JP7736618B2 - racket - Google Patents

Description

The present invention relates to a racket, particularly a soft tennis racket.

In racket sports such as tennis, players swing a racket to hit a ball. The racket has a grip that the player holds, a shaft with the grip attached to one end, and a loop-shaped frame attached to the other end of the shaft. Strings are stretched in a grid pattern inside the frame, and these strings form a hitting surface for hitting the ball (see, for example, Patent Document 1).

JP 2009-261914 A

Rackets are required to improve both their ball control and ball repulsion performance in order to increase the accuracy and performance of play. Control refers to the ease with which a player can control the ball, and performance can be improved by making the hitting surface less likely to wobble when hitting the ball. Therefore, to improve control, a shape design that makes it difficult for the shaft to twist is generally adopted.

Furthermore, repulsion performance is determined by the initial speed of the ball when it is hit, and performance can be improved by making the ball leave the club quickly upon impact. Therefore, to improve repulsion performance, a shaft design that makes it less likely to bend is generally adopted.

Therefore, in order to improve both control and repulsion performance, one possible design would be to increase the shaft's rigidity to reduce flex and twist. However, simply increasing the shaft's rigidity would increase the sense of impact felt by the player when hitting the ball, making it difficult to evaluate each of the above performance characteristics.

The present invention was made in consideration of the above-mentioned circumstances, and aims to provide a racket that can exhibit both good control and repulsion performance and can reduce the feeling of impact.

The racket of the present invention comprises a frame on which strings are stretched to form a hitting surface, and a shaft formed between the frame and a grip. The shaft comprises a shaft body connected to the upper end of the grip, and a recessed portion and a non-recessed portion formed on both thickness-wise sides of the shaft body. The recessed portion extends upward adjacent to the upper end of the grip, and the non-recessed portion is formed in at least the area sandwiched between the upper end of the recessed portion and the lower end of the frame.

According to the present invention, the shaft is formed with non-depressed sections, which suppress twisting of the shaft and make the hitting surface less likely to wobble, improving ball control. Furthermore, the non-depressed sections suppress shaft flex, while the depressed sections prevent this flex from being suppressed excessively. In other words, the depressed and non-depressed sections moderately suppress shaft flex. This moderate shaft flex increases the initial velocity of the ball when hit, improving repulsion performance and mitigating the feeling of impact when hitting the ball. In this way, the depressed and non-depressed sections of the shaft simultaneously improve both ball control and repulsion performance, while mitigating the feeling of impact when hitting the ball.

1A and 1B are external views of a racket according to an embodiment in one mode of use, in which FIG. 1A is a front view of the racket, and FIG. 1B is a side view of the racket. FIG. 2 is a partial schematic perspective view of the racket. FIG. 1B is a partially enlarged view of FIG. 1A. 1B is a cross-sectional view taken along line AA in FIG. 1A. 10 is a graph showing the results of fluid analysis of the embodiment and the second comparative example.

Embodiments of the present invention will be described in detail below with reference to the drawings. Note that, while the following describes an example in which the present invention is applied to a soft tennis racket, the scope of application is not limited to this and can be changed. For example, the present invention may also be applied to tennis rackets for hard tennis, squash rackets, etc.

Figure 1 shows an external view of one mode of use of a racket according to an embodiment of the present invention, with Figure 1A being a front view of the racket and Figure 1B being a side view of the racket. Note that for the sake of clarity, some components have been omitted from the following figures.

As shown in FIG. 1, the racket 10 comprises a head 11, which is the part that hits the ball, a grip 12, which is the part that the player holds the racket 10, and a shaft 13 formed between the head 11 and the grip 12. The head 11 and shaft 13 are formed by molding hollow cylinders made of, for example, fiber-reinforced resin, but they may also be solid and filled with foam, or made of wood or metal.

In the following explanation, as shown by the arrows in Figure 1, the longitudinal direction of the racket 10 is referred to as the up-down direction, with the side where the head 11 is located referred to as the upper side and the side where the grip 12 is located referred to as the lower side. Furthermore, the direction perpendicular to the up-down direction on the hitting surface of the racket 10 (i.e., on a plane along the hitting surface) is referred to as the left-right direction, and the direction perpendicular to the hitting surface of the racket 10 is referred to as the front-to-rear direction. The left-to-right direction refers to the width direction of the racket 10 and may be referred to as the width direction in the following explanation, and the front-to-rear direction refers to the thickness direction of the racket 10 and may be referred to as the thickness direction in the following explanation.

The head 11 includes a loop-shaped frame 15 that resembles an ellipse that is long in the vertical direction. A string (not shown) is stretched around the frame 15 in a grid pattern to form a hitting surface (face) on the inside. The outer surface 15a of the frame 15 is provided with a groove 16 that is recessed in the center in the thickness direction. The groove 16 is provided continuously along the circumferential direction of the frame 15. The frame 15 is provided with a plurality of holes 17 through which the strings are inserted. These holes 17 are formed from the bottom of the groove 16 on the outer surface 15a of the frame 15 to the inner surface 15b. A plurality of holes 17 are provided along the circumferential direction of the frame 15.

The shaft 13 has a shaft body 20 that connects to the upper end of the grip 12 and extends linearly in the vertical direction. The shaft 13 also has a throat 21 that connects to the upper end of the shaft body 20 and branches into two from the upper end of the shaft body 20 toward the frame 15 when viewed from the front to back. A yoke 18 that forms part of the frame 15 is formed between the left and right throats 21. The throat 21 is formed in a shape that curves gently in an arc between the grip 12 and the head 11.

An opening 23 is formed that is open in the front-to-rear direction and is surrounded by the yoke 18 of the frame 15 and the left and right throats 21 of the shaft 13. Here, as also shown in Figure 2, the area adjacent to the opening 23 is the opening-forming surface 25. Figure 2 is a partial, schematic perspective view of the racket. The opening-forming surface 25 forms the inner peripheral surface of the throat 21, which is formed to bulge toward the opening 23. The opening-forming surface 25 also forms the lower end 23a of the opening 23. This lower end 23a is the boundary between the shaft body 20 and the throat 21 in the vertical direction, and this boundary position is the upper end of the shaft body 20 and the lower end of the throat 21.

At the upper end of the shaft body 20, an opening-side recess 27 is formed, continuing from the opening-forming surface 25. The opening-side recess 27 is formed on both sides of the shaft body 20 in the thickness direction. The opening-side recess 27 is formed so that its width dimension gradually decreases downward in the up-down direction. Furthermore, the opening-side recess 27 is formed so that its depth (recess width) gradually decreases downward in the thickness direction.

The shaft 13 further includes a recessed portion 30 and a non-recessed portion 31 formed on both thickness-wise sides of the shaft body 20.

The recessed portion 30 extends upward adjacent to the upper end of the grip 12 and is recessed in a direction that reduces the thickness of the shaft body 20. The recessed portion 30 is formed so that its width dimension gradually decreases upward in the vertical direction. Specifically, when viewed from the front-to-back direction, the recessed portion 30 is formed across the entire left-to-right direction of the shaft body 20 near the grip 12. Furthermore, when viewed from the front-to-back direction, the recessed portion 30 has a pair of left and right inclined edges that gradually approach each other upward from the grip 12, and a semicircular arc-shaped upper edge (upper end) that connects the inclined edges.

Figure 3 is a partially enlarged view of Figure 1A. As shown in Figure 3, the upper edge of the recessed portion 30 is formed above the vertical center position C of the shaft body 20. In other words, the recessed portion 30 is formed in more than half of the shaft body 20 in the vertical direction.

The non-depressed portion 31 is formed on both thickness-wise sides of the shaft body 20, extending in an X-shape when viewed from the front to back. The portion of the non-depressed portion 31 sandwiched between the upper end of the depressed portion 30 and the lower end of the opening-side recess 27 is the vertical intermediate portion 31a. Furthermore, the non-depressed portion 31 is formed extending vertically from the intermediate portion 31a to both the left and right sides of the opening-side recess 27 and to both sides of the depressed portion 30. The region in which the intermediate portion 31a is formed in the non-depressed portion 31 is also the region sandwiched between the upper end of the depressed portion 30 and the lower end of the throat 21.

The intermediate portion 31a is formed at a position including the center of the shaft body 20 in the left-right direction. Because the upper edge of the recessed portion 30 is formed above the center position C in the up-down direction of the shaft body 20, the intermediate portion 31a adjacent to and above the upper edge is also formed above the center position C in the up-down direction of the shaft body 20.

The shaft body 20 has an area in the vertical direction where neither the recessed portion 30 nor the opening-side recess 27 is formed, due to the intermediate portion 31a of the non-recessed portion 31. In other words, the recessed portion 30 and the opening-side recess 27 are separated in the vertical direction by the intermediate portion 31a, and the intermediate portion 31a is raised between the recessed portion 30 and the opening-side recess 27.

Figure 4 is a cross-sectional view taken along line A-A in Figure 1A. As shown in Figure 4, the cross-sectional shape of the shaft body 20, perpendicular to the vertical direction, in the region where the non-depressed portion 31 is formed, is formed into a substantially octagonal shape. The non-depressed portion 31 is formed by both the front and rear sides of this octagon (both sides in the thickness direction).

Here, the octagon formed by the cross section of the shaft body 20 has sloped surfaces 33 formed on both the front-to-back and left-to-right sides. The front-to-back width of each sloped surface 33 is set within a range of 25 to 35% of the total front-to-back width of the shaft body 20, and the left-to-right width of each sloped surface 33 is set within a range of 25 to 35% of the total left-to-right width of the shaft body 20.

In the area where the recess 30 is formed, the cross section perpendicular to the vertical direction is formed into a roughly octagonal shape, and is recessed on both the front and rear sides as shown by the dotted lines in Figure 4.

Next, we will explain the analysis of the stiffness of the shaft in both the bending and twisting directions. This analysis was performed on the racket of the above embodiment and first to third comparative examples, which have shaft shapes different from those of the above embodiment.

In the first comparative example, the shaft body 20 of the above embodiment does not have a non-depressed portion 31, but has a depressed portion 30 that extends continuously from the opening-side recess 27 in the vertical direction. In the second comparative example, the shaft body 20 of the above embodiment does not have a depressed portion 30, but has a cross-sectional shape perpendicular to the vertical direction that is approximately rectangular. In the third comparative example, the shaft body of the second comparative example has a cross-sectional shape perpendicular to the vertical direction that is approximately octagonal. Note that the first comparative example has a conventional, common shape, and the shapes of the second and third comparative examples and the embodiment were designed to improve on this shape of the racket.

In the analysis, the racket grip was fixed, and a specified load was applied in the front-to-back direction to the upper end of the frame. The amount of deformation in the front-to-back direction at the upper end of the frame compared to before the load was applied was measured as the amount of flex. Similarly, the racket grip was fixed, and a specified load was applied in opposite front-to-back directions to the left and right sides of the frame. The amount of deformation in the front-to-back direction at both ends of the frame compared to before the load was applied was measured as the amount of torsion.

In measurements conducted on each embodiment and each comparative example, the amount of flex and twist for the first comparative example was set to 100, and the amounts of flex and twist for the other comparative examples and embodiments were measured relative to the first comparative example. The measurement results are shown in Table 1 below.

As shown in Table 1, the second and third comparative examples and the embodiment all had smaller amounts of flex and torsion than the first comparative example, and were able to increase both flexural rigidity and torsional rigidity. However, the second comparative example had too little flex compared to the first comparative example. As a result, the flexural rigidity of the second comparative example was too high, resulting in a stronger impact feeling when hitting the ball and making it impractical.

The third comparative example had a smaller amount of flex than the first comparative example, but a larger amount of flex than the second comparative example, allowing for a moderate increase in flex rigidity. As a result, the third comparative example was able to increase the initial velocity of the ball when hit, exhibiting good repulsion performance and reducing the feeling of impact when hitting the ball. However, the third comparative example had only a slight change in the amount of torsion compared to the first comparative example, and was unable to sufficiently increase torsional rigidity. As a result, the third comparative example experienced wobble on the hitting surface, making it impossible to improve control performance compared to the first comparative example.

The embodiment had the same amount of flex as the third comparative example, and by appropriately increasing flex rigidity, it was possible to exhibit good ball-hitting performance and reduce the sense of impact when hitting the ball. Furthermore, the embodiment was able to reduce the amount of twist compared to the first and third comparative examples, and was able to sufficiently increase torsional rigidity. As a result, the embodiment was able to make the hitting surface less likely to wobble when hitting the ball, and was able to exhibit good control performance. Therefore, the embodiment was able to simultaneously improve both ball-hitting control performance and ball-hitting performance while reducing the sense of impact when hitting the ball.

Fluid analysis was also performed on the shafts of the embodiment and the second comparative example. In this fluid analysis, the drag values were analyzed when wind was blown from the front for one second under the same conditions on each shaft of the embodiment and the second comparative example. The results are shown in Figure 5. Figure 5 is a graph showing the results of the fluid analysis of the embodiment and the second comparative example.

In the graph of Figure 5, if the average drag value for the second comparative example is set to 100, the average drag value (relative value) for the embodiment is 94. Therefore, the second comparative example has a shaft with a substantially rectangular cross-sectional shape, while the embodiment, which has a substantially octagonal cross-sectional shape, was able to reduce air resistance by approximately 6%. As a result, the embodiment can improve swingability and swing speed compared to the second comparative example.

In the above embodiment, the upper end of the recessed portion 30 is formed above the vertical center position C of the shaft body 20, so the formation range of the recessed portion 30 can be ensured to maintain appropriate bending rigidity. Furthermore, the formation position and range of the non-recessed portion 31 in the vertical direction can be set to ensure good torsional rigidity. This makes it possible to achieve both good ball control and repulsion performance.

In addition, the left-right width of the recessed portion 30 gradually decreases upward, and the non-recessed portion 31 extends in an X-shape, which also contributes to the excellent flexural rigidity and torsional rigidity.

The present invention is not limited to the above-described embodiment and can be modified in various ways. The size, shape, direction, etc. shown in the accompanying drawings in the above-described embodiment are not limited to these and can be modified as appropriate within the scope of the effects of the present invention. Other modifications can be made as appropriate within the scope of the purpose of the present invention.

For example, the shapes and positions of the recessed portion 30 and non-recessed portion 31 can be modified in various ways, as long as the non-recessed portion 31 is formed in the area sandwiched between at least the upper end of the recessed portion 30 and the lower end of the throat 21 and functions similarly to the above embodiment.

Alternatively, the shaft 13 may not have a bifurcated throat 21, but may have a single shaft body 20 extending vertically, with the upper end connected to the lower end of the frame 15. In such a configuration, the non-depressed portion 31 is formed in at least the area sandwiched between the upper end of the depressed portion 30 and the lower end of the frame 15. With this configuration, similar to the above embodiment, both control performance and repulsion performance can be exhibited well, and the feeling of impact can be reduced.

The present invention is a racket that exhibits both excellent control and repulsion performance, and has the effect of reducing the feeling of impact.

10: Racket 12: Grip 13: Shaft 15: Frame 20: Shaft body 21: Throat 30: Depressed portion 31: Non-depressed portion C: Center position in the vertical direction

Claims (6)

A racket comprising a frame on which strings are stretched to form a hitting surface, and a shaft formed between the frame and a grip,
The shaft includes a shaft body connected to an upper end of the grip;
a recessed portion and a non-recessed portion formed on both sides of the shaft body in the thickness direction,
the recess extends upward adjacent an upper end of the grip;
The racket is characterized in that the non-depressed portion is formed at least in an area sandwiched between an upper end of the depression portion and a lower end of the frame. The shaft further includes a throat that is connected to an upper end of the shaft body and that branches into two branches from the upper end toward the frame,
2. The racket according to claim 1, wherein the non-depressed portion is formed at least in an area sandwiched between an upper end of the depression and a lower end of the throat. The racket described in claim 1 or claim 2, characterized in that the upper end of the recessed portion is formed above the vertical center position of the shaft body. The racket described in claim 1 or claim 2, characterized in that the recessed portion is formed so that its width dimension gradually decreases toward the top. The racket described in claim 1 or claim 2, characterized in that the non-depressed portion is formed to extend in an X-shape when viewed in the thickness direction of the shaft body. The racket described in claim 1 or claim 2, characterized in that the non-depressed portion has a cross-sectional shape perpendicular to the up-down direction that is approximately octagonal.