Tennis racket and method

Abstract

A tennis racket is provided that has a rectangular ball striking face with rounded corners. The racket is formed of a carbon fiber sandwich with light material mounted therebetween. A strip of carbon fiber is attached to the outer edge spanning the two carbon fiber top and bottom sheets. The rectangular frame is formed with outwardly bowed sides so as to be pulled into a straight sided configuration by the string tension. Locking grommets of various constructions are provided to hold the strings at predetermined tensions. Testing equipment and methods are provided for testing tennis rackets.

1 . A sports racket, comprising:
 a racket body including:
 a racket head having a substantially rectangular face shape, said substantially rectangular face shape including rounded corners, said racket head defining a plurality of string mounting positions in a predetermined arrangement on the four opposing sides of said rectangular face shape; 
 a racket handle affixed to said racket head; and 
   at least one string mounted at said string mounting positions to define main string portions and cross string portions, said main string portions each being of substantially equal length and substantially equal tension, said cross string portions each being of substantially equal length and substantially equal tension.   
     
     
         2 . A sports racket as claimed in  claim 1 , wherein said racket body with said at least one string weighs less than 14 ounces. 
     
     
         3 . A sports racket as claimed in  claim 1 , wherein said racket body with said at least one string weighs less than 12 ounces. 
     
     
         4 . A sports racket as claimed in  claim 1 , wherein said racket body with said at least one string weighs less than 10 ounces. 
     
     
         5 . A sports racket as claimed in  claim 1 , wherein said main string portions and said cross string portions are of substantially equal string tensions when strung in said racket head. 
     
     
         6 . A sports racket as claimed in  claim 1 , wherein said rectangular racket head is formed with a shape having outwardly bowed sides such that when strung the racket head sides are drawn into substantially straight sides by the string tension. 
     
     
         7 . A sports racket, comprising:
 a racket body including:
 a racket head having a substantially rectangular face shape, said substantially rectangular face shape including rounded corners, said racket head defining a plurality of string mounting positions in a predetermined arrangement on four opposing sides of said rectangular face shape; 
 a racket handle affixed to said racket head; and 
   at least one string mounted at said plurality of string mounting locations to define main string portions and cross string portions, said main string portions each having a main string fundamental vibration frequency where each main string frequency is substantially the same, said cross string portions each having a cross string fundamental vibration frequency where each cross string frequency is substantially the same.   
     
     
         8 . A sports racket as claimed in  claim 7 , wherein said racket body and string weighs less than 14 ounces. 
     
     
         9 . A sports racket as claimed in  claim 7 , wherein said racket body and string weighs less than 12 ounces. 
     
     
         10 . A sports racket as claimed in  claim 7 , wherein said racket body and string weighs less than 10 ounces. 
     
     
         11 . A sports racket as claimed in  claim 7 , wherein said at least one string has a substantially constant linear string density, and wherein (√ti)/li=constant and (√sj)/kj=constant, where ti is a string tension of a main string portion, li is a string length of the main string portion, sj is a string tension of a cross string portion, and kj is a string length of the cross string portion. 
     
     
         12 . A sports racket as claimed in  claim 7 , wherein said at least one string has a variable linear string density, and wherein that (√ti/mi)/li=constant and (√sj/m′j)/kj=constant, where ti is a string tension of a main string portion, mi is a string density of the main string portion, li is a string length of the main string portion, sj is a string tension of a cross string portion, m′j is a string density of the cross string portion, and kj is a string length of the cross string portion. 
     
     
         13 . A sports racket as claimed in  claim 7 , wherein (√ti/mi)/li=(√sj/m′j)/kj. 
     
     
         14 . A sports racket as claimed in  claim 7 , further comprising:
 lockable grommets mounted at least some of said string mounting locations to hold said string portions in place.   
     
     
         15 . A sports racket as claimed in  claim 7 , further comprising:
 a lockable grommet at one end of each of said main string portions and at one end of each of said cross string portions to hold said string portions in place.   
     
     
         16 . A sports racket as claimed in  claim 7 , further comprising:
 a lockable grommet at each end of each of said main strings and at each end of each of said cross strings to hold said strings in place.   
     
     
         17 . A sports racket as claimed in  claim 14 , wherein said lockable grommets hold said string portions at said string mounting locations to maintain a predetermined tension on predetermined ones of the string portions. 
     
     
         18 . A sports racket as claimed in  claim 17 , wherein said lockable grommets on said cross string portions maintain tensions on said cross string portions so that (√sj)/kj=constant, where sj is the tension on the cross string portions and kj is the length of the cross string portions, and
 wherein said lockable grommets on said main string portions maintains tension on said main string portions so that (√ti)/li=constant, where ti is the tension on the main string portions and li is the length of the main string portions. 
 
     
     
         19 . A sports racket as claimed in  claim 17 , wherein said lockable grommets on said cross string portions maintain tensions on the cross string portions such that (√sj/m′j)/kj=constant, where sj is the tension on the cross string portions, m′j is the mass density of the cross string portions, and kj is the length of the cross string portions; and
 wherein said lockable grommets on said main string portions maintain tensions on the main string portions such that (√ti/mi)/li=constant, where ti is the tension on the main string portions, mi is the mass density of the main string portions, and li is the length of the main string portions. 
 
     
     
         20 . A sports racket, comprising:
 a racket head including an open frame defining an arrangement of string holes at opposing sides of said open frame, said string holes including substantially conical hole portions;   a handle affixed to said racket head;   at least one string disposed through said string holes and extending across said open frame to define a racket face; and   a plurality of lockable grommets disposed in ones of said string holes, said grommets including substantially conical grommet portions inserted into said substantially conical hole portions, said lockable grommets engaging and restraining said at least one string under tension by frictional engagement between said substantially conical hole portions and said substantially conical grommet portions and said string.   
     
     
         21 . A sports racket, comprising;
 a racket head including an open frame defining an arrangement of string holes at opposing sides of said open frame, said string holes including substantially conical hole portions, said substantially conical hole portions being threaded;   a handle affixed to said racket head;   at least one string disposed through said string holes and extending across said open frame to define a racket face; and   a plurality of lockable grommets disposed in ones of said string holes, said grommets including threaded substantially conical grommet portions inserted into said threaded substantially conical hole portions, said lockable grommets engaging and restraining said at least one string under tension by threaded engagement between said threaded substantially conical hole portions and said threaded substantially conical grommet portions and said string.   
     
     
         22 . A sports racket, comprising:
 a racket head including an open frame defining an arrangement of string holes at opposing sides of said open frame, said string holes including substantially conical hole portions;   a handle affixed to said racket head;   at least one string disposed through said string holes and extending across said open frame to define a racket face; and   a plurality of lockable grommets disposed in ones of said string holes, said grommets each including a substantially cylindrical bar disposed in said substantially conical hole portions, said grommets each including a stopping block in said substantially conical hole, said substantially cylindrical bar being wedged in said substantially conical hole to hold said at least one string in place under tension, said substantially cylindrical bar permitting said at least one string to be pulled through said grommet to increase tension on the string but preventing movement of the string in an opposite direction.   
     
     
         23 . A sports racket, comprising:
 a racket head including an open frame defining an arrangement of string holes at opposing sides of said open frame;   a handle affixed to said racket head;   at least one string disposed through said string holes and extending across said open frame to define a racket face; and   a plurality of lockable grommets disposed in ones of said string holes, said grommets including first and second locking portions and a biasing member, said biasing member biasing said first and second locking portions toward one another to engage said at least one string to hold said at least one string under tension, said first and second locking members permitting said at least one string to move through said locking portions in a direction to increase tension on the string but preventing movement of the string in an opposite direction.   
     
     
         24 . A sports racket, comprising:
 a racket head including an open frame defining an arrangement of string holes at opposing sides of said open frame;   a handle affixed to said racket head;   at least one string disposed through said string holes and extending across said open frame to define a racket face; and   a plurality of lockable grommets disposed at ones of said string holes, said grommets including a string passageway and a threaded bore opening onto said string passageway and a threaded member threadably engaged in said threaded bore, said threaded member bearing against said at least one string in said string passageway to secure said at least one string in said string passageway.   
     
     
         25 . A sports racket as claimed in  claim 24 , further comprising:
 an external block defining said string passageway and said threaded bore and into which said threaded member is engaged.   
     
     
         26 . A sports racket as claimed in  claim 24 , further comprising:
 a portion of said racket head defining said threaded bore and into which said threaded member is engaged.   
     
     
         27 . A sports racket, comprising:
 a racket head including an open frame defining an arrangement of string holes at opposing sides of said open frame;   a handle affixed to said racket head;   at least one string disposed through said string holes and extending across said open frame to define a racket face; and   a plurality of lockable grommets disposed at ones of said string holes, said grommets each including a compressible elastic string gripping element engaging said string, said grommets each including a threaded cone engaged with said gripping element, said grommets each including a threaded nut threadably engaged on said threaded cone so as to compress said gripping element and thereby secure the string in position.   
     
     
         28 . A sports racket, comprising:
 a racket head including an open frame defining an arrangement of string holes at opposing sides of said open frame;   a handle affixed to said racket head;   at least one string disposed through said string holes and extending across said open frame to define a racket face; and   a plurality of lockable grommets disposed at ones of said string holes, said grommets each including a compressible elastic string gripping element engaging said string, said string gripping elements being held in threaded nuts, and threaded portions being provided at said string holes onto which said threaded nuts are threadably engaged so as to hold said string under tension in said string holes.   
     
     
         29 . A sports racket, comprising:
 a racket frame;   a racket handle connected to said racket frame,   said racket frame and said racket handle being formed of a carbon fiber composite materials and having an sandwich structure, said sandwich structure including first and second opposed carbon fiber sheets between which is disposed a light core material.   
     
     
         30 . A sports racket as claimed in  claim 29 , wherein said racket frame and said racket handle is in a single piece and has a structure characterized by having been cut from a single sheet of sandwich material. 
     
     
         31 . A sports racket as claimed in  claim 30 , wherein said sports racket has a moment of inertia of a face cross section at least twice as large as an annular cross section of a same area and similar dimensions. 
     
     
         32 . A sports racket as claimed in  claim 29 , further comprising:
 a carbon fiber strip affixed to an outer perimeter face of at least portions of said sports racket.   
     
     
         33 . A sports racket as claimed in  claim 32 , wherein said carbon fiber strip is of a “C” shape and has first and second portions overlapping first and second outer layers of the sandwich structure, respectively. 
     
     
         34 . A sports racket as claimed in  claim 32 , further comprising:
 a plurality of layers of Kevlar material applied to said carbon fiber strip.   
     
     
         35 . A sports racket as claimed in  claim 32 , wherein an area moment of inertia of a face cross section is at least 1.8 times as large as a moment of inertia of an annulus of a same area. 
     
     
         36 . A sports racket as claimed in  claim 32 , wherein said racket weighs less than 14 ounces. 
     
     
         37 . A sports racket as claimed in  claim 32 , wherein said racket weighs less than 12 ounces. 
     
     
         38 . A sports racket as claimed in  claim 32 , wherein said racket weighs less than 10 ounces. 
     
     
         39 . A sports racket as claimed in  claim 32 , wherein said racket frame has a inner face length is between 11 inches and 15 inches, said racket frame having a inner face width of between 9 inches and 11 inches, said racket frame has a face side width of between 0.25 inches and 0.75 inches, said racket frame has a face side depth is between 0.5 inches and 1 inch, and said racket frame has a sandwich plate thickness is between 0.025 inches and 0.15 inches. 
     
     
         40 . A sports racket as claimed in  claim 39 , wherein stress induced in side portions of the racket frame by string tensions of less than 70 pounds is less than 80 percent of a rupture force of the frame face material. 
     
     
         41 . A sports racket as claimed in  claim 32 , wherein said racket frame is of a substantially rectangular face shape, said substantially rectangular face shape including rounded corners, said racket head defining a plurality of string mounting positions in a predetermined arrangement on four opposing sides of said rectangular face shape;
 a racket handle affixed to said racket head; and   
       at least one string mounted at said plurality of string mounting locations to define main string portions and cross string portions, said main string portions each having a main string fundamental vibration frequency, said cross string portions each having a cross string fundamental vibration frequency, said main string fundamental vibration frequency being substantially equal to said cross string fundamental vibration frequency. 
     
     
         42 . A sports racket as claimed in  claim 39 , further comprising:
 lockable grommets mounted so as to hold at least one string in said racket frame.   
     
     
         43 . A sports racket as claimed in  claim 42 , wherein said lockable grommets maintain a predetermined string tension on at least one string strung in said racket frame. 
     
     
         44 . A sports racket as claimed in  claim 42 , wherein said lockable grommets maintain predetermined tension on said at least one string, said predetermined tension being such that main string portions of the at least one string have substantially equal fundamental vibration frequencies, said predetermined tension being such that cross string portions of the at least one string have substantially equal fundamental vibration frequencies. 
     
     
         45 . A sports racket as claimed in  claim 44 , wherein said fundamental vibration frequencies of said main string portions is substantially equal to said fundamental vibration frequencies of said cross string portions. 
     
     
         46 . A sports racket as claimed in  claim 29 , wherein said sports racket weighs less than 14 ounces. 
     
     
         47 . A sports racket as claimed in  claim 29 , wherein said sports racket weighs less than 12 ounces. 
     
     
         48 . A sports racket as claimed in  claim 29 , wherein said sports racket weighs less than 10 ounces. 
     
     
         49 . A method for providing a sports racket, comprising the steps of:
 forming a racket frame so that said frame has a substantially rectangular shape;   stringing the racket frame with at least one string to provide main string portions and cross string portions extending between opposing sides of said substantially rectangular frame;   tensioning the main string portions so that each of the main string portions is of substantially equal length and substantially equal tension; and   tensioning the cross string portions so that each of the cross string portions is of substantially equal length and substantially equal tension.   
     
     
         50 . A method as claimed in  claim 49 , wherein said step of forming includes forming the substantially rectangular racket frame with outwardly bowed sides such that said steps of tensioning the main string portions and tensioning the cross string portions exerts sufficient force on the bowed sides to draw the sides into substantially straight sides under string tension. 
     
     
         51 . A method as claimed in  claim 49 , wherein said step of stringing applies initial tension to the main string portions and the cross string portions; and
 wherein said tensioning steps apply final tension to the main string portions and the cross string portions.   
     
     
         52 . A method as claimed in  claim 49 , wherein said tensioning steps applied substantially the same tension to the main string portions and the cross string portions. 
     
     
         53 . A method as claimed in  claim 49 , wherein said steps of tensioning include the sub-steps of locking the string portions in lockable grommets to maintain tension on the string portions. 
     
     
         54 . A method as claimed in  claim 53 , wherein said substep of locking includes locking the string portions in the lockable grommets by wedging force. 
     
     
         55 . A method as claimed in  claim 53 , wherein said sub-step of locking includes locking the string portions in the lockable grommets by threadably engaging a first threaded member with a second threaded member.