CROSS-REFERENCE TO RELATED APPLICATION
This application claims priority on and the benefit of Patent Application No. 2019-050966 filed in JAPAN on Mar. 19, 2019 and Patent Application No. 2019-050967 filed in JAPAN on Mar. 19, 2019. The entire disclosures of these Japanese Patent Applications are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to rackets for use in tennis, etc.
Description of the Related Art
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. JPH5-345052 and JP2015-217192 disclose proposals regarding the shapes of grommets.
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 with which a stable trajectory can be obtained even when a ball is hit at a position shifted from the center of a face.
Another object of the present invention is to provide a racket having excellent spin performance.
SUMMARY OF THE INVENTION
A racket according to an aspect of the present invention includes
- (1) a frame,
- (2) a grommet mounted on the frame and having a plurality of tubular portions, and
- (3) a string forming a face.
Each of the tubular portions has a through hole through which the string is passed. The through hole has a base-side opening, a side wall, and a tip-side opening. At least one of the tubular portions has a non-circular tip-side opening in which an inner dimension in a direction parallel to the face is larger than an inner dimension in a direction perpendicular to the face. In the tubular portion having the non-circular tip-side opening, the string is in contact with the side wall from the base-side opening to the tip-side opening.
With the racket according to the present invention, the string easily becomes deformed, and thus a contact time between the string and a ball upon a stroke is long. The racket can contribute to a large launch angle.
Preferably, a longitudinal string is passed through the tubular portion having the non-circular tip-side opening. Preferably, the tubular portion having the non-circular tip-side opening is disposed near a top of the frame. Preferably, in the tubular portion having the non-circular tip-side opening, the string is in contact with a wall surface, at an inner side in a width direction, of the side wall.
Preferably, the tubular portion having the non-circular tip-side opening has a through hole having a uniform cross-sectional shape from the base-side opening to the tip-side opening.
Preferably, a contour of the non-circular tip-side opening 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 non-circular tip-side opening to an inner dimension L2, in the direction perpendicular to the face, of the non-circular tip-side opening is not less than 1.3.
Preferably, a ratio (L1/D) of an inner dimension L1, in the direction parallel to the face, of the non-circular tip-side opening to a diameter D of the string is not less than 1.5.
A racket according to another aspect of the present invention includes
- (1) a frame,
- (2) a grommet mounted on the frame and having a plurality of tubular portions, and
- (3) a string forming a face.
Each of the tubular portions has a through hole through which the string is passed. The tubular portions include parallel movement tubular portions that mainly permit movement of the string in a direction parallel to the face, and vertical movement tubular portions 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 of the parallel movement tubular portions has a through hole in which an inner dimension in the direction parallel to the face 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 1.3. 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 1.5.
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.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a front view of a racket according to an embodiment of the present invention;
FIG. 2 is an enlarged view of a part of the racket in FIG. 1;
FIG. 3 is an exploded view of a part of the racket in FIG. 1;
FIG. 4 is an enlarged view of a part of a grommet of the tennis racket in FIG. 3;
FIG. 5(a) is an enlarged cross-sectional view of a part of the grommet in FIG. 4;
FIG. 5(b) is a cross-sectional view taken along a line B-B in FIG. 5(a);
FIG. 6(a) is an enlarged cross-sectional view of a part of the grommet in FIG. 4;
FIG. 6(b) is a cross-sectional view taken along a line B-B in FIG. 6(a);
FIG. 7(a) is a cross-sectional view of the grommet in FIGS. 5(a) and 5(b) with a string;
FIG. 7(b) is a cross-sectional view taken along a line B-B in FIG. 7(a);
FIG. 8 is an enlarged view of an area near the top of the racket in FIG. 1;
FIG. 9 is a front view of the racket in FIG. 1 with a tennis ball;
FIG. 10 is a front view of the area near the top in FIG. 8;
FIG. 11 is a bottom view of a tubular portion of the grommet in FIGS. 5(a) and 5(b) with the string;
FIG. 12(a) is a cross-sectional view of a part of a grommet of a racket according to another embodiment of the present invention;
FIG. 12(b) is a cross-sectional view taken along a line B-B in FIG. 12(a);
FIG. 13 is a bottom view of a tubular portion of the grommet in FIGS. 12(a) and 12(b) with a string;
FIG. 14(a) is a cross-sectional view of a part of a grommet of a racket according to still another embodiment of the present invention;
FIG. 14(b) is a cross-sectional view taken along a line B-B in FIG. 14(a);
FIG. 15 is a bottom view of a tubular portion of the grommet in FIGS. 14(a) and 14(b) with a string;
FIG. 16 is an enlarged view of an area near the top of a racket according to still another embodiment of the present invention;
FIG. 17 is a front view of a racket according to still another embodiment of the present invention;
FIG. 18 is an enlarged view of a part of the racket in FIG. 17;
FIG. 19 is an exploded view of a part of the racket in FIG. 17;
FIG. 20 is an enlarged view of a part of a grommet of the tennis racket in FIG. 19;
FIG. 21(a) is a front view of a part of the grommet in FIG. 20;
FIG. 21(b) is a cross-sectional view taken along a line B-B in FIG. 21(a);
FIG. 21(c) is a cross-sectional view taken along a line C-C in FIG. 21(a);
FIG. 22(a) is a front view of a part of the grommet in FIG. 20;
FIG. 22(b) is a cross-sectional view taken along a line B-B in FIG. 22(a);
FIG. 22(c) is a cross-sectional view taken along a line C-C in FIG. 22(a);
FIG. 23(a) is a front view of the grommet in FIGS. 21(a) to 21(c) with a string;
FIG. 23(b) is a cross-sectional view taken along a line B-B in FIG. 23(a);
FIG. 24(a) is a front view of the grommet in FIGS. 22(a) to 22(c) with the string;
FIG. 24(b) is a cross-sectional view taken along a line B-B in FIG. 24(a);
FIG. 25 is an enlarged view of an area near the top of the racket in FIG. 17;
FIG. 26 is a front view of the racket in FIG. 17 with a tennis ball;
FIG. 27 is a front view showing another state of the area near the top in FIG. 25;
FIG. 28 is a cross-sectional view of a first tubular portion of the racket in FIG. 17;
FIG. 29 is a bottom view of a parallel movement tubular portion in FIGS. 21(a) to 21(c) with the string;
FIG. 30 is a bottom view of a vertical movement tubular portion in FIGS. 22(a) to 22(c) with the string;
FIG. 31 is a bottom view of a parallel movement tubular portion of a tennis racket according to still another embodiment of the present invention with a string;
FIG. 32 is a bottom view of a parallel movement tubular portion of a tennis racket according to still another embodiment of the present invention with a string;
FIG. 33(a) is a front view of a parallel movement tubular portion of a tennis racket according to still another embodiment of the present invention;
FIG. 33(b) is a cross-sectional view taken along a line B-B in FIG. 33(a); and
FIG. 33(c) is a cross-sectional view taken along a line C-C in FIG. 33(a).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The following will describe in detail the present invention based on preferred embodiments with appropriate reference to the drawings.
First Invention
First Embodiment
FIGS. 1 to 3 show a tennis racket 2. The tennis racket 2 includes a frame 4, a grip 6, grommets 8, and a string 10. The tennis racket 2 can be used in regulation-ball tennis. In FIGS. 1 and 2, an arrow X represents the width direction of the tennis racket 2, and an arrow Y represents the axial direction of the tennis racket 2.
The frame 4 includes a head 12, two throats 14, and a shaft 16. The head 12 forms the contour of a face 17 (described in detail later). The front shape of the head 12 is substantially an ellipse. The major axis direction of the ellipse coincides with the axial direction Y of the tennis racket 2. The minor axis direction of the ellipse coincides with the width direction X of the tennis racket 2. One end of each throat 14 is connected to the head 12. The throat 14 is connected at the vicinity of the other end thereof to the other throat 14. The throats 14 extend from the head 12 to the shaft 16. The shaft 16 extends from the location where the two throats 14 are connected to each other. The shaft 16 is formed so as to be integrally connected to the throats 14. A portion, of the head 12, located between the two throats 14 is a yoke 18. The head 12 may have a shape other than an ellipse.
The frame 4 is composed of a pipe. In other words, the frame 4 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 6 is formed by a tape wound on the shaft 16. The grip 6 suppresses slip between a hand of a player and the tennis racket 2 when the tennis racket 2 is swung.
As shown in FIG. 3, the tennis racket 2 includes a first grommet 8a, two second grommets 8b, and a third grommet 8c. Each grommet 8 includes a base 20 and a plurality of tubular portions 100. Each tubular portion 100 is formed so as to be integrated with the base 20. A typical material of the grommet 8 is a synthetic resin that is more flexible than the frame 4.
The first grommet 8a is mounted onto a portion at and near the top of the head 12 as shown by an arrow A1 in FIG. 3. As a result of the mounting, each tubular portion 100 of the first grommet 8a penetrates a hole (not shown) provided in the head 12. Each second grommet 8b is mounted onto a side of the head 12 as shown by an arrow A2 in FIG. 3. As a result of the mounting, each tubular portion 100 of the second grommet 8b penetrates a hole (not shown) provided in the head 12. The third grommet 8c is mounted onto the yoke 18 as shown by an arrow A3 in FIG. 3. As a result of the mounting, each tubular portion 100 of the third grommet 8c penetrates a hole (not shown) provided in the head 12.
The string 10 is stretched on the head 12. The string 10 is stretched along the width direction X and the axial direction Y. Of the string 10, portions extending along the width direction X are referred to as transverse strings 10a. Of the string 10, portions extending along the axial direction Y are referred to as longitudinal strings 10b. The face 17 (see FIG. 1) is formed by a plurality of transverse strings 10a and a plurality of longitudinal strings 10b. The face 17 generally extends along an X-Y plane.
FIG. 4 is an enlarged view of a part of the grommet 8 of the tennis racket 2 in FIG. 3. As described above, the grommet 8 includes the base 20 and the plurality of tubular portions 100.
FIGS. 5(a) and 5(b) show a part of the grommet 8. FIG. 5(a) is a cross-sectional view taken along a plane including the axis of a tubular portion 100a. FIG. 5(b) 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. 5(b), 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 17 (the right-left direction in FIG. 5(b)) is larger than the inner dimension in a direction perpendicular to the face 17 (the up-down direction in FIG. 5(b)).
FIGS. 6(a) and 6(b) show another part of the grommet 8. FIG. 6(a) is a cross-sectional view taken along a plane including the axis of a tubular portion 100b. FIG. 6(b) 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. 6(b), 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 17 (the right-left direction in FIG. 6(b)) is equal to the inner dimension in the direction perpendicular to the face 17 (the up-down direction in FIG. 6(b)).
FIGS. 7(a) and 7(b) show the tubular portion 100a in FIGS. 5(a) and 5(b). FIGS. 7(a) and 7(b) also show the string 10. The string 10 is passed through the through hole 24a. The string 10 is in contact with the side wall 28a from the base-side opening 26a to the tip-side opening 30a. The string 10 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 10 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 FIGS. 7(a) and 7(b), the inner dimension in the right-left direction of the through hole 24a is sufficiently larger than the diameter of the string 10. Therefore, the string 10 can move rightward in the tubular portion 100a. The tubular portion 100a mainly permits movement of the string 10 in the right-left direction (the direction parallel to the face 17).
In FIG. 2, reference character CL indicates a center line. The tennis racket 2 has a symmetrical shape with respect to the center line CL. As shown in FIG. 2, the tennis racket 2 includes a first tubular portion 101, a second tubular portion 102, a third tubular portion 103, a fourth tubular portion 104, a fifth tubular portion 105, a sixth tubular portion 106, a seventh tubular portion 107, an eighth tubular portion 108, a ninth tubular portion 109, a tenth tubular portion 110, an eleventh tubular portion 111, a twelfth tubular portion 112, a thirteenth tubular portion 113, a fourteenth tubular portion 114, a fifteenth tubular portion 115, a sixteenth tubular portion 116, a seventeenth tubular portion 117, an eighteenth tubular portion 118, a nineteenth tubular portion 119, a twentieth tubular portion 120, a twenty-first tubular portion 121, a twenty-second tubular portion 122, a twenty-third tubular portion 123, a twenty-fourth tubular portion 124, a twenty-fifth tubular portion 125, a twenty-sixth tubular portion 126, a twenty-seventh tubular portion 127, a twenty-eighth tubular portion 128, a twenty-ninth tubular portion 129, a thirtieth tubular portion 130, a thirty-first tubular portion 131, a thirty-second tubular portion 132, a thirty-third tubular portion 133, a thirty-fourth tubular portion 134, and a thirty-fifth tubular portion 135. FIG. 2 shows 35 tubular portions 100. Since the tennis racket 2 has a symmetrical shape with respect to the center line CL as described above, the number of tubular portions 100 in the tennis racket 2 is 70.
As shown in FIG. 2, the longitudinal strings 10b are passed through the first tubular portion 101, the second tubular portion 102, the third tubular portion 103, the fourth tubular portion 104, the fifth tubular portion 105, the sixth tubular portion 106, the seventh tubular portion 107, the ninth tubular portion 109, the twenty-seventh tubular portion 127, the twenty-ninth tubular portion 129, the thirtieth tubular portion 130, the thirty-first tubular portion 131, the thirty-second tubular portion 132, the thirty-third tubular portion 133, the thirty-fourth tubular portion 134, and the thirty-fifth tubular portion 135. The transverse strings 10a are passed through the eighth tubular portion 108, the tenth tubular portion 110, the eleventh tubular portion 111, the twelfth tubular portion 112, the thirteenth tubular portion 113, the fourteenth tubular portion 114, the fifteenth tubular portion 115, the sixteenth tubular portion 116, the seventeenth tubular portion 117, the eighteenth tubular portion 118, the nineteenth tubular portion 119, the twentieth tubular portion 120, the twenty-first tubular portion 121, the twenty-second tubular portion 122, the twenty-third tubular portion 123, the twenty-fourth tubular portion 124, the twenty-fifth tubular portion 125, the twenty-sixth tubular portion 126, and the twenty-eighth tubular portion 128.
In the present embodiment, the second tubular portion 102 and the fourth tubular portion 104 each have a through hole 24a (see FIGS. 5(a) and 5(b)) with a cross-sectional shape that is an elongated circle. The other tubular portions 100 each have a through hole 24b (see FIGS. 6(a) and 6(b)) with a cross-sectional shape that is a circle. The tubular portions 100 other than the second tubular portion 102 and the fourth tubular portion 104 may each have a through hole 24a with a cross-sectional shape that is an elongated circle. For example, the sixth tubular portion 106 may have a through hole 24a with a cross-sectional shape that is an elongated circle.
FIG. 8 is an enlarged view of an area near the top of the tennis racket 2 in FIG. 1. In FIG. 8, the frame 4 and the transverse strings 10a are not shown. FIG. 8 shows the base 20, the first tubular portion 101, the second tubular portion 102, the third tubular portion 103, and the fourth tubular portion 104. The first tubular portion 101 has a through hole 24b (see FIGS. 6(a) and 6(b)) with a cross-sectional shape that is a circle. The second tubular portion 102 has a through hole 24a with a cross-sectional shape that is an elongated circle. The third tubular portion 103 has a through hole 24b with a cross-sectional shape that is a circle. The fourth tubular portion 104 has a through hole 24a with a cross-sectional shape that is an elongated circle. In the second tubular portion 102, the string 10 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 104, the string 10 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. 9 shows a tennis ball 32 together with the tennis racket 2. FIG. 9 shows the moment of impact between the tennis racket 2 and the tennis ball 32. In FIG. 9, the tennis ball 32 collides against the face 17 at the lower side (the ground G side) with respect to the center line CL. In this state, the player swings the tennis racket 2 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 102. The inner dimension in the width direction of the through hole 24a of the second tubular portion 102 (100a) is sufficiently large. Therefore, the longitudinal string 10b becomes deformed without being obstructed by the second tubular portion 102, and moves outward in the width direction. FIG. 10 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 104 (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 2 and the tennis ball 32. With the tennis racket 2, the tennis ball 32 is launched at a large launch angle. With the tennis racket 2, even when the tennis ball 32 is hit at the lower side with respect to the center line CL, a high trajectory can be obtained.
As described above, the string 10 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 32 collides against the face 17 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 2, the difference in trajectory is small between when the tennis ball 32 collides against the face 17 at the upper side with respect to the center line CL and when the tennis ball 32 collides against the face 17 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 2, the tubular portion 100a may be formed such that the string 10 is in contact with the wall surface at the outer side in the width direction.
In FIG. 8, 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 15% and not greater than 80%, and particularly preferably not less than 20% and not greater than 70%, of the half width W1 (see FIG. 1) of the tennis racket 2.
In the tennis racket 2, the tubular portions 100a (the second tubular portion 102 and the fourth tubular portion 104) located near the top each have the through hole 24a with a cross-sectional shape that is non-circular. The tubular portions 100 located at the yoke 18 may each have a through hole 24a with a cross-sectional shape that is non-circular. The tubular portions 100 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 100 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 32 collides against a predetermined area.
In the tennis racket 2, as described above, the second tubular portion 102 and the fourth tubular portion 104 each have the through hole 24a with a cross-sectional shape that is non-circular. Since the tennis racket 2 has a symmetrical shape with respect to the center line CL, the tennis racket 2 includes two second tubular portions 102 and two fourth tubular portions 104. 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 2 and not greater than 16, and more preferably not less than 4 and not greater than 12.
FIG. 11 is a bottom view of the tubular portion 100a of the grommet 8 in FIGS. 5(a) and 5(b). FIG. 11 shows the tip of the tubular portion 100a. In FIG. 11, 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. 11, an arrow L1 indicates the inner dimension, in the direction parallel to the face 17, of the tip-side opening 30a. The inner dimension L1 is also the long diameter of the elongated circle. In FIG. 11, an arrow L2 indicates the inner dimension, in the direction perpendicular to the face 17, 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 10 easily becomes deformed in the direction parallel to the face 17 and is less likely to become deformed in the direction perpendicular to the face 17, the ratio (L1/L2) is preferably not less than 1.3 and particularly preferably not less than 1.5. The ratio (L1/L2) is preferably not greater than 4.0. L1 is preferably not less than 2.0 mm and not greater than 3.0 mm.
In FIG. 11, an arrow D indicates the diameter of the string 10. From the viewpoint that the string 10 easily becomes deformed in the direction parallel to the face 17, the ratio (L1/D) is preferably not less than 1.5 and particularly preferably not less than 1.8. The ratio (L1/D) is preferably not greater than 4.5.
Second Embodiment
FIG. 12(a) is a cross-sectional view of a part of a grommet 34 of a tennis racket according to another embodiment of the present invention, and FIG. 12(b) is a cross-sectional view taken along a line B-B in FIG. 12(a). The structure of the tennis racket other than the grommet 34 is the same as that of the tennis racket 2 shown in FIGS. 1 to 11.
The grommet 34 includes a base 36 and a tubular portion 38. The tubular portion 38 has a through hole 40. The through hole 40 has a base-side opening 42, a side wall 44, and a tip-side opening 46. As shown in FIG. 12(b), the cross-sectional shape of the through hole 40 is an ellipse. The through hole 40 has a uniform cross-sectional shape from the base-side opening 42 to the tip-side opening 46.
FIG. 13 is a bottom view of the tubular portion 38 of the grommet 34 in FIGS. 12(a) and 12(b). FIG. 13 shows the tip of the tubular portion 38. FIG. 13 also shows a string 10. In FIG. 13, a direction perpendicular to the surface of the sheet is the axial direction of the tubular portion 38. The shape of the tip-side opening 46 is an ellipse.
In FIG. 13, an arrow L1 indicates the inner dimension, in a direction parallel to a face, of the tip-side opening 46. The inner dimension L1 is also the major diameter of the ellipse. In FIG. 13, an arrow L2 indicates the inner dimension, in a direction perpendicular to the face, of the tip-side opening 46. The inner dimension L2 is also the minor diameter of the ellipse. From the viewpoint that the string 10 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 1.3 and particularly preferably not less than 1.5. The ratio (L1/L2) is preferably not greater than 4.0. The inner dimension L2 is preferably not less than 1.8 mm and not greater than 2.2 mm.
In FIG. 13, an arrow D indicates the diameter of the string 10. From the viewpoint that the string 10 easily becomes deformed in the direction parallel to the face, the ratio (L1/D) is preferably not less than 1.5 and particularly preferably not less than 1.8. The ratio (L1/D) is preferably not greater than 4.5.
Third Embodiment
FIG. 14(a) is a cross-sectional view of a part of a grommet 44 of a tennis racket according to still another embodiment of the present invention, and FIG. 14(b) is a cross-sectional view taken along a line B-B in FIG. 14(a). The structure of the tennis racket other than the grommet 44 is the same as that of the tennis racket 2 shown in FIGS. 1 to 11.
The grommet 44 includes a base 46 and a tubular portion 48.
The tubular portion 48 has a through hole 50. The through hole 50 has a base-side opening 52, a side wall 54, and a tip-side opening 56. As shown in FIG. 14(b), the cross-sectional shape of the through hole 50 is an elongated circle. The long axis of the elongated circle is tilted relative to a direction parallel to a face. The through hole 50 has a uniform cross-sectional shape from the base-side opening 52 to the tip-side opening 56.
FIG. 15 is a bottom view of the tubular portion 48 of the grommet 44 in FIGS. 14(a) and 14(b). FIG. 15 shows the tip of the tubular portion 48. FIG. 15 also shows a string 10. In FIG. 15, a direction perpendicular to the surface of the sheet is the axial direction of the tubular portion 48. The shape of the tip-side opening 56 is an elongated circle.
In FIG. 15, an arrow L1 indicates the inner dimension, in the direction parallel to the face, of the tip-side opening 56. In FIG. 15, an arrow L2 indicates the inner dimension, in the direction perpendicular to the face, of the tip-side opening 56. The inner dimension L1 is larger than the inner dimension L2. Therefore, the string 10 can easily move in the through hole 50 in the direction parallel to the face. From the viewpoint that the string 10 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 1.3 and particularly preferably not less than 1.5. The ratio (L1/L2) is preferably not greater than 4.0.
In FIG. 15, an arrow D indicates the diameter of the string 10. From the viewpoint that the string 10 easily becomes deformed in the direction parallel to the face, the ratio (L1/D) is preferably not less than 1.5 and particularly preferably not less than 1.8. The ratio (L1/D) is preferably not greater than 4.5.
Fourth Embodiment
FIG. 16 is an enlarged view of an area near the top of a racket according to still another embodiment of the present invention. In FIG. 16, a frame and transverse strings 10a are not shown. FIG. 16 shows a base 60 and five tubular portions 62. Each tubular portion 62 has a through hole 64 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. 16). The through hole has a side wall 66.
As is obvious from FIG. 16, 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. 16), of a side wall 66, 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. 16), of a side wall 66. 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.
Still Another Embodiment
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 1.3 and particularly preferably not less than 1.5. The ratio (L1/L2) is preferably not greater than 4.0.
Second Invention
First Embodiment
FIGS. 17 to 20 show a tennis racket 82. The tennis racket 82 includes a frame 84, a grip 86, grommets 88, and a string 90. The tennis racket 82 can be used in regulation-ball tennis. In FIGS. 17 and 18, an arrow X represents the width direction of the tennis racket 82, and an arrow Y represents the axial direction of the tennis racket 82.
The frame 84 includes a head 92, two throats 94, and a shaft 96. The head 92 forms the contour of a face 97 (described in detail later). The front shape of the head 92 is substantially an ellipse. The major axis direction of the ellipse coincides with the axial direction Y of the tennis racket 82. The minor axis direction of the ellipse coincides with the width direction X of the tennis racket 82. One end of each throat 94 is connected to the head 92. The throat 94 is connected at the vicinity of the other end thereof to the other throat 94. The throats 94 extend from the head 92 to the shaft 96. The shaft 96 extends from the location where the two throats 94 are connected to each other. The shaft 96 is formed so as to be integrally connected to the throats 94. A portion, of the head 92, located between the two throats 94 is a yoke 98.
The frame 84 is composed of a pipe. In other words, the frame 84 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 86 is formed by a tape wound on the shaft 96. The grip 86 suppresses slip between a hand of a player and the tennis racket 82 when the tennis racket 82 is swung.
As shown in FIG. 19, the tennis racket 82 includes a first grommet 98a, two second grommets 88b, and a third grommet 98c. Each grommet 98 includes a base 240 and a plurality of tubular portions 200. Each tubular portion 200 is formed so as to be integrated with the base 240. A typical material of the grommet 98 is a synthetic resin that is more flexible than the frame 84.
The first grommet 98a is mounted onto a portion at and near the top of the head 92 as shown by an arrow A1 in FIG. 19. As a result of the mounting, each tubular portion 200 of the first grommet 98a penetrates a hole (not shown) provided in the head 92. Each second grommet 98b is mounted onto a side of the head 92 as shown by an arrow A2 in FIG. 19. As a result of the mounting, each tubular portion 200 of the second grommet 98b penetrates a hole (not shown) provided in the head 92. The third grommet 98c is mounted onto the yoke 98 as shown by an arrow A3 in FIG. 19. As a result of the mounting, each tubular portion 200 of the third grommet 98c penetrates a hole (not shown) provided in the head 92.
The string 90 is stretched on the head 92. The string 90 is stretched along the width direction X and the axial direction Y. Of the string 90, portions extending along the width direction X are referred to as transverse strings 90a. Of the string 90, portions extending along the axial direction Y are referred to as longitudinal strings 90b. The face 97 (see FIG. 17) is formed by a plurality of transverse strings 90a and a plurality of longitudinal strings 90b. The face 97 generally extends along an X-Y plane.
FIG. 20 is an enlarged view of a part of the grommet 98 of the tennis racket 82 in FIG. 19. As described above, the grommet 98 includes the base 240 and the plurality of tubular portions 200. These tubular portions 200 include parallel movement tubular portions 200a and vertical movement tubular portions 200b. These tubular portions 200 can also include tubular portions 200 other than the parallel movement tubular portions 200a and the vertical movement tubular portions 200b.
FIG. 21(a) is a front view of a part of the grommet 98 in FIG. 20, FIG. 21(b) is a cross-sectional view taken along a line B-B in FIG. 21(a), and FIG. 21(c) is a cross-sectional view taken along a line C-C in FIG. 21(a). FIGS. 21(a) to 21(c) 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 97 (the right-left direction in FIG. 21(a)) is larger than the inner dimension in a direction perpendicular to the face 97 (the up-down direction in FIG. 21(a)).
FIG. 22(a) is a front view of a part of the grommet 98 in FIG. 20, FIG. 22(b) is a cross-sectional view taken along a line B-B in FIG. 22(a), and FIG. 22(c) is a cross-sectional view taken along a line C-C in FIG. 22(a). FIGS. 22(a) to 22(c) 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 97 (the right-left direction in FIG. 22(a)) is uniform from the base-side opening 246b to the tip-side opening 250b. The inner dimension in the direction perpendicular to the face 97 (the up-down direction in FIG. 22(a)) 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 97 is larger than the inner dimension in the direction parallel to the face 97.
FIG. 23(a) is a front view of the grommet 98 in FIGS. 21(a) to 21(c) with the string 90, and FIG. 23(b) is a cross-sectional view taken along a B-B in FIG. 23(a). The string 90 is passed through the through hole 244a. The string 90 is in contact with the side wall 248a from the base-side opening 246a to the tip-side opening 250a. The string 90 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 90 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. 23(a), the inner dimension in the right-left direction of the through hole 244a is sufficiently larger than the diameter of the string 90. Therefore, the string 90 can move rightward in the parallel movement tubular portion 200a. The string 90 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 90 in the direction parallel to the face 97.
FIG. 24(a) is a front view of the grommet 98 in FIGS. 22(a) to 22(c) with the string 90, and FIG. 24(b) is a cross-sectional view taken along a line B-B in FIG. 24(a). The string 90 is passed through the through hole 244b. The string 90 extends so as to substantially coincide with the axis of the through hole 244b. As is obvious from FIG. 24(a), the inner dimension in the up-down direction of the tip-side opening 250b is sufficiently larger than the diameter of the string 90. Therefore, the string 90 can move in the up-down direction in the vertical movement tubular portion 200b. The string 90 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 90 in the direction perpendicular to the face 97.
In FIG. 18, reference character CL indicates a center line. The tennis racket 82 has a symmetrical shape with respect to the center line CL. As shown in FIG. 18, the tennis racket 82 includes a first tubular portion 201, a second tubular portion 202, a third tubular portion 203, a fourth tubular portion 204, a fifth tubular portion 205, a sixth tubular portion 206, a seventh tubular portion 207, an eighth tubular portion 208, a ninth tubular portion 209, a tenth tubular portion 210, an eleventh tubular portion 211, a twelfth tubular portion 212, a thirteenth tubular portion 213, a fourteenth tubular portion 214, a fifteenth tubular portion 215, a sixteenth tubular portion 216, a seventeenth tubular portion 217, an eighteenth tubular portion 218, a nineteenth tubular portion 219, a twentieth tubular portion 220, a twenty-first tubular portion 221, a twenty-second tubular portion 222, a twenty-third tubular portion 223, a twenty-fourth tubular portion 224, a twenty-fifth tubular portion 225, a twenty-sixth tubular portion 226, a twenty-seventh tubular portion 227, a twenty-eighth tubular portion 228, a twenty-ninth tubular portion 229, a thirtieth tubular portion 230, a thirty-first tubular portion 231, a thirty-second tubular portion 232, a thirty-third tubular portion 233, a thirty-fourth tubular portion 234, and a thirty-fifth tubular portion 235. FIG. 18 shows 35 tubular portions 200. Since the tennis racket 82 has a symmetrical shape with respect to the center line CL as described above, the number of tubular portions 200 in the tennis racket 82 is 70.
As shown in FIG. 18, the longitudinal strings 90b are passed through the first tubular portion 201, the second tubular portion 202, the third tubular portion 203, the fourth tubular portion 204, the fifth tubular portion 205, the sixth tubular portion 206, the seventh tubular portion 207, the ninth tubular portion 209, the twenty-seventh tubular portion 227, the twenty-ninth tubular portion 229, the thirtieth tubular portion 230, the thirty-first tubular portion 231, the thirty-second tubular portion 232, the thirty-third tubular portion 233, the thirty-fourth tubular portion 234, and the thirty-fifth tubular portion 235. The transverse strings 90a are passed through the eighth tubular portion 208, the tenth tubular portion 210, the eleventh tubular portion 211, the twelfth tubular portion 212, the thirteenth tubular portion 213, the fourteenth tubular portion 214, the fifteenth tubular portion 215, the sixteenth tubular portion 216, the seventeenth tubular portion 217, the eighteenth tubular portion 218, the nineteenth tubular portion 219, the twentieth tubular portion 220, the twenty-first tubular portion 221, the twenty-second tubular portion 222, the twenty-third tubular portion 223, the twenty-fourth tubular portion 224, the twenty-fifth tubular portion 225, the twenty-sixth tubular portion 226, and the twenty-eighth tubular portion 228.
FIG. 25 is an enlarged view of an area near the top of the tennis racket 82 in FIG. 17. In FIG. 25, the frame 84 and the transverse strings 90a are not shown. FIG. 25 shows the base 240, the first tubular portion 201, the second tubular portion 202, the third tubular portion 203, the fourth tubular portion 204, and the fifth tubular portion 205. In the present embodiment, the first tubular portion 201, the third tubular portion 203, and the fifth tubular portion 205 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 FIGS. 22(a) to 22(c)). The second tubular portion 202 and the fourth tubular portion 204 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 FIGS. 21(a) to 21(c)). In the tennis racket 82, 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. 25, in the second tubular portion 202, 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 204, 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. 26 shows a tennis ball 32 together with the tennis racket 82. FIG. 26 shows the moment of impact between the tennis racket 82 and the tennis ball 32. In FIG. 26, the tennis ball 32 collides against the face 97 at the lower side (the ground G side) with respect to the center line CL. In this state, the player swings the tennis racket 82 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 202. The inner dimension in the width direction of the through hole 244a of the second tubular portion 202 is sufficiently large. Therefore, the longitudinal string 90b becomes deformed without being obstructed by the second tubular portion 202, and moves outward in the width direction. FIG. 27 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 204 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 82 and the tennis ball 32. The tennis ball 32 is launched with a high spin rate.
FIG. 28 is a cross-sectional view of the first tubular portion 201 of the racket in FIG. 17. In FIG. 28, an arrow Z represents the thickness direction of the tennis racket 82. As described above, in the first tubular portion 201, the shape of the tip-side opening 250b is a vertically elongated circle. Therefore, the longitudinal string 90b passed through the first tubular portion 201 becomes deformed in the Z direction upon reception of pressure from the tennis ball 32. This deformation is not inhibited by the first tubular portion 201. Therefore, the longitudinal string 90b can become sufficiently deformed in the Z direction. FIG. 28 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 203 and the longitudinal string 90b passed through the fifth tubular portion 205 can also similarly become sufficiently deformed in the Z direction.
In the parallel movement tubular portion 200a (the second tubular portion 202 or the fourth tubular portion 204), 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 82 and the tennis ball 32, 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 32 upon impact. Through the biting, high-rate spin is imparted to the tennis ball 32.
In FIG. 25, 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 15% and not greater than 60%, and particularly preferably not less than 20% and not greater than 50%, of the half width W1 (see FIG. 17) of the tennis racket 82.
For the purpose of imparting performance intended by a designer to the tennis racket 82, the tubular portion 200 may be formed such that the string 90 is in contact with the wall surface at the outer side in the width direction.
The tennis racket 82 has the parallel movement tubular portions 200a and the vertical movement tubular portions 200b near the top. The tennis racket 82 may have a parallel movement tubular portion 200a and a vertical movement tubular portion 200b at the yoke 98. The tennis racket 82 may have a parallel movement tubular portion 200a and a vertical movement tubular portion 200b at each side.
In the tennis racket 82, as described above, the second tubular portion 202 and the fourth tubular portion 204 are parallel movement tubular portions 200a. Since the tennis racket 82 has a symmetrical shape with respect to the center line CL, the tennis racket 82 includes two second tubular portions 202 and two fourth tubular portions 204. Therefore, the total number N1 of the parallel movement tubular portions 200a is four. The total number N1 is preferably not less than 2 and not greater than 16, and more preferably not less than 4 and not greater than 12.
In the tennis racket 82, as described above, the first tubular portion 201, the third tubular portion 203, and the fifth tubular portion 205 are vertical movement tubular portions 200b. Since the tennis racket 82 has a symmetrical shape with respect to the center line CL, the tennis racket 82 includes two first tubular portions 201, two third tubular portions 203, and two fifth tubular portions 205. Therefore, the total number N2 of the vertical movement tubular portions 200b is six. The total number N2 is preferably not less than 2 and not greater than 16, and more preferably not less than 4 and not greater than 12.
FIG. 29 is a bottom view of the parallel movement tubular portion 200a in FIGS. 21(a) to 21(c) with the string 90. FIG. 29 shows the tip of the parallel movement tubular portion 200a. In FIG. 29, 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. 29, an arrow L1 indicates the inner dimension, in the direction parallel to the face 97, of the tip-side opening 250a. The inner dimension L1 is also the long diameter of the elongated circle. In FIG. 29, an arrow L2 indicates the inner dimension, in the direction perpendicular to the face 97, 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 90 easily becomes deformed in the direction parallel to the face 97 and is less likely to become deformed in the direction perpendicular to the face 97, the ratio (L1/L2) is preferably not less than 1.3 and particularly preferably not less than 1.5. The ratio (L1/L2) is preferably not greater than 4.0.
In FIG. 29, an arrow D indicates the diameter of the string 90. From the viewpoint that the string 90 easily becomes deformed in the direction parallel to the face 97, the ratio (L1/D) is preferably not less than 1.5 and particularly preferably not less than 1.8. The ratio (L1/D) is preferably not greater than 4.5.
FIG. 30 is a bottom view of the vertical movement tubular portion 200b in FIGS. 22(a) to 22(c) with the string 90. FIG. 30 shows the tip of the vertical movement tubular portion 200b. In FIG. 30, 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. 30, an arrow L3 indicates the inner dimension, in the direction parallel to the face 97, of the tip-side opening 250b. The inner dimension L3 is also the short diameter of the elongated circle. In FIG. 30, an arrow L4 indicates the inner dimension, in the direction perpendicular to the face 97, 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 90 easily becomes deformed in the direction perpendicular to the face 97, the ratio (L4/L3) is preferably not less than 1.3 and particularly preferably not less than 1.5. The ratio (L4/L3) is preferably not greater than 4.0.
In FIG. 30, an arrow D indicates the diameter of the string 90. From the viewpoint that the string 90 easily becomes deformed in the direction perpendicular to the face 97, the ratio (L4/D) is preferably not less than 1.5 and particularly preferably not less than 1.8. The ratio (L4/D) is preferably not greater than 4.5.
Second Embodiment
FIG. 31 is a bottom view of a parallel movement tubular opening 254 of a tennis racket according to another embodiment of the present invention with a string 90. The structure of the tennis racket other than the parallel movement tubular opening 254 is the same as that of the tennis racket 82 shown in FIGS. 17 to 30.
The parallel movement tubular opening 254 has a through hole. The through hole has a base-side opening, a side wall, and a tip-side opening 256. The cross-sectional shape of the through hole is uniform from the base-side opening to the tip-side opening 256. As shown in FIG. 31, the shape of the tip-side opening 256 is an ellipse. In FIG. 31, an arrow L1 indicates the inner dimension, in a direction parallel to a face, of the tip-side opening 256. The inner dimension L1 is also the major diameter of the ellipse. In FIG. 31, an arrow L2 indicates the inner dimension, in a direction perpendicular to the face, of the tip-side opening 256. The inner dimension L2 is also the minor diameter of the ellipse. From the viewpoint that the string 90 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 1.3 and particularly preferably not less than 1.5. The ratio (L1/L2) is preferably not greater than 4.0.
In FIG. 31, an arrow D indicates the diameter of the string 90. From the viewpoint that the string 90 easily becomes deformed in the direction parallel to the face, the ratio (L1/D) is preferably not less than 1.5 and particularly preferably not less than 1.8. The ratio (L1/D) is preferably not greater than 4.5.
Third Embodiment
FIG. 32 is a bottom view of a parallel movement tubular portion 258 of a tennis racket according to still another embodiment of the present invention with a string 90. The structure of the tennis racket other than the parallel movement tubular portion 258 is the same as that of the tennis racket 82 shown in FIGS. 17 to 30.
The parallel movement tubular portion 258 has a through hole. The through hole has a base-side opening, a side wall, and a tip-side opening 260. The cross-sectional shape of the through hole is uniform from the base-side opening to the tip-side opening 260. As shown in FIG. 32, the shape of the tip-side opening 260 is an elongated circle. The long axis of the elongated circle is tilted in a direction parallel to a face. In FIG. 32, an arrow L1 indicates the inner dimension, in the direction parallel to the face, of the tip-side opening 260. In FIG. 32, an arrow L2 indicates the inner dimension, in a direction perpendicular to the face, of the tip-side opening 260. From the viewpoint that the string 90 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 1.3 and particularly preferably not less than 1.5. The ratio (L1/L2) is preferably not greater than 4.0.
In FIG. 32, an arrow D indicates the diameter of the string 90. From the viewpoint that the string 90 easily becomes deformed in the direction parallel to the face, the ratio (L1/D) is preferably not less than 1.5 and particularly preferably not less than 1.8. The ratio (L1/D) is preferably not greater than 4.5.
Fourth Embodiment
FIG. 33(a) is a front view of a parallel movement tubular portion 262 of a tennis racket according to still another embodiment of the present invention, FIG. 33(b) is a cross-sectional view taken along a line B-B in FIG. 33(a), and FIG. 33(c) is a cross-sectional view taken along a line C-C in FIG. 33(a). The structure of the tennis racket other than the parallel movement tubular portion 262 is the same as that of the tennis racket 82 shown in FIGS. 17 to 30.
The parallel movement tubular portion 262 has a through hole 264. The through hole 264 has a base-side opening 266, a side wall 268, and a tip-side opening 270. The shape of the base-side opening 266 is a circle. The shape of the tip-side opening 270 is an elongated circle. The inner dimension, in a direction parallel to a face, of the through hole 264 gradually increases from the base-side opening 266 toward the tip-side opening 270. In the tennis racket, a longitudinal string passed through the parallel movement tubular portion 262 can easily become deformed in the direction parallel to the face.
Still Another Embodiment
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 1.3 and particularly preferably not less than 1.5. The ratio (L1/L2) is preferably not greater than 4.0.
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 1.3 and particularly preferably not less than 1.5. The ratio (L4/L3) is preferably not greater than 4.0.
The racket according to the present invention can be used in various sports such as soft tennis, squash, and badminton. The above descriptions are merely illustrative examples, and various modifications can be made without departing from the principles of the present invention.
Patent Grant
11161016
