Abstract:
In accordance with the embodiments of the present invention, a resilient and elastic single-filament string for a sports racquet, and an accompanying complete sports racquet is provided. The string includes a central body with ridges that extend axially along the length of said central body, where the ridges and central body are initially formed as a single homogeneous structure. The sports racquet incorporates at least one of these single-filament strings, along with a frame formed of a rigid material containing a number of holes.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is related to U.S. Provisional Patent Application Ser. No. 61/818,658 titled “STRING FOR TENNIS RACQUET AND TENNIS RACQUET WITH IMPROVED STRING” filed on May 2, 2013, the complete subject matter of which is incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE DISCLOSURE 
       [0002]    A sports racquet string, preferably a tennis racquet string, and more specifically an improved string configuration that imparts more spin to a ball upon contact, recovers more quickly from such contact, maintains its structural integrity for a longer period of time, and a sports racquet that includes the improved string. 
       BACKGROUND 
       [0003]    The traditional and most popular cross-section of a sports racquet string is circular. Such strings are typically made from natural gut (animal fiber) or from synthetic materials, such as nylon. Conventionally, strings are constructed by twisting many fine filaments of these materials together, with or without a center filament, into a round core strand and then by passing the core strand through a round die to apply an outer layer coating. Thus the prior art teaches the use of a multi-filament string. Such multi-filament strings provide an increase in elasticity over traditional single-filament synthetic strings, but fall short of single-filament strings in terms of their durability. 
         [0004]    The prior art also discloses the idea of a multi-filament string that is not round in cross-section but that ,may include a plurality of external ribs. These concepts are illustrated and described, for example, in PCT Application No. PCT/US90/01698, published as WO 91/11549 in the names of CHEN and LIN. 
         [0005]    As described in the aforementioned PCT Application, it is generally desirable that the sting exhibits various characteristics such as small damping, that is, low energy loss and high resilience, and good elasticity, that is, a low modulus of elasticity. These elements contribute to the playability of the string. As an illustration, a low modulus of elasticity promotes the ability of the player to carefully control the spin and direction of the balls they hit, thereby providing greater accuracy and spin amount. It is also desirable that the string be sufficiently durable. This aspect of durability is the most troublesome deficiency among all multi-filament string designs. 
         [0006]    The overall diameter of any sports racquet string is very important, as it affects the durability and playability of the string. Generally, thin strings have superior playability. Thin strings exhibit good elasticity, which allows them to maintain longer contact with the ball for greater control. However, thin strings may stretch and are more easily broken. On the other hand, thick strings are stronger and more durable but lack the playability of thin strings. 
         [0007]    An additional important characteristic of a string is its ability to impart a spin, preferably top spin, on the ball. The failure to consistently impart significant top spin frequently results in the ball traveling greater distance than intended before hitting the ground. Thus the failure to impart a top spin on the ball frequently requires that the ball be struck with lesser force, to limit the distance of travel before the ball hits the ground. This means hitting shots that are slower, and more easily returned. More spin allows for more speed. 
         [0008]    To put spin on the ball, the ball is struck with the racket face at an angle to the flight path and the racket face is moved in a parallel direction to the plane of the face. Increasing the friction between the strings and the ball has been thought to enhance imparting spin on the ball. 
         [0009]    The aforementioned PCT Application, as well as U.S. Pat. Nos. 4,805,393 (&#39;393 patent) and 4,860,531 (&#39;531 patent), all three of which are hereby incorporated in their entirety by reference, each propose variations in string configuration, but suffer from the limitation that they are unable to provide all of the desired benefits of the current invention. Rather, the approach taken in each reference is merely an unsatisfactory compromise in performance, based on a misunderstanding of the contribution of the string shape or configuration to the playing of the game. 
         [0010]    The strings mentioned in these references are all comprised of either fused or bonded multi-filament combinations, or helically-oriented twisting of a non-circular single-filament. Such types of string share the disadvantage of not having enough durability to match their elasticity, and therefore impart a consistently high amount of spin on a ball after prolonged usage. The single-filament string described herein maintains a higher degree of durability compared to the prior art strings, while simultaneously providing more elasticity than a traditional single-filament string when contacting a ball. The present invention&#39;s ridged homogenous construction solves the problem of providing a high degree of playability coupled with a high degree of overall string durability. 
       BRIEF SUMMARY OF THE INVENTION 
       [0011]    An improved string for a sports racquet is formed as of a single-filament or monofilament, not as of a multi-filament configuration, and includes a plurality of spaced-apart projections or ridges extending along the length of the string&#39;s outer surface that are formed as part of the string when it is first created. The ridges may be spaced equally apart from one another around the circumference of the central string body, and may extend axially along the outer surface of the single-filament string. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0012]    In the drawings, wherein like reference numerals identify corresponding components: 
           [0013]      FIG. 1A  is a perspective illustration of one form of the racquet string; 
           [0014]      FIG. 1B  is a cross-section of one form of the racquet string; 
           [0015]      FIG. 2  is a cross-section of another form of the racquet string; 
           [0016]      FIG. 3  is a cross-section of another form of the racquet string; and 
           [0017]      FIG. 4  is a cross-section of another form of the racquet string. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]    In the following description, it is to be understood and appreciated that while one or more forms of the current invention are described or illustrated, the present disclosure is not to be limited to the specific form or arrangement herein described and shown. It will be apparent to those skilled in the art that various changes may be made without departing from the scope of the present contribution and thus the present contribution is not to be considered limited to what is shown and described in the specification and/or any drawings or figures included herein. 
         [0019]    Thus any embodiments, methods, procedures and techniques described herein are merely representative, are intended to be only exemplary, and are not intended as limitations on the scope of the claimed invention. Changes therein and other uses will occur to those skilled in the art, and should be considered as encompassed within the spirit of the present disclosure. All dimensions, configurations, materials, etc., should be interpreted in a non-limiting manner. 
         [0020]    Referring first to  FIG. 1A  , the present invention is illustrated as a tennis racquet string  10 , presented in a perspective view. The string  10  is a single-filament having a central body  12 , with a series of spaced-apart, axially or longitudinally extending ribs or ridges  14 . Preferably, the ridges are equally spaced apart around the circumference of the body  12  of the string. 
         [0021]    Preferably, the string  10  including the ridges  14  is made as a single extrusion. The material of the string  10  may be a PET-based polymer, but any other form of string heretofore used for tennis racquet strings may be used as well. 
         [0022]      FIG. 1B  is a direct cross-sectional illustration of the string  10 , having the central body  12 , and the series of distinct rectangular ribs or ridges  14 . In this  FIG. 1B , the ribs or ridges are formed as relatively small rectangular protrusions that extend perpendicularly from surface of the cylindrical central body  12 . 
         [0023]    In another embodiment of the present invention,  FIG. 2  illustrates in cross-section a string  20 , having a central body  22 , and a series of ridges  26 . Six ridges are illustrated, thus the center-points of each ridge would be spaced 60 degrees apart from one another, measured radially around the circumference of the central body  22 . In  FIG. 2  , the ridges  26  are formed as truncated triangles, whose bases completely cover the smoothly-curved surface of the central body  22 . 
         [0024]    In another embodiment of the present invention,  FIG. 3  illustrates in cross-section a string  30 , having a central body  32 , and a series of ridges  38 . Six equally-spaced ridges are illustrated, and thus the ridges would be spaced 60 degrees apart from one another, measured radially around the circumference of the single central body  32 . The ridges  38  are formed as pointed triangles, whose bases completely cover the smoothly-curved surface of the single central body  32 . 
         [0025]    In another embodiment of the present invention,  FIG. 4  illustrates in cross-section a string  40 , having a central body  42 , and a series of ridges  44 . The ridges  44  are formed as triangles. In this embodiment, the ridges  44  are not equally spaced around the entire circumference of the central body  42 , but are instead present only on one half of the central body&#39;s outer surface. 
         [0026]    As noted above, the number of ridges ( FIGS. 1A ,  1 B,  2 ,  3 , and  4 ) as well as the ridge configuration (e.g., rectangular ( FIGS. 1A and 1B ) or pointed ( FIGS. 3 and 4 )) is described in general, non-limiting terms. More or fewer ridges, and different configurations or shapes that make contact with the ball, are within the spirit and scope of the present disclosure. 
         [0027]    The inventor has determined that the configurations of the present invention generally described herein provide numerous advantages over the prior art. For example, while the ridges are compressed upon impact with the ball, the sting recovers or resumes its normal configuration more quickly, thus imparting greater spin to the ball. The ridged-configuration of the present invention results in more friction between the ball and each string, due to a pinching effect that results from the deformation of the ridged-shape of the string upon contact with the ball, and a decrease in friction between the horizontal and vertical racquet strings because of the smaller contact area of between each string. The degree of deformation of strings when contacting a ball changes the amount of string surface area that the ball is in contact with. More contact translates to a higher degree of friction, and thus a greater ability to impart spin upon the ball. 
         [0028]    The increase in playability is enhanced by the fact that the present invention is formed as a single monofilament extrusion, where the ridges and the central body are formed as one structure when the string is first created. This allows for greater ridge deformation and an improvement in overall string consistency, elasticity, and resilience. 
         [0029]    The present invention provides an enhanced surface area for ball contact, not only by virtue of the fact that the strings themselves have more surface area due to their ridged surfaces, but also because the ridges may deform to a greater degree upon ball contact. These same ridges also allow the strings to touch each other with a smaller contact point, thus allowing for greater string mobility when installed in a racquet. The prior art attempted to accomplish the same goal with a combination of outer string structures that were fused or bonded to a central string, after the central core (or cores) of the string had already been formed. Having ridges initially formed with the central body as a monofilament string allows for improvements in elasticity, resilience, and playability. 
         [0030]    It is the combination of greater ridge deformation and smaller inter-string contract that imparts more spin than prior configurations. The present configuration allows for more movement of the strings due to fewer contact points between the horizontal and vertical racquet strings, and therefore less friction on the strings. However, there is greater friction between the ball and the ridged-strings, due to the increase in surface area that the ball may deform onto when contacting the string, so that a greater benefit of the friction (i.e., all of the energy imparted upon movement or deformation of the string) may be imparted to the ball. 
         [0031]    A typical sports racquet has a fixed number of horizontally-oriented strings, and a fixed number of vertically-oriented strings within its face, with the strings extending through grommets and holes found within the frame. The present string may be greater in overall diameter than conventional strings, because of its ridges or ribs, thus allowing for larger holes in the racquet frame. Larger holes mean an overall reduction in the weight of the racquet, as well as the use of fewer strands of crossing string in the face of the racquet, thereby reducing the density of a racquet&#39;s string pattern. 
         [0032]    In one embodiment of the present invention, the strings may be spiral wound or twisted either during creation or installation, to impart even more spin to the ball. 
         [0033]    Typically, a sports racquet string may have a diameter of between about 1.00-1.30 millimeters. The ridges heretofore proposed for multi-filament strings are of approximately 0.25 millimeters in height, from the surface of the central string body. Thus, a string described in the prior art could have an overall cross-sectional diameter as great as 1.80 millimeters, i.e., the core thickness added to the height of two ridges opposed form one another by 180 degrees measured around the circumference of the central string body. As noted above, the present invention may thus be thicker than the prior art strings, but still enjoy the benefits provided by a substantially elastic string of a thinner overall diameter. 
         [0034]    Many synthetic materials are available for use in sports racquet strings, including but not limited to: Nylon, Polyester, Kevlar, Zyex (polyetheretherketon), Boron, Graphite Fiber, Vectran, Polyolefin, and Polyurethane.