Abstract:
An adjustable aperture forming mechanism provides a tapered hole, an O-ring located in the tapered hole, and a pusher that pushes the O-ring and compresses it into the tapered hole in order to reduce the size of the aperture. When the pusher is retracted, the O-ring returns to its uncompressed, enlarged shape, enlarging the shape of the aperture.

Description:
This application claims priority from Provisional Application Ser. No. 60/115,568 filed Jan. 12, 1999 now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a mechanism for adjusting the size of an aperture. This adjustable aperture mechanism may be used to control the flow of light, gas, or fluid, or it may be used as a collet or chuck to hold a solid object in place. 
     In target shooting, an adjustable aperture is desirable, because it allows the shooter the ability to fine tune his or her sight picture for optimum performance. Until now, the only way to change aperture diameters for an AR-15/M-16 service rifle was to use a system consisting of interchangeable fixed diameter inserts. This system is slow and tedious to use, prone to inadequate adjustment, and is prone to the loss of individual parts. 
     SUMMARY OF THE INVENTION 
     The present invention provides a tapered hole, an O-ring located in the tapered hole, and a pusher that pushes the O-ring into the tapered hole, to reduce the size of the aperture. When the pusher is retracted, the O-ring returns to its enlarged shape, enlarging the size of the aperture. This mechanism permits periodic or continuously-variable control of the size of the aperture by adjusting the position of the pusher. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an exploded side view of an adjustable aperture made in accordance with the present invention; 
     FIG. 2 is an exploded side sectional view of the adjustable aperture of FIG. 1; 
     FIG. 3 is a side sectional view of the assembled adjustable aperture of FIG. 1 in the open position; and 
     FIG. 4 is the same view as FIG. 3 but in the reduced aperture position. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     The preferred embodiment of the adjustable aperture mechanism shown in FIGS. 1-4 is configured for use as an adjustable aperture for the rear sight of a target rifle. The adjustable aperture mechanism  10  includes an aperture body  12 , which is substantially cylindrical in shape. The aperture body  12  has a small diameter portion  14  and a large diameter portion  16 . The aperture body  12  defines an axial aperture  18 , extending throughout the length of the body  12 . The axial aperture  18  is enlarged in the large diameter portion  16 , and the aperture  18  defines a tapered portion  20 , having a frustro-conical shape, at the intersection of the large diameter portion  16  and the small diameter portion  14 . An O-ring  22  lies at the large-diameter end of the tapered aperture  18 . It may be desirable to apply a light film of light machine oil to the interface between the O-ring  22  and the tapered aperture to ensure that the O-ring will slide smoothly along the aperture without binding. There are threads  29 A on the outer surface of the small diameter portion  14  and threads  27 A on the inner surface of the large diameter portion  16 . There is a reduced-diameter step  24  in the outer surface of the small diameter portion  14 , and there is an enlarged-diameter step  26  in the inner surface of the large diameter portion  16 . 
     The adjustable aperture mechanism  10  also includes an eye piece  28 , which is substantially cylindrical in shape and defines an axial aperture  30  extending throughout its entire length. There are threads  27  on the outer surface of the eyepiece  28 , which mate with the internal threads  27 A on the enlarged diameter portion  16  of the aperture body  12 . As the eyepiece  28  is threaded into the aperture body  12 , it serves as a pusher. The eyepiece  28  includes a flange  32  at its back end and a flat surface  33  at its forward end. The adjustable aperture mechanism  10  also includes a retainer  34 , which is substantially cylindrical in shape and defines an axial aperture  36 . The retainer  34  has internal threads  29  which mate with the external threads  29 A on the reduced diameter portion  14  of the aperture body  12 . The retainer  34  is used to hold the adjustable aperture mechanism on a rifle. 
     As shown in FIG. 3, when the aperture is in the “open” position, the O-ring  22  is lying at the outer edge of the tapered surface  20 . The eyepiece  28  is threaded into the aperture body  12  just far enough to contact the O-ring  22 . At this point, the inside diameter of the O-ring  22  is approximately equal to the smallest diameter of the aperture  18  of the aperture body  12 , so the O-ring  22  is not reducing the size of the aperture. In order to reduce the diameter of the aperture, the eyepiece  28  is threaded further into the aperture body  12 , pushing the O-ring  22  down into the tapered hole  20 . This squeezes the O-ring uniformly around its circumference, thereby reducing the inside diameter of the O-ring and restricting the opening through which light can pass. As the eye piece  28  is threaded further into the aperture body  12 , the O-ring is pushed further into the tapered hole  20 , which reduces the inside diameter of the O-ring  22  still further, until the flat end surface  33  of the eye piece  28  abuts the aperture body  12 , as shown in FIG. 4, at which point the O-ring inside diameter is reduced as far as it will go in this mechanism. Depending upon the sizes of the O-ring and the tapered hole, the aperture may be completely closed at this point or it may be at some desired small diameter. 
     To increase the size of the aperture, the process is reversed, and the resilient O-ring automatically expands and moves toward the larger diameter opening as the pressure of the eye piece  28  is released. 
     When this adjustable aperture mechanism is used on a rifle, the assembled mechanism forms a hood, which cancels out any shadows caused by the sun shining directly on the rear sight of the rifle. There are rules of competition which limit the dimensions of the hood. The length “L” (see FIG. 3) can be no greater than 0.650 inches, and the diameter “D” can be no greater than 0.375 inches. In this preferred embodiment, the length is 0.350 inches, plus or minus 0.010 inches, and the diameter is 0.350 inches, plus or minus 0.010 inches. The O-ring diameter in this preferred embodiment is {fraction (3/16)}-inch outside diameter and {fraction (1/16)}-inch inside diameter, with a wall thickness of {fraction (1/16)}-inch when at rest. In this preferred embodiment, the O-ring  22  is made of standard Buna-N neoprene rubber. The tapered hole  20  tapers at an angle α (See FIG. 3) of 60°, which means that the angle between the tapered surface  20  and the straight cylindrical surface of the aperture  18  is 210°. This produces an aperture that varies in size from approximately 0.015 inches to 0.0625 inches in diameter. The movement of the pusher into and out of the aperture body is completely reversible, with no permanent deformation of the pusher, the O-ring, or the aperture body. 
     While the foregoing description describes the adjustable aperture mechanism being used for the sight for a particular rifle, with certain specific dimensions, it is clear that the dimensions may vary depending upon the application. For example, the adjustable aperture mechanism could be used as a valve for intravenous fluid; it could be used to focus beams of light for other purposes, and it could be used as a collet or chuck to hold a small-diameter solid member in place. It will be obvious to those skilled in the art that other modifications may be made to the embodiment described above without departing from the scope of the present invention.