Patent Application
20100331126
The present application claims priority upon Japanese Patent Application No. 2009-155789 filed on Jun. 30, 2009, which is herein incorporated by reference.
1. Technical Field
The present invention relates to a tennis racket.
2. Related Art
It is well known that a tennis racket generally includes a frame and a string. The frame has a structure including a looped frame body (hereinafter referred to as a loop portion) that serves as a ball hitting face (hitting face) and a shaft portion provided with a grip at an end thereof. The hitting face is formed by stringing across a string inwardly of the loop portion.
As described in JP-A-6-269514, there are various performances required for the tennis racket and one of the important performances required is a “hitting feel”. The hitting feel is a performance related to a feel that is transmitted to an arm or a hand holding the racket upon hitting the ball and can be quantitatively expressed, for example, by an amplitude of vibration of the string, time taken for the amplitude to damp, or a coefficient of restitution when the racket is supported at a grip position in the air with the hitting face horizontal to the ground surface and a ball is dropped from a predetermined height to the hitting face in such a state.
Qualitatively, the hitting feel is often expressed with an expression such as “hard” and “soft”. Generally, “hard” represents a feel in which there is a strong impact in hitting the ball but a high ball speed can be obtained and the racket can be quickly swung through, and may also be referred to as a “agile feel/speed feel”. On the other hand, with the “soft” feel, even if the ball is hit outside a central region in the hitting face, a so-called sweet spot, which provides an easier repulsion of the ball, the impact is weak. Also, it represents a feel with which a high ball speed cannot be achieved but a ball direction can be positively controlled. This may also be referred to as a “refreshing feel/comfort feel”.
Preference between such feels certainly differs between players depending on their age, sex, skill level and physical strength and also differs for the same player depending on his or her training hours and time, season and physical condition. For example, a player may prefer a hard feel at the beginning of the training since he/she has physical strength, whereas he/she may prefer a soft hitting feel as he/she gets exhausted by the training and a power of the arm to receive the shock from the ball is reduced. Further, a string expands and contracts in accordance with temperature and humidity. Further, a repulsion force of the ball changes due to a change in an elasticity of rubber forming the ball in accordance with the temperature. Therefore, even if the same racket is used, the hitting feel may change through the year.
Whether being a professional or an amateur, there is a wide variety of tennis players. There is a wide range of physical strength and skill for individuals between different age and sex and even between those of the same age and sex. Accordingly, there are various the hitting feels preferred by individual players. Recently, there are many players who wish to play with different hitting feels depending on the physical strength or the mood that occasionally change or depending on the season, etc.
In the past, since the hitting feel relied on a tension of a string or a flexibility of the frame itself of the racket, if the player wanted to play with different hitting feels, he/she needed to posses a plurality of rackets with frames of different hitting feels or rackets strung with different tensions, or, depending on the season, to restring by specifying the tension to obtain a preferred hitting feel.
However, for an ordinary amateur tennis player, it is a great economic burden to possess a plurality of rackets. Further, with a training using rackets of different frames in turn, the player cannot get used to the rackets and, particularly, it takes time for a beginner to improve his/her skill. In a case of having it restrung by specifying the tension, it is difficult to obtain a preferred hitting feel unless he/she is an experienced or an advanced-level player since an experience or a professional knowledge on correlation between the tension and the hitting feel is required.
The invention has been made in view of such drawbacks and its object is to provide a racket with which different hitting feels can be easily obtained and which can be offered to a use without a great financial burden.
In order to achieve the object described above, the main aspect of the invention is a tennis racket including:
a frame that includes a shaft and a looped frame portion, the shaft having a grip formed on one end side thereof, the frame portion being joined to the other end side of the shaft and forming a hitting face with a string being strung across; and
a plurality of insertion holes that provide communication between an inner peripheral side surface and an outer peripheral side surface of the frame portion and through which the string is inserted,
shock absorbing portions and hard portions being provided in an alternating fashion on at least a part of the outer peripheral side surface of the frame portion, each shock absorbing portion being formed between insertion holes that are adjacent to each other, each hard portion being formed between insertion holes that are adjacent to each other and being less elastically deformable than the shock absorbing portion.
Other aspects of the present invention shall be elucidated in the specification with reference to accompanying drawings.
At least the following matters will be disclosed in the present specification and accompanying drawings.
As has been described above, recently, there is a need for a tennis racket that is cost effective and with which different hitting feels can be obtained easily. Accordingly, in order to meet such a need, the inventors considered that, basically using only one frame, it is necessary that different hitting feels can be obtained while maintaining a tension of a string. Further, the inventors considered that with the different hitting feels being achieved, it is desired to provide the racket with functions and performances that can widely meet the needs for the hitting feels for a variety of players with different skills, physical strengths and preferences. Aspects of the invention have been contrived based on such idea. The scope of the invention includes the above-mentioned main aspect of the invention, as well as a tennis racket having the features as follows:
The shock absorbing portion is made of a material that is more elastically deformable than a material of the hard portion. Alternatively, the shock absorbing portion is thicker than the hard portion;
The looped frame portion includes a frame main body portion forming a main body of the loop and a strip-like side surface member attached to an outer peripheral side surface of the frame main body portion,
each of the insertion holes being a hollow portion of a hollow cylindrical tube portion,
the side surface member having an opening of the insertion hole formed in a front surface thereof and is provided with the tube portion protruding from a back surface thereof,
the frame main body portion being provided with guide holes and projections, each of the guide holes providing communication between the outer peripheral side surface and the inner peripheral side surface of the frame main body portion, the tube portion being inserted through the guide hole, the projections being alternately formed between the guide holes that are adjacent to each other,
the shock absorbing portion being formed by attaching the side surface member to the outer peripheral side surface of the frame main body portion and deforming the front surface of the side surface member by each of the projections into a protruded shape that protrudes outwardly of the frame portion;
The string is strung across by being guided from an inner side of the looped frame portion via the insertion hole to an outer side of the looped frame portion, flexed back and then guided to the inner side via another insertion hole,
the frame member being provided with an indicating portion that specifies either or both a stringing start position for a case in which the string is flexed back at the shock absorbing portion of the frame portion and a stringing start position for a case in which the string is flexed back at the hard portion;
With a direction normal to the hitting face being a front-back direction and a direction extending from the frame portion to the grip being an up-down direction, the frame portion is provided with regions having no shock absorbing portion formed therein arranged at four positions on the outer peripheral side surface at upper left, upper right, lower left and lower right thereof; and
With a plane parallel to the hitting face being a flat plane, the shaft branches on the flat plane in a Y-shape from the grip side towards the frame portion and joins to the frame portion to form an opening portion that provides communication from a front side of the flat plane towards a depth direction, a hollow portion being formed in a side face of the shaft, the hollow portion providing communication in and out of the opening portion to arrange the insertion holes in a continuous manner along the loop shape of the frame portion.
In
The racket 1 of the present embodiment includes mainly a frame 2 that is formed by integrally joining a shaft 20 to a frame portion of a substantially elliptical shape (loop portion) 10. A net-like hitting face 3 is formed by stringing across a string (31, 32) in each of a lateral direction and a transverse direction and inwardly of the loop portion 10. The shaft 20 is formed in a continuous manner below the loop portion 10. It is to be noted that an end of the shaft serves as the grip 21 with a tape-like rubber and the like being wound thereon.
At the racket top 13, a cover made of resin (40a: a meshed hatching portion in the figure) that protects the loop portion 10 is attached. The substantially elliptical loop portion 10 is provided with insertion holes 41, through which the string (31, 32) is inserted, in a side surface (11, 12) thereof including the cover 40a.
The string (31, 32) includes a main string 31 that is strung across in a longitudinal direction and a cross string 32 that is strung across in a lateral direction each of which being guided to an outer side via a certain insertion hole 41 from an inner side of the loop portion 10, flexed back along a side surface of the loop portion 10 and then guided to an inner side of the loop portion 10 again via another insertion hole 41. In this manner, each of the longitudinal and lateral string (31, 32) is strung across at an inner side of the loop portion 10. Accordingly, the hitting face 3 is formed in which the string (31, 32) is strung across in a net-like manner.
The shaft 20 has a planar configuration of a Y-shape that branch upwardly to the left and right and a substantially triangular opening portion 22, which provides communication in the front-back direction, is formed by a lower end 14 of the loop portion 10 and the Y-shaped branching portion. In the present embodiment, the frame 2 has a special structure in which a cavity portion 23, which provides communication between an inner side and an outer side of the opening portion 22, is formed in the side surface of the shaft 20. A central portion of an outer peripheral side surface of the loop portion 10 continues in and out of the opening portion 22 of the shaft 20 via the cavity portion 23 and thus the insertion holes 41 are arranged along the substantially elliptical shape of the loop portion 10.
In this example, five grommet members (40a-40e) are attached to a periphery of the frame main body portion 15 and, as shown in
As has been described above, the racket 1 of the present embodiment can provide different hitting feels to a player without changing tensions of the strings (31, 32) for a single frame 2. The racket 1 of the present embodiment achieves a hitting feel selecting function that enables a selection between either a “hard” hitting feel or a “soft” hitting feel by contriving the structure of the grommet member (40a-40e).
Hereinafter, the hitting feel selecting function of the racket of the present embodiment will be described. As shown in
Specifically, the trapezoidal protruded portion 50 is more elastically deformable compared to the recessed portion 60. Accordingly, in a case where the string (31, 32) is flexed back at this protruded portion 50, when a ball hits the hitting face 3, the string (31, 32) exerts a force directed inwardly of the loop portion 10 onto the flexing back portion (50, 60) due to an impulsion. The trapezoidal protruded portion 50 is more elastically deformable than the recessed portion 60 and thus elastically deforms due to a force produced by the string (31, 32) and provides a shock absorbing function.
In other words, in a case where the string (31, 32) flexes back at the protruded portion 50, the protruded portion 50 serves as a “shock absorbing portion” 50 that alleviates the shock from the ball and, as a result, a soft hitting feel can be obtained. On the other hand, in a case where the string (31, 32) is strung by flexing back at the recessed portion 60, since an elastic deformation due to the shock from the ball is less likely to occur, a solid hitting feel is obtained. That is to say, the recessed portion 60 functions as a “hard portion 60” having a hard property.
In the present embodiment, a difficulty level of elastic deformation is relatively altered between the hard portion 60 and the shock absorbing portion 50 by manufacturing the grommet member (40a-40e) by double molding of a hard resin forming the hard portion 60 and a soft resin forming the shock absorbing portion 50. In this example, Pebax (Trade Mark) including a polyether block amide copolymer is used as a double mold resin in which the hard resin is Pebax 7033 and the soft resin is Pebax 3533.
Further, in the present embodiment, as for the string (31, 32) strung across a central portion of the loop portion 10, i.e., a region which is a so-called sweet spot, the grommets 42 at the central eight positions of the left and right grommet members (40b, 40c) at which the cross string 32 is strung across (in
In
Further, in an example shown in
How to String in Accordance with the Hitting Feel
As has been described above, the above-mentioned racket 1 can obtain different hitting feels by appropriately selecting the insertion holes 42 through which the strings (31, 32) are to be inserted through and thus selecting whether to flex back on the shock absorbing portions 50 or on hard portions 60 when stringing the strings (31, 32) across the loop portion 10.
In
Further, the grommet 42 that firstly guides the string (31, 32) from an outer side to an inner side of the loop portion 10 is taken as a stringing start position and the grommet 42 that lastly guides the string (31, 32) from an inner side to an outer side of the loop portion 10 is taken as a stringing end position. The stringing start position and the stringing end position of the main string 31 are indicated by a white circle and a black circle, respectively, and the stringing start position and the stringing end position of the cross string 32 are indicated by a white square and a black square, respectively. Knots of the string (31, 32) are indicated with white triangles.
In the present embodiment, the shock absorbing portion 50 and the hard portion 60 are, except for a part such as a part 46 near the stringing end position of the string (31, 32), arranged to surely oppose each other at the left and right and at the top and bottom, and when the string (31, 32) is inserted through the grommets 42 at opposing positions in the up-down direction and the left-right direction, it flexes back on either the shock absorbing portion 50 or the hard portion 60.
The main string 31 is strung across in a left-right symmetrical manner from the top end 13 or the bottom end 14 of the loop portion 10 and the cross string 32 is strung across from either a left or right upper portion of the loop portion 10 towards a lower portion in a meandering manner. In the case of the stringing fashion for the hard hitting feel, as shown in
The racket 1 of the present embodiment provides different hitting feels in response to the stringing fashion of the strings (31, 32). Accordingly, using the same frame 2, a difference in the hitting feels was actually measured for cases in which the string (31, 32) was strung with two stringing fashions to obtain different hitting feels. Of course, the tension for stringing the string (31, 32) across was made the same. As for the hitting feel, measurement was taken for two properties, i.e., a cushioning characteristic and a shock range. The cushioning characteristic indicates the difficulty level of relative deformation between the hard portion 60 and the shock absorbing portion 50 and is a deformation ratio in a thickness direction at the strip-like portion 45 of the grommet member (40a-40e). The shock range is a maximum amplitude obtained when a ball is dropped from a predetermined height to a center of the hitting face 3 and the string (31, 32) is vibrated while the hitting face 3 of the racket 1 is held horizontally. Both measured properties are indicated by relative values by taking a numerical value of a case where the string is strung with the hard hitting feel as 100.
Table 1 below shows the result of the measurement.
It can be seen from Table 1 that, depending on the stringing position of the string (31, 32), there is a significant difference between the hitting feels. In other words, according to the racket 1 of the present embodiment, significantly different two types of hitting feels can be obtained with the single frame 2.
Position at which Shock Absorbing Portion is Formed
As has been described above, in the present embodiment, the shock absorbing portion 50 and the hard portion 60 are arranged so as to surely oppose at the left and right and at the top and bottom of the loop portion 10, except for the part 46 such as near the stringing end position of the string (31, 32). In other words, on the outer peripheral side surface 11 of the loop portion 10, the shock absorbing portion 50 and the hard portion 60 are not provided continuously along the entire side surface of the loop. Specifically, explaining with reference to
The region 46 in which the shock absorbing portion 50 is not formed corresponds to the stringing end portion of the main string 31 and to the stringing start position and the stringing end position of the cross string 32. In a case where the shock absorbing portion 50 exists at this position, when the string (31, 32) is strung for the hard hitting feel, the outer most string 33 and the second one from the outer most string 34 in the hitting face 3 flex back on the shock absorbing portions 50 as shown in
Normally, when the ball is hit outside the sweet spot, as the string (31, 32) strung across in up-down and left-right directions gradually becomes shorter from the center of the hitting face 3 towards a direction of the frame of the loop portion 10, the hitting feel also gradually becomes harder. However, in a case where the outer most string 33 and the second one from the outer most string 34 in the hitting face 3 flex back on the shock absorbing portions 50, while the hitting feel is being hardened gradually, the hitting feel may be inverted and may sharply become soft. If the hitting feel changes sharply, the hitting feel expected by the player will be impaired. Also, if the hitting feel changes, it will of course become difficult to control the direction and the speed of the ball. Accordingly, in the present embodiment, as has been described above, the region 46 in which the shock absorbing portion 50 is deliberately not formed is provided, and the string (31, 32) is prevented from flexing back at any of the shock absorbing portions 50 when the string (31, 32) is strung across for the hard hitting feel.
According to the racket 1 of the present embodiment, different hitting feels can be obtained with the single frame 2 by simply changing stringing fashion or the stringing start position of the string (31, 32). In order not to start from a wrong stringing start position, on a front surface (back surface) of the loop portion 10, marks are indicated at start stringing positions corresponding to the hitting feels.
In
Of course, it is not necessary that the main string 31 and the cross string 32 are both strung across for the same hitting feel. For example, the main string 31 may be strung across to flex back on the hard portions 60 and the cross strings 32 may be strung across to flex back on the shock absorbing portion 50 to enable freedom in customization in accordance with a user's choice or preference. Thus, even in a case in which the stringing positions of the string (31, 32) differ for the main string and the cross string, the stringing positions will not be mistaken with the above-mentioned marks (70Mh, 70Ch, 70Ms, 70Cs).
As has been described above, according to the racket 1 of the present embodiment, the substantially elliptical shape providing a contour of the loop portion 10 continues in and out of the opening 22 via the hollow portion 23 provided in the side surface of the shaft 20, and the insertion holes 41 are arranged in a continuous manner along the shape of the loop. This shaft structure also improves properties related to the hitting feel.
With the stringing fashion of the known racket 1b shown in part (A) and part (C), since a shaft 20b does not have the hollow portion 23, the main string 31 will flex back through the shaft 20b and thus a length of a main string 31L strung at a joining portion 24 between the shaft 20b and the loop portion 10 and a length of a main string 31S that is adjacent to the main string 31L and that is flexed back along an ellipse will be extremely different. Accordingly, while the string becomes gradually shorter from the center of the hitting face 3 towards the frame portion of the loop portion 10, the main string 31 will become extremely long and thus the hitting feel will be discontinuous from the center of the hitting face 3 towards the frame portion. Therefore, there is a possibility that it becomes difficult to control the ball.
On the other hand, according to the racket 1 of the present embodiment shown in part (B) and part (D), the hollow portion 23 is provided in the side surface of the shaft 20 and the main string 31 flexes back along the substantially elliptical shape of the loop portion 10 also at the joining portion 24 between the shaft 20 and the loop portion 10. Accordingly, the main string 31 becomes gradually shorter from the center of the loop portion 10 towards the frame portion direction and the hitting feel gradually changes from the sweet spot at the center of the hitting face 3 towards an outward direction.
Further, with the racket 1 of the present embodiment, different hitting feels can be obtained by changing the stringing start positions of the main string 31 for the top and bottom of the loop portion 1 and it is the shaft structure of the present embodiment that substantially enables the change in the stringing start position. Specifically, the cross string 32 is not influenced by the structure of the shaft 20 since it may be started stringing from either the top left or top right end of the loop portion 10 depending on the different hitting feels. However, as has been shown in part (C) and part (D) of
In the embodiment described above, the grommet member (40a-40e) formed by double molding is attached to the frame main body portion 15, which is a main body of the loop portion 10, and thus the hard resin and the soft resin are selectively provided at positions where the string (31, 32) flexes back. There are grommets 42 through which the insertion holes 41 penetrate that are made of the soft resin and that are made of the hard resin. Accordingly, as in the grommet member 141 shown in
Further, in the embodiment described above, the shock absorbing portion 50 made of the soft resin protrudes in a trapezoidal shape outwardly of the loop portion 10. However, it is not limited to such a configuration but may be any structure as long as the difficulty level of elastic deformation of the flexed back portion is relatively different when the string (31, 32) flexes back along the side surface of the loop portion 10.
For example, as in the grommet member 142 shown in
Further, the shock absorbing portion can be formed by devising the shape of the frame main body portion.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2009-155789 | Jun 2009 | JP | national |
