SPORTS RACQUET WITH HYBRID STRINGING ARRANGEMENT

Technical Field

The present invention generally relates to racquets for use in sports games and, more particularly, is concerned with a sports racquet having a hybrid stringing arrangement of longitudinal and cross strings of dissimilar materials.

Background Art

A conventional sports racquet, such as a tennis racquet, has a frame which includes a head portion, a throat portion and a handle portion formed as an integral structure. Typically, the racquet frame is fabricated of composite-type material composed of high modulus fibers such as graphite fibers or glass fibers in a matrix of an epoxy resin. Alternatively, racquet frames have been fabricated from other materials, such as aluminum, wood and plastics. The head portion of the racquet frame typically has a round or oval configuration and contains a plurality of holes aligned in a common plane. A grid pattern of stringing extends through the holes and is applied under tension across the head portion to provide a ball striking area of the racquet. The handle portion of the racquet frame is usually covered with an outer sheath for facilitating gripping of the racquet by the user's hand.

Commonly, stringing for sports racquet is made of animal gut, synthetic materials, or in rare instances metallic wire. Animal gut stringing is normally made from beef or sheep intestines. It is generally considered to have optimum playing characteristics for racquet sports. However, it is costly, affected adversely by weather, has a relatively short play life, and breaks easily. Synthetic stringing for sports racquets is normally made from polymeric materials, such as nylon, polyester, or other engineered polymer composites. Certain synthetic materials, such as nylon, polyester or polyolephine, can be engineered to

provide good playing characteristics. Other synthetic string materials, such as strings made from high strength aramid fibers, can be engineered to provide good durability. However, there is not a synthetic material or combination of such materials which provides an optimum combination of playability and durability.

Metallic stringing for sports racquets is normally made from ferrous alloys, such as steel, or a stainless steel alloy, or other metallic alloys. If properly designed, metallic strings provide good durability; however, they are too stiff to provide an acceptable level of playability. They also produce high levels of shock and vibration which are damaging to the racquet frame and are hazardous to the wrist and arm of the player. Consequently, a need still exists for improvement of racquet stringing so as to optimize the playability and durability of the racquet strings.

Disclosure of Invention The present invention provides a sports racquet with a hybrid stringing arrangement designed to satisfy the aforementioned needs by optimizing the combination of playability and durability of racquet stringing. Accordingly, the present invention relates to a sports racquet which comprises: (a) a frame having a head portion encompassing an open region; and (b) a hybrid arrangement of stringing applied under tension to the head portion and extending across the open region in an interwoven grid pattern defined by a plurality of longitudinal strings and a plurality of cross strings providing a striking area of the racquet. All of the longitudinal strings of the stringing arrangement are composed of a core of metallic material. All of the cross strings of the stringing arrangement are composed of a non-metallic material, preferably a synthetic material or an animal gut material.

More particularly, the metallic material composing the core of the longitudinal strings is a metal selected from the group consisting of ferrous alloys, such as steel or stainless

steel, or non-ferrous metals or alloys> such as titanium or a titanium alloy. Also, the core of metallic material is preferably coated externally with an outer layer of a low friction, abrasion resistant, synthetic material. The synthetic material composing the cross strings and the outer layer surrounding the core of the longitudinal strands is a polymer material, such as a polyamide, such as nylon and aramids, polyester, polyolephine, polyetheretherketone, or polyethylene. These and other features and advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed description when taken in conjunction with the drawings wherein there is shown and described an illustrative embodiment of the invention.

Brief Description of Drawings

Fig. 1 is a plan view of a prior art tennis racquet to which can be applied a hybrid stringing arrangement in accordance with the present invention. Fig. 2 is an enlarged fragmentary plan view of the hybrid stringing arrangement in accordance with the present invention.

Fig. 3 is an enlarged cross-sectional view of a cross string of the hybrid stringing arrangement taken along line 3—3 of Fig. 2.

Fig. 4 is an enlarged cross-sectional view of a longitudinal string of the hybrid stringing arrangement taken along line 4—4 of Fig. 2.

Best Mode for Carrying Out the Invention

Referring now to the drawings, and particularly to Fig. 1, there is shown a prior art tennis racquet, generally indicated by the numeral 10. While the present invention is illustrated in Figs. 2-4 and described below in conjunction with the tennis racquet 10, the present invention is believed to be applicable to the racquets used in playing other sports comparable to tennis, such as squash and badminton. Thus, the reference hereafter to a tennis racquet 10 should be construed

in a generic sense as applicable to other sports racquets.

In its basic construction, the tennis racquet 10 has a frame 12, preferably of a one-piece structure, which includes a head portion 14, a handle portion 16 and a throat portion 18 extending between and interconnecting the head and handle portions 14, 16. The racquet frame 12 typically is fabricated of a composite- ype material composed of high modulus fibers such as graphite fibers or glass fibers in a matrix of an epoxy resin. Alternatively, the racquet frame 12 can be fabricated from other materials, such as aluminum, wood and plastics.

The handle portion 16 of the racquet frame 10 typically includes an outer sheath (not shown) for facilitating gripping of the racquet by the user's hand. The throat portion 18 typically is in the form of a pair of shafts or legs 20 having a generally V-shaped configuration.

The head portion 14 of the racquet frame 12 typically has a round or oval configuration and a hollow construction. The hollow interior of the head portion 14 is preferably filled with filler foam material (not shown) whose purpose is to prevent chips which are produced in the head portion during fabrication from later making noise during use of the tennis racquet 10. The head portion 14 contains a plurality of spaced stringing holes (not shown) extending between an inwardly facing surface 1 A and along a narrow recess (not shown) formed in an outwardly facing surface 14B of the head portion 14. The stringing holes are aligned in a common plane. In a known manner, a conventional stringing 22 is applied under tension through the holes and across the open region 24 encompassed by the head portion 14 in an interwoven grid pattern that provides a ball or other object striking area of the racquet 10.

Referring to Figs. 2-4, a hybrid stringing arrangement 26 of the present invention can be employed in the tennis racquet 10 instead of the conventional stringing 22. The hybrid stringing arrangement 26 is applied under tension to the head portion 14 and extended across the open region 24 in the same interwoven grid pattern as provided by the conventional stringing 22 to also define the ball striking area of the racquet 10.

However, unlike the conventional stringing 22, the hybrid arrangement 26 of stringing is defined by a plurality of longitudinal strings 28 and a plurality of cross strings 30 which are composed of different or dissimilar materials. All of the vertical or longitudinal main strings 28 of the stringing arrangement 26 are composed of at least a core 32 of metallic material. Preferably, the core 32 of metallic material of all the longitudinal strings 28 is coated externally with an outer layer 34 of a low friction, abrasion resistant, synthetic material. All of the horizontal or cross strings 30 of the stringing arrangement 26 are composed of a non-metallic material, such as a synthetic material or an animal gut material.

More particularly, the metallic material composing the core 32 of the longitudinal strings 28 can be a ferrous alloy, such as stainless steel or another steel alloy, or a non- ferrous metal, such as titanium or a titanium alloy. Other metallic materials can also be used due to the high strength and resiliency of metallic materials. Preferably, the metal core of the longitudinal strings 28 is stainless steel or titanium. The non-metallic material composing the cross strings 30 and the outer layer 34 surrounding the core 32 of the longitudinal strings 28 can be a synthetic polymer, such as nylon, polyester, polyolephine, or an aramid, or animal gut (for the cross strings) .

The combination of the longitudinal strings 28 of metallic material and cross strings 30 of non-metallic material which comprise the hybrid arrangement 26 of stringing in accordance with the present invention provide improved stringing durability, while retaining acceptable stringing playability. The durability of the longitudinal strings 28 is improved since the wear of these strings is greatly reduced due to the hardness of the metal compared to that of non-metallic material. Further, when compared to a stringing arrangement formed of metallic longitudinal and metallic cross strings, metal-to-synthetic material (such as nylon) contact, as in the case of the invention, has a much lower coefficient of friction, than metal-to-metal contact (0.2 compared to 0.8).

Additionally, the stiffness of the metallic longitudinal strings in comparison to the synthetic material or natural gut is stiffer, resulting in less string movement compared to all- synthetic or all natural gut longitudinal and cross strings, which results in greater synthetic or natural gut cross string durability. Therefore, the durability of the combination of metallic longitudinal strings and non-metallic cross strings is vastly improved.

Tests have been performed to measure the durability of the hybrid stringing arrangement 26 of the present invention for comparison with that of the prior art. The results are summarized in Table I. These tests involved a cross section of advanced players using various racquet stringing under routine playing conditions, and measuring the amount of time required for the stringing to break.

TABLE I Stringing Combination Equivalent Hours of Match

(Longitudinal/Cross) Play Before Strand Breakage

Animal Gut/Animal Gut 6

Nylon/Nylon 9

Steel/Steel 6 Steel/Nylon 24

Steel/Animal Gut 9

These tests were conducted using a stainless steel alloy for the longitudinal strings 28, as being representative of the metallic materials, and nylon or animal gut material for the cross strings 30, as being representative of the non-metallic materials.

The playability of the hybrid stringing arrangement 26 of the present invention is also vastly improved over all-metallic or all-non-metallic stringing. The resiliency provided by the metallic longitudinal strings 28 and the elasticity provided by the non-metallic cross strings 30 in the hybrid stringing arrangement 26 results in greater stringing bed flexibility and thus a softer, more preferred feeling. This combination also

results in a much better energy transfer to the struck ball (greater ball velocity) .

Tests have also been performed to measure the playability of the hybrid stringing arrangement 26 and compare it to that of the prior art. The results are summarized in Table II. These tests involved measurement of struck ball velocities while keeping incoming ball velocities constant. These tests were conducted using stainless steel for the longitudinal strings 28, as being representative of the metallic materials, and nylon or animal gut material for the cross strings 30, as being representative of the non-metallic materials.

TABLE II

Stringing Combination Velocity of Struck Ball

(Longitudinal/Cross) fMiles Per Hour)

Animal Gut/Animal Gut 49

Nylon/Nylon 48

Steel/Steel 39 Steel/Nylon 46

Steel/Animal Gut 46

From the tests conducted, the combined ranking of durability and playability is best with a combination of metallic longitudinal strings 28 and non-metallic cross strings 30 as provided in the hybrid stringing arrangement 26 of the present invention. An added advantage to the present invention is the ability to reduce the diameter of the metallic longitudinal strings 28 due to the improved durability of the metallic longitudinal strings and non-metallic cross strings 30 as provided in the hybrid stringing arrangement 26 of the present invention. The smaller diameter strings provide more penetration into the surface of the ball, thus providing for more ball control and spin. The diameter reduction can be greatly improved over that of prior art stringing by at least

thirty percent.

It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement of the parts thereof without departing from the spirit and scope of the invention or sacrificing all of its material advantages, the form hereinbefore described being merely a preferred or exemplary embodiment thereof.