Racket

Abstract

To provide a racket 2 which is excellent in repulsion performance and controllability and suppresses a player's discomfort.SOLUTION: A racket 2 has a frame 4, a grip 6, a grommet 10 and a string 12. The frame 4 has a head 14, a first throat 16a, a second throat 16b and a shaft 18. Maximum value of thickness of the frame 4 is below 26.0 mm. In-plane rigidity index Gi of the racket 2 to be the product of a top pressure rigidity value Git(kgf / cm) and a lateral pressure rigidity value Gis(kgf / cm) is between 5000 and 8000. Out-of-plane rigidity index Go of the racket 2 to be the product of a throat rigidity value Gos(kgf / cm) and a ball hitting surface rigidity value Goh(kgf / cm) is between 45000 and 60000.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] This specification discloses a racket suitable for tennis, soft tennis, squash, padel, badminton, and the like. [Background technology]

[0002] 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 a high speed. A high flight speed is advantageous in tennis. Japanese Patent Application Laid-Open No. 5-15617 discloses a tennis racket with excellent resilience. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-15617 Summary of the Invention [Problem to be solved by the invention]

[0004] Tennis players require a tennis racket to have not only good repulsion performance but also good controllability. Especially, experienced tennis players have a strong demand for good controllability.

[0005] The applicant's intention is to provide a racket that is excellent in resilience and controllability. [Means for solving the problem]

[0006] The racket disclosed in this specification is Frame including head and A string that is strung on the head and forms a hitting surface. The maximum thickness of this frame is less than 26.0 mm. In this racket, the in-plane stiffness index Gi, which is the product of the top pressure stiffness value Git (kgf / cm) and the side pressure stiffness value Gis (kgf / cm), is 5,000 or more and 8,000 or less. The out-of-plane stiffness index Go, which is the product of the throat stiffness value Gos (kgf / cm) and the hitting surface stiffness value Goh (kgf / cm), is 45,000 or more and 60,000 or less. Effect of the Invention

[0007] This racket has excellent resilience. A ball hit with this racket can fly at high speed. The contact time of this racket with the ball when hit is long. This racket also has excellent controllability. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a front view showing a tennis racket according to an embodiment. [Diagram 2] FIG. 2 is a side view of the tennis racket of FIG. [Diagram 3] FIG. 3 is an enlarged exploded view of a portion of the tennis racket of FIG. [Figure 4] FIG. 4 is a perspective view showing a part of the manufacturing process of the racket of FIG. [Diagram 5] FIG. 5 is an enlarged cross-sectional view taken along line VV in FIG. [Figure 6] FIG. 6 is an enlarged view of the area indicated by the arrow VI in FIG. [Figure 7] FIG. 7 is an enlarged view showing a portion of the prepreg for the first fiber-reinforced layer of the frame of FIG. [Figure 8] FIG. 8 is an enlarged view showing a portion of the prepreg for the second fiber-reinforced layer of the frame of FIG. [Figure 9] FIG. 9 is an enlarged view showing a portion of the prepreg for the third fiber-reinforced layer of the frame of FIG. [Figure 10] FIG. 10 is a front view showing a method for measuring the top pressure stiffness value of the tennis racket in FIG. [Figure 11] FIG. 11 is a front view showing a method for measuring the side pressure stiffness value of the tennis racket in FIG. [Figure 12] FIG. 12(a) is a plan view showing a method for measuring the throat stiffness value of the tennis racket in FIG. 1, and FIG. 12(b) is a front view thereof. [Figure 13] FIG. 13(a) is a plan view showing a method for measuring the stiffness value of the ball-striking surface of the tennis racket of FIG. 1, and FIG. 13(b) is a front view thereof. [Figure 14] FIG. 14 is a cross-sectional view showing a part of a tennis racket according to another embodiment. [Figure 15] FIG. 15(a) is a front view showing a method for measuring the out-of-plane natural frequency of the tennis racket in FIG. 14, and FIG. 15(b) is a side view thereof. [Figure 16] FIG. 16 is a graph showing the relationship between frequency and transfer function of the tennis racket of FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, preferred embodiments will be described in detail with reference to the drawings as appropriate.

[0010] [First embodiment] [Components] A tennis racket 2 is shown in Figures 1-3. The racket 2 has a frame 4, a grip 6, an end cap 8, a grommet 10, and strings 12. The racket 2 can be used for hard tennis. In Figure 1, an arrow X indicates the width direction of the racket 2, an arrow Y indicates the axial direction of the racket 2, and a direction Z indicates the thickness direction of the racket 2. In Figure 2, the grommets 10 and the strings 12 are omitted.

[0011] 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 a face 20 (described in detail later). The front shape of the head 14 is approximately elliptical. The major axis direction of the ellipse coincides with the axial direction Y of the racket 2. The minor axis direction of the ellipse coincides with the width direction X of the racket 2. The first throat 16a extends from the head 14. The second throat 16b extends from the head 14. The second throat 16b joins with 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 throat 16. The portion of the head 14 sandwiched between the two throats 16 is a yoke 22. This frame 4 is hollow.

[0012] The main material of the frame 4 is a fiber-reinforced resin. The fiber-reinforced resin has a resin matrix and a large number of reinforcing fibers. The frame 4 includes a plurality of fiber-reinforced layers. The fiber-reinforced layers will be described in detail later.

[0013] Examples of the base resin of 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. A resin that is particularly suitable for the frame 4 is an epoxy resin.

[0014] Examples of reinforcing fibers for the frame 4 include carbon fibers, metal fibers, glass fibers, and aramid fibers. A particularly suitable fiber for the frame 4 is a long carbon fiber. A plurality of types of fibers may be used in combination.

[0015] 2 and 3, the head 14 has a groove 24. This groove 24 is recessed from the outer circumferential surface of the head 14. The groove 24 is formed over almost the entire circumference of the head 14, excluding the yoke 22. The head 14 further has a plurality of holes 26. The plurality of holes 26 are arranged over almost the entire circumference of the head 14.

[0016] The grip 6 is formed by a tape wound 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.

[0017] As shown in FIG. 3, the grommet 10 has a base 28 and a plurality of pipes 30. The base 28 has a belt shape. Each pipe 30 is integrally formed 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 a plurality of grommets 10. The number of pipes 30 in each grommet 10 may be one.

[0018] 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.

[0019] 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 large number of threads 32. A portion of the strings 12 extending along the width direction X is referred to as a horizontal thread 32a. A portion of the strings 12 extending along the axial direction Y is referred to as a vertical thread 32b. The horizontal threads 32a and the vertical threads 32b form a face 20. The face 20 is generally aligned along the XY plane. The face 20 may be formed from two or more strings 12.

[0020] [Manufacturing method] Hereinafter, an example of a method for manufacturing a tennis racket 2 will be described with reference to FIG. 4. In this manufacturing method, a mandrel, a tube, and a plurality of prepregs 34 are prepared. Each prepreg 34 is made of a plurality of reinforcing fibers arranged in parallel and a matrix resin. In this manufacturing method, a mandrel is first inserted into a tube. The prepregs 34 are wound around the tube in sequence. By being wound, the prepregs 34 assume a cylindrical shape. FIG. 4 shows a cylindrical prepreg 34p and a sheet-like prepreg 34s. The mandrel and the tube are not shown in FIG. 4.

[0021] As the mandrel is rotated, prepreg 34s is wound around prepreg 34p. This winding causes prepreg 34s to assume a cylindrical shape. Another prepreg 34 is wound around prepreg 34s as necessary to obtain laminate 36. Arrow A1 in FIG. 4 indicates the longitudinal direction of laminate 36.

[0022] After the mandrel is removed from the tube, the tube and laminate 36 are set in a mold. In the mold, the tube is filled with gas and expands. This expansion presses the prepreg 34 against the cavity surface of the mold. The prepreg 34 is heated and the matrix resin hardens. The hardening results in a molded body. The molded body has a shape that is the inverse of the shape of the cavity surface.

[0023] Holes 26 are drilled in this molded body. Furthermore, this molded body is subjected to processing such as surface polishing and painting to obtain the frame 4. A grip 6, grommets 10, etc. are attached to this frame 4. Furthermore, a string 12 is strung on this frame 4 to complete the tennis racket 2.

[0024] [Fiber reinforced layer] Fig. 5 is an enlarged cross-sectional view taken along line VV in Fig. 1. Fig. 6 is an enlarged view of the portion indicated by arrow VI in Fig. 5. Figs. 5 and 6 show the frame 4. As described above, the frame 4 has a plurality of fiber-reinforced layers 38. In this embodiment, the frame 4 includes two first fiber-reinforced layers 38a, two second fiber-reinforced layers 38b, and eight third fiber-reinforced layers 38c.

[0025] FIG. 7 shows a first prepreg 34a for the first fiber reinforced layer 38a. The first prepreg 34a includes a matrix 40 and a plurality of first reinforcing fibers 42a arranged in parallel. Each of the first reinforcing fibers 42a is inclined with respect to the longitudinal direction A1. In FIG. 7, an arrow θa indicates an inclination angle (absolute value) of the first reinforcing fiber 42a with respect to the longitudinal direction A1. The inclination angle θa is 30° or more and 60° or less. In this specification, reinforcing fibers with an inclination angle of 30° or more and 60° or less are referred to as "bias type reinforcing fibers." The first fiber reinforced layer 38a includes bias type reinforcing fibers.

[0026] FIG. 8 shows a second prepreg 34b for the second fiber reinforced layer 38b. The second prepreg 34b includes a matrix 40 and a plurality of second reinforcing fibers 42b arranged in parallel. Each of the second reinforcing fibers 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 FIG. 7). In FIG. 8, an arrow θb indicates 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 more 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.

[0027] FIG. 9 shows a third prepreg 34c for the third fiber reinforced layer 38c. The third prepreg 34c includes a matrix 40 and a plurality of third reinforcing fibers 42c arranged in parallel. Each of the third reinforcing fibers 42c extends along the longitudinal direction A1. The inclination angle (absolute value) of the third reinforcing fibers 42c with respect to the longitudinal direction A1 is zero. The third reinforcing fibers 42c may be slightly inclined with respect to the longitudinal direction A1. In this specification, reinforcing fibers with an inclination angle (absolute value) of 10° or less with respect to the longitudinal direction A1 are referred to as "straight type reinforcing fibers". The third fiber reinforced layer 38c includes straight type reinforcing fibers.

[0028] 6, the frame 4 has fiber reinforced layers 38 containing bias type reinforcing fibers and fiber reinforced layers 38 containing straight type reinforcing fibers. The number of fiber reinforced layers 38 containing bias type reinforcing fibers is four, and the number of fiber reinforced layers 38 containing straight type reinforcing fibers is eight.

[0029] [In-plane stiffness index Gi] The in-plane stiffness index Gi is appropriate for this tennis racket 2. The in-plane stiffness index Gi is calculated by the following formula. Gi = Git × Gis In this formula, Git is the apical pressure stiffness value (kgf / cm) and Gis is the lateral pressure stiffness value (kgf / cm).

[0030] FIG. 10 shows a method for measuring the top pressure stiffness value Git. In FIG. 10, the tennis racket 2 is fixed to a support 44. The support 44 has a spacer 46, and the yoke 22 is placed on the spacer 46. The width direction X of the racket 2 coincides with the horizontal direction. The axial direction Y of the racket 2 coincides with the vertical direction. A rigid plate 48 abuts against the top of the racket. The plate 48 descends, and a load is applied to the racket 2. The displacement (cm) of the plate 48 from a state where the load is 25 kgf to a state where the load is 50 kgf is measured. The load difference of 25 kgf is divided by the displacement (cm) to calculate the side pressure stiffness value Gis. The side pressure stiffness value Gis is measured with the string 12 removed from the frame 4.

[0031] From the viewpoint of resilience performance, the apex pressure stiffness value Git is preferably 60kgf / cm or more, more preferably 70kgf / cm or more, and particularly preferably 80kgf / cm or more. From the viewpoint of control performance, the apex pressure stiffness value Git is preferably 110kgf / cm or less, more preferably 100kgf / cm or less, and particularly preferably 90kgf / cm or less.

[0032] FIG. 11 shows a method for measuring the lateral pressure stiffness value Gis. In FIG. 11, a tennis racket 2 is placed on a rigid base 50. 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 52 descends, and a load is applied to the racket 2. The displacement (cm) of the plate 52 from a load of 25 kgf to a load of 50 kgf is measured. The load difference of 25 kgf is divided by the displacement (cm) to calculate the lateral pressure stiffness value Gis. The lateral pressure stiffness value Gis is measured with the string 12 removed from the frame 4.

[0033] From the viewpoint of resilience performance, the lateral pressure stiffness value Gis is preferably 45 kgf / cm or more, more preferably 50 kgf / cm or more, and particularly preferably 60 kgf / cm or more. From the viewpoint of control performance, the lateral pressure stiffness value Gis is preferably 100 kgf / cm or less, more preferably 90 kgf / cm or less, and particularly preferably 80 kgf / cm or less.

[0034] The in-plane rigidity index Gi is preferably 5000 or more and 8000 or less. A tennis racket 2 having an in-plane rigidity index Gi of 5000 or more has excellent resilience performance. From this viewpoint, the in-plane rigidity index Gi is more preferably 5100 or more, and particularly preferably 5150 or more. A tennis racket 2 having an in-plane rigidity index Gi of 8000 or less has excellent controllability. From this viewpoint, the in-plane rigidity index Gi is more preferably 7500 or less, and particularly preferably 7200 or less.

[0035] The ratio (Git / Gis) of the apical pressure stiffness value Git to the lateral pressure stiffness value Gis is preferably 1.0 or more and 1.8 or less. A tennis racket 2 having a ratio (Git / Gis) within this range bends appropriately in the in-plane direction when a ball is struck, so that twisting of the face 20 is unlikely to occur. This racket 2 has excellent resilience performance. From the viewpoint of resilience performance, the ratio (Git / Gis) is more preferably 1.1 or more, and particularly preferably 1.2 or more. From the viewpoint of resilience performance, the ratio (Git / Gis) is more preferably 1.7 or less, and particularly preferably 1.6 or less.

[0036] [Out-of-plane stiffness index Go] The out-of-plane stiffness index Go is appropriate for this tennis racket 2. The out-of-plane stiffness index Go is calculated by the following formula. Go = Gos × Goh In this formula, Gos is the throat stiffness value Gos (kgf / cm), and Goh is the hitting face stiffness value (kgf / cm).

[0037] 12(a) and (b) show a method for measuring the throat stiffness value Gos. In this measurement, a first bar 54a, a second bar 54b, and a third bar 54c are prepared. The material of these bars 54 is steel. The cross-sectional shape of each bar 54 is a circle with a radius of 5.0 mm. The bars 54 extend along the width direction X. The axial distance between the first bar 54a and the third bar 54c is 100 mm, and the axial distance between the third bar 54c and the second bar 54b is 100 mm. The first bar 54a is located closer to the head 14 than one end P1 of the throat 16. The second bar 54b is located closer to the grip 6 than the other end P2 of the throat 16. The racket 2 is placed on the first bar 54a and the second bar 54b. The width direction X and the axial direction Y of the racket 2 coincide with the horizontal direction. The third bar 54c descends, and a load is applied to the tennis racket 2. The displacement (cm) of the third bar 54c 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 throat stiffness value Gos. The throat stiffness value Gos is measured with the string 12 removed from the frame 4.

[0038] From the viewpoint of resilience performance, the throat stiffness value Gos is preferably 350 kgf / cm or more, more preferably 370 kgf / cm or more, and particularly preferably 400 kgf / cm or more. From the viewpoint of control performance, the throat stiffness value Gos is preferably 480 kgf / cm or less, more preferably 460 kgf / cm or less, and particularly preferably 440 kgf / cm or less.

[0039] 13(a) and (b) show a method for measuring the hitting surface stiffness value Goh. In this measurement, a first bar 56a, a second bar 56b, and a third bar 56c are prepared. The material of these bars 56 is steel. The cross-sectional shape of each bar 56 is a circle with a radius of 10.0 mm. The bars 56 extend along the width direction X. The axial distance between the first bar 56a and the third bar 56c is 170 mm, and the axial distance between the third bar 56c and the second bar 56b is 170 mm. The first bar 56a is located at the top of the head 14. The racket 2 is placed on the first bar 56a and the second bar 56b. The width direction X and the axial direction Y of the racket 2 coincide with the horizontal direction. The third bar 56c is lowered, and a load is applied to the tennis racket 2. The displacement (cm) of the third bar 56c from a state where the load is 25 kgf to a state where the load is 50 kgf is measured. The load difference of 25 kgf is divided by the displacement (cm) to calculate the ball-hitting surface stiffness value Goh. The ball-hitting surface stiffness value Goh is measured with the strings 12 removed from the frame 4.

[0040] From the viewpoint of resilience performance, the stiffness value Goh of the ball-hitting surface is preferably 100 kgf / cm or more, more preferably 110 kgf / cm or more, and particularly preferably 120 kgf / cm or more. From the viewpoint of control performance, the stiffness value Goh of the ball-hitting surface is preferably 170 kgf / cm or less, more preferably 160 kgf / cm or less, and particularly preferably 150 kgf / cm or less.

[0041] The out-of-plane stiffness index Go is preferably 45,000 or more and 60,000 or less. A tennis racket 2 having an out-of-plane stiffness index Go of 45,000 or more has excellent resilience performance. From this viewpoint, the out-of-plane stiffness index Go is more preferably 46,000 or more, and particularly preferably 47,000 or more. A tennis racket 2 having an out-of-plane stiffness index Go of 60,000 or less has excellent controllability. From this viewpoint, the out-of-plane stiffness index Go is more preferably 55,000 or less, and particularly preferably 51,000 or less.

[0042] [Tennis racket performance] This tennis racket 2 achieves an in-plane stiffness index Gi of 5,000 or more and 8,000 or less, and an out-of-plane stiffness index Go of 45,000 or more and 60,000 or less. This tennis racket 2 has excellent resilience performance, yet has a long contact time with the ball when struck. This tennis racket 2 can achieve both resilience performance and controllability.

[0043] As described above, the tennis racket 2 includes bias-type reinforcing fibers. The bias-type reinforcing fibers can contribute to achieving both an in-plane stiffness index Gi of 5,000 or more and 8,000 or less and an out-of-plane stiffness index Go of 45,000 or more and 60,000 or less. From this perspective, the ratio of the mass of the bias-type reinforcing fibers to the total mass of the reinforcing fibers is preferably 15% or more, more preferably 20% or more, and particularly preferably 23% or more. This ratio is preferably 50% or less, more preferably 40% or less, and particularly preferably 35% or less.

[0044] By adjusting the material, thickness, density, etc. of the reinforcing fibers, it is possible to achieve both an in-plane stiffness index Gi of 5,000 or more and 8,000 or less and an out-of-plane stiffness index Go of 45,000 or more and 60,000 or less.

[0045] In FIG. 2, the symbol Pt represents the top of the head 14, the symbol P1 represents one end of the throat 16, and the symbol P2 represents the other end of the throat 16. The one end P1 is also the joint between the head 14 and the throat 16. As is clear from FIG. 2, the head 14 has a constant thickness from the top to the joint P1 (see also FIG. 1). In FIG. 2, the arrow T1 represents the thickness of the top. The throat 16 has a constant thickness from the one end P1 to the other end P2 (see also FIG. 1). In FIG. 2, the arrow T2 represents the thickness of the throat 16. The shaft 18 has a constant thickness throughout. In FIG. 2, the arrow T3 represents the thickness of the shaft 18. The thicknesses T2 and T3 are equal to the thickness T1. In other words, the thickness of the frame 4 is constant except for the yoke 22. In this tennis racket 2, an in-plane stiffness index Gi of 5,000 or more and 8,000 or less and an out-of-plane stiffness index Go of 45,000 or more and 60,000 or less can be simultaneously achieved.

[0046] The maximum thickness of the frame 4 is preferably less than 26.0 mm. In other words, the thickness of the frame 4 is preferably less than 26.0 mm at any point. In this tennis racket 2, an in-plane stiffness index Gi of 5000 or more and 8000 or less and an out-of-plane stiffness index Go of 45000 or more and 60000 or less can be achieved at the same time. From this viewpoint, the maximum thickness is more preferably 24.5 mm or less, and particularly preferably 23.5 mm or less. From the viewpoint of durability of the tennis racket 2, this maximum thickness is preferably 17.0 mm or more, more preferably 19.0 mm or more, and particularly preferably 20.0 mm or more.

[0047] [Second embodiment] FIG. 14 is a cross-sectional view showing a portion of a tennis racket 58 according to another embodiment. FIG. 14 shows a frame 60. The frame 60 has a damper 62. The damper 62 is sandwiched between fiber-reinforced layers. The damper 62 can suppress vibrations transmitted to a tennis player. The player can obtain an excellent hitting feel. The configuration of the members of the racket 58 other than the damper 62 is the same as that of the racket 2 shown in FIG. 1-9.

[0048] The damper 62 is formed from a polymer composition. The polymer composition includes a base polymer. The polymer composition may include additives, if necessary. Examples of base polymers suitable for the damper 62 include polyurethane, styrene-based elastomers, and acrylic-based elastomers. The damper 62 may be a foam.

[0049] A preferred location for the damper 62 is on the outer side of the head in the width direction X. Another preferred location is the throat.

[0050] The vibration damping rate in the out-of-plane direction of this tennis racket 58 is preferably 0.5% or more. A racket 58 with this vibration damping rate of 0.5% or more provides an excellent shot feeling. From this viewpoint, the vibration damping rate is more preferably 0.6% or more, and particularly preferably 0.7% or more.

[0051] FIG. 15 shows a method for measuring the out-of-plane natural frequency of a tennis racket 58. In this method, the racket 58 is suspended by a string 64. The axial direction Y of the racket 58 coincides with the vertical direction. The head 66 is located above the shaft 68. The grip tape is peeled off from the shaft 68. The strings are removed from the head 66. An acceleration pickup 70 is attached to the head 66. The acceleration pickup 70 is attached to the outermost part of the head 66 in the width direction X. The acceleration pickup 70 faces the thickness direction Z. The acceleration pickup 70 has a mass of 3.5 g. The point Ph of the head 66 opposite the acceleration pickup 70 is excited by an impulse hammer (not shown). 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 70 are sent to a frequency analyzer via an amplifier. A typical frequency analyzer is the Dynamic Signal Analyzer from Hewlett-Packard. The damping rate of the out-of-plane natural vibration is calculated based on the transfer function obtained by this device. The vibration damping rate (ζ) is calculated by the following formula: ζ = (1 / 2) × (Δω / ωn) In this formula, ωn is the out-of-plane primary natural frequency, and Δω is the width of the peak when the transfer function is To (see FIG. 15). The transfer function To is calculated by the following formula. To = Tn / (2 1 / 2 ) In this formula, Tn is the transfer function for the out-of-plane primary natural vibration. EXAMPLES

[0052] The effects of the racket according to the embodiment will be explained below, but the scope of the disclosure in this specification should not be construed as being limited based on the description of this embodiment.

[0053] [Example 1] A tennis racket was manufactured. The racket frame had multiple fiber-reinforced layers. The ratio of the mass of bias-type reinforcing fibers to the total mass of the reinforcing fibers was 25%. The maximum thickness of the racket was 21.5 mm.

[0054] [Examples 2 and 3 and Comparative Examples 1-6] Tennis rackets were obtained in Examples 2 and 3 and Comparative Examples 1 to 6. The specifications of these tennis rackets are shown in Tables 1 and 2 below.

[0055] [Mass velocity] Two advanced tennis players were asked to play rallies using each tennis racket. The ball velocity was measured. The results of multiple measurements are shown in Tables 1 and 2 below.

[0056] [Ball feel] The tennis players were asked to rate the hitting feel during the rallies according to the following criteria. A: Good B: Not bad C: Bad The results are shown in Tables 1 and 2 below.

[0057] [Table 1]

[0058] [Table 2]

[0059] As is clear from Tables 1 and 2, the tennis rackets of the examples are excellent in both resilience performance and controllability. The superiority of these rackets is clear from these evaluation results.

[0060] [Disclosure items] Each of the following sections is a disclosure of a preferred embodiment.

[0061] [Item 1] Frame including head and A string that is strung on the head and forms a hitting surface. Equipped with The maximum thickness of the frame is less than 26.0 mm, The in-plane stiffness index Gi, which is the product of the apex pressure stiffness value Git (kgf / cm) and the lateral pressure stiffness value Gis (kgf / cm), is 5000 or more and 8000 or less; A racket whose out-of-plane stiffness index Go, which is the product of the throat stiffness value Gos (kgf / cm) and the hitting surface stiffness value Goh (kgf / cm), is 45,000 or more and 60,000 or less.

[0062] [Item 2] the frame has a pair of throats each connected to the head and a shaft connected to the throats; the head has a constant thickness T1 from its top to its junction with the throat; The throat has a constant thickness T2, The shaft has a constant thickness T3, 2. The racket according to item 1, wherein the thickness T2 and the thickness T3 are the same as the thickness T1.

[0063] [Item 3] 3. The racket according to item 1 or 2, wherein the ratio (Git / Gis) of the apical pressure stiffness value Git to the side pressure stiffness value Gis is 1.0 or greater.

[0064] [Item 4] The frame includes a damper, 4. The racket according to any one of items 1 to 3, wherein the vibration damping rate in the out-of-plane direction is 0.5% or more. [Industrial Applicability]

[0065] The aforementioned racket is also suitable for soft tennis, squash, padel, badminton, etc. [Explanation of symbols]

[0066] 2. Tennis racket 4. Frame 6. Grip 10 Grommet 12···string 14 Head 16. Throat 18. Shaft 20... Face 22. York 24...Groove 26...hole 28...Base 30 Pipe 32... threads 32a Horizontal thread 32b...Vertical thread 34...Prepreg 34a First prepreg 34b Second prepreg 34c: Third prepreg 36...Laminate 38...Fiber reinforced layer 38a First fiber reinforced layer 38b...Second fiber reinforced layer 38c Third fiber reinforced layer 40. Matrix 42a...First reinforcement fiber 42b Second reinforcing fiber 42c...Third reinforcement fiber 58. Tennis racket 60... Frame 62 Damper

Claims

1. Frame including head and A string that is strung on the head and forms a hitting surface. It is equipped with The maximum thickness of the frame is less than 26.0 mm; The in-plane stiffness index Gi, which is the product of the apex pressure stiffness value Git (kgf / cm) and the lateral pressure stiffness value Gis (kgf / cm), is 5,000 or more and 8,000 or less, The racket has an out-of-plane stiffness index Go, which is the product of a throat stiffness value Gos (kgf / cm) and a ball-hitting surface stiffness value Goh (kgf / cm), of 45,000 or more and 60,000 or less.

2. the frame has a pair of throats each connected to the head and a shaft connected to the throats; the head has a constant thickness T1 from its top to its junction with the throat; The throat has a constant thickness T2, The shaft has a constant thickness T3, 2. The racket of claim 1, wherein said thickness T2 and said thickness T3 are the same as said thickness T1.

3. 3. The racket according to claim 1, wherein a ratio (Git / Gis) of the apex pressure stiffness value Git to the side pressure stiffness value Gis is 1.0 or greater.

4. The frame includes a damper, 3. The racket according to claim 1, wherein the vibration damping rate in the out-of-plane direction is 0.5% or more.

Images