Patent Publication Number: US-2022226708-A1

Title: Vibration damping coupler for a ball bat

Description:
RELATED APPLICATION 
     This application claims the benefit of U.S. Provisional Application Ser. No. 63/138,738 filed Jan. 18, 2021 and entitled VIBRATION DAMPENING BAT CONNECTION AND METHODS OF MAKING THE SAME, which is hereby incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE INVENTION 
     This application relates to ball bats and, more specifically, to structures and methods for connecting a bat barrel to a handle. 
     BACKGROUND OF THE INVENTION 
     Many bat manufacturers have endeavored to improve the performance of baseball and softball bats. In the case of a bat, improved performance can come in the form of, among other things, improved swing weight or moment of inertia (MOI), improved accuracy, improved feel, improved barrel length, improved sound, or increased coefficient of restitution or batted ball speed. 
     Bat manufacturers have attempted to improve the enjoyment of the bat, and to some level the batter&#39;s performance, of the batted ball game. This enjoyment can be substantially affected by the “feel”, or perception, a batter has with a particular bat. Some of this qualitative “feel” concept is controlled by the management of the vibrational energy transferred, or imparted, to the hands of the user when a ball impacts the barrel of the bat. The concept, also known as shock or “sting”, is well known in the art. 
     Vibration at impact between a bat and ball can generally be reduced by striking the ball within the bat&#39;s “sweet spot” or center of percussion. However, a ball struck on either side of the bat&#39;s sweet spot (e.g., between the sweet spot and the end cap or between the sweet spot and the handle) may cause vibrations to transmit through the bat and into the user&#39;s hands. For example, as shown in  FIG. 1A , a bat may have a sweet spot (S). Striking a ball between the sweet spot and the handle (A) can cause a bat to bend or deform as shown in  FIG. 1B . Striking a ball between the sweet spot and the cap (B) can cause a bat to bend or deform as shown in  FIG. 1C . 
     The bending or deformation may result in vibrations that may create an unpleasant or painful sensation for the user and/or may injure the user&#39;s psyche, which may inhibit the user&#39;s performance during use of the bat. The discomfort or pain may be particularly prevalent among children or aged users. Generally, a bat has a first flexural bending mode and a second flexural bending mode. The first mode generally has a natural frequency of approximately 150 Hz to approximately 200 Hz and, generally, has a bending node approximately 6 inches from the knob (i.e., the end of the bat nearest the handle). This typically results in a low amount of vibration at the bending node of the first flexural bending mode (i.e., 6 inches from the knob) but also typically results in a high amount of deflection (i.e., vibration) at the knob, which is where a user&#39;s lower hand is typically positioned. The second flexural bending mode generally has a natural frequency of approximately 600 Hz, and generally has a bending node approximately 2 inches from the knob. Thus, while there may be little to no vibration at or near the knob, a high amount of vibration may be felt where a user&#39;s upper hand is typically located. 
     One method to combat these vibrations and improve the “feel” of the bat has been to create separate handle and barrel portions and create what is referred to as a two-piece bat. The two components are then bonded together either through mechanical means and/or through adhesives. However, these types of constructions might still allow vibration to be transferred to the user&#39;s hands. Therefore, more effective solutions are required to improve the user&#39;s enjoyment of the bat by eliminating or at least substantially damping the high vibrations from impacts. 
     There have been numerous attempts to improve a batter&#39;s enjoyment by controlling the energy transfer to the user&#39;s hands. For example, U.S. Pat. Nos. 10,384,106, 10,252,127, 10,245,488, 10,016,667, 9,814,956, 9,669,277, 9,486,680, 9,101,810, 8,226,505, 7,601,083, 7,572,197, 7,410,433, 7,311,620, 7,201,679, 7,128,670, 6,945,886, 6,929,573, 6,863,628, 6,743,127, 6,702,698, 5,593,158, 5,219,164, and U.S. Patent Application Publication Nos. 2008/0064538, 2011/0111892, and 2016/0184680 disclose various attempts to improve the energy control or the shock attenuating features of a bat. 
     Most conventional bats include only a single vibration isolator such that vibration is reduced for only one of the bending modes. Some bats may use high damping materials to absorb shock. High damping materials may limit the transmission of vibrations at frequencies lower than the natural frequency but may allow more vibration above the natural frequency. Other bats may use low damping materials. Low damping materials may better limit vibration at frequencies above the natural frequency but tend to transmit more vibration at the natural frequency. 
     An example of a bat design aiming to absorb vibration is U.S. Pat. No. 5,593,158. This bat comprises a single elastomeric isolation union element between a separately manufactured handle and barrel. An elastomer is used to damp vibration but is only capable of damping a single mode. 
     Yet another bat design aiming to reduce vibration is shown in U.S. Pat. No. 9,669,277 which describes a joint connecting a handle and a barrel. The joint comprises a collar and a spacer that separates the collar from the distal end of the handle. The joint is used to damp vibration but again is only capable of damping a single mode. 
     It would be an advancement in the art to provide an improved vibration isolator for ball bats. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a ball bat includes a barrel portion having a substantially cylindrical outer surface. A transition portion is connected to the barrel portion and is tapered inwardly from the barrel portion. A handle portion has a distal portion positioned within the transition portion. An elastomeric coupler is secured around the distal portion. A rigid sleeve is secured around the elastomeric coupler and is interposed between the transition portion and the elastomeric coupler. 
     The distal portion may be flared. The elastomeric coupler may have an inner frustoconical surface and an outer frustoconical surface. The elastomeric coupler may further define one or more ridges extending outwardly from the outer frustoconical surface. The rigid sleeve may define a sleeve frustoconical surface and one or more grooves extending outwardly from the sleeve frustoconical surface. The one or more ridges may be positioned within the one or more grooves. In some embodiments, the inner frustoconical surface further defines one or more grooves extending outwardly from the inner frustoconical surface. An adhesive may be positioned between the elastomeric coupler and the distal portion, the adhesive at least partially filling the one or more grooves. The inner frustoconical surface may have a smaller cone angle than the outer frustoconical surface. 
     In some embodiments, the outer frustoconical surface is a first outer frustoconical surface. The elastomeric coupler may further define a second outer frustoconical surface and a transition extending inwardly from the second outer frustoconical surface to the first outer frustoconical surface. The rigid sleeve may be positioned around the first outer frustoconical surface and have a proximal edge positioned abutting the transition. 
     In some embodiments, the elastomeric coupler defines an inner surface contacting the distal portion, the distal portion being larger than an undeformed size of the inner surface. The rigid sleeve may define an inner surface sized such that the elastomeric coupler is compressed between the inner surface and the distal portion. The elastomeric coupler may be made of or include a material having a hardness less than 95 Shore A. The transition portion may connect to the handle portion exclusively through the elastomeric coupler. In some embodiments, all connections between the transition portion and the handle portion includes a member having a hardness of less than 95 Shore A. In some embodiments, the rigid sleeve includes or is made of a material that has a higher hardness than the elastomeric coupler. The rigid sleeve  42  may include or be made of a material having a hardness of at least 20 Shore D. In some embodiments, the elastomeric coupler has a hardness between 40 and 95 Shore A and the rigid sleeve has a hardness between 20 and 90 Shore D. 
     In another aspect of the invention, a method for manufacturing a ball bat includes (a): positioning an elastomeric coupler around a handle portion and sliding the elastomeric coupler from a proximal end of a handle portion to a distal portion of the handle portion such that the elastomeric coupler is stretched outwardly to fit over the distal portion. The method may further include (b): following (a), passing a rigid sleeve from the proximal end of the handle portion to the distal portion such that the rigid sleeve is positioned around the elastomeric coupler and compresses the elastomeric coupler. The method may further include (c): following (b), positioning a barrel and tapered transition portion around the handle portion and sliding the barrel and tapered transition portion to the distal portion such that the rigid sleeve nests within the tapered transition portion with the barrel extending distally of the handle portion. The rigid sleeve has higher hardness than the elastomeric coupler. 
     In some embodiments, the method includes applying adhesive between the elastomeric coupler and the distal portion and applying adhesive between the rigid sleeve and the tapered transition portion. 
     The elastomeric coupler may have a hardness of less than 95 Shore A and the rigid sleeve may have a hardness of more than 20 Shore D. 
     In some embodiments, the elastomeric coupler defines outwardly extending ridges and the rigid sleeve defines grooves extending outwardly from an interior surface of the rigid sleeve. The method may further include inserting the outwardly extending ridges within the grooves. 
     In some embodiments, following (c) no connection between the tapered transition portion and the handle portion exists that that is not through the elastomeric coupler. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative examples of the present invention are described in detail below with reference to the following drawings: 
         FIGS. 1A to 1C  are schematic illustrations showing bending modes of a ball bat; 
         FIG. 2  is a top view of a ball bat in accordance with an embodiment of the present invention; 
         FIGS. 3A to 3D  are views illustrating assembly of a ball bat in accordance with an embodiment of the present invention; 
         FIG. 4A  is a top view of an elastomeric coupler in accordance with an embodiment of the present invention; 
         FIG. 4B  is a cross-sectional view of the elastomeric coupler of  FIG. 4A  in accordance with an embodiment of the present invention; 
         FIG. 4C  is a side view of the elastomeric coupler of  FIG. 4A ; 
         FIG. 5A  is an isometric view of a rigid sleeve in accordance with an embodiment of the present invention; 
         FIG. 5B  is a cross-sectional view of the rigid sleeve of  FIG. 5A ; 
         FIG. 6A  is a cross-sectional view of a ball bat incorporating the rigid sleeve and elastomeric coupler in accordance with an embodiment of the present invention; 
         FIG. 6B  is a cross-sectional view of a ball bat incorporating the rigid sleeve and a second embodiment of the elastomeric coupler in accordance with an embodiment of the present invention; 
         FIG. 6C  is a cross-sectional view of a ball bat incorporating the rigid sleeve and a third embodiment of the elastomeric coupler in accordance with an embodiment of the present invention; and 
         FIG. 6D  is a cross-sectional view of a ball bat incorporating the rigid sleeve and a fourth embodiment of the elastomeric coupler in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 2 , a baseball bat  10  may be understood with respect to a longitudinal direction  12   a  and a radial direction  12   b  defined as an orientation radiating outwardly from the longitudinal direction  12   a  without regard to angle. A circumferential direction  12   c  may be defined as tangential movement or orientation about a center line  14  parallel to the longitudinal direction  12   a  and offset from the longitudinal direction  12   a  along the radial direction  12   b . In addition, the baseball bat  10  and components thereof may be understood with respect to the terms “proximal end” and “distal end.” As used herein “proximal end” shall be understood to refer to an end of the bat or component that is closer to a user&#39;s hands when the bat is in use than the distal end. Likewise, “distal end” shall be understood as an end of the bat or component that is farther from the user&#39;s hand when the bat is in use than the proximal end. 
     The baseball bat  10  may include a barrel portion  16 , a handle portion  18 , and a transition portion  20  (i.e., the taper) between the barrel portion  16  and the handle portion  18 . The barrel portion  16  and the handle portion  18  may be cylindrical about the center line  14 , an outer diameter of the barrel portion  16  being greater, e.g., between 2 and 4 times greater, than the outer diameter of the handle portion  18 . The transition portion  20  may have a frustoconical shape that transitions from the greater diameter of the barrel portion  16  to a smaller diameter. Curved or rounded transitions between the barrel portion  16  and the transition portion  20  and between the handle portion  18  and the transition portion  20  may also be present. The portions  16  and  18  may be substantially cylindrical or include cylindrical and substantially cylindrical portions. For example, “substantially cylindrical” may be understood as a frustoconical shape with a cone angle of between 0 and 3 degrees. 
     The barrel portion  16  and transition portion  20  may be monolithically formed such as by co-molding, casting, or other approach. The portions  16 ,  18 ,  20  may be made of the same material or different materials and each may be any of metal, plastic, composite (e.g., carbon fiber, fiberglass, etc.), wood, or any other material suitable for withstanding the impact forces imposed on a baseball bat when striking a ball. Examples of suitable composite materials include carbon fiber, fiberglass, boron, or aramid (e.g., KEVLAR®) composite. Where a composite is used, fibers may be within a matrix comprising thermoset polymers like epoxy and phenolics, thermoplastic polymers such as low-density polyethylene, high-density polyethylene, polypropylene, nylon, and acrylics. 
     For example, the barrel portion  16  and transition portion  20  may be made of a metal alloy while the handle  18  is made of another material such as wood, composite, or rigid plastic. In another example, the barrel portion  16  is formed of a combination of a composite material (carbon fiber composite, fiberglass composite) in combination with another material such as an aluminum alloy, titanium alloy, scandium alloy, steel, other alloys, thermoplastic material, thermoset material, wood, or other polymer matrix composite materials. 
     The barrel portion  16  may be a hollow cylinder of uniform wall thickness and may also have non-uniform thickness or have other non-symmetrical features about the center line  14 . The handle portion  18  may be a hollow cylinder of uniform thickness or may also be non-uniform or have non-symmetrical features. In some embodiments, outer surfaces of the barrel portion  16 , transition portion  20  and handle portion  18  are symmetrical about the center line  14  but the thicknesses of one or both of the barrel portion  16 , transition portion  20 , and handle portion  18  vary along the center line  14 . 
     The barrel portion  16  may also include “inserts” designed to alter the performance of batted balls when impacted on the specified striking region of the barrel portion  16 . Examples of such inserts can be found in U.S. Pat. No. 9,498,690, which is hereby incorporated herein by reference in its entirety. Such barrel inserts, or any other aspects of the striking region of the bat designed to improve batted ball performance may all be used in conjunction with the invention described herein. 
     The barrel portion  16  can be sized with a variety of different weights, lengths, and diameters to meet the user&#39;s needs. The barrel portion  16  includes a primary tubular ball impact region that is commonly or preferably used for impacting the ball during use. The ball impact region includes the location of the center of percussion (“COP”) of the ball bat. The COP is typically identified in accordance with the ASTM Standard F2219. The COP is also known as the center of oscillation or the length of a simple pendulum with the same period as a physical pendulum as a bat oscillating about a pivot. The COP is often used synonymously with the term “sweet spot.” The “sweet spot” can include the COP and an area plus or minus 3 inches of the COP along the longitudinal direction  12   a.    
     Outer surfaces of some or all of the barrel portion  16 , and handle portion  18 , and transition portion  20  may be anodized, coated, and/or painted with one or more layers of paint, clear coat, inks, coatings, primers, and/or other outer surface coatings. Outer surfaces of some or all of the barrel portion  16 , and handle portion  18 , and transition portion  20  may include alpha numeric and/or graphic distinguishing marks indicative of designs, trademarks, graphics, specifications, certifications, instructions, warning, and/or markings. These can include a trademark that is applied as a decal, as a screening, or through other conventional means. 
     A knob  24  may secure to a proximal end of the handle  18  and an end cap  22  may secure to a distal end of the barrel portion  16 . The knob  24  may slide over a proximal end portion of the handle portion  18  and be secured by means of welds, adhesive, rivets, screws, or other fastening means. The knob  24  might be an integral part of the handle. A grip may be attached to the handle portion  18  adjacent the knob  24 . The end cap  22  may include a portion that slides within the distal end of the hollow barrel portion  16  and may be secured therein by means of welds, adhesive, rivets, screws, or other fastening means. 
       FIGS. 3A to 3C  illustrate a method for assembling a bat  10  incorporating improved vibration damping both in terms of degree of vibration damping and ease of manufacture. 
     Referring specifically to  FIGS. 3A and 3B , the handle portion  18  may include a flared distal portion  30 . The handle portion  18  may include other non-cylindrical portions. For example, moving from the proximal end to the distal end of the handle portion  18  along the center line  14  there may be a cylindrical portion  32  that is substantially cylindrical, a flared proximal portion  34  that flares outwardly from the cylindrical portion  32 , a tapered portion  36  that tapers inwardly, and the flared distal portion  30  that flares outwardly. As is apparent in  FIG. 3A , this arrangement may result in a recess  38  between the flared distal portion  30  and the tapered portion  36 . The recess  38  may be defined by a rounded transition between the flared distal portion  30  and the tapered portion  36 . 
     The portions  30 ,  32 ,  34 ,  36  may have cone angles between 3 and 15 degrees and may have cone angles that are equal to one another or different form one another. For example, the flared proximal portion  34  may be longer than the flared distal portion  30  and have a smaller flare angle. 
     During manufacture, an elastomeric coupler  40  is positioned over the flared distal portion  30 . The elastomeric coupler  40  may be deformed, i.e., stretched, in order to fit over the flared distal portion  30 . A restoring force exerted by the elastomeric coupler  40  on the flared distal portion  30  may increase frictional forces between the elastomeric coupler  40  and the flared distal portion  30 . 
     Positioning the elastomeric coupler  40  may include sliding the elastomeric coupler  40  over the proximal end of the handle portion  18  and sliding the elastomeric coupler  40  along the handle portion  18  until it is over the flared distal portion  30 . As shown in  FIG. 3B , after positioning, one end of the elastomeric coupler  40  may be in or near the recess  38 , such as within 3 mm of the smallest diameter of the handle portion  18  between the flared distal portion  30  and the tapered portion  36 . Adhesive may be applied to one or both of the flared distal portion  30  and an interior surface of the elastomeric coupler  40  prior to positioning of the elastomeric coupler on the flared distal portion  30 . 
     The elastomeric coupler  40  may function as a vibration damping member and may be made of a suitable material to form this function. For example, the elastomeric coupler  40  may be made of silicone. Other elastomeric materials may be used. For example, natural or synthetic rubber, styrene-butadiene rubber (SBR), ethylene propylene diene monomer (EPDM), nitrile, flexible plastic, or other elastomeric material may be used. For example, the elastomeric coupler  40  may be made of or include a material having a hardness of between 40 and 95 Shore A may be used. The hardness may be selected to achieve a desired degree of damping. 
     Referring to  FIGS. 3B and 3C , a rigid sleeve  42  may then be positioned over the flared distal portion  30  and the elastomeric coupler  40 . Positioning the rigid sleeve  42  may include sliding the rigid sleeve  42  over the proximal end of the handle portion  18  and sliding the rigid sleeve  42  until it is over the flared distal portion  30 . The sleeve  42  may be positioned over the elastomeric coupler  40  before or after any adhesive between the elastomeric coupler  40  and flared distal portion  30  has cured. Adhesive may also be applied to the outer surface of the elastomeric coupler  40  and/or an interior surface of the rigid sleeve  42  prior to positioning of the rigid sleeve  42  over the elastomeric coupler  40 . Positioning the rigid sleeve  42  over the elastomeric coupler  40  may require deformation (i.e., compression) of the elastomeric coupler  40  and the rigid sleeve  42  may continue to compress the elastomeric coupler  40  once positioned over the elastomeric coupler  40 . 
     The rigid sleeve  42  may be made of a rigid plastic such as polymethyl pentene (also known as TPX), polyamide, acrylonitrile butadiene styrene (ABS), polypropylene, nylon, or other plastic. The rigid sleeve  42  may also be made of a composite material, such as carbon fiber, fiberglass, boron, or aramid (e.g., KEVLAR) composite. Where a composite is used, fibers may be within a matrix comprising thermoset polymers like epoxy and phenolics, thermoplastic polymers such as low-density polyethylene, high-density polyethylene, polypropylene, nylon, and acrylics. The rigid sleeve  42  may be made of metal, such as steel or aluminum. The rigid sleeve  42  may include or be made of a material having a hardness greater than the elastomeric coupler  40 . For example, a hardness of 20 to 90 Shore D. 
     Referring to  FIGS. 3C and 3D , the barrel portion  16  and transition portion  20  may then be slid over the proximal end of the handle portion  18  and slid along the handle portion  18  until the flared distal portion  30 , elastomeric coupler  40 , and rigid sleeve  42  are positioned within the transition portion  20 . The transition portion  20  may be positioned over the rigid sleeve  42  before or after any adhesive between the rigid sleeve  42  and the elastomeric coupler  40  has cured. The combined flared distal portion  30 , elastomeric coupler  40 , and rigid sleeve  42  are flared outwardly with distance from the proximal end of the handle portion  18  and sized such that passage completely through the transition portion  20  is prevented. 
     The interior surface of the transition portion  20  may have a cone angle and size matching the cone angle and size of the rigid sleeve  42 . The rigid sleeve  42  may fit within the transition portion  20  with an interference fit. Alternatively, the rigid sleeve  42  may slide freely into the transition portion  20 . In either case, adhesive may be applied to the rigid sleeve  42  and/or the interior surface of the transition portion  20  prior to positioning to fasten the rigid sleeve  42  within the transition portion  20 . 
     After assembling the handle portion  18 , barrel portion  16 , and transition portion  20  as shown in  FIG. 3D , the cap  22  may be secured to the barrel portion  16  and the knob  24  may be secured to the proximal end of the handle portion  18  as shown in  FIG. 2 . The knob  24  may be according to any knob known in the art. In the illustrated embodiment, the knob  24  is shown as an “axe” type knob. In other embodiments, a round knob  24  may be used. 
     Referring to  FIGS. 4A to 4C , the elastomeric coupler  40  may have a first surface  50  conforming to a frustoconical shape. The outer surface  50  may have a cone angle of between 3 and 15 degrees and may be equal to or different from the cone angle of the flared distal portion  30 . In some embodiments, the elastomeric coupler  40  defines a second surface  52  that also has a frustoconical shape that may have the same or a different cone angle as the first surface  50  such that a distal end of the second surface  52  has a greater diameter than the proximal end of the first surface  50 . A stepped or curve transition  54  may be defined by the elastomeric coupler between the distal end of the second surface  52  and the proximal end of the first surface  50 . In some embodiments, the second surface  52  includes a chamfer or bevel  56  at the proximal end thereof to facilitate insertion into the rigid sleeve  42 . 
     In the illustrated embodiment, ridges  58  are formed on the first surface  50  and extend partially or completely between the proximal end and distal ends of the first surface  50 . For example, in the illustrated embodiment, the ridges  58  extend from the distal end partially to the proximal end of the first surface  50 , such as between 50 and 75 percent of the distance between the proximal end and distal end of the first surface  50 . In the illustrated embodiment, there are two ridges  58  positioned opposite one another. In other embodiments, a single ridge  58  or three or more ridges  58  may be used. As shown in  FIG. 4C , the ridges  58  may have a semi-circular cross-sectional shape in a plane parallel to the radial direction  12   b  and perpendicular to the longitudinal direction  12   a , though other shapes may also be used. In the illustrated embodiment, the ridges  58  are oriented parallel to the axis of symmetry of the frustoconical shape defined by the first surface  50  (e.g., in a plane parallel to the longitudinal direction  12   a  and center line  14 ). As discussed in greater detail below, the ridges  58  may engage corresponding grooves in the rigid sleeve  42  to resist rotation of the elastomeric coupler  40  relative to the rigid sleeve  42 . 
     An inner surface  60  of the elastomeric coupler  40  may also conform to a frustoconical shape. The inner surface  60  may have the same or different cone angle as the first surface  50 . For example, in the illustrated embodiment, the inner surface  60  has a smaller cone angle than the first surface  50  such that the thickness of the elastomeric coupler  40  at the distal end of the first surface  50  is greater than the thickness of the elastomeric coupler  40  at the proximal end of the first surface  50  (thickness being defined herein as being thickness parallel to the radial direction  12   b ). However, in other embodiments, the elastomeric coupler has substantially constant (e.g., within 0.5 mm) thickness between the distal and proximal ends of the first surface  50 . 
     The inner surface  60  may extend along the longitudinal direction  12   a  overlapping both the first and second surfaces  50 ,  52 . The proximal end of the elastomeric coupler  40  may further include an interior chamfer or bevel  62  to facilitate insertion of the flared distal portion  30  into the elastomeric coupler  40 . 
     Grooves  64  may extend outwardly from the inner surface  60  and extend parallel to the longitudinal direction  12   a  partially or completely between the distal end and proximal end of the inner surface  60 . The grooves  64  may be partially or completely filled with adhesive used to secure the elastomeric coupler  40  to the flared distal portion  30  thereby increasing the amount of area engaged with the adhesive and providing mechanical interference to resist rotation of the elastomeric coupler  40  relative to the flared distal portion  30 . 
     In the illustrated embodiment, the grooves  64  are distributed substantially (e.g., within 2 degrees of) uniformly about the axis of symmetry of the inner surface  60 , such as every 20 degrees, 30 degrees, or some other angular separation. The depth of the grooves may be between 0.1 and 0.5 times the minimum thickness of the elastomeric coupler  40  (e.g., at the proximal end of the first surface  50 ). The width of the grooves may be such that the each groove occupies an arc of between 2 and 10 degrees along the circumferential direction  12   c.    
     In some embodiments, the flared distal portion  30  ( FIGS. 3A, 6A ) has one or more asymmetric features formed thereon either to resist rotation of the elastomeric coupler  40  or to provide asymmetric properties to the completed bat  10 . Accordingly, the elastomeric coupler  40  may further define one or more asymmetric cavities  66  that extend outwardly from the frustoconical shape defined by the inner surface  60 . For example, in the illustrated embodiment, the cavity  66  conforms to a portion of an ovoid or ellipsoid shape. 
       FIGS. 5A and 5B  illustrate an example configuration of the rigid sleeve  42 . The rigid sleeve  42  may include an outer surface  70  conforming to a frustoconical shape. The outer surface  70  may be sized to conform to the interior surface of the transition portion  20 . The rigid sleeve  42  may further include an inner surface  72  conforming to a frustoconical shape. The inner surface  72  may have the same or different cone angle as the outer surface  70  such that the thickness of the rigid sleeve  42  is either substantially (e.g., within 0.5 mm) constant or varying along the longitudinal direction  12   a.    
     The inner surface  72  engages the first surface  50  of the elastomeric coupler  40 . As noted above, when the elastomeric coupler  40  is positioned over the flared distal portion  30 , the rigid sleeve  42  may compress the elastomeric coupler  40  against the flared distal portion. Accordingly, upon assembly, each point on the inner surface  72  along the longitudinal direction  12   a  may have a smaller diameter than the undeformed diameter of the first surface  50  of the elastomeric coupler  40  at that point along the longitudinal direction  12   a.    
     In the illustrated embodiment, grooves  74  extend outwardly from the inner surface  72  of sleeve  42  and extend partially or completely between the proximal end and distal ends of the inner surface  72 . For example, in the illustrated embodiment, the grooves  74  extend from the distal end partially to the proximal end of the inner surface  72 . In the illustrated embodiment, there are two grooves  74  positioned opposite one another. In other embodiments, a single groove  74  or three or more grooves  84  may be used. As shown in  FIG. 5B , the grooves  74  may have a semi-circular cross-sectional shape in a plane parallel to the radial direction  12   b  and perpendicular to the longitudinal direction  12   a , though other shapes may also be used. The diameter of the semi-circular shape may be the same as or greater than the diameter of the semi-circular shape of the ridges  58  to provide a gap for receiving adhesive. Alternatively, the diameter of the semi-circular shape may be the smaller than the diameter of the semi-circular shape of the ridges  58  such that deformation (such as compression) of the ridges  58  is required for the ridges  58  to insert within the grooves  74 . 
     In the illustrated embodiment, the grooves  74  are oriented parallel to the axis of symmetry of the frustoconical shape defined by the inner surface  72  (e.g., in a plane parallel to the longitudinal direction  12   a  and center line  14 ). As discussed above, the grooves  74  may engage corresponding ridges  58  on the elastomeric coupler  40  to resist rotation of the elastomeric coupler  40  relative to the rigid sleeve  42 . Note that the placement of the ridges  58  and grooves  74  may be reversed, with grooves  74  being defined on the elastomeric coupler and ridges  58  protruding inwardly from the inner surface  72  of the rigid sleeve  42 . 
     In some embodiments, a chamfer or bevel  76  extends between the inner surface  72  and the proximal end of the rigid sleeve  42 . In some embodiments, a chamfer or bevel  78  extends between the inner surface  72  and the distal end of the rigid sleeve  42 . The chamfer or bevel  76  may avoid a sharp contact point between the rigid sleeve  42  and the elastomeric coupler  40 . The chamfer or bevel  76  may seat within the transition  54  between the first surface  50  and the second surface  52  of the elastomeric coupler  40 . The chamfer or bevel  78  may facilitate sliding the rigid sleeve  42  over the elastomeric coupler  40 . 
       FIG. 6A  illustrates the assembled handle portion  18 , transition portion  20 , elastomeric coupler  40 , and rigid sleeve  42 . When assembled the rigid sleeve  42  is positioned around the elastomeric coupler and the proximal end of the rigid sleeve is positioned at the transition  54  between the first surface  50  and the larger diameter second surface  52 . The transition  54  therefore resists sliding of the rigid sleeve  42  off the elastomeric coupler  40 . The thicker region between the second surface  52  and inner surface  60  further provides a greater amount of damping material to absorb energy from relative rotation of the transition portion  20  relative to the handle portion  18 . 
     As noted above, the inner surface  72  of the rigid sleeve  42  is sized such that the elastomeric coupler is compressed thereby when assembled. As also noted above, the thickness of the elastomeric coupler  40  along the first surface  50  increases with distance from the proximal end of the first surface  50 . In some embodiments, the amount of compression varies along the length of the first surface  50 . In particular, the amount of compression may be greater at the distal end of the surface  50  than at the proximal end. In this manner, the elastomeric coupler  40  functions as a wedge that increases friction between the rigid sleeve  42  and the elastomeric coupler  40  when assembled, thereby resisting collapse of the handle portion  18  into the transition portion  20 . 
     As shown, the transition portion  20  defines a frustoconical interior surface  90 . The interior surface  90  engages the outer surface  70  of the rigid sleeve  42  either with or without deformation of the rigid sleeve  42 . The undeformed second surface  52  may be larger than the portion of the surface  90  within which it is engaged such that the elastomeric coupler  40  is compressed between the flared distal portion  30  and the surface  90  in the region of the second surface  52 . 
     Adhesive may be positioned between interior surface  90  and one or both of the surface  70  of the rigid sleeve  42  and the second surface  52  of the elastomeric coupler  40 . The adhesive may resist collapse of the bat by the handle  18  being forced into the transition portion  20 . The flared shape of the rigid sleeve  42  resists removal of the rigid sleeve  42  upon swinging of the bat  10  along with any adhesive used. 
     As noted above, the handle portion  18  may have asymmetric features formed thereon, such as the asymmetric bulge  92 . The asymmetric bulge  92  may seat within the cavity  66  of the elastomeric coupler  40  after assembly. In other embodiments, the asymmetric bulge  92  and cavity  66  are omitted. 
     As shown in  FIG. 6A , the proximal bevel or chamfer  76  is positioned near (e.g., within 3 mm of) the recess  38 . This may function as a rocker or pivot point for the transition portion  20  relative to the handle portion  18 . 
     The illustrated approach for incorporating an elastomeric coupler into a bat  10  may provide various advantages relative to prior approaches. The elastomeric coupler  40  is not adhered directly to the transition portion  20  when the rigid sleeve  42  is put in place. The relatively soft elastomer of the elastomeric coupler  40  is difficult to fasten with adhesive. In the illustrated embodiment, the elastomeric coupler  40  secures to the rigid sleeve  42  and the rigid sleeve  42  is secured to the transition portion  20 . The elastomeric coupler  40  may secure to the rigid sleeve  42  with an interference fit and may have ridges  58  engaging corresponding grooves  74  on the rigid sleeve  42 , which individually or in combination provide a connection that is less susceptible to sliding along the longitudinal direction  12   a  and rotation in the circumferential direction  12   c.    
     The rigid sleeve  42  in combination with the transition portion  20  increases the stiffness of the joint between the transition portion  20  and the handle  18 . The compression of the elastomeric coupler  40  by the rigid sleeve  42  increases the internal pressure acting on the transition portion  20 , which further increases stiffness of the joint. This alters the natural frequency of the bat  10  and reduces the vibrations felt by the user. The stiffness of the joint raises the natural frequency of the bat to higher frequencies and the elastomeric coupler  40  increases damping at low frequencies, both of which decrease the amount of vibration and shock felt by the user in response to impacts outside the sweet spot. 
     In addition, the handle  18  is completely isolated from the transition portion by the elastomeric coupler  40 . Stated differently, there is no connection between the transition portion  20  and the handle portion  18  that does not pass through material within the hardness range defined above for the material of the elastomeric coupler  40 . The material of the elastomeric coupler is interposed between the handle portion  18  and both of the rigid sleeve  42  and transition portion  20 . The elastomeric coupler  40  is therefore effective at reducing the vibration or shock felt by a player, particularly for impacts outside the sweet spot. 
       FIGS. 6B, 6C, and 6D  illustrate various alternative embodiments for implementing a vibration damper for a bat  10 . The embodiments of  6 B,  6 C, and  6 D may be understood as having some or all of the same features (e.g., all listed features, ranges, and alternative features) as for the embodiment of  FIGS. 2 to 6A  except as noted in the description below. 
     Referring specifically to  FIG. 6B , in some embodiments, the flared distal portion  30  may be secured to a handle portion  18  that is exclusively cylindrical. For example, the flared distal portion  30  may be formed on a sleeve  100  that secures to the cylindrical handle portion  18  by means of adhesive, co-curing, or other fastening means. Accordingly, the sleeve  100  may define a cylindrical inner surface for conforming to the handle portion  18  and a frustoconical outer surface having some or all of the attributes described above with respect to the flared distal portion  30 . The sleeve  100  may be formed of any of the materials listed above as being suitable for forming the handle portion  18 . The sleeve  100  may be formed of the same or different type of material as is used to form the handle portion  18 . Where the sleeve  100  is used, the asymmetric bulge  92  may be formed on the sleeve  100  or omitted. 
     Referring to  FIG. 6C , in some embodiments, the flared distal portion is omitted and the elastomeric coupler  40  secured directly to a cylindrical outer surface  110  of the handle portion  18 . In the embodiment of  FIG. 6C , the tapered portion  36  and flared proximal portion  34  are retained. However, in other embodiments the handle portion  18  is exclusively cylindrical as shown in  FIG. 6B . In the illustrated embodiment, the inner surface  60  of the elastomeric coupler  40  may also be cylindrical. When undeformed, the inner surface  60  may have a smaller diameter than the cylindrical outer surface  110  such that stretching of the elastomeric coupler  40  is required to place the elastomeric coupler over the handle portion  18 . The thickness of the elastomeric coupler  40  at the distal end thereof is greater in the embodiment of  FIG. 6B  and may provide a higher amount of damping relative to other embodiments disclosed herein. 
     In some embodiments, resistance to slipping of the handle portion  18  within the elastomeric coupler  40  may be improved by forming a substantially flat axial surface  112  on the asymmetric bulge  92  that engages a corresponding substantially flat axial surface  114  on the elastomeric coupler  40 , such as part of the cavity  66 . “Substantially flat” may be understood as having all points within 0.5 mm of a plane parallel to the radial direction  12   b  and perpendicular to the longitudinal direction  12   a . Substantially flat may also be defined as being within 0.5 mm of a cone with a cone angle greater than 80 and less than 90 degrees (90-degree cone angle being a flat plane). 
     The embodiment of  FIG. 6D  may be modified relative to the embodiment of  FIG. 6C . In particular, a flared distal portion  120  is formed on the handle portion  18  between the distal end and the cylindrical outer surface  110 . The cone angle of the flared distal portion  120  may be between 30 and 55 degrees, such as 45 degrees. The flared distal portion  120  may be formed on a separate member that is secured over a distal portion of the cylindrical outer surface  110  by means of adhesive, threads, co-curing, or other fastening means such that a portion of the cylindrical outer surface  110  remains uncovered by the separate member. The flared distal portion  120  may also be formed on a separate member secured to the handle portion  18  by inserting the separate member within the handle portion  18 , which may be hollow. The separate member may be secured within the handle portion  18  by means of adhesive, threads, co-curing, or other fastening means. 
     The elastomeric coupler  40  may define a beveled surface  122  sized to engage the flared distal portion  120 . The beveled surface  122  may have substantially (e.g., within 3 degrees of) the same cone angle as the flared distal portion  120 . 
     While the preferred embodiments of the invention have been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.