TECHNICAL FIELD 
     The subject invention generally concerns firearm equipment. More particularly, the present invention relates to a charging handle for a firearm utilizing a cog and a spring. 
     BACKGROUND OF THE INVENTION 
     A firearm&#39;s charging handle (otherwise known in the art as a “cocking handle” or a “bolt handle”) is a device used to cock the hammer, which allows the operator to engage the bolt assembly of a firearm. Charging handles are typically used in rifles and similar firearms, such as the M-16 rifle, the AR-15 rifle, the M-4 carbine, and the Short Barreled Rifle (SBR). Operation of the charging handle facilitates many actions, including, for example, loading a preliminary cartridge, ejecting a spent shell casing or unfired cartridge, clearing an obstruction in the chamber of the rifle, and verifying that the chamber is empty. Typically, a charging handle is T-shaped with a long, slim body and a shorter horizontal crossbar at one end. The charging handle is mounted parallel to the bolt assembly. 
     The user of a firearm manually operates the charging handle. The user hooks the forefinger of one hand over one end of the crossbar and the middle finger of the same hand over the second end of the crossbar. The user pulls the crossbar rearward, which results in the bolt assembly being moved to the rear. The typical charging handle includes a spring-biased, rotating latch with a hook that engages the firearm receiver when the charging handle is in a forward position. The latch is attached to the charging handle with a pin. When the user pulls the crossbar rearward, the latch disengages from the receiver and allows the charging handle to be pulled rearward. 
     There are several disadvantages associated with the traditional charging handle design, which requires two fingers to operate. The use of two fingers to operate the charging handle requires that the user move the firearm off target. An improved prior art design includes using paddles on the latch such that the user can press either paddle with one finger or either hand, which releases the latch and moves the charging handle backward. This makes the latch easier to reach and allows the firearm to stay on target. However, this design causes stress on the pin holding the latch to the charging handle. 
     An improved design includes a lever system that uses one male lever and one female lever that interlock inside the body of the charging handle. An example is described in U.S. Pat. No. 7,240,600, entitled “Rifle Charging Handle with Ambidextrous Latch” issued to Bordson on Jul. 10, 2007, which is incorporated herein by reference. Similarly, an alternate improved design includes an internal lever system with two cam-style, interfacing levers. Examples of such designs are described in U.S. Pat. No. 8,336,436, entitled “Ambidextrous Cam Style Charging Handle” issued to Kincel on Dec. 25, 2012, and U.S. Pat. No. 8,356,537, entitled “Ambidextrous Charging Handle” issued to Kincel on Jan. 22, 2013, which are incorporated herein by reference. 
     These systems are improvements over prior ambidextrous charging handles because metal fatigue and torque are reduced. However, these systems utilize protruding elements on the crossbar of the charging handle, as well as internal lever systems that are subject to stress and potential breakage after repeat usage. Previous designs that require force to be applied to two surfaces would often result in the user&#39;s hand being pinched. Moreover, repeated application of force causes the pivot shaft/roll pin to fail. 
     The present invention is aimed at one or more of the problems identified above. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein: 
         FIG. 1A  is an exploded view of a fully assembled charging handle with cog and an upper receiver of an exemplary firearm; 
         FIG. 1B  is a side view of a fully assembled charging handle with cog on an exemplary firearm; 
         FIG. 1C  is a top view of a fully assembled charging handle with cog on an exemplary firearm; 
         FIG. 2A  is a top plan view of a charging handle with cog; 
         FIG. 2B  is a bottom plan view of a charging handle with cog; 
         FIG. 3  is an exploded perspective view of a charging handle with cog and spring bar; 
         FIG. 4  is a top cross-sectional view of a partial charging handle with cog and spring bar; 
         FIGS. 5A and 5B  are cross-sectional views of a partial charging handle with cog and spring bar illustrating operation of the charging handle assembly; 
         FIG. 6  is an exploded perspective view of a charging handle with cog and coil spring; 
         FIG. 7  is a top cross-sectional view of a partial charging handle with cog and coil spring; 
         FIG. 8  is a perspective view of a plunger with cogs engaged with a coil spring; and 
         FIGS. 9A and 9B  are cross-sectional views of a partial charging handle with cog and coil spring illustrating operation of the charging handle assembly. 
     
    
    
     Corresponding reference characters indicate corresponding parts throughout the drawings. 
     SUMMARY OF THE INVENTION 
     In one aspect of the present invention, a firearm comprising an upper receiver and a charging handle is disclosed. A charging handle has a handle assembly with two handles and a main body. The first handle includes a latch parallel to the main body. When the latch interfaces with the upper receiver, the charging handle is in a first “locked” position. The handle assembly also includes a plunger interfacing with the first handle and the second handle near the main body, and a spring bar spanning the first handle, the plunger, and the second handle. When force is applied to either handle, tension from the spring bar is applied equally across the first handle and the second handle, and the plunger is pushed into the main body, moving the latch away from the upper receiver into a second “unlocked” position. 
     In another aspect of the present invention, a charging handle with cog and spring bar is disclosed. A handle assembly has two handles and a main body. The first handle includes a latch parallel to the main body. When the latch interfaces with the upper receiver, the charging handle is in a first “locked” position. The handle assembly also includes a plunger interfacing with the first handle and the second handle near the main body, and a spring bar spanning the first handle, the plunger, and the second handle. When force is applied to either handle, tension from the spring bar is applied equally across the first handle and the second handle, and the plunger is pushed into the main body, moving the latch away from the upper receiver into a second “unlocked” position. 
     In yet another aspect of the present invention, a firearm comprising an upper receiver and a charging handle is disclosed. A charging handle has a handle assembly with two handles and a main body. The first handle includes a latch parallel to the main body. When the latch interfaces with the upper receiver, the charging handle is in a first “locked” position. The handle assembly also includes a plunger interfacing with the first handle and the second handle near the main body, and a coil spring inside the plunger. When force is applied to either handle, tension from the coil spring pushes the plunger into the main body, and energy is transferred to the handles, moving the latch away from the upper receiver into a second “unlocked” position. 
     In yet another aspect of the present invention, a charging handle with cog and spring bar is disclosed. A handle assembly has two handles and a main body. The first handle includes a latch parallel to the main body. When the latch interfaces with the upper receiver, the charging handle is in a first “locked” position. The handle assembly also includes a plunger interfacing with the first handle and the second handle near the main body, and a coil spring inside the plunger. When force is applied to either handle, tension from the coil spring pushes the plunger into the main body, and energy is transferred to the handles, moving the latch away from the upper receiver into a second “unlocked” position. 
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to the drawings and in operation, the present invention overcomes at least some of the disadvantages of known charging handles. The present invention allows the user to apply force with one hand to a single surface (i.e., the lever) rather than two or more surfaces. 
     Referring now to  FIG. 1A , an exploded view of a fully assembled charging handle  100  and a cut-away of an upper receiver  110  of an exemplary firearm is shown. Main body  120  is T-shaped and coupled to handle assembly  130 . Handle assembly  130  includes a latch  140 . When coupled to the upper receiver  110 , main body  120  of charging handle  100  slides into an opening  150 . Latch  140  interfaces with upper receiver  110  at a latch aperture  160 . When latch  140  is engaged in latch aperture  160 , the charging handle  100  is in the “locked” position and remains stationary. 
     Referring now to  FIGS. 1B and 1C , views of a fully assembled charging handle with cog on an exemplary firearm are shown, wherein the charging handle assembly is shown in a locked position. Charging handle  100  is positioned partially within upper receiver  110  with the portion of charging handle  100  containing handle assembly  130  exposed for operator manipulation. 
     Referring now to  FIGS. 2A-2B , top plan and bottom plan views of a fully assembled charging handle (independent of the firearm) are shown. 
     Cog and Spring Bar 
     Referring now to  FIG. 3 , an exploded view of a charging handle with cog and spring bar is illustrated. Main body  120  is T-shaped and coupled to handle assembly  130  with pins  170 . Handle assembly  130  consists of a first handle  180  and a second handle  190 . First handle  180  and second handle  190  each comprise two connected plates (upper and lower) with a cavity in the center. First handle  180  includes latch  140 . First handle  180  includes an external edge furthest away from main body  120  and an internal edge closest to main body  120 . First handle  180  may further include gear teeth  200  on the internal edge closest to main body  120 . Second handle  190  includes an external edge furthest away from main body  120 , and an internal edge closest to main body  120 . 
     First handle  180  and second handle  190  may be injection-molded from any high-strength, temperature-resistant material. This construction would help prevent wear on the parts and render the charging handle lighter. 
     Plunger  210  connects to the T-shaped handle of main body  120 . Plunger  210  includes one or more cogs  220 . Spring bar  230  is also shown. Plunger  210  and spring bar  230  are described in more detail below. 
     As can be seen from  FIG. 3 , pins  170  pass through apertures  240  in the first plates of first handle  180  and second handle  190 , apertures  250  in main body  120 , and apertures  260  in the second plates of first handle  180  and second handle  190 , to secure the handle assembly  130  to main body  120 . 
     Referring again to  FIG. 3 , first handle  180  and second handle  190  may contain a number of apertures, one of which is labeled  270 , in the second plate, which serve a dual purpose of making the charging handle lighter by removing mass from the assembly, and of allowing dirt or debris to pass through instead of collecting in the handle assembly. 
     Referring now to  FIG. 4 , a top cross-sectional view of a partial charging handle with cog and spring bar is illustrated. Plunger  210  is shown interfacing on a first side with the internal edge of first handle  180 , and on a second side the internal edge of second handle  190 . Cogs  220  (not shown) interface with the gear teeth  200  (not shown) of first handle  180 , such that the cogs  220  and the gear teeth  200  interact in a rack-and-pinion manner. 
     Spring bar  230  connects at a first end to first handle  180 , spans the T-handle of main body  120  between cogs  220  of plunger  210 , and connects at a second end to second handle  190 . 
     Thus, the traditional lever system in the charging handle has been replaced in the present invention by a handle and cog system that eliminates the necessity of interlocking or interfacing latches. 
     Referring now to  FIGS. 5A and 5B , cross-sectional views of a partial charging handle with cog and spring bar illustrating operation of the charging handle assembly are shown. As seen in  FIG. 5A , pressure may be applied by the user (with one finger, for example) in a rearward direction  280  to finger surface  290  of first handle  180 . This motion causes the gear teeth  200  of first handle  180  to push plunger  210  into main body  120 , which in turn moves latch  140  in an outward direction  300 , which ultimately disengages the firearm receiver into an “unlocked” position. Spring bar  230  applies equal tension on both first handle  180  and second handle  190 , as well as the plunger  210  to prevent rattling during operation. 
     Similarly, as shown in  FIG. 5B , pressure may be applied by the user (with one finger, for example) in a rearward direction  310  to finger surface  320  of second handle  190 . This motion causes the movement of latch  140  in an outward direction  330 , which disengages the latch from the firearm receiver into an “unlocked” position. This motion causes the gear teeth  200  of first handle  180  to push plunger  210  into main body  120 , which in turn moves latch  140  in an outward direction, which ultimately disengages the firearm receiver into an “unlocked” position. Spring bar  230  applies equal tension on both first handle  180  and second handle  190  as well as the plunger  210 , to prevent rattling during operation. 
       FIGS. 5A and 5B  illustrate that a user may use a single finger to disengage latch  140  by applying pressure either to first handle  180  or to second handle  190 . Alternatively, the user may use more than one finger to disengage latch  140  by applying pressure to both first handle  180  and second handle  190  simultaneously. No pressure is applied, either directly or by transfer, to main body  120 . 
     Cog and Coil Spring 
     Referring now to  FIG. 6 , an exploded view of a charging handle with cog and coil spring is illustrated. Main body  120  is T-shaped and coupled to handle assembly  130  with pins  170 . Handle assembly  130  consists of a first handle  180  and a second handle  190 . First handle  180  and second handle  190  each comprise two connected plates (upper and lower) with a cavity in the center. First handle  180  includes latch  140 . First handle  180  includes an external edge furthest away from main body  120  and an internal edge closest to main body  120 . First handle  180  may further include gear teeth  200  on the internal edge closest to main body  120 . Second handle  190  includes an external edge furthest away from main body  120 , and an internal edge closest to main body  120 . 
     First handle  180  and second handle  190  may be injection-molded from any high-strength, temperature-resistant material. This construction would help prevent wear on the parts and render the charging handle lighter. 
     Plunger  210  connects to the T-shaped handle of main body  120 . Plunger  210  includes one or more cogs  220 . Coil spring  310  is also shown. Plunger  210  and coil spring  310  are described in more detail below. 
     As can be seen from  FIG. 6 , pins  170  pass through apertures  240  in the first plates of first handle  180  and second handle  190 , apertures  250  in main body  120 , and apertures  260  in the second plates of first handle  180  and second handle  190 , to secure the handle assembly  130  to main body  120 . 
     Referring again to  FIG. 6 , first handle  180  and second handle  190  may contain a number of apertures, one of which is labeled  270 , in the second plate, which serve a dual purpose of making the charging handle lighter by removing mass from the assembly, and of allowing dirt or debris to pass through instead of collecting in the handle assembly. 
     Referring now to  FIG. 7 , a top cross-sectional view of a partial charging handle with cog and coil spring is illustrated. Plunger  210  is shown interfacing on a first side with the internal edge of first handle  180 , and on a second side the internal edge of second handle  190 . Cogs  220  (not shown) interface with the gear teeth  200  (not shown) of first handle  180 , such that the cogs  220  and the gear teeth  200  interact in a rack-and-pinion manner. Coil spring  310  fits inside plunger  210 , as shown in  FIG. 8 . 
     Thus, the traditional lever system in the charging handle has been replaced in the present invention by a handle and cog system that eliminates the necessity of interlocking or interfacing latches. 
     Referring now to  FIGS. 9A and 9B , cross-sectional views of a partial charging handle with cog and coil spring illustrating operation of the charging handle assembly are shown. As seen in  FIG. 9A , pressure may be applied by the user (with one finger, for example) in a rearward direction  320  to finger surface  330  of first handle  180 . This motion causes the gear teeth  200  of first handle  180  to push plunger  210  into main body  120 , which in turn moves latch  140  in an outward direction  340 , which ultimately disengages the firearm receiver into an “unlocked” position. Coil spring  310  applies tension to the plunger  210  only, which in turn transfers the tension through the gear teeth  200 , which in turn transfers the tension to first handle  180  and second handle  190 . 
     Similarly, as shown in  FIG. 9B , pressure may be applied by the user (with one finger, for example) in a rearward direction  350  to finger surface  360  of second handle  190 . This motion causes the movement of latch  140  in an outward direction  370 , which disengages the latch from the firearm receiver into an “unlocked” position. This motion causes the gear teeth  200  of first handle  180  to push plunger  210  into main body  120 , which in turn moves latch  140  in an outward direction, which ultimately disengages the firearm receiver into an “unlocked” position. Coil spring  310  applies tension to the plunger  210  only, which in turn transfers the tension through the gear teeth  200 , which in turn transfers the tension to first handle  180  and second handle  190 . 
       FIGS. 9A and 9B  illustrate that a user may use a single finger to disengage latch  140  by applying pressure either to first handle  180  or to second handle  190 . Alternatively, the user may use more than one finger to disengage latch  140  by applying pressure to both first handle  180  and second handle  190  simultaneously. No pressure is applied, either directly or by transfer, to main body  120 . 
     Obviously, many modifications and variations of the present invention are possible in light of the above teachings. In addition, the reference numerals in the claims are merely for convenience and are not to be read in any way as limiting.
A firearm comprising an upper receiver and a charging handle is disclosed. A charging handle is coupled to the upper receiver and comprises a handle assembly rotationally coupled to a main body about a first and a second pivot point. The handle assembly includes a first handle having an edge nearest the main body and a latch extending from the first handle parallel to the main body for interfacing with the upper receiver in a first position, a second handle having an edge nearest the main body, and a plunger interfacing with the edge of the first handle and the edge of the second handle, and a spring, such that when force is applied to either handle, the plunger is pushed into the main body and energy is transferred to the handles, moving the latch into a second position.