Racket Frame and Racket

Abstract

A racket frame includes a face portion and a grip portion that are arranged side by side in a first direction. Face portion includes a first part including a first end located on a side opposite to grip portion in first direction and a second part including a second end located on a side of grip portion, second part being disposed apart from first part. A plurality of first through-holes that extend along first direction and are arranged at intervals in a second direction are formed in first part. The plurality of first through-holes include a first hole closest to a center of first part in second direction and a second hole located on an opposite side of the center with respect to first hole. In a third direction intersecting with first direction and second direction, a width of first hole is larger than a width of second hole.

Description

TECHNICAL FIELD

The present invention relates to a racket frame and a racket.

BACKGROUND ART

There are spin performance and repulsion performance as evaluation indices of performance of a racket frame and a racket. Japanese Patent Laying-Open No. 2017-121431 discloses a racket frame for tennis having the good repulsion performance and spin performance.

In addition, conventionally, the racket frame is known in which a partial region of a face portion is designed as a first region in which the spin performance is relatively enhanced and another partial region of the face portion is designed as a second region in which the repulsion performance is relatively enhanced in planer view of the face portion. In the first region, string is designed to easily move in a direction along a batting surface during batting. The second region is designed such that the string is less likely to move in the direction along the batting surface during the batting as compared with the first region.

CITATION LIST

Patent Literature

• • PTL 1: Japanese Patent Laying-Open No. 2017-121431

SUMMARY OF INVENTION

Technical Problem

A main object of the present invention is to provide a racket frame and a racket in which the spinning performance of the partial region of the face portion is further improved as compared with the conventional racket frame and racket.

Solution to Problem

A racket frame according to one aspect of the present invention includes a face portion and a grip portion that are arranged side by side in a first direction A. The face portion includes a first part including a first end located on a side opposite to the grip portion in the first direction A and a second part including a second end located on a side of the grip portion in the first direction A, the second part being disposed apart from the first part. A plurality of first through-holes that extend along the first direction A and are arranged at intervals in a second direction B perpendicular to the first direction A are formed in the first part. The plurality of first through-holes include a first hole closest to a center of the first part in the second direction B and a second hole located on the opposite side of the center with respect to the first hole. In a third direction C intersecting with the first direction A and the second direction B, a width of the first hole is larger than a width of the second hole.

Advantageous Effects of Invention

According to the present invention, the racket frame and the racket in which the spinning performance of the partial region of the face portion is further improved as compared with the conventional racket frame and racket can be provided.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a plan view illustrating a racket frame according to an embodiment.

FIG. 2 is a side view illustrating a string protector fixed to a first end of a face portion of the racket frame in FIG. 1 as viewed from a grip portion side or a second end side.

FIG. 3 is a perspective view illustrating the string protector in FIG. 2.

FIG. 4 is a perspective view illustrating the string protector in FIG. 2 as viewed from a viewpoint different from that in FIG. 3.

FIG. 5 is a plan view illustrating the racket of the embodiment.

FIG. 6 is a view illustrating a relationship between the racket frame and a string in the racket in FIG. 5.

FIG. 7 is a side view illustrating the string protector fixed to the first end of the face portion of the racket in FIG. 5 as viewed from the grip portion side.

FIG. 8 is a graph comparing spin performances of sample 1 and sample 2.

FIG. 9 is a graph comparing spin performances of samples 2 and sample 3.

FIG. 10 is a photograph illustrating an experimental system in which an amount of strain generated in each of a third main string portion and a fourth main string portion of Example is measured.

FIG. 11 is a graph illustrating the amount of strain that is generated in each of the third main string portion and the fourth main string portion and measured from a start to an end of pressurization to each of the third main string portion and the fourth main string portion in the experimental system in FIG. 10.

DESCRIPTION OF EMBODIMENT

Hereinafter, an embodiment of the present invention will be described. In the following drawings, the same or corresponding component is designated by the same reference numeral, and the overlapping description will be omitted.

<Configuration of Racket Frame>

As illustrated in FIG. 1, a racket frame 100 according to the embodiment includes a face portion 1, a shaft portion 2, and a grip portion 3. Face portion 1, shaft portion 2, and grip portion 3 are arranged side by side in a first direction A. Shaft portion 2 is disposed between face portion 1 and grip portion 3 in first direction A.

For example, a material used for the racket frame is carbon fiber reinforced plastic (CFRP). However, the material used for the racket frame is not limited thereto. For example, glass fiber reinforced plastic (GFRP) or the like can be used.

Face portion 1 has an elliptical annular shape in planar view. A longitudinal direction of face portion 1 in planar view is along first direction A. A lateral direction in planar view is along a second direction B perpendicular to first direction A. A third direction C perpendicular to first direction A and second direction B is a hitting direction of a racket 110.

Face portion 1 includes a first end 1a and a second end 1b in first direction A. First end 1a is an end located on an opposite side of face portion 1 from grip portion 3 in first direction A. Second end 1b is an end located on the side of grip portion 3 in first direction A.

Face portion 1 includes a first part 11 including first end 1a and a second part 12 including second end 1b. First part 11 extends along second direction B around first end 1a. Second part 12 extends along second direction B around second end 1b. Second part 12 is disposed apart from first part 11 in first direction A.

Face portion 1 further includes a third part 13 and a fourth part 14. Third part 13 is disposed between first part 11 and second part 12, and connects one end of first part 11 and one end of second part 12. Fourth part 14 is disposed between first part 11 and second part 12, and connects the other end of first part 11 and the other end of second part 12. Fourth part 14 is disposed apart from third part 13 in second direction B.

Each of first part 11, second part 12, third part 13, and fourth part 14 of face portion 1 includes an inner periphery 1c and an outer periphery 1d. A plurality of through-holes through which the string passes are formed in face portion 1. The plurality of through-holes are opened in each of inner periphery 1c and outer periphery 1d. The plurality of through-holes include a plurality of first through-holes 21, a plurality of second through-holes 24, a plurality of third through-holes 25, and a plurality of fourth through-holes 26, which are described below.

The plurality of first through-holes 21 are made in first part 11. Each of the plurality of first through-holes 21 extends along first direction A and is disposed at intervals in second direction B. A detailed configuration of the plurality of first through-holes 21 will be described later.

The plurality of second through-holes 24 are made in second part 12. Each of the plurality of second through-holes 24 is disposed at intervals in second direction B. The interval between two second through-holes 24 adjacent to each other in second direction B gradually increases, for example, as a distance from a center line CL passing through first end 1a and second end 1b increases.

The plurality of third through-holes 25 are made in third part 13. Each of the plurality of third through-holes 25 is disposed at intervals in first direction A.

The plurality of fourth through-holes 26 are made in fourth part 14. Each of the plurality of fourth through-holes 26 is disposed at intervals in first direction A.

Shaft portion 2 includes a first branch member 2A and a second branch member 2B. Grip portion 3 includes a grip member 3A and a grip 3B. First branch member 2A and second branch member 2B branch from grip member 3A. Grip 3B is formed so as to cover grip member 3A. For example, polyurethane is used for grip 3B.

With reference to FIGS. 2 to 5, details of the plurality of first through-holes 21 will be described below. The plurality of first through-holes 21 are holes through which a main string portion 201 of a string 200 passes in racket 110.

As illustrated in FIGS. 2 to 5, for example, racket frame 100 further includes a grommet 15 attached to first part 11. As illustrated in FIG. 3, grommet 15 includes a grommet main body 15a and a plurality of protrusions 15b. Each of the plurality of protrusions 15b protrudes toward the side of second part 12 in first direction A with respect to grommet main body 15a. As illustrated in FIGS. 2 to 5, each of the plurality of first through-holes 21 is made in the plurality of protrusions 15b of grommet 15. Grommet 15 protects main string portion 201 of string 200. Preferably grommet 15 is separate from face portion 1. For example, a material constituting grommet 15 is a nylon resin.

As illustrated in FIGS. 2 and 3, a plurality of insertion holes 11a through which the plurality of protrusions 15b are inserted are made in first part 11. Each of the plurality of insertion holes 11a may have any configuration as long as each of the plurality of protrusions 15b can be inserted. When viewed from first direction A, for example, a planar shape of each of the plurality of insertion holes 11a is a circular shape.

As illustrated in FIG. 2, each of the plurality of first through-holes 21 is made line-symmetrically with respect to a center line CL (virtual line) passing through first end 1a and second end 1b. The plurality of first through-holes 21 include a first hole 22a, a second hole 23a, a third hole 23b, a fourth hole 22b, a fifth hole 22c, and a sixth hole 23c arranged on each of one side and the other side in second direction B with respect to center line CL. First hole 22a, second hole 23a, third hole 23b, fourth hole 22b, fifth hole 22c, and sixth hole 23c are arranged so as to be separated from center line CL of first part 11 in the above-described order. Center line CL passes through the center axis of grip portion 3.

First hole 22a is disposed at a position closest to center line CL in second direction B among the plurality of first through-holes 21.

Second hole 23a is disposed on the opposite side of center line CL with respect to first hole 22a. Second hole 23a is adjacent to first hole 22a. Second hole 23a is disposed at a position second closest to center line CL of first part 11 in second direction B among the plurality of first through-holes 21.

Third hole 23b is disposed on the opposite side of second hole 23a with respect to first hole 22a. Third hole 23b is adjacent to second hole 23a. Third hole 23b is disposed at a position third closest to center line CL of first part 11 in second direction B.

Fourth hole 22b is disposed on the side opposite to second hole 23a with respect to third hole 23b. Fourth hole 22b is adjacent to third hole 23b. Fourth hole 22b is disposed at a position fourth closest to center line CL of first part 11 in second direction B.

Fifth hole 22c is disposed on the side opposite to third hole 22b with respect to fourth hole 23b. Fifth hole 22c is adjacent to fourth hole 22b. Fourth hole 22b is disposed at a position fifth closest to center line CL of first part 11 in second direction B.

Sixth hole 23c is disposed on the side opposite to fourth hole 22b with respect to fifth hole 22c. Sixth hole 23c is adjacent to fifth hole 22c. Sixth hole 23c is disposed at a position sixth closest to center line CL of first part 11 in second direction B.

As illustrated in FIGS. 2 and 3, the planar shape of each of first hole 22a and fourth hole 22b is an elliptical shape elongated in third direction C when viewed from first direction A. When viewed from first direction A, the longitudinal direction of each of first hole 22a and fourth hole 22b is along third direction C. When viewed from first direction A, the lateral direction of each of first hole 22a and fourth hole 22b is along second direction B. When viewed from first direction A, for example, the planar shape of fifth hole 22c is a circular shape.

As illustrated in FIGS. 2 and 3, for example, the planar shape of each of second hole 23a, third hole 23b, and sixth hole 23c is a circular shape when viewed from first direction A.

As illustrated in FIG. 2, in third direction C, a width W1 of first hole 22a is wider than a width W2 of second hole 23a. For example, the width of first hole 22a may be equal to the width of second hole 23a in second direction B.

As illustrated in FIG. 2, a width W3 of third hole 23b is narrower than a width W4 of fourth hole 22b in third direction C. For example, the width of third hole 23b may be equal to the width of fourth hole 22b in second direction B.

As illustrated in FIG. 2, a width W5 of fifth hole 22c may be wider than a width W6 of sixth hole 23c in third direction C, and for example, the width of fifth hole 22c may be wider than the width of sixth hole 23c in second direction B.

For example the widths of the plurality of first through-holes 21 may be equal to each other in second direction B.

The planar shape of each of the plurality of first through-holes 21 viewed from first direction A is not particularly limited as long as a magnitude relationship of each width described above is implemented. When viewed from first direction A, the planar shape of fifth hole 22c may be an elliptical shape. In this case, the longitudinal direction of fifth hole 22c is along third direction C as viewed from first direction A. When viewed from first direction A, the lateral direction of fifth hole 22c is along second direction B.

In third direction C, the width of each of first hole 22a, fourth hole 22b, and fifth hole 22c is larger than the width of each of the plurality of second through-holes 24.

As illustrated in FIGS. 5 and 7, the width in third direction C and the width in second direction B of each of the plurality of first through-holes 21 are greater than or equal to an outer diameter of string 200, and is preferably wider than the outer diameter of string 200. The width in third direction C and the width in second direction B of each of the plurality of first through-holes 21 are narrower than the width in third direction C and the width in second direction B of each of the plurality of insertion holes 11a.

As illustrated in FIG. 2, in second direction B, a distance L1 between two first holes 22a adjacent to each other across center line CL is shorter than a distance L2 between first hole 22a and second hole 23a. In other words, in second direction B, distance L1/2 between center line CL and first hole 22a is shorter than half of distance L2 between first hole 22a and second hole 23a.

As illustrated in FIG. 2, in second direction B, a distance L3 between second hole 23a and third hole 23b is shorter than distance L2 between first hole 22a and second hole 23a. In second direction B, a distance L4 between third hole 23b and fourth hole 22b is longer than distance L3 between second hole 23a and third hole 23b. In second direction B, a distance L5 between fourth hole 22b and fifth hole 22c is shorter than distance L4 between third hole 23b and fourth hole 22b. In second direction B, a distance L6 between fifth hole 22c and sixth hole 23c is longer than distance L5 between fourth hole 22b and fifth hole 22c. Distance L1 to distance L6 are distances between the centers of the holes in second direction B.

<Configuration of Racket>

With reference to FIGS. 5 to 7, racket 110 of the embodiment will be described below. As illustrated in FIGS. 5 to 7, racket 110 includes racket frame 100 and string 200 pitched on face portion 1 of racket frame 100.

As illustrated in FIG. 6, string 200 passes through each of the plurality of first through-holes 21, the plurality of second through-holes 24, the plurality of third through-holes 25, and the plurality of fourth through-holes 26. String 200 includes a plurality of main string portions 201, a plurality of folded portions 202, a plurality of folded portions 203, and a plurality of cross-string portions 204.

The plurality of main string portions 201 extend along first direction A between the plurality of first through-holes 21 and the plurality of second through-holes 24. The plurality of cross-string portions 204 extend in second direction B between the plurality of third through-holes 25 and the plurality of fourth through-holes 26.

The plurality of folded portions 202 are disposed outside the plurality of first through-holes 21. The plurality of folded portions 202 include a first folded portion 202a disposed between first hole 22a and second hole 23a, a second folded portion 202b disposed between third hole 23b and fourth hole 22b, and a third folded portion 202c disposed between fifth hole 22c and sixth hole 23c.

In other words, string 200 is folded back outside first hole 22a and second hole 23a between first hole 22a and second hole 23a. Main string portion 201 extending from first hole 22a along first direction A and main string portion 201 extending from second hole 23a along first direction A are connected to each other with first folded portion 202a interposed therebetween.

String 200 is folded back outside third hole 23b and fourth hole 22b between third hole 23b and fourth hole 22b. Main string portion 201 extending from third hole 23b along first direction A and main string portion 201 extending from fourth hole 22b along first direction A are connected to each other with second folded portion 202b interposed therebetween.

String 200 is folded back outside fifth hole 22c and sixth hole 23c between fifth hole 22c and sixth hole 23c. Main string portion 201 extending from fifth hole 22c along first direction A and main string portion 201 extending from sixth hole 23c along first direction A are connected to each other with third folded portion 202c interposed therebetween.

As illustrated in FIGS. 6 and 7, the plurality of folded portions 203 are disposed outside the plurality of second through-holes 24. The plurality of folded portions 203 include a fourth folded portion 203a disposed between first folded portion 202a and second folded portion 202b and a fifth folded portion 203b disposed between second folded portion 202b and third folded portion 202c.

Main string portion 201 extending from second hole 23a along first direction A and main string portion 201 extending from third hole 23b along first direction A are connected to each other with fourth folded portion 203a interposed therebetween. Main string portion 201 extending from fourth hole 22b along first direction A and main string portion 201 extending from fifth hole 22c along first direction A are connected to each other with fifth folded portion 203b interposed therebetween.

String 200 passes through two second through-holes 24 among the plurality of second through-holes 24 between second hole 23a and third hole 23b. Between second hole 23a and third hole 23b, string 200 passes through two second through-holes 24 (first-group second through-holes) disposed at positions close to center line CL in second direction B among the plurality of second through-holes 24, and includes fourth folded portion 203a.

String 200 passes through two second through-holes 24 among the plurality of second through-holes 24 between fourth hole 22b and fifth hole 22c. Between fourth hole 22b and fifth hole 22c, string 200 passes through two second through-holes 24 (second-group second through-holes) disposed at positions farther from center line CL than the first-group second through-holes among the plurality of second through-holes 24, and includes fifth folded portion 203b.

For example, a knot of two strings connected to each other and connected in series is disposed in fifth hole 22c.

As illustrated in FIG. 7, in second direction B, a distance L12 between main string portions 201 passing through first holes 22a and main string portions 201 passing through second holes 23a is longer than a distance L11 between main string portions 201 passing through respective first holes 22a.

In second direction B, distance L12 between main string portion 201 passing through first hole 22a and main string portion 201 passing through second hole 23a is longer than a distance L13 between main string portion 201 passing through second hole 23a and main string portion 201 passing through third hole 23b.

In second direction B, distance L13 between main string portion 201 passing through second hole 23a and main string portion 201 passing through third hole 23b is shorter than a distance L14 between main string portion 201 passing through third hole 23b and main string portion 201 passing through fourth hole 22b.

In second direction B, distance L14 between main string portion 201 passing through third hole 23b and main string portion 201 passing through fourth hole 22b is longer than a distance L15 between main string portion 201 passing through fourth hole 22b and main string portion 201 passing through fifth hole 22c.

In second direction B, distance L15 between main string portion 201 passing through fourth hole 22b and main string portion 201 passing through fifth hole 22c is shorter than a distance L16 between main string portion 201 passing through fifth hole 22c and main string portion 201 passing through sixth hole 23c.

As illustrated in FIG. 5, a first region R1 located closer to first part 11 than the center of face portion 1 in second direction B and a second region R2 including the center of face portion 1 in second direction B are formed in face portion 1 of racket 110. First region R1 is closer to first part 11 than second region R2. For this reason, the spin performance and the repulsive performance during the hitting in first region R1 are more susceptible to the configuration of the plurality of first through-holes 21 than the spin performance and the repulsive performance during the hitting in second region R2.

The manner of pitching string 200 to face portion 1 of racket frame 100 is not particularly limited. Hereinafter, an example of how to pitch main string portion 201 will be described.

For example, string 200 is first passing through a hole closest to center line CL among the plurality of second through-holes 24 from the outside to the inside as indicated by an arrow in FIG. 6. Subsequently, string 200 passes through first hole 22a (see FIGS. 2 and 7) outward from the inner side, then is folded back at the outer side (first folded portion 202a), and passes through second hole 23a (see FIGS. 2 and 7) from the outside toward the inside.

Subsequently, string 200 passes through the hole second closest to center line CL among the plurality of second through-holes 24 from the inside to the outside, then is folded back at the outside (fourth folded portion 203a), and passes through the hole third closest to center line CL among the plurality of second through-holes 24 from the outside to the inside. Subsequently, string 200 passes through third hole 23b (see FIGS. 2 and 7) from the inside to the outside, then is folded back at the outside (second folded portion 202b), and passes through fourth hole 22b (see FIGS. 2 and 7) from the outside to the inside.

Subsequently, string 200 passes through a hole fourth closest to center line CL among the plurality of second through-holes 24 from the inside to the outside, is folded back at the outside (fifth folded portion 203b), and passes through a hole fifth closest to center line CL among the plurality of second through-holes 24 from the outside to the inside. Subsequently, string 200 passes through fifth hole 22c (see FIGS. 2 and 7) from the inside to the outside, then is folded back at the outside (third folded portion 202c), and passes through sixth hole 23c (see FIGS. 2 and 7) from the outside to the inside.

Subsequently, string 200 passes through a hole sixth closest to center line CL among the plurality of second through-holes 24 from the inside to the outside. As described above, the plurality of main string portions 201 can be formed by passing string 200 through the plurality of first through-holes 21 and the plurality of second through-holes 24 so as to sequentially form first folded portion 202a, fourth folded portion 203a, second folded portion 202b, fifth folded portion 203b, and third folded portion 202c.

String 200 may be pitched by being reversed in first direction A with respect to the pitching method described above. Prepared string 200 may first pass through first hole 22a from the outside to the inside, and then pass through the hole closest to center line CL among the plurality of second through-holes 24 from the inside to the outside.

Examples of racket frame 100 and racket 110 of the embodiment will be described below.

Example 1

In Example 1, the spin performance of the racket frame according to samples 1 to 3 having different configurations of the plurality of first through-holes was evaluated.

(Samples 1 to 3)

In the racket frame according to sample 1, as a comparative example, the intervals in the second direction B of the plurality of first through-holes were equal to each other, and the widths in the third direction C of the plurality of first through-holes were equal to each other.

In the racket frame of sample 2, the intervals of the plurality of first through-holes in second direction B were equal to each other, but the distance between two first holes adjacent to each other across center line CL in second direction B was shorter than the distance between the first hole and the second hole.

Sample 3 was racket frame 100. That is, sample 1 was different from sample 3 only in that the intervals in second direction B of the plurality of first through-holes were equal to each other and the widths in third direction C of the plurality of first through-holes were equal to each other. Sample 2 was different from sample 3 only in that the intervals in second direction B of the plurality of first through-holes were equal to each other. Sample 2 was different from sample 1 only in that the distance between two first holes adjacent to each other across center line CL in second direction B was shorter than the distance between the first hole and the second hole.

In sample 3, in second direction B, the distance between the main string portion passing through the first hole and the main string portion passing through the second hole was longer than the distance between the main string portion passing through the second hole and the main string portion passing through the third hole.

(Evaluation Method)

A tennis ball launched from a tennis ball launcher was collided with the first region of the racket in which the grip portion was fixed to a jig, and the number of rotations of the spin of the tennis ball rebounded by the collision was measured. The tennis ball launcher launched the tennis ball onto the racket such that the center of the tennis ball overlaps the center line. The direction in which the tennis ball launcher launched the tennis ball was set such that the direction was perpendicular to the center line of the racket and the angle of inclination formed by the direction in which the tennis ball was launched with respect to second direction B of the racket was 15 degrees or 30 degrees. A hard tennis ball was used as the tennis ball. A high-speed camera was used to measure the rotation speed of the spin.

(Evaluation Results)

FIG. 8 is a graph comparing evaluation results of sample 1 and sample 2. FIG. 9 is a graph comparing evaluation results of sample 2 and sample 3.

As illustrated in FIG. 8, the number of spin rotations of the tennis ball rebounded from sample 2 was larger than the number of spin rotations of the tennis ball rebounded from sample 1 regardless of the inclination angle. At the time of hitting a ball with the inclination angle of 15 degrees, the spin rate of the tennis ball bouncing back from sample 2 was 17% higher than the number of spin rotations of the tennis ball rebounded from sample 1. During the hitting with the inclination angle of 30 degrees, the number of spin rotations of the tennis ball rebounded from sample 2 was 6% higher than the number of spin rotations of the tennis ball rebounded from sample 1.

In general, the spin during the hitting with the inclination angle of 30 degrees is more likely to be applied than the spin during the hitting with the inclination angle of 15 degrees. That is, it was checked that the spin performance of sample 2 was higher than the spin performance of sample 1 even under the hitting condition in which the inclination angle was 30 degrees at which the spin was likely to be applied to sample 1.

As illustrated in FIG. 9, the number of spin rotations of the tennis ball rebounded from sample 3 was larger than the number of spin rotations of the tennis ball rebounded from sample 2 even under the hitting condition in which the inclination angle at which the spin is likely to be applied is 30 degrees. During the hitting with the inclination angle of 30 degrees, the number of spin rotations of the tennis ball rebounded from sample 3 was 7% higher than the number of spin rotations of the tennis ball rebounded from sample 2.

That is, it was checked that the spin performance of sample 3 is higher than the spin performance of sample 2 even under the hitting condition in which the inclination angle at which the spin is likely to be applied is 30 degrees. Furthermore, from these results, it was checked that the spin performance of sample 3 was higher than the spin performance of sample 1.

Example 2

In Example 2, a distortion characteristic in the first region of the racket of sample 3 was evaluated.

(Evaluation Method)

First, a strain sensor was attached to each of two main string portions 201 extending along first direction A from each of third hole 23b and fourth hole 22b (see FIGS. 2 and 7) of sample 3. The attachment position of the strain sensor in each main string portion 201 was between each of third hole 23b and fourth hole 22b and a part intersecting with cross-string portion 204 closest to first end 1a in second direction B. As described above, each main string portion 201 is configured of one string and is folded back by second folded portion 202b.

Subsequently, as illustrated in FIG. 10, a hemispherical indenter having an outer diameter equal to the outer diameter of the tennis ball was pressed against the first region of sample 3 fixed in third direction C in third direction C, and the change in each strain amount from the start to the end of the pressing was evaluated. The indenter was disposed such that the top of the indenter overlaps the midpoints in second direction B of two main string portions 201 and third direction C in the first region. That is, each of two main string portions 201 was pressed by the indenter under the same condition.

FIG. 11 is a graph illustrating the above evaluation result. A horizontal axis in FIG. 11 represents time (unit: ms) from the start to the end of the pressing, and a vertical axis in FIG. 11 represents a strain amount. A line segment D in FIG. 11 indicates the strain amount of main string portion 201 extending from third hole 23b along first direction A, and a line segment E in FIG. 11 indicates the strain amount of main string portion 201 extending from fourth hole 22b along first direction A.

As illustrated in FIG. 11, a time difference Δt was checked between main string portion 201 extending from fourth hole 22b and main string portion 201 extending from third hole 23b before the start of distortion. Width W4 in third direction C of fourth hole 22b is larger than width W3 in third direction C of third hole 23b. For this reason, main string portion 201 extending from fourth hole 22b is more likely to move in third direction C than main string portion 201 extending from third hole 23b. Because each of two main string portions 201 starts to be distorted after moving in third direction C, it is considered that time difference Δt is caused by a difference in ease of movement in third direction C between two main string portions 201.

Furthermore, as illustrated in FIG. 11, a maximum strain amount difference ΔST was checked between main string portion 201 extending from fourth hole 22b and main string portion 201 extending from third hole 23b. Furthermore, until the distortion amount of each main string portion 201 was maximized, the distortion amount of main string portion 201 extending from fourth hole 22b was always smaller than the distortion amount of main string portion 201 extending from third hole 23b. The movement of each main string portion 201 in third direction C is implemented by a part of force applied to each main string portion 201, and the distortion of each main string portion 201 is implemented by the remainder of force applied to each main string portion 201. Thus, it is considered that the strain amount difference when the predetermined time elapses and the maximum strain amount difference ΔST are also caused by the difference in ease of movement in third direction C between two main string portions 201.

Because time difference Δt is formed between two main string portions 201 connected to each other with second folded portion 202b interposed therebetween, two main string portions 201 are likely to move in first direction A for the time from when they are pressed in third direction C until time difference Δt elapses. Furthermore, because the difference in the strain amount when a predetermined time elapses and the maximum strain amount difference ΔST are formed between two main string portions 201 connected to each other with second folded portion 202b interposed therebetween, two main string portions 201 are likely to move in first direction A for a time from when two main string portions 201 are pressed in third direction C until two main string portions 201 are no longer pressed.

As a result, for example, main string portion 201 extending from fourth hole 22b is pulled toward the side of main string portion 201 extending from third hole 23b, and easily moves toward the side of first part 11 in first direction A. When two main string portions 201 move as described above, the tennis ball colliding with two main string portions 201 in the first region is likely to spin. This action is achieved not only between two main string portions 201 extending from each of third hole 23b and fourth hole 22b, but also between two main string portions 201 extending from each of first hole 22a and second hole 23a, and between two main string portions 201 extending from each of fifth hole 22c and sixth hole 23c.

The present inventors consider that the evaluation result in FIG. 9 of Example 1 was obtained for the above reason considered from the evaluation result of Example 2.

<Function and Effect>

Function and effect of the racket frame and the racket of the embodiment will be described based on Example 1 and Example 2.

Racket frame 100 includes face portion 1 and grip portion 3 that are arranged side by side in first direction A. Face portion 1 includes first part 11 including first end 1a located on the side opposite to grip portion 3 in first direction A and second part including second end 1b located on the side of grip portion 3 in first direction A, the second part being disposed apart from first part 11. The plurality of first through-holes 21 extending along first direction A and arranged at intervals in second direction B perpendicular to first direction A are formed in first part 11. The plurality of first through-holes 21 include first hole 22a closest to the center of first part 11 in second direction B and second hole 22a located on the opposite side of the center with respect to first hole 23a. In third direction C intersecting with first direction A and second direction B, the width of first hole 22a is larger than the width of second hole 23a.

As described in Example 1, the present inventors have found that in racket frame 100 having the above configuration (samples 3 of Examples 1 and 2 described above), the spin performance is improved by 7% as compared with the case where the interval in second direction B and the width in third direction C of each first through-hole are equal to each other (sample 1 in Example 1 described above) and the case where the interval in second direction B of each first through-hole is different from each other but the width in third direction C of each first through-hole is equal to each other (sample 2 in Example 1 described above).

In racket frame 100, distance L1/2 between center line CL and first hole 22a in second direction B is shorter than half of distance L2 between first hole 22a and second hole 23a. That is, distance L1 is shorter than distance L2.

As described in Example 1, the present inventors have found that when distance L1/2 between center line CL and first hole 22a in second direction B is shorter than half of distance L2 between first hole 22a and second hole 23a (sample 2 in Example 1 described above), the spin performance is improved by 6% as compared with the case where distance L1/2 between center line CL and first hole 22a in second direction B is equal to half of distance L2 between first hole 22a and second hole 23a (sample 1 in Example 1 described above).

Regarding this, as the distance between two main string portions 201 adjacent in second direction B in first region R1 is longer, the relative positional relationship between two main string portions 201 and the tennis ball tends to be different during the hitting in first region R1, and the difference tends to be generated in the force applied to two main string portions 201 during the hitting. The longer the distance in second direction B between two main string portions 201 connected to each other with folded portion 202 interposed therebetween, the larger the difference in the force between two main string portions 201, and two main string portions 201 are likely to move to one side in first direction A. As a result, the tennis balls colliding with the two main string portions 201 are likely to spin. That is, as distance L2 is longer, the tennis ball colliding with the main string portion 201 passing through first hole 22a and main string portion 201 passing through second hole 23a is likely to spin.

On the other hand, main string portions 201 passing through respective first holes 22a are not connected with folded portion 202 interposed therebetween, and even when distance L1 is increased, main string portions 201 passing through respective first holes 22a do not easily move in first direction A. When distance L1 is shorter than distance L2, distance L2 can be lengthened by that amount. That is, when distance L1 is shorter than distance L2, the spinning performance of racket frame 100 is efficiently improved.

In racket frame 100, the plurality of first through-holes 21 further include third hole 23b located on the opposite side of second hole 22a with respect to first hole 23a, and fourth hole 23b located on the opposite side of third hole 22b with respect to first hole 22a. In third direction C, width W4 of fourth hole 22b is larger than width W3 of third hole 23b.

In such racket frame 100, high spin performance is exhibited when the ball is hit by two main string portions 201 extending from each of first hole 22a and second hole 23a in first region R1, when the ball is hit by two main string portions 201 extending from each of third hole 23b and fourth hole 22b, and when the ball is hit by four main string portions 201 extending from each of first hole 22a to fourth hole 22b. Accordingly, in racket frame 100, first width W1 is wider than second width W2, but the region where the high spin performance is exhibited is wider as compared with the configuration in which fourth width W4 is equal to third width W3.

In racket frame 100, distance L3 between second hole 23a and third hole 23b in second direction B is shorter than distance L2 between first hole 22a and second hole 23a and distance L4 between third hole 23b and fourth hole 22b.

When distance L3 is shorter than distance L2 and distance L4, the spinning performance of racket frame 100 is efficiently improved for the same reason as the case where distance L1 is shorter than distance L2.

Racket 110 includes racket frame 100 and string 200 that is pitched on face portion 1 and includes the plurality of main string portions extending between first part 11 and second part 12 along first direction A. String 200 passes through the plurality of first through-holes 21, and is folded back outside first hole 22a and second hole 23a between first hole 22a and second hole 23a (first folded portion 202a).

Racket 110 includes racket frame 100, so that an effect equivalent to that of racket frame 100 can be achieved.

In racket 110, in second direction B, the distance between the main string portion passing through first hole 22a and the main string portion passing through second hole 23a is longer than the distance between the main string portion passing through second hole 23a and the main string portion passing through third hole 23b.

It should be considered that the disclosed embodiment is illustrative and non-restrictive in every respect. The scope of the present invention is defined not by the embodiment but by the claims, and is intended to include meanings equivalent to the claims and all modifications within the scope.

REFERENCE SIGNS LIST

1: face portion, 1a: first end, 1b: second end, 1c: inner periphery, 1d: outer periphery, 2: shaft portion, 2A: first branch member, 2B: second branch member, 3: grip portion, 3A: grip member, 3B: grip, 11: first part, 11a: insertion hole, 12: second part, 13: third part, 14: fourth part, 15: grommet, 15a: grommet main body, 15b: protrusion, 21: first through-hole, 22a: first hole, 22b: fourth hole, 22c: fifth hole, 23a: second hole, 23b: third hole, 23c: sixth hole, 24: second through-hole, 25: third through-hole, 26: fourth through-hole, 100: racket frame, 110: racket, 200: string, 201: main string portion, 202, 203: folded portion, 202a: first folded portion, 202b: second folded portion, 202c: third folded portion, 203a: fourth folded portion, 203b: fifth folded portion, 204: cross-string portion

Claims

1. A racket frame comprising a face portion and a grip portion arranged side by side in a first direction, wherein the face portion includes a first part including a first end located on a side opposite to the grip portion in the first direction and a second part including a second end located on a side of the grip portion in the first direction, the second part being disposed apart from the first part,a plurality of first through-holes that extend along the first direction and are disposed at intervals in a second direction perpendicular to the first direction are formed in the first part,the plurality of first through-holes include a first hole closest to the first end in the second direction and a second hole located on a side opposite to the first end with respect to the first hole, anda width of the first hole is wider than a width of the second hole in a third direction intersecting with the first direction and the second direction.

2. The racket frame according to claim 1, wherein in the second direction, a distance between an imaginary line passing through the first end and the second end and the first hole is shorter than a half of a distance between the first hole and the second hole.

3. The racket frame according to claim 1, wherein the plurality of first through-holes further include a third hole located on a side opposite to the first hole with respect to the second hole and a fourth hole located on a side opposite to the first hole with respect to the third hole, anda width of the fourth hole is wider than a width of the third hole in the third direction.

4. The racket frame according to claim 3, wherein a distance between the second hole and the third hole in the second direction is shorter than a distance between the first hole and the second hole and a distance between the third hole and the fourth hole.

5. The racket frame according to claim 1, wherein a plurality of second through-holes that extend along the first direction and are disposed at intervals in the second direction are formed in the second part, andthe width of the first hole is wider than a width of each of the plurality of second through-holes in the third direction.

6. A racket comprising: the racket frame according to claim 1; anda string that is pitched over the face portion and includes a plurality of main string portions extending along the first direction between the first part and the second part, whereinthe string passes through the plurality of first through-holes, and is folded back outside the first hole and the second hole between the first hole and the second hole.

7. The racket according to claim 6, wherein the string passes through two second through-holes of the plurality of second through-holes between the second hole and the third hole.

8. A racket comprising: a face portion arranged side by side in a first direction;a grip portion; anda string that is pitched over the face portion, whereinthe face portion includes a first part including a first end located on a side opposite to the grip portion in the first direction and a second part including a second end located on a side of the grip portion in the first direction, the second part being disposed apart from the first part,a plurality of first through-holes that extend along the first direction and are disposed at intervals in a second direction perpendicular to the first direction are formed in the first part,the plurality of first through-holes include a first hole closest to the first end in the second direction, a second hole located on a side opposite to the first end with respect to the first hole, a third hole located on a side opposite to the first hole with respect to the second hole, and a fourth hole located on a side opposite to the first hole with respect to the third hole,a width of the first hole is wider than a width of the second hole in a third direction intersecting with the first direction and the second direction,the string includes a plurality of main string portions extending along the first direction between the first part and the second part,the string passes through the plurality of first through-holes, andin the second direction, a distance between the main string portion passing through the first hole and the main string portion passing through the second hole is longer than a distance between the main string portion passing through the second hole and the main string portion passing through the third hole.

9. The racket frame according to claim 2, wherein the plurality of first through-holes further include a third hole located on a side opposite to the first hole with respect to the second hole and a fourth hole located on a side opposite to the first hole with respect to the third hole, anda width of the fourth hole is wider than a width of the third hole in the third direction.

10. The racket frame according to claim 9, wherein a distance between the second hole and the third hole in the second direction is shorter than a distance between the first hole and the second hole and a distance between the third hole and the fourth hole.

11. The racket frame according to claim 2, wherein a plurality of second through-holes that extend along the first direction and are disposed at intervals in the second direction are formed in the second part, andthe width of the first hole is wider than a width of each of the plurality of second through-holes in the third direction.

12. The racket frame according to claim 3, wherein a plurality of second through-holes that extend along the first direction and are disposed at intervals in the second direction are formed in the second part, andthe width of the first hole is wider than a width of each of the plurality of second through-holes in the third direction.

13. The racket frame according to claim 4, wherein a plurality of second through-holes that extend along the first direction and are disposed at intervals in the second direction are formed in the second part, andthe width of the first hole is wider than a width of each of the plurality of second through-holes in the third direction.

14. The racket frame according to claim 9, wherein a plurality of second through-holes that extend along the first direction and are disposed at intervals in the second direction are formed in the second part, andthe width of the first hole is wider than a width of each of the plurality of second through-holes in the third direction.

15. The racket frame according to claim 10, wherein a plurality of second through-holes that extend along the first direction and are disposed at intervals in the second direction are formed in the second part, andthe width of the first hole is wider than a width of each of the plurality of second through-holes in the third direction.

16. A racket comprising: the racket frame according to claim 2; anda string that is pitched over the face portion and includes a plurality of main string portions extending along the first direction between the first part and the second part, whereinthe string passes through the plurality of first through-holes, and is folded back outside the first hole and the second hole between the first hole and the second hole.

17. A racket comprising: the racket frame according to claim 3; anda string that is pitched over the face portion and includes a plurality of main string portions extending along the first direction between the first part and the second part, whereinthe string passes through the plurality of first through-holes, and is folded back outside the first hole and the second hole between the first hole and the second hole.

18. A racket comprising: the racket frame according to claim 4; anda string that is pitched over the face portion and includes a plurality of main string portions extending along the first direction between the first part and the second part, whereinthe string passes through the plurality of first through-holes, and is folded back outside the first hole and the second hole between the first hole and the second hole.

19. A racket comprising: the racket frame according to claim 5; anda string that is pitched over the face portion and includes a plurality of main string portions extending along the first direction between the first part and the second part, whereinthe string passes through the plurality of first through-holes, and is folded back outside the first hole and the second hole between the first hole and the second hole.

20. A racket comprising: the racket frame according to claim 9; anda string that is pitched over the face portion and includes a plurality of main string portions extending along the first direction between the first part and the second part, whereinthe string passes through the plurality of first through-holes, and is folded back outside the first hole and the second hole between the first hole and the second hole.