion is a description of exemplary embodiments only, and is not intended as limiting the broader aspects of the present invention, which broader aspects are embodied in the exemplary constructions. 
       FIGS. 1 and 2  illustrate a thermal imager  10  constructed in accordance with the present invention. Imager  10  includes a housing  12  in which the components of a thermal image camera are located. Preferably, housing  12  is formed by complementary left and right housing portions  12   a  and  12   b  which are joined together during assembly. While any suitable material can be utilized, housing portions  12   a  and  12   b  are preferably formed of a rigid high impact plastic material. Selected regions of housing  12  may be desirably overmolded with a softer polymeric material. 
     Referring now also to  FIG. 3 , housing  12  includes a front portion defining a hood  14  where the device&#39;s lens  16  is located. One skilled in the art will recognize that the target energy enters the device through lens  16 . As will be described more fully below, a pair of light sensors  18  and  20  are positioned at respective left and right positions below lens  16 . Preferably, light sensors  18  and  20  are robust optical sensors, such as silicon photo transistors mounted to a printed circuit board which is installed in the hood. 
     Referring now also to  FIG. 2 , a lens cover  22  is provided to cover lens  16  when imager  10  is not in use. Preferably, lens cover  22  is opaque so as to protect the imager&#39;s internal components from the passage of infrared radiation when the unit is not being used. 
     In this case, lens cover  22  slides up and down in a channel provided in front shroud  24 . Shroud  24  extends to a location under handle  26  to facilitate placement of the entire unit in a computer docking station for recharging and specialized programming. A trigger  28  is located on handle  26 , as shown. Trigger  28  permits the user to store selected images in the device&#39;s internal memory. In the illustrated embodiment, laser diode  30  projects a dot of light forward of the imager to facilitate aiming. 
     As will be described more fully below, cover  22  may be adapted to serve as the means by which the user turns the unit on and off. In this regard, cover  22  can be moved to the down position (shown) when imager  10  is in use. Cover  22  is moved to an up position in front of hood  14  when imager  10  is turned off. An appropriate mechanism turns the unit either on or off depending on the position of cover  22 . 
     As noted above, exposure to high radiation sources, such as sunlight, can often damage the focal plane array located inside of imager  10 . Because the user will slide lens cover  22  into a position over hood  14  when the unit is turned off, the unit will always be protected from sunlight exposure when in a powered off state. 
     Referring now particularly to  FIG. 1 , a display  32  is preferably located at the rear of imager  10 . In  FIG. 1 , a variety of information is being shown on the display, including a thermal image of the device being inspected. A temperature gradient scale and other information may also be provided in different regions of the display. For example, this depiction indicates that the machine being inspected is a “compressor” based on stored information. Various buttons  34 ,  36  and  38  may also be provided on the rear portion of housing  12  to allow the user to perform various tasks. 
     Referring now to  FIGS. 4 and 5 , imager  10  includes a further mechanism for protecting the focal plane array when the unit is in use. When potentially damaging exposure is detected, the unit can advantageously enter a “sun protection mode.” (As one skilled in the art will appreciate, the term “sun protection mode” indicates that potentially harmful levels of radiation have been detected from whatever source, including but not limited to the sun.) As shown in  FIG. 4 , display  32  will preferably depict a graphical representation so informing the user. In one preferred embodiment, the unit will remain in the protection mode until powered off and then on again. The user may accomplish this by sliding the lens cover  22  to a position over hood  14  and then back down. 
     Certain additional details will now be described with particular reference to  FIG. 5 . When lens cover  22  is moved to the power on position, incident radiation is allowed to enter hood  14 . The radiation passes through lens  16  and impinges focal plane array (FPA)  40 . In presently preferred embodiments, FPA  40  is an infrared (IR) FPA of any suitable type, such as alpha-silicon or vanadium oxide. FPA  40  converts the incident radiation into electrical signals which are then provided to signal processing circuitry  42 . Circuitry  42  processes the raw signals to produce IR video and data that can be shown on display  32 . 
     One technique for using lens cover  22  as a means to turn the unit off and on is also illustrated in  FIG. 5 . In this case, a small magnet  44  is in lens cover  22 . (In presently preferred embodiments, magnet  44  is actually located near the top of lens cover  22 .) When lens cover  22  is moved to the down position, reed switch  46  will close, providing power from battery  48  to the various components within imager  10 . While a magnet/reed switch mechanism is shown in this embodiment, one skilled in the art will appreciate that other suitable mechanisms for turning the unit on and off can also be utilized. 
     Imager  10  includes a shutter which can protect FPA  40  from extensive sun exposure during operation. In this case, the shutter is configured as a “flag”  50  which is also used for offset correction during normal operation. Specifically, flag  50  will periodically rotate during normal operation to a position in front of FPA  40  to provide a temperature reference. Flag  50  is rotated by a small motor  52  which is operated by shutter controller circuitry  54 . 
     The sun protection mechanism operates as follows in the illustrated embodiment. As imager  10  is raised in a direction toward the sun  56 , excessive radiation will begin to enter hood  14 . In most cases, however, this sunlight will encounter light sensors  18  and  20  before lens  16 . This is illustrated in the diagram where radiation from the sun is shown impinging light sensor  20 , but not lens  16 . The sun&#39;s radiation will not directly impinge lens  16  unless and until imager  10  is moved to the position  58  relative to the sun. 
     Output signals from light sensors  18  and  20  are fed to circuitry  54 . When the level of radiation detected by light sensors  18  and  20  exceeds a predetermined threshold, flag  50  will be rotated to a position in front of FPA  40  (as indicated at  60 ). As a result, flag  50  will prevent the incident radiation from impinging and possibly damaging FPA  40 . In the illustrated embodiment, the graphical representation depicted in  FIG. 4  will then be shown on display  32 , informing the user that the device is in the sun protection mode. 
     It can thus be seen that the present invention provides a thermal imager having an effective sun protection mechanism. While preferred embodiments of the invention have been shown and described, modifications and variations may be made thereto by those of ordinary skill in the art without departing from the spirit and scope of the present invention. In addition, it should be understood that aspects of the various embodiments may be interchanged both in whole or in part. Furthermore, those of ordinary skill in the art will appreciate that the foregoing description is by way of example only, and is not intended to be limitative of the invention as further described in the appended claims.