CA2047076A1

CA2047076A1 - Racket for ball games, in particular a tennis racket

Info

Publication number: CA2047076A1
Application number: CA002047076A
Authority: CA
Inventors: Siegfried Kuebler
Original assignee: Individual
Current assignee: Individual
Priority date: 1990-07-27
Filing date: 1991-07-15
Publication date: 1992-01-28
Also published as: DE59105564D1; MY107222A; ATE122907T1; EP0468263A1; JPH04236973A; CN1064414A; JP3129772B2; EP0468263B1; DK0468263T3; ES2076423T3; DE4106067A1

Abstract

ABSTRACT

A racket for ball games, in particular a tennis racket, comprising stringing provided in a stringing frame comprising a profile bar, a throat region adjoining the stringing and a handle (20) on a racket shaft on the longitudinal axis of the racket, which preferably forms a straight line of symmetry, is improved in regard to so-called impact shock in that the racket, between the throat region and the end of the handle (20), has a hinge location (44) whose hinge axis extends parallel to the stringing.
The hinge location (44) is preferably disposed in the region of the handle (20) and is formed by a limb portion of the handle (20) which is preferably defined on both sides by groove-like channels (40) and is filled by an elastic shaped mass (42).

Figure 7

Description

2 Q ~

KU-128.01 Racket for ball g~es, in particular a tennls racket Description The invention relates to a racket for ball games, in p2rticular a tennis racket, comprising stringing in a stringing frame comprising a shaped bar, a thr~at region which adjoins the stringing and a handle on a racket shaft on the longitudinal axis of the racket which preferably forms a straight line of symmetry, wherein the free end of the handle is defined by a handle end face.
Tenni~ rackets of that kind are to be found for example in German laid-open application (DE-06) Nb 30 18 354. When clamped in the region of the handle, tests showed that they have a natural frequency of between 25 and a maximum of 50 Hz; unstrung tennis rackets generally have slightly higher values. me frequency of the orerall system comprising the racket -and the stringing ha& a sub3tantial influence on the hand which is playing with the racket and thus also on the occurrence of what is kncwn as tennis arm.
In consideration thereof the inventor set himself the aim of eliminating or at.lQa~t alleviating the influences acting on the hand of the perEOn pl~ying with such a racket, in parti~l~r the sD-called imçact shock which occurs upon oont wt with the ball, with~ut in that respect giving up the ~dvantages of a very stiff frame, as are afforded for example by ra~ket~ in accordance with Ger~an patent specification No 3 343 898.
That ob~ect i3 attained by the 03ncept that the racket has a hinge location between the throat region ~nd the end fa oe of the handla and the hinge ~xi~ e~tends parallel to the ~tringing, that iR to s~y in the plane defined by ~he racket frame. In other words, providad at the pivot point which occu~s or ad~cent that pivot point, in the racket ~haft or in the handle, i~ ~ ela~tic hinge locatlon ~hlch alters the frsquency 2~ ~s~ 76 characteristics of the racket and compensates for impact shock.
Ihe above-mentioned pivot point of the racket when a ball is struck is referred to in the language in the art as the 'pivot po mt of rotation'. No forces occur at that point but a turning moment acts thereabout~ When the ball hits the racket, forces in the direction of the arriving ~all act on the racket, as viewed from that point towards the head end of the racket. Fxom the pivot point towards the end of the handle hcwever the forces act in the oQposite dlrection. merefore, when playing a forehand, a racket tends to tilt out of the player's hand wherea~ when a backhand stroke is played it tends to fom e itself into the palm of the hand. That is possibly th~ reason why players suffering from what i known as tennis arn can hit a forehand stroke in a relatively pain-frse manner but paln occurs to a greater extent when playing a back~nd.
lS It ha~ be#~l found advantageous for the 2bove-indicated hinge location to be disposed in the region of the handle ~lthough it is also in accordance with the invention for the hinge location to be displaced out of the handle region; thu~, in ~ccordance wi~h the invention, the elastic hinge can be dispcsed in ~ range of dist~nce of 60 thrnugh 200 m~ from the end face of the handle. That i~ al~o ~he region in which the above-mentione~ piv~t point lie~.
In Dccordance with the invention the hinge location is formed by a block of elastio matexial, a rubber b~ock, which is preferably vulcanised at both ends on to plates o the h~ndl~ pcrtions and connects two 25 portions of the handle.
In anoth~ ~linent of the i~tion ~e hinge location ~ a linb portil of the ~te or the rælcet ~ihaft, which i delimited on both 5~ 3 b5~ like ch~ls formed t~. The width of ~e channel or grwve, ~8 ms~ured in the longit~i~ ~Kis of tbe racket, m~y be up to 100 mn but it will generally b~ considerably ~rter. In t~at connection , the d#pth of the limb portion cpproxim~tely o~rrespond~ to the depth of the ch~hnel for~sd in the racket, whi~h ~cl~uçpc~e~ that the shaft cross-2~17~
.

section is divided into three portions of approxim2tely equal width.
Preferably the two grooves of that construction are filled by ashaped mass of low flexural stiffness, particularly when the two grooves are provided in the handle region and must be covered by the handle S leather.
m e object according to the invention is also db~rEd by a racket with a plurality of parallel axes, which are directed transversely with respect to the longitudinal axis of the racket, of adjacent hinge locations. In thfit arrangement flexing in the elastic region of the racket which is clamped f ct as far as the f;rst hinge location at the handle, under the effect of a foree which acts at a spacing of 400 mm from the hinge axis towards the head, is to be between 1.2 and 9 times as great as the flexing of a h m ge-less racket, which however is otherwise of aorresponding configuration, when it is fixedly clamped at the handle, as ~ar ~Q the hinge axis.
A~vantageously the hinge location or locations produces or produce a reduction in the frequency of a racket which is fixedly claTped as far as the first hinge at the hanile by between ~ 2 and ~ relative to an identical racket ~ithout a hin g location.
Tennis r~ckets with an o~en throat region which is defined by two pIDfile portl~n~ with D frame limb portion connecting same, and of increased cross-sectio,n in the region thereof, which have p m ven in practice to be extremely effective, can ~e ~sde even more efficient by virtue of the provi~ion of at least o~e such hinge location.
An ~ t of additional slgnificance to the present invention is the possibility of providing the racket shaft ~nd a shaft portio~ forming the handle with at le~st one gsp which extends oontinuously into ~he throat region and which contains at least m a portion-wise mEnner an elastic mZS8 which bears at bDth s~es against the surface~ which del;neate the gap in the shaft, constituting an intermedi~te layer or intermediate '. elament between the bar part~ o~ the shaft. In acoordance with a further feature of the invention, as viewed in CroB8-8aCtion, th2 intermediate 2~-~ 7~ 7~

layer may also c ~ prise a plurality of strips or cord portions which leave cavities or gaps free between them. In a particular emkcdiment there is provided a round cord portion which holds the tw~ associated shaft bar parts at a spacing and keeps the remaining portions of the gap in the shaft free.
In addition it has proven to be advantageous for the elastic material to bear at both sides against the surfaces defining the gap in the shaft and for the bar Fr- ts of the shaft to be at least partially laterally mc~able relative to each other in the direction of striking.
With a syTnmetrical racket design configuration, s~paration of the handle is parallel to the direction of ~triking or pexpendicular to the striking surface and preferably along the longitudinal axis of the racket. If the ~eparating gap in the shaft is outside the center line, or is curved, inclined or of a zig-zag configuration, the damping results which can be acJhieved are admittedly not quite so good but they are still acceptable. Thu8, in accordance with a further feature of the invention, the substantially rectangul_r cross-section of the gap in the shaft extends linearly in a plane or surfaoe, but the cross-section can also be of a wavy or zig-zag oonfiguration.
m e elARt~c ccnnecting el~ments of correctly separated shaft or handle b~r part~ nN~y be continuous, oonsisting for exa~ple of a silicone rubber laye~. Hb*~n~er it i8 al80 possible to envi~age them being arranged in a punctiform f~shLLon or only in a strip-like configuration for exAmple at the cut edge or the e~ds of the gap. Tbe conu~cting elements may be produced from hLse or tubP portio~s, round ru~*~er oQrd portions or IG~iliently in some other way. It is alas possible to e~vi~age a partial oFening, for e ~ e slots, ~hich can also be unfilled a firn oonnection cx~iJd rennin only at the end of ~he h~ndle, while the slot disposed th~r~#~ao~ oould oontain a dkn~ping material.
It ha8 p~ven to be ~dvantageou~ for the described surface ~o be of a '. fl~t oonfiguration- ~n a particl~Lar oonstructiDn the fiurf~ce i~ curved in cro~s-~ection, snd ~ plurality of surfaces moy be ~&ociated kith each other.

Depending on the respective design configuration of the racket according to the invention, flat bar portions of elastic material are used, which are linear or curved in cross-section and which, as described, may entirely or only partially fill the gap in the shaft.
5Therefore, an elastic connection - or interruption - is put into the handle or the center line thereof, to absorb and damp the torsion effect in the lower region of the racket. That eliminates inter alia the disadvantages invelved in handles which are foamed on the racket, with a virtually elastic characteristic, namely making the racket 'soft' in its longitudinal ~;rection, so that the oscillation characteristics are altered, the degree of striking precision deteriorates and the positive properties referred to, in a super-hard racket, are lost. If the handle which i8 otherwise made fxom re or less non-elastic materials such as for example wcod, metal, pressed fibers in a plastic bed, plastic materials or hard foam, is separaterl along the center 1ine or axis of symmetry or c~ely ad~acent thereto substantially peIFendicularly to the ~triking surface, and re ~oined for example with an elastic mass such as si1;cone rubt~r, that alte s the hardness of the racket in its lDngi~ ~1n~1 direction just as little as the o~cillation characteristics of the racket. The latter Are ~180 not altered when the ball is hit on the longitudln41 ~xis of the r~cket. Hbwever ln the case of balls which hit the ~triking surfaoe of the r~cket outslde that ~Xi5, torsional oscillations are produced: admittedly, those tor3ional o~cillations are superimposed o~ the longit ~ 08cillati4n, but then, due to the resultiny rel~tive noveTent of the dhaft and handle bar portions relative to each other, they ar~ damped ~nd 8uppres8ed by nE2nS of the ela~tic intermediate l~yer and c~n thus paB8 to a lessar degree into the striking aDm. The connection of the d of the handle by the handle csp which is principally not divided or also o~ es ela8tic ~terial, and the influen oe of ~ ~ e leather which ~R wr~pped aroun~ the handle, mLst '. aiao be t~ken into acoount when selecting the raqu~rqd el~stlcity of the intermediate layer. Test~ have confirmed thAt racket~ of such a 20A 7~7~

construction reduce the impact shock when balls are struck at an off-center position, and give an improved 'feel for the ball'. This invention can substantially eliminate the disadvantages of super-hard rackets while however ma m taining the advantages therecf.
Further ~advantages, features and details of the m vention are apparent from the following description of preferIed embodinents and with reference to the drawings in which:
Figure 1 is a plan view of p~rt of a tennis racket wlth a head oomprising a hollow profile bar and a handle on a racket shaft, Figure 2 is a side view of the Figure 1 racket, Figure 3 is a vi~w on an enlarged scale in cross-section through Figure 1 taken along line III-III therein, Figure 4 is a view on an enlarged scale in cross-section through Figure 1 taken along line rv-rv therein, Figures 5 and 6 show two partly sectional plan views of handles on an enlarged scale in oomparison with Figures 1 and 2, Figures 7 ~nd 8 shcw various partly sectional side views of handles on an enlarged sc~le, Figure 9 shows a view of a portion fram Figure 1 an an enlaryed scale, in another embodiment, Figure 10 shows the portion illustrated in Figure 9, turned through 90 ~
Figures 11 through 15 show views on ~n enl~rged ~cale in cross-section through th~ handle taken along line XI-XV in Figure 10, in relation to different oonstructions.
A tennis racket 10 ~hich is shown by way of exaTçle in Figures 1 thrDugh 4 h2s an oval rackPt head or ~tringing frare 14 formed by a suitably curved prDfile bar 12. The profile bar 12 of the racket head 14 terminates on both sides of the longitudinal ~xis M of the racket m pLufile arms 16 which laterally delimit an open throat region H and which Dre connected by a frame limb portion 18 and which go into a racket shaft 19.

Adjoining the racket shaft 19 is a handle 20 of a thickness h of from about 26 through 32 mm; that thickness h is measured on the handle 20 without a wrapping leather 21 and without taking æ count of a handle cap 22 which in Figures 1 and 2 is covered by the leather.
S The racket hea~ 14 and the liTb portion 18 define a stringing area or surface Q comprising transverse string~ 24 and longitudinal strings 25 which cross thè transverse strings 24. The preferred point of impact A
for a tennis ball (not shcwn) lie in Figure 1 approximately at the point of intersection of the longitudinal ~Kis M of the racket and the section line III-III, and in Figure 2, zç~y~x~ltely on a line K.
The racket head 14 or its holJow profile bsr 12 is substantially of extended eval cross-section, the side w~Lls 26 thereof extending at an internal spacing as indicated at a of for example 8 mm (outside width m about 10 mm~ a~d blending into arcuate portions 27 with an internal profile height b of 20 mm and an external profile height as indicated at n of in this c~se about 25 mm.
The profile b r 12 i8 formed from a tubular bl~nk 30 in which longitudinal fib~r ~trands 31 are arranged in the arcuate portions 27.
m e ends of the blank 30 are brought together at the racket ~haft 19 in ~u~h ~ way that two ch2ni~ers 29 are formed in the ahaft and in the handle 20. m e two ends of the blank 30, as shcwn in Figure 4, form the octagDnal cro5s-section of the handle 20.
In the entx~diment shcwn in Figure 5 th~ handle 20 is m~de fm m two portions 32 and 32a which ~re connected together at 2 ~pasing e by an elastic inte ~ ate portion 34. The latt~r ccn~y~ises two transverse plates 36 of metal ~r another suitable m~terial, and a rubber block 38 which i~ fiXP~ly vulcanised t ~ . It forms a hinge i~csti~n of limited fleoLLbility, the hinge axis B of ~hich extends at a spacing t of from 60 th~x~ugh 220 nnn relative to the end face 21 of the handle cap 22, constituting the end face of the handle. The 6pacing of the hinge aKis B
. from the end 15 of the racket he3d 14 is iientified by ~.

7~

The hinge location shcwn in Figures 6 and 7 is defined by grooves 40 of a greatest width as indicated at z, the grooves 40 being formed at both sides in the handle 20 and reducing in size towar~s the axis M of the handle. The grooves 40 are filled for example by plastic blocks 42 S with a low , level of flexural stiffness. The depth i of the grooves 40 in Figure 7 is somewhat shorter than the thickness c of an interTediate portion 44 which remains in the handle 20; the surfaces of the intermediate portio4 44 each form the lcwest point 41 of the respective groove. Mor0over lDngitudinal strands or cords 31 of the blank 30 are laid arcund the grooves 40 and are therefore not interrupted at the hinge location.
In Figure 8 the hinge location oomprising the intenmediate limb portion 44 which i8 flanked by the grcoves 40 is disposed adjacent the end of ~he racket shaft 19.
If the thLckness c of the Lntermediate linb portion 44 which is formed by the grooves 40 cver the length z snd which does not only have to be of the shape shcwn in the illustrated cmbod~nent measures about half the thLckness h of the handle 20, the flexing which occurs in response to a force acting on the racket, by virtue of the lower mcrent o~ inertia in the cros~-section of the limb portion, per unit of length, i8 about 4.3 time8 ~R high as the flexing which occurs with a full handle cross-section if the mDdulus of ela8ticity i3 assumed to be unalter~d;
mrreover the degree of flexing is inversely proportional to the product of the noment of inertia x modulus of elasticity~
If tbe thickne~s c of the limb portion is only one third of the thi ~ 88 h of the handle 20, the oorrespond~ng vnlue is 12.5 an~
finally, at a one quarter situation, it R twenty times as hi~h~ Those init;~lly calculated value~ are confirm3d u$on nEasurcments carried out on cc~llYqxmdlng r~cket configurations, a preferred nfesu:enent in respect of the thickness c be m g when it mea~ures about 4 through 6 mm, '. that iR to say the thickness h of the handle 20 i etween five and eight times the thicXness c.

The hinge location 34 m~st be fairly elastic in order to cause small variations in frequency. That wil1 ncw be described by means of an example with reference to the construction shown in Figures 5 and 6.
The thickness c of the limb portion 44 should be half the thickness h of the handle of the tennis racket 10, with the width z being 20 ~m. The spacing t from the handle end 23 is fixed at 120 mm. m e ball hits the stringing Q at the location A which in the illustrated example is 400 mm away from the hinge ?XlS B. Fbr the sake of sImplicity it is assumed that the nrmen$ of inertia for the full handle cross-section is unaltered for all racket cross-sections, that is to say CVOE the entire length of the racket, no torsional moments occur and the mDdulus of elasticity remain constant~ Calcu~tion shows that flexing of the tennis racket 10 with the above-described hinge Joc~tion 34 und OE the fo m e of a ball acting th~30n is 1.22 times as high as that of an identical racket without hinge. The frec~ency of the tennis racket wDuld then change with the reciprocal value of the root of the flexing. If the tennis racket 10 had a frequency of 80 Hz, the racket provided with that hinge would have a frequency of 80 x 1~ r 22 Hz, that i8 to say 72.5 Hz.
A further e~u~q?le is inte~ded to show how it is po~sible to achieve a ~ 3at OE dbn~p in freque~cy.
The height c of the l$nb portion is selected to be a quarter of the thicXness h of the h~ndle, wlth the width z being 1~0 ~m. In other r~#~p#:ts the dat~ of the first e~rnple apply.
In thl~ c~se the db~ree of flexing being sGught ~niid be ~ix times as great ~nd the fr~xa~ency bx~l~y s~ught wc~ild also be six tiTes lower, that is to say only 33 Hz inste2d of 80 Hz. That freqyency relates to a tennis racket 10 which is f;xP~ly clan~ed AQ fRr ~8 the first hinge at the handle 20.
In the enilXl~nent ahcwn in Figures 9 and 10 ~he racket shaft 19 anl the adjoining shaft portion vf the handle 20 are ~ymnetrically divided in . the di~rection of th~ longitudin~1 axis M of the racket, that is to say each of the pr~file ~rms 16 $s extended with its own ~haft hA- pa~t 46a 7 ~7~

in the handle 20, wherein the two shaft bar parts 46a to~ether determine the external contour of a handle shaft portion 46 and delimit between them a shaft gap 48 which, as shown in Figure 9, accommodates an elastic intermediate layer 50 and defines a plane E ~hich passes through the stringing surface or area Q, substantially perpendicularly in Figures 11 through 14.
In the erbodirent shown in Figures 9 through 1l the shaft bar parts 46a~ apart from the hinge location 40/44, are symmetrical ~ull profiles with an interposed strip of elastic material AC a filling intermediate layer 50 in the shaft gap 48 which is here linear in cross-section, whereas Figure L2 shcws shaft bar parts 46b~ 46C of different cross-sectional configurations, with between them, and at different spacings f, g relative to the side contours 52, a shaft gap 48C which is of a substanti.ally wavy or corrugated configurat~on and which is entirely L5 filled by the elastic intenmediate layer 50c.
Figure 13 ~hows a handle 20 with a holJow profile which is divided symmetrically in the plane E into shaft bar parts 46d~ with an elastic round strand or oord 50d. The construction shown ~Ln Figure 14 corresponds to that shown in Figure 11 with the difference that the ahaft bar parts 46e are hollow pr~files each having a profile cha~ber 47 defined therein.
Finally Figure 15 8how8 a three-part handle shaft portion 46f cu.~i ing two side bar part~ 54 and a oore or oentral bar p3rt 55;
between then Figure 15 shows intenmediate layers 50k which are curved in a part-circular oGnfiguration relative to each other. Ins~ead of the aboYe-describ~d plane E, two curved surfaces F can be &een herein.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A racket for ball games, in particular a tennis racket, comprising stringing in a stringing frame comprising a shaped bar, a throat region which adjoins the stringing and a handle on a racket shaft on the longitudinal axis of the racket which preferably forms a straight line of symmetry, wherein the free end of the handle is defined by a handle end face, characterised in that the racket (10) has a hinge location (34, 44) between the throat region (H) and the handle end (23) of the handle (20) and the hinge axis (B) extends parallel to the stringing (Q).

2. A racket as set forth in claim 1 characterised in that the hinge location (34, 44) is disposed in the region of the handle (20).

3. A racket as set forth in claim 2 characterised in that the center or hinge axis (B) of the hinge location (34, 44) is disposed at a spacing (t) of from 60 mm through 220 mm from the handle end (23).

4. A racket as set forth in one of claims 1 through 3 characterised in that the hinge location (34) is formed by an elastic material block (38), for example a rubber block, which connects two portions (32, 32a) of the handle (20).

5. A racket as set forth in claim 4 characterised in that the block (38) is vulcanised at both ends on to plates of the handle portions (32, 32a).

6. A racket as set forth in one of claims 1 through 3 characterised in that the hinge location is formed by a limb portion (44) of the handle (20) or the racket shaft (19), which is delimited at least at one side and preferably at both sides by a groove-like channel (40) formed therein.

7, A racket as set forth in claim 6 characterised in that the width (Z) of the groove or channel (40), as measured on the longitudinal axis (M) of the racket, is up to 100 mm.

8. A racket as set forth in claim 6 or claim 7 characterised in that the thickness (c) of the limb portion (44) approximately corresponds to the depth (i) of the groove or channel (40).

9. A racket as set forth in claim 6 or claim 7 characterised in that the thickness (h) of the handle (20) corresponds to between four and ten times and preferably five and eight times the thickness (c) of the limb portion (44).

10. A racket as set forth in at least one of claims 6 through 9 characterised m that the groove or channel (40) is filled by a shaped mass (42) with a low level of flexural stiffness.

11. A racket as set forth m at least one of claims 1 through 10 characterised by a plurality of axially adjacent hinge locations (34, 44).

12. A racket as set forth in at least one of claims 1 through 11 characterised in that the flexing in the elastic region of the racket (10) which is fixedly clamped as far as the first hinge location (34, 44) by the handle 120), under the action of a force which act at a spacing of about 400 mm from the hinge axis towards the head, is between 1.2 and 9 times as great as the flexing of a hinge-less racket which otherwise corresponds thereto when fixedly clamped at the handle (20) as far as the hinge axis (B).

13. A racket as set forth in at least one of claims 1 through 12 characterised in that the racket shaft (19) and the racket shaft portion forming the handle (20) has a shaft gap (48, 48c, 48k) which extends continuously into the throat region (H) and which at least in a portion-wise manner contains an elastic mass (50) which bears at both sides against surfaces delimiting the shaft gap, as an intermediate element between shaft bar parts (46a through 46e; 54, 55).

14. A racket as set forth in at least one of claims 1 through 13 characterised in that the shaft bar parts (46a through 46e; 54, 55) are at least partially movable relative to each other in the striking direction.

15. A racket as set forth in claim 13 or claim 14 characterised in that the shaft gap (48) defines a surface (E, F) extending transversely with respect to the stringing surface (Q).

16. A racket as set forth in claim 15 characterised in that the surface (E) which extends transversely to the stringing plane defines a plane of symmetry.

17. A racket as set forth in claim 13 or claim 15 characterised in that the surface (F) defined by the shaft gap (48k) is curved in cross-section.

18. A racket as set forth in at least one of claims 13 through 17 characterised in that the cross-section of the shaft gap (48c) is of a wavy or zig-zag configuration.

19. A racket as set forth in one of claims 1 through 18 characterised in that the handle (20) is formed by at least one hollow profile member.

20. A racket as set forth in one of claims 13 through 19 characterised by a plurality of surfaces (E, F) or shaft gaps (48, 48c, 48k) in the cross-section of the handle (20).