RACKET
A grommet of a racket includes a tubular part. The tubular part includes a through hole through which a string is passed. The through hole includes a base opening, a side wall, and a non-circular tip opening. Assuming an imaginary dividing plane that is perpendicular to a face of the racket and that divides the non-circular tip opening into a first opening portion and a second opening portion shorter than the first opening portion in a direction parallel to the face, an inside dimension of the first opening portion in the direction perpendicular to the face increases gradually from one end of the non-circular tip opening in the direction parallel to the face to the dividing plane. In the tubular part, the string passes through the first opening portion and is in contact with the side wall from the base opening to the tip opening.
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This application claims priority to and the benefit of Japanese Patent Application No. 2021-182156, filed on Nov. 8, 2021, the entire disclosure of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION 1. Field of the InventionThe present disclosure relates to a racket for use in tennis or the like.
2. Description of the Related ArtA tennis racket includes a frame and strings. In the tennis racket, the strings are typically passed through holes via a grommet. A proposal relating to the shape of the grommet is disclosed in Japanese Laid-Open Patent Application Publication No. 2015-217192.
SUMMARY OF THE INVENTIONA tennis player tries to hit the ball at the center of the face of the racket. However, in tennis playing, the ball is often hit at a point away from the center of the face. When the ball is hit at a point below the center of the face (point toward the ground), the ball flies at a small launch angle due to a change in the angle of the face. The small launch angle leads to a low trajectory of the ball. The ball flying in a low trajectory is likely to fail to pass over the net.
The present applicant aims to provide a racket capable of producing a stable trajectory of a ball even in the event that the ball is hit at a point away from the center of the face of the racket.
A racket according to the present disclosure includes:
(1) a frame;
(2) a grommet mounted on the frame, the grommet including a plurality of tubular parts; and
(3) strings forming a face of the racket.
Each of the tubular parts includes a through hole through which a corresponding one of the strings is passed. The through hole includes a base opening, a side wall, and a tip opening. At least one of the plurality of tubular parts includes a non-circular tip opening. Assuming an imaginary dividing plane that is perpendicular to the face and that divides the non-circular tip opening into a first opening portion and a second opening portion shorter than the first opening portion in a direction parallel to the face, an inside dimension of the first opening portion in a direction perpendicular to the face increases gradually from one end of the non-circular tip opening in the direction parallel to the face to the dividing plane. In the tubular part including the non-circular tip opening, the string passes through the first opening portion and is in contact with the side wall from the base opening to the tip opening.
With the use of the racket according to the present disclosure, a stable trajectory can be achieved even in the event that the ball is hit at a point away from the center of the face.
The above and further objects, features and advantages of the present disclosure will be more apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings.
Hereinafter, the present disclosure will be described in detail based on preferred embodiments with appropriate reference to the drawings.
First EmbodimentThe frame 4 includes a head 12, two throats 14, and a shaft 16. The head 12 defines the outline of the face 17 (described in detail later). The head 12 as viewed from the front is generally shaped as an ellipse. The direction of the major axis of the ellipse coincides with the axial direction Y of the tennis racket 2. The direction of the minor axis 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. The throat 14 joins the other throat 14 in the vicinity of the other end. The throat 14 extends from the head 12 to the shaft 16. The shaft 16 extends from the point where the two throats 14 join each other. The shaft 16 is continuous and integral with the throats 14. The portion of the head 12 that is located between the two throats 14 is a yoke 18. The head 12 may have a shape other than an elliptical shape.
The frame 4 is formed of a pipe. That is, the frame 4 is hollow. The pipe is made of a fiber-reinforced resin material. The matrix resin of the fiber-reinforced resin material is a thermosetting resin. The thermosetting resin is typically an epoxy resin. The fibers of the fiber-reinforced resin material are typically carbon fibers. The fibers are continuous fibers.
The grip 6 is formed by a tape wound around the shaft 16. The grip 6 reduces slip between the hand(s) of the player and the tennis racket 2 when the player swings the tennis racket 2.
As shown in
As shown by the arrow A1 in
The strings 10 are strung on the head 12. The strings 10 are strung along the width direction X and the axial direction Y. The strings 10 that extend along the width direction X may be referred to as “transverse strings 10a”. The strings 10 that extend along the axial direction Y may be referred to as “longitudinal strings 10b”. The plurality of transverse strings 10a and the plurality of longitudinal strings 10b form the face 17 (see
The tubular part 100 has a through hole 24 (24a or 24b) through which the string 10 is passed. The plurality of tubular parts 100 include a plurality of tubular parts 100a each of which has a through hole 24a having a generally triangular cross-section and a plurality of tubular parts 100b each of which has a through hole 24b having an elliptical cross-section.
In
The shape of the tip opening 30a will be described in more detail with reference to
In
One end of the tip opening 30a in the direction parallel to the face 17 is referred to as a “first end P1”, which is an end of the first opening portion 31 as well. The other end of the tip opening 30a in the direction parallel to the face 17 is referred to as a “second end P2”, which is an end of the second opening portion 32 as well. The length L1 of the first opening portion 31 is a distance between the first end P1 and the dividing plane S in the direction parallel to the face 17. The length L2 of the second opening portion 32 is a distance between the second end P2 and the dividing plane S in the direction parallel to the face 17.
The first opening portion 31 is generally shaped as a triangle having a vertex at the first end P1 of the tip opening 30a in the direction parallel to the face 17. The inside dimension Lh of the first opening portion 31 in a direction perpendicular to the face 17 increases gradually from the first end P1 to the dividing plane S. In the present embodiment, as shown in
As shown in
The angle θ between extensions of the two straight portions 33 is 120 degrees or less and preferably 90 degrees or less. The magnitude of the angle θ may differ from one tubular part 100a to another. This will be described in detail later.
As shown by a dashed-double dotted line in
In
As shown in
As shown in
In the present embodiment, each of the second, fourth, and sixth tubular parts 102, 104, and 106 has the through hole 24a having a generally triangular cross-section (see
As shown in
In the tip opening 30a of each of the second, fourth, and sixth tubular parts 102, 104, and 106, the first opening portion 31 is closer to the centerline CL of the racket 2 than the second opening portion 32.
As a result of the swing, the longitudinal string 10b passed through the second tubular part 102 is subjected to a force acting perpendicular to the face 17 and outward in the width direction. In
As previously stated, the string 10 is in contact with the inner one of the opposite wall surfaces of the side wall 28a of the through hole 24a in the width direction. Thus, when the tennis ball B collides with the face 17 at a point above the centerline CL, the deformation of the longitudinal string 10b is not facilitated by the generally triangular through hole 24a. As such, a long time of contact is not achieved, and correction of the trajectory does not occur. With the use of the racket 2, there is little difference in trajectory between collision of the tennis ball B with the face 17 at a point above the centerline CL and collision of the tennis ball B with the face 17 at a point below the centerline CL.
As previously stated, the string 10 is pushed by the ball B and moves toward the dividing plane S along the edge of the first opening portion 31 that is opposite from the ball B. As the movement direction of the string 10 is restricted in this manner, a stable trajectory can be achieved with reduced variations in both the launch angle and flight distance. As the tip opening 30a is symmetrical about a plane parallel to the face 17, a stable trajectory can be achieved regardless of which side of the face 17 the ball B collides with.
In the first tubular part 101, the tip opening 30b is shaped as an ellipse having a minor axis the direction of which coincides with the direction parallel to the face 17. Thus, the longitudinal string 10b passed through the first tubular part 101 is deformed in the direction perpendicular to the face 17 under the action of the pressing force applied from the tennis ball B. The first tubular part 101 does not hinder this deformation. However, the first tubular part 101 hinders the deformation of the string 10 in the direction parallel to the face 17. Thus, the string 10 passed through the through hole 24b of the first tubular part 101 and the string 10 passed through the through hole 24a of the second tubular part 102 adjacent to the first tubular part 101 move away from each other under the action of the pressing force applied from the tennis ball B. Thus, the distance between the two strings 10 is increased upon contact of the ball B with the face 17, and this makes it easier to spin the ball B.
Likewise, the distance between the string 10 passed through the through hole 24b of the third tubular part 103 and the string 10 passed through the through hole 24a of the fourth tubular part 104 is increased under the action of the pressing force applied from the tennis ball B. The distance between the string 10 passed through the through hole 24b of the fifth tubular part 105 and the string 10 passed through the through hole 24a of the sixth tubular part 106 is also increased under the action of the pressing force applied from the tennis ball B.
The edges of the first opening portion 31 of each of the second, fourth, and sixth tubular parts 102, 104, and 106 include the two straight portions 33 which are symmetrical to each other about a plane parallel to the face 17. Extensions of the two straight portions 33 in each of the second, fourth, and sixth tubular parts 102, 104, and 106 form an angle θ with each other, and the closer the tubular part is to the centerline CL of the racket 2, the smaller the angle θ between the extensions is (that is, θ1<θ2<θ3). This allows the string 10 to move in an appropriate direction in each tubular part. In general, the flight distance of the ball decreases as the ball hitting point becomes more distant from the center of the face of the racket. However, in the present embodiment, the angle θ between extensions of the two straight portions 33 increases with increasing distance from the tubular part to the centerline CL of the racket 2, so that the farther the tubular part is from the centerline CL, the more easily the string 10 can move in a direction perpendicular to a ball hitting plane. Thus, a desired flight distance is likely to be achieved even in the event that the ball is hit at a point away from the centerline CL of the racket 2.
In order to endow the tennis racket 2 with performance intended by the designer, the tubular part 100a may be formed such that the string 10 is in contact with the outer one of the opposite wall surfaces in the width direction.
In the tennis racket 2, each of the tubular parts 100a located in the vicinity of the top of the tennis racket 2 (second, fourth, sixth tubular parts 102, 104, and 106) has the through hole 24a having a generally triangular cross-section. Any of the tubular parts 100 located on the yoke 18 may have the through hole 24a having a generally triangular cross-section. Any of the tubular parts 100 located on the sides of the head 12 may have the through hole 24a having a generally triangular cross-section. Any of the transverse strings 10a may be passed through the tubular part 100 having the through hole 24a having a generally triangular cross-section. In any case, the height of trajectory exhibited upon collision of the tennis ball B with a given area of the face 17 can be increased.
In the tennis racket 2, as previously stated, each of the second, fourth, and sixth tubular parts 102, 104, and 106 has the through hole 24a having a generally triangular cross-section. Being symmetrical about the centerline CL, the tennis racket 2 includes two second tubular parts 102, two fourth tubular parts 104, and two sixth tubular parts 106. Thus, the total number N of the tubular parts 100a having the through hole 24a, which has a generally triangular cross-section and in which the string 10b is in contact with the inner one of the opposite wall surfaces in the width direction, is six. The total number N need not be 6. For example, the total number N is preferably from 2 to 16 and more preferably from 4 to 12.
Evaluation Test
An evaluation test was conducted in which the effect of the racket 2 including the tubular part 100a having the through hole 24a having a generally triangular cross-section was evaluated by comparing the racket 2 with other rackets. In the evaluation test, three types of rackets, i.e., rackets of Example, Comparative Example 1, and Comparative Example 2 were produced first.
A racket including second, fourth, and sixth tubular parts was produced as the racket of Example. Each of the second, fourth, and sixth tubular parts had a through hole 24a having a generally triangular cross-section, like the second, fourth, and sixth tubular parts 102, 104, and 106 described in the above embodiment.
In each of the rackets of Example, Comparative Example 1, and Comparative Example 2, the through holes of tubular parts other than the second, fourth, and sixth tubular parts had the same circular cross-section. Specifically, the shape of the through holes of tubular parts other than the second, fourth, and sixth tubular parts was the same as the shape of the through hole 201 shown in
After production of the three types of rackets of Example, Comparative Example 1, and Comparative Example 2 as described above, players were allowed to play rallies using the different types of rackets. The ball trajectories were tracked for each racket, and the average and standard deviation of the launch angle of the ball were calculated. The average and standard deviation of the flight distance of the ball were also calculated. The calculation results are listed in Table 1.
As seen from Table 1, the average of the launch angle was greater in Example 1 than in Comparative Examples 1 and 2. The average of the flight distance was also greater in Example than in Comparative Examples 1 and 2. This verifies that the racket of Example is superior to the rackets of Comparative Examples 1 and 2 in both the launch angle and flight distance.
Additionally, the standard deviation from the average of the launch angle was smaller in Example than in Comparative Examples 1 and 2, and the standard deviation from the average of the flight distance was also smaller in Example than in Comparative Examples 1 and 2. This verifies that the racket of Example produces a more stable trajectory with smaller variations in both the launch angle and flight distance than the rackets of Comparative Examples 1 and 2.
Second EmbodimentThe grommet 40 includes a base 20 and tubular parts 100. Each tubular part 100 has a through hole 24 thorough which a string 10 is passed. The cross-section of the through hole 24 is congruent from the base opening to the tip opening. The plurality of tubular parts 100 include tubular parts 100a and 100c each of which has a through hole 24a or 24c having a cross-section shaped as described in the first embodiment. Each of the through holes 24a and 24c has a generally triangular cross-section just as does the through hole 24a described in the first embodiment. The orientation of the generally triangular shape differs between the through holes 24a and the through holes 24c.
Specifically, as shown in
The angle between extensions of the two straight portions included in the edges of the tip opening is the same for all of the tubular parts 100a and 100c shown in
The present embodiment differs from the first embodiment also in that in the tubular parts 100a and 100c, the first opening portion 31 need not be closer to the centerline CL of the racket 2 than the second opening portion 32. For example, when the first opening portion 31 is closer to the centerline CL of the racket 2 than the second opening portion 32 in one of the two tubular parts 100a and 100c adjacent to each other, the first opening portion 31 may be farther from the centerline CL of the racket 2 than the second opening portion 32 in the other of the adjacent tubular parts 100a and 100c.
The grommet 40 is mounted around the top of the head 12. The grommet 40 may be mounted on one of the sides of the head 12 or on the yoke 18.
The present embodiment, like the first embodiment, has the advantage of increasing both the launch angle and flight distance. Additionally, the present embodiment, like the first embodiment, has the advantage of producing a stable trajectory with reduced variations in both the launch angle and flight distance.
Furthermore, in the present embodiment, the string 10 passed through the through hole 24a of the tubular part 100a and the string 10 passed through the through hole 24a of the tubular part 100c adjacent to the tubular part 100a move away from each other. Thus, the maximum value of the distance between the two adjacent strings 10 is increased upon contact of the ball with the face. This makes it easier to spin the ball.
Other EmbodimentsAlthough in the above embodiments the imaginary dividing plane S is at a location where the inside dimension of the tip opening 30a in the direction perpendicular to the face 17 reaches a maximum, the imaginary dividing plane S is not limited to being at this location. The dividing plane may be defined at any location, provided that the first opening portion is longer than the second opening portion in the direction parallel to the face and that the inside dimension of the first opening portion in the direction perpendicular to the face increases gradually from one end of the first opening portion in the direction parallel to the face to the dividing plane.
Although in the above embodiments the cross-section of the through hole is congruent from the base opening to the tip opening, the cross-section of the through hole need not be congruent from the base opening to the tip opening. For example, the through hole may have a generally triangular tip opening as described in the above embodiments and a base opening having a shape other than a generally triangular shape, such as a circular base opening. For example, the through hole may have a generally triangular tip opening as described in the above embodiments, and the cross-section of the through hole may change continuously or stepwise toward the base opening.
Although in the above first embodiment the direction of the minor axis of the ellipse of the tip opening 30b coincides with the direction parallel to the face 17 (the left-right direction in
The tip opening including the first and second opening portions need not be generally triangular. The tip opening may be generally shaped as a rectangle composed of a generally triangular first opening portion and a generally triangular second opening portion that is shorter than the generally triangular first opening portion in the direction parallel to the face. The tip opening may be fan-shaped. The tip opening may be asymmetrical about a plane parallel to the face.
[Disclosed Items]
The following items disclose preferred embodiments.
[Item 1]
A racket including: a frame; a grommet mounted on the frame, the grommet including a plurality of tubular parts; and strings forming a face of the racket, wherein: each of the tubular parts includes a through hole through which a corresponding one of the strings is passed; the through hole includes a base opening, a side wall, and a tip opening; at least one of the plurality of tubular parts includes a non-circular tip opening; assuming an imaginary dividing plane that is perpendicular to the face and that divides the non-circular tip opening into a first opening portion and a second opening portion shorter than the first opening portion in a direction parallel to the face, an inside dimension of the first opening portion in a direction perpendicular to the face increases gradually from one end of the non-circular tip opening in the direction parallel to the face to the dividing plane; and in the tubular part including the non-circular tip opening, the string passes through the first opening portion and is in contact with the side wall from the base opening to the tip opening.
[Item 2]
The racket according to item 1, wherein the first opening portion is generally shaped as a triangle having a vertex at the one end of the non-circular tip opening.
[Item 3]
The racket according to item 1 or 2, wherein the first opening portion is closer to a centerline of the racket than the second opening portion.
[Item 4]
The racket according to any one of items 1 to 3, wherein the first opening portion includes an edge extending from the one end to the dividing plane, the edge including a straight portion that is straight when viewed in a direction in which the through hole extends, and a ratio of a length of the straight portion in the direction parallel to the face to a length of the first opening portion in the direction parallel to the face is 0.3 or more.
[Item 5]
The racket according to any one of items 1 to 4, wherein the string passed through the tubular part including the non-circular tip opening is a longitudinal string.
[Item 6]
The racket according to item 5, wherein the tubular part including the non-circular tip opening is located in the vicinity of a top of the frame.
[Item 7]
The racket according to any one of items 1 to 6, wherein: the plurality of tubular parts include two or more tubular parts each of which includes the non-circular tip opening, the two or more tubular parts being located in the vicinity of a top of the frame; edges of the first opening portion of each of the two or more tubular parts include two straight portions each of which is straight when viewed in a direction in which the through hole extends, the two straight portions being symmetrical to each other about a plane parallel to the face; extensions of the two straight portions in each of the two or more tubular parts form an angle with each other; and the closer the tubular part is to a centerline of the racket, the smaller the angle between the extensions is.
The racket according to the present disclosure can be used in various kinds of sports such as soft tennis, squash, and badminton.
From the foregoing description, numerous modifications and other embodiments of the present disclosure are obvious to those skilled in the art. Accordingly, the foregoing description is to be construed as illustrative only, and is provided for the purpose of teaching those skilled in the art the best mode for carrying out the present disclosure. The structural and/or functional details may be substantially modified without departing from the scope of the present disclosure.
Claims
1. A racket comprising:
- a frame;
- a grommet mounted on the frame, the grommet including a plurality of tubular parts; and
- strings forming a face of the racket, wherein
- each of the tubular parts includes a through hole through which a corresponding one of the strings is passed,
- the through hole includes a base opening, a side wall, and a tip opening,
- at least one of the plurality of tubular parts includes a non-circular tip opening,
- assuming an imaginary dividing plane that is perpendicular to the face and that divides the non-circular tip opening into a first opening portion and a second opening portion shorter than the first opening portion in a direction parallel to the face, an inside dimension of the first opening portion in a direction perpendicular to the face increases gradually from one end of the non-circular tip opening in the direction parallel to the face to the dividing plane, and
- in the tubular part including the non-circular tip opening, the string passes through the first opening portion and is in contact with the side wall from the base opening to the tip opening.
2. The racket according to claim 1, wherein the first opening portion is generally shaped as a triangle having a vertex at the one end of the non-circular tip opening.
3. The racket according to claim 1, wherein the first opening portion is closer to a centerline of the racket than the second opening portion.
4. The racket according to claim 1, wherein
- the first opening portion includes an edge extending from the one end to the dividing plane, the edge including a straight portion that is straight when viewed in a direction in which the through hole extends, and
- a ratio of a length of the straight portion in the direction parallel to the face to a length of the first opening portion in the direction parallel to the face is 0.3 or more.
5. The racket according to claim 1, wherein the string passed through the tubular part including the non-circular tip opening is a longitudinal string.
6. The racket according to claim 5, wherein the tubular part including the non-circular tip opening is located in the vicinity of a top of the frame.
7. The racket according to claim 1, wherein
- the plurality of tubular parts include two or more tubular parts each of which includes the non-circular tip opening, the two or more tubular parts being located in the vicinity of a top of the frame,
- edges of the first opening portion of each of the two or more tubular parts include two straight portions each of which is straight when viewed in a direction in which the through hole extends, the two straight portions being symmetrical to each other about a plane parallel to the face,
- extensions of the two straight portions in each of the two or more tubular parts form an angle with each other, and
- the closer the tubular part is to a centerline of the racket, the smaller the angle between the extensions is.
Type: Application
Filed: Oct 13, 2022
Publication Date: May 11, 2023
Applicant: SUMITOMO RUBBER INDUSTRIES, LTD. (Kobe-shi)
Inventors: Kohei MIMURA (Kobe-shi), Yosuke YAMAMOTO (Kobe-shi)
Application Number: 17/965,384