JP2022103633A - Badminton racket - Google Patents

Abstract

To provide a badminton racket 2 by which a variation of trajectories of a shuttle can be suppressed in shots the hit points of which are closer to a top 24 and which involve a cut.SOLUTION: A badminton racket 2 has a shaft 4, a grip 10 in which a portion of the shaft 4 closer to a butt end 20 is inserted, and a frame 6 attached to a portion of the shaft 4 closer to a tip end 22. An out-of-plane primary natural frequency ωi1 (Hz) and an out-of-plane secondary natural frequency ωi2 (Hz) in the natural vibration of the badminton racket 2 under a free constraint condition satisfies a following equation (1): ωi2≥3.6×ωi1+5.0 (1). A favorable out-of-plane secondary natural frequency ωi2 is 203 Hz or more.SELECTED DRAWING: Figure 1

Description

The present invention relates to a racket used for badminton.

The badminton racket has a frame, a string and a shaft. The frame has a top and a bottom. The strings form a face. The player shoots the shuttle with a racket. The shot causes the face to collide with the shuttle. The impact of the collision is transmitted from the string through the frame to the shaft. The shot deforms the frame and shaft. An attempt to optimize the deformation behavior at the time of collision is described in Japanese Patent Application Laid-Open No. 2001-70481.

Japanese Unexamined Patent Publication No. 2001-70481

In a badminton game, players make different types of shots. Players perform shots such as smash, lobing, drop, and clear.

Unlike normal lobing, cut lobing involves a cut operation. In cut lobing, the shuttle flies at high speed while spinning at high speed. Cut lobing is often struck from near the net on the player's court. Cut lobing is a shot intended to carry the shuttle to the back of the opponent's court. The trajectory of the shuttle in cut lobing is high. Players need a high degree of skill to fly the shuttle at the intended height. Players who make heavy use of cut lobing want a stable trajectory (speed, height, etc.) for the shuttle.

In a statistical survey, the typical RBI in cut lobing is closer to the top. Even in shots other than cut lobing, the shuttle can be shot at the RBI near the top.

An object of the present invention is to provide a badminton racket in which the hitting point is closer to the top and the variation in the trajectory of the shuttle can be suppressed in a shot accompanied by a cut.

The badminton racket according to the present invention is
Shafts with bad ends and tip ends,
A grip where the vicinity of the bad end of this shaft is inserted,
It also has a frame attached to the shaft in the vicinity of this chip end. In the natural vibration of this badminton racket under the free restraint condition, the in-plane primary natural frequency ωi1 (Hz) and the in-plane secondary natural frequency ωi2 (Hz) satisfy the following formula (1).
ωi2 ≧ 3.6 × ωi1 + 5.0 (1)

Preferably, the badminton racket satisfies the following mathematical formula (2).
ωi2 ≧ 3.6 × ωi1 + 16.0 (2)
Preferably, the badminton racket satisfies the following mathematical formula (3).
ωi2 ≧ 3.6 × ωi1 + 29.0 (3)

Preferably, the frequency ωi2 is 203 Hz or higher. Preferably, the frequency ωi2 is 208 Hz or higher.

The player who uses the badminton racket according to the present invention has a hitting point closer to the top and is easy to make a shot accompanied by a cut. This racket can contribute to the victory of the game.

FIG. 1 is a front view showing a badminton racket according to an embodiment of the present invention. FIG. 2 is a right side view showing the racket of FIG. FIG. 3 is an enlarged cross-sectional view showing a part of the shaft of the racket of FIG. FIG. 4 is an enlarged cross-sectional view taken along the line IV-IV of FIG. FIG. 5 is a developed view showing a prepreg for the shaft of the racket of FIG. FIG. 6 is an explanatory diagram showing a method of measuring the frequency of the natural vibration of the racket of FIG. FIG. 7 is a graph showing the results obtained by the measurement of FIG. FIG. 8 is a graph showing the relationship between the in-plane primary natural frequency ωi1 and the in-plane secondary natural frequency ωi2 of the badminton racket of FIG. FIG. 9 is a development view showing a prepreg for a shaft of a badminton racket according to a seventh embodiment of the present invention. FIG. 10 is a development view showing a prepreg for a shaft of a badminton racket according to a sixth embodiment of the present invention.

Hereinafter, the present invention will be described in detail based on a preferred embodiment with reference to the drawings as appropriate.

The badminton racket 2 is shown in FIGS. 1 and 2. The racket 2 has a shaft 4, a frame 6, a neck 8, a cap 9, a grip 10, and a string 12. In FIGS. 1 and 2, the arrow X represents the width direction, the arrow Y represents the axial direction, and the arrow Z represents the thickness direction.

The shaft 4 has a bad portion 14, a middle portion 16, and a tip portion 18. The shaft 4 further has a bad end 20 and a tip end 22. The shaft 4 is hollow. The shaft 4 is made of a fiber reinforced resin. This fiber reinforced resin has a resin matrix and a large number of reinforced fibers. The shaft 4 includes a plurality of fiber reinforcing layers (described in detail later).

As the base resin of the shaft 4, thermocurable resins such as epoxy resin, pismareimide resin, polyimide and phenol resin; and polyether ether ketone, polyether sulfone, polyetherimide, polyphenylene sulfide, polyamide and polypropylene. Thermoplastic resin is exemplified. A resin particularly suitable for the shaft 4 is an epoxy resin.

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

The frame 6 is annular and hollow. The frame 6 is made of a fiber reinforced resin. As the fiber reinforced resin, a base resin similar to the base resin of the shaft 4 can be used. As the fiber reinforced resin, the same reinforcing fibers as the reinforcing fibers of the shaft 4 can be used. The frame 6 is tightly coupled to the tip end 22 of the shaft 4 via the neck 8. The frame 6 has a top 24 and a bottom 26.

The grip 10 has a hole 27 extending in the axial direction (Y direction). The vicinity of the bad end 20 of the shaft 4 is inserted into this hole 27. The inner peripheral surface of the hole 27 and the outer peripheral surface of the shaft 4 are joined with an adhesive.

The string 12 is stretched on the frame 6. The string 12 is stretched along the width direction X and the axial direction Y. The portion of the string 12 extending along the width direction X is referred to as a lateral thread 28. The portion of the string 12 extending along the axial direction Y is referred to as a vertical thread 30. The face 32 is formed by the plurality of horizontal threads 28 and the plurality of vertical threads 30. The face 32 is generally along the XY plane.

In FIG. 1, reference numeral 34 represents an exposed portion of the shaft 4. The exposed portion 34 is exposed from the neck 8 and is exposed from the grip 10. In FIG. 1, reference numeral L is the length of the exposed portion 34. The length L is usually 150 mm or more and 210 mm or less.

FIG. 3 is an enlarged cross-sectional view showing a part of the shaft 4 of the racket 2 of FIG. FIG. 4 is an enlarged cross-sectional view taken along the line IV-IV of FIG. As described above, the shaft 4 is hollow. As shown in FIG. 4, the cross-sectional shape of the shaft 4 is a circle. In other words, the shaft 4 has a cylindrical shape.

In FIGS. 3 and 4, the arrow Di represents the inner diameter of the shaft 4. A typical inner diameter Di is 3 mm or more and 10 mm or less. In FIGS. 3 and 4, the arrow Do represents the outer diameter of the shaft 4. A typical outer diameter Do is 5 mm or more and 15 mm or less.

As described above, the shaft 4 is made of a fiber reinforced resin. The shaft 4 can be manufactured by a seat winding method. In this sheet winding method, multiple prepregs are wrapped around a mandrel. Each prepreg has a plurality of fibers and a matrix resin. This matrix resin is not cured.

FIG. 5 is a developed view showing a prepreg configuration for the shaft 4 of the racket 2 of FIG. This prepreg configuration has 11 prepregs (ie, sheets). Specifically, this prepreg configuration includes a first sheet S1, a second sheet S2, a third sheet S3, a fourth sheet S4, a fifth sheet S5, a sixth sheet S6, a seventh sheet S7, and an eighth sheet S8. It has a ninth sheet S9, a tenth sheet S10, and an eleventh sheet S11. From these prepregs, a plurality of fiber reinforcing layers are formed by the method described later. Specifically, the first fiber reinforcing layer is formed from the first sheet S1, the second fiber reinforcing layer is formed from the second sheet S2, the third fiber reinforcing layer is formed from the third sheet S3, and the fourth sheet. The fourth fiber reinforcing layer is formed from S4, the fifth fiber reinforcing layer is formed from the fifth sheet S5, the sixth fiber reinforcing layer is formed from the sixth sheet S6, and the seventh fiber reinforcing layer is formed from the seventh sheet S7. It is formed, the eighth fiber reinforcing layer is formed from the eighth sheet S8, the ninth fiber reinforcing layer is formed from the ninth sheet S9, the tenth fiber reinforcing layer is formed from the tenth sheet S10, and the eleventh sheet S11 is formed. The eleventh fiber reinforcing layer is formed from.

The left-right direction in FIG. 5 is the axial direction of the shaft 4. In FIG. 5, the positions of the bad end 20 and the chip end 22 are indicated by arrows. For convenience of explanation, in FIG. 5, the scale in the left-right direction (axial direction) does not match the scale in the up-down direction.

The first sheet S1 is present throughout the shaft 4. The shape of the first sheet S1 is generally rectangular. The first sheet S1 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber is inclined with respect to the axial direction. The angle of the extending direction of the carbon fiber with respect to the axial direction is 30 ° or more and 60 ° or less. In this embodiment, this angle is 45 °. The first sheet S1 has a width of 82 mm and a length of 340 mm.

The second seat S2 is present throughout the shaft 4. The shape of the second sheet S2 is generally rectangular. The second sheet S2 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber is inclined with respect to the axial direction. The angle of the extending direction of the carbon fiber with respect to the axial direction is −60 ° or more and −30 ° or less. In this embodiment, this angle is −45 °. The second sheet S2 has a width of 82 mm and a length of 340 mm.

The inclination direction of the carbon fibers in the second sheet S2 is opposite to the inclination direction of the carbon fibers in the first sheet S1. Therefore, the inclination direction of the carbon fibers in the second fiber reinforcing layer is opposite to the inclination direction of the carbon fibers in the first fiber reinforcing layer. In this shaft 4, a bias structure is achieved by the first fiber reinforced layer and the second fiber reinforced layer. The first fiber reinforced layer and the second fiber reinforced layer contribute to the flexural rigidity and the torsional rigidity of the shaft 4. The first fiber reinforced layer and the second fiber reinforced layer particularly contribute to the torsional rigidity of the shaft 4.

The third sheet S3 is located substantially in the center of the shaft 4. The shape of the third sheet S3 is approximately a parallelogram. The third sheet S3 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber is inclined with respect to the axial direction. The angle of the extending direction of the carbon fiber with respect to the axial direction is 30 ° or more and 60 ° or less. In this embodiment, this angle is 45 °. The third sheet S3 has a width of 38 mm and a length of 70 mm.

The fourth seat S4 exists substantially in the center of the shaft 4. In the axial direction, the position of the fourth sheet S4 coincides with the position of the third sheet S3. The shape of the fourth sheet S4 is generally a parallelogram. The fourth sheet S4 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber is inclined with respect to the axial direction. The angle of the extending direction of the carbon fiber with respect to the axial direction is −60 ° or more and −30 ° or less. In this embodiment, this angle is −45 °. The fourth sheet S4 has a width of 38 mm and a length of 70 mm.

The inclination direction of the carbon fibers in the fourth sheet S4 is opposite to the inclination direction of the carbon fibers in the third sheet S3. Therefore, the inclination direction of the carbon fibers in the fourth fiber reinforcing layer is opposite to the inclination direction of the carbon fibers in the third fiber reinforcing layer. In this shaft 4, a bias structure is achieved by a third fiber reinforced layer and a fourth fiber reinforced layer. The third fiber reinforcing layer and the fourth fiber reinforcing layer contribute to the flexural rigidity and the torsional rigidity of the middle portion 16. The third fiber reinforcing layer and the fourth fiber reinforcing layer particularly contribute to the torsional rigidity of the middle portion 16.

The fifth sheet S5 is biased toward the tip end 22 side of the shaft 4. The shape of the fifth sheet S5 is generally trapezoidal. The fifth sheet S5 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber coincides with the axial direction. In other words, the angle of the extending direction of the carbon fiber with respect to the axial direction is substantially 0 °. In the fifth sheet S5, the width is 76 mm, the length of the upper base is 105 mm, and the length of the lower base is 115 mm.

As described above, the carbon fibers contained in the fifth sheet S5 are substantially axially oriented. Therefore, even in the fifth fiber reinforcing layer, the carbon fibers are substantially axially oriented. As used herein, a structure in which the carbon fibers are substantially axially oriented is referred to as a "straight structure". The fifth fiber reinforcing layer has a straight structure. When the shaft 4 bends, a large tension is applied to these carbon fibers. This tension suppresses further deflection of the shaft 4. In other words, these carbon fibers contribute to the flexural rigidity of the shaft 4. The fifth fiber reinforcing layer particularly contributes to the bending rigidity of the tip portion 18.

The sixth seat S6 is biased toward the bad end 20 side of the shaft 4. The shape of the sixth sheet S6 is generally trapezoidal. The sixth sheet S6 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber coincides with the axial direction. In other words, the angle of the extending direction of the carbon fiber with respect to the axial direction is substantially 0 °. In the sixth sheet S6, the width is 76 mm, the length of the upper base is 155 mm, and the length of the lower base is 165 mm.

As described above, the carbon fibers contained in the sixth sheet S6 are substantially axially oriented. Therefore, even in the sixth fiber reinforcing layer, the carbon fibers are substantially axially oriented. The sixth fiber reinforcing layer has a straight structure. When the shaft 4 bends, a large tension is applied to these carbon fibers. This tension suppresses further deflection of the shaft 4. In other words, these carbon fibers contribute to the flexural rigidity of the shaft 4. The sixth fiber reinforcing layer particularly contributes to the bending rigidity of the bad portion 14.

The seventh sheet S7 is located substantially in the center of the shaft 4. The shape of the seventh sheet S7 is approximately a parallelogram. The seventh sheet S7 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber is inclined with respect to the axial direction. The angle of the extending direction of the carbon fiber with respect to the axial direction is 30 ° or more and 60 ° or less. In this embodiment, this angle is 45 °. The seventh sheet S7 has a width of 38 mm and a length of 110 mm.

The eighth sheet S8 is located substantially in the center of the shaft 4. In the axial direction, the position of the eighth sheet S8 coincides with the position of the seventh sheet S7. The shape of the eighth sheet S8 is approximately a parallelogram. The eighth sheet S8 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber is inclined with respect to the axial direction. The angle of the extending direction of the carbon fiber with respect to the axial direction is −60 ° or more and −30 ° or less. In this embodiment, this angle is −45 °. The eighth sheet S4 has a width of 38 mm and a length of 110 mm.

The ninth sheet S9 is biased toward the tip end 22 side of the shaft 4. The shape of the ninth sheet S9 is generally trapezoidal. The ninth sheet S9 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber coincides with the axial direction. In other words, the angle of the extending direction of the carbon fiber with respect to the axial direction is substantially 0 °. In this ninth sheet S9, the width is 76 mm, the length of the upper base is 85 mm, and the length of the lower base is 95 mm.

As described above, the carbon fibers contained in the ninth sheet S9 are substantially axially oriented. Therefore, even in the ninth fiber reinforcing layer, the carbon fibers are substantially axially oriented. The ninth fiber reinforcing layer has a straight structure. When the shaft 4 bends, a large tension is applied to these carbon fibers. This tension suppresses further deflection of the shaft 4. In other words, these carbon fibers contribute to the flexural rigidity of the shaft 4. The ninth fiber reinforcing layer particularly contributes to the bending rigidity of the tip portion 18.

The tenth sheet S10 is biased toward the bad end 20 side of the shaft 4. The shape of the tenth sheet S10 is generally trapezoidal. The tenth sheet S10 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber coincides with the axial direction. In other words, the angle of the extending direction of the carbon fiber with respect to the axial direction is substantially 0 °. In the tenth sheet S10, the width is 76 mm, the length of the upper base is 135 mm, and the length of the lower base is 145 mm.

As described above, the carbon fibers contained in the tenth sheet S10 are substantially axially oriented. Therefore, even in the tenth fiber reinforced layer, the carbon fibers are substantially axially oriented. The tenth fiber reinforced layer has a straight structure. When the shaft 4 bends, a large tension is applied to these carbon fibers. This tension suppresses further deflection of the shaft 4. In other words, these carbon fibers contribute to the flexural rigidity of the shaft 4. The tenth fiber reinforcing layer particularly contributes to the bending rigidity of the bad portion 14.

The eleventh sheet S11 exists over the entire shaft 4. The shape of the eleventh sheet S11 is substantially rectangular. The eleventh sheet S11 contains a plurality of carbon fibers arranged in parallel. The extending direction of each carbon fiber coincides with the axial direction. In other words, the angle of the extending direction of the carbon fiber with respect to the axial direction is substantially 0 °. The eleventh sheet S11 has a width of 4 mm and a length of 340 mm.

As described above, the carbon fibers contained in the eleventh sheet S11 are substantially axially oriented. Therefore, even in the eleventh fiber reinforced layer, the carbon fibers are substantially axially oriented. The eleventh fiber reinforced layer has a straight structure. When the shaft 4 bends, a large tension is applied to these carbon fibers. This tension suppresses further deflection of the shaft 4. In other words, these carbon fibers contribute to the flexural rigidity of the shaft 4.

In this shaft 4, the first fiber reinforcing layer, the second fiber reinforcing layer and the eleventh fiber reinforcing layer exist from the bad end 20 to the tip end 22. These fiber reinforced layers can contribute to the durability of the shaft 4.

In the manufacture of the shaft 4, the sheet shown in FIG. 5 is sequentially wound around a mandrel. The first sheet S1 and the second sheet S2 may be overlapped and wound around a mandrel. The third sheet S3 and the fourth sheet S4 may be overlapped and wound around a mandrel. The sixth sheet S6 and the seventh sheet S7 may be overlapped and wound around a mandrel. Along with these sheets, other sheets may be wrapped around the mandrel. Examples of other sheets include those containing glass fiber.

Wrapping tape is further wrapped around these sheets. These mandrels, prepregs (sheets S1-S8) and wrapping tapes are heated in an oven or the like. The heating causes the matrix resin to flow. Further heating causes the resin to undergo a curing reaction, and a molded product is obtained. The end face is processed, polished, painted, and the like to complete the shaft 4.

The material of the shaft 4 is a fiber reinforced resin. The material of the shaft 4 may be a resin composition containing no fibers. The material of the shaft 4 may be metal, wood, or the like.

FIG. 6 is an explanatory diagram showing a method of measuring the frequency of the natural vibration of the racket 2 of FIG. In this method, the racket 2 is suspended by the string 36. This racket 2 does not have the string 12. In other words, the racket 2 without the string 12 is provided for measuring the frequency of the natural vibration. In FIG. 6, the axial direction (Y direction) of the shaft 4 coincides with the vertical direction. In FIG. 6, the shaft 4 is located below the frame 6.

As shown in FIG. 6, an acceleration pickup 38 is attached to the racket 2. The position of the acceleration pickup 38 is the tip of the grip 10. The direction of the acceleration pickup 38 is the X direction. The acceleration pickup 38 has a mass of 3.5 g. Next, the point Ph of the grip 10 facing the acceleration pickup 38 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 38 are sent to the frequency analyzer (“Dynamic Signal Analyzer” of Hewlett-Packard Co., Ltd.) via the amplifier. Based on the transfer function obtained by this device, the frequency of the natural vibration in the plane is calculated. The direction of the natural vibration in the plane is mainly the X direction. In this method, the natural frequency is measured without being firmly fixed to any part of the racket 2. In other words, the natural frequency is measured under free constraints.

FIG. 7 is a graph showing the results obtained by the measurement of FIG. In FIG. 7, the horizontal axis is the frequency (Hz), and the vertical axis is the magnitude of acceleration (m / s ² / N). In FIG. 7, reference numeral P1 is a primary peak. The frequency at this primary peak P1 is the in-plane primary natural frequency ωi1. In FIG. 7, reference numeral P2 is a secondary peak. The frequency at this secondary peak P2 is the in-plane secondary natural frequency ωi2.

FIG. 8 is a graph showing the relationship between the in-plane primary natural frequency ωi1 and the in-plane secondary natural frequency ωi2 of the badminton racket 2. In this graph, the reference numeral Pr represents the point of the racket 2 shown in FIG. 1-5.

The straight line represented by the reference numeral L1 in FIG. 8 can be represented by the following mathematical formula.
ωi2 = 3.6 x ωi1 + 5.0
As shown in FIG. 8, the point Pr is located above the straight line L1. In other words, the coordinates (ωi1, ωi2) of the racket 2 include the following mathematical formula (1).
ωi2 ≧ 3.6 × ωi1 + 5.0 (1)
According to the knowledge obtained by the present inventor, the racket 2 satisfying this mathematical formula (1) is suitable for cut lobing. A player who performs cut lobing using this racket 2 can easily obtain the trajectory intended by the shuttle. In this racket 2, the variation in the trajectory of the shuttle in cut lobing is small.

According to the findings obtained by the present inventor, when the shuttle is hit at the portion of the face 32 near the bottom 26, the vibration in the in-plane secondary mode is mainly excited. According to the findings obtained by the present inventor, when the shuttle is struck in the portion of the face 32 near the top 24, the vibration in the in-plane primary mode is mainly excited. A typical RBI in cut lobing is closer to the top 24. Therefore, in cut lobing, vibration in the in-plane primary mode is mainly excited. However, even in cut lobing, the hit points vary. In the racket 2 satisfying the above formula (1), the in-plane primary natural frequency ωi1 is relatively small, and the in-plane secondary natural frequency ωi2 is relatively large. According to the findings obtained by the present inventor, in the cut lobing by the racket 2 in which the in-plane primary natural frequency ωi1 is small and the in-plane secondary natural frequency ωi2 is large, the variation in the initial speed of the shuttle is small even if the hitting points vary. .. The reason is that the repulsion of the racket 2 is not extremely small even if the shuttle is hit at a position deviated from the intended position. Since the variation in the initial velocity of the shuttle is small, the variation in the trajectory of the shuttle is also small. This racket 2 is suitable for a player who makes heavy use of cut lobing. This racket 2 is also suitable for players who place importance on cut lobing.

As mentioned above, a typical RBI in cut lobing is closer to the top 24. The racket 2 according to the present invention is also suitable for shots other than cut lobing, in which the shuttle is hit and accompanied by a cut at a portion of the face 32 near the top 24.

A small frequency ωi1 and a large frequency ωi2 are achieved by changing the position of the prepreg, the number of prepregs, the width of the prepreg, the length of the prepreg, the angle of the fiber, the amount of the grain of the fiber, the elastic modulus of the fiber, etc. on the shaft 4. Can be done. As a concrete means
(A) The fiber reinforcing layer having a straight structure is unevenly distributed in the bad portion 14.
(B) The number of fiber reinforced layers of the bad portion 14 is set large.
(C) The fiber reinforced layer having a large basis weight is unevenly distributed in the bad portion 14.
(D) A fiber reinforcing layer having fibers having a large elastic modulus is unevenly distributed in the bad portion 14.
(E) The number of fiber reinforced layers of the chip portion 18 is set small.
(F) The fiber reinforced layer having a small basis weight is unevenly distributed in the chip portion 18.
(G) A fiber reinforcing layer having fibers having a small elastic modulus is unevenly distributed in the chip portion 18.
Etc. are exemplified. In the present embodiment, as described above, the high rigidity of the bad portion 14 is achieved by the fifth fiber reinforcing layer obtained from the fifth sheet S5 and the eighth fiber reinforcing layer obtained from the eighth sheet S8. As a result, a small frequency ωi1 and a large frequency ωi2 are achieved.

Depending on the specifications of the members other than the shaft 4, a small frequency ωi1 and a large frequency ωi2 may be achieved. As a member other than the shaft 4 that may be involved in the frequency, the frame 6 can be mentioned. A small frequency ωi1 and a large frequency ωi2 are achieved by changing the position of the prepreg, the number of prepregs, the width of the prepreg, the length of the prepreg, the angle of the fiber, the amount of the grain of the fiber, the elastic modulus of the fiber, etc. in the frame 6. Can be done. As a concrete means
(A) The fiber reinforcing layer having a straight structure is unevenly distributed in the vicinity of the bottom 26 of the frame 6.
(B) The number of fiber reinforced layers in the vicinity of the bottom 26 of the frame 6 is set large.
(C) Fiber reinforced layers having a large basis weight are unevenly distributed in the vicinity of the bottom 26 of the frame 6.
(D) Fiber reinforced layers having fibers having a high elastic modulus are unevenly distributed in the vicinity of the bottom 26 of the frame 6.
(E) The number of fiber reinforced layers in the vicinity of the top 24 of the frame 6 is set small.
(F) Fiber reinforced layers having a small basis weight are unevenly distributed in the vicinity of the top 24 of the frame 6.
(G) Fiber reinforced layers having fibers having a small elastic modulus are unevenly distributed in the vicinity of the top 24 of the frame 6.
Etc. are exemplified.

The straight line represented by the reference numeral L2 in FIG. 8 can be represented by the following mathematical formula.
ωi2 = 3.6 x ωi1 + 16.0
As shown in FIG. 8, the point Pr is located above the straight line L2. In other words, the coordinates (ωi1, ωi2) of the racket 2 include the following mathematical formula (2).
ωi2 ≧ 3.6 × ωi1 + 16.0 (2)
According to the knowledge obtained by the present inventor, the racket 2 satisfying this mathematical formula (2) is suitable for cut lobing. A player who performs cut lobing using this racket 2 can easily obtain the trajectory intended by the shuttle. In this racket 2, the variation in the trajectory of the shuttle in cut lobing is small.

The straight line represented by the reference numeral L3 in FIG. 8 can be represented by the following mathematical formula.
ωi2 ≧ 3.6 × ωi1 + 29.0
As shown in FIG. 8, the point Pr is located above the straight line L3. In other words, the coordinates (ωi1, ωi2) of the racket 2 include the following mathematical formula (3).
ωi2 ≧ 3.6 × ωi1 + 29.0 (3)
According to the knowledge obtained by the present inventor, the racket 2 satisfying this mathematical formula (3) is suitable for cut lobing. A player who performs cut lobing using this racket 2 can easily obtain the trajectory intended by the shuttle. In this racket 2, the variation in the trajectory of the shuttle in cut lobing is small.

The straight line represented by the reference numeral L4 in FIG. 8 can be represented by the following mathematical formula.
ωi2 = 203
As shown in FIG. 8, the point Pr is located above the straight line L4. The frequency ωi2 of the point Pr is 203 or more. In other words, the coordinates (ωi1, ωi2) of the racket 2 include the following mathematical formula (4).
ωi2 ≧ 203 (4)
According to the knowledge obtained by the present inventor, the racket 2 satisfying this mathematical formula (4) is suitable for cut lobing. In the cut lobing using this racket 2, the shuttle flies at high speed.

The straight line represented by the reference numeral L5 in FIG. 8 can be represented by the following mathematical formula.
ωi2 = 208
As shown in FIG. 8, the point Pr is located above the straight line L5. The frequency ωi2 of the point Pr is 208 or more. In other words, the coordinates (ωi1, ωi2) of the racket 2 include the following mathematical formula (5).
ωi2 ≧ 208 (5)
According to the knowledge obtained by the present inventor, the racket 2 satisfying this mathematical formula (5) is suitable for cut lobing. In the cut lobing using this racket 2, the shuttle flies at high speed.

Hereinafter, the effects of the present invention will be clarified by Examples, but the present invention should not be construed in a limited manner based on the description of these Examples.

[Example 1]
A shaft having the prepreg configuration shown in FIG. 5 was manufactured. Each prepreg contained carbon fiber. The tensile elastic modulus of this carbon fiber was 24 tf / mm ² . A badminton racket was manufactured by attaching a frame, neck, cap and grip used in a commercially available badminton racket having standard hardness and mass to this shaft. The in-plane primary natural frequency ωi1 of this racket was 52 Hz, and the in-plane secondary natural frequency ωi2 was 217 Hz. The coordinates of this racket are indicated by the reference numeral Pr in FIG.

[Example 2-10 and Comparative Example 1-8]
The badminton rackets of Example 2-10 and Comparative Example 1-8 were obtained in the same manner as in Example 1 except that the prepreg configuration was as shown in Table 1-4. The widths of the prepregs for the shafts of these rackets are shown in Table 1-4 below. The in-plane primary natural frequency ωi1 and the in-plane secondary natural frequency ωi2 of these rackets are shown in Tables 1-4 and FIG. 8 below.

[Stability]
The shuttle was launched by the launch machine. The player was asked to cut and lob the shuttle, and the trajectory of the shuttle was photographed. The images were analyzed and the height of the shuttle passing over the net was measured. Twenty measurements were taken to determine the standard deviation of height. The racket was rated based on this standard deviation. The rating criteria are as follows. The results are shown in Table 1-4 below.
A: Standard deviation is less than 0.14m B: Standard deviation is 0.14m or more and less than 0.20m C: Standard deviation is 0.20m or more

[Repulsion]
In the above stability assessment, the speed of the shuttle passing over the net was measured. The measurement was performed 20 times, and the average value of the speed was calculated. The racket was rated based on this average value. The rating criteria are as follows. The results are shown in Table 1-4 below.
A: Average speed is 19.0 m / s or more B: Average speed is 18.0 m / s or more and less than 19.0 m / s C: Average speed is less than 18.0 m / s

As is clear from Table 1-4, in the badminton racket of each embodiment, the trajectory of the shuttle in cut lobing is stable. From this evaluation result, the superiority of the present invention is clear.

The badminton racket according to the present invention is suitable for a player in a style that makes heavy use of cut lobing. This racket is also suitable for players who have a RBI near the top and make heavy use of other shots with cuts.

2 ... Badminton racket 4 ... Shaft 6 ... Frame 8 ... Neck 10 ... Grip 12 ... String 14 ... Bad part 16 ... Middle part 18 ... Chip part 20・ ・ ・ Bad end 22 ・ ・ ・ Chip end 24 ・ ・ ・ Top 26 ・ ・ ・ Bottom 28 ・ ・ ・ Horizontal thread 30 ・ ・ ・ Vertical thread 32 ・ ・ ・ Face 34 ・ ・ ・ Exposed part 38 ・ ・ ・ Accelerometer pickup S1 ... 1st sheet S2 ... 2nd sheet S3 ... 3rd sheet S4 ... 4th sheet S5 ... 5th sheet S6 ... 6th sheet S7 ... 7th sheet S8 ...・ ・ Eighth sheet S9 ・ ・ ・ Ninth sheet

Claims (5)

Shafts with bad ends and tip ends,
A grip on which the vicinity of the bad end of the shaft is inserted,
It also has a frame attached to the shaft in the vicinity of the chip end.
A badminton racket in which the in-plane primary natural frequency ωi1 (Hz) and the in-plane secondary natural frequency ωi2 (Hz) satisfy the following formula (1) in the natural vibration under free restraint conditions.
ωi2 ≧ 3.6 × ωi1 + 5.0 (1) The badminton racket according to claim 1, which satisfies the following formula (2).
ωi2 ≧ 3.6 × ωi1 + 16.0 (2) The badminton racket according to claim 2, which satisfies the following formula (3).
ωi2 ≧ 3.6 × ωi1 + 29.0 (3) The badminton racket according to any one of claims 1 to 3, wherein the frequency ωi2 is 203 Hz or higher. The badminton racket according to claim 4, wherein the frequency ωi2 is 208 Hz or higher.

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