Abstract:
A multi-walled, tubular baseball bat has a barrel portion with a mid-section wherein the radial stiffness of the overall barrel wall varies along the barrel length to provide an enlarged sweetspot, improved soft feel and performance, plus unique sounds upon impact. The bat has a frame with a barrel portion of consistent diameter. A secondary member, or members, of tubular form extend internally along the barrel. The secondary member provides the required radial stiffness variation by: 1) variations in the thickness of the wall of the secondary member or by, 2) secondary members with unique geometric external surface profiles or by, 3) the presence of functional air cavities, with or without closed ends, between the main bat frame and the secondary member or members or by, 4) the presence of numerous annular secondary members located side by side less than one-half the length of the barrel portion.

Description:
[0001]     This application claims the benefit of priority of U.S. Provisional Patent Application 60/745,806, filed 27 Apr. 2006, and is a continuation-in-part of U.S. patent application Ser. No. 10/672,060, filed 29 Sep. 2003. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to baseball bats and more particularly to tubular baseball bats, constructed of a variety of materials, and more particularly to baseball bats designed to improve player performance. More particularly, baseball bats according to the invention have variable radial stiffness along the barrel length resulting in larger sweet spots, improved batting performance as defined by greater hitting distance, a vibration soft feel, and unique sounds upon contact with a ball while meeting existing, new, or changed performance standards established by regulatory bodies.  
       BACKGROUND OF THE INVENTION AND PRIOR ART  
       [0003]     Baseball and softball bats, hereinafter referred to simply as “baseball bats” or “bats”, are today typically made solely from aluminum alloys, or aluminum alloys in combination with composite materials (hybrid bats), or most recently solely from composite materials (with the exception of solid wooden bats for the Major Leagues). Such bats are tubular (hollow inside) in construction in order to meet the weight requirements of the end user, have a cylindrical handle portion for gripping, a cylindrical barrel portion for hitting, and a tapered mid-section connecting the handle and barrel portions. Traditionally, such bats have generally had a constant radial stiffness along their barrel portion length, measuring the radial stiffness along the barrel wall as independent annular segments of the barrel wall at any location along the barrel wall length.  
         [0004]     When aluminum alloys initially replaced wooden bats in most bat categories, the original aluminum bats were formed as a single member, that is, they were made in a unitary manner as a single-walled aluminum tube for the handle, taper, and barrel portions. Such bats are often called single-wall aluminum bats and were known to improve performance relative to wooden bats as defined by increased hit distance. More recently (in the mid  1990 &#39;s), improvements in bat design largely concentrated on further improving bat performance. This was accomplished primarily by thinning the barrel wall of the single wall bat frame, and adding inner or internal, and or outer or external, secondary members extending along the entire barrel length. These members are often referred to respectively as inserts or sleeves; while the main member is often referred to as a body, shell or frame. Such bats are often called double-wall bats or multi-walled bats in the case of more than two walls resulting from two or more secondary members.  
         [0005]     Such double walled and multi-walled tubular bats generally obtained improved performance in terms of hitting distance by reason of the improved elastic deflection that is characteristic of a multilayer barrel wall. The efficient batting of a ball is maximized by minimizing plastic deformation, both within the bat and within the ball. Ideally, during the collision, the barrel wall of the bat should not deform beyond its elastic limit. Use of a multi-wall two or more member construction along the entire barrel length allows the barrel portion of the bat to elastically deflect or flex more upon ball impact which propels the ball faster and further than prior art single wall bats.  
         [0006]     The scientific principle governing improved bat performance is bending theory. When a ball impacts a bat it has kinetic energy that must be absorbed by the bat in order to stop the ball. The bat stores most of this energy by flexing. The ball as well deforms. After the ball is stopped, the bat returns the energy it has stored by rebounding and sending the ball back towards where it came from. The more the bat barrel or striking portion deforms upon ball impact without failing (denting or breaking) or experiencing plastic deformation, the lower the energy loss and the greater the energy returned to the ball from the bat as the tubular bat barrel portion impacted returns to its original shape.  
         [0007]     To allow the bat barrel portion to deform, requires lowering the radial stiffness of the barrel portion. The prior art double walled and multi-walled tubular bats have traditionally accomplished this by thinning the main member of the barrel portion and adding thin secondary member insert(s) and/or sleeve(s) which are not bonded to the main member, but which generally extend throughout the full length of the barrel portion. Such inserts and sleeves are not coupled to the barrel wall portion of the frame, and these two contacting components may slide with respect to each other in the same manner as leafs within a leaf spring. The resultant lowered radial stiffness along the barrel portion length permits the barrel wall to deflect elastically.  
         [0008]     U.S. Pat. No. 5,415,398 to Eggiman is an example of a multiwalled bat that discloses use of a frame and internal insert of constant thickness running full length of the barrel portion of the bat in a double-wall construction.  
         [0009]     Other similar bat designs are described in U.S. Pat. No. 5,303,917 to Uke which discloses a two member bat of thermoplastic and composite materials and U.S. Pat. No. 5,364,095 to Easton which discloses a two member bat consisting of an external metal tube and an internal composite sleeve bonded to the inside of the external metal tube and running full length of the barrel portion of the bat.  
         [0010]     U.S. Pat. No. 6,251,034 discloses a polymer composite second tubular member running throughout the full length of the barrel portion of the bat with the members joined at the ends only of the barrel portion with the balance of the composite member freely movable relative to the primary member. U.S. Pat. Nos. 6,440,017 and 6,612,945 to Anderson also disclose two member bats with an outer sleeve and inner shell of constant thickness running full length of the barrel portion. Other references include U.S. Pat. No. 6,063,828 to Pitzenberger, U.S. Pat. No. 6,461,760 to Higginbotham; U.S. Pat. No. 6,425,836B1 to Mizuno, and U.S. Patent Pub. 2001/0094882 A1 to Clauzin.  
         [0011]     In all the prior art multi-walled tubular bats cited so far, the bat secondary member, or insert, extends along the entire frame barrel length, have constant diameters and thickness resulting in uniform cross-sectional geometry along the secondary member length. Also, the bat members are not joined, except at their ends, in order to reduce radial stiffness of the barrel portion to improve bat performance. Also, in all cases, the radial stiffness of the barrel portion is uniform or constant full length of the barrel portion of the bats.  
         [0012]     While the prior art single member, and more particularly, double-walled and multi-walled tubular bats have demonstrated improved performance as claimed, various regulatory bodies have raised safety concerns regarding improved performance bats and thus, some have established maximum performance standards for various categories of baseball bats under their jurisdiction. As a result, manufacturers of baseball bats are required to pass various controlled laboratory tests, such as, bbf (batted ball performance), bbs (batted ball speed), etc. Further, for a given bat category (eg. slowpitch softball), there may be two or more regulatory bodies each of which may establish a different standard. Further, any of the regulatory bodies may change their standard from time to time. Such new or changed or varying regulations are extremely problematic, costly, and disruptive for both manufacturers and players.  
         [0013]     It is not generally desirable to lower the performance of a bat by simply increasing the thickness of the barrel wall of one or more of the barrel members along its full length. Lowering the performance of the bat by merely increasing the wall thickness can increase weight such that the finished bat weight standard or objective is exceeded. On the other hand, it is desirable to increase the wall thickness only in the sweetspot, or mid region, of the barrel portion of the bat without significantly increasing the weight.  
         [0014]     Therefore, what is needed is a simple, low cost invention to vary, e.g. decrease, bat performance of tubular bats in a controlled manner, in order to meet lowered or changed bat performance standard requirements without significantly increasing or departing from standard bat weight. Further, in conjunction with causing a decrease in batting performance it would be desirable to improve another bat characteristic such as “sweetspot” size.  
         [0015]     The sweet spot of a bat is generally the portion of the barrel which, with when struck by the ball, provides maximum batting performance. It is the location on the barrel at which the collision occurs with maximum efficiency and with the transmission of minimum vibration through the handle to the hands of a user. While highly subjective, many players would accept that the sweet spot portion on the bat has a dimension of approximately 2 inches, possibly up to 4 inches, in length and is located generally midway along the barrel portion. It is highly desirable to provide improved bats with a predetermined maximum allowable bat performance and a larger sweetspot region than bats of the prior art. This is one of the primary objectives of the present invention. Further, multi-wall bats of the present invention with inventive secondary members with non-uniform cross-sections along their length provide a vibration free soft feel and produce unique sounds upon contact with a ball.  
         [0016]     U.S. published patent application No. 2005/0070384 with patent application filed Sep. 29, 2003, by the inventors of the current application, addresses the larger sweetspot region objective by varying radial stiffness along the barrel length by adding a stiffener, or by changing fibre properties along the barrel length, or by thickening the barrel wall generally in the area of the sweetspot.  
         [0017]     U.S. Pat. No. 6,949,038 issued to Fritzke filed Jan. 21, 2004 also addresses this objective. The Fritzke &#39;038 reference purports to achieve an improved sweet spot characteristic by providing a secondary member, located either inside or outside the barrel of a standard frame, wherein the secondary member has a constant outside diameter with an internal wall whose thickness increases while proceeding from its ends inwardly towards the opposing ends. Generally, this thickening is shown to increase to a maximum around the mid-portion of the length of the secondary member. In one figure,  FIG. 12 , this thickness is shown to partially decrease around the mid-portion of the length of the secondary member, providing two laterally placed regions of maximum thickness on either side of the mid-portion.  
         [0018]     While the present inventor&#39;s earlier publication and the Fritzke patent represent different means of achieving an enlarged sweet spot of a baseball bat, the present invention includes other means to achieve the same result plus additional benefits regarding performance, feel and sound. Field testing has repeatedly shown that a “soft” feel upon ball impact and/or a “pleasing” sound are both player perceptions which are often favoured by the player over absolute performance as measured by hit distance.  
       SUMMARY OF THE INVENTION  
       [0019]     Therefore, in view of the foregoing, what is needed is a tubular baseball bat with a specific distribution of variable radial stiffness along their barrel portions in order to vary bat performance along the barrel hitting portion length, to make the bat feel “soft” when striking a ball, and to produce a pleasing sound upon impact with the ball. To achieve these objectives, the bats of the present invention are stiffened in the barrel area of peak bat performance commonly referred to as the sweetspot. Typically, this is an area approximately 2″ to 4″ in width as compared to barrel portion lengths of 4″ to 16″. This is achieved by the presence of an inventive geometric secondary member, or members, with non-constant outside diameters positioned internally within the bat frame, or by independent numerous annular secondary members located along the inner surface of the barrel portion of an external bat frame, or by inserting or adding to the bat a circumferential stiffener in the region of the sweetspot, or by making the barrel wall thicker in the region of the sweetspot, or by having stiffer material in the region of the sweetspot. Such embodiments also can provide variable bat performance along the barrel length, enlarge the sweetspot size, improve bat performance, have a softer feel upon ball impacts, and produce unique pleasing sounds upon ball impact.  
         [0020]     In one embodiment of the present invention, the inventive internal secondary members have a variable outside diameter and constant wall thickness and are characterized by variations in the surface profile on one side of the secondary member wall being reflected by a corresponding profile on the other side of the secondary wall that provide at least two or more contact regions with the internal barrel portion of the frame barrel wall that in turn create at least one functional air cavity that is closed at both ends. In one variant of the invention internal secondary members have constant internal diameters.  
         [0021]     In another embodiment of the present invention, two or more independent annular or ring like, members of generally consistent cross-sectional geometry with variable dimensions and with length less than one-half the barrel portion length are internally located in unbonded contact along the inner wall of the barrel portion of an external bat frame. An additional secondary bat member of length approaching the barrel length may be located internally to the annular secondary members.  
         [0022]     In another embodiment, a short light weight polymer composite circumferential stiffener of the invention as employed adds only minimal weight to a given bat thus allowing the stiffened bat to continued to be used within the required weight requirements set by the relevant governing body. The stiffener of the present invention can be added to previously constructed tubular bats returned from players for modification to meet a changed regulation allowing such previously manufactured bats to meet a changed standard. Though somewhat heavier, a short metallic stiffener could also be employed. An alternative method of varying stiffness, and thus bat performance, along the barrel portion is to vary thickness along the barrel portion.  
         [0023]     Another alternative solution of the present invention for all composite bats is accomplished by engineering calculation considering selection of the composite fiber type, the fibre size, the angles of the fibers, and the thickness of the polymer composite stiffener to be employed to precisely lower the bat performance.  
         [0024]     While tubular bats of the present invention have variable radial stiffness along their barrel portions to achieve a specific predetermined bat maximum bat performance, it is simultaneously possible to achieve a sweetspot which is larger than the sweetspot typically found in tubular bats of the prior art. In the present invention this is accomplished by selectively radially stiffening only the peak performance area (generally the sweetspot area) of the bat to provide a radial stiffness therein which is greater than the radial stiffness of the barrel portion area immediately adjacent on both sides of the sweetspot. The resultant effect can be to approximately double the sweetspot size (that is, the area of the barrel portion which provides maximum bat performance). Further, bats of the present invention with secondary members with a variable outside diameter, with or without thickened end portions have a softer feel upon impact and produce unique impact sounds.  
         [0025]     The foregoing summarizes the principal features of the invention and some of its optional aspects. The invention may be further understood by the description of the preferred embodiments, in conjunction with the drawings, which follow. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0026]      FIG. 1  shows a longitudinal cross-section of a typical prior art single wall tubular bat with a singular frame, or member, construction.  
         [0027]      FIG. 1A  shows a cross-sectional area taken at any location through the barrel portion of the  FIG. 1  prior art tubular bat.  
         [0028]      FIG. 2  shows a longitudinal cross-section of a typical prior art double-wall tubular bat with two separate members, a frame or main member with an internal insert as a secondary member in the barrel area. Both the frame and insert run the full length of the barrel portion and are not joined full length.  
         [0029]      FIG. 2A  shows a cross-sectional area taken at any location through the barrel portion of the  FIG. 1  prior art tubular bat.  
         [0030]      FIG. 3  shows a longitudinal cross-section of a typical prior art double-wall tubular bat with two separate members, a frame or main member with an external sleeve secondary member in the barrel portion. Both the frame and sleeve run the full length of the barrel portion and are not joined full length.  
         [0031]      FIG. 3A  shows a cross-sectional area taken at any location through the barrel portion of the  FIG. 3  prior art tubular bat.  
         [0032]      FIG. 4  shows a longitudinal cross-section of one embodiment of the present invention showing a single wall tubular bat in accordance with the present invention showing an internal stiffener generally confined to the sweetspot area of the barrel portion and joined to the barrel portion.  
         [0033]      FIG. 4A  shows a cross-sectional area of a barrel location not within the sweetspot area.  
         [0034]      FIG. 4B  shows a cross-sectional area within the sweetspot area showing the internal stiffener of the present invention.  
         [0035]      FIG. 5  shows a longitudinal cross-section of a second embodiment of the present invention showing a single wall tubular bat in accordance with the present invention with an external stiffener generally confined to the sweetspot area of the barrel portion and joined to the barrel portion.  
         [0036]      FIG. 5A  shows a cross-sectional area at a barrel location not within the sweetspot area.  
         [0037]      FIG. 5B  shows a cross-sectional area within the sweetspot area showing an external stiffener of the present invention.  
         [0038]      FIG. 6  shows a longitudinal cross-section of a third embodiment of the present invention showing a single wall polymer composite tubular bat in accordance with the present invention showing a localized area of the fiber type and/or angle change resulting in increased radial stiffness generally confined to the sweetspot area of the barrel portion.  
         [0039]      FIG. 6A  shows a cross-sectional area at a barrel location not within the sweetspot area.  
         [0040]      FIG. 6B  shows a cross-sectional area within the sweetspot area showing a stiffened area of changed fiber angles and/or type.  
         [0041]      FIG. 6 . 1  shows a longitudinal cross section of a single wall polymer composite tubular bat in accordance with the present invention showing the alternative construction incorporating a thickened barrel wall  21  resulting in increased radial stiffness generally confined to the sweetspot area of the barrel portion.  
         [0042]      FIG. 6 . 1 A shows a cross-sectional area at a barrel location not within the sweetspot area.  
         [0043]      FIG. 6 . 1 B shows a cross-sectional area within the sweetspot area showing a stiffened area with thicker barrel wall.  
         [0044]      FIG. 6 . 2  shows a longitudinal cross-section of an alternative double wall polymer composite bat in accordance with the present invention showing a localized area of the fibre type and/or fibre angle change within the insert resulting in increased radial stiffness generally confined to the sweetspot area of the barrel portion.  
         [0045]      FIG. 6 . 2 A shows a cross-sectional area at a barrel location not within the sweetspot area.  
         [0046]      FIG. 6 . 2 B shows a cross-sectional area within the sweetspot area showing a stiffened area of changed fibre angles and/or type.  
         [0047]      FIG. 6 . 3  shows a longitudinal cross-section of a double wall polymer composite bat in accordance with the present invention with an alternative construction showing a thickened barrel wall  21  within the insert resulting in increased radial stiffness generally confirmed to the sweetspot areas of the barrel portion.  
         [0048]      FIG. 6 . 3 A shows a cross-sectional area of a barrel location not within the sweetspot area.  
         [0049]      FIG. 6 . 3 B shows a cross-sectional area within the sweetspot area showing a stiffened area with thicker barrel wall.  
         [0050]      FIG. 7  shows a longitudinal cross-section of a fourth embodiment of the present invention showing a double-wall tubular bat with two separate members, a frame or main member with an internal insert as a secondary member full length in the barrel portion, and in accordance with the present invention, showing an internal stiffener generally confined to the sweetspot area of the barrel portion and joined to the barrel portion.  
         [0051]      FIG. 7A  shows a cross-sectional area at a barrel location not within the sweetspot area.  
         [0052]      FIG. 7B  shows a cross-sectional area within the sweetspot area showing the internal stiffener.  
         [0053]      FIG. 8  shows a longitudinal cross-section of a fifth embodiment of the present invention showing a double-wall tubular bat with two separate members, a frame or main member with an external sleeve as a secondary member full length in the barrel portion, and in accordance with the present invention showing an external stiffener generally confined to the sweetspot area of the barrel portion and joined to the barrel portion.  
         [0054]      FIG. 8A  shows a cross-sectional area at a barrel location not within the sweetspot area.  
         [0055]      FIG. 8B  shows a cross-sectional area within the sweetspot area showing the external stiffener.  
         [0056]      FIG. 9  shows in graphical form the typical relationship between tubular bat performance and barrel location and sweetspot size.  
         [0057]      FIG. 10  shows in graphical form a typical relationship between tubular bat performance of a bat of the present invention and barrel location and sweetspot size.  
         [0058]      FIG. 11A  shows a longitudinal cross-section of the barrel portion of a typical prior art single wall tubular bat with a singular frame, or main member. Not shown in  FIG. 11A  and all following figures is the traditional bat handle portion located at the proximal end of the taper portion.  
         [0059]      FIG. 11B  shows a longitudinal cross-section of the barrel portion of a typical prior art single wall tubular bat with a singular frame, or main member, construction wherein the barrel wall is inwardly thickened generally in the area of the sweetspot.  
         [0060]      FIG. 11C  shows a longitudinal cross-section of the barrel portion of a typical prior art double wall tubular bat with an external frame and a secondary internal member, or insert.  
         [0061]      FIG. 11D  shows a longitudinal cross-section of the barrel portion of a typical prior art double wall tubular bat with an external frame and a secondary internal member, or insert, wherein the insert is inwardly thickened generally in the area of the sweetspot.  
         [0062]      FIG. 11E  shows a longitudinal cross-section of the barrel portion of a typical prior art double wall tubular bat with an external frame and a secondary internal member, or insert, wherein both the frame and the insert are inwardly thickened generally in the area of the sweetspot.  
         [0063]      FIG. 12A  shows a longitudinal cross-section of the barrel portion of one embodiment of the present invention showing a double wall tubular bat with an external frame and a primary secondary member, or insert, located internally within the frame wherein the primary secondary member has an outer diameter which varies along the length of the member, a constant wall thickness, two contact regions with the frame barrel portion inner surface, and one air cavity that is closed at both ends.  
         [0064]      FIG. 12B  shows a variant of the bat of  FIG. 12A  wherein the primary secondary member has a constant wall thickness, there are two contact regions, and one closed air cavity, wherein the thickness of the air cavity is reduced generally in the area of the barrel mid portion.  
         [0065]      FIG. 12C  shows a variant of the bat of  FIG. 12A  wherein the primary secondary member has a constant wall thickness, there are three contact regions and two closed air cavities.  
         [0066]      FIG. 12D  shows a variant of the bat of  FIG. 12A  wherein the primary secondary member has a constant wall thickness and the outer diameter of the primary secondary member oscillates periodically along its length between a maximum and a minimum diameter, creating multiple contact regions and multiple closed air cavities.  
         [0067]      FIG. 12E  shows a variant of the bat of  FIG. 12D  wherein the period of the oscillation of outside diameter of the primary secondary member increases away from the barrel mid portion.  
         [0068]      FIG. 12F  shows a variant of the bat of  FIG. 12A  with a primary secondary member and an additional secondary member located internally to the primary secondary member wherein both secondary members have outer diameters which vary along the length of the secondary members, have constant wall thicknesses, two contact regions each, and one closed air cavity each.  
         [0069]      FIG. 12G  shows a variant of the bat of  FIG. 12A  wherein the primary secondary member has a constant diameter internal surface, a non-constant diameter external surface, a non-constant wall thickness, two contact regions with the internal frame wall, and one air cavity that is closed at both ends.  
         [0070]      FIG. 12H  shows a variant of the bat of  FIG. 12G  wherein the primary secondary member has two contact regions and one closed air cavity that has a non-uniform cross-section.  
         [0071]      FIG. 12I  shows a variant of the bat of  FIG. 12G  wherein the primary secondary member has three contact regions and two closed air cavities.  
         [0072]      FIG. 12J  shows a variant of the bat of  FIG. 12D  wherein the primary secondary member has a constant diameter internal surface.  
         [0073]      FIG. 12K  shows a variant of the bat of  FIG. 12E  wherein the primary secondary member has a constant diameter internal surface.  
         [0074]      FIG. 12L  shows a variant of the bat of  FIG. 12F  wherein the primary secondary member has a constant diameter internal surface.  
         [0075]      FIG. 13A  shows a longitudinal cross-section of the barrel portion of a second embodiment of the present invention showing a double wall tubular bat with an external frame, and six independent annular secondary members, or rings, each of length less than one-half the frame barrel portion length and varying thickness, each internally located side by side, with or without spaces between, along the frame barrel portion length against the barrel portion inner surface of the external bat frame.  
         [0076]      FIG. 13B  shows a multi-wall bat variant of the bat of  FIG. 13A  wherein there are six independent annular secondary members each of length less than one-half the frame barrel portion length, each internally located along the frame inner wall surface, and a tubular additional secondary member with length approaching the frame barrel portion length and located internally to the annular secondary members and in contact with at least one annular secondary member, generally extending co-extensively with the frame barrel portion.  
         [0077]      FIG. 13C  shows a variant of the bat of  FIG. 13B  wherein there are six independent annular secondary members each of length less than one-half the frame barrel portion length, each internally located along the additional secondary member outer wall surface and internally to the external frame inner wall surface.  
         [0078]      FIG. 13D  shows a variant of the bat of  FIG. 13B  wherein there are three independent annular secondary members of constant thickness each internally located between and abutting against the external frame inner wall surface and the additional secondary member outer wall surface forming three closed air cavities.  
         [0079]      FIG. 13E  shows a variant of the back of  FIG. 13D  wherein there are multiple annular secondary members with or without multiple air cavities.  
         [0080]      FIG. 13F  shows a longitudinal cross-section of the barrel portion of another embodiment of the present invention showing a multi-wall tubular bat with an external frame, and two annular secondary members, or rings, each of length less than one-half the frame barrel portion length, wherein each annular secondary member is located between the outer frame and an additional secondary member with length approaching the frame barrel portion length, wherein the wall of the additional secondary member is thickest generally in the frame barrel mid portion providing a contact area between the inner surface of the frame and the outer surface of the additional secondary member. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0081]     The present invention is directed to providing tubular baseball bats with variable radial stiffness along the length of the barrel or hitting portion  1 , of the bats. Bats of the present invention can have a larger sweetspot size  19 , have a soft feel with substantially reduced vibrations, and produce unique pleasing sounds upon impact with a baseball or softball. Further, such bats can be produced at reasonably low costs.  
         [0082]     Unless otherwise indicated, the term stiffness as used in this disclosure is equivalent to the modulus of elasticity and is a measure of the change in length of a material under loading. For a tubular body, such as a baseball bat, stiffness of the material can be measured in the axial direction, parallel to the longitudinal axis of the tube, or the radial or transverse direction perpendicular to the longitudinal axis of the tube. Radial stiffness is a measure of the force required to depress any given a section of the tube in the radial direction. Radial stiffness is a function of modulus of the material, the tube thickness and the tube diameter. Radial stiffness is measured along the barrel wall as independent annular segments of the barrel wall at each measurement location.  
         [0083]     The prior art bats are shown in  FIGS. 1, 2 ,  3 , and  11 .  FIGS. 1 and 11 A show a single wall tubular bat with main member or frame  16 .  FIGS. 2 and 11 C show a double wall tubular bat with an insert or primary secondary member  13 , formed separately from the main member  16 , which is fitted into the entire barrel length  1  of the main member  16 .  FIG. 3  shows a double wall tubular bat with a sleeve  14 , formed separately from the main member  16 , which is fitted over the entire barrel length  1  of the main member  16 .  FIG. 11B  shows a single wall tubular bat with the main member  16  being internally thickened in the barrel mid-section.  FIGS. 11D and 11E  show double wall tubular bats with an internally thickened secondary member  13  and in the case of  FIG. 11E  also an internally thickened main member  16 .  
         [0084]     Though not indicated in  FIGS. 1 through 8 , and  11  through  14 , bats of the present invention, similarly to bats of the prior art, include a traditional knob at the handle portion end  5 , or proximal end of the bat, and a traditional end cap  21  (not shown in  FIGS. 1 through 8 ) at the barrel portion end  4 , the distal end, both of which can be made from a variety of materials.  
         [0085]     Most adult tubular baseball bats of the prior art have maximum outside barrel portion diameter  2  of either 2.625 inches or 2.75 inches. Depending on the taper portion geometry of the mid-section  8 , and the total length of the bat, the barrel length  1  as defined by length of constant maximum diameter  2 , ranges from 4 to 12 inches. Total barrel wall thickness  6  ranges from 0.100 inches to 0.140 inches for aluminum bats and up to 0.220 inches for all composite bats and is measured at any point along the barrel wall as the outside diameter of the frame or member with the largest outside diameter minus the inside diameter of the member with the smallest outside diameter including any gaps, or spaces, between the two extreme diameters.  
         [0086]     Most youth baseball bats and softball bats of the prior art have maximum outside barrel portion diameter  2  of 2.25 inches. Depending on the taper portion geometry of the mid-section  8 , the barrel length  1  ranges from 4 to 16 inches. Barrel wall thickness  6  ranges from 0.060 inches to 0.090 inches for aluminum bats and up to 0.220 inches for all composite bats.  
         [0087]     The bats of the present invention, shown in  FIGS. 4 through 8 , and  12  through  14 , have similar dimensions to the foregoing prior art bats shown in  FIGS. 1, 2 ,  3 , and  11 .  
         [0088]     A first embodiment of the present invention  FIG. 4  is a single wall tubular baseball bat consisting of a cylindrical handle portion  7  for gripping, a cylindrical tubular barrel portion  9  for striking or hitting, and a tapered portion  8  connecting the handle  7  and barrel  9  portions, with a thin polymer composite stiffener  18  having a stiffener wall located internally within the barrel portion  9  and extending longitudinally in the mid-section, sweetspot area  19  of the barrel length  1 .  
         [0089]     A polymer composite is a non-homogenous material consisting of continuous fibers embedded in, and wetted by, a polymeric resin matrix whereby the properties of the material are superior to those of its constituent fibers and resin taken separately. Such polymer composites are anistropic materials since they exhibit different responses to stresses applied in different directions depending on how the fibers are aligned or angled within the matrix.  
         [0090]     Other materials commonly used in bat constructions such as aluminum, wood and plastics are not anistropic and are thus limited in controlling bat performance; for example, radial stiffness is equal to longitudinal stiffness and cannot be graduated along the barrel length  1 . However, with composite materials, which are preferred, properties of bats made in accordance with the present invention, such as radial stiffness which determines bat performance can be controlled (i.e. designed to a given requirement) by altering such parameters as the fiber alignments along the barrel length  1 , and/or the type of fibers chosen, their demier or layout density and/or the thickness of the polymer composite structure.  
         [0091]     Generally, the fiber materials used are selected from a group consisting of fiberglass, graphite or carbon, aramid, boron, nylon, or hybrids of any of the foregoing, all of which are commercially available. The resins used to impregnate, wet out, and encapsulate or imbed the fiber materials are generally selected from a group consisting of epoxy, polyester, vinyl ester, urethane, or a thermoplastic such as nylon, or mixtures thereof.  
         [0092]     The first embodiment of the present invention, depicted in  FIG. 4 , consists of a thin polymer composite stiffener  18  located internally within the barrel portion  9  generally in the sweetspot area  19  located in proximity to the middle or mid-section area of the barrel length  1  of a single wall tubular bat. The resultant stiffened bat results in a predetermined calculated lower performance, with an enlarged sweetspot  19 , as subsequently explained.  
         [0093]     The sweetspot area  19  of a baseball bat is generally referred to as that area along the barrel length  1  in which bat performance is greatest; that is, a ball struck within the sweetspot area  19  will travel further than a ball struck on either side of the sweetspot area. Typically, the sweetspot area  19  is located around the middle of the barrel length  1  and is in the order of about 2 inches to 4 inches in length when compared to overall barrel lengths  1  which range from approximately 4 inches to 16 inches or more.  
         [0094]     In actual practice, the performance of a baseball bat of the prior art follows a statistical normal distribution along the barrel length  1 , usually centered near the middle of the barrel length  1  in the sweetspot area  19 .  FIG. 9  shows a typical bat performance distribution example with a 12-inch barrel length  1 .  
         [0095]     In  FIG. 9 , the maximum bbs (one measure of bat performance standard) is 100 while most players would describe the sweetspot as being approximately 2 inch long (that is, the portion of the barrel length equal to or greater than 98 bbs). The bat of this particular sample meets a bat performance factor standard of 100 bbs maximum if so regulated.  
         [0096]     If the applicable regulatory body for the bat in the  FIG. 9  example changed the bat performance standard from 100 bbs maximum to say 96 bbs maximum, the bat of the present invention could be provided with a specifically designed 4 inch polymer composite stiffener  18  located in the center of the barrel length  1 .  FIG. 10  shows the bbs versus barrel length for this example.  
         [0097]     In  FIG. 10 , in an example of the present invention, the combined barrel wall, with the polymer composite stiffener  18  present, is approximately twice as stiff in the center 2 inches of the sweetspot area  19  as in the  1  inch area immediately adjacent to the center or mid-section area on each side of the center area. The polymer composite stiffener  18  fiber type, fiber angles and thicknesses are designed such as to reduce the bbs from 100 to 96 in the center 2 inch area of the barrel length  1  and from 98 to 96 bbs in the 1 inch areas immediately adjacent to the center area. As a result of the present invention, the resultant typical example bat meets the lowered regulatory standard of 96 bbs with a sweetspot area  19  which has been increased in size by 100% (from 2 inches wide to 4 inches wide). At the same time the regions around points A and B have been introduced into the batting performance curve of  FIG. 10  that were not present in the curve of  FIG. 9 , with the more flattened portion there-between that is characteristic of an enlarged sweet spot.  
         [0098]     Alternatively, thickening the total barrel wall with the same material, the same thickness, and the same location as the stiffener results in the identical reduced bat performance.  
         [0099]     The first embodiment (i.e. as shown in  FIG. 4 ) of the present invention is particularly suited to retrofitting used bats returned by players and making them legally playable under a revised standard.  
         [0100]     The thin polymer composite stiffener  18  of the present invention has a stiffener wall which is typically in the order of 0.010 inches to 0.040 inches in thickness, preferably 0.020″ with a length of 2 inches to 6 inches which is typically less than 50% of the barrel length, such as 16⅔% of the barrel length, as is apparent from  FIG. 10 . A 4 inch stiffener, as referenced in paragraph [0059], in a 12 inch barrel as referenced in  FIG. 10 , would represent 33.3% of the barrel length; a 4 inch stiffener in a 16 inch barrel would represent 25%, and a 2 inch stiffener in a 16 inch barrel would represent 12.5% of the barrel length. The stiffener  18  is preferably bonded, fully or partially, to the main member  16 , or to the secondary member insert  13  of  FIG. 7  or to the secondary member sleeve  14  of  FIG. 8 , or combinations thereof on either the internal or external barrel walls, as shown in  FIGS. 4, 5 ,  7  and  8 . Analogous to  FIGS. 4, 5 ,  7  and  8  an alternative solution (since stiffness is proportional to thickness) to the stiffener  18  is to vary the barrel thickness  6  to the same extent and manner along any portion of the barrel length  1  of any bat according to the invention, including the bat of  FIG. 6  in order to vary bat performance. The barrel portion&#39;s effective wall thickness in the mid-section can be greater by 8⅓% or more over the thickness of the barrel in the lateral, adjacent portions. Conversely, the barrel wall&#39;s thickness beyond its central portion, in the lateral regions proceeding towards the end portions of the barrel, may be at least 8⅓% thinner than the thickness of the barrel wall in the mid-section. Just as the stiffener wall may be typically in the order of 0.005 inches to 0.040 inches in thickness, or 0.010 inches to 0.040 inches in thickness, or 0.015 inches to 0.040 inches in thickness, or 0.015 inches to 0.030 inches, so too the analogous increase in barrel wall thickness along the mid-section may fall within the same ranges.  
         [0101]     A second embodiment of the present invention, as shown in  FIG. 5 , is a single wall tubular baseball bat which in accordance with the present invention has a thin polymer composite stiffener  18  located externally to the barrel portion  9  generally in the sweetspot area  19  located in proximity to the middle area of the barrel length  1 . The resultant stiffened bat results in a calculated lower performance, with a bigger (longer) sweetspot  19 , as previously explained.  
         [0102]     A third embodiment of the present invention, as shown in  FIG. 6 , is a single wall tubular polymer composite baseball bat which in accordance with the present invention has a localized area of fiber type of greater stiffness and/or angle change  20  resulting in increased radial stiffness generally in the sweetspot area  19  located in proximity to the middle area of the barrel length  1 . This embodiment applies equally well to double-wall and multi-wall (more than two walls) tubular all polymer composite baseball bats and is limited to newly designed polymer composite single wall, double-wall, and multi-walled new bats as opposed to field returned bats. The fiber types, and/or fiber angles, and/or fiber sizes, and/or composite thickness can be designed such as to graduate the radial stiffness of the barrel wall within the barrel portion  1  along its entire length. That is, the radial stiffness could be higher in the peak performance area (generally the sweetspot area  19 ) than in the lateral regions immediately adjacent to the sweetspot area  19 . In fact, by duplicating the increase in radial stiffness in the barrel mid-section as achieved by the stiffener  18  of  FIG. 4  or  7 , the exact same bat performance change as shown in  FIG. 10  and enlarged in sweetspot size  19  can be achieved by bats of  FIG. 6 . Similarly, the alternative solution  FIG. 6 . 1  showing a single wall tubular bat with a thickened barrel wall  21  and the alternative solution  FIG. 6 . 3  showing a double wall tubular bat with a thickened barrel wall  21 , with the same material, location, and thickness of the stiffener  18  will result in the same bat performance change, as shown in  FIG. 10 , and resultant enlarged sweetspot size  19 .  
         [0103]     A fourth embodiment of the present invention, as shown in  FIG. 7 , is a double-wall tubular bat showing two separate members, a frame or main member  16  with an internal insert  13  as a secondary member full length in the barrel length  1  and, in accordance with the present invention, a stiffener  18  located internally within the insert  13  generally confined to the sweetspot area  19 , along the barrel length  1 . Though not shown, the stiffener  18  could be located externally to the main member  16  or between the main member  16  and the internal insert  13 . Also, though not shown, in multi-walled bats the stiffener  18  could be located internally, or externally, or between the members, or combinations thereof.  
         [0104]     A fifth embodiment of the present invention, as shown in  FIG. 8 , is a double-wall tubular bat showing two separate members, a frame or main member  16  with an external sleeve  14  as a secondary member full length in the barrel length  1  and, in accordance with the present invention, a stiffener  18 , located externally to the sleeve  14 , generally in the area of the sweetspot area  19  along the barrel length  1 . Though not shown, the stiffener  18  could be located internally to the main member  16  and the external sleeve  14 . Also, though not shown, in multi-walled bats, the stiffener  18  could be located internally, or externally, or between the members, or combinations thereof.  
         [0105]     All embodiments of the present invention, as shown in  FIGS. 4, 5 ,  6 ,  7 ,  8 ,  12 C,  12 I,  13 A,  13 B,  13 C,  13 D, and  13 F, exhibit greater radial stiffness in the mid-section of the barrel length  1  relative to the lateral regions immediately adjacent to the mid-section, resulting in an enlarged sweetspot area  19 .  
         [0106]     Besides an enlarged sweetspot, other objectives of bats of the present invention include providing a user with a “soft feel”, having substantially less vibrations transmitted to the user&#39;s hand while striking a ball, unique impact sounds, and higher performance for average or below average players when making contact away from the normal sweetspot. These further objectives are achieved by bats of the present invention with secondary members with a variable outside diameter and by bats with two or more independent annular secondary members internally located along the inside diameter of the external bat frame.  
         [0107]     All bats of the present invention shown in  FIG. 12  are characterized by inventive primary secondary members, or inserts  13 , located internally within an external main member, or frame  16 , with frame wall thickness  44 , within the barrel length  1  of the hitting portion of the bat. The primary secondary member  13  has an inner surface  53 , an outer surface  55 , an inner diameter  29 , an outer diameter  25 , a wall thickness  27 , a length  26 , a proximal end  58 , and a distal end  59 . Not shown in the  FIGS. 12 and 13  bats is the normal handle portion located adjacent to the taper proximal portion and knob located at the proximal end of the frame  16  traditional bats. A traditional endcap  21  encloses the distal end  49  of the barrel portion  9 . The inventive primary secondary members  13  of the bats of  FIG. 12  have outer diameters  25  that vary along the majority of the barrel length  1 . The variations in outer diameter  25  of the inserts  13  in all bats of FIGS.  12  are dimensioned to produce two or more contact areas  30  with the inside surface  45  of the frame  16 . In some variants of the bats of  FIG. 12 , the primary secondary member  13  contact areas  30  have substantially flattened portions of constant maximum outer diameter, while in others the contact portions are much smaller. The contact areas  30  create at least one enclosed air cavity  22  with a maximum air cavity thickness  23  of at least 0.010″. The air cavities  22  of the present invention are closed at both ends to produce the desired feel and sound objectives upon ball contact. Varying positioning and quantities of the air cavities  22 , and contact areas  30 , produce bats with different performance levels, feel, and sound upon barrel portion  9  impact with a ball. To produce the desired unique soft bat feel and sound upon impact, the ideal thickness  23  of the air cavities  22  has been found by field testing to be 0.020″ to 0.050″ which is considerably thicker than prior art bats, where any such air spaces exist only due to manufacturing tolerances of the frame  16  and secondary member  13 . The air cavities  22  of the present invention can be filled with an elastomeric material with further performance, feel, and sound effects. Such prior art secondary members  13  do not have variable outer diameters. Due to the variable outer diameter  25 , all bats of  FIG. 12  can have variable radial stiffness along the barrel length  1 . However, when the frame  16  and/or the primary secondary member  13  is made with composite materials, fiber types and laminating angles can be manipulated to achieve either constant or variable radial stiffness along the barrel length  1  regardless of dimensional variations.  
         [0108]     As seen in  FIGS. 12A through 12F  bats of the present invention are further characterized by the inventive primary secondary member  13  having a variable outer diameter  25  and a variable inner diameter  29 . The variable outer diameter  25  of the insert  13  produces variations in the surface profile of the insert  13  which are generally reflected by a corresponding profile on the inner surface  53  of the insert  13  wall. The resulting total bat wall thickness  6  variations along the barrel length  1  vary the performance, feel, and sound of the bats of  FIGS. 12A through 12F .  
         [0109]     The bat variant of  FIG. 12A  has a single annular air cavity  22  where the external frame  16  wall acts independently of the insert  13  wall until the contact force between the ball and the external frame  16  increases enough to deflect the external frame inner surface  45  into contact with the insert&#39;s outer surface  55 . At that point, the two members  16  and  13  act together, thus creating a non-linear spring. This decreases the peak contact force between the ball and the bat, which reduces the energy losses in the ball, and therefore improves performance.  
         [0110]     The bat variant of  FIG. 12B  has an insert  13  outside diameter  25  which increases near the barrel mid-portion  50 , narrowing the air cavity  22  thickness. This reduces the performance improvement due to the effect of the gap, discussed in the previous paragraph, near the mid-portion  50  of the barrel length  1  and therefore gives a more uniform bat performance along the barrel length  1 .  
         [0111]     The bat variant of  FIG. 12C  is similar to  12 B where the insert  13  makes contact with the frame  16  inner surface  45  near the mid-portion  50  of the barrel length  1  at the insert  13  proximal  58  and distal  59  portions near the barrel ends. This eliminates the performance improvement imparted on the bat by the air cavity  22  at the barrel mid-portion  50 , but creates two independent annular air cavities  22  away from the barrel mid-portion  50 .  
         [0112]     The bat variant of  FIG. 12D  has an insert  13  where the outside diameter  25  oscillates, or varies periodically along the barrel length  1 . When the period of the oscillations is reduced the insert  13  becomes stiffer and stronger for a given weight, or lighter for a given stiffness. The radial stiffness of the insert  13  increases with increased insert wall thickness  27 , reduced period of oscillation, or increased magnitude of oscillation.  
         [0113]     The bat variant of  FIG. 12E  has an insert  13  where the outside diameter  25  oscillates, or varies periodically along the barrel length  1 , and where the period of the oscillation increases away from the mid-portion  50  of the barrel length  1 . The resultant reduced radial stiffness away from the sweetspot creates a more uniform performance along the barrel length  1 .  
         [0114]     The bat variant of  FIG. 12F  is a triple wall version of the bat of  FIG. 12A  created by an additional secondary member  31 . Though not shown, additional such members could be added to create a multi-wall bat with more than three walls. Similarly, though not shown, additional secondary members  31  of any configuration could be added to the bats of  FIGS. 12B, 12C ,  12 D, and  12 E.  
         [0115]      FIGS. 12G through 12L  depict bats characterized by an inventive primary secondary member  13  with a variable outer diameter  25  and a constant inner diameter  29  along the barrel length  1 . Otherwise, the bat variants of  FIGS. 12G  through L are similar to the bat variants of  FIGS. 12A  through F.  
         [0116]     In another embodiment of the present invention, the bats of  FIG. 13  have two or more independent annular, or ring-like, secondary members  61  of similar cross-section shape of variable dimensions with individual length  62 , along the barrel portion  19 , less than one-half the barrel portion length  1  and are internally located along the inner surface  45  of the external frame  16 . The annular secondary members  61  have a length  62 , a wall thickness  63 , an inner surface  64 , an inner diameter  65 , an outer surface  66 , and an outer diameter  67 .  
         [0117]     The bat variant of  FIG. 13A  has the external frame  16  reinforced by a series of independent inner annular secondary members  61  generally in the form of annular rings. The secondary members  61  have a common outer diameter  67  which is equal to or less than the inner diameter  25  of the frame  16  and are generally thicker near the barrel mid-portion  50  of the barrel length  1  and thinner away from it. The rings  61  are generally thicker towards the barrel distal end  49  and thinner towards the barrel proximal end  48  because the bat is moving faster at the distal end  49 . Although not shown, the annular secondary members  61  could be of constant thickness and have varying material properties to accomplish varying radial stiffness and resultant more uniform performance.  
         [0118]     The bat variant of  FIG. 13B  has an external frame  16  reinforced by a series of independent annular secondary members  61  in the form of annular rings, in combination with an inner additional secondary continuous member  31  extending along the majority of the barrel length  1 . The annular secondary members  61  provide a more uniform bat performance along the barrel length, while the inner additional secondary member  31  supports the impact force.  
         [0119]     The bat variant of  FIG. 13C  is similar to that of  13 B; however, the annular secondary members  61  have a constant inner diameter  29 .  
         [0120]     The bat variant of  FIG. 13D  has internal annular secondary members  61  with a uniform inner diameter  29  and outer diameter  25 , which create closed air cavities  22 .  
         [0121]     The bat variant of  FIG. 13E  has an external frame  16  and axially continuous inner additional secondary member  31  with a series of annular secondary members  61  between the two. One candidate for the intermediate members  61  is a series of elastomeric O-rings with higher stiffness near the barrel mid portion  50 .  
         [0122]     The bat variant of  FIG. 13F  has an axially continuous inner additional secondary member  31  that is thicker in its mid-portion and could, or could not be, in contact with the external frame  16  near the barrel mid-portion  50  and has a reduced outer diameter at the barrel proximal  48  and distal  49  ends. The bat has two or more annular secondary members  61  located at the barrel portion  9  proximal  48  and diesel  49  ends. In effect, this bat is double walled at the barrel mid-portion  50  and triple walled away from the barrel mid-portion  50 , giving more uniform bat performance along the barrel length  1  resulting in a broadened sweetspot.  
         [0123]     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.  
         [0000]     Conclusion  
         [0124]     The foregoing has constituted a description of specific embodiments showing how the invention may be applied and put into use. These embodiments are only exemplary. The invention in its broadest, more specific aspects, is further described and defined in the claims which now follow.  
         [0125]     These claims, and the language used therein, are to be understood in terms of the variants of the invention which have been described. They are not to be restricted to such variants, but are to be read as covering the full scope of the invention as is implicit within the invention and the disclosure that has been provided herein.  
         [0126]     The invention may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The present embodiments are therefore to be considered as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.