GB2391819A

GB2391819A - Tennis racket with vibration-damping member

Info

Publication number: GB2391819A
Application number: GB0316006A
Authority: GB
Inventors: Hiroyuki Takeuchi; Kunio Niwa
Original assignee: Sumitomo Rubber Industries Ltd
Current assignee: Sumitomo Rubber Industries Ltd
Priority date: 2002-07-10
Filing date: 2003-07-09
Publication date: 2004-02-18
Anticipated expiration: 2023-07-09
Also published as: FR2842117B1; GB2391819B; FR2842117A1; GB0316006D0

Abstract

A racket is formed in one piece comprising a string-stretching part (13) surrounding a ball-hitting face (F), a bifurcated throat part (14A, 14B), a shaft part (15), and a grip part (16). A yoke (17) mounted on a portion of connection between the string-stretching part (13) and the throat part (14) A vibration-damping member (20)preferably made of a viscoelastic material is mounted on the string-stretching part (13) by spanning the vibration-damping member (20) overthe ball-hitting face (F) between a left frame of the string-stretching part (13) and a right frame thereof, with the vibration-damping member (20)preferably not in contact with the strings stretched on the ball-hitting face (F). The vibration-damping member 20 may be of two parts, one on either side of the ball hitting face F. A spacer of viscoelatic material may be provided on the vibration-damping member 20 and may contact the strings.

Description

RACKET

BACKGROUND OF THE INVENTION

Field of the Invention

5 Thepresentinventionrelatestoaracket. Moreparticularly, the present invention relates to a racket that is preferably used for tennis, badminton, squash, and in particular regulation-ball tennis and that has enhanced vibration-damping performance without reducing the repulsive performance thereof.

10 Descrlption of the Related Art In recent years, there is provided a "thick. racket" which isthickintheout-of-planedirectionofaballhittingfacethereof. Female and senior tennis players desire to use the "thick racket', because they want to hit tennis ball at a high speed with a small 15 power. That is, powerless people desire to use a racket which is lightweight and has ball flight performance. Therefore a fiber reinforced resin having a high specific strength and a high degree of freedom in design is most popular as the material for the racket.

However, as the tennis racket becomes more lightweight, the 20 extent of a shock to be applied by the ball to the tennis racket at the time of hitting the ball becomes increasingly large and a player feels an unpleasant vibration. Further the shock applied to the racket is liable to be transmitted to an elbow, which is a cause of so-called tennis elbow. Therefore there is a growing 25 demand for development of a racket that is lightweight and has high

vibration-absorbing performance.

Recently a lightweight racket having a weight less than280g is supplied. Moreover a lightweight racket having a weight less than 25Qg is designed. It has become clear that the durability of 5 the lightweight racket frame changes very greatly, when the weight oftheamountoffiberreinforcedresinchangesslightly,forexample, 4g to 5g.

Therefore there are proposed a large number of lightweight rackets having a vibration-damping member mounted thereon to allow 10 them to have en appropriate degree of vibration-damping performance and vibrationabsorbing performance in dependence on the strength thereof. For example, in the tennis racket disclosed in Japanese Examined Patent Publication No. 52-13455, the cantilevered damper 15 composed of the long and narrow elastic material is installed at the end of the grip end. The base of the steelwire haying the weighs installed on its front end is embedded in the racket frame. In the disclosure made in Japanese Patent Application LaidOpen

No.52-156031, the base of the vibration-damping member is fixed 20 to the throat part of the racket frame, and the body of the dynamic damper is connected to the base via the neck to vibrate the body.

In the apparatus for absorbing vibrations of aracet frame disclosed in Japanese Patent Application Laid-Open No.62-192182, the vibrationabsorbing member of the apparatus has the rod having the 25 mass-adding member mounted on its free end. The rod is supported

on the body of the racket frame by the viscoelastic material.

In the vibration-cushioning apparatus proposed by the present applicant and disclosed in Japanese Patent Application Laid-Open No.2000-2414 Q. the vibrating weight is received in the hollow portion 5 of the flexible cap surrounding the grip end. The weight is spaced at a certain interval from the grip end. The vibration-cushioning apparatus is mounted at the free end of the grip of a hitting tool in such a way that the vibrationcushioning apparatus is disposed in the vicinity of the antipode of vibration.

10 In the vibration-damping member proposed by the present applicant and disclosed in Japanese Patent Application Laid-Open No.2000-157649, the weighting material is disposed in the vicinity of a position having a large amplitude of vibrations generated by the racket frame, with the weighting material connected to the 15 viscoelastic material. That is, the vibration-damping member is disposed in the thickness andwidthwise directions to dampvibrations in each vibration mode.

In the vibration-damping member disclosed in Japanese Patent Application Laid-Open No.2001-37916, the vibration-damping merrber 20 is mounted in the string hole formed on the racket frame to thereby damp the vibration of the string and the racket frame.

However, in the disclosure made in Japanese Examined Patent

Publication No.52-13455 and Japanese Patent Application Laid-Open Nos. 52156031 and 62-192182, the weight of each of the racket frames 25 contributes to only damping of vibrations in a specific mode

(out-of-planeprlmaryvibration). Theweighttheracketframeheavy and does not affect the property of the body of the racket frame.

Further each of the racket frames has a member that interrupts a prayer when the prayer swings and does not have a member contributing 5 to improvement of the repulsive performance.

The vibration-cushioni.ng apparatus disclosed in Japanese Examined Patent Publication No. 2000-24140 contributes to damping of vibrations in each vibration mode but it is difficult to allow the end cap to have a lid. Thus a measure for preventing a sound 10 generated by a fragment in the hollow member is insufficient. Thus the end cap does not contribute to the improvement of the repulsive performance. The natural frequency is adjusted by the auxiliary weight, which increases the weight of the racket.

In the disclosure made in Japanese Patent Application

15 Laid-Open Nos.2000-lS7649 and 2000-37916, the members mounted on the racket frameis not soheavyasthemembersof the above-described otherproposalsandfavorableinthevibrati.on-dampingperformance. However, there is a growing demand for development of a vibration-damping member haying a more favorable vibration-damping 20 performance.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above-described problems. Thus it is an object of the present 25 invention to provide a racket having improved vibration-damping

performance without increasing the weight thereof and superior in the repulsive performance thereof.

To achieve the object, according to the present invention, there is provided a racket whose frame is formed in one piece 5 comprisingastringstretchingpartsurroundingaball-hittingface, a bifurcated throat part, a shaft part, and a grip part; and a yoke mounted on a portion of connection between the string-stretching part and the throat part.

In this construction, a vibration-damping member for the 10 ballhittingfacespanningmadeofaviscoelasticmaterialismounted on the stringstretching part by spanning the vibration-damping member over the ballhitting face between a left frame of the string-stretching part and a right frame thereof, with the vibration-damping member not in contact with the strings stretched 15 on the ball-hitting face.

The vibration-damping member, made of the viscoelastic material, isspannedovertheball-hittingfaceliketheyokebetween the left frame of the string-stretching part and the right frame thereof. Thus the vibrationdamping member enhances the 20 vibration-damping performance and allowing a player to recognize that the racket frame is provided with a vibrationdampingfunction.

Thatis, both endsof the vibration-dampingmember are fixedly fitted on the left and right frames of the string-stretching part or the throat part. In this fixing, a face contact is made between 25 the vibration-damping member and the string-stretching part or the

throat part. Thus vibrations generated on the racket frame are transmitted to the vibration-damping membermade of the viscoelastic material. Consequently the vibration-damping member resonates, thus absorbing vibrations in a good balance at the left and right 5 racket frames owing to the viscoelastic characteristic of the vibration-damping member. A mass-adding material such as a weight is not mounted on the racket frame. Therefore the vibration-damping member is light and has enhanced vibration-damping performance.

Because the vibration-damping member is mounted on the 10 stringstretching part, the repulsive performance of the vibration-damping member can be improved. That is, the vibration-damping performance is enhanced with a possible smallest amount of weight of the vibration- damping member. Further an increase of a small amount of weight thereof can be related to 15 improvement of the repulsive performance. By connecting the viscoelastic material different from the material of the racket frame to the racket frame as described above, a shear force generated when the racket frame deforms is concentrated on the connection surface of the racket frame and that of the viscoelastic material.

20 Thereby the vibration-damping performance can be enhanced.

The vibration-damping member for the ball-hitting face spanning does not contact the string. Therefore the repulsive performance of the string does not deteriorate.

In terms of balance, it is preferable that both ends of the 25 vibrationdamping member are disposed on the left and right frames

of the gut-stretching part symmetrically not only with respect to the central longitudinal line of the ball-hitting face but also with respect to the ball-hitting face.

It is preferable that the vibration-damping member is made 5 of a synthetic resin and has a flexural modulus of elasticity not less than 100 MPa nor more than 1500 MPa.

If the vibration-damping member has a flexural modulus of elasticity less than 100 MPa, the vibration-damping member is so soft that the frequency of the vibration-damping member does not 10 match not only the out-ofplane secondary vibration having a comparatively high natural frequency but also the out-of-plane primary vibration having a comparatively low natural frequency.

On the other hand, if the vibration-damping member has a flexural modulus of elasticity more than 1500 MPa, the vibration-damping 15 member is so herd that the frequency of the vibration-damping member does not match not only the out-of-plane primary vibration having a comparatively low natural frequency but also the out-of-plane secondary vibration having a comparatively high natural frequency.

It is possible to use rubber, resin or elastomer having the 20 flexural modulus of elasticity in the above-described range as the vibrationdamping member. A thermoplastic resin such as nylon can be preferably used. Polyether block amide (PEB.X), polystyrene-vinyl isoprene blockcopolymer(HYBRAR), end polyester elastomer (HYTREL) are particularly preferable.

25 Itispreferablethatthevibration-dampingmemberhasaweight

not less than 4g nor more than leg.

If the weight of the vibration-damping member is less than 4g, it is difficult to resonate the vibration-damping member with the racket frame and hence it is difficult to obtain sufficient 5 vibration-damping performance. On the other hand, if the weight of the vibration-damping member is more than leg, the weight of the racket and the moment of inertia become large. Consequently the operability of the racket becomes poor.

The vibration-damping member to be spanned over the 10 ball-hitting face comprises left and right mounting parts fixedly fitted on the left frame of the string-stretching part and the right frame thereof respectively; and a spanning part, integral with the left and right mounting parts, disposed between the left and right mounting parts.

15 The spanning part is divided into front and back portions spaced at a predetermined interval from front surface of string faces and back surfaces thereof respectively; a string insertion hole is formed in a gap between the front and back portions of the spanning parts end allstringsstretchedinalongitudinaldirection 20 to be inserted through the yoke are inserted through the string insertion hole.

It is possible to form the same number of string insertion holes as that of the strings so that the strings are freely inserted into the string insertion holes respectively by providing a gap 25 between the surface of the string and the inner peripheral surface

. of the string insertion hole.

One of a pair of vibration-damping membersisspannedat fornt side of the ball-hitting face and the other of the vibration-damping members is spanned at back side of the kall-hitting face, with a 5 gaptormedbetweenapairofthevibration-dampingmembers. A spacer made of a viscoelastic material is disposed at a portion of the gapbetweenthevibration-dampingmembers,withthespacerincontact with at least trio strings stretched in a longitudinal direction.

By disposing the spacer in the gap between a pair of the 10 vibrationdamping members spaced at a certain interval from the front and back surfaces of the strings respectively, with the vibrationdampingmembersnotincontact withthestrings,thespacer serves as a means for placing the vibration-damping members at a position where the vibrationdamping members do not contact the 15 strings. Therebywhenatennisballishit,thestringadonotcontact the vibration-damping members end the repulsive force of the strings is not reduced.

The spacer made of the viscoelastic material is in contact with at least two strings stretched in a longitudinal direction.

20 Thereby the spacer absorbs vibrations of the strings generated when the ball is hit, thus improving vibration-damping performance.

Further since the spacer is bonded to the vibration-damping member, the spacer and the vibration-damping member display the function of a dynamic damper cooperatively, thus improving the 25 vibration-damping performance.

. The reason the spacer is in contact with at least two strings stretched in a longitudinal direction is as follows: If the spacer is not in contact with two or more strings, it is impossible to place the vibration-damping member at a position where the 5 vibrationdampingmemberdoesnotcontactthestrings. Inthiscase, the strings contact the vibration-damping member when the ball is hit and the repulsive force thereof deteriorate. Further a sufficient vibration-damping effect of the string cannot be obtained. 10 By forming the spacer of a material more elastic than the material for the vibration-damping member and adjusting the elasticity of the material for the spacer' it is possible to improve the vibration-damping performance of the string and adjust the vibrationdamping performance of the racket frame.

15 It is preferable to dispose the spacer at the center of the ballhitting face.

The above-described construction prevents the racket from being unbalanced and enhances the vibration-damping performance owing to contact between the spacer and the centralstring stretched 20 in a longitudinal direction having a large amount of vibrations when the ball is hit.

The complex elastic modulus E* of the viscoelastic material composing the spacer is less than 2.00X109dyn/cm2when the complex elasticmodulus is measured ata frequency oflO Hzanda temperature 25 of 0 C to 10 C.

When the viscoelastic material has the complex elastic modulus in the above range, the spacer has a sufficient elasticity. Thus it is possible to improve the vibration-damping performance of the string and that of the racket frame.

5 As the viscoelasticmaterial for the spacer, styrene butadiene rubber and silicone rubber can be preferably used.

It is preferable that the spacer has a weight not less than 0.3g nor more than 2g.

If the spacer has a weight less than 0.3g, the volume of the 10 spacer is insufficient for the spacer to contact the string. On the other hand, if the spacer has a weight more than 2g, the weight of the racket and the moment of inertia become large. Consequently the racket has a low operability. One or a plurality of the spacers can be mounted on the racket frame.

15 It is preferable that the total of the area where both sides of the vibration-damping member contact the string-stretching part is set to not less than 20cm2. Thereby it is possible to increase the resonant property of the vibration-damping member and improve the vibration-damping performance thereof. It is preferable that 20 the length of the spanning part of the vibration-damping merrier is set to not less than 60mrn. Thereby it is possible to increase the vibration-damping performance of the spanning part.

It is preferable that the vibration-damping member is fitted on essentially an inner surface of the string-stretching part in 25 its thickness direction and both surfaces thereof in its widthwise

direction. It is possible to form a concavity on the string-stretching part on which the vibration-damping member is mounted to fit the left and right mounting parts of the vibration-damping member in the concavity. In this case, no step 5 is formed between the surface of the stringstretching part and that ofthevlbration-dampingmember. The vibrationdampingmember may be mounted on the string-stretching part at a desired position thereofwithoutformingtheconcavityonthestring-stretchinUpart. A second vibration-damping member for the throat spanning 10 composed of a viscoelastic material may be spanned between a left frame of the throat part and a right frame thereof by spacing the vibration-damping member for the throat spanning at a certain interval from the yoke or by laying the vibration-damping member for the throat spanning on a surface of the yoke.

15 In the case where vibration-damping member for the throat spanning is spanned between left and right throat parts, it is unnecessary to form the string insertion hole thereon. Thus the vibration-damping member for the throat spanning may be solid rod-shaped, sheet-shaped or tube-shaped.

20 In addition to the vibration-damping member for the ball-hitting face spanning spanned over the ball-hitting face, the vibration-damping member for the throat spanning made of the viscoelastic material mounted on only the throat part has a vibration-damping effect.

25 The racket frame haslargeamplitudesintheprimaryvibration

mode at the top, the grip, and the center thereof. It is possible to damp vibrations most effectively by disposing the vibration-damping member at a position in the vicinity of the neighborhood of the center of the racket frame in the region between 5 the grip end and the top of the gutstretching part, namely, at apositionlocated scarer to the yoke then the position ofalowermost string stretched in a latitudinal direction in such a way that the vibration-damping member crosses the ball-hitting face.

In the case where the vibration-damping member is mounted 10 in the vicinity of the top of the gut-stretching part, a play has difficulty in swinging the racket. In the case where the vibration-damping member is mounted on the grip part of the racket gripped by the player, the vibration-damping member has a low vibration-damping effect.

15 More specifically, the vibration-damping member is mounted on the string-stretching part or the throat part by spacing the vibrationdamping member at an interval of not less than 0.3L nor more than 0.6L from the grip end, supposing that an entire length of the racket frame is L. 20 It is favorable to dispose the vibration-damping member at the antipode of each vibration mode. The antipode of the out-of-plane primary vibration mode is present at an interval of 0.3L to 0.7L from the grip end. The antipode of the out-of-plane secondary vibration mode is present at an interval of O.1L to 0.4L 25 andO.6LtoO.9Lfromthegripend. Therefore todamp the out-of-plane

primary vibration and the out-of-plane secondary vibration, favorably the vibration-damping member is disposed at an interval of 0.3L to 0.6L and more favorably in the vicinity of 0.45L from the grip end.

5 It is preferable that the length of strings stretched on the ballhitting face in a longitudinal direction of the racket is set to not less than 340mm nor more than 420mm.

The string (main string) long in the longitudinal direction of the racket has a high restitution coefficient, thins causing the 10 yoke to be disposed at a lower position. Thus it is possible to improve the restitution coefficient efficiently without increasing theweight/balance. Inthecasewherethelengthsofallmainstrings are in the above-described range, they have excellent restitution performance. But it is possible that at least one main string is 15 in the above-described range. As main strings become longer, the restitution performance thereof becomes increasingly high.

Ifthemainstringhasalengthlessthan3fiOmm,itisdifficult to obtain sufficient restitution performance. On the other hand, if the main string has a length more than 420mm, the length of the 20 yoke becomes shorter accordingly. Consequently the in-plane rigidity deteriorates and the face stability deteriorates.

The racket frame body can be formed of a fiber reinforced resin, a resin, a metal, wood or a composite material thereof. It is preferable to form the racket frame body of a hollow pipe-shaped 25 laminateofprepregs. Athermosettingresinorathermoplasticresin

can tee used es the fiber reinforced resin. The thermosetting resin is more favorable than the thermoplastic resin in terms ofatrength and rigidity. Epoxy resin is particularly preferable. Fibers to be used as high-performance reinforcing fibers can be used as the 5 reinforcing fiber. Carbon fiber is preferable as the reinforcing fiber since it is lightweight and has a high strength. Continuous fibersarealsopreferableasthereinforcingfiber. Thedisposition mode of the reinforcing fiber can be appropriately set. Asa method of forming the racket frame, the reinforcing fiber is wound around 10 a mandrel by filament winding to form a layup. Then the layup is put into a die to fill the thermoplastic resin such as rim nylon intothelayup. It is preferable that the weight of the racket frame on which the viscoelastic material is mounted is 200g to 280g.

BRIEF DESCRIPTION OF THE DRAWINGS

Figs. 1A and 1B are a schematic view of a racket according to a first embodiment of the present invention.

Fig. 2A is a front view showing a vibration-damping member 20 made of a viscoelastic material.

Fig. 2B is a plan view showing the vibration-damping member made of the viscoelastic material.

Fig. 2C is a sectional view taken along a line C-C of Fig. 2A. 25 Fig. 2D is a sectional view taken along a line D-D of Fig.

2A. Fig. 2E is a sectional view taken along a line E-E of Fig. -

2A. Fig. 2F is a sectional view taken along a line F-F of Fig. 5 2A. -

Fig. 3A is a sectional view showing a mounted situation of the vibrationdamping member.

Fig. 3B shows the relationship between a string insertion -

hole of the vibration-damping member and a string.

10 Fig. 4A and 4B are an enlarged perspective view showing main -

portionsofa racket according to a second embodiment of the present invention. Fig. 5A is a front view showing a vibration-damping member according to a second embodiment of the present invention.

15 Fig. 5B is a plan view showing the vibration-damping member shown in Fig. 5A.

Fig. 5C is a sectional view taken along a line I1-I1 of Fig. 5A. Fig. 5D is a sectional view taken along a line I2-I2 of Fig. -

90 5A.

Fig. 5E is a sectional view taken along a line I3-I3 of Fig. 5 5A. Fig. 6A shows a state in which the vibration-damping member made of a viscoelastic material is mounted on the racket frame.

25 Fig. 6B is a perspective view showing the viscoelastic

material. Fig. 6C is a plan view showing the viscoelastic material.

Fig. 7A and 7B show a modification of the present invention.

Figs. 8A and 8B show a modification of the mounting situation 5 of mounting the viscoelastic material on the racket frame.

Figs. 9 shows a method of measuring the moment of inertia in a swing direction.

Figs. 10A, JOB, 10C, and 10D are schematic views showing a methodefmeasuringthevibration-dampingfactoroftheracketframe. 10 Fig. llshowsamethodoEmeasuringtherestitutioncoefflcient of the racket frame.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The embodiments of the present invention will be described 15 below with reference to drawings.

Figs. 1 through 3 show a racket of a first embodiment of the present invention. The racket is used for regulation-ball tennis.

A racket frame 11 of the racket has a string-stretching part (head part) 13 surrounding a ball-hitting face F. a bifurcated throat 2Q part 14 (14A, 14B), a shaft part 15, and a grip pert 16. These parts are in one pipe made of a fiber reinforced resin. A yoke 17 made of a materiel different from the fiber reinforced resinis connected to the racket frame 11 at the throat part 15 to surround the ball-hitting face F with the stringstretching part 13 and the yoke 25 17.

A vibration-dampingmember20 made ofaviscoelasticmaterial is mounted on the string-stretching part 13 like a double yoke by spanning the vibration-damping member 20 over and below the ballhittingfaceFbetweenaleftframe13Aofthestring-stretching 5 part 13 and a right frame 13B thereof, with the vibration-damping member20nctin contact with stringag stretched on the ball-hitting face F. Theviscoelastiomaterialconstitutingthevibration-damping member 20 is made ofpolyether block amide which is a kind of nylon.

10 The flexural modulus of elasticity of the vibration-damping member 20 is 730 MPa.

Supposing that the overall length of the racket frame 11 is L, the vibration-damping member 2Q is spaced by 0.3L to 0.6L from a grip end 16a.

15 In the first embodiment, the vibration-damping member 20 is disposedontheball-hittingfaceFbyspacingitatacertaininterval from the yoke 17. The vibration-damping member 20 is connected to the left frame 13A of the string-stretching part 13 and the right frame 13B thereof by spacing the vibration-damping member 20 at 20 an interval of 0.46L from the grip end 16a. The vibration-damping member 20 is disposed symmetrically not only with respect to the central line of the racket in its longitudinal direction, but also with respect to the ball-hitting face F. In the first embodiment, thelengthofthestringg(mainstring)stretchedinthelongitudinal 25 direction of the racket is set to 240mm to 400mm.

AS shown in Fig. 2, the vibration-damping member 20 has left and right mounting parts 20Aa, 20Ab fixedly fitted on the left and right frames13A, 13Bofthe string-stretching part 13 respectively; and a spanning part 20B integral with the left and right mounting 5 parts 20Aa, 20Ab and interposed therebetween, with the spanning part20B spaced at a certain interval from the front end beck surfaces of the ball-hitting face F. The spanning pert 20B is divided into front and beck portions 20Ba, 20Bb spaced at a predetermined interval from the front and 10 beck aurfacesof the ball-hitting face E (string face) respectively.

A string insertion hole 21 is formed in the gap between the front and back portions 20Ba and 20Bb. The string insertion hole 21 is approximately elliptic. All strings stretched in a longitudinal direction(lOstringsinthe first embodiment) tobeinserted through the yoke 17 are inserted through the string insertion hole 21.

Because the string insertion hole 21 is approximately elliptic, the thickness of each of the front and back portions 20Ba, 20Bb of the spanning part20Bbecomea gradually thinner toward the center of the spanning part SOB. The thickness tl of the stringinsertion 20 hole 21 at the center thereof is set to 2mm.

The length of the spanning part 20B of the vibration-damping member 20 is set to 135mm. The width W1 of the spanning part 20B is set to 14.85mm. The length HI of the string insertion hole 21 is set to 115.0mm. The area where the 'ibration-damping member 20 25 and the string-stretching part 13 are connected with each other

is set to 28cm2. The thickness t2 of the left and right mounting parts20Aaand20Abat which the vibration-dampingmember20 contacts i the string-stretching part 13 is set to tom. The weight of the vibrationdamping member 90 is set to lOg.

5 As shown in Fig. 3, the vibration-damping member 20 contacts aninnersurfacel3aofthestring-stretchinggartl3initsthickness directionEbothsurfaces13b,13cChereofinitswidthwisedirection, and an outer surface 13d thereof in its thickness direction and connectedLoeachofthem.More specifically, aconcavityl3e haying 10 a configuration conforming to that of the left and right mounting part20Aaand20AbisformedonthestringstretchingDart13connected to the vibration-damping member 20. The vibration-damping member 20 is mounted on the string-stretching part 13 with an adhesive agent by bringing the inner peripheral surface of the left and right 15 mounting part20Aa and 20Ab into contact with the peripheralsurface of the concavity 13e. The depth of the concavity 13e is equal to the thickness of the left and right mounting part 20Aa and 20Ab.

The vibration-damping member 20 and the string-stretching part 13 are so configured that no step is formed between the surface of 20 the stringstretching part 13 and that of the vibration-damping member 20, when the vibration-damping member 20 is mounted on the string-stretching part 13.

Theracket frame ll is formedasapipemadeofafiberreinforced resin. More specifically, the racket frame 11 is made ofalaminate 25 of prepregs composed of epoxy resin serving as the matrix resin

and reinforcing fibers of carbon impregnated with the epoxy resin.

Asdescribedabove,thevibration-dampingmember20ismounted on the racket frame 11 by connecting the left and right ends of the vibration-damping member 20 to the left and right frames 13A, 5 13Bof the string-stretching partly respectively. Thus vibrations transmitted from both sides of the racket frame 11 can be absorbed in a good balance by the elasticity of the viscoelastic material constituting the vibration-damping member 20. That is, the racket framell and the vibration-damping member 20 play a role of a dynamic 10 damper. Further the spanning part 20B vibrates readily. Thus the vibration-damping performance can be enhanced.

Because the vibration-dmping member 20 is mounted on the stringstretching part 13 proximate to the ball-hitting face F. the repulsive performance of the strings can be improved. That is, 15 although the vibration-damping member is very lightweight, it has enhanced vibrationdamping performance. Further an increase of a small amount thereof added to the racket allows the strings to have improved repulsive performance. It is possible to set the lengths i of the strings (main strings) to be stretched on the ball-hitting 20 face F in the longitudinal direction of the racket to not less than 340mmnormorethan420mmtotherebyimprovetherepulsiveperformance of the strings.

Figs. 4 through 6 show a second embodiment. A vibration-damping 20' comprised of a pair of vibration-damping 25 members 200 and 201 is spanned over and below the ball-hitting face

F respectively between a left frame of the string-stretching part 13 and a right frame thereof by disposing the vibration-damping member 200 over the front surface of the string g and the vibration-damping member 201 under the back surface thereof, with 5 a gap formed between the vibrationdamping members 200 and 201.

A spacer 30 composed of a viscoelastic material is disposed at a portion of the gap between the vibration-damping members 200 and 201, with the spacer 30 in contact with two main strings g stretched in a longitudinal direction. A convexity 13a is disposed on each 10 of the front and back surfaces of the string-stretching part 13 at a position where the vibration-damping members 200 and 201 is mounted. As shown in Fig. 5, each of a pair of the left and right vibration-damping members 200 and 201 has left and right mounting 15 parts COAa' and 20Ab' to be fixedly fitted on the left and right frames of the string-stretching part13respectively;anda spanning part 20B' integral with the left and right mounting parts 20Aa' 20Ab' and interposed therebetween.

The width of the spanning part 20B' in the out-of-plane 20 direction of the racketbecomee gradually thinner towardits center.

A string insertion groove 20B-1' is formed on the ball-hitting face side of the spanning part COB'. A convexity 20B-2' on which the spacer 30 is mounted is formed at approximately the center of the string insertion groove 20B-1' in its longitudinal direction (weft 25 direction). A pin 20B-3' is projected from one end of the spanning

part 20B' toward the ball-hitting face F. A concavity 20B-4' into which the pin 20B-3' is inserted is formed on the spanning part 20B' at the other end thereof. The concavity 20B-4' and the pin 20B-3' are symmetrical with respect to the center of the spanning 5 part SOB'.

As shown in Figs. 5C through BE, the left and right mounting parts 20Aa' and 20Ab' of each of the vibration-damping members 200 and 201 are bent in conformity to the configuration of the frame of the string-stretching part 13. through-hole 20A-1' is formed 10 at the center of each of the left and right mounting parts 20Aa' and 20Ab'.

When a pair of the vibration-damping members 200 and 201 is mounted on the racket frame 11, a string insertion hole 20C' is formed by confronting the string insertion groove 20B-1' of the 15 vibration- dampingmember2QO and the string insertion groove 20B-1' of the vibration- damping member 201 each other.

As shown in Fig. 6, the spacer 30 is disposed at the center - of the string insertion hole 20C' lo the longitudinal direction thereof. 20 A Vshaped groove 31 is formed at both ends of the spacer 30. A notch is formed at a lower end 31a of the groove 31 to form a concavity 32. In conformity to the configuration of the vibration-damping member 20' (200 and 201), an upper surface 31b of the spacer 30 is gently concave, namely, circular arc-shaped, 25 andalowersurface31cthereofisalsogentlycurved, namely,circular

arc-shaped. In conformity to the configuration of the string insertion hole 20C', a side surface 31d of the spacer 30 in its longitudinal direction is gently curved, namely, circular arc-shaped A groove 31e is formed on the side surface 31d.

5 The length of the spacer 30 is set to 21.11rrn. The width of the spacer 30 is set to 7.65mm. The thickness of the spacer 30 is set to 4.91mm. The length of the groove 31e is set to llmm. The width of the groove 31e is set to 3.61mm. The depth of the groove 31e is set to 1.00mm. In the first embodiment, the complex elastic 10 modulus E* of the spacer 30 is 1. 41X107 dyn/cm2 when it is measured at a frequency of 10 Hz and a temperature of 0 C to 10 C.

The left and right mounting parts 20Aa', 20Ab' of each of the vibrationdamping members 200 and 201 are mounted on the string-stretching part 13, with the vibration-damping member 200 15 disposed at the upper side of the string-stretching part 13 in the out-of-plane direction of the racket and the vibration-damping member 201 disposed at the lower side of the string-stretching part 13 in the out-of-plane direction of the racket. More specifically, the convexity 13a formed on the string-stretching part 13 is fitted 20 in the through-hole 20A-1' formed on each of the left and right mounting parts 20Aa', 20Ab' of each of the vibration-dampingmembers 200 and 201. Further the pin 20B-3, of each of the vibration-damping member 200 and 201 is inserted into the concavity 20B-4' of each of the vibration-damping member 201 and 200. In this manner, the 25 vibrationdamping members 200, 201 are installed on the racket frame

11. The racket frame 11 and the vibration-damping member 200, 201 are bonded to each other by applying an adhesive agent between the racket frame 11 and the vibration-damping member 200 as well as the vibrationdamping member 201.

5 After a pair of the vibration-damping members 200, 201 is mounted on the racket frame 11 in the above-described manner, the convexity2oB2'formedatthecenterofthevibration-dampingmember 20' (200 and 201) and the concavity 31e formed on the spacer 30 are fitted on each other, and the vibration-damping members 200, 10 201andthespacer30 are bonded to each other by applying the adhesive agent therebetween, with the spacer 30 disposed in the string insertion hole 20C' of the vibration-damping member 20'.

The string g is stretched in the string-stretching part 13 in this state. Of all main strings g stretched in a longitudinal 15 direction to be inserted into the string insertion hole 20C' of the vibration-damping member 20', two central main strings g are fitted into the concavity 32 of the spacer 30.

Supposing that the overall length of the racket frame 11 is L, the vibration-damping member20' is disposed on the ball-hitting 20 face by spacing it at an interval 0.3L to 0.6L from the grip end 16a. The vibration-damping member 20' is disposed on the ball-hitting face F by spacing it at a certain interval from the yoke 17. The vibration-damping member 20' is connected to theleft and right frames of the stringstretching part 13 at a position 25 spaced et 0.46L from the grip end 16a. The vibration-dampingmember

20' is disposed symmetrically not only with respect to the central lineoftheracketinitslongitudinaldirectionbutalsowithrespect to the ballhitting face F. In the second embodiment, the length of the string g (mainstring)stretchedinthelongitudinaldirection 5 of the racket is 340mm to 420mm.

The other construction of the racket of the second embodiment are similar to those of the first embodiment. Thus description

thereof is omitted herein.

In the racket ofthesecondembodiment,the vibration-damping 10 member 20' (200 and 201) is spaced at a certain interval from the front and back surfaces of the string g, with the vibration-damping member 20' not in contact with the string g. Since the spacer 30 is disposed between the vibration-damping members 200 and 201, the vibration-damping member 20' is placed at a position where the 15 vibration-dampingmember20' does not contact the string g. Thereby when a ball is hit with the racket, the string g does not contact the vibration-damping member 20'. Therefore the repulsive force of the string g is not reduced.

The spacer 30 is in contact with the string g, thus absorbing 20 vibrations of the string g generated when the ball is hit. Thus the string g has improved vibration-damping performance. Further since the spacer 30 is bonded to the vibration-damping member 20', the spacer 30 and the vibration-damping member 20' display the function of a dynamic damper cooperatively, thus improving the 25 vibration-damping performance. Otheroperationsandeffectsof the

second embodiment are similar to those of the first embodiment.

Fig. 7 shows a modification of the vibration-damping member of the present invention. As shown in Fig. 7A, two string insertion holes 20X and 20Y long in its left-to-right direction may be formed 5 on the spanning part of the vibration-damping member 20. As shown in Fig. 7B, the same number of string Insertion holes 20Z as that of strings may be formed on the spanning part in such a way that each string does not contact the corresponding string insertion hole 20Z.

10 Fig, 8 shows a third embodiment. As a vibration-damping member 20" to be spanned over the ball-hitting face, vibration-damping members 200' and 201' composed of a sheet-shaped viscoelastia materiel are spanned over one side of the ball-hitting face and under the other side thereof respectively in such a way IS that the vibration-damping members 200' and 201' do not contact strings g. In addition to the vibration-damping member 20", a vibration-damping member 42 composed of a viscoelastic material is mounted on the throat part from one side 14A thereof to the other side 14B thereof by spacing the vibration-damping member 42 at a 20 certainintervalfromtheyoke17. Supposing that the overalllength of the racket frame 11 is L, the vibration-damping member 42 is connected to the throat part at a position spaced at 0.36L from the grip end. Similarly to the first embodiment, the vibration-damping member 42 has left and right mounting parts and 25 a spanning part. A hole may be formed on the spanning part or the

spanning part may be hollow.

One of the vibration-damping members 200' and 201' may be spanned over the ball-hitting face, and the other thereof may be spanned over the throat part.

5 The sheet-shaped vibration-damping member may be mounted directly on the inner surface of the string-stretching part and the throat part in the thickness direction thereof or directly on both surfaces of the string-stretching part and the throat part in the widthwise direction thereof without fanning a concavity 10 thereon.

Rackets of examples of the present invention and those of comparison examples were prepared to examine the vibration-damping performance thereof and feeling players had for them in qucstionnairing. 15 The thickness of each racket frame was set to28mn. The width of the racket frame was set to 13 to 14.5mm. The area of the face of the racket was set to 125.1lmm2. The rackets of the examples and the comparison examples had the same configuration.

More specifically, CFprepregs (produced byToray Industries 20 Inc., T300, T700, T80Q, M46J) were layered on a tube made of nylon 66 to form a vertical lamination of the CF prepregs. A mandrel of 14.5 was used as the core of the nylon tube. The CE prepregs were layered et angles of0 , 22 , 30 , and 90 . A die was heated to 150 C.

The inside of the nylon tube was pressurized and kept at 9kgf/cm2 25 by air for 30 minutes. A viscoelastic material or a dynamic damper

was mounted on each prepared racket frame, as shown in table 1.

TheabbreviationPB7233and PB5533shownintableldenotesPEBAX7233 and PEBAX5533 respectively.

O N |

_ ire_ _ _ __ -1 volt 0 m. m r rim us 0 <9 0 Ln _ Inure _ _ _ 11:;; -m v v 0 =' O m r 0 0 0 r _ Boar _ _ _ 0 t: it., C- --i 1 V o 0 o m O 0 O O co L1,.!;, . U

_ Viva _ 1 v v 0 0 o m r us 0 r 0 w 0 U) _ _

'.,. u e 7= ud - a r

a: us 0 rn to an 0 0 rn to - ho -

o o - - - - -

O O rr);r n n cn r r rn o - - co co c) cc) O O) 1

- o o o O r r r o o ;r r.

o o O r U) 4J - --. o h C c O O O 1 O >, _.-

S O oP O q -) h U C C Q O C (U O -- 1 -1 (I - C O -H

1 0 Ll = 4U Q 1 CJ u 0) O) Q -

- - O - -,1 Q 3

O 03 > Q O

: t | N v -a Ir) CSi Oo 1 O O o N to{). r m. a) Fir NIX O Q)

_. _ _ _ _ _

T j o o e = '': o-r=1 O O h h C O OC s h q I C a) 1 C Q) C C 1 O O _ > ql _ 1 1 O O O -,1 CO O C C C.- C

t -- O O O O o\o O o\ -,1.- 1 1 -1 1 ---

u, - - C. - - - h C C C O h: S Y C O O CO O O S O GS O. -. - O. a, t (J > < u tp a' a' 1 U) =, a).- Q Q _,, c 3 E s E Q E o c o o c. o s

Example l

The racket of the example 1 had a construction similar to that of the first embodiment. As the vibration-damping member to tee spanned over the ball-hittingface, a viscoelastic material made 5 of PEBAX7233 (manufactured by ATOCHEM) is used. The thickness of the spanning part at its center was set to l.Omm. The weight of theviscoelasticmaterialwassettolOg. Supposing that the overall length of the racket frame was L, the vibration-damping member was bonded to the gut-stretching part by spacing it at an interval of 10 0.46L from the grip end.

Example 2

As the viscoelastic material, 12-NYLON (produced by Toray Industries Inc., "Rilsan ANN 0", flexural modulus of elasticity: 1100 MPa) was used. The other specifications of the racket were

15 similar to those of the example 1.

Example 3

Astheviscoelastiomaterial,PEBAX5533 (producedbyATOCHEM, flexural modulus of elasticity: 160 MPa) was used. The other specifications of the racket were similar to those of the example

20 1. Example 4

The thickness of the spanning part at its center was set to 0.7mm. The weight of the viscoelastic material was set to 7g. The other specifications of the racket were similar to those of the

25 example 1.

Example 5

The thickness of the spanning part at its center was set to 3.Omm. The weighs of the viscoelastic materiel was set to 14g. The other specifications of the racket were similar to those of the

5 example 1.

Example 6

As the viscoelastic material, 6-NYLON (produced by Unitika, flexural modulus of elasticity: 2500 MPa) was used. The other specifications of the racket were similar to those of the example

10 1. Example 7

Astheviscoelasticmaterial, PEBAX4033(producedbyATOCHEM, flexural modulus of elasticity: 84 MPa) was used. The other specifications of the racket were similar to those of the example

15 1. Example 8

The thickness of the spanning part at its center was set to 0.3mm. The weight of the viscoelastic material was set to 3g. The other specifications of the racket were similar to those of the

20 example 1.

Example 9

The thickness of the spanning part at its center was set to 5.0mm. The weight of the viscoelasticmaterial was set to leg. The other specifications of the racket were similar to those of the

25 example 1.

Comparison Example 1 Avibration-dampingmembertobespannedovertheballhitting facewas not mounted on the racket frame. Avibration-dampingmember such as a dynamic damper was not mounted on the racket frame.

5 Comparison Example 2 Supposing that the ball-hitting face of the racket frame was the surface of a clock and that the top position of the racket frame was 12 o'clock, a two-layer construction damper having a weight of lOg (5g at one side) composed of a matrix of a tungsten sheet 10 and Cepton (produced by Kuraray, styrene thermoplastic elastomer) wasmountedat the position of three o'clockandnineo'clock(spaced by 500mm (0.72L) from grip end).

The vibration-damping factor end the restitution coefficient of each of the racket frames of the examples of the present invention 15 end the comparison examples were measured. Aball-hitting test was conducted by the method described later. Table 1 shows results of evaluation. The flexuralmodulusof elasticity of each racket frame was measured in accordance with A5TMD790.

Measurement of Moment of Inertia 20 As shown in Fig. 9, required accessory parts were mounted on each racket frame. Each tennis racket was hung, with the grip thereof located uppermost to measure the period Ts thereof by an instrument for measuring the moment ofinertia "hereof. The moment of inertia Is in the direction (out-of-plane direction) of a swing 25 which is made about the grip end was calculated by the following

equations, because the moment of inertia indicates the operability of the tennis racket.

The moment of inertia Is in the direction (out-of-plane direction) of the swing which is made about the grip end: Is[g-cm2] 5 Is = MXgXh (Ts/2/)2 The center of swing means the center of rotation of the racket gripped by a player. In the above equation, M is the weight of the racket; g is tile gravity; and h is the distance from the center of rotation to the gravity.

10 Measurement of Out-of-Plane Primary Vibration-Damping Factor As shown in Fig. 10A, the racket was hung with a string 81 at the upper end of the string-stretching part 13 thereof. An acceleration pick-tip meter83wasfixeUperpendicularlytothefrarne surface at one connection point between the string-stretching part 15 13 and the throat part 14. As shown in Figs. JOB, in this state, the other connection portion between the string-stretching part 13 end the throat part 14 was hit with animpact hammer 85 to vibrate the racket frame. An input vibration(F)measuredbya force pick-tip meter installed on the impact hammer 85 and a response vibration 20 (a) measured by the acceleration pick-up meter 83 were inputted to a frequency analyzer 87 (dynamic single analyzer HP3562A manufactured by Fuhret Packard Inc.) through amplifiers 86A and 86B. A transmission function in the frequency region obtained by an analysis was calculated to obtain the frequency of the racket 25 frame. Thevibrationdampingratio()oftheracketframe,namely,

the out-of-plane primary vibration-damping factor thereof was computed by an equation shown below. Table 1 shows the average of measured values of the racket frame of each of the examples and the comparison examples.

5 = (1/2) x (in) To = Tn/12 Measurement of Out-of-Plane Secondary Vibration-Damping Factor AsshowninFig.10C,withtheupperendofthestringstretching part 13Ofthe racket of each of the examples and comparison examples 10 hung with the string 81, the acceleration pick-up meter 83 was installed on one connection portion between the throat part 14 and the shaft part 15, with the acceleration pick-up meter 83 perpendicular to the face of the racket frame. In this state, the rear side of the racket frame at a portion thereof confronting the pick-up meter-installed position was hit with the impact hammer 85 to vibrate the racket frame. The damping factor, namely, the gut-of-plane secondary vibration-damping factor of each racket was computed by a method equivalent to the method of computing the out-of-plane primary vibration-damping factor. Table 1 shows the 20 average value of the measured values of the racket frame of each of the examples and the comparison examples.

Measurement of Restitution Coefficient As shown in Fig. 11, the grip pert of each of the racket frames of the examples and the comparison examples was hung in such a way 25 that the racket frame was free in a vertical posture. A tennis ball

waslaunched from aballlauncherat a constant speed ofVl (30m/sec) end collided with the ball-hittingiace to measure the rebound speed V2 of the tennis ball. The restitution coefficient is the ratio of the rebound speed V2tothelaunched speed V1 (V2/V1). Thelarger 5 the restitution coefficient, thelonger the tennis ballflies. The restitution coefficient of each racket was measured at the center of its ball-hitting face, at a position (X) lower by 80mm from the center of its ball-hitting face, and at a position located at the side of the position (X) and spaced by 50mm from the position (X).

10 The restitution coefficient shown in table 1 is the average value of the three restitution coefficients. That is, the restitution coefficient of each racket frame was measured at the three points thereof. Evaluation in Ball-Hitting Test 15 Toexaminethevibration, flightperformance, andoperability of each of the rackets of the examples and the comparison examples, questionnairing was conducted on fifty middle-class and high-class players who hit balls and gave any one of one mark to five marks (the more, the belter) on the above items. The prayers had not less 20 than 10 years' experience in tennis, and play tennis not less than three times a week. The average of the marks the 50 players gave was computed.

Asindicatedintablel,thepositionsofthevibration-damping members mounted on the racket frame of the examples 3 and 4 and 25 the comparison examples 1 and 2 were compared with one another.

As the vibration-damping member of the comparison example 2, the twolayerconstructiondampercomposedofthemetalsheetwasmounted at positions in the vicinity of the center of the ball-hitting face and was not spanned (spanning construction) over the 5 string-stretching part 13.

The racket frame of the comparison example 2 and the examples 1 and 2 had the effect of the dynamic damper. Thus they had a vibration-damping factor higher than the racket frame of the comparisonexamplelineachvibrationmode. Sincetheracket frames 10 other than that of the comparison example 1 had an increase in the weight thereof, they had improvement in the repulsive performance thereof. The vibration-damping member of the comparison example 2 was disposed in the vicinity of the top position of the racket frame. Therefore the racket frame of the comparison example 2 had 15 a large moment of inertia in the swing direction and thus a low operability. The racket of the example 2 had a higher vibration-damping factor than the racket of the comparison example 2, because the racket of the example 2 had the construction in which the 20 vibration-damping member was spanned over the ball-hitting face.

The racket of the example 3 had a higher out-of-plane secondary vibrationdamping factor than the racket of the comparison example 2. The racket of the example 3 had a more favorable result than thatofthecomparisonexample2intheball-hittingtest. Therefore 25 itispreferable that supposing that the overalllengthof the racket l 3g

frame is I, the vibration-damping member is spaced by 0.3L to 0.6L from the grip end.

The extents of vibration of the viscoelastic materials of the examples 1, 2, 3, 6, and 7 having the same weight (leg) were 5 compared with each other according to the differencein the flexural modulus of elasticity thereof. The racket of the example 6 having a comparatively high flexural modulus of elasticity and the racket of the example 7 having a comparatively low flexural modulus of elasticity were superior to the racket of the comparison example 10 1 in the vibration-damping performance thereof, although a little inferior to the rackets of the examples 1, 2, and 3 in the vibration-damping performance thereof. The racket of the example 2 having a comparatively high flexural modulus of elasticity of 1100 Mpa had improvement in its out-of-plane primary 15 vibration-damping factor. The racket of the example 4 having a comparatively low flexural modulus of elasticity of 730 Mpa had improvementinitsout-of-planesecondaryvibration-dampinsfactor. Therefore it is preferable that the flexural modulus of elasticity of the viscoelastic material is not less than 100 MPa nor more than 20 1500 MPa.

The vibration-damping performances of the rackets of the examples 1, 4, 5, 8, and 9 made of the same viscoelastic material (PB7233) were compared with each other according to the difference in the weight thereof. It is considered that it is difficult for 25 the frequency of the v1scoelastic material of the example 8 thin

and light to match the frequency of the racket frame. Thus the viscoelastic material of the racket of the example g was inferior to the viscoelastic material of the racket of the examples 1, 4, 5,and 9 in the gut-of-plane primary end secondary vibration-damping 5 factors thereof, but was superior to the viscoelastic material of the racket of the comparison example 1 in the out-of-plane primary andsecondaryvibrationdampingfactorsthereof. The viscoelastic materialoftheracketoftheexampleShadlowerout-of-planeprimary and secondary vibration-damping factors than the viscoelastic 10 material of the racket of the comparison example 2 having a weight of log. However, since the viscoelastic material of the racket of the comparison example 2 was lightweight, namely, had a weight of fig, the viscoelastic material of the racket of the example 8 had excellent vibration-damping member.

Theracketoftheexamplesl,g,5,and9havingalargethickness had improved vibration damping factors. The racket of the example 9 which was heavy had excellent vibration-damping effect but had a large moment of inertia and hence low operability. Therefore it is preferable that the vibrationdamping member has a weight not 20 less than 4g nor more than leg.

Rackets of examples of the present invention and those of comparison examples were prepared to examine the vibration-damping performance thereof. A spacer was interposed between a pair of vibration-damping members spanned over the ball-hitting face of 25 each racket.

The racket frame of each of the examples and the comparison examples had a thickness of 28mm, a width of 13 to 14.5mm, and a face area of 125.11 in2.

More specifically, CFprepregs (produced byToray Industries 5 Inc., T300, T700, T800, M46J) were layered on a tube made of nylon 66 to form a vertical lamination of the CF prepregs. A mandrel of 614.5 was used as the core of the nylon tube. The CF prepregs were layered at angles of 0, 22, 30, and 90 . A die was heated to 150 C.

The inside of the nylon tube was pressurized and kept at 9kgf/cm2 10 by air for 30 minutes. A viscoelastic material similar to that of the second embodiment was mounted on the racket frame at a position spacedby325mm(0. 46L) fromthegripend. Theviscoelasticmaterial was formed by molding PEBAX7033 (produced by ATOCHEM). The vibration-damping member of the examples 10 to 13 shown in table 15 2 was identical to that of the second embodiment.

0 m+ u 0 0 Àn o R O:1 N O O O

+ x m 0 U] U _ _ _ _ _ N C: x m 0 c N r 0 _ C u C 0 0 _ U) _ U _ _ 0 0 O C1 cvl O O O N r r m | 5

r w r - 1 E c 0 c N 0 r N O u) C C C C O O O ( X -- 3. 0 0 0

u' s u c:. _ _ _ _ U 1 _

u rG 0 O rO 0 v' 0 O O 3 U Qu Q U Q Q O Q4 -a -(r >ra '>m '> '>-

E: U oO a O 1 O O 1 O

O =:.= O S

v' a) a) oo c:: a, a, C X

a) 0 >1:: a) 0 S O C1, O

X 4 1 1.- X 1 1.- O

u q s q C 4 v' O O O O.-

O, E: O.- s c =--.Q =-- 4J s Q -O O s.- .- O O 3 3 a). .=. U _ _ O Q 0 v' u,.. O O O Q O v, _ O C C.- 4 cn 3 o 4 4 c.= -4 q C U) o o V) o o ,1 O O O O - -

N I tt 0' -,- 4J -1 tl CD.- 4) - 1 C) a' a' 4J (J Q) o S l S::, 1 O S S t 3 1 O) 0 Q) s a' 1 Q V] -,' Q U) -,' Q

a a' ra,- > ra.- :> R5 s E _ t> _ _ 3 Q _ O} Q _ _ _ Q _ 0) 3

À Example 10

A spacer made of silicone rubber was bonded to the central portionofavibration-absorbingmaterial,withthespacerincontact with strings.

5 À Example 11

A spacer composed of lOOparts by welghL ofstyrene butadiene rubber (SBR) and 1.5 parts by weight of sulfur was bonded to the centralportion ofa vibration-absorbing material, with the spacer in contact with strings.

10 À Example 12 A spacer composed of 100 parts by weight of styrene butadiene rubber (SBR), 40 parts by weight of carbon black, and 1.5 parts by weight of sulfur was bonded to the central portion of a vibrationabsorbing material, with the spacer in contact with 15 strings.

À Example 13

A spacer composed of 100 parts by weight ofstyrene butadiene rubber (SBR), 60 parts by weight of carbon black, and 1.5 parts by weight of sulfur was bonded to the central portion of a 20 vibration-absorbing material, with the spacer in contact with strings. À Comparison Example 3 A spacer was not installed at the central portion of a vibration-absorbing material.

25 À Comparison Example 4

A spacer composed of PEBAX 5533 was bonded to the central portion of a vibration-absorbing material, but the spacer was not in contact with strings.

The vibration-damping factor end the restitution coefficient 5 of each of the racket frames of the examples 10 through 13 and the comparison examples 3 and 4 were measured. A ball-hitting test was conducted. Table 2 shows results of evaluation.

The method of measuring the out-of-plane primary vibration-damping factor and the method of measuring the 10 out-of-plane secondary vibrationdamping factor were the same as the above-described measuring method.

As shown in Fig. lOD, with a string stretched, the upper end of the head part 13 was hung with the string 81. The acceleration pick-up meter 83 was fixed perpendicularly to the face of the frame 15 at one connection point between the throat part 14 and the shaft part IS. In this state, with the impact hammer 85, vibration was applied to the string et the center of the head part13. The natural frequency of the string was obtained in a method similar to that for measuring the gut-of-plane secondary vibration-damping factor.

20 Table 2 shows the natural frequency of the string of the racket of each of the examples and the comparison examples.

* À Evaluation of Ball Hitting To examine the vibration-absorbing performance of each racket, questionnairing was conducted on 42 middleclass and high-class 25 female players who hit balls and gave any one of one mark to five

marks (themore, thebetter). TheplayershadnotlessthanlOyears' experience in tennis, and play tennis not less than three times a week. The average of the marks the 42 players gave was computed.

In the comparison example 3, the spacermade of the viscoelastic 5 material was mounted at the center of the vibration-absorbing material. The vibration-clamping factor of the frame was not good because the spacer restricted the vibration of the vibration-absorbing material. The string did not have a good vibration-damping factor because the spacer did not contact the 10 string.

In the racket of the comparison example 4, the string had a vibrationdamping factor a little higher than that of the racket of the comparison example 3 because the spacer contacted the string.

However, a vibration-damping factor of the racket frame was lower than that of the comparison example 3 because the spacer restricted the vibration of the vibration-absorbing material.

The racket of the example 10 had the highest out-of-plane primary vibration-damping factor, since nothing was disposed at the central portion of the vibration-absorbing material. However, 20 the string had a low vibration-damping factor since the viscoelastic material was not mounted on the Packet frame.

Because the comparatively soft viscoelastic material was disposed at the central portion of the vibration-absorbing material of the racket frame of the examples 11 to 13, the out-of-plane primary 25 vibration-damping factor and the vibration-damping factor of the

string of the racket of each of the examples 11 to 13 were lower than those of the racket of the example 1Q, but were higher than those of the racket of the comparison examples 3 and 4.

As apparent from the foregoing description, according to the

5 racket of the present invention, the vibration-absorbing member made of the viscoelastic material is spanned at front and back side of the ballhitting face by connecting the left and right ends thereof to the left and right frames of the string-stretching part respectively. Thus vibrations transmitted from both sides of the 10 racket frame can be absorbed in a good balance by the elasticity of the viscoelastic material having an appropriate flexural modulus of elasticity. That is, the racket frame and the vibration-damping member play the role of a dynamic damper. Thus the vibration-damping performance can be enhanced.

15 By disposing the spacer in the gap between a pair of the vibrationdamping members spaced at a certain interval from the front and back surfaces of the strings respectively, with the vibration-damping members not in contact with the strings, the spacer serves as a means for placing the vibration-damping members at a 20 position where the vibrationdamping members do not contact the strings. Therebywhen a tennis ball is hit, the strings do not contact the vibration-damping members and the repulsive force of the strings is not reduced.

The spacer made of the viscoelastic material is in contact 25 with the strings stretched in a longitudinal direciton. Thereby

the spacer absorbs vibrations of the strings generated when the ballishit, thusimprovingvibration-dampingperformance. Further since the spacer is bonded to the vibration-damping member, the spacer and the vibrationdamping member display the function of 5 adynamicdampercooperatively, thusimprovingthevibration-damping performance. By forming the spacer of a material more elastic than the material for the vibration-damping member and adjusting the elasticity of the material for the spacer, it is possible to improve 10 the vibration-damping performance of the spacer and adjust the vibration-damping performance of the racket frame.

In the present invention, since a mass-adding material such as a weight is not mounted on the racket frame. Therefore the vibrationdampingmererislightandhasenhancedvibration-damping 15 performance. Further by forming the viscoelastic material of a materialdifferentiromthematerialcomposingthestring-stretching part, ashearforcageneratedwhentheracketframedeformsisabsorbed by concentrating the shear force on the connection surface of the racketframeandtheconnectionsurfaceoftheviscoelasticmaterial. 20 Thereby the vibration-damping performance can be enhanced.

Claims

WHAT IS CLAIMED IS:

1. A racket whose frame is formed in one piece comprising a stringstretching part surrounding a ball-hitting face, a bifurcated throat part, a shaft part, and a grip part; and a yoke 5 mounted on a portion of connection between said string-stretching part and said throat part r wherein a vibration-damping member for the ball-hitting face spanning made of a viscoelastic material is mounted on said string-stretching part by spanning said vibration-damping member 10 over said ball-hitting face between a left frame of said string-stretching part and a right frame thereof, with said vibration-damping member not in contact with said strings stretched on said ball-hitting face.

2. The racket according to claim 1, wherein said 15 vibration-damping member to be spanned over said ball-hitting face comprises left and right mounting parts fixedly fitted on said left frame of said stringstretching part and said right frame thereof respectively;anda spanning part, integral with saidleft end right mounting parts, disposed between saidleft and right mounting parts, 20 wherein said spanning part is divided into front and back portions spaced at a predetermined interval from front surface of string faces and back surfaces thereof respectively; a string insertionholeisformedina gap between said front end beck portions of said spanning part; and all strings stretched in a longitudinal 25 direction to be inserted through said yoke are inserted through

said string insertion hole.

3. The racket according to claim 1, wherein one of a pair of vibrationdamping members is spanned at front side of said ball-hitting face and the other of said vibration-damping members 5 is spanned at back side of said ball-hitting face, with a gap formed between a pair of said vibration-damping members; end a spacer made of a viscoelastic material is disposed at a portion of said gap between said vibration- dampingmembers, with said spacerin contact with at least two strings stretched in a longitudinal direction.

10

4. The racket according to claim 3, wherein said spacer interposed between a pair of said vibration-damping members is disposed at a central portion of a ball-hitting face where said spacer does not interfere with strings stretched in a latitudinal direction. 15

5. The racket according to claim 3 or 4, wherein a complex elasticmodulus E* of a viscoelastic material composing said spacer is less than 2.00X109 dyn/cm2 when said complex elastic modulus is measured at a frequency of 10 Hz and a temperature of 0 C to 10 C.

6. The racket according to any one of claims 1 through 5, 20 wherein a vibration-damping member for the throat spanning composed of a viscoelastic material is spanned between a left frame of said throat part and a right frame thereof by spacing said vibration-damping member for the throat spanning at a certain interval from said yoke or by laying said vibration-damping member 25 for the throat spanning on a surface of said yoke.

7. The racket according to any one of claims 1 through 6, wherein said vibration-damping member is mounted on said string-stretching part or said throat part by spacing said vibration-damping member at an interval of not less than 0 3L nor 5 more than 0.6L from said grip end, supposing that an entire length of said racket frame is L.

8. The racket according to any one of claims 1 through 7, wherein said vibration-damping member has a flexural modulus of elasticity not less than 100 MPa nor more than 1500 MPa.

10

9. The racket according to any one of claims 1 through 8, wherein said vibration-damping member has a weight not less than 4g nor more than 16g.

10. The racket according to any one of claims 1 through 9, wherein a length of strings stretched on said ball-hitting face 15 in a longitudinal direction of said racket is set to not less than 340mm nor more than 420mm.

11. A racket having a frame with a grip part, a shaft part, a bifurcated throat part diverging from said shaft part into left and right-hand frame parts which merge into each other opposite said bifurcated throat part, with said bifur-

cated throat part and said left and right-hand frame parts forming a head part of said racket, said head part being adapted in use to support strings forming the stringing of the racket, there being a vibrationdamping member for the head part of the racket extending between said left and right-hand frame parts.

12. A racket in accordance with claim 11, wherein said grip part, said shaft part, said bifurcated throat part and said left and right-hand frame parts are integrally formed of a composite material.

13. A racket in accordance with claim ll or claim 12, wherein said vibration-damping member comprises a visco-

elastic material.

14. A racket in accordance with any one of the claims 11 to 13, wherein said vibration-damping member extends on opposite sides of said head part.

15. A racket in accordance with any one of the claims 11 to 14, wherein said stringing comprises longitudinal strings extending essentially parallel to said shaft part and transverse strings extending between said right and left-hand frame parts and wherein said vibration-damping member is spaced from at least some of the longitudinal strings of said stringing.

16. A racket in accordance with claim 15, or in said vibration-damper includes a spacer member disposed between said left and right-hand frame parts and contacting at least one or several central longitudinal strings.

17. A racket in accordance with any one of the claims 11 to 16, wherein said vibration-damping member is bonded to said right and left-hand frame parts.

18. A racket in accordance with any one of the preced-

ing claims 11 to 17, there being a yoke part joining diver-

gent limbs of said bifurcated throat part and forming part of said head part, said vibration-damping member being disposed adjacent to and generally parallel to the yoke part, but spaced therefrom.

19. A racket in accordance with claim 18, wherein some of said longitudinal strings pass through said vibration-

damping member to said yoke part.

20. A racket in accordance with claim 19, wherein no transverse strings are provided at said head part between said vibration-damping member and said yoke part.

21. A racket substantially as herein described with reference to and as illustrated in the accompanying drawings.