RACQUET HAVING ELONGATED GROMMET BARRELS WITH IMPROVED DAMPING CHARACTERISTICS

Abstract

A sports racquet with enhanced string vibration damping has grommets with elongated barrels on many of the cross strings. The internal diameter of the barrels is selected so as to preserve a minimum clearance between the cross string and its enclosing barrel, thereby mitigating vibration. The barrel lengths vary as a function of their distance from the top of the frame, so that their free ends are positioned near the nearest main string.

Description

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, but the strings vibrate after the initial impact. 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, or an incorrect feel for ball response.

Vibration damping devices have been incorporated into racquets in an effort to absorb and reduce these vibrations, which may lead to reduced performance because of incorrect feel, discomfort or fatigue. 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 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 unwanted vibration in the string bed. Such vibration as is felt should be better correlated to how well the ball has been struck, and should be more uniform between on-center and off-center hits.

The inventor has previously introduced a racquet in which several of the grommets are extended as barrels into the string bed, and this has had salutary vibration-dampening effects. But it has been discovered that extending these barrels even further has created additional and unforeseen vibrations that have detracted from optimum feel by the user. A need therefore persists for improvements in vibration dampening and stability in sports racquets.

SUMMARY OF THE INVENTION

The invention accordingly provides a sports racquet in which many of the cross strings are equipped with grommets having vibration-dampening extended barrels. The preferably plastic barrels extend into the string bed from the boundary which the string bed makes with the racquet frame, so that at least about 75% of the cross string, from the cross string boundary to the first main string, is covered. Alternatively, a free end of the barrel is disposed so as to no more than about 15 mm from the nearest main string. The string gauge and interior diameter of the barrel are chosen such that there is at least 0.14 mm, preferably at least 0.16 mm, and more preferably at least 0.19 mm of clearance between the interior surface of the barrel and the exterior surface of the string. Alternatively, an interior diameter of the barrel should be at least 21% greater than an exterior diameter of the string, and more preferably should be at least 33% greater than an exterior diameter of the string. It has been discovered that if at least this amount of clearance is maintained, the result is a dampened racquet with good stability and without an unwanted “buzz” or undamped vibration. The barrels may be integrally formed with one or more grommet strips which are placed in proximity to the grommet holes of the frame, preferably on the lateral exterior of the frame. In order to bring the free ends of the grommet barrels closer to the nearest main string, the lengths of the barrels on any one grommet strip generally, but not always, increase as one proceeds from the top of the frame head to the throat.

BRIEF DESCRIPTION OF THE DRAWINGS

Further aspects of the invention and their advantages can be discerned in the following detailed description, in which like characters denote like parts and in which:

FIG. 1 is an isometric view of a sports racquet showing a head, a handle, a string bed, and grommets according to the prior art;

FIG. 2 is a plan view of a sports racquet according to a first embodiment of the invention;

FIG. 3 is a plan view of a second embodiment of the invention, in which most of the cross strings are jacketed or enclosed by long-barrel grommets having free ends that are within a predetermined distance of the nearest main string;

FIG. 4 is a side view of the prior art grommet strip having grommets with short barrels;

FIG. 5 is a side view of a grommet strip having grommets with elongated barrels;

FIG. 6 is a side view of a grommet strip having grommets with elongated barrels and varied lengths, ends of the barrels disposed at a more constant distance from the nearest main string once the grommet strip is installed;

FIG. 7 is a detail of an individual grommet with an elongated barrel;

FIG. 8 is a sectional detail taken substantially along line 8-8 of FIG. 3;

FIG. 9 is a cross section taken substantially along line 9-9 of FIG. 8;

FIG. 10 is an isometric view of a test fixture used to test the vibration damping effects of the invention;

FIG. 11 is a top view of the test fixture;

FIG. 12 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 2, strung with 16 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on a center of the string bed;

FIG. 13 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, the barrels having an internal diameter of 1.5-1.6 mm and being strung with 16 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on a center of the string bed;

FIG. 14 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, with barrels having an internal diameter of 2.6 mm and as strung with 16 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on a center of the string bed;

FIG. 15 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 2, strung with 17 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on a center of the string bed;

FIG. 16 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, the barrels having an internal diameter of 1.5-1.6 mm and being strung with 17 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on a center of the string bed;

FIG. 17 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, with barrels having an internal diameter of 2.6 mm and as strung with 17 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on a center of the string bed;

FIG. 18 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 2, strung with 18 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on a center of the string bed;

FIG. 19 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, the barrels having an internal diameter of 1.5-1.6 mm and being strung with 18 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on a center of the string bed;

FIG. 20 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, with barrels having an internal diameter of 2.6 mm and being strung with 18 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the center of the string bed;

FIG. 21 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 2, strung with 16 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location;

FIG. 22 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, the barrels having an internal diameter of 1.5-1.6 mm and being strung with 16 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location;

FIG. 23 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, with barrels having an internal diameter of 2.6 mm and as strung with 16 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location;

FIG. 24 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 2, and being strung with 17 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location;

FIG. 25 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, with barrels having an internal diameter of 1.5-1.6 mm and being strung with 17 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location;

FIG. 26 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, with barrels having an internal diameter of 2.6 mm and as strung with 17 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location;

FIG. 27 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 2, strung with 18 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location;

FIG. 28 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, the barrels having an internal diameter of 1.5-1.6 mm and being strung with 18 gauge string, as measured using the test fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location; and

FIG. 29 is a graph showing vibration intensity versus time for a racquet substantially as shown in FIG. 3, with barrels having an internal diameter of 2.6 mm and being strung with 18 gauge string, as measured using the text fixture of FIGS. 10 and 11 after a ball is dropped on the string bed at a predetermined off-center location.

DETAILED DESCRIPTION

Referring to FIG. 1, a sports racquet, indicated generally at 100, has a frame 102 with a handle 103, a head 104, a string bed 105, and a plurality of grommet holes 106 disposed around at least a portion of the head 104. The frame 102 is defined to exclude any throat piece (not shown) or other structure at the throat area of the racquet where the head 104 and the handle 103 or shaft join. The string bed 105 substantially resides in a string bed plane P. The string bed has a number of cross strings 107 that laterally traverse the head 104 of the racquet 100 and a number of main strings 108 that longitudinally traverse the head 104. The cross strings 107 intersect the main strings 108 at a considerable angle, and typically intersect the racquet longitudinal axis X (FIGS. 2 and 3) at ninety degrees. Even though the cross strings 107 and main strings 108 are referred to in the discussion below as individual strings, it is contemplated that each of the cross strings 107 and main strings 108 be segments of a longer string or strings which are used to string the racquet 100. 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 string 107 and main string 108 may have the same diameter as the other strings or may have its own separate string diameter. Cross strings 107 typically are parallel and spaced apart from each other.

The cross strings 107 extend between and enter respective grommet holes 106. The frame head 104 has a laterally inward facing surface 112. A string bed boundary 111 is defined as the intersection of the plane P with surface 112. Grommet holes 106 each adjoin the string bed boundary 111. One or more grommet strips 109 may be adjacent to the grommet holes 106 and are usually assembled to the lateral exterior of the frame 102.

As shown, sports racquet 100 may be a racquetball racquet of the “long string” type in which most or all of the main strings 108 are fed into a hollow handle 103 and are anchored at an anchor (not shown) at or near a handle end 110, or may be of a more conventional type in which some or all of the main strings 108 have lower anchoring points on the frame 102 or throat piece (not shown). The invention may also be employed on other racquets such as those used for tennis, badminton or squash. If one end of a main string 108 is fed into a hollow handle, the opposing end will extend into a grommet hole 106 on top of the racquet. Otherwise, the main strings 108 will extend between and enter grommet holes 106. In this racquet 100, each of the grommet holes 106 is fitted with a grommet that does not appreciably extend into the string bed, as its primary purpose is to serve as a bushing for the string as the string is routed through the frame 102.

Referring to FIG. 2, a sports racquet of the type of FIG. 1 is shown, but with some of the grommets including or constituting barrels 202 being disposed on seven cross strings 107. Barrels 202 are of a moderate and mostly uniform length. A racquet 200 of the form seen in FIG. 2 is sold by Applicant under the mark “Heatseeker 2.0”. This racquet has barrels 202 which extend about 29 mm from their junctions with the grommet strips 109 to their free ends 204, and extend into the string bed 105 by a substantially uniform 26 to 27 mm. The free ends 204 are disposed at greatly varying distances from the nearest or most lateral main strings 210 (that is, the main strings closest to the string bed boundary 111), ranging from zero to more than 18 mm away from these closest main strings 210. The cross strings 107 jacketed by barrels 202 may make up a portion of the “sweet spot,” the center of which is illustrated by point or center 206, for the racquet or the specific location on the racquet string bed 105 where optimal contact with the projectile is desired. The sweet spot is a general area on the string bed 105 where the coefficient of restitution is closest to one or at a maximum. The sweet spot may vary according to user, string tension, materials, string type, frame construction, and style of play. However, for the tests described below, the sweet spot center 206 was controlled to be in the same place in terms of its distance from the frame top 212 and always to be on the racquet longitudinal axis X. Also seen on this FIG. 2 is an intentionally off-center target 208 that has been displaced toward the handle 103 and is off-axis. The location of target 208 was controlled to stay the same, from one racquet to the next, for the off-center ball drop tests illustrated by FIGS. 21-29.

FIG. 3 shows a sports racquet 298 in which the long barrel grommets 300-320 are of substantially different lengths, with their free ends 324 tending to be disposed at a closer and more even distance from a nearest main string 210. In one embodiment the barrels range in length from about 24 to 26 mm at the top jacketed string (barrel 300) to about 39 to 42 mm at the bottom jacketed string (barrel 320). These barrel lengths are measured from the string bed boundary 111, or the point at which the string departs from the interior sidewall 112 of the frame 102, to the free end 324 of the barrel. The distance between the free end 324 of the barrel and the nearest main string 210 also has a tendency to increase (with some exceptions) as the handle 103 is approached. This distance is as short as about 2 mm at barrel 300 and may be as long as 15 mm at barrel 318. In an embodiment, the range of distances can be 2 mm to 13 mm. More than seven cross strings 107 can be jacketed, and it is preferred that most of the cross strings 107 be jacketed or equipped with long barrels. In the embodiment illustrated in FIG. 3, eleven cross strings 107, or the fifth through fifteenth cross strings 107, have end segments which are mostly enclosed or jacketed by barrels 300-320.

The amount of cross string 107 from the interior racquet frame sidewall 112 to the nearest main string 210 (as sometimes used herein, the string's “outer length”) that is jacketed by a barrel also varies by percentage as one proceeds from barrel 300 to barrel 320. Barrel 300 covers as much as 90% of the outer length of string 107; barrel 318 covers as little as 75% of the outer length of its respective cross string 107. More preferably this coverage is in the range of about 76% to 90%. The percentage of coverage has a tendency to drop as one approaches the handle 103.

Referring to FIG. 4, attached to the prior art grommet strip 109 are prior art grommets 401 which have not been elongated into a vibration damping barrel. The prior art grommets 401 are typically of a length that extends about 3 mm into the string bed from the string bed boundary. The length of prior art grommets 401 is conventionally chosen to be enough to extend through frame 102 at a respective grommet hole 106. While grommets 401 are shown to be of uniform length, their length can be variable if the racquet head cross section thickness varies from place to place.

Referring to FIG. 5, a grommet strip 500 has attached to it vibration damping grommets 501 with moderately elongated barrels 503. The primary purpose for the elongated grommet barrels 503 is to dampen the vibration of the string bed 105 when the string bed 105 impacts a projectile. When the string bed 105 receives vibratory forces from the strike of a projectile, those forces are transferred to head 104 of the racquet 100 and eventually to the user. Grommets 501 may also act to produce a more stable playing surface. Also present on the illustrated embodiment of grommet strip 500 are grommets 502 that do not have elongated barrels. A grommet strip 500 may contain a combination of short grommets 502 and grommets 501 with elongated barrels 503. Each grommet 501 with an elongated barrel 503 extends into the string bed 105 from the string bed boundary 111 by about at least 0.55 inches. In the commercial “Heatseaker 2.0” embodiment tested below, the grommets 501 extend into the string bed 105 from the string bed boundary 111 by about 26.7 to about 28.2 mm, and are each a little more than about 29 mm long as measured from their grommet strip backing.

A set of three improved grommet strip segments is seen in FIG. 6. A grommet strip segment 600A has, integrally molded with it, barrels 300-320. Grommet strip 600A will be assembled to the left side of the racquet 298 and receives eleven cross strings 107. As measured from the segment proper to their free ends, barrels 300-320 have lengths which generally increase as a function of the distance from frame top 326 and as a function of their increasing proximity to the handle 103. In the commercial embodiments tested below (the “Invasion” and the “Invasion X”), barrels 300-320 have respective lengths approximating 27.6 mm, 30.4 mm, 33.0 mm, 35.6 mm, 37.7 mm, 39.3 mm, 42.8 mm, 42.9 mm, 42.5 mm, 42.9 mm and 43.0 mm as measured from the grommet strip to the free end. Barrels 312-320 are nearly of the same length while the length of barrels 300-310 increases more dramatically as a function of their distance from the top 326 of the frame. As inserted into grommet holes 106, a varying amount of these barrel lengths will be taken up in proceeding through the frame 102. Hence, a length of the barrels 300-320 as measured from the string bed boundary 111 to their free ends 324 will exhibit more variance as installed. Strip segment 600A terminates, at an end proximate to barrel 300, with a grommet 602 without an extended barrel. This end grommet 602 receives a peg or sleeve 604 of a head grommet strip segment 606. The head grommet trip segment 606 has no elongated barrels on it in the illustrated embodiment. Grommet strip segment 606 is assembled to the frame 102 around the top of the head 104. A grommet strip 600B, identical to the previously described grommet strip segment 600A, is provided for the right side of the racquet frame 102. In the place of three grommet strip segments 600A, 606, 600B, a unitary grommet strip may be provided, or more grommet strip segments could be provided, as is convenient for molding or assembly.

Referring to FIG. 7, a single grommet 700 with an elongated barrel 702 may be provided separately from a multiple-grommet grommet strip segment 600A, 600B. In both cases, the single grommet 700 and any of the barrels 300-320 on grommet strips 600A, 600B has a barrel interior diameter 704 and a preferably a slightly tapered exterior diameter for ease in injection-molding the barrel-equipped grommets 700, 300-320. An individual grommet 700 may be extended through a respective grommet hole 106 (FIG. 2). Racquets 298 according to the invention may be provided with one or more grommet strip segments, such as grommet strip segments 600A, 600B, a plurality of single long-barreled grommets 700, or both. It is contemplated that the grommets or barrels 700, 300-320 be placed on many, and preferably most, of the cross strings 107 of racquet 298 (FIG. 3).

Referring to FIG. 8, the illustrated and tested frame 102 is a dual barrel frame, but no limitation as to the type of frame should be inferred. The frame 102 has a grommet hole 106 through which a grommet with an elongated barrel 800 is inserted. The long barreled grommet closely encloses a cross string 107. For the purposes of this invention, a grommet barrel will be considered to closely enclose a string 107 if it has a vibration-damping effect thereon. Referring to FIG. 9, the string 107 has an outer diameter 900. Common string sizes used in sports racquets include 18 gauge, with an outer diameter of 1.22 mm +/−0.02 mm; 17 gauge, with an outer diameter of 1.27 mm +/−0.02 mm; and 16 gauge, with an outer diameter of 1.32 mm +/−0.02 mm. For example, the grommet barrel 800, as found on the “Invasion” and for which test results are illustrated by FIGS. 13, 16, 19, 22, 25 and 28, may have an interior diameter 704 that is in the range of about 1.5-1.6 mm for racquetball, tennis and squash applications. This interior diameter is therefore from 1.2 times to about 1.33 times the string diameter 900. There will be a clearance 902 between the inner wall 904 of the barrel 800 and the surface of the string 107. In the “Invasion” and “Heatseeker 2.0” embodiments, this clearance is in the range of 0.09 to 0.19 mm. The grommet 800 may be attached to a grommet strip 600A, 600B (FIG. 6) or may be an individual grommet 700 (FIG. 7). It is preferred that the inner diameter of the barrel be at least 21% greater than the string diameter. In another embodiment, the inner diameter of the barrel can be 33% greater than the string diameter.

In the tested “Invasion X” embodiment, the barrel interior diameter is about 2.6 mm. As enclosing 18 ga.-16 ga. strings, this means that the interior diameter of the barrel 800 is about 1.9 to 2.2 times the outer diameter of the cross string it is enclosing. For these string gauges, the clearance 902 is in the range of about 0.64 to 0.69 mm. To mitigate the vibration transmitted by the cross strings 107 to the long barrels, the clearance 902 should be at least 0.14 mm, preferably should be at least 0.16 mm, and more preferably should be at least 0.19 mm.

Relative to the composition of barrel 800, 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. 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 a polyether with an amide blocker, 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.

The tested strings were E-Force Oxygen™ 16-18 gauge strings each strung to a finish tension of 30 pounds. The Oxygen™ strings are made from hundreds of composite microfibers bonded together.

Referring to FIGS. 10 and 11, a test apparatus 1000 was constructed to perform the tests on the vibration damping qualities of the grommets with elongated barrels. Commercial embodiments of racquets 200 (FIG. 2) and 298 (FIG. 3) were tested. The racquet being tested was positioned in the fixture 1000 and held in a fixed position. In the fixed position, the racquet frame 102 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 height 1002 of two feet and oriented to strike a point 206 equidistant from both sides of the racquet frame and four inches from the top of the frame 102. The vibration was measured via a microphone 1004 (FIG. 11) located five inches above the string bed just above the top of the racquet frame 102. The microphone 1004 identified sound waveforms caused by vibration when the racquet was struck with the ball. The microphone 1004 was connected to a computer that was using a software bundle called NCH Audio Essentials 2012 Edition which includes the following sub-programs:

• • WavePad Sound Editor
  • MixPad Multi-track Mixer
  • RecordPad Sound Recorder
  • Golden Records Vinyl Converter
  • Switch Audio File Converter
  • Zulu DJ Software.

The two programs used from the above list were WavePad and RecordPad.

Referring to FIGS. 12-29, data were taken on the vibration characteristics of nine different racquets, resulting from both center drops (onto location 206) and drops on an off-center location 208. The center location 206 and the off-center location 208 were controlled to be in the same location throughout the tests, relative to the degree of lateral displacement from racquet axis, and the degree of longitudinal displacement from the top margin of the head. Throughout the tests, a 170 gram racquet was used, and the end tension used in stringing the racquet was 30 pounds. Three models of racquets, differing from each other in the length, number and internal diameter of cross-string barrels, were strung with 16 gauge string (the heaviest), 17 gauge string and then 18 gauge string. The model tested in FIGS. 12, 15, 18, 21, 24 and 27 was the E-Force Heatseeker™ 2.0, depicted in FIG. 2. The model tested in FIGS. 13, 16, 19, 22, 25 and 28 was the E-Force Invasion™, depicted in FIG. 3, with barrels having an internal diameter of 1.5-1.6 mm. The model tested in FIGS. 14, 17, 20, 23, 26 and 29 was the E-Force Invasion X™, also depicted in FIG. 3 but with barrels having an internal diameter of 2.6 mm. The largest spike in these audio recordings occurs when the dropped ball first hits the string bed, the small spikes occurring to the left of this event being ambient noise.

In the racquet tested in FIG. 13, the barrels are significantly longer than those on the racquet tested in FIG. 12, and there are 22 of them instead of 14. All other variables were controlled to be the same. FIG. 13 shows a second peak that is almost as large as the first peak, and this vibration takes about 0.3 seconds to significantly damp out. This lengthened dampening is felt by the players as an undesirable buzz.

FIG. 14 shows a racquet similar to that tested in FIG. 13, the only difference being that the barrels used in this racquet have an internal diameter of 2.6 mm rather than 1.5-1.6 mm. There is a noticeable increase in dampening characteristic and the dampening is also superior to the shorter- and thinner-barrel version tested in FIG. 12.

FIGS. 15-17 show similar vibration test data, for a racquet strung with 17 gauge string rather than a 16 gauge string. The improvement in dampening is still present as seen in FIG. 17, although the improvement is not as dramatic as that seen for 16 gauge string.

FIGS. 18-20 record the same data for racquets in which 18 gauge string is used. Here, increasing the diameter of the longer-length barrels (FIG. 20) produces a dampening that is better than that produced by the narrow long barrels seen in FIG. 19. There is not as much of a continuing “buzz” seen in FIG. 19 as there is in FIG. 13 or 16 for corresponding racquets strung with heavier (17 or 16 gauge) string. The inventor believes that this is due to the fact that the clearance of the smaller-diameter string inside the barrel is greater.

FIGS. 21-29 display data from intentionally off-center hits, and correspond to the data for center hits appearing in FIGS. 12-20. For each of these experiments, a ball was dropped on location 208 on the racquet. This set of data is useful for analyzing the “stability” of the racquet, which is its propensity to behave in a more uniform way regardless of where on the string bed the ball hits. FIGS. 21-23 are racquets strung with 16-gauge string and may be compared with FIGS. 12-14. The differences between a center hit and an off-center hit on a racquet equipped with narrow long barrels (1.5-1.6 mm interior diameter; FIGS. 13 and 22) are noticeable. Increasing the internal diameter of these barrels to 2.6 mm (FIGS. 14 and 23) makes this difference go away, and thus a more “stable” racquet results. This effect is most pronounced in racquets strung with 16—gauge string.

Because of the difference in behavior of 16 gauge, 17 gauge and 18 gauge string in the narrower, long barrels having an interior diameter of 1.5-1.6 mm, the data suggest a minimum clearance 902 between the inner wall 904 of the barrel and the string 107 of about 0.14 mm, preferably 0.16 mm, and more preferably 0.19 mm. At clearances below this threshold and with long barrels, an annoying and insufficiently damped buzz obtained; at clearances above this, this buzz went away.

The improved vibration dampening and stability of these racquets has been qualitatively proven out by play-testing them. Racquets with the improved vibration-dampening barrels will enhance racquet stability while reducing wear on a player's hand, arm and shoulders, providing more comfort and reproducibility during play.

In summary, the claimed invention provides increased vibration damping and stability 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.

Claims

1. A sports racquet comprising:

a racquet frame having an axis, a head of the racquet frame laterally surrounding a string bed, the head having a lateral interior surface, the string bed residing in a string bed plane, a string bed boundary formed by the intersection of the interior surface of the head and the string bed plane;

a plurality of spaced-apart grommet holes formed through the frame and disposed around at least a portion of the head;

the string bed having a plurality of strings including main strings and cross strings, the cross strings strung at an angle to the axis, strung in spaced relation to each other, and strung to intersect the main strings, at least some of the cross strings received into respective grommet holes in the head, an outer length of the cross string defined to extend between the string bed boundary and an intersection of the cross string with the nearest main string;

each of the grommet holes being provided with a grommet, a plurality of elongated, vibration-dampening barrels formed as portions of ones of the grommets, each barrel enclosing a respective enclosed cross string, each barrel extending through a grommet hole and extending into the string bed, the barrel covering at least about 75% of said outer length.

2. The racquet of claim 1, wherein the barrel covers between about 76% and about 90% of said outer length of said enclosed cross string.

3. The racquet of claim 1, wherein each barrel has an inner wall with an inner radius and the cross strings have an outer surface with an outer radius, a difference between the inner radius and the outer radius preselected to be at least about 0.14 mm.

4. The racquet of claim 3, wherein the difference between the inner radius and the outer radius is preselected to be at least about 0.16 mm.

5. The racquet of claim 4, wherein the difference between the inner radius and the outer radius is preselected to be at least about 0.19 mm.

6. The racquet of claim 5, wherein the difference between the inner radius and the outer radius is preselected to be in the range of 0.64 mm to 0.69 mm.

7. The racquet of claim 1, wherein each of a majority of the cross strings strung on the racquet are strung through at least one of said barrels.

8. The racquet of claim 1, wherein each of more than seven cross strings strung on the racquet is strung through at least one of said barrels.

9. The racquet of claim 1, wherein the barrels are provided in pairs, one barrel of each pair extending into the string bed from the frame on one side of the string bed, a second barrel of the pair extending into the string bed from the frame on an opposite side of the string bed, a respective cross string being strung through each pair of barrels.

10. The racquet of claim 1, wherein each barrel has an inner diameter and the cross strings each have an outer diameter, the inner diameter of the barrel being greater than the outer diameter of the cross string enclosed by the barrel by at least 21%.

11. The racquet of claim 10, wherein the inner diameter of the barrel is greater than the outer diameter of the cross string enclosed by the barrel by at least 33%.

12. The racquet of claim 11, wherein the inner diameter of the barrel is in the range of about 1.9 to about 2.2 times the cross string diameter.

13. The racquet of claim 1, wherein a plurality of the barrels are integrally formed with a grommet strip disposed laterally exterior to the frame.

14. The racquet of claim 13, wherein the racquet frame has a top, barrels formed on the grommet strip having lengths which generally increase as a function of the barrel's distance from the top of the racquet frame.

15. The racquet of claim 13, wherein first and second grommet strips are disposed on opposite sides of the frame, a plurality of elongated barrels integrally formed with and extending from each grommet strip.

16. The racquet of claim 1, wherein the racquet frame has a top, the plurality of barrels include a spaced-apart array of barrels enclosing respective cross strings, a length of the barrels in the array generally increasing as a function of the barrel's distance from the top of the frame.

17. The racquet of claim 1, wherein each elongated barrel is made of a material consisting essentially of a polyether with an amide blocker.

18. The racquet of claim 1, wherein each elongated barrel is made of a material consisting essentially of a polyamide.

19. A sports racquet comprising:

a racquet frame having an axis, a head laterally surrounding a string bed, the head having a lateral interior surface, the string bed residing in a string bed plane, a string bed boundary formed by the intersection of the lateral interior surface of the head and the string bed plane;

a plurality of spaced-apart grommet holes formed through the frame and disposed around at least a portion of the head;

the string bed having a plurality of strings including main strings and cross strings, the cross strings strung at an angle to the axis, strung in spaced relation to each other, and strung to intersect the main strings, at least some of the cross strings received into respective grommet holes in the head, an outer length of the cross string defined to extend between the string bed boundary and an intersection of the cross string with the main string nearest to the string bed boundary;

a plurality of grommets inserted into the grommet holes, a plurality of elongated, vibration-dampening barrels formed as portions of ones of the grommets, each barrel having a free end and enclosing a respective enclosed cross string, each barrel extending through a grommet hole and into the string bed so that the free end of the last said barrel is no more than about 15 mm from the main string nearest the string bed boundary.

20. The racquet of claim 19, wherein the free ends of the barrels are each displaced from the nearest main string by a distance in the range of about 2 mm to about 13 mm.

21. The racquet of claim 19, wherein the grommets with elongated barrels are disposed on at least eleven cross strings.

22. The racquet of claim 19, wherein a plurality of the barrels are integrally formed with a grommet strip disposed laterally exterior to the frame.

23. The racquet of claim 19, wherein first and second grommet strips are disposed on opposite sides of the frame, a respective plurality of elongated barrels integrally formed with each of the first and second grommet strips.

24. The racquet of claim 19, wherein each elongated barrel is made of a material consisting essentially of a polyether with an amide blocker.

25. The racquet of claim 19, wherein each elongated barrel is made of a material consisting essentially of a polyamide.

26. The racquet of claim 19, wherein the cross string has a predetermined diameter, an interior diameter of each barrel being at least 21% greater than the enclosed cross string diameter.

27. The racquet of claim 26, wherein the interior diameter of each barrel is at least 33% greater than the cross string diameter.

28. The racquet of claim 27, wherein the interior diameter of each elongated barrel is in the range of about 1.9 to about 2.2 times the cross string diameter.

29. The racquet of claim 19, wherein a clearance between an inner surface of each elongated barrel and an outer surface of the cross string enclosed by the last said elongated barrel is at least 0.14 mm.

30. The racquet of claim 29, wherein the clearance between the inner surface of each elongated barrel and the outer surface of the cross string enclosed by the last said elongated barrel is at least 0.16 mm.

31. The racquet of claim 30, wherein the clearance between the inner surface of each elongated barrel and the outer surface of the cross string enclosed by the last said elongated barrel is at least 0.19 mm.

32. The racquet of claim 31, wherein the clearance between the inner surface of each elongated barrel and an outer surface of the cross string enclosed by the last said elongated barrel is in the range of about 0.64 mm to about 0.69 mm.

33. The racquet of claim 19, wherein at least 22 grommets with elongated barrels are disposed on the cross strings.

34. The racquet of claim 19, wherein for each cross string on which a grommet with an elongated barrel is disposed, a second grommet with an elongated barrel is disposed at an opposed intersection of the string bed boundary and the cross string.

35. The racquet of claim 19, wherein each of the elongated barrels is integrally formed on one of a first and a second grommet strip segment.

36. The racquet of claim 19, wherein each grommet with an elongated barrel is made of a material consisting essentially of polyether with an amide blocker.

37. The racquet of claim 19, wherein each grommet with an elongated barrel is made of a material consisting essentially of a polyamide.