JP2000061004A - Tennis racket - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the effective length of a gut without lowering the strength of a gut-strung part. SOLUTION: At least a part of string holes bored in a gut-strung part 12 surrounding a face side 11 of a hollow frame formed of a fiber-reinforced resin in communication between the interior part and the exterior part 20 thereof are made smaller in the exterior part 20 than in the interior part thereof. The diameter of the holes at the exterior part 20 thereof is set in a range of 3.7 mm-3.0 mm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tennis racket, and more particularly, to improving a gut hole to increase a coefficient of restitution and a sweet area when hitting a tennis ball and to suppress uncomfortable vibration. To do.

[0002]

2. Description of the Related Art In a conventional tennis racket frame, as shown in FIGS. 16 (I), (II) and (III), a gut stretched portion 2 surrounding a face portion 1 is attached to a gut at the center in the thickness direction. The groove 3 is provided along the entire circumference, and the gut holes 4 are formed in the bottom surface 3a of the gut groove 3 at predetermined intervals, and the gut 5 is stretched while sequentially passing through the gut hole 4.

Usually, the string of gut 5 is a gut hole 4
17 (I) and (II), the bumper 6 is attached to the top side and the yoke side, and the grommets 7 are attached to both side sides of the bumper 6 and the grommet 7. The tubular legs 6a and 7a are passed through the gut holes 4, and the strings are passed through the legs 6a and 7a to stretch the gut 5 on the face portion 1. The bumper 6 and the grommet 7 are usually resin molded products.

The gut hole 4 connects the inner hole 4a formed in the inner frame 2a (face side frame) of the hollow gut tension portion 2 and the outer hole 4b formed in the outer frame 2b to communicate with each other. The inner hole 4a and the outer hole 4b have the same diameter, and are set to a size that allows the foot portions 6a and 7a of the bumper 6 and the grommet 7 to be closely fitted. Usually, the gut hole diameter is set to 4.0 mm to 4.5 mm. In this way, the outer peripheral surfaces of the foot portions 6a and 7a of the bumper and the grommet are held immovably in close contact with the inner peripheral surfaces of the inner hole 4a and the outer hole 4b, and the string of the gut 5 that passes through the foot portions 6a and 7a. Is fixed at the inner end point P1 of the inner frame 2a of the gut tension portion 2.

As described above, the bumper 6 and the grommet 7 are fixed in the gut holes 4 of the gut tension portion 2, and the gut 5
Strings are bumpers 6 and grommets 7 feet 6
Since the gut 5 is tightly fitted and held in the a and 7a, the gut 5 is fixed at the tip of the inner side surface of the gut tension portion 2. Therefore, the fulcrum of the gut that deforms at the time of a ball collision becomes the inner end point of the gut stretched portion 2, and the effective length of the gut is limited to the area of the face portion 1 surrounded by the inner side surface of the gut stretched portion 2.

The longer the effective length of the gut, the greater the actual face area, which in turn increases the sweet area,
In addition, since the amount of deformation of the gut becomes large, the contact time between the ball and the gut becomes long, and a racket having a high resilience and a good shot feeling can be obtained.

In view of the above points, a tennis racket shown in FIG. 18 has been conventionally proposed (JP-A-5-3450).
No. 52). In this tennis racket, the inside hole 4a 'and the outside hole 4'of the gut hole 4'drilled in the gut tension portion 2'are provided.
The hole diameter of the leg portion 7a 'of the grommet 7'which fits into the gut hole 4'is expanded inward while having the same diameter as b'. The string of the gut 5 to be passed through the gut hole 4 ′ has a gap C on the inner peripheral surface of the tubular portion inside the leg portion 7a ′.
The fulcrum of is moved to the outside. With this configuration, the effective length of the gut 5 that can be deformed can be increased to slightly less than twice the width W of the gut stretched portion 2 ′ (W × 2 on both left and right sides), and the actual face area is increased. The sweet area can be expanded.

[0008]

However, as shown in FIG.
The configuration shown in (1) has the following problems. First, as the weight of the racket has been reduced in recent years, the wall thickness T of the frame including the gut stretched portion 2 ′ has become smaller. On the other hand, gut hole 4 '
In order to provide an effective gap C between the inside of the foot portion 7a 'of the grommet 7'that fits in and the gut 5, the outer diameter of the grommet foot portion 7a' needs to be about 5 mm. Therefore,
The diameter of the inner hole 4a 'and the outer hole 4b' of the gut hole 4'in which the grommet foot portion 7a 'is fitted is set to 5 mm or more and needs to be larger than the normal gut hole diameter of 4.0 mm to 4.5 mm. is there. Thickness T is small, usually 20 to 3
If a gut hole of 5 mm or more is provided in a portion of about 0 mm,
There is a problem that the durability of the racket decreases.

Particularly, in order to reduce the weight of recent rackets,
Most of them are made of fiber reinforced plastics, and PAN-based carbon fibers are mainly used because of their low specific gravity and high strength. This PAN-based carbon fiber has lower compressive strength than tensile strength. With the gut 5 stretched over the gut stretched portion 2 ', the outer frame 2b' of the gut stretched portion 2 '
The gut 5 is stretched on the outer frame 2b ', and the outer frame 2b' has a large compressive stress. Therefore, if the diameter of the gut hole 4 ′ is increased and the outer hole 4b ′ formed in the outer frame 2b ′ is also increased as described above, the durability of the outer frame 2 ′ is greatly reduced and the outer hole 4b ′ is There is a problem that becomes the starting point of destruction.

If a gap C is to be provided between the gut string and the string of the gut fitted in the gut hole without increasing the diameter of the gut hole provided in the gut stretched portion, the grommet foot part 7a '. It would be better to thin the. Conventionally, the grommet is resin-molded with 66 nylon or 12 nylon, and if the thickness of the foot portion 7a 'of the grommet made of this material is thin, there is a problem that the grommet is likely to tear after the gut is tightened. That is, 66 nylon and 12 nylon have a glass transition temperature (Tg) of 18 ° C., which is the peak temperature of tan δ, so it is difficult to follow the movement of the gut at room temperature, and therefore stress from the gut is applied.
The thin wall makes it easier to tear.

Further, in the racket shown in FIG. 18, since the effective face of the gut 5 is enlarged to enlarge the substantial face surface, there is an advantage that the sweet area is enlarged, but the vibration of the gut is easily excited. Since the grommet 7'is a resin molded product, the vibration of the gut 5 is transmitted to the frame of the gut tension portion via the grommet, and the vibration of the frame after hitting becomes great, which makes the player uncomfortable. There are also problems.

In order to suppress the vibration of the gut, conventionally, as a gut vibration stop, a vibration suppressing material of about 5 to 15 g of rubber or urethane material may be fixed to the gut surface or the like.
If these gut vibration stoppers are attached, the weight of the racket increases correspondingly, and even if vibration of the gut surface can be suppressed, it does not suppress the vibration of the frame, and it does not reduce the discomfort given to the player. Can not.

The present invention has been made in view of the above problems, and improves the gut hole provided in the gut stretched portion to increase the effective length of the gut to increase the sweet area and improve the resilience performance. Eliminates the strength reduction of the gut tension section,
Another object of the present invention is to provide a tennis racket that also damps vibrations of the gut and the gut stretched portion.

[0014]

In order to solve the above-mentioned problems, the present invention is provided with a hollow frame made of fiber reinforced resin, and a gut tension portion surrounding the face surface of the frame is provided with an inner portion and an outer portion thereof. At least a part of the gut hole communicating with the hole is made smaller than the hole provided in the outer part than the hole provided in the inner part, and the hole diameter of the outer part is 3.7 mm to.
We provide a tennis racket with a range of 3.0 mm.

As described above, the tennis racket of the present invention has a diameter of 4.0 mm to 4.5 mm, which is a normal gut hole diameter, and is 3.7 mm to 3.0 mm, preferably,
It is set to 3.5 mm to 3.2 mm. If it is larger than 3.7 mm, the durability of the outer portion of the gut stretched portion is reduced, and cracks are more likely to be formed than the gut holes. On the other hand, 3.0
If it is less than mm, the outer diameter of the string of gut is 1.3.
Since the thickness is mm, it is necessary to extremely reduce the wall thickness of the grommet and the bumper that are fitted in the gut hole, and the durability is reduced and the tear tends to occur.

The inner hole is 4.5 mm to 6.5 m.
It is preferable that m is a circular hole.

As described above, the diameter of the gut hole is smaller than that of the conventional gut hole provided in the outer part of the gut where the compressive stress is applied, so that the durability of the outer part of the gut tension portion can be improved. Therefore, even if the frame is molded with fiber reinforced plastic made of PAN-based carbon fiber having low compressive strength,
It is possible to prevent a crack from being generated from the gut hole in the gut tension portion to which the gut compressive stress is applied.

The gut hole in which the hole on the outer side is smaller than the hole on the inner side is at least one of 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock when the face surface surrounded by the gut tension portion is regarded as a clock face. It is provided within a range of ± 5 ° or more and ± 45 ° or less from the position. That is, the gut holes may be provided at all positions of 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock, or at 3 o'clock and 6 o'clock.
It may be provided only at the hour position, or at the three o'clock, nine o'clock, and twelve o'clock positions. In addition, ± 4 from the above four positions
If it is provided at 5 °, all the gut holes provided in the gut tension portion will be smaller in the outer part hole than in the inner part.

12 o'clock (top position), 6 o'clock, 3 o'clock,
It is preferable that the gut hole near the 9 o'clock position has the above-described configuration, because the gut tension portion surrounding the face surface is deformed vertically and horizontally by in-plane vibration when hitting a ball, and the maximum vibration position is 12 o'clock in the vertical direction. It depends on the position of 6 o'clock and the position of 3 o'clock and 9 o'clock in the lateral direction. Further, the maximum vibration width portion of the secondary vibration in the out-of-plane direction is at 3 o'clock and 9 o'clock. That is, the gut hole at the position where the vibration width is large has the hole diameter of the outer portion smaller than the hole diameter of the inner portion.

The grommet or bumper for attaching the outer hole to the gut hole which is smaller than the inner hole is a molded product made of rubber or elastomer provided with a cylindrical foot portion, and a gut mat of the outer portion of the gut tension portion. It is configured by combining with a resin molded product consisting of a cover to be attached to the outer surface, and the above-mentioned foot part is tightly fitted and fixed in the hole on the outer side of the gut tension section, and a gap is opened between it and the hole on the inner side. Attached,
The deformation fulcrum of the gut which is passed through the hole of the cover from the hollow part of the foot is the outer part of the gut tension part.

Bumpers and grommets, which are a combination of a molded product made of rubber or elastomer constituting the above-mentioned foot portion and a resin molded product constituting the cover, have the same form as a conventional resin bumper or grommet. So there is no weight gain.

Rubber of the above bumper or grommet,
The outer diameter of the foot made of elastomer is 3.0 mm to 3.5
It is set to be mm, and the gut is tightly fitted in the hole on the outer side of the stretched portion, and a gap is formed between the hole and the hole on the inner side.
This gap is preferably 0.8 mm to 1.5 mm.

The rubber or elastomer is tan δ
It is preferable to use a rubber or an elastomer having a glass transition point (Tg) of 10 ° C. or lower, which is the peak temperature of When the foot is molded using such a rubber or elastomer, it has rubber-like properties at room temperature, so it is easy to follow the movement of the gut that is in close contact with the hollow part of the foot,
In addition, since it stretches, it will not tear even if the thickness of the foot is reduced.

The molded product made of rubber or elastomer is a resin molded product which constitutes at least two legs by connecting them through a connecting piece and has a connecting hole in the connecting piece while forming the cover. Is provided with a projection for press-fitting and fixing in the coupling hole, and a gut hole communicating with the hollow portion of the foot portion at the time of coupling. In the grommet, the cover is fitted in the gut groove provided on the outer side of the gut stretched portion, and is attached to the gut stretched portions on both the left and right sides of the face surface. The bumper covers the entire outer surface of the outer side of the gut stretched portion, and is attached to the top portion and the 6 o'clock side of the yoke mounting side.

The cover of the above resin molded product has a thickness of 2.3 mm at least at a portion where the gut straddles between the gut holes.
It is preferable to provide a thick portion having the above thickness.

As described above, when the grommets and the foot of the bumper for mounting the outer hole in the gut hole which is smaller than the inner hole are molded with rubber or elastomer having elasticity, the grommet and the foot of the bumper are in close contact with the hollow of the foot. It makes it easier for the foot to follow the movement of the inserted gut. Moreover, while the foot is tightly fitted and held in the hole on the outer side, there is a gap between the foot and the inner peripheral surface of the hole on the inner side. To follow. As a result, the effective length of the gut can be increased, the face surface can be substantially expanded, and the sweet area can be expanded, and the time in which the gut contacts the ball is lengthened, the shot feeling is mild, and the resilience performance is also improved. Can be increased. Furthermore,
The longer contact time of the ball also improves the hold performance and can improve the control performance when the ball is hit hard.

Further, since there is a gap between the inner peripheral surface of the hole in the inner part and the outer peripheral surface of the foot part, the moving direction of the foot part following the movement of the gut is not limited. In particular, if the inner hole is a circular hole and an annular gap is provided between the inner hole and the outer circumference of the foot, the foot of the grommet can move in any direction following the gut when hitting a ball. Recently, tennis playing styles are diversifying, and the gut makes various movements when striking not only flat hits but also spins and sliced balls. You can

Further, since the foot portion that the gut passes through closely contacts the foot portion made of rubber or elastomer, it is possible to suppress unpleasant high frequency vibration of the gut. Moreover, since the connecting piece for connecting the foot portions is attached to and contacts the outer surface of the outer side portion of the gut stretched portion, it is possible to suppress high-frequency vibration of the frame of the gut stretched portion. In particular, when the thick portion is provided on the cover that overlaps the outside of the contact portion, the vibration of the gut is less likely to be transmitted to the frame, and the vibration of the frame can be effectively suppressed. In this way, both the vibration of the strings of the gut itself and the vibration of the frame can be damped.

In particular, a gut hole having a foot portion made of the above rubber or elastomer and a gut hole for mounting a bumper is provided at a portion of the gut tension portion where the vibration width at 12 o'clock, 6 o'clock, 3 o'clock, and 9 o'clock is large. Therefore, the vibration damping effect is large.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a tennis racket according to the present invention will be described below in detail with reference to the drawings.

The frame 10 of the tennis racket of the embodiment shown in FIG. 1 has a hollow shape made of fiber reinforced resin and surrounds a face surface 11 on which the gut 5 is stretched, a gut tension portion 12, a throat portion 13, and a shaft portion. 14 and the grip portion 15 are continuously formed. The above-mentioned gut tension portion 12 has a yoke portion 16 which is a separate member and has an annular shape which continuously surrounds the frame surface 11 on the throat side.

A gut groove 22 is formed in the outer side portion 20 of the gut stretched portion 12 of the frame 10 and gut holes 23 are formed along the length direction at a required interval. These gut holes 23 are the outer holes 24 provided in the bottom surface of the gut groove 22 of the outer part 20 and the inner part 2 of the gut tension part 12.
1 and the inner hole 25 provided in the first hole 1. The outer hole 24 and the inner hole 25 are provided at positions communicating with each other through the hollow portion 26.

Two types of the gut holes 23 are provided. In this embodiment, as shown in FIG.
The gut hole 23A shown in FIG. 2 is provided within a range of ± 12 ° with the position of 2 o'clock as a fulcrum (A) and within a range of ± 30 ° with the positions of 3 o'clock and 9 o'clock on both sides as a fulcrum (B) (C). ing. In addition, the yoke 16 is also ±
A gut hole 23A 'is provided in the range (D) of 7 °.

That is, the hole diameter r1 of the outer hole 24A provided on the bottom surface of the gut groove of the outer portion 20 is set to the inner hole 2 provided in the inner portion 21.
It is set smaller than the hole diameter r2 of 5A (r1 <r
2). The outer hole 24A is 3.0 mm to 3.7 mm, preferably 3.2 mm to 3.5 mm. On the other hand, the inner hole 25A of the inner portion 21 is 4.5 mm to 6.5 mm. Both the outer hole 24A and the inner hole 25A are circular holes, and their center points are located on the same line. The only difference is that the yoke 16 is not provided with a gut groove, and the size of the gut hole 23A 'is the same as that of the gut hole 23A.

The gut holes 23B provided near 2 o'clock (E), 10 o'clock (F), 5 o'clock (G), and 7 o'clock (H) outside the above range (A, B, C, D) are As shown in FIG. 3 (II), the hole diameter r3 of the outer hole 24B and the inner hole 24B.
Is the same as 4.0 mm to 4.5 mm, which is substantially the same as the conventional gut hole.

One bumper 30 is attached to the top side of the ranges A, E and F, and the range B and G and the range C and H are set.
Grommets 31 are attached to the respective areas of No. 3 and bumpers 32 are attached to the area of D.

As shown in FIGS. 4 and 5, the bumper 30 is composed of a rubber molded product 35 and a resin molded product 36. The rubber molded product 35 is resin molded within the range (A) in which the gut holes 23A are provided. It is connected to the item 36. The rubber molded product 35 includes a cylindrical foot portion 37 that is inserted into the gut hole 23A, and a connecting piece 38 that connects the outer ends of these foot portions 37.
8 is provided with a coupling hole 39. The outer diameter of the foot portion 37 is press-fitted into the outer hole 24A so as to be closely fixed thereto, and is set to a size such that an annular gap 40 is formed between the foot portion 37 and the inner hole 25A. Outer diameter is 3.0 mm
~ 3.5 mm. The leg portion 37 is dimensioned such that the tip of the leg portion 37 protrudes from the inner portion 21 of the gut tension portion in a state where the leg portion 37 is inserted in the gut hole 23A, and the connecting piece 38 that connects the outer end of the leg portion is fitted along the bottom surface of the gut groove 22. I am trying to do it.

The resin molded product 36 has different shapes at the positions corresponding to the ranges (A) and (E) (F). In a range corresponding to (A), the cross-section concave portion 41a fitted in the gut groove 22 and the collar portion 4 protruding from the tip ends on both sides thereof.
1b is provided, and a gut insertion hole 42 communicating with the hollow portion 37a of the foot portion 37 is provided on the bottom surface of the concave portion 41a in cross section, and the coupling hole 39 is press-fitted between the gut insertion holes 42. A protrusion 43 for fixing is provided. Further, the concave portion 41 in cross section between the gut insertion holes 42
Since the stretched gut 5 hits the groove a, a thick portion 44 is provided in the widthwise central portion on the inner surface side of the groove bottom, and the gut positioning is performed on both widthwise edges of the thick portion 44. Protrusion 44a
Is provided.

The protrusion 43 of the resin molded product 36 is connected to the coupling hole 3
The cover 41 of the resin molded product 36 is superposed on and coupled to the connecting piece 38 of the rubber molded product 35 by being press-fitted and fixed to the rubber molded product 9. With the resin molded product 36 and the rubber molded product 35 attached to the gut tension section 12, a concave section 41 is formed.
a is fitted in the gut groove 22, and the collar portions 41 b on both sides cover the outer portions 20 on both sides of the gut groove 22.

The resin molded product 36 is provided with a gut insertion hole 46 in the bottom surface of the cross-section concave portion 41a of the cover 41 in a range corresponding to (E) and (F), and a tubular foot portion 45 from the outer periphery of the gut insertion hole 46. And the foot portion 45 is fitted into the gut hole 23B. The outer diameter of the foot portion 45 is set so as to be fitted into the outer hole 24B and the inner hole 25B of the gut hole 23B without any clearance.

The grommet 31 attached to the side is as shown in FIGS. 6 and 7, and is substantially the same as the bumper 30 shown in FIGS. 4 and 5, and has a rubber molded product 35 and a resin molded product 36.
The difference is that both side flange portions 41 of the resin molded product 36 are
Since there is only b, the same reference numerals are given and description thereof is omitted.

The bumper 32 attached to the yoke side is substantially the same as the bumper 30 and is composed of a rubber molded product and a resin molded product. The foot 37 of the rubber molded product is passed through the gut hole 23A, and the legs of the resin molded product on both sides are formed. The portion 45 is passed through the gut hole 23B, and the cover 41 of the resin molded product 45 is provided with the yoke 16
Mounted on the outer surface of the.

As described above, the bumpers 30 and 32 and the grommet 31 are attached to the outer surface of the gut tension portion 12, and in this state, the gut 5 is passed through the gut holes 23A and 23B, and as shown in FIG. Gut is stretched over 11.

The gut 5 passes through the foot of the bumper and the grommet passed through the gut hole, and the tension of the gut 5 causes the rubber molded product 37 that passes through the inner hole 25A of the gut hole 23A to
It is held at the center position of the inner hole 25A, and holds an annular space 40 between the outer peripheral surface of the foot portion 37 and the inner peripheral surface of the inner hole 25A. On the other hand, the outer side of the foot portion 37 is press-fitted into the outer hole 24A and tightly fitted and fixed, so that the deformation fulcrum of the gut 5 is the outer portion 20 of the gut tension portion 12 provided with the outer hole 24A. As a result, the effective length of the gut 5 that can be deformed at the time of a ball collision reaches a position where the gut 5 reaches the outer part 20 of the gut tension frame 12, and the inner part 21 serves as a fulcrum, compared with the inner part 21 to the gut groove 22. The width W'becomes wider, and the face surface 11 is increased by W '* 2 on both sides.

Example 1 The above tennis racket was prepared as follows. An epoxy resin, which is a thermosetting resin, was used as a prepreg sheet reinforced with carbon fibers arranged in one direction, and the prepreg sheet was wrapped around a tube covered with a mandrel. After laminating and winding the required number of sheets, it was pulled out from the mandrel to form a layup. The layup was placed in the cavity of the mold, and an internal pressure of 7 kgf / cm ² was applied to the tube, and the layup was performed at 145 ° C. for 5 hours.
It was held for 0 minutes and molded. The mold used was a racket frame having a frame thickness of 24 mm and a total length of 27.5 inches.

Gut holes are formed in the molded racket frame to form eight gut holes 23A in the 12 o'clock (A) range, and at the 3 o'clock (B) range and 9 o'clock (C). Nine gut holes 23B were drilled in the range. These gut holes 23A have a diameter of the outer hole 24A of 3.5 mm,
The diameter of the inner hole 25A was set to 5.5 mm. Other than the above, the gut hole 23B was used, and the inner hole 25B and the outer hole 24B were 4.3 mm in diameter.

A bumper 30 is provided in the area (A) on the top side.
And the grommets 31 were respectively attached to the areas (B) and (C) on the side side. The resin molded product 36 of the bumper 30 and the grommet 31 was molded from 12 nylon. Further, the thick portion 44 of the portion of the resin molded product 36 with which the gut 5 abuts has a maximum thickness of 3.0 mm.

The product weight of the racket with the grommet and bumper attached was 240 g, and the balance position was 335 mm from the grip end.

(Second Embodiment) Similar to the first embodiment, a gut hole 23A is provided in the area (A) on the top side and the area (B) and (C) on the side], and the outer hole 24A of the gut hole 23A is provided.
Has a diameter of 3.7 mm. This example is different from Example 1 in that the diameter of the outer hole is changed, and other points are the same.

(Example 3) Example 1 and resin molded product 36
The difference is that the maximum thickness of the thick portion 44 is 2.3 mm, and the others are the same.

(Example 4) Example 1 and the gut hole 23A
The difference is that the diameter of the inner hole 25A is 4.6 mm, and the others are the same.

(Embodiment 5) Embodiment 1 and the gut hole 23A.
The inside diameter of the inner hole 25A is different from that of the first embodiment except that the diameter of the inner hole 25A is set to 6.4 mm, and the others are the same.

For comparison with the above-described examples of the present invention, the following tennis rackets of Comparative Examples 1 to 6 were prepared.

(Comparative Example 1) The gut holes in the areas (A) on the top side and the areas (B) and (C) on the sides are the same as the gut holes in the other areas. 4.0 mm
And That is, all of the gut holes are provided in the gut hole 2
3B. The gut holes 23B were fitted with grommets and bumpers formed of 12 nylon, which have been conventionally used. That is, a grommet and a bumper, which are integrally resin-molded for the foot and the cover, were attached, and the foot was immovably fitted into the gut hole 23B. Others were the same as in Example 1.

(Comparative Example 2) The gut holes in the range (A) on the top side and in the ranges (B) and (C) on the sides were 5 mm in diameter for both the inner and outer holes. A grommet and a bumper, which are integrally resin-molded with a foot and a cover, were attached to these gut holes, and the foot had an outer diameter of 5 mm. The inner diameter of the foot was enlarged inward. That is,
The structure is similar to that of the conventional example shown in FIG. Others were the same as in Example 1.

(Comparative Example 3) The diameter of the outer hole of the gut hole 23A was 3.8 mm, and the bumpers and grommets to be attached were all made of rubber. That is, in the present invention, the member which is a resin molded product is also a rubber molded product. Others were the same as in Example 1.

(Comparative Example 4) The difference from Example 1 is that the maximum thickness of the thick portion of the resin molded product of the bumper and grommet mounted in the gut hole 23A is 15 mm, and the resin molded product has a coupling protrusion. The point is that the resin molded product and the rubber molded product are fixed without providing the coupling hole in the rubber molded product. Others were the same as in Example 1.

(Comparative Example 5) A difference from Example 1 is that the hole diameter of the inner hole 25A of the gut hole 23A is 4.3 mm, and the other points are the same as in Example 1.

(Comparative Example 6) A difference from Example 1 is that the diameter of the inner hole 25A of the gut hole 23A is 6.8 mm, and the other points are the same as in Example 1.

Seven tennis rackets of each of Examples 1 to 5 and Comparative Examples 1 to 6 were prepared, and the rebound coefficient, the sweet area, and the damping of the gut (string) were each stretched with the gut stretched. Rate, frame damping rate, top pressure strength, lateral pressure strength, contact rate between the foot of the grommet and the inner hole, and a durability test and a paint crack test were performed. In addition, a shot feeling test by actual hit was also conducted.
The results are shown in Table 1 below.

[0061]

[Table 1]

The restitution coefficient is measured as shown in FIG.
The racket with the gut stretched is held so that the top part is hung so as to be free in the vertical state, and in this state, the ball is made to collide with the face surface at a constant speed V ₁ , and the speed V ₂ of the bounced ball is changed. It was measured. The coefficient of restitution is velocity V ₁ , V
_{It is} a ratio of ₂ (V ₁ / V ₂ ), and the larger the restitution coefficient is, the better the flight of the ball is.

As shown in Table 1, Examples 1 to 5 have a coefficient of restitution of 0.446 to 0.454, and Comparative Examples 1 to 1
It was larger than the coefficient of restitution of Comparative Example 5. In Comparative Example 6, the inner hole was made large so that the feet of the grommets could be moved, so the coefficient of restitution was the same as that of the example.
However, Comparative Example 6 has a drawback that paint cracks, which will be described later, are likely to occur.

As with the measurement of the restitution coefficient, the gut damping ratio is measured by holding the top part of the racket on which the gut is stretched so as to be free in the vertical state, and in this state, vibrating the frame with an impact hammer. Then, the displacement and acceleration of the gut at that time were read by a laser and measured.

As shown in Table 1, Examples 1 to 5 have a gut attenuation rate of 0.48 to 0.55, and Comparative Examples 1 to 1
Comparative example 5 was 0.11 to 0.39, and it was confirmed that the example was superior in gut damping property. In Comparative Example 6, the inner hole was made large so that the foot portion of the grommet could be moved, and thus the gut damping ratio showed the same value as that of the example.

The frame damping factor was measured by measuring the damping factor of the out-of-plane secondary natural frequency of the racket with the gut stretched.
In this measurement, as shown in FIG. 12, the top of the racket was hung with a string and freely supported, and in this state, the acceleration pickup 100 was attached to one surface at the 3 o'clock position, and the impact hammer 101 vibrated from the back surface. . The input vibration measured by the force pickup attached to the impact hammer and the response vibration measured by the acceleration pickup were analyzed by the frequency analysis device 104 via the amplifiers 102 and 103. The transfer function in the frequency domain was obtained by this analysis, and the out-of-plane secondary natural frequency was obtained. The attenuation rate was calculated from FIG. 13 by the following formula.

Ζ = (1/2) × (Δω / ωn) T0 = Tn / √2

As shown in Table 1, the frame attenuation rates of Examples 1 to 5 were 0.73 to 0.77. Comparative Examples were 0.41 to 0.72 except for Comparative Example 3. In Comparative Example 3, since the bumper and the grommet were entirely made of rubber, vibration of the gut was absorbed by the bumper and the grommet and transmitted to the frame, so that the frame damping ratio was 0.7.
It was as big as 4. However, it has a drawback that the coefficient of restitution is poor and that the shot feeling is poor as described later.

The measurement of the top pressure strength is as shown in FIG.
The racket with the gut stretched (12 o'clock) was placed vertically with the top as the upper end, both sides were fixed and held, and a load was applied from the upper end until the frame broke, and the maximum load value at that time was measured.

As shown in Table 1, in Examples 1 to 5, the top pressure strength was 208 to 223 kgf. In Comparative Example 2 in which the gut hole was larger than that of the example, the pressure was 162 kg / cm. Therefore, it was confirmed that the top pressure strength was reduced when the configuration of Comparative Example 2 was used, but the top pressure strength was not reduced when the configuration of this example was used.

The lateral pressure strength is measured as shown in FIG.
With the racket with the gut stretched upright,
One side of the gut stretched portion was placed on the base, and a load was applied from above to the other side positioned above until the frame broke, and the maximum load value at that time was measured.

As shown in Table 1, in Examples 1 to 5, the lateral pressure strength was 161 to 172 kg / cm. The comparative example 2 in which the gut hole is larger than the example is 141 kg / cm.
Met. Therefore, it was confirmed that the lateral pressure strength was reduced with the configuration of Comparative Example 2, but the lateral pressure strength was not reduced with the configuration of this example.

The contact between the leg of the grommet and the frame was measured by measuring the tension of the warp and weft of the gut at 601b (27 kg).
When stretched with × 601b (27 kg), 601b × 5
The contact ratio at that time was measured for the case of stretching with 41b and the case of stretching with 601b × 481b. Specifically, the presence or absence of contact between the frame and the foot of the grommet with respect to the target gut hole was examined, and the ratio to the total number of target holes was calculated.

As shown in Table 1, Examples 1 to 5
Is 0% to 2.0%, the grommet foot and the inner hole of the frame hardly contact each other, so even if the foot is made of rubber,
It was confirmed that the feet were in contact with the frame and were less likely to wear or crack. Comparative Examples 1 and 2 are 100% naturally, but Comparative Examples 3 to 5 have a contact rate of 29% to 58%, and the rubber feet are likely to contact the frame,
It was confirmed that the gut damping effect was small.

In the durability test, the ball was made to strike a position 6 cm below the top at a speed of 55 m / sec. 500
The case where the frame did not break even after repeated collisions was regarded as OK.

As shown in Table 1, all of the present examples were OK in the durability test, but in the conventional racket of Comparative Example 1 and the racket proposed in FIG. 18 of Comparative Example 2, the outer gut holes were formed. It was confirmed that the frame had no durability due to its large diameter.

In the paint crack test, when the warp and weft of the gut were stretched by 601b × 601b, it was observed whether or not a crack was generated in the paint (painting) inside the gut tension portion.

As shown in Table 1, in all of the examples, no cracks were generated in the paint, but in Comparative Example 6, cracks were generated. Therefore, if the gap between the rubber foot and the inner hole of the frame is too large, the distance between the holes will be small, and the deformation of the gut tensioner when hitting the gut tensioner will increase. It was confirmed that the paint did not follow and cracks occurred.

In the hit feeling test, 24 testers hit the ball and scored an average of 5 points.

As shown in Table 1, Examples 1 to 5 were able to obtain an evaluation of 4.05 or more, but Comparative Examples 1 to 1
In the case of 5, only a rating of less than 4 could be obtained. In particular,
The general conventional type has an evaluation of 2.78, and it was confirmed that the hitting feeling of the racket of the present invention was improved as compared with the conventional racket.

[0081]

As is apparent from the above description, the tennis racket of the present invention has an improved shape of the gut hole provided in the gut tension portion of the frame, so that the durability of the frame is maintained and the gut is effective. The length can be increased, and as a result, the face surface can be substantially enlarged, the coefficient of restitution when hitting a ball can be increased, and the sweet area can be increased.

Further, the foot portion to be inserted into the gut hole of the grommet or bumper is made of rubber, and a gap is provided between the rubber foot portion and the inner hole of the gut tension portion, and the foot portion is provided at the outer portion. If the structure is fixed, uncomfortable vibration generated in the gut and the frame can be suppressed while increasing the contact time between the ball and the gut. In particular, the present invention has various advantages such that the vibration of the gut transmitted to the frame can be suppressed and the shot feeling of the player can be improved.

[Brief description of drawings]

FIG. 1 shows a tennis racket frame according to an embodiment of the present invention, (I) is a plan view, and (II) is a side view.

FIG. 2 is a partially enlarged view of a gut tension portion of the racket frame seen from the inner surface side, (I) is a drawing when the gut is not stretched, and (II) is a diagram when the gut is stretched. It is a drawing.

FIG. 3 shows a gut tension portion, (I) shows a gut hole 23.
A sectional view of a portion provided with A, (II) is a sectional view of a portion provided with a gut hole 23B.

FIG. 4 is an exploded perspective view of a bumper.

FIG. 5 shows a resin molded product of the bumper, wherein (I) is a plan view and (II) is a bottom view.

FIG. 6 is an exploded perspective view of a grommet.

FIG. 7 shows a resin molded product of the above grommet, (I)
Is a plan view and (II) is a bottom view.

8 (I) and (II) are cross-sectional views showing a state in which the bumper is attached to the gut tension portion.

9 (I) and (II) are cross-sectional views showing a state in which the grommet is attached to the gut tension portion.

FIG. 10 is a partial plan view of the tennis racket with the gut stretched.

FIG. 11 is a schematic diagram showing a method for measuring a coefficient of restitution.

FIG. 12 is a schematic diagram showing a method of measuring a vibration damping rate.

FIG. 13 is a diagram showing the relationship between frequency and transfer function.

FIG. 14 is a schematic view showing a method of measuring the top pressure strength.

FIG. 15 is a schematic diagram showing a method for measuring lateral pressure strength.

16 (I) (II) (III) are drawings showing a conventional example.

FIG. 17 (I) is a sectional view with a bumper attached, and (II) is a sectional view with a grommet attached.

FIG. 18 is a cross-sectional view showing another conventional example.

[Explanation of symbols]

5 Gut 10 tennis racket 11 face 12 Gut tension section 20 Outer part 21 Inside 22 gut groove 23 (23A, 23B) Gut hole 24A, 24B Outer hole 25A, 25B inner hole 30 bumper 31 Grommet 35 Rubber molded products 36 Resin molded products 37, 45 feet 38 Connection piece 39 coupling protrusion 40 voids 41 cover 42, 46 Gut insertion hole 43 coupling protrusion 44 Thick part

Claims (4)

[Claims] 1. A hollow frame made of fiber reinforced resin, wherein at least a part of a gut hole is formed in a gut stretched portion surrounding a face surface of the frame so as to communicate with an inner part and an outer part thereof. Is smaller than the hole provided in the inner part, and the hole diameter of the outer part is 3.7 mm to
A tennis racket with a range of 3.0 mm. 2. At least 12 o'clock, 3 o'clock, 6 o'clock, and 9 o'clock when the gut hole in which the outer hole is smaller than the inner hole is viewed as the face surface surrounded by the gut tension portion is a watch face. The tennis racket according to claim 1, wherein the tennis racket is provided within a range of ± 5 ° or more and ± 45 ° or less from any position. 3. A grommet or bumper for mounting the outer hole in a gut hole which is smaller than the inner hole, wherein the grommet or the bumper is a molded product made of rubber or elastomer provided with a cylindrical foot, and the gut stretched outside It is configured by combining with a resin molded product consisting of a cover to be attached to the outer surface of the part, and the foot part made of the above rubber or elastomer is tightly fitted and fixed in the hole of the outer part of the gut stretched part and the hole of the inner part. 3. The gut deformation fulcrum, which is attached with a gap between the gut and is closely attached to the hole provided in the cover from the hollow part of the foot part, is an outer part of the gut tension part.
Tennis racket described in. 4. The molded article made of rubber or elastomer has at least two legs connected via a connecting piece, and a connecting hole is formed in the connecting piece, while a resin forming the cover. The tennis racket according to claim 3, wherein the molded product includes a protrusion for press-fitting and fixing in the coupling hole, and a gut hole communicating with the hollow portion of the foot portion at the time of coupling.