WO1994015674A2

WO1994015674A2 - Long string tennis racquet

Info

Publication number: WO1994015674A2
Application number: PCT/US1993/007204
Authority: WO
Inventors: Stephen J. Davis; Andre Terzaghi
Original assignee: Prince Sports Group, Inc.
Priority date: 1992-07-31
Filing date: 1993-07-30
Publication date: 1994-07-21
Also published as: JPH08506739A; CA2141438A1; AU6811694A; EP0652795A1; WO1994015674A3

Abstract

A tennis racquet has a standard overall length and strung surface width. The length of the strung surface is elongated to 14.5 inches or more, e.g., 14.9 inches, and formed as an egg shape to produce improved stability while retaining good power. In a preferred embodiment, the ends of the main and cross strings engage the frame in a staggered configuration such that the strings engage the outermost crossing string on the surface facing one side of the center stringing plane and engage the frame on opposite side of the central stringing plane.

Description

DESCRIPTION

LONG STRING TENNIS RACQUET

FIELD OF INVENTION The present invention relates to an improvement in oversized tennis racquets.

BACKGROUND OF THE INVENTION

Howard Head U.S. patent No. 3,999,756 discloses a tennis racquet having a strung surface with a length between 12 and 15 inches, a maximum width in the range of 9 to 11*. inches, and a strung surface area between 85 and 130 square inches. Racquets made in accordance with the principles of the Howard Head invention have a larger sweet spot, and exhibit better power and performance, than prior racquets, and accordingly most tennis racquets made today are made according to the Howard Head invention.

While most tennis racquets have a conventional overall length of about 27 inches, racquets are made in varying head sizes. Two of the more common head sizes are, respectively, the so-called "mid-size" racquet, with a head strung surface size of about 90-95 square inches, and the "oversize" racquet, with a head size of about 110 square inches, although these can vary.

While the Howard Head patent discloses head sizes larger than 110 square inches, as a practical matter racquets with a strung surface area much above 110 square inches are not popular. This is due to the fact that, aside from the weight penalty, the racquet becomes unwieldy if the frame is made too large, particularly if the width increases excessively.

Another problem with increasing the head size is that, as the length of the strung surface increases, vibration tends to increase in the main strings. This vibration can be annoying to players and thus is undesirable.

In recent years, the power of tennis racquets has increased, resulting in higher ball speeds and the need for quicker reactions. Shot making involves more short quick swings, or "whacking" the ball, rather than long smooth swings. For quicker reaction, it would thus be desirable to use a racquet which is relatively light weight, particularly in the head. However, if a head light, lightweight racquet were to be used, the racquet would tend to jump back upon impact with the ball. Not only would this impart undesirable shock to the arm tendons, but the racquet would not be stable.

Recently, tennis racquets have been introduced which are lighter in weight. Such weight savings have been achieved, for example, by using lighter weight handles, such as molded-in handles. Such racquets are designed to be head heavy, however, to avoid the problems mentioned above. However, a head heavy racquet tends to be less maneuverable, and thus less desirable for some players.

SUMMARY OF THE INVENTION

It has been found that a tennis racquet which is provided with certain structural characteristics can be made light weight, and at the same time exhibit a surprising improvement in maneuverability and stability while retaining good power. These properties are achieved by providing a lightweight racquet with properties including an increased mass moment of inertia and increased radius of gyration about the center of mass, compared to conventional racquets; by elongating the stringing area without increasing the maximum width or polar moment of inertia; by locating the longest cross strings (the widest portion of the frame) between the geometric center of the stringing area and the tip; by making the racquet slightly head heavy; and by providing a certain minimum frequency to maintain good power. In accordance with another aspect of the present invention, a tennis racquet frame and bridge piece are configured so as to define a novel, egg-shape stringing area containing interwoven main and cross strings. As used herein, the term "egg-shape" refers to a geometry wherein the border of the stringing area is a continuous convex curve, formed of a multitude of radii, and wherein the radius of curvature at the six o'clock position (the end of the stringing area adjacent the handle) is smaller than at the 12 o'clock position (the racquet tip) . Preferably, the radius at the 12:00 o'clock position (tip) is between 100 -170 mm, and the radius at the 6:00 o'clock position is between 30 - 100 mm. Preferably, also, the stringing area has an aspect ratio (ratio of length/width) in the range of 1.3 - 1.7, and most preferably about 1.4. Preferably, also, the widest point of the strung surface is located at a point greater than 5% of the distance from the geometric center of the strung surface (the mid-point of the long axis of the strung surface) toward the tip, and most preferably about 17 mm from the geometric center toward the tip. In addition to having an egg shape geometry, preferably, also, the frame is sized so that the major axis of the egg (length of the stringing surface) is at least 14-s inches, the maximum width of the stringing surface is less than 10.75 inches, and the overall string plane area defined by the egg is between 112 in² and 120 in².

It has been found that this egg-shape frame, due to its novel geometry, produces a surprisingly controllable, yet quite powerful, racquet which is stronger than comparable racquets of other shapes. Moreover, by providing such a geometry, the shorter cross strings are disposed at the highest power zone of the racquet (i.e., closer to throat), whereas the longest cross strings are located at a lower coefficient of restitution zone nearer the tip. Thus, the geometry of the cross strings helps even out the power zone.

In an exemplary embodiment of the invention, a tennis racquet has a standard overall length of about 27 inches and includes a head portion and throat bridge defining a generally egg-shape stringing area. A plurality of interwoven main and cross strings form a strung surface and are received in holes in the frame. The stringing area has a maximum width of about 10.75 inches or less, and a length greater than 14 inches, and preferably about 15 inches or more.

A conventional 110 square inch racquet has a strung surface length of about 13 h inches, and a maximum width of about 10.4 inches. Thus, a racquet according to the present invention has an increased strung surface length while at least generally maintaining the same overall width. This may be accomplished by using a similar frame head shape but relocating the bridge piece toward the handle.

In one embodiment, the holes for at least some, and preferably most or all, of the main and cross strings are staggered such that the strings cross their respective outer-most crossing string on one string surface, i.e., facing one side of the central stringing plane, and engage the frame on the opposite side of the central plane.

It has been found that, by staggering the locations where the string ends engage the frame, the stringing area can be elongated in the manner disclosed without encountering the problems that would occur using conventional stringing. In particular, due to the geometry of the string ends, string vibration is kept to acceptable levels, while allowing a larger strung surface. Moreover, because the ends of the strings are splayed, it is possible to utilize a greater proportion of zero degree fibers in the frame to produce a frame which is stiffer and less subject to deformation when strung. The use of longer strings also contributes to an increase in the power of the racquet. Moreover, while in a conventional stringing system increasing the length of the main strings would produce increased stress, upon ball impact, on the cross-strings (due to the fact that the longer main strings are able to elongate more) , by utilizing the staggered string geometry according to the invention, the strung surface exhibits a more uniform string plane response.

For a better understanding of the invention, reference is made to the following detailed description of the preferred embodiments, taken in conjunction with the drawings accompanying the application.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a front view of a tennis racquet according to the invention;

Fig. 2 is a side view of the tennis racquet of Fig. 1, in which the strings have been omitted for clarity;

Fig. 3 is a view a portion of the frame of the racquet of Fig. 1, with the strings omitted for clarity, taken in the direction of lines 3-3 of Fig. 1; Fig. 4 is a view of a portion of the frame of the racquet of Fig. 1, with the strings omitted for clarity, taken in the direction of lines 4-4 of Fig. 1; and

Fig. 5 is a view, taken in the direction of lines 5-5 of Fig. 1, showing the string ends of a pair of cross strings intersecting the outermost main string. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to Fig. 1, a tennis racquet according to the invention includes generally a frame 10 and a handle 12. The frame is preferably formed of a composite material (e.g., fiber-reinforced thermoset or thermoplastic resin), but may also be formed of metal. Preferably, the handle is a light weight handle, such as a molded in handle such as used in the Prince Graphite Lite XB tennis racquet. The racquet has a standard overall length of about 27 inches. The frame 10 includes a head portion 14, a pair of converging frame portions 16 extending from said head portion 14 and forming a throat region, a shaft 18 extending from the converging frame portions 16 and supporting the handle 12, and a bridge piece 20 arranged between said converging frame portions 16 to define, with said head portion 14, a generally egg shape stringing area 22. The head portion 14, converging frame portions 16, shaft 18, and handle 12 may have conventional dimensions, e.g., for a 110 square inch racquet. As compared to a conventional racquet, however, the bridge piece 20 is located further toward the handle 12, so that the strung surface area 22 is larger than 110 square inches, e.g. 116 square inches.

As shown in Figure 1, the head portion and throat piece define an egg shape stringing area. In the exemplary embodiment, the radius of the stringing area at the 12:00 o'clock position is 124 mm, whereas the radius at 6:00 is 50 mm, and increases to a maximum radius of 209 mm at about the 3:30 and 8:30 positions. In the embodiment shown in Figures 1-5, the racquet frame has a constant cross sectional height (the dimension perpendicular to the stringing plane) , preferably between 22 and 26mm. In an alternate preferred embodiment, the frame employs a constant taper system geometry, as disclosed in U.S. patent No. 5,037,098. In an illustrative embodiment, the frame height varies from 24mm just above the handle to 34mm at the tip. However, other dimensions, such as 24mm at the handle to 30mm at the tip, may be employed, depending on the desired frame characteristics.

In an exemplary embodiment, the stringing area 22 has a conventional maximum width which is less than about 10.75 inches, and a length (along the central axis 24) of greater than 14% inches, and most preferably between about 15 inches (e.g., 14.9 inches) and about 15 inches. The racquet further includes a plurality of interwoven main 26 and cross 28 strings forming a strung surface.

In the preferred embodiment of a 27 inch racquet, the racquet is constructed so as to have certain properties. In particular, the strung weight of the racquet should preferably be less than 300 grams. The polar moment of inertia (the mass moment of inertia about the longitudinal axis of the racquet) should be less than 1.90 gram-m², and preferably between 1.6 - 1.7 gram-m², and the balance point (center of gravity) should be located at least 13.4 inches from the butt end. As noted above, the strung surface length should be greater than 14% inches, and the frame should have a minimum free space frequency of 140 Hz for a composite racquet (100 Hz for a metal racquet) . Preferably, the cross sectional width of the frame is 11% - 12 mm.

In a racquet as disclosed herein, the throat piece is located further away from the center of gravity than in conventional racquets. This acts not only to increase the string length, but also to increase the mass moment of inertia about the center of gravity and improve the stability of the racquet by reducing the tendency of the racquet to kick upon impact of balls away from the center of percussion. In accordance with a preferred embodiment of the invention, the ends of the respective main and cross strings are arranged in a staggered pattern, described further below. The main strings 26 include a pair of strings 30 located outermost from the geometric center GC of the strung surface at opposed locations; similarly, the cross strings include a pair of strings 32 located outermost from the geometric center. Each of these outermost strings 30, 32 form the last crossing string of the respective cross or main string before it engages the frame head portion 13.

Fig. 2 illustrates holes 34 which have been drilled in the frame head portion 14 for receiving the racquet strings. As can be seen in Figure 2, the holes are not located in the central stringing plane 36, but rather are staggered such as to lie alternatively on opposite sides of the plane 36. Moreover, it will be noted that, in this embodiment, the amount of stagger is reduced in the corners of the racquet, as described further in connection with Figures 3-5.

Referring to Fig. 3, it will be seen that the holes 40 for the cross strings, except for holes 42, lie at a constant distance from the center stringing plane 36, but on alternate sides. This will be referred to herein as a full stagger, and is employed for most of the cross strings 28 and for the upper ends of the main strings 26, except for the upper corners.

Referring to Fig. 5, which illustrates a full stagger for two successive cross strings 28a and 28b, the first 28a of the two cross strings extends over the outermost main string 30, and is thereafter directed to engage the frame head portion 14, through grommet 40a, which extends through a pair of string holes 40a formed in the hollow frame, which is located below the central stringing plane 36. As a result, the cross string 28a engages the outermost main string 30 at an angle α which is less than 180°. The string 28a passes through string hole 40a and enters the stringing groove 15, where it crosses the central plane 36 to string hole 40b. From string hole 40b, the next cross string 28b extends under the outermost main string 30, and then extends upwardly to engage the next main string (not shown) . For purposes of clarity, the angle by which the cross strings 28a, 28b diverge toward the center of the stringing surface (i.e. toward the right in Fig. 5) has been exaggerated slightly in Fig. 5.

As can be seen in Fig. 1, in the corners of the racquet there is only a short distance between the intersection of the crossing strings and the frame. As a result, if a full stagger were to be employed, the strings would need to diverge at a sharp angle. To reduce this angle, the amount of stagger is reduced in the four corners of the racquet, as exemplified in Fig. 4 by corner string holes 42, to a half stagger. In an exemplary embodiment, the string holes in bridge piece 20 are also at a half, rather than a full stagger. In this manner, all of the string holes between the lower two corners are at a half stagger. However, a full stagger can be employed in the bridge piece 20 if desired. Also, rather than half stagger, the strings can be left unstaggered (zero stagger) in the corners and/or the throat piece 20.

As alternative embodiments to the stringing configuration shown in Figures 2-5, a conventional stringing pattern, in which none of the strings are staggered, may be employed. Also, a constant stagger may be employed completely around the frame. In the latter case, the amount of stagger would be generally reduced, compared to Figures 2-5, to avoid sharp angles in the corners (e.g., a half stagger).

The foregoing represent preferred embodiments of the invention. Variations and modifications of the foregoing composition and method will be apparent to persons skilled in the art, without departing from the inventive concepts disclosed herein. All such modifications and variations are intended to be within the scope of the invention, as defined in the following claims.

Claims

We claim:

1. In a tennis racquet comprising a frame and a handle; said racquet having a standard overall length; said frame including a head portion, a pair of converging frame portions extending from said head portion and forming a throat region, a shaft extending from said converging frame portions and supporting said handle, and a bridge piece arranged between said converging frame portions to define, with said head, a stringing area; wherein said stringing area has a conventional maximum width of less than about 10.75 inches; wherein said head portion and throat piece include holes for receiving strings; said racquet further comprising a plurality of interwoven main and cross strings forming a strung surface, said main strings and cross strings each including a pair of strings located outermost from the geometric center of the strung surface at opposed locations, each outer-most string having opposed surfaces facing opposite sides of the central stringing plane; the improvement wherein said stringing area is generally egg- shaped has a strung surface length of at least 14% inches, and wherein successive ends of at least some of said main and cross strings are staggered such that the associated strings cross their respective outer-most crossing string on one surface, facing one side of the central stringing plane, and engage the frame on the opposite side of the central string plane.

2. A tennis racquet according to claim 1, wherein said head includes opposed side portions, a tip portion, a pair of upper corners separating said side portions from said tip portion; and a pair of lower corners separating said side portions from said bridge piece; wherein said strings have a constant stagger at least in said side portions and tip portion.

3. A tennis racquet according to claim 2, wherein said strings, in said corners and bridge piece, have a stagger which is less than said constant stagger.

4. A tennis racquet according to claim 2, wherein said stringing area is at least about 15 inches in length.

5. A tennis racquet according to claim 4, wherein said stringing area length is less than about 15% inches.

6. A tennis racquet according to claim 2, wherein said strung surface area is greater than 110 square inches.

7. A tennis racquet according to claim 2, wherein said strung surface area is about 116 square inches.

8. In a tennis racquet comprising a frame and a handle; said racquet having a standard overall length; said frame including a head portion, a pair of converging frame portions extending from said head portion and forming a throat region, a shaft extending from said converging frame portions and supporting said handle, and a bridge piece arranged between said converging frame portions to define, with said head, a stringing area; wherein said stringing area has a conventional maximum width of less than about 10.75 inches; said racquet further comprising a plurality of interwoven main and cross strings forming a strung surface; the improvement wherein said stringing area is egg-shaped.

9. A racquet according to claim 8, wherein the racquet has a strung surface length of at least 14% inches and a stringing area greater than 110 square inches.

10. A tennis racquet comprising a frame and a handle; said racquet having a standard overall length of about 27 inches; said frame including a head portion defining a stringing area and a shaft supporting said handle, and a plurality of interwoven strings; wherein said stringing area has a conventional maximum width of about 9 to 10.75 inches; wherein said racquet has a polar moment of inertia less than 1.9 gram-m²; a balance point greater than 13.4 inches away from the butt end of the frame; a maximum weight of 300 grams; a strung surface length of at least 14% inches; and a minimum free space frequency of 100 Hz, wherein such racquet is lightweight, maneuverable, and stable.

11. A tennis racquet according to claim 10, wherein said frame is formed of a composite material and has a free space frequency of at least 140 Hz.