GROMMET AND RACKET

Structures with racket performance varied according to the configurations of cylindrical parts can be easily used. A grommet (25-28) includes a cylindrical part (32) which is mounted pierced through a through hole (23) formed in a frame (20) of a racket (10) and through which a string (21) passes. The string is extended in a tensioned state on the frame so as to form front and back faces as hitting faces (22). The cylindrical part includes a first formation section (35) forming both sides of a central axis position (C) of the cylindrical part and a second formation section (36) rotationally shifted with reference to the central axis position by 90 degrees relative to the first formation section and forming both sides of the central axis position. One of the first and second formation sections is disposed on both sides in a front/back direction. The first and second formation sections each have a different rigidity.

TECHNICAL FIELD

The present invention relates to a grommet to be mounted on a racket frame so as to prevent a string and the frame from being in contact with each other, and to a racket using the grommet.

BACKGROUND ART

As disclosed in patent document 1, tennis rackets and badminton rackets are provided with a loop-shaped frame and have a hitting face (a face) formed by extending a string in a tensioned state inside the frame. The frame has formed therein many holes which are arranged at certain spacings and through which the string is inserted. Grommets are mounted in the holes, and cylindrical portions of the grommets are positioned between the inner circumferential faces of the holes and the string so as to prevent the inner circumferential faces and the string from being in contact with each other.

PRIOR ART DOCUMENT

Patent Document

Patent Document 1: Japanese National Publication of International Patent Application No. 2012-517873

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

When a racket hits a ball, strings receive a force in the front/back direction of a hitting face, and the force also acts on grommets via the strings. When, for example, a ball is hit with spin, a string extended in a tensioned state in a longitudinal direction also receives a force in a lateral direction, and the force in the lateral direction also acts on the grommets. The inventors focused on the fact that forces act on the grommets like this, and has allowed structures with varied grommet rigidities to be used, thereby arriving at an invention that allows various performances of a racket to be varied.

The present invention was created in view of such a fact, and an object thereof is to provide a grommet and a racket for which structures with racket performance varied according to the configurations of cylindrical parts can be easily used.

Means for Solving Problems

A grommet in one aspect of the present invention includes a cylindrical part which is mounted pierced through a hole formed in a frame of a racket and through which a string passes, wherein the string is extended in a tensioned state on the frame so as to form front and back faces as hitting faces, the cylindrical part includes a first formation section forming both sides of a central axis position of the cylindrical part and a second formation section rotationally shifted with reference to the central axis position by 90 degrees relative to the first formation section and forming both sides of the central axis position, one of the first and second formation sections is disposed on both sides in a front/back direction, and the first and second formation sections each have a different rigidity.

This configuration allows for implementation of a structure in which the cylindrical part can be oriented in such a manner as to allow for the selecting of which of the first and second formation sections is to be disposed in the front/back direction. Thus, the rigidities of the cylindrical part in the front/back direction and in a direction orthogonal thereto can be varied, and various performances pertaining to ball hitting, such as ball repulsive-performance and spin performance, can be varied, thereby allowing structures meeting various user needs to be easily implemented.

In the grommet of the present invention, the cylindrical part, when viewed in a direction in which a central axis thereof extends, may include a circular inner edge and an oval or ellipsoidal outer edge, so as to provide the first and second formation sections. In accordance with this configuration, with the cylindrical part having a simple and non-complicated shape, the rigidity of the cylindrical part in the longer direction, in which the oval or ellipsoidal shape is formed, can be relatively enhanced, and the rigidity thereof in the shorter direction can be relatively decreased.

A racket in one aspect of the present invention includes: the grommet, which includes a plurality of the cylindrical parts; and a frame on which strings are extended in a tensioned state in a longitudinal direction and a lateral direction, the strings forming front and back faces as hitting faces, wherein the cylindrical parts are pierced through holes formed in the frame, so as to mount the grommet on the frame, and the strings are extended in a tensioned state by being passed through the plurality of cylindrical parts.

In the racket of the present invention, positions at which are formed the first and second formation sections of cylindrical parts through which the string extended in a tensioned state in the longitudinal direction is inserted may be different, by 90 degrees with reference to the central axis positions of the cylindrical parts, from positions at which are formed the first and second formation sections of cylindrical parts through which the string extended in a tensioned state in the lateral direction is inserted. In accordance with this configuration, the ball hitting performance can be obtained under a condition in which the cylindrical parts through which the string in the longitudinal direction is inserted and the cylindrical parts through which the string in the lateral direction is inserted are different from each other in terms of the orientations of the first and second formation sections.

In the racket of the present invention, the first formation sections may have a higher rigidity than the second formation sections, cylindrical parts through which the string extended in a tensioned state in the longitudinal direction is inserted may each have the first formation section formed on both sides in the front/back direction, and cylindrical parts through which the string extended in a tensioned state in the lateral direction is inserted may each have the second formation section formed on both sides in the front/back direction. In accordance with this configuration, the cylindrical parts through which the string in the longitudinal direction is inserted can have a relatively low rigidity in the lateral direction and thus have a large motion range in the lateral direction when a ball is hit, thereby allowing the string in the longitudinal direction to enhance the spin performance upon ball hitting. Moreover, the cylindrical parts through which the string in the lateral direction is inserted can have a relatively low rigidity in the front/back direction and thus have a large motion range in the front/back direction when a ball is hit, thereby allowing the string in the lateral direction to enhance the ball repulsive-performance.

In the racket of the present invention, the holes have a circular shape, and the first and second formation sections of each of the cylindrical parts may be different from each other in terms of a distance in a radial direction to an inner circumferential edge of a hole through which the cylindrical part is pierced. In accordance with this configuration, with respect to the relationship with the holes in the frame through which the cylindrical parts are pierced, each of the formation sections that desirably have a larger motion range, among the first and second formation sections, can have a large space between the formation section and the hole. Thus, the motion range of the cylindrical part can be increased not only by the first and second formation sections of the cylindrical part, but also in terms of the relationship with the hole through which the cylindrical part is pierced.

In the racket of the present invention, the first and second formation sections may be formed in each of cylindrical parts, among the plurality of cylindrical parts, through which a string extended in a tensioned state in the longitudinal and/or lateral direction and passing through a central region of the hitting faces is inserted. In accordance with this configuration, the ball hitting performance of the strings forming a so-called sweet spot can be enhanced effectively.

In the racket of the present invention, the cylindrical parts in which the first and second formation sections are formed may protrude from an inner circumferential face of the frame by a smaller amount than the cylindrical parts in which the first and second formation sections are not formed. In accordance with this configuration, owing to the cylindrical parts with a small amount of protrusion, a large motion range can be enhanced for the string inserted through these cylindrical parts.

Effect of the Invention

In the present invention, the cylindrical parts are, as described above, provided with the first and second formation sections having different rigidities, thereby allowing the structure enhancing the racket performance to be easily used.

The following specifically describes embodiments of the present invention by referring to the drawings. Although the following descriptions are given for examples in which the grommet of the present invention is applied to a soft tennis racket, the application of the grommet is not limited to this and can be changed. For example, the grommet may be applied to a tennis racket, a squash racket, or a badminton racket.

FIG. 1is an appearance view of a racket in accordance with embodiments of the present invention,FIG. 1Abeing a front view of the racket,FIG. 1Bbeing a side view of the racket. Note that indications of some components are omitted for descriptive purposes in the drawings described in the following.

As depicted inFIG. 1, a racket10includes: a head11, i.e., a site for hitting a ball; a grip12, i.e., a site to be gripped by a player to hold the racket10; and a shaft13integrally coupling the head11and the grip12. In the following descriptions, as indicated by arrows inFIG. 1, the longer direction of the racket10is defined as a longitudinal direction, the side in the longitudinal direction on which the head11is located is defined as a top-end side, and the side in the longitudinal direction on which the grip12is located is defined as a grip-end side. A direction orthogonal to the longitudinal direction on a hitting face22of the racket10(i.e., on a plane along the hitting face22) is defined as a lateral direction (or a left-right direction). A direction orthogonal to the hitting face22of the racket10is defined as a front/back direction (or a forward/backward direction). The near side of the plane ofFIG. 1A(left side of the plane ofFIG. 1B) is defined as a front side, and the opposite side from the front side is defined as a back side.

When seen in the forward/backward direction, the shaft13includes throats15constituted by two branches extending from the grip12toward the head11. A yoke17forming a portion of the head11is formed between the left and right throats15. The shaft13is not limited to this and may not include two branches.

The head11includes an oval frame20that is long in the longitudinal direction, and strings21that are extended inside the frame20in a tensioned state in the longitudinal direction and the lateral direction. The strings21form hitting faces (faces)22on both of the front and back sides of the inside of the frame20. For example, the frame20may be provided by forming a cylindrical hollow body formed from fiber-reinforced plastic into an oval shape. Alternatively, the frame20may not be a hollow body but may be filled with a foam material, or may be a wooden or metal body.

An outer peripheral face20aof the frame20includes a groove section20bformed by a central portion of the outer peripheral face20ain the thickness direction being recessed relative to both side portions thereof. The groove section20bis continuously provided in the circumferential direction of the frame20. The frame20includes through holes (holes)23. The through holes23extend in a pierced manner from the bottom side of the groove section20bof the frame20to an inner circumferential face20cof the frame20. The through holes23, i.e., a plurality of through holes, are arranged in the circumferential direction of the frame20.

FIG. 2is an explanatory front view of a situation in which grommets have been removed from the frame. Four grommets25-28are mounted, as indicated inFIG. 2, onto the frame20from the outer-edge side, and strings21are extended in a tensioned state on the frame20via the grommets25-28. In the present embodiment, the grommet25on the top-end side extends, with reference to the front view of the frame20inFIG. 2, from a site of approximately 10 o'clock to a site of approximately 2 o'clock and protects the portion of the frame20on a top-20A side. The left and right grommets26and27are respectively provided extending from the vicinities of the left and right end portions of the grommet25on the top-end side to positions reaching the lowermost through holes23formed in the left and right side faces of the frame20. The grommet28on the grip-end side is provided on the yoke17. The lengths of the grommets25-27, i.e., the grommets other than the grommet28on the grip-end side, in the circumferential direction of the frame20may be varied in accordance with various conditions.

As an example, the grommets25-28may each be a molded product obtained through injection molding with thermoplastic. The grommets25-28each include a band-like part31extending in the circumferential direction of the frame20and a plurality of cylindrical parts32protruding from a back face of the band-like part31, i.e., one face of the band-like part31. The band-like part31has a forward-backward width that is greater than or equal to that of the groove section20band less than that of the frame20. The band-like part31of the grommet25on the top-end side has a forward-backward width substantially equal to that of the frame20and protects the top-20A side of the frame20.

The cylindrical parts32each include a base section on the band-like-part-31side and a leading-end section on an opposite side from the base section, and the leading-end sections are pierced through the through holes23from outside the frame20. The piercing causes the grommets25-28to be mounted on the frame20, with the leading-end sides of the cylindrical parts32disposed protruding inward from the inner-circumferential-face-20cside of the frame20. An inner space of each of the cylindrical parts32is formed as an insertion path33(seeFIG. 3) through which a string21is inserted. The inner diameter of the insertion path33is substantially the same as or slightly larger than the diameter of the string21, i.e., the inner diameter of the insertion path33is made to be closer to that of the string21to be suppressed from being displaced relative to the insertion path33when a ball is hit. The inner diameter of the insertion path33is within a range from 100 to 165, where the diameter of the string21is 100.

Next, the specific configuration of the cylindrical part is described by referring toFIG. 3.FIG. 3Ais an A-A line cross-sectional view ofFIG. 1.FIG. 3Bis a B-B line cross-sectional view ofFIG. 1.FIG. 3Arepresents a cylindrical part32through which a string21extended in a tensioned state in the longitudinal direction is inserted (hereinafter, “longitudinal cylindrical part32A”).FIG. 3Brepresents a cylindrical part32through which a string21extended in a tensioned state in the lateral direction is inserted (hereinafter, “lateral cylindrical part32B”).

FIGS. 3A and 3Bare seen in the direction in which the central axis of the string21extends (a direction orthogonal to the plane of the figures). As depicted inFIGS. 3A and 3B, the longitudinal cylindrical part32A and the lateral cylindrical part32B each include a circular inner edge forming an insertion path33and an oval outer edge, and the inner edge and the outer edge share the same central axis position C. The longitudinal cylindrical part32A and the lateral cylindrical part32B each include a first formation section35forming, in a major axis direction, both sides of the central axis position C, and a second formation section36forming, in a minor axis direction, both sides of the central axis C. Thus, the second formation section36is positioned rotationally shifted with reference to the central axis position C by 90 degrees relative to the first formation section35.

The first formation section35is a certain region including the major axis of the oval, and the second formation section36is a certain region including the minor axis of the oval. Accordingly, in each of the longitudinal cylindrical part32A and the lateral cylindrical part32B, the first formation section35has a different thickness from the second formation section36and thus has a different rigidity from the second formation section36. In the present embodiment, the first formation section35has a higher rigidity than the second formation section36. As an example, the certain regions may be regions depending on the diameter of the insertion path33or regions within a range of about 90 degrees with reference to the central axis position C with the major axis and the minor axis as centers.

The positions at which the first formation section35and the second formation section36of the longitudinal cylindrical part32A are formed are different, by 90 degrees with reference to the central axis positions C, from the positions at which the first formation section35and the second formation section36of the lateral cylindrical part32B are formed. In particular, in the longitudinal cylindrical part32A inFIG. 3A, the first formation section35is formed on both sides in the front/back direction, and the second formation section36is formed on both sides in a direction orthogonal to the front/back direction with reference to the face direction of the hitting face22(seeFIG. 1), i.e., both sides in the lateral direction. In the lateral cylindrical part32B inFIG. 3B, by contrast, the second formation section36is formed on both sides in the front/back direction, and the first formation section35is formed on both sides in a direction orthogonal to the front/back direction with reference to the face direction of the hitting face22, i.e., both sides in the longitudinal direction.

The through holes23formed in the frame20are circular openings (openings shaped like exact circles), and the longitudinal cylindrical parts32A and the lateral cylindrical parts32B that have oval outer edges are mounted into the circular through holes23by being pierced therethrough. Accordingly, the first formation section35formed on both sides in the major axis direction of the oval and the second formation section36formed on both sides in the minor axis direction of the oval are different from each other in terms of the distance in the radial direction to the inner circumferential edge of the through hole23. In particular, spaces S are formed between the second formation sections36and the inner circumferential edges of the through holes23, thereby forming deformation allowances allowing the cylindrical parts32A and32B to be deformed in directions such that the cylindrical parts32A and32B tilt toward the spaces S (see the white arrows in the figures). Meanwhile, the first formation sections35and the inner circumferential edges of the through holes23contact each other or have small spaces therebetween, and the inner circumferential edge of each of the through holes23restricts deformation that would occur when the cylindrical parts32A and32B tilt toward the first formation section35.

The longitudinal cylindrical part32A and the lateral cylindrical part32B are, as described above, different in terms of the positions at which the first formation section35and the second formation section36are formed, and thus each have a different position (orientation) for formation of the space S. In particular, in the lateral cylindrical part32B inFIG. 3B, spaces S are formed on both sides in the front/back direction, and in the longitudinal cylindrical part32A inFIG. 3A, spaces S are formed on both sides in a direction orthogonal to the face direction of the hitting face22(both sides in the lateral direction), in comparison with the front/back direction.

Although every longitudinal cylindrical part32A and every lateral cylindrical part32B may include a first formation section35and a second formation section36, some of the longitudinal cylindrical parts32A and the lateral cylindrical parts32B may have a circular outer edge shape so as to attain a uniform thickness in the circumferential direction (seeFIG. 4). For example, the longitudinal cylindrical parts32A and the lateral cylindrical parts32B, through which the string21that passes through the central region of the hitting face22, which is so-called a sweet spot, is inserted, may include first formation sections35and second formation sections36. In particular, the longitudinal cylindrical parts32A within a region SS1inFIG. 1and the lateral cylindrical parts32B within a region SS2inFIG. 1may include first formation sections35and second formation sections36.

The longitudinal cylindrical parts32A and the lateral cylindrical parts32B that include first formation sections35and second formation sections36may protrude from the inner circumferential face20cof the frame20by a smaller amount than the longitudinal cylindrical parts32A and the lateral cylindrical part32B without first formation sections35and second formation sections36. In this case, the string21inserted into the cylindrical parts32A and32B that include first formation sections35and second formation sections36tends to be more easily flexure-deformed when hitting a ball.

When a ball is hit with spin by the racket10, the string21extended in a tensioned state in the longitudinal direction is flexed by receiving a force in the lateral direction, and spin is applied to the ball owing to the force of the string21restoring from the flexed state. In the longitudinal cylindrical part32A, as described above, the second formation section36is formed on both sides in the lateral direction and has a lower rigidity than the first formation section35, so the amount of motion (deformation) of the longitudinal cylindrical part32A in the lateral direction can be increased (seeFIG. 3A), thereby increasing the elastic force of the longitudinal cylindrical part32A in the lateral direction when the longitudinal cylindrical part32A is restored after being moved. Hence, the spin rate of a ball can be increased so that the spin performance in ball hitting can be enhanced.

When a ball is hit by the racket10, the string21receives a force in the front/back direction and is flexed in the front/back direction, and the ball is repulsively hit by receiving the force of the string21restoring from the flexed state. When the lateral cylindrical part32B is configured such that, as described above, a second formation section36is formed on both sides in the front/back direction and has a lower rigidity than a first formation section35, the amount of motion (deformation) of the lateral cylindrical part32B in the front/back direction can be increased, thereby increasing the elastic force of the lateral cylindrical part32B in the front/back direction when the lateral cylindrical part32B is restored after being moved. Hence, the repulsive force applied to the ball can be increased so that the ball repulsive-performance can be enhanced.

The longitudinal cylindrical part32A includes a first formation section35having a high rigidity and formed on both sides in the front/back direction, so when attention is focused only on the string21extended in a tensioned state in the longitudinal direction, it may seem as if the longitudinal cylindrical part32A does not tend to be deformed in the front/back direction and decreases the repulsive-performance. However, since the string in the longitudinal direction in the racket10is longer than that in the lateral direction, the string21extended in a tensioned state in the lateral direction, which is relatively short, more largely affects the repulsive-performance. The lateral cylindrical parts32B, and thus the string21in the lateral direction, have a large amount of motion, so the amount of motion of the longitudinal string21and that of the lateral string21can be made close to each other so as to increase the amount of flexure deformation of the entirety of the strings21, thereby enlarging the sweet spot with the repulsive-performance enhanced. In one possible configuration, material for the longitudinal cylindrical part32A may be different from that for the lateral cylindrical part32B such that the lateral cylindrical part32B is more flexible (deformable) than the longitudinal cylindrical part32A. In accordance with this configuration, the lateral cylindrical part32B and the string21in the lateral direction can have an even larger amount of motion, and the amount of motion of the longitudinal string21can be made even closer to that of the lateral string21, thereby enlarging the sweet spot with the repulsive-performance enhanced.

In the present embodiment, as described above, a structure can be easily implemented in which the longitudinal cylindrical part32A and the lateral cylindrical part32B are different in terms of the orientations of formation sections35and36having different rigidities. Thus, the formation sections35and36having different amounts of motion (deformation) for ball hitting can be disposed as described above so as to enhance both the repulsive-performance and the spin performance.

In the meantime, structures from the prior art adopt configurations in which the area of the opening of the insertion path in a cylindrical part is large relative to a string so as to increase the amount of motion of the string. In such configurations, however, when the string is flexed upon hitting a ball, the string is displaced within the insertion path and less likely to receive a force from the cylindrical part.

In this regard, in the present embodiment, the diameter of the string21is made close to the inner diameter of the insertion path33, so the cylindrical part32is deformed in accordance with flexure of the string21upon ball hitting. Thus, the force of the cylindrical part32restoring from a deformed state resulting from ball hitting can act on the string21, and thus on the ball, so that the ball hitting performance can be enhanced in comparison with the structures from the prior art. In addition, when a ball is hit, displacement of the string21relative to the insertion path33can be suppressed, and unnecessary vibrations, which would be unpleasant for the player, can be prevented from being generated, so the unclear feeling of ball hitting can be avoided.

In such an embodiment, the first formation section35and the second formation section36are formed with the cylindrical part32having an oval outer edge, so the rigidities of the first formation section35and the second formation section36can be varied by means of the simple and non-complicated shape, thereby achieving the above-described ball hitting performance. Moreover, a configuration can be easily used in which the longitudinal cylindrical part32A and the lateral cylindrical part32B are different in terms of the orientations of a first formation section35and a second formation section36in the front/back direction.

Since the outer edge of the cylindrical part32has an oval shape, spaces S can be formed between the through hole23and the second formation section36forming both sides in the minor axis direction, with the cylindrical part32inserted into the circular through hole23. The cylindrical part32can be easily moved (deformed) in a direction such that the cylindrical part32leans toward the second formation section36having a low rigidity, and the above-described ball hitting performance can be better achieved by the spaces S ensuring larger motion ranges for the cylindrical part32toward the spaces S.

The present invention is not limited to the embodiments described above and can be implemented with various changes made thereto. The above-described embodiments are not limited to the sizes, shapes, directions, or the like illustrated in the attached drawings and can have changes made thereto, as appropriate, as long as the effect of the invention can be achieved. In addition, the invention can be implemented with changes made thereto, as appropriate, without deviating from the scope of the purpose of the invention.

For example, the orientations of the first formation sections35and the second formation sections36in the longitudinal cylindrical part32A and the lateral cylindrical part32B are not limited to the abovementioned ones, and in comparison with the abovementioned embodiments, the orientations of the first formation section(s)35and the second formation section(s)36of both/either the longitudinal cylindrical part32A and/or the lateral cylindrical part32B may be shifted by 90 degrees with reference to the central axis position C. Meanwhile, the second formation section36may have a higher rigidity than that of the first formation section35. Thus, although, for example, the spin performance or the repulsive-performance provided by the cylindrical parts32A and32B could be reduced, the racket10can be implemented with a structure achieving a balanced overall performance owing to the ball hitting performance associated with, for example, the structures of, or the materials for, the frame20and the shaft13. In the present invention, as described above, a structure can be implemented in which the cylindrical parts32A and32B can be oriented in such a manner as to allow for the selecting which of the first formation section35and the second formation section36is to be disposed in the front/back direction, thereby producing the racket10that can meet various user needs.

In the embodiments described above, the cylindrical part32has an oval outer edge. However, the first formation section35and the second formation section36can also be formed in the manner described above by making it so that the cylindrical part32has an ellipsoidal outer shape.

The first formation section35and the second formation section36of the cylindrical part32may have the same thickness but may each have a different rigidity by each being formed from a different material. In this case, the opening of the through hole23through which the cylindrical part32is pierced may have an oval or ellipsoidal shape such that the first formation section35and the second formation section36each have a different distance to the inner circumferential edge of the through hole23in the radial direction.

INDUSTRIAL APPLICABILITY

The present invention pertains to a grommet and a racket using the same, for which structures with racket performance varied according to the configurations of the cylindrical parts can be easily used.

The present application is based upon Japanese Patent Application No. 2019-042724, filed on Mar. 8, 2019, the entire contents of which are incorporated herein.