JP2023044826A - badminton racket - Google Patents

Abstract

To provide a badminton racket 2 which can suppress variation of a projectile path of a shuttle in both a shot a hit point of which is closer to a bottom and a shot a hit point of which is closer to a top.SOLUTION: A badminton racket 2 has a shaft 4, a frame 6, and a grip 12. In the racket 2, a ratio (ωo2/ωo1) of an out-of-plane secondary natural vibration frequency ωo2(Hz) to an out-of-plane primary natural vibration frequency ωo1(Hz), and a (ωi2/ωi1) of an in-plane secondary natural vibration frequency ωi2(Hz) to an in-plane primary natural vibration frequency ωi1(Hz) satisfy the following numerical expression (1): (ωi2/ωi1)≥1.3*(ωo2/ωo1)-0.2 (1).SELECTED DRAWING: Figure 1

Description

This specification discloses a racket for use in badminton.

A badminton racket has a frame, strings and a shaft. The frame has a top and a bottom. The strings form the face. A player shoots a shuttle with a racket. The shot causes the face to collide with the shuttle. The impact from the collision is transmitted from the string through the frame to the shaft. The shot deforms the frame and shaft. An attempt to optimize deformation behavior is described in JP-A-2021-23724.

Japanese Unexamined Patent Application Publication No. 2021-23724

In a game of badminton, players make different types of shots. Players make shots such as smashes, lobs, drops, and clears.

A smash is a shot intended to prevent an opposing player from receiving. In Smash, the player must have the skill to fly the shuttle on the intended trajectory. Players who use smashes often want a stable shuttle trajectory (speed, height, etc.).

Unlike normal lobbing, cut lobbing involves a cutting motion. In cut-robbing, the shuttle flies at high speed while rotating at high speed. Cut lobbing is often hit from within the player's court, near the net. A cut lobbing is a shot intended to carry the shuttle deep into the opposing player's court. The trajectory of the shuttle in cut lobbing is high. A player must have a high degree of skill to fly the shuttle at the intended height. Players who use a lot of cut lobbing want a stable shuttle trajectory (speed, height, etc.).

Statistical studies have shown that typical hit points in smashes are closer to the bottom, and typical hit points in cut lobbing are closer to the top. Even in shots other than smashes, the shuttle can be shot at the hitting point near the bottom. Even in shots other than cut lobbing, the shuttle can be shot at the hit point closer to the top.

The present inventor intends to provide a badminton racket capable of suppressing variation in the trajectory of the shuttle in both shots where the hitting point is closer to the bottom and shots where the hitting point is closer to the top.

A preferred badminton racket is
a shaft having a pad and a tip;
a grip attached to the shaft in this bad;
and has a frame attached to the shaft at the tip. The ratio (ωo2/ωo1) of the out-of-plane secondary natural frequency ωo2 (Hz) to the out-of-plane primary natural frequency ωo1 (Hz) of this badminton racket, and the in-plane secondary to the in-plane primary natural frequency ωi1 (Hz) The ratio (ωi2/ωi1) of the natural frequency ωi2 (Hz) satisfies the following formula (1).
(ωi2/ωi1) ≧ 1.3 * (ωo2/ωo1) − 0.2 (1)

Players using this badminton racket tend to hit shots with a hit point closer to the bottom, and hit points closer to the top. This racket can contribute to winning the game.

FIG. 1 is a front view showing a badminton racket according to one embodiment. 2 is a right side view of the badminton racket of FIG. 1; FIG. 3 is an enlarged sectional view showing a part of the shaft of the badminton racket of FIG. 2. FIG. FIG. 4 is an enlarged cross-sectional view taken along line IV--IV of FIG. 5 is a cross-sectional perspective view showing an example of a prepreg for the shaft of the badminton racket of FIG. 1. FIG. 6 is an exploded view showing the prepreg construction for the shaft of the badminton racket of FIG. 1; FIG. FIG. 7 is an exploded view showing a type A prepreg configuration. FIG. 8 is a schematic diagram showing a type A prepreg configuration. 9 is an enlarged sectional view showing a part of the shaft of the badminton racket of FIG. 1. FIG. 10 is an enlarged sectional view showing a part of the shaft of the badminton racket of FIG. 2. FIG. 11 is an enlarged cross-sectional view taken along line XI-XI of FIG. 10. FIG. 12 is an enlarged cross-sectional view taken along line XII-XII of FIG. 10. FIG. FIG. 13 is a schematic diagram showing a type B prepreg configuration. FIG. 14 is an explanatory diagram showing a method of measuring the out-of-plane natural frequency of the racket of FIG. FIG. 15 is a graph showing the results obtained from the measurements of FIG. FIG. 16 is an explanatory diagram showing a method of measuring the in-plane natural frequency of the racket of FIG. FIG. 17 is a graph showing the results obtained from the measurements of FIG. 18 is a graph showing the relationship between the ratio (ωo2/ωo1) and the ratio (ωi2/ωi1) of the badminton racket of FIG. 1. FIG. FIG. 19 is a schematic diagram showing a type C prepreg configuration. FIG. 20 is a schematic diagram showing a type D prepreg configuration. FIG. 21 is a schematic diagram showing a type E prepreg structure. FIG. 22 is a schematic diagram showing a type F prepreg configuration. FIG. 23 is a schematic diagram showing a type G prepreg structure. FIG. 24 is a schematic diagram showing a type H prepreg configuration. FIG. 25 is a schematic diagram showing a Type I prepreg configuration. FIG. 26 is a schematic diagram showing a type J prepreg structure. FIG. 27 is a schematic diagram showing a type K prepreg configuration. 28 is an exploded view showing the prepreg configuration of Comparative Example 1. FIG. FIG. 29 is an exploded view showing the prepreg configuration of Comparative Example 2. FIG. 30 is an exploded view showing the prepreg configuration of Comparative Example 3. FIG.

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

A badminton racket 2 is shown in Figures 1 and 2 . This racket 2 has a shaft 4 , a frame 6 , a neck 8 , a cap 10 , a grip 12 and strings 14 . 1 and 2, arrow X represents the width direction, arrow Y represents the axial direction, and arrow Z represents the thickness direction. The width direction X is also called an in-plane direction. The thickness direction Z is also called the out-of-plane direction.

Shaft 4 is hollow. Arrow Ls in FIG. 1 indicates the length of shaft 4 . In this embodiment, the length Ls is 340 mm. Shaft 4 has pad 16 , middle 18 and tip 20 . Shaft 4 also has a bad end 22 and a tip end 24 . A bad 16 is defined herein as the zone between the bad end 22 and a location whose distance from the bad end 22 is 44% of the length Ls. The middle 18 is defined as the zone between the distance from the bad end 22 of 44% of the length Ls and the distance from the bad end 22 of 71% of the length Ls. Tip 20 is defined as the zone between tip end 24 and a location 71% of length Ls from bad end 22 .

The shaft 4 is made of fiber reinforced resin. This fiber-reinforced resin has a resin matrix and a large number of reinforcing fibers. The shaft 4 includes multiple fiber reinforced layers (discussed in more detail below).

Thermosetting resins such as epoxy resins, pismaleimide resins, polyimides and phenolic resins; thermoplastic resins are exemplified. A particularly suitable resin for the shaft 4 is an epoxy resin.

Carbon fibers, metal fibers, glass fibers, and aramid fibers are examples of reinforcing fibers for the shaft 4 . A particularly suitable fiber for shaft 4 is carbon fiber. A plurality of types of fibers may be used in combination.

The frame 6 is annular and hollow. The frame 6 is made of fiber reinforced resin. A base resin similar to the base resin of the shaft 4 can be used for this fiber-reinforced resin. A reinforcing fiber similar to the reinforcing fiber of the shaft 4 may be used for this fiber-reinforced resin. Frame 6 is rigidly connected to tip end 24 of shaft 4 via neck 8 . Frame 6 has a top 26 and a bottom 28 .

The grip 12 has a hole 30 extending in the axial direction (Y direction). The vicinity of the bad end 22 of the shaft 4 is inserted into this hole 30 . The inner peripheral surface of the hole 30 and the outer peripheral surface of the shaft 4 are joined with an adhesive.

A string 14 is strung on the frame 6 . The string 14 is stretched along the width direction X and the axial direction Y. As shown in FIG. The portion of string 14 that extends along width direction X is transverse thread 32 . The portion of string 14 that extends along axial direction Y is longitudinal thread 34 . A face 36 is formed by a plurality of horizontal threads 32 and a plurality of vertical threads 34 . Face 36 generally lies along the XY plane.

FIG. 3 is an enlarged cross-sectional view showing a portion of the shaft 4 of the racket 2 of FIG. 1. FIG. FIG. 4 is an enlarged cross-sectional view taken along line IV--IV of FIG. As mentioned above, this shaft 4 is hollow. As shown in FIG. 4, the cross-sectional shape of this shaft 4 is circular. In other words, this shaft 4 is cylindrical. No foreign matter is accommodated inside the shaft 4 .

The arrow Di in FIGS. 3 and 4 represents the inner diameter of the shaft 4 . A typical inner diameter Di is between 3 mm and 10 mm. In this embodiment, the inner diameter Di from the bad end 22 (see FIG. 2) to the tip end 24 is substantially constant. Arrow Do in FIGS. 3 and 4 represents the outer diameter of shaft 4 . A typical outer diameter Do is 5 mm or more and 15 mm or less. In this embodiment, the outer diameter Do from the bad end 22 to the tip end 24 is substantially constant.

Reference SC in FIG. 4 represents the center point of the shaft 4 . In this embodiment, the shaft 4 is divided into four zones for convenience. In FIG. 4, the zone indicated by arrow Q1 is the first quarter, the zone indicated by arrow Q2 is the second quarter, the zone indicated by arrow Q3 is the third quarter, and the zone indicated by arrow Q4 is It is the fourth quarter. The central angle at point SC of each quarter is 90°. The first quarter Q1 is separated from the center point SC in the in-plane direction. The second quarter Q2 is spaced out-of-plane with respect to the center point SC. The third quarter Q3 is separated in the in-plane direction from the center point SC. The fourth quarter Q4 is spaced out-of-plane with respect to the center point SC.

As described above, the shaft 4 is made of fiber-reinforced resin. This shaft 4 can be manufactured by a sheet winding method. In this sheet winding method, multiple prepregs are wound around a mandrel.

An example of the prepreg 38 is shown in FIG. This prepreg 38 has a plurality of fibers 40 and matrix resin 42 . These fibers 40 are parallel. Matrix resin 42 is not cured. The arrow θ in FIG. 5 is the angle of the fiber 40 with respect to the Y direction.

FIG. 6 is an exploded view showing the prepreg construction for shaft 4 of racket 2 of FIG. This prepreg configuration has nine prepreg sheet groups. Specifically, this prepreg configuration includes a first sheet group S1, a second sheet group S2, a third sheet group S3, a fourth sheet group S4, a fifth sheet group S5, a sixth sheet group S6, and a seventh sheet group. S7, an eighth sheet group S8 and a ninth sheet group S9. The horizontal direction in FIG. 6 is the axial direction of the shaft 4 . The positions of the bad end 22 and the tip end 24 are indicated by arrows in FIG. For convenience of explanation, in FIG. 6, the scale in the horizontal direction (axial direction) does not match the scale in the vertical direction.

The first sheet group S<b>1 includes a single prepreg 44 . This prepreg 44 exists over the entire shaft 4 . The shape of this prepreg 44 is generally rectangular. This prepreg 44 includes a plurality of parallel carbon fibers. The extending direction of each carbon fiber is inclined with respect to the axial direction. The angle θ of this carbon fiber is 45°. The tensile modulus E of this carbon fiber is 24 tf/mm ² . The width W of this prepreg 44 is 80 mm.

The second sheet group S2 includes a single prepreg 46. As shown in FIG. This prepreg 46 exists over the entire shaft 4 . The shape of this prepreg 46 is generally rectangular. This prepreg 46 includes a plurality of parallel carbon fibers. The extending direction of each carbon fiber is inclined with respect to the axial direction. The angle θ of this carbon fiber is -45°. The tensile modulus E of this carbon fiber is 24 tf/mm ² . The width W of this prepreg 46 is 80 mm. The inclination direction of the carbon fibers in the second sheet group S2 is opposite to the inclination direction of the carbon fibers in the first sheet group S1. In this shaft 4, the first seat group S1 and the second seat group S2 form a bias structure.

Each of the third sheet group S3, the fifth sheet group S5 and the seventh sheet group S7 has a type A prepreg construction. The Type A prepreg construction will be detailed later. Each of the fourth sheet group S4, the sixth sheet group S6 and the eighth sheet group S8 has a type B prepreg construction. The Type B prepreg construction will be detailed later.

A ninth sheet group S9 includes a single prepreg 48 . This prepreg 48 exists over the entire shaft 4 . The shape of this prepreg 48 is generally rectangular. This prepreg 48 includes a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . The width W of this prepreg 48 is 54 mm.

FIG. 7 is an exploded view showing the prepreg structure of type A, and FIG. 8 is a schematic diagram thereof. This prepreg configuration includes eight prepregs. The width of each prepreg corresponds to 1/4 of the circumferential length of the shaft 4 at the position of the prepreg. This width in the third sheet group S3 is approximately 4 mm, in the fifth sheet group S5 this width is approximately 5 mm and in the seventh sheet group S7 this width is approximately 5 mm.

The prepreg A1 exists between the bad end 22 and a position at a distance of 240 mm from the bad end 22 . The shape of this prepreg A1 is generally rectangular. This prepreg A1 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 55 tf/mm ² . This prepreg A1 exists in the first quarter Q1.

The prepreg A2 exists between a position at a distance of 240 mm from the bad end 22 and a position at a distance of 340 mm from the bad end 22 . The shape of this prepreg A2 is generally rectangular. This prepreg A2 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . This prepreg A2 is present in the first quarter Q1.

The prepreg A3 is present between the bad end 22 and a position at a distance of 150 mm from the bad end 22 . The shape of this prepreg A3 is generally rectangular. This prepreg A3 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . This prepreg A3 is present in the second quarter Q2.

The prepreg A4 exists between a position at a distance of 150 mm from the bad end 22 and a position at a distance of 340 mm from the bad end 22 . The shape of this prepreg A4 is generally rectangular. This prepreg A4 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 55 tf/mm ² . This prepreg A4 is present in the second quarter Q2.

The prepreg A5 is present between the bad end 22 and a position at a distance of 240 mm from the bad end 22 . The shape of this prepreg A5 is generally rectangular. This prepreg A5 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 55 tf/mm ² . This prepreg A5 is present in the third quarter Q3.

The prepreg A6 exists between a position at a distance of 240 mm from the bad end 22 and a position at a distance of 340 mm from the bad end 22 . The shape of this prepreg A6 is generally rectangular. This prepreg A6 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . This prepreg A6 is present in the third quarter Q3.

The prepreg A7 is present between the bad end 22 and a position at a distance of 150 mm from the bad end 22 . The shape of this prepreg A7 is generally rectangular. This prepreg A7 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . This prepreg A7 is present in the fourth quarter Q4.

The prepreg A8 exists between a position at a distance of 150 mm from the bad end 22 and a position at a distance of 340 mm from the bad end 22 . The shape of this prepreg A8 is generally rectangular. This prepreg A8 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 55 tf/mm ² . This prepreg A8 is present in the fourth quarter Q4.

Shaft 4 is shown in FIGS. 9-12. 9-12 show cross-sections of the third sheet group S3. Illustration of other seat groups is omitted. The third sheet group S3 has a type A prepreg structure, as described above.

As shown in FIGS. 9-12, prepreg A1 and prepreg A2 are located in the first quarter Q1, prepreg A3 and prepreg A4 are located in the second quarter Q2, and prepreg A5 and prepreg A6 are located in the third quarter Q2. It is located in quarter Q3, and prepreg A7 and prepreg A8 are located in fourth quarter Q4.

As shown in FIGS. 9-12, prepreg A1 resides from bad 16 to middle 18, prepreg A2 resides at tip 20, prepreg A3 resides at bad 16, and prepreg A4. is present from middle 18 to tip 20, prepreg A5 is present from bad 16 to middle 18, prepreg A6 is present at tip 20, and prepreg A7 is present at bad 16. , and the prepreg A8 exists from the middle 18 to the tip 20.

FIG. 13 is a schematic diagram showing a Type B prepreg configuration. This prepreg configuration includes eight prepregs. The width of each prepreg corresponds to 1/4 of the circumferential length of the shaft 4 at the position of the prepreg. In the fourth sheet group S4 this width is about 4 mm, in the sixth sheet group S6 this width is about 5 mm and in the eighth sheet group S8 this width is about 6 mm.

The prepreg B1 exists between the bad end 22 (see FIG. 2) and a position at a distance of 150 mm from the bad end 22. As shown in FIG. The shape of this prepreg B1 is generally rectangular. This prepreg B1 includes a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 55 tf/mm ² . This prepreg B1 exists in the first quarter Q1.

The prepreg B2 exists between a position at a distance of 150 mm from the bad end 22 and a position at a distance of 340 mm from the bad end 22 . The shape of this prepreg B2 is generally rectangular. This prepreg B2 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . This prepreg B2 exists in the first quarter Q1.

The prepreg B3 exists between the bad end 22 and a position at a distance of 240 mm from the bad end 22 . The shape of this prepreg B3 is generally rectangular. This prepreg B3 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . This prepreg B3 exists in the second quarter Q2.

The prepreg B4 exists between a position at a distance of 240 mm from the bad end 22 and a position at a distance of 340 mm from the bad end 22 . The shape of this prepreg B4 is generally rectangular. This prepreg B4 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 55 tf/mm ² . This prepreg B4 exists in the second quarter Q2.

The prepreg B5 is present between the bad end 22 and a position at a distance of 150 mm from the bad end 22 . The shape of this prepreg B5 is generally rectangular. This prepreg B5 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 55 tf/mm ² . This prepreg B5 exists in the third quarter Q3.

The prepreg B6 exists between a position at a distance of 150 mm from the bad end 22 and a position at a distance of 340 mm from the bad end 22 . The shape of this prepreg B6 is generally rectangular. This prepreg B6 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . This prepreg B6 is present in the third quarter Q3.

The prepreg B7 is present between the bad end 22 and a position at a distance of 240 mm from the bad end 22 . The shape of this prepreg B7 is generally rectangular. This prepreg B7 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 7.4 tf/mm ² . This prepreg B7 is present in the fourth quarter Q4.

The prepreg B8 exists between a position at a distance of 240 mm from the bad end 22 and a position at a distance of 340 mm from the bad end 22 . The shape of this prepreg B8 is generally rectangular. This prepreg B8 contains a plurality of parallel carbon fibers. The extending direction of each carbon fiber is located in the axial direction. The angle θ of this carbon fiber is 0°. The tensile modulus E of this carbon fiber is 55 tf/mm ² . This prepreg B8 is present in the fourth quarter Q4.

The prepreg B1 and the prepreg B2 are located in the first quarter Q1, the prepreg B3 and the prepreg B4 are located in the second quarter Q2, the prepreg B5 and the prepreg B6 are located in the third quarter Q3, and the prepreg B7. and prepreg B8 are located in the fourth quarter Q4.

The prepreg B1 is present in the bud 16, the prepreg B2 is present from the middle 18 to the tip 20, the prepreg B3 is present from the bud 16 to the middle 18, and the prepreg B4 is present at the tip 20. , the prepreg B5 is present in the bud 16, the prepreg B6 is present from the middle 18 to the tip 20, the prepreg B7 is present from the bud 16 to the middle 18, and the prepreg B8 is Present at tip 20.

In the type A prepreg configuration, the prepregs A1, A2, A5 and A6 are spaced apart in the in-plane direction with respect to the center point SC (see FIG. 4). In the type B prepreg configuration, the prepregs B1, B2, B5 and B6 are spaced apart from the center point SC in the in-plane direction. The tensile modulus E of the carbon fibers contained in the prepregs A1, A5, B1 and B5 is large, and the tensile modulus E of the carbon fibers contained in the prepregs A2, A6, B2 and B6 is small. The elastic modulus E of each carbon fiber affects the bending stiffness of the shaft 4 . This shaft 4 has the following formula.
RiB > RiM > RiT
RiB: in-plane bending rigidity of the pad 16 RiM: in-plane bending rigidity of the middle 18 RiT: in-plane bending rigidity of the tip 20

In the Type A prepreg configuration, prepregs A3, A4, A7 and A8 are spaced out-of-plane with respect to center point SC. In the type B prepreg configuration, prepregs B3, B4, B7 and B8 are spaced out-of-plane with respect to center point SC. The tensile modulus E of the carbon fibers contained in the prepregs A3, A7, B3 and B7 is small, and the tensile modulus E of the carbon fibers contained in the prepregs A4, A8, B4 and B8 is large. The elastic modulus E of each carbon fiber affects the bending stiffness of the shaft 4 . This shaft 4 has the following formula.

RoB < RoM < RoT
RoB: out-of-plane bending stiffness of the pad 16 RoM: out-of-plane bending stiffness of the middle 18 RoT: out-of-plane bending stiffness of the tip 20

This shaft 4 further comprises at the buds 16 the following formula:
RiB > RoB
This shaft 4 further comprises at the tip 20 the following formula.
RiT < RoT

In this specification, the tensile modulus E is measured according to the standard of "JIS R 7608". The tensile elastic modulus E is calculated based on the change in stress when the elongation rate changes from 0.3% to 0.7%.

As is clear from FIG. 6, the prepregs of the first sheet group S1, the second sheet group S2 and the ninth sheet group S9 are present from the bad end 22 to the tip end 24. As shown in FIG. These sheet groups can contribute to the durability of the shaft 4 .

In the manufacture of this shaft 4, the sheets shown in FIG. 6 are successively wound around a mandrel. Along with these sheets, other sheets may be wrapped around the mandrel. Other sheets are exemplified by those containing glass fibers. Wrapping tape is further wrapped around these sheets. These mandrels, prepregs (sheet groups S1-S9) and wrapping tapes are heated in an oven or the like. Heating causes the matrix resin to flow. By further heating, this resin undergoes a curing reaction to obtain a molded article. The molded body is subjected to processing such as end surface processing, polishing, and painting, and the shaft 4 is completed.

As described above, the material of the shaft 4 is fiber reinforced resin. The material of the shaft 4 may be a resin composition that does not contain fibers. The material of the shaft 4 may be metal, wood, or the like.

FIG. 14 is an explanatory diagram showing a method of measuring the out-of-plane natural frequency of the racket 2 of FIG. In this method, the string 50 suspends the racket 2 . This racket 2 does not have a string 14 (see FIG. 1). In other words, the racket 2 without the strings 14 is used for the measurement of the natural frequency. In FIG. 14, the axial direction (Y direction) of the shaft 4 coincides with the vertical direction. In FIG. 14, the frame 6 is positioned above the shaft 4 .

As shown in FIG. 14, the racket 2 is attached with an acceleration pickup 52 . The position of the acceleration pickup 52 is the tip of the grip 12 . The orientation of this acceleration pickup 52 is the Z direction. This acceleration pickup 52 has a mass of 3.5 g. A point Ph on the opposite side of the acceleration pickup 52 of the grip 12 is vibrated by an impact hammer (not shown). The input vibration measured by the force pickup of the impact hammer and the response vibration measured by the acceleration pickup 52 are sent to a frequency analyzer (Hewlett-Packard "Dynamic Signal Analyzer") via an amplifier. Out-of-plane natural frequencies are calculated based on the transfer function obtained with this device. The direction of the out-of-plane natural vibration is primarily in the Z direction. In this method, the natural frequency is measured without any part of the racket 2 being rigidly fixed. In other words, out-of-plane natural frequencies under free constraint conditions are measured.

FIG. 15 is a graph showing the results obtained from the measurements of FIG. In FIG. 15, the horizontal axis is frequency (Hz) and the vertical axis is acceleration (m/s ² /N). A primary peak is indicated by P1 in FIG. The frequency at this primary peak P1 is the out-of-plane primary natural frequency ωo1. A secondary peak is indicated by symbol P2 in FIG. The frequency at this secondary peak P2 is the out-of-plane secondary natural frequency ωo2.

FIG. 16 is an explanatory diagram showing a method of measuring the frequency of natural vibration in the in-plane direction of the racket 2. As shown in FIG. In this measuring method, the racket 2 is suspended by the string 50, similarly to the measuring method shown in FIG. As shown in FIG. 16, the orientation of the acceleration pickup 52 is the X direction. A point Ph of the grip 12 facing the acceleration pickup 52 is vibrated by an impact hammer (not shown). The input vibration measured by the force pickup of the impact hammer and the response vibration measured by the acceleration pickup 52 are sent to a frequency analyzer (Hewlett-Packard "Dynamic Signal Analyzer") via an amplifier. Based on the transfer function obtained by this device, the frequency of the in-plane natural vibration is calculated. The direction of the in-plane natural vibration is mainly the X direction. In this method, in-plane natural frequencies are measured under free constraint conditions.

FIG. 17 is a graph showing the results obtained from the measurements of FIG. In FIG. 17, the horizontal axis is frequency (Hz) and the vertical axis is acceleration (m/s ² /N). A primary peak is indicated by P1 in FIG. The frequency at this primary peak P1 is the in-plane primary natural frequency ωi1. A secondary peak is indicated by P2 in FIG. The frequency at this secondary peak P2 is the in-plane secondary natural frequency ωi2.

18 is a graph showing the relationship between the ratio (ωo2/ωo1) and the ratio (ωi2/ωi1) of the badminton racket 2. FIG. In this graph, the symbol Pr represents the points of racket 2 shown in FIGS. 1-13.

A straight line indicated by symbol L1 in FIG. 18 can be represented by the following formula.
(ωi2/ωi1) = 1.3 * (ωo2/ωo1) − 0.2
As shown in FIG. 18, the point Pr is located above the straight line L1. In other words, the coordinates ((ωo2/ωo1), (ωi2/ωi1)) of the racket 2 have the following formula (1).
(ωi2/ωi1) ≧ 1.3 * (ωo2/ωo1) − 0.2 (1)
According to knowledge obtained by the present inventors, the racket 2 that satisfies this formula (1) is suitable for smashing and cut-robbing. A player who uses this racket 2 to smash or cut-lob is likely to obtain the intended trajectory of the shuttle. With this racket 2, the variation in the trajectory of the shuttle in smashes is small, and the variation in the trajectory of the shuttle in cut robbing is also small.

The badminton racket 2 satisfying the above formula has a relatively small out-of-plane vibration ratio (ωo2/ωo1) and a relatively large in-plane vibration ratio (ωi2/ωi1).

According to the inventor's findings regarding out-of-plane vibrations, when the shuttle is struck at a portion of the face 36 closer to the bottom 28, the out-of-plane secondary natural frequency is mainly excited. According to the knowledge obtained by the present inventors, when the shuttle is hit on the portion of the face 36 near the top 26, the first out-of-plane natural frequency is mainly excited. A typical hitting point in a smash is near the bottom 28 . Therefore, in the smash, the out-of-plane secondary natural vibration is mainly excited. However, even in the smash, the RBI varies. A racket 2 having a small ratio (ωo2/ωo1) has a relatively large out-of-plane primary natural frequency ωo1 and a relatively small out-of-plane secondary natural frequency ωo2. According to the knowledge obtained by the present inventors, in a smash with a racket 2 having a large out-of-plane primary natural frequency ωo1 and a small out-of-plane secondary natural frequency ωo2, even if the hitting point varies, the initial velocity of the shuttle has little variation. The reason is that even if the shuttle is hit at a position deviated from the intended position, the rebound of the racket 2 is not extremely small. Since the variation in the initial speed of the shuttle is small, the variation in the trajectory of the shuttle is also small. This racket 2 is suitable for players who frequently use smashes. This racket 2 is also suitable for players who emphasize smash.

As described above, a typical hitting point in a smash is near the bottom 28 . This racket 2 is also suitable for shots other than smashes, in which the shuttle is hit with the part of the face 36 closer to the bottom 28 .

According to the inventor's findings regarding in-plane vibration, when the shuttle is struck at a portion of the face 36 closer to the bottom 28, the in-plane secondary mode vibration is mainly excited. According to the knowledge obtained by the present inventors, when the shuttle is hit by a portion of the face 36 near the top 26, the in-plane primary mode vibration is mainly excited. A typical hitting point in cut lobbing is toward the top 26. Therefore, cut-lobing mainly excites the in-plane primary mode vibration. However, even in cut lobbing, the hitting point varies. A racket 2 having a large ratio (ωi2/ωi1) has a relatively small in-plane primary natural frequency ωi1 and a relatively large in-plane secondary natural frequency ωi2. According to the knowledge obtained by the present inventors, when the racket 2 has a small in-plane primary natural frequency ωi1 and a large in-plane secondary natural frequency ωi2, the variation in the initial speed of the shuttle is small even if the hitting point varies. . The reason is that even if the shuttle is hit at a position deviated from the intended position, the rebound of the racket 2 is not extremely small. Since the variation in the initial speed of the shuttle is small, the variation in the trajectory of the shuttle is also small. This racket 2 is suitable for players who frequently use cut-robbing. This racket 2 is also suitable for players who emphasize cut-robbing.

As mentioned above, the typical hitting point in cut lobbing is towards the top 26. This racket 2 is also suitable for shots other than cut lobbing, in which the shuttle is hit on a portion of the face 36 closer to the top 26 and involves a cut.

As described above, in the shaft 4 , the in-plane bending rigidity of the tip 20 is lower than the in-plane bending rigidity of the pad 16 , and the out-of-plane bending rigidity of the tip 20 is higher than the out-of-plane bending rigidity of the pad 16 . big. In the badminton racket 2 having this shaft 4, the above formula (1) can be achieved.

Adjustment of the rigidity distribution of the frame 6 is another means for achieving the above formula (1). The frame 6 having high bending rigidity in the in-plane direction and low bending rigidity in the out-of-plane direction in the vicinity of the bottom 28 can contribute to the achievement of the above formula (1).

As still another means for achieving the above formula (1), adjustment of the rigidity distribution of the entire racket 2, adjustment of the mass distribution of the shaft 4, adjustment of the mass distribution of the frame 6, adjustment of the mass distribution of the entire racket 2, adjustment of the shaft 4 volume distribution adjustment, frame 6 volume distribution adjustment, and overall racket 2 volume distribution adjustment are exemplified.

From the viewpoint of suitability for smashing and cut-robbing, it is more preferable that the racket 2 satisfies the following formula.
(ωi2/ωi1) ≥ 1.3 * (ωo2/ωo1) − 0.1
From the viewpoint of suitability for smashing and cut-robbing, it is particularly preferable for the racket 2 to satisfy the following formula.
(ωi2/ωi1) ≥ 1.3 * (ωo2/ωo1) + 0.1

A straight line indicated by symbol L2 in FIG. 18 can be represented by the following formula.
(ωi2/ωi1) = 1.11 * (ωo2/ωo1) + 0.391
As shown in FIG. 18, the point Pr is positioned above the straight line L2. In other words, the coordinates ((ωo2/ωo1), (ωi2/ωi1)) of this racket 2 have the following formula (2).
(ωi2/ωi1) ≥ 1.11 * (ωo2/ωo1) + 0.391 (2)
According to knowledge obtained by the present inventor, the racket 2 that satisfies this formula (2) is suitable for smashing and cut-robbing. A player who uses this racket 2 to smash or cut-lob is likely to obtain the intended trajectory of the shuttle. With this racket 2, the variation in the trajectory of the shuttle in smashes is small, and the variation in the trajectory of the shuttle in cut robbing is also small.

A straight line indicated by symbol L3 in FIG. 18 can be represented by the following formula.
(ωi2/ωi1) = 2.5 * (ωo2/ωo1) - 3.42
As shown in FIG. 18, the point Pr is located on the straight line L3. In other words, the coordinates ((ωo2/ωo1), (ωi2/ωi1)) of this racket 2 have the following formula (3).
(ωi2/ωi1) ≧ 2.5 * (ωo2/ωo1) − 3.42 (3)
According to knowledge obtained by the present inventors, the racket 2 that satisfies this formula (3) is suitable for smashing and cut-robbing. A player who uses this racket 2 to smash or cut-lob is likely to obtain the intended trajectory of the shuttle. With this racket 2, the variation in the trajectory of the shuttle in smashes is small, and the variation in the trajectory of the shuttle in cut robbing is also small.

A straight line indicated by symbol L4 in FIG. 18 can be represented by the following formula.
(ωo2/ωo1) = 2.99
As shown in FIG. 18, point Pr is positioned to the left of straight line L4. In other words, the ratio of points Pr (ωo2/ωo1) is 2.99 or less. This racket 2 is suitable for smashing. From this point of view, the ratio (ωo2/ωo1) is more preferably 2.95 or less, particularly preferably 2.94 or less. The ratio (ωo2/ωo1) is preferably 2.50 or more.

A straight line indicated by symbol L5 in FIG. 18 can be represented by the following formula.
(ωi2/ωi1) = 3.61
As shown in FIG. 18, the point Pr is positioned above the straight line L5. In other words, the ratio of points Pr (ωi2/ωi1) is 3.61 or more. This racket 2 is suitable for cut robbing. From this point of view, the ratio (ωi2/ωi1) is more preferably 3.65 or more, particularly preferably 3.68 or more. The ratio (ωi2/ωi1) is preferably 4.3 or less.

A preferred specification determination method for the badminton racket 2 will be described below. This determination method is
(A) Out-of-plane primary natural frequency ωo1 (Hz), out-of-plane secondary natural frequency ωo2 (Hz), in-plane primary natural frequency ωi1 (Hz), and in-plane secondary natural frequency ωi2 (Hz) of the standard racket ),
(B) Based on these natural frequencies ωo1, ωo2, ωi1 and ωi2, a step of determining whether the above-mentioned formula (1) is satisfied;
and (C) determining the characteristics of the shaft 4 or frame 6 of the target racket 2 to have a ratio (ωo2/ωo1) that is less than that of the standard racket if this equation (1) is not satisfied. .

The characteristics determined in step (C) include the length of the shaft 4, the thickness of the shaft 4, the stiffness of the shaft 4, the stiffness distribution of the shaft 4, the length of the frame 6, the thickness of the frame 6, and the thickness of the frame 6. and the stiffness distribution of the frame 6 are illustrated.

Another preferred specification determination method is
(A) Out-of-plane primary natural frequency ωo1 (Hz), out-of-plane secondary natural frequency ωo2 (Hz), in-plane primary natural frequency ωi1 (Hz), and in-plane secondary natural frequency ωi2 (Hz) of the standard racket ),
(B) Based on these natural frequencies ωo1, ωo2, ωi1 and ωi2, a step of determining whether the above-mentioned formula (1) is satisfied;
and (C) determining the characteristics of the shaft 4 or frame 6 of the target racket 2 to have a ratio (ωi2/ωi1) greater than that of the standard racket if Equation (1) below is not satisfied. .

The characteristics determined in step (C) include the length of the shaft 4, the thickness of the shaft 4, the stiffness of the shaft 4, the stiffness distribution of the shaft 4, the length of the frame 6, the thickness of the frame 6, and the thickness of the frame 6. and the stiffness distribution of the frame 6 are illustrated.

Although the effects of the badminton rackets according to the examples will be clarified below, the scope disclosed in the present specification should not be interpreted in a limited manner based on the description of the examples.

[Example 1]
A badminton racket as shown in Figures 1-13 was constructed. This racket has a primary out-of-plane natural frequency ωo1 of 59 Hz, a secondary out-of-plane natural frequency ωo2 of 172 Hz, a primary in-plane natural frequency ωi1 of 51 Hz, and a secondary in-plane natural frequency ωi2 of It was 200Hz. The coordinates of this racket are indicated by symbol Pr in FIG.

[Example 2]
A badminton racket was obtained in the same manner as in Example 1, except that the prepreg structure of the shaft was changed. In this shaft, a type C prepreg structure is adopted for the sheet groups S3 to S8. Further, in this shaft, a prepreg having a width of 54 mm was adopted for the ninth sheet group S9. A Type C prepreg configuration is shown in FIG.

[Example 3]
A badminton racket was obtained in the same manner as in Example 1, except that the prepreg structure of the shaft was changed. For this shaft, the following types of prepreg construction were employed.
Third seat group S3: Type D
Fourth sheet group S4: Type E
Fifth sheet group S5: Type F
Sixth sheet group S6: Type G
Seventh sheet group S7: Type H
Eighth seat group S8: Type G
These prepreg configurations are shown in Figures 20-24. Further, in this shaft, a prepreg having a fiber elastic modulus of 16 tf/mm ² was adopted for the ninth sheet group S9.

[Example 4]
A badminton racket was obtained in the same manner as in Example 1, except that the prepreg structure of the shaft was changed. In this shaft, prepreg having a fiber elastic modulus of 30 tf/mm ² was used for the first sheet group S1 and the second sheet group S2. For this shaft, the following types of prepreg construction were employed.
Third seat group S3: Type I
Fourth sheet group S4: Type I
Fifth sheet group S5: Type I
Sixth sheet group S6: Type I
Seventh sheet group S7: Type J
Eighth seat group S8: Type K
These prepreg configurations are shown in Figures 25-27. Further, in this shaft, a prepreg having a fiber elastic modulus of 30 tf/mm ² is used for the ninth sheet group S9.

[Comparative Example 1]
A badminton racket was obtained in the same manner as in Example 1, except that the prepreg structure of the shaft was changed. This prepreg configuration is shown in FIG.

[Comparative Example 2]
A badminton racket was obtained in the same manner as in Example 1, except that the prepreg structure of the shaft was changed. This prepreg configuration is shown in FIG.

[Comparative Example 3]
A badminton racket was obtained in the same manner as in Example 1, except that the prepreg structure of the shaft was changed. This prepreg configuration is shown in FIG.

[smash]
Launched the shuttle with the launch machine. The player was allowed to smash the shuttle and the trajectory of the shuttle was photographed. The images were analyzed to measure the height of the shuttle as it passed over the net. Twenty measurements were taken and the standard deviation of height was determined. Racquets were rated based on this standard deviation. The rating criteria are as follows. The results are shown in Tables 1 and 2 below.
3: Standard deviation is less than 0.06 m 2: Standard deviation is 0.06 m or more and less than 0.10 m 1: Standard deviation is 0.10 m or more

[Cut Robbing]
Launched the shuttle with the launch machine. The player cut-robbed the shuttle and photographed the trajectory of the shuttle. The images were analyzed to measure the height of the shuttle as it passed over the net. Twenty measurements were taken and the standard deviation of height was determined. Racquets were rated based on this standard deviation. The rating criteria are as follows. The results are shown in Tables 1-4 below.
3: Standard deviation is less than 0.14 m 2: Standard deviation is 0.14 m or more and less than 0.20 m 1: Standard deviation is 0.20 m or more

As is clear from Tables 1 and 2, the badminton rackets of each example were rated "3" or "2" for smash stability, and "3" or "2" for cut-robbing stability. be. On the other hand, the rackets of each comparative example scored "1" for the evaluation of smash stability or cut-robbing stability. From this result, the superiority of this badminton racket is clear.

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

[Item 1]
a shaft having a pad and a tip;
a grip attached to the shaft in the pad;
and a frame attached to said shaft at said tip,
The ratio (ωo2/ωo1) of the out-of-plane secondary natural frequency ωo2 (Hz) to the out-of-plane primary natural frequency ωo1 (Hz), and the in-plane secondary natural frequency ωi2 to the in-plane primary natural frequency ωi1 (Hz) (Hz) ratio (ωi2/ωi1) satisfies the following formula (1).
(ωi2/ωi1) ≧ 1.3 * (ωo2/ωo1) − 0.2 (1)

[Item 2]
A badminton racket according to item 1, which satisfies the following formula (2).
(ωi2/ωi1) ≥ 1.11 * (ωo2/ωo1) + 0.391 (2)

[Item 3]
A badminton racket according to item 1, which satisfies the following formula (3).
(ωi2/ωi1) ≧ 2.5 * (ωo2/ωo1) − 3.42 (3)

[Item 4]
4. The badminton racket according to any one of items 1 to 3, wherein the ratio (ωo2/ωo1) is 2.99 or less.

[Item 5]
5. The badminton racket according to any one of items 1 to 4, wherein the ratio (ωi2/ωi1) is 3.61 or more.

[Item 6]
6. The badminton racket according to any one of items 1 to 5, wherein the shaft is made of a fiber-reinforced resin containing a plurality of reinforcing fibers.

[Item 7]
In the pad, the tensile modulus of the reinforcing fibers contained in the zone away from the center point of the shaft in the in-plane direction is the tensile modulus of the reinforcing fibers contained in the zone away from the center point of the shaft in the out-of-plane direction. 7. A badminton racket according to item 6, which is greater than the modulus of elasticity.

[Item 8]
In the tip, the tensile modulus of the reinforcing fibers contained in the zone away from the center point of the shaft in the in-plane direction is the tensile modulus of the reinforcing fibers contained in the zone away from the center point of the shaft in the out-of-plane direction. A badminton racket according to item 6 or 7, which is less than the modulus of elasticity.

[Item 9]
9. Any one of items 6 to 8, wherein the tensile modulus of reinforcing fibers contained in the pad is greater than the tensile modulus of reinforcing fibers contained in the tip in a zone away from the center point of the shaft in the in-plane direction. The badminton racket described in Kani.

[Item 10]
10. Any one of items 6 to 9, wherein the tensile modulus of reinforcing fibers contained in the pad is smaller than the tensile modulus of reinforcing fibers contained in the tip in a zone away from the center point of the shaft in the out-of-plane direction. The badminton racket described in Kani.

[Item 11]
a shaft having a pad and a tip;
a grip attached to the shaft in the pad;
and a specification determination method for a badminton racket comprising a frame attached to the shaft at the tip, comprising:
(A) Out-of-plane primary natural frequency ωo1 (Hz), out-of-plane secondary natural frequency ωo2 (Hz), in-plane primary natural frequency ωi1 (Hz), and in-plane secondary natural frequency ωi2 (Hz) of the standard racket ),
(B) Based on these natural frequencies ωo1, ωo2, ωi1 and ωi2, a step of determining whether the following formula (1) is satisfied;
and (C) determining the properties of the shaft or frame of the target racket to have a ratio (ωo2/ωo1) that is less than that of a standard racket when Equation (1) below is not satisfied. specification determination method.
(ωi2/ωi1) ≧ 1.3 * (ωo2/ωo1) − 0.2 (1)

[Item 12]
a shaft having a pad and a tip;
a grip attached to the shaft in the pad;
and a specification determination method for a badminton racket comprising a frame attached to the shaft at the tip, comprising:
(A) Out-of-plane primary natural frequency ωo1 (Hz), out-of-plane secondary natural frequency ωo2 (Hz), in-plane primary natural frequency ωi1 (Hz), and in-plane secondary natural frequency ωi2 (Hz) of the standard racket ),
(B) Based on these natural frequencies ωo1, ωo2, ωi1 and ωi2, a step of determining whether the following formula (1) is satisfied;
and (C) determining the characteristics of the shaft or frame of the target racket to have a ratio (ωi2/ωi1) greater than that of a standard racket if Equation (1) below is not satisfied. specification determination method.
(ωi2/ωi1) ≧ 1.3 * (ωo2/ωo1) − 0.2 (1)

The badminton racket described above is suitable for players whose styles involve heavy use of smashes and cut lobbing. This racket is also suitable for a player whose style frequently uses other shots with hitting points near the bottom and other shots with hitting points near the top and accompanied by cuts.

2 Badminton Racket 4 Shaft 6 Frame 8 Neck 10 Cap 12 Grip 14 String 16 Bad 18 Middle 20 Tip 22 Bad end 24 Tip end 26 Top 28 Bottom 36 Face 38 Prepreg 40 Fiber 42 Matrix resin 44 Prepreg 46 ... prepreg 48 ... prepreg S1 ... first sheet group S2 ... second sheet group S3 ... third sheet group S4 ... fourth sheet group S5 ... fifth sheet group S6 Sixth sheet group S7 Seventh sheet group S8 Eighth sheet group S9 Ninth sheet group

Claims (12)

a shaft having a pad and a tip;
a grip attached to the shaft in the pad;
and a frame attached to said shaft at said tip,
The ratio (ωo2/ωo1) of the out-of-plane secondary natural frequency ωo2 (Hz) to the out-of-plane primary natural frequency ωo1 (Hz), and the in-plane secondary natural frequency ωi2 to the in-plane primary natural frequency ωi1 (Hz) (Hz) ratio (ωi2/ωi1) satisfies the following formula (1).
(ωi2/ωi1) ≧ 1.3 * (ωo2/ωo1) − 0.2 (1) The badminton racket according to claim 1, which satisfies the following formula (2).
(ωi2/ωi1) ≥ 1.11 * (ωo2/ωo1) + 0.391 (2) The badminton racket according to claim 1, which satisfies the following formula (3).
(ωi2/ωi1) ≧ 2.5 * (ωo2/ωo1) − 3.42 (3) The badminton racket according to any one of claims 1 to 3, wherein the ratio (ωo2/ωo1) is 2.99 or less. The badminton racket according to any one of claims 1 to 4, wherein the ratio (ωi2/ωi1) is 3.61 or more. The badminton racket according to any one of claims 1 to 5, wherein the shaft is made of fiber-reinforced resin containing a plurality of reinforcing fibers. In the pad, the tensile modulus of the reinforcing fibers contained in the zone away from the center point of the shaft in the in-plane direction is the tensile modulus of the reinforcing fibers contained in the zone away from the center point of the shaft in the out-of-plane direction. 7. The badminton racket of claim 6, wherein the modulus of elasticity is greater than the modulus of elasticity. In the tip, the tensile modulus of the reinforcing fibers contained in the zone away from the center point of the shaft in the in-plane direction is the tensile modulus of the reinforcing fibers contained in the zone away from the center point of the shaft in the out-of-plane direction. A badminton racket according to claim 6 or 7, wherein the modulus of elasticity is less than the modulus of elasticity. The tensile elastic modulus of the reinforcing fibers contained in the pad is greater than that of the reinforcing fibers contained in the tip in zones spaced in the in-plane direction from the center point of the shaft. A badminton racket according to any one of the preceding claims. 10. The method according to any one of claims 6 to 9, wherein the tensile modulus of reinforcing fibers contained in the pad is smaller than the tensile modulus of reinforcing fibers contained in the tip in zones spaced apart in the out-of-plane direction from the center point of the shaft. A badminton racket according to any one of the preceding claims. a shaft having a pad and a tip;
a grip attached to the shaft in the pad;
and a specification determination method for a badminton racket comprising a frame attached to the shaft at the tip, comprising:
(A) Out-of-plane primary natural frequency ωo1 (Hz), out-of-plane secondary natural frequency ωo2 (Hz), in-plane primary natural frequency ωi1 (Hz), and in-plane secondary natural frequency ωi2 (Hz) of the standard racket ),
(B) Based on these natural frequencies ωo1, ωo2, ωi1 and ωi2, a step of determining whether the following formula (1) is satisfied;
and (C) determining the properties of the shaft or frame of the target racket to have a ratio (ωo2/ωo1) that is less than that of a standard racket when Equation (1) below is not satisfied. specification determination method.
(ωi2/ωi1) ≧ 1.3 * (ωo2/ωo1) − 0.2 (1) a shaft having a pad and a tip;
a grip attached to the shaft in the pad;
and a specification determination method for a badminton racket comprising a frame attached to the shaft at the tip, comprising:
(A) Out-of-plane primary natural frequency ωo1 (Hz), out-of-plane secondary natural frequency ωo2 (Hz), in-plane primary natural frequency ωi1 (Hz), and in-plane secondary natural frequency ωi2 (Hz) of the standard racket ),
(B) Based on these natural frequencies ωo1, ωo2, ωi1 and ωi2, a step of determining whether the following formula (1) is satisfied;
and (C) determining the characteristics of the shaft or frame of the target racket to have a ratio (ωi2/ωi1) greater than that of a standard racket if Equation (1) below is not satisfied. specification determination method.
(ωi2/ωi1) ≧ 1.3 * (ωo2/ωo1) − 0.2 (1)

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