JP2025179357A - racket - Google Patents

Abstract

To provide a racket excellent in repulsion performance.SOLUTION: A racket has a frame 4. The frame 4 includes a head 14. The head 14 has a first high-elasticity layer 37a and a second high-elasticity layer 37b. Each high-elasticity layer 37 is positioned outside the head 14 in a thickness direction. The high-elasticity layers 37 include a reinforced fiber of a straight type. In the frame 4, the ratio of a ball hitting face rigidity value G2 to a lateral pressure rigidity value G1 (G2/G1) is 3.20 or larger. In the frame 4, the ratio of thickness Tf to width Wf (Tf/Wf) is desirably 2.0 or larger.SELECTED DRAWING: Figure 5

Description

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

In tennis, a ball is hit with a racket. This hit transfers the kinetic energy of the racket to the ball, causing it to fly. A ball hit with a tennis racket with excellent resilience can fly at high speeds. A high flight speed is advantageous in tennis. Japanese Patent Application Laid-Open Publication No. 5-15617 discloses a tennis racket with excellent resilience.

Japanese Patent Application Publication No. 5-15617

Tennis players desire even greater repulsion performance. The applicant's intention is to provide a racket with excellent repulsion performance.

The racket disclosed in this specification has a frame including a head. The ratio (G2/G1) of the hitting surface stiffness value G2 to the side pressure stiffness value G1 of this frame is 3.20 or greater.

This racket has excellent resilience. A ball hit with this racket can fly at high speed.

FIG. 1 is a front view showing a tennis racket according to an embodiment. FIG. 2 is a right 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 a perspective view showing a part of the manufacturing process of the racket of FIG. FIG. 5 is an enlarged cross-sectional view taken along line VV in FIG. FIG. 6 is an enlarged cross-sectional view taken along line VI-VI in FIG. FIG. 7 is an enlarged view showing a portion of the prepreg for the first fiber reinforced layer of the head of FIG. FIG. 8 is an enlarged view showing a portion of the prepreg for the second fiber-reinforced layer of the head of FIG. FIG. 9 is a perspective view showing a part of the high-elasticity layer of the head of FIG. FIG. 10 is an enlarged view showing a part of the prepreg for the high-elasticity layer of FIG. FIG. 11 is a graph showing the relationship between the side pressure stiffness value and the hitting surface stiffness value of the tennis racket frame of FIG. FIG. 12 is a front view showing a method for measuring the side pressure stiffness value of the frame of the tennis racket shown in FIG. FIG. 13(a) is a plan view showing a method for measuring the stiffness value of the ball-hitting surface of the frame of the tennis racket shown in FIG. 1, and FIG. 13(b) is a front view thereof.

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 Figures 1 and 2, 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. The grommets 10 and strings 12 are not shown in Figure 2.

The frame 4 has a head 14, a first throat 16a, a second throat 16b, and a shaft 18. The head 14 forms the outline of the face 20 (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. In FIG. 1, the symbol Ch represents the center of the head 14. The first throat 16a extends from the head 14. The second throat 16b extends from the head 14. The second throat 16b joins the first throat 16a at a position away from the head 14. The shaft 18 extends from the point where the two throats 16 join. The shaft 18 is continuous with the throats 16. The portion of the head 14 sandwiched between the two throats 16 is a yoke 22. 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. The fiber-reinforced layers will be described in detail later.

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 groove 24. This groove 24 is recessed from the outer peripheral surface of the head 14. The groove 24 is formed around almost the entire circumference of the head 14, excluding the yoke 22. The head 14 also has a plurality of holes 26. The plurality of holes 26 are arranged around almost the entire circumference of the head 14.

The grip 6 is formed by tape wrapped around the shaft 18. The grip 6 prevents slippage between the player's hand and the racket 2 when the tennis racket 2 is swung.

As shown in FIG. 3, the grommet 10 has a base 28 and multiple pipes 30. The base 28 has a belt shape. Each pipe 30 is formed integrally with the base 28. The pipes 30 stand upright from the base 28. 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 30 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 28 is housed in the groove 24. A portion of the base 28 may protrude from the groove 24. Furthermore, when the grommet 10 is attached to the head 14, the pipe 30 passes through the hole 26.

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 30. The strings 12 form a number of threads 32. The portions of the strings 12 that extend along the width direction X are referred to as horizontal threads 32a. The portions of the strings 12 that extend along the axial direction Y are referred to as vertical threads 32b. The multiple horizontal threads 32a and multiple vertical threads 32b form a face 20. The face 20 generally extends along the X-Y plane. Only a portion of the face 20 is shown in FIG. 1. The face 20 may be formed from two or more strings 12.

An example of a method for manufacturing a tennis racket 2 will now be described with reference to Figure 4. In this manufacturing method, a mandrel, a tube, and multiple prepregs 34 are prepared. Each prepreg 34 is made of multiple parallel reinforcing fibers and a matrix resin. In this manufacturing method, a mandrel is first inserted into a tube. The prepregs 34 are then wound around the tube in sequence. Once wound, the prepregs 34 assume a cylindrical shape. Figure 4 shows a cylindrical prepreg 34p and a sheet-like prepreg 34s. The mandrel and tube are not shown in Figure 4.

As the mandrel is rotated, prepreg 34s is wound onto prepreg 34p. This winding causes prepreg 34s to assume a cylindrical shape, resulting in laminate 36. If necessary, another prepreg 34 is wound onto this laminate 36. Multiple sheet-like prepregs 34s may be stacked and wound onto the mandrel or prepreg 34p. In Figure 4, arrow A1 indicates the longitudinal direction of laminate 36.

After the mandrel is removed from the tube, the tube and laminate 36 are set in a mold. Inside the mold, the tube is filled with gas, causing it to expand. This expansion presses the prepreg 34 against the cavity surface of the mold. The prepreg 34 is heated, causing the matrix resin to harden. Upon hardening, a molded body is obtained. The molded body has a shape that is the inverse of the shape of the cavity surface.

Holes 26 are drilled in this molded body. The molded body is then subjected to further surface polishing, painting, and other processes to obtain the frame 4. The grip 6, grommets 10, and other components are attached to this frame 4. Strings 12 are then strung around this frame 4 to complete the tennis racket 2.

Figure 5 is an enlarged cross-sectional view taken along line V-V in Figure 1. This cross-section is taken along a plane perpendicular to the axial direction of the frame 4 and passing through the center Ch of the head 14. This head 14 has a first high-elasticity layer 37a and a second high-elasticity layer 37b (see also Figure 2). Each high-elasticity layer 37 is located on the inner side of the head 14 in the thickness direction.

Figure 6 is an enlarged cross-sectional view taken along line VI-VI in Figure 5. Figure 6 shows the head 14. The head 14 has multiple fiber-reinforced layers 38. In this embodiment, the head 14 includes multiple first fiber-reinforced layers 38a, multiple second fiber-reinforced layers 38b, and multiple third fiber-reinforced layers 38c. In this embodiment, the number of first fiber-reinforced layers 38a is five, the number of second fiber-reinforced layers 38b is five, and the number of third fiber-reinforced layers 38c is four. The first fiber-reinforced layers 38a and the second fiber-reinforced layers 38b are alternately positioned along the thickness direction of the head 14 (the vertical direction in Figure 6). The multiple third fiber-reinforced layers 38c form the aforementioned first high-elasticity layer 37a. The first high-elasticity layer 37a is positioned on the inner side of the head 14 in the thickness direction (the lower side in Figure 6). Although not shown, the second high-elasticity layer 37b has a shape that is mirror-symmetrical to the shape of the first high-elasticity layer 37a.

Figure 7 shows the first prepreg 34a for the first fiber-reinforced layer 38a. This first prepreg 34a includes a matrix 40 and a plurality of parallel-arranged first reinforcing fibers 42a. Each of the first reinforcing fibers 42a is inclined with respect to the longitudinal direction A1. In Figure 7, the arrow θa represents the inclination angle (absolute value) of the first reinforcing fiber 42a with respect to the longitudinal direction A1. The inclination angle θa is 30° or greater and 60° or less. In this specification, reinforcing fibers 42 with an inclination angle of 30° or greater and 60° or less are referred to as "bias-type reinforcing fibers." The first fiber-reinforced layer 38a includes bias-type reinforcing fibers.

Figure 8 shows the second prepreg 34b for the second fiber-reinforced layer 38b. This second prepreg 34b includes a matrix 40 and a plurality of parallel-arranged second reinforcing fibers 42b. Each second reinforcing fiber 42b is inclined with respect to the longitudinal direction A1. The inclination direction of the second reinforcing fibers 42b is opposite to the inclination direction of the first reinforcing fibers 42a (see Figure 7). In Figure 8, arrow θb represents the inclination angle (absolute value) of the second reinforcing fibers 42b with respect to the longitudinal direction A1. The inclination angle θb is 30° or greater and 60° or less. The second reinforcing fibers 42b are "bias-type reinforcing fibers." The second fiber-reinforced layer 38b includes bias-type reinforcing fibers.

Figure 9 shows a portion of the high-elasticity layer 37. As mentioned above, the high-elasticity layer 37 has four third fiber-reinforced layers 38c. These third fiber-reinforced layers 38c are obtained by winding and folding a sheet-like third prepreg 34c.

Figure 10 shows the third prepreg 34c for the high-elasticity layer 37. This third prepreg 34c includes a matrix 40 and a plurality of third reinforcing fibers 42c arranged in parallel. Each third reinforcing fiber 42c extends along the longitudinal direction A1. The inclination angle (absolute value) of the third reinforcing fiber 42c with respect to the longitudinal direction A1 is zero. The third reinforcing fiber 42c may be slightly inclined with respect to the longitudinal direction A1. In this specification, reinforcing fibers 42 with an inclination angle (absolute value) with respect to the longitudinal direction A1 of 10° or less are referred to as "straight-type reinforcing fibers." The third fiber-reinforced layer 38c includes straight-type reinforcing fibers. In other words, the high-elasticity layer 37 includes straight-type reinforcing fibers.

11 shows the relationship between the side pressure rigidity value G1 and the ball-striking surface rigidity value G2 of the frame 4. The straight line designated by the symbol S1 in this graph is expressed by the following mathematical formula.
G2 = 3.20 ・G1
For a tennis racket 2 that is plotted on this line S1 or above this line S1, the ratio (G2/G1) is 3.20 or more.
Satisfy the following formula:
G2 ≧ 3.20 ・G1 (1)
In a tennis racket 2 that satisfies this formula (1), the side pressure rigidity value G1 is relatively small and the hitting surface rigidity value G2 is relatively large.

As mentioned above, a tennis racket 2 that satisfies formula (1) has a relatively small side pressure stiffness value G1. According to the inventor's findings, with this racket 2, the mode amplitude of the tennis ball is relatively large in the vibration mode excited during impact with the tennis ball. Therefore, the speed of the tennis ball in the traveling direction at the end of impact is high. In other words, a racket 2 with a relatively small side pressure stiffness value G1 has excellent resilience performance.

As mentioned above, a tennis racket 2 that satisfies formula (1) has a relatively large ball-striking surface stiffness value G2. According to the inventor's findings, with this racket 2, the mode amplitude of the tennis ball is relatively large in the vibration mode excited during impact with the tennis ball. Therefore, the tennis ball's forward velocity at the end of impact is high. In other words, a racket 2 with a relatively large ball-striking surface stiffness value G2 has excellent resilience performance.

As mentioned above, the high-elasticity layer 37 is located on the inner side of the head 14 in the thickness direction. When the ball-striking surface rigidity value G2 of this tennis racket 2 is measured, a force is applied to the head 14 in the thickness direction (Z direction). This force causes the head 14 to bend in the thickness direction relative to the shaft 18. Because the third reinforcing fibers 42c are straight-type reinforcing fibers, this bending generates a large tensile stress in the third reinforcing fibers 42c of the high-elasticity layer 37. The third reinforcing fibers 42c suppress this bending. The high-elasticity layer 37 contributes to a large ball-striking surface rigidity value G2.

When the side pressure stiffness value G1 of this tennis racket 2 is measured, a force is applied to the head 14 in the width direction (X direction). This force causes the head 14 to bend inward in the width direction. The stress generated in the third reinforcing fibers 42c by this bending is small. The third reinforcing fibers 42c do not hinder this deformation. A tennis racket 2 having a high-elasticity layer 37 can achieve a small side pressure stiffness value G1.

Figure 12 shows a method for measuring the side pressure stiffness value G1. In Figure 12, a tennis racket 2 is placed on a rigid base 44. The width direction X of the racket 2 coincides with the vertical direction. The axial direction Y of the racket 2 coincides with the horizontal direction. A rigid plate 46 descends, and a load is applied to the racket 2. The displacement (cm) of the plate 46 from a load of 25 kgf to a load of 50 kgf is measured. The load difference, 25 kgf, is divided by the displacement (cm) to calculate the side pressure stiffness value G1. The side pressure stiffness value G1 is measured with the strings 12 removed from the frame 4.

From the standpoint of resilience performance, the side pressure stiffness value G1 is preferably 90 kgf/cm or less, more preferably 80 kgf/cm or less, and particularly preferably 75 kgf/cm or less. The side pressure stiffness value G1 of a tennis racket 2 that can be used in practical applications is 20 kgf/cm or more.

Figures 13(a) and (b) show a method for measuring the hitting surface rigidity value G2. For this measurement, a first bar 48a, a second bar 48b, and a third bar 48c are prepared. These bars 48 are made of steel. The cross-sectional shape of each bar 48 is a circle with a radius of 10.0 mm. These bars 48 extend along the width direction X. The axial distance between the first bar 48a and the third bar 48c is 170 mm, and the axial distance between the third bar 48c and the second bar 48b is 170 mm. The first bar 48a is located at the top of the head 14. The racket 2 is placed on the first bar 48a and the second bar 48b. The width direction X and the axial direction Y of the racket 2 coincide with the horizontal direction. The third bar 48c is lowered, and a load is applied to the tennis racket 2. The displacement (cm) of the third bar 48c from a load of 25 kgf to a load of 50 kgf is measured. The difference in load, 25 kgf, is divided by the displacement (cm) to calculate the ball striking surface rigidity value G2. The ball striking surface rigidity value G2 is measured with the strings 12 removed from the frame 4.

From the standpoint of resilience performance, the ball-striking surface rigidity value G2 is preferably 100 kgf/cm or greater, more preferably 200 kgf/cm or greater, and particularly preferably 250 kgf/cm or greater. The ball-striking surface rigidity value G2 of a tennis racket 2 that can be used in practical applications is 500 kgf/cm or less.

In Figure 2, the arrow Lh represents the axial length of the high-elasticity layer 37. In this embodiment, this length Lh is the axial distance from the top Pt of the head 14 to the end Ed of the high-elasticity layer 37. From the perspective of achieving a large hitting surface rigidity value G2, the length Lh is preferably 170 mm or greater, more preferably 250 mm or greater, and particularly preferably 340 mm or greater.

In Figure 5, the arrow Tf represents the thickness of the frame 4, and the arrow Wf represents the width of the frame 4. The ratio (Tf/Wf) of the thickness Tf to the width Wf is preferably 2.0 or greater. A tennis racket 2 with a ratio (Tf/Wf) within this range is likely to achieve a large ratio (G2/G1). From this perspective, the ratio (Tf/Wf) is more preferably 2.2 or greater, even more preferably 2.4 or greater, and particularly preferably 2.8 or greater. The ratio (Tf/Wf) of a tennis racket 2 that can be used in practical applications is 4.0 or less.

From the viewpoint of making it easier to achieve a large ratio (G2/G1), the thickness Tf is preferably 20.0 mm or greater, more preferably 26.0 mm or greater, even more preferably 28.5 mm or greater, and particularly preferably 33.0 mm or greater. The thickness Tf of a tennis racket 2 that can be used in practical applications is 40.0 mm or less.

The straight line indicated by the symbol S2 in the graph of FIG.
G2 = 3.55 ・G1
For tennis rackets 2 plotted on this line S2 or above but away from this line S2, the ratio (G2/G1) is 3.55 or greater. For this tennis racket 2, the side pressure rigidity value G1 is relatively small and the ball-striking surface rigidity value G2 is relatively large. According to the findings of the inventors, this tennis racket 2 has even better resilience performance. In other words, a tennis racket 2 that satisfies the following formula has even better resilience performance.
G2 ≧ 3.55 ・G1

The straight line indicated by the symbol S3 in the graph of FIG. 11 is expressed by the following mathematical formula.
G2 = 3.90 ・G1
For tennis rackets 2 plotted on this line S3 or above this line S3 but away from it, the ratio (G2/G1) is 3.90 or greater. For this tennis racket 2, the side pressure rigidity value G1 is relatively small and the hitting surface rigidity value G2 is relatively large. According to the findings of the inventors, this tennis racket 2 has even better resilience performance. In other words, a tennis racket 2 that satisfies the following formula has even better resilience performance.
G2 ≧ 3.90 ・G1

The straight line indicated by the symbol S4 in the graph of FIG.
G2 = 4.10 ・G1
For tennis rackets 2 plotted on this line S4 or above this line S4 but away from it, the ratio (G2/G1) is 4.10 or greater. For this tennis racket 2, the side pressure rigidity value G1 is relatively small and the ball-striking surface rigidity value G2 is relatively large. According to the findings of the inventors, this tennis racket 2 has extremely excellent resilience performance. In other words, a tennis racket 2 that satisfies the following formula has extremely excellent resilience performance.
G2 ≧ 4.10 ・G1

[evaluation]
[Sample 1]
A tennis racket model for simulation was created with the following specifications:
Width of first prepreg and second prepreg: 250 mm
Frame thickness Tf: 29.9 mm
Elastic modulus of reinforcing fiber of high elastic layer: 80 tf/mm ²
High elastic layer thickness: 0.825 mm

[Sample 2-120]
A tennis racket model of Sample 2-120 was produced in the same manner as Sample 1, except that the specifications were as shown in Table 1-6 below.

[simulation]
The side pressure stiffness value G1 and the ball striking surface stiffness value G2 of each sample were calculated by simulation. Furthermore, the velocity of a tennis ball when it impacted each sample and rebounded was calculated by simulation. The results are shown in Tables 1 to 6 below.

For each sample shown in Table 1, the ratio (G2/G1) is 4.10 or greater. The ball speed for this sample is 5950 mm/s or greater.

For each sample shown in Table 2, the ratio (G2/G1) is greater than or equal to 3.90 and less than 4.10. The ball speed for this sample is greater than or equal to 5930 mm/s and less than 5950 mm/s.

For each sample shown in Table 3, the ratio (G2/G1) is greater than or equal to 3.55 and less than 3.90. The ball speed for this sample is greater than or equal to 5900 mm/s and less than 5930 mm/s.

For each sample shown in Table 4, the ratio (G2/G1) is greater than or equal to 3.20 and less than 3.55. The ball speed for this sample is greater than or equal to 5870 mm/s and less than 5900 mm/s.

For each sample shown in Tables 5 and 6, the ratio (G2/G1) is less than 3.20. The ball speed for this sample is less than 5870 mm/s.

These evaluation results clearly show the superiority of tennis rackets with a higher ratio (G2/G1).

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

[Item 1]
It has a frame that includes a head,
In this racket frame, the ratio (G2/G1) of the hitting surface rigidity value G2 to the side pressure rigidity value G1 is 3.20 or more.

[Item 2]
Item 2. The racket according to item 1, wherein the head has a high-elasticity layer located on the outer side in the thickness direction and including straight-type reinforcing fibers.

[Item 3]
3. The racket according to item 2, wherein the high-elasticity layer is present in a cross section along a plane perpendicular to the axial direction of the frame and passing through the center of the head.

[Item 4]
4. The racket according to any one of items 1 to 3, wherein a ratio (Tf/Wf) of a thickness Tf of the frame to a width Wf of the frame in a cross section taken along a plane perpendicular to the axial direction of the frame and passing through the center of the head is 2.0 or greater.

[Item 5]
5. The racket according to any one of items 1 to 4, wherein the ratio (G2/G1) is 3.55 or more.

[Item 6]
Item 6. The racket according to item 5, wherein the ratio (G2/G1) is 3.90 or more.

[Item 7]
Item 7. The racket according to item 6, wherein the ratio (G2/G1) is 4.10 or more.

[Item 8]
8. The racket according to any one of items 1 to 7, wherein the side pressure rigidity value G1 is 90 kgf/cm or less.

[Item 9]
9. The racket according to any one of items 1 to 8, wherein the ball-striking surface rigidity value G2 is 100 kgf/cm or more.

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

DESCRIPTION OF SYMBOLS 2...Tennis racket 4...Frame 6...Grip 10...Grommet 12...String 14...Head 16...Throat 18...Shaft 20...Face 22...Yoke 24...Groove 26...Hole 28...Base 30...Pipe 32...Thread 32a...Horizontal thread 32b...Vertical thread 34...Prepreg 34a...First prepreg 34b...Second prepreg 34c...Third prepreg 36...Laminate 37...High elasticity layer 37a...First high elasticity layer 37b...Second high elasticity layer 38...Fiber reinforced layer 38a...First fiber reinforced layer 38b...Second fiber reinforced layer 38c...Third fiber reinforced layer 40...Matrix 42a...First reinforcing fiber 42b...Second reinforcing fiber 42c...Third reinforcing fiber

Claims (9)

It has a frame that includes a head,
In this racket frame, the ratio (G2/G1) of the hitting surface rigidity value G2 to the side pressure rigidity value G1 is 3.20 or more. The racket of claim 1, wherein the head has a high-elasticity layer located on the outside in the thickness direction and containing straight-type reinforcing fibers. The racket of claim 2, wherein the high-elasticity layer is present in a cross section along a plane perpendicular to the axial direction of the frame and passing through the center of the head. The racket of claim 1 or 2, wherein the ratio (Tf/Wf) of the thickness Tf of the frame to the width Wf of the frame in a cross section taken along a plane perpendicular to the axial direction of the frame and passing through the center of the head is 2.0 or greater. The racket described in claim 1 or 2, wherein the ratio (G2/G1) is 3.55 or greater. The racket described in claim 5, wherein the ratio (G2/G1) is 3.90 or greater. The racket described in claim 6, wherein the ratio (G2/G1) is 4.10 or greater. The racket according to claim 1 or 2, wherein the side pressure stiffness value G1 is 90 kgf/cm or less. The racket according to claim 1 or 2, wherein the hitting surface rigidity value G2 is 100 kgf/cm or greater.