Stamping tools

Abstract

The vibrations of multiple frequency components transmitted from the striking tool to the batter's hand during a hit are reduced by a single structure built into the striking tool, thereby effectively reducing the vibrations transmitted to the batter's hand. [Solution] The striking tool 1 comprises a striking tool body 10 having a grip portion 21 and a striking portion connected to the grip portion 21. The striking tool 1 further comprises a core rod structure 11 provided as a dynamic vibration absorber, which is disposed inside the striking tool body 10 and has a core rod 25 that extends along the long axis in which the grip portion 21 and the striking portion are aligned, with at least one end fixed to the striking tool body 10. A specific set of natural frequencies (ω1, ω2) among the natural frequencies of the core rod structure 11 are set to frequencies that dampen the natural vibration of the striking tool body 10, corresponding to a specific set of natural frequencies (Ω1, Ω2) among the natural frequencies of the striking tool body 10.

Description

[Technical Field]

[0001] The present invention relates to a striking device having a grip portion and a striking portion connected to the grip portion. [Background technology]

[0002] When a ball is struck with a bat in baseball or softball, a tennis racket, or a golf club, the vibrations generated by the ball's impact with the batting part of the batting tool are transmitted to the batter's hand via the grip. To reduce the transmission of vibrations to the batter's hand during impact, batting tools equipped with mechanisms to absorb and mitigate vibrations are known.

[0003] For example, Patent Document 1 discloses a striking tool equipped with a vibration damping device on the grip portion. This vibration damping device consists of a cap 1 attached to the end of the grip portion, a protective ring 3 integrally molded with the cap 1 and provided on the cap 1, a protrusion 4 on the inside of the protective ring 3, and an auxiliary weight 6 held at the center of the protective ring 3 by the protrusion 4. By adjusting the density of the auxiliary weight 6, the natural frequency of the vibration damping device is matched to the natural frequency of the striking tool, thereby enhancing the vibration absorption effect.

[0004] Furthermore, Patent Document 2 discloses a cylindrical vibration absorbing member 1 that is attached to the grip portion of a striking tool. The vibration absorbing member 1 consists of a rod-shaped mass body 4 that acts as a vibrator and an elastic layer 5 that covers the mass body 4. The elastic layer 5 consists of an inner foamed elastic layer 6 that covers the mass body 4 and an outer elastic layer 7 that covers the inner foamed elastic layer 6 via an adhesive layer 8 and has a smaller elastic deformation range than the inner foamed elastic layer 6. The purpose is to absorb vibrations by allowing relatively free movement of the mass body 4 within the inner foamed elastic layer 6, while absorbing larger movements of the mass body 4 with the outer foamed elastic layer 7, which has a smaller elastic deformation range, thereby allowing the member to function as a vibrator and absorb vibrations. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2003-236019 [Patent Document 2] Japanese Patent Publication No. 2000-24140 [Overview of the project] [Problems that the invention aims to solve]

[0006] When hitting a ball with a batting tool, if the ball is struck off-center, the batter's hand gripping the tool will experience numbness. This numbness is thought to be caused by vibrations generated when the ball collides with the tool and transmitted to the batter's hand via the grip. When the ball is struck with the center of the tool, the tool does not vibrate significantly, and the energy of the impact is efficiently converted into the ball's kinetic energy. However, when the ball is struck off-center, a large portion of the energy of the impact is converted into vibrational energy in the tool, resulting in increased vibration. This increased vibration in the tool is then transmitted to the batter's hand, causing numbness. Since batting tools have multiple natural frequencies, the vibrations transmitted from the tool to the batter's hand during impact have multiple frequency components. Furthermore, the position where the batter grips the tool and the position where the ball collides with the batting area will affect which of these frequency components becomes more pronounced.

[0007] The vibration damping device disclosed in Patent Document 1 is configured to absorb vibrations at the natural frequency of the hitting tool by adjusting the density of an auxiliary weight 6 held at the center of a protective ring 3 in a cap 1 attached to the end of the grip portion. Therefore, it is configured to absorb vibrations at a single natural frequency of the hitting tool by adjusting it to match that natural frequency. The vibration absorbing member 1 disclosed in Patent Document 2 is configured to allow a single rod-shaped mass body 4, which acts as a vibrator, to vibrate relatively freely within an inner foamed elastic layer 6, while the outer elastic layer 7 absorbs the large movement of the mass body 4. Therefore, it is configured to absorb vibrations at a single natural frequency of the hitting tool by adjusting it to match that natural frequency. Consequently, the structures disclosed in Patent Document 1 or Patent Document 2 can only reduce the vibration of a single frequency component among the multiple frequency components of vibration generated in the hitting tool when the ball collides with it and transmitted from the grip portion to the batter's hand, making it difficult to sufficiently reduce the vibrations transmitted from the grip portion to the batter's hand. Furthermore, in order to suppress the increase in size and complexity of the structure that reduces the vibration of multiple frequency components transmitted from the batting tool to the batter's hand during impact, it is desirable that the structure be provided as a single structure built into the batting tool, rather than as multiple structures that individually reduce the vibration of multiple frequency components.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a striking tool that can reduce vibrations of multiple frequency components transmitted from the striking tool to the batter's hand during striking using a single structure built into the striking tool, thereby effectively reducing the vibrations transmitted to the batter's hand. [Means for solving the problem]

[0009] (1) The hitting tool of the present invention comprises a hitting tool body having a grip portion and a hitting portion connected to the grip portion. The hitting tool of the present invention further comprises a core rod structure provided as a dynamic vibration absorber, which is disposed inside the hitting tool body and extends along the long axis direction in which the grip portion and the hitting portion are aligned, with at least one end of the core rod fixed to the hitting tool body, wherein a specific plurality of natural frequencies among the natural frequencies of the core rod structure are set to frequencies that dampen the natural vibration of the hitting tool body, corresponding to a specific plurality of natural frequencies among the natural frequencies of the hitting tool body.

[0010] According to the above-described batting device, the vibration of the batting device is reduced by absorbing vibrations of the batting device through a core rod structure, which acts as a dynamic vibration absorber and has a core rod extending along the long axis of the batting device body with at least one end fixed to the batting device body. Furthermore, a specific set of natural frequencies in the core rod structure is set to frequencies that dampen the natural vibrations of the batting device body, corresponding to a specific set of natural frequencies in the batting device body. Therefore, the core rod structure resonates with vibrations at each natural frequency of the batting device body, thereby absorbing the natural vibrations at each natural frequency of the batting device body and reducing the vibration of the batting device body. Consequently, it is possible to reduce the vibrations of multiple frequency components that occur in the batting device body when the ball collides with the hitting part of the batting device body and are transmitted from the grip to the batter's hand. In addition, according to the above-described batting device, the structure that reduces the vibrations of multiple vibration components is configured as a core rod structure, which acts as a dynamic vibration absorber and is placed inside the batting device body, with at least one end fixed to the batting device body and having a core rod extending along the long axis of the batting device body. Therefore, the vibrations of multiple frequency components transmitted from the striking tool to the batter's hand during a hit can be reduced by a single structure built into the striking tool.

[0011] As described above, with the above configuration, it is possible to provide a striking tool that can reduce the vibrations of multiple frequency components transmitted from the striking tool to the batter's hand during hitting using a single structure built into the striking tool, thereby suitably reducing the vibrations transmitted to the batter's hand.

[0012] (2) In the striking tool described above, the core rod structure has weights attached to the core rod, and it is preferable that the position and mass of the weights attached to the core rod are adjusted so that one of a set of specific natural frequencies in the core rod structure corresponds to one of a set of specific natural frequencies in the striking tool body and dampens the natural vibration of the striking tool body. The mass of the weights can be adjusted by changing the number, material and size of the weights.

[0013] With this configuration, by adjusting the position and mass of the weight attached to the core rod, a desired natural frequency among several specific natural frequencies in the core rod structure can be easily set to a frequency that dampens a desired natural frequency among several specific natural frequencies in the striking tool body. Therefore, it becomes even easier to adjust the reduction of multiple frequency components of vibration transmitted from the striking tool to the hitter's hand during striking using a single structure built into the striking tool.

[0014] (3) In the striking tool described above, the core rod structure preferably has a plurality of weights attached to the core rod, and the plurality of weights are attached to the core rod with a gap in the longitudinal direction.

[0015] When adjusting the natural frequency of the core rod structure to a frequency that dampens the natural vibration of the striking tool body by corresponding to the natural frequency of the striking tool body, it is possible to adjust the natural frequency of the core rod structure by increasing the mass of the weights attached to the core rod by attaching multiple weights to the core rod. However, if multiple weights are attached to the core rod in contact with each other, the weights as a whole contribute to an increase in rigidity, making it difficult to lower the natural frequency of the core rod structure. In contrast, with the above configuration, the weights are attached to the core rod with gaps in between, which suppresses the contribution of the weights as a whole to an increase in rigidity. Therefore, it is possible to lower the natural frequency of the core rod structure by increasing the mass of the weights while suppressing the increase in rigidity caused by attaching multiple weights to the core rod, making it easier to adjust the natural frequency of the core rod structure.

[0016] (4) In the striking tool described above, it is preferable that the length of the core rod is adjusted so that one of the specific natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body in correspondence with one of the specific natural frequencies in the striking tool body, and that the position and mass of the weight attached to the core rod are adjusted so that another of the specific natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body in correspondence with another of the specific natural frequencies in the striking tool body.

[0017] With this configuration, by adjusting the length of the core rod, any desired natural frequency among several specific natural frequencies in the core rod structure can be easily set to a frequency that dampens any desired natural frequency among several specific natural frequencies in the striking tool body. Furthermore, by adjusting the position and mass of the weight attached to the core rod, any other desired natural frequency among several specific natural frequencies in the core rod structure can be easily set to a frequency that dampens any other desired natural frequency among several specific natural frequencies in the striking tool body. Therefore, it becomes even easier to adjust the reduction of multiple frequency components of vibration transmitted from the striking tool to the hitter's hand during striking using a single structure built into the striking tool.

[0018] (5) In the striking tool described above, it is preferable that the position in which a first weight, which is one of the multiple weights, is attached to the core rod and the mass of the first weight are adjusted so that one of the multiple specific natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body in correspondence with one of the multiple specific natural frequencies in the striking tool body, and that the position in which a second weight, which is another of the multiple weights, is attached to the core rod and the mass of the second weight are adjusted so that another of the multiple specific natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body in correspondence with another of the multiple specific natural frequencies in the striking tool body.

[0019] With this configuration, by adjusting the position and mass of the first weight attached to the core rod, any desired natural frequency among several specific natural frequencies in the core rod structure can be easily set to a frequency that dampens any desired natural frequency among several specific natural frequencies in the striking tool body. Furthermore, by adjusting the position and mass of the second weight attached to the core rod, any other desired natural frequency among several specific natural frequencies in the core rod structure can be easily set to a frequency that dampens any other desired natural frequency among several specific natural frequencies in the striking tool body. Therefore, it becomes even easier to adjust the reduction of multiple frequency components of vibration transmitted from the striking tool to the hitter's hand during striking using a single structure built into the striking tool.

[0020] (6) In the striking tool described above, it is preferable that a damping material is arranged inside the striking tool body around the core rod to dampen the vibration of the core rod.

[0021] With this configuration, since damping material is arranged around the core rod within the striking tool body, the vibration of the core rod can be quickly dampened after it begins to vibrate. Therefore, when the core rod structure resonates with the vibrations of the striking tool body at each natural frequency and absorbs the natural vibrations of the striking tool body at each natural frequency, the vibration of the resonating core rod can also be further dampened. As a result, the vibrations transmitted from the striking tool to the hitter's hand during striking can be further reduced. [Effects of the Invention]

[0022] According to the present invention, it is possible to provide a striking tool that can reduce vibrations of multiple frequency components transmitted from the striking tool to the batter's hand during a strike using a single structure built into the striking tool, thereby effectively reducing the vibrations transmitted to the batter's hand. [Brief explanation of the drawing]

[0023] [Figure 1] This figure shows a striking tool according to a first embodiment of the present invention, and is a cross-sectional view of the striking tool. [Figure 2] This figure shows the core rod structure in the striking tool shown in Figure 1. [Figure 3] This figure shows the relationship between the length of the core rod and the natural frequency in a core rod structure. [Figure 4] This figure shows the core rod structure of a striking tool according to a second embodiment of the present invention. [Figure 5] This figure shows the core rod structure of a striking tool according to the third embodiment of the present invention. [Figure 6] This figure shows the test results for the striking tool of Example 1, and is a diagram showing the vibration acceleration waveform during the hammering test. [Figure 7] This figure shows the test results for the striking tool of Example 1, and is a power spectrum obtained from the vibration acceleration waveform obtained in the hammering test. [Figure 8] This figure shows the core rod structure of the striking tool in Example 2. [Figure 9] This figure shows the test results for the striking tool of Example 2, and is a diagram showing the vibration acceleration waveform during the hammering test. [Figure 10] This figure shows the test results for the striking tool of Example 2, and is a power spectrum obtained from the vibration acceleration waveform obtained in the hammering test. [Modes for carrying out the invention]

[0024] The embodiments for carrying out the present invention will be described below with reference to the drawings. The present invention is a striking tool that comprises a striking tool body having a grip portion and a striking portion connected to the grip portion, and can be widely applied to various uses. Examples of striking tools to which the present invention can be applied include baseball bats, softball bats, tennis rackets, golf clubs, and the like.

[0025] [First Embodiment] (batting tool) Figure 1 is a diagram showing a striking tool 1 according to a first embodiment of the present invention, and is a diagram showing a cross-section of the striking tool 1. In Figure 1, the striking tool 1 of this embodiment is illustrated as being configured as a baseball bat. The striking tool 1 comprises a striking tool body 10 and a core rod structure 11. The striking tool body 10 has a grip portion 21 and a hitting portion 22 arranged alongside the grip portion 21 and connected to the grip portion 21. The core rod structure 11 is arranged inside the striking tool body 10 and is provided as a dynamic vibration absorber that dampens the natural vibrations of multiple modes in the striking tool body 10.

[0026] (Striking tool body) The batting tool body 10 is provided as the body of a baseball bat, and in this embodiment, it has a hollow structure with an internal space extending from the grip portion 21 to the hitting portion 22. The grip portion 21 of the batting tool body 10 is the part that is held by the batter, and the hitting portion 22 of the batting tool body 10 is the part that collides with the ball and directly hits the ball when the batting tool 1 is used to strike the ball. In the batting tool body 10, a tapered portion 23 is provided between the grip portion 21 and the hitting portion 22, which has a larger diameter than the grip portion 21. That is, the grip portion 21 and the hitting portion 22 are connected via the tapered portion 23, and the grip portion 21, tapered portion 23, and hitting portion 22 are arranged in series and provided as a single unit. The materials forming the grip portion 21, tapered portion 23, and hitting portion 22 of the batting tool body 10 are metal, wood, or CFRP (Carbon Fiber Reinforced Plastic), for example, an aluminum alloy.

[0027] Furthermore, the striking tool body 10 is equipped with an end knob 24 that is attached to the grip portion 21 so as to close the end of the hollow cylindrical grip portion 21. The end knob 24 is attached to the grip portion 21 so as to close the end of the grip portion 21 opposite to the hitting portion 22. One end of the core rod 25, described later in the core rod structure 11, is fixed to the end knob 24. The material of the end knob 24 is a resin material, a composite material such as CFRP, or a metal material, and in this embodiment, the end knob 24 is made of a resin material, for example. The striking tool body 10 is also equipped with a cap member 29 that is attached inside the grip portion 21. The other end of the core rod 25, described later in the core rod structure 11, is fixed to the cap member 29. The material of the cap member 29 is a resin material, a composite material such as CFRP, or a metal material, and in this embodiment, the cap member 29 is made of a resin material, for example.

[0028] (core rod structure) Figure 2 is a diagram showing the core rod structure 11 in the striking tool 1, and is an enlarged view of the core rod structure 11 and its surrounding area in Figure 1. The core rod structure 11 is provided as a dynamic vibration absorber that is placed inside the striking tool body 10 and dampens the natural vibrations of multiple modes in the striking tool body 10. In this embodiment, the core rod structure 11 is provided inside the hollow cylindrical grip portion 21 of the striking tool body 10. The core rod structure 11 comprises a core rod 25, a weight 26, and a cylindrical member 27.

[0029] The core rod 25 extends along the long axis direction of the striking tool body 10, which is the direction in which the grip portion 21 and the striking portion 22 are aligned in a straight line, and at least one end of the core rod 25 is fixed to the striking tool body 10. In this embodiment, the core rod 25 extends linearly along the long axis direction of the striking tool body 10 within the grip portion 21 of the striking tool body 10, and both ends of the core rod 25 in the long axis direction are fixed to the striking tool body 10. The core rod 25 is preferably made of a metal material, but may be made of a material other than metal, such as a composite material such as CFRP or a resin material. In this embodiment, the core rod 25 is made of a metal material, for example, it is made of a rod-shaped member made of brass. The core rod 25 is provided as a round rod-shaped member that extends linearly with a substantially circular cross-section, and in this embodiment, it is provided as a screw shaft with a thread formed along its entire length in the long axis direction to facilitate the attachment of the weight 26. Furthermore, the core rod 25 is not limited to a round rod shape with a circular cross-section of a uniform diameter, but may also be formed in a shape in which the diameter changes along the long axis and the middle part bulges out.

[0030] One end of the core rod 25 in the longitudinal direction is fixed to the striking tool body 10 by being secured to an end knob 24 attached to the end of the grip portion 21. The end knob 24 of the striking tool body 10 has a thick, disc-shaped basic outer shape, and one end face of the end knob 24 is provided with a cylindrical wall portion 24a into which the end of the grip portion 21 fits. The end knob 24 is attached to the grip portion 21 by fitting the end of the grip portion 21 into the cylindrical wall portion 24a with the outer circumference of the end of the grip portion 21 in close contact with the inner circumference of the cylindrical wall portion 24a. The end knob 24 is also provided with a protrusion 24b on the inside of the cylindrical wall portion 24a that fits onto a cylindrical member 27 inserted into the grip portion 21. The protrusion 24b has a hexagonal prism-shaped recess 24c on its inner circumference into which a hexagonal nut 28a is fitted. A nut 28a is fitted into the recess 24c, and the nut 28a is fixed to the recess 24c with adhesive. A hole 24d is formed at the bottom of the recess 24c into which one end of the core rod 25 is inserted. One end of the core rod 25 is fixed to the end knob 24 by screwing it into the hole 24d and simultaneously screwing it into the nut 28a fixed in the recess 24c against the protrusion 24b. The end knob 24 is made of resin, and the end of the core rod 25, which is provided as a metal screw shaft, is inserted into the hole 24d while rotating, causing the inner circumference of the hole 24d to be threaded, and the end of the core rod 25 to screw into the end knob 24. The end knob 24, with one end of the core rod 25 fixed to it, is attached to the grip portion 21, thereby fixing one end of the core rod 25 to the grip portion 21.

[0031] The other end of the core rod 25 in the longitudinal direction is fixed to the striking tool body 10 by being fixed to a cap member 29 attached inside the grip portion 21. The cap member 29 of the striking tool body 10 has a basic cylindrical shape and is made of resin material. The cap member 29 is provided with a disc-shaped large-diameter portion 29a that fits onto the inner circumference of the grip portion 21, and a small-diameter portion 29b that is provided concentrically with the large-diameter portion 29a and extends cylindrically in a stepped manner relative to the large-diameter portion 29a. The small-diameter portion 29b is formed to fit onto a cylindrical member 27 inserted into the grip portion 21. The small-diameter portion 29b has a hexagonal prism-shaped recess 29c on its inner circumference into which a hexagonal nut 28b is fitted. The nut 28b is fitted into the recess 29c and fixed to the recess 29c with adhesive. Furthermore, a hole 29d is formed at the bottom of the recess 29c into which one end of the core rod 25 is inserted. The other end of the core rod 25 is fixed to the cap member 29 by screwing it into the hole 29d while simultaneously screwing it into the nut 28b fixed to the small diameter portion 29b in the recess 29c. The cap member 29 is made of resin, and as the end of the core rod 25, which is provided as a metal screw shaft, is rotated and inserted into the hole 29d, the inner circumference of the hole 29d is threaded, and the end of the core rod 25 is screwed into the cap member 29. The cap member 29, to which the other end of the core rod 25 is fixed, is attached to the grip portion 21, thereby fixing the other end of the core rod 25 to the grip portion 21.

[0032] The cylindrical member 27 is provided as a cylindrical member formed of a resin material, and in this embodiment, it is formed of acrylic resin. A core rod 25 is arranged inside the cylindrical member 27, and end knobs 24 and cap members 29 are attached to both ends of the cylindrical member 27 in the longitudinal direction. The cylindrical member 27, with the core rod 25 arranged inside and the end knobs 24 and cap members 29 attached to both ends, is attached to the striking tool body 10 by being inserted into and fitted into the grip portion 21. When the core rod 25, end knobs 24 and cap members 29 are attached to the cylindrical member 27, for example, first, one end of the core rod 25 is screwed into the end knob 24 to which a nut 28a is fixed. Next, the core rod 25 attached to the end knob 24 is inserted into the cylindrical member 27, and the protrusion 24b of the end knob 24 is fitted into and fixed to one end of the cylindrical member 27. Subsequently, the small-diameter portion 29b of the cap member 29, to which the nut 28b is attached, is fitted onto the other end of the cylindrical member 27 while rotating, and the other end of the spindle 25 is screwed into the cap member 29. At this time, the large-diameter portion 29a of the cap member 29 abuts against the end face of the other end of the cylindrical member 27, so that the cylindrical member 27 is fixed to the end knob 24 and the cap member 29, sandwiched between the end knob 24 and the cap member 29, which are connected via the spindle 25. The cylindrical member 27, to which the spindle 25, end knob 24 and cap member 29 are attached, is inserted into the grip portion 21 and fitted into the grip portion 21 in a state where it slides against the inner circumference of the grip portion 21. The cylindrical member 27 is fitted into the grip portion 21 until the end of the grip portion 21 fits into the cylindrical wall portion 24a of the end knob 24 and the end knob 24 is attached to the grip portion 21.

[0033] The weight 26 is attached to the core rod 25 and is provided to adjust the natural frequency of the core rod structure 11, as will be described later. The weight 26 is preferably made of a metal material, but may be made of a material other than metal, such as a composite material like CFRP, a resin material, silicone, rubber, or urethane. In this embodiment, the weight 26 is made of a metal material and is provided as a nut made of brass, for example. The weight 26, provided as a brass nut, is attached to the core rod 25, which is provided as a screw shaft, by screwing it in. The position and amount of the weight 26 attached to the core rod 25 are adjusted so that the natural frequency of the core rod structure 11 is set to the desired frequency, as will be described later. The weight 26, whose position on the core rod 25 has been adjusted, is fixed to the core rod 25 by being secured by welding or pinning to prevent rotation.

[0034] Furthermore, in the core rod structure 11, one or more weights 26 are provided to be attached to the core rod 25. If there are multiple weights 26, they are attached to the core rod 25 with a gap in the longitudinal direction. If the weights 26 are attached to the core rod 25 in a state of contact and lined up, the weights 26 as a whole will contribute to an increase in rigidity, increasing the rigidity of the core rod structure 11 and making it difficult to adjust the natural frequency of the core rod structure 11. However, by attaching the weights 26 to the core rod 25 with a gap in between, it is possible to easily adjust the natural frequency of the core rod structure 11 while suppressing the increase in rigidity of the weights 26 as a whole. The dimension of the gap between adjacent weights 26 attached to the core rod 25 in the longitudinal direction is preferably 0.25 mm or more in order to avoid contact between the weights 26 when the core rod structure 11 vibrates.

[0035] Furthermore, a cylindrical member 27, to which a core rod 25 with a weight 26 attached is positioned on the inside and end knobs 24 and cap members 29 are attached to both ends, is filled with a damping material 30 to dampen the vibration of the core rod 25. The damping material 30 filled inside the cylindrical member 27 is preferably a material such as gel, wax, or oil, but any material that can dampen the vibration of the core rod 25 is acceptable, and may be a granular material or other viscous liquid material. In the striking tool 1, because the cylindrical member 27 is filled with damping material 30, the damping material 30 that dampens the vibration of the core rod 25 is arranged around the core rod 25 inside the striking tool body 10. In this embodiment of the striking tool 1, the damping material 30 that dampens the vibration of the core rod 25 is arranged around the core rod 25, but a form in which the damping material 30 is not arranged may also be implemented. In other words, a form of the striking tool 1 may be implemented in which the inside of the cylindrical member 27 is not filled with damping material 30, and the inside of the striking tool body 10 is not equipped with damping material 30 to dampen the vibration of the core rod 25. Also, although a cylindrical member 27 is provided in the striking tool 1 of this embodiment, a form of the striking tool 1 may be implemented in which the cylindrical member 27 is not provided.

[0036] In this embodiment of the striking tool 1, a damping material 30 made of a material such as gel, wax, or oil is filled into the cylindrical member 27, so that the damping material is arranged around the core rod 25 over almost the entire length of the core rod 25. However, a configuration in which the damping material is arranged partially around the core rod 25 may also be implemented. In this case, the damping material made of a material such as urethane, silicone, or rubber may be attached to the core rod 25 so as to partially cover the area around the core rod 25. When such damping material is attached to the core rod 25, it is preferable that the damping material be attached to the core rod 25 so as to cover the area around the weight 26 at the part of the core rod 25 to which the weight 26 is attached. This allows the vibration of the core rod 25 to be efficiently dampened by the damping material.

[0037] The mandrel structure 11 is configured as a dynamic vibration absorber that suppresses the natural vibrations of a plurality of modes in the striking tool body 10. In order to suppress the natural vibrations of a plurality of modes in the striking tool body 10, in the striking tool 1, among the natural frequencies ω of the mandrel structure 11, a specific plurality of natural frequencies ω i are set to the vibration frequencies that suppress the natural vibrations of the striking tool body 10 corresponding respectively to a specific plurality of natural frequencies Ω among the natural frequencies Ω of the striking tool body 10. i Here, the natural frequency ω of the mandrel structure 11 i represents the vibration frequency of the natural vibration of the i-th mode in the mandrel structure 11, and i represents any one of natural numbers such as 1, 2, 3, ···. Similarly, the natural frequency Ω of the striking tool body 10 i represents the vibration frequency of the natural vibration of the i-th mode in the striking tool body 10, and i represents any one of natural numbers such as 1, 2, 3, ···. i Note that i representing the order of the mode of the natural vibration at the natural frequency Ω of the striking tool body 10 and i representing the order of the mode of the natural vibration at the natural frequency ω i of the mandrel structure 11 both simply represent any natural number, including cases where the orders match and cases where they do not. Therefore, the order of the mode of the natural vibration at the natural frequency Ω i of the striking tool body 10 to be suppressed and the natural frequency ω i of the mandrel structure 11 set to the vibration frequency that suppresses the natural vibration of the striking tool body 10 corresponding to that natural frequency Ω i may or may not match in the order of the mode of the natural vibration. That is, the natural frequency ω i of the mandrel structure 11 that suppresses the natural vibration of the striking tool body 10 is merely set to the vibration frequency that suppresses the natural vibration of the striking tool body 10 corresponding to any i-th mode natural frequency Ω i of the striking tool body 10, and the order of the mode of the natural vibration at the natural frequency ω i of the mandrel structure 11 and the order of the mode of the natural vibration at the natural frequency Ω i of the striking tool body 10 may or may not match. [[]]

[0038] [[]] [[]]The striking tool body 10 has numerous natural frequencies Ω, such as the first natural frequency Ω1, which is the natural frequency of the first mode; the second natural frequency Ω2, which is the natural frequency of the second mode; the third natural frequency Ω3, which is the natural frequency of the third mode; and so on. In the striking tool 1, a specific set of natural frequencies Ω among the natural frequencies Ω possessed by the striking tool body 10 are used. i The natural vibrations at the core rod structure 11 are damped. Multiple specific natural frequencies Ω are damped. i For example, the primary natural frequency Ω1 of the first mode, which has a large amplitude of vibration, and the secondary natural frequency Ω2 of the second mode are selected. The core rod structure 11 has many natural frequencies ω, such as the primary natural frequency ω1, which is the natural frequency of the first mode, the secondary natural frequency ω2, which is the natural frequency of the second mode, the tertiary natural frequency ω3, which is the natural frequency of the third mode, and so on. In the striking tool 1, a specific set of natural frequencies ω among the natural frequencies ω of the core rod structure 11 are selected. i However, the striking tool body 10 has several specific natural frequencies Ω i Each of these is set to a frequency that dampens the natural vibration of the striking tool body 10. The specific multiple natural frequencies Ω of the striking tool body 10 that are damped are set accordingly. i If the primary natural frequency is Ω1 and the secondary natural frequency is Ω2, then a specific set of natural frequencies ω in the core rod structure 11 iFor example, the natural frequencies of any two specific modes are selected, such as the primary natural frequency ω1 and the secondary natural frequency ω2, or the secondary natural frequency ω2 and the tertiary natural frequency ω3, or the tertiary natural frequency ω3 and the quaternary natural frequency ω4, etc. Then, for example, the primary natural frequency ω1 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. Alternatively, the secondary natural frequency ω2 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the tertiary natural frequency ω3 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. Alternatively, the tertiary natural frequency ω3 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the quaternary natural frequency ω4 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0039] (Setting the natural frequency of the core rod structure) Next, the specific natural frequencies ω of the core rod structure 11 i This section explains the settings. Specific multiple natural frequencies ω of the core rod structure 11 i This refers to a specific set of natural frequencies Ω of the striking tool body 10. i The vibration frequencies corresponding to each of these are set to dampen the natural vibration of the striking tool body 10. Specific multiple natural frequencies ω of the core rod structure 11 i When setting this, first, the natural frequency Ω of the striking tool body 10 i The natural frequency Ω of the striking tool body 10 is measured. iThis is measured by performing a hammering test on the striking tool body 10 without the core rod structure 11 attached. In the hammering test, the striking tool body 10 is suspended by a string, an accelerometer is attached to the grip portion 21 of the striking tool body 10, the striking portion 22 of the striking tool body 10 is vibrated with a hammer, and the acceleration of the vibration of the striking tool body 10 when vibrated with the hammer is measured with the accelerometer. The power spectrum is calculated from the acceleration waveform obtained from the accelerometer measurement. That is, the power for each frequency is determined by performing an FFT analysis on the acceleration waveform obtained as the power of the time signal, and the power spectrum is calculated. Then, based on the obtained power spectrum, the natural frequency Ω of the striking tool body 10 is determined. i This is checked. Note that if the desired natural vibrations to be damped are, for example, the natural vibrations of the first mode and the natural vibrations of the second mode, the natural frequency Ω of the striking tool body 10 to be measured should be determined. i The primary natural frequency Ω1 and the secondary natural frequency Ω2 are measured.

[0040] Natural frequency Ω of the striking tool body 10 i Once obtained, the known mass m is then added to the striking tool body 10. a Add a known mass m a The natural frequency Ω of the striking tool body 10 with the added component ai Measure the mass m. a The natural frequency Ω of the striking tool body 10 with the added component ai The known mass m a This represents the frequency of the i-th mode natural vibration in the striking tool body 10 to which the element is attached, where i is one of the natural numbers such as 1, 2, 3, ..., and the known mass m a The natural frequency Ω of the striking tool body 10 with the added component ai The measurement is the natural frequency Ω of the striking tool body 10. i Similar to the measurement, the vibration acceleration waveform is obtained by a hammering test, and the power spectrum is calculated by performing FFT analysis on that acceleration waveform. Based on the obtained power spectrum, the known mass m a The natural frequency Ω of the striking tool body 10 with the added component ai Check.

[0041] Natural frequency Ω of the striking tool body 10i and known mass m a The natural frequency Ω of the striking tool body 10 with the added component ai Once obtained, the equivalent mass M can be calculated using the mass-sensitive method in the following equation (1). i The equivalent mass M is calculated. i This is the equivalent mass in the i-th mode of vibration, where i represents one of the natural numbers such as 1, 2, 3, ... JPEG2026082472000002.jpg22153 Next, the equivalent mass M obtained using equation (1) above. i The mass m of the core rod structure 11, which is a dynamic vibration absorber. d Therefore, the mass ratio μ is calculated using the following equation (2). i Calculate the mass ratio μ. i This is the mass ratio in the i-th mode of vibration, where i represents one of the natural numbers such as 1, 2, 3, ... JPEG2026082472000003.jpg19153

[0042] Then, the mass ratio μ obtained by equation (2) above i The natural frequency Ω of the striking tool body 10, measured based on the hammering test. i Therefore, the natural frequency ω of the core rod structure 11 is given by equation (3) below. i The optimal natural frequency f is the natural frequency of the core rod structure 10 that is referenced when setting the optimal natural frequency. i This calculates the natural frequency ω of the core rod structure 11. i The natural frequency Ω of the striking tool body 10 i The optimal natural frequency f of the core rod structure 11 is referenced when setting the frequency to dampen the natural vibration of the striking tool body 10 in accordance with this setting. i The optimal natural frequency f is calculated using the following equation (3). i This is the optimal natural frequency of the i-th mode, where i represents one of the natural numbers such as 1, 2, 3, ... JPEG2026082472000004.jpg18153 The optimal natural frequency f of the core rod structure 11, obtained by equation (3) above, is determined by equation (3). i The natural frequency Ω of the striking tool body 10 is iThis is the median frequency that dampens the natural vibration of the striking tool body 10. Natural frequency ω of the core rod structure 11 i The optimal natural frequency f is obtained using equation (3) above. i Or the optimal natural frequency f i The frequency is set to fall within a range of a predetermined percentage change relative to ω. Natural frequency ω of the core rod structure 11 i The optimal natural frequency is f i Or the optimal natural frequency f i By setting the frequency to fall within a predetermined range of change relative to the value, the natural frequency Ω of the striking tool body 10 is achieved. i The frequency is set to a frequency that dampens the natural vibration of the striking tool body 10 in accordance with this. Furthermore, experimental results were obtained from the sensations felt by the batter in their hand when the striking tool 1 held by the batter is vibrated, and the natural frequency ω of the core rod structure 11 was determined to be i However, the optimal natural frequency f i By setting the frequency to fall within a range of ±15% of the original frequency, the natural frequency Ω of the striking tool body 10 is achieved. i It was confirmed that the natural vibration of the striking tool body 10 can be effectively dampened in response to this. Therefore, the natural frequency ω of the core rod structure 11 i The optimal natural frequency f is obtained using equation (3) above. i By setting the frequency to fall within a range of ±15% of the original frequency, the natural frequency Ω of the striking tool body 10 is achieved. i The frequency may be set to a frequency that dampens the natural vibration of the striking tool body 10 in accordance with this. Furthermore, in order to further dampen the natural vibration of the striking tool body 10, the natural frequency ω of the core rod structure 11 may be set. i The optimal natural frequency is f i The frequency may be set to a range of ±10% relative to the value, and more preferably, the optimal natural frequency f i The frequency may be set to fall within a range of ±5% of the value.

[0043] (Adjustment of the natural frequency of the core rod structure) Next, the natural frequency ω of the core rod structure 11 i The frequency that dampens the natural vibration of the striking tool body 10 is the optimal natural frequency f, which can be determined by equation (3) above. i Or the optimal natural frequency fi In order to set the frequency within the range of a predetermined rate of change with respect to, the natural frequency ω of the mandrel structure 11 i will be described. That is, the natural frequency ω of the mandrel structure 11 i is set to the frequency that damps the natural vibration of the striking tool body 10 corresponding to the natural frequency Ω of the striking tool body 10, the natural frequency ω of the mandrel structure 11 i will be described. As a method for adjusting the natural frequency ω of the mandrel structure 11 i will be described. As a method for adjusting the natural frequency ω of the mandrel structure 11 i there are five methods of the following adjustment methods (i) to (v).

[0044] Adjustment method (i) is a method of adjusting the natural frequency ω of the mandrel structure 11 by adjusting the length of the mandrel 25 i By shortening the length of the mandrel 25, the natural frequency ω of the mandrel structure 11 can be adjusted to increase, and by lengthening the length of the mandrel 25, the natural frequency ω of the mandrel structure 11 i can be adjusted to decrease. i

[0045] Adjustment method (ii) is a method of adjusting the natural frequency ω of the mandrel structure 11 by changing the types of the mandrel 25 and the weight 26 by changing the material, size, etc. to adjust the mass of the mandrel 25 and the weight 26 i By reducing the mass of the mandrel 25 and the weight 26, the natural frequency ω of the mandrel structure 11 can be adjusted to increase, and by increasing the mass of the mandrel 25, the natural frequency ω of the mandrel structure 11 i can be adjusted to decrease. i [[ID=3l]]

[0046] Adjustment method (iii) is a method of adjusting the natural frequency ω of the mandrel structure 11 by changing the number of weights 26 attached to the mandrel 25 to adjust the mass of the weight 26 i By reducing the number of weights 26 and reducing the mass of the weight 26, the natural frequency ω of the mandrel structure 11 can be adjusted to increase, and by increasing the number of weights 26 and increasing the mass of the weight 26, the natural frequency ω of the mandrel structure 11 i can be adjusted to increase, and by increasing the number of weights 26 and increasing the mass of the weight 26, the natural frequency ω of the mandrel structure 11" iIt can be adjusted to decrease.

[0047] Adjustment method (iv) is a method of adjusting the natural frequency ω of the mandrel structure 11 by adjusting the position of the weight 26 attached to the mandrel 25. By adjusting the position of the weight 26 attached to the mandrel 25 to approach the node of vibration, the natural frequency ω of the mandrel structure 11 i can be adjusted to increase, and by adjusting the position of the weight 26 attached to the mandrel 25 to approach the antinode of vibration, the natural frequency ω of the mandrel structure 11 i can be adjusted to decrease. i It can be adjusted to decrease.

[0048] Adjustment method (v) is a method of adjusting the natural frequency ω of the mandrel structure 11 by adjusting the tension applied to the mandrel 25. By adjusting the tension applied to the mandrel 25 to increase, the natural frequency ω of the mandrel structure 11 i can be adjusted to increase, and by adjusting the tension applied to the mandrel 25 to decrease, the natural frequency ω of the mandrel structure 11 i can be adjusted to decrease. In the mandrel structure 11, for the end knob 24 and the cap member 29 that are arranged sandwiching the cylindrical member 27 and the both ends of the mandrel 25 are screwed respectively, by relatively rotating the mandrel 25 in the direction of screwing into each of them, the tension applied to the mandrel 25 can be adjusted to increase. Also, by relatively rotating the end knob 24 and the cap member 29 in the direction in which the mandrel 25 comes off from the end knob 24 and the cap member 29, the tension applied to the mandrel 25 can be adjusted to decrease.

[0049] The natural frequency ω of the mandrel structure 11 i is set to the vibration frequency that damps the natural vibration of the tool body 10 corresponding to the natural frequency Ω of the tool body 10. When adjusting the natural frequency ω of the mandrel structure 11 <00​​​​​​This adjusts the following: that is, a specific set of natural frequencies ω in the core rod structure 11. i The striking tool body 10 has a specific set of natural frequencies Ω i In order to set the vibration frequency of the striking tool body 10 to a frequency that dampens the natural vibration corresponding to each of these, the natural frequency ω of the core rod structure 11 i When adjusting, select one or more of the adjustment methods (i) to (v) described above, and specify a number of natural frequencies ω in the core rod structure 11. i This is adjusted. Once this adjustment is complete, a specific set of natural frequencies ω in the core rod structure 11 will be determined. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The vibration frequencies corresponding to each of these are set to dampen the natural vibration of the striking tool body 10.

[0050] In the striking tool 1 of this embodiment, by adjusting the length of the core rod 25, a specific set of natural frequencies ω in the core rod structure 11 are achieved. i One of the natural frequencies ω i However, there are several specific natural frequencies Ω in the striking tool body 10. i Any of the natural frequencies Ω i The vibration frequency is set to a frequency that dampens the natural vibration of the striking tool body 10 in accordance with this. In the striking tool 1 of this embodiment illustrated in Figures 1 and 2, there are a specific set of multiple natural vibration frequencies ω in the core rod structure 11. i The primary natural frequency ω1 and the secondary natural frequency ω2 are identified, and a specific set of natural frequencies Ω in the striking tool body 10 are identified. i The primary natural frequency Ω1 and the secondary natural frequency Ω2 have been identified. In the striking tool 1, by adjusting the length of the core rod 25, one of the specific secondary natural frequencies (ω1, ω2) in the core rod structure 11, which is ω2, corresponds to one of the specific secondary natural frequencies (Ω1, Ω2) in the striking tool body 10, and is set to a frequency that dampens the natural vibration of the striking tool body 10.

[0051] Furthermore, in the striking tool 1 of this embodiment, by adjusting the position and mass of the weight 26 attached to the core rod 25, a specific set of natural frequencies ω in the core rod structure 11 can be achieved. i Other natural frequencies among them ω i However, there are several specific natural frequencies Ω in the striking tool body 10. i Other natural frequencies among them Ω i The frequency is set to a frequency that dampens the natural vibration of the striking tool body 10 in accordance with this. As described above, in the striking tool 1 of this embodiment illustrated in Figures 1 and 2, there are a specific set of multiple natural frequencies ω in the core rod structure 11. i The primary natural frequency ω1 and the secondary natural frequency ω2 are identified, and a specific set of natural frequencies Ω in the striking tool body 10 are identified. i The primary natural frequency Ω1 and the secondary natural frequency Ω2 have been identified. In the striking tool 1, by adjusting the position and mass of the weight 26 attached to the core rod 25, one of the other primary natural frequencies (ω1, ω2) in the core rod structure 11, ω1, is set to a frequency that dampens the natural vibration of the striking tool body 10, corresponding to one of the other primary natural frequencies (Ω1, Ω2) in the striking tool body 10.

[0052] Here, in the striking tool 1, the optimal natural frequency f, which is obtained by equation (3) above, corresponds to the frequency that dampens the natural vibration of the striking tool body 10, with a specific set of natural frequencies (ω1, ω2) in the core rod structure 11 corresponding to a specific set of natural frequencies (Ω1, Ω2) in the striking tool body 10. i Or the optimal natural frequency f i Further explanation will describe a specific example of adjusting the natural frequencies (ω1, ω2) of the core rod structure 11 in order to set the frequency to fall within a predetermined range of change.

[0053] In adjusting the natural frequencies (ω1, ω2) of the core rod structure 11, first, the type of core rod 25 is selected considering the material and diameter of the core rod 25, and then the type of weight 26 is selected considering the material and size of the weight 26. If a compact structure is desired by shortening the length of the core rod 25, a core rod 25 with a small diameter and high specific gravity is selected. In the striking tool 1 of this embodiment, for example, a brass screw shaft with a diameter of 4 mm is selected as the core rod 25, and a brass nut that screws onto the core rod 25 is selected as the weight 26.

[0054] After selecting the type of core rod 25 and weight 26, several core rods 25 of different lengths are prepared, and a hammering test is performed on each of the several lengths of core rods 25 to measure the vibration acceleration of each length of core rod 25. For example, if the core rod 25 is made of brass with a diameter of 4 mm, five lengths of core rods 25 of 10 cm, 15 cm, 20 cm, 25 cm, and 30 cm are prepared, and a hammering test is performed on each length of core rod 25 to measure the vibration acceleration. In the hammering test, each of the five lengths of core rods 25 is suspended by a string, an accelerometer is attached to the end, and it is excited with a hammer, and the vibration acceleration of the core rod 25 when excited with the hammer is measured with the accelerometer.

[0055] After obtaining the acceleration waveforms for each of the five core rods 25 of different lengths by measurement with an accelerometer, the power spectrum of each core rod 25 of each length is calculated from the obtained acceleration waveforms. Then, based on the obtained power spectrum, the natural frequency ω of each core rod 25 is determined. i Check the natural frequencies ω of the core rods 25 of each length. i Upon checking, based on the results of that check, the length of the core rod 25 and the natural frequency of each mode (natural frequency ω) i An approximate formula is created for the relationship between the length of the core rod 25 and the natural frequency ω. Figure 3 shows the relationship between the length of the core rod 25 and the natural frequency ω. i This figure shows the relationship. Figure 3 shows the natural frequencies ω of each mode confirmed for each of the five lengths of core rods 25. i Each is represented by a symbol, and the length of the core rod 25 and the natural frequency ω of each mode are shown. iThe approximation curve showing the relationship is shown as a solid line, and the approximation formula is also displayed. Specifically, in Figure 3, the natural frequencies (ω1, ω2, ω3) of the first, second, and third modes, which were confirmed for each of the five lengths of the core rod 25, are shown as circles, squares, and triangles, respectively, and the approximation curve showing the relationship between the length of the core rod 25 and the natural frequencies (ω1, ω2, ω3) of each mode, along with the approximation formula, is displayed.

[0056] As shown in Figure 3, the length of the core rod 25 and the natural frequency ω of each mode i Once an approximate formula showing the relationship is obtained, the length of the core rod 25 is determined based on this approximate formula such that the second natural frequency ω2, which is the frequency of the natural vibration of the second mode of the core rod 25, falls within the range of the optimal natural frequency f2 obtained by equation (3) above or a frequency that changes by a predetermined ratio relative to the optimal natural frequency f2. That is, based on the obtained approximate formula, the length of the core rod 25 is determined such that the second natural frequency ω2 of the core rod 25 corresponds to the second natural frequency Ω2 of the striking tool body 10 and dampens the natural vibration of the second mode of the striking tool body 10. In the core rod structure 11 of the striking tool 1, the core rod 25 is attached to the striking tool body 10 with both ends fixed, but a configuration in which the core rod 25 is attached to the striking tool body 10 with one end fixed may also be implemented. When the core rod 25 is fixed to the striking tool body 10 on one side, the secondary natural frequency Ω2 of the core rod 25 is theoretically 0.357 times that of the case where both ends are fixed. Therefore, when the core rod 25 is fixed to the striking tool body 10 on one side, the length of the core rod 25 is determined by considering that the secondary natural frequency Ω2 is 0.357 times that of the case where both ends are fixed.

[0057] Furthermore, to determine the length of the core rod 25, hammering tests were performed on multiple core rods 25 of different lengths to obtain acceleration waveforms and calculate the power spectrum, and the natural frequency ω was determined. i Check the length of the core rod 25 and the natural frequency ω of each mode. i An example was given of creating an approximate formula for the relationship and determining the length of the core rod 25 based on that approximate formula, but the length of the core rod 25 can also be determined by other methods. The natural frequency ω of a uniform rodi The theoretical value can be calculated using the rod length, Young's modulus, moment of inertia, and density. Therefore, a hammering test was performed on a core rod 25 of one length to obtain the acceleration waveform and calculate the power spectrum, and the natural frequency ω i The natural frequency ω is calculated as the theoretical value mentioned above. i By making adjustments to this, the length of the core rod 25 and the natural frequency ω of each mode are determined. i Alternatively, an equation can be created regarding the relationship between the two, and the length of the core rod 25 can be determined based on that equation.

[0058] By adjusting the length of the core rod 25 to the length determined as described above, the secondary natural frequency ω2 of the core rod 25 is adjusted to a frequency that dampens the natural vibration of the second mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. After the secondary natural frequency ω2 of the core rod 25 is adjusted, the primary natural frequency ω1 of the core rod structure 11 is then adjusted by the weight 26. When the primary natural frequency ω1 of the core rod structure 11 is adjusted by the weight 26, the weight 26 is attached to the node of the secondary natural vibration of the core rod 25 and its mass is adjusted so as not to affect the secondary natural frequency ω2 of the core rod 25. Therefore, when the primary natural frequency ω1 of the core rod structure 11 is adjusted by the weight 26, the secondary natural frequency ω2 of the core rod 25 does not change, and the secondary natural frequency ω2 of the core rod 25 becomes the secondary natural frequency ω2 of the core rod structure 11. As a result, the length of the core rod 25 is adjusted, and the secondary natural frequency ω2 of the core rod 25 is adjusted, so that the secondary natural frequency ω2 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0059] Once the length of the core rod 25 is adjusted and the second natural frequency ω2 of the core rod structure 11 is set, the first natural frequency ω1 of the core rod structure 11 is then adjusted by adjusting the position and mass of the weights 26 attached to the core rod 25. The weights 26 are attached to the nodes of the second mode natural vibrations, which are located near the center of the core rod 25 in the longitudinal axis direction. The first natural frequency ω1 of the core rod structure 11 is adjusted by adjusting the mass of the weights 26 attached to the core rod 25 at the nodes of the second mode natural vibrations. The mass of the weights 26 is adjusted by changing the number of weights 26 attached to the core rod 25. The first natural frequency ω1 of the core rod structure 11 is adjusted by performing a hammering test on the core rod structure 11 while changing the mass of the weights 26 attached to the core rod 25, obtaining the acceleration waveform, calculating its power spectrum, and confirming the first natural frequency ω1 of the core rod structure 11. Then, by changing the mass of the weight 26, the primary natural frequency ω1 of the core rod structure 11 is adjusted, and the mass of the weight 26 is determined such that the primary natural frequency ω1 of the core rod structure 11 corresponds to the primary natural frequency Ω1 of the striking tool body 10 and is a frequency that dampens the natural vibration of the primary mode of the striking tool body 10, and is within the range of the optimal natural frequency f1 obtained by equation (3) above or a frequency that changes by a predetermined ratio with respect to the optimal natural frequency f1.

[0060] Furthermore, the change in the primary natural frequency ω1 of the core rod structure 11 due to changing the mass of the weight 26 attached to the node position of the second natural vibration can also be calculated by vibration simulation using a model in which weights are attached to a rod. For this reason, the adjustment of the primary natural frequency ω1 of the core rod structure 11 by changing the mass of the weight 26 may be performed by simulation. In addition, in the core rod structure 11 of the striking tool 1, the core rod 25 is attached to the striking tool body 10 with both ends fixed, but a configuration in which the core rod 25 is attached to the striking tool body 10 with one side fixed may also be implemented. When the core rod 25 is attached to the striking tool body 10 with one side fixed, the adjustment of the primary natural frequency ω1 of the core rod structure 11 by changing the mass of the weight 26 may be performed by simulation, or the adjustment of the primary natural frequency ω1 of the core rod structure 11 may be performed while confirming the vibration damping effect by hammering the striking tool 1 with the core rod structure 11 with the changed mass of the weight 26 attached.

[0061] As described above, by adjusting the mass of the weight 26 attached to the core rod 25 at the node position of the second natural vibration, the primary natural frequency ω1 of the core rod structure 11 is adjusted to a desired frequency without changing the secondary natural frequency ω2 of the core rod structure 11. Then, by adjusting the weight 26 attached to the core rod 25 and adjusting the primary natural frequency ω1 of the core rod structure 11, the primary natural frequency ω1 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10.

[0062] (Effects of this embodiment) According to the striking tool 1 of this embodiment, the vibration of the striking tool 1 is reduced by a core rod structure 11, which acts as a dynamic vibration absorber and has a core rod 25 that is fixed at least one end to the striking tool body 10 and extends along the long axis of the striking tool body 10, thereby absorbing the vibration of the striking tool body 10. Furthermore, there are a certain number of natural frequencies ω in the core rod structure 11. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The frequency is set to dampen the natural vibration of the striking tool body 10 in accordance with the corresponding frequency. i In response to vibrations, the core rod structure 11 resonates, thereby affecting the natural frequencies Ω of the striking tool body 10. i This absorbs natural vibrations and reduces vibrations of the hitting tool body 10. Therefore, it is possible to reduce the vibrations of multiple frequency components that occur in the hitting tool body 10 when the ball collides with the hitting portion 22 of the hitting tool body 10 and are transmitted from the grip portion 21 to the batter's hand. Furthermore, according to the hitting tool 1 of this embodiment, the structure that reduces the vibrations of multiple vibration components is configured as a core rod structure 11 as a dynamic vibration absorber, which is arranged inside the hitting tool body 10 and has a core rod 25 with at least one end fixed to the hitting tool body 10 and extending along the long axis of the hitting tool 1. Therefore, the vibrations of multiple frequency components transmitted from the hitting tool 1 to the batter's hand during hitting can be reduced with a single structure built into the hitting tool 1.

[0063] As described above, according to this embodiment, the vibrations of multiple frequency components transmitted from the striking tool 1 to the batter's hand during hitting can be reduced by a single structure built into the striking tool 1, thereby effectively reducing the vibrations transmitted to the batter's hand.

[0064] Furthermore, according to the striking tool 1 of this embodiment, by adjusting the position and mass of the weight 26 attached to the core rod 25, a specific set of natural frequencies ω in the core rod structure 11 can be achieved. i The desired natural frequency ω i The striking tool body 10 has a specific set of multiple natural frequencies Ω i The desired natural frequency among them Ω i The vibration frequency can be easily set to a level that dampens vibrations. Therefore, it becomes even easier to adjust the reduction of multiple frequency components of vibration transmitted from the striking tool to the batter's hand during impact using a single structure built into the striking tool.

[0065] Natural frequency ω of core rod structure 11 i The natural frequency Ω of the striking tool body 10 i In order to adjust the frequency of the striking tool body 10 to a frequency that dampens the natural vibration, by attaching multiple weights 26 to the core rod 25, the mass of the weights 26 attached to the core rod 25 is increased, thereby increasing the natural vibration frequency ω in the core rod structure 11. i It can be adjusted to reduce the value. However, when multiple weights 26 are attached to the core rod 25 in a state where they are in contact and lined up, the multiple weights 26 contribute to an increase in overall rigidity, and the rigidity of the core rod structure 11 becomes high, thus reducing the natural frequency ω of the core rod structure 11. i This makes it difficult to reduce the stiffness. In contrast, with the striking tool 1 of this embodiment, since the multiple weights 26 are attached to the core rod 25 with gaps in between, it is possible to suppress the multiple weights 26 contributing to an increase in stiffness as a whole. Therefore, while suppressing the increase in stiffness by attaching the multiple weights 26 to the core rod 25, the mass of the weights 26 can be increased to increase the natural frequency ω in the core rod structure 11. i This can reduce the natural frequency ω of the core rod structure 11. i This makes adjustment easier.

[0066] Furthermore, according to the striking tool 1 of this embodiment, by adjusting the length of the core rod 25, a specific set of natural frequencies ω in the core rod structure 11 can be achieved. i Any of the desired natural frequencies ω i The striking tool body 10 has a specific set of multiple natural frequencies Ω i Any of the desired natural frequencies Ω i The vibration frequency can be easily set to a frequency that dampens vibrations. Furthermore, by adjusting the position and mass of the weight 26 attached to the core rod 25, a specific set of natural frequencies ω in the core rod structure 11 can be set. i Other desired natural frequencies ω i The striking tool body 10 has a specific set of multiple natural frequencies Ω i Other desired natural frequencies Ω i The vibration frequency can be easily set to a level that dampens vibrations. Therefore, it becomes even easier to adjust the reduction of multiple frequency components of vibrations transmitted from the striking tool 1 to the batter's hand during impact using a single structure built into the striking tool 1.

[0067] Furthermore, according to the striking tool 1 of this embodiment, since the damping material 30 is arranged around the core rod 25 within the striking tool body 10, the vibration of the core rod 25 can be quickly dampened after it begins to vibrate. Therefore, each natural frequency Ω of the striking tool body 10 i The core rod structure 11 resonates with vibrations, and each natural frequency Ω of the striking tool body 10 is generated. i When absorbing the natural vibrations, the vibrations of the resonant core rod 25 can also be attenuated. This further reduces the vibrations transmitted from the striking tool 1 to the batter's hand during impact. In this embodiment, a configuration in which damping material 30 to attenuate the vibrations of the core rod 25 is arranged around the core rod 25 is illustrated, but this is not required. That is, a striking tool 1 may be implemented in a form in which damping material 30 to attenuate the vibrations of the core rod 25 is not arranged inside the striking tool body 10. Even with a striking tool 1 in a form in which damping material 30 is not arranged around the core rod 25, the vibrations of multiple frequency components transmitted from the striking tool 1 to the batter's hand during impact can be reduced by a single structure built into the striking tool 1, thereby effectively reducing the vibrations transmitted to the batter's hand.

[0068] [Second Embodiment] Next, a striking tool 2 according to the second embodiment of the present invention will be described. Figure 4 is a diagram showing the core rod structure 12 of the striking tool 2 according to the second embodiment of the present invention. The striking tool 2 of the second embodiment is configured in the same way as the striking tool 1 of the first embodiment, but the natural frequency ω of the core rod structure 12 i In terms of the manner in which the adjustment is made, it differs from the striking tool 1 of the previously described embodiment. Hereinafter, only the configuration of the striking tool 2 according to the second embodiment that differs from the striking tool 1 of the previously described embodiment will be described. For elements that are configured in the same way as in the previously described embodiment and elements that are configured in correspondence with the previously described embodiment, the same reference numerals are used in the drawings, or the same reference numerals are used for reference, and redundant explanations will be omitted.

[0069] Referring to Figure 4, the hitting tool 2 is configured as a baseball bat, similar to the hitting tool 1 in the previously described embodiment, and comprises a hitting tool body 10 and a core rod structure 12. The hitting tool body 10 is configured in the same way as in the previously described embodiment and has a grip portion 21, a tapered portion 23, and a hitting portion 22. The core rod structure 12 is positioned inside the hitting tool body 10 and is provided as a dynamic vibration absorber to dampen the natural vibration of the hitting tool body 10.

[0070] The core rod structure 12, like the core rod structure 11 of the previously described embodiment, comprises a core rod 25, a weight 26, and a cylindrical member 27. The inside of the cylindrical member 27 is filled with damping material 30, and, as in the previously described embodiment, the damping material 30 is arranged around the core rod 25 to dampen the vibration of the core rod 25. However, in the core rod structure 12, by adjusting the position and mass of the weight 26 attached to the core rod 25, a specific set of natural frequencies ω in the core rod structure 12 can be controlled. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The vibration frequencies corresponding to each of these are set to dampen the natural vibration of the striking tool body 10. In addition, in the core rod structure 12, a sponge member 31, which is a damping material, is provided between the weights 26 and attached to the core rod 25.

[0071] The core rod structure 12 is configured as a dynamic vibration absorber that dampens the natural vibrations of multiple modes in the striking tool body 10, similar to the core rod structure 11 in the previously described embodiment. And, similar to the previously described embodiment, in order to dampen the natural vibrations of multiple modes in the striking tool body 10, the striking tool 2 has a specific set of natural frequencies ω in the core rod structure 12. i However, there are several specific natural frequencies Ω in the striking tool body 10. i Each of these is set to a frequency that dampens the natural vibration of the striking tool body 10. The specific multiple natural frequencies Ω of the striking tool body 10 that are damped are set accordingly. i For example, the primary natural frequency Ω1 of the first mode with a large vibration amplitude and the secondary natural frequency Ω2 of the second mode are selected. Then, corresponding to this, a certain number of natural frequencies ω in the core rod structure 12 are selected. i These correspond to the primary natural frequency ω1 and the secondary natural frequency ω2. The primary natural frequency ω1 of the core rod structure 12 is set to a frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10. Then, the secondary natural frequency ω2 of the core rod structure 12 is set to a frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0072] In the striking tool 2 of this embodiment, the position and mass of the weight 26 attached to the core rod 25 are adjusted, thereby allowing for a specific set of natural frequencies ω in the core rod structure 12. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The vibration frequencies corresponding to each of these are set to dampen the natural vibration of the striking tool body 10. In the core rod structure 12, the first weight 26a, which is one of the weights 26, and the second weight 26b, which is the other weight 26, are individually adjusted in terms of the position and mass to which they are attached to the core rod 25, thereby setting a specific set of natural vibration frequencies ω in the core rod structure 12. i However, there are several specific natural frequencies Ω in the striking tool body 10. iThe natural vibrations at each point are set to frequencies that dampen them. That is, in the striking tool 2, the position of the first weight 26a attached to the core rod 25 and the mass of the first weight 26a are adjusted, thereby controlling a specific set of natural vibrations ω in the core rod structure 12. i One of the natural frequencies ω i However, there are several specific natural frequencies Ω in the striking tool body 10. i Any of the natural frequencies Ω i The frequency is set to a frequency that dampens the natural vibration of the striking tool body 10 in accordance with this. Then, in the striking tool 2, the position of the second weight 26b attached to the core rod 25 and the mass of the second weight 26b are adjusted so that a specific set of natural frequencies ω in the core rod structure 12 are controlled. i Other natural frequencies among them ω i However, there are several specific natural frequencies Ω in the striking tool body 10. i Other natural frequencies among them Ω i The frequency is set to a level that dampens the natural vibration of the striking tool body 10.

[0073] In addition, in the striking tool 2 of this embodiment illustrated in Figure 4, there are a specific set of natural frequencies ω in the core rod structure 12. i The primary natural frequency ω1 and the secondary natural frequency ω2 are identified, and a specific set of natural frequencies Ω in the striking tool body 10 are identified. iThe primary natural frequency Ω1 and the secondary natural frequency Ω2 have been identified. In the striking tool 2, by adjusting the position of the first weight 26a attached to the core rod 25 and the mass of the first weight 26a, one of the primary natural frequencies (ω1, ω2) in the core rod structure 12, ω1, is set to a frequency that dampens the natural vibration of the striking tool body 10, corresponding to one of the primary natural frequencies (Ω1, Ω2) in the striking tool body 10, Ω1. Furthermore, in the striking tool 2, by adjusting the position of the second weight 26b attached to the core rod 25 and the mass of the second weight 26b, one of the specific multiple natural frequencies (ω1, ω2) in the core rod structure 12, another secondary natural frequency ω2 corresponds to one of the specific multiple natural frequencies (Ω1, Ω2) in the striking tool body 10, and is set to a frequency that dampens the natural vibration of the striking tool body 10.

[0074] Furthermore, in the striking tool 2 of this embodiment, a sponge member 31, which is a damping material attached to the core rod 25, is provided. The sponge member 31 is attached to the core rod 25 between the first weight 26a and the second weight 26b, which are attached to the core rod 25. The sponge member 31 is provided, for example, as a cylindrical member with a through hole into which the core rod 25 is inserted. The sponge member 31 is made of a material such as urethane, silicone, or rubber, and is arranged as a damping material to dampen the vibration of the core rod 25.

[0075] Here, in the striking tool 2 of this embodiment, the optimal natural frequency f, which is determined by equation (3) above, corresponds to the frequency that dampens the natural vibration of the striking tool body 10, with a specific set of natural frequencies (ω1, ω2) in the core rod structure 12 corresponding to a specific set of natural frequencies (Ω1, Ω2) in the striking tool body 10. i Or the optimal natural frequency f i Further explanation will describe a specific example of adjusting the natural frequencies (ω1, ω2) of the core rod structure 12 in order to set the frequency to fall within a predetermined range of change.

[0076] In adjusting the natural frequencies (ω1, ω2) of the core rod structure 12, first, the type of core rod 25 is selected considering the material and diameter of the core rod 25, and then the type of weights 26 used as the first weight 26a and the second weight 26b is selected considering the material and size of the weights 26. If a compact structure is desired by shortening the length of the core rod 25, a core rod 25 with a small diameter and high specific gravity is selected. In the striking tool 2 of this embodiment, for example, a brass screw shaft with a diameter of 4 mm is selected as the core rod 25, and brass nuts that are screwed onto the core rod 25 are selected as the weights 26 used as the first weight 26a and the second weight 26b.

[0077] After selecting the types of core rods 25 and weights 26, several core rods 25 of different lengths are prepared, and a hammering test is performed on each of the core rods 25 of different lengths to measure the vibration acceleration of each core rod 25. As for the several core rods 25 of different lengths, for example, five core rods 25 of lengths 10cm, 15cm, 20cm, 25cm, and 30cm are prepared, and a hammering test is performed on each core rod 25 of different lengths in the same manner as in the above embodiment to measure the vibration acceleration.

[0078] Once the acceleration waveforms of the five core rods 25 of different lengths are obtained through measurements in the hammering test, the power spectrum of each core rod 25 of each length is calculated from these acceleration waveforms, and based on these power spectra, the natural frequency ω of each core rod 25 of each length is determined. i Check the natural frequencies ω of the core rods 25 of each length. i Upon checking, based on the results of that check, the length of the core rod 25 and the natural frequency of each mode (natural frequency ω) are determined, similar to the case of the striking tool 1 in the embodiment described above. i An approximate formula is created for the relationship between the length of the core rod 25 and the natural frequency ω, as shown in Figure 3. That is, similar to the striking tool 1 of the embodiment described above, an approximate formula is created for the relationship between the length of the core rod 25 and the natural frequency ω. i We will find the relationship between the length of the core rod 25 and the natural frequency ω of each mode. iAn approximate formula is created to show the relationship between the two. Then, using the created approximate formula as a reference, the first natural frequency ω1, which is the natural frequency of the first mode of the core rod 25, and the second natural frequency ω2, which is the natural frequency of the second mode, are found to be the optimal natural frequency f obtained by equation (3) above. i The length of the core rod 25 is determined so that each of these values ​​is slightly greater than the optimal natural frequency f. i By determining the length of the core rod 25 so that it is slightly greater than the first weight 26a and the second weight 26b, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12 can be individually adjusted to decrease them. In the core rod structure 12 of the striking tool 2, the core rod 25 is attached to the striking tool body 10 with both ends fixed, but a configuration in which the core rod 25 is attached to the striking tool body 10 with one end fixed may also be implemented. When the core rod 25 is attached to the striking tool body 10 with one end fixed, the primary natural frequency Ω1 of the core rod 25 is theoretically 0.157 times that of the case where both ends are fixed, and the secondary natural frequency Ω2 of the core rod 25 is theoretically 0.357 times that of the case where both ends are fixed. For this reason, when the core rod 25 is attached to the striking tool body 10 with one end fixed, the length of the core rod 25 is determined taking these points into consideration.

[0079] Once the length of the core rod 25 is determined, the second natural frequency ω2 of the core rod structure 12 is then adjusted by adjusting the position and mass of the second weights 26b attached to the core rod 25. The second weights 26b are attached to the antinodes of the second mode natural vibration of the core rod 25. The second natural frequency ω2 of the core rod structure 12 is adjusted by adjusting the mass of the second weights 26b attached to the antinodes of the second mode natural vibration of the core rod 25. The mass of the second weights 26b is adjusted by the number of second weights 26b attached to the core rod 25. The change in the second natural frequency ω2 of the core rod structure 12 due to changing the mass of the second weights 26b attached to the antinodes of the second mode natural vibration can be calculated by vibration simulation using a model in which weights are attached to a rod. Therefore, the adjustment of the second natural frequency ω2 of the core rod structure 12 by changing the mass of the second weights 26b is examined by simulation. Through simulation studies, the second natural frequency ω2 of the core rod structure 12 is adjusted by changing the mass of the second weight 26b, and the mass of the second weight 26b is determined such that the second natural frequency ω2 of the core rod structure 12 corresponds to the second natural frequency Ω2 of the striking tool body 10, is a frequency that dampens the natural vibration of the second mode of the striking tool body 10, and is within the range of the optimal natural frequency f2 obtained by equation (3) above or a frequency that changes by a predetermined ratio to the optimal natural frequency f2.

[0080] When the mass of the second weight 26b is adjusted to the mass determined as described above, the secondary natural frequency ω2 of the core rod structure 12 is adjusted to a frequency that dampens the natural vibration of the second mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. After the secondary natural frequency ω2 of the core rod structure 12 is adjusted, the primary natural frequency ω1 of the core rod structure 12 is then adjusted by the first weight 26a. When the primary natural frequency ω1 of the core rod structure 12 is adjusted by the first weight 26a, the first weight 26a is attached to the node of the secondary natural vibration of the core rod 25 and its mass is adjusted so as not to affect the secondary natural frequency ω2 of the core rod structure 12. Therefore, when the primary natural frequency ω1 of the core rod structure 12 is adjusted by the first weight 26a, the secondary natural frequency ω2 of the core rod structure 12 does not change. Therefore, by adjusting the mass of the second weight 26b, the secondary natural frequency ω2 of the core rod structure 12 is set to a frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0081] Once the second weight 26b is adjusted to set the second natural frequency ω2 of the core rod structure 12, the first natural frequency ω1 of the core rod structure 12 is then adjusted by adjusting the position and mass of the first weight 26a attached to the core rod 25. The first weight 26a is attached to the position of the node of the second mode natural vibration, which is located near the center in the longitudinal axis direction of the core rod 25. The first natural frequency ω1 of the core rod structure 12 is adjusted by adjusting the mass of the first weight 26a attached to the core rod 25 at the node of the second mode natural vibration. The mass of the first weight 26a is adjusted by the number of first weights 26a attached to the core rod 25. The change in the first natural frequency ω1 of the core rod structure 12 due to changing the mass of the first weight 26a attached to the node of the second natural vibration can be calculated by vibration simulation using a model in which weights are attached to a rod. Therefore, the adjustment of the primary natural frequency ω1 of the core rod structure 12 by changing the mass of the first weight 26a is investigated by simulation. Through simulation, the primary natural frequency ω1 of the core rod structure 12 is adjusted by changing the mass of the first weight 26a, and the mass of the first weight 26a is determined so that the primary natural frequency ω1 of the core rod structure 12 corresponds to the primary natural frequency Ω1 of the striking tool body 10, and is a frequency that dampens the natural vibration of the first mode of the striking tool body 10, and falls within the range of the optimal natural frequency f1 obtained by equation (3) above or a frequency that changes by a predetermined ratio to the optimal natural frequency f1.

[0082] As described above, by adjusting the mass of the first weight 26a attached to the core rod 25 at the node position of the second natural vibration, the primary natural frequency ω1 of the core rod structure 12 is adjusted to a desired frequency without changing the secondary natural frequency ω2 of the core rod structure 12. Then, by adjusting the first weight 26a attached to the core rod 25 and adjusting the primary natural frequency ω1 of the core rod structure 12, the primary natural frequency ω1 of the core rod structure 12 is set to a frequency that dampens the natural vibration of the first mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10.

[0083] According to the striking tool 2 of this embodiment, a specific set of natural frequencies ω in the core rod structure 12 i However, there are several specific natural frequencies Ω in the striking tool body 10. i The frequency is set to dampen the natural vibration of the striking tool body 10 in accordance with the corresponding frequency. i In response to vibrations, the core rod structure 12 resonates, causing each natural frequency Ω of the striking tool body 10 to resonate. i This absorbs natural vibrations and reduces vibrations of the hitting tool body 10. Therefore, it is possible to reduce the vibrations of multiple frequency components that occur in the hitting tool body 10 when the ball collides with the hitting portion 22 of the hitting tool body 10 and are transmitted from the grip portion 21 to the batter's hand. Furthermore, according to the hitting tool 2 of this embodiment, the structure that reduces the vibrations of multiple vibration components is arranged inside the hitting tool body 10 and is configured as a core rod structure 12 as a dynamic vibration absorber having a core rod 25 extending along the long axis of the hitting tool 2 and a weight 26 attached to the core rod 25. Therefore, the vibrations of multiple frequency components transmitted from the hitting tool 2 to the batter's hand during hitting can be reduced by a single structure built into the hitting tool 2.

[0084] Furthermore, according to the striking tool 2 of this embodiment, by adjusting the position and mass of the first weight 26a among the weights 26 attached to the core rod 25, a specific set of natural frequencies ω in the core rod structure 12 can be achieved. i Any of the desired natural frequencies ω i The striking tool body 10 has a specific set of multiple natural frequencies Ω i Any of the desired natural frequencies Ω iThe vibration damping frequency can be easily set. Furthermore, by adjusting the position and mass of the second weight 26b of the weight 26 attached to the core rod 25, a specific set of natural frequencies ω in the core rod structure 12 can be controlled. i Other desired natural frequencies ω i The striking tool body 10 has a specific set of multiple natural frequencies Ω i Other desired natural frequencies Ω i The vibration frequency can be easily set to a level that dampens vibrations. Therefore, it becomes even easier to adjust the reduction of multiple frequency components of vibrations transmitted from the striking tool 2 to the batter's hand during impact using a single structure built into the striking tool 2.

[0085] Furthermore, according to the striking tool 2 of this embodiment, since the damping material 30 is arranged around the core rod 25 within the striking tool body 10, the vibration of the core rod 25 can be quickly dampened after it begins to vibrate. Therefore, each natural frequency Ω of the striking tool body 10 i The core rod structure 12 resonates with vibrations, and each natural frequency Ω of the striking tool body 10 is affected. i When absorbing the natural vibrations, the vibrations of the resonant core rod 25 can also be attenuated. Furthermore, according to the striking tool 2 of this embodiment, a sponge member 31, which acts as a damping material, is attached to the core rod 25 between the first weight 26a and the second weight 26b attached to the core rod 25. Therefore, the vibrations of the core rod 25 after it has started to vibrate can be attenuated even more quickly. In this embodiment, a configuration in which the damping material 30 and the sponge member 31 that attenuate the vibrations of the core rod 25 are arranged around the core rod 25 is illustrated, but this is not required. That is, a striking tool 2 in a form without the damping material 30 or the sponge member 31 may be implemented. Even with a striking tool 2 in a form without the damping material 30 or the sponge member 31, the vibrations of multiple frequency components transmitted from the striking tool 2 to the batter's hand during a strike can be reduced by a single structure built into the striking tool 2, and the vibrations transmitted to the batter's hand can be suitably reduced.

[0086] [Third Embodiment] Next, a striking tool 3 according to the third embodiment of the present invention will be described. Figure 5 is a diagram showing the core rod structure 13 of the striking tool 3 according to the third embodiment of the present invention. The striking tool 3 of the third embodiment is configured similarly to the striking tool 1 of the first embodiment, but the core rod structure 13 does not have a weight, and the natural frequency ω of the core rod structure 13 i In terms of the form in which the adjustment is made, it differs from the striking tool 1 of the previously described embodiment. Hereinafter, only the configuration of the striking tool 3 according to the third embodiment that differs from the striking tool 1 of the previously described embodiment will be described. For elements that are configured in the same way as in the previously described embodiment and elements that are configured in correspondence with the previously described embodiment, the same reference numerals are used in the drawings, or the same reference numerals are used for reference, and redundant explanations will be omitted.

[0087] Referring to Figure 5, the striking tool 3 is configured as a baseball bat, similar to the striking tool 1 in the previously described embodiment, and comprises a striking tool body 10 and a core rod structure 13. The striking tool body 10 is configured in the same way as in the previously described embodiment and has a grip portion 21, a tapered portion 23, and a hitting portion 22. The core rod structure 13 is positioned inside the striking tool body 10 and is provided as a dynamic vibration absorber to dampen the natural vibration of the striking tool body 10.

[0088] The core rod structure 13, like the core rod structure 11 of the previously described embodiment, comprises a core rod 25 and a cylindrical member 27. The inside of the cylindrical member 27 is filled with damping material 30, and, as in the previously described embodiment, the damping material 30 is arranged around the core rod 25 to dampen the vibration of the core rod 25. However, the core rod structure 13 does not have a weight 26, and by adjusting the type and length of the core rod 25, a specific set of natural frequencies ω in the core rod structure 13 can be controlled. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The vibration frequencies corresponding to each of these are set to dampen the natural vibration of the striking tool body 10.

[0089] The core rod structure 13 is configured as a dynamic vibration absorber that dampens the natural vibrations of multiple modes in the striking tool body 10, similar to the core rod structure 11 in the previously described embodiment. And, similar to the previously described embodiment, in order to dampen the natural vibrations of multiple modes in the striking tool body 10, the striking tool 3 has a specific set of natural frequencies ω in the core rod structure 13. i However, there are several specific natural frequencies Ω in the striking tool body 10. i Each of these is set to a frequency that dampens the natural vibration of the striking tool body 10. The specific multiple natural frequencies Ω of the striking tool body 10 that are damped are set accordingly. i For example, the primary natural frequency Ω1 of the first mode with a large vibration amplitude and the secondary natural frequency Ω2 of the second mode are selected. Then, corresponding to this, a certain number of natural frequencies ω in the core rod structure 13 are selected. i These correspond to the primary natural frequency ω1 and the secondary natural frequency ω2. The primary natural frequency ω1 of the core rod structure 13 is set to a frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10. Then, the secondary natural frequency ω2 of the core rod structure 13 is set to a frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0090] In the striking tool 3 of this embodiment, by adjusting the type and length of the core rod 25, a specific set of natural frequencies ω in the core rod structure 13 can be achieved. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The vibration frequencies corresponding to each of these are set to dampen the natural vibration of the striking tool body 10. Note that the natural frequency of a uniform rod is ω i Regarding this, theoretical values ​​can be calculated using the length of the rod, Young's modulus, moment of inertia of area, and density. As is clear from these theoretical values, if the core rod 25 is a uniform rod, changing its length or diameter will not change any of the natural frequencies ω in the core rod 25. i and other natural frequencies ω iThe ratio between the primary natural frequency ω1 and the secondary natural frequency ω2 does not change. Therefore, if the core rod 25 is a uniform rod, the ratio between the primary natural frequency ω1 and the secondary natural frequency ω2 in the core rod 25 does not change even if the length or diameter of the core rod 25 is changed. Accordingly, in the striking tool 3 of this embodiment, the type of core rod 25 is selected such that the ratio between the primary natural frequency ω1 and the secondary natural frequency ω2 of the core rod 25 matches the ratio between the frequency that dampens the natural vibration of the primary mode of the striking tool body 10 corresponding to the primary natural frequency Ω1 of the striking tool body 10 and the frequency that dampens the natural vibration of the secondary mode of the striking tool body 10 corresponding to the secondary natural frequency Ω2 of the striking tool body 10. In other words, in the striking tool 3, the type of core rod 25 is selected such that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod 25 matches the ratio of the optimal natural frequency f1 of the primary mode to the optimal natural frequency f2 of the secondary mode, which is obtained by equation (3) above. The type of core rod 25 whose ratio of primary natural frequency ω1 to secondary natural frequency ω2 matches the desired frequency ratio that dampens the natural vibration of the striking tool body 10 is investigated experimentally or by simulation.

[0091] Once a type of core rod 25 is selected in which the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 matches the desired frequency ratio, the length of the core rod 25 is then adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 match the frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. As a result, the primary natural frequency ω1 of the core rod structure 13 is set to a frequency that dampens the primary natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 13 is set to a frequency that dampens the secondary natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0092] Here, in the striking tool 3 of this embodiment, the optimal natural frequency f, which is determined by equation (3) above, corresponds to the frequency that dampens the natural vibration of the striking tool body 10, with a specific set of natural frequencies (ω1, ω2) in the core rod structure 13 corresponding to a specific set of natural frequencies (Ω1, Ω2) in the striking tool body 10. i Or the optimal natural frequency f iFurther explanation will describe a specific example of adjusting the natural frequencies (ω1, ω2) of the core rod structure 13 in order to set the frequency to fall within a predetermined range of change.

[0093] In adjusting the natural frequencies (ω1, ω2) of the core rod structure 13, first, the type of core rod 25 is selected such that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod 25 matches the ratio of the optimal natural frequency f1 of the primary mode to the optimal natural frequency f2 of the secondary mode, which is obtained by equation (3) above.

[0094] After selecting the type of core rod 25, several core rods 25 of different lengths are prepared, and a hammering test is performed on each of the core rods 25 of different lengths to measure the vibration acceleration of each core rod 25. For example, five core rods 25 of lengths 10cm, 15cm, 20cm, 25cm, and 30cm are prepared, and a hammering test similar to that of the above embodiment is performed on each core rod 25 to measure the vibration acceleration.

[0095] Once the acceleration waveforms of the five core rods 25 of different lengths are obtained through measurements in the hammering test, the power spectrum of each core rod 25 of each length is calculated from these acceleration waveforms, and based on these power spectra, the natural frequency ω of each core rod 25 of each length is determined. i Check the natural frequencies ω of the core rods 25 of each length. i Upon checking, based on the results of that check, the length of the core rod 25 and the natural frequency of each mode (natural frequency ω) are determined, similar to the case of the striking tool 1 in the embodiment described above. iAn approximate formula is created for the relationship between ( ) and ). Then, using the created approximate formula as a reference, the length of the core rod 25 is determined so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 match, for example, the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode obtained by equation (3) above. Note that the ratio of the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 matches the ratio of the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode obtained by equation (3) above. Therefore, by adjusting the length of the core rod 25, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 can be made to match the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode obtained by equation (3) above simultaneously. Alternatively, the length of the core rod 25 may be determined such that the primary natural frequency ω1 and the secondary natural frequency ω2 of the core rod 25 coincide with frequencies that fall within a predetermined range of change relative to the optimal natural frequency f1 of the primary mode and frequencies that fall within a predetermined range of change relative to the optimal natural frequency f2 of the secondary mode, respectively.

[0096] As described above, by adjusting the length of the core rod 25, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 are adjusted to frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. Since the core rod 25 does not have a weight 26, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 become the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 13. By adjusting the core rod 25 as described above, the primary natural frequency ω1 of the core rod structure 13 is set to a frequency that dampens the primary natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 13 is set to a frequency that dampens the secondary natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0097] According to the striking tool 3 of this embodiment, a specific set of natural frequencies ω in the core rod structure 13 i However, there are several specific natural frequencies Ω in the striking tool body 10. iThe frequency is set to dampen the natural vibration of the striking tool body 10 in accordance with the corresponding frequency. i In response to vibrations, the core rod structure 13 resonates, thereby affecting the natural frequencies Ω of the striking tool body 10. i This absorbs natural vibrations and reduces vibrations of the hitting tool body 10. Therefore, it is possible to reduce the vibrations of multiple frequency components that occur in the hitting tool body 10 when the ball collides with the hitting portion 22 of the hitting tool body 10 and are transmitted from the grip portion 21 to the batter's hand. Furthermore, according to the hitting tool 3 of this embodiment, the structure that reduces the vibrations of multiple vibration components is configured as a core rod structure 13 as a dynamic vibration absorber, which is arranged inside the hitting tool body 10 and has a core rod 25 extending along the long axis of the hitting tool 3. As a result, the vibrations of multiple frequency components transmitted from the hitting tool 3 to the batter's hand during hitting can be reduced by a single structure built into the hitting tool 3.

[0098] In this embodiment, the striking tool 3 is illustrated in which the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 13 are set to frequencies that dampen the natural vibrations of the striking tool body 10, corresponding to the primary natural frequency Ω1 and secondary natural frequency Ω2 of the striking tool body 10, respectively. However, this is not required. A striking tool 3 may be implemented in which the natural vibrations of other modes of the striking tool body 10 are dampened. For example, a configuration may be implemented in which the primary natural frequency ω1 and tertiary natural frequency ω3 of the core rod structure 13 are set to frequencies that dampen the natural vibrations of the striking tool body 10, corresponding to the primary natural frequency Ω1 and tertiary natural frequency Ω3 of the striking tool body 10, respectively. Alternatively, the second natural frequency ω2 and third natural frequency ω3 of the core rod structure 13 may be set to frequencies that dampen the natural vibration of the striking tool body 10, corresponding to the second natural frequency Ω2 and third natural frequency Ω3 of the striking tool body 10, respectively. In these cases, the type of core rod 25 is selected such that the ratio of the first natural frequency ω1 to the third natural frequency ω3 of the core rod 25 matches the ratio of the frequency that dampens the natural vibration of the first mode of the striking tool body 10 to the frequency that dampens the natural vibration of the third mode. Alternatively, the type of core rod 25 is selected such that the ratio of the second natural frequency ω2 to the third natural frequency ω3 of the core rod 25 matches the ratio of the frequency that dampens the natural vibration of the second mode of the striking tool body 10 to the frequency that dampens the natural vibration of the third mode.

[0099] Furthermore, in this embodiment, the striking tool 3 is shown as having a damping material 30 arranged around the core rod 25 to dampen the vibration of the core rod 25, but this is not required. In other words, a striking tool 3 without the damping material 30 may be implemented. Even with a striking tool 3 without the damping material 30, the vibrations of multiple frequency components transmitted from the striking tool 3 to the batter's hand during impact can be reduced by a single structure built into the striking tool 3, thereby effectively reducing the vibrations transmitted to the batter's hand.

[0100] [Fourth Embodiment] Next, a striking tool according to the fourth embodiment of the present invention will be described. The striking tool of the fourth embodiment is configured similarly to the striking tool 3 of the third embodiment, but the natural frequency ω of the core rod structure 13 is different. iIn terms of the manner in which the adjustment is made, it differs from the striking tool 3 of the third embodiment. Hereinafter, only the configuration of the striking tool according to the fourth embodiment that differs from the striking tool 3 of the third embodiment described above will be explained. Note that the striking tool of the fourth embodiment is configured similarly to the striking tool 3 of the third embodiment shown in Figure 5, so the striking tool of the fourth embodiment will be described with reference to Figure 5, using the same reference numerals for elements configured similarly to the third embodiment.

[0101] Referring to Figure 5, the fourth embodiment of the striking tool is configured as a baseball bat, similar to the striking tool 3 of the third embodiment described above, and comprises a striking tool body 10 and a core rod structure 13. The striking tool body 10 has a grip portion 21, a tapered portion 23, and a hitting portion 22. The core rod structure 13 is positioned inside the striking tool body 10 and is provided as a dynamic vibration absorber that dampens the natural vibrations of multiple modes in the striking tool body 10.

[0102] The core rod structure 13 of the striking tool in the fourth embodiment includes a core rod 25 and a cylindrical member 27, similar to the core rod structure 13 of the third embodiment. The inside of the cylindrical member 27 is filled with damping material 30, and damping material 30 is arranged around the core rod 25 to dampen the vibration of the core rod 25. However, in the core rod structure 13 of the striking tool in the fourth embodiment, by adjusting the type, length and tension of the core rod 25, a specific set of natural frequencies ω in the core rod structure 13 can be achieved. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The vibration frequencies corresponding to each of these are set to dampen the natural vibration of the striking tool body 10. Although the fourth embodiment of the striking tool is shown as an example in which damping material 30 is arranged around the core rod 25 to dampen the vibration of the core rod 25, the striking tool of the fourth embodiment may also be implemented in a form in which the damping material 30 is not arranged.

[0103] In the striking tool of the fourth embodiment, a specific set of natural frequencies ω in the core rod structure 13 i However, there are several specific natural frequencies Ω in the striking tool body 10. iThe frequencies are set to dampen the natural vibrations of the striking tool body 10, corresponding to each of the above. More specifically, in the striking tool of the fourth embodiment, the primary natural frequency ω1 of the core rod structure 13 is set to a frequency that dampens the natural vibrations of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 13 is set to a frequency that dampens the natural vibrations of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0104] In the striking tool of the fourth embodiment, by adjusting the type, length, and tension of the core rod 25, the primary natural frequency ω1 and secondary natural frequency ω2 in the core rod structure 13 are set to frequencies that dampen the natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 and secondary natural frequency Ω2 in the striking tool body 10, respectively. Note that if the core rod 25 is a uniform rod, the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 in the core rod 25 does not change even if the length or diameter of the core rod 25 is changed. Therefore, in the striking tool of the fourth embodiment, the type of core rod 25 is selected such that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod 25 matches the ratio of the frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. In other words, in the striking tool of the fourth embodiment, the type of core rod 25 is selected such that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod 25 matches the ratio of the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode, which can be obtained by equation (3) above. Furthermore, the type of core rod 25 whose ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 matches the desired frequency ratio for damping the natural vibration of the striking tool body 10 will be investigated experimentally or through simulation.

[0105] Once a type of core rod 25 is selected in which the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 matches the desired frequency ratio, the length of the core rod 25 is then determined so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 can be adjusted to the desired frequency. Then, the tension applied to the core rod 25 is adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 match the frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. As a result, the primary natural frequency ω1 of the core rod structure 13 is set to a frequency that dampens the primary natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 13 is set to a frequency that dampens the secondary natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. Furthermore, the tension applied to the core rod 25 can be adjusted by rotating the end knobs 24 and cap members 29, which are positioned on either side of the cylindrical member 27 and to which both ends of the core rod 25 are screwed, relative to each other.

[0106] Here, in the striking tool of the fourth embodiment, the optimal natural frequency f obtained by equation (3) above corresponds to the frequency that dampens the natural vibration of the striking tool body 10, with a specific set of natural frequencies (ω1, ω2) in the core rod structure 13 corresponding to a specific set of natural frequencies (Ω1, Ω2) in the striking tool body 10. i Or the optimal natural frequency f i Further explanation will describe a specific example of adjusting the natural frequencies (ω1, ω2) of the core rod structure 13 in order to set the frequency to fall within a predetermined range of change.

[0107] In adjusting the natural frequencies (ω1, ω2) of the core rod structure 13 of the striking tool in the fourth embodiment, first, the type of core rod 25 is selected such that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod 25 matches the ratio of the optimal natural frequency f1 of the primary mode to the optimal natural frequency f2 of the secondary mode, which is obtained by equation (3) above.

[0108] After selecting the type of core rod 25, several core rods 25 of different lengths are prepared, and a hammering test is performed on each of the core rods 25 of different lengths to measure the vibration acceleration of each core rod 25. For example, five core rods 25 of lengths 10cm, 15cm, 20cm, 25cm, and 30cm are prepared, and a hammering test similar to that of the above embodiment is performed on each core rod 25 to measure the vibration acceleration.

[0109] Once the acceleration waveforms of the five core rods 25 of different lengths are obtained through measurements in the hammering test, the power spectrum of each core rod 25 of each length is calculated from these acceleration waveforms, and based on these power spectra, the natural frequency ω of each core rod 25 of each length is determined. i Check the natural frequencies ω of the core rods 25 of each length. i Upon checking, based on the results of that check, the length of the core rod 25 and the natural frequency of each mode (natural frequency ω) are determined, similar to the case of the striking tool 1 in the embodiment described above. i An approximate formula is created for the relationship between ( ). Then, using the created approximate formula as a reference, the length of the core rod 25 is determined such that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 are reasonably close to the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode, for example, obtained by equation (3) above.

[0110] Once the length of the core rod 25 is determined, the tension applied to the core rod 25 is then adjusted to match the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 to the frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. The ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod 25 matches the ratio of the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode, which can be obtained using equation (3) above. Therefore, by adjusting the tension applied to the core rod 25, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 can be simultaneously matched to the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode, which can be obtained using equation (3) above. Furthermore, the tension applied to the core rod 25 may be adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 match frequencies that fall within a predetermined range of change relative to the optimal natural frequency f1 of the primary mode and frequencies that fall within a predetermined range of change relative to the optimal natural frequency f2 of the secondary mode, respectively. In adjusting the tension applied to the core rod 25, the tension can be increased by rotating the end knob 24 and the cap member 29 relative to each other in the direction in which the core rod 25 is screwed into each of them. Alternatively, the tension can be decreased by rotating the end knob 24 and the cap member 29 relative to each other in the direction in which the core rod 25 is detached from the end knob 24 and the cap member 29.

[0111] When adjusting the tension applied to the core rod 25 to adjust the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25, for example, a hammering test of a striking tool to which the core rod structure 13 with the core rod structure 13 has been modified can be used. By changing the tension applied to the core rod 25 and performing a hammering test of the striking tool to which the core rod structure 13 has been attached to confirm the vibration damping effect, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 can be adjusted.

[0112] As described above, by adjusting the tension on the core rod 25, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 are adjusted to frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. Since the core rod 25 does not have a weight 26, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 become the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 13. By adjusting the core rod 25 as described above, the primary natural frequency ω1 of the core rod structure 13 is set to a frequency that dampens the primary natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 13 is set to a frequency that dampens the secondary natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0113] According to the striking tool of the fourth embodiment, a specific set of natural frequencies ω in the core rod structure 13 i However, there are several specific natural frequencies Ω in the striking tool body 10. i The frequency is set to dampen the natural vibration of the striking tool body 10 in accordance with the corresponding frequency. i In response to vibrations, the core rod structure 13 resonates, thereby affecting the natural frequencies Ω of the striking tool body 10. i This absorbs the natural vibrations of the batting tool body 10, thereby reducing the vibration of the batting tool body 10. Therefore, it is possible to reduce the vibration of multiple frequency components that occur in the batting tool body 10 when the ball collides with the hitting portion 22 of the batting tool body 10 and are transmitted from the grip portion 21 to the batter's hand. Furthermore, according to the batting tool of the fourth embodiment, the structure that reduces the vibration of multiple vibration components is configured as a core rod structure 13 as a dynamic vibration absorber, which is arranged inside the batting tool body 10 and has a core rod 25 extending along the long axis of the batting tool. As a result, the vibration of multiple frequency components transmitted from the batting tool to the batter's hand during hitting can be reduced by a single structure built into the batting tool.

[0114] [Fifth Embodiment] Next, a striking tool according to the fifth embodiment of the present invention will be described. The striking tool of the fifth embodiment is configured similarly to the striking tool 1 of the first embodiment, but the natural frequency ω of the core rod structure 11 is different. iThe method of adjusting differs from that of the striking tool 1 of the first embodiment. Hereinafter, only the configuration of the striking tool according to the fifth embodiment that differs from that of the striking tool 1 of the first embodiment described above will be explained. Note that the striking tool of the fifth embodiment is configured similarly to the striking tool 1 of the first embodiment shown in Figure 2, so the striking tool of the fifth embodiment will be described with reference to Figure 2, using the same reference numerals for elements configured similarly to those of the first embodiment.

[0115] Referring to Figure 2, the fifth embodiment of the striking tool is configured as a baseball bat, similar to the striking tool 1 of the first embodiment, and comprises a striking tool body 10 and a core rod structure 11. The striking tool body 10 has a grip portion 21, a tapered portion 23, and a hitting portion 22. The core rod structure 11 is positioned inside the striking tool body 10 and is provided as a dynamic vibration absorber that dampens the natural vibrations of multiple modes in the striking tool body 10.

[0116] The core rod structure 11 of the striking tool in the fifth embodiment includes a core rod 25, a weight 26, and a cylindrical member 27, similar to the core rod structure 11 of the first embodiment. The inside of the cylindrical member 27 is filled with damping material 30, and damping material 30 is arranged around the core rod 25 to dampen the vibration of the core rod 25. However, in the core rod structure 11 of the striking tool in the fifth embodiment, by adjusting the type and length of the core rod 25, the position and mass of the weight 26, and the tension of the core rod 25, a specific set of natural frequencies ω in the core rod structure 11 can be achieved. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The vibration frequencies corresponding to each of these are set to dampen the natural vibration of the striking tool body 10. Although the striking tool of the fifth embodiment is shown as having a damping material 30 arranged around the core rod 25 to dampen the vibration of the core rod 25, the striking tool of the fifth embodiment may be implemented in a form in which the damping material 30 is not arranged.

[0117] In the striking tool of the fifth embodiment, a specific set of natural frequencies ω in the core rod structure 11 i However, there are several specific natural frequencies Ω in the striking tool body 10. iThe frequencies are set to dampen the natural vibrations of the striking tool body 10, corresponding to each of the above. More specifically, in the striking tool of the fifth embodiment, the primary natural frequency ω1 of the core rod structure 11 is set to a frequency that dampens the natural vibrations of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 11 is set to a frequency that dampens the natural vibrations of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0118] In the striking tool of the fifth embodiment, the type and length of the core rod 25, the position and mass of the weight 26, and the tension of the core rod 25 are adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 in the core rod structure 11 correspond to the primary natural frequency Ω1 and secondary natural frequency Ω2 in the striking tool body 10, respectively, and the frequencies that dampen the natural vibration of the striking tool body 10.

[0119] In the striking tool of the fifth embodiment, first, the type of core rod 25 is selected, and then the length of the core rod 25 is determined so that the length of the core rod 25 allows the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 to be adjusted to the desired frequencies. Then, the ratio of the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11 is adjusted by adjusting the position and mass of the weight 26 attached to the core rod 25. At this time, the position and mass of the weight 26 attached to the core rod 25 are adjusted so that the ratio of the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11 matches the ratio of the frequency that dampens the natural vibration of the primary mode of the striking tool body 10 corresponding to the primary natural frequency Ω1 of the striking tool body 10 and the frequency that dampens the natural vibration of the secondary mode of the striking tool body 10 corresponding to the secondary natural frequency Ω2 of the striking tool body 10. In other words, in the striking tool of the fifth embodiment, the position and mass of the weight 26 attached to the core rod 25 are adjusted so that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 matches the ratio of the optimal natural frequency f1 of the primary mode to the optimal natural frequency f2 of the secondary mode, which is obtained by equation (3) above.

[0120] By adjusting the position and mass of the weight 26 attached to the core rod 25, the tension applied to the core rod 25 is then adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11 match the frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. As a result, the primary natural frequency ω1 of the core rod structure 11 is set to a frequency that dampens the primary natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 11 is set to a frequency that dampens the secondary natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. The tension applied to the core rod 25 can be adjusted by relatively rotating the end knobs 24 and cap members 29, which are positioned on either side of the cylindrical member 27 and to which both ends of the core rod 25 are screwed.

[0121] Here, in the striking tool of the fifth embodiment, the optimal natural frequency f, which is obtained by equation (3) above, corresponds to the frequency that dampens the natural vibration of the striking tool body 10, with the specific multiple natural frequencies (ω1, ω2) in the core rod structure 11 corresponding to the specific multiple natural frequencies (Ω1, Ω2) in the striking tool body 10. i Or the optimal natural frequency f i Further explanation will describe a specific example of adjusting the natural frequencies (ω1, ω2) of the core rod structure 11 in order to set the frequency to fall within a predetermined range of change.

[0122] In adjusting the natural frequencies (ω1, ω2) of the core rod structure 11 of the striking tool in the fifth embodiment, first, the type of core rod 25 is selected considering the material and diameter of the core rod 25, and then the type of weight 26 is selected considering the material and size of the weight 26. If a shorter length of the core rod 25 is desired to create a more compact structure, a core rod 25 with a smaller diameter and higher specific gravity is selected. In the striking tool of the fifth embodiment, for example, a brass screw shaft with a diameter of 4 mm is selected as the core rod 25, and a brass nut that screws onto the core rod 25 is selected as the weight 26.

[0123] After selecting the types of core rods 25 and weights 26, several core rods 25 of different lengths are prepared, and a hammering test is performed on each of the core rods 25 of different lengths to measure the vibration acceleration of each core rod 25. For example, five core rods 25 of lengths 10cm, 15cm, 20cm, 25cm, and 30cm are prepared, and a hammering test similar to that in the first embodiment is performed on each core rod 25 to measure the vibration acceleration.

[0124] Once the acceleration waveforms of the five core rods 25 of different lengths are obtained through measurements in the hammering test, the power spectrum of each core rod 25 of each length is calculated from these acceleration waveforms, and based on these power spectra, the natural frequency ω of each core rod 25 of each length is determined. i Check the natural frequencies ω of the core rods 25 of each length. i Upon checking, based on the results of that check, the length of the core rod 25 and the natural frequency of each mode (natural frequency ω) are determined, similar to the case of the striking tool 1 of the first embodiment. i An approximate formula is created for the relationship between ( ). Then, using the created approximate formula as a reference, the length of the core rod 25 is determined within a range in which the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 do not exceed, for example, the optimal natural frequency f1 of the desired primary mode and the optimal natural frequency f2 of the secondary mode, which are obtained by equation (3) above. Note that by setting the length of the core rod 25 within a range in which the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 do not exceed the desired frequencies, it is possible to adjust the tension on the core rod 25 while increasing it to raise the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25.

[0125] After determining the length of the core rod 25, the position and mass of the weights 26 attached to the core rod 25 are then adjusted to match the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11, which corresponds to the ratio of the frequency that dampens the primary mode natural vibration of the striking tool body 10 to the frequency that dampens the secondary mode natural vibration. The weights 26 are attached to the node of the secondary mode natural vibration, which is located near the center of the core rod 25 in the longitudinal axis direction. By adjusting the mass of the weights 26 attached to the core rod 25 at the node of the secondary mode natural vibration, the primary natural frequency ω1 of the core rod structure 11 is changed without changing the secondary natural frequency ω2 of the core rod structure 11, thereby adjusting the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11. The mass of the weights 26 is adjusted by the number of weights 26 attached to the core rod 25. The ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 is adjusted by performing a hammering test on the core rod structure 11 while changing the mass of the weight 26 attached to the core rod 25, obtaining the acceleration waveform, calculating its power spectrum, and confirming the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11. Then, the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 is adjusted by changing the mass of the weight 26, and the mass of the weight 26 is determined so that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 matches the ratio of the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode obtained by equation (3) above. Note that the adjustment of the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 by changing the mass of the weight 26 may also be performed by vibration simulation using a model in which a weight is attached to a rod.

[0126] By adjusting the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 to match the desired frequency ratio, the tension applied to the core rod 25 is then adjusted to match the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 to the frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. Since the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 matches the ratio of the optimal natural frequency f1 of the primary mode to the optimal natural frequency f2 of the secondary mode, which is obtained by equation (3) above, the tension applied to the core rod 25 can be adjusted to simultaneously match the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11 to the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode, which are obtained by equation (3) above. Furthermore, the tension applied to the core rod 25 may be adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11 match frequencies that fall within a predetermined range of change relative to the optimal natural frequency f1 of the primary mode and frequencies that fall within a predetermined range of change relative to the optimal natural frequency f2 of the secondary mode, respectively. In adjusting the tension applied to the core rod 25, the tension applied to the core rod 25 is increased by relatively rotating the end knob 24 and the cap member 29 in the direction in which the core rod 25 is screwed into each, thereby raising the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11.

[0127] When adjusting the tension applied to the core rod 25 to adjust the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11, for example, a hammering test of a striking tool to which the core rod structure 11 with the tension of the core rod 25 has been changed can be used. By changing the tension applied to the core rod 25 and performing a hammering test of a striking tool to which the core rod structure 11 has been attached, the vibration damping effect can be confirmed, thereby adjusting the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11.

[0128] As described above, by adjusting the tension applied to the core rod 25, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11 are adjusted to frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. In this way, by adjusting the length of the core rod 25, the position and mass of the weight 26 attached to the core rod 25, and the tension applied to the core rod 25, the primary natural frequency ω1 of the core rod structure 11 is set to a frequency that dampens the primary natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 11 is set to a frequency that dampens the secondary natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0129] According to the striking tool of the fifth embodiment, a specific set of natural frequencies ω in the core rod structure 11 i However, there are several specific natural frequencies Ω in the striking tool body 10. i The frequency is set to dampen the natural vibration of the striking tool body 10 in accordance with the corresponding frequency. i In response to vibrations, the core rod structure 11 resonates, thereby affecting the natural frequencies Ω of the striking tool body 10. i This absorbs the natural vibrations of the batting tool body 10, thereby reducing the vibration of the batting tool body 10. Therefore, it is possible to reduce the vibration of multiple frequency components that occur in the batting tool body 10 when the ball collides with the hitting portion 22 of the batting tool body 10 and are transmitted from the grip portion 21 to the batter's hand. Furthermore, according to the batting tool of the fifth embodiment, the structure for reducing the vibration of multiple vibration components is configured as a core rod structure 13 as a dynamic vibration absorber, which is arranged inside the batting tool body 10 and has a core rod 25 extending along the long axis of the batting tool and a weight 26 attached to the core rod 25. As a result, the vibration of multiple frequency components transmitted from the batting tool to the batter's hand during hitting can be reduced by a single structure built into the batting tool.

[0130] [Sixth Embodiment] Next, a striking tool according to the sixth embodiment of the present invention will be described. The striking tool of the sixth embodiment is configured similarly to the striking tool 2 of the second embodiment, but the natural frequency ω of the core rod structure 12 is different. iIn terms of the manner in which the adjustment is made, it differs from the striking tool 2 of the second embodiment. Hereinafter, only the configuration of the striking tool according to the sixth embodiment that differs from the striking tool 2 of the second embodiment described above will be explained. Note that the striking tool of the sixth embodiment is configured similarly to the striking tool 2 shown in Figure 4, so the striking tool of the sixth embodiment will be described with reference to Figure 4, and the same reference numerals will be used for elements configured similarly to the second embodiment.

[0131] Referring to Figure 4, the striker of the sixth embodiment is configured as a baseball bat, similar to the striker 2 of the second embodiment, and comprises a striker body 10 and a core rod structure 12. The striker body 10 has a grip portion 21, a tapered portion 23, and a hitting portion 22. The core rod structure 12 is positioned inside the striker body 10 and is provided as a dynamic vibration absorber that dampens the natural frequencies of multiple modes in the striker body 10.

[0132] The core rod structure 12 of the striking tool in the sixth embodiment, like the core rod structure 12 of the second embodiment, comprises a core rod 25, a weight 26 including a first weight 26a and a second weight 26b, and a cylindrical member 27. The inside of the cylindrical member 27 is filled with damping material 30, and the damping material 30 is arranged around the core rod 25 to dampen the vibration of the core rod 25. In addition, a sponge member 31 is attached to the core rod 25 between the first weight 26a and the second weight 26b attached to the core rod 25. However, in the core rod structure 12 of the striking tool in the sixth embodiment, by adjusting the type and length of the core rod 25, the position and mass of the first weight 26a and the second weight 26b, and the tension of the core rod 25, a specific set of natural frequencies ω in the core rod structure 12 can be achieved. i However, there are several specific natural frequencies Ω in the striking tool body 10. i The natural frequency of the striking tool body 10 is set to a vibration damping frequency corresponding to each of these. Although the striking tool of the sixth embodiment is exemplified by having a damping material 30 and a sponge member 31 arranged around the core rod 25 to dampen the vibration of the core rod 25, the striking tool of the sixth embodiment may be implemented in a form in which the damping material 30 and sponge member 31 are not arranged.

[0133] In the striking tool of the sixth embodiment, a specific set of natural frequencies ω in the core rod structure 12 i However, there are several specific natural frequencies Ω in the striking tool body 10. i The frequencies are set to dampen the natural vibrations of the striking tool body 10, corresponding to each of the above. More specifically, in the striking tool of the sixth embodiment, the primary natural frequency ω1 of the core rod structure 12 is set to a frequency that dampens the natural vibrations of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 12 is set to a frequency that dampens the natural vibrations of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0134] In the striking tool of the sixth embodiment, the type and length of the core rod 25, the position and mass of the weights 26 including the first weight 26a and the second weight 26b, and the tension of the core rod 25 are adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 in the core rod structure 12 correspond to the primary natural frequency Ω1 and secondary natural frequency Ω2 in the striking tool body 10, respectively, and the frequencies that dampen the natural vibration of the striking tool body 10.

[0135] In the striking tool of the sixth embodiment, first, the type of core rod 25 is selected, and then the length of the core rod 25 is determined so that the length of the core rod 25 allows the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 to be adjusted to the desired frequencies. Then, the position and mass of the first weight 26a and the position and mass of the second weight 26b attached to the core rod 25 are adjusted to adjust the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12. At this time, the position and mass of the first weight 26a and the position and mass of the second weight 26b attached to the core rod 25 are adjusted so that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 matches the ratio of the frequency that dampens the natural vibration of the primary mode of the striking tool body 10 corresponding to the primary natural frequency Ω1 of the striking tool body 10 and the frequency that dampens the natural vibration of the secondary mode of the striking tool body 10 corresponding to the secondary natural frequency Ω2 of the striking tool body 10. In other words, in the striking tool of the sixth embodiment, the position and mass of the first weight 26a and the position and mass of the second weight 26b attached to the core rod 25 are adjusted so that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 matches the ratio of the optimal natural frequency f1 of the primary mode to the optimal natural frequency f2 of the secondary mode, which is obtained by equation (3) above.

[0136] By adjusting the positions and masses of the first weight 26a and the second weight 26b attached to the core rod 25, the tension on the core rod 25 is then adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12 match the frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. As a result, the primary natural frequency ω1 of the core rod structure 12 is set to a frequency that dampens the primary natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 12 is set to a frequency that dampens the secondary natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. The tension on the core rod 25 can be adjusted by relatively rotating the end knobs 24 and cap members 29, which are positioned on either side of the cylindrical member 27 and to which both ends of the core rod 25 are screwed.

[0137] Here, in the striking tool of the sixth embodiment, the optimal natural frequency f obtained by equation (3) above corresponds to the frequency that dampens the natural vibration of the striking tool body 10, with a specific set of natural frequencies (ω1, ω2) in the core rod structure 12 corresponding to a specific set of natural frequencies (Ω1, Ω2) in the striking tool body 10. i Or the optimal natural frequency f i Further explanation will describe a specific example of adjusting the natural frequencies (ω1, ω2) of the core rod structure 12 in order to set the frequency to fall within a predetermined range of change.

[0138] In adjusting the natural frequencies (ω1, ω2) of the core rod structure 12 of the striking tool in the sixth embodiment, first, the type of core rod 25 is selected considering the material and diameter of the core rod 25, and then the type of weight 26 is selected considering the material and size of the weight 26. If a compact structure is desired by shortening the length of the core rod 25, a core rod 25 with a small diameter and high specific gravity is selected. In the striking tool of the sixth embodiment, for example, a brass screw shaft with a diameter of 4 mm is selected as the core rod 25, and a brass nut that screws onto the core rod 25 is selected as the weight 26.

[0139] After selecting the types of core rods 25 and weights 26, several core rods 25 of different lengths are prepared, and a hammering test is performed on each of the core rods 25 of different lengths to measure the vibration acceleration of each core rod 25. For example, five core rods 25 of lengths 10cm, 15cm, 20cm, 25cm, and 30cm are prepared, and a hammering test similar to that in the second embodiment is performed on each core rod 25 to measure the vibration acceleration.

[0140] Once the acceleration waveforms of the five core rods 25 of different lengths are obtained through measurements in the hammering test, the power spectrum of each core rod 25 of each length is calculated from these acceleration waveforms, and based on these power spectra, the natural frequency ω of each core rod 25 of each length is determined. i Check the natural frequencies ω of the core rods 25 of each length. iUpon checking, based on the results of that check, the length of the core rod 25 and the natural frequency of each mode (natural frequency ω) are determined, similar to the case of the striking tool 2 of the second embodiment. i An approximate formula is created for the relationship between ( ) and ). Then, using the created approximate formula as a reference, the length of the core rod 25 is determined such that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 exceed, for example, the optimal natural frequency f1 of the desired primary mode and the optimal natural frequency f2 of the secondary mode, which can be obtained using equation (3) above. Note that by setting the length of the core rod 25 so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25 exceed the desired frequencies, when attaching and adjusting the first weight 26a and the second weight 26b to the core rod 25, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12 can be reduced.

[0141] After determining the length of the core rod 25, the position and mass of the first weight 26a and the second weight 26b attached to the core rod 25 are then adjusted to match the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12, which matches the ratio of the frequency that dampens the primary mode natural vibration of the striking tool body 10 to the frequency that dampens the secondary mode natural vibration. The second weight 26b is attached to the antinode of the secondary mode natural vibration of the core rod 25. The secondary natural frequency ω2 of the core rod structure 12 is adjusted by adjusting the mass of the second weight 26b attached to the antinode of the secondary mode natural vibration relative to the core rod 25. The first weight 26a is attached to the node of the secondary mode natural vibration located near the center in the longitudinal axis direction of the core rod 25. By adjusting the mass of the first weight 26a attached to the core rod 25 at the node position of the second-order mode natural vibration, the primary natural frequency ω1 of the core rod structure 11 can be changed without changing the secondary natural frequency ω2 of the core rod structure 12, thereby adjusting the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11. The mass of the first weight 26a and the mass of the second weight 26b are adjusted by the number of first weights 26a and second weights 26b attached to the core rod 25, respectively. The changes in the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12 due to changing the mass of the second weight 26b attached at the antinode position of the second-order natural vibration and the mass of the first weight 26a attached at the node position of the second-order natural vibration can be calculated by vibration simulation using a model in which weights are attached to a rod. Therefore, the adjustment of the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 by changing the mass of the first weight 26a and the mass of the second weight 26b is investigated by simulation. Through simulation, the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 is adjusted by changing the mass of the first weight 26a and the mass of the second weight 26b, and the masses of the first weight 26a and the second weight 26b are determined so that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 matches the ratio of the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode obtained by equation (3) above.

[0142] By adjusting the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 to match the desired frequency ratio, the tension applied to the core rod 25 is then adjusted to match the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 to the frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. Since the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 matches the ratio of the optimal natural frequency f1 of the primary mode to the optimal natural frequency f2 of the secondary mode, which is obtained by equation (3) above, the tension applied to the core rod 25 can be adjusted to simultaneously match the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 12 to the optimal natural frequency f1 of the primary mode and the optimal natural frequency f2 of the secondary mode, which are obtained by equation (3) above. Furthermore, the tension applied to the core rod 25 may be adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12 match frequencies that fall within a predetermined range of change relative to the optimal natural frequency f1 of the primary mode and frequencies that fall within a predetermined range of change relative to the optimal natural frequency f2 of the secondary mode, respectively. In adjusting the tension applied to the core rod 25, the tension applied to the core rod 25 is increased by rotating the end knob 24 and the cap member 29 relative to each other in the direction in which the core rod 25 is screwed into each, thereby increasing the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11. Alternatively, the tension applied to the core rod 25 is decreased by rotating the end knob 24 and the cap member 29 relative to each other in the direction in which the core rod 25 is detached from the end knob 24 and the cap member 29.

[0143] When adjusting the tension applied to the core rod 25 to adjust the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12, for example, a hammering test of a striking tool to which the core rod structure 12 with the tension of the core rod 25 has been changed can be used. By changing the tension applied to the core rod 25 and performing a hammering test of a striking tool to which the core rod structure 12 has been attached, the vibration damping effect can be confirmed, thereby adjusting the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12.

[0144] As described above, by adjusting the tension applied to the core rod 25, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12 are adjusted to frequencies that dampen the primary and secondary natural vibrations of the striking tool body 10, respectively. In this way, by adjusting the length of the core rod 25, the position and mass of the first weight 26a attached to the core rod 25, the position and mass of the second weight 26b attached to the core rod 25, and the tension applied to the core rod 25, the primary natural frequency ω1 of the core rod structure 12 is set to a frequency that dampens the primary natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 12 is set to a frequency that dampens the secondary natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0145] According to the striking tool of the sixth embodiment, a specific set of natural frequencies ω in the core rod structure 12 i However, there are several specific natural frequencies Ω in the striking tool body 10. i The frequency is set to dampen the natural vibration of the striking tool body 10 in accordance with the corresponding frequency. i In response to vibrations, the core rod structure 12 resonates, causing each natural frequency Ω of the striking tool body 10 to resonate. i This absorbs natural vibrations and reduces vibrations of the hitting tool body 10. Therefore, it is possible to reduce the vibrations of multiple frequency components that occur in the hitting tool body 10 when the ball collides with the hitting portion 22 of the hitting tool body 10 and are transmitted from the grip portion 21 to the batter's hand. Furthermore, according to the hitting tool of the sixth embodiment, the structure for reducing vibrations of multiple vibration components is configured as a core rod structure 13 as a dynamic vibration absorber, which is arranged inside the hitting tool body 10 and has a core rod 25 extending along the long axis of the hitting tool, and a first weight 26a and a second weight 26b attached to the core rod 25. As a result, vibrations of multiple frequency components transmitted from the hitting tool to the batter's hand during hitting can be reduced by a single structure built into the hitting tool. [Examples]

[0146] The following describes embodiments of the present invention. As embodiments of the present invention, a striking tool of Embodiment 1, which corresponds to the second embodiment described above, and a striking tool of Embodiment 2, which corresponds to the fifth embodiment, were manufactured, and a hammering test was performed to confirm the vibration reduction effect.

[0147] [Example 1] As the striking tool for Example 1, a striking tool corresponding to the striking tool 2 of the second embodiment described above was manufactured. Referring to Figure 4, the striking tool for Example 1 was manufactured as a metal bat. That is, the grip portion 21, tapered portion 23, and hitting portion 22 of the striking tool body 10 of Example 1 were formed from metal material. The end knob 24 and cap member 29 of the striking tool body 10 were formed from resin material. The core rod structure 11 of the striking tool for Example 1 was attached to the striking tool body 10 so as to be positioned inside the grip portion 21. Furthermore, in the core rod structure 11 of the striking tool for Example 1, a brass screw shaft with a diameter of 4 mm and a total length of 17 cm was used as the core rod 25, a brass nut that screws onto the core rod 25 was used as the weight 26, and an acrylic cylindrical member with an outer diameter of 16 mm and a thickness of 2 mm was used as the cylindrical member 27. The weights 26 attached to the core rod 25 were attached to the core rod 25 with a gap of 0.25 mm or more in the direction of the core rod 25's long axis. A sponge member 31 was placed between the first weight 26a and the second weight 26b attached to the core rod 25. No damping material 30 such as oil was filled inside the cylindrical member 27.

[0148] Furthermore, in the striking tool of Example 1, the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 12 were set to frequencies that dampen the natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 and secondary natural frequency Ω2 of the striking tool body 10, respectively. More specifically, by adjusting the position and mass of the first weight 26a attached to the core rod 25, the primary natural frequency ω1 of the core rod structure 12 was set to a frequency that dampens the natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10. By adjusting the position and mass of the second weight 26b attached to the core rod 25, the secondary natural frequency ω2 of the core rod structure 12 was set to a frequency that dampens the natural vibration of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0149] A hammering test was performed on the striking tool of Example 1 described above to confirm the vibration reduction effect. In the hammering test, the striking tool of Example 1 was suspended by a string, an accelerometer was attached to the grip portion 21 of the striking tool body 10, and the striking point on the grip portion 21 side of the striking part 22 of the striking tool body 10 was vibrated with a hammer. The acceleration of the vibration of the striking tool body 10 when vibrated with the hammer was measured with the accelerometer. For comparison, a hammering test was also performed on a striking tool without the core rod structure 12 attached, and the vibration acceleration was measured in the same manner.

[0150] Figure 6 shows the test results for the hammering tool of Example 1, and is a diagram showing the vibration acceleration waveform during the hammering test. Figure 6(A) is the vibration acceleration waveform obtained by performing a hammering test on a hammering tool without the core rod structure 12 for comparison, and Figure 6(B) is the vibration acceleration waveform obtained by performing a hammering test on the hammering tool of Example 1 with the core rod structure 12. Figure 7 also shows the test results for the hammering tool of Example 1, and is a diagram showing the power spectrum (frequency function) obtained from the vibration acceleration waveform obtained in the hammering test. Figure 7(A) is the power spectrum obtained from a hammering test on a hammering tool without the core rod structure 12 for comparison, and Figure 7(B) is the power spectrum obtained from a hammering test on the hammering tool of Example 1 with the core rod structure 12.

[0151] As shown in Figure 6, it was confirmed that the core rod structure 12 in the striking tool of Example 1 significantly reduces vibrations generated in the grip portion 21. In other words, it was confirmed that the striking tool of Example 1 significantly reduces vibrations transmitted to the batter's hand during striking. Furthermore, as shown in Figure 7, it was confirmed that the core rod structure 12 in the striking tool of Example 1 significantly reduces both the first-order mode vibrations and the second-order mode vibrations generated in the grip portion 21 simultaneously. Thus, it was confirmed that the striking tool of Example 1 can reduce multiple frequency components of vibrations transmitted from the striking tool to the batter's hand during striking with a single structure built into the striking tool.

[0152] [Example 2] As the striking tool for Example 2, a striking tool corresponding to the fifth embodiment described above was manufactured. Figure 8 is a diagram showing the core rod structure 11a of the striking tool 1a of Example 2, and is a diagram showing a cross-section of the striking tool 1a. Figure 8(A) is a diagram showing the overall configuration of the core rod structure 11a, and Figure 8(B) is an enlarged cross-sectional view showing the weight 33 and the surrounding portion of the core rod structure 11a.

[0153] Referring to Figure 8, the striking tool 1a of Example 2 was manufactured as a metal bat. Specifically, the grip portion 21, tapered portion 23, and hitting portion 22 of the striking tool body 10 of the striking tool 1a of Example 2 were made of metal. The end knob 24 and the cap member 29 were made of metal. The core rod structure 11a of the striking tool 1a of Example 2 was attached to the striking tool body 10 so as to be positioned inside the grip portion 21. In the core rod structure 11a of the striking tool 1a of Example 2, a brass screw shaft with a diameter of 4 mm and a total length of 24 cm was used as the core rod 25. One end of the core rod 25 was fixed to the end knob 24 by a stainless steel nut 37, passing through a hole provided in the center of the end knob 24. The other end of the core rod 25 was attached to the cap member 29 by screwing it into a screw hole provided in the metal cap member 29. Furthermore, the cap member 29 is secured to the grip portion 21 by bolts 38 that pass through the grip portion 21 and are screwed into the screw holes of the cap member 29, with multiple screw holes provided on the side of the cap member 29.

[0154] The weight 33 of the core rod structure 11a was formed by stacking multiple brass washers in the axial direction, each having a hole larger than the diameter of the core rod 25. The weight 33, which was placed around the core rod 25 with the weight passing through it, was attached to the core rod 25 by being sandwiched from both sides in the axial direction by silicone washers 34 and stainless steel nuts 35. With this configuration, the weight 33 does not directly contact the core rod 25, but is fastened to the core rod 25 via the silicone washers 34 by stainless steel nuts 35 that are screwed onto the core rod 25 on both sides in the axial direction. Because the weight 33 does not directly contact the core rod 25, it is possible to easily adjust the natural frequency of the core rod structure 11a by lowering it while suppressing the weight 33 from increasing the rigidity of the core rod structure 11a. In addition, a sponge member 36 as a damping material was placed around the weight 33 in the core rod structure 11a. As the sponge member 36, a cylindrical form made of a material such as urethane, silicone, or rubber was used and arranged to completely cover the outer circumference of the weight 33. In the core rod structure 11a, the cylindrical member 27 was not provided, and no damping material 30 such as oil was placed inside the striking tool body 10.

[0155] Furthermore, in the striking tool 1a of Example 2, the length of the core rod 25, the position and mass of the weight 33, and the tension of the core rod 25 were adjusted to set the primary natural frequency ω1 and secondary natural frequency ω2 in the core rod structure 11a to frequencies that dampen the natural vibration of the striking tool body 10, corresponding to the primary natural frequency Ω1 and secondary natural frequency Ω2 of the striking tool body 10, respectively. More specifically, the length of the core rod 25 was first adjusted so that the length of the core rod 25 could be adjusted to the desired frequencies for both the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod 25. Next, the position and mass of the weight 33 attached to the core rod 25 were adjusted so that the ratio of the primary natural frequency ω1 to the secondary natural frequency ω2 of the core rod structure 11a matched the ratio of the frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10. Then, the tension applied to the core rod 25 was adjusted so that the primary natural frequency ω1 and secondary natural frequency ω2 of the core rod structure 11 matched the frequencies that dampen the natural vibrations of the primary and secondary modes of the striking tool body 10, respectively. The tension applied to the core rod 25 was adjusted by changing the degree of tightening of the nut 37 screwed onto the end of the core rod 25. In this way, the primary natural frequency ω1 of the core rod structure 11a is set to a frequency that dampens the natural vibration of the primary mode of the striking tool body 10, corresponding to the primary natural frequency Ω1 of the striking tool body 10, and the secondary natural frequency ω2 of the core rod structure 11 is set to a frequency that dampens the natural vibration of the secondary mode of the striking tool body 10, corresponding to the secondary natural frequency Ω2 of the striking tool body 10.

[0156] A hammering test was performed on the striking tool 1a of Example 2 described above to confirm the vibration reduction effect. In the hammering test, the striking tool 1a of Example 2 was suspended by a string, an accelerometer was attached to the grip portion 21 of the striking tool body 10, and the striking point on the grip portion 21 side of the striking part 22 of the striking tool body 10 was vibrated with a hammer. The acceleration of the vibration of the striking tool body 10 when vibrated with the hammer was measured with the accelerometer. For comparison, a hammering test was also performed on a striking tool without the core rod structure 11a attached, and the vibration acceleration was measured in the same manner.

[0157] Figure 9 shows the test results for the hammering tool 1a of Example 2, and is a diagram showing the vibration acceleration waveform during the hammering test. Figure 9(A) is the vibration acceleration waveform obtained from a hammering test performed on a hammering tool without the core rod structure 11a for comparison, and Figure 9(B) is the vibration acceleration waveform obtained from a hammering test performed on the hammering tool 1a of Example 2 with the core rod structure 11a. Figure 10 also shows the test results for the hammering tool 1a of Example 2, and is a diagram showing the power spectrum (frequency function) obtained from the vibration acceleration waveform obtained from the hammering test. Figure 10(A) is the power spectrum obtained from a hammering test performed on a hammering tool without the core rod structure 11a for comparison, and Figure 10(B) is the power spectrum obtained from a hammering test performed on the hammering tool 1a of Example 2 with the core rod structure 11a.

[0158] As shown in Figure 9, it was confirmed that the core rod structure 11a of the striking tool 1a of Example 2 significantly reduces vibrations generated in the grip portion 21. In other words, it was confirmed that the striking tool 1a of Example 2 significantly reduces vibrations transmitted to the batter's hand during striking. Furthermore, as shown in Figure 10, it was confirmed that the core rod structure 11a of the striking tool 1a of Example 2 significantly reduces both the first-order mode vibrations and the second-order mode vibrations generated in the grip portion 21 simultaneously. Thus, it was confirmed that the striking tool 1a of Example 2 can reduce multiple frequency components of vibrations transmitted from the striking tool to the batter's hand during striking with a single structure built into the striking tool.

[0159] While embodiments for carrying out the present invention have been described above, the embodiments described above are illustrative examples of the present invention, and the present invention is not limited to the examples of the embodiments described above. It can be applied with various modifications as long as they are described in the claims. For example, the examples of the embodiments described above may be combined with well-known technology, conventional technology, or prior art, or parts of them may be replaced with well-known technology, etc. [Explanation of symbols]

[0160] 1,2,3,1a Striking tool, 10 Striking tool body, 11,12,13,11a Core rod structure, 21 Grip section, 22 Striking section, 23 Tapered section, 24 End knob, 24a Cylindrical wall section, 24b Convex section, 24c Recessed section, 24d Hole, 25 Core rod, 26 Weight, 26a First weight, 26b Second weight, 27 Cylindrical member, 28a,28b Nut, 29 Cap member, 29a Large diameter section, 29b Small diameter section, 29c Recessed section, 29d Hole, 30 Damping member, 31 Sponge member

Claims

1. A striking tool comprising a striking tool body having a grip portion and a striking portion connected to the grip portion, The device further comprises a core rod structure provided as a dynamic vibration absorber, which is arranged inside the main body of the striking tool, extends along the long axis in which the grip portion and the striking portion are aligned, and has at least one end fixed to the main body of the striking tool. A striking tool in which a specific set of natural frequencies among the natural frequencies of the core rod structure are set to frequencies that dampen the natural vibration of the striking tool body, corresponding to a specific set of natural frequencies among the natural frequencies of the striking tool body.

2. The aforementioned core rod structure has a weight attached to the core rod, The striking tool according to claim 1, wherein the position and mass of the weight attached to the core rod are adjusted so that one of a set of specific natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body, corresponding to one of a set of specific natural frequencies in the striking tool body.

3. The core structure has a plurality of weights attached to the core, The striking tool according to claim 2, wherein the plurality of weights are attached to the core rod with gaps in the longitudinal direction.

4. By adjusting the length of the core rod, one of the specific natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body, corresponding to one of the specific natural frequencies in the striking tool body. The striking tool according to claim 2, wherein the position and mass of the weight attached to the core rod are adjusted so that one of the other natural frequencies among a specific set of natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body, corresponding to one of the other natural frequencies among a specific set of natural frequencies in the striking tool body.

5. The position at which the first weight, which is one of the multiple weights, is attached to the core rod and the mass of the first weight are adjusted so that one of the specific multiple natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body, corresponding to one of the specific multiple natural frequencies in the striking tool body. The striking tool according to claim 3, wherein the position at which a second weight, which is another weight among the plurality of weights, is attached to the core rod and the mass of the second weight are adjusted so that another natural frequency among a specific plurality of natural frequencies in the core rod structure is set to a frequency that dampens the natural vibration of the striking tool body, corresponding to another natural frequency among a specific plurality of natural frequencies in the striking tool body.

6. The striking tool according to any one of claims 1 to 5, wherein a damping material is arranged around the core rod inside the striking tool body to dampen the vibration of the core rod.

Images