Patent Publication Number: US-2013232845-A1

Title: Battery free light emitting diode reflective dot gunsight

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a nonprovisional patent application that relies for priority under 35 U.S.C. 120 on Provisional Application Ser. No. 61/600,904 filed on Feb. 20, 2012, which is incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to firearms sighting systems, and more particularly to reflective light emitting diode (LED) dot type sights. This invention provides a means for powering the LED lamp in the gunsight by a hand cranked mechanism. 
     2. Statement of the Prior Art 
     There are several major classes of gunsights. The first and the oldest class of gunsights are called “iron sights.” This class of gunsights typically consist of a metal pin and notch that, when aligned with a target, ensure that the gun is positioned such that a projectile from the gun barrel will likely impact the target. While these gunsights are simple, and require no power, it is difficult to focus on the target and the gunsights at the same time. This in turn leads to degraded accuracy. 
     A second class of gunsights uses a telescope with cross hairs. This class of gunsights has the advantage that the cross hairs and the target are in the same focal plane, but several disadvantages. Telescopes are often bulky and they significantly reduce the shooter&#39;s field of view, making them useful only in “slow fire” situations. 
     A third class of gunsights project a laser beam onto the target. The laser is aligned to the gun barrel such that the projectile from the gun will likely impact the target at the location of the projected laser spot on the target. This apparatus allows for a “point and shoot” operation, but the range is limited by the visibility of the projected laser spot. Considerable power is required to project the laser for any significant distance, especially in bright ambient light. 
     The above limitation is overcome by a fourth class of gunsight—the reflective dot gunsight. Here the shooter views the target through a partially reflective glass lens. An LED (light emitting diode) projects a spot of light onto the glass lens such that it is reflected back into the eye of the shooter. The position of the reflected dot is adjusted so that it appears to be overlaid on the target. 
     Since the projected dot is in the same focal plane as the target, there is no need to shift focus while sighting. Unlike the projected laser, the reflective dot gunsight can be used at any practical range and is not affected by ambient light. One major drawback of the reflective red dot gunsight is the need to carry batteries for power. In the event that no charged battery is available, the gunsight becomes useless. This limitation forces shooters to either have back-up “iron sights”, thus compromising the accuracy of the gun or to always have a supply of spare batteries. Invariably when a gun is retrieved for use from storage, it is found that the reflective dot gunsight has accidently been left on and the battery is dead. The anxiety of having to worry about battery failure at an inopportune moment is often sufficient for hunters and combat shooters to avoid using the technically advanced and accurate reflective red dot gunsights and instead opt for inferior “iron sights.” 
     SUMMARY OF THE INVENTION 
     These and other objects, advantages, and novel features are provided by embodiments of the present invention, which overcome all these difficulties and provides all the desired features by powering the LED reflective dot gunsight using a hand cranked mechanism. Cranking the power generator for about 10 to 15 seconds is often sufficient to operate the reflective dot gunsight for 10 minutes or more. The device can be cranked again at any time to top up the available power reserve. Thus, the disclosed invention eliminates the need for batteries to power the reflective dot gunsight. Use of means such as a supercapacitor instead of rechargeable batteries eliminates the need for replacing batteries for 10 years or more providing true “battery-free” operation. Moreover, electrical circuits as disclosed herein are used to efficiently utilize energy stored in the supercapacitor. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The foregoing and other features of the present invention will become more apparent from the following description of exemplary embodiments, as illustrated in the accompanying drawings wherein: 
         FIG. 1  is a side view of a reflective dot gunsight with a hand crank mechanism according to the present invention; 
         FIG. 2  is a schematic drawing of the major components of the present invention; and 
         FIG. 3  is a circuit diagram of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Exemplary embodiments are discussed in detail below. While specific exemplary embodiments are discussed, it should be understood that this is done for illustration purposes only. In describing and illustrating the exemplary embodiments, specific terminology is employed for the sake of clarity. However, the embodiments are not intended to be limited to the specific terminology so selected. Persons of ordinary skill in the relevant art will recognize that other components and configurations may be used without departing from the true spirit and scope of the embodiments. It is to be understood that each specific element includes all technical equivalents that operate in a similar manner to accomplish a similar purpose. Therefore, the examples and embodiments described herein are non-limiting examples. 
     Referring now to the drawings, wherein like reference numbers generally indicate identical, functionally similar, and/or structurally similar elements, there is shown in  FIG. 1  a human-powered reflective dot gunsight according to one embodiment of the present invention. In general, the gunsight comprises a housing  10 , which contains an LED lamp  12 . Light from the LED lamp  12  is reflected from the partially reflective eye lens  14  on to the objective lens  16 , which may also be partially reflective. The reflective light passes through the eye lens  14  and is viewed by the shooter&#39;s eye as a red dot superimposed on to the target  18 , when viewed through lenses  14  and  16 . Inside housing  10  is also a power generator  20 , coupled to gearbox  22  which, in turn, is driven by hand crank  24 . Power is stored in supercapacitor  26 . Switch  28  is used to power the LED lamp  12  from the supercapacitor  26 . 
       FIG. 2  illustrates the operation of certain major components of the present invention. The preferred embodiment utilizes a hand crank  24  to drive a gear train  22 . This is necessary to raise the rotational speed for the DC motor  20  used as a generator. These low cost toy motors typically require 2000 to 6000 rpm in order to generate an output voltage of at least 3 volts. Hand cranking is comfortable between 30 and 60 rpm, so gearbox  22  preferably has a ratio in the range of about 1:50 to 1:200 to raise the output speed to the desired range. A diode  30  may be used between the generator  20  and the supercapacitor  26  to prevent the charged supercapacitor  26  from back-driving the generator  20 . 
     A boost and regulation circuit  32  may be used between supercapacitor  26  and LED lamp  12 . Devices such as the LT1932, manufactured by Linear Technology Corporation of Milpitas, California may be used. Use of a boost/regulation chip allows operation down to 0.8 volts while maintaining a constant current supply to the LED lamp  12 . 
     The LT1932 is a fixed frequency step-up DC/DC converter designed to operate as a constant-current source. Because it directly regulates output current, the LT1932 is ideal for driving light emitting diodes (LEDs) whose light intensity is proportional to the current passing through them, not the voltage across their terminals. 
     Without boost and regulation circuit  32 , LED  12  will become dimmer as the voltage in supercapacitor  26  decays. It will not be lit once the voltage drops below 2.2 volts. The single cell supercapacitor can be charged to a maximum voltage of 2.7 volts so only the voltage range from 2.7 volts down to 2.2 volts is usable without a voltage boost circuit. This would leave a considerable charge in the capacitor unutilized. However, the boost and regulation circuit  32  used in this invention maintains a constant current to the LED lamp  12 , ensuring uniform brightness at voltages down to 1 V. This allows for a more complete utilization of the energy stored in the supercapacitor  26 . Switch  28  may be used to turn the LED lamp  12  on and off. The electrical circuit is shown in  FIG. 3 . 
     In the preferred embodiment, supercapacitor  26  had a capacitance of 3.3F (manufactured by Nichicon Corporation of Kyoto, Japan). In this configuration, cranking the device for 10 to 15 seconds provides for the LED lamp  12  to be lit for 10 to 15 minutes. 
     The hand crank generator could have been coupled to a rechargeable battery for energy storage. This technique has significant drawbacks. Firstly, the rechargeable battery takes much longer to come to a full charge and the charging voltage must be carefully controlled to avoid damaging the battery. Secondly, any rechargeable battery only functions for a finite number of charge-discharge cycles. Typically, rechargeable batteries are rated for 200 to 500 cycles before they must be replaced. Having to change the rechargeable battery periodically negates some of the advantage of a maintenance-free human powered gunsight. In contrast to a battery, supercapacitor can be charged very quickly. With a single cell supercapacitor as used in the disclosed invention there is no need to regulate the charging process. The supercapacitor cannot be overcharged. A supercapacitor does not have any limitation on the number of charge-discharge cycles, but eventually ages due to chemical degradation. A working life of 10 years or more is typical. In addition, supercapacitors can now be obtained for about the same price as a rechargeable battery and furthermore do not contain toxic chemicals. 
     While the disclosure has been described with reference to several embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiments disclosed as the best mode contemplated for caring out this disclosure.