Patent Grant
8562462
This application claims priority on Patent Application No. 2011-162026 filed in JAPAN on Jul. 25, 2011. The entire contents of this Japanese Patent Application are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to frames for tennis rackets and the like. Specifically, the present invention relates to racket frames that include vibration-damping portions.
2. Description of the Related Art
When a ball is hit with a tennis racket, vibrations are transmitted to the player. Some players feel uncomfortable with the vibrations. Players desire mild feel at impact. The vibrations can also cause tennis elbow.
There have been various proposals for damping the vibrations. JP4-236973 discloses a tennis racket that includes an elastic body in a grip thereof. The elastic modulus of the elastic body can contribute to vibration damping. JP2003-10362 discloses a tennis racket that includes a damper in a head thereof. The damper can contribute to vibration damping.
Players request tennis rackets to have desired resilience. When a ball is hit with a racket having excellent resilience, the ball can fly at a high speed. Players also request tennis rackets to have desired operability.
Tennis rackets having excellent resilience and operability are suitable to players who participate in competitions. However, tennis rackets having excellent resilience and operability generally have inferior vibration-damping performance.
An object of the present invention is to provide a racket frame having excellent vibration-damping performance, resilience, and operability.
A racket frame according to the present invention includes a body and a first vibration-damping portion fixed to the body. The body includes a head, a shaft, a pair of throats extending from the head to the shaft, and a grip connected to the shaft. The body includes a second vibration-damping portion. A material of the second vibration-damping portion is different from a material of the first vibration-damping portion. In the racket frame, a ratio (R2/R4) of a side pressure rigidity R2 to a throat rigidity R4 is equal to or greater than 0.26. A moment of inertia around an axis at a position of 10 cm from a grip end is less than 300 kg·cm2. A vibration damping rate in an out-of-plane secondary mode is equal to or greater than 0.70 but equal to or less than 1.0.
Preferably, the first vibration-damping portion is formed from a fiber reinforced nylon. Preferably, the second vibration-damping portion is formed from an epoxy resin.
Preferably, the first vibration-damping portion is fixed to each throat, the shaft, or the grip, and the second vibration-damping portion is included in the head or each throat. Preferably, the first vibration-damping portion extends from each throat to the grip.
Preferably, the head includes a pair of second vibration-damping portions. These second vibration-damping portions are located so as to be symmetrical about the axis of the racket frame.
Each throat may include the second vibration-damping portion. These second vibration-damping portions are located so as to be symmetrical about the axis of the racket frame.
Preferably, the side pressure rigidity R2 is equal to or greater than 95 kgf/cm, and the throat rigidity R4 is equal to or less than 350 kgf/cm. Preferably, the ratio (R2/R4) is equal to or greater than 0.28. Preferably, the moment of inertia is less than 295 kg·cm2.
The following will describe in detail the present invention, based on preferred embodiments with reference to the accompanying drawings.
A racket frame 2 shown in
The head 8 forms the contour of a ball-hitting face. The head 8 has a substantially elliptical front shape. One end of each throat 10 is connected to the head 8. Each throat 10 is connected at the vicinity of the other end thereof to the other throat 10. The throats 10 extend from the head 8 to the shaft 12. The shaft 12 extends from the location where the two throats 10 are connected to each other. The shaft 12 is formed so as to be integrally connected to the throats 10. The grip 14 is formed so as to be integrally connected to the shaft 12. The portion of the head 8 that is sandwiched between the two throats 10 is a yoke 16.
The body 4 is composed of fiber reinforced resinous layers. The matrix resin of the fiber reinforced resinous layers is an epoxy resin. The reinforced fiber of the fiber reinforced resinous layers is a carbon fiber. The reinforced fiber is a long fiber. As is obvious from
The first vibration-damping portions 6 are fixed to the body 4. As shown in
The first vibration-damping portions 6 can be fixed to the throats 10, the shaft 12, or the grip 14. As is obvious from
Each first vibration-damping portion 6 is formed from a fiber reinforced nylon including a short fiber. A preferable short fiber is a carbon fiber. A preferable matrix is 66 nylon. The content of the short fiber in the fiber reinforced nylon is equal to or greater than 10% by weight but equal to or less than 30% by weight. The first vibration-damping portion 6 in which the content is equal to or greater than 10% by weight has a high elastic modulus and excellent dimensional accuracy. In this respect, the content is particularly preferably equal to or greater than 15% by weight. The first vibration-damping portion 6 in which the content is equal to or less than 30% by weight has excellent vibration-damping performance. In this respect, the content is preferably equal to or less than 25% by weight.
In the tennis racket in which the racket frame 2 is used, vibrations generated at hitting are damped by the first vibration-damping portions 6. The tennis racket has excellent feel at impact. With the tennis racket, tennis elbow is unlikely to occur.
What is indicated by a reference sign L1 in
What is indicated by a reference sign Ti in
As shown in
As shown in
In the tennis racket in which the racket frame 2 is used, vibrations generated at hitting are damped by the second vibration-damping portions 18. The tennis racket has excellent feel at impact. With the tennis racket, tennis elbow is unlikely to occur. The material of the second vibration-damping portions 18 is different from the material of the first vibration-damping portions 6. Since the two types of the vibration-damping portions whose materials are different from each other are provided, the racket frame 2 is very excellent in vibration-damping performance.
What is indicated by each reference sign L2 in
In the present embodiment, the head 8 and the throats 10 include the second vibration-damping portions 18. Only the head 8 may include the second vibration-damping portions 18, or only each throat 10 may include the second vibration-damping portion 18.
In light of vibration-damping performance, each angle θ is preferably equal to or greater than 30° and particularly preferably equal to or greater than 45°. In light of vibration-damping performance, each angle θ is preferably equal to or less than 120° and particularly preferably equal to or less than 90°.
In light of resilience and operability, the top pressure rigidity R1 is preferably equal to or greater than 110 kgf/mm and particularly preferably equal to or greater than 120 kgf/mm. In light of feel at impact, the top pressure rigidity R1 is preferably equal to or less than 135 kgf/mm and particularly preferably equal to or less than 130 kgf /mm.
In light of resilience and operability, the side pressure rigidity R2 is preferably equal to or greater than 95 kgf/mm and particularly preferably equal to or greater than 100 kgf/mm. In light of feel at impact, the side pressure rigidity R2 is preferably equal to or less than 120 kgf/mm and particularly preferably equal to or less than 110 kgf/mm.
A. The compressing tool 32 presses the head 8. Due to this pressing, a load is applied to the racket frame 2. By the movement of the compressing tool 32, the load gradually increases. A movement distance X (mm) of the compressing tool 32 from the state in which the load is 25 kgf to the state in which the load is 50 kgf is measured. A value obtained by dividing 25 kgf by X is the plane rigidity R3. The measurement of the plane rigidity R3 is conducted in a state in which the grommet is attached to the racket frame 2 having vibration-damping performance and the gut is not mounted on the racket frame 2 having vibration-damping performance.
In light of resilience and operability, the plane rigidity R3 is preferably equal to or greater than 50 kgf/mm and particularly preferably equal to or greater than 55 kgf/mm. In light of feel at impact, the plane rigidity R3 is preferably equal to or less than 65 kgf/mm and particularly preferably equal to or less than 60 kgf/mm.
The distance L in
In light of resilience and operability, the throat rigidity R4 is preferably equal to or greater than 310 kgf/mm and particularly preferably equal to or greater than 320 kgf/mm. In light of feel at impact, the throat rigidity R4 is preferably equal to or less than 350 kgf/mm and particularly preferably equal to or less than 340 kgf /mm.
In light of resilience and operability, the ball-hitting face rigidity R5 is preferably equal to or greater than 130 kgf/mm and particularly preferably equal to or greater than 140 kgf/mm. In light of feel at impact, the ball-hitting face rigidity R5 is preferably equal to or less than 170 kgf/mm and particularly preferably equal to or less than 160 kgf/mm.
The ratio (R2/R4) of the side pressure rigidity R2 to the throat rigidity R4 is preferably equal to or greater than 0.26. The racket frame 2 in which the ratio (R2/R4) is equal to or greater than 0.26 has both excellent feel at impact and excellent resilience. In this respect, the ratio (R2/R4) is more preferably equal to or greater than 0.28 and particularly preferably equal to or greater than 0.31. The ratio (R2/R4) that can be achieved in a practical racket frame 2 is equal to or less than 0.40.
Rv=(½)×(Δω/ωn) (1)
T0=Tn/√2 (2)
In the equation (1), ωn is the frequency of a primary maximal value.
The vibration damping rate in the out-of-plane secondary mode is preferably equal to or greater than 0.70 and particularly preferably equal to or greater than 0.80. In light of resilience, the vibration damping rate is preferably equal to or less than 1.0.
The vibration damping rate in the out-of-plane primary mode is preferably equal to or greater than 0.50 and particularly preferably equal to or greater than 0.60. In light of resilience, the vibration damping rate is preferably equal to or less than 0.80.
The vibration damping rate in the in-plane secondary mode is preferably equal to or greater than 1.3 and particularly preferably equal to or greater than 1.5. In light of resilience, the vibration damping rate is preferably equal to or less than 2.0.
In light of operability, a moment of inertia around the axis at a position of 10 cm from the grip end is preferably less than 300 kg·cm2 and particularly preferably less than 295 kg·cm2. The moment of inertia that can be achieved in a practical racket frame 2 is equal to or greater than 250 kg·cm2. The moment of inertia is measured by racket diagnostic center manufactured by Babolat VS.
In light of resilience, the weight of the racket frame 2 is preferably equal to or greater than 300 g and particularly preferably equal to or greater than 310 g. In light of operability, the weight is preferably equal to or less than 340 g and particularly preferably equal to or less than 330 g.
The following will show the effects of the present invention by means of Examples, but the present invention should not be construed in a limited manner based on the description of these Examples.
The racket frame shown in
A racket frame of Example 2 was obtained in the same manner as Example 1, except the positions of the second vibration-damping portions in the head were as shown in Table 1 below.
A racket frame of Example 3 was obtained in the same manner as Example 1, except no second vibration-damping portions were provided in the throats. A racket frame of Example 4 was obtained in the same manner as Example 1, except no second vibration-damping portions were provided in the head.
A racket frame of Comparative Example 1 was obtained in the same manner as Example 1, except no first vibration-damping portions were provided. A racket frame of Comparative Example 2 was obtained in the same manner as Example 1, except no second vibration-damping portions were provided. A racket frame of Comparative Example 3 was obtained in the same manner as Example 1, except no first vibration-damping portions and no second vibration-damping portions were provided.
Racket frames of Examples 5 and 6 were obtained in the same manner as Example 1, except the weight and the positions of the second vibration-damping portions in the head were as shown in Tables 2 and 3 below.
Racket frames of Comparative Examples 4 to 6 are commercially available racket frames. The racket frame of Comparative Example 4 includes second vibration-damping portions in a shaft thereof. In the racket frame of Comparative Example 5, a matrix is a nylon obtained by reaction injection molding, and a reinforced fiber is a carbon long fiber. In the racket frame of Comparative Example 6, a carbon short fiber is dispersed in a nylon matrix.
[Evaluation]
Grommets, grip tapes, end caps, and guts were mounted onto the racket frames to produce tennis rackets. Ten advanced players conducted rallies with the tennis rackets and were asked about feel at impact, resilience, and operability. The evaluation was categorized as follows on the basis of the number of players who answered, “good”.
A: 8 or more
B: 6 or 7
C: 4 or 5
D: 3 or less
The results are shown in Tables 1 to 3.
As shown in Tables 1 to 3, the racket frames of Examples are excellent in various performance characteristics. From the results of evaluation, advantages of the present invention are clear.
The above descriptions are merely for illustrative examples, and various modifications can be made without departing from the principles of the present invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2011-162026 | Jul 2011 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5178387 | Kuebler | Jan 1993 | A |
| 5538243 | Yamamoto et al. | Jul 1996 | A |
| 7131920 | Ashino | Nov 2006 | B2 |
| 8137221 | Ashino | Mar 2012 | B2 |
| 20130029793 | Yamamoto et al. | Jan 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 4-236973 | Aug 1992 | JP |
| 2001286581 | Oct 2001 | JP |
| 2002065904 | Mar 2002 | JP |
| 2003-10362 | Jan 2003 | JP |
| 2011015885 | Jan 2011 | JP |
| 2013022361 | Feb 2013 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20130029793 A1 | Jan 2013 | US |
