CN108348806B - Tennis racket string - Google Patents

Abstract

The inventive net thread for racket has the advantages of forming hollow part and improving durability. The disclosed device is provided with: a core wire (11); and a string (10) for a racket wound around the outer periphery of the core wire and having a plurality of side wires (12). The core wire is provided with: a solid portion (20) formed in a predetermined region including a central axis position (C); and a plurality of hollow portions (21) formed in the periphery of the solid portion and extending in the extending direction of the core wire. The number of the hollow portions is odd, and the hollow portions are arranged at equal angles around the solid portion.

Description

Tennis racket string

Technical Field

The present invention relates to a racket string used for tennis, badminton, squash, and the like, and more particularly, to a racket string in which a plurality of side wires are wound around the outer periphery of a core wire.

Background

In a tennis racket or a badminton racket, strings are stretched in a net shape on a racket face portion. Further, as a net string for a racket, a net string is widely used in which a monofilament serving as a thin side line is wound around a monofilament serving as a core line or a net string outside a multifilament. The mesh wire described above is generally called "monofilament type" when the core wire is monofilament, and is called "multifilament type" when the core wire is multifilament.

As a monofilament type mesh wire, as shown in patent document 1, a structure in which a hollow portion is formed at a central axis position of a core wire is proposed. By forming the hollow portion, there can be obtained an advantage that the elastic force of the net string is improved and the shock absorbing performance at the time of hitting the ball can be improved.

Documents of the prior art

Patent document 1: japanese patent laid-open publication No. 2005-237877

Disclosure of Invention

However, in the mesh wire of patent document 1, when a force is applied in the radial direction of the cross section, there is a problem that the hollow portion is easily crushed in the radial direction. The crush of the hollow portion is likely to occur not only at the intersection of the vertical line and the horizontal line of the net string, but also at the time of hitting a ball, and there is a problem that the durability of the net string is lowered due to the crush.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a racket string which can obtain advantages of forming a hollow portion and improve durability.

The string for a racket according to the present invention extends in a predetermined direction, and includes: a solid portion formed in a predetermined region including a position of the central axis; and a plurality of hollow portions formed at the periphery of the solid portion and extending in the extending direction. Further, the racket string according to the present invention includes a core string; and a plurality of side wires wound around an outer peripheral side of the core wire, the core wire including: a solid portion formed in a predetermined region including a position of the central axis; and a plurality of hollow portions formed at the periphery of the solid portion and extending in the extending direction of the core wire.

According to these configurations, since the central axis position is a solid portion and the hollow portion is formed in the periphery of the solid portion, it is possible to suppress a strong force from acting on the hollow portion from both sides in the radial direction (thickness direction) of the net string by tightening or hitting the racket. This makes it possible to prevent the hollow portion from being easily crushed, to obtain advantages such as a vibration absorbing effect at the time of hitting a ball, and to prevent a decrease in durability due to an increase in stress concentration caused by crushing. Further, since a plurality of hollow portions are formed in the periphery of the solid portion, not only the sum of the opening areas of the hollow portions can be obtained, but also the opening areas of the respective hollow portions can be reduced, thereby making it difficult to crush the hollow portions.

In the racket string according to the present invention, the number of the hollow portions may be odd, and the hollow portions may be arranged at equal angles around the solid portion. According to this configuration, the hollow portions can be arranged so as to be dispersed around the solid portion, and two hollow portions can be arranged in the diameter direction of the mesh wire. Thus, even if a force from the radial direction is applied to one of the plurality of hollow portions and temporarily collapsed by stretching the racket, it is possible to suppress a large force from the radial direction from being applied to the other hollow portion. As a result, the two hollow portions can be prevented from being crushed at the same time, and the advantages of the hollow portions can be more easily and satisfactorily exhibited.

In the racket string according to the present invention, the number of the hollow portions may be 3, 5, or 7. According to this structure, the size and layout of the hollow portion can be maintained in a well-balanced manner, stress concentration on the hollow portion can be more favorably relaxed to improve durability, and the advantage of the hollow portion can be favorably exhibited while maintaining the state in which the hollow portion is formed.

In the racket string according to the present invention, the plurality of hollow portions may be formed in the same shape. According to this structure, even if the orientation of the circumferential direction of the net string is changed, the performance relating to the hitting of the hollow portion can be stabilized without change.

In the racket string according to the present invention, the ratio of the opening area of the hollow portion in the cross section of the entire racket string may be 3.0% to 8.0%. According to this numerical range, both improvement in durability against cutting and improvement in feeling of hitting a ball, which are contradictory, can be favorably achieved.

According to the present invention, the solid portion is formed at the central axis position, and the plurality of hollow portions are formed at the periphery of the solid portion, so that advantages of forming the hollow portions can be obtained, and durability can be improved.

Drawings

Fig. 1 is a cross-sectional view of a mesh wire according to embodiment 1.

Fig. 2 is a cross-sectional view of a wire associated with a comparative configuration.

Fig. 3 is a cross-sectional view of the mesh wire according to embodiment 2.

Fig. 4 is a graph showing a relationship between a void ratio of a mesh wire, a natural frequency, and a cutting strength.

Fig. 5 is a graph showing a relationship between the gauge (gauge) of the mesh wire and the natural frequency.

Detailed Description

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. The string of the present invention can be applied to various rackets such as a soft tennis racket, a tennis ball, a badminton racket, and a squash as long as it is stretched over a frame of the racket to form a racket face.

(embodiment 1)

Fig. 1 is a cross-sectional view of a mesh wire according to embodiment 1. As shown in fig. 1, the mesh wire 10 includes: a core wire 11 located at the center to form a circular outer periphery in cross section; a plurality of side wires 12 spirally wound around the outer peripheral side of the core wire 11; and a resin coating layer 13 further formed on the outer periphery thereof, the outer shape of which is formed in a circular shape in cross section. The core wire 11 and the lateral wire 12 are integrally bonded by an adhesive.

A monofilament made of a synthetic fiber, preferably a polyamide fiber of nylon 6 or nylon 66 is used for the core wire 11. In addition, a synthetic fiber monofilament, multifilament or multifilament, preferably, polyamide fiber such as nylon 6 or nylon 66 is used for the side thread 12. Preferably, a polyamide resin is used for the resin coating layer 13. In addition, polyester (polybutylene terephthalate, polyethylene terephthalate, or the like), polyolefin, polyphenylene sulfide, polyether ether ketone, or the like may be used for the core wire 11 and the side wire 12.

The core wire 11 includes: a solid portion 20 formed in a predetermined region including a central axis position C thereof; and a plurality of hollow portions 21 formed around the solid portion 20. In other words, in the core wire 11, as shown by the two-dot chain line in fig. 1, a region having a substantially circular cross section inside the plurality of hollow portions 21 becomes the solid portion 20. The solid portion 20 and the plurality of hollow portions 21 are formed to extend in the extending direction of the core wire 11, respectively.

The number of the hollow portions 21 is odd, and in embodiment 1, 5 hollow portions 21 are formed. The 5 hollow portions 21 are disposed at equal angles (about 72 degrees, respectively) around the solid portion 20. Therefore, all the hollow portions 21 have a positional relationship in which no other hollow portion 21 is present on a line L (broken line in fig. 1) connecting the hollow portion 21 and the central axis position C, and a plurality of arbitrary hollow portions 21 are not arranged in the radial direction of the core wire 11.

The 5 hollow portions 21 are formed in substantially the same inner peripheral shape, and in embodiment 1, are formed in substantially a rectangular shape in cross section. Specifically, the device is provided with: 2 sides forming an interior angle of substantially right angle; and 2 sides of an inner angle of which the diagonal angle is an obtuse angle, are formed into an elongated shape so as to be tapered toward the radial outside of the core wire 11. The distances from the central axis position C of the 5 hollow portions 21 are substantially the same, and the distances from the outer periphery of the core wire 11 are also set substantially the same.

The ratio of the opening area (sum) of all the hollow portions 21 in the cross section of the entire mesh wire 10 (hereinafter referred to as "hollow ratio") is preferably set to 3.0% to 8.0%, for the reason described below.

Next, the deformation of the hollow portion 21 when the mesh wire 10 is stretched will be described in comparison with the comparative structure of fig. 2.

The string 10 is stretched in a mesh shape over a frame (not shown) of the racket, and receives a tensile force in an extending direction. At the same time, the crossing portions of the vertical threads and the horizontal threads stretched in a mesh shape receive compressive forces from both sides in the radial direction in the cross section. Further, in the case of hitting a ball with a racket, the string 1O also receives a compressive force from both sides in the diameter direction in the cross section. Such a compressive force acts on the wire 10 from various directions depending on a change in the orientation of the stretched wire 10 in the circumferential direction, as long as the wire is in the radial direction in the cross section. Here, as an example, a case where a compressive force acts in the direction of arrow F in fig. 1 is considered.

When the compressive force acts, the uppermost hollow portion 21 in fig. 1 is deformed so as to be crushed in the vertical direction in the radial direction. However, since the other 4 hollow portions 21 are not located on the line of the arrow F on which the compressive force acts, the acting compressive force becomes extremely weak, and the deformation of the hollow portions 21 can be suppressed. That is, 4 hollow portions 21 not on the line of the arrow F can maintain the opened state. Even if the diameter position on which the compressive force acts is changed, since 2 hollow portions 21 are not arranged in the diameter direction, at least 4 hollow portions 21 can maintain the opened state as described above.

In the uppermost hollow portion 21, a compressive force from below acts via the solid portion 20. Therefore, the force of deforming the hollow portion 21 so as to crush is dispersed in the solid portion 20, and the amount of deformation by crushing is supposed to be reduced. Further, it is presumed that the solid portion 20 acts to support the uppermost hollow portion 21 as a base against the compressive force from above, and the uppermost hollow portion 21 is less likely to be crushed. Therefore, even the uppermost hollow portion 21 is in a state in which deformation by crushing is suppressed.

Here, since the 5 hollow portions 21 are formed at an interval of about 72 ° around the shaft center position C in the cross section and have the same shape, when the position of action of the compression force indicated by the arrow F in fig. 1 is changed by a multiple of about 72 °, the hollow portions 21 are deformed in the same manner as described above. Depending on the change in the diameter position where the compressive force acts, all the hollow portions 21 may not overlap the diameter position, and in this case, the crushing deformation of the hollow portions 21 can be suppressed more favorably.

Fig. 2 is a cross-sectional view of a wire associated with a comparative configuration. The position and shape of the hollow portion 21 of the mesh wire 10 according to embodiment 1 are changed from the mesh wire 10A according to the comparative structure, and one hollow portion 21A is formed at the axial center position C of the core wire 11A. In the mesh wire 10A of such a comparative structure, when the compressive force acts in the direction of the arrow F in the same manner as described above, as shown by the two-dot chain line in the figure, the hollow portion 21A is crushed on both sides in the up-down direction (diameter direction) so as to be flat. The reason for this is that the hollow portion 21A is located at the shaft center position C, and the opening area of the hollow portion 21A is large.

Stress is concentrated on the left and right sides of the crushed hollow portion 21A, and cracks are generated from the stress concentrated portion, which causes adverse effects such as deterioration of durability and cutting strength. In contrast, the mesh wire 10 of embodiment 1 can suppress the occurrence of stress concentration as in the comparative structure, because the total opening area of the hollow portions 21 can be obtained and the opening areas of the hollow portions 21 can be reduced, and the collapse of the hollow portions 21 can be suppressed as described above. This can prevent the occurrence of cracks in the stress concentration portion of the comparative structure, for example, and can improve the durability and the cutting strength. As a result, the life of the network cable 10 can be extended, high performance can be maintained for a long period of time, and the cost burden can be reduced by reducing the replacement frequency.

Here, by forming a plurality of hollow portions 21 in the core wire 11 as in the mesh wire 10, there are advantages described below as compared with a mesh wire (hereinafter, referred to as "solid mesh wire") in which the core wire 11 having no hollow portion 21 is solid.

By forming the hollow portion 21, the gauge (diameter size) can be made thicker without changing the weight per unit length as compared with a solid mesh wire. Therefore, the contact area between the net string 10 and the ball (badminton) can be enlarged, controllability and drivability can be improved, and the hitting power can be increased. Further, when the mesh wire 10 having the same specification as the solid mesh wire is formed, the displacement of the mesh wire 10 can be improved according to the amount of the plurality of hollow portions 21, and high rebound due to recovery can be realized, and the hitting sound can be improved in addition to the light and sharp feeling of hitting the ball.

The advantages as above are not obtained with solid mesh wires, and are not easily obtained in the case where the hollow portion 21A is crushed as in the comparative configuration. That is, the above-described advantage can be said to be a peculiar significant effect obtainable by forming the plurality of hollow portions 21 as the above-described mesh wire 10.

(embodiment 2)

Next, embodiment 2 different from embodiment 1 will be described with reference to fig. 3. Fig. 3 is a cross-sectional view of the mesh wire according to embodiment 2. In embodiment 2, the same reference numerals are given to the components common to embodiment 1, and the description thereof will be omitted.

The mesh wire 10 according to embodiment 2 has 3 hollow portions 31 formed in the core wire 11. The 3 hollow portions 31 are arranged at equal angles, that is, about 120 ° around the solid portion 20. Therefore, in embodiment 2, all the hollow portions 31 are also in a positional relationship where no other hollow portion 31 is present on a line L (broken line in fig. 3) connecting the hollow portions 31 and the central axis position C, and a plurality of arbitrary hollow portions 31 are not arranged in the radial direction of the core wire 11.

The 3 hollow portions 31 are formed in substantially the same inner peripheral shape, and in embodiment 2, are formed in a substantially triangular shape in cross section. Specifically, the base is formed in a substantially isosceles triangular shape, and the base is positioned on the center axis position C side and is curved in a concentric circle shape with respect to the core wire 11, and the inner angles of the other 2 sides are obtuse angles and positioned radially outward of the core wire 11. The 3 hollow portions 31 are set to have the same distance from the central axis position C and the same distance from the outer periphery of the core wire 11. The 3 hollow portions 31 are formed at positions closer to the central axis position C than the hollow portions 21 of embodiment 1 and farther from the outer periphery of the core wire 11.

The ratio of the opening area (sum) of all the hollow portions 31 in the cross section of the entire core wire 11 is also set to be 3.0% to 8.0%.

A groove 11a formed by cutting out in a V shape is formed on the outer peripheral surface of the core wire 11 radially outside each hollow portion 31. The groove 11a may be omitted, and the core wire 11 may have a substantially cylindrical outer periphery.

According to embodiment 2 as described above, the same effects as those of embodiment 1 can be obtained, and the number of hollow portions 31 to be formed is reduced, so that the manufacturing can be facilitated by simplifying the mold and the like.

Next, an experiment performed to evaluate a feel of hitting a ball, a hitting sound, and durability with respect to the network cable according to embodiment 1 will be described. In the experiment, the mesh wire of embodiment 1 shown in fig. 1 was manufactured as examples 1 and 2, and the hollow ratio of the hollow portion 21 was set to 4.2% in example 1 and 2.3% in example 2. Further, as a comparative example, a mesh wire in which the core wire 11 is solid was manufactured. Except for these, the conditions were the same for each example and comparative example.

For the net strings of examples 1 and 2 and comparative examples, an experiment for measuring the natural vibration frequency of the net string was performed in order to evaluate the feel of hitting a ball and the sound of hitting a ball. Further, for the wires of examples 1 and 2, an experiment was performed to measure the cutting strength of the wire for the purpose of evaluating durability. The measurement results are shown in fig. 4A and 4B. Fig. 4A and 4B are graphs showing the relationship between the void fraction of the network cable, the natural frequency, and the breaking strength. Fig. 4A shows the measurement results of the natural frequency and the cutting strength of the string stretched in the racket for hard tennis. Fig. 4B shows the measurement results of the natural frequency and the cutting strength of the string stretched in the racket for soft tennis.

In an experiment for measuring the natural frequency of the string, the strings of examples 1 and 2 and comparative example were stretched at a tension of 50 pounds in a racket for hard tennis and at a tension of 30 pounds in a racket for soft tennis. An acceleration sensor was attached to the grip portion of the stretched racket, and the output of the acceleration sensor was analyzed using an FFT analyzer DS-2000 (manufactured by mini-perimeter measuring instruments, ltd.). And (3) impacting the intersection point of the network cable by using an impact hammer, carrying out Fourier transform on the obtained time axis vibration waveform, and measuring the first-order natural vibration frequency of the network cable. The measurement results are shown in fig. 4A and 4B.

Further, using the racquets stretched with the strings of examples 1 and 2 and comparative example, the hitting feeling and hitting sound of the player at the time of hitting the ball were evaluated. In this evaluation, example 1 in which the hollow ratio was 4.2% was the most preferable, and example 2 in which the hollow ratio was 2.3% was the next more preferable, and the variation amount of the natural frequency of the change in the hitting feel and the hitting sound felt by the player, which was inferior to example 1, was about 1OHz or more in the comparative example. In the graphs of fig. 4A and 4B, the hollow percentage of the value obtained by subtracting 1OHz from the natural frequency of example 1 on the straight line obtained by the least square method from each measurement result of the natural frequency was about 3%. Therefore, when the hollow ratio is 3.0% or more, a high hitting sound and a good feeling of hitting can be obtained. The difference between examples 1 and 2 is estimated to be due to the influence of the hollow ratio on the number of hollow portions not formed.

In an experiment for measuring the cutting strength of the wire, the wires of examples 1 and 2 were measured for the cutting strength by autograph AGS-J (manufactured by Shimadzu corporation). The measurement conditions were as defined in JIS L1013:2010 edition "chemical fiber yarn test method", and the test article was held at a distance of 250mm, a tensile strength of 300mm/min, and the number of tests was 3. The measurement results of the average value of 3 tests are shown in fig. 4A and 4B. The lower limit of the cutting strength that the mesh can withstand in actual use is 300N. In the graphs of fig. 4A and 4B, the void ratio is greater than 8% when the straight-line breaking strength of each measurement result of the connection breaking strength is less than 300N. Therefore, when the void ratio is 8.0% or less, excellent cutting durability can be exhibited. As described above, when the hollow ratio is 3.0% to 8.0%, both improvement in the cutting durability and improvement in the hitting feeling, which are inverse relationships, can be favorably realized.

Fig. 5 is a graph showing a relationship between the specification of the mesh wire and the natural frequency. To examine the relationship between the gauge of the mesh wire and the presence or absence of the hollow portion in the core wire, 3 types of mesh wires (core wire is solid) of comparative examples having the gauge of 1.15mm, 1.2mm, and 1.25mm and the mesh wire of example 1 having the gauge of 1.25mm were prepared. Further, the natural frequency was measured by stretching the racket for soft tennis as described above. The measurement results are shown in fig. 5.

As can be understood from the graph of fig. 5, under the condition that the mesh wire is 1.25mm, the value of the natural frequency after the measurement becomes large in example 1 in which the hollow portion is formed in the core wire, as compared with the comparative example in which the core wire is solid. Therefore, as long as the specification is the same, the one forming the hollow portion is light and obtains a sharp hitting feeling, and the hitting sound can be improved.

In addition, in the graph of fig. 5, a straight line obtained by the least square method from each measurement result of the natural frequency of the comparative example is depicted. On this straight line, the specification of 1.215mm, which is the same as the natural frequency of example 1 having the specification of 1.25mm, is set. That is, as long as the natural frequency is the same, a thicker specification can be formed in the example 1 in which the hollow portion is formed in the core wire, as compared with the comparative example in which the core wire is solid. Thus, the contact area between the net string and the ball (badminton) can be increased while maintaining the feeling of hitting the ball and the hitting sound.

The present invention is not limited to the above embodiments, and can be implemented by being variously modified. In the above-described embodiments, the size, shape, orientation, and the like shown in the drawings are not limited thereto, and may be appropriately modified within the range in which the effects of the present invention are exhibited. In addition, the present invention can be modified and implemented as appropriate within a range not departing from the object of the present invention.

For example, even if the number of hollow portions 21 and 31 formed in the core wire 11 is 7, the same effects as those of the above embodiments can be obtained. Further, although the number of hollow portions 21, 31 formed may be changed to an even number, it is advantageous that the hollow portions 21, 31 are arranged at equal angles with the solid portion 20 as the center as an odd number, and that the hollow portions 21, 31 are not arranged in the radial direction of the core wire 11, so that simultaneous crushing of the hollow portions 2 can be avoided. The number of hollow portions 21, 31 formed may be an odd number of 9 or more, but the number of hollow portions 21, 31 formed may be 3, 5, 7, which improves the balance between the size and layout of the hollow portions 21, 31, and provides excellent durability and hitting performance.

The opening shape of the hollow portions 21 and 31 is not limited to the illustrated example, and may be changed from the viewpoint of workability, hitting performance, and durability.

In addition, the wire 10 may be configured such that all the side wires 12 wound around the core wire 11 are omitted. In this case, it is preferable to use synthetic fiber monofilaments and polyester for the mesh wire 10. However, polyamide fibers of nylon 6 and nylon 66 may be used.

(availability in industry)

The racket net wire of the present invention forms a hollow part and has an effect of improving durability.

The present application is based on Japanese patent application 2015-221973, filed on 11/12/2015. The contents of which are all incorporated herein.

Claims (2)

1. A string for a racket, which is characterized in that it extends in a predetermined direction,

the string for racket includes: a solid portion formed in a region that becomes circular including a central axis position in a cross section; and five hollow portions formed at the periphery of the solid portion and extending in the extending direction,

the hollow portion is disposed in a quadrangular shape having 2 sides including the side on the side of the central axis position of the cross section and having an inner angle forming a right angle and 2 sides including an inner angle forming an obtuse angle at the diagonal angle, and the quadrangular shape is formed in an elongated shape so as to be tapered outward in the radial direction of the mesh wire, and the sides on the side of the central axis position of the cross section extend in the circumferential direction of a circle concentric with the solid portion,

the five hollow portions are formed in the same shape and arranged at equal angles with the solid portion as the center,

the ratio of the opening area of the hollow portion in the cross section of the entire racket string is 3.0% to 8.0%.

2. A string for a racket, comprising a core thread; and a plurality of side wires wound around an outer peripheral side of the core wire,

the core wire is provided with: a solid portion formed in a region that becomes circular including a central axis position in a cross section; and five hollow portions formed at the periphery of the solid portion and extending in the extending direction of the core wire,

the hollow portion is disposed in a quadrangular shape extending in a circumferential direction concentric with the solid portion on a side of a central axis position of a cross section, the quadrangular shape including 2 sides having an inner angle forming a right angle including the side on the side of the central axis position and 2 sides having an inner angle forming an obtuse angle at a diagonal angle thereof, and the quadrangular shape being formed in an elongated shape so as to be tapered toward a radial outside of the core wire,

the five hollow portions are formed in the same shape and arranged at equal angles with the solid portion as the center,

the ratio of the opening area of the hollow portion in the cross section of the entire racket string is 3.0% to 8.0%.

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