Abstract:
A racket stringing clamp for clamping diagonal racket strings which clamp has generally configured teeth projecting into spaces which are to be bordered by string segments. The clamp includes jaws for gripping two substantially parallel string segments. A handle including a cam serves to move the jaw.

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of pending U.S. patent application Ser. No. 09/118,456 filed Jul. 17, 1998 which is related to U.S. Provisional Application Ser. No. 60/070,431 filed Jan. 5, 1998 entitled “Improved Method And Product For Stringing Game Racket”; U.S. Provisional Application Ser. No. 60/073,891 filed Feb. 6, 1998 entitled “Racket Frame With Improved String Support Means For Stringing Game Racket”; and U.S. Provisional Application Ser. No. 60/078,981 filed Mar. 19, 1998 entitled “Markings For String, Frame And Grommets Of Game Rackets”. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention is an improvement in game rackets and their stringing and, in particular an improvement directed to the teachings of U.S. Pat. No. 4,184,679 including overcoming certain difficulties stringers found in stringing such rackets. There was resistance on the part of the stringers to learn the pattern disclosed in the &#39;679 patent as it was found by many to be complicated to learn and too time consuming in practice. Certain tennis playing consumers, for example, did not want to buy the product disclosed in the &#39;679 patent because it was difficult to get it restrung. Further the prior art rackets which included diagonal and horizontal string segments had the drawback that during the stringing process, when any reasonable tension was applied to the strings, distortion of the frame would occur. 
     Prior art three string rackets had the further complication that restringing could not in many instances be done on conventional stringing machines. Special clamps were needed to string the diagonal strings which clamps were not compatible with many stringing machines and the process of inserting verticals first took much more time than conventional stringing. 
     SUMMARY OF THE PRESENT INVENTION 
     The present inventive racket, method of stringing and stringing apparatus provide a simpler and improved system permitting racket stringing and restringing be accomplished on all stringing machines using conventional clamps or the improved clamp of the present invention. The first step in the present invention stringing method is to determine the stringing pattern having diagonal string segments and vertical or horizontal string segments. The number of string segments and the size of angles of intersection or crossovers are selected depending on the shape and size of the racket to be strung. Formulas assist in pattern formation. Once the pattern is determined holes or other siring supports are located on the racket head and the racket is ready for stringing. 
     Stringing starts with the placing of first and second sets of opposing diagonals on or in the string supports such that the second set overlies the first diagonal set or vice versa. The stringing of the first and second diagonal sets are accomplished by alternately inserting and subsequently tensioning string segments in each direction, generally starting at the top, mid-region or bottom of the frame. When all or substantially all of the diagonal string segments have been inserted, a set of verticals (or horizontals) are then strung by weaving them over the upper diagonals and under the lower diagonals. 
     The angle of the diagonal string segments are selected to avoid any shortening, widening, narrowing or other distortion of the frame. The angle of the diagonals to the racket horizontal centerline and the angle of intersection of each of the diagonals is determined based on a number of factors discussed below. Preferably, diagonal segments at approximately 45° to the horizontal centerline are used; however, diagonals more or less vertical in orientation may be used provided the diagonals have the ability to counteract the horizontal forces that would otherwise warp the racket when stringing rackets in this diagonals-first method. Preferably diagonals are in the ranges of 35°-55° or 40°-50° or 43° to 47°. Algebraic formulae serve to calculate the symmetric three-directional vertical-diagonal pattern across the racket face. A method and formula for assuring that an over/under weave is achieved throughout the string pattern is also included in the present invention. 
     Orthogonal crossing diagonals permit use of conventional swivel or floating clamps. Floating clamps may also be used on machines that do not have swivel clamps but use rail clamps for mains and floating clamps for diagonals. 
     The present invention also includes a method of stringing using racket and string identifications which are coordinated to assist in stringing. 
     Finally, the invention includes improved clamps which are helpful in three set stringing on some machines. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a partial perspective View of a stringing machine with a racket frame positioned for stringing; 
     FIG. 2 is a front elevational view of the racket in the process of having its diagonals strung; 
     FIG. 3 is a front elevational view of the racket with its diagonals in place and vertical stringing commenced; 
     FIG. 3 a  is a view similar to FIG. 3 with vertical stringing continuing; 
     FIG. 3 b  is a partial elevational view showing a string segment weave; 
     FIG. 4 is a three-string racket strung with diagonals and verticals; 
     FIG. 5 is a racket strung with diagonals and horizontals; 
     FIG. 6 is an elevational view of the clamp of the present invention showing the side of the clamp handle; 
     FIG. 7 is an elevational view of the clamp showing the front surface of the handle; 
     FIG. 8 is a top plan view of the clamp in the open position; 
     FIG. 9 is a view similar to FIG. 8 of the clamp in the closed position (handle omitted); 
     FIG. 10 is an alternative embodiment of the clamp with holes to receive removable additional projection teeth; 
     FIG. 11 is a perspective view of an alternative clamp adapted to be used in a clamp holder associated with a stringing machine; 
     FIG. 12 is a side sectional view of the alternative clamp and its holder mounted on the stringing machine; 
     FIG. 13 is a side elevational view of an alternative string clamp; 
     FIG. 14 is a perspective view of the clamp of FIG. 13 showing shaped teeth; 
     FIG. 15 is a plan view of the clamp with the jaws open; 
     FIG. 16 is a plan view of the clamp with the jaws closed; 
     FIG. 17 is a tennis racket frame strung in three directions including vertical and diagonal string segments and showing the clamp of FIG. 13 positioned with its teeth in openings between string segments; and 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In FIG. 1 a conventional stringing machine  5  is shown for stringing a three-string racket  3  of the present invention. Also shown is stringing machine tension arm  5   a , machine frame  5   b  and clamp  5   c.    
     Turning to FIGS. 2,  3 ,  3   a  and  4 , stringing is commenced with left diagonal segments underneath right diagonal segments  16 . A string segment is a straight tensioned length of string extending from one inside edge of the frame to another inside frame edge. All left diagonal segments are under all right diagonal segments or vice versa. After stringing the diagonals  15 ,  16 , a group of vertical segments  17  which segments are individually assigned designations  1 RV and  1 LV (first right and left verticals) on either side of the vertical centerline through head midpoint (MP) are strung using vertical string length  19  (FIG.  3 ). Verticals may, alternatively, be started at other locations. Further vertical stringing is shown in FIG. 3 a . Stringing is clamped by starting clamp  20 , clamp  21  of the present invention (described in detail below) and machine tensioning arm  5   a . Vertical segments are woven over the upper diagonals and under the lower diagonals. Turning to FIG. 3 b , the weave of string segments is seen in which vertical segments  17  are positioned over the upper left diagonal segments  15  and vertical segments  17  are positioned under the lower right diagonal segment  16  and left diagonal segment  15  is over right diagonal segment  16 . Stringing is preferably at low to mid tension range. 
     The method of stringing a racket comprises the steps of alternately stringing and then tensioning substantially both sets of opposing diagonals with conventional or improved tensioning equipment, then interlacing and tensioning the set of vertical strings, using conventional tensioning clamps that accompany stringing machines or clamps of the present invention clamps. 
     FIG. 4 shows a fully strung racket  3  having vertical segments, and FIG. 5 illustrates a racket head in which horizontal segments are used instead of vertical segments. The stringing patterns of the present invention provide (1) intersection of diagonals at points midway between verticals  17  (i.e. points A and B, FIG.  14 ), and (2) provide a plurality of hexagonal and triangular openings  8 ,  9  and  10 . Opening  10  is the same size and shape of the area defined by points A, L, T, B, S and M. Openings  8 ,  9  and  10  vary in size and shape depending on spacing of the string segments and the angles of crossing of the string segments. 
     Turning to FIGS. 6-10, portable string clamp unit  21  includes body  23  with two side walls  23   a ,  23   b , lower handle  25  and clamp plates  27 ,  28 . Unit body  23  has two (2) upwardly extending projections or teeth  31 ,  32  and two projection bases  33 ,  34  each having holes  33   a,b  and  34   a,b . Clamp unit  21  includes clamping arrangement  40  including bolt  41  with head  41   h  and stem  41   s . Stem  41   s  is connected to cross pin  42  in clamp lever  43 , which pivots on axle  45  mounted on clamp body extensions  47 ,  48 . Clamp lever  43  has cam section  43   c  which rides on the outside surface  28   o  of plate  28 . Also shown are alignment pins  35  and plate extensions  36  and  37 . 
     In operation, clamp unit  21  is positioned with teeth  31  and  32  engaging racket segment strings. With reference to FIG. 10, a string (S) is positioned between head surface  23   a  and plate  28 . When lever  43  is moved downward cam  43   c  engages plate surface  28   o  pulling bolt  41  to move surface  23   a  and plate  28  toward one another to grip string (S). As cam  43   c  rotates further clockwise (FIG. 6) it snaps into a lock position (shown in dashed lines FIG. 6) holding string (S) without the operator gripping the clamp unit  21 . 
     Turning to FIG. 10, additional projections  51 ,  52  having pegs  52   a,b  and  53   a,b  are fitted into spaced apart holes  33   a,b  and  34   a,b  of bases  33 ,  34  to provide additional projections for string engagement when needed for racket stringing. Portable string clamp unit  21  has the versatility of being operated with two, three, four, five or more teeth or projections. 
     In FIGS. 11 and 12, a string clamp unit  55 , similar in construction to unit  21  is mounted in a holder  56  which holder  56  in turn is mounted in track  57  of stringing machine  58  for reciprocation therein. Clamp unit  55  has a lower cylindrically shaped stem  55   s . Holder  56  includes skirt  56   s  which rides on horizontal machine surface  58   s  while holder guide  56   g  assists in stabilizing holder  56  as it is manipulated. Also shown is clamp handle  55   c.    
     A feature of the present invention is to provide a sequence of stringing which is easy to string on conventional stringing equipment with or without use of the above-described clamps depending on the equipment. Where the angles and spacing of the strings are such that conventional clamps do not fit between or among the string segments, the clamps  21 ,  55  of the present invention may be used. Clamp  21 ,  55  are sized and shaped at their upper clamping end to permit positioning the clamp in string openings  8 ,  9  and  10  (FIG.  14 ). 
     The present invention is useful for all types of rackets used in the sports of tennis, racquetball squash and badminton. 
     Turning to FIGS. 13-16, there is shown an alternative string-gripping clamp  61  which includes central body  62 , right jaw  64 , left jaw  66  pivoted about pivot pin  67 . Jaws  64 ,  66  are clamped against body surfaces  62   a, b  by central bar with cap unit  68  pulled by operation of handle  70  pivoted about pin  71 . Bar with cap unit  68  when articulated by handle  70  causes jaws  64 ,  66  to move toward body surfaces  62   a, b  to grip and hold string segments SS 1  and SS 2  (see FIGS.  20  and  21 ). 
     Teeth projection pairs  76 ,  77  on the top of right jaw  64  and teeth projection pairs  78 ,  79  on left jaw  66  are generally triangular in cross section with each projection tooth having surfaces a, b, c, d and e. Surface a is the small top surface. Surfaces d and e intersect along lines and those surfaces d and e together with surface b create a tooth which gets generally smaller from its larger bottom adjacent jaws  64 ,  66  to its top at surface a. The shape of the projections  76 - 79  facilitates inserting such projections in between string segments (FIG.  17 ). Projections  76 - 79  will be positioned in open places between string segments where needed as the weave is being developed. The body portion of clamp  61  also carries a pair of larger teeth projections  80 ,  81  each having nine ( 9 ) surfaces aa-ii. Each projection  80 ,  81  has two small vertical surfaces aa, bb and two large vertical surfaces cc, dd. Each projection  80 ,  81  in addition has four tapering surfaces ee, ff, gg and hh. Finally, each projection  80 ,  81  has a flat surface ii. The tapering surfaces facilitate positioning the projections between and among string segments. 
     Further with respect to clamp  61  and strung racket of FIG. 7, it is seen how teeth projections  76 - 81  fit into string openings  85 ,  86 ,  87  and  88 . String openings  85 ,  86  are triangular and string openings  87 ,  88  are polygonal. Finally, while the pattern shown in FIG. 17 includes verticals and diagonals; alternatively, horizontals and diagonals may be used.