GB2393129A - Sports racket - Google Patents

Abstract

A racket frame comprising a head, a shaft, a bifurcated throat and a connecting yoke 17 across the throat is equipped with a vibration-damping mounting for the stretched strings S. The mounting comprises a viscoelastic member 20 placed where the vertical strings are longest, on the outside of either the yoke 17 and/or the crown of the head, and preventing direct contact of the frame with a curved plate member 30; the strings S pass through opening(s) in the frame and the elastic member 20 and are wound round the plate 30 via string holes 32. The openings 17a and 21 may each receive a plurality of strings so that the degree of freedom of movement of the strings S is increased for better rebound performance. A twin-yoke embodiment, Fig 9A (not shown) may have a through hole for strings in the upper yoke, and the vibration-damping mounting on the outside of the lower yoke, nearer to the handle and grip.

Description

( .cr. 23931 29 iAr.;KGROrvi,!D OF T'J:E IL.v'i'.ITION =_,...e -..--e._ -.

T'-= 'ese.:-i.;Ai-..-:'e-As..= -_;'e- a..;-.-.--- _ _, 5 a racket tv be sed for regulatio,i.-ball teiir.is, bact,,ir.tc.., and s--as:. '-;e 'ese.. t intvrent o-. is ir..ene tc enina.r._e che vration-ampiny ue..-:or,,ance o the racet a.v t..e r.-bon e__ r:C_..e - r A __ - \d'V' - _ cJ 1 _._ v yr " r __ÀST_ v of a strTr.g-supporting portion ^' the ra_ket.

10 rescriotion of the Reated Ar.

I,.recent years, the racket far.e is der.andedLo have a ght weight, and a high rigidity, strength, and d=aoility. The.ioe- I reinforcev resinis the most popularmaterial for the racket frame.

Normally the racket frame is formed by molding a thermosetting :- es n re nforce with - fiber sc" as a ca-^cn fiber having a high s,... .:.. _... s. _ s.

he fiber reinforce -esiri con a,....y t"e c;.er,mase-.i..y resi-.as s.r. a_ri.res ninasahlybrgidit-,a,rebo,,-.erf^r.n.ance, bttheeiberreinfccedresirisapttovibracower.itissvJec.ed c a shvc'., t;.us csi-.g a er..-: 5 piaye- -. sfer frvm e.n s e bow.

=^ ovrer_v.'^.e -^.e ?-cb_e.nm,.n ece-.t ea-s, -.e- is pr!ose a raci.-.et frame corr.pose;^ of a fiber-reinorcethermovlas.ic -esn ^.-se.-._ r:- -s-. -s S5 -^.e-m.-,p_.s res r. s-er_s -

-r r _ ',.i a;-- G r r' r.. a r.,.1:ns, e,f: r:_ n i<,e

( cvrsists o c^ritincs -icers..:o-e spec_f _al i'y'' S..e -_be -ei-.f.,-. ei resin cortainir,.y the tnerrn^ ast c rcs_-., pol,arride esi..s sed as À e m-.a r: r*s r., a:d:-e _ ti..c s.ibe-s o short fibers are Jsed as -,h reinorcirig fiber.

_ The -ac:e frame made o- the be-e orceit er.mo?las,ic resir.re.le.s a high t_ughness, t.hvs pr^vicling characteristics si_:r.ssa.;..c-res s. an_e tc s-.o_-,..;-.ah-.gr.c--v- bra- o-.-;ia..p--.

2e-formance than he conver.tiona -ac'.et frame.iave o- the therrcseht-in. g resin.

O Hoever, the thermoplastic resin de?ends on arienvriro.n.ent for its e ast c rod '1:is and st-enyth.- a.-iybe. e.tent tha.n. tr.

thermosetting resin. Thus in dependence vn environme.lt in hich the racket frame is used, the characteristic of the thermcplastic resin such as rigidity is liable to change.

_. r'.''iii t i C in _ O COrr p t.; W 2 Ferrtal e a' d se. i or p2 a,e-s' e.ma.-ds of:n tir a bali a l^nJ d_srarce w_t- a smal p^-..er, pe.b.lit a-. d reLv ni per--r..ar.ce cf a racr.e are r eyarded as Mpvr 24- t.

Th,srhe racket isdesiredLobemoeanm.no-ellyhtweiht (decrease c.rmomen of nertia) a..d have a hlyLer reLvvnd peforma..e.

2- The ball-hittiny face of tn.e racket fo- comr?eitos is derair.ded -o be slab e. I. '-.as bee.. -e-ea.ed rece... j ha the rigid t;inthein-p anedirectio.is ani irporaint.Fact_- Fo- r.ak..g --.e a''-..ace s-ab:e.

ia._ lA i,r- tirie."'S 2 <^S __ '_ e.;-:_-. ti.e ;__-- _ -:.;i.-.._-.e r _..=!' _ i;.. _ _ r i. e,..i=-__= r _,

( of he raicet r- e, there are ^cpGe-i r c..ets,, À^r,r '' C6 a stri<.4-s?porti.,iy ? ' O'| is poviie;.J't r 2 i C i. '_i a T.p i i -. g e' -A ce.

he s r ng re e_. on me.,rAe- as 5-O;;i-i - i-. i yr. " d S_' -Se.-i 5 inJapanese PatentApplicatior.=aid-OpenNo. S-lC7952 isdescried belo^. TAe str_n-, ?rCect on me.;rer 1 in-i_-ies a pl.Aality of strirg_nse.to.._y iniria'po-.ivri,-..wh c,istr-r.gSisi.lser.ed and a be 1 r vcr io. 3 _on.. e r.g the cyl inJi-' ca p_ r. n S, À v eac'.

Other. The belt portion 3 has the upper laye' 3A a.nd the lower 10 layer 33. A concavity is formed on tre pper aver 3A. The pper layer 3A is overlaid on the lower layer 3B to orm a throuc,h-ho'e 4. I.. the string protecticn merbe- 1 having his construction, the through-hole 4 absorbs shocks applied to strings S when a ball is hit, thus enhancing the v-. bration-damp.ng cericrmance of the 15 racket -rame. ecause the 'o..er a, er 3B is rr,ore elastic than :"e -,e 3, r. e _:i=' e' 3- r, S '' S,r_ S,r, .' C >: S, r ro _ i to the strings S. t.n.us further enhancing tAe vibraticn-da.T.pi..

perEcrmancetherec. The'pperaer3Ais.m2veof 2 r'' i.m..ateria_ to enha..e the rebound performance of the racke', frame.

20 The string protection me.mber i absorbs vioraticns o the strings when the ball is hit. Damping of the vibration cf the racke -ra.me is rCr considere'. hat s rhe erring.oie_i.i n e,,be. ' s.r.-acac'e,c SG=-;C'I., e-.la..- ': i,, _ v r,, _.> _.... e. r,!'.; 2'2 _ _.-...; tr.e' beca=e <e s-.ri ^-e - r=._e' -s t'=

( !_6r0'y-;-itO_e A' 2r'e s-i.^g votec-r.c.me- ' haa a vw s re^.gh ar.en_e m..ay be hroken.

j,v- v..-E!..-i C. 5 The presen invention;.as been mae in v-iew v- _he acove-esc bed prole.s. ''hs, - s an cb-,ect o te present inven o. to v oiide a ra_ke.;.at s si,ve-ior in ts ibra cr.-vampng verfor,m.ance, tigh. weg;, staole.- -s rigidity, and high in its rebound perform.ance.

10 rO achieve the object, accordiny to the resent inven,ior,, tAere is provided a racket having a acket fram.e inc'''9ing 2 heai part; a shat part; a bifurcated throat pat connecting the head pert end the shaft part; and a yoke both ends of which are connected w.h the throat part. Strings are monted Gn a string-streching 5 secTivn ircldi..g -e hea' pa-- a-_;ne, oe a-..d surro,ri.ng --' ^-' -- -- - ace bys re-cr r.g-es:r -.gs. n:-s_ons-r -, a plate-shaped memer is r..ounted on an outer surace of the s='ing-strehc.ir.y, sect cn at a pcs tion -.^erec. wnere a longes_ main s, ring is disposed, with a v7iscoelastic mem,hver intervosed 7 <etweer.-;-e ycke and t:n.e plate-sr.aped.e.m.er; a.-d -.e st.ings are stretchedinthestring-stretchingsectionLyinserting'hestrings -'r:oJ- -,.^e rvrisc_e:as",ic.e.,ce ard w..din he s-r r.gs ro Àn,- ar.

O,'er s'-ace c= the ?2'ate-sh.aped m.ember.

_.. = -., a. _._..,... c. _ _..' _._.. -..... i _ _ _ a _.,.. _:: 2_ -,-. est; s Fe,o.- at a n, - '.= '.,,in. a t - e.ea';,r -,=

( tor,j. rhe iscoe-as i_.,e.mber a..d n e p'ate-sr.aped.;e.;ber a' be mounted at botn. te -,oke an t.h.e cro.,n or at eiher he o'e o- _;,e _rcn. ,:.e- he;er. ca_ s-r.-.gs r,, be.,,:-.-d;- rec-.

B-tprererably,t.n.evris_oelastc.m.e;;berandheplate-shaped.;e.m;Lber 5 are. ;,onted a...e y ke.

-his s be.-=use by m;;ou-.'r.g tne viscoe'ast -.;.erer and he plate-s,. apedmemve. n lle yoke close to tcleposit.cr?o? t;-le _enier of?ravi yothec;-e. rarn;e, tiSpQSS iQ1 ecreducebad.r. ue.^ce oftheviscoelasticmemberandthep'ate-shapedmemberontheT,leight 10 of the racket fr=.m,e and the bala..ce.

The vscoe'astic member is sheet-shaped to contact it',vith the strTr.gstretc;.ing section. The plate-shapedmember-'s 'orme of a risid material. The plate-shaped merrber is not in contact or onr.ecticn.i:.h,he stri.;gstrechng sectio.n but has a 15 corfiuation sir.. lar to tie outer suface of the riscoeast__ eriAe 0 co-ver --he o_:er s_rfa_e -.^ereo-. he.e-.-a s- -s are inserted into the viscoelastic mernbe- and the plate-shaped merrber hro-gh. s- ns holes orme<4 theeon.

Ir.the racket having the above-described co..structio.., t;.e 20 plateshaped.n;e.r.ber is layere< on the is_oelasic m.e.mher so ha the vis_oelastic.,;ember and the plate-s.aped merrber constitue a siny protec n.m,em.erandse--vreas a d,r.a.m;ic ar;pe-. As--ir.-

inser.-or. cyi-^r se_ grGie t -'s. D t D;..^ r.-Agr a'ly,_-. r : ' '' i ?. -. À r.. e_-s ?_ ;,;. _ a __ _ _ ____.__ _. _._ _ 25 and the plate-sh=ped.rre.m.?-r nct ^n as tee r?'ommei -Dr g i i;..:

( he ' r.ys oy ir.ser -r.g rhe s -i. s h-!C_''''' he ra_Ke. '-ame ar.;i h hm;.-= 1 h; - rqerhQ r _ J. S__ S C,.L.,_.

3 i..-e-?vs ny -.-.e.'T. s__e as.._:G.mbe- ^e. ween -he piate-s.^aped rfember made cf the ig d mete rise andi the 5 str nv-stre.hintysec.ior,i. such avvat..a. --e vate-shavecimember is not co-.n.ectedtvvith the sh ring-strerchTi-i!ysectior., t s pcss b'e _. _ _.. ... _

o; ra-.ali__ cl -.!al_e __=.,_.;_ at..-S c..; a....03_..-e gererated vvLen a ball is hit to the viscoe'as.ic...errber an ' tra..sr.it hhe tensile force uniformly ^ the risccelastic merbe'.

10That is, theviscoelasticmemberand the plate-shapedmernber tor. the dl. lamic dampe, and he rriscce_asti- memnver serves as a spring, thereby absorbing vibrations and damping the vibrations.

At ieast one part of the string holes formed on the racket frame,,he viscoelas.ic member, and the plate-shaped meler is 15set _-qer than other st- r!y h es. r.e o_ ? -a' ' of st-.-gs rm r= I - r i ns= - '=,J,; nt h mc, ' -= rr= r sh r; nr 1 CS J _ _. À._ .. _ _ _ y _ _.....

The ra_ket cf the p.eser.. i.^er.tior. is no' proided.vi,h the gro.m.um.. et mounted on the conventional string protecion me.m.=cr.

Thus t s ossible o a'lvr i:.e s. - ng -_ move i.. a v de ra..ge 20 vher. the ball is hit and hence im-ove the rebound performance thereo'. The -_' low.nq rbree r.ethd a-e ccne.ntioral 1r adcp-e as a;eans -or m?o- r. t;.e re _nd,erf.'r,a.e O '- _IlA racker.

r r;--:5...,..>* O_.f=' -_.=. a ':. ctS-;_ *i j_..f 2),m rle n c r i ne r t ia.

( :6 Ike area of the face o- the racket s i-creased.

:( Theot-of-oiane rigiditlisincreaseia-.dthein-piar,erigidity 5 e,eased.

.oweve, tr.eraehvv j: causes reduc' on 0 "he o?erabi i i 5 of the ra_.et frame and is incapable of mating the racket frame lightweight. hemethvdi in_reasestreweiaLtv tneracketrame - and the moment of inertia, thus deteriGrain he operate _.ty-.

The.metnca:ó causes the isyering conarruccion and sect-one configuration to be altered. In the case here the racket frame 10 has a high elasticity, it has a low strength. In, t;.e case where the racket frame has a high strength, its weight increases.

On the other hand, according to the present invention, the viscoelastic member and the plate-shaped member are disposed at a port-on where the weight of the racket frame and the balance 15 treeo are r.o- affected adversely,, r.ame2y, a portion where the i.'.r.=S:.'--___-- S--_!'-, is _ spouse''. -re'2-oe _-e above-described problems do not occur and the rebound pe-for.mance of the racket can be imp-3ved.

Themountingpositior.of the yokels shifted toward the shaft 20 side of tr. e throat part. r.adiit-;on, a yoke-shapei memwer.made o' a vibra.ion-da... ping material s mounted on the head paint by p acting:he oe-shapedrer. herat a pcs_- o..ir.wari-r m t:.e,oke.

B to ends o; the yGke-shaped r,erbe are contin,is with -.h^ L '.L''_-''' 1.:_.-.__'^'-_-;G''';''.et_.'..-_v'\_2,. S a, 3 I', *- 2-.C1S -;\r'' i''. em.

25.. hole -ross..is lord Is torAmi;ei on. tee;,cke-s"apei meter. I

this acket, t..e,errica_ st- ngs;S are< scsev o-.the hea part bl insert ing them r,n roJhthestir.g..o'e^=..e,oke-shapedmem.ver, mon-.g -.e v_.ie. s- _.ee- an t:A.e _ s..aped me.er s-.

the yoke disposed et.heshaftsdeaft;-etA.r,at part,ar.di..se--ng 5 -he ertical strings t..ere n..

In this cor.str,_tior., the yoke-shaped.me.,ber as well as the yke ar,sv-s i'.-a. _.-s;, -;.e s.rl.gs,..-;iis er,;.ancir.g.-e vibration-damping performance of the rac.et rame.

It is preferakle rhat vertical strinyscisposed at both ens 10 of the yoke in a longitudinal direction t..ereof are round round an outer surrace cf t..e plte-shaped.m.el-.^er, wit:n the ve-tca stringsincontactrithbothendsurfacesoftheviscoelasticmember and the plateshaped member in a lor.gitudi-.al direction thereof; and other vertical strings clisposed between the vertical strings t dispose_ a- o h ens o_ t. -e ',,eare nser e--.rA_gh st-in- -oles ormed on:n.e s_celast c me:^er ani the pA1 a-e-shaped mem.ber.

This cons -uctior. allows he nurnoe _ string Aoles o be formed on the v'scoelastic member and the plate-shaped member tc besmalla..ihencee.. AaAicest:-ies.re r. (A) l- _1ie p_ae-shapemeiie-.

20 It s preferable -hat in the p'ae-sha?eAo member, a portio-.

thereo. rvu..i-h _. tiie ver;ca' s.riny -s._u..v is projeced ^.

the shape ot a ci-cula. arc and that the ver i_a1 string is oun_ o:.-..e: _ S___=i. ?;,. - - - A _ _ A A A _ _.._ _ r.. _ _.

pro,e_t c.-. ma1 e - rme:i. the pla-e-sap me.,wer so th'-i::: -i:; <- -:_.. s:_ e -:-a _- j-. - iscce_?is-

( member. fain -o,e_ti. may, be fo-m.ed -i'- bat; e.ds or Me plat-shapd member in its wthnise direction so that the -v save as. c.e.m her 5 me d be-^e'n the _.-.- pr. e_- Ens.

R bber or carbon black-co-.tair.i.ng rubber car.be preferably 5 used for. h.e vscoelas'c mel.,ber. I, _s pre,e-ao e Ada- Me viscoelastic me..oer has a thickness tom to 6m and has a complex e astir moue 'JS.-.c,r less than '.X;i2' lye''.;-- icr..,o:-e..har. '.0 Xi01 dyn/cm2 when tr.e compiox elastic modulus is measured at a temperature of 0 to 10 C and a frequency of 10 Hz.

10 If the thickness of the viscoelastic member is less than stem' it is impossible to so fiiently mprove the rebound performance of the racket frame and the vibration-damping performance thereof. On the other hand, if the thickness of the viscoelastic member is more than 6mm, the weight of the racket lo _-ar.,e -;c-eases Ann hence the.,^era laity Stereo -s offs.

To sG i.-] t'r.e c0.mpe e''=kS" m.c!lus it; -.e -,'iscOelas_ic membettneabove-descrioedra..ye,h.e-vr-scoeastiCmem!erseries as a dynamic damper. Thus the vibration-absorbing performance of r.he racie, fra..e can be imroro-ved.

20 To form the p'ahe-shaped member of a rigid material, the c' a-e-shaped me.-,-e.,;aybe fvr.,.ed by molding a themose ting resin h.avinga,alitysa.. ,easthah othe racket frame oratheri,oplas-ic -es r... s.a-v-.-ab'e,.a.-._.ae-shape me,.be- s cme.> Or aFiber':ei.for e-r.e r.,.op as-; yes.'._re. ai..pe,s.,or-:-irbo;-: _ _, ALL, a,= _, r -it. _.

( he resin o-use i..the racker 'ra.T,e _ the aresen in/en.ion Àr.cludes the theroset'ing resin anci the therQplastic rcsir., as es_r oeii arbo-ve. ..e t..er..,ose---n res n..- u;ies e?c y resir, nsatu-ateri polyester resin, phencl resin, melamine resin, urea resin, -ailyl p-thalate -esn, polyure:a-.e resi.., colyi,ide resin, and silicon esir.. Tre thermolasic resin inc udes ?G'yam-;ie -esn, sa-uae.-,:ies.e- res..,.i_arbc^.ate r.-s ., ARSresin,polyvinylchlo.ideresin,polyacetalresin,polystyrene resin, polyethylene resin, polyvinyl acetate, AS resn, 10 methacrylate resin, polypropylene resin, and fluorine resin.

As reinforcing fibers fcr,se in the f ber reinforced res_r., fibers which are used as high-performance reinforcing fibers can tee used. Forexample, it is possible to use carbon fiber, graphite fiber, aramid fiber, silicon carbide fiber, alumina fiber, boron - o _iber, g ass 'ibe, aro.a- -c I'5i=''-e iber, ar4.mta-i- pO] yes er r_ber, u ra-;nigh-m.o_ecJ2a--. isight poye_-/le.ne fihve, and ne iYe. Meral fibers 'ay be use as the re nforcing fiber. ne carbon fiber is preferable because it is lightweight and has a h. gh strength. 'n:-ese rei..for_ -.g f vbers _ar. be sed in he for.

20 of long or short fibers. A m.ixture of to or more of these reinfe, rcngfibers.T,aycousea. he_or.fig:aionandarrance.T.er..

Of the reinforcir. fibers are r,_i mited to s?ecific ones. or e::amL-, --. ey,la; be ara-- - a si r J e i r.A 1_ in r a ra-.i-

i rest-.,...e reir. rc A, - bQ2'S...ay a'-e ie shae., r shee's, S _ _ i. i c! _ r, i -;:. ' ' -=l _. _.. 1 L _ _ _ _ _ I _ _ À / À À _ À _ _ _ À À _ -

( =:r.e racket-fra.e bc,. is nc. 'i...itei r_ a la."nate of f be' reinforced pr=2regS. Th.e racket-frame cdy.na be forme!-4 by ^,g _=,Tr_ _es. a r..a.nc-e: _, - a...en- -,vldi..-, o form a layu, disposing the layp n a aie, and filling the 5 thermoplastic res n sUCil as.im nylon --.. o he oe.

BRIEF 3_SCRIDTION O'' THE DRArPIING-S Fig. i is a schema ic fcnt vie SGW' ng a racket -rame according to a first embodiment of the present invention.

10 E'ig. 2 is a perspe;_tive -view sho.-ing a yoke.

Fig. 3 is a perspective view showing a clate-shaped member according to the first embodiment of tr.e present invention.

Fig. 4 shows the plate-shaped membe- according to the first embodiment of the oresent invention, in:.'hich: 15 Fg. '1A iS a plan iiew; . 3 _s a o. v_..; Fig. 4C is a sectional view taken a o..g a line I1-I1 of Fig. 4A; and Fig. 'D is a sectiona vie,vLaken as. a line I9-I? o F-g.

20 4A.

r g. 5A is plan v-iew s;^ic,virig a s oelas.i_ meer.

Fig. 5B 's a sectional viev taker: al,ng a line I3-I3.

. _,, _ _. _: ',- -,' - A

-:,. __ a a a=; i l:. -. = -..'.A:i.,._. ': - _-.

Eig. 6 is a se_r,..;_e;, so,v..:- e-_-i-ye-> ai' por os a - ' t -::;; ,=: a - - -: a r:-: -:-, / ', _,',,,,,;,,,, _! _,,,,',_,,,,,., _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ -' _ _

1 1

( l invention. Fig. 7 is a perspective view showing a plate-shaped member accord-

ing to a second embodiment of the present invention.

Fig. 8 is a sectional view showing enlarged main portions of the yoke according to the second embodiment of the present invention.

Fig. 9A is a sectional view showing enlarged main portions of a racket according to a third embodiment of the present invention.

Fig. 9B is a schematic front view showing a viscoelastic member and a plate-shaped member.

Fig. 10 shows the method of measuring a restitution coefficient.

Figs. 11A, 11B, and 11C are schematic views showing a method of measuring the vibration-damping factor of the racket frame.

Fig. 12 shows a conventional art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Embodiments of the present invention will be described below with reference to the drawings.

Figs. 1 and 6 show a first embodiment of the present invention.

A racket frame 10 is composed of one continuous pipe made of a fiber reinforced resin. A head part 12, a throat part 13, a shaft part 14, and a grip part 15 are continuously formed on the racket frame 10. A yoke 17 is connected to the throat part 13 at both sides so that the head part l,

12 and the yoke 17 form a string-stretching section G surrounding a ball-

hitting face F. As shown in Fig. 2, a string hole 17a is formed on the yoke 17 in almost the entire length thereof in its longitudinal direction (horizontal string direction). A plate-shaped member 30 made of a rigid material is mounted at a side of the yoke 17 opposite to the ball-hitting face F. with a viscoelastic member 20 interposed between the yoke 17 and the plate-

shaped member 30.

Similarly to the racket frame 10, the plate-shaped member 30 is made of the fiber reinforced resin. In conformity to the configuration of the yoke 17, a flat plate-shaped substrate or plate portion 31 of the plate-

shaped member 30 is gently curved in its longitudinal direction. As shown in Figs. 3 and 4, the plate-shaped member 30 has six string holes 32 (32a, 32b, 32c, 32d, 32e, and 32f) formed thereon at equal intervals. A circular arc-shaped projection 33 is formed between the string holes 32a and 32b, between the string holes 32c and 32d, and between the string holes 32e and 32f. A string insertion groove 34 connecting the adjacent string holes 32 to each other is formed on each circular arc-shaped projection 33. A shut-in projection 35 is formed on the plate-shaped member 30, except at an edge of its substrate portion 31, to be joined with the viscoelastic member 20.

( Similarly to the plate-shaped member 30 and as shown in Fig. 5, the viscoelastic member 20 to be interposed between the plate-shaped mem- j ber 30 and the yoke 17 is gently curved in conformity to the configuration of the yoke 17. The viscoelastic member 20 has a through- hole 21 formed therein, except at the periphery thereof, into which the fit-in projection 35 of the plate-shaped member 30 is fitted.

The thickness of the viscoelastic member 20 is set to a value typi-

cally between 2mm and 6mm. In the first embodiment, the thickness of the viscoelastic member 20 is set to 5mm. The viscoelastic member 20 is made of a material whose complex elastic modulus is not less than 2.0 x107 dyn/cm2 nor more than 1.0x10 dyn/cm2 when it is measured at a temperature of O to 10 C and a frequency of 10 Hz. In the first embodi-

ment, the viscoelastic member 20 is made of a material, containing 100 parts by weight of rubber (styrene-butadiene rubber) and 1.5 parts by weight of sulfur. The complex elastic modulus E* of the material is set to 5. 07x107 dyn/cm2 when it is measured at a temperature of 0 to 10 C and a frequency of 10 Hz.

Referring to Fig. 6, with the fit-in projection 35 fitted in the through-

hole 21 of the viscoelastic member 20, the string S is stretched on the yoke 17 by inserting the string S into the string hole 17a of the yoke 17, the through-hole 21 of the viscoelastic member 20, and the string hole 32

( of the plate-shaped member 30 in such a way that only the viscoelastic member 20 contacts the yoke 17.

At this time, the string S is passed through the string insertion groove 34 of the plate-shaped member 30 from the inner peripheral side of the yoke 17 to the outer peripheral side thereof and turned or folded back toward the ball-hitting face F. In the above-described construction, the plate-shaped member 30 functioning as a string protection member and the viscoelastic member 20 are not provided with a cylindrical grommet into which the string S is inserted. Thus this construction increases the degree of freedom of the string S. i.e., increases the movable range of the string S when a ball is hit, thus improving the rebound performance of the string S. The viscoelastic member 20 interposed between the yoke 17 and the plate-shaped member 30 serves as a spring, thus improving the rebound performance of the string S. The string hole 17a of the yoke 17 and the through-hole 21 of the viscoelastic member 20 are so constructed that not just one string S is inserted into them, but rather a plurality of strings S is inserted into them. Therefore it is possible to increase the degree of freedom of the string S. i.e. increase the movable range of the string S. when the ball is hit and hence improve the rebound performance of the string S. Since the yoke 17 at which the longest string can be disposed has the above

( described construction, the rebound performance of the string S can be improved effectively.

Since the viscoelastic member 20 serves as a dynamic damper, the vibration-damping performance of the racket frame 10 can be improved.

Since the plate-shaped member 30 is not in direct contact with the racket frame 10, the tensile force and impact force of the string S generated when the ball is hit are easily transmitted to the viscoelastic member 20. There-

fore the vibration-damping performance of the racket frame 10 can be improved. The big string hole 17a is formed on the yoke 7. But the plate-

shaped member 30 formed by molding the fiber reinforced resin is mounted on the yoke 17. Thus the plate-shaped member 30 does not affect the rigidity of the racket frame 10 adversely. Therefore the rigidity in the in-plane direction can be maintained and control performance can be kept. Further the plate-shaped member 30 is capable of maintaining the strength of the yoke 17.

In the first embodiment, as in the case of the racket frame 10, the plateshaped member 30 is made of a fiber reinforced thermosetting resin.

But the plate-shaped member 30 may be formed by molding a thermoplas-

tic resin such as nylon.

It is most suitable to apply the above-described construction to the yoke. However, through the viscoelastic member, the plate-shaped mem

( her may be mounted at the crown of the head part 12, where the longest string can be disposed, or at both the yoke and the crown.

Figs. 7 and 8 show a second embodiment of the present invention.

Unlike the first embodiment, the number of the string holes to be formed on a yoke 17' of the second embodiment is not one but four. More specifically, of the four string holes, two string holes 17a' disposed at the left and right ends of the yoke 17' are approximately circular in section, whereas two string holes 17b' disposed at the center of the yoke 17' are elliptic in section. In the embodiment shown the string holes 17b' are disposed at opposite ends of a long slot in the yoke 17'. One string S is inserted into each of the string holes 17a', whereas two strings S are inserted into each of the string holes 17b'. Thus six strings S are inserted through the yoke 17'.

The configuration of a string hole 32a' disposed at both ends of the plate-shaped member 30' is similar to that of the string hole 32 of the plate-shaped member 30 of the first embodiment. A long through-hole 32b' is formed between the string holes 32b and 32c of the plate-shaped member 30 of the first embodiment and between the string holes 32d and 32e of the plate-shaped member 30. Other constructions of the plate-

shaped member 301 are similar to that of the plate-shaped member 30 of the first embodiment.

( As shown in Fig. 8, with a shut-in projection 35' fitted in the through-

hole 21 of the viscoelastic member 20, the string S is stretched on the head part 12 along the yoke 17' by inserting the string S into the string holes 17a' and 17b' of the yoke 17", the through-hole 21 of the viscoelastic member 20, and the string holes 32a' and 32b' of the plateshaped mem-

ber 30'.

The above-described construction maintains the degree of freedom of the string S when the ball is hit, provides an effect similar to that of the first embodiment, and improves the strength of the yoke 17'.

Fig. 9 shows a third embodiment.

The mounting position of a yoke 17" is shifted toward the shaft side of the throat part. In addition, a yoke-shaped member 170 made of a vibration-damping material is mounted on the head part by placing the yoke-shaped member 170 at a position (mounting position of the yoke 17 of the first and second embodiments) inward from the yoke 17". Both ends of the yoke-shaped member 170 are continuous with the right-hand and lefthand head parts. Thus the racket of the third embodiment has two yokes. A long hole 171 extending crosswise of the head of the racket is formed in the yoke-shaped member 170. A viscoelastic member 20" and a plate-shaped member 30" are mounted on the yoke 17". The viscoelastic member 20" has a configuration similar to that of the viscoelastic member

( 20 of the first embodiment. Instead of the fit-in projection, a fit-in projec tion 35" is formed at both ends of the substrate portion of the plate- | shaped member 30" in its widthwise direction (i.e. across the head of the l racket from the left side limb to the right side limb) to accommodate the viscoelastic member 20" between the fit-in projections 35".

Because other constructions of the third embodiment are similar to those of the second embodiment, description thereof is omitted herein.

In the racket, the vertical strings S are stretched by inserting them through the string hole 171 of the yoke- shaped member 170, the string hole of the yoke 17", and through the viscoelastic member 20" and the plate-shaped member 30".

This construction allows the yoke-shaped member 170 to absorb vibrations of the strings, thus enhancing the vibration-damping perform-

ance of the racket frame.

The racket frame of each of examples 1 through 4 of the present invention and comparison examples 1 through 4 will be described below in detail. The racket frame of each of the examples and comparison examples was made of a fiber reinforced resin. They were hollow and had the same shape. More specifically, each racket frame had a thickness of 28 mm, a width of 13 mm- 16 mm, and a ball-hitting area of 116 square inches.

They were prepared in the following method.

( Prepreg sheets (CF prepreg (foray T300, 700, 800, M46J)) made of fiber reinforced thermosetting resin containing carbon fibers as the rein-

forcing fiber thereof were layered at angles of 0 , 22 , 30 , and 90 on a mandrel (0 0 14.5) coated with an internal-pressure tube made of 66-

nylon to mold the material into a vertical laminate. After the mandrel was removed from the laminate, the laminate was set in a die. In this state, the die was clamped and heated to 150 C for 30 minutes, with an air pressure of 9 kgf/cm2 kept in the internal tube to prepare racket frames.

The plate-shaped member of each of the examples and comparison examples was made of the fiber reinforced thermoplastic resin composed of 12-nylonserving as its matrix resin and carbon short fibers serving as its reinforcing fibers.

The kind, thickness, complex elastic modulus, weight of the racket frame, and the balance of the racket frame were set as shown in table 1.

r,,, I. I 1 1. llj I.,, L) ' i=] | (9 | r ' t 0, I O ' (] (! I l ' O I I O I [; I. ('j I t-1. j C O ' O,, , 1 I, ,:G! i I O '; O vn. ('-; I L1 À l!,,.;::. 1 j 1 j, i..,I. j '.;....Z. (! j. j., 1,- ' i, 1 j; ! ' ' 1 _,; ' 2 I, i . ' iXJ, I L _. 0; i X C C. O t ' ; r ', C ' 9! rC Lj r-,, r, + ' e J.. [ l l;;. ( I -! ' V >1, _i! C'i _ (n ' ' +. g I,, O. 0, I I -. U I! 0 1 m; À:. j j | À, I::: Ir', -] ' j ' ';. ' | I -, 'j. I::; ' ' I |- ---i I, L.---------'---1! ---i ------'-, --: - ' ' - ' -;- --4 j I r,. j j, . i 5-1,, j, I.;;. 05 I ' j ',, . ''. Q., I; r', 1 C '' ' ' O . n O r] () Lr r C j;; c- cJ ::, I v I O + l-i O 0 0 -n,-; C D =' N U):

II ' I CT >! 2 ' I I L ' r. U) ' O rx' 1 r<), 9 j O ', CC: c0 ' I. | |-. fa I.! I v r n. ( rn O 1 0. ! r. r. I I ., ie.= i '.., --.. 1,,. 1 ., r C I, C' C,. l.,. C _ | 0 n l I ra (0 rJ i:,, rO:!: I I,.: ' I: 5 , r I. Q O\o,E >_,,\0 _ 0\o, _ IQ C 5--i I Li i -! I 0 ' ' in > ' r -. . i_i . l ; i ' ' >. tv. r; Iv i'i I 5 i,,,' , r: rJ. ,,, 3; r, | |: ' -! ' L': C I ' r ra, , O '. i C ' _ I ' C rO 1 4J r ' 3 ' --, rv Q j, E _ I ' r I::. -; tJ j ' I r; -i!:,,, j!:: v: I; vu a i, 0, ';, C) '75 v),15 1; 0 i rn. I, C i ' ' 1 i ' ' 'n j ': I C C j >1 j d l., ra. | -: ra I! IJ I i (rv ' i ra I ra I I V;; I | | n::; rri; - 4 C 1 -d 0 C |! r I 1 C C j --; C rn 2 rj),,, < jO j, Q C!, rn Cv ' Q _;, Q r; Q. O r-, I CV! Q. o: | - r] | -; ; . r] | I v) i | - rd |. r] j - r1 - r] C 2 X I _' t=d 1 ' v v I C X 1 V, , I L ' 0 rV l rQa ra I I cl'. I 3 r, o ra I l-v, _ ' ra I j r: , _, I.;' -: v - :; l i TVt r;: . I I: I itt itl; i-1 | 3 | _ -r4 8' I i I VU Q v), 1 . Q I I C ' -- rL ' | 4-J Q 1J,Q j rL - - Q I v jar4, C r)!.!a r r-1.rt! Àrd; _ O I Àrt - j Q -1;._l; _ ! '; j-_ <, j j!o '4 0 > 'O;:> . =;i,-;r,!o > o >.o i l "V r-i r c I r_ r| j r_ I;;_ C --t I ri; _ _ ,,! J _I-r, _ À n c,..,. .., _,;_. r _ a ll;r; ' r _ _, =

--.; ' _ r,,., '.. -i; ' =; r j t C _ r. _ I r,, o;rt v 4j '! r; I;; -- C. -

rt I; a vn) V I.. -: j -t V: ra::,: ' - r l -ri ' (' I; 4a' -c I!,-. j v r - I ' '.. v..! =-i 1 I rJ I -r] v I r r-] C, t l v I r,, Q | n I Àrd | Q | r r, I rD I | r] r r I Q la r C ra l r1; v) a ru l-rl ' > ia.; -rt; I vJ i J j F-t I l::,! 3 ' a) I rY I:> i Q,! L 1! 3 m j.

_.. 1 J

( À E.'amole 1 T-.e is_ae.astic member i-.terncse- between he yoke and the plate-shaped member was formed by.,.olding rubber con,aining 'CC Qa_sby weight o styrer.e-btacie-.e r oberand1. arts'ovweia.-, 5 of sulfur. The thickness of the viscoelastic member was set to 5mm. Other - cnstruction.s of the racket frame were the same as those of One racket frame of the first embodiment.

À Example 22

The viscoelastic member interposed between the yoke and the 10 plateshaped member was formed by molding rubber containing 100 parts by weight of SBR, 40 parts by weight of carbon black, and 1.5 parts by weight of sulfur. The thickness of the viscoelastic member was set to 2mm. Other constructions of the racket frame were the same as those of the racket frame of the example 1.

15 À E.-.a,ole 3 The viscce_as.ic member -.-erpcse-'-e-ween -he yoke and the plate-shaped mer.ber was formed by molding rubber containing 100 parts by weight of SBR, 40 parts by weight of carbon black, and 1.5 parts by weight of sulfur. The thickness of the viscoelast_ 23 member was set to 5mm. Other constructions of the racket frame were the same as those of the racket frame of the example 1.

À:'ample d Tr.e-,isc^easri member.erpcse,_ewee.:he 'Ike G'7 -.'-.-

'are-shape me..ner was fQrl.;ed by l g PE=.aX::3. The 2:,:- caress;_ e:iscoe us- _ member -..-as set to,. O nerd )., _ a_

( constrictions o. the racket Frame were the same as these of he racket frame th^-- first embodiment.

À oa-son E:.axple i rue v'scoe'astic T.e-ber was Hot inrerp^se<>be weed the yoke 5 and the plate-shaped member. Other constructions of the racket frame were the same as those of' the racket frame of the first embodiment. À Colrr,parison E ample Silicone rubber having a thickness of 5mm was interposed 10 between the yoke end the plate-shapedmember. Other constructions of the racket frame were the same as those of the racket frame of the first embodiment.

À Comparison Example 3 Nylon 11 having a thickness of 5mm was interposed between 15 the yoke and the ^' ale-shaped member. Other constructions of the ra.-i2et_ '-:3rie w=.e The same as hose o r..e cache-: -awe of he first embodiment.

À Comparison Sample 4 The viscoelasic member interposed between the yoke and the 20 plate-shaped member was formed by molding rubber containing 100 carts by weight of BBR, 40 parts by weigh.- of carbon black, and 1.5 parts by we',ght of sulfur. The thickness of the viscoelastic .ebe- was set to 8r. ^ her cor.s=-cc r.s Of The racket -am2 were the same as h_se c; the racket 'ra.-r.e of the e:ampe i.

ri5 The Sac,;' G --ar.e Q- each.,:e e ales::-rs:-h: anti hi

( _ompa-isc.. e.ampes 1 thrc!ugh Ar was measured by the metr.cc1 which will be described later on the restitution _oefficicnt, the out-o--p_a-.e a. a-;- Vera or-damp-r.c factor, and:-de out-of-plane secor.dary vibration-damming factor. In addition, 5 a ball-hitting tes' was conducted. Table shows test results.

À MEASUREMENT OF RESTITUTION COEFFICIENT

As shown -I r 1C, str-r.gs cede ste._:-ieo on the tennis racket of each of the examples and comparison examples at a tensile force of 60 pounds (vertical) and 55 pounds (horizontal). Each 10 tennis racket was held vertically free, with a grip part 15 fixed gently. T. tennis ball was launched from a ball launcher at a constant speed of V1 (30m/sec) to allow the tennis ball to collide with the ball-hitting plane of the tennis racket. A rebound speed V2 of the tennis ball was measured. The restitution coefficient is the rat 0 Of the redound speed VAz to he 'bunched speed V1.

The higher the restitution coe--ic end is, the onger the Penn s ball flies. The restitution coe-f Lied was measured in this way.

À Measurement of Out-of-Plane Primary Vibration Damping Factor As shown in Fig. llA, wi h the upper end of the head par 2012 hung with a string 5i, an acceleration pick-up meter 53 was installed on one conned ion polio.. between. heinead part 12 a.d the throat part 13, with the acceleration pick-up meter 53 erper.!i _:_ar o the 'a e of he a.-'e ra.-e. As SihON.i '.- i_g5.

113, in th s state, the other cc.ne_-'AlA. po'.__on between e.he2:-

- Add -> v--:-> -.-e Ada- a' ', As -- -.v t-: - roach:ae': 2}

o vibrate the racket frame. Ar.nput vi-aon I-) measured by aforcepickupmeterinstalledontheimpactnam.e'D5andaresponse v bratiQn (at peas e,by the a_ce''era- i- _ -k-Jp.e-e- 3 were inputtedtoafrequencyanalyzer57(dynamicsngleanalyzerHP3562A 5 mar.ufactued by Hewlett-Packard Company! -..-Qugh amplifiers 56A and 56B. A transmission function in the frequency region obtained by ananays s was calculatei.c ob air the -equen_y o. the racket frame. Thevibrationdampingratio()oftheracketframe,namely, the out-of-plane primary vibrationdamping factor thereof was 10 computed by an equation shown below. Table 1 shows the average of values obtained by measurement conducted for a plurality of the racket frames of each of the examples and the comparison examples.

= (1/2) x (in) To = in/ À v^asurer,n,en 0 Ou--c-Plane Alec nda-y, Crag ^, n amp_ng "acto-

As shown in Fig. llC, with the upper end of the head part i2 of the racket frame hung with the stair. 51, the acceleration pick-up meter 53 was installed on one correction portion between 20 the throat part 13 and the shaft- part lo, w.h the acceleration pick-up meter 53 perpendicular to the face of the racket frame.

In his state, tine rearsideo..he racketrameaapor- ontr.ereo' confronting the pick-up meter-installed pos Lion was hot with the -.:Tn.er T-_r-=te e -----it - a-. We an--..;A---.., 25 namely, the ou--of-piane secon;'arf vibra -n-dampinq fas:o- ^.

( "r.e racket frame was computed by a method eqivaler.t to the.metnod of computing the out-of-plane primary vibration-damping factor.

Cache; shows 'he average o- values c.a-ned by,measure.men.

conidCtedforapluralityoftheracketEramesofeachoftheexam.ples 5 and the comparison examples.

À Evaluation in Ball-Hitting Test TO e-;ami..ehe o?erabiiiy, f'igri. performance, v_^>ration, andimpact of each of the rackets oftheexamples end the comparison examples, questionnaires was conducted on 53 middlegrade and 10 high-grade players who hiLballs and gave any one ofonemark through five marks ithe more, the better) on the above items. The players have not less than 10 years' experience in tennis, and recently play tennis not less than three times a week. The average of the marks the 53 prayers gave was computed. Table [shows the results.

5 As shown n.ab_e -', the 0 t-of-pla.ne _r_mary vibration-damping factors of the racket -raves of the examples 1 through 4 were 0.75 to 0.81. The out-of-plane secondary vibration-damping factors of the racket frames thereof were 0.90 to 1.34. Tr.e ou-of-plar.e primary vibraion-damping factors of 20 the racket frames of the comparison examples 1 through 4 were 0.42 to 0.50. The out-o'-plane secondary vibration-damping factors of the racket frames thereof were 0.64 to 0.69. Thins it was confirmed t.- .a ile racks- f-a.es o The e:;=m-les; 'h-o:;g^ ha super.oir vib-ationdamp_nq per'-or.,arice -o -he -ark=- frames Of > '^= --a'; stun a-'s r v .;q /, 3 I TV -..v, _

( As a whole, the racket frames of me ea,mples 1 through 4 had highsrestitution coefficients than the racket frames of the _ompariso.r e:a., pies 1 through A, Tha- is, -.as coni-me:n.at the racket frames of the examples 1 through 4 had superior rebound 5 performance co the racket frames of the _cmparison e^.amples 1 through 4.

It was also Confirmed.ha n the a. -h-t-_ng es., The racket frames of the examples 1 through 4 were superior to the racket framesofthecomparisone. xamplesirbrough4inoperability, 10 flight performance, and vibration&impact thereof.

As apparent from the foregoing description, according to

the present invention, the plate-shaped member is not provided with the erring insertion cylindrical part. Thus the degree of freedom of the string, i.e., the movable range of the string i5 ire-eases v-.-e-. a ball is:.-. That is, --e -ebor.d pe--o-mance of the stringcanbemproved. The viscoeiasticmember-n-er?osed between the racket frame and:e plate-s;aped member serves as a spring, thus improving the rebound performance of the string Lo a h.ighe- en ent.

90 The strtr.g hole formed on the portion of the race. frame where the plate-shaped member is mounted and the through-hole of theviscoe2asricmemberinte.?osedbetwee! 'ne?iae-snapedTembe and the frame are so construct-d that a pears its Of s- -as ca He -semen Were -,:c. 'hee-_re - s _.ss_2e Lo Disease -':'? 2i degree of freedom of the string, i. e., increase the mov-2e ran e - t

( of the string, when the ball is hit and hence improve the rebound per-

formance of the string. Since the yoke at which the longest string can be disposed has the above-described construction, the rebound performance of the string can be improved effectively.

By setting the complex elastic modulus of the viscoelastic member to the range described previously, the viscoelastic member serves as a dynamic damper. Thus the vibration-damping performance of the racket frame can be improved. Since the plate-shaped member is not in direct contact with the racket frame, the tensile force of the string and an impact force generated when the ball is hit are easily transmitted to the viscoelas-

tic member. Therefore the vibration-damping performance of the racket frame can be improved.

It is noted that the strings extending through the yoke can be and usually will be sections of one continuous string looped to and fro between the yoke and the crown of the racket, i.e. the end of the head part of the racket opposite to the yoke. They could, however, also be separate strings anchored at both ends to the head part of the racket opposite to the yoke and forming one loop or a plurality of loops at the yoke around the plate-

shaped member, i.e. over a portion of the surface of the plate-shaped member between adjacent holes therein. Thus, if individual strings are used, they could each form two longitudinal strings, four longitudinal strings or any even number of longitudinal strings having space on the 2Y

( head of the racket. Ultimately, it would also be conceivable to use at least one single string (or a plurality of single strings) anchored at one end to the plate-shaped member and at the other end to the head part of the racket opposite to the yoke.

Claims (12)

1. ( WHAT IS CLAIMED rib:

   A racr.e- hater ng a race- frame Comprising a;nicad park; a shaft part; a bifurcated throat part connecting said head par and said shaft par- to each other; and a yc'e both ends o. whic., 5 are connected with said throat part, strings being mounted on a strirg-stretching section including said head part and said yoke and surrounding a ball-pitting face by stretchi^.g said str figs, wherein a plate-shapedmemberis mounted on an outer surface 10 of said string-stretching section at a position thereof where a longest vertical string is disposed, with a viscoelastic member interposed between said yoke and said plae-shaped member; and said strings are stretched in said string-stretching section by insertingsaidstringsthroughsaidv'scoelasicmemberandwindins 15 said strings round an outer surface Of said p' ale-shaped member.
2. 2. The racke'- accord ng So claim l, wherein said! scce asti_ member is sheet-shaped to contact said viscoelastic member with saIdstringstretchingsection;saidpiae-shapedmemberisfcrmed of a rigid material and not in contact or connection with said 20 string-stretching section but has a configuration similar to an outer surface of said viscoelastic member to cover said outer stir-ace thereon; and vertical s rib. s a-e Inserted --.-o said vis_oelast.c Vetoer and said olate-s.haped ime.ber through s'in : =s --.e<4 s-: s-es- -!:_e::^ said --e-s.are 2o member.

   JO

   (
3. 3. The rac<.er accord rg tc, claim 1 or i, w:-le-ein said viscoelastic member and said plare-shaped merrier are mounted on
4. 4. The racket according to any one of claims 1 through 3, wherein said viscoelastic member has a thickness '.nm to am and a comple.< elastic modulus not less than AZ.Ox107 dyn/cm2 nor more than 1.0 l a I e at s sTie therec,. opE:osie to a bal-..itt-- i -ace.

   X 0 iyn/cm when said, omcle:. elastic mode us is measured a.

   a temperature of O to 10 C and a frequency of 10 Fiz.
5. 5. The racket frame according to any one of claims 1 through 10 4, wherein said plate-shaped member is formed by molding a material having a quality same as the, of said racket frame, a thermoplastic resin or a fiber reinforced thermoplastic resin.
6. 6. The racket according to any one of claims 1 through 5, wherein at least one part of string holes formed on said racket frame, 1 sa; 1scoelast crrembe<, a.n.dsid?;ate-sriapedmemhe- s set larger than other string holes; and one o' a plura By "f strtr.gs i S freely inser ed into said larger string ho es.
7. 7. The racket according to ar.y one of claims 1 through 6, wherein vertical strings disposed a- both ends of said yoke in a longitudinal 20 direction thereof are wound round an outer surface of said plate-shaped member, with said vertical strings in contact with both end surfaces of said iscoelastic merrber and said plate-sr.a?ed -,ember n git udina_ re_ _ irereo; a-.i 0 her -ier-ca sir r'.s disposed bAetweeri said vertical s Fir As d spsed at both i:: ems of Sal -he -'e insea ^< aim s' -.A=S -: -T. e;^. said s; elastic nether and as.- -e-s..aed me.T=e.

   3'
8. 8. A racket having a racket frame comprising a head part; a shaft part; a bifurcated throat part connecting said head part and said shaft part to each other; and a yoke both ends of which are connected with said throat part, strings being mounted on a string-stretching section including said head part and said yoke and surrounding a ball-hitting face, wherein a string holder, e.g. in the form of a plate-shaped member, is mounted on an outer surface of said string-stretching section at a position thereof where a longest vertical string is disposed, with a visco-

   elastic member interposed between said yoke and said plate-shaped mem-

   ber; and some of said strings being stretched in said string-stretching section by inserting said strings through said viscoelastic member and looping said strings around an outer surface of said plate-shaped member.
9. 9. The racket according to claim 1, wherein said viscoelastic member is sheet-shaped for contact at an inner surface with said string- stretching section; said plate-shaped member is formed of a rigid material and is not in contact or connection with said string-stretching section but has a configuration similar to an outer surface of said viscoelastic member to cover an outer surface thereof; and vertical strings are inserted into said viscoelastic member and said plate-shaped member through string holes formed on said viscoelastic member and said plate-shaped member.

   (
10. 10. The racket frame according to any one of claims 8 or 9, wherein said plate-shaped member is formed by molding a material having a composi-

    tion same as that of said racket frame, a thermoplastic resin or a fiber reinforced thermoplastic resin.
11. 11. A racket having a racket frame comprising a head part; a shaft part; a bifurcated throat part connecting said head part and said shaft part to each other; and a yoke both ends of which are connected with said throat part, strings being mounted on a string-stretching section including said head part and said yoke and surrounding a ball-hitting face, wherein a string holder is provided at at least one of a shaft side of said yoke and at a crown part of said stringing section opposite to said yoke at a side of said crown part remote from said yoke, with a viscoelastic part disposed between said at least one string holder and the associated one of said yoke and said crown part; and some of said strings being stretched in said string-stretching section by inserting said strings through said viscoelastic member and looping said strings around an outer surface of said plate-shaped member.
12. 12. A racket substantially as herein described with reference to and as illustrated in the accompanying drawings.