Patent Description:
A tennis racket includes a frame and a string. In the old days, a string is directly inserted through holes formed in a frame. In a recent tennis racket, a string is inserted through holes with grommets therebetween. <CIT> and <CIT> disclose proposals regarding the shapes of grommets. Documents <CIT> and <CIT> disclose a tennis racket in accordance with the preamble of claim <NUM>. In particular, <CIT> discloses in Fig. 8a a grommet with two holes that are each oval shaped. These holes may be arranged parallel to the face of the racket as shown in Fig. 8a or in a direction perpendicular to the face of the racket. <CIT> discloses further prior art.

A tennis player tries to hit a ball at the center of the face of a racket. However, in tennis play, hitting at a position shifted from the center frequently occurs. When a ball is hit at the lower side (ground side) with respect to the center, the ball flies at a small launch angle due to a change in the angle of the face. This launch angle causes a low trajectory. A ball with a low trajectory is less likely to pass over the net.

With enhancement of the performance of tennis rackets, drive shots are frequently used in recent tennis. Upon a drive shot, overspin is imparted to a tennis ball. Players desire tennis rackets with which spin is easily imparted.

An object of the present invention is to provide a racket having excellent spin performance.

A racket according to an aspect of the present invention includes.

Each of the tubular portions has a through hole through which the string is passed. The tubular portions include parallel movement tubular portions, wherein each through hole of the parallel movement tubular portions has a shape that mainly permits movement of the string in a direction parallel to the face, and vertical movement tubular portions, wherein each through hole of the vertical movement tubular portions has a shape that mainly permit movement of the string in a direction perpendicular to the face.

With the racket according to the present invention, upon impact with a ball, the string passed through each of the parallel movement tubular portions becomes greatly deformed in the direction parallel to the face. Thereafter, the string returns to the original shape. By the deformation and the return, high-rate spin is imparted to the ball.

With the racket according to the present invention, upon impact with a ball, the string passed through each of the vertical movement tubular portions becomes greatly deformed in the direction perpendicular to the face. Meanwhile, deformation, in the direction perpendicular to the face, of the string passed through each of the parallel movement tubular portions is small. Therefore, great pressure is applied to the ball from the string passed through each of the parallel movement tubular portions. By this pressure, high-rate spin is imparted to the ball.

Preferably, each of the parallel movement tubular portions is adjacent to at least one vertical movement tubular portion. Preferably, each of the vertical movement tubular portions is adjacent to at least one parallel movement tubular portion.

Preferably, each through hole of the parallel movement tubular portions has an inner dimension in the direction parallel to the face that is larger than an inner dimension in the direction perpendicular to the face. Preferably, a cross-sectional shape of the through hole of each of the parallel movement tubular portions is an ellipse or an elongated circle. Preferably, a ratio (L1/L2) of an inner dimension L1, in the direction parallel to the face, of the through hole of each of the parallel movement tubular portions to an inner dimension L2, in the direction perpendicular to the face, of the through hole of each of the parallel movement tubular portions is not less than <NUM>. Preferably, a ratio (L1/D) of an inner dimension L1, in the direction parallel to the face, of the through hole of each of the parallel movement tubular portions to a diameter D of the string is not less than <NUM>.

The through hole of each of the parallel movement tubular portions can have a base-side opening, a side wall, and a tip-side opening. Preferably, in each of the parallel movement tubular portions, the string is in contact with the side wall from the base-side opening to the tip-side opening. Preferably, in each of the parallel movement tubular portions, the string is in contact with a wall surface, at an inner side in a width direction, of the side wall.

Preferably, each of the parallel movement tubular portions has a through hole having a uniform cross-sectional shape from the base-side opening to the tip-side opening.

Preferably, a longitudinal string is passed through each of the parallel movement tubular portions, and another longitudinal string is passed through each of the vertical movement tubular portions.

Preferably, the parallel movement tubular portions and the vertical movement tubular portions are disposed near a top of the frame.

<FIG> show a tennis racket <NUM>. The tennis racket <NUM> includes a frame <NUM>, a grip <NUM>, grommets <NUM>, and a string <NUM>. The tennis racket <NUM> can be used in regulation-ball tennis. In <FIG> and <FIG>, an arrow X represents the width direction of the tennis racket <NUM>, and an arrow Y represents the axial direction of the tennis racket <NUM>.

The frame <NUM> includes a head <NUM>, two throats <NUM>, and a shaft <NUM>. The head <NUM> forms the contour of a face <NUM> (described in detail later). The front shape of the head <NUM> is substantially an ellipse. The major axis direction of the ellipse coincides with the axial direction Y of the tennis racket <NUM>. The minor axis direction of the ellipse coincides with the width direction X of the tennis racket <NUM>. One end of each throat <NUM> is connected to the head <NUM>. The throat <NUM> is connected at the vicinity of the other end thereof to the other throat <NUM>. The throats <NUM> extend from the head <NUM> to the shaft <NUM>. The shaft <NUM> extends from the location where the two throats <NUM> are connected to each other. The shaft <NUM> is formed so as to be integrally connected to the throats <NUM>. A portion, of the head <NUM>, located between the two throats <NUM> is a yoke <NUM>. The head <NUM> may have a shape other than an ellipse.

The frame <NUM> is composed of a pipe. In other words, the frame <NUM> is hollow. The material of the pipe is a fiber-reinforced resin. The matrix resin of the fiber-reinforced resin is a thermosetting resin. A typical thermosetting resin is an epoxy resin. Typical fibers of the fiber-reinforced resin are carbon fibers. The fibers are long fibers.

The grip <NUM> is formed by a tape wound on the shaft <NUM>. The grip <NUM> suppresses slip between a hand of a player and the tennis racket <NUM> when the tennis racket <NUM> is swung.

As shown in <FIG>, the tennis racket <NUM> includes a first grommet 8a, two second grommets 8b, and a third grommet 8c. Each grommet <NUM> includes a base <NUM> and a plurality of tubular portions <NUM>. Each tubular portion <NUM> is formed so as to be integrated with the base <NUM>. A typical material of the grommet <NUM> is a synthetic resin that is more flexible than the frame <NUM>.

The first grommet 8a is mounted onto a portion at and near the top of the head <NUM> as shown by an arrow A1 in <FIG>. As a result of the mounting, each tubular portion <NUM> of the first grommet 8a penetrates a hole (not shown) provided in the head <NUM>. Each second grommet 8b is mounted onto a side of the head <NUM> as shown by an arrow A2 in <FIG>. As a result of the mounting, each tubular portion <NUM> of the second grommet 8b penetrates a hole (not shown) provided in the head <NUM>. The third grommet 8c is mounted onto the yoke <NUM> as shown by an arrow A3 in <FIG>. As a result of the mounting, each tubular portion <NUM> of the third grommet 8c penetrates a hole (not shown) provided in the head <NUM>.

The string <NUM> is stretched on the head <NUM>. The string <NUM> is stretched along the width direction X and the axial direction Y. Of the string <NUM>, portions extending along the width direction X are referred to as transverse strings 10a. Of the string <NUM>, portions extending along the axial direction Y are referred to as longitudinal strings 10b. The face <NUM> (see <FIG>) is formed by a plurality of transverse strings 10a and a plurality of longitudinal strings 10b. The face <NUM> generally extends along an X-Y plane.

<FIG> is an enlarged view of a part of the grommet <NUM> of the tennis racket <NUM> in <FIG>. As described above, the grommet <NUM> includes the base <NUM> and the plurality of tubular portions <NUM>.

<FIG> show a part of the grommet <NUM>. <FIG> is a cross-sectional view taken along a plane including the axis of a tubular portion 100a. <FIG> is a cross-sectional view taken along a plane perpendicular to the axis of the tubular portion 100a. As shown in these drawings, the tubular portion 100a has a through hole 24a. The through hole 24a has a base-side opening 26a, a side wall 28a, and a tip-side opening 30a. As shown in <FIG>, the cross-sectional shape of the through hole 24a is an elongated circle. The through hole 24a has a uniform cross-sectional shape from the base-side opening 26a to the tip-side opening 30a. Therefore, the shape of the tip-side opening 30a is an elongated circle (that is, non-circular). In the tip-side opening 30a, the inner dimension in a direction parallel to the face <NUM> (the right-left direction in <FIG>) is larger than the inner dimension in a direction perpendicular to the face <NUM> (the up-down direction in <FIG>).

<FIG> show another part of the grommet <NUM>. <FIG> is a cross-sectional view taken along a plane including the axis of a tubular portion 100b. <FIG> is a cross-sectional view taken along a plane perpendicular to the axis of the tubular portion 100b. As shown in these drawings, the tubular portion 100b has a through hole 24b. The through hole 24b has a base-side opening 26b, a side wall 28b, and a tip-side opening 30b. As shown in <FIG>, the cross-sectional shape of the through hole 24b is a circle. The through hole 24b has a uniform cross-sectional shape from the base-side opening 26b to the tip-side opening 30b. Therefore, the shape of the tip-side opening 30b is a circle. In the tip-side opening 30b, the inner dimension in the direction parallel to the face <NUM> (the right-left direction in <FIG>) is equal to the inner dimension in the direction perpendicular to the face <NUM> (the up-down direction in <FIG>).

<FIG> show the tubular portion 100a in <FIG>. <FIG> also show the string <NUM>. The string <NUM> is passed through the through hole 24a. The string <NUM> is in contact with the side wall 28a from the base-side opening 26a to the tip-side opening 30a. The string <NUM> is in contact with a left side wall surface of the side wall 28a. Since the inner dimension in the right-left direction of the base-side opening 26a is equal to the inner dimension in the right-left direction of the tip-side opening 30a, the string <NUM> can be in contact with the side wall 28a from the base-side opening 26a to the tip-side opening 30a. The inner dimension in the right-left direction of the base-side opening 26a may be larger than the inner dimension in the right-left direction of the tip-side opening 30a. As is obvious from <FIG>, the inner dimension in the right-left direction of the through hole 24a is sufficiently larger than the diameter of the string <NUM>. Therefore, the string <NUM> can move rightward in the tubular portion 100a. The tubular portion 100a mainly permits movement of the string <NUM> in the right-left direction (the direction parallel to the face <NUM>).

In <FIG>, reference character CL indicates a center line. The tennis racket <NUM> has a symmetrical shape with respect to the center line CL. As shown in <FIG>, the tennis racket <NUM> includes a first tubular portion <NUM>, a second tubular portion <NUM>, a third tubular portion <NUM>, a fourth tubular portion <NUM>, a fifth tubular portion <NUM>, a sixth tubular portion <NUM>, a seventh tubular portion <NUM>, an eighth tubular portion <NUM>, a ninth tubular portion <NUM>, a tenth tubular portion <NUM>, an eleventh tubular portion <NUM>, a twelfth tubular portion <NUM>, a thirteenth tubular portion <NUM>, a fourteenth tubular portion <NUM>, a fifteenth tubular portion <NUM>, a sixteenth tubular portion <NUM>, a seventeenth tubular portion <NUM>, an eighteenth tubular portion <NUM>, a nineteenth tubular portion <NUM>, a twentieth tubular portion <NUM>, a twenty-first tubular portion <NUM>, a twenty-second tubular portion <NUM>, a twenty-third tubular portion <NUM>, a twenty-fourth tubular portion <NUM>, a twenty-fifth tubular portion <NUM>, a twenty-sixth tubular portion <NUM>, a twenty-seventh tubular portion <NUM>, a twenty-eighth tubular portion <NUM>, a twenty-ninth tubular portion <NUM>, a thirtieth tubular portion <NUM>, a thirty-first tubular portion <NUM>, a thirty-second tubular portion <NUM>, a thirty-third tubular portion <NUM>, a thirty-fourth tubular portion <NUM>, and a thirty-fifth tubular portion <NUM>. <FIG> shows <NUM> tubular portions <NUM>. Since the tennis racket <NUM> has a symmetrical shape with respect to the center line CL as described above, the number of tubular portions <NUM> in the tennis racket <NUM> is <NUM>.

As shown in <FIG>, the longitudinal strings 10b are passed through the first tubular portion <NUM>, the second tubular portion <NUM>, the third tubular portion <NUM>, the fourth tubular portion <NUM>, the fifth tubular portion <NUM>, the sixth tubular portion <NUM>, the seventh tubular portion <NUM>, the ninth tubular portion <NUM>, the twenty-seventh tubular portion <NUM>, the twenty-ninth tubular portion <NUM>, the thirtieth tubular portion <NUM>, the thirty-first tubular portion <NUM>, the thirty-second tubular portion <NUM>, the thirty-third tubular portion <NUM>, the thirty-fourth tubular portion <NUM>, and the thirty-fifth tubular portion <NUM>. The transverse strings 10a are passed through the eighth tubular portion <NUM>, the tenth tubular portion <NUM>, the eleventh tubular portion <NUM>, the twelfth tubular portion <NUM>, the thirteenth tubular portion <NUM>, the fourteenth tubular portion <NUM>, the fifteenth tubular portion <NUM>, the sixteenth tubular portion <NUM>, the seventeenth tubular portion <NUM>, the eighteenth tubular portion <NUM>, the nineteenth tubular portion <NUM>, the twentieth tubular portion <NUM>, the twenty-first tubular portion <NUM>, the twenty-second tubular portion <NUM>, the twenty-third tubular portion <NUM>, the twenty-fourth tubular portion <NUM>, the twenty-fifth tubular portion <NUM>, the twenty-sixth tubular portion <NUM>, and the twenty-eighth tubular portion <NUM>.

In the present embodiment, the second tubular portion <NUM> and the fourth tubular portion <NUM> each have a through hole 24a (see <FIG>) with a cross-sectional shape that is an elongated circle. The other tubular portions <NUM> each have a through hole 24b (see <FIG>) with a cross-sectional shape that is a circle. The tubular portions <NUM> other than the second tubular portion <NUM> and the fourth tubular portion <NUM> may each have a through hole 24a with a cross-sectional shape that is an elongated circle. For example, the sixth tubular portion <NUM> may have a through hole 24a with a cross-sectional shape that is an elongated circle.

<FIG> is an enlarged view of an area near the top of the tennis racket <NUM> in <FIG>. In <FIG>, the frame <NUM> and the transverse strings 10a are not shown. <FIG> shows the base <NUM>, the first tubular portion <NUM>, the second tubular portion <NUM>, the third tubular portion <NUM>, and the fourth tubular portion <NUM>. The first tubular portion <NUM> has a through hole 24b (see <FIG>) with a cross-sectional shape that is a circle. The second tubular portion <NUM> has a through hole 24a with a cross-sectional shape that is an elongated circle. The third tubular portion <NUM> has a through hole 24b with a cross-sectional shape that is a circle. The fourth tubular portion <NUM> has a through hole 24a with a cross-sectional shape that is an elongated circle. In the second tubular portion <NUM>, the string <NUM> is in contact with the wall surface, at the left side (the inner side in the width direction), of the side wall 28a of the through hole 24a. In the fourth tubular portion <NUM>, the string <NUM> is in contact with the wall surface, at the left side (the inner side in the width direction), of the side wall 28a of the through hole 24a.

<FIG> shows a tennis ball <NUM> together with the tennis racket <NUM>. <FIG> shows the moment of impact between the tennis racket <NUM> and the tennis ball <NUM>. In <FIG>, the tennis ball <NUM> collides against the face <NUM> at the lower side (the ground G side) with respect to the center line CL. In this state, the player swings the tennis racket <NUM> forward and then upward.

By this swing, outward force in the width direction is applied to the longitudinal string 10b passed through the second tubular portion <NUM>. The inner dimension in the width direction of the through hole 24a of the second tubular portion <NUM> (100a) is sufficiently large. Therefore, the longitudinal string 10b becomes deformed without being obstructed by the second tubular portion <NUM>, and moves outward in the width direction. <FIG> shows the longitudinal string 10b after the movement. Thereafter, the longitudinal string 10b returns to the original shape. The longitudinal string 10b passed through the fourth tubular portion <NUM> (100a) also similarly becomes deformed and returns to the original shape. The deformation and the return of these longitudinal strings 10b achieve a long contact time between the tennis racket <NUM> and the tennis ball <NUM>. With the tennis racket <NUM>, the tennis ball <NUM> is launched at a large launch angle. With the tennis racket <NUM>, even when the tennis ball <NUM> is hit at the lower side with respect to the center line CL, a high trajectory can be obtained.

As described above, the string <NUM> is in contact with the wall surface, at the inner side in the width direction, of the side wall 28a of the through hole 24a. Therefore, when the tennis ball <NUM> collides against the face <NUM> at the upper side with respect to the center line CL, promotion of deformation of the longitudinal strings 10b due to the through holes 24a, which have elongated circle shapes, is not achieved. Accordingly, a long contact time is not obtained, and the trajectory is not corrected. With the racket <NUM>, the difference in trajectory is small between when the tennis ball <NUM> collides against the face <NUM> at the upper side with respect to the center line CL and when the tennis ball <NUM> collides against the face <NUM> at the lower side with respect to the center line CL.

For the purpose of imparting performance intended by a designer to the tennis racket <NUM>, the tubular portion 100a may be formed such that the string <NUM> is in contact with the wall surface at the outer side in the width direction.

In <FIG>, an arrow W2 indicates the distance in the width direction from the center line CL to the tubular portion 100a that is located at the outermost side in the width direction, that has the non-circular tip-side opening 30a, and in which the string 10b is in contact with the wall surface at the inner side in the width direction. The distance W2 is preferably not less than <NUM>% and not greater than <NUM>%, and particularly preferably not less than <NUM>% and not greater than <NUM>%, of the half width W1 (see <FIG>) of the tennis racket <NUM>.

In the tennis racket <NUM>, the tubular portions 100a (the second tubular portion <NUM> and the fourth tubular portion <NUM>) located near the top each have the through hole 24a with a cross-sectional shape that is non-circular. The tubular portions <NUM> located at the yoke <NUM> may each have a through hole 24a with a cross-sectional shape that is non-circular. The tubular portions <NUM> located at the side may each have a through hole 24a with a cross-sectional shape that is non-circular. The transverse string 10a may be passed through a tubular portion <NUM> that has a through hole 24a with a cross-sectional shape that is non-circular. In any of these cases, improvement of a trajectory height can be achieved when the tennis ball <NUM> collides against a predetermined area.

In the tennis racket <NUM>, as described above, the second tubular portion <NUM> and the fourth tubular portion <NUM> each have the through hole 24a with a cross-sectional shape that is non-circular. Since the tennis racket <NUM> has a symmetrical shape with respect to the center line CL, the tennis racket <NUM> includes two second tubular portions <NUM> and two fourth tubular portions <NUM>. Therefore, the total number N of the tubular portions 100a that have a through hole 24a with a non-circular cross-sectional shape and in which the string 10b is in contact with the wall surface at the inner side in the width direction, is four. The total number N is preferably not less than <NUM> and not greater than <NUM>, and more preferably not less than <NUM> and not greater than <NUM>.

<FIG> is a bottom view of the tubular portion 100a of the grommet <NUM> in <FIG>. <FIG> shows the tip of the tubular portion 100a. In <FIG>, a direction perpendicular to the surface of the sheet is the axial direction of the tubular portion 100a. The tubular portion 100a has the tip-side opening 30a. As described above, the shape of the tip-side opening 30a is an elongated circle.

In <FIG>, an arrow L1 indicates the inner dimension, in the direction parallel to the face <NUM>, of the tip-side opening 30a. The inner dimension L1 is also the long diameter of the elongated circle. In <FIG>, an arrow L2 indicates the inner dimension, in the direction perpendicular to the face <NUM>, of the tip-side opening 30a. The inner dimension L2 is also the short diameter of the elongated circle. From the viewpoint that the string <NUM> easily becomes deformed in the direction parallel to the face <NUM> and is less likely to become deformed in the direction perpendicular to the face <NUM>, the ratio (L1/L2) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/L2) is preferably not greater than <NUM>. L1 is preferably not less than <NUM> and not greater than <NUM>.

In <FIG>, an arrow D indicates the diameter of the string <NUM>. From the viewpoint that the string <NUM> easily becomes deformed in the direction parallel to the face <NUM>, the ratio (L1/D) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/D) is preferably not greater than <NUM>.

<FIG> is a cross-sectional view of a part of a grommet <NUM> of a tennis racket according to another embodiment of the present disclosure, and <FIG> is a cross-sectional view taken along a line B-B in <FIG>. The structure of the tennis racket other than the grommet <NUM> is the same as that of the tennis racket <NUM> shown in <FIG>.

The grommet <NUM> includes a base <NUM> and a tubular portion <NUM>. The tubular portion <NUM> has a through hole <NUM>. The through hole <NUM> has a base-side opening <NUM>, a side wall <NUM>, and a tip-side opening <NUM>. As shown in <FIG>, the cross-sectional shape of the through hole <NUM> is an ellipse. The through hole <NUM> has a uniform cross-sectional shape from the base-side opening <NUM> to the tip-side opening <NUM>.

<FIG> is a bottom view of the tubular portion <NUM> of the grommet <NUM> in <FIG>. <FIG> shows the tip of the tubular portion <NUM>. <FIG> also shows a string <NUM>. In <FIG>, a direction perpendicular to the surface of the sheet is the axial direction of the tubular portion <NUM>. The shape of the tip-side opening <NUM> is an ellipse.

In <FIG>, an arrow L1 indicates the inner dimension, in a direction parallel to a face, of the tip-side opening <NUM>. The inner dimension L1 is also the major diameter of the ellipse. In <FIG>, an arrow L2 indicates the inner dimension, in a direction perpendicular to the face, of the tip-side opening <NUM>. The inner dimension L2 is also the minor diameter of the ellipse. From the viewpoint that the string <NUM> easily becomes deformed in the direction parallel to the face and is less likely to become deformed in the direction perpendicular to the face, the ratio (L1/L2) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/L2) is preferably not greater than <NUM>. The inner dimension L2 is preferably not less than <NUM> and not greater than <NUM>.

In <FIG>, an arrow D indicates the diameter of the string <NUM>. From the viewpoint that the string <NUM> easily becomes deformed in the direction parallel to the face, the ratio (L1/D) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/D) is preferably not greater than <NUM>.

<FIG> is a cross-sectional view of a part of a grommet <NUM> of a tennis racket according to still another embodiment of the present disclosure, and <FIG> is a cross-sectional view taken along a line B-B in <FIG>. The structure of the tennis racket other than the grommet <NUM> is the same as that of the tennis racket <NUM> shown in <FIG>.

The grommet <NUM> includes a base <NUM> and a tubular portion <NUM>. The tubular portion <NUM> has a through hole <NUM>. The through hole <NUM> has a base-side opening <NUM>, a side wall <NUM>, and a tip-side opening <NUM>. As shown in <FIG>, the cross-sectional shape of the through hole <NUM> is an elongated circle. The long axis of the elongated circle is tilted relative to a direction parallel to a face. The through hole <NUM> has a uniform cross-sectional shape from the base-side opening <NUM> to the tip-side opening <NUM>.

<FIG> is a bottom view of the tubular portion <NUM> of the grommet <NUM> in <FIG>. <FIG> shows the tip of the tubular portion <NUM>. <FIG> also shows a string <NUM>. In <FIG>, a direction perpendicular to the surface of the sheet is the axial direction of the tubular portion <NUM>. The shape of the tip-side opening <NUM> is an elongated circle.

In <FIG>, an arrow L1 indicates the inner dimension, in the direction parallel to the face, of the tip-side opening <NUM>. In <FIG>, an arrow L2 indicates the inner dimension, in the direction perpendicular to the face, of the tip-side opening <NUM>. The inner dimension L1 is larger than the inner dimension L2. Therefore, the string <NUM> can easily move in the through hole <NUM> in the direction parallel to the face. From the viewpoint that the string <NUM> easily becomes deformed in the direction parallel to the face and is less likely to become deformed in the direction perpendicular to the face, the ratio (L1/L2) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/L2) is preferably not greater than <NUM>.

<FIG> is an enlarged view of an area near the top of a racket according to still another embodiment of the present disclosure. In <FIG>, a frame and transverse strings 10a are not shown. <FIG> shows a base <NUM> and five tubular portions <NUM>. Each tubular portion <NUM> has a through hole <NUM> with a cross-sectional shape that is an elongated circle. The long axis of the elongated circle coincides with the width direction of the racket (the right-left direction in <FIG>). The through hole has a side wall <NUM>.

As is obvious from <FIG>, the racket has first tubular portions 62a in each of which a longitudinal string 10b is in contact with the wall surface, at the inner side in the width direction (the left side in <FIG>), of a side wall <NUM>, and second tubular portions 62b in each of which a longitudinal string 10b is in contact with the wall surface, at the outer side in the width direction (the right side in <FIG>), of a side wall <NUM>. The longitudinal strings 10b passed through the first tubular portions 62a can sufficiently become deformed outward in the width direction. The longitudinal strings 10b passed through the second tubular portions 62b can sufficiently become deformed inward in the width direction.

In a tubular portion that mainly permits movement of a string in a direction parallel to a face, various shapes can be used for a tip-side opening. In the tip-side opening having any of the various shapes, the inner dimension L1 in the direction parallel to the face is larger than the inner dimension L2 in a direction perpendicular to the face. The ratio (L1/L2) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/L2) is preferably not greater than <NUM>.

The frame <NUM> includes a head <NUM>, two throats <NUM>, and a shaft <NUM>. The head <NUM> forms the contour of a face <NUM> (described in detail later). The front shape of the head <NUM> is substantially an ellipse. The major axis direction of the ellipse coincides with the axial direction Y of the tennis racket <NUM>. The minor axis direction of the ellipse coincides with the width direction X of the tennis racket <NUM>. One end of each throat <NUM> is connected to the head <NUM>. The throat <NUM> is connected at the vicinity of the other end thereof to the other throat <NUM>. The throats <NUM> extend from the head <NUM> to the shaft <NUM>. The shaft <NUM> extends from the location where the two throats <NUM> are connected to each other. The shaft <NUM> is formed so as to be integrally connected to the throats <NUM>. A portion, of the head <NUM>, located between the two throats <NUM> is a yoke <NUM>.

As shown in <FIG>, the tennis racket <NUM> includes a first grommet 98a, two second grommets 88b, and a third grommet 98c. Each grommet <NUM> includes a base <NUM> and a plurality of tubular portions <NUM>. Each tubular portion <NUM> is formed so as to be integrated with the base <NUM>. A typical material of the grommet <NUM> is a synthetic resin that is more flexible than the frame <NUM>.

The first grommet 98a is mounted onto a portion at and near the top of the head <NUM> as shown by an arrow A1 in <FIG>. As a result of the mounting, each tubular portion <NUM> of the first grommet 98a penetrates a hole (not shown) provided in the head <NUM>. Each second grommet 98b is mounted onto a side of the head <NUM> as shown by an arrow A2 in <FIG>. As a result of the mounting, each tubular portion <NUM> of the second grommet 98b penetrates a hole (not shown) provided in the head <NUM>. The third grommet 98c is mounted onto the yoke <NUM> as shown by an arrow A3 in <FIG>. As a result of the mounting, each tubular portion <NUM> of the third grommet 98c penetrates a hole (not shown) provided in the head <NUM>.

The string <NUM> is stretched on the head <NUM>. The string <NUM> is stretched along the width direction X and the axial direction Y. Of the string <NUM>, portions extending along the width direction X are referred to as transverse strings 90a. Of the string <NUM>, portions extending along the axial direction Y are referred to as longitudinal strings 90b. The face <NUM> (see <FIG>) is formed by a plurality of transverse strings 90a and a plurality of longitudinal strings 90b. The face <NUM> generally extends along an X-Y plane.

<FIG> is an enlarged view of a part of the grommet <NUM> of the tennis racket <NUM> in <FIG>. As described above, the grommet <NUM> includes the base <NUM> and the plurality of tubular portions <NUM>. These tubular portions <NUM> include parallel movement tubular portions 200a and vertical movement tubular portions 200b. These tubular portions <NUM> can also include tubular portions <NUM> other than the parallel movement tubular portions 200a and the vertical movement tubular portions 200b.

<FIG> is a front view of a part of the grommet <NUM> in <FIG>, <FIG> is a cross-sectional view taken along a line B-B in <FIG> is a cross-sectional view taken along a line C-C in <FIG> show a parallel movement tubular portion 200a. The parallel movement tubular portion 200a has a through hole 244a. The through hole 244a has a base-side opening 246a, a side wall 248a, and a tip-side opening 250a. The cross-sectional shape of the through hole 244a is an elongated circle. The through hole 244a has a uniform cross-sectional shape from the base-side opening 246a to the tip-side opening 250a. In the through hole 244a, the inner dimension in a direction parallel to the face <NUM> (the right-left direction in <FIG>) is larger than the inner dimension in a direction perpendicular to the face <NUM> (the up-down direction in <FIG>).

<FIG> is a front view of a part of the grommet <NUM> in <FIG>, <FIG> is a cross-sectional view taken along a line B-B in <FIG> is a cross-sectional view taken along a line C-C in <FIG> show a vertical movement tubular portion 200b. The vertical movement tubular portion 200b has a through hole 244b. The through hole 244b has a base-side opening 246b, a side wall 248b, and a tip-side opening 250b. In the through hole 244b, the inner dimension in the direction parallel to the face <NUM> (the right-left direction in <FIG>) is uniform from the base-side opening 246b to the tip-side opening 250b. The inner dimension in the direction perpendicular to the face <NUM> (the up-down direction in <FIG>) gradually increases from the base-side opening 246b toward the tip-side opening 250b. The shape of the base-side opening 246b is generally a circle. The shape of the tip-side opening 250b is an elongated circle. In the tip-side opening 250b, the inner dimension in the direction perpendicular to the face <NUM> is larger than the inner dimension in the direction parallel to the face <NUM>.

<FIG> is a front view of the grommet <NUM> in <FIG> with the string <NUM>, and <FIG> is a cross-sectional view taken along a B-B in <FIG>. The string <NUM> is passed through the through hole 244a. The string <NUM> is in contact with the side wall 248a from the base-side opening 246a to the tip-side opening 250a. The string <NUM> is in contact with a left side wall surface of the side wall 248a. Since the inner dimension in the right-left direction of the base-side opening 246a is equal to the inner dimension in the right-left direction of the tip-side opening 250a, the string <NUM> can be in contact with the side wall 248a from the base-side opening 246a to the tip-side opening 250a. As is obvious from <FIG>, the inner dimension in the right-left direction of the through hole 244a is sufficiently larger than the diameter of the string <NUM>. Therefore, the string <NUM> can move rightward in the parallel movement tubular portion 200a. The string <NUM> can hardly move in the up-down direction in the parallel movement tubular portion 200a. In other words, the parallel movement tubular portion 200a mainly permits movement of the string <NUM> in the direction parallel to the face <NUM>.

<FIG> is a front view of the grommet <NUM> in <FIG> with the string <NUM>, and <FIG> is a cross-sectional view taken along a line B-B in <FIG>. The string <NUM> is passed through the through hole 244b. The string <NUM> extends so as to substantially coincide with the axis of the through hole 244b. As is obvious from <FIG>, the inner dimension in the up-down direction of the tip-side opening 250b is sufficiently larger than the diameter of the string <NUM>. Therefore, the string <NUM> can move in the up-down direction in the vertical movement tubular portion 200b. The string <NUM> can hardly move in the right-left direction in the vertical movement tubular portion 200b. In other words, the vertical movement tubular portion 200b mainly permits movement of the string <NUM> in the direction perpendicular to the face <NUM>.

As shown in <FIG>, the longitudinal strings 90b are passed through the first tubular portion <NUM>, the second tubular portion <NUM>, the third tubular portion <NUM>, the fourth tubular portion <NUM>, the fifth tubular portion <NUM>, the sixth tubular portion <NUM>, the seventh tubular portion <NUM>, the ninth tubular portion <NUM>, the twenty-seventh tubular portion <NUM>, the twenty-ninth tubular portion <NUM>, the thirtieth tubular portion <NUM>, the thirty-first tubular portion <NUM>, the thirty-second tubular portion <NUM>, the thirty-third tubular portion <NUM>, the thirty-fourth tubular portion <NUM>, and the thirty-fifth tubular portion <NUM>. The transverse strings 90a are passed through the eighth tubular portion <NUM>, the tenth tubular portion <NUM>, the eleventh tubular portion <NUM>, the twelfth tubular portion <NUM>, the thirteenth tubular portion <NUM>, the fourteenth tubular portion <NUM>, the fifteenth tubular portion <NUM>, the sixteenth tubular portion <NUM>, the seventeenth tubular portion <NUM>, the eighteenth tubular portion <NUM>, the nineteenth tubular portion <NUM>, the twentieth tubular portion <NUM>, the twenty-first tubular portion <NUM>, the twenty-second tubular portion <NUM>, the twenty-third tubular portion <NUM>, the twenty-fourth tubular portion <NUM>, the twenty-fifth tubular portion <NUM>, the twenty-sixth tubular portion <NUM>, and the twenty-eighth tubular portion <NUM>.

<FIG> is an enlarged view of an area near the top of the tennis racket <NUM> in <FIG>. In <FIG>, the frame <NUM> and the transverse strings 90a are not shown. <FIG> shows the base <NUM>, the first tubular portion <NUM>, the second tubular portion <NUM>, the third tubular portion <NUM>, the fourth tubular portion <NUM>, and the fifth tubular portion <NUM>. In the present embodiment, the first tubular portion <NUM>, the third tubular portion <NUM>, and the fifth tubular portion <NUM> are vertical movement tubular portions 200b. In each vertical movement tubular portion 200b, the shape of the tip-side opening 250b is a vertically elongated circle (see <FIG>). The second tubular portion <NUM> and the fourth tubular portion <NUM> are parallel movement tubular portions 200a. In each parallel movement tubular portion 200a, the shape of the tip-side opening 250a is a horizontally elongated circle (see <FIG>). In the tennis racket <NUM>, a plurality of parallel movement tubular portions 200a and a plurality of vertical movement tubular portions 200b are alternately arranged. Each of the parallel movement tubular portions 200a is adjacent to at least one vertical movement tubular portion 200b. Each of the vertical movement tubular portions 200b is adjacent to at least one parallel movement tubular portion 200a.

As shown in <FIG>, in the second tubular portion <NUM>, the longitudinal string 90b is in contact with the wall surface, at the left side (the inner side in the width direction), of the side wall 248a of the through hole 244a. In the fourth tubular portion <NUM>, the longitudinal string 90b is in contact with the wall surface, at the left side (the inner side in the width direction), of the side wall 248a of the through hole 244a.

<FIG> shows a tennis ball <NUM> together with the tennis racket <NUM>. <FIG> shows the moment of impact between the tennis racket <NUM> and the tennis ball <NUM>. In <FIG>, the tennis ball <NUM> collides against the face <NUM> at the lower side (the ground G side) with respect to the center line CL. In this state, the player swings the tennis racket <NUM> forward and then upward. This swing is a drive swing.

By this swing, outward force in the width direction is applied to the longitudinal string 90b passed through the second tubular portion <NUM>. The inner dimension in the width direction of the through hole 244a of the second tubular portion <NUM> is sufficiently large. Therefore, the longitudinal string 90b becomes deformed without being obstructed by the second tubular portion <NUM>, and moves outward in the width direction. <FIG> shows the longitudinal string 90b after the movement. Thereafter, the longitudinal string 90b returns to the original shape. The longitudinal string 90b passed through the fourth tubular portion <NUM> also similarly becomes deformed and returns to the original shape. The deformation and the return of these longitudinal strings 90b achieve a long contact time between the tennis racket <NUM> and the tennis ball <NUM>. The tennis ball <NUM> is launched with a high spin rate.

<FIG> is a cross-sectional view of the first tubular portion <NUM> of the racket in <FIG>. In <FIG>, an arrow Z represents the thickness direction of the tennis racket <NUM>. As described above, in the first tubular portion <NUM>, the shape of the tip-side opening 250b is a vertically elongated circle. Therefore, the longitudinal string 90b passed through the first tubular portion <NUM> becomes deformed in the Z direction upon reception of pressure from the tennis ball <NUM>. This deformation is not inhibited by the first tubular portion <NUM>. Therefore, the longitudinal string 90b can become sufficiently deformed in the Z direction. <FIG> shows the longitudinal string 90b after the deformation. Thereafter, the longitudinal string 90b returns to the original shape. The longitudinal string 90b passed through the third tubular portion <NUM> and the longitudinal string 90b passed through the fifth tubular portion <NUM> can also similarly become sufficiently deformed in the Z direction.

In the parallel movement tubular portion 200a (the second tubular portion <NUM> or the fourth tubular portion <NUM>), as described above, the shape of the tip-side opening 250b is a horizontally elongated circle. Therefore, the parallel movement tubular portion 200a inhibits movement of the longitudinal strings 90b in the Z direction. The longitudinal string 90b passed through the parallel movement tubular portion 200a does not become sufficiently deformed in the Z direction.

Upon impact between the tennis racket <NUM> and the tennis ball <NUM>, the amount of deformation in the Z direction of the longitudinal string 90b passed through the parallel movement tubular portion 200a is small, and the amount of deformation in the Z direction of the longitudinal string 90b passed through the vertical movement tubular portion 200b is large. In other words, by the impact, only the longitudinal string 90b passed through the vertical movement tubular portion 200b is greatly moved back. The longitudinal string 90b passed through the parallel movement tubular portion 200a is not greatly moved back. The longitudinal string 90b passed through the parallel movement tubular portion 200a sufficiently bites into the tennis ball <NUM> upon impact. Through the biting, high-rate spin is imparted to the tennis ball <NUM>.

In <FIG>, an arrow W2 indicates the width of a zone near the top. The parallel movement tubular portions 200a and the vertical movement tubular portions 200b are preferably disposed in the zone near the top. The width W2 is preferably not less than <NUM>% and not greater than <NUM>%, and particularly preferably not less than <NUM>% and not greater than <NUM>%, of the half width W1 (see <FIG>) of the tennis racket <NUM>.

For the purpose of imparting performance intended by a designer to the tennis racket <NUM>, the tubular portion <NUM> may be formed such that the string <NUM> is in contact with the wall surface at the outer side in the width direction.

The tennis racket <NUM> has the parallel movement tubular portions 200a and the vertical movement tubular portions 200b near the top. The tennis racket <NUM> may have a parallel movement tubular portion 200a and a vertical movement tubular portion 200b at the yoke <NUM>. The tennis racket <NUM> may have a parallel movement tubular portion 200a and a vertical movement tubular portion 200b at each side.

In the tennis racket <NUM>, as described above, the second tubular portion <NUM> and the fourth tubular portion <NUM> are parallel movement tubular portions 200a. Since the tennis racket <NUM> has a symmetrical shape with respect to the center line CL, the tennis racket <NUM> includes two second tubular portions <NUM> and two fourth tubular portions <NUM>. Therefore, the total number N1 of the parallel movement tubular portions 200a is four. The total number N1 is preferably not less than <NUM> and not greater than <NUM>, and more preferably not less than <NUM> and not greater than <NUM>.

In the tennis racket <NUM>, as described above, the first tubular portion <NUM>, the third tubular portion <NUM>, and the fifth tubular portion <NUM> are vertical movement tubular portions 200b. Since the tennis racket <NUM> has a symmetrical shape with respect to the center line CL, the tennis racket <NUM> includes two first tubular portions <NUM>, two third tubular portions <NUM>, and two fifth tubular portions <NUM>. Therefore, the total number N2 of the vertical movement tubular portions 200b is six. The total number N2 is preferably not less than <NUM> and not greater than <NUM>, and more preferably not less than <NUM> and not greater than <NUM>.

<FIG> is a bottom view of the parallel movement tubular portion 200a in <FIG> with the string <NUM>. <FIG> shows the tip of the parallel movement tubular portion 200a. In <FIG>, a direction perpendicular to the surface of the sheet is the axial direction of the parallel movement tubular portion 200a. The parallel movement tubular portion 200a has the tip-side opening 250a. As described above, the shape of the tip-side opening 250a is an elongated circle.

In <FIG>, an arrow L1 indicates the inner dimension, in the direction parallel to the face <NUM>, of the tip-side opening 250a. The inner dimension L1 is also the long diameter of the elongated circle. In <FIG>, an arrow L2 indicates the inner dimension, in the direction perpendicular to the face <NUM>, of the tip-side opening 250a. The inner dimension L2 is also the short diameter of the elongated circle. From the viewpoint that the string <NUM> easily becomes deformed in the direction parallel to the face <NUM> and is less likely to become deformed in the direction perpendicular to the face <NUM>, the ratio (L1/L2) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/L2) is preferably not greater than <NUM>.

<FIG> is a bottom view of the vertical movement tubular portion 200b in <FIG> with the string <NUM>. <FIG> shows the tip of the vertical movement tubular portion 200b. In <FIG>, a direction perpendicular to the surface of the sheet is the axial direction of the vertical movement tubular portion 200b. The vertical movement tubular portion 200b has the tip-side opening 250b. As described above, the shape of the tip-side opening 250b is an elongated circle.

In <FIG>, an arrow L3 indicates the inner dimension, in the direction parallel to the face <NUM>, of the tip-side opening 250b. The inner dimension L3 is also the short diameter of the elongated circle. In <FIG>, an arrow L4 indicates the inner dimension, in the direction perpendicular to the face <NUM>, of the tip-side opening 250b. The inner dimension L4 is also the long diameter of the elongated circle. From the viewpoint that the string <NUM> easily becomes deformed in the direction perpendicular to the face <NUM>, the ratio (L4/L3) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L4/L3) is preferably not greater than <NUM>.

In <FIG>, an arrow D indicates the diameter of the string <NUM>. From the viewpoint that the string <NUM> easily becomes deformed in the direction perpendicular to the face <NUM>, the ratio (L4/D) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L4/D) is preferably not greater than <NUM>.

<FIG> is a bottom view of a parallel movement tubular opening <NUM> of a tennis racket according to another embodiment of the present invention with a string <NUM>. The structure of the tennis racket other than the parallel movement tubular opening <NUM> is the same as that of the tennis racket <NUM> shown in <FIG>.

The parallel movement tubular opening <NUM> has a through hole. The through hole has a base-side opening, a side wall, and a tip-side opening <NUM>. The cross-sectional shape of the through hole is uniform from the base-side opening to the tip-side opening <NUM>. As shown in <FIG>, the shape of the tip-side opening <NUM> is an ellipse. In <FIG>, an arrow L1 indicates the inner dimension, in a direction parallel to a face, of the tip-side opening <NUM>. The inner dimension L1 is also the major diameter of the ellipse. In <FIG>, an arrow L2 indicates the inner dimension, in a direction perpendicular to the face, of the tip-side opening <NUM>. The inner dimension L2 is also the minor diameter of the ellipse. From the viewpoint that the string <NUM> easily becomes deformed in the direction parallel to the face and is less likely to become deformed in the direction perpendicular to the face, the ratio (L1/L2) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/L2) is preferably not greater than <NUM>.

<FIG> is a bottom view of a parallel movement tubular portion <NUM> of a tennis racket according to still another embodiment of the present invention with a string <NUM>. The structure of the tennis racket other than the parallel movement tubular portion <NUM> is the same as that of the tennis racket <NUM> shown in <FIG>.

The parallel movement tubular portion <NUM> has a through hole. The through hole has a base-side opening, a side wall, and a tip-side opening <NUM>. The cross-sectional shape of the through hole is uniform from the base-side opening to the tip-side opening <NUM>. As shown in <FIG>, the shape of the tip-side opening <NUM> is an elongated circle. The long axis of the elongated circle is tilted in a direction parallel to a face. In <FIG>, an arrow L1 indicates the inner dimension, in the direction parallel to the face, of the tip-side opening <NUM>. In <FIG>, an arrow L2 indicates the inner dimension, in a direction perpendicular to the face, of the tip-side opening <NUM>. From the viewpoint that the string <NUM> easily becomes deformed in the direction parallel to the face and is less likely to become deformed in the direction perpendicular to the face, the ratio (L1/L2) is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/L2) is preferably not greater than <NUM>.

<FIG> is a front view of a parallel movement tubular portion <NUM> of a tennis racket according to still another embodiment of the present invention, <FIG> is a cross-sectional view taken along a line B-B in <FIG> is a cross-sectional view taken along a line C-C in <FIG>. The structure of the tennis racket other than the parallel movement tubular portion <NUM> is the same as that of the tennis racket <NUM> shown in <FIG>.

The parallel movement tubular portion <NUM> has a through hole <NUM>. The through hole <NUM> has a base-side opening <NUM>, a side wall <NUM>, and a tip-side opening <NUM>. The shape of the base-side opening <NUM> is a circle. The shape of the tip-side opening <NUM> is an elongated circle. The inner dimension, in a direction parallel to a face, of the through hole <NUM> gradually increases from the base-side opening <NUM> toward the tip-side opening <NUM>. In the tennis racket, a longitudinal string passed through the parallel movement tubular portion <NUM> can easily become deformed in the direction parallel to the face.

For a parallel movement tubular portion, through holes with various shapes that mainly permit movement of a string in a direction parallel to a face can be used. In each of the through holes, the ratio (L1/L2) of the inner dimension L1, in the direction parallel to the face, of a tip-side opening to the inner dimension L2, in a direction perpendicular to the face, of the tip-side opening is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L1/L2) is preferably not greater than <NUM>.

For a vertical movement tubular portion, through holes with various shapes that mainly permit movement of the string in the direction perpendicular to the face can be used. In each of the through holes, the ratio (L4/L3) of the inner dimension L4, in the direction perpendicular to the face, of a tip-side opening to the inner dimension L3, in the direction parallel to the face, of the tip-side opening is preferably not less than <NUM> and particularly preferably not less than <NUM>. The ratio (L4/L3) is preferably not greater than <NUM>.

Claim 1:
A racket (<NUM>) comprising a frame (<NUM>), a grommet (<NUM>) mounted on the frame (<NUM>) and having a plurality of tubular portions (<NUM>), and a string (<NUM>) forming a face (<NUM>), wherein
each of the tubular portions (<NUM>) has a through hole (<NUM>) through which the string (<NUM>) is passed, and
the tubular portions (<NUM>) include parallel movement tubular portions (200a), wherein each through hole (244a) of the parallel movement tubular portions (200a) has a shape that mainly permits movement of the string (<NUM>) in a direction parallel to the face (<NUM>),
characterized in that
the tubular portions (<NUM>) further include vertical movement tubular portions (200b), wherein each through hole (244b) of the vertical movement tubular portions (200b) has a shape that mainly permits movement of the string (<NUM>) in a direction perpendicular to the face (<NUM>).