Revolutionary New Tennis Racquet by Dr Paul Zarda

Dr. Paul Zarda of Orlando and Sanford Florida has developed a revolutionary new tennis racquet. He has applied for a patent for the racquet and that patent application can be found here: https://www.google.com/patents/US20140274494

His invention is directed to a racquet design with an inner and outer frame connected by an isolation system. Uniquely adapted to tennis racquets, the natural motion of the inner frame relative to the outer frame, upon impact of the tennis ball on the inner frame, will generate spin when the ball contacts the inner frame. The relationship between the inner frame, outer frame and isolation system can control the spin imparted to the ball for a given tennis swing. The tuning of the isolators relative to conventional racquet characteristics will increase the amount of ball spin caused by conventional racquets. This invention will also increase the accuracy of the tennis ball’s trajectory.

The use of spin in the sport of tennis is a strategy employed by players at all levels. At intermediate and advanced levels, mastery of topspin and underspin offers a significant competitive advantage. For example, tennis players, who are able to hit the ball causing significant ball topspin, can aim the ball’s trajectory well above the actual net (minimizing the error of the ball hitting the net) while relying on the spin to bring the ball down inside the opponent’s boundary lines. This clearance allows players to hit the ball with greater speed with the confidence that it will land in the field of play. In addition, both topspin and underspin/slice will also cause difficulties for the opponent to respond. In the case of topspin, the ball will bounce and 'jump' off of the court making it difficult for the opponent to adjust.  In the case of underspin, the ball will skid or die making it equally difficult for the opponent to adjust. It is accepted in the sport of tennis that those capable of consistently mastering topspin and underspin have reached a higher level of ability that will favorably impact their game. 

In the 1970s the spaghetti tennis racquet (or more appropriately named “the spaghetti strings”; almost any racquet could be strung using the spaghetti strings) offered a noticeable increase in spin rate over conventionally strung racquets for an equivalent tennis stroke. The spaghetti stringing technique was revolutionary and historically significant, and the present invention’s design will be contrasted against the design of the spaghetti. The concept of the design of the spaghetti tennis racquet is shown in Figure 1. The racquet frame 101 supports 6 cross strings 102. There are 2 pair groups of main strings (103 and 104) that are on either side of the cross strings. In Figure 2, the front and back main strings (103 and 104) are shown as they lock into the slider-bars (105 and 106 in Figures 1). Most importantly, the 2 sets of main string are not interwoven with the cross strings as seen in more traditional stringing configurations.

The spaghetti is designed so that the front set of main strings (103), locked into the 4 slider bars (105), moves together as they slide on the 4 cross strings (102).  Since they are not interwoven this movement is much easier than in traditionally strung rackets. 

The back set of main strings (104) and slider-bars (106) function in the same way as the front assembly (although independent of the front assembly). Both sets of main string assemblies can flex for out-of-plane loading. For in-plane loading, only the side that contacts the ball flexes in the plane of the string bed. 

Another problem with the spaghetti is that the in-plane and out-of-plane stiffness was not controlled.   Most tennis players (pros and amateurs alike) hit with racquets whose out-of-plane string bed stiffness is 140/150 lbs/in to 250 lbs/in. A stiffness softer than this makes the ball “trampoline” off the string bed, which both significantly hampers control and significantly hampers keeping the ball “in the court”; and stiffness higher than this make the racquet hit like a board with a significant loss in power. The spaghetti system offers out-of-plane stiffness in the order of 90/100 lbs/in, making it almost impossible to control if the motion of a player's stroke did not lend itself to generating topspin.  Because of the double string assembly and the plastic roughed-up inserts 103 and 104 of the spaghetti design shown, the spaghetti system no longer meets United States Tennis Association and International Tennis Federation rules for a strung tennis racquet to be used in sanctioned tournament play. It will become obvious that the present invention can provide an in-plane and out of plane stiffness better suited to current expectations. 

Tennis players and tennis manufacturers, over the last several years, have found another way to help increase ball spin: open string patterns. Figure 2 shows a racquet that is strung with a conventional stringing pattern (16 mains x 19 cross).

 Figure 3 shows the same racquet strung with an open string pattern of 16 main strings (110) and 10 cross strings (109). There are other open string patterns that have significantly less strings, but the principle on which the open string pattern causes increased top spin is the same: the string kickback and the in-plane compliance of the main strings is the key. As the ball strikes the open string bed, in exactly the same manner outlined previously for the spaghetti, the main strings slide on the cross strings, and then rebound. Once again, slow motion video during this contact shows the added spin may be due to this kick back tangential force, but it is also clear that the X-direction compliance of the main string allows the ball to not slip on the string bed, causing added rotation. With less cross strings, the interweaving the main strings are able to move more than traditional stringing patterns, though still less than that of the spaghetti system.

 The open string pattern has several problems in its use. The open string pattern has the same directional limitation that was explained in the spaghetti system: an open strung racquet making an angle to the tennis court as it impacts the ball will get only a partial advantage of the spin generated by the open pattern (compared to the same racquet, same conditions, but the racquet is swung parallel to the court). Another disadvantage of the open string pattern racquet is the significantly increased wear of the string bed causing a shorter string life. Since the movement of the main strings sliding over the cross strings is fundamental to the advantage of the open string system, it is no surprise to see the cross strings essentially “sawing” the main strings in half. And this is indeed the case, where the more effective the open string pattern is to cause increased spin, the shorter the main string life. In addition, this frictional sliding reduces the amount of in-plane-motion returnable energy that is available for spin generation. It will become obvious that the present invention overcomes these limitations in the open stringing pattern.

The present invention (Figure 4) is directed to a tennis racquet design with an inner and outer frame connected by an isolation system.   When a tennis ball strikes the inner frame string bed, its dynamic loads will be transmitted into the string bed. The normal load will deflect the strings and isolators and, depending on the combined stiffness out of plane of the isolator/inner frame/string bed, those strings can re-bound just like conventionally strung racquets.  However, the in-plane movement and compliance of the string bed helps maintain adequate frictional force between the ball and string bed so the ball does not slip on the string bed. After impact, this results in an increase in ball rotation compared to conventional racquets. The minimization of the weight of the inner frame (compared to the weight of the ball) will decrease the opportunity of the ball to slip against the strings. The elimination of that slippage will result in increase rotation (topspin or underspin) of the ball.  In addition, during impact, the isolators store more energy in them (in-plane deformation) and then return that energy, through the non-slip frictional load, back into spinning the ball.

Objectives of the invention:

1) An objective of the invention is to employ an inner frame that, relative to an outer frame, will generate spin when a tennis ball contacts the inner frame.

2) Another objective of the invention is to minimize ball slipping on the tennis racquet string bed.

3) Another objective of the invention is that when the ball contacts the inner frame it will create a deflection of the inner frame in the x-y plane.

4) Another objective of the invention is to teach a relationship between an inner frame, an outer frame and an isolation system to control the spin imparted to a tennis ball for a given tennis swing.

5) Yet another objective of the invention is to permit tuning of isolators relative to conventional racquet characteristics to increase the amount of ball spin compared to conventional racquets.

6) Another objective of the instant invention is a tuning of the isolator system for the in-plane and out-of-plane stiffness to maximize spin for a given swing motion/speed.

7) Another objective of the instant invention is to offer optimized combinations of inner frame, outer frame and isolator to maximize spin for a full range of skill sets and swing speeds/styles.

Please refer to the referenced patent application for more details of this revolutionary design.