Patent Description:
A 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 <CIT>.

Patent Document <CIT> discloses a racket with a grommet having tubular parts. The tubular parts include tubular parts with a non-circular opening. These tubular parts are designed with non-circular openings so that two strings can be passed through said non-circular opening.

Patent Document <CIT> discloses a racket with a grommet having tubular parts. These tubular parts originally form a circular opening but form a non-circular opening when they are collapsed.

A 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:.

Each of the tubular parts includes a through hole through which a corresponding single 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.

<FIG> show a tennis racket <NUM>. The tennis racket <NUM> includes a frame <NUM>, a grip <NUM>, grommets <NUM>, and strings <NUM>. The tennis racket <NUM> is usable for regular tennis. In the drawings, the arrow X represents the width direction of the tennis racket <NUM>, and the arrow Y represents the axial direction of the tennis racket <NUM>. The reference sign CL represents the centerline of the tennis racket <NUM>. The tennis racket <NUM> is symmetrical about the centerline CL.

The frame <NUM> includes a head <NUM>, two throats <NUM>, and a shaft <NUM>. The head <NUM> defines the outline of the face <NUM> (described in detail later). The head <NUM> 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 <NUM>. The direction of the minor axis of the ellipse coincides with the width direction X of the tennis racket <NUM>. One end of each throat <NUM> is continuous with the head <NUM>. The throat <NUM> joins the other throat <NUM> in the vicinity of the other end. The throat <NUM> extends from the head <NUM> to the shaft <NUM>. The shaft <NUM> extends from the point where the two throats <NUM> join each other. The shaft <NUM> is continuous and integral with the throats <NUM>. The portion of the head <NUM> that is located between the two throats <NUM> is a yoke <NUM>. The head <NUM> may have a shape other than an elliptical shape.

The frame <NUM> is formed of a pipe. That is, the frame <NUM> 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 <NUM> is formed by a tape wound around the shaft <NUM>. The grip <NUM> reduces slip between the hand(s) of the player and the tennis racket <NUM> when the player swings the tennis racket <NUM>.

As shown in <FIG>, the tennis racket <NUM> includes a first grommet 8a, two second grommets 8b, and a third grommet 8c. Each grommet <NUM> includes a base <NUM> and a plurality of tubular parts <NUM>. Each tubular part <NUM> is integral with the base <NUM>. The grommet <NUM> is typically made of a synthetic resin material softer than the material of the frame <NUM>.

As shown by the arrow A1 in <FIG>, the first grommet 8a is mounted around the top of the head <NUM>. With the first grommet 8a mounted on the head <NUM>, each tubular part <NUM> of the first grommet 8a extends through a corresponding one of holes (not shown) of the head <NUM>. As shown by the arrow A2 in <FIG>, each second grommet 8b is mounted on a corresponding one of the sides of the head <NUM>. With the second grommet 8b mounted on the head <NUM>, each tubular part <NUM> of the second grommet 8b extends through a corresponding one of holes (not shown) of the head <NUM>. As shown by the arrow A3 in <FIG>, the third grommet 8c is mounted on the yoke <NUM>. With the third grommet 8c mounted on the yoke <NUM>, each tubular part <NUM> of the third grommet 8c extends through a corresponding one of holes (not shown) of the head <NUM>.

The strings <NUM> are strung on the head <NUM>. The strings <NUM> are strung along the width direction X and the axial direction Y. The strings <NUM> that extend along the width direction X may be referred to as "transverse strings 10a". The strings <NUM> 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 <NUM> (see <FIG>). The face <NUM> extends generally along the X-Y plane.

<FIG> is an enlarged perspective view showing a portion of the grommet <NUM> of the tennis racket <NUM> of <FIG>. The reference sign CP represents a plane passing through the centerline CL of the tennis racket <NUM> and perpendicular to the width direction X of the tennis racket <NUM> (this plane will be referred to as "reference plane" hereinafter). The tennis racket <NUM> is symmetrical about the reference plane CP. As previously stated, the grommet <NUM> includes the base <NUM> and the plurality of tubular parts <NUM>.

The tubular part <NUM> has a through hole <NUM> (24a or 24b) through which the string <NUM> is passed. The plurality of tubular parts <NUM> 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.

<FIG> is a cross-sectional view taken along a plane including the axis of the tubular part 100a. <FIG> is a cross-sectional view taken along a plane perpendicular to the axis of the tubular part 100a. The through hole 24a includes a base opening 26a, a side wall 28a, and a tip opening 30a. As previously stated, the through hole 24a has a generally triangular cross-section. The cross-section of the through hole 24a is congruent from the base opening 26a to the tip opening 30a. Thus, the tip opening 30a is generally triangular.

In <FIG>, the string <NUM> is shown by a dashed-double dotted line. In the tubular part 100a having the tip opening 30a, the string <NUM> is in contact with the side wall 28a from the base opening 26a to the tip opening 30a which is generally triangular.

The shape of the tip opening 30a will be described in more detail with reference to <FIG>. In <FIG>, the edges of the tip opening 30a as viewed in the direction in which the through hole 24a extends are shown by a bold solid line. The direction in which the through hole 24a extends is parallel to the axial direction of the tubular part 100a. The tip opening 30a is symmetrical about a given plane R parallel to the face <NUM> (this plane R will be referred to as "face plane R" hereinafter). The tip opening 30a is shaped as a triangle with rounded corners. The tip opening 30a has three rounded vertices. The face plane R crosses one of the three vertices. Each of the vertices is formed by a curve but may be formed as a point.

In <FIG>, an imaginary dividing plane S dividing the tip opening 30a into a first opening portion <NUM> and a second opening portion <NUM> in a direction parallel to the face <NUM> is shown by a dashed-double dotted line. The dividing plane S is perpendicular to the face <NUM>. The dividing plane S is parallel to the direction in which the through hole 24a extends. The length L1 of the first opening portion <NUM> in the direction parallel to the face <NUM> is greater than the length L2 of the second opening portion <NUM> in the direction parallel to the face <NUM>.

One end of the tip opening 30a in the direction parallel to the face <NUM> is referred to as a "first end P1", which is an end of the first opening portion <NUM> as well. The other end of the tip opening 30a in the direction parallel to the face <NUM> is referred to as a "second end P2", which is an end of the second opening portion <NUM> as well. The length L1 of the first opening portion <NUM> is a distance between the first end P1 and the dividing plane S in the direction parallel to the face <NUM>. The length L2 of the second opening portion <NUM> is a distance between the second end P2 and the dividing plane S in the direction parallel to the face <NUM>.

The first opening portion <NUM> 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 <NUM>. The inside dimension Lh of the first opening portion <NUM> in a direction perpendicular to the face <NUM> increases gradually from the first end P1 to the dividing plane S. In the present embodiment, as shown in <FIG>, the imaginary dividing plane S is at a location where the inside dimension Lh of the tip opening 30a in the direction perpendicular to the face <NUM> reaches a maximum.

As shown in <FIG>, each of the two edges of the first opening portion <NUM> that extend from the first end P1 to the dividing plane S includes a straight portion <NUM> that is straight when viewed in the direction in which the through hole 24a extends. The two straight portions <NUM> are symmetrical to each other about the face plane R. The ratio of the length L3 of the straight portion <NUM> in the direction parallel to the face <NUM> to the length L1 of the first opening portion <NUM> in the direction parallel to the face <NUM> (L3/L1) is <NUM> or more, preferably <NUM> or more, and more preferably <NUM> or more.

The angle θ between extensions of the two straight portions <NUM> is <NUM> degrees or less and preferably <NUM> 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 <FIG>, the string <NUM> is placed to pass through the first opening portion <NUM> (see <FIG>). More specifically, when viewed in the direction in which the through hole 24a extends, the string <NUM> is in contact with that rounded vertex of the tip opening 30a which includes the first end P1. As the cross-section of the through hole 24a is congruent from the base opening 26a to the tip opening 30a, the string <NUM> can be in contact with the side wall 28a from the base opening 26a to the tip opening 30a. As is clear from <FIG>, the length L1 of the first opening portion <NUM> in the direction parallel to the face <NUM> is significantly greater than the diameter of the string <NUM>. In the vicinity of the dividing plane S, the length of the first opening portion <NUM> in the direction perpendicular to the face <NUM> is significantly greater than the diameter of the string <NUM>, while in the vicinity of the first end P1, the length of the first opening portion <NUM> in the direction perpendicular to the face <NUM> is not significantly greater than the diameter of the string <NUM>. The tubular part 100a permits the movement of the string <NUM> toward the dividing plane S.

<FIG> is a cross-sectional view taken along a plane including the axis of the tubular part 100b. <FIG> is a cross-sectional view taken along a plane perpendicular to the axis of the tubular part 100b. The through hole 24b includes a base opening 26b, a side wall 28b, and a tip opening 30b. As previously stated, the through hole 24b has an elliptical cross-section. The cross-section of the through hole 24b is congruent from the base opening 26a to the tip opening 30a. Thus, the tip opening 30b is elliptical. The direction of the minor axis of the ellipse of the tip opening 30b coincides with the direction parallel to the face <NUM> (the left-right direction in <FIG>).

In <FIG>, the string <NUM> is shown by a dashed-double dotted line. The string <NUM> is placed to pass through the center of the ellipse of the tip opening 30b. More specifically, the minor axis of the ellipse of the tip opening 30b crosses the string <NUM> when viewed in the direction in which the through hole 24b extends. For example, the string <NUM> may be in contact with the side wall 28b in the direction parallel to the face <NUM> from the base opening 26b to the tip opening 30b. As is clear from <FIG>, the inside dimension of the tip opening 30b in the direction perpendicular to the face <NUM> is significantly greater than the diameter of the string <NUM>. The tubular part 100b permits the movement of the string <NUM> mainly in the direction perpendicular to the face <NUM>.

As shown in <FIG>, the tennis racket <NUM> includes a first tubular part <NUM>, a second tubular part <NUM>, a third tubular part <NUM>, a fourth tubular part <NUM>, a fifth tubular part <NUM>, a sixth tubular part <NUM>, a seventh tubular part <NUM>, an eighth tubular part <NUM>, a ninth tubular part <NUM>, a tenth tubular part <NUM>, an eleventh tubular part <NUM>, a twelfth tubular part <NUM>, a thirteenth tubular part <NUM>, a fourteenth tubular part <NUM>, a fifteenth tubular part <NUM>, a sixteenth tubular part <NUM>, a seventeenth tubular part <NUM>, an eighteenth tubular part <NUM>, a nineteenth tubular part <NUM>, a twelfth tubular part <NUM>, a twenty-first tubular part <NUM>, a twenty-second tubular part <NUM>, a twenty-third tubular part <NUM>, a twenty-fourth tubular part <NUM>, a twenty-fifth tubular part <NUM>, a twenty-sixth tubular part <NUM>, a twenty-seventh tubular part <NUM>, a twenty-eighth tubular part <NUM>, a twenty-ninth tubular part <NUM>, a thirtieth tubular part <NUM>, a thirty-first tubular part <NUM>, a thirty-second tubular part <NUM>, a thirty-third tubular part <NUM>, a thirty-fourth tubular part <NUM>, and a thirty-fifth tubular part <NUM>. In <FIG>, <NUM> tubular parts <NUM> are shown. As previously stated, the tennis racket <NUM> is symmetrical about the centerline CL. Thus, the number of the tubular parts <NUM> in the tennis racket <NUM> is <NUM>.

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

In the present embodiment, each of the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM> has the through hole 24a having a generally triangular cross-section (see <FIG>). Each of the other tubular parts <NUM> has the through hole 24b having an elliptical cross-section (see <FIG>). Any of the tubular parts <NUM> other than the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM> may have the through hole 24a having a generally triangular cross-section or have a through hole having a circular cross-section.

<FIG> is an enlarged view of the vicinity of the top of the racket <NUM> of <FIG> as viewed from the front. <FIG> is a view of the vicinity of the top of the racket <NUM> of <FIG> as viewed in the axial direction Y. In <FIG> and <FIG>, the frame <NUM> and the transverse strings 10a are omitted. In <FIG>, there are shown the base <NUM>, first tubular part <NUM>, second tubular part <NUM>, third tubular part <NUM>, and fourth tubular part <NUM>. In <FIG>, there are shown the base <NUM>, first tubular part <NUM>, second tubular part <NUM>, third tubular part <NUM>, fourth tubular part <NUM>, fifth tubular part <NUM>, and sixth tubular part <NUM>. Each of the first, third, and fifth tubular parts <NUM>, <NUM>, and <NUM> has the through hole 24b having an elliptical cross-section (see <FIG>). Each of the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM> has the through hole 24a having a generally triangular cross-section (see <FIG>). In each of the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM>, the string <NUM> is in contact with the left wall surface (inner one of the opposite wall surfaces in the width direction) of the side wall 28a of the through hole 24a.

As shown in <FIG>, the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM> are identical in that each of them has the generally triangular tip opening 30a; however, the generally triangular shape slightly differs among the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM>. Specifically, in the second tubular part <NUM>, the angle θ1 between extensions of the two straight portions <NUM> included in the edges of the tip opening 30a is <NUM> degrees. In the fourth tubular part <NUM>, the angle θ2 between extensions of the two straight portions <NUM> included in the edges of the tip opening 30a is <NUM> degrees. In the sixth tubular part <NUM>, the angle θ3 between extensions of the two straight portions <NUM> included in the edges of the tip opening 30a is <NUM> degrees. That is, the closer the tubular part is to the centerline CL of the racket <NUM>, the smaller is the angle θ between extensions of the two straight portions (θ1 < θ2 < θ3). The angle θ between extensions of the two straight portions <NUM> included in the edges of the tip opening 30a may be the same for the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM>.

In the tip opening 30a of each of the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM>, the first opening portion <NUM> is closer to the centerline CL of the racket <NUM> than the second opening portion <NUM>.

<FIG> shows the tennis racket <NUM> along with a tennis ball B. <FIG> illustrates the moment of impact between the tennis racket <NUM> and the tennis ball B. In <FIG>, the tennis ball B collides with the face <NUM> at a point below the centerline CL (point toward the ground G). In this state, the player swings the tennis racket <NUM> forward and upward.

As a result of the swing, the longitudinal string 10b passed through the second tubular part <NUM> is subjected to a force acting perpendicular to the face <NUM> and outward in the width direction. In <FIG>, the longitudinal string 10b moved by the force is shown. In <FIG>, the direction in which the ball B contacts the face <NUM> is shown by the arrow B1, and the direction in which the longitudinal string 10b moves upon contact of the ball B with the face <NUM> is shown by the arrow depicted inside the through hole 24a. The longitudinal string 10b is deformed without being disturbed by the second tubular part <NUM> and moves outward in the width direction. In the tip opening 30a, the longitudinal string 10b is pushed by the ball B and moves toward the dividing plane S along the edge of the first opening portion <NUM> that is opposite from the ball B. After that, the longitudinal string 10b is restored to its original shape. Likewise, the longitudinal strings 10b passed through the fourth tubular part <NUM> (100a) and sixth tubular part <NUM> (100a) are deformed and then restored to their original shapes. The deformation and restoration of the longitudinal strings 10b ensure a long time of contact between the tennis racket <NUM> and the tennis ball B. With the use of the tennis racket <NUM>, the tennis ball B is shot at a large launch angle. With the use of the tennis racket <NUM>, a high trajectory of the tennis ball B can be achieved even in the event that the tennis ball B is hit at a point below the centerline CL.

As previously stated, the string <NUM> 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 <NUM> 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 <NUM>, there is little difference in trajectory between collision of the tennis ball B with the face <NUM> at a point above the centerline CL and collision of the tennis ball B with the face <NUM> at a point below the centerline CL.

As previously stated, the string <NUM> is pushed by the ball B and moves toward the dividing plane S along the edge of the first opening portion <NUM> that is opposite from the ball B. As the movement direction of the string <NUM> 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 <NUM>, a stable trajectory can be achieved regardless of which side of the face <NUM> the ball B collides with.

In the first tubular part <NUM>, 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 <NUM>. Thus, the longitudinal string 10b passed through the first tubular part <NUM> is deformed in the direction perpendicular to the face <NUM> under the action of the pressing force applied from the tennis ball B. The first tubular part <NUM> does not hinder this deformation. However, the first tubular part <NUM> hinders the deformation of the string <NUM> in the direction parallel to the face <NUM>. Thus, the string <NUM> passed through the through hole 24b of the first tubular part <NUM> and the string <NUM> passed through the through hole 24a of the second tubular part <NUM> adjacent to the first tubular part <NUM> 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 <NUM> is increased upon contact of the ball B with the face <NUM>, and this makes it easier to spin the ball B.

Likewise, the distance between the string <NUM> passed through the through hole 24b of the third tubular part <NUM> and the string <NUM> passed through the through hole 24a of the fourth tubular part <NUM> is increased under the action of the pressing force applied from the tennis ball B. The distance between the string <NUM> passed through the through hole 24b of the fifth tubular part <NUM> and the string <NUM> passed through the through hole 24a of the sixth tubular part <NUM> is also increased under the action of the pressing force applied from the tennis ball B.

The edges of the first opening portion <NUM> of each of the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM> include the two straight portions <NUM> which are symmetrical to each other about a plane parallel to the face <NUM>. Extensions of the two straight portions <NUM> in each of the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM> form an angle θ with each other, and the closer the tubular part is to the centerline CL of the racket <NUM>, the smaller the angle θ between the extensions is (that is, θ1 < θ2 < θ3). This allows the string <NUM> 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 <NUM> increases with increasing distance from the tubular part to the centerline CL of the racket <NUM>, so that the farther the tubular part is from the centerline CL, the more easily the string <NUM> 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 <NUM>.

In order to endow the tennis racket <NUM> with performance intended by the designer, the tubular part 100a may be formed such that the string <NUM> is in contact with the outer one of the opposite wall surfaces in the width direction.

In the tennis racket <NUM>, each of the tubular parts 100a located in the vicinity of the top of the tennis racket <NUM> (second, fourth, sixth tubular parts <NUM>, <NUM>, and <NUM>) has the through hole 24a having a generally triangular cross-section. Any of the tubular parts <NUM> located on the yoke <NUM> may have the through hole 24a having a generally triangular cross-section. Any of the tubular parts <NUM> located on the sides of the head <NUM> 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 <NUM> 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 <NUM> can be increased.

In the tennis racket <NUM>, as previously stated, each of the second, fourth, and sixth tubular parts <NUM>, <NUM>, and <NUM> has the through hole 24a having a generally triangular cross-section. Being symmetrical about the centerline CL, the tennis racket <NUM> includes two second tubular parts <NUM>, two fourth tubular parts <NUM>, and two sixth tubular parts <NUM>. 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 <NUM>. For example, the total number N is preferably from <NUM> to <NUM> and more preferably from <NUM> to <NUM>.

An evaluation test was conducted in which the effect of the racket <NUM> including the tubular part 100a having the through hole 24a having a generally triangular cross-section was evaluated by comparing the racket <NUM> with other rackets. In the evaluation test, three types of rackets, i.e., rackets of Example, Comparative Example <NUM>, and Comparative Example <NUM> 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 <NUM>, <NUM>, and <NUM> described in the above embodiment.

<FIG> shows a second tubular part <NUM> of the racket of Comparative Example <NUM>. The through hole <NUM> of the second tubular part <NUM> has a circular cross-section. The cross-section of the through hole <NUM> is congruent from the base opening to the tip opening. The diameter of the through hole <NUM> is only slightly greater than the diameter of the string <NUM>, and the string <NUM> is hardly movable in the through hole <NUM>. In Comparative Example <NUM>, the cross-sections of the through holes of the fourth and sixth tubular parts have the same shape as the cross-section of the through hole <NUM> of the second tubular part <NUM>.

<FIG> shows a second tubular part <NUM> of the racket of Comparative Example <NUM>. The through hole <NUM> of the second tubular part <NUM> has a circular cross-section. The cross-section of the through hole <NUM> is congruent from the base opening to the tip opening. The diameter of the through hole <NUM> is significantly greater than the diameter of the string <NUM>. The diameter of the through hole <NUM> is two or more times the diameter of the string <NUM>. In the tubular part <NUM>, the string <NUM> is in contact with the inner one of the opposite wall surfaces of the side wall of the through hole <NUM> in the width direction. The tubular part <NUM> restricts the string <NUM> from moving inward along the width direction in the through hole <NUM>, and does not restrict the movement of the string <NUM> in other directions. In Comparative Example <NUM>, the cross-sections of the through holes of the fourth and sixth tubular parts have the same shape as the cross-section of the through hole <NUM> of the second tubular part <NUM>.

In each of the rackets of Example, Comparative Example <NUM>, and Comparative Example <NUM>, 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 <NUM> shown in <FIG>.

After production of the three types of rackets of Example, Comparative Example <NUM>, and Comparative Example <NUM> 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 <NUM>.

As seen from Table <NUM>, the average of the launch angle was greater in Example <NUM> than in Comparative Examples <NUM> and <NUM>. The average of the flight distance was also greater in Example than in Comparative Examples <NUM> and <NUM>. This verifies that the racket of Example is superior to the rackets of Comparative Examples <NUM> and <NUM> 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 <NUM> and <NUM>, and the standard deviation from the average of the flight distance was also smaller in Example than in Comparative Examples <NUM> and <NUM>. 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 <NUM> and <NUM>.

<FIG> shows a portion of a grommet <NUM> of a tennis racket according to a second embodiment. This tennis racket has the same structural components as the tennis racket <NUM> shown in <FIG>, except for the grommet <NUM>. In the following description, the structural components of the grommet <NUM> that are the same as those of the grommet of the first embodiment are denoted by the same reference signs and will not be described in detail.

The grommet <NUM> includes a base <NUM> and tubular parts <NUM>. Each tubular part <NUM> has a through hole <NUM> thorough which a string <NUM> is passed. The cross-section of the through hole <NUM> is congruent from the base opening to the tip opening. The plurality of tubular parts <NUM> 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 <FIG>, the through hole 24c of the tubular part 100c has a cross-section that is symmetrical to that of the through hole 24a of the tubular part 100a about a line perpendicular to the face <NUM>. The cross-section of the through hole 24a and the cross-section of the through hole 24c are in different orientations but are congruent to each other. The tubular parts 100a and the tubular parts 100c alternate with one another.

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 <FIG>. However, the angle between extensions of the two straight portions included in the edges of the tip opening may differ for each tubular part 100a or100c. The magnitude of the angle between extensions of the two straight portions may be chosen as appropriate.

The present embodiment differs from the first embodiment also in that in the tubular parts 100a and 100c, the first opening portion <NUM> need not be closer to the centerline CL of the racket <NUM> than the second opening portion <NUM>. For example, when the first opening portion <NUM> is closer to the centerline CL of the racket <NUM> than the second opening portion <NUM> in one of the two tubular parts 100a and 100c adjacent to each other, the first opening portion <NUM> may be farther from the centerline CL of the racket <NUM> than the second opening portion <NUM> in the other of the adjacent tubular parts 100a and 100c.

The grommet <NUM> is mounted around the top of the head <NUM>. The grommet <NUM> may be mounted on one of the sides of the head <NUM> or on the yoke <NUM>.

<FIG> is a view for illustrating how the string <NUM> moves upon contact of a ball with the face of the racket of <FIG> shows one tubular part 100a and one tubular part 100c which are adjacent to each other.

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 <NUM> passed through the through hole 24a of the tubular part 100a and the string <NUM> 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 <NUM> is increased upon contact of the ball with the face. This makes it easier to spin the ball.

Although 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 <NUM> 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 <NUM> (the left-right direction in <FIG>), the minor axis of the ellipse of the tip opening 30b may cross the direction parallel to the face <NUM> (the left-right direction in <FIG>). The tip opening 30b may be circular. In this case, the tip opening 30b may be, for example, an opening as shown in <FIG> which permits little movement of the string or an opening as shown in <FIG> which permits movement of the string.

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.

The racket according to the present disclosure can be used in various kinds of sports such as soft tennis, squash, and badminton.

Claim 1:
A racket (<NUM>) comprising:
a frame (<NUM>);
a grommet (<NUM>) mounted on the frame (<NUM>), the grommet (<NUM>) including a plurality of tubular parts (<NUM>); and
strings (<NUM>) forming a face (<NUM>) of the racket (<NUM>), wherein
each of the tubular parts (<NUM>) includes a through hole (<NUM>) through which a corresponding single one of the strings (<NUM>) is passed,
the through hole (<NUM>) includes a base opening (26a), a side wall (28a), and a tip opening (30a),
at least one of the plurality of tubular parts (<NUM>) includes a non-circular tip opening (30a),
assuming an imaginary dividing plane (S) that is perpendicular to the face (<NUM>) and that divides the non-circular tip opening (30a) into a first opening portion (<NUM>) and a second opening portion (<NUM>) shorter than the first opening portion (<NUM>) in a direction parallel to the face, an inside dimension (Lh) of the first opening portion (<NUM>) in a direction perpendicular to the face increases gradually from one end (P1) of the non-circular tip opening (30a) in the direction parallel to the face (<NUM>) to the dividing plane (S), and
in the tubular part (<NUM>) including the non-circular tip opening (30a), the string (<NUM>) passes through the first opening portion (<NUM>) and is in contact with the side wall (28a) from the base opening (26a) to the tip opening (30a).