Classifications

• • A—HUMAN NECESSITIES
  • A63—SPORTS; GAMES; AMUSEMENTS
  • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
  • A63B60/00—Details or accessories of golf clubs, bats, rackets or the like
  • A63B60/54—Details or accessories of golf clubs, bats, rackets or the like with means for damping vibrations

Definitions

• U.S. Patent 3,907,292 concerns a tennis racket the rim and the handle of which are surrounded by a tubular organ containing a series of fly-weights which normally rest in the throat portions of the tube due to the action of helical springs. Under use, the weights move toward the head of the racket because of the centrifugal force resulting from the racket swinging motion during play and increase the "sweet spot" of the stringed area; this also ensures a better bouncing control on the ball and an increased hitting power.
• U.S. Patent 3,941,380 (Lacoste) discloses a tennis racket in which the head oscillations are damped by means of a secondary oscillator working along the handle axis thereof at vibration antinodes. Since the oscillating bodies are located on the longitudinal axis of the racket, they do not affect the center of percussion and do not reduce the torque around the axis which results from an off-centered impact.
• U.S. Patent 4,057,250 discloses means to generate a reactive force for diminishing the bouncing of the racket after ball impact. For achieving this, masses producing the force must be able to move as freely as possible and, in this connection, the masses can even consist of loose metal shot.
• the device is not a secondary oscillator.
• the effect is distinguishable from the present invention since the increase of the moment of inertia of the racket in Kuban will only take place when the body has reached the end of its free elastic displacement which may be too late after the impact for being effective to increase the center of percussion. Moreover no damping of vibration is contemplated by an oscillator.
• French Patent 2,387,670 concerns a golf club, the head of which is provided with balancing weights which can vibrate in a direction perpendicular to the longitudinal axis of said head. This oscillating motion ensures that the orientation of the head is maintained during the interval starting from the moment the ball is hit by the head to the moment it loses contact therewith after being hit.
• the balancing weights increase the moment of inertia of the club in relationship to the hitting point of the head.
• these weights have first a static effect because they increase the club inertia and, second, they have a dynamic effect because they move in a direction perpendicular to the hitting plane of the head.
• Such displacements' generate moments of inertia around the striking point which are substantially equal and enable the head to stay properly oriented after striking the ball, this action being effective for the full distance where the head and the ball stay in contact.
• the object of the present invention is to increase the moment of inertia and the area of the "sweet spot" or center of percussion both longitudinally and transversely on a tennis racket to increase a players chance of striking the center, and at the same time to ensure the damping of the oscillation of the racket when the ball is nevertheless struck off-center. It is also an object to provide a tennis racket with improved angular stability over standard rackets, or those with static weights, on off- centered impacts.
• the invention provides a tennis racket having moveable or dynamic weights attached to the rim of the racket's head on both sides relative to the handle of the racket between the racket throat and the transverse axis of the head.
• the position of these weights increases the moment of inertia around both the longitudinal and transverse axes of the racket effectively enlarging the sweet spot or center of percussion in all directions.
• the moveable weights are coupled to said rim by elastic means whereby they can oscillate in a direction substantially perpendicular to the plane of the racket head with an intrinsic frequency 1.4-2 times that of the fundamental frequency of oscillation of the racket itself.
• This arrangement provides an unique weighting system chosen in a manner such that when the system consisting of the moveable weights and the elastic means is driven into vibration at the frequency 1.4-2 times that of the racket, the weights complete the first half of their cycle and apparently restore energy to the racket before the ball leaves the racket. Moreover, the moveable weights " with this critical frequency improve the angular stability of the racket over fixed weights or dynamic weights without the critical frequency.
• Figure 1 is a view partially in perspective of one embodiment of the invention using weights held in moveable straps.
• Figure 2 is a diagram showing the damping effect of a two-section oscillator chain which we believe may help explain the invention.
• Figure 3 is a comparative diagram of the vibration in two rackets of the same type, one of which is provided with the moveable weights according to the invention.
• Figure 4 is a perspective view of an alternative configuration of the present invention.
• Figure 5 is a perspective view at a greater scale of the weight system of Figure 4.
• Figure 6 is a graph showing the improvement in angular stability due to moveable weights having the critical intrinsic frequency range.
• Figure 1 shows a conventional tennis racket 1 comprising the head 2, the strings 3 attached to the head 2 and two side members 4 and 5 forming the throat of the racket connecting the head to the handle (not pictured) .
• the longitudinal and transverse axes are along lines 20 and 20 respectively.
• the racket comprises six moveable weights 6, consisting in this example of small cylinders of about 3g each, which are coupled to the head 2 by means of straps 7.
• the straps 7 consist of energy absorbent polyurethane or equivalent elastomer, 1 mm thick, glued at the top of the arcuate section of each strap on the underside thereof to the frame. These straps 7 constitute elastic means for allowing movement of the weights generally perpendicular to the plane of the racket head.
• the system composed of the straps and the moveable weights has an intrinsic oscillatory frequency and constitutes, with the racket itself, a two-section oscillator chain, each oscillator starting to vibrate with its own independent oscillating frequency whenever a ball impacts the racket strings 3.
• the straps and/or the weights are made of energy absorbent materials which may aid the damping of the racket vibration in addition to the attenuating effect of the oscillator chain.
• the moveable weights have multiple effects.
• the first effect of the weights 6 is to increase the moment of inertia of the racket around both the longitudinal and transverse axes of the racket and to increase the angular stability to an of -centered impact of a ball on the racket.
• Static weights would have a similar effect in increasing the effective size of the center of percussion, popularly known as the "sweet spot" of the racket, but the moveable weights, with the critical frequency, improve the angular stability over static weights as shown in Figure 6.
• the ordinate of the graph in Figure 6 is the ratio of the angular rotation for moveable weights over that for static weights.
• the abscissa shows the ratio of the intrinsic frequency of the weight system to the fundamental frequency of the racket. This analytical curve shows that over the frequency range of about 1.3-2 and also above 2.7, the angular stability is up to about 3% better with moveable weights than fixed weights.
• the additional weights be as light as possible relative to the racket so as not to impose an additional burden on the player.
• the weights make a total of about 20 g.
• the location of the weights must also be optimized in connection with the center of gravity and the moment of inertia of the racket. Placement of the weights as far as possible away from the longitudinal axis would maximize the moment of inertia but would require a larger compensating weight in the handle to retain the center of gravity at about point C in Figure 1, thereby increasing the total weight of the racket.
• Placement nearest the throat would require minimal compensating weight but would not have much effect on the sweet spot in the transverse directions.
• a compromise is preferably struck, according to the invention, by symmetrically locating the weights on the rim at angles between about 30 and 70 degrees from the longitudinal axis on both sides thereof between the transverse axis and the throat. This position also has the advantage that the sweet spot of the racket is elongated in both the longitudinal and the transverse directions of the racket thereby increasing the possibility of a good return of a tennis ball.
• the second and third effects of the weights are to damp racket vibration after impact and to restore a small but significant portion of the impact energy to the racket while the ball is still in contact.
• the reason for the energy restoration is complicated and not easily explained.
• the absolute values of the amplitudes , and A 2 related to a two-section oscillator chain system, as proposed for the present case are related to the impact excitation frequency ⁇ as schematically represented on the diagram of
• the oscillation period T, of the racket was measured by means of a strain gauge placed on a sample racket and was found to be 0.01 sec.
• the spring constant c legally must be between about 235 g(force)/mm and 485 g(force)/mm to ensure damping and restoration of energy to the racket prior to the impacting ball leaving the racket.
• the energy restored by two weight Q systems each consisting of 3 three-gram weights secured by three straps having spring constants in the range calculated above and weighing a total of one gram (therefore 2 ten gram weight systems) would be on the order of 5 2%, a seemingly small yet significant gain.
• Weights 6 and straps 7 having the properties determined above were divided into two groups, each group of three weights being located symmetrically on one side of the longitudinal 0 axis of the racket such as shown in Figure 1, at an angle of about 45° to the longitudinal axis.
• Various experiments and measurements have been performed on this racket. Firstly, comparative measurements have been effected on two identical rackets, one of them being provided with the added weights of the invention, the other being unmodified. Vibration damping coefficients on both rackets were measured.
• Figure 3 represents two diagrams, "a” and “b", of the damping of the vibrations, curve “a” corresponding to the control racket without the weights and curve “b” corresponding to the racket equipped with two groups of ten gram weights (three 3g weights held by a lg strap) . It can be seen that the damping rate of "b" is much faster than "a” as impact energy is transmitted to the moveable weights and the energy absorbing materials and then has been partially restored to the racket on the first cycle of the weights.
• racket "b" provided a better control of the ball especially in the case of overspin or sliced balls, i.e. when the surface of the racket is at a non-orthogonal angle with the path of the incoming ball.
• the half period of vibration of the added weights corresponds to about 60-70% of the contact time of the ball and the racket during the impact. Consequently, we have found that, as the weights move to the opposite side of the racket relative to the ball, energy temporarily stored in the moving weights is restored to the racket when the ball is still touching the strings. And the contact time is increased leading to better ball control. Moreover, after impact, the inventive weight system attenuates the vibration better than fixed weights and only slightly less' effectively than moveable weights having frequencies equal to the fundamental mode of vibration of the racket.
• FIG. 4 and Figure 5 illustrates a racket embodiment according 5 to the invention in which the weights and the suspending elastic means are incorporated within the frame of the head. Suitable adsorbent materials can be used in their construction. This frame, which is somewhat enlarged to accommodate
• each housing 8 is
• weights which are in the form of small cylinders 10, for example weighing 3g, and having each an annular groove 10a in their side wall.
• the cylindrical weights 10 are mounted axially within a helical
• 25 11 is assembled by putting each weight into its tubular housing 8, the base plate being inserted in a hollow area (not visible) located at one end of said housings 8. Another identical plate (not shown) is inserted in another similar
• Weight of the cylinders and stiffness of the springs are selected as in the case of the straps discussed above. Total added weight of about 20 grams is preferred. The important feature, however, is the frequency of the added mass/spring assembly.

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• Health & Medical Sciences (AREA)
• General Health & Medical Sciences (AREA)
• Physical Education & Sports Medicine (AREA)
• Golf Clubs (AREA)
• Vibration Dampers (AREA)
• Vibration Prevention Devices (AREA)

Priority Applications (2)

Applications Claiming Priority (2)

Publications (1)

Family

ID=22033325

Family Applications (1)

Country Status (6)

Cited By (7)

Families Citing this family (2)

Citations (8)

Family Cites Families (1)

• 1980
  • 1980-07-23 JP JP50193180A patent/JPS56500955A/ja active Pending
  • 1980-07-23 DE DE8080901593T patent/DE3067259D1/de not_active Expired
  • 1980-07-23 WO PCT/US1980/000943 patent/WO1981000214A1/en not_active Ceased
  • 1980-07-24 IE IE1541/80A patent/IE49957B1/en unknown
  • 1980-07-25 CA CA000357071A patent/CA1140608A/en not_active Expired
• 1981
  • 1981-02-09 EP EP80901593A patent/EP0032506B1/en not_active Expired

Patent Citations (8)

Non-Patent Citations (1)

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