FI89334B - Spelracket - Google Patents

Description

1 39334

Playground - Spelracket

The present invention relates generally to a racket for ball play with limited flexibility, such as a tennis racket. In particular, the invention relates to a racket as defined in the preamble of the claim.

In a traditional racket, the rigidity of the frame and arm portion is such that when the ball hits a threaded surface of the racket, the top of the frame is forced away from the longitudinal axis of the racket. This deflection adversely affects the flight path of the bouncing ball.

A complex oscillation reaction occurs in any part exposed to the input load. This complex, deformed shape of a body can be transformed into the sum of an infinite number of simple oscillation state shapes with varying amplitude and frequency. The specific frequencies, state modes, and amplitudes associated with an oscillating body depend on several factors. These include the stiffness and weight distribution of the part and the degree of compression of the part.

Stiffness and weight distribution can be adjusted in two ways. One way would be to use special reinforcement materials in the parts of the body, so that these materials have a higher strength to weight ratio and stiffness to weight ratio. Another method of regulating stiffness and weight distribution would be to change the cross-sectional geometry of the part; more specifically, by using a constant amount of material in the cross section and varying the moment of inertia in the cross section area so that the ratio of stiffness to weight varies. Higher stiffness increases oscillation frequencies and decreases dynamic deformation amplitudes. Higher weight reduces oscillation frequencies and reduces dynamic deformation amplitudes.

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Two specific coercive situations are of interest in this context. The other extreme, the “free-free” coercion situation, represents a body that oscillates freely in space. This can be simulated in the laboratory by hanging the piece with elastic bands and allowing it to vibrate freely. The first two forms of vibration mode of a simple rod that bends under "free-free" forcing conditions are illustrated in Figure 10.

The opposite extreme is a "fixed-free" forced lumbar, where one end of the body is firmly attached to the support bracket, while the other end is allowed to oscillate freely. The first three forms of vibration mode of a simple bar that bends under "fixed-free" forcing conditions are illustrated in Figure 11. It should be noted that modes 1 and 2 of Figure 10 have approximately the same shapes as corresponding modes 2 and 3 of Figure 11. Adding a Tight Fastener to a body that bends in a "free-to-free" situation causes an additional tuning of the low-frequency oscillation state (state 1 in Fig. 11).

The frequencies of states 1 and 2 under "free-to-free" forcing conditions are not the same as the frequencies of the corresponding state modes (states 2 and 3, respectively) under "fixed-free" conditions. The frequency of the state mode in either of the forcing situations is approximated by the frequency of the state mode in the other situation using the following equation:

Freqcf = Freqff x (Lff / Lcf) 2 (Equation 1) ^ cf 'kff "^ cc

Freqcf = frequency of the state mode in the "fixed-free" situation.

Freqff = frequency of the state mode in the "free-free" situation.

Lff = length of the bar in the "free-free" situation.

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Lcc = length of the bar below the fastener la.

Lcf = the corresponding length of the bar in the "fixed-free" situation.

Tennis rackets have similar vibration characteristics to the simple bars described above due to the strokes between the ball and the racket during the game. Several different rackets were tested in the laboratory. The test results show that for traditional tennis rackets under "free-free" forcing conditions, the first deflection state is in the order of 100-170 Hz. Under "attached-free" forcing conditions, the frequency of the first and second bending states of conventional rackets is in the order of 25-50 Hz and 125-210 Hz, respectively. U.S. Patent 4,664,380 (West German DE-OS 3434898) mentions that the resonant frequency of the racket described therein in a "fixed-free" forcing situation is 70-200 Hz.

Studies have shown that in a "free-to-free" situation, an oscillating tennis racket is closer to the behavior of a tennis racket during a game than a racket in "fixed-free" conditions. If "fixed-free" forcing conditions prevail during testing, Equation 1 shall be used to change the frequency values so that under "fixed-free" conditions, the second deflection state is an approximation of the frequency values of the first state of the "free-free" situation.

It has been found that with a traditional tennis ball, the stroke times between the ball and the racket are 2-7 milliseconds with an average of 2-3 milliseconds. During this time, the top of the racket bends backwards due to the power supply to the ball. In a traditional racket, the ball leaves strands of impact between the ball and the racket at some point when the racket begins to change shape and shortly after the racket has reached its maximum or bounce point. As a result, the flight path of the impact is affected (see Figure 12) and energy is wasted, 4 39334 because the racket has not returned to its inflexible position where the recoil angle is zero and the speed of the racket tip is maximum.

If the ball remains in the strands as the racket bends and does not leave the strands until the racket has returned to its inflexible position, the flight path of the ball is not affected and the accuracy of the stroke is improved (see Figure 13). In addition, since the speed of the racket tip is at its maximum at this point, more energy is transferred to the ball and the stroke becomes stronger. Changing the deformation time of a tennis ball is not considered a desirable solution to the problem. For this reason, the most favorable performance of a tennis racket must be designed so that the frequency of the predominant vibration space generated during the game corresponds to the duration of contact between the ball and the racket. More specifically, one and a half times the duration of the first bending state of a tennis racket under "free-free" compression conditions should be the same as the contact ball of the tennis ball to the strands. The first recovery mode of the "free-free" forced state is selected because this is the prevailing vibration state generated during the game.

According to the present invention, it has been possible to provide a racket structure whose oscillation frequency of different bending states is more advantageous for the player and the game ball than with known racket structures. The main features of the racket according to the invention appear from the characterizing part of the appended claim.

The first bending state of an ideal tennis racket under "free-to-free" conditions would be 170-250 Hz, as 2-3 millisecond contact times between the ball and the racket are common. Using Equation 1, the frequency size class under "fixed-free" conditions, if a 70 cm long racket is hung suspended from a rigid support at 7.5 cm from the handle, would be 215-315 Hz in the second bending mode. The frequency range of one particular embodiment of the racket is 200 to 210 Hz in the first bending state under "free-free" forcing conditions and 230 to 265 Hz in the second bending state under "fixed-free" conditions.

The present invention will be described with reference to the illustrative embodiment shown in the accompanying drawings.

Figure 1 is a top plan view of a tennis racket made in accordance with the present invention.

Figure 2 is a side view of the club of Figure 1.

Figure 3 is a top plan view of the racket frame of Figure 1 without the strands and shank lining.

Figure 4 is a side view of the racket frame of Figure 3.

Figure 5 is a cross-sectional view taken along line 5-5 of Figure 3.

Figure 6 is a cross-sectional view taken along line 6-6 of Figure 3.

Figure 7 is a cross-sectional view taken along line 7-7 of Figure 3.

Figure 8 is a cross-sectional view taken along line 8-8 of Figure 3.

Figure 9 is a partial perspective view of a portion of the club frame showing multiple layers of graphite fibers.

Figure 10 illustrates the first and second bend-rack space of a tennis racket under free-free forcing conditions.

Figure 11 illustrates the first, second, and third bending states of a tennis racket under fixed-free forcing conditions.

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Figure 12 illustrates the deformation of a traditional, prior art racket as a traditional tennis ball bounces back from the racket after an impact.

Figure 13 illustrates the deformation of a racket according to the present invention when a conventional tennis ball bounces back from the racket after an impact.

As described above, it is desirable to adjust the stiffness of the tennis racket so that after a traditional tennis ball strikes the racket, the racket returns to its original, inflexible position before the ball leaves the racket strands. Under these conditions, the flight path of the ball before and after hitting the racket is not affected, and the accuracy of the stroke is improved, as illustrated in Figure 13. In addition, more energy is transferred back to the bouncing ball, and the blows are stronger.

It is desirable to adjust the stiffness of the tennis racket so that the first deflection state of the racket in free-to-force forcing conditions is 170 to 250 Hz. Because the second bending state of such a racket in the fixed-free forcing conditions is 215 to 315 Hz in the second bending state. Figures 1 to 9 illustrate one particular embodiment of a tennis racket 15 having such frequencies.

Referring first to Figures 1 and 2, the racket 15 includes frames 17 having a handle portion 18, a neck portion 19, and a tip portion 20. The neck portion 19 includes a pair of frame portions 21, 22 extending from the handle portion 18 and joining the tip portion 20. The connector 23 extends between the neck pieces 21 and 22 and forms the base of the tip portion, which is usually loop-shaped or oval.

The tennis racket also includes a plurality of longitudinal strands 24 and transverse strands 25 extending in the tip portion 20 and 7 to the traditional openings in the connector 23 89334. The plastic buffer 26 extends around the top of the tip portion to protect the tip from abrasion and wear. The bumper is held in place by the strands, and the bumper also protects the strands from rubbing against the openings in the racket frame. The mold flap 27 extends between the end of the bumper 26 and the neck portion 19 to protect the strands at the bottom of the tip.

The racket also includes a conventional handle cover 28 and an end cap 19 in the handle portion 18. The handle cover can be formed from a helically wrapped leather strip.

Figures 3 and 4 illustrate a racket frame 17 without strands and handle cladding.

Referring to Figures 5-8, each of the frame portions 18 to 23 is formed of a tubular frame portion having a wall thickness of 0.114 to 0.127 cm. The tubular frame portion is formed of layers of resin-impregnated graphite fibers that are wound around an air-filled bladder. As is well known in the art, once the club frame is placed in the mold, the bladder is blown full of air to force layers of graphite fibers against the mold until the resin cures.

Figure 9 illustrates layers 31-42 of resin impregnated graphite fibers used to form the tubular frame portions of the preferred embodiment. Each of the layers 31 to 42 includes non-directional graphite fibers oriented in the direction indicated by the marking. Layers 31, 32 and 35 to 42 contain graphite fibers having a modulus of elasticity of about 33,000,000. Layers 33 and 34 contain graphite fibers having a modulus of elasticity of about 45,000,000. About 10 to 51 of the graphite fibers used in the club frame have a higher modulus of elasticity, and 8 89334 of about 80 to 90 ft. Of the graphite fibers has a lower modulus of elasticity. The use of graphite fibers with a higher modulus of elasticity increases the rigidity of the racket without increasing the weight of the racket. The outermost layer 43 of the racket frame, illustrated in Figure 9, is a paint layer.

Referring to Figures 3-6, the outer surface of the tip is provided with a groove AS in which the thread openings A6 are located. The groove AS also serves to place the buffer 25 and the insert 26 in place (Figure 2).

The height of the racket frame is determined with respect to Fig. A, and measures the dimension of the racket perpendicular to the median plane MP extending through the longitudinal centerline CL of the handle portion 18. The longitudinal centerline CL also forms the longitudinal axis of the racket of Figure 3. The strands of the racket are located in the central plane MP, and the bending of the racket illustrated in Figures 10a and 11 takes place in a plane extending perpendicular to the central plane.

In Fig. A, the height of the frame of the racket continuously digs from the dimension A of the top of the frame to the dimension B of the neck B. The height of the racket continuously decreases from dimension B to the dimension C of the handle 18. The height of the handle increases with dimension C to D and remains the same until the bottom of the handle.

The maximum height B of the racket frame is located in the area where the neck portions 21 and 22 join the tip portion 20. When comparing Figures 3 and A, the maximum dimension B is generally parallel to the center of the connector 23 where the longitudinal centerline CL intersects the connector. When comparing Figures 6 and 7, the height of the connecting piece 23 is substantially smaller than the height of the connecting parts 21 and 22 and the tip part 20 in the region of the maximum height B.

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In one particular embodiment, where the racket has a large tip portion, the longitudinal inner dimension E of the tip portion was 34.9623 cm, the transverse inner dimension of the tip portion was 25.7970 cm, and the total length L was 68.478 cm. The height A of the top of the tip was 2.769 cm, the maximum height B was 3.81 cm, the height C was 2.54 cm and the height D varied depending on the size of the handle according to the traditional dimensions of the handle. Referring to Figure 5, the total width G of the top of the tip portion was 0.965 cm. Referring to Figure 7, the height H of the connecting piece 23 was 2.743 cm, and the width I was 1.016 cm. The maximum height B Buhde to the minimum height A of the tip was 1.5 / 1.09 or 1.376.

The moment of inertia in the area of the club at the point where the cross-sectional height of the club was at its highest was 0.84 cma. The frequency of the first bending mode under free-free forcing conditions was 204 Hz, and the frequency of the second bending mode under fixed-free conditions was 230 Hz.

In one particular embodiment of the medium-sized racket, the longitudinal inner dimension E of the tip portion was 31.801 cm, the transverse inner dimension of the tip portion was 23.698 cm, and the total length L was 68.423 cm. The height A of the top of the tip portion was 2.337 cm, the maximum height B was 3.175 cm, the height C was 2.54 cm, and the height D varied depending on the size of the handle. The total width G of the top of the tip was 1.029 cm. The height H of the connecting piece 23 was 2.299 cm, and the width I was 1.1422 cm. The ratio of the maximum height B to the minimum height A of the tip portion was 1.25 / 0.92 or 1.3587.

The frequency of the first bending mode under free-free forcing conditions was 208 Hz, and the frequency of the second bending mode under fixed-free conditions was 230 Hz.

The shape and dimensions of the frame of the racket illustrated in Figures 3-9 provide, in relation to the mean plane MP, such swing moments that the racket is stiffer than conventional rackets and has the desired frequency of 170-250 Hz for the first bending mode in free-force forcing or 215-315 Hz for the second bending mode. attached-free coercion. The ratio of the maximum height B to the minimum height A is preferably a ratio of about 1.35 to about 1.38.

The use of graphite fibers with a relatively high modulus of elasticity in layers 33 and 34 allows the weight of the frame to be reduced sufficiently to include the buffer 26 while maintaining the total weight of the club in the normal order of magnitude. About 270 grams of graphite fibers and resin, which may be traditional resin, have been used in the frame.

A racket having a large tip portion and a medium sized racket having a defined shape and dimensions are described herein to achieve the desired stiffness and frequency. It is to be understood, however, that other shapes and dimensions may be used as long as the resulting stiffness provides the desired frequency. An important goal is to achieve a frequency of 170 to 250 Hz for the first bending mode in free-free forcing and a frequency of 215 to 315 Hz for fixed-free forcing for the second bending mode.

Since detailed descriptions of certain embodiments of the present invention have been set forth in the foregoing description, it is to be understood that those skilled in the art can make significant changes to many of the details provided herein without departing from the spirit and scope of the invention.

Claims (14)

A racket (15) having a handle (18), a loop-shaped main portion (20), a neck portion (19) connecting the hand position and the main portion, and a longitudinal axis (22) parallel to the centerline and center plane of the handle (MP). ) extending through a longitudinal axis parallel to the plane of the loop-shaped main part (20), characterized in that the racket (15) has a frequency of the first bending state under free-free-forcing conditions in a plane extending perpendicular to said central plane (MP) between 170 Hz and 250 Hz. Racket according to Claim 1, characterized in that the frequency is between 200 Hz and 210 Hz. A racket according to claim 1, characterized in that the frequency of the racket (15) in the second bending state under fixed-free-forcing conditions and in a plane perpendicular to the central plane (MP) is between 215 Hz and 315 Hz. Racket according to Claim 1 or 3, characterized in that the frequency of the second bending state under fixed-free-forcing conditions is between 230 Hz and 265 Hz. Racket according to at least one of Claims 1 to 4, characterized in that the racket is made of a tube consisting of several layers (31-42) of resin-impregnated graphite fibers, and that the fibers in some layers have a modulus of elasticity of about 227528 x 101 N / m 2 and in others the modulus of elasticity of the fibers in the layers is about 310266 x 101 N / m2. Racket according to at least one of Claims 1 to 5, characterized in that the racket is made of a tube consisting of twelve layers (31 to 42) of resin-impregnated graphite fibers and that the modulus of elasticity of the fibers in the two layers is about 310266 x 106 N / m2 and the modulus of elasticity of the fibers in the second layers is about 227528 x 106 N / m2. Racket according to claim 5 or 6, characterized in that about 10 to 20% of the fibers have an elastic modulus of about 310266 x 10 6 N / m 2 and about 80 to 90% of the fibers have an elastic modulus of about 227528 x 106 N / m2. Racket according to Claim 6 or 7, characterized in that the two inner layers (31, 32) and the eight outer layers comprise graphite fibers with a modulus of elasticity of approximately 227528 x 106 N / m 2. Racket according to at least one of Claims 1 to 8, characterized in that the wall thickness of the tube is approximately 1.14 to 1.27 mm. Racket according to at least one of Claims 1 to 9, characterized in that the neck part (19) comprises a pair of frame members (21, 22) which branch from the handle (18) and join the main part (20) so that the racket has a connecting piece (23). passing between the bifurcated parts (21, 22) and forming the base of the loop-shaped main part (20) that the height (B) of the racket (15) relative to the median plane (MP) is at its maximum at the bifurcated frame parts (21, 22) in the area where the connector (23) aligns with the branching frame portions (21, 22). Racket according to Claim 10, characterized in that the ratio of the maximum height (B) of the racket to the height of the apex (A) of the main part (20) is approximately 1.35 to 1.38. Racket according to Claim 10 or 11, characterized in that the moment of inertia at the maximum cross-sectional height (B) of the frame (17) is approximately 13.73 cm 4. 13 89334 Racket according to Claim 10 or 11, characterized in that the height of the racket decreases continuously from the maximum height (B) to the tip (A) of the main part (20) and from the maximum height (B) to the tip of the handle part (18). A racket according to claim 1, characterized in that its length is about 685 mm.