JP7748665B2 - racket - Google Patents

Description

This specification discloses a racket suitable for tennis, soft tennis, squash, padel, badminton, etc.

When a ball is hit with a tennis racket, vibrations are generated in the racket. These vibrations are transmitted to the player, causing discomfort to the player.

JP 2005-328923 A discloses a tennis racket with a grip and a dynamic damper housed in the grip. This dynamic damper damps vibrations generated in the racket.

JP 2005-328923 A

The racket disclosed in JP 2005-328923 A does not adequately suppress vibrations transmitted to the player, causing discomfort to the player. In soft tennis, squash, padel, badminton, and other sports, the transmission of vibrations from the racket to the player also causes discomfort to the player.

The inventor's intention is to provide a racket that reduces discomfort for the player.

Preferred rackets have a natural frequency of 100 Hz or less in an unconstrained state.

This racket can reduce player discomfort caused by arm vibration.

FIG. 1 is an exploded front view showing a tennis racket according to an embodiment. FIG. 2 is a side view of the tennis racket of FIG. FIG. 3 is an exploded view of a portion of the tennis racket of FIG. 1, shown enlarged. FIG. 4 is an enlarged, partially cut-away view of a portion of the tennis racket of FIG. FIG. 5 is an enlarged, partially cut-away view of a portion of the tennis racket of FIG. FIG. 6 is a schematic diagram showing a method for measuring the in-plane natural frequency of the tennis racket of FIG. FIG. 7 is a graph showing a schematic representation of the natural frequency of the tennis racket of FIG. 1 in an unconstrained state. FIG. 8 is a front view showing a tennis racket according to another embodiment. FIG. 9 is a side view of the tennis racket of FIG. FIG. 10 is an enlarged cross-sectional view showing the dynamic damper of the tennis racket of FIG. FIG. 11 is an enlarged cross-sectional view showing the dynamic damper of the tennis racket of FIG.

A preferred embodiment will be described in detail below, with appropriate reference to the drawings.

Figures 1-3 show a tennis racket 2. The racket 2 has a frame 4, a grip 6, an end cap 8, grommets 10, and strings 12. The racket 2 can be used for hard tennis. In Figure 1, arrow X represents the width direction of the racket 2, arrow Y represents the axial direction of the racket 2, and direction Z represents the thickness direction of the racket 2. In Figure 2, the grommets 10 and strings 12 are not shown.

The frame 4 has a head 14, a first throat 16, a second throat 18, and a shaft 20. The head 14 forms the outline of the face 22 (described in detail later). The front shape of the head 14 is approximately elliptical. The major axis of the ellipse coincides with the axial direction Y of the racket 2. The minor axis of the ellipse coincides with the width direction X of the racket 2. The first throat 16 extends from the head 14. The second throat 18 extends from the head 14. The second throat 18 joins the first throat 16 at a position away from the head 14. The shaft 20 extends from the point where the two throats 16, 18 join. The shaft 20 is continuous with the throats 16, 18. The portion of the head 14 sandwiched between the two throats 16, 18 is a yoke 24. The frame 4 is hollow.

The main material of this frame 4 is fiber-reinforced resin. This fiber-reinforced resin has a resin matrix and a large number of reinforcing fibers. The frame 4 includes multiple fiber-reinforced layers.

Examples of the base resin for the frame 4 include thermosetting resins such as epoxy resin, bismaleimide resin, polyimide, and phenolic resin; and thermoplastic resins such as polyetheretherketone, polyethersulfone, polyetherimide, polyphenylene sulfide, polyamide, and polypropylene. Epoxy resin is a particularly suitable resin for the frame 4.

Examples of reinforcing fibers for the frame 4 include carbon fiber, metal fiber, glass fiber, and aramid fiber. A particularly suitable fiber for the frame 4 is long carbon fiber. Multiple types of fiber may be used in combination.

As shown in Figures 2 and 3, the head 14 has a grommet groove 26. This grommet groove 26 is recessed from the outer peripheral surface of the head 14. The grommet groove 26 is formed around almost the entire circumference of the head 14, excluding the yoke 24.

The head 14 further has a plurality of holes 28. Each hole 28 penetrates the head 14. The plurality of holes 28 are arranged around almost the entire circumference of the head 14.

The grip 6 is formed by tape wrapped around the shaft 20. The grip 6 prevents slippage between the player's hand and the tennis racket 2 when the tennis racket 2 is swung.

As shown in FIG. 3, the grommet 10 has a base 30 and multiple pipes 32. The base 30 has a belt shape. Each pipe 32 is formed integrally with the base 30. The pipes 32 stand upright from the base 30. The grommet 10 is typically made of a synthetic resin that is softer than the frame 4. The tennis racket 2 may have multiple grommets 10. The number of pipes 32 in each grommet 10 may be one.

The grommet 10 is attached to the head 14. When the grommet 10 is attached to the head 14, the base 30 is housed in the grommet groove 26. A portion of the base 30 may protrude from the grommet groove 26. Furthermore, when the grommet 10 is attached to the head 14, the pipe 32 passes through the hole 28.

As shown in FIG. 1, the strings 12 are strung on the head 14. The strings 12 are strung along the width direction X and the axial direction Y. The strings 12 pass through a pipe 32. The strings 12 form a number of threads 34. The portions of the strings 12 that extend along the width direction X are referred to as horizontal threads 34a. The portions of the strings 12 that extend along the axial direction Y are referred to as vertical threads 34b. The multiple horizontal threads 34a and multiple vertical threads 34b form a face 22. The face 22 generally extends along the X-Y plane. The face 22 may be formed from two or more strings 12.

Figures 4 and 5 show the vicinity of the shaft 20. As shown in these figures, the tennis racket 2 has a case 36, a dynamic damper 38, a first holder 40, and a second holder 42. The case 36 is cylindrical. The case 36 has a chamber 44. The dynamic damper 38 is housed in the chamber 44. The case 36 is housed in the shaft 20. In other words, the dynamic damper 38 is housed in the shaft 20 via the case 36. The dynamic damper 38 may also be housed in the shaft 20 without the case 36. The first holder 40 and the second holder 42 are each fixed to the case 36. The dynamic damper 38 has a weight 46, a first leaf spring 48, and a second leaf spring 50. The dynamic damper 38 may include a damping material. A typical damping material is gel.

The weight 46 has a high specific gravity. Preferred materials for the weight 46 include copper, copper alloy, lead, lead alloy, tungsten, tungsten alloy, carbon steel, and alloy steel. In Figure 4, the arrow Lw represents the length of the weight 46, and the arrow Tw represents the thickness of the weight 46. In Figure 5, the arrow Ww represents the width of the weight 46.

One end of the first leaf spring 48 is connected to the weight 46. The other end of the first leaf spring 48 is connected to the first holder 40. One end of the second leaf spring 50 is connected to the weight 46. The other end of the second leaf spring 50 is connected to the second holder 42. The first leaf spring 48 and the second leaf spring 50 hold the weight 46 away from the case 36. In FIG. 4, arrow Ls1 represents the length of the first leaf spring 48, arrow Ls2 represents the length of the second leaf spring 50, and arrow Ts represents the thickness of each leaf spring. In FIG. 5, arrow Ws represents the width of each leaf spring. The sum of length Ls1 and length Ls2 is the total length Ls of the springs 48, 50.

As is clear from comparing Figures 4 and 5, the thickness direction of the first leaf spring 48 is the X direction. Therefore, the first leaf spring 48 can bend in the X direction. The thickness direction of the second leaf spring 50 is the X direction. Therefore, the second leaf spring 50 can bend in the X direction. The bending of the first leaf spring 48 and the second leaf spring 50 can move the weight 46 in the X direction. The weight 46 oscillates as the first leaf spring 48 and the second leaf spring 50 alternately bend to the right in Figure 4 and to the left in Figure 4. The direction of the oscillation is the X direction (i.e., the in-plane direction).

Figure 6 shows a method for measuring the in-plane natural frequency of a tennis racket 2. In this method, the racket 2 is suspended by a string 52. The axial direction (Y direction) of the racket 2 is aligned with the vertical direction. The head 14 is positioned above the shaft 20. The grip tape has been removed from the shaft 20. An acceleration pickup 54 is attached to the shaft 20 of the racket 2. The acceleration pickup 54 is attached 90 mm from the bottom end 56. The acceleration pickup 54 faces the X direction. The acceleration pickup 54 has a mass of 3.5 g. An impulse hammer (not shown) vibrates the shaft 20 at a point Ph opposite the acceleration pickup 54. A typical impulse hammer is manufactured by PCB Corporation. The input vibration measured by the force pickup of the impulse hammer and the response vibration measured by the acceleration pickup 54 are sent to a frequency analyzer via an amplifier. A typical frequency analyzer is a Hewlett-Packard "Dynamic Signal Analyzer." The in-plane natural frequency is calculated based on the transfer function obtained by this device. With this method, the natural frequency is measured without any part of the racket 2 being rigidly fixed. In other words, the natural frequency of the racket 2 in an unconstrained state is measured.

Fig. 7 is a graph showing the natural frequency of the tennis racket 2 in the X direction (i.e., in-plane direction). In Fig. 7, the horizontal axis is frequency (Hz) and the vertical axis is acceleration (m/ ^s2 /N). In Fig. 7, the reference symbol P1 indicates the primary peak and the reference symbol P2 indicates the secondary peak. The frequency f1 at the primary peak P1 is lower than the frequency f2 at the secondary peak P2. The frequency f1 is the natural frequency of the racket 2 in the in-plane direction.

As mentioned above, the direction of oscillation of the weight 46 in the dynamic damper 38 is the in-plane direction. This oscillation affects the in-plane natural frequency of the tennis racket 2. The in-plane natural frequency of this tennis racket 2 is lower than that of a tennis racket that does not have the dynamic damper 38.

The player's hands and arms and the tennis racket 2 form a coupled system. According to the inventor's findings, the natural frequency of the coupled system is low. The in-plane natural frequency of a conventional tennis racket without a dynamic damper 38 is approximately 200 Hz. The tennis racket 2 according to the present disclosure has an in-plane natural frequency of 100 Hz or less. The in-plane natural frequency of the racket 2 is close to the natural frequency of the coupled system. Therefore, hand and arm vibrations in the coupled system including the racket 2 have a small amplitude and a large damping rate. The racket 2 can suppress impacts on the player caused by arm vibrations. From this perspective, the in-plane natural frequency of the racket 2 is more preferably 50 Hz or less, and particularly preferably 30 Hz or less. The in-plane natural frequency is preferably 5 Hz or more. The racket 2 may have two or more dynamic dampers 38.

Conventional tennis rackets with dynamic dampers do not take into account the natural frequency of the coupled system. The in-plane natural frequency of these rackets is high. With these rackets, discomfort is not sufficiently suppressed. In contrast, with the tennis racket 2 disclosed herein, the natural frequency of the coupled system is taken into account, and an appropriate dynamic damper 38 is selected.

The racket may have a dynamic damper in which the weight oscillates in an out-of-plane direction. This dynamic damper achieves a low out-of-plane natural frequency. The racket may also have a dynamic damper in which the weight oscillates in a direction that is neither in-plane nor out-of-plane. According to the inventor's findings, in-plane vibrations are well transmitted to the arm. Therefore, a dynamic damper 38 in which the weight 46 oscillates in an in-plane direction is preferred.

An example of a method for determining the specifications of the dynamic damper 38 is described below. The parameters of the dynamic damper 38 are calculated using the following formula:

M: Mass of coupled system (kg)
K: Spring constant of the coupled system (N/m)
μ: mass ratio m: mass of the dynamic damper 38 (m)
k: spring constant of the dynamic damper 38 (N/m)
c: damping coefficient of the dynamic damper 38 (Ns/m)

The mass M and spring constant K in the coupled system can be estimated experimentally.

The dynamic damper 38 shown in Figures 4 and 5 has both the first leaf spring 48 and the second leaf spring 50 fixed to the case 36. The spring constant k of this dynamic damper 38 is calculated using the following formula:

This formula can be transformed to derive the following formula:

This formula calculates the width b (= Ws) of the first leaf spring 48 and the second leaf spring 50.

The damping factor of the dynamic damper 38 is calculated using the following formula:

ζ: damping ratio η: loss coefficient K1: storage modulus K2: loss modulus K': complex modulus

The relationship between damping ratio ζ and loss coefficient η is as follows:

As mentioned above, the grip 6 is wrapped around the shaft 20. Therefore, the player cannot see the dynamic damper 38. The player can use the tennis racket 2 without feeling uncomfortable. A transparent grip 6 may be used to allow the dynamic damper 38 to be seen.

This method allows for the design of a dynamic damper 38 that can reduce impact on the player.

Figure 8 is a front view of a tennis racket 58 according to another embodiment, and Figure 9 is a side view thereof. Similar to the tennis racket 2 shown in Figures 1-3, this tennis racket 58 has a frame 60, a grip 62, an end cap 64, grommets, and strings 66. This racket 58 also has a dynamic damper 68. The frame 60 has a head 70, a first throat 72, a second throat 74, and a shaft 76. Unlike the racket 2 shown in Figures 1-3, the shaft 76 does not house a damper. This tennis racket 58 can be used for hard tennis. In Figures 8 and 9, arrow X represents the width direction of the racket 58, arrow Y represents the axial direction of the racket 58, and direction Z represents the thickness direction of the racket 58.

The dynamic damper 68 is fixed to the first throat 72, the second throat 74, and the shaft 76. This fixation is achieved by adhesive. Fixation may be achieved by other means. Examples of other means include bolts, ties, and welding. The housing of the dynamic damper 68 (described in more detail below) may be integrally molded with the frame 60. The tennis racket 58 may have a dynamic damper 68 that can be attached to and detached from the frame 60.

Figures 10 and 11 show a dynamic damper 68. This dynamic damper 68 has a housing 78, a weight 80, and a pair of leaf springs 82. The weight 80 is made of the same material as the weight 46 shown in Figures 4 and 5. The leaf springs 82 are made of the same material as the first leaf spring 48 and second leaf spring 50 shown in Figures 4 and 5.

One end of the leaf spring 82 is connected to the weight 80. The other end of the leaf spring 82 is connected to the housing 78. The leaf spring 82 holds the weight 80 at a distance from the housing 78. In FIG. 10, the arrow Lw represents the length of the weight 80, the arrow Tw represents the thickness of the weight 80, the arrow Ls represents the length of the leaf spring 82, and the arrow Ts represents the thickness of the leaf spring 82. In FIG. 11, the arrow Ww represents the width of the weight 80, and the arrow Ws represents the width of the leaf spring 82.

As is clear from comparing Figures 10 and 11, the thickness direction of the leaf spring 82 is the X direction. Therefore, the leaf spring 82 can bend in the X direction. The bending of the leaf spring 82 can move the weight 80 in the X direction. The weight 80 oscillates as the leaf spring 82 alternates between bending to the right in Figure 10 and bending to the left in Figure 10. The direction of the oscillation is the X direction (i.e., the in-plane direction).

The oscillation of the weight 80 in the in-plane direction affects the in-plane natural frequency of the tennis racket 58. The in-plane natural frequency of this racket 58 is lower than that of a racket without a dynamic damper 68. The hand-arm vibration in a coupled system including this racket 58 has a small amplitude and a large damping rate. This racket 58 can suppress the impact on the player caused by arm vibration. From this perspective, the in-plane natural frequency is preferably 100 Hz or less, more preferably 50 Hz or less, and particularly preferably 30 Hz or less. The in-plane natural frequency is preferably 5 Hz or more.

In the dynamic damper 68 shown in Figures 10 and 11, one end of the leaf spring 82 is fixed to the housing 78. The spring constant k of this dynamic damper 68 is calculated using the following formula:

This formula can be transformed to derive the following formula:

This formula calculates the width b (= Ws) of the leaf spring 82.

A player swinging this racket 58 can see the dynamic damper 68. Players who are concerned about impacts to their elbows can easily distinguish this racket 58 from a conventional racket that generates a large impact. The dynamic damper 68 may be located between the first throat 72 and the second throat 74. The leaf spring 82 may be fixed directly to the frame 60 without using the housing 78.

The effects of the racket according to the example will be explained below, but the scope of the disclosure in this specification should not be interpreted as being limited based on the description of this example.

[Example 1]
The tennis racket shown in Figures 1-5 was manufactured. This racket had a dynamic damper housed in the shaft. In this dynamic damper, the weight was made of brass, the spring was made of stainless steel (SUS303), and the damping material was gel. The vibration direction of the weight was in-plane. The specifications of the weight and leaf spring of this dynamic damper are shown in Table 1 below.

[Examples 2 to 5 and Comparative Example 1]
Tennis rackets of Examples 2-5 and Comparative Example 1 were obtained in the same manner as in Example 1, except that the specifications of the weights, leaf springs, and damping materials were as shown in Tables 1 and 2 below.

[Example 6]
A tennis racket of Example 6 was obtained in the same manner as Example 1, except that a dynamic damper was provided in which the vibration direction of the weight was out of plane.

[Example 7]
The tennis racket shown in Figures 8-11 was manufactured. This racket has a dynamic damper fixed to the throat and shaft. The vibration direction of the weight of this dynamic damper is in the in-plane direction. The specifications of the weight, leaf spring, and damping material of this dynamic damper are shown in Table 2 below.

[Comparative Example 2]
A tennis racket of Comparative Example 2 was obtained in the same manner as in Example 1, except that no dynamic damper was provided.

[Sensory evaluation]
A sensory evaluation was conducted by an advanced player with a history of tennis elbow. This player regularly hits the ball while taking into consideration damage to the elbow caused by impact. This player is sensitive to vibrations transmitted from the racket to the arm. Five players were asked to evaluate the reduction in impact to the elbow, and an average score was calculated. The results are shown in Tables 1 and 2 below.

As is clear from Tables 1 and 2, the tennis rackets of each example inflict less impact on the player. When hitting shots with this racket, the player is less likely to feel uncomfortable. The superiority of this racket is clear from these evaluation results.

[Disclosure items]
Each of the following sections is a disclosure of a preferred embodiment.

[Item 1]
A racket having a natural frequency of 100 Hz or less in an unconstrained state.

[Item 2]
Item 1. The racket according to item 1, having an in-plane natural frequency of 100 Hz or less in an unconstrained state.

[Item 3]
3. The racket according to item 1 or 2, comprising a frame and a dynamic damper attached to the frame.

[Item 4]
The dynamic damper includes a spring and a weight fixed to the spring,
4. The racket according to item 3, wherein the weight vibrates due to repeated deformation of the spring.

[Item 5]
5. The racket according to item 4, wherein the vibration direction of the weight is an in-plane direction.

[Item 6]
6. The racket according to any one of items 3 to 5, wherein the dynamic damper is housed within the frame.

[Item 7]
the frame includes a head, a first throat and a second throat extending from the head, and a shaft connected to the first throat and the second throat;
7. The racket according to item 6, wherein the dynamic damper is housed in the shaft.

[Item 8]
6. The racket according to any one of items 3 to 5, wherein the dynamic damper is bonded to the surface of the frame.

[Item 9]
the frame includes a head, a first throat and a second throat extending from the head, and a shaft connected to the first throat and the second throat;
9. The racket according to item 8, wherein the dynamic damper is joined to the first throat, the second throat, or the shaft.

The aforementioned rackets are also suitable for soft tennis, squash, padel, badminton, etc.

2...Tennis racket 4...Frame 6...Grip 16...First throat 18...Second throat 20...Shaft 36...Case 38...Dynamic damper 44...Chamber 46...Weight 48...First leaf spring 50...Second leaf spring 58...Tennis racket 60...Frame 62...Grip 68...Dynamic damper 72...First throat 74...Second throat 76...Shaft 78...Housing 80...Weight 82...Leaf spring

Claims (5)

In an unconstrained state, the bearing has an in-plane natural frequency of 50 Hz or less,
The vehicle is provided with a frame and a dynamic damper attached to the frame,
the dynamic damper includes a spring and a weight fixed to the spring, and the weight vibrates in an in-plane direction due to repeated deformation of the spring;
The racket has a lower in-plane natural frequency due to the vibration of the weight . 2. The racket of claim 1 , wherein the dynamic damper is housed within the frame. the frame includes a head, a first throat and a second throat extending from the head, and a shaft connected to the first throat and the second throat;
3. The racket of claim 2 , wherein the dynamic damper is housed in the shaft. 2. The racket of claim 1 , wherein the dynamic damper is bonded to the surface of the frame. the frame includes a head, a first throat and a second throat extending from the head, and a shaft connected to the first throat and the second throat;
5. The racket according to claim 4 , wherein the dynamic damper is joined to the first throat, the second throat, or the shaft.