JP5230835B1 - Method for manufacturing shaft used in badminton racket - Google Patents

Abstract

A badminton racket having a shaft with appropriately improved both bending rigidity and torsional rigidity is provided.
A prepreg sheet in which a first reinforcing fiber group extending in a direction inclined with respect to a central axis of a mandrel and a second reinforcing fiber group extending in a direction crossing the first reinforcing fiber group are impregnated with a resin. 20, a first winding stage of winding the mandrel so that the number of windings at the front end of the mandrel is greater than the number of windings at the rear end of the mandrel, and a reinforcing fiber group extending substantially parallel to the central axis of the mandrel. A second winding step of winding the prepreg sheet 22 impregnated with the mandrel so that the number of windings at the front end of the mandrel is less than the number of windings at the rear end of the mandrel, and the prepreg sheet wound around the mandrel Heating and curing 20 and 22.
[Selection] Figure 4

Description

  The present invention relates to a method of manufacturing a shaft used in a badminton racket.

  Japanese Patent Application Laid-Open No. 2001-137390 (Patent Document 1) discloses that a shaft of a badminton racket is formed using a unidirectional carbon fiber reinforced resin to increase the bending rigidity of the shaft. Patent Document 1 also discloses that the torsional rigidity of the shaft is increased by winding a unidirectional carbon fiber reinforced resin in the bias direction.

JP 2001-137390 A

  In general, the badminton racket needs to be able to stabilize the frame surface by making the shaft difficult to twist in order to allow the shuttle to fly where the player aims. In addition, the badminton racket needs to have a moderate and repulsive shaft so that the player can hit the shuttle strongly and fly away. Such a requirement cannot be satisfied simply by using a unidirectional carbon fiber reinforced resin without any ingenuity as described in Patent Document 1.

  Thus, according to various embodiments of the present invention, a badminton racket having a shaft with appropriately improved both bending rigidity and torsional rigidity is provided.

A method of manufacturing a shaft used for a badminton racket according to an aspect of the present invention includes a first reinforcing fiber group extending in a direction inclined with respect to a central axis of a mandrel, and a first extending in a direction intersecting the first reinforcing fiber group. A first winding step of winding the prepreg sheet impregnated with resin in the two reinforcing fiber groups around the mandrel so that the number of windings at the front end of the mandrel is larger than the number of windings at the rear end of the mandrel; A prepreg sheet in which a reinforcing fiber group extending substantially parallel to the central axis of the mandrel is impregnated with resin is wound around the mandrel so that the number of windings at the front end of the mandrel is less than the number of windings at the rear end of the mandrel. A second winding step of rotating, and a step of heating and curing the prepreg sheet wound around the mandrel.
A shaft used for a badminton racket according to an aspect of the present invention, the first reinforcing fiber group extending in a direction inclined with respect to the central axis of the shaft, and the second extending in a direction intersecting the first reinforcing fiber group A first cylindrical member that is formed of a prepreg sheet in which a reinforcing fiber group is impregnated with a resin and that has a thickness at the front end that is greater than a thickness at the rear end, and a reinforcement that extends substantially parallel to the central axis. A second cylinder, which is constituted by a prepreg sheet in which a fiber group is impregnated with a resin, is formed so that the thickness at the front end is smaller than the thickness at the rear end, and is arranged coaxially with the first cylindrical member. And a member.

  Various embodiments of the present invention can provide a badminton racket having a shaft with appropriately improved both bending and torsional rigidity.

FIG. 1 is a schematic view showing a configuration of a badminton racket according to an embodiment of the present invention. FIG. 2 is a schematic diagram for explaining the torsional rigidity of the badminton racket according to the embodiment of the present invention. FIG. 3 is a schematic diagram illustrating an example of bending rigidity and torsional rigidity of a badminton racket shaft according to an embodiment of the present invention. FIG. 4 is a schematic view showing a specific example of a prepreg sheet used for a shaft of a badminton racket according to an embodiment of the present invention. FIG. 5 is a schematic view showing a method for producing a prepreg sheet used for a shaft of a badminton racket according to an embodiment of the present invention. FIG. 6 is a schematic diagram for explaining a method of joining a shaft and a frame of a badminton racket according to an embodiment of the present invention. FIG. 7 is a schematic diagram showing a configuration of a prepreg sheet used for a shaft of a badminton racket according to an embodiment of the present invention.

  Hereinafter, various embodiments will be described with reference to the drawings as appropriate. In addition, the same referential mark is attached | subjected to the common component in drawing. Further, the drawings are not necessarily shown to the same scale for convenience.

  FIG. 1 is a schematic view showing a configuration of a badminton racket according to an embodiment of the present invention. As shown in FIG. 1, a badminton racket (hereinafter simply referred to as a “racquet”) 10 according to the present embodiment includes a frame 12, a shaft 14 coupled to the frame 12, a grip 16 coupled to the shaft 14, including.

  The frame 12 and the shaft 14 are integrally formed. The shaft 14 and the grip 16 are joined together by inserting and bonding the rear end of the shaft 14 into a hole formed at the tip of the grip 16. The length (adhesion length) of the portion inserted into the grip 16 at the rear end of the shaft 14 is, for example, about 60 to about 70 mm.

  As a racket that can be used in an official game, the overall length of the frame 12 is generally within about 280 mm, the overall length of the grip 16 is within about 200 mm, and the overall length of the racket 10 is within about 680 mm. . In order to satisfy such constraint conditions, the overall length of the shaft 14 is approximately about 300 mm.

In addition, the weight of the shaft 14 is about 11 to about 13 g in order to make the swinging feeling and the balance point (center of gravity) of the racket 10 appropriate due to restrictions in the integral molding of the frame 12 and the shaft 14. It is standard that the inner diameter and outer diameter of the shaft 14 are about 3.5 to about 4.0 mm and about 7.0 to about 8.0 mm, respectively.
Furthermore, in this embodiment, the shaft 14 is formed so that the outer diameter is substantially the same from the front end to the rear end. This is for improving the feeling of swinging the racket 10.

The role of the shaft 14 in the racket 10 is as follows: (a) The player can control the shuttle so that it can fly, (b) The player can hit the shuttle strongly to fly away. (C) The role that the player can react quickly is given.
Regarding the role (a), it is required that the frame surface is stable and that the shaft 14 is difficult to twist. As for the role (A) and the role (C), the shaft 14 is required to have an appropriate repulsive force.

  However, as described above, the size of the inner diameter and the outer diameter of the shaft 14 is restricted. In other words, the shaft 14 needs to be designed with torsional rigidity and bending rigidity within a limited thickness.

  Therefore, in one embodiment, with regard to “bending rigidity”, the shaft 14 has a moderate rigidity and a repulsive force. Therefore, the thickness is about 100 μm or less and the resin content (RC) is less than the thickness due to the limitation of the wall thickness. It is formed using a prepreg sheet that is about 15 to about 25%. Specifically, the shaft 14 has, for example, a bending rigidity (EI) of about 5.38E + 05 at the front end, a bending rigidity of about 6.48E + 05 at the rear end, and a bending rigidity from the front end toward the rear end. Is formed to increase. The bending rigidity of the shaft 14 may increase continuously from the front end toward the rear end, or may increase rapidly at one or more points.

この運動エネルギーは、シャフト１４がしなり、ねじれるといった仕事量と略等しいと考えられる。しなり及びねじれがこの運動エネルギー（仕事量）を半分ずつ受け持つと仮定する。 On the other hand, the “torsional rigidity” of the shaft 14 can be designed from the viewpoint described below, for example.
The world record for smash speed in badminton is 421 km / h, but at a general level, smash speed is said to be about 200 to about 300 km / h. The weight of the shuttle is about 5 g, and the kinetic energy given to the shuttle launched by the smash is obtained by the following equation (1).

This kinetic energy is considered to be substantially equal to the amount of work that the shaft 14 bends and twists. Suppose that bending and twisting are responsible for half of this kinetic energy (work).

スマッシュ時にラケット１０に作用する力をＦとすると、次式（３）及び次式（４）が得られる。

ここで、ｍは、シャトルの重量（≒５ｇ）であり、ｖは、スマッシュ時に与えられるシャトルの速度（≒２００ｋｍ／ｈ）であり、ｘは、ねじれ量（≒２π×０.１×１０／３００[ｍ]）である。 As shown in FIG. 2, when the distance between the central axis of the racket 10 and the end of the frame 12 is 0.1 m and the twist angle is 10 °, the twist amount x is obtained by the following equation (2).

When the force acting on the racket 10 during smashing is F, the following equations (3) and (4) are obtained.

Here, m is the shuttle weight (≈5 g), v is the shuttle speed (≈200 km / h) given during smashing, and x is the twist amount (≈2π × 0.1 × 10 / 300 [m]).

  Substituting each numerical value into the above equation (4) and combining the units gives F = 2.3 [kgf]. In other words, the force acting on the racket 10 when hitting a smash of about 200 km / h is about 2.3 kgf.

  On the other hand, when the smash is struck at the end of the frame 12 which is displaced by about 10 cm from the central axis of the racket 10 (smash is struck by about 10 cm off-center), the torsional rigidity is about 5.18E + 05 to about 5.61E + 05. Then, the twist angle can be suppressed to about 8 ° (about 7.9 to about 8.6 °).

  Here, the twist angle of the shaft 14 becomes maximum at the joint portion with the frame 12, becomes zero at the joint portion with the grip 16, and decreases linearly (linearly) from the front end to the rear end of the shaft 14.

  As one embodiment, in the shaft 14, a frame joint portion (front end) that greatly affects shuttle control (frame surface stability), and L / 3 from the front end toward the rear end (L is the total length of the shaft 14). ) By setting the torsional rigidity in the portion between the portion advanced by about 8.00E + 05 and the torsion angle to about 5 °.

  In consideration of the above points, in one embodiment, due to thickness restrictions, a prepreg sheet having a thickness of about 30 to about 100 μm or less and a resin content (RC) of about 20 to about 30% is used. It is formed. Specifically, for example, the shaft 14 has a torsional rigidity (GI) of about 8.00E + 05 at the front end, a torsional rigidity of about 5.18E + 05 at the rear end, and a torsional rigidity from the front end toward the rear end. Is formed to decrease. The torsional rigidity of the shaft 14 may decrease continuously from the front end toward the rear end, or may decrease rapidly at one or more points.

  FIG. 3 is a schematic diagram illustrating an example of bending rigidity and torsional rigidity of a badminton racket shaft according to an embodiment of the present invention. As shown in FIG. 3, the shaft 14 of the racket 10 according to one embodiment has a bending rigidity of about 5.00E + 05 and about 7.00E + 05 at the front end and the rear end, respectively, and increases from the front end toward the rear end. Has bending rigidity. The shaft 14 has a torsional rigidity of about 8.00E + 05 and about 5.00E + 05 at the front end and the rear end, respectively, and has a torsional rigidity that decreases from the front end toward the rear end.

Next, a method for manufacturing the racket 10 according to the present embodiment will be described.
First, a method for manufacturing the shaft 14 will be described with reference to FIG. FIG. 4 is a schematic view showing a specific example of a prepreg sheet used for a shaft of a badminton racket according to an embodiment of the present invention. FIG. 4 shows specific examples 1 to 3 as specific examples of the prepreg sheet used for the shaft 14 in the upper, middle, and lower stages, respectively.

(Specific example 1)
Paying attention to Example 1, the prepreg sheet 20 (prepreg sheet (1)) and the prepreg sheet 22 (prepreg sheet (2)) are used.

The prepreg sheet 20 (prepreg sheet (1)) has a length (left and right direction in FIG. 4) extending from the front end to the rear end of the mandrel. The mandrel is not shown in FIG. 4, but is formed in a columnar shape extending in the left-right direction in FIG. 4 and having substantially the same outer diameter from the front end to the rear end. The prepreg sheet 20 includes a prepreg sheet obtained by impregnating a resin in a first reinforcing fiber group extending in a direction inclined with respect to the central axis of the mandrel, and a second reinforcement extending in a direction intersecting the extending direction of the first reinforcing fiber group. A prepreg sheet formed by superimposing a prepreg sheet in which a fiber group is impregnated with a resin. Each reinforcing fiber included in the first reinforcing fiber group is disposed so as to form an angle of, for example, about 45 ° with respect to the central axis of the mandrel, and each reinforcing fiber included in the second reinforcing fiber group includes, for example, the first reinforcing fiber For example, it may be arranged so as to form an angle of about 90 ° with respect to the extending direction of each reinforcing fiber included in the fiber group. The prepreg sheet 20 functions to impart torsional rigidity to the finally obtained shaft 14.
The prepreg sheet 20 is formed, for example, as shown in FIG. First, as shown in FIG. 5 (a), a prepreg sheet 20a obtained by impregnating a first reinforcing fiber group disposed so as to extend in a direction that forms an angle of, for example, about 45 ° with respect to the central axis of the mandrel, And the prepreg sheet | seat 20b which impregnated resin to the 2nd reinforcement fiber group arrange | positioned so that it may extend in the direction which makes an angle of about 90 degrees with respect to the extending direction of a 1st reinforcement fiber group is prepared. The prepreg sheet 20a and the prepreg sheet 20b have substantially the same shape (rectangular shape). The back surface of the prepreg sheet 20a and the surface of the prepreg sheet 20b are bonded together using an adhesive. The prepreg sheet bonded in this way is cut as shown in FIG. 5 (b) so as to have a desired shape (triangular portion 20c is cut). Thereby, the trapezoidal prepreg sheet 20 shown in FIG. 4 is formed. Note that the prepreg sheets (3), (5), and (6) in specific examples described later are also formed by the same method.

  The reinforcing fibers included in each of the first reinforcing fiber group and the second reinforcing fiber group include various reinforcing fibers including, for example, carbon fibers, metal fibers, glass fibers, and aramid fibers. As the resin impregnated in the reinforcing fiber, either a thermosetting resin or a thermoplastic resin may be used. Available thermosetting resins include, for example, epoxy, pismaleimide, polyimide, phenol, and the like. Available thermoplastic resins include, for example, polyetheretherketone (PEEK), polyethersulfone (PES), polyetherimide (PEI), polyphenylene sulfide (PPS), polyamide (PA) and polypropylene (PP). including. In specific examples 2 and 3 to be described later, the same reinforcing fibers and resins as those in specific example 1 can be used as the reinforcing fibers and resins constituting the prepreg sheet.

  Returning to FIG. 4, the prepreg sheet 20 has a width that decreases from the front end 20T (corresponding to the front end of the mandrel) toward the rear end 20B (corresponding to the rear end of the mandrel). As an example, the prepreg sheet 20 has a width that linearly decreases from the front end 20T toward the rear end 20B. The prepreg sheet 20 has a width of about 8 turns around the mandrel tip at the tip 20T, and about 6 turns around the mandrel rear end at the rear end 20B. The width is as large as possible. The number of windings is considered to bring about the torsional rigidity shown in FIG. 3 in consideration of the reinforcing fiber and resin used, the thickness (inner diameter and outer diameter) of the shaft 14 finally obtained, the weight and the length, and the like. Can be determined.

  Like the prepreg sheet 20, the prepreg sheet 22 (prepreg sheet (2)) has a length (left and right direction in FIG. 4) extending from the front end to the rear end of the mandrel. The prepreg sheet 22 is a prepreg sheet in which a reinforcing fiber group extending substantially parallel to the central axis of the mandrel is impregnated with a resin. The prepreg sheet 22 functions to impart bending rigidity to the shaft 14 finally obtained. As the reinforcing fibers included in the reinforcing fiber group and the resin impregnated in the reinforcing fiber group, the same resins as those used for the prepreg sheet 20 can be used.

  The prepreg sheet 22 has a width that increases from the front end 22T (corresponding to the front end of the mandrel) toward the rear end 22B (corresponding to the rear end of the mandrel). As an example, the prepreg sheet 22 has a width that linearly increases from the front end 22T toward the rear end 22B. The prepreg sheet 22 has a width that is wound, for example, about 3 times around the tip of the mandrel at the tip 22T, and is wound around, for example, about 5 times around the rear end of the mandrel at the rear end 22B. The width is as large as possible. The number of windings is considered to bring about the bending rigidity shown in FIG. 3 in consideration of the reinforcing fiber and resin to be used, the thickness (inner diameter and outer diameter), the weight and the length of the shaft 14 finally obtained. Can be determined.

  After the prepreg sheet 20 is wound around the mandrel (first winding stage), the prepreg sheet 22 is wound around the mandrel (second winding stage). Since the prepreg sheet 20 is wound eight times and the prepreg sheet 22 is wound three times at the tip of the mandrel, two types of prepreg sheets are wound a total of 11 times. Since the prepreg sheet 20 is wound 6 times and the prepreg sheet 22 is wound 5 times at the rear end of the mandrel, two types of prepreg sheets are wound 11 times in total. As described above, since the number of windings is 11 at the front end and the rear end of the mandrel, if the thickness of the prepreg sheet 20 and the thickness of the prepreg sheet 22 are substantially the same, The thickness at the front end and the rear end is substantially the same. The width from the front end 20T to the rear end 20B of the prepreg sheet 20 and the front end 22T of the prepreg sheet 22 so that substantially the same thickness is maintained from the front end to the rear end of the shaft 14 as well as the front end and rear end of the shaft 14. To the rear end 22B is adjusted. Thereby, the formed shaft 14 has substantially the same outer diameter from the front end to the rear end.

(Specific example 2)
Focusing on the specific example 2, the prepreg sheet 24 (prepreg sheet (3)) and the prepreg sheet 26 (prepreg sheet (4)) are used. Only the difference between the prepreg sheets 24 and 26 and the prepreg sheets 20 and 22 described above will be described.

  The prepreg sheet 24 (prepreg sheet (3)) has a width that decreases from the front end 24T toward the rear end 24B. As an example, the prepreg sheet 24 includes a plurality of rectangular portions (here, three rectangular portions 24a, 24b, and 24c) having different widths. The rectangular portion 24a has the largest width, the rectangular portion 24c has the smallest width, and the rectangular portion 24b has a width between the width of the rectangular portion 24a and the width of the rectangular portion 24c. .

  The prepreg sheet 26 (prepreg sheet (4)) has a width that increases from the front end 26T toward the rear end 26B. As an example, the prepreg sheet 26 includes a plurality of rectangular portions (here, three rectangular portions 26a, 26b, and 26c) having different widths. The rectangular portion 26a has the largest width, the rectangular portion 26c has the smallest width, and the rectangular portion 26b has a width between the width of the rectangular portion 26a and the width of the rectangular portion 26c. .

  The width of each rectangular portion of the prepreg sheet 24 and the prepreg sheet 26 is such that the thickness of the shaft 14 formed by winding both prepreg sheets around a mandrel has substantially the same outer diameter from the front end to the rear end. Can be determined as appropriate. For example, when the rectangular parts 24a, 24b, 24c are wound around the mandrel by 8, 6, and 4 respectively, the rectangular parts 26a, 26b, 26c are respectively 3 times, 5 times, and 7 around the mandrel. If it is wound, the total number of windings of the prepreg sheet is 11 in any part of the mandrel. Therefore, if the thicknesses of the prepreg sheet 24 and the prepreg sheet 26 are substantially the same, the thickness of the obtained shaft 14 is also substantially the same from the front end to the rear end.

(Specific example 3)
Paying attention to Example 3, a prepreg sheet 30 (prepreg sheet (5)), a prepreg sheet 32 (prepreg sheet (6)), and a prepreg sheet 34 (prepreg sheet (8)) are used. Only the differences between these prepreg sheets 20 and 22 will be described.

The prepreg sheet 30 (prepreg sheet (5)) differs from the prepreg sheet 20 (prepreg sheet (1)) described above in that it has substantially the same width from the front end 30T to the rear end 30B.
The prepreg sheet 32 (prepreg sheet (6)) has a shorter length than the prepreg sheet 20 (prepreg sheet (1)) described above. Specifically, the prepreg sheet 32 has a length corresponding to, for example, about 1/3 of the entire length of the mandrel. The prepreg sheet 32 has substantially the same width from the front end 32T to the rear end 32B. The prepreg sheet 32 may have a linearly decreasing width at the rear end 32B.
By winding these two types of prepreg sheets around a mandrel, the resulting shaft 14 has a torsional rigidity in the portion between the front end and a portion advanced about 1/3 from the front end toward the rear end. This is larger than the torsional rigidity in the remaining (2/3 portion). In addition, the torsional rigidity in the other part (the remaining part of about 2/3) is substantially constant along the extending direction.

The prepreg sheet 34 (prepreg sheet (7)) differs from the prepreg sheet 22 (prepreg sheet (2)) described above in that it has substantially the same width from the front end 34T to the rear end 34B.
The prepreg sheet 36 (prepreg sheet (8)) has a shorter length than the prepreg sheet 22 (prepreg sheet (2)) described above. Specifically, the prepreg sheet 26 has a length corresponding to, for example, about 1/3 of the entire length of the mandrel. The prepreg sheet 36 has substantially the same width from the front end 36T to the rear end 36B. The prepreg sheet 36 may have a linearly increasing width at the tip 36T.
By winding these two types of prepreg sheets around a mandrel, the resulting shaft 14 has a bending rigidity in the portion between the rear end and a portion advanced about 1/3 from the rear end toward the front end. This is larger than the bending rigidity in the portion (the remaining portion of about 2/3). In addition, the bending rigidity in other portions (the remaining portion of about 2/3) is substantially constant along the extending direction.

  In the specific examples 1 to 3 described above, the prepreg sheet used has a thickness in the range of about 30 to about 100 μm, a resin content in the range of about 15 to about 25%, and about 24 to about It is preferable to have an elastic modulus in the range of 26 tons.

  Moreover, in each specific example, there is no limitation in the order which winds a several prepreg sheet | seat around a mandrel. For example, in the first specific example, after the prepreg sheet 20 is wound around the mandrel, the prepreg sheet 22 may be wound around the mandrel, or both prepreg sheets may be wound around the mandrel in the reverse order. This is also true of other examples. Accordingly, the technical scope of the claimed invention is that the first winding stage is executed after the second winding stage is executed, and the second winding stage is executed after the first winding stage is executed. Note that the description is intended to include both cases where the winding phase is performed.

(Other examples)
Combination of prepreg sheets (1) and (4), combination of prepreg sheets (2) and (3), combination of prepreg sheets (1), (7) and (8), prepreg sheets (1) and ( The shaft 14 can be configured by using any of the combinations of 6), (2), and (8), and the combination of the prepreg sheets (3), (6), (4), and (8). is there.

  The shaft 14 manufactured as described above can be expressed as follows. That is, the shaft 14 extends in a direction intersecting (for example, orthogonal to) the first reinforcing fiber group extending in a direction inclined with respect to the central axis of the shaft (for example, about 45 °) and the second reinforcing fiber group. A prepreg sheet in which a reinforcing fiber group is impregnated with resin is formed such that the thickness at the front end (end on the frame side) is larger than the thickness at the rear end (end on the grip side). A cylindrical member is provided. Further, the shaft 14 is constituted by a prepreg sheet in which a reinforcing fiber group extending substantially parallel to the central axis of the shaft is impregnated with a resin, and the thickness at the front end (frame side end) is the rear end (grip side end). ) And a second cylindrical member that is formed coaxially with the first cylindrical member. The first tubular member may be disposed on the second tubular member, or the second tubular member may be disposed on the first tubular member. .

In addition to this, an additional outermost layer may be formed in order to improve the impact resistance of the resulting shaft 14. The additional outermost layer is formed by a prepreg sheet obtained by impregnating a resin into reinforcing fiber groups extending substantially perpendicular to the central axis of the mandrel. As the reinforcing fiber contained in the reinforcing fiber group and the resin impregnated in the reinforcing fiber group, those mentioned above can be used.
Although glass fiber can be used as the reinforcing fiber, in this case, the hit feeling of the finally obtained racket 10 may be dull. Therefore, it is more preferable to use carbon fiber as the reinforcing fiber.

  This additional outermost layer is wound on the prepreg sheet after the prepreg sheet described with reference to FIG. 4 is wound. For example, the outermost layer has a length extending from the front end to the rear end of the mandrel, and has substantially the same width from the front end to the rear end. Thereby, the obtained shaft 14 maintains substantially the same outer diameter from the front end to the rear end.

  Thereafter, a taping process is performed. A molding tape such as polyester is spirally wound around the outer peripheral surface of the mandrel (more precisely, the prepreg sheet shown in FIG. 4 or an additional outermost layer). By this taping process, the gap generated between the prepreg sheets is removed as much as possible.

  Next, the mandrel around which the forming tape is wound by the taping process is accommodated in the pot, baked (baking process), and cured (curing process). Thereafter, the mandrel is pulled out from the laminated structure formed on the mandrel. The laminated structure is further made into a shaft 14 by performing a cutting process or a polishing process as necessary.

In the case where the above-described additional outermost layer is provided, when the outermost layer is subjected to a polishing treatment, the impact resistance of the shaft 14 is reduced as compared with the case where the outermost layer is not provided. Can be increased. Specifically, the additional outermost layer has a group of reinforcing fibers extending substantially perpendicular to the central axis of the mandrel. When considered microscopically, a minute gap is formed between adjacent reinforcing fiber groups. If an external force is applied to this gap, the additional outermost layer may be damaged. Therefore, by subjecting this additional outermost layer to polishing, at least a part of the plurality of reinforcing fibers is divided, and extends substantially perpendicular to the central axis of the mandrel from the central axis of the mandrel. To be inclined and extended. Thereby, the additional outermost layer forms a structure like a dispersion of long fibers. That is, the additional outermost layer forms a structure in which reinforcing fibers extending substantially perpendicular to the central axis of the mandrel and reinforcing fibers extending obliquely with respect to the central axis of the mandrel are mixed. Thereby, since the gap | interval produced between adjacent reinforcement fibers can be suppressed, the impact resistance of the shaft 14 can be increased.
As the outermost layer, for example, after winding the mandrel having a thickness in the range of about 30 to about 80 μm about 6 times and performing the taping process and the firing process described above, the number of windings is about 6 times. It is preferable to perform the polishing process from a thickness corresponding to 1 to a thickness that decreases to a thickness corresponding to about 3 windings.

  Next, a method of joining the shaft 14 and the frame 12 manufactured in this way will be described with reference to FIG. FIG. 6 is a schematic diagram for explaining a method of joining a shaft and a frame of a badminton racket according to an embodiment of the present invention.

  The shaft 14 and the frame 12 can be coupled using an internal pressure molding method. Since this internal pressure forming method is a method known by those skilled in the art, this method will be briefly described.

  As shown in FIG. 6, in the mold 40, an annularly extending region 42 for forming the frame 12 and a linearly extending region 44 for communicating with the region 42 and forming the shaft 14 are provided. , Is formed. The inner diameter of the region 44 is formed to be substantially the same from one end to the other end of the region 44.

  In the region 42, an uncured prepreg (which will be referred to as the frame 12 later, which will be referred to as “frame 12” for convenience) disposed in a hollow tubular shape is disposed. In the region 44, the shaft 14 that has been subjected to the firing process and the curing process described above is disposed. A belt-shaped prepreg sheet is wound around the joint 50 between the frame 12 and the shaft 14 as many times as necessary. An expandable tube 52 is inserted into the shaft 14 and the frame 12.

  Next, the tube 52 is expanded using compressed air or the like, pressure is applied from the inside of the prepreg, the prepreg is pressed against the inner wall surface of the mold, and the prepreg is heated and cured in this state. Thereby, the racket 10 is formed.

As described above, according to various embodiments of the present invention, the shaft is formed such that the torsional rigidity decreases from the front end to the rear end of the shaft, so that the frame surface is less likely to be twisted and stable when the shuttle is struck. It will be a thing. In addition, since the shaft is formed so that the bending rigidity increases from the front end to the rear end of the shaft, the shaft is appropriately bent in the vicinity of the front end to generate a repulsive force. Is thrown away.
In addition, in order to reduce the torsional rigidity from the front end of the shaft toward the rear end, a prepreg sheet having a “decreasing width” from the front end to the rear end is used, while the front end of the shaft is moved from the rear end to the rear end. In order to increase the bending rigidity, the outer diameter of the finally obtained shaft is maintained substantially constant from the front end to the rear end by using a prepreg sheet having an “increasing width” from the front end to the rear end. be able to. Thereby, the feeling of swinging can be improved while stabilizing the frame surface and increasing the repulsive force of the shaft.

  Next, a shaft having different twisting direction torques when rotated clockwise and counterclockwise will be described with reference to FIG. FIG. 7 is a schematic diagram showing a configuration of a prepreg sheet used for a shaft of a badminton racket according to an embodiment of the present invention.

  In a sport called badminton, a player sometimes performs an action of twisting a grip at the moment of hitting a shuttle. In order to manufacture a racket that can withstand such a twisting operation, the following device can be applied to the shaft.

  Here, as an example, a case will be described in which a prepreg sheet 20 'obtained by improving the prepreg sheet 20 shown in the specific example 1 of FIG. 4 is used. In addition, the detailed description is abbreviate | omitted about the structure similar to the prepreg sheet | seat 20 among the structures of the prepreg sheet | seat 20 '.

  The prepreg sheet 20 ′ shown in FIG. 7B is formed by laminating a trapezoidal prepreg sheet 20′a and a trapezoidal prepreg sheet 20′b as shown in FIG. 7A. It is. The reinforcing fiber group included in the prepreg sheet 20'a and the reinforcing fiber group included in the prepreg sheet 20'b intersect (for example, orthogonal).

The width of the prepreg sheet 20′a is formed larger than the width of the prepreg sheet 20′b so as to increase, for example, by one turn with respect to the number of turns on the mandrel. Thus, in the shaft with the prepreg sheets 20 ', twisting direction torque direction D ₁ is larger than the twisting direction torque direction D _2. Such a shaft is suitable for a right-handed player that twists the grip downward at the moment of hitting the shuttle.

On the contrary, the width of the prepreg sheet 20′a may be formed so as to be smaller than the width of the prepreg sheet 20′b, for example, by one turn with respect to the number of turns on the mandrel. . In this case, in the shaft with the prepreg sheets 20 ', twisting direction torque direction D ₂ is larger than the twisting direction torque direction D _1. Such a shaft is suitable for an operation in which the left-handed player twists the grip downward at the moment of hitting the shuttle.

  Such a method can be similarly applied to the prepreg sheet (3) and the prepreg sheets (5) and (6) used in each of the above-described specific example 2 and specific example 3.

10 Badminton racket 12 Frame (frame surface)
14 Shaft 16 Grip

Claims (3)

A shaft used for a badminton racket,
The first reinforcing fiber group extending in the direction inclined with respect to the central axis of the shaft and the prepreg sheet impregnated with resin in the second reinforcing fiber group extending in the direction intersecting the first reinforcing fiber group, A first tubular member formed such that the thickness is greater than the thickness at the rear end;
It is composed of a prepreg sheet in which a reinforcing fiber group extending substantially parallel to the central axis is impregnated with resin, and the thickness at the front end is smaller than the thickness at the rear end, and the thickness at the rear end is the first cylindrical member. A second tubular member formed to be smaller than the thickness at the tip, and disposed coaxially with the first tubular member;
Equipped with,
A shaft having substantially the same outer diameter from the front end to the rear end .   The shaft according to claim 1, wherein the second cylindrical member is disposed on the first cylindrical member.   The shaft according to claim 1, wherein the first cylindrical member is disposed on the second cylindrical member.

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