EP0310169B2 - Rackets for ball games, especially tennis rackets - Google Patents

Abstract

The tennis racket (30) has strings in a frame (32) of profiled rod (33), a heart zone adjacent to the frame and flanked by rod sections, a frame member (34) joining its sections, and a handle (16) on the longitudinal axis (M). The maximum height (n1) of the profiled rod at right angles to the string plane (Q) is greater than the thickness of the handle in the same direction. The profile height (h) of the frame member can be less than this max. height.

Description

The invention relates to a racket for ball games, in particular a tennis racket, with covering provided in a tensioning frame made of a profile bar in one plane, a heart zone adjoining the tensioning frame with flanking profile bar sections of the tensioning frame and a frame part connecting these profile bar sections, the profile bar sections with the frame part open heart boundaries, as well as with an end handle in the longitudinal axis of the racket, in particular in the axis of symmetry.

A tennis racket with a plate-like frame part can be found in DE-A-30 18 354, a frame bridge between profile sections shows DE-A-29 08 872. The thickness of the uncovered handle of such tennis rackets measures between 23 and 32 mm, and the height of the Tensioning frame - seen in the direction of impact, i.e. at right angles to the covering - is below the handle thickness.

On such - clamped in the area of the handle - tennis rackets of this type, a natural frequency of 25 to max. 50 Hz detected; unstrung tennis rackets generally show slightly higher values.

As is known, a ball hitting the covering forces the tenter frame out of the longitudinal axis of the racket and leads to a deterioration in the accuracy; the described deflection of the tenter is responsible for the direction of the ball.

Due to the different dimensions of the natural frequency of the tennis racket on the one hand and the "ball resonance" of approximately 125 Hz on the other hand, there are demonstrable deviations of up to one meter from the desired airline of the ball over the entire length of a playing field. The precision of known tennis rackets leaves much to be desired.

US-A-15 39 019 describes the development of a tennis racket whose center of vibration lies in the center of the stringing surface. Its handle continues up to the racket oval in an "intermediate portion", whose - to reduce the air resistance - the oval cross-section near the racket frame is knotted higher than its cross-section. The club head is heavier at the head end due to a larger cross-section and supplemented by an additional weight in the form of a metal strip.

US-A-4 176 841 discusses the disadvantages of a racket by deflecting its frame in the direction of the stroke, and then the object is to design a mass-produced metal tennis racket so that low elasticity strings can be used without additional spring loading . Such a racket is shown with the profile end surrounded by the handle and given as a typical profile width, which always remains constant over the profile length, with 22.5 mm. In addition, the wall thickness for a hollow profile made of at least 95%, preferably 100%, titanium alloy is given as 0.6 to 0.8 mm. Since the constant profile width can be 25 to 40 times - in particular 30 times - and the profile thickness 5 to 20 times, in particular 10 times, larger than that wall thickness, comparatively high values for the profile height result. These height values, however, at the same time cause a significant weight gain in the case of the racket described, which makes it unplayable at higher profile heights - no reason for a person skilled in the art to take such paths.

In view of these circumstances, the inventor has set himself the goal of significantly reducing the described deviations in a racket of the type mentioned at the beginning and of improving its impact behavior overall. Above all, the profile stiffness should be increased.

To achieve this object, the greatest cross-sectional height of the profile bar running transversely to the plane of the covering on both sides of the longitudinal axis of the racket in the area of the heart zone is greater than the thickness of the handle, the cross-sectional height of the profile bar decreasing approximately from the heart zone of the racket to the club head. It has been shown that such an increase in the profile bar cross-section - especially on both sides of the longitudinal axis of the racket, that is to say in the side regions of the frame - makes the racket stiffer and significantly improves its impact behavior.

Particular embodiment strings of the invention are set out in claims 2 to 10.

In the racket according to the invention, the usual thickness of the handle without casing - that is, without grip leather, foam rubber covering or the like. Components not belonging to the structural racket profile - and without taking into account the grip cap, is between about 23 and 32 mm. Its racket axis forms a line of symmetry, and the height of the cross section of the tenter frame is - without prejudice to the frame design outside the specified area in this - greater than that thickness of the handle. The latter is determined by the human hand and therefore remains without influence on the club design. According to the invention, the above stipulation of the ratio of handle thickness to the height of a cross section also applies to a profile rod from which the stenter frame is made.

The preferred max. The height of the cross-section of the profile bar and / or stenter has proven to be a measure of the thickness of the handle up to about 45 mm.

It has proven to be advantageous that the racket tapers from the greatest cross-sectional height of its profile bar in the area of the heart zone both to the handle and to the racket head, that is to say in both directions of the longitudinal axis. In a preferred embodiment, the greatest height of the profiled bar in the specified area should be in the vicinity of the connection point between the profiled bar and the frame web, advantageously on both sides of this frame web. It is also advantageous if this greatest height is constant in an area running on both sides of the heart zone.

The greatest height may decrease steadily while creating a straight longitudinal contour of the profile, but it is also possible to produce the contour curved or curved.

According to the invention, the height of the cross-section or profile of the racket or stenter, which is perpendicular to the covering, increases abruptly or gradually compared to the grip thickness and can also decrease again from the point of greatest extent to the racket head.

The racket according to the invention - which corresponds to known rackets insofar as its tenter frame or a profile rod resulting from this has a cross-sectional width between 8 and 16 mm measured in the plane of the covering - has an moment of inertia which is 4 to 16 times higher than the moment of inertia a tennis racket according to the prior art, the cross-sectional height of which is equal to or less than the thickness of its handle.

Insofar as a cross-sectional dimension is mentioned above, it must be taken into account that the longitudinal axis of the racket is also an axis of symmetry, ie the cross-section of the clamping frame described is on the other side of the axis of symmetry a corresponding cross-section. In addition, the covering determines a plane of symmetry.

Fig. 1:

die teilweise wiedergegebene Draufsicht auf einen bekannten Tennisschläger mit Spannrahmen aus Profilrohr;

Fig. 2:

die Seitenansicht zu Fig. 1;

Fig. 3:

den vergrößerten Querschnitt durch Fig. 1 nach deren Linie III - III;

Fig. 4:

eine Schwingungsgrafik für den Tennisschläger nach Fig. 1 bis 4;

Fig. 5:

eine Schemaskizze zu einem Belastungsfall;

Fig. 6:

eine Teildraufsicht auf eine bevorzugte Ausführungsform eines erfindungsgemäßen Tennisschlägers mit Spannrahmen;

Fig. 7:

die der Fig. 2 entsprechende Darstellung des Tennisschlägers der Fig. 6;

Fig. 8:

einen Querschnitt des Spannrahmens des erfindungsgemäßen Tennisschlägers;

Fig. 9:

eine Schwingungsgrafik zu Fig. 6 bis 8;

Fig.10,11:

schematisierte Seitenansichten zu ausgewählten bevorzugten Ausführungsformen des erfindungsgemäßen Tennisschlägers.

Further advantages, features and details of the invention result from the following description and from the drawing; this shows in:

Fig. 1:

the partially reproduced top view of a known tennis racket with a frame made of profile tube;

Fig. 2:

the side view of Fig. 1;

Fig. 3:

the enlarged cross section through Figure 1 along the line III - III.

Fig. 4:

a vibration diagram for the tennis racket of Figures 1 to 4.

Fig. 5:

a schematic sketch of an exposure case;

Fig. 6:

a partial plan view of a preferred embodiment of a tennis racket with tensioning frame according to the invention;

Fig. 7:

the representation corresponding to FIG. 2 of the tennis racket of FIG. 6;

Fig. 8:

a cross section of the frame of the tennis racket according to the invention;

Fig. 9:

a vibration graph to Figures 6 to 8.

Fig. 10,11:

schematic side views of selected preferred embodiments of the tennis racket according to the invention.

A tennis racket 10 of known type shown in FIGS. 1 to 3 has an oval clamping frame 12 made of a correspondingly curved profile bar 13, which ends on both sides of the racket longitudinal axis M in - defining a plate-shaped heart 14 - profile arms 15. The latter are fixed in a handle 16 with a thickness i of 26 to 32 mm; the thickness i is measured on handles 16 without wrapping leather and without considering a handle cap 17.

Tensioning frame 12 and heart 14 surround a stringing surface Q made of cross strings 18 and longitudinal strings 19 crossing them. The preferred point of impact for a tennis ball (not shown) is designated by S in FIG. 1.

According to FIG. 3, the tensioning frame 12 or its profiled bar 13 is rectangular in cross section, the side walls 20 of which run, for example, at a distance a of 7 mm and the transverse walls 21 of which run at a distance b of 17 mm.

With a wall thickness q of the side or transverse wall 20 or 21 of 2 mm, the outer width m is 11 mm and the outer height n is 21 mm. The latter is otherwise far lower than the thickness i of the handle 16.

The cross-sectional area 0 that can be calculated from the above dimensions for the profile rod 13 is in mm ² : $$\text{21. 2. 2 + 7. 2. 2 = 112.}$$

The natural frequency f _o of the tennis racket 10 clamped in accordance with the diagram according to FIG. 5 can be measured by suddenly removing a force P acting on the longitudinal axis M of the racket.

worin 1 die vom Schreibband abgelesene Schwingungslänge in mm ist.If the natural frequency is written on a writing tape running at 3000 mm / _s , the following applies $${\text{f}}_{\text{O}}\text{=}\frac{\text{3000}}{\text{1}}\text{(HZ),}$$

where 1 is the oscillation length in mm read from the writing tape.

In the range of elasticity, the dimension d is proportional to the deflection of the force P made clear in FIG. 5. But it is also related to the natural frequency of the tennis racket 10 in the longitudinal direction; If a tennis racket has a deflection of d ₁ and another one of d ₂ under the same force P, the natural frequency of the second tennis racket can be calculated approximately according to the following relationship: $${\text{fo}}_{\text{2nd}}{\text{= fo}}_{\text{1}}\sqrt{\frac{{\text{d}}_{\text{1}}}{{\text{d}}_{\text{2nd}}}}\text{(Hz)}$$

The contact time between tennis racket 10 and ball has been tried many times - u. a. through high-speed photography - with 2 to max. 6 ms found, on average 4 ms, which results in a whole oscillation t = 8 ms or 125 Hz.

FIG. 4 shows a longitudinal vibration curve for a conventional tennis racket 10 according to FIGS. 1 to 3. At point A, a ball touches the net of covering Q and forces the tenter 12 to follow the ball frequency. This movement seeks to counteract dynamic inertial forces of the tenter frame 12. Arrived at point B, the ball reverses its direction and leaves the string Q following the ball approximately at point C. The tennis racket 10 oscillates at its natural frequency and is only at point D when the ball is clear of the string Q at C. separates (t = 8 ms, t / ₄ = 2 ms).

The different dimensions of the natural frequency of the tennis racket 10 from 25 to 50 Hz on the one hand and the excitation frequency of the ball of about 125 Hz on the other hand - seen over the entire length of a playing field - lead to significant deviations of the ball from the desired airline; as mentioned, this deviation can be up to one meter.

The design of a tennis racket 30 according to FIGS. 6 to 8 has a resonance frequency, which remedies the described defect; the cross section of the profile rod 33 contains the following dimensions according to FIG. 8: inner width a ₁ 8 mm, outer width m ₁ 10 mm, inner height b ₁ 32.2 mm, outer height n ₁ 37 mm as the result of a calculation which confirms the agreement of the natural frequency of this tennis racket 30 and the "ball resonance", that is to say the agreement of the excitation frequency with the natural frequency.

gleicht also der Querschnittsfläche von Tennisschläger 10, der nachfolgend mit TS₁₀ bezeichnet sei.
Bei

d₁₀ =

Durchbiegung von TS₁₀

d₃₀ =

Durchbiegung Tennisschläger 30 (TS₃₀)

FR₁₀ =

Eigenresonanz von TS₁₀ = 50 Hz*)

FR₃₀ =

Eigenresonanz von TS₃₀ = 125 Hz

ist $$\begin{array}{c}\begin{array}{c}\frac{{\text{FR}}_{}}{}\end{array}\end{array}$$$$\begin{array}{c}\begin{array}{c}\frac{{}_{\text{10}}}{{\text{<figure-callout id="30" label="FR" filenames="imgf0002.png" state="{{state}}">FR</figure-callout>}}_{\text{30}}}\text{=}\frac{\hfill \text{50}}{\hfill \text{125}}\text{= 0,4}\\ \text{0,4 =}\sqrt{\frac{{\text{d}}_{\text{10}}}{{\text{d}}_{\text{30}}}}\\ {\text{<figure-callout id="30" label="d" filenames="imgf0002.png" state="{{state}}">d</figure-callout>}}_{\text{30}}{\text{= 0,16 . <figure-callout id="10" label="d" filenames="imgf0001.png" state="{{state}}">d</figure-callout>}}_{\text{10}}\end{array}\end{array}$$

Fußnote : *) Werte gelten für Graphitschläger, also für harte WerkstoffeThe calculable cross-sectional area is here $$\begin{gathered} \text{37. 1. 2 + 8. × .2 and at × = 2.4} \\ {\text{112 mm}}^{\text{2nd}}\text{,} \end{gathered}$$

is therefore equal to the cross-sectional area of tennis racket 10, which is referred to below as TS ₁₀ .
At

d ₁₀ =

Deflection of TS ₁₀

d ₃₀ =

Deflection tennis racket 30 (TS ₃₀ )

FR ₁₀ =

Natural resonance of TS ₁₀ = 50 Hz *)

FR ₃₀ =

Natural resonance of TS ₃₀ = 125 Hz

is $$\begin{array}{c}\begin{array}{c}\frac{{\text{FR}}_{\text{10th}}}{{\text{FR}}_{\text{30th}}}\text{=}\frac{\hfill \text{50}}{\hfill \text{125}}\text{= 0.4}\\ \text{0.4 =}\sqrt{\frac{{\text{d}}_{\text{10th}}}{{\text{d}}_{\text{30th}}}}\\ {\text{d}}_{\text{30th}}{\text{= 0.16. d}}_{\text{10th}}\end{array}\end{array}$$

Footnote: *) Values apply to graphite mallets, i.e. hard materials

The deflection under a load P must be 1/6 compared to TS ₁₀ with TS ₃₀ . The cross-sectional areas in FIGS. 3 and 5 lead to $$\begin{gathered} \begin{array}{c}\begin{array}{c}{\text{J}}_{\text{10th}}\text{=}\frac{{\text{11.21}}^{\text{3rd}}}{\text{12th}}\text{-}\frac{{\text{7.17}}^{\text{3rd}}}{\text{12th}}\text{=} \\ \text{8490 - 2870 = 5620}\\ {\text{J}}_{\text{30th}}\text{=}\frac{{\text{10.37}}^{\text{3rd}}}{\text{12th}}\text{-}\frac{{\text{8.32.2}}^{\text{3rd}}}{\text{12th}} \\ \text{42210 - 22250 = 19960}\end{array}\end{array} \end{gathered}$$

.The deflection d is a function of $\frac{\text{1}}{\text{J}}$

.

die Einfederung ist mit dem Querschnitt nach Fig. 5 : 0,28.This means $$\frac{{\text{J}}_{\text{10th}}}{{\text{J}}_{\text{30th}}}\text{= 0.28;}$$

the deflection with the cross section according to FIG. 5: 0.28.

The resonance frequency is $${\text{FR}}_{\text{30th}}{\text{= FR}}_{\text{10th}}\sqrt{\frac{\text{1}\hfill }{\text{0.28}\hfill }}{\text{= FR}}_{\text{10th}}\sqrt{\text{3.57}}\text{= 1.9.50 = 95 Hz}$$

One assumes
b ₁ = 37 mm,
n ₁ = 42 mm,
so is $$\begin{array}{c}\begin{array}{c}{\text{J}}_{\text{30th}}\text{=}\frac{{\text{10.42}}^{\text{3rd}}}{\text{12th}}\text{-}\frac{{\text{8.37}}^{\text{3rd}}}{\text{12th}}\\ \text{61740 - 31000 = 30,000}\\ \frac{{\text{J}}_{\text{10th}}}{{\text{J}}_{\text{30th}}}\text{= 0.18}\\ {\text{FR}}_{\text{30th}}{\text{= FR}}_{\text{10th}}\text{. 2.36 ≅ 120 Hz}\end{array}\end{array}$$

FIG. 7 shows a frame shape that takes these findings into account, in which an area E with a projecting profile height n ₁ extends on both sides of a frame web 34. From the area E, the profile height n _o to the head 40 on the one hand and to the handle attachment 41 decreases continuously. The frame web 34 shown in section in FIG. 7 replaces the previously described heart 14 and has a lower average profile height h than the profile bar 33.

The vibration behavior of the tennis racket 30 according to the invention in the longitudinal direction can be seen in FIG. 9. The natural frequency of the racket now matches the excitation frequency of the ball. When it is lifted off the covering Q, the tennis racket 30 has reached point C or in the immediate vicinity thereof, and the ball receives, in addition to an additional acceleration, the tension frame 32 of the tennis racket 30 an exact trajectory which is no longer falsified by the dimension Z of the deflection, as can be seen in FIG. 4. In the case of balls hitting the tennis racket 30 or its covering Q outside the longitudinal axis M inaccurately, a torsional vibration occurs about the longitudinal axis M. This torsional vibration is superimposed on the longitudinal vibration.

If this vibration is also brought to preferably 125 Hz by tuning the frame web 34 from FIG. 7, the entire tennis racket 30 only vibrates sinusoidally at a frequency when touching the ball and also compensates for torsional deflection by timely swinging back.

The handles 16 of the tennis racket 30 (FIGS. 6 to 8) and the embodiments 30 _a and 30 _{b shown} in FIGS. 10, 11 are of conventional thickness i, which - as said - measures 23 to 32 mm compared to this Thickness i have the adjoining profile bars - better designated as frame profiles 33 for the sake of their changing heights - in all cases a longer outer height n ₁ .

The max. Height n ₁ of frame profile 33 _a (FIG. 10) ends approximately at heart zone H and decreases as height n _o to racket head 40.

The embodiments shown in the drawing show the max. Height n ₁ outgoing straight line, i.e. a constant decrease in the variable height n _o . Instead of this continuous course, the corresponding cross-sectional contours can also be curved, as indicated at 33 _b in FIG. 11.

Claims (10)

1. Racket (30) for ball games, in particular tennis racket, with strings in one plane provided in a clamping frame (32) consisting of a profile bar (33), a core zone (H) adjoining the clamping frame (32) and flanked by profile bar sections of the clamping frame (32), a frame portion (34) connecting these profile bar sections, the profile bar sections with the frame portion delimiting an open heart-shaped portion, and an end handle (16) in the longitudinal axis (M) of the racket, in particular in the plane of symmetry, characterised in that the maximum cross-sectional height (n₁) of the profile bar (33, 33_a, 33_b) extending transversely to the plane of the strings (Q) on both sides of the longitudinal axis (M) in the region of the core zone (H), is greater than the thickness (i) of the handle (16), with a cross-sectional heigth (n_o) of the profile bar decreasing from approximately the racket core zone towards the racket head (40).
2. Racket according to claim 1 with a frame web (34) as the frame portion connecting the profile sections, characterised in that a profile height (h) of the frame web (34) is shorter than the maximum height (n₁) of the profile bar (33, 33_a, 33_b) in the region of the core zone (H).
3. Racket according to claim 1 or 2, characterised in that the maximum cross-sectional height (n₁) of the profile bar (33) in the region of the core zone (H) is provided at both ends of the frame web (34).
4. Racket according to any of claim 1 to 3, characterised in that the maximum cross-sectional height (n₁) of the profile bar (30, 30_a, 30_b) is constant in a region (E) of the core zone (H) on both sides of the longitudinal axis (M) of the racket.
5. Racket according to any of claims 1 to 4, characterised in that the profile bar (33, 33_b) decreases both towards the handle (16) and also towards the racket head (40).
6. Racket according to any of claims 1 to 5, characterised in that the reduction in its cross-sectional height (n₀) is constant, or that its height (n) decreases, giving a curved contour.
7. Racket according to any of claims 1 to 6 characterised in that the profile bar (33, 33_a, 33_b) is in the form of a hollow profile.
8. Racket according to any of claims 1 to 7, characterised in that the first-order resonant frequency of the stringed racket (30) approximately corresponds to the frequency converted from the half-oscillation of the period of ball/stringing (Q) contact, and is 80 to 200 Hz, in particular 100 to 140 Hz, in the case of the racket (30) fixed at the handle (16), for games with a ball in contact with the stringing (0) over a duration of approximately 2 to 6 ms for a half-oscillation.
9. Racket according to claim 8, characterised in that the natural frequency of the racket (30) approximately concides with the excitation frequency of the ball.
10. Racket according to any of claims 1 to 9 with a cross-sectional width of between 8 and 16 mm of the profile bar providing the clamping frame, characterised in that the moment of inertia of the cross-section of the clamping frame (32) or profile bar (33) of the racket (30) is 4 to 16 times the moment of inertia of a racket (10) of which the cross-sectional height is equal to or less than the thickness (i) of the handle (16).

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