Patent Publication Number: US-7896763-B2

Title: Ball bat exhibiting optimized performance via selective placement of interlaminar shear control zones

Description:
This application is a Continuation of U.S. patent application Ser. No. 11/873,326, filed Oct. 16, 2007 now U.S. Pat. No. 7,527,570, which is a Continuation of U.S. patent application Ser. No. 11/457,542, filed Jul. 14, 2006, now issued as U.S. Pat. No. 7,361,107, which is a Continuation of U.S. patent application Ser. No. 10/903,493, filed Jul. 29, 2004, now issued as U.S. Pat. No. 7,115,054, all of which are incorporated herein by reference. 
    
    
     BACKGROUND 
     Baseball and softball bat manufacturers are continually attempting to develop ball bats that exhibit increased durability and improved performance characteristics. Ball bats typically include a handle, a barrel, and a tapered section joining the handle to the barrel. The outer shell of these bats is generally formed from aluminum or another suitable metal, and/or one or more composite materials. 
     Barrel construction is particularly important in modern bat design. Barrels having a single-wall construction, and more recently, a multi-wall construction, have been developed. Modern ball bats typically include a hollow interior, such that the bats are relatively lightweight and allow a ball player to generate substantial “bat speed” or “swing speed.” 
     Single-wall bats generally include a single tubular spring in the barrel section. Multi-wall barrels typically include two or more tubular springs, or similar structures, that may be of the same or different material composition, in the barrel section. The tubular springs in these multi-wall bats are typically either in contact with one another, such that they form friction joints, are bonded to one another with weld or bonding adhesive, or are separated from one another forming frictionless joints. If the tubular springs are bonded using a structural adhesive, or other structural bonding material, the barrel is essentially a single-wall construction. U.S. Pat. No. 5,364,095, the disclosure of which is herein incorporated by reference, describes a variety of bats having multi-walled barrel constructions. 
     It is generally desirable to have a bat barrel that is durable, while also exhibiting optimal performance characteristics. Hollow bats typically exhibit a phenomenon known as the “trampoline effect,” which essentially refers to the rebound velocity of a ball leaving the bat barrel as a result of flexing of the barrel wall(s). Thus, it is desirable to construct a ball bat having a high “trampoline effect,” so that the bat may provide a high rebound velocity to a pitched ball upon contact. 
     The “trampoline effect” is a direct result of the compression and resulting strain recovery of the bat barrel. During this process of barrel compression and decompression, energy is transferred to the ball resulting in an effective coefficient of restitution (COR) of the barrel, which is the ratio of the post impact ball velocity to the incident ball velocity (COR=Vpost impact/Vincident). In other words, the “trampoline effect” of the bat improves as the COR of the bat barrel increases. 
     Multi-walled bats were developed in an effort to increase the amount of acceptable barrel deflection beyond that which is possible in typical single-wall designs. These multi-walled constructions generally provide added barrel deflection, without increasing stresses beyond the material limits of the barrel materials. Accordingly, multi-wall barrels are typically more efficient at transferring energy back to the ball, and the more flexible property of the multi-wall barrel reduces undesirable deflection and deformation in the ball, which is typically made of highly inefficient material. 
     An example of a multi-wall ball bat  100  is illustrated in  FIG. 1 . The barrel  102  of the ball bat  100  includes an inner wall  104  separated from an outer wall  106  by an interface shear control zone  108  or layer, such as an elastomeric layer, a friction joint, a bond-inhibiting layer, or another suitable layer. Each of the inner and outer walls  104 ,  106  includes one or more plies  110  of one or more fiber-reinforced composite materials. Alternatively, one or both of the inner and outer walls  104 ,  106  may include a metallic material, such as aluminum. A ball bat having this construction is described in detail U.S. patent application Ser. No. 10/712,251, filed on Nov. 13, 2003, the disclosure of which is hereby incorporated by reference. 
     One way that a multi-wall bat differs from a single-wall bat is that there is no shear energy transfer through the interface shear control zone(s) (“ISCZ”) in the multi-wall barrel, i.e., through the region(s) between the barrel walls that de-couple the shear interface between those walls. As a result of strain energy equilibrium, this shear energy, which creates shear deformation in a single-wall barrel, is converted into bending energy in a multi-wall barrel. And since bending deformation is more efficient in transferring energy than is shear deformation, the walls of a multi-wall bat typically exhibit a lower strain energy loss than does a single wall design. Thus, multi-wall barrels are generally preferred over single-wall designs for producing efficient bat-ball collision dynamics, or a better “trampoline effect.” 
     To illustrate,  FIG. 2  shows a graphical comparison of the relative performance characteristics of a typical wood bat barrel, a typical single-wall bat barrel, and a typical double-wall bat barrel. As  FIG. 2  illustrates, double-wall bats generally perform better along the length of the barrel than do single-wall bats and wood bats. While double-wall bats have generally produced improved results along the barrel length, these results still decrease to an extent as impact occurs away from the barrel&#39;s “sweet spot.” 
     The sweet spot is the impact location in the barrel where the transfer of energy from the bat to the ball is maximal (i.e., where the trampoline effect is greatest), while the transfer of energy to a player&#39;s hands is minimal. The sweet spot is generally located at the intersection of the bat&#39;s center of percussion (COP), and the first three fundamental nodes of vibration. This location, which is typically about 4 to 8 inches from the free end of the barrel (it is shown at 6 inches from the free end of the barrel in  FIG. 2 , by way of example), does not move when the bat is vibrating in its first (or fundamental) bending mode. As a result, when a ball impacts the sweet spot, the bat does not vibrate, and none of the initial energy of the ball is lost to the bat. Moreover, a player swinging the bat does not feel vibration when the ball impacts the sweet spot. 
     The barrel region between the sweet spot and the free end of the barrel, and the barrel region between the sweet spot and the tapered section of the bat, in particular, do not exhibit the optimal performance characteristics that occur at the sweet spot. Indeed, in a typical ball bat, the barrel performance, or trampoline effect, decreases considerably as the impact location moves away from the sweet spot. As a result, a player is required to make very precise contact with a pitched ball to achieve optimum results, which is generally very challenging. Thus, a need exists for a ball bat that exhibits improved performance, or trampoline effect, at barrel regions away from the sweet spot. 
     SUMMARY 
     The invention is directed to a ball bat that exhibits improved feel, compliance, and/or performance as a result of strategic placement of interface shear control zones in the bat handle and/or other regions of the ball bat. 
     Other features and advantages of the invention will appear hereinafter. The features of the invention described above can be used separately or together, or in various combinations of one or more of them. The invention resides as well in sub-combinations of the features described. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the drawings, wherein the same reference number indicates the same element throughout the several views: 
         FIG. 1  is a partially cutaway view of a multi-wall ball bat. 
         FIG. 2  is a graph comparing relative performance characteristics of a typical wood bat barrel, a typical single-wall bat barrel, and a typical double-wall bat barrel. 
         FIG. 3  is side view of a ball bat. 
         FIGS. 4-7  and  11  are cross-sections of Zones  1 - 3  of the bat barrel shown in  FIG. 3 , according to five separate “multi-wall” embodiments. 
         FIG. 8  is a graph comparing relative performance characteristics of a typical double-wall bat barrel and a bat barrel utilizing multiple interface shear control zones to create a “multi-wall” bat. 
         FIGS. 9-10  are cross-sections of Zones  1 - 3  of the bat barrel shown in  FIG. 3 , according to two alternative embodiments. 
     
    
    
     DETAILED DESCRIPTION OF THE DRAWINGS 
     Turning now in detail to the drawings, as shown in  FIG. 3 , a baseball or softball bat  10 , hereinafter collectively referred to as a “ball bat” or “bat,” includes a handle  12 , a barrel  14 , and a tapered section  16  joining the handle  12  to the barrel  14 . The free end of the handle  12  includes a knob  18  or similar structure. The barrel  14  is preferably closed off by a suitable cap  20  or plug. The interior of the bat  10  is preferably hollow, which allows the bat  10  to be relatively lightweight so that ball players may generate substantial bat speed when swinging the bat  10 . 
     The ball bat  10  preferably has an overall length of 20 to 40 inches, more preferably 26 to 34 inches. The overall barrel diameter is preferably 2.0 to 3.0 inches, more preferably 2.25 to 2.75 inches. Typical bats have diameters of 2.25, 2.625, or 2.75 inches. Bats having various combinations of these overall lengths and barrel diameters, as well as any other suitable dimensions, are contemplated herein. The specific preferred combination of bat dimensions is generally dictated by the user of the bat  10 , and may vary greatly between users. 
     For purposes of this discussion, as illustrated in  FIGS. 3-7 , the bat barrel  14  is divided into three zones. The first zone  21 , or “Zone  1 ,” extends approximately from the tapered section  16  of the ball bat  10  to a location near the “sweet spot” (as described above) of the bat barrel  14 . The second zone  22 , or “Zone  2 ,” extends approximately from the free end of the bat barrel  14  to a location near the sweet spot. The third zone  24 , or “Zone  3 ,” extends between the first and second zones  21 ,  22 , and includes the sweet spot of the barrel  14 . The actual dimensions and locations of these zones may vary, as may the total number of zones. For example, Zone  1  may extend into the tapered section  16  of the ball bat  10 . For ease of description, however, the three zones  21 ,  22 ,  24  detailed above will be described herein. 
     The bat barrel  14  preferably comprises a plurality of composite plies  25 . The composite materials that make up the plies are preferably fiber-reinforced, and may include glass, graphite, boron, carbon, aramid, ceramic, kevlar, metallic, and/or any other suitable reinforcement material, preferably in epoxy form. Each composite ply preferably has a thickness of approximately 0.003 to 0.020 inches, more preferably 0.005 to 0.008 inches. Alternatively, nano-tubes, such as high-strength carbon nano-tube composite structures, may be used to construct the bat barrel  14 . 
     As explained above, increasing the number of walls in a bat barrel increases the acceptable deflection in the bat barrel, and also converts shear energy into bending energy, via the strategic placement of one or more ISCZs. As a result, the bat&#39;s trampoline effect is improved. In existing multi-wall bats, however, optimum results are not achieved throughout the entire length of the barrel, since barrel performance naturally deteriorates the further that impact occurs from the sweet spot. 
     To improve barrel performance in Zones  1  and/or  2 , a separate “multi-wall” approach, created by strategic placement of ISCZs in one or both of those zones, may be utilized (see, for example,  FIG. 11 , including ISZCs  96  in Zones  1  and  2 ). Each ISCZ used preferably has a radial thickness of approximately 0.001 to 0.010 inches, more preferably 0.005 to 0.006 inches. Any other suitable size ISCZ may alternatively be used. An ISCZ may include a bond-inhibiting layer, a friction joint, a sliding joint, an elastomeric joint, an interface between two dissimilar materials (e.g., aluminum and a composite material), or any other suitable means for separating the barrel into “multiple walls.” If a bond-inhibiting layer is used, it is preferably made of a fluoropolymer material, such as Teflon® (polyfluoroethylene), FEP (fluorinated ethylene propylene), ETFE (ethylene tetrafluoroethylene), PCTFE (polychlorotrifluoroethylene), or PVF (polyvinyl fluoride), and/or another suitable material, such as PMP (polymethylpentene), nylon (polyamide), or cellophane. 
     In a first barrel embodiment shown in  FIG. 4 , a first ISCZ  30  is located in Zone  3  of the bat barrel  14 . The first ISCZ  30  is preferably located at or near the neutral axis of the bat barrel  14 , where the shear stresses in the barrel  14  are the highest. In this manner, an optimal amount of shear stress can be converted into bending stress. The first ISCZ  30  may alternatively be located at any other radial location in Zone  3  of the bat barrel  14 . The neutral axis is located approximately at the radial midpoint of the barrel wall if the barrel  14  is made up of homogeneous isotropic layers. If more than one composite material is used in the barrel  14 , and/or if the material is not uniformly distributed, the neutral axis may reside at a different radial location. 
     For ease of description, the composite barrel material(s) used in the embodiments shown in  FIGS. 4-7  will be considered to be homogeneous, isotropic layers, such that the neutral axis of the barrel  14  is located approximately at the radial midpoint of the barrel wall. In practice, however, any suitable combination of composite and/or metallic materials may be used to construct the barrel  14 , such that the neutral axis may be located at other locations in the barrel  14 . Moreover, once an ISCZ is added to the barrel  14 , it divides the barrel  14  into two barrel “walls,” each of which has its own neutral axis, as described in detail in U.S. patent application Ser. No. 10/712,251. 
     Returning to the first embodiment shown in  FIG. 4 , Zone  1  includes two ISCZs  32 ,  34 , and Zone  2  includes two ISCZs  36 ,  38 . Each of the ISCZs  32 ,  34 ,  36 ,  38  may be located approximately at thirds of the radial barrel thickness, or may be positioned in another manner. By locating two ISCZs in each of Zones  1  and  2  of the bat barrel  14 , those regions essentially perform as tri-wall structures, and thus exhibit increased deflection as compared to Zone  3 , which is essentially a double-wall structure. As a result, the barrel deflection and trampoline effect of Zones  1  and  2  are improved relative to Zone  3 , thus causing them to better approximate the performance of Zone  3  of the bat barrel  14 . Accordingly, when a ball impacts the barrel  14  at either Zone  1  or Zone  2 , the barrel  14  produces a trampoline effect that is closer to that which is produced at the sweet spot than do existing ball bats. 
     In the first embodiment shown in  FIG. 4 , the ISCZs  32 ,  34 ,  36 ,  38  are oriented such that they are continuous with the first ISCZ  30  in Zone  3 . Additionally, the ISCZs  32 ,  34  in Zone  1  are substantially symmetrical with the ISCZs  36 ,  38  in Zone  3 . One or more of the ISCZs  32 ,  34 ,  36 ,  38  may alternatively be discontinuous with the first ISCZ  30 , and the ISCZs  32 ,  34  in Zone  1  may be asymmetrical with the ISCZs  36 ,  38  in Zone  3 , as described below. 
     In the barrel embodiments shown in  FIGS. 5 and 6 , a greater number of ISCZs are located in Zone  1  than in Zone  2  of the bat barrel  14 . Such an arrangement may be preferable due to the effects of rotational inertia. During a typical bat swing, the rotational inertia produced in Zone  1  is less than that produced in Zone  2 , due to the relative proximity of Zone  1 , as compared to Zone  2 , to the bat handle  12 . Accordingly, bat performance is typically inferior in Zone  1  than in Zone  2 . To counteract this difference in performance, in the embodiments shown in  FIGS. 5 and 6 , a greater number of ISCZs are included in Zone  1  than in Zone  2 , to increase the barrel deflection in Zone  1  to a greater extent than in Zone  2 . 
     In the barrel embodiment shown in  FIG. 5 , a continuous ISCZ  40  runs through Zones  1 ,  2 , and  3 , approximately at the radial midpoint of the barrel wall. Two separate discontinuous ISCZs  42 ,  44  are located in Zone  1  between the ISCZ  40  and the central axis of the bat barrel  14 , while an additional discontinuous ISCZ  46  is located in Zone  1  between the ISCZ  40  and the outer surface of the bat barrel  14 . Thus, Zone  1  includes a total of four ISCZs, such that the barrel  14  essentially performs like a 5-wall structure in Zone  1 . Zone  2  includes one discontinuous ISCZ  48  located between the ISCZ  40  and the central axis of the bat barrel  14 , add an additional discontinuous ISCZ  50  located between the ISCZ  40  and the outer surface of the bat barrel  14 . Thus, Zone  2  includes a total of three ISCZs, such that the barrel  14  essentially performs like a 4-wall structure in Zone  2 . 
     In the barrel embodiment shown in  FIG. 6 , Zone  3  includes one ISCZ  60  located approximately at the radial midpoint of the barrel wall. Zone  1  includes two ISCZs  62 ,  64  located between the radial midpoint and the outer surface of the barrel wall, and one ISCZ  66  located between the radial midpoint of the barrel wall and the central axis of the barrel  14 . Thus, Zone  1  includes a total of three ISCZs, such that the barrel  14  essentially performs like a 4-wall structure in Zone  1 . Zone  2  includes one ISCZ  68  located between the radial midpoint and the outer surface of the barrel wall, and one ISCZ  70  located between the radial midpoint of the barrel wall and the central axis of the barrel  14 . Thus, Zone  2  includes a total of two ISCZs, such that the barrel  14  essentially performs like a 3-wall structure in Zone  2 . The three ISCZs  62 ,  64 ,  66  in Zone  1 , and the two ISCZs  68 ,  70  in Zone  2 , are all continuous with the ISCZ  60  in Zone  3 . 
     The barrel embodiments shown in  FIGS. 5 and 6  illustrate the design flexibility contemplated by the present invention. For example, one or more ISCZs in Zones  1  and  2  may be continuous or discontinuous with one or more ISCZs in Zone  3 . one or more ISCZs in any of Zones  1 - 3  may be located between the radial midpoint and the outer surface of the barrel wall, at or near the radial midpoint of the barrel wall, and/or between the radial midpoint of the barrel wall and the central axis of the bat barrel  14 , etc. Additionally, Zones  1  and  2  may include the same or a different number of ISCZs than one another. 
     Importantly, the termination of an ISCZ need not occur specifically where two zones meet. Indeed, an ISCZ may overlap, or reside in, more than one zone, and the zones may be wider or narrower than those which are depicted in the drawings. Moreover, a greater or lesser number of zones may be specified. Indeed, the “zones” are used for illustrative purposes only, and do not provide a physical or theoretical barrier of any kind. Thus, ISCZs may be positioned in the bat barrel  14  (as well as in the tapered section  16  and the handle  12 ) at a wide variety of locations, according to an infinite number of designs, to achieve desired barrel and overall ball bat performance characteristics. 
     To this end, the invention is generally directed to a ball bat having a greater number of ISCZs in at least one barrel region located away from the sweet spot, than the number of ISCZs that are located in a barrel region including the sweet spot, in order to provide improved barrel deflection and trampoline effect in those regions. Additionally, in some embodiments, it may be desirable to include a greater number of ISCZs in a barrel region between the tapered section of the bat and the sweet spot, than in a region between the sweet spot and the free end of the barrel, to compensate for the differences in the effects of rotational inertia in those regions. It is recognized, however, that any suitable number of ISCZs may be located in any regions of the barrel (and other portions of the ball bat), in any suitable configuration, depending on the design goals for a particular ball bat. 
       FIG. 7  illustrates an alternative barrel embodiment in which the bat barrel  14  includes a metal outer region  80  and a composite inner region  82 . The metal outer region  80  is preferably separated from the composite inner region  82  by a suitable ISCZ  86 , such as a bond-inhibiting layer. Alternatively, the non-bonded interface between the metal outer region  80  and the composite inner region may itself form an ISCZ. 
     The metal outer region  80  preferably includes aluminum and/or another suitable metallic material. The composite inner region  82  preferably includes one or more ISCZs  84 , in at least Zones  1  and  2  of the barrel  14 , to provide increased barrel deflection in those regions. This hybrid metal/composite construction provides increased durability, due to the presence of the metal outer region  80 , while still providing the advantages of increased regional barrel deflection, due to the placement of one or more ISCZs in specific zones of the composite inner region  82 . In an alternative embodiment, the barrel  14  may include a composite outer region and a metal inner region. 
       FIG. 8  shows a graphical comparison of the relative performance characteristics of a typical double-wall bat barrel (the double-wall barrel curve in the graph of  FIG. 8  is the same as the double-wall barrel curve shown in the graph of  FIG. 2 ), and a “multi-wall” bat barrel incorporating additional ISCZs in Zones  1  and  2  of the bat barrel  14 . As  FIG. 8  illustrates, by locating additional ISCZs in Zones  1  and  2  of the bat barrel  14 , performance is generally improved along the length of the barrel  14  as compared to a typical double-wall bat. 
       FIGS. 9 and 10  illustrate alternative embodiments in which a single continuous ISCZ passes through Zone  1 , Zone  3 , and Zone  2  of the bat barrel, essentially forming a double-wall bat barrel. The single continuous ISCZs in these embodiments, however, intersect more than one ply in each of Zones  1 ,  2 , and  3 , i.e., the thickness of each of the barrel walls varies throughout the length of the barrel. Accordingly, the bat barrel does not perform like a typical double-wall barrel having a single continuous ISCZ running along the length of the barrel at substantially the same radial location. 
       FIG. 9  illustrates a bat barrel including a single continuous ISCZ  90  that runs closer to the outer surface of the barrel  14  in Zone  3  than in Zones  1  and  2 . 
       FIG. 10  illustrates a bat barrel including a single continuous “stepped” ISCZ  92  that runs closer to the outer surface of the barrel  14  in Zone  2  than in Zone  3 , and closer to the outer surface of the barrel  14  in Zone  3  than in Zone  1 . The continuous ISCZ need not be symmetric, and it may be positioned inversely to the embodiments shown in  FIGS. 9 and 10 , or it may be oriented in any other suitable fashion. By varying the location of the single continuous ISCZ throughout the bat barrel, the sweet spot of the barrel may be increased and/or modified. In an alternative embodiment, the continuous ISCZ may intersect greater than one ply in a lesser number of zones or barrel regions, such that the thickness of the barrel walls varies only in those regions. 
     The present invention further contemplates locating ISCZs in the bat handle  12  and/or the tapered section  16  (to provide increased deformation for off-barrel hits) of the ball bat  10 , to provide increased deflection in those regions. Use of ISCZs in the bat handle  12  provides increased handle compliance, due to the efficient energy transfer resulting from bending deformation, as opposed to shear deformation. In addition, by using one or more ISCZs to de-couple the handle  12 , the “feel” of the bat  10  is improved, as a greater number of interfaces are provided for dissipating vibration energy. 
     When one or more ISCZs are placed in the handle  12  near the tapered section  16 , the ball bat  10  exhibits a quicker “snap back” to axial alignment during a swing than if the ISCZ(s) are placed closer to the user grip location of the handle  12 . This quicker snap back is generally preferred by skilled players who generate high swing speeds. Placing ISCZs closer to the grip location on the handle  12  tends to rob skilled players of control, as the bat  10  is too slow to return to the axial position at or just prior to the time of ball impact. 
     For novice players, however, it may be preferable to locate ISCZ(s) in the bat handle  12  closer to user the grip location, since lesser-skilled players tend to “push” the bat through the strike zone, and therefore do not cause the bat  10  to “bend” significantly out of axial alignment. Those skilled in the art, therefore, will recognize that the placement of the ISCZs in the handle  12  is generally dependent upon the flexibility of the remaining bat handle  12 , the weight of the bat barrel  14 , the skill level of the intended user, and the materials used in the handle  12 . 
     The ball bat  10  is generally constructed by rolling the various layers of the bat  10 , including the ISCZs, onto a mandrel or similar structure having the desired bat shape. The ISCZs are strategically placed and oriented, as described in the above embodiments, to achieve increased deflection and trampoline effect in Zone  1  and/or Zone  2  of the bat barrel  14 . Additionally, or alternatively, ISCZs may be placed in the handle  12  and/or the tapered section  16  of the ball bat  10  to increase deflection in those regions. 
     The ends of the layers are preferably “clocked,” or offset, from one another so that they do not all terminate at the same location before curing. Accordingly, when heat and pressure are applied to cure the bat  10 , the various barrel layers blend together into a distinctive “one-piece,” or integral, multi-wall construction. Put another way, all of the layers of the bat are “co-cured” in a single step, and blend or terminate together at least one end, resulting in a single-piece, multi-wall structure with no gaps (at the at least one end), such that the barrel  14  is not made up of a series of tubes, each with a wall thickness that terminates at the ends of the tubes. As a result, all of the layers act in unison under loading conditions, such as during striking of a ball. 
     The blending of the layers into a single-piece, multi-wall construction, like tying the ends of a leaf spring together, offers an extremely durable assembly, particularly when impact occurs at the extreme ends of the layer separation zones. By blending the multiple layers together, the barrel  14  acts as a unitized structure where no single layer works independently of the other layers. One or both ends of the barrel  14  may terminate together in this manner to form the one-piece barrel  14 . In an alternative design, neither of the barrel ends terminates together in this manner. 
     The described bat construction, and method of making the same, provides a bat  10  having excellent “trampoline effect” throughout the length of the barrel  14 . These results are primarily due to the selection and strategic placement of ISCZs (which may also be placed in the handle  12  and/or the tapered section  16  of the bat  10  to increase deflection in those regions) in the barrel  14 . Additionally, the optional step of blending the barrel layers together in a single curing step provides for increased durability, especially during impact at the extreme ends of the barrel layers. 
     Thus, while several embodiments have been shown and described, various changes and substitutions may of course be made, without departing from the spirit and scope of the invention. The invention, therefore, should not be limited, except by the following claims and their equivalents.