Patent Publication Number: US-2007109638-A1

Title: Fused thermal and direct view aiming sight

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is a divisional of U.S. application Ser. No. 11/043,627, filed Jan. 26, 2005. 
    
    
     BACKGROUND OF THE INVENTION  
      1. Field of the Invention  
      The present invention generally relates to aiming sights for use with firearms and, more particularly, to a fused thermal and a direct view aiming sight.  
      2. Background Art  
      Conventional aiming sights superimpose an aiming reticle on the view of a target scene for the use of firearms during the day-time. For the use of guns, such conventional aiming sights include non-magnified (1×) aiming sights such as a reflex (red-dot) aiming sight as taught in U.S. Pat. No. 3,905,708; and also include holographic aiming sights as taught in U.S. Pat. Nos. 5,483,362 and 6,490,060. For the use of rifles, such conventional aiming sights include magnified aiming sights such as a rifle scope.  
      Conventional aiming sights for night-time use of firearms typically include a thermal imager, an image intensified night vision tube, or a low-light CCD sensor. The target scenes provided by these night-time use aiming sights are displayed on a screen together with an electronically generated reticle.  
      A visible imaging sensor such as a CCD sensor or an image intensifier tube provides high image resolution and a familiar view (i.e., visible/near IR electronic image) of the target. However, a well-camouflaged target can be difficult for the CCD sensor to detect because camouflages are designed to blend into the background in the visible to near infrared (400 nm to 900 nm) spectral region. A thermal imager operating in the LWIR (8 μm to 12 μm) spectral range can detect warm well-camouflaged bodies such as human beings. However, target identification (e.g., friend or foe) with a thermal imager is difficult. The thermal imager provides a thermal electronic image or map of the target at modest resolution which is quite unlike the familiar visible image. Attempts have been made to combine a CCD sensor and a thermal imager in order to fuse the visible/near IR and thermal electronic images in order to combine the strengths of the CCD sensor and the thermal imager.  
      CCD video sensors and image displays have limited resolution and dynamic range. The amount of information conveyed is a fraction of the information provided by the human eye. Moreover, target aiming by looking at a display screen is indirect and relatively slower than by looking through a conventional aiming sight. This is particularly true in close quarter battles where a 1× electronic sight such as a holographic aiming sight or a red-dot aiming sight allows an operator to keep both eyes open and focused at the target scene.  
     SUMMARY OF THE INVENTION  
      Accordingly, it is an object of the present invention to provide a fused thermal and a direct view aiming sight.  
      It is another object of the present invention to provide an aiming sight having a thermal imaging sight and an optical gun sight.  
      It is a further object of the present invention to provide an aiming sight which provides an image display having a thermal image superimposed on a direct view image.  
      It is still another object of the present invention to provide an aiming sight having a thermal imager for providing a thermal image and a magnified optical weapon sight for providing a direct view image in which the thermal image and the direct view image are combined such that an operator sees the two images superimposed on one another.  
      It is still a further object of the present invention to provide an aiming sight having a thermal imager for providing a thermal image and a non-magnified optical weapon sight for providing an intermediate image in which the thermal image and the intermediate image are combined such that an operator sees the two images superimposed on one another.  
      It is still yet another object of the present invention to provide an aiming sight having a thermal imaging sight and an optical gun sight to generate a superimposed thermal and direct view image for an operator to see.  
      It is still yet a further object of the present invention to provide an aiming sight system having a fused thermal and a direct view aiming sight which function with a night-vision scope to provide a light-intensified superimposed thermal and direct view image for an operator to see during night-time use.  
      The aiming sight in accordance with the present invention generally fuses a thermal image display with a direct image viewed through a conventional weapon sight. The red or amber color monochromic thermal image cues all the warm targets in the field of the direct view image of the weapon sight. An operator can then interrogate the cued targets to determine threats and engage the targets if needed.  
      In carrying out the above objects and other objects, the present invention provides an aiming sight having an optical gun sight, a thermal image sight assembly, and a spectral beam combiner assembly. The optical gun sight generates a direct view image of an aiming point or reticle superimposed on a target scene. The thermal image sight assembly generates a thermal image of the target scene. The spectral beam combiner assembly is positioned behind the optical gun sight and the thermal image sight assembly and is positioned in front of an exit pupil. The spectral beam combiner assembly receives and passes the direct view image from the optical gun sight to the exit pupil and receives and reflects the thermal image from the thermal image sight assembly to the exit pupil such that the thermal image is superimposed onto the direct view image of the optical gun sight for an operator to see as a superimposed thermal and direct view image when the operator positions an eye at the exit pupil.  
      In one embodiment, the beam combiner assembly includes a folding mirror and a spectral beam reflector. The mirror is generally positioned behind the thermal image sight assembly. The reflector is generally positioned behind the optical gun sight and in front of the exit pupil. The mirror receives and reflects the thermal image from the thermal image sight assembly to the reflector. The reflector passes the direct view image from the optical gun sight to the exit pupil and reflects the thermal image from the mirror to the exit pupil in order to superimpose the thermal image onto the direct view image of the optical gun sight for the operator to see as a superimposed image composed of a monochromic thermal image and a direct view image of the target scene together with the aiming reticle.  
      In one embodiment, the thermal image assembly includes a thermal imager, a liquid crystal display (LCD), and a long eye relief eyepiece. The thermal imager generates the thermal image of the target scene. The LCD displays the thermal image as a monochromic image, and the relief eyepiece provides the thermal image displayed by the LCD to the mirror for the mirror to reflect to the reflector.  
      The reflector is a narrow-band spectral reflector which is tuned to reflect the wavelength of the thermal image received from the mirror to the exit pupil while allowing any other light of other wavelengths to pass. The thermal imager includes a narrow-band light emitting diode (LED) to illuminate the LCD screen. The LCD displays the thermal image as a monochromic image on the LCD screen. The brightness of the LED is controllable in order to match brightness of the thermal image with brightness of the direct view image such that the superimposed thermal and direct view image has an even brightness.  
      The thermal image data can be processed such that the thermal image includes targets in the target scene which have a temperature falling within a given temperature range and excludes all other targets in the target scene. The thermal imager and the LCD are controllable to be turned-off such that the direct view image provided from the optical gun sight is passed to the exit pupil without a thermal image superimposed thereon when the thermal image sight assembly is turned-off.  
      A focal length of the thermal imager, a size of the LCD, and a magnification of the eyepiece can be selected such that the thermal image is made to be the same angular size as the direct view image in order for the superimposed thermal and direct view image to have an even size.  
      The system can be used at night with an image intensified night vision device if the brightness of the LCD screen and the brightness of the aiming reticle of the direct view sight can both be dimmed to a level that can be used with an image intensified night vision device. The brightness of the LED used to illuminate the LCD screen can be reduced to a very low level by controlling the driving voltage and the use of pulse width modulation. The effective brightness of the display is proportional to the product of the driving voltage and the duty cycle of the pulse width modulation. For example, a 200-to-1 voltage adjustment range together with a 10,000-to-1 range in the modulation duty cycle produce a total brightness adjustment range of 2,000,000-to-1.  
      The optical gun sight may be either a night vision device compatible non-magnified reflex optical sight or a holographic optical sight in which brightness of the aiming reticle is adjustable over a wide range. A night-vision scope may be positioned at the exit pupil of the optical gun sight. The night-vision scope light-intensifies the superimposed thermal and direct view image for night-time use of the aiming sight.  
      Also, in carrying out the above objects and other objects, the present invention provides another aiming sight. This aiming sight generally includes a magnified optical sight, a thermal image sight assembly, and a spectral beam combiner assembly. The optical sight includes an objective lens and an aiming reticle which is placed at an intermediate image plane of the objective lens. The optical sight has an exit pupil at a position behind the eyepiece lens assembly which collimates the image at the intermediate image plane. The thermal image sight assembly generates a thermal image of the target scene. The beam combiner assembly has a spectral beam reflector positioned at the intermediate image plane. The reflector receives and passes the intermediate image having the superimposed aiming reticle from the optical sight to the exit pupil and receives and reflects the thermal image from the thermal image sight assembly to the exit pupil such that the thermal image is superimposed over the aiming reticle and the intermediate image for an operator to see as one combined image when the operator positions an eye at the exit pupil.  
      The optical power of the thermal imager and the size of the LCD may be selected to match magnification power of the objective lens such that a size of the intermediate image plane of the optical sight and a size of the LCD are the same. Brightness of the LCD is controllable in order to match brightness of thermal image with brightness of the intermediate image such that the combined image has an even brightness.  
      The above objects and other objects, features, and advantages of the present invention are readily apparent from the following detailed description of the preferred embodiment(s) when taken in connection with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1   a  illustrates a side perspective view of a fused thermal and a direct view aiming sight in accordance with the present invention mounted on a firearm;  
       FIG. 1   b  illustrates a backside perspective view of the aiming sight and the firearm shown in  FIG. 1   a;    
       FIG. 2  illustrates a conceptual drawing of the fused thermal and the direct view aiming sight in accordance with the present invention;  
       FIG. 3  illustrates a conceptual drawing of the fused thermal and the direct view aiming sight used with a night-vision scope or goggle for operation at night in accordance with the present invention; and  
       FIG. 4  illustrates a conceptual drawing of the fused thermal and the direct view aiming sight in accordance with another embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)  
      Referring now to  FIG. 1 , a fused thermal and a direct view aiming sight  10  in accordance with an embodiment of the present invention mounted on a firearm  11  is shown. It is to be appreciated that the aiming sight in accordance with the present invention may be similarly mounted on other firearms such as carbines and machine guns.  
      Referring now to  FIG. 2 , with continual reference to  FIG. 1 , a conceptual drawing of fused thermal and direct view aiming sight  10  is shown. As shown in  FIGS. 1 and 2 , aiming sight  10  generally includes an optical gun sight  12 , a thermal image sight assembly  14 , and a spectral beam combiner assembly  16 .  
      Optical gun sight  12  is a conventional gun sight for use in close quarters may be a non-magnified (1×) reflex (red-dot) gun sight as taught in U.S. Pat. No. 3,905,708 which is hereby incorporated by reference in its entirety. Alternatively, optical gun sight  12  may be a holographic gun sight as taught in U.S. Pat. Nos. 5,483,362 and 6,490,060, which are both hereby incorporated by reference in their entirety. In operation, optical gun sight  12  superimposes an aiming point (i.e., aiming reticle) on the view of a target scene. The non-magnified optical gun sight has unlimited eye relief and the aiming reticle and the target from any position behind the optical gun sight. As such, optical gun sight  12  provides a direct view image which is viewed through the optical gun sight.  
      Thermal image sight assembly  14  generally includes a thermal sensor or imager  22 , a monochromic liquid crystal display (LCD)  24  illuminated by a light emitting diode (LED), and a long eye relief eyepiece  26 . Thermal imager  22  is preferably an un-cooled micro-bolometer array thermal imager. Thermal imager  22  includes thermal imaging processing electronics and a thermal sight for generating a thermal image of a target scene. LCD  24  is preferably a miniature monochromic image which is illuminated by a high-brightness LED. LCD  24  generally displays the thermal image generated by thermal imager  22  as a high-brightness monochromic image.  
      Spectral beam combiner assembly  16  generally includes a folding mirror  30  and a spectral beam reflector  32 . Mirror  30  is positioned generally behind thermal image sight assembly  14 . Reflector  32  is positioned generally behind optical gun sight  12  and is in front of exit pupil  20 . Mirror  30  is configured to direct the thermal image displayed by LCD  24  to reflector  32 . Reflector  32  is configured to reflect light having the wavelength of monochromic image  24  while transmitting all other light. As such, reflector  32  reflects the thermal image displayed by LCD  24  and is a narrow-band spectral beam reflector. As will be described below, reflector  32  reflects the thermal image displayed by LCD  24  and passes the direct view image provided by optical gun sight  12  to exit pupil  20  for operator  18  to see as one fused thermal and direct view image.  
      In operation of aiming sight  10 , thermal imager  22  generates a thermal image of a target scene. Thermal imager  22  generates the thermal image by detecting targets in a target scene having a temperature falling within a temperature range (e.g., between 90° F. and 110° F.) for display as the thermal image. Thermal imager  22  may employ more sophisticated target detection processing. LCD  24  then displays the thermal image as a high-brightness monochromic image.  
      The thermal image displayed by LCD  24  is viewed through long eye relief eyepiece  26 . Long eye relief eyepiece  26  has an eye relief of at least 80 mm. Mirror  30  and reflector  32  finction to place the thermal image displayed by LCD  24  in line with optical gun sight  12 . By properly choosing (i) the focal length of an imaging lens of the thermal sight of thermal imager  22 , (ii) the display size of LCD  24 , and (iii) the magnification of eyepiece  26 , the thermal image displayed by the LCD is made the same size as the direct view image provided through optical gun sight  12 .  
      By then adjusting the alignment of the thermal sight and/or by adjusting the alignment of mirror  30 , operator  18  sees two superimposed images of a target scene by placing his eye at the position of exit pupil  20 . The two superimposed images include the direct view image provided by optical gun sight  12  and the thermal image provided by thermal image sight assembly  14 . That is, operator  18  sees the direct view image target scene and amber color spots indicating objects in the target scene which have the temperature of human beings (i.e., temperatures falling within the range of 90° F. to 110° F.).  
      Thermal sight assembly  14  further includes a power supply such as a battery  34 . Battery  34  supplies power to thermal imager  22  and its processing electronics and also supplies power to LCD  24 . Thermal imager  22  and LCD  24  are set in a standby mode to save the life of battery  34 . Operator  18  turns-on thermal imager  22  and LCD  24  by pressing a remote switch or the like. In response to the actuation of the remote switch, thermal imager  22  and LCD  24  instantly turn-on and stay on for a minute or so. Operator  18  generally turns-on thermal imager  22  and LCD  24  when the operator desires to search for hidden or camouflaged targets in a target scene. When operator  18  cues a target from its thermal signature, the operator can turn off thermal sight assembly  14  in order to remove the superimposed thermal image from the direct view image target scene and then concentrate on the target without distraction.  
      Referring now to  FIG. 3 , with continual reference to  FIG. 2 , a conceptual drawing of the fused thermal and direct view aiming sight  10  used with a night-vision scope or goggle  36  for operation of the aiming sight at night is shown. A holographic gun sight  12  has a reticle brightness that can be lowered to a relatively low, night-vision device compatible level. As such, with the use of a holographic gun sight  12 , aiming sight  10  can be used with image intensified night-vision scope or goggle  36  for night-time operation. Night-vision scope or goggle  36  is placed at exit pupil  20  of optical gun sight  12  and thermal image sight assembly  14 . When an eye of operator  18  is positioned at exit pupil  20 , the operator sees through night-vision scope  36  a superimposed light-intensified thermal image generated by thermal image sight assembly  14  and a light-intensified aiming reticle of the direct view image generated by holographic gun sight  12 .  
      The brightness of the LED used to illuminate LCD  24  is lowered to a level suitable for use by night-vision scope  36 . This is done so that the light-intensified thermal image seen through night-vision scope  36  has a brightness suitable for viewing by operator  18 . The LED brightness may be adjusted by varying the driving voltage and by using pulse-width modulation as taught in U.S. Pat. No. 5,483,362 in order to adjust both the intensity and the duty cycle of the modulated LED. Once again, the thermal image generated by thermal image sight assembly  14  can be used by operator  18  to cue warm targets such as human bodies and the high-resolution light-intensified direct view image generated by holographic gun sight  12  can be used by the operator for target recognition, identification, and aiming.  
      In either of the configurations shown in  FIGS. 2 and 3 , LCD  24  and relief eyepiece  26  are attached firmly to optical gun sight  12 . Thermal imager  22  with its thermal sight can also be attached to optical gun sight  12  with LCD  24  and eyepiece  26  as an integrated unit. Alternatively, thermal imager  22  with its thermal sight can be mounted forward near the tip of the barrel of a weapon and connected to LCD  24  via a cable (as shown in  FIG. 1 ). In this configuration, LCD  24  receives the video signal indicative of the thermal image generated by thermal imager  22  via the cable. Placing thermal imager  22  at the front will avoid having the heat from the barrel getting into the field of view of thermal imager  22 . Such heat could overwhelm the LWIR thermal sensor array.  
      Referring now to  FIG. 4 , a fused thermal and direct view aiming sight  40  in accordance with another embodiment of the present invention is shown. Aiming sight  40  implements the direct view thermal fusion with a rifle scope. As is known in the art, a rifle scope is a magnified optical aiming scope. Similar to aiming sight  10 , aiming sight  40  generally includes an optical rifle aiming scope, a thermal sight assembly, and a spectral beam combiner assembly.  
      As shown in  FIG. 4 , the optical rifle aiming scope of aiming sight  40  includes an objective lens  42 , a Pechan prism  44 , a reticle  46 , and an eyepiece  48 . These elements of the optical rifle aiming scope are configured to generate an aiming reticle superimposed over a direct view image of a target scene for an operator to see. The optical rifle aiming scope is modified such that spectral beam reflector  32  is placed right behind the intermediate image plane where reticle  46  is located. As such, spectral beam reflector  32  is placed between reticle  46  and eyepiece  48  of the optical rifle aiming scope. (In contrast, in aiming sight  10  spectral beam reflector  32  is placed behind optical gun sight  12  as shown in  FIGS. 1, 2 , and  3 .)  
      In operation, LCD  24  receives a thermal image of a target scene generated by thermal imager  22  and then displays the thermal image as a monochromic image. Reflector  32  receives the thermal image displayed by LCD  24  as the LCD is illuminated by a narrow-band LED. Reflector  32  reflects the thermal image displayed by LCD  24  and superimposes the displayed thermal image over reticle  46  and the intermediate image of the target scene.  
      The displayed thermal image of LCD  24  is aligned with the direct view image viewed through the optical rifle aiming scope. The optical power of the thermal sight of thermal imager  22  and the size of LCD  24  are chosen to match the power of objective lens  42  of the optical rifle aiming scope such that the image sizes of the intermediate image plane formed by the objective lens and the LCD thermal image formed by LCD  24  are the same. Thermal imager  22  is steered in order to make these two images coincide.  
      When operator  18  looks through eyepiece  48  of the optical rifle aiming scope, the operator sees the magnified direct image view of the target scene (generated by the optical rifle aiming scope) and superimposed on this direct image view is the monochromic red thermal image view (displayed by LCD  24 ). By displaying only warm targets within the desired temperature range, operator  18  can use the thermal image view to locate and cue possible camouflaged human and animal targets.  
      Thus, it is apparent that there has been provided, in accordance with the present invention, a fused thermal and a direct view aiming sight that fully satisfies the objects, aims, and advantages set forth above. While embodiments of the present invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the present invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the present invention.