EP0106850B1 - Tennis or squash racket - Google Patents

Abstract

In a tennis or squash racket, the strings (22, 24) are mounted without friction on the frame (12) and arranged at the surface of the frame in such a way that two parallel strands (22c, 22d) of the same string are distant by at least one ball diameter. Between said two parallel strands two other strands (24d) belonging to an other string (24) are arranged. Such arrangement of the strings allows to distribute the tension resulting from a stroke on the ball in areas which have not been in contact with the ball.

Description

The invention relates to a tennis or squash racket with an essentially elliptical frame, a handle connected to this and a string attached within the frame made of strings crossing each other, the at least one on the frame with low friction and several times stretched over the frame with in includes essentially parallel string sections.

In conventional tennis rackets, the strings are passed over the frame surface with a uniform or slightly differentiated tension and fixed at their ends in the frame. Since a large number of parameters are involved in the playing behavior of a tennis racket, some of which have opposing characteristics, it is at most possible with such a covering to give the stringing at the ideal point of impact of the ball, the "sweet spot", favorable tension and impact loss properties . When the "sweet spot" is optimized, it is generally not possible to optimize other areas of the covering at the same time. As a result, balls that do not hit the "sweet spot" are relatively difficult to control and strain the wrist of the player.

A tennis racket is known from GB-A-380 915, in which the strings are guided over deflection rollers mounted in the frame and a number of tensioning devices are provided on the frame for individually tensioning individual strings. To a certain extent, this solution enables the tension behavior of the strings to be corrected, but is still tied to essential parameters which impair optimal tension distribution, such as, in particular, the stretchable string length and the course of the string.

FR-A-784 057 describes a tennis racket in which a continuous, endless string is also guided over rollers in the frame and is connected to a tensioning device in the transition area between the handle and the frame, which is referred to as the heart of the tennis racket change of the total tension by the player himself. Apart from the fact that this solution does not allow individual selection of the tension of individual strings and the tension gradient in the racket, it has also only proven to be of limited functionality, since the considerable friction occurring at the crossing points of the strings leads to the tensioning device applying Preload is only spread over the entire stringing in a very slow creep process.

Similar solutions with deflection rollers in the frame and a tensioning device in the handle are shown in GB-A-2 029 241 and US-A-4 057 249. These constructions are also opposed to the concerns previously expressed.

From US-A-2 206 548 a racket is known, in which the stringing consists of several strings.

The object of the invention is to improve the elastic properties of the strings, in particular when the ball contact is not central.

This object is achieved in that the immediately adjacent parallel string sections belong to different strings and that the distance between the string sections belonging to the same string is at least about a ball radius.

With this type of string guide, the stretching of the string sections directly involved in the ball contact leads to an increased tension in those sections of the same string which run in the region of the edges of the ball contact zone. In this way there is a tension distribution, which is characterized by high elasticity in the ball contact zone, while the stringing in an area surrounding this zone is more tensioned and is correspondingly less deflected, so that the ball receives better guidance during the stroke. While in conventional rackets the position of the "sweet spot" is fixed once and for all, in the racket according to the invention the "sweet spot" is formed at the point of contact with the ball.

The strings are preferably at least partially extended beyond the frame area, and the string sections extending beyond the frame area are freely stretchable and connected to the string sections lying in the frame area via a low-friction deflection. The strings are preferably extended into the hollow handle and possibly down to the bottom.

This solution offers the possibility to extend the stretchable length of individual or all strings, which is of course essential for the elasticity behavior, in any way.

The advantage of this extension is particularly evident in the example of the relatively short strings lying in the edge region of the frame, the tension behavior of which is always unsatisfactory in conventional rackets. However, there are corresponding advantages for the entire sowing.

The elongated strings are preferably fastened within the handle in arbitrarily selectable longitudinal positions of an elongated slider which can be displaced longitudinally in the handle; that can be moved with the help of a clamping device. This tensioning device offers the user the possibility of raising and lowering the overall tension of the tennis racket, which is optimized with regard to the tension distribution. It is quite possible and under certain circumstances it is even intended that the tensioning process will produce effects of different strengths according to the different string lengths.

In conventional tennis rackets, the frame is usually designed in such a way that it is capable of absorbing shock losses within certain limits. The absorption of impact losses, which occur particularly in non-central ball contacts, can take place according to the invention in that the slider as such is suspended elastically or elastically damped.

In a further preferred embodiment of the invention, the deflection between the string section lying within the frame and the string section extending beyond the frame is admittedly reduced in the pulling direction into the interior of the frame surface, that is to say when a string is deflected upon impact, it is braked in the opposite direction. This enables a high reduction of impact losses, since the ball is taken up softly and resiliently by the racket but is not immediately thrown back by the springing back of the string immediately.

Brief description of the drawings

• Fig. 1 shows a schematic, partially cutaway plan view of an embodiment of a tennis racket according to the invention;
• 2 schematically illustrates the deflection of the stringing of a tennis racket according to the invention;
• 3 is a view of an embodiment of a slider;
• Fig. 4 is a partially cutaway left side view in Fig. 3;
• Fig. 5 shows a further embodiment of the slider;
• 6 and 7 illustrate the storage of the rollers in the frame;
• 8 to 11 illustrate further forms of deflection of the strings in the frame;
• Fig. 12 is a partial cutaway view of the handle of another embodiment of a tennis racket;
• 13 shows a junction between two crossed strings of the tennis racket according to the invention.

Preferred embodiments of the

invention

A tennis racket shown in FIG. 1 comprises a handle 10 and a frame 12. The handle is hollow and has a plate 14 closing the handle at its free end. Within the area formed by the frame 12 there is a string, generally designated 16, which is indicated in FIG. 1 only by a single, completely drawn-in string 22 and a further string 24, which is only partially shown. A longitudinally displaceable slide piece 18 is attached within the hollow handle 10. Through the plate 14 closing the handle, a clamping bolt 20 is freely rotatable, which enters with thread engagement in the lower end of the slider 18, so that a longitudinal displacement of the slider 18 can be achieved within the handle 10 by rotating the clamping bolt. The individual strings of the strings 16 extend through bores 26 arranged in longitudinal sections in the sliding piece 18 and can thus be re-tensioned by the user together with the aid of the tensioning bolt 20.

In the exemplary embodiment shown, the tennis racket has a diagonal covering. The string 22 is fixed to the frame at point A at the bottom left in FIG. 1 and extends with a first section 22a diagonally across the frame surface to a deflection roller 28. From there, the string 22 is outside the frame 12 to a further deflection roller 30 guided. A subsequent section 22b of the string 22 runs parallel to the section 22a to a deflection roller 32 (point C). From the deflection roller 32, the string 22 runs through one of the bores 26 of the slide piece 18 within the hollow handle 10 (point D) to a further deflection roller 34. Two further sections 22c, 22d of the string 22 which are parallel to one another are symmetrical to the string sections via deflection rollers 38 22a, 22b. The end of the string section 22d is fixed at point B on the frame 12. The distance between the parallel string sections 22a and 22b or 22c and 22d corresponds approximately to the radius of a tennis ball.

The other strings of the strings 16 are essentially similar to the strings 22. The parallel string sections of the individual strings have essentially the same distances and accommodate the string sections of other strings between them. For example, a string section 24d of a string 24 extends between the string sections 22c, 22d of the string 22, while the string section 24c parallel thereto extends outside the string sections 22c, 22d.

If, for example, a ball hits a point P at a stroke, the string sections 22a, 22c and 24d are hit directly by the ball and stretched accordingly. The tensile force occurring in these string sections is transmitted almost undiminished to the string sections 22b, 22d and 24c by the deflection rollers, so that there is an increased tension in an annular area around the point P. The resulting deflection of the strings 16 is shown schematically in FIG. 2. While the stringing is curved concavely to the ball in the usual way directly in the area of the ball contact zone, due to the increased tension there is a in the adjacent sections F of the stringing convex curvature recognizable. The ball 42 is therefore received in a relatively narrow trough, which gives the ball guidance and ensures that the ball 42 is accelerated in a direction perpendicular to the plane E of the frame surface when the strings spring back.

In order to reduce the friction in the nodes at which the individual string sections intersect, the parallel groups of string sections, which in FIG. 1 are represented on the one hand by the string sections 22a, 22b and on the other hand by the string sections 22c, 22d, 24c and 24d, are in arranged on two different levels. The strings are not networked with each other, but run freely past each other. On the other hand, to avoid undesired distortion of the strings when the ball strikes, the string sections are connected to one another at the crossing points by connecting pieces. Such a connector is shown in Fig. 13 and designated 110. The connecting piece 110 is formed by two rings 112, 114 which are firmly connected to one another and which are oriented perpendicularly to one another with their central axes and each run through with low friction on a string section 70 or 70 '.

In another embodiment of the tennis racket according to the invention, the strings are networked with one another in the usual way. In this case, the strings advantageously have a flattened cross-section, the dimensions of which are reduced in the direction perpendicular to the plane of the frame surface, so that the strings which are networked with one another are pressed against one another with only a relatively small force at the nodes.

The flattened strings advantageously comprise two cores of tensile material which are square or round in cross-section and which are surrounded by a common casing made of friction-reducing material. The sheath has a rectangular or elliptical cross section, or consists of two cross-sectional areas each receiving a core, which are connected to one another by a web.

The use of two cores made of tensile material gives the string a twist resistance similar to that of a conventional string with a round cross-section.

In a modified embodiment, the string is provided with only one core. A reduction in node friction can also be achieved with strings with a round cross-section if the overall diameter of the strings is reduced. In this case, the strings should be made of a particularly tensile material, possibly with a friction-reducing coating.

As already described with reference to FIG. 1, in the racket according to the invention the strings, for example the string 22, are extended beyond the frame surface into the handle 10. Between points C and D in FIG. 1, the string 22 is guided essentially without contact, so that the entire length A-B can participate in the elastic stretching of the string 22 when a ball hits it.

The extent to which the individual strings can be extended in this way is largely freely selectable, since the slider 18 is elongated and, as can be seen from FIG. 1, has a large number of superimposed fastening positions, for example bores 26. When the string is fastened in the lower region of the slider 18, the lengthening of the string increases accordingly. After a suitable stretchable length and - when the string is pulled in - a suitable pre-tension is selected in this way for each string, after completion of the stringing there is the possibility of tensioning the overall string synchronously stronger or weaker with the aid of the tensioning bolt 20. Again, the effect can be exploited that the tension in the string fixed in the upper region of the slider 18, the overall length of which is shorter, is increased or decreased more. Because of the friction at the crossing points of the strings - especially if none of the abovementioned friction-reducing measures are taken - the pretension emanating from the tensioning device in the handle 10 of the racket is increasingly reduced to the apex of the frame 12 opposite the handle 10. Such a drop in tension or tension gradient can be used in a targeted manner if, for example, larger or smaller impact losses and / or smaller force increases in the edge region of the stringing are desired.

Fig. 3 is an enlarged view of the slider 18 already shown in Fig. 1. The slider 18 has a number of bores 26 lying one above the other in the longitudinal direction, which allow the strings to be passed through at different heights. In FIG. 4, which shows a further side view of the slider 18, two adjacent bores are shown in the lower area, which allow the accommodation of two different strings at the same height. Otherwise, a threaded bore 44 for receiving the clamping bolt 20 is indicated in the lower region of FIGS. 3 and 4.

Fig. 5 shows another embodiment of a slider, which in this case is designated 18 '. Instead of the bores 26 according to FIGS. 3 and 4, undercut recesses 26 'are provided in this case on the two opposite strings, which allow the individual strings to be suspended at any height. A threaded bore 44 in turn serves to receive a clamping bolt, not shown. As such, the slider can also be made of elastic material, such as rubber or elastic plastic that it has a certain spring and damping effect and can absorb shock losses. Since a deformation in the longitudinal direction of the slider from bottom to top in FIGS. 3 to 5 is added, this effect is particularly evident in the upper region of the sliders shown. This can be used specifically.

6 shows a schematic cross section through the frame 12. The frame consists of two box profiles 46, 48 connected by a web. At the level of the cutting height in FIG. 6, the web for receiving a roller 50 is interrupted. The reel is spherical in the example shown and has a circumferential groove 52 for guiding a string, not shown. The roller 50 is rotatably arranged on an axle pin 54, which is inserted into opposite bores of the box profiles 46, 48, which are not described in more detail. A corresponding bore 56 is provided on the upper side of the box section 46 in FIG. 6 for inserting the axle pin. 7 is a side view of the frame 12 and shows the web 58 and circular recesses 51 for the rollers 50.

FIG. 8 shows a partial section through the web 58, not shown in FIG. 6, and in a view of one of the box profiles, which is designated by 60 in FIG. 8. An insert 64 made of slidable material is inserted into a bore 62 of the web 58 and has a bead-shaped rounding 68 in the region of the deflection of a string 66, which allows the string 66 to slide largely without friction. Such a solution results in a similarly low-friction connection between the string section 70 lying within the frame and the string section 72 lying outside the frame.

Fig. 9 shows a similar deflection of a string 66. An insert designated 74 engages again in the bore 62, but instead of the rounding 68 has a foldable in the direction of the arrow, rounded at its free end support 76, which when pulled in the direction of Inside the frame surface, i.e. upwards in Fig. 9 by folding the movement of the string 66 practically no resistance, in the rest position shown in Fig. 9, however, is held by a stop 78, so that the string is retracted only by overcoming a certain amount of friction can be. This ensures that the string 66 yields slightly when a ball hits the string, but does not spring back with the same speed and ease, so that the ball springs back only with a certain loss of impact.

A further embodiment of the deflection is illustrated in FIGS. 10 and 11. In these figures it is assumed as an example that the deflection is located in the vicinity of the lower apex of the frame 12, so that the string section extends freely from the frame to the slider 18. In this embodiment, the string 66 extends through a bore 100 of the support 76, which can be pivoted about an axis pin 102 in a region delimited by the web 58 and an inclined surface 104 of the support. By tilting the bore 100 with respect to the longitudinal direction of the string 66, the friction increases considerably when the support 76 is pivoted by a pull on the string section 70 into the position shown in FIG. 10.

If a further extension beyond the previously described lengthening of the string is required, a string 80 according to FIG. 12 can also be moved back and forth several times in the hollow handle via rollers 82, 84 on the bottom plate 14 and in the area of the frame 12 be brought here.

In the above description, the features of the invention were explained using a tennis racket. However, the invention can be applied in a corresponding manner to other rackets, in particular to squash rackets.

Claims (13)

1. Tennis or squash racket having a substantially elliptical frame (12), a handle (10) connected thereto and a stringing (16) inside the frame (12) consisting of crossing strings generally parallel to each other, the strings being deviated with low friction on the frame several times and being strung over the frame several times, characterized in that the string sections (22c,24d) next to each other are parts of different strings (22,24) and that the spacing between parallel string sections (22a,22b) belonging to the same string is at least one ball radius.

2. Racket as claimed in claim 1, characterized in that the strings are deviated with low friction by way of pulleys (28-40,50).

3. Racket as claimed in claim 2, characterized in that the pulleys (50) have a spherical form.

4. Racket as claimed in any one of claims 1 to 3, characterized in that the crossing strings (70,70') are placed in different planes to run free past each other and at their cross-overs are joined together by connection links (110) slidingly taking up the strings.

5. Racket as claimed in any one of claims 1 to 3, characterized in that the strings are so flattened in cross section that the size thereof in the plane (E) of the frame is greater than in a direction normal to that plane and in that the strings have at least one core of high-tensile material and a casing of low-friction material.

6. Racket as claimed in any one of claims 1 to 5, characterized in that the strings (22,24) are lengthened out of the frame and that the string sections (72) outside the frame are joined with the string sections (22b,22c,70) inside the frame over a low-friction deviation (32,34,68,76).

7. Racket as claimed in claim 6, characterized in that the string sections (72) running out past the frame (12) are trained into the hollow handle (10).

8. Racket as claimed in claim 7, characterized in that the string sections (72) trained out past the frame (12) are trained along the outer surface of the frame into the handle (10).

9. Racket as claimed in any one of claims 6 to 8, characterized in that the strings are trained over one-way friction brakes (76), such brakes making possible slipping of the strings towards the inside of the frame and braking them in the opposite direction.

10. Racket as claimed in any one of claims 7 to 9, characterized in that in the handle (10) the strings are fixed to a tightening means (18,20) that may be moved along in said handle.

11. Racket as claimed in claim 10, characterized in that the tightening means is made up of a slider (18) able to be moved along in the handle, such slider making it possible to fix or deviate the strings at different positions of length for the purpose of adjustment the length of the string sections (72) running out past the frame (12).

12. Racket as claimed in claim 11, characterized in that the slider (19) is made of an elastic material and/or is elastically kept in position. 13. Racket as claimed in any one of claims 1 to 12, characterized in that the strings are stretched tight diagonally in relation to the length axis of the racket.

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