Arrangement for rackets

Technical field:

The present invention relates to an arrangement for rackets for ball games, comprising a frame with a handle and a plurality of mutually crosswise laid strings which are secured in the frame. A representa¬ tive type of such rackets is tennis rackets, and the invention relates primarily to these.

Background:

In ball games using rackets, especially tennis, problems arise for many players because of the movement of the strings due to the transverse forces which arise upon impact of the ball. This is especially noticeable in the case of so-called topped and sliced strokes, whereby the principle plane of the racket is held at an angle to the intended direction of the ball. Improper positions of the strings can have an unfavorable effect upon the playing characteristics of the racket so that the player must repeatedly adjust the position of the strings. These transverse motions, especially of the longitudinal strings and for rackets strung tightly, lead to greatly increased wear on the strings at the points of intersection, not least because of the fact that particles often accumulate at the points of inter¬ section of the strings, which significantly shortens the life span of the strings.

Another problem is the vibrations which are created in the strings during ball impact and which give rise to sound phenomena, especially in the case of rackets with metal parts and, furthermore, have been shown to be a cause of joint injuries, so-called tennis elbow, to the player.

It is previously known from, for example US-A 4 078 796, to provide plastic inserts at the points of

intersection of the strings, but these consist of sepa¬ rate elements which are made of a smooth, relatively hard plastic material and which may reduce wear to a certain extent but which, however, do not hinder the motion of the points of intersection.

Bodies of soft material have also been proposed, as in DE-B 25 21 578.

Technical problem:

Using previously known devices it has only been possible to achieve a limited effect and only in cer¬ tain cases , such as damping the sound in metal-strung rackets. Other desirable improvements, in part pre¬ venting the sideways motion of the strings during sliced strokes and in part reduced physiological stresses by reducing vibrations, have not been able to be achieved to any great extent or at the same time.

The solution:

The solution according to the invention is a number of tubular flexible units which are provided to encase certain chosen ones of the strings of the racket and to extend in their longitudinal direction. Each unit exhibits an inward longitudinal channel and an enveloping surface, against which crossing strings are provided to lie. The desired effect of the invention is obtained by applying the units to specific ones of the strings of the rackets and by making the units from a chosen material.

Advantages:

By means of the invention, the sought-after effect, that is, 'n part, the position-holding effect upon the strings, so that these do not move so that the racket must be re-strung, but, however, not with such holding power that the impact effectivness of the racket is diminished, and in part, a damping of the vibrations of the strings, so that these vibrations

decay quickly and the physiologically injurious effect on the arm of the player is reduced.

Brief description of the drawings:

The invention will now be explained below in more detail using exemplifying embodiments with reference to the enclosed drawings in which fig. 1 shows a partially broken view of a tennis racket, provided with a first exemplifying embodiment of the arrangement according to the invention, fig. 2 shows a likewise partially broken view of a tennis racket, provided with a second exem¬ plifying embodiment of the arrangement according to the invention, fig. 3 is a partially broken view, viewed along the cut III-III in fig. 1, fig. 4 is a view in enlarged scale, viewed along the cut IV-IV in fig. 1, while fig. 5 is a corresponding sectional view of an alternative embodiment of the arrangement according to the invention.

Best mode of carrying out the invention:

The arrangement according to the invention con¬ sists of a number of tubular units 1, 2, 3 and 4, which are provided to surround certain chosen strings 5 and 6 on a racket 7, for example, a tennis racket, the head of which is shown, but the handle -of which is deleted for reasons of space. In conventional manner, the handle consists of a lengthwise extending unit, which is firmly joined to the head and extends in the general plane of the head, i.e., the general plane in which the frame 8 and the strings 5 and 6 extend. In conventio¬ nal manner, the strings are secured in the frame 8 and consist either of separate strings for each longitudi¬ nal or lateral extension or of continuous strings, which are redirected through holes in the frame. In the example shown, the tubular units 1-4 are four in number, whereby two tubular units 1 and 2 are arranged on longitudinal strings 5, while two of the tubular units 3 and 4 are arranged each on one of the trans¬ verse strings 6. By "longitudinal strings" is meant

those strings which extend in the longitudinal direc¬ tion of the racket, i.e., over the length of the oval frame, whereas the transverse strings 5 extend in the transverse direction of the racket, i.e., over the breadth of the frame. The longitudinal strings 5 ex¬ tend consequently generally parallel to the handle. The tubular units are preferably placed so that they divide the surface within the frame, i.e., the impact surface of the racket, into suitable sections, whereby placement of the tubular units on the transverse strings has been chosen in such a manner that the longi¬ tudinal strings 5 are divided in three by the trans¬ verse tubular units 3 and 4 so that at least two of the three portions, more specifically, the central portion and the portion located closest to the handle, have been chosen to be generally of the same size, which provides optimal reduction of the sideways motion of the strings. The transverse strings 6 are divided in three in a similar manner which, in the example shown, is done in a symmetrical manner by positioning the two longitudinal tubular units 1 and 2 at the same general distance from the edge of the frame, in the example shown, placed on the third one of the longitudinal strings 5, counting from the respective edge of the frame. In this manner the longitudinal ^" tubular units 1 and 2 are placed in the outer region of the impact surface of the racket which comprises the part of the impact surface which provides pure and satisfactory impact with the ball. Of the transverse tubular units 3 and 4 the upper unit 3 extends in the outer region of the impact surface, while the lower unit 4 is placed further in in the impact surface, but not at the center of it. In this way the motion of the strings, i.e., the movement of the points of intersection 9 between the longitudinal strings 5 and the transverse strings will consequently be reduced to a minimum.

In the exemplifying embodiment shown in fig. 1 both the longitudinal tubular units 1 and 2 and the transverse tubular units 3 and 4 extend generally over

the entire length of the strings 5 and 6 while, in the exemplifying embodiment shown in fig. 2, the longitudi¬ nal tubular units 1 and 2 have been shortened so as to extend only between the two transverse tubular units 3 and 4, more precisely, generally equal to the distance between these units. In this way the increase in thick¬ ness which otherwise arises at the points of intersec¬ tions between the tubular units is avoided.

The tubular units therefore consists of tubes, that is to say, flexible encasing elements having an internal longitudinal channel, through which each res¬ pective string 5 and 6 extends when mounted. The tubes exhibit an inner diameter or inner transverse dimension which corresponds as closely as possible to the outer transverse dimension or outer diameter of the strings 5 and 6. The manner in which the strings extend in the tubular units 1 and 3 is seen more clearly in the de¬ tailed views in figs. 3, 4 and 5. In one advantageous embodiment the tubes are completely closed, thereby forming a continuous enveloping surface around the strings in question and are in such case mounted in connection with the stringing of the racket when it is manufactured or during subsequent occasions for string¬ ing. In connection with stringing, the tubular unit in question is threaded on when the respective string is drawn between the securing points of the frame. Accord¬ ing to the alternative embodiment shown in fig. 5 the tubular units can be slotted with a longitudinal slit 10 extending over the entire length of the unit, there¬ by making it possible to mount the tubular units onto a racket which is already strung. The tubular unit is thereby threaded sideways over the string in such a way that the string is inserted through the longitudinal slit 10. Since the tubular unit is preferably made of an elastic material the slit will generally close after application of the unit. In combination with the tubu¬ lar unit being held in position against the strings 5, which run in the lateral direction of the unit, this

prevents the unit from inadvertently coming loose from its respective string.

The tubular units are made of a flexible, deform- able, preferably elastic material, which makes it possible for the units to follow the slightly zig-zag shaped extension of the strings and to follow the small elastic motions of the strings in a direction trans¬ verse the impact surface, which arise upon impact with a ball. During this the strings are stretched slightly in their longitudinal direction and, because of the elastic properties of the strings, they return to an initial position in the principal plane of the racket. Because of the deformability of the tubular units a deformation arises at each point of intersection of the tubular units on the one hand and the strings 5 and 6, which run perpendicular to the tubular units, on the other hand and also at the points of intersection of the tubular units in the embodiment of fig. 1, the deformation being in the form of an impression in the enclosing surface of the tubular units, thereby provid¬ ing shaped engagement for the strings which run perpen¬ dicular to the tubular units, so that they are general¬ ly locked into position as far as movements in the said principal plane are concerned. This means that the strings are locked not only at their points of attach¬ ment to the frame but locking against sideways motion, i.e., in the principle plane, is provided in both of the embodiments principally along two intermediate positions over the length of the majority of the strings 5 ^" and 6. This means that, by means of the said division into three of the strings, the length of each string which can stretch freely is greatly reduced to being a smaller part of the total length of the strings, which greatly reduces the possibility of side¬ ways motion of the strings and, consequently, of their points of intersection 9.

Even for impacts which cause lateral forces in the strings, the strings will consequently yield to a lesser extent and will maintain their principle

positions even between the tubular units. Some small motion at the points of intersection is naturally per¬ mitted in order to give the racket its good playing characteristics, which, to a certain extent, will be improved due to the limited sideways give of the strings. Impact forces will consequently be transfer¬ red to the ball during topped and sliced strokes to a greater extent because of the reduced give of the strings, which leads to an increased spin effect and to greater velocity of the ball. Furthermore, it has been demonstrated that the tubular elements also have a vibration damping effect which, consequently, solves a serious problem of modern tennis rackets of metal and composite materials to which, otherwise, special vibra¬ tion damping elements are often applied between the strings. In this way, arm injuries to the player are counteracted to a great degree. Suitable material for the tubular units is, e.g., relatively hard rubber material or plastic material.

It is advantageous to mount the tubular units using special tools or fixtures ^' . When threading the tubes in connection with stringing a stiff metal thread can for example be used, whereby it is inserted through the tubular units and is provided with a securing ele¬ ment for the end of the string, whereby the string is drawn through the tubular unit when the stiff thread is drawn back. The slotted tubular units are mounted with suitable tools, provided to separate the transverse and longitudinal strings from one another at each point of intersection, either one point of intersection at a time or all points of intersection over the entire length of the tube, so that the tubular unit can be applied.

The invention is not limited to the exemplifying embodiment described above and shown in the drawings but can be varied within the scope of the following patent claims, especially in view of the fact that it is conceivable that the arrangement be applied to other rackets than tennis rackets, such as rackets for squash.

The strings can for example be locked against the tubu¬ lar units by providing the tubular units with a surface having. such friction that a friction locking instead arises, however, a shaped locking is judged to give less wear unless the friction is so great that the point of intersection with the tubular unit cannot be moved. The points of intersection with the tubular units move because of the deformation and flexibility of the tubular units in the longitudinal direction of the units, i.e., so that these follow the extension and elastic compression of the respective strings, which means that the distance between the points of intersec¬ tion will vary somewhat upon impact. The points of intersection are, however, consequently locked against a residual motion so that an uneven distribution is avoided as far as the distance between the strings is concerned. The greatest problem with respect to the motion of the strings is with the longitudinal strings 5 which are longest and are exposed to the greatest extent to lateral forces upon impact with the ball. In certain cases it may therefore be sufficient to use only one, for example, centrally placed, transverse tubular unit in order to lock the longi- tudinal strings, or two transverse tubular units, in accordance with the exemplifying embodiments shown, whereby the longitudinal tubular units may possibly be left out. The number of tubular units can therefore be varied from one to several units. From what has been stated above it is obvious that the longitudinal strings 5 are locked by -means of the transverse tubular units 3 and 4, which are applied to one or several transverse strings, while the transverse strings 6 are locked by means of the tubular units 1 and 2, which are applied to longitudinal strings.