EP0176021B1 - Tennis racket - Google Patents

Abstract

A racket for playing a game using a ball of limited resiliency such as a tennis racket comprises a racket head frame portion provided with stringing, a handle, and a shaft arrangement connecting the racket head frame portion and the handle. The resonance frequency of the racket head frame portion at least approximately corresponds to the period of time for which a ball is in contact with the strings of the racket when struck thereby, and the natural frequency of the racket substantially corresponds to the excitation frequency of the ball. The thickness of the racket frame as measured in a direction normal to the plane of the stringing is greater than the thickness of the handle as measured in a corresponding direction.

Description

The invention relates to a tennis racket with a covering provided in a tenter frame from a profile bar in a plane for games with a ball in contact with the covering in a period of about 2 to 6 ms for half a vibration, and a ball adjoining the tenter frame. of intersecting sections of the profile bar and a frame web connecting them - heart zone and an end handle in the longitudinal axis of the racket.

A conventional tennis racket has a height of the uncovered handle of 23 to 32 mm, and the height of the tensioning frame - seen in the direction of impact, that is to say at right angles to the covering - is below the handle thickness. A racket of this customary dimension is given, for example, in DE-A-30 18 354.

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

As is well known, a ball tied to the stringing 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 about 125 Hz on the other hand, there are demonstrable deviations of up to one meter from the desired flight line of the ball over the entire length of a 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. His handgrip continues in an "intermediate portion" up to the racket oval, the oval cross section of which near the racket oval is higher than the cross section of the frame of the racket oval. The club head is heavier due to a larger cross section and supplemented by an additional weight in the form of a metal strip.

In an article "Physics of the tennis racket" (American Journal of Physics, 47 (6), June 1979, pp. 482-487), the measurement of the oscillation periods in different tennis rackets is made and it is mentioned that half the vibration in some of the tennis rackets about twice the time the ball stayed on the fabric. In order to keep the loss of energy due to deformation as low as possible, the tennis racket could be made stiffer and equipped with a shorter period of vibration.

In view of these circumstances, the inventor has set himself the goal of creating a racket of the type mentioned at the beginning in which the deviations described are considerably reduced. Overall, the striking behavior of the racket should be improved.

A tennis racket leads to the solution of this task according to the teaching of claim 1. In addition, the torsional vibration superimposed on the longitudinal vibration should advantageously correspond to the resonance vibration and, in the preferred case, be approximately 125 Hz.

Of particular importance for the racket according to the invention is the configuration of the heart zone as a narrow frame web, the height of which is less than the height of the profile bar.

The tennis racket according to the invention - which corresponds to known rackets insofar as its tenter frame or a profile rod resulting from it has a cross-sectional width between 8 and 16 mm measured in the plane of the covering - has an moment of inertia which is four to 16 times higher than the moment of inertia of 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.

In the racket according to the invention, the usual thickness of the handle is without casing, ie without grip leather, foam rubber covering or the like. Ingredients not belonging to the structural racket profile and without taking the handle cap into account between about 23 and 32 mm. Its racket axis forms a line of symmetry and the height of a cross section of the tenter frame is 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.

It has proven to be advantageous that the largest cross-sectional height of the racket in the area of its heart zone is greater than the thickness of the handle. This "greatest height" can taper towards both the handle and the club head, ie in both directions of the longitudinal axis, whereby its "greatest height" is preferably constant in an area running on both sides of the heart zone.

According to another feature of the invention, the greatest height of the racket is arranged at the transition to the handle - the racket or cross-sectional height can decrease from this transition or at a distance from it towards the racket head. The acceptance may take place continuously while producing a straight longitudinal contour of the profile, but it is also possible to produce the contour in a curved or curved manner.

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

The height of the cross-section or profile of the racket or stenter, which is perpendicular to the covering, can increase suddenly or gradually compared to the grip thickness and / or - suddenly or gradually - decrease from the point of greatest dimension to the racket head.

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 has a corresponding cross-section on the other side of the axis of symmetry. In addition, within the scope of the invention - as is known per se - 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 bis Fig. 12:

schematisierte Seitenansichten zu ausgewählten bevorzugten Ausführungsformen des erfindungsgemäßen Tennisschlägers.

Further advantages, features and details of the invention emerge 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 tenter frame of the tennis racket according to the invention;

Fig. 9:

a vibration graph of Figures 6 to 8.

Fig. 10 to Fig. 12:

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

A tennis racket 10 of known type shown by way of example in FIGS. 1 to 3 has an oval clamping frame 12 made of a correspondingly curved profile rod 13, which ends on both sides of the racket longitudinal axis M in - delimiting 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 composed of transverse 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.

3, the clamping frame 12 or its profile rod 13 is rectangular in cross section, the side walls 20 of which, for example, run 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 for the profile rod 13, which can be calculated from the above dimensions, is in mm 2:

$\text{21st 2nd 2 + 7. 2nd 2 = 112.}$

The natural frequency f₀ of the tennis racket 10 clamped in accordance with the diagram according to FIG. 5 can be measured by an attacking on the racket longitudinal axis M. Force P is suddenly removed.

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

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

Die Kontaktzeit zwischen Tennisschläger 10 und Ball wurde durch viele Versuche -- u. a. durch Hochgeschwindigkeitsfotografie -- mit 2 bis max. 6 ms festgestellt, im Mittel also mit 4 ms, was für eine ganze Schwingung t = 8 ms oder 125 Hz erbringt.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 under the same force P has a deflection of d₁ and another has a deflection of d₂, the natural frequency of the second tennis racket can be calculated approximately according to the following relationship:

The contact time between tennis racket 10 and ball has been through many attempts - including high-speed photography - with 2 to max. 6 ms determined, 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 the covering Q and forces the tensioning frame 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.

als Ergebnis einer Berechnung, welche die Übereinstimmung der Eigenfrequenz dieses Tennisschlägers 30 und der "Ballresonanz" bestätigt, also die Übereinstimmung der Erregerfrequenz mit der Eigenfrequenz.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:

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 von Tennisschläger 30 (TS₃₀)

FR₁₀

= Eigenresonanz von TS₁₀ = 50 Hz ^*)

FR₃_u

= Eigenresonanz von TS₃₀ = 125 Hz

ist


Fußnote: *) Werte gelten für Graphitschläger, also für harte Werkstoffe

$\text{<figure-callout id="30" label="d" filenames="imgf0002.png,imgf0003.png" state="{{state}}">d</figure-callout> ₃₀ = 0,16 . d₁₀}$

The calculable cross-sectional area is here

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

d₁₀

= Deflection of TS ₁₀

d ₃₀

= Deflection of tennis racket 30 (TS ₃₀ )

FR ₁₀

= Natural resonance of TS ₁₀ = 50 Hz ^* )

FR₃ _u

= Natural resonance of TS ₃₀ = 125 Hz

is


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

$\text{<figure-callout id="30" label="d" filenames="imgf0002.png,imgf0003.png" state="{{state}}">d</figure-callout> ₃₀ = 0.16. d₁₀}$

The deflection under a load P must be 1/6 compared to TS ₁₀ with TS ₃₀ .

Die Durchbiegung d ist eine Funktion von $\frac{\text{1}}{\text{J}}$

.
The cross-sectional areas in FIGS. 3 and 5 lead to

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

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

The resonance frequency is

One assumes

b ₁ = 37 mm,
n₁ = 42 mm,

so is

A frame shape that takes these findings into account is shown in FIG. 7, in which an area E with the above profile height n 1 extends on both sides of a frame web 34. The profile height n₀ to the club head 40 on the one hand and to the handle attachment 41 decreases continuously from the area E. 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 excitation frequency of the ball now corresponds to its natural frequency. When it is lifted off the covering Q, the tennis racket 30 has reached point C or in the immediate vicinity thereof, and in addition to an additional acceleration from the clamping frame 32 of the tennis racket 30, the ball receives an exact trajectory which is no longer falsified by the dimension Z of the deflection is, as shown in Fig. 4. If inaccurate - d. H. outside the longitudinal axis M on the tennis racket 30 or its strings Q - hitting balls, a torsional vibration occurs about the longitudinal axis M. This torsional vibration is superimposed on the longitudinal vibration.

If this oscillation 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 it touches 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 _b to 30 _{c shown} in FIGS. 10 to 12 are of conventional thickness i, which - as said - measures 23 to 32 mm compared to this Thickness i have the adjoining profile bars - better known as frame profiles 33 for their changing heights - in all cases a longer outer height n 1.

The frame profile 33 _{b of} FIG. 10 is a total of that max. Height n 1 _, while the max. Height n ₁ of frame profile 33 _c (Fig. 11) ends approximately at heart zone H and decreases as height n ₀ to the club head 40.

The embodiments shown in the drawing show the max. Height n₀ outgoing straight line, that is to say a constant decrease in the variable height n _0. Instead of this continuous profile, the corresponding cross-sectional contours can also be curved, as is indicated in FIG. 12 at 33 _a .

Claims (12)

1. Tennis racket (30) with strings in one plane provided in a clamping frame (32) consisting of a profile bar (33), for games with a ball which is in contact with the strings in a period of approximately 2 to 6 ms for a semi-oscillation, a core zone (H) adjoining the clamping frame (32) and flanked by profile bar sections adjoining each other and by a frame web (34) connecting the latter, and an end handle (16) in the longitudinal axis (M) of the racket, wherein the primary resonant frequency of the strung tennis racket (30) approximately corresponds to the frequency converted from the semi-oscillation, of the period of ball/string (0) contact, in the case of the tennis racket (30) anchored to the handle (16) is 83 to 200 Hz, preferably 100 to 140 Hz, and the frame web (10) is adjusted in such a way that when torsional oscillations occur, the racket oscillates only sinusoidally in one frequency on contact with the ball.
2. Tennis racket according to claim 1, characterised in that the torsional oscillation superimposed on the longitudinal oscillation is around 125 Hz.
3. Tennis racket according to claim 1 or 2 with a cross-sectional width of the profile bar producing the clamping frame between 8 and 16 mm, 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 tennis racket (10) of which the cross-sectional height is equal to or less than the thickness (i) of the handle (16).
4. Tennis racket according to any of claims 1 to 3, characterised in that the profile height (h) of the frame web (34) is shorter than the maximum height (n₁) of the profile bar (33, 33_a to 33_c).
5. Tennis racket according to any of claims 1 to 4, characterised in that the maximum cross-sectional height (n₁) of the profile bar (33 or 33_a to 33_c) extending transversely to the plane of the strings (Q) in the region of the core zone (H) is greater than the thickness (i) of the handle (16).
6. Tennis racket according to claim 4 or 5, characterised in that the maximum cross-sectional height (n₁) of the profile bar (33, 33_a to 33_c) in the region of the core zone (H) is provided at both ends of the frame web (34).
7. Tennis racket according to any of claims 1 to 6, characterised in that the height (n₁) of the profile bar (33, 33_a to 33_c) is constant in a region (E) on both sides of the core zone (H).
8. Tennis racket according to any of claims 1 to 7, characterised in that the height (n₀) of the profile bar 33_c) decreases approximately from the core zone (H) of the tennis racket (30_c) towards the racket head (40) thereof.
9. Tennis racket according to any of claims 1 to 8, characterised in that the profile bar (33, 33_a to 33_c) tapers both towards the handle (16) and towards the racket head (33, 33_a to 33_c).
10. Tennis racket according to any of claims 1 to 8, characterised in that the reduction in height (n₀) of the profile bar (33, 33_a to 33_c) is constant.
11. Tennis racket according to any of claims 1 to 8, characterised in that the height (n₀) of the profile bar (33, 33_a to 33_c) decreases to produce a curved contour.
12. Tennis racket according to any of claims 1 to 11, characterised in that the profile bar (33, 33_a to 33_c) is a hollow profile.

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