Patent Publication Number: US-4093220-A

Title: Tennis racket string network

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to tennis rackets, and more particularly the manner in which the strings are strung in an ordinary tennis racket. 
     Nearly all tennis rackets now sold and used are strung in a regular `basket weave` pattern. The longitudinal direction is usually strung first then the cross strings are woven alternately under and over the longitudinal strings. This stringing method entraps each string so that there is very little movement when side forces are imparted to the strings, such as when the ball is struck to impart a spin to the ball. The restoring forces created by the weave pattern try to maintain the regular spacing between the strings. 
     This common stringing method is fine if the ball is struck on the center of the striking face or slightly below center which is usually the percussion center, frequently referred to as the sweet spot of most tennis rackets. Away from the center up or down or on either side, the strings are shorter between supports, consequently, the resilience decreases, effective spring constant increase. The resilience further decreases because the ball is struck closer to the frame which anchors the strings. Consequently, when the ball is hit off center, the net effect of the decreased resilience is to: increase the shock, increase the turning or twisting forces as felt in the hand of the player. Even if the player can hold the racket firmly enough to resist the twisting forces, the ball will still move off the racket in unexpected and unwanted directions. 
     When the ball contacts the string, it will flatten. Therefore, the rate of change in resilience will affect the direction the ball leaves the striking face. For example, imagine the ball rising when it is struck. If the ball is struck near the top side of the string face with a flat stroke, the stiffer strings at the top side will tend to direct the ball downward into the net. If the same ball is struck with an intended top spin where the tendency would be to strike the ball near the bottom side of the hitting face, the stiffer strings at the bottom side will lift the ball higher than intended and direct the ball beyond the court. 
     Some tennis racket designers have made frame structural changes to make the string network a more uniform striking surface. The `Prince` tennis racket made the striking surface larger, proportionally wider and varied the string network spacing, closer near the center. The Wilson metal racket also made the striking head rounder and varied the spacing. C. L. Godfrey in his U.S. Pat. No. 1,733,960, Oct. 29, 1929, added additional string at the center. A new tennis racket market by Sabine Tennis Project under the trade name SweetSpot varied the spacing more than previously designed tennis rackets by eliminating both vertical and cross strings near the frame. 
     SUMMARY OF THE INVENTION 
     The object of this invention is to provide improved stringing network usable in ordinary tennis rackets without any modification to the frame that gives a more uniform striking surface characteristic at the center, at the percussion center and away from center than is possible with a common stringing arrangement. The improved stringing network(s) will: 
     1. Improve ball control because: 
     (a) twisting movements are reduced. 
     (b) more even reaction forces on surface of ball which is flattened on the string network. 
     (c) the stringing network is less sensitive to the spin of the ball imparted by opponent. 
     2. Allow a player to hit the ball harder for the same reasons given above. 
     3. Allow a player tactics not now easily possible with an ordinary stringing network. For example, blocking a hard serve with a lot of spin on the ball. 
     4. Reduce the shock and strain a player usually feels due to off-center hits. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front view of a racket head strung with a regular weave pattern at the center and 2, 2 pattern at the sides and 1, 2, 2 pattern at both ends. 
     FIG. 2 is a front view of a racket head strung with a regular weave pattern at the center and 1, 2 pattern at the sides and 2, 3 pattern at the top. 
     FIG. 3 is a front view of a racket head strung with a regular weave pattern at the center and at both ends, and with a 1,3 pattern at both sides. 
     FIG. 4 is a front view of a racket head strung with a regular weave pattern at the center and both sides, and with a 2 pattern at the bottom and 2, 1, 2 pattern at the top. 
     FIG. 5 is a front view of a racket head strung with a regular weave pattern at the center with a 1,2 pattern at each side and both ends, and with the third cross string, 3C, at both ends and the third longitudinal strings, 3V, at each side omitted. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, the drawing represents a typical tennis racket frame with provisions for stringing network having eighteen strings in the longitudinal direction, V direction, and twenty cross strings, C direction. FIG. 1 also illustrates the improved stringing network. At the center of the striking face starting with 6C string at each end and with 5V at each side the string network is the regular `basket weave` pattern. Around center on all four sides of the regular `basket weave` pattern the network is modified. 
     At the sides starting with longitudinal string 4V, the cross strings are alternately strung over and under two longitudinal strings. The result of this method is to pull longitudinal strings, 1V and 2V closer together, also longitudinal strings 3V and 4V closer together by the forces of the cross strings. Longitudinal strings 3V and 4V will be closer together than 1V and 2V as shown in the diagram. 
     At the top and bottom the stringing network is again altered to increase and decrease the string spaces in the longitudinal direction. Starting at the top, the first cross string 1C is strung in a regular manner. The second cross string 2C is strung opposite the first strings, that is, the second cross string goes under the longitudinal string where the first went over. The third cross string 3C is strung identical to 2C. Fourth 4C and fifth 5C cross strings are strung identically and opposite to 2C and 3C strings. This stringing schedule will cause strings 2C and 3C pulled closer together, also strings 4C and 5C are pulled closer together. 
     The described stringing network provides a suspension for the center striking face strung in a regular `basket weave` pattern. It also increases the relative resilience of the shorter outer strings with respect to the inner strings. The resultant network gives a more uniform resilience over nearly the complete usable striking area. This particular network is identified as 2, 2 at the sides and 1, 2, 2 at the ends. 
     It is obvious that a number of string networks can be derived using minor variations of the string network just described. For example, the weave pattern at the sides can be extended towards the center to make a 1, 2, 2 or a 2, 2, 2 pattern or retracted to a 1, 2 or 2 pattern. FIG. 2 shows a racket head strung with a 1, 2 pattern at the sides. Similarly, in the longitudinal direction, the pattern can be changed from 1, 2, 2 pattern at the ends to 2, 1, 2 pattern, or extended, or retracted to include more or less strings in the altered pattern. FIG. 4 shows a racket head strung with a 2, 1, 2 pattern at the top and a 2 pattern at the bottom. Elimination of one of the peripheral strings is also possible. On wood rackets, the second string, 2C, from the bottom or closest to the throat can be easily eliminated. At the sides and top, elimination of a string is more difficult except on many composite and metal rackets, which employ a continuous groove to protect the strings or don&#39;t extend the strings to the outside of the frame. FIG. 5 is a front view of a racket head strung with a regular weave pattern at the center and with a 1, 2 pattern at each side and both ends, and with the third cross strings, 3C, at both ends and the third longitudinal strings, 3V, at each side omitted. 
     Another variation is to surround the regular `basket weave`  pattern at the center with three string arrangement. At the sides the 2, 2 pattern can be changed to 1, 3. FIG. 3 shows a racket head with the sides altered to a 1, 3 pattern. At top and bottom the 1, 2, 2 pattern can be changed to 2, 3 pattern. FIG. 2 shows a racket head strung to a 2, 3 pattern at the top and a regular `basket weave` pattern at the center and bottom.