JPH0562553B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a racket frame in which the ball repulsion characteristics when a ball is hit at the stringing part of the frame are improved.

[Prior Art] The materials used for tennis racket frames have been diversified, including wooden rackets, metal rackets, and fiber-reinforced plastic (hereinafter abbreviated as FRP) rackets. As shown in the figure, the total weight of the frame body 1 is generally 260 to 370 g, and the frame shape of the frame stringing section 2 on which the strings are stretched is also generally approximately oval.

Conventionally, in this type of racket frame,
When a ball is hit on the stringed part of a frame, immediately after the ball makes contact with the gut surface, vibration behavior occurs independently in both the frame system and the ball system, but the natural frequency of the frame is For rackets, the frequency is set to about 90 to 140 Hz, so the vibration behavior of the racket system and the vibration behavior of the ball system do not match, and the vectors do not match.

Therefore, in order to measure the behavior of the racket frame and the ball, as shown in FIG.
A clamp 5 that can be freely rotated in the direction of the ball, which is latched by
The frame main body 1 is thereby made swingable in a pendulum shape, and the ball B is fired toward the frame stringing section 2. Ball B at off-spot areas such as the tip side 2a of the racket and the grip side 2b of the racket stringing part 2.
Using a high-speed camera, we take continuous photographs of the vibrations of the ball and racket as they hit the ball at intervals of 1/2000 seconds. From the state of contact of the ball B at the tip of the frame stringing part, or the grip side part of the frame stringing part as shown in Figs. In the release state shown in FIGS. 6-j and especially in the release shown in FIGS. 7-i-j, the behavior of the racket frame 1 around the ball B moves in the opposite direction to the traveling direction of the ball B. , not only cannot be a positive factor for propulsion when the ball is reflected, but also the vibration energy of the ball system and racket system cannot be effectively used to accelerate the ball, which adversely affects the repulsion characteristics of the ball. There were problems such as:

In addition, FIGS. 6 a to l and FIGS. 7 a to l are
As shown in the figure, the grip portion 3 of the frame body 1
is supported by a clamp 5 that is rotatable in the direction of ball hitting on a rotating shaft 4, and the collision state between the ball B and the frame stringing part 2 is observed with the frame body 1 hanging down. In order to make it easier to compare the changes in the figures, each figure has been rotated by 90 degrees so that the shaft portion of the frame body 1 is in a nearly horizontal direction. and FIGS. 3a to 3 are also shown in the same manner.

[Problems to be Solved by the Invention] Therefore, as a result of various studies in view of the above circumstances, the inventor determined that the frequency of the natural vibration of the frame caused by the collision with the ball and the elasticity of the ball caused by the collision with the frame. This invention was completed by focusing on the correlation between the recovery of deformation energy and the repulsion characteristics.
When the ball is released from the frame, by making the deformation recovery direction of the ball and the vibration behavior direction of the surrounding frame the same direction, the behavior of the surrounding frame will be in the same direction with respect to the ball's traveling direction. To provide a racket frame that can effectively utilize vibration energy for acceleration and propulsion when a ball is reflected.

[Means for Solving the Problems] In order to solve the above-mentioned problems, the present invention provides a racket frame whose total weight is in the range of 260 to 370 g, and the primary natural frequency of the frame is set to 200 to 270 Hz. The racket mass and the racket primary natural frequency are preferably set within the range defined by the four coordinate points shown in FIG. The method for measuring the natural frequency of a racket frame used in As shown in the figure, the unstrung racket frame is supported in a suspended state by tying rubber strings 6, 6 at positions corresponding to one or two nodes at which the primary natural vibration occurs. The vibration is generated by striking the racket frame at a position corresponding to the most extreme part of the frame stringing part (section P shown in Fig. 8) using, for example, a plastic hammer. is applied once to generate bending vibration in the racket frame, and an accelerometer is fixed to the opposite side of the frame at the impact position P to measure the frequency.

[Operation] That is, by having the above configuration, the present invention can reduce the primary eigenfrequency of the frame to 200 to 270Hz.
Since the ball is set within the range of Since the behavior of the frame acts positively, vibration energy can be effectively used for acceleration and propulsion when the ball is reflected, thereby making it possible to improve the speed at which the ball is hit back.

[Examples] The present invention will be described below with reference to the embodiments shown in FIGS. 1 to 3. In the illustrated embodiment of the present invention, parts that have the same structure as the conventional racket frame shown in FIGS. 4 and 5 will be described using the same reference numerals.

That is, the racket frame according to the present invention has the primary natural frequency of the frame body 1 within the range of 200 to 270 Hz when the overall weight of the frame body 1 is in the range of 260 to 370 g as shown in FIG. Preferably, as shown in FIG. 1, the values of the racket mass (g) and the racket's primary natural frequency (Hz) are as follows.
Coordinates A (260, 220), B (260, 270), C (370,
250) and D(370, 200) within a range corresponding to the coordinates located within the diagonal line surrounded by the quadrilateral.

Here, the reason why the range of the primary natural frequency of the frame body 1 is set to 200 to 270 Hz is that if the primary natural frequency is less than 200 Hz, when the ball B is released from the frame stringing part 2 when hitting the ball at an off-spot, etc. The behavior (vibration) direction of ball B and the surrounding frame is opposite, and the behavior (vibration) of the surrounding frame is not only a positive factor in the propulsion of ball B, but also a negative factor. Because it will be.

On the other hand, the primary natural frequency of the frame body 1 is
Even if the frequency exceeds 270Hz, the behavior (vibration) of the frame will not be a negative factor for the repulsion performance of ball B, but in order to manufacture a highly rigid racket frame with a primary natural frequency exceeding 270Hz, This is because the weight of the racket exceeds the allowable weight (370g) using current manufacturing technology, making it unsuitable for use as a racket. By the way, when setting the primary natural frequency of the racket as described above, it is not necessarily specified by the constituent materials, shape elements, or molding method of the frame, but by the cross-sectional shape of the frame and the Young's modulus (EI distribution) of the material used. ) and weight distribution, and uses 100% of currently available high-modulus materials (e.g., high-modulus carbon fibers or boron fibers). In that case,
It is quite difficult to obtain the racket frame of the present invention with the general cross-sectional dimensions and shapes found in current products.

Therefore, specifically, the racket frame of the present invention has an outer shell structure in which the periphery is made of FPR, for example.
170mm in the same direction from the center point in the long axis direction of the frame stringing part, where a groove is formed along the circumferential direction of the frame, preferably on the outer periphery and, if necessary, on the inner periphery as well.
The primary frame required by setting the frame thickness distribution to the maximum within the range and setting the frame shape so that the average value of the frame thickness in that range is 22 mm or more. The natural frequency can be set, and for example, the cross-sectional shape of the frame stringing part 2 of the frame body 1 on which strings are stretched, that is, the cross-sectional moment of inertia, can be set to 2 to 3 times that of current conventional rackets. 7000
It is designed to have a diameter of about 9000 mm ⁴ and further has a high elastic modulus material such as high elastic modulus carbon fiber or boron fiber arranged at the optimum position.

According to the above configuration, since the primary natural frequency of the racket frame 1 is set within the range of 200 to 270 Hz, as shown in FIG. 3 in a fixed state, the ball B is fired toward the frame stringing section 2, and the ball B is hit back at off-spot portions such as the tip 2a side of the frame stringing section 2 and the grip section side 2b of the frame stringing section 2. Using a high-speed photographic camera, the vibrations of the frame were photographed continuously under the same conditions as before at time intervals of 1/2000 seconds. part or third
From the state of contact of the ball B at the grip side part of the frame stringing part as shown in Figures a to g, Figures 2h to 2
l, or the released state shown in FIG. 3 h to l,
In particular, when the ball B is released from the frame stringing section 2 when hitting the ball at an off-spot, at the time of release shown in Fig. 2 i to j or Fig. 3 i to j, the movement direction of the ball and the surrounding frame is the same direction. As a result, the behavior of the frame stringing section 2 around it will have a positive effect on the propulsion of the ball B, and there will be no vibrational loss for the propulsion when the ball is reflected, and the acceleration of the ball will be reduced. It becomes possible to use it effectively for promotion.

In the above embodiment, as a means of setting the primary natural frequency of the frame, for example, the second moment of area is increased by increasing the thickness in the bending direction of the frame having a CFRP outer shell structure using carbon fiber as a reinforcing fiber. and increased, but is not necessarily limited to this means, e.g. forming an outer shell structure
By using a higher modulus of FRP reinforcing fiber, or by changing the outer shell structure from a parallelogram to increasing the area of the outer shell material parallel to the bending direction, the partition wall surface forming grooves is increased. The same actions and effects as the present invention can be achieved by doing the following.

In addition, this invention can be modified in various ways without departing from the gist of the invention.

[Effect of the invention] As is clear from the above explanation, this invention has the following effects:
Since the primary natural frequency of the frame is set within the range of 200 to 270 Hz, when the ball is released from the frame at bat, the direction of reflection of the ball and the direction of movement due to vibration from the surrounding frame are the same. direction, and the behavior of the frame around it has a positive effect on the propulsion of the ball, so
Energy can be effectively used for acceleration and propulsion when the ball is reflected, thereby producing an excellent effect of improving the speed at which the ball is hit back.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram showing the setting range according to the relationship between the racket mass and the racket primary natural frequency of the racket frame according to the present invention, and Figs. Explanatory diagrams showing the continuous behavior from the state of contact between the frame and the ball when hitting the ball to the released state, Figures 3a to 1 also show the state of contact between the frame and the ball when hitting the ball at the off-spot part on the grip side of the stringed part of the frame. An explanatory diagram showing the continuous behavior up to the release state, Fig. 4 is a plan view showing a conventional general racket frame, and Fig. 5 also shows a state in which the ball collides with the racket at the off-spot portion of the racket frame. The explanatory diagrams, Figures 6a to 6f, show the continuous behavior of a conventional general racket frame from the contact state of the frame and the ball to the release state when the ball is hit at the off-spot portion on the tip end side of the frame stringing part when hitting the ball. The explanatory diagrams shown in FIGS. 7a to 7l are explanatory diagrams showing the continuous behavior from the contact state of the frame and the ball to the release state when hitting the ball at the off-spot part on the grip part side of the frame stringing part,
FIG. 8 is an explanatory diagram showing a racket supporting method for measuring the primary natural frequency of the racket frame. 1... Frame body, 2... Frame stringing section.

Claims (1)

[Scope of Claims] 1. A racket frame having a total frame weight in the range of 260 to 370 g, characterized in that the primary natural frequency of the frame is set within the range of 200 to 270 Hz.