Abstract:
A dual powered fiber optic sight for a gun, which can be illuminated either by ambient light or by a light source. The light source is preferably a light-emitting diode (LED). Ambient light and light from the LED are carried by a fiber optic rod and the rod appears as a bright dot on the front sight of the gun. The electronics are enclosed and protected from the environment by a water-proof adhesive. The end of the fiber optic rod may be cut at a 45 degree angle to increase the rod&#39;s light-gathering ability.

Description:
This is a continuation-in-part of application Ser. No. 09/845,939, filed Apr. 30, 2001 now U.S. Pat. No. 6,571,504. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to an illuminated open sight for a gun, such as a rifle or shotgun. 
     Present fiber optic gun sights, which function using ambient light, perform good to excellent when there is sufficient existing light. Their performance becomes less effective as the existing light diminishes. At or around daybreak and sunset are good examples of this. 
     It is well known that you cannot see stars during daylight hours. This is because the light being reflected or generated by the star is not as great as the surrounding light. The surrounding light washes out the light received from the star. When it comes to fiber optic gun sights they tend to fail when you need them the most. 
     Often times the light produced or collected by a fiber optic gun sight is not sufficient to be seen when the target is a bird flying across a clear blue sky. This can happen when you the shooter might be in the shade of a tree or on the back side of a hill or building. Since existing fiber optic gun sights fail when a good sight picture is needed the most, the need for an optional power source is of utmost importance. 
     Tritium is a radioisotope of hydrogen and a phosphor glows in the dark. Gun sights using tritium are faint when compared to the light emitted by an LED. Manufacturers of this type of gun sight claim that battery powered systems have a tendency to fail. This may have been the norm but not any more. This gun sight uses batteries that are inexpensive, very obtainable and will perform well beyond 100 hours. 
     Laser sights are of little value outdoors during daylight hours. They also reveal where you are as the shooter. Red dot sights and scopes do not have the field of view that open sights have. With some it is a struggle locating the red dot inside this tube that you must look through. 
     U.S. Pat. No. 4,434,560 discloses an aiming aid for an aiming device in a low light level environment. The aiming aid includes a light source that transmits light to fiber optics in a front sight and by a light-scattering rod to fiber optics in the rear sight. However, the patent has the disadvantage that the barrel of the weapon must be extensively modified (i.e., cut out) to accommodate the apparatus. Also, the patent does not disclose the use of ambient light to power the front sight. 
     There is a need for a dual-powered fiber optic sight for a gun, which can be illuminated either by ambient light or by a light source. 
     SUMMARY OF THE INVENTION 
     A dual powered fiber optic sight for a gun, which can be illuminated either by ambient light or by a light source. The light source is preferably a light-emitting diode (LED). Ambient light and light from the LED are carried by a fiber optic rod to a target screen and the rod appears as a bright dot on the target screen on the front sight of the gun. 
     This system being dual powered has an LED that provides illumination in the instances where existing fiber optic gun sights fail to function adequately. The invention ensures 24 hour performance and does it when it is needed most. This is accomplished by placing an LED at the opposite end of the target screen (front sight). A fiber optic rod becomes a light pipe to transmit light from the LED to the target screen. The rod also transmits ambient light to the target screen. In addition, the rod polarizes the light so that there is much less glare than there would be if you were looking directly into the LED. 
     In mode one or when ambient light is sufficient, the fiber optic rod which emits green light will appear green on the target screen. In mode two or when the ambient light generated is less than the surrounding light, the LED will take over and appears as a red dot on the target screen, red being the color emitted by the LED. 
     The illuminated dot is surrounded by a black target screen, which has two beneficial advantages. First, it provides more contrast between the illuminated dot and the surrounding area. Open sights often blend in with the surroundings, making it more difficult to see the sight. Another advantage of this target screen is that it encourages the shooter to aim and shoot with both eyes open (because the target screen blocks the target from view by the sighting eye). Most experienced shooters using open sights suggest that you keep both eyes open. It is faster and optimizes the unlimited field of view that you have with open sights. With both eyes open you can prepare your second shot at the same time you are taking the first shot. 
     The batteries uses by this invention are inexpensive, very obtainable, and will perform well beyond 100 hours. Even if the sight is left on over night, there will be plenty of power to get through a long weekend of hunting. Even if the batteries run out, the sight can still be powered by ambient light. 
     The surface mounted device (SMD) LED is mounted on a flex circuit to ensure reliability. The LED has a life estimated at 100,000 hours, or more than eleven (11) years of continuous use. 
     The sight is designed so that it can be completely disassembled without any tools or wrenches. Since all parts are accessible, any mechanical or electrical problem can be pinpointed by the user with a basic understanding of the system. 
     Many hunters have given up hunting because they have problems seeing the sights. As we age our eyes&#39; ability to focus on more than one object becomes more and more difficult. A system that provides a bright sight is easier to see, both consciously and unconsciously. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front perspective view of a first embodiment of the present invention. 
     FIG. 2 is a rear perspective view of a first embodiment of the present invention. 
     FIG. 3 is an exploded perspective view of a first embodiment of the present invention. 
     FIG. 4 is a side elevational view of a gun barrel with the first embodiment mounted thereon. 
     FIG. 5 is similar to FIG. 4, showing a second embodiment of the present invention. 
     FIG. 6 is an elevational view of the rear sight of FIG.  5 . 
     FIG. 7 is similar to FIG. 5, but shows a third embodiment of the present invention. 
     FIG. 8 is similar to FIG. 1, but shows a fourth embodiment of the present invention. 
     FIG. 9 is a cross-sectional view of the fourth embodiment of FIG.  8 . 
     FIG. 10 is a schematic side-elevational view of the fourth embodiment. 
     FIG. 11 is a cross-section along the lines  11  of FIG.  10 . 
     FIG. 12 is a cross-section along the lines  12  of FIG.  10 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The dual-powered, illuminated open sight of the present invention is generally shown in the Figures as reference numeral  10 . 
     A first embodiment of the present invention has a front sight only, and is mounted directly to the gun barrel. 
     FIG. 1 shows that the sight  10  may be mounted on the barrel B of a gun. A typical mounting utilizes the rail R on the barrel B, which is found on guns such as shotguns. Holding members  14  such as screws may attach the sight  10  to the rail R. However, other mounts are possible. In any case, the sight  10  can be mounted on the gun barrel B without significantly modifying the gun barrel. 
     The sight  10  further comprises a window  12  adapted to gather ambient light. The window  12  may be made of any material that transmits ambient light, such as glass or plastic. 
     The sight  10  further comprises an artificial light source  16 . The artificial light source  16  is preferably a light-emitting diode  18 . The preferred LED is a Stanley Model number BR1113F (red). Others include PG1113F (green) and PY1113F (yellow). 
     The sight  10  further comprises a target screen  20 . Preferably, the target screen presents a dark or black surface to the light from the ambient or artificial light source, to improve contrast. 
     The sight  10  further comprises a fiber optic device  22  adapted to transmit light from the window  12  and from the artificial light source  16  to the target screen  20 . The fiber optic device  22  appears as an illuminated dot on the target screen  22  (see FIG.  2 ). Preferably, the fiber optic device  22  is a monofilament plastic rod  24 . A suitable rod is obtainable from Poly-optical Products, Inc., 17475 Gillette Ave., Irvine, Calif. 92614-5612 (Optibright® Scintillating Fibers). The rod is preferably about 2 mm in diameter. 
     The LED  18  is preferably mounted on a flexible circuit  26 , which also provides a contact for the batteries  28 . The flexible circuit cooperates with a sliding switch  30  to turn the LED on and off. A piece of foam tape  32  may be inserted to act as a spring for the sliding switch. 
     A housing  40  encloses the window  12 , LED  18 , fiber optic device  22 , flexible circuit  26 , and batteries  28 . The sliding switch  30  forms a portion of the housing  40 . O-rings  44  hold the halves  42  of the housing  40  together and enable the user to assemble and disassemble the sight  10  without the use of tools. 
     If the fiber optic device  22  has a green color and the LED is red, the fiber optic device will appear green when illuminated by ambient light (mode 1) and red when illuminated by the LED (mode 2). As the ambient light decreases, the fiber optic device will turn from green to red. This occurs at the point where the ambient light is approximately equal to the light from the LED. White light may be briefly transmitted during the shift from mode 1 to mode 2, if there is enough yellow light coming from the fiber optic device to form the three primary colors (red, green, and yellow). It may be desirable to have the LED and the fiber optic device be the same color in order to avoid this white light effect. 
     When (2) #10 hearing aid batteries  28  are placed in series they should produce 2.8 volts. When two of these batteries are placed under the load of a Stanley BR1113F SMD LED  18 , the voltage drops to 1.6 volts. By nature of this combination the LED  18  draws less current and the result is far more battery life. The battery life of this combination is between 100 and 125 hours of continuous use. 
     FIG. 4 shows the sight  10  mounted on the rib R of a shotgun. 
     A second embodiment of the present invention includes a rear sight, and the rear sight is also mounted directly on the gun barrel. 
     FIG. 5 shows the second embodiment, which adds a rear sight  50 , also mounted on the rib R of the shotgun. A second fiber optic device  52  connects the front sight  10  to the rear sight  50 . This may be a monofilament plastic rod  54  as described above. FIG. 6 shows a detail of the rear sight  50 . There may be two rods  54 , in which case two illuminated dots are presented on the rear target screen  56 , as shown in the Figure. The rods or filaments  54  are preferably 1 mm and may be encased in a protective covering such as 3M heat shrink tubing from Minnesota Mining and Manufacturing, Inc., St. Paul, Minn. The filaments  54  and protective covering may be woven between the supports of the rib R. 
     A third embodiment of the present invention has the front sight and rear sight mounted on rails which extend above the gun barrel. 
     FIG. 7 shows the third embodiment in which the front sight  10  is modified so that the fiber optic device  22  extends above the standard shotgun rib R. In this case, the fiber optic device  22  is extended outside the housing  40  as an extension  23 , which may typically be two to three inches longer. The extension  23  is mounted on a rail  70  which in turn is mounted on the rib R. No target screen is used in this case. Because the fiber optic device  22  is approximately three inches longer, it appears much brighter. Also, the rear sight  50  is mounted on a second rail  72 , which in turn is mounted on the rib R. The rails  70 ,  72  may butt together and may be mounted to the rib R by tape such as (0.020) 3M-VHB Tape from Minnesota Mining and Manufacturing, Inc., St. Paul, Minn. The rear sight  50  may slide into a slot  80  in the second rail  72 . This makes the rear sight interchangeable for elevation. Windage can be adjusted by sliding the rear sight  50  to the left or right inside the slot  80 . 
     A fourth embodiment of the gun sight is shown in the Figures as reference numeral  110 . It differs from the other embodiments in that the fiber optic device or rod  122 ,  124  is not enclosed in a housing, but instead collects light directly from the ambient environment. Also, there is no target screen. In addition, a cap  140  is provided which is sealed to a mount  150  using a silicone adhesive, to protect the LED  16  and flex circuit from moisture. A suitable silicone adhesive is the DAP-Silicone Titanium-enriched maximum flexibility adhesive ASTM C920, Class 25, available from Dow Corning, marketed by DAP (www.dap.com). Furthermore, a battery pack  160  is preferably mounted under the barrel B, with wires  162  leading to the flex circuit within the cap  140 . 
     To provide the maximum amount of light-gathering power from the LED  16 , the rod  124  is cut at an angle {grave over (α)} to the long axis of the rod  124 . Optimally, the angle {grave over (α)} is about 45°. With the angle {grave over (α)} at 45°, the cut end of the rod  124  forms a right triangle with sides a and b and hypotenuse c, as shown in FIG.  10 . Under the Pythagorean Theorem, the length of the hypotenuse c will be: 
     
       
         
           c 
           2 
           =a 
           2 
           +b 
           2  
         
       
     
     
       
           c =( a   2   +b   2 )  
       
     
     FIG. 11 shows that the cut at the end of the rod  124  will be in the form of an ellipse with major axis c/2 and minor axis a/2. The formula for the area of an ellipse with major axis b and minor axis a is: 
     
       
         
           A=Πab  
         
       
     
     Substituting for a and b, we get: 
     
       
           A   1 =Π( c/ 2)( a/ 2)  
       
     
     
       
           A   1 =Π( a   2   +b   2 )/2( a/ 2)  
       
     
     In contrast, the area of cut transversely to the long axis of the rod, as shown in FIG. 12, will be a circle with area: 
     
       
           A   2 =Π( a/ 2) 2    
       
     
     Then the ratio of the area of the 45° cut to the transverse cut will be:                  A   1     /     A   2       =                  (     Π          √     (       a   2     +     b   2       )       /   2          (     a   /   2     )       )     /     ∏       (     a   /   2     )     2                     =                  √     (       a   2     +     b   2       )       /   a                                  
     With a 45° cut, a=b, therefore, the ratio becomes: 
     
       
         =(2 a   2 )/ a= (2) a    
       
     
     It can be seen that the 45° cut will have an increased surface area of: 
     
       
         2*2=1.414  
       
     
     times the surface area of the transverse cut. 
     The increased surface area should increase the light-gathering ability of the rod  124  proportionately. 
     Also, light from the light source  116  will impinge more directly on the rod  124  if the rod is cut an angle as shown in FIG.  10 . 
     The present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof, and it is therefore desired that the present embodiment be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than to the foregoing description to indicate the scope of the invention.