Abstract:
The invention is directed to a compound archery crossbow wherein the power cables and the bowstring remain substantially parallel allowing the bowstring to be positioned for increased power and accuracy of an arrow and/or wherein the power stroke has been extended by positioning the bowstring farther from the string catch.

Description:
FIELD OF THE INVENTION 
       [0001]    This invention relates to an improved compound archery crossbow. 
       BACKGROUND OF THE INVENTION 
       [0002]    Crossbows conventionally include an elongated barrel of wood, metal or composite composition that forms a mounting base for the remainder of the crossbow hardware. A pair of resilient limbs of wood, steel, aluminum, and/or composite composition project in opposite directions from one end of the barrel, with the free ends of the limbs being joined by a bowstring cable. A support is provided on the upper surface of the barrel for holding an arrow. A trigger mechanism is carried by the barrel for engaging, and holding the bowstring cable in the drawn or cocked position, and for selectively releasing the cable so as to propel the bolt from the bow. 
         [0003]    Conventional dual-cam compound crossbows have a power cam mounted at the end of each of the two bow limbs to control the draw force on the bowstring and the bending of the limbs as the bowstring is drawn back to cock the crossbow. Each power cam includes grooved segments to control let-out of the bowstring cable and take-up of the power cables. Those cams typically include two grooved segments (hereinafter, “two-groove cams”). But, with two-groove cams, the cams can get out of sync when the bowstring is drawn back to cock the bow, which can offset the nock travel so it is no longer straight with the barrel, thereby causing the arrow to launch incorrectly. Latching the bowstring off center from the correct nocking point when cocking the bow can also cause erratic arrow flight. Those issues do not occur, however, when cams with two let-out grooves and a take-up groove are used (hereinafter, a “three-groove cam”). In a dual cam bow with three-groove cams, the distal ends of both power cables are each attached to opposite cams so that each cam becomes a slave to the other, thereby forcing the cams to rotate in unison, which helps maintain straight nock travel and makes it possible to get a higher level of stored energy to peak weight from the bow. 
         [0004]    Commonly in dual-cam crossbows, the power cables or cable segments are anchored near the end of one or both bow limbs, typically at the mounting axles of the pulleys and/or cams. Accordingly, a continuous problem with compound bows is the inherently unequal application of force to opposite sides of the mounting axles of the pulleys and/or cams as the bowstring is drawn. Moreover, placing the power cables all on one cam creates more load on one side of the limb. 
         [0005]    In an effort to overcome that out of balance system, configurations have been proposed that distribute the force load applied to the mounting axles. For example, a “yoke” or “Y harness” configuration was proposed wherein the terminal, or anchor end, of a cable is divided into two strands that extend to opposite sides of a pulley or cam, thereby evenly distributing the force applied by that cable to its respective attachment points. A “yoke” or “Y harness” configuration is described in commonly-owned U.S. Pat. No. 6,990,970, the subject matter of which is incorporated by reference in its entirety. A yoke system, however, is not effective to balance the load on the limbs with a front mounted (i.e., reverse draw) bowstring because it is not possible to draw the bowstring past the split in the cables because they are anchored at the axle on each side of the pulleys and/or cams. And, anchoring the power cables to the limb still affects the timing of the cams and causes problematic twisting of the limbs. In addition, riggings that position all of the power cables on one side of the bowstring can generate cable forces on one side of the pulley or cam, which results in a design that tends to lean, tip, or twist the limbs of a bow with respect to the plane of the bowstring, thereby causing an arrow to launch incorrectly. Accordingly, there is a need for a dual-cam crossbow with synchronized cams and with minimal twisting of the limbs. 
         [0006]    Hybrid dual-cam two-groove “slave” systems are another configuration that can be utilized in crossbows. A dual-cam two-groove “slave” systems configuration is described in commonly owned and co-pending U.S. patent application Ser. No. 12/290,750, the subject matter of which is incorporated by reference in its entirety. In that configuration, each cam includes a first let-out groove for letting out the bowstring and a hybrid groove that includes both a let-out portion for letting out a first power cable and a take-up portion for taking up a second power cable in the same groove. Because there are only two grooves and the power cables are both anchored at the hybrid groove, the load center of the cam is narrow and can be located near the center of the limb without introducing much torque during the draw cycle. The power cables, however, must still be deflected to move them out of the path of the bowstring and an arrow, which will still cause some twisting of the limbs. 
       BRIEF SUMMARY OF THE INVENTION 
       [0007]    In a first embodiment, the invention is directed to a compound archery crossbow having a barrel supported by a stock. The crossbow further includes an upper pair and a lower pair of limbs, wherein the upper pair of limbs has a first member with a distal end and a proximal end, and a second member having a distal end and a proximal end. Similarly, the lower pair of limbs has a first member having a distal end and a proximal end, and a second member having a distal end and a proximal end. The upper pair and the lower pair of limbs are mounted to the stock by a riser, wherein an attachment means attaches the proximal end of the first member and the second member of the upper pair of limbs and the proximal end of the first member and the second member of the lower pair of limbs to the riser. The upper pair and the lower pair of limbs remain parallel at all times. 
         [0008]    The invention further includes a first three-groove cam and a second three-groove cam, wherein the first cam has a first let-out groove, a second let-out groove, and a take-up groove. Similarly, the second cam also has a first let-out groove, a second let-out groove, and a take-up groove. The first let-out groove, the second let-out groove, and the take-up groove of the first cam are inverted in configuration from the first let-out groove, the second let-out groove, and the take-up groove of the second cam. 
         [0009]    The invention further includes a first power cable extending from the first let-out groove of the first cam to the take-up groove of the second cam and a second power cable extending from the first let-out groove of the second cam to the take-up groove of the first cam. Additionally, a bowstring extends from the second let-out groove of the first cam to the second let-out groove of the second cam, wherein the first and second power cables are positioned between the riser and the bowstring. 
         [0010]    A first axel assembly includes a first part that extends through the first cam, the distal end of the first member of the upper pair of limbs, and the distal end of the first member of the lower pair limbs. A second axel assembly includes a first part that extends through the second cam, the distal end of the second member of the upper pair of limbs, and the second member of the lower pair of limbs. Drawing the bowstring away from the riser lets out the bowstring from the second let-out groove of the first and second cam, which causes the first cam and second cams to rotate around the first and second axel assemblies so as to let out the first and second power cables from the first let-out groove of the first and second cam, respectively. 
         [0011]    The bowstring, the first power cable, and the second power cable are substantially parallel to each other, and the first part of the first and second axel assemblies have opposite rotational movement with respect to one another. 
         [0012]    Each of the first let-out groove, the second let-out groove, and the take-up groove of the first and second cam includes a base having a periphery on which the bowstring, the first power cable, and the second cable are disposed. The base of the first let-out groove, the base of the second let-out groove, and the base of the take-up groove of the first and second cam are of substantially the same dimension. 
         [0013]    At least one base of the first let-out groove, the second let-out groove, and the take-up groove of the first and second cam includes posts mounted thereto for anchoring the power cables and bowstring. 
         [0014]    The crossbow further comprises a receiver attached to the barrel, wherein the receiver comprises a bowstring catch, safety, and trigger linkage. The stock includes a trigger attached to the trigger linkage for releasing the bowstring from the bowstring catch when the bowstring is in the loaded position in the receiver. A channel in the barrel can be positioned to hold an arrow so that the vanes, or fletches, on the arrow will not contact the first or second power cable as the arrow moves past the first and second power cable. The arrow may also be nocked to the bowstring to accomplish substantially same thing result without the use of the channel to support or guide the arrow. 
         [0015]    In another embodiment, the cams are reversed in orientation with the bowstring positioned horizontally between cams and the riser so the power stroke can be increased, which results in better performance. 
         [0016]    In yet another embodiment, a shoot-through design includes two-groove cams with the power cables anchored to the axle assemblies on the side opposite the take-up groove instead of the cam. 
         [0017]    In still another embodiment, a hybrid two-groove cam is utilized that includes a let-out groove and a hybrid groove with let-out portion on take-up portions on the same grooved element. That embodiment provides a shoot-over design. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0018]      FIG. 1  is a top view of an exemplary embodiment of a crossbow according to the present invention; 
           [0019]      FIG. 2  is a front view of the crossbow illustrated in  FIG. 1 ; 
           [0020]      FIG. 3  is a side view of the crossbow illustrated in  FIG. 1 ; 
           [0021]      FIG. 4  is a top view of the crossbow illustrated in  FIG. 1 , modified to have a reverse draw; 
           [0022]      FIG. 5  is a top view of the crossbow illustrated in  FIG. 1 , modified to include a tunnel for protecting the bowstring; 
           [0023]      FIG. 6  is a rear view of the crossbow illustrated in  FIG. 5 ; 
           [0024]      FIG. 7  is a side view of the crossbow illustrated in  FIG. 6 ; 
           [0025]      FIG. 8  is a top view of an exemplary embodiment of a three-groove cam according to the present invention; 
           [0026]      FIG. 9  is a top view of a another exemplary embodiment of a crossbow according to the present invention; 
           [0027]      FIG. 10  is a front view of the crossbow illustrated in  FIG. 9 ; 
           [0028]      FIG. 11  is a side view of the crossbow illustrated in  FIG. 9 ; 
           [0029]      FIG. 12  is a top view of the crossbow illustrated in  FIG. 9 , modified to have a reverse draw; 
           [0030]      FIG. 13  is a bottom view of another exemplary embodiment of a crossbow according to the present invention; 
           [0031]      FIG. 14  is a front view of the crossbow illustrated in  FIG. 13 ; 
           [0032]      FIG. 15  is a side view of the crossbow illustrated in  FIG. 13 ; 
           [0033]      FIG. 16  is a top view of the crossbow illustrated in  FIG. 13 , modified to have a reverse draw; 
           [0034]      FIG. 17  is a top view of yet another exemplary embodiment of a crossbow according to the present invention with the limbs forward; and 
           [0035]      FIG. 18  is a top view of the crossbow illustrated in  FIG. 17 , modified to have a reverse draw. 
       
    
    
       [0036]    Reference will now be made in detail to non-limiting embodiments of the present invention by way of reference to the accompanying drawings, wherein like reference numerals refer to like parts, components, and structures. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0037]    Certain terminology is used herein for convenience only and is not to be taken as a limitation on the present invention. The terminology includes the words specifically mentioned, derivatives thereof, and words of similar import. The embodiments discussed herein are not intended to be exhaustive or to limit the invention to the precise form disclosed. Those embodiments are chosen and described to best explain the principles of the invention and its application and practical use and to enable others skilled in the art to best utilize the invention. 
         [0038]    Referring now to the drawings,  FIGS. 1-3  illustrate a first embodiment of the present invention directed to a compound archery crossbow  10  that may have a barrel  12  supported by a stock  14 . The crossbow  10  may include an upper pair  16 A &amp; B and a lower pair  18 A &amp; B of limbs, wherein the upper pair of limbs  16 A &amp; B has a first member  16 A with a distal end  16 A 1  and a proximal end  16 A 2  and a second member  16 B with a distal end  16 B 1  and a proximal end  16 B 2 . Similarly, the lower pair of limbs  18 A &amp; B also has a first member  18 A with a distal end  18 A 1  and a proximal end  18 A 2  and a second member  18 B with a distal end  18 B 1  and a proximal end  18 B 2 . The upper pair of limbs  16 A &amp; B and the lower pair of limbs  18 A &amp; B are mounted to the stock  14  by a riser  20 , wherein attachment portion  22  attach the proximal end  16 A 2  of the first member  16 A, the proximal end  16 B 2  of the second member  16 B of the upper pair of limbs  16 , and the proximal end of the first member  18 A 2 , and the second member  18 B 2  of the lower pair of limbs  18  to the riser  20 . In the illustrated embodiment, the attachment portions  22  are limb caps. The upper pair of limbs  16 A &amp; B and the lower pair of limbs  18 A &amp; B are substantially parallel at all times. 
         [0039]    It will appreciated by those of skill in the art that the limb configuration can vary from the embodiment illustrated in  FIGS. 1-3  without deviating significantly from the spirit of the present invention. The illustrated configurations are not intended to be limiting, but rather to provide an appreciation of the function of the limb(s) of the present invention, regardless of the configuration that one skilled in the art chooses. Accordingly, the limbs could be a single structure or they could include a single upper limb with a single parallel lower limb. Thus, the limb configuration could be one, two, or four pieces and still adhere to the basic concept of the present invention. 
         [0040]    The crossbow  10  may include a three-groove first cam  24  and a three-groove second cam  26 , wherein the first cam  24  has a first let-out groove  24 A, a second let-out groove  24 B, and a take-up groove  24 C, and the second cam  26  has a first let-out groove  26 A, a second let-out groove  26 B, and a take-up groove  26 C. The first let-out groove  24 A, the second let-out groove  24 B, and the take-up groove  24 C of the first cam  24  are inverted with respect to the first let-out groove  26 A, the second let-out groove  26 B, and the take-up groove  26 C of the second cam  26 . Accordingly, the first let-out groove  24 A of the first cam  24  is disposed at the top of the first cam  24 , the second let-out groove  24 B of the first cam  24  is disposed at the middle of the first cam  24 , and the take-up groove  24 C of the first cam  24  is disposed at the bottom of the first cam  24 . Conversely, the first let-out groove  26 A of the second cam  26  is disposed at the bottom of the second cam  26 , the second let-out groove  26 B of the second cam  26  is disposed in the middle of the second cam  26 , and the take-up groove  26 C of the second cam  26  is disposed at the top of the second cam  26 . 
         [0041]    The crossbow  10  may also include a first power cable  28  extending from the first let-out groove  24 A of the first cam  24  to the take-up groove  26 C of the second cam  26 ; a second power cable  30  extending from the first let-out groove  26 A of the second cam  26  to the take-up groove  24 C of the first cam  24 ; and a bowstring  32  extending from the second let-out groove  24 B of the first cam  24  to the second let-out groove  26 B of the second cam  26 . The first power cable  28 , the second power cable  30 , and the bowstring  32  are each separate cables and are each anchored at their distal ends to the first cam  24  and second cam  26 . Accordingly, the first power cable  28 , the second power cable  30 , and the bowstring  32  extend substantially parallel to each other between the first cam  24  and second cam  26 , with the bowstring  32  being vertically disposed in between the first power cable  28  and the second power cable  30  (hereinafter, the “shoot-through” configuration). 
         [0042]    Horizontally, the first power cable  28  and second power cable  30  may be disposed between the riser  20  and the bowstring  32  (see, e.g.,  FIG. 1 ), or the bowstring  32  may be disposed between the riser  20  and the first power cable  28  and second power cable  30  (see, e.g.,  FIG. 4 ). The crossbow  10 ′ of the latter configuration (hereinafter, the “reverse draw” configuration) is substantially the same as the crossbow  10  illustrated in  FIGS. 1-3 , except the first cam  24  and second cam  26  are flipped so that the take-up groove  24 C of the first cam  24  is at the top of the first cam  24  and the take-up groove  26 C of the second cam  26  is at the bottom of the second cam  26 . That reverse draw configuration increases the distance that the bowstring  32  can be pulled away from the riser, thereby increasing the power stroke and improving the performance of the crossbow  10 ′. The shoot-through configuration enables the reverse draw configuration by allowing the bowstring  32  to be pulled away from the riser  20  and through the first power cable  28  and second power cable  30 . 
         [0043]    Because the first power cable  28  and second power cable  30  are substantially parallel to each other and are anchored at the top and bottom of the first cam  26  and second cam  28 , they can be provided a sufficient vertical distance apart to allow the arrow pass between them. Accordingly, the first power cable  28  and second power cable  30  do not have to be deflected in the vertical direction to remove them from the path of the arrow. Moreover, the second power cable  30  can be run through a forked opening  54  in the barrel  12  to protect it from the arrow&#39;s sharp arrowhead when loading and shooting the arrow. And, although the first power cable  28  runs over the barrel  12 , a tunnel  56  can be attached to the barrel  12  to surround the arrow and avoid a potential problem of the arrowhead cutting the first power cable  28  when loading the arrow.  FIGS. 5-7  illustrate a crossbow  10 ″ with a tunnel  56  attached to the barrel  12 . Or, in the alternative, the first power cable  28  can be covered with a protective material, such as KEVLAR brand protective material, that is very difficult to cut. The bowstring  32  does not require such protection in either of those configurations because it is held out of the way when the an arrow is loaded. 
         [0044]    In addition, because the distal ends of the first power cable  28  and second power cable  30  are anchored at the first cam  24  and second cam  26  instead of the limbs  16 A &amp; B and  18 A &amp; B or the axle assemblies  34 A and  34 B, the present invention also resolves timing issues between the first cam  24  and second  26 . Anchoring the distal ends first power cable  28  and second power cable  30  at the first cam  24  and second cam  26  cam causes the first cam  24  and the second cam  26  become slaves to each other, thereby forcing the cams to rotate in unison, which helps maintain straight nock travel and prevents a user from attaching the bowstring off center of the bowstring catch  48 . Both of those factors contribute to better arrow flight. 
         [0045]    As  FIGS. 1-3  also illustrate, a first axel assembly  34 A extends through the distal end  16 A 1  of the first member  16 A of the upper pair of limbs  16 A &amp; B, through the first cam  24 , and through the distal end  18 A 1  of the first member  18 A of the lower pair limbs  18 A &amp; B. And, a second axel assembly  34 B extends through the distal end  16 B 1  of the second member  16 B of the upper pair of limbs  16 A &amp; B, through the second cam  26 , and through the distal end  18 B 1  of the second member  18 B of the lower pair of limbs  18 A &amp; B. The first cam  24  rotates about the first axel assembly  34 A, and the second cam  26  rotates about the second axel assembly. Accordingly, drawing the bowstring  32  away from the riser  20  pulls the bowstring  32  out of the second let-out grooves  24 B and  26 B of the first cam  24  and second cam  26 , respectively, as the first cam  24  and second cam  26  rotate about the first axel assembly  34 A and second axel assembly  34 B, respectively. The rotation of the first cam  24  about the first axel assembly  34 A is in the opposite direction of the rotation of the second cam  26  about the second axel assembly  34 B. And, the rotation of the first cam  24  pulls the second power cable  30  out of the first let-out groove  26 A of the second cam  26  and into the take-up groove  24 C of the first cam  24  while the rotation of the second cam  26  simultaneously pulls the first power cable  28  out of the first let-out groove  24 A of the first cam  26  and into the take-up groove  26 C of the second cam  26 , thereby synchronizing the first cam  24  with the second cam  26  as the bowstring  32  is drawn away from the riser  20 . As discussed above, by pulling one cable out of one groove on one cam and into a groove on another cam, each cam becomes a slave to the other, which provides the synchronization required to prevent the possibility of the nock point shifting from center when the bowstring  32  is drawn away from the riser  20 . That configuration therefore improves the accuracy of the crossbow  10 . 
         [0046]    When the bowstring  32  is drawn back to cock the crossbow  10 , the first power cable  28 , the second power cable  30 , and the bowstring  32  remain substantially parallel to each other, just as in the “relaxed” position. And, because the first power cable  28  is anchored at the top of the first cam  24  and second cam  26 , the second power cable  30  is anchored at the bottom of the first cam  24  and second cam  26 , and the bowstring  32  is anchored substantially in the middle of the first cam  24  and second cam  26 , the torque on the first axel assembly  34 A and the second axel assembly is effectively neutralized, which substantially eliminates twisting forces on the limbs  16 A &amp; B and  18 A &amp; B of the crossbow  10 . Eliminating those twisting forces helps further improve the accuracy of the crossbow  10 . 
         [0047]    As  FIG. 8  illustrates, the first let-out groove  24 A, the second let-out groove  24 B, and the take-up groove  24 C of the first cam  24  are each disposed at different diameters R 1 , R 2 , and R 3 , respectively, from the first axle assembly  34 A. Each of those diameters R 1 , R 2 , and R 3  may vary as required to produce the smoothest torque curve when drawing the bowstring  32  back and releasing it. Accordingly, the first let-out groove  24 A, the second let-out groove  24 B, and the take-up groove  24 C of the first cam  24  may be formed in a circular shape, a kidney shape, or a combination thereof. It will be appreciated by those of skill in the art, however, that the shape of the first let-out groove  24 A, the second let-out groove  24 B, and the take-up groove  24 C of the first cam  24  can be varied significantly without deviating significantly from the spirit of the present invention. 
         [0048]    The first let-out groove  26 A, the second let-out groove  26 B, and the take-up groove  26 C of the second cam  26  have substantially the same shape as the first let-out groove  24 A, the second let-out groove  24 B, and the take-up groove  24 C of the first cam  24 , respectively. That symmetry substantially equalizes the load on each side of the first axle assembly  34 A and second axle assembly  34 B, which thereby eliminates torque at the distal ends  16 A 1 ,  16 B 1 ,  18 A 1 , and  18 B 1  of the limbs  16 A &amp; B and  18 A &amp; B of the crossbow  10 . Accordingly, that symmetry causes the limbs  16 A &amp; B and  18 A &amp; B to deflect an equal amount as the bowstring  32  is drawn away from the riser  20 . Equalizing the amount of deflection of the limbs  16 A &amp; B and  18 A &amp; B helps improve the accuracy of the crossbow  10 . 
         [0049]    In addition to being of substantially identical dimensions, the first cam  24  and second cam  26  also both include a first post  40 , a second post  42 , and a third post  44  extending therefrom for anchoring the distal ends of first power cable  28 , the second power cable  30 , and the bowstring  32 , respectively. The first cam  24  and second cam  26  may also include a draw stop (not illustrated) extending therefrom to prevent the cams  24  and  26  from being over-rotated and to allow the bow to be locked at full draw with no tension on the bowstring  32 . 
         [0050]    As  FIG. 3  illustrates, the barrel of the crossbow  10  may include a receiving portion  46  formed therein for receiving the bowstring  32  when it is draw away from the riser  20 . The receiver portion  46  includes a bowstring catch  48 , a safety mechanism  50 , and a trigger linkage (not shown) connecting the bowstring catch  48  to a trigger  52  disposed in the stock  14 . Through interaction with the trigger linkage, moving the trigger  52  will pull the bowstring catch  48  downward toward the barrel  10  and release the bowstring  32  from the receiving portion  46 . And, as  FIG. 1  illustrates, the barrel  12  may also include a channel  58  running lengthwise down the barrel  12  for receiving the vane of an arrow so the arrow can remain flush with the barrel  12  when the arrow is loaded into and shot from the crossbow  10 . The channel  58  also helps prevent the arrow from contacting the first power cable  28  and the second power cable  30  as it moves past them when it is shot from the crossbow  10 . As an alternative to the channel  58 , an arrow with a nock can be used so the arrow can be attached to the bowstring  32  after the bowstring  32  is held by the bowstring catch  48 . 
         [0051]      FIGS. 9-12  illustrate another embodiment of a crossbow  60  according to the present invention that utilizes the shoot-through configuration described above, but with a two-groove first cam  70  and two-groove second cam  72  in lieu of a three-groove first cam  24  and three-groove second cam  26 . The two-groove first cam  70  includes a take-up groove  70 A and a let-out groove  70 B, and the second two-groove cam  72  includes a take-up groove  72 A and a let-out groove  72 B. But, instead of including a second let-out groove  24 A or  26 A like the first three-groove cam  24  and the second three-groove came  26 , a first anchor  74  is provided between the first two-groove cam  70  and the distal end  16 A 1  of the first member  16 A of the upper pair of limbs  16 A &amp; B, and a second anchor  76  is provided between the second two-groove cam  72  and the distal end  18 A 1  of the first member  18 A of the lower pair limbs  18 A &amp; B. The first anchor  74  is disposed on the first axle assembly  34 A, and the second anchor  76  is disposed on the second axle assembly  34 B. 
         [0052]    The take-up groove  70 A of the first cam  70 , the let-out groove  70 B of the first cam  70 , and the first anchor  74  are inverted with respect to the take-up groove  72 A of the second cam  72 , the let-out groove  72 B of the second cam  72 , and the second anchor  76 . Accordingly, the take-up groove  70 A of the first cam  70  is disposed at the bottom of the first cam  70 , the let-out groove  70 B of the first cam  70  is disposed at the top of the first cam  70 , and the first anchor  74  is disposed above the first cam  70 . Conversely, the take-up groove  72 A of the second cam  72  is disposed at the top of the second cam  72 , the let-out groove  72 B of the second cam  72  is disposed at the bottom of the second cam  72 , and the second anchor  76  is disposed below the second cam  72 . 
         [0053]    In that configuration, the first power cable  28  extends from the take-up groove  72 A of the second cam  72  to the first anchor  74 ; the second power cable  30  extends from the take-up groove  70 A of the first cam  70  to the second anchor  76 ; and the bowstring  32  extends from the let-out groove  70 B of the first cam  70  to the let-out groove  70 B of the second cam  72 . The first power cable  28 , the second power cable  30 , and the bowstring  32  are each separate cables. One end of the first power cable  28  is anchored at the second cam  72  and the other end is anchored at the first anchor  74 ; one end of the second power cable  30  is anchored at the first cam  70  and the other end is anchored at the second anchor  76 ; and the bowstring is anchored at its distal ends at the first cam  70  and second cam  72 . Accordingly, the first power cable  28 , the second power cable  30 , and the bowstring  32  extend substantially parallel to each other between the first cam  70  and second cam  72  in a shoot-through configuration. 
         [0054]    Also in that configuration, the first power cable  28  and second power cable  30  may be horizontally disposed between the riser  20  and the bowstring  32  (see, e.g.,  FIG. 9 ), or the bowstring  32  may be horizontally disposed between the riser  20  and the first power cable  28  and second power cable  30  (see, e.g.,  FIG. 12 ). The crossbow  60 ′ of the latter configuration (i.e., the reverse draw configuration) is substantially the same as the crossbow  60  illustrated in  FIGS. 9-11 , except the first cam  70  and second cam  72  are flipped so that the take-up groove  70 A of the first cam  70  is at the top of the first cam  70  with the first anchor  74  disposed below the first cam  70 , and the take-up groove  72 A of the second cam  72  is at the bottom of the second cam  72  with the second anchor  76  disposed above the second cam  72 . And, when provided in reverse draw configuration, the bowstring  32  does not interference with the first power cable  28  or the second power cable  30  when the bowstring  32  is drawn back to cock the crossbow  60 ′. 
         [0055]    The features of the crossbows  60  and  60 ′ illustrated in  FIGS. 9-12  provide substantially the same advantages as those described for the corresponding features of the crossbows  10  and  10 ′ illustrated in  FIGS. 1-4 . The primary difference between those configurations is that, unlike the three-groove cam configuration illustrated in  FIGS. 1-4 , the ends of the first power cable  28  and the second power cable  30  that are attached to the first anchor  74  and second anchor  76 , respectively, in the configuration illustrated in  FIGS. 9-12  do not rotate at the point of attachment as the opposite ends of those cables rotate via the take-up groove  72 A of the second cam  72  and the take-up groove  70 A of the first cam  70 , respectively. Thus, the two-groove cam configuration illustrated in  FIGS. 9-12  does not provide the advantage of improved cam synchronization as is provided by the three-groove cam configuration illustrated in  FIGS. 1-5 . 
         [0056]      FIGS. 13-15  illustrate yet another embodiment of a crossbow  100  according to the present invention that does not utilize the shoot-through configuration, but uses hybrid two-groove first cam  102  and hybrid two-groove second cam  104  to provide improved cam synchronization similar to that of the three-groove cam configuration illustrated in  FIGS. 1-4 . (NOTE:  FIG. 13  shows a bottom view of the crossbow  100  so as to more clearly illustrate the hybrid two-groove first cam  102  and hybrid two-groove second cam  104 .  FIG. 14  shows a view taken along line  14 - 14  as if  FIG. 13  were a top view.) The hybrid two-groove first cam  102  includes a let-out groove  102 A and a hybrid groove  102 B, wherein the hybrid groove  102 B includes a let-out portion  102 B 1  and a take-up portion  102 B 2 . And, the second hybrid two-groove cam  104  includes a let-out groove  104 A and a hybrid groove  104 B, wherein that hybrid groove  104 B also includes a let-out portion  104 B 1  and a take-up portion  104 B 2 . The hybrid groove  102 B of the first cam  102  and the hybrid groove  104 B of the second cam  104  allow the distal ends of the first power cable  28  and second power cable  30  to be attached to the first cam  102  and the second cam  104  so that each cam is a slave to the other, as described above. Accordingly, a first anchor  74  and second anchor  76  are not required as in the configurations illustrated in  FIGS. 9-12 . 
         [0057]    In that configuration, the first power cable  28  extends from the let-out portion  102 B 1  of the first cam  102  to the take-up portion  104 B 2  of the second cam  104 ; the second power cable  30  extends from the let-out portion  104 B 1  of the second cam  104  to the take-up portion  102 B 2  of the first cam  102 ; and the bowstring  32  extends from the let-out groove  102 A of the first cam  102  to the let-out groove  104 A of the second cam  104 . Unlike the configurations illustrated in  FIGS. 1-12 , however, the let-out groove  102 A and hybrid groove  102 B of the first cam  102  are in the same orientation as the let-out groove  104 A and the hybrid groove  104 B of the second cam  104  in the configurations illustrated in  FIGS. 13-16 . Thus, the hybrid groove  102 B of the first cam  102  and the hybrid groove  104 B of the second cam  104  are each disposed at the bottom of the first cam  102  and second cam  104 , respectively, and the first power cable  28  and the second power cable  30  therefore extend between the hybrid groove  102 B of the first cam  102  and the hybrid groove  104 B of the second cam  104  such that both the first power cable  28  and the second power cable  30  are vertically disposed below bowstring  32  (hereinafter, the “shoot-over” configuration). 
         [0058]    In the shoot-over configuration, the barrel  12  may include a forked opening  54  through which the first power cable  28  and the second power cable  30  extend to provide clearance for the arrow and to protect the first power cable  28  and the second power cable  30  from an arrow&#39;s sharp arrowhead when loading and shooting the arrow. That configuration, however, requires that the first power cable  28  and the second power cable  30  be deflected slightly. A low friction guide  108  can be positioned within the forked opening  54  to guide the first power cable  28  and the second power cable  30  through the forked opening  54 , to prevent them from fouling each other as they pass over one another, and to prevent them from abrading against the surfaces of the forked opening  54 . 
         [0059]    Also in the shoot-over configuration, the first power cable  28  and second power cable  30  may be horizontally disposed between the riser  20  and the bowstring  32  (see, e.g.,  FIG. 13 ), or the bowstring  32  may be horizontally disposed between the riser  20  and the first power cable  28  and second power cable  30  (see, e.g.,  FIG. 16 ). The crossbow  100 ′ of the latter configuration (i.e., the reverse draw configuration) is substantially the same as the crossbow  100  illustrated in  FIGS. 13-15 , except that the first cam  102  and second cam  104  switch positions at the distal ends  16 A 1  &amp;  18 A 1  and  16 B 1  &amp;  18 B 1  of the limbs  16 A &amp; B and  18 A &amp; B without changing their orientation with respect to each other so that the let-out groove  102 A of the first cam  102  and the let-out groove  104 A of the second cam  104  both remain at the top of the first cam  102  and second cam  104 , respectively. 
         [0060]    The features of the crossbows  100  and  100 ′ illustrated in  FIGS. 13-16  provide substantially the same advantages as those described for the corresponding features of the crossbows  10 ,  10 ′,  10 ″,  60 , and  60 ′ illustrated in  FIGS. 1-12 . The primary difference between those configurations is that, unlike those configurations, the first power cable  28  and the second power cable  30  are both located at the bottoms of the first cam  102  and second cam  104  and must therefore be deflected. That deflection may result in twisting forces being exerted on the limbs  16 A &amp; B and  18 A &amp; B. That twisting force, however, is significantly reduced because the let-out grooves  102 A and  104 A are disposed close to the hybrid grooves  102 B and  104 B on the first axle assembly  34 A and second axle assembly  34 B, respectively, thereby reducing the torque produced on the limbs  16 A &amp; B and  18 A &amp; B when the bowstring is drawn away from the riser  20 . In addition, the hybrid two-groove cam configuration illustrated in  FIGS. 13-16  also provides the benefit of improved cam synchronization, similar to that provided by the three-groove cam configuration illustrated in  FIGS. 1-8 . 
         [0061]    Each of the configurations illustrated in  FIGS. 1-16  and discussed above can also be provided with the limbs  16 A &amp; B and  18 A &amp; B and the riser  142  facing in the opposite direction (hereinafter, the “reverse limb” or “limb forward” configuration).  FIGS. 17 and 18  illustrate a crossbow  140  and  140 ′ according to the hybrid two-groove cam shoot-over configuration of the present invention (see, e.g.,  FIGS. 13-16 ) with both a standard draw and a reverse draw, respectively. In addition, any of the configurations illustrated in  FIGS. 1-18  can be modified and combined as required to provide any of the benefits discussed above. For example, the three-groove cam can be modified so that the first let out grooves  24 A and  26 A and the take-up grooves  24 C and  26 C are both below their associated second let-out grooves  24 B and  26 C on the first cam  24  and second cam  26 , respectively, so that the first power cable  28  and second power cable  30  are vertically disposed below the bowstring  32 , thereby providing a three-groove cam shoot-over configuration with either a standard or reverse draw. 
         [0062]    The foregoing description and drawings should be considered as illustrative only of the principles of the invention. The invention may be configured in a variety of shapes and sizes and is not intended to be limited by the preferred embodiment. Numerous applications of the invention will readily occur to those skilled in the art. Therefore, it is not desired to limit the invention to the specific examples disclosed or the exact construction and operation shown and described. Rather, all suitable modifications and equivalents may be resorted to, falling within the scope of the invention.