Racket with reduced yoke rigidity

Details Racket with reduced yoke rigidity Racket with reduced yoke rigidity

2002-07-03

2004-02-10

Chiu, Raleigh W. (Department: 3711)

Games using tangible projectile

Player held and powered, nonmechanical projector, per se,...

Racket or paddle; accessory therefor

C473S521000, C473S537000, C473S546000

Reexamination Certificate

active

06688997

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a racket frame and in particular, a tennis racket frame lightweight and excellent in its restitution performance.
2. Description of the Related Art
In recent years, there is proposed a so-called “thick racket” which is thick in an out-of-plane direction (ball-hitting direction) of the ball-hitting face of the racket frame. Females and seniors need the thick racket because they want to hit a tennis ball thereby at a high speed with a small force. The tennis racket they want is lightweight and excellent in ball-flying performance.
However, in consideration of a collision between the racket frame and a ball, the lightweight racket frame has a low restitution coefficient, according to the principle of the conservation of energy. That is, the light weight of the racket frame causes deterioration of its restitution performance. As a method of improving the restitution performance of the racket frame without increasing its weight, partly changing the rigidity of the racket frame [partly] is proposed.
For example, to improve the restitution performance of the racket frame, the tennis racket disclosed in Japanese Patent Application Laid-Open No.9-285569 has a highly rigid material extended from its face-side part to an extension direction of its face part to improve the rigidity value of the face-side part and reduce the deformation of the face part when a tennis ball is hit.
The present applicant proposed a racket frame as disclosed in Japanese Patent Application Laid-Open No.10-295855. The sectional peripheral length of the racket frame is constant, and only the sectional configuration of a particular portion is altered to reduce the moment of inertia of the section and increase the rigidity in the out-of-plane direction of the ball-hitting face. This racket frame has improved restitution performance.
However, the tennis racket disclosed in Japanese Patent Application Laid-Open No.9-285569 has the problem that although the tennis racket is lightweight, it does not have sufficient restitution performance, and the balance is great owing to the extension of the highly rigid material in the face-side part. Thus the tennis racket has a low operability. Also, the insertion of the highly rigid material into a part of the face part causes concentration of a stress and hence the strength of the racket frame deteriorates.
The racket frame disclosed in Japanese Patent Application Laid-Open No.10-295855 is lightweight and has preferable restitution performance. However since the sectional peripheral length of the racket frame is constant, it is impossible to change its rigidity value greatly. Thus there is room for improvement in its restitution performance.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-described demands. Thus, it is an object of the present invention to provide a racket frame that is lightweight without deteriorating its strength and superior in its restitution performance.
In order to achieve this object, according to the present invention, there is provided a pipe-shaped racket frame having a racket-frame body made of a fiber reinforced resin and composed of a string-stretched part (head), a throat part, a shaft part, and a grip part sequentially arranged and a yoke connected to the racket-frame body. In this construction, supposing that the head is a clock face and that a top position of the head is 12 o'clock, a yoke rigidity value at a central position, which is a vertical direction to a ball-hitting face, of the yoke in a longitudinal direction, is in a range of 10% to 70% of a face rigidity value which is an average of a rigidity value of a vertical direction to the ball-hitting face at a 12 o'clock position of the head and at a three o'clock position of the head.
As a result of their energetic researches, the present inventors found out that a racket frame that is lightweight and has improved restitution performance without deteriorating its strength is obtained by setting the yoke rigidity value at the central position of the yoke vertical to the ball-hitting face smaller than the face rigidity value which is the average of the rigidity value at the 12 o'clock position of the head vertical to the ball-hitting face and the rigidity value at the three o'clock position of the head vertical to the ball-hitting face and by integrally molding a fiber reinforced resin having a hollow portion to form the racket-frame body.
By setting the yoke rigidity value vertical to the ball-hitting face smaller than the face rigidity value vertical thereto, the head does not deform easily owing to its high rigidity, whereas the yoke flexes easily with the ball-hitting face, owing to its low rigidity, when a ball collides with the string-stretched ball-hitting face. Thereby vertical strings (guts) can be deformed greatly. Thus it is possible for the racket frame whose body is made of a fiber reinforced resin to have improved restitution performance without deteriorating its strength.
The yoke rigidity value is set not less than 10% of the face rigidity value nor more than 70% thereof, favorably not less than 30% thereof nor more than 70% thereof, and more favorably not less than 35% thereof nor more than 50% thereof.
If the yoke rigidity value is set less than 10% of the face rigidity value, the yoke has a low strength. On the other hand, if the yoke rigidity value is set more than 70% of the face rigidity value, the yoke is not flexible sufficiently and thus the restitution performance of the racket frame cannot be improved.
The yoke rigidity value is measured at the central position of the yoke in its longitudinal direction, vertical (frame thickness direction) to the ball-hitting face. As will be described later, the rigidity value is measured by a three-point bending method at the central position between two racket frame-supporting points (the central position in the longitudinal direction of the yoke) 70 mm (2.75 in.) apart from each other. Supposing that the head is a clock face, the top position of the head is 12 o'clock. The face rigidity value is the average of the rigidity value at the 12 o'clock position vertical to the ball-hitting face and the rigidity value at the three o'clock position vertical to the ball-hitting face measured in a method similar to the above method.
The yoke rigidity value is not less than 60 kgf/cm (338 lbf/in) nor more than 500 kgf/cm (2820 lbf/in), favorably not less than 100 kgf/cm (564 lbf/in) nor more than 450 kgf/cm (2538 lbf/in), and more favorably not less than 200 kgf/cm (1128 lbf/in) nor more than 350 kgf/cm 1974 lbf/in).
If the yoke rigidity value is set less than 60 kgf/cm (338 lbf/in), the yoke has a low strength. On the other hand, if the yoke rigidity value is set more than 500 kgf/cm (2820 lbf/in), the yoke is not flexible sufficiently and thus the restitution coefficient of the racket frame cannot be improved.
It is preferable that the yoke consists of a fiber reinforced resin, a resin, a metal, a wood or a composite material thereof.
As a metal, it is favorable to use lightweight metal such as aluminum, titanium, magnesium, and the like or alloys containing one of these lightweight metals as the main component. To allow the racket frame to have a high vibration-damping effect, it is more favorable to use a fiber-reinforced thermoplastic resin. As a matrix resin, polyamide resin and a mixture of polyamide and ABS resin are preferably used. As a reinforcing fiber, a short carbon fiber is preferably used.
The yoke is manufactured by a method of injection-molding a thermoplastic resin or the like reinforced with short carbon fibers or the like; a molding method of weaving co-mingled yarns of a polyamide fiber and a carbon fiber into a braid and fusing a polyamide to impregnate the reinforcing fiber therewith; or a method of forming RIM nylon by injecting a RIM nylon monomer into a laminate consisting of foamed epoxy, a nylon tube coating the foamed epoxy, and a carbon br

Affiliated with

Also associated with

Rating

Racket with reduced yoke rigidity does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Racket with reduced yoke rigidity, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Racket with reduced yoke rigidity will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-3355300