Device for rackets

Technical field:

The present invention relates to a device for rackets which have a frame in which a number of intersecting strings are tensioned, in which respect spring elements are arranged on at least some of the said strings for exerting a spring force on the said strings in their longitudinal direction for the purpose of counteracting changes in the tension of the said strings, and the said spring elements are designed to be run through by the string in question and have an arched, curved convex part.

Technical problem: In racket games, such as tennis, squash, badminton and- the like, the properties of the strings are of particu¬ larly great importance for the playing characteristics of the racket and, thus, the ability of the player to manage the ball in the desired manner. An extremely important factor for the properties of the strings is the tension of the strings, i.e. the tensile force which is applied to the strings during the stringing process, which tensile force affects the spring flexibility of the strings and, thus, the ball which hits the striking surface of the racket.

Experience has shown that in a racket it is the longest strings situated in the centre of the striking surface of the racket, i.e. in the hitting area of the racket, that are particularly exposed, during the first hours after stringing the racket, to a considerable reduction in tension, which thereby changes the playing characteris¬ tics of the racket. This can of course to a certain extent be compensated by giving the racket an overten- sioning, corresponding to the reduction in tension. However, this instead means that, during the first hours, the playing characteristics are not those desired, until the string tension required for a particular player is

obtained .

Moreover, in the case of conventional rackets there are difficulties involved in achieving optimal playing characteristics, since maximum ball control requires a certain level of tensioning, while maximum transmission of power to the ball requires another level of tension¬ ing.

Prior art:

US-A-1,542,177 discloses an arrangement in which spring elements are arranged on the outside of the frame and each act on two strings. However, a change in the form of the spring elements results in a sideways displacement of the position of the strings, which can affect their useful life as a result of increased wear at the inter- section points.

The aim of the present invention is to eliminate the abovementioned disadvantages of known rackets in such a way that the reduction in tension after stringing the racket is kept to a minimum and optimal playing charac- teristics are thus achieved.

Solution:

The said aim is achieved by means of a device which is characterized in that the said spring elements are situated inside the frame and are designed to produce, in the string in question, an arched deviation from its essentially rectilinear extension, in that the said spring elements are designed with a central, arched part which forms the said convex part over which the string runs and which is designed to be deformed in an elastic- ally flexible manner in order to counteract changes in the tension of the string, and has two end parts, each with an opening through which the string extends, and in that the said end parts are curved in the opposite direction to the central part forming, outside the associated openings away from the convex bearing surface of the central part, likewise convex bearing surfaces for

the string, over which the latter is deflected. Description of figures:

The invention will be illustrated in greater detail below on the basis of two exemplary embodiments and with reference to the attached drawings, in which Fig. 1 shows a broken view of a tennis racket provided with the device according to the invention. Fig. 2 shows a side view and Fig. 3 a front view of the device according to the invention in a first embodiment. Figs. 4, 5 and 6 show three different views of the first embodiment according to the invention assembled on a string belonging to a racket. Fig. 7 shows, on a larger scale, a partially broken section of the upper part of the element according to Fig. 4. Fig. 8 shows a side view of a second embodi- ment of the device according to the invention assembled, on a string belonging to a racket.

Preferred embodiments:

Fig. 1 shows the head 1 of a racket 2, for example a tennis racket, whose elongate shaft 3 is essentially cut away for reasons of space. The head consists in a conven¬ tional manner essentially of a frame 4 which encloses an area over which there extends a set of crosslaid strings 5, 6. The frame 2 is, in accordance with conventional design, made of a relatively rigid material, such as wood, metal, graphite, carbon fibre, polymer material or a composite material or the like, which affords suitable characteristics for the racket game in question. The crosslaid strings consist of two main types, namely lengthwise strings which extend essentially in the longitudinal direction of the shaft, and transverse strings β which extend at right-angles to the lengthwise strings. Another arrangement of the strings is of course conceivable. The strings can consist, for example, of a single continuous string or of two or more individual lengths, which are secured in the frame 4 of the racket. The strings are secured by extending through channels in the frame (see broken lines in Fig. 1) and usually form loops and thus extend in a serpentine pattern, except

at the ends of the lengths where these are secured by means of a knot or another locking element. The set of strings thus forms a striking surface for the racket, whose central area is usually called the hitting surface and constitutes the surface where the best hitting characteristics are achieved and which it is thus attemp¬ ted to use during play. The crosslaid strings are inter¬ twined in a conventional manner so that each string length alternately runs over and under the crosslaid strings.

According to the present invention, spring elements 7 are arranged on at least some of the strings 5, 6 and are designed to counteract changes in the tension of the strings.

The first embodiment of the spring element shown in Figs. 1-6 consists of a leaf spring, expediently of spring steel, through which the actual strings are thread. The spring elements are, as shown in Fig. 1, suitably posi¬ tioned in the vicinity of the frame, i.e. outside the hitting surface and in one of the areas where the strings are not crosslaid. The spring element 7 is pre-formed with a central arched part 8 which extends between the two ends 9, 10 of the element where the central curvature merges into two smaller arch parts bent in the opposite direction. In these end parts there are openings 11, 12, one for each end part, which are expediently formed by punching-out so that a lug 13, 14 is formed which is turned up so that each of the openings can allow a string to pass through.

Figs. 4, 5, 6 and 7 show how one of the strings 5 extends through the spring element 7, namely through the two openings 11, 12, so that, at the end parts outside the two openings, the string bears against the convex side of the end parts and, at the openings, changes to the other ^' side of the spring element and bears against the convex side of its central arched part 8. As a result of the

arrangement of the punched-out lugs 13, 14, which are moreover rounded, the string does not bear against the edge of any opening but acquires a bearing surface against the inside of the lugs, which merges continuously into the convex side of the arched end parts. This eliminates the risk of such wear as would weaken and break the string.

The spring element according to the first embodiment is, as a result of the chosen tension of the string, only partially sprung so that an additional spring to a desired radius of curvature is possible, which occurs when hitting the ball, and as a result of this the playing characteristics of the racket are extremely favourable. Upon impact with the ball, there is thus an additional tendency for the spring element to straighten out, accompanied by an extremely rapid return to the initial shape which is maintained in the rest position under the string tension chosen. This therefore affords a combination of the favourable characteristics which are obtained in a looser or a harder string racket, namely - despite a chosen and, for example, high tension force, good flexibility and elasticity of the string.

After stringing the racket 1 provided with the device according to the invention, the considerable reduction in the string tension which occurs in conventional rackets during the first playing hours is eliminated by virtue of the fact that the extension of the active length of the

^• strings, occurring in those strings which are longest and at the same time most exposed to the ball, i.e. the length of each string between its securing points in the frame, is taken up by the deformation of the spring element so that the desired tension force is essentially maintained or subjected to a minimal reduction. This minimizes the change in the playing characteristics of the racket after stringing, which is particularly desir¬ able for all players. In the case of the element accord¬ ing to Figs. 2-7, this is achieved by means of the

distance between the ends of the spring element being reduced under the action of a spring force.

Fig. 8 shows a second embodiment in which the spring element, which is designated 15, comprises an elastically flexible cushion 16 whose one side 17 forms an arched, central surface over which the string 5 is essentially deflected, in which respect the ends of the spring element have the same design as in the first example with openings 18, 19 and lug flaps 20, 21 and the curve directed in the opposite direction relative to the central arched part. For the frame of the spring element, a leaf spring of the same type as in the first example can be used, but the part 24 lying between the ends can be straight or even arched in the opposite direction to. the outside of the elastic cushion 16.

In the second -embodiment according to Fig. 8, a spring resilience is obtained by means of the material proper¬ ties of the cushion 16, in which connection a change in the tension of the string results in a changed deflection of the string in a part which runs through the spring element by means of deformation of the cushion, which is compressed at a higher tension and expands at a lower tension of the string in the part which is situated in front of the string.

The difference between the two spring elements at varying tension of the string lies in the fact that, in the first embodiment, there is a variation between the securing of the string in the spring element, i.e. essentially at its openings 11, 12, while in the second embodiment there is a change in the length of the extension of the string through the spring element, although the effect in principle remains the same, namely taking up a change in the active length of the string as a function of changes in the string either on account of the string being stretched or tightened or on account of a momentary force transverse to the longitudinal direction of the string.

such as when hitting the ball.

The invention is not limited to the exemplary embodiments described above and shown in the drawings, but can be varied within the scope of the subsequent patent claims. For example, another number of spring elements than that shown in the drawing can be assembled, for example a greater number of spring elements for the lengthwise strings and, if appropriate, also for some of the trans¬ verse strings, in which respect the spring elements are positioned inside the frame and outside the area with crosslaid strings. The material of choice for the strings is, for example, polymer material in which stretching is greater than in natural strings. The spring element according to the invention thus affects the elastic properties which a string normally has on account of the. material properties of the string.