Racquet with elongated grommet barrels

A sports racquet with increased string vibration damping has grommets with elongated barrels. The barrels conform closely to the strings, are capable of absorbing vibration, and may be placed on the main strings, the cross strings, or both.

BACKGROUND OF THE INVENTION

Today's sports racquets, such as tennis, racquetball, squash and badminton racquets, each have a frame with a head portion supporting a string bed, coupled to a shaft or handle. The size and length of the head varies, depending on the particular sport for which the racquet is being used. As the racquet strikes a projectile such as a ball or shuttlecock, the strings deflect and propel the projectile from the racquet. The resulting string vibration is transmitted to the frame of the racquet and eventually the handle or shaft, and, finally, to the hand, arm and shoulder of the user. This string vibration may cause user discomfort.

Vibration damping devices have been incorporated into racquets in an effort to absorb and reduce these uncomfortable and potentially harmful vibrations. While there are many different types of damping devices, most attempt to absorb the vibration in the string bed before it is transmitted to the frame. Many such devices attach to the strings themselves in or near the throat of the racquet and are made of a rubber or silicone-type material that is conducive to absorbing vibration. Because these devices must be lightweight in order to minimally affect the balance and feel of the racquet, and because many of them are located to be remote from the main racquet hitting area, they may not provide sufficient damping to significantly reduce the vibration. Further, many are difficult to install and some are prone to fall off during play.

However, grommets are usually incorporated into racquets to prevent premature string wear. Thus, it would be advantageous to incorporate a light-weight damping device into a racquet, near the hitting area, in the form of an elongated grommet, made from an elastic material that minimally affects the weight, balance and feel of the racquet, yet significantly reduces vibration in the string bed.

SUMMARY OF THE INVENTION

The problems mentioned above are solved by the invention, which in a first aspect provides a sports racquet. The sports racquet has a head, which laterally surrounds a string bed. The string bed resides in a plane, and a string bed boundary is formed at the intersection of the string bed plane and the interior surface of the head. A shaft of the sort used in tennis, squash, badminton, or some racquetball racquets, or a handle as used in other racquetball racquets, is connected directly to the head. The racquet further includes a frame having a plurality of grommet holes disposed around at least a portion of the head. The string bed has a plurality of strings at least some of which are received into respective grommet holes in the head.

On the exterior lateral surface of the head, elongate grommet strips are disposed adjacent to the grommet holes. Grommets are attached to the grommet strips at an angle to the grommet strip. Due to the flexibility and elasticity of the materials and due to the frame shape, the angle may vary. The grommets that are attached to the grommet strip are spaced apart to coincide with the grommet holes in the racquet and are inserted into the grommet holes. In an alternative embodiment of the invention, the grommets are not attached to a grommet strip. In still another embodiment, the long barreled grommets vary in length on the grommet strip.

A predetermined number of the grommets have vibration-damping, elongated barrels. In one embodiment, when inserted into the grommet hole, the elongated barrel extends into the string bed from the string bed boundary by about at least 0.55 inches. In other embodiments, the vibration damping elongated barrel extends into the string bed from the string bed boundary by at least 0.8 inches or even by at least 1.05 inches.

In a further aspect of the present invention, the grommets with elongated barrels are disposed on, or jacket, ones of the cross strings. For each cross string on which a grommet with an elongated barrel is disposed, a second grommet with an elongated barrel may be disposed at the opposed intersection of the string bed boundary and the cross string. Grommets with elongated barrels may also be disposed on every other cross string or on alternating sides, or on random strings where the specific placement of grommets is selected as a function of the balance point or other play characteristics (such as vibration) of the racquet. In one embodiment, the long barreled grommets on the cross strings extend into the string bed such that their free ends are no more than about 33 millimeters from the nearest or outermost main string. In still another embodiment, the long barreled grommets on the cross strings cover an area of 30% of the length of the cross string between the string bed boundary and the outermost main string. The grommets with elongated barrels can be disposed on only the cross strings which are at least five cross strings removed from the handle of the racquet. In a further aspect of the present invention, the grommets with elongated barrels are disposed on several adjacent cross strings.

DETAILED DESCRIPTION

Referring toFIG. 1, a sports racquet, indicated generally at100, has a frame102with a handle103, a head104, a string bed105, and a plurality of grommet holes106disposed around at least a portion of the head104. The frame102is defined to exclude any throat piece (not shown) or other structure at the throat area of the racquet where the head104and the handle103or shaft join. The string bed105resides in a string bed plane P. The string bed has a number of cross strings107that laterally traverse the head104of the racquet100and a number of main strings108that longitudinally traverse the head104. Even though the cross strings107and main strings108are referred to in the discussion below as individual strings, it is contemplated that each of the cross strings107and main strings108are segments of a longer string or strings which are used to string the racquet100. No limitation regarding the string bed, the strings themselves, the number, diameter, or length of the strings, the connectivity of the strings, the string physical or chemical composition, or any other string quality should be inferred by the discussion of the strings individually. Thus, each cross string107and main string108may have the same diameter as the other strings or may have its own separate string diameter. The cross strings107extend between and enter grommet holes106. The frame head104has a laterally inward facing surface112. A string bed boundary111is defined as the intersection of the plane P with surface112. Grommet holes106each adjoin the string bed boundary111. The grommet strip109is adjacent to the grommet holes106.

As shown, sports racquet100may be a racquetball racquet of the “long string” type in which most or all of the main strings108are fed into a hollow handle103and are anchored at an anchor (not shown) at or near a handle end110, or may be of a more conventional type in which some or all of the main strings have lower anchoring points on the frame102or throat piece (not shown). The invention may also be employed on other racquets such as those used for tennis or squash. If one end of a main string108is fed into a hollow handle, the opposing end will extend into a grommet hole106on top of the racquet. Otherwise, the main strings108will extend between and enter grommet holes106.

Referring toFIG. 2, a sports racquet100of the type ofFIG. 1is shown, but with long barrel grommets202disposed on seven cross strings107. The cross strings107jacketed by grommets202may make up a portion of the “sweet spot,” the center of which is illustrated by “x”206, for the racquet or the specific location on the racquet string bed105where optimal contact with the projectile is desired. The sweet spot206is a general area on the string bed105where the coefficient of restitution is closest to one or at a maximum. The sweet spot106may vary according to user, string tension, materials, string type, frame construction, and style of play. Alternatively or additionally, the ones of cross strings107having long barreled grommets may all reside in the racquet hitting area, which extends from about the center of the racquet to the head end or tip opposite of the handle.

FIG. 3Ashows an alternative embodiment with long barrel grommets202disposed on main strings108only.

FIG. 3Bshows an alternative embodiment with long barrel grommets202disposed on main strings108and cross strings107.

Referring toFIG. 4, attached to the prior art grommet strip109are prior art grommets401that do not have an elongated vibration damping barrel. The prior art grommets401are typically of a length that extends about 0.12 inches into the string bed from the string bed boundary. The length of prior art grommets401is conventionally chosen to be enough to extend through frame102at a respective grommet hole106. While grommets401are shown to be of uniform length, their length can be variable if the racquet head cross section thickness varies from place to place.

Referring toFIG. 5, a grommet strip500, according to the invention, has attached to it vibration damping grommets501with elongated barrels503. The primary purpose for the elongated grommet barrels503is to dampen the vibration of the string bed105when the string bed105impacts a projectile. When the string bed105receives vibratory forces from the strike of a projectile, those forces are transferred to head104of the racquet100and eventually to the user. Grommets501may also act to produce a more stable playing surface. Also present on the illustrated embodiment of grommet strip500are grommets502that do not have elongated barrels. A grommet strip500may contain a combination of short grommets502and grommets501with elongated barrels503, as well as a combination of grommets501with elongated barrels503of different lengths, depending on the application and vibration damping effects desired. Each grommet501with an elongated barrel503extends into the string bed105from the string bed boundary111by about at least 0.55 inches. More preferably, the grommets501extend into the string bed105from the string bed boundary111by about at least 0.8 inches or about at least 1.05 inches. While in the illustrated embodiment the entirety of the long-barrel grommets501are of uniform length, they could also vary according to any variance in frame thickness.

Referring toFIG. 5A, a single grommet520with an elongated barrel522may be provided separately from a multiple-grommet grommet strip500. In both cases, the single grommet520and the grommet501on a grommet strip502, the grommet501,520, has a barrel interior diameter504and a preferably a slightly tapered exterior diameter for ease in injection-molding the grommets520. An individual grommet520may be extended through a respective grommet hole106(FIG. 2). Racquets200according to the invention may be provided with one or more grommet strips500, a plurality of single long-barreled grommets520, or both. It is contemplated that the grommets501,520may be placed on one or more of the cross strings107(FIG. 2), or one or more of the main strings108(FIG. 3), or a combination of both (FIG. 3B). Different grommets520can be provided to be of different lengths.

Referring toFIG. 6, the illustrated frame102is a dual barrel frame, but no limitation as to the type of frame should be inferred. The frame102has a grommet hole106through which a grommet604with an elongated barrel605is inserted. The long barreled grommet closely encloses a string606. For the purposes of this invention, a grommet barrel will be considered to closely enclose a string if it has a vibration-damping effect thereon. The string606may be a cross string107or a main string108. Referring toFIG. 6A, the string606has a diameter608. For example, the grommet604may have an interior diameter504that is in the range of about 1.2 times to about 1.5 times the string diameter608. The interior diameter504is preferably about 1.5-1.6 millimeters for racquetball, tennis and squash applications. The tighter the fit between the string606and the barrel605, the more vibration damping will occur, however the fit cannot be so tight that the string606cannot be pulled through the barrel605. The grommet604may be attached to a grommet strip500(FIG. 5) or may be an individual grommet (FIG. 5A).

Referring toFIG. 7, when a long-barrel grommet604is placed on a cross string702, the grommet604will closely enclose the cross string702and in one embodiment will extend into the string bed105from the string bed boundary111to at least a distance of no more than 33 millimeters from the nearest main string704. In the illustrated embodiment, the spacing is smallest on the topmost cross string702on which a long-barrel grommet604is disposed, and largest on the bottommost cross string equipped with a long-barrel grommet604. In this embodiment and due to the shape of the head, and the angle of the outside-most main string704, the distance between the free end610of the barrel605and the nearest main string704will increase the closer the cross string702is to the handle103. Preferably, when the grommets604with elongated barrels605are placed on cross strings702, the grommets are placed on several, such as at least seven adjacent cross strings702. Additionally, for each cross string702on which a grommet604is disposed, usually there is a second grommet604with an elongated barrel605disposed at the opposed intersection of the string bed boundary111and cross string702(SeeFIG. 2). To maximize the placement of grommets604with elongated barrels605in the range of the sweet spot206, in the illustrated embodiment, when the grommets604with elongated barrels605are placed on seven consecutive cross strings702, the cross strings702on which the grommets are disposed are at least five cross strings removed from the handle103. Stated differently, for a racquet with a length (L) of twenty-two inches, the location of the group of cross strings702upon which the grommets604are disposed can be in the range between about length (B) of 15.5 inches and length (T) of 19 inches from the terminus of the racquet handle103(SeeFIG. 2). In yet another embodiment, all of the cross strings702can have grommets604disposed upon them. Alternatively the long barrel-equipped or jacketed cross strings702can all reside within the racquet's hitting area.

Further referring toFIG. 7, the grommet604with an elongated barrel605covers a portion, but not all, of the cross string702between the string bed boundary111and the outside-most main string704. The grommet604with an elongated barrel605covers about at least 30% of the length of the cross string702between the string bed boundary and the nearest main string704. More preferably, the grommet with an elongated barrel covers about at least 44% of the length of the cross string702between the string bed boundary and the nearest main string704. Even more preferably, the grommet with an elongated barrel covers about at least 58% of the length of the cross string702between the string bed boundary and the nearest main string704.

The inventors have determined that a non-brittle polymer which will flex and not break upon the impact of a projectile into the string bed should be used for the grommets604with elongated barrels605. The polymer should be more flexible than the frame, yet should still be plastic enough to exhibit damping properties. Preferably the polymer should have a flexural modulus in the range of 280-1730 MPa as measured under ISO 178 test methods. More preferably the flexural modulus is 390 MPa as measured under ISO 178 test methods. Preferably the polymer should have a Charpy Notched Impact Strength of between about 5 and 125 kJ/m2 under ISO 179 test methods. More preferably the polymer should have a Charpy Notched Impact Strength of 120 kJ/m2 at 23 degrees Celsius and 20 kJ/m2 at −30 degrees Celsius. Preferably the polymer should not break in Charpy Unnotched Impact Strength tests under ISO 178 test methods. A preferred polymer can be polyether block amide, such as the amide formulation sold under the mark PEBAX 7033 SP 1. Another polymer that may be considered is a polyamide, such as the formulations commercially available as nylon 11 or nylon 12.

Referring toFIGS. 10 through 13, the tests performed show that the elongated grommet barrels605significantly dampen post-strike string vibration in comparison to prior art, short-barreled grommets. Referring toFIGS. 8 through 13, the racquet that was tested was an E-Force® Heatseeker Model 170, strung with Oxygen™ 17 gauge string to a finish tension of 32 pounds. The Oxygen™ 17 gauge string is made from hundreds of composite microfibers bonded together. A number of trials were performed with varying grommet barrel lengths on the same seven cross strings (two grommets per cross string): (1) prior art grommets of about 0.12 inches; (2) grommets of about 1.05 inches; (3) grommets of about 0.8 inches; and (4) grommets of about 0.55 inches.

Referring toFIGS. 8 and 9, a test apparatus800was constructed to perform the tests on the vibration damping qualities of the grommets with elongated barrels. The racquet802being tested was positioned in the fixture800and held in a fixed position. In the fixed position, the racquet frame did not move, only the strings moved when struck with a ball. A Pro Penn HD racquetball ball with a diameter of 2.5 inches and a weight of 1.4 ounces was dropped from a fixed position height804of two feet and oriented to strike a point equidistant from both sides of the racquet frame and four inches from the top of the frame902. The vibration was measured via a microphone901located five inches above the string bed just above the top of the racquet frame. The microphone901identified sound waveforms caused by vibration when the racquet was struck with the ball. The microphone901was connected to a computer that was using Adobe Sound Booth Master Suite CS5 software.

In the data for both the racquet with the grommet strip with elongated barrels that extended 1.05 inches into the string bed (graphed onFIG. 11) and the prior art racquet without the elongated grommet barrels (i.e. grommets that extend no more than about 0.125 inches into the string bed shown inFIG. 1) (graphed onFIG. 10), during the strike of the ball or the initial “pop,” the sound level was very intense. The sound level recorded upon the strike had a peak of approximately 18 decibels above the ambient noise level. For the prior art racquet, the initial vibration lasted for 0.02 seconds. The initial vibration lasted 0.01 seconds for the dampened racquet with the barrel extending about 1.05 inches into the string bed.

As can also be seen by comparingFIG. 10toFIG. 11, vibration falls off immediately after the ball strike with the dampened racquet but vibration continues on the undampened racquet. Specifically, vibration decayed to approximately zero with no residual vibration within 0.14 seconds of the ball strike for the dampened racquet. There is a low frequency wave that continues before decaying to zero.

Additionally,FIG. 12demonstrates the vibration damping effects of a grommet with an elongated barrel that extends about 0.8 inches into the string bed. Here, the vibration decayed to zero in approximately 0.32 seconds. InFIG. 13, the vibration damping effects of a grommet with an elongated barrel that extends about 0.55 inches into the string bed demonstrated a decay to zero in approximately 0.38 seconds.

Thus, the elongated grommet barrels provide much improved vibration damping characteristics that will reduce wear on a players hand, arm and shoulders and provide more comfort during play.

In summary, the claimed invention provides increased vibration damping while minimally affecting the weight and balance of the racquet. While illustrated embodiments of the present invention have been described and illustrated in the appended drawings, the present invention is not limited thereto but only by the scope and spirit of the appended claims.