racket

Abstract

To provide a racket which can achieve a high projectile line, even when a ball is hit at a position deviated from a center of a face.SOLUTION: A grommet 8 of a racket has a cylindrical part 100a. The cylindrical part 100a has an open hole 24a for passing a string 10 therethrough. The open hole 24a comprises: a base side opening 26a; a side wall 28a; and a tip side opening 30a. When dividing a non-circular tip side opening 30a into a first opening 31 and a second opening 32 whose length in a direction parallel to the face is shorter than that of the first opening 31, in a virtual division plane S which is vertical to the face, an inner dimension of the first opening 31 in a direction vertical to the face is increased gradually from one end P1 of the non-circular tip end opening 30a to the division plane S in the direction parallel to the face. In the cylindrical part 100a, the string 10 passes through the first opening 31, and contacts the side wall 28a in a range from the base side opening 26a to the tip side opening 30a.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present disclosure relates to a racket used in tennis or the like. [Background technology]

[0002] A tennis racket has a frame and strings. Generally, in a tennis racket, the strings are threaded through holes via grommets. A proposal regarding the shape of the grommet is disclosed in JP 2015-217192 A. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-217192 Summary of the Invention [Problem to be solved by the invention]

[0004] Tennis players strive to hit the ball with the center of the racket face. However, off-center hits occur frequently in tennis. When the ball is hit below the center (toward the ground), the angle of the face changes, causing the ball to fly at a small launch angle. This launch angle results in a low trajectory. A ball with a low trajectory is less likely to fly over the net.

[0005] An object of the present disclosure is to provide a racket that can obtain a stable trajectory even when the ball is hit at a position shifted from the center of the face. [Means for solving the problem]

[0006] The racket according to the present disclosure comprises: (1) Frame, (2) a grommet attached to the frame and having a plurality of tubular portions; and (3) The strings that form the face It has. Each tubular portion has a through hole through which a string is threaded. This 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. When the non-circular tip-side opening is divided by an imaginary dividing plane perpendicular to the face into a first opening and a second opening that is shorter in length in a direction parallel to the face than the first opening, the inner dimension of the first opening in a direction perpendicular to the face gradually increases from one end of the non-circular tip-side opening in a direction parallel to the face to the dividing plane. In a tubular portion having a non-circular tip-side opening, a string passes through the first opening and abuts against the side wall from the base-side opening to the tip-side opening. [Effects of the Invention]

[0007] With the racket according to the present disclosure, a stable trajectory can be obtained even when the ball is hit at a position shifted from the center of the face. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a front view showing a racket according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is an enlarged view of a portion of the racket of FIG. [Figure 3] FIG. 3 is a partial exploded view of the racket of FIG. [Figure 4] 4 is an enlarged perspective view showing a portion of a grommet of the racket of FIG. 3. FIG. [Figure 5] 5(a) is an enlarged cross-sectional view of a portion of the grommet in FIG. 4 viewed from the front, FIG. 5(b) is a cross-sectional view taken along line BB in FIG. 5(a), and FIG. 5(c) is a diagram for explaining the shape of the tip-end opening in FIG. 5(b). [Figure 6] 6(a) is an enlarged cross-sectional view of a portion of the grommet of FIG. 4 as viewed from the front, and FIG. 6(b) is a cross-sectional view taken along line BB of FIG. 6(a). [Figure 7]FIG. 7 is an enlarged cross-sectional view of the top and vicinity of the racket in FIG. 1 as viewed from the front. [Figure 8] FIG. 8 is a view of the top and vicinity of the racket in FIG. 1 as viewed in the axial direction Y of the racket. [Figure 9] FIG. 9 is a front view of the racket of FIG. 1 shown with a ball. [Figure 10] FIG. 10(a) is an enlarged cross-sectional view of the top vicinity of the racket in FIG. 9 as viewed from the front, and FIG. 10(b) is a diagram for explaining the movement of the string when the ball contacts the face. [Figure 11] FIG. 11 is a diagram for explaining a grommet according to a first comparative example. [Figure 12] FIG. 12 is a diagram for explaining a grommet according to a second comparative example. [Figure 13] FIG. 13 is a diagram showing a portion of a grommet of a racket according to a second embodiment of the present disclosure. [Figure 14] FIG. 14 is a diagram for explaining the movement of the string when the ball comes into contact with the face of the racket in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, the present disclosure will be described in detail based on preferred embodiments, with appropriate reference to the drawings.

[0010] (First embodiment) 1-3 show a tennis racket 2. This tennis racket 2 has a frame 4, a grip 6, grommets 8, and strings 10. This tennis racket 2 can be used for hard tennis. In the drawings, arrow X indicates the width direction of the tennis racket 2, and arrow Y indicates the axial direction of the tennis racket 2. The symbol CL indicates a center line. The tennis racket 2 has a shape that is symmetrical with respect to the center line CL.

[0011] The frame 4 has a head 12, two throats 14, and a shaft 16. The head 12 forms the outline of a face 17 (described in detail later). The front shape of the head 12 is approximately elliptical. 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 continuous with the head 12. This throat 14 joins with another throat 14 near the other end. The throat 14 extends from the head 12 to a shaft 16. The shaft 16 extends from the point where the two throats 14 join. The shaft 16 is formed continuously and integrally with the throats 14. The portion of the head 12 sandwiched between the two throats 14 is a yoke 18. The head 12 may have a shape other than an ellipse.

[0012] The frame 4 is made 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. A typical fiber of the fiber-reinforced resin is a carbon fiber. The fiber is a long fiber.

[0013] The grip 6 is formed by a tape wound around the shaft 16. The grip 6 prevents slippage between the player's hand and the tennis racket 2 when the tennis racket 2 is swung.

[0014] As shown in Figure 3, the tennis racket 2 has a first grommet 8a, two second grommets 8b, and a third grommet 8c. Each grommet 8 has a base 20 and a plurality of tubular portions 100. Each tubular portion 100 is formed integrally with the base 20. The grommets 8 are typically made of a synthetic resin that is softer than the frame 4.

[0015] As shown by arrow A1 in FIG. 3, the first grommet 8a is attached near the top of the head 12. With this attachment, the tubular portion 100 of each first grommet 8a passes through a hole (not shown) formed in the head 12. As shown by arrow A2 in FIG. 3, the second grommets 8b are attached to the side of the head 12. With this attachment, the tubular portion 100 of each second grommet 8b passes through a hole (not shown) formed in the head 12. As shown by arrow A3 in FIG. 3, the third grommet 8c is attached to the yoke 18. With this attachment, the tubular portion 100 of each third grommet 8c passes through a hole (not shown) formed in the head 12.

[0016] The strings 10 are strung around the head 12. The strings 10 are strung along a width direction X and an axial direction Y. The portions of the strings 10 that extend along the width direction X are called cross strings 10a. The portions of the strings 10 that extend along the axial direction Y are called main strings 10b. The multiple cross strings 10a and the multiple main strings 10b form a face 17 (see FIG. 1). The face 17 generally lies along the XY plane.

[0017] 4 is an enlarged perspective view showing a portion of the grommet 8 of the tennis racket 2 of FIG. 3. The reference symbol CP indicates a plane (hereinafter referred to as the "reference plane") that passes through the center line CL of the tennis racket 2 and is perpendicular to the width direction X of the tennis racket 2. The tennis racket 2 has a shape that is symmetrical with respect to the reference plane CP. As described above, the grommet 8 has a base 20 and a plurality of tubular portions 100.

[0018] The tubular portion 100 has through holes 24 (24a, 24b) through which the string 10 is passed. The multiple tubular portions 100 include multiple tubular portions 100a in which the cross-sectional shape of the through hole 24a is approximately triangular and multiple tubular portions 100b in which the cross-sectional shape of the through hole 24b is elliptical.

[0019] FIG. 5(a) is a cross-sectional view taken along a plane including the axis of the tubular portion 100a. FIG. 5(b) is a cross-sectional view taken along a plane perpendicular to the axis of the tubular portion 100a. The through-hole 24a has a base-side opening 26a, a side wall 28a, and a tip-side opening 30a. As described above, the cross-sectional shape of the through-hole 24a is approximately triangular. The through-hole 24a has a congruent 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 approximately triangular.

[0020] 5(a) and 5(b), the string 10 is indicated by a two-dot chain line. In the tubular portion 100a having the tip-side opening 30a, the string 10 abuts against the side wall 28a from the base-side opening 26a to the approximately triangular tip-side opening 30a.

[0021] The shape of the tip-side opening 30a will be described in more detail with reference to FIG. 5(c). In FIG. 5(c), the edge of the tip-side opening 30a when viewed in the penetrating direction of the through-hole 24a is indicated by a thick solid line. The penetrating direction of the through-hole 24a is parallel to the axial direction of the tubular portion 100a. The tip-side opening 30a is symmetrical with respect to a predetermined plane (hereinafter referred to as the "face surface") R parallel to the face 17. The shape of the tip-side opening 30a is a rounded triangle. The tip-side opening 30a has three rounded vertices. The face surface R intersects with one of the three vertices. The vertices are configured as curves, but may also be points.

[0022] 5(c), an imaginary dividing plane S that divides the tip-side opening 30a into a first opening 31 and a second opening 32 in a direction parallel to the face 17 is shown by a two-dot chain line. The dividing plane S is a plane perpendicular to the face 17. The dividing plane S is parallel to the penetrating direction of the through-hole 24a. The length L1 of the first opening 31 in the direction parallel to the face 17 is longer than the length L2 of the second opening 32 in the direction parallel to the face 17.

[0023] One end of the tip side opening 30a in a direction parallel to the face 17, which is also an end of the first opening 31, is referred to as a first end P1, and the other end of the tip side opening 30a in a direction parallel to the face 17, which is also an end of the second opening 32, is referred to as a second end P2. The length L1 of the first opening 31 is the length between the first end P1 in a direction parallel to the face 17 and the dividing surface S. The length L2 of the second opening 32 is the length between the second end P2 in a direction parallel to the face 17 and the dividing surface S.

[0024] The shape of the first opening 31 is a substantial triangle having a first end P1 of the tip-side opening 30a in a direction parallel to the face 17 as its vertex. Starting from this first end P1 and reaching the dividing plane S, the inner dimension Lh of the first opening 31 in a direction perpendicular to the face 17 gradually increases. In this embodiment, as shown in FIG. 5(c), the imaginary dividing plane S is located at a position where the inner dimension of the tip-side opening 30a in the direction perpendicular to the face 17 is maximum.

[0025] 5(c), each of the two edges of the first opening 31 extending from the first end P1 to the dividing surface S includes two straight line portions 33 that are linear when viewed in the penetrating direction of the through-hole 24a. The two straight line portions 33 are symmetrical with respect to the face surface R. The ratio (L3 / L1) of the length L3 of the straight line portions 33 in the direction parallel to the face 17 to the length L1 of the first opening 31 in the direction parallel to the face 17 is 0.3 or more, preferably 0.5 or more, and more preferably 0.7 or more.

[0026] The angle θ formed by the extensions of the two straight portions 33 is 120 degrees or less, and preferably 90 degrees or less. The size of the angle θ may vary for each tubular portion 100a. This will be described in detail later.

[0027] As shown by the two-dot chain lines in FIGS. 5(a) and 5(b), the string 10 is positioned to pass through the first opening 31 (see FIG. 5(c)). More specifically, when viewed in the direction of penetration of the through-hole 24a, the string 10 contacts the rounded apex of the tip-side opening 30a, which includes the first end P1. Because the through-hole 24a has a congruent cross-sectional shape from the base-side opening 26a to the tip-side opening 30a, the string 10 can contact the sidewall 28a from the base-side opening 26a to the tip-side opening 30a. As is clear from FIGS. 5(a) and 5(b), the length L1 of the first opening 31 in the direction parallel to the face 17 is sufficiently larger than the diameter of the string 10. Furthermore, the length of the first opening 31 near the parting plane S in the direction perpendicular to the face 17 is sufficiently larger than the diameter of the string 10, but the length of the first opening 31 near the first end P1 in the direction perpendicular to the face 17 is not sufficiently larger than the diameter of the string 10. The tubular portion 100a allows the string 10 to move in the direction toward the parting plane S.

[0028] FIG. 6(a) is a cross-sectional view taken along a plane including the axis of the tubular portion 100b. FIG. 6(b) is a cross-sectional view taken along a plane perpendicular to the axis of the tubular portion 100b. The through hole 24b has a base-side opening 26b, a side wall 28b, and a tip-side opening 30b. As described above, the cross-sectional shape of the through hole 24b is elliptical. The through hole 24b has a congruent 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 elliptical. The minor axis of the ellipse of the tip-side opening 30b coincides with the direction parallel to the face 17 (the left-right direction in FIG. 6(b)).

[0029] In Figures 6(a) and 6(b), the string 10 is indicated by a two-dot chain line. The string 10 is positioned so as to pass through the center of the ellipse of the tip side opening 30b. More specifically, when viewed in the direction of penetration of the through-hole 24b, the string 10 intersects with the minor axis of the ellipse of the tip side opening 30b. For example, the string 10 may abut against the side wall 28b in a direction parallel to the face 17 from the base side opening 26b to the tip side opening 30b. As is clear from Figures 6(a) and 6(b), the inner dimension of the tip side opening 30b in a direction perpendicular to the face 17 is sufficiently larger than the diameter of the string 10. The tubular portion 100b primarily allows movement of the string 10 in a direction perpendicular to the face 17.

[0030] As shown in FIG. 2 , the tennis racket 2 includes a first cylindrical portion 101, a second cylindrical portion 102, a third cylindrical portion 103, a fourth cylindrical portion 104, a fifth cylindrical portion 105, a sixth cylindrical portion 106, a seventh cylindrical portion 107, an eighth cylindrical portion 108, a ninth cylindrical portion 109, a tenth cylindrical portion 110, an eleventh cylindrical portion 111, a twelfth cylindrical portion 112, a thirteenth cylindrical portion 113, a fourteenth cylindrical portion 114, a fifteenth cylindrical portion 115, a sixteenth cylindrical portion 116, a seventeenth cylindrical portion 117, an eighteenth cylindrical portion 118, The tennis racket 2 has a nineteenth barrel portion 119, a twentieth barrel portion 120, a twenty-first barrel portion 121, a twenty-second barrel portion 122, a twenty-third barrel portion 123, a twenty-fourth barrel portion 124, a twenty-fifth barrel portion 125, a twenty-sixth barrel portion 126, a twenty-seventh barrel portion 127, a twenty-eighth barrel portion 128, a twenty-ninth barrel portion 129, a thirty-tenth barrel portion 130, a thirty-first barrel portion 131, a thirty-second barrel portion 132, a thirty-third barrel portion 133, a thirty-fourth barrel portion 134, and a thirty-fifth barrel portion 135. Thirty-five barrel portions 100 are shown in FIG. 2 . As described above, the tennis racket 2 has a symmetrical shape with respect to the center line CL, and therefore the number of barrel portions 100 in the tennis racket 2 is 70.

[0031] As shown in FIG. 2, the main string 10b is threaded through the first barrel portion 101, the second barrel portion 102, the third barrel portion 103, the fourth barrel portion 104, the fifth barrel portion 105, the sixth barrel portion 106, the seventh barrel portion 107, the ninth barrel portion 109, the twenty-seventh barrel portion 127, the twenty-ninth barrel portion 129, the thirty-tenth barrel portion 130, the thirty-first barrel portion 131, the thirty-second barrel portion 132, the thirty-third barrel portion 133, the thirty-fourth barrel portion 134, and the thirty-fifth barrel portion 135. The cross string 10a is threaded through the eighth tube portion 108, the tenth tube portion 110, the eleventh tube portion 111, the twelfth tube portion 112, the thirteenth tube portion 113, the fourteenth tube portion 114, the fifteenth tube portion 115, the sixteenth tube portion 116, the seventeenth tube portion 117, the eighteenth tube portion 118, the nineteenth tube portion 119, the twentieth tube portion 120, the twenty-first tube portion 121, the twenty-second tube portion 122, the twenty-third tube portion 123, the twenty-fourth tube portion 124, the twenty-fifth tube portion 125, the twenty-sixth tube portion 126 and the twenty-eighth tube portion 128.

[0032] In this embodiment, the second cylindrical portion 102, the fourth cylindrical portion 104, and the sixth cylindrical portion 106 have through holes 24a (see FIG. 5) whose cross-sectional shape is approximately triangular. The other cylindrical portions 100 have through holes 24b (see FIG. 6) whose cross-sectional shape is elliptical. The cylindrical portions 100 other than the second cylindrical portion 102, the fourth cylindrical portion 104, and the sixth cylindrical portion 106 may have through holes 24a whose cross-sectional shape is approximately triangular. Furthermore, the cylindrical portions 100 other than the second cylindrical portion 102, the fourth cylindrical portion 104, and the sixth cylindrical portion 106 may have through holes 24a whose cross-sectional shape is approximately triangular, or may have through holes whose cross-sectional shape is circular.

[0033] FIG. 7 is an enlarged front view of the top and vicinity of the racket 2 of FIG. 1. FIG. 8 is a view of the top and vicinity of the racket 2 of FIG. 1 as viewed in the axial direction Y of the racket 2. The frame 4 and cross strings 10a are omitted from FIGS. 7 and 8. FIG. 7 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. FIG. 8 shows the base 20, 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, and the sixth tubular portion 106. The first tubular portion 101, the third tubular portion 103, and the fifth tubular portion 105 have through holes 24b (see FIG. 6) with an elliptical cross section. The second tubular portion 102, the fourth tubular portion 104, and the sixth tubular portion 106 have through holes 24a (see FIG. 5) with a substantially triangular cross section. In the second tubular portion 102, the fourth tubular portion 104, and the sixth tubular portion 106, the string 10 abuts against the left (inner in the width direction) wall surface of the side wall 28a of the through-hole 24a.

[0034] As shown in FIG. 8 , the second, fourth, and sixth cylindrical portions 102, 104, and 106 all share a generally triangular tip-side opening 30a, but the generally triangular shapes are slightly different. Specifically, in the second cylindrical portion 102, the angle θ1 formed by the extensions of the two straight portions 33 included in the edge of the tip-side opening 30a is 30 degrees. In the fourth cylindrical portion 104, the angle θ2 formed by the extensions of the two straight portions 33 included in the edge of the tip-side opening 30a is 60 degrees. In the sixth cylindrical portion 106, the angle θ formed by the extensions of the two straight portions 33 included in the edge of the tip-side opening 30a is 90 degrees. In other words, the angle θ formed by the extensions of the two straight portions decreases with increasing distance from the center line CL of the racket 2 (i.e., θ1<θ2<θ3). However, in the second cylindrical portion 102, the fourth cylindrical portion 104, and the sixth cylindrical portion 106, the angles formed by the extension lines of the two straight line portions 33 included in the edge portion of the tip side opening 30a may be the same.

[0035] In addition, in each of the tip side openings 30a of the second tubular portion 102, the fourth tubular portion 104, and the sixth tubular portion 106, the first opening 31 is located closer to the center line CL of the racket 2 than the second opening 32.

[0036] Fig. 9 shows a tennis ball B together with the tennis racket 2. Fig. 9 also shows the moment of impact between the tennis racket 2 and the tennis ball B. In Fig. 9, the tennis ball B collides with the face 17 below the center line CL (towards the ground G). In this state, the player swings the tennis racket 2 forward and then upward.

[0037] This swing applies a force perpendicular to the face 17 and outward in the width direction to the main string 10b threaded through the second tubular portion 102. FIG. 10(a) shows the main string 10b after movement, and FIG. 10(b) shows the contact direction of the ball B indicated by arrow B1, and the movement direction of the main string 10b when the ball B contacts the face 17 indicated by the arrow in the through-hole 24a. The main string 10b deforms and moves outward in the width direction without being hindered by the second tubular portion 102. At the tip-side opening 30a, the main string 10b is pushed by the ball B and moves toward the dividing plane S along the edge of the first opening 31 opposite the ball B. The main string 10b then returns to its original shape. The main strings 10b threaded through the fourth tubular portion 104 (100a) and the sixth tubular portion 106 (100a) also deform and return to their original shape in a similar manner. These deformations and restorations of the main strings 10b achieve a long contact time between the tennis racket 2 and the tennis ball B. The tennis racket 2 hits the tennis ball B at a large launch angle. The tennis racket 2 can achieve a high trajectory even when the tennis ball B is hit below the center line CL.

[0038] As mentioned above, the strings 10 abut on the inner wall surfaces of the side walls 28a of the through-holes 24a in the width direction. Therefore, when the tennis ball B hits the face 17 above the center line CL, the approximately triangular shape of the through-holes 24a does not promote deformation of the main strings 10b. Therefore, a long contact time is not obtained, and no correction of the trajectory is made. With this racket 2, there is little difference in trajectory between when the tennis ball B hits the face 17 above the center line CL and when the tennis ball B hits the face 17 below the center line CL.

[0039] As described above, the string 10 is pushed by the ball B and moves in a direction toward the dividing surface S along the edge of the first opening 31 on the side opposite the ball B. Because the direction of movement of the string 10 is restricted in this way, a stable trajectory with reduced variation in both launch angle and distance can be obtained. Furthermore, because the tip-side opening 30a has a shape that is symmetrical with respect to a plane parallel to the face 17, a stable trajectory can be obtained regardless of which side of the face 17 the ball B contacts.

[0040] As described above, the string 10 is pushed by the ball B and moves in a direction toward the dividing surface S along the edge of the first opening 31 on the side opposite the ball B. Because the direction of movement of the string 10 is restricted in this way, a stable trajectory with reduced variation in both launch angle and distance can be obtained. Furthermore, because the tip-side opening 30a has a shape that is symmetrical with respect to a plane parallel to the face 17, a stable trajectory can be obtained regardless of which side of the face 17 the ball B contacts.

[0041] On the other hand, the shape of the tip-side opening 30b of the first tubular portion 101 is an ellipse with its minor axis coinciding with a direction parallel to the face 17. Therefore, under pressure from the tennis ball B, the main string 10b threaded through the first tubular portion 101 deforms in a direction perpendicular to the face. The first tubular portion 101 does not hinder this deformation. However, the first tubular portion 101 does hinder the deformation of the string 10 in a direction parallel to the face 17. Therefore, under pressure from the tennis ball B, the string 10 threaded through the through-hole 24b of the first tubular portion 101 and the adjacent string 10 threaded through the through-hole 24a of the second tubular portion 102 move away from each other. Therefore, when the ball B contacts the face 17, the distance between the two strings 10 increases, making it easier to apply spin.

[0042] In addition, the string 10 passing through the through hole 24b of the third tubular portion 103 and the string 10 passing through the through hole 24a of the fourth tubular portion 104 also receive pressure from the tennis ball B, causing the distance between them to similarly increase, and the string 10 passing through the through hole 24b of the fifth tubular portion 105 and the string 10 passing through the through hole 24a of the sixth tubular portion 106 also receive pressure from the tennis ball B, causing the distance between them to similarly increase.

[0043] The edge of each first opening 31 of the second, fourth, and sixth cylindrical portions 102, 104, and 106 includes two straight portions 33 that are symmetrical to each other in a plane parallel to the face 17. Furthermore, in the second, fourth, and sixth cylindrical portions 102, 104, and 106, the angle θ formed by the extensions of the two straight portions 33 becomes smaller the closer the cylindrical portion is to the center line CL of the racket 2 (i.e., θ1<θ2<θ3). This optimizes the direction of movement of the strings 10 in each cylindrical portion. Generally, the farther the ball is struck from the center of the racket face, the more difficult it is to achieve a long ball flight distance. However, in this embodiment, the farther the cylindrical portion is from the center line CL of the racket 2, the greater the angle θ formed by the extensions of the two straight portions 33, making it easier for the strings 10 to move perpendicular to the hitting surface. Therefore, it becomes easier to achieve a long flight distance even when the ball is struck from a position farther from the center line CL of the racket 2.

[0044] For the purpose of imparting the performance intended by the designer to the tennis racket 2, the tubular portion 100a may be formed so that the strings 10 come into contact with the outer wall surface in the width direction.

[0045] In this tennis racket 2, the tubular portions 100a (second tubular portion 102, fourth tubular portion 104, and sixth tubular portion 106) located near the top have through holes 24a whose cross-section is approximately triangular. The tubular portion 100 located at the yoke 18 may have through holes 24a whose cross-section is approximately triangular. The tubular portion 100 located at the side may have through holes 24a whose cross-section is approximately triangular. The cross strings 10a may be threaded through the tubular portion 100 having through holes 24a whose cross-section is approximately triangular. In either case, an improvement in trajectory height can be achieved when a tennis ball B impacts a predetermined point.

[0046] As described above, in this tennis racket 2, the second tubular portion 102, the fourth tubular portion 104, and the sixth tubular portion 106 each have a through hole 24a whose cross section is approximately triangular. Because this tennis racket 2 is symmetrical with respect to the center line CL, it has two second tubular portions 102, two fourth tubular portions 104, and two sixth tubular portions 106. Therefore, the total number N of tubular portions 100a whose cross section is approximately triangular and whose inner wall surface in the width direction has through holes 24a with which the strings 10b come into contact is six. The total number N does not have to be six, and is preferably, for example, 2 to 16 inclusive, and more preferably, 4 to 12 inclusive.

[0047] (Evaluation test) An evaluation test was conducted to evaluate the effect of the racket 2 having the tubular portion 100a in which the cross-sectional shape of the through-hole 24a is approximately triangular by comparing it with other rackets. In the evaluation test, three types of rackets were first produced: an example, a comparative example 1, and a comparative example 2.

[0048] As an example racket, a racket was produced having a second cylindrical portion, a fourth cylindrical portion, and a sixth cylindrical portion in which the cross-sectional shape of the through hole 24a is approximately triangular, similar to the second cylindrical portion 102, the fourth cylindrical portion 104, and the sixth cylindrical portion 106 described in the above embodiment.

[0049] FIG. 11 shows the second cylindrical portion 200 of the racket of Comparative Example 1. The cross-sectional shape of the through hole 201 in the second cylindrical portion 200 is circular. The through hole 201 has a congruent cross-sectional shape from the base-side opening to the tip-side opening. The diameter of the through hole 201 is slightly larger than the diameter of the string 10, so that the string 10 can hardly move within the through hole 201. In Comparative Example 1, the shapes of the through holes in the fourth and sixth cylindrical portions are the same as the cross-sectional shape of the through hole 201 in the second cylindrical portion 200.

[0050] FIG. 12 shows the second tubular portion 300 of the racket of Comparative Example 2. The cross-sectional shape of the through hole 301 of the second tubular portion 300 is circular. The through hole 301 has a congruent cross-sectional shape from the base-side opening to the tip-side opening. The diameter of the through hole 301 is sufficiently larger than the diameter of the string 10. The diameter of the through hole 301 is at least twice the diameter of the string 10. In the tubular portion 300, the string 10 abuts on the inner wall surface of the side wall of the through hole 301 in the width direction. The tubular portion 300 restricts the movement of the string 10 inward in the width direction within the through hole 201, but does not particularly restrict the movement of the string 10 in other directions. In Comparative Example 2, the shapes of the through holes of the fourth and sixth tubular portions are the same as the cross-sectional shape of the through hole 201 of the second tubular portion 200.

[0051] In each of the rackets of Example, Comparative Example 1, and Comparative Example 2, the through holes in the cylindrical portions other than the second, fourth, and sixth cylindrical portions had the same circular cross-sectional shape. Specifically, the through holes in the cylindrical portions other than the second, fourth, and sixth cylindrical portions had the same shape as through hole 201 shown in FIG. 11.

[0052] After producing the three types of rackets described above, namely, Example, Comparative Example 1, and Comparative Example 2, players were asked to play rallies using each racket. The trajectory of the ball when using each racket was then tracked and measured, and the average launch angle and its standard deviation were calculated, as well as the flight distance and its standard deviation. The calculation results are shown in Table 1.

[0053] [Table 1]

[0054] As shown in Table 1, the average launch angle of the Example was greater than the average launch angles of Comparative Examples 1 and 2. The average flight distance of the Example was also greater than the average flight distances of Comparative Examples 1 and 2. This confirmed that the racket of the Example was superior to the rackets of Comparative Examples 1 and 2 in both launch angle and flight distance.

[0055] Furthermore, the standard deviation of the average launch angle for the Example was smaller than the standard deviation of the average launch angle for Comparative Examples 1 and 2, and the standard deviation of the average flight distance for the Example was smaller than the standard deviation of the average flight distance for Comparative Examples 1 and 2. This confirms that the racket for the Example provides a more stable trajectory with less variation in both launch angle and flight distance compared to the rackets for Comparative Examples 1 and 2.

[0056] Second Embodiment Figure 13 shows a portion of grommet 40 of a tennis racket according to a second embodiment. The structure of this tennis racket, other than grommet 40, is the same as that of tennis racket 2 shown in Figures 1-12. In the following description, the same components of grommet 40 as those in the first embodiment are designated by the same reference numerals, and detailed description thereof will be omitted.

[0057] The grommet 40 has a base 20 and a tubular portion 100. The tubular portion 100 has a through hole 24 through which the string 10 is passed. The through hole 24 has a congruent cross-sectional shape from the base-side opening to the tip-side opening. The multiple tubular portions 100 have tubular portions 100a, 100c having through holes 24a, 24c with the cross-sectional shapes described in the first embodiment. The cross-sectional shapes of the through holes 24a, 24c are both approximately triangular, the same as the through hole 24a described in the first embodiment. However, the orientation of the approximately triangular shape of the through holes 24a, 24c is different from each other.

[0058] 11, the through-hole 24c of the cylindrical portion 100c has a cross-sectional shape that is symmetrical to the through-hole 24a of the cylindrical portion 100a with respect to a line perpendicular to the face 17. That is, the through-hole 24a and the through-hole 24c have the same cross-sectional shape but face in different directions. A plurality of cylindrical portions 100a and a plurality of cylindrical portions 100c are arranged alternately.

[0059] 11, the angle formed by the extension lines of the two straight lines included in the edge of the tip-side opening is the same for all of the tube portions 100a, 100c, but the angle formed by the extension lines of the two straight lines included in the edge of the tip-side opening may be different for multiple tube portions 100a, 100c. In addition, the angle formed by the extension lines of the two straight lines can also be set appropriately.

[0060] In this embodiment, unlike the first embodiment, the first opening 31 in the tube portions 100a, 100c does not have to be located closer to the center line CL of the racket 2 than the second opening 32. For example, if the first opening 31 in one of the adjacent tube portions 100a, 100c is located closer to the center line CL of the racket 2 than the second opening 32, the first opening 31 in the other of the tube portions 100a, 100c may be located farther from the center line CL of the racket 2 than the second opening 32.

[0061] The grommet 40 is attached near the top of the head 12. However, the grommet 40 may also be attached to the side of the head 12 or to the yoke 18.

[0062] Fig. 14 is a diagram for explaining the movement of the string 10 when a ball comes into contact with the face of the racket in Fig. 13. Fig. 14 shows one cylindrical portion 100a and one cylindrical portion 100c that are adjacent to each other.

[0063] This embodiment, like the first embodiment, also has the effect of increasing both the launch angle and the flight distance. Furthermore, this embodiment, like the first embodiment, also has the effect of reducing the variation in both the launch angle and the flight distance, thereby achieving a stable trajectory.

[0064] Furthermore, in this embodiment, the string 10 passing through the through-hole 24a of the tubular portion 100a and the adjacent string 10 passing through the through-hole 24a of the tubular portion 100c move in directions away from each other. This increases the maximum distance between the two adjacent strings 10 when the ball contacts the face. This makes it easier to apply spin.

[0065] (Other embodiments) In the above-described embodiment, the imaginary dividing plane S is located at a position where the inner dimension of the tip-side opening 30a in the direction perpendicular to the face 17 is maximized, but the position of the imaginary dividing plane S is not limited to this. The dividing plane can be set arbitrarily at a position that satisfies the conditions that the length of the first opening in the direction parallel to the face is longer than the length of the second opening in the direction parallel to the face, and the inner dimension of the first opening in the direction perpendicular to the face gradually increases from one end of the first opening in the direction parallel to the face to the dividing plane.

[0066] Although the through hole has a congruent cross-sectional shape from the base-side opening to the tip-side opening, the cross-sectional shape of the through hole does not have to be congruent from the base-side opening to the tip-side opening. For example, the through hole may have a tip-side opening with a generally triangular shape as described in the above embodiment and a base-side opening with a shape other than a generally triangular shape, such as a circular shape. For example, the cross-sectional shape of the through hole may be a generally triangular shape as described in the above embodiment at the tip-side opening, and may change continuously or stepwise toward the base-side opening.

[0067] In the first embodiment, the minor axis of the ellipse of the tip side opening 30b coincides with the direction parallel to the face 17 (the left-right direction in FIG. 6(b)). However, the minor axis of the ellipse of the tip side opening 30b may intersect with the direction parallel to the face 17 (the left-right direction in FIG. 6(b)). The tip side opening 30b may be circular. In this case, the tip side opening 30b may be an opening that hardly allows string movement, as shown in FIG. 11, for example, or an opening that allows string movement, as shown in FIG. 12, for example.

[0068] The shape of the tip side opening including the first opening and the second opening may be other than a substantially triangular shape. For example, the tip side opening may be a substantially quadrilateral shape composed of a substantially triangular first opening and a substantially triangular second opening that is shorter in length in a direction parallel to the face than the substantially triangular first opening. The shape of the tip side opening may also be a sector shape. The shape of the tip side opening does not have to be asymmetric with respect to a plane parallel to the face.

[0069] Disclosure (1) is a racket comprising a frame, a grommet attached to the frame and having a plurality of tubular portions, and a string forming a face, each tubular portion having a through hole through which the string passes, the through hole having a base-side opening, a side wall, and a tip-side opening, at least one of the tubular portions having a non-circular tip-side opening, wherein when the non-circular tip-side opening is divided by an imaginary dividing plane perpendicular to the face into a first opening and a second opening having a length shorter than that of the first opening in a direction parallel to the face, the inner dimension of the first opening in a direction perpendicular to the face gradually increases from one end of the non-circular tip-side opening in the direction parallel to the face to the dividing plane, and in the tubular portion having the non-circular tip-side opening, the string passes through the first opening and abuts against the side wall from the base-side opening to the tip-side opening.

[0070] The present disclosure (2) is the racket according to the present disclosure (1), wherein the shape of the first opening is a substantially triangular shape having the one end of the non-circular tip-side opening as a vertex.

[0071] The present disclosure (3) is the racket according to the present disclosure (1) or (2), wherein the first opening is located closer to the center line of the racket than the second opening.

[0072] The present disclosure (4) is a racket in any combination with any of the present disclosures (1) to (3), in which the edge of the first opening extending from the one end to the dividing surface includes a straight portion that is linear when viewed in the penetrating direction of the through hole, and the ratio of the length of the straight portion in a direction parallel to the face to the length of the first opening in a direction parallel to the face is 0.3 or more.

[0073] The present disclosure (5) is a racket that is an arbitrary combination with any of the present disclosures (1) to (4), in which the main strings are threaded through the tubular portion having the non-circular tip-side opening.

[0074] The present disclosure (6) is the racket according to the present disclosure (5), in which the tubular portion having the non-circular tip-side opening is disposed near the top of the frame. 5. The racket of claim 4.

[0075] The present disclosure (7) is a racket in any combination with any of the present disclosures (1) to (6), in which a plurality of tubular portions having the non-circular tip-side openings are arranged near the top of the frame, and the edge of the first opening corresponding to each of the plurality of tubular portions having the non-circular tip-side openings includes two straight portions that are symmetrical to each other in a plane parallel to the face and are each straight when viewed in the penetrating direction of the through-hole, and in the plurality of tubular portions having the non-circular tip-side openings, the angle formed by the extension lines of the two straight portions becomes smaller the closer the tubular portion is to the center line of the racket. [Industrial Applicability]

[0076] The racket according to the present disclosure can be used in various sports such as soft tennis, squash, and badminton. [Explanation of symbols]

[0077] 2. Tennis rackets 4. Frame 6. Grip 8, 40... Grommet 8a First grommet 8b Second grommet 8c···Third grommet 10 strings 10a horizontal string 10b... Vertical string 12 heads 20...Base 24a, 24b, 24c...Through hole 26a, 26b... Base side opening 28a, 28b...side wall 30a, 30b...Tip side opening 100, 101-135, 100a, 100b...Cylinder part 200, 300...Cylinder part 201, 301...through holes S...Divided surface

Claims

1. The golf club includes a frame, a grommet attached to the frame and having a plurality of tubular portions, and a string forming a face, Each cylindrical portion has a through hole through which the string is passed, the through hole has a base opening, a side wall, and a tip opening, At least one of the cylindrical portions has a non-circular distal end opening, when the non-circular tip side opening is divided by an imaginary dividing plane perpendicular to the face into a first opening and a second opening having a length in a direction parallel to the face shorter than that of the first opening, an inner dimension of the first opening in a direction perpendicular to the face gradually increases from one end of the non-circular tip side opening in the direction parallel to the face to the dividing plane, the first opening has a substantially triangular shape having the one end of the non-circular tip-side opening as a vertex, In the tubular portion having the non-circular tip side opening, the string passes through the first opening and abuts against the side wall from the base side opening to the tip side opening.

2. The racket of claim 1 , wherein the first opening is located closer to a center line of the racket than the second opening.

3. an edge portion of the first opening portion extending from the one end portion to the dividing surface includes a linear portion that is linear when viewed in a penetrating direction of the through hole, 3. The racket according to claim 1, wherein a ratio of a length of the straight portion in a direction parallel to the face to a length of the first opening in a direction parallel to the face is 0.3 or greater.

4. 4. The racket according to claim 1, wherein the main strings are threaded through the tubular portion having the non-circular tip end opening.

5. 5. The racket of claim 4, wherein the tubular portion having the non-circular tip opening is located near the top of the frame.

6. A racket comprising a frame, a grommet attached to the frame and having a plurality of tubular portions, and strings forming a face, Each cylindrical portion has a through hole through which the string is passed, the through hole has a base opening, a side wall, and a tip opening, At least one of the cylindrical portions has a non-circular distal end opening, when the non-circular tip side opening is divided by an imaginary dividing plane perpendicular to the face into a first opening and a second opening having a length in a direction parallel to the face shorter than that of the first opening, an inner dimension of the first opening in a direction perpendicular to the face gradually increases from one end of the non-circular tip side opening in the direction parallel to the face to the dividing plane, In the tubular portion having the non-circular tip side opening, the string passes through the first opening and abuts against the side wall from the base side opening to the tip side opening, a plurality of cylindrical portions having the non-circular distal end openings are disposed near a top of the frame; an edge portion of the first opening portion corresponding to each of the plurality of cylindrical portions having the non-circular tip side openings includes two straight line portions that are symmetrical with each other in a plane parallel to the face and that are each straight when viewed in a penetrating direction of the through hole, In the racket, among the plurality of tubular portions having the non-circular tip-side opening, the angle formed by the extension lines of the two straight portions becomes smaller as the tubular portion is closer to the center line of the racket.

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