Abstract:
An apparatus has structure with a reticle oriented approximately parallel to and adjacent an imaginary plane. The structure includes on one side of the plane a portion transmissive to visible radiation, the portion having a surface that is spaced from and angled with respect to the plane, and that faces away from the reticle. A reticle illumination section emits radiation adjacent the surface. According to a different aspect, a method involves: providing a reticle oriented approximately parallel to an imaginary plane and disposed immediately adjacent the plane; providing on one side of the plane a structural portion that is transmissive to visible radiation; forming on the portion a surface spaced from the plane, oriented at an angle to the plane, and oriented to face away from the reticle; and emitting radiation adjacent the surface.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates in general to weapon sights and, more particularly, to techniques for illuminating a reticle in a weapon sight. 
       BACKGROUND 
       [0002]    Over the years, various techniques have been developed to help a person accurately aim a weapon such as a rifle. One common approach is to mount a sight or scope on the weapon. A person then uses the sight or scope to view an image of a scene that includes an intended target. Existing sights usually superimpose a reticle on the image of the scene. For example, the reticle may be in the form of crosshairs. 
         [0003]    Under certain circumstances, including low levels of ambient light, it may be advantageous if the reticle is illuminated to increase its visibility. Various techniques have previously been developed for illuminating a reticle. Although these known techniques have been generally adequate for their intended purposes, they have not been satisfactory in all respects. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0004]    A better understanding of the present invention will be realized from the detailed description that follows, taken in conjunction with the accompanying drawings, in which: 
           [0005]      FIG. 1  is a diagrammatic fragmentary sectional side view of an apparatus that is part of a weapon sight, and that in particular is an illuminated reticle assembly. 
           [0006]      FIG. 2  is a diagrammatic sectional view taken along the section line  2 - 2  in  FIG. 1 . 
       
    
    
     DETAILED DESCRIPTION  
       [0007]      FIG. 1  is a diagrammatic fragmentary sectional side view of an apparatus that is part of a weapon sight, and that in particular is an illuminated reticle assembly  10 .  FIG. 2  is a diagrammatic sectional view of the assembly  10 , taken along the section line  2 - 2  in  FIG. 1 . With reference to  FIGS. 1 and 2 , the assembly  10  includes an approximately cylindrical tube  12 . In the disclosed embodiment, the tube  12  is made of aluminum, but it could alternatively be made of any other suitable material. The tube  12  has at one end an axially-facing annular end surface  14 . The interior of the tube  12  includes three radially-inwardly surfaces  16 ,  17  and  18  that are each approximately cylindrical. The surfaces  16 ,  17  and  18  decrease progressively in diameter in a direction away from the end surface  14 . An axially-facing annular shoulder  21  is provided between the surfaces  16  and  17 , and an axially-facing annular surface  22  is provided between the surfaces  17  and  18 . The axial half of surface  16  that is closest to the end surface  14  has internal threads  26 . 
         [0008]    The assembly  10  also includes a holding ring  31 . The holding ring  31  has external threads  32  that engage the internal threads  26  on the tube  12 . In the disclosed embodiment, the holding ring  31  is made of aluminum, but it could alternatively be made of any other suitable material. The holding ring  31  has one end  33  that is approximately flush with the end surface  14  on the tube  12 . At the opposite axial end, the ring  31  has an axially-facing annular end surface  36 . Adjacent the end surface  36 , the ring  31  has a radially outwardly facing support surface  37  that is approximately cylindrical. At the end of the support surface  37  remote from end surface  36 , the holding ring  31  has an annular shoulder  38  that faces in the same axial direction as the end surface  36 . 
         [0009]    The assembly  10  further includes a glass plate  46  that is a circular disc. The plate  46  is transmissive to visible radiation. The plate  46  has a radially-outwardly facing peripheral edge surface  47  that is adjacent the cylindrical surface  17  on the tube  12 . The plate  46  also has planar and parallel side surfaces  48  and  49  on opposite sides thereof. The outer edge of the side surface  48  engages the annular shoulder  22  on the tube  12 . 
         [0010]    The assembly  10  includes a further glass plate  51  that is a circular disc. The plate  51  has a radially-outwardly facing peripheral edge surface  52  that is adjacent the surface  17  on the tube  12 . The plate  51  has two planar and parallel side surfaces  53  and  54  on opposite sides thereof. The side surface  53  is in direct contact with the side surface  49  on the plate  46 . The outer edge of the side surface  54  engages the annular end surface  36  on the holding ring  31 . Thus, the plates  46  and  51  are both held against axial movement by the surfaces  22  and  36 , and are both held against radial movement by the surface  17 . 
         [0011]    The plate  51  has, between the peripheral edge surface  52  and the side surface  54 , an annular bevel surface  57 . The bevel surface  57  is a polished frustoconical surface with an axis that is coincident with a central axis  58  of the assembly  10 . The axis  58  is perpendicular to an imaginary plane defined by the adjacent side surfaces  49  and  53 . The bevel surface  57  extends at an angle with respect to the plane of the surfaces  49  and  53 . This angle may be within a range of approximately 25° to 65°. In the disclosed embodiment, the angle is approximately 45°. 
         [0012]    In the region of adjacent side surfaces  49  and  53 , a reticle  66  is provided ( FIG. 2 ). In the disclosed embodiment, the reticle  66  has a simple “crosshair” configuration. However, the reticle  66  could have any other desired configuration. The axis  58  extends through a central region of the reticle  66 . In the disclosed embodiment, the reticle  66  is formed by using a known glass etching or engraving technique to etch or engrave the pattern of the reticle into either the side surface  49  of glass plate  46  or the side surface  53  of glass plate  51 . The grooves or other recesses resulting from the etching or engraving are optionally filled with a material that is reflective, florescent or phosphorescent, as discussed in more detail later. In the disclosed embodiment, this material is titanium oxide and sodium silicate, but it could alternatively be any other suitable material. After the recesses are filled with this material, the side surfaces  49  and  53  of the glass plates  46  and  51  are bonded together with an optical grade cement of a type that is known in the art and readily commercially available. In the disclosed embodiment, this is a type of cement that cures when exposed to ultraviolet (UV) radiation. however, the cement could alternatively be cured in any other suitable manner. 
         [0013]    The assembly  10  includes two tritium light sources  76  and  77 , each of which is a component that is readily commercially available. Each light source  76  and  77  is elongate and arcuate, where the angle of arc is in the range of approximately 120° to 180°. In the disclosed embodiment, the light sources  76  and  77  are identical, but they could alternatively be different. Each of the light sources  76  and  77  is a radioluminescent capsule having a tubular shell that is made of glass or some other suitable material, and that is closed at each end. A phosphor coating is provided on the inner surface of the capsule. The capsule contains tritium, which is a radioactive isotope of hydrogen having atoms with three times the mass of ordinary light hydrogen atoms. As the tritium material decays, it emits soft beta rays that, when they strike the phosphor coating, are converted into visible light. The half life of tritium is approximately 12.5 years. Thus, as a practical matter, the tritium light sources  76  and  77  each have a usable life of more than 15 years. Consequently, the tritium light sources  76  and  77  each glow continuously for a long time, thereby providing a safe and reliable source of light, without any need for a power source such as a battery. 
         [0014]    The tritium light sources  76  and  77  are supported on the holding ring  31  at respective locations that are circumferentially offset. Each of the light sources  76  and  77  engages the support surface  37 , and also the axial shoulder  38 . Each of the light sources  76  and  77  is fixedly secured to the axial shoulder  38  by a suitable adhesive, such as a commercially-available epoxy adhesive. With reference to  FIG. 1 , when the holding ring  31  is installed in the tube  12 , each of the light sources  76  and  77  is adjacent the cylindrical surface  16  on the tube  12 , and adjacent the bevel surface  57  on the glass plate  54 . 
         [0015]    Radiation emitted by the light sources  76  and  77  is represented diagrammatically in  FIG. 1  by broken-line arrows. This radiation passes through the bevel surface  57 , and then travels through the plate  57  to the reticle  66  ( FIG. 2 ). In the disclosed embodiment, the reticle  66  is reflects this radiation. However, depending on the wavelength of the radiation and the material used for the reticle, it would alternatively be possible for the reticle to fluoresce or phosphoresce in response to the radiation, or to respond in some other manner to the radiation. 
         [0016]    When the eye  86  of a user views a distant scene  87  through the assembly  10 , the reticle  66  is superimposed on the image of the scene  87 . The reticle  66  is more readily visible to the user as a result of the radiation from the light sources  76  and  77 , particularly when the ambient light external to the sight is relatively low. The use of the bevel surface  57  allows for a relatively compact and lightweight assembly, which can be particularly beneficial for use on small, portable weapons, such as a rifle. The reticle is reliably illuminated, without obstructing the optical view of the user, in devices where backlighting of the reticle is not practical (for example where a device has only spherical lenses and no reflecting prism surfaces that could be backlit). Although the invention encompasses the use of battery powered light sources, the disclosed tritium sources are advantageous because they avoid the need to periodically replace a battery. 
         [0017]    Although the disclosed embodiment uses two tritium light sources,  76  and  77 , it would alternatively be possible to use only a single tritium light source having a longer arc length, or a larger number of tritium light sources each having a shorter arc length. In addition, it would be possible to use types of light sources other than tritium light sources. For example, instead of the tritium light sources, it would be possible to use a light pipe that receives illumination at one end region from a light emitting diode (LED), or from ambient daylight outside the weapon sight, and that has an opposite end regions extending along the bevel surface  57  and emitting the illumination. The light pipe could, for example, be a fluorescent fiber of a known type. As is known in the art, a fluorescent fiber has a core that is made from a material such as polystyrene, and that is surrounded by a cladding made from a material such as a clear acrylic. The core is doped with a special fluorescent dye. Ultraviolet light (for example from ambient daylight) can pass through the cladding and into the core, where the fluorescent dye absorbs the ultraviolet light and then emits visible light. The material of the dye determines the color of the visible light that is produced. Due to differences in the refractive indexes of the cladding and core, the visible light is trapped within the core, and is reflected toward an end region of the fiber. In that end region, the cladding may be a material with a different index of refraction that allows the visible light to escape. 
         [0018]    Although one selected embodiment has been illustrated and described in detail, it should be understood that a variety of substitutions and alterations are possible without departing from the spirit and scope of the present invention, as defined by the claims that follow.