Abstract:
A weapon aiming system may utilize a laser diode and a reflective coating on an optical element to generate a red dot aim point for a shooter with a bright view to the target with minimal color distortion. The optical element may utilize an off-axis parabolic lens to reduce parallax to improve sighting accuracy. The weapon aiming system may utilize visible and infrared aim lasers that are coaligned to simplify boresighting of the weapon and to simplify target acquisition. The weapon aiming system may include a magnifier and a sight being disposed along a longitudinal rail of a weapon in a position with the close quarter combat sight being disposed between the magnifier and the weapon muzzle.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims the benefit of U.S. provisional patent application Ser. No. 60/568,528, filed May 6, 2004, the disclosure of which is incorporated herein by reference in its entirety. 
    
    
     TECHNICAL FIELD 
     This invention relates to a weapon-aiming device, and more particularly to a weapon-mountable red dot sight. 
     BACKGROUND OF THE INVENTION 
     In close quarter combat, typically in the ranges of 2-800 meters, soldiers are required to rapidly acquire, identify, and accurately fire on enemy targets. Soldiers may use weapon-mounted sights with visible and infrared light sources to assist in the aiming process during daytime and nighttime missions. These sights may be mounted on handheld weapons such as the M4A1 carbine and other small arms and are used to provide better target observation, illumination, and marking. 
     Traditional weapon-mounted sights utilize red dot sights that incorporate a light emitting diode (LED) as a source of illumination in conjunction with a pinhole aperture. Light emitted from the LED and passing through the pinhole is reflected by an optical element and forms an aim point that can be seen by a shooter looking through the close quarter combat sight. Because the LED has a relatively large emitting area and practical transmission and machining capability limitations limit how small a pinhole can be used, the resulting aim point is relatively large in size. Such a large aim point is undesirable and impairs accuracy especially when aiming at a relatively small target or a target at a relatively long distance. 
     Red dot sights may be used both during the day without assistance or at night with the assistance of a night vision device such as a monocular or goggle. Red dot sights utilizing tritium (a radioactive isotope) exist, but suffer because the brightness can not be increased during the day and decreased during the night to be compatible with night vision devices. 
     A dichroic coating is commonly used on a lens surface of a red dot sight to partially reflect or transmit light and to provide a simultaneous view of the red dot and the target scene. Because a visible LED has a relatively weak, apertured light intensity, the optical element typically needs to have a highly reflective coating if a significant amount of the light energy is to be reflected toward the shooter. This highly reflective coating effectively blocks light from the target scene in transmission at wavelengths similar to those being reflected from the LED. Therefore if the a red dot sight employs a red LED, the optical element commonly has a coating that reflects a relatively high percentage of the red light energy from the LED to increase the brightness of the LED visible to the eye, and thus also blocks a high percentage of red light from the target scene. The result is the target scene has an undesirable blue tint. Not only does this blue tint cause the scene to look unnatural, it also impairs one&#39;s ability to use the sight with two eyes open because one eye sees the target scene in normal color while the eye seeing the target scene through the sight sees a bluish scene. The blue tint also makes target acquisition difficult in low light conditions such as dusk or dawn because a lack of light transmission. Depending on the nature of the reflective coating, the coating impairs the transmission of light in a portion of the electromagnetic spectrum that the night vision device is sensitive thereby reducing the performance capabilities of the night vision device, in turn affecting the ability of the operator to detect and direct fire on the target. This can be quite distracting. The large aim point and the distorted color of the target scene are two major limitations of existing red dot sights. 
     Traditional red dot sights have optical elements having spherical optical elements or in some cases holographic elements. With such elements, parallax is present to a significant degree. That is, as the observer looking through the red dot sight moves his eye relative to the sight optical aperture, the point of aim moves with respect to the target. This results in a loss of aiming accuracy. Also, since different shooters hold their eye differently relative to the sight, no single boresight or zero setting of the sight is suitable for all users. This means that each shooter may need to boresight or zero the red dot sight for himself. 
     BRIEF SUMMARY OF THE INVENTION 
     A weapon mountable sight has a housing configured to be coupleable to a weapon, where the housing houses a laser diode for a light source and a reflective element to reflect light emitted from the laser diode towards a user looking through the housing. 
     A close quarter combat sight has a housing, where the housing houses a source of light and a parabolic element. The parabolic element having a reflective coating capable of reflecting light in a narrow band within the visible passband, with a transmission of 10%-40% relative intensity. 
     A weapon aiming system has a weapon with rails along at least a portion of a longitudinal axis between a butt and a muzzle, a magnifier, and a close quarter combat sight. The close quarter combat sight being disposed along the rail in a position between the magnifier and the muzzle. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a better understanding of the present invention, together with other objects, features and advantages, reference should be made to the following detailed description which should be read in conjunction with the following figures wherein like numerals represent like parts: 
         FIG. 1  is a relative comparison of the emitting dimensions of an LED versus a laser diode. 
         FIG. 2  is a profile view of a red dot sight with an LED light source and a spherical optical element. 
         FIG. 3  is an eyepiece eye-box diagram. 
         FIG. 4  is a profile view of a red dot sight with a laser diode light source and a parabolic lens consistent with the invention. 
         FIG. 5  is a profile view of a red dot sight with an optical element consistent with the invention. 
         FIG. 6  is a plot of reflection versus wavelength comparing a coating transmission spectrum for an LED coating and a laser coating. 
         FIG. 7  is a profile view of a weapon with a close quarter combat sight and magnifier. 
         FIG. 8  is a profile view of a weapon with a close quarter combat sight and magnifier consistent with the invention. 
         FIG. 9  is a profile view of a magnifier consistent with the invention. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  is a relative comparison of the emitting dimensions of a light emitting diode (LED) versus a laser diode. A typical LED has an emitting dimension of 100 microns square or larger whereas a typical laser diode has an emitting dimension of 1 micron×5 microns. When using an LED in a close quarter combat optics, for example a red dot sight, a light blocking plate with an aperture is placed in front of the LED to reduce the size of the exiting light beam. The aperture size is approximately 0.0005″ to 0.002″ in diameter. The aperture is typically formed in the plate, as a secondary step after molding or machining, with a laser due to the small aperture size requirement. The plate with this secondary step can add significant cost to the sight. The light emitted from the LED that is blocked by the plate (&gt;95%) is trapped inside the optics housing and adds heat within the enclosure and wastes energy and battery or electric source life. Close quarter combat sights are run off of batteries and this wasted light can greatly reduce the overall battery life. 
     By using a laser diode as the light source in a close quarter combat optic, the emitting area is reduced to a fraction of the size of an LED. As can be seen in  FIG. 1  this smaller emitting area enables the sight to have a smaller and therefore more precise aiming point. The smaller emitting area can also eliminate the need for a blocking plate with an aperture. Due to the more efficient use of light within the optics housing, the laser diode can be driven with less power, which can result in improved battery life. 
     In addition, by using a laser diode, the light energy is intense, concentrated, and is essentially monochromatic. This means the reflective coating on the optical element can be a relatively low reflectance coating and still allow for an easily observable dot in the brightest environments. Such narrow band reflective coating reflects a small portion of the light emitted by the laser diode, but because of the low reflectance, blocks only a small percentage of light from the target scene. This results in the target scene retaining its natural color. This in turn results in a brighter and more natural looking scene. This also facilitates using the close quarter combat optic with two eyes open since both eyes see the same scene in terms of brightness, color, and all other scene attributes. 
       FIG. 2  is a profile view of a red dot sight with an LED light source and a spherical optical element. The LED  3  is mounted off of an optical axis OA of the red dot sight  1 . It should be noted that as rays from an LED light source  3  are reflected by the spherical optical element  2  they form a ray pattern at a viewing plane  4 . The rays within the pattern are not exactly parallel at the viewing plane, and the angle of the ray to the observer&#39;s eye is dependent upon the exact position in the plane where the bundle is sampled. This is shown in  FIG. 3  where the exit pupil (solid circle) position can be moved left, right, up, and down (clear circle), and still stay within the eye-box. The transmitted rays through the spherical optical element from a very distant target are nearly perfectly parallel, and the difference in angle between rays from the target and rays from the LED light source appear as a physical separation between the target and the image of the source. Thus, the point at which the aiming dot appears on the target is dependent on the shooter&#39;s eye position relative to the red dot sight. 
       FIG. 4  is a profile view of a red dot sight with a laser diode light source  13  and a parabolic lens  12  consistent with the invention. The laser diode light source  13  is mounted off of an optical axis OA of the red dot sight  10 . Although reference is made to a red dot sight, other color sights, for example green, are considered within the invention. By incorporating a parabolic lens  12  as the optical element off of which the aiming dot is reflected, parallax can be reduced to a negligible amount at close in ranges and less than 0.25 milliradians at ranges beyond 200 meters. It should be noted that as rays from a laser diode light source  13  are reflected by the parabolic optical element  12  they form a ray pattern at a viewing plane  15 . Reduced parallax enables a red dot sight containing the present advanced optical element to be boresighted or zeroed once and effectively used by virtually all shooters to accurately direct weapon fire. It also ensures that a shooter can be highly accurate without having to maintain a consistent eye position or cheek weld relative to the sight or weapon. The result is quicker engagement times, more accurate shooting, and the ability to readily transfer one weapon among several individuals. The parabolic lens may be sealed within the housing to keep it sheltered from the elements (closed sight configuration) or may be exposed to the elements (open sight configuration). 
       FIG. 5  is a profile view of a red dot sight  500  with an optical element  504  consistent with the invention. Surfaces  1  and  2  of the optical element  504  generally conform to a parabola and the dimensions of the parabola and the thickness of the optical element may be selected by a person of ordinary skill in the art to suit the desired size constraints. The formula for surfaces  1  and  2  respectively may be: 
     
       
         
           
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     (where: r=radial position on lens surface
         c=surface curvature (=1/radius)   k=conic constant   A1, A2=aspheric coefficients       

     The material may be glass or plastic, for example optical grade Xeonex E48R. The optical element  504  may be retained in a housing  502 . The housing  502  houses a laser diode  526  that is mounted off-axis from the optical axis OA of the housing  502 . The housing  502  may incorporate a mechanism  520  for mounting the red dot sight  500  to a weapon  530 , for example a handgun or long gun. The mechanism  520  may have a moveable actuator  522  that travels in an opening  524  for connection to and disconnection from the weapon  530 . The red dot sight  500  may be mounted to a weapon using a variety of mounting mechanism, including those disclosed in more detail in U.S. Pat. No. 5,430,967, titled, Aiming Assistance Device for a Weapon, issued on Jul. 11, 1995; U.S. Pat. No. 6,574,901, titled, Auxiliary Device for a Weapon and Attachment Thereof, issued Jun. 10, 2003; and U.S. Pat. No. 6,705,038, titled, Mounting Assembly for a Weapon, issued on Mar. 16, 2004, all of which are incorporated herein by reference in their entirety. Additionally, the auxiliary device may utilize a mounting mechanism compatible with a mounting rail disclosed in military specifications (e.g., MIL-STD-1913), a “rail grabber” mounting mechanism, screws, bolts, and/or the like. In a closed sight configuration, the optical element  504  may be disposed within the housing  502  between an objective window  508  and an eyepiece window  506 . The objective window  508  and the eyepiece window  506  may protect the optical element  504  from the environment, for example water and sand. In an open sight configuration, one or more of the objective window  508  and the eyepiece window  506  may not be included. In this configuration the optical element  504  may be exposed to the environment and the laser diode  526  may be protected by a cover  510 . A power setting actuator  540  coupled to a power control circuit allows a user to control the brightness of the red dot. 
       FIG. 6  is a plot of reflection versus wavelength in nanometers comparing a coating transmission spectrum for an LED coating and a laser coating consistent with the invention. The laser coating is selected such that there is a hi-fidelity retention of colors in the scene when a viewer looks through the red dot sight. A coating for surface  1  consistent with the invention has reflectance between about 10% and 50%, preferably between about 10% and 40%, more preferably 20±5% at 650 nm and 11 degree angle of incidence and an average photophic transmission greater than 75%, more preferably about 90% at 11 degrees, preferably ±6 degree angle, more preferably ±3 degree angle of incidence to surface normal. The coated optics in transmission preferably should not shift the apparent CIE 1976 white source by more than 0.06 in (U,V) coordinate radius. A coating for surface  2  consistent with the invention preferably has 0.25% reflectance at 650 nm at an 11 degree angle of incidence. As shown in  FIG. 6 , the coating consistent with the invention has a greater retention of color of the scene (around 650 nm) when looking through the red dot sight than the LED coating. This results in the scene coloring being more realistic. 
     As shown in  FIG. 6 , the reflective element reflects light in a narrow band (less than 100 nm) within the visible passband, with the transmission band as measured at the 10%-40% relative intensity points. 
     The coating disclosed above is for use with a red light source, which has a wavelength of about 650 nm. If a different color light source were used, for example a green light source, which has a wavelength of about 510 nm, the coating requirement would shift to about 510 nm. 
     The transmission and reflectance sums to 100% in a non-absorbing coating. The coating described in  FIG. 6  has a low averaged reflectance in the visible waveband from 450 nm to 680 nm. This low average visible reflectance corresponds to a high transmittance from the target to the observer. 
       FIG. 7  is a profile view of a weapon  700  with a close quarter combat sight  702  and magnifier  704 . The close quarter combat sight  702  may be mounted to rails  708  on the weapon  700  and the magnifier  704  may mount directly to the close quarter combat sight  702  by screw threads or bayonet mounting. In close quarter combat, the target  706  may be from 2-800 meters away and a soldier needs to clearly see the target  706  throughout this range. Close quarter combat sights typically do not have any magnification capabilities and require the addition of a removeable magnifier to better see longer distance targets. The magnifier is removeable because at shorter distances a magnifier is unnecessary, but at longer distances a magnifier may help the soldier more easily acquire and identify a target. As shown, the magnifier  704  is positioned between the close quarter combat sight  702  and the target  706 . 
     Placement of the magnifier  704  between the close quarter combat sight  702  and the target  706  has drawbacks due to magnification and manufacturing tolerances. Magnifiers have one or more lenses that make the target appear larger. These lenses are typically machined and often have undesired imperfections that may cause the aim point to shift when a magnifier is placed in front of the close quarter combat sight. This shift in aimpoint requires a soldier to either boresight the weapon once without the magnifier and once again with the magnifier or to mentally compensate for the difference in the heat of battle. In addition, if the soldier uses a different magnifier, he will have to reboresight the weapon because of different anomalies in the second magnifier or different rotational alignment of the magnifier to the red dot sight. Another problem with placing the magnifier  704  between the close quarter combat sight  702  and the target  706  is that the magnifier  704  needs to be larger and longer as the required size scales with increasing distance from the eye piece. 
       FIG. 8  is a profile view of a weapon  800  with a close quarter combat sight  802  and magnifier  804  consistent with the invention. The magnifier  804  is disposed between a soldier (not shown) and the close quarter combat sight  802 . The close quarter combat sight  802  may be consistent with the sight disclosed in  FIGS. 4 ,  5 , and  6 . This mounting arrangement allows the soldier to boresight the weapon once for use with and without the magnifier. The close quarter combat sight  802  may be mountable to rails  808  that extend along at least a portion of a longitudinal axis of the weapon  800  between a butt  810  and a muzzle  812 . The magnifier  804  may mount directly to the rails  808  as described above with reference to  FIG. 5  or may be coupleable to the rear end of the close quarter combat sight  802 , for example by screw threads or bayonet mounting. The magnifier  804  and the close quarter combat sight  802  may be mounted in a variety of locations along the longitudinal axis of the weapon  800  as desired by the soldier. 
       FIG. 9  is a profile view of a magnifier consistent with the invention. The magnifier  804  may have a magnification of 2 or greater, preferably 3-5×. The magnifier  804  has one or more lenses  820  that are housed in a housing  822 . One or more of the lenses  820  in the magnifier  804  may be moveable relative to housing  822  or one of the other lenses  820  to allow the soldier to adjust the magnification. 
     Although reference is made to a soldier, the present invention has applications outside of military applications. 
     Although several preferred embodiments of the present invention have been described in detail herein, the invention is not limited hereto. It will be appreciated by those having ordinary skill in the art that various modifications can be made without materially departing from the novel and advantageous teachings of the invention. Accordingly, the embodiments disclosed herein are by way of example. It is to be understood that the scope of the invention is not to, be limited thereby.