EP0104930A1 - Rahmen für Sportschläger - Google Patents

Rahmen für Sportschläger Download PDF

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Publication number
EP0104930A1
EP0104930A1 EP83305749A EP83305749A EP0104930A1 EP 0104930 A1 EP0104930 A1 EP 0104930A1 EP 83305749 A EP83305749 A EP 83305749A EP 83305749 A EP83305749 A EP 83305749A EP 0104930 A1 EP0104930 A1 EP 0104930A1
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EP
European Patent Office
Prior art keywords
frame
string
region
racket
strings
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EP83305749A
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English (en)
French (fr)
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EP0104930B1 (de
Inventor
Tsai Chen Soong
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Individual
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Individual
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    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B49/00—Stringed rackets, e.g. for tennis
    • A63B49/02—Frames
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B49/00—Stringed rackets, e.g. for tennis
    • A63B49/02—Frames
    • A63B49/022—String guides on frames, e.g. grommets
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B49/00—Stringed rackets, e.g. for tennis
    • A63B49/02—Frames
    • A63B49/028—Means for achieving greater mobility of the string bed
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B49/00—Stringed rackets, e.g. for tennis
    • A63B49/02—Frames
    • A63B2049/0217—Frames with variable thickness of the head in the string plane
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B49/00—Stringed rackets, e.g. for tennis
    • A63B49/02—Frames
    • A63B49/03—Frames characterised by throat sections, i.e. sections or elements between the head and the shaft
    • A—HUMAN NECESSITIES
    • A63—SPORTS; GAMES; AMUSEMENTS
    • A63B—APPARATUS FOR PHYSICAL TRAINING, GYMNASTICS, SWIMMING, CLIMBING, OR FENCING; BALL GAMES; TRAINING EQUIPMENT
    • A63B51/00—Stringing tennis, badminton or like rackets; Strings therefor; Maintenance of racket strings
    • A63B51/02—Strings; String substitutes; Products applied on strings, e.g. for protection against humidity or wear
    • A63B51/023—Strings having characteristics varying along the length of the string, e.g. diameter or elasticity
    • 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

  • Frames for sports rackets, and particularly for tennis rackets present an engineering challenge. They must be strong enough to withstand enormous loads, be as nearly rigid as possible, and yet use only a few ounces of material.
  • a conventional tennis racket weighs approximately 355 to 411 grams; and its center of gravity is in the vicinity of its throat, which makes the weight attributed to the frame extending around the ball-hitting region from 170 to 199 grams.
  • This low weight of material must sustain a tremendous string load of up to 36 kilograms per string and a ball-hitting load of 46 kilograms or more, repeated for perhaps 40,000 shots without a failure. Understandably, sports racket frames have not yet-fully met such a challenge.
  • Steel frame rackets are known to be too flexible or "whippy". Since steel is heavy, its walls have to be made thin to remain light in. weight, giving its.-frame section insufficient moment of inertia for resisting bending and torsion loads.
  • Frame sections formed of aluminum alloy can have thicker walls and be more rigid, but they tend to permanently deform due to lower yield strength.
  • Alcoa heat-treatable 60-T6 series or 70 series improve the strength of aluminum considerably, but not enough to eliminate frame problems.
  • Frame strips presently used in metal rackets fall into two categories--oval or rectangular tubular section and I-beam section with solid or tubular flanges.
  • the tubular flange on both ends of the web provides torsional and bending rigidity resisting ball impact; and the thick web provides a bearing seat supporting string holes.
  • the I-beam section has the inherent problem of a marginal moment of inertia to resist the pulling load from the strings in the plane of the string surface, since most of the sectional mass is along the longitudinal axis of the frame to provide a solid seating for the strings.
  • the moment-of-inertia ratio between the axis perpendicular to the web and the axis coinciding with the web for the HEAD EDGE racket frame section is 7.6 to 1.0.
  • Another important advantage of my improved frame section is a longer free vibrational length for the strings, which substantially improves the performance of the string network.
  • the outer perimeter region may be formed with a central recess where the strings are supported, where the inner perimeter region is formed as an open channel having spaced apart edges, these channel edges may be turned inward toward the plane of the string network, where the inner perimeter region has a wall extending between the side regions and formed to provide clearance openings around the strings, this inner perimeter wall may be formed as a separate perforated strip secured to the side regions, foamed resin material may be disposed within the side regions and shaped to clear the strings, the outwardly facing surfaces of the side regions may have shallow central recesses, the sides of the lateral side regions having a string clearance depth of at least 0.64 cms, this string clearance depth may also extend to a nose region between the lateral side regions, the clearance of the support region from the strings is preferably sufficient to accommodate vibration of the strings on average impact with the ball without the
  • my improved frame anchors the strings at the outer perimeter of the frame strip and forms. a support region of the frame extending inward from the outer perimeter toward the ball-hitting region. Providing the support or mechanical strength for the frame section in regions formed inwardly from the outer perimeter anchorage adds a small but significant extra length to the nominal string length and thus enlarges the free vibrational area of the string network for the same size racket head.
  • FEM finite-element structural mechanical analysis
  • the major and minor radii of the ellipse are 16.33 cms and 14.05 cms, respectively.
  • the two lateral sides converge to the handle, and the analysis assumes that the end of the grip towards the shank region provides a fixed-end support to the racket. Since the racket and the load are symmetric with respect to the longitudinal axis of the racket, only one-half of the racket needs to be meshed.
  • FIG. 1 shows the mesh of the analyzed racket.
  • Nodes 1 and 29 are nodes to maintain symmetry with the right half of the racket.
  • the throat piece is joined rigidly with the side frame at node 20.
  • each node except nodes 1 and 29 in the elliptical circumference are loaded with a force of 987 grams in the z direction of FIG. 1.
  • the sum is 45.4kgs at the center of the network.
  • This static load is equivalent to a tennis ball having a weight of 57.9 grams traveling at 129 kph and being stopped within 0.0046 seconds in a constant deceleration. If a frame can sustain this static load for an indefinite time, it should be able to sustain a transient load with a peak load of much greater magnitude. So, this 45 kg sustained load may be taken as a realistic field load on a racket to repeatedly sustain a volley at a 160 kph ball speed.
  • each node from node 2 to 9 and from 17 to 27 bears a longitudinal string
  • each node from 5 to 21 bears a lateral string load.
  • FIGS. 2 and 3 show preferred cross-sectional shapes made according to the invention for frame strips analyzed and compared with a prior art frame as explained below.
  • FIGS. 2 and 3 show preferred cross-sectional shapes made according to the invention for frame strips analyzed and compared with a prior art frame as explained below.
  • Section 1 of FIG. 2 has a string hole or grommet seat 2 located at the outer perimeter where string 3 enters the frame and leads into the network.
  • the width 4 of seat 2 is as short as possible, about 0.5 cms or less. There is ample opening or cutout at the inner perimeter 5 to let the string vibrate without interference.
  • the height 6 in the sections of FIGS. 2 and 3 is about 2 to 2.5 cms but it can be reduced when stronger material than the Alcoa 6061-T6 is used.
  • the width 7, designated as d, is 2.5 cm for section 1 of FIG. 2 but can vary from 1.14 to 3.05 cms depending on objectives.
  • the height 6 is taken as 2.5 cms and d is varied from 1.14 to 2.54 cms
  • widths 7 less than 1.14 cms the design will not yield enough effective string length increase to benefit the performance. Widths greater than 3 cm. will make the frame strip too bulky.
  • the string clearance opening 8 can be round, oval, or rectangular in shape; and each string can have its own opening, or use an enlarged opening to accommodate several strings, so that in between holes 8, there is ample material to form a web to connect the upper side region 9 and lower side region 10.
  • the material removed from opening 8 can be added to the web between the neighboring openings, so that the wall thickness 11 can be the same as the side regions 9 and 10, whose thickness in section 1 is preferably about 0.14 cms for aluminum, for example.
  • inner perimeter 5 can form a continuous angle section with sides 9 and 10; and no web is needed for connecting the two sides at the inner perimeter.
  • openings 8, 12, and 13 are all illustrated in section 1 'for convenience, in actual practice, I prefer staggering or spacing openings 8, 12, and 13 along the length of a frame strip so that they do not all lie on a single section, for evenly distributing the material and strength along the frame strip length.
  • Openings 12 and 13 can be round, oval, or rectangular in shape, with the remaining web extending between side regions 9 and 16 and between 10 and 17. Openings 12 and 13 can also be shaped as triangles, leaving panels between openings inclined as in a truss assembly. Then the frame will have its outer and inner perimeters supported by a plane truss on each side of the string plane. This can be structurally more rigid.
  • Openings 12 and 13 reduce weight, as well as reduce air resistance when the racket is swung. This may be necessary when the section width 7 is more than '1.8 cms
  • For narrower sections one may simply omit the openings 12 and 13 and reduce the wall thickness to 0.064 cms shown in the section of FIG. 3, where only opening 8 remains. This narrower section is especially adaptable to graphite rackets.
  • FIG. 2 applies to the section of FIG. 3 except it has a shorter width 7, which is about 1.5 cms In the FIG. 3 section, there are no air openings 12 and 13. All wall thicknesses are the same as the larger width section of FIG. 2.
  • the side regions 9 and 10 in FIGS. 2 and 3 are 0.64 cms wide and -0.14 cms thick, and side regions 16 and 17 are 0.5 ems and 0.14 ems thick. These are'continuous flanges providing major bending rigidity to resist moments due to the string and ball impact loads. They also provide necessary mass to guard against damage when the racket hits the ground.
  • the thickness of string anchorage wall 2 at the outer perimeter of the frame section can be 0.089 cms for an aluminum section.
  • a plastic cushion strip can be provided to resist court-scuffing damage.
  • Side regions 14 and 15 can be inwardly curved or recessed along their outer surfaces to reduce damage when the racket hits the ground.
  • the inventive sections Due to the well balanced mass distribution, the inventive sections have extremely high ratios of strength to weight for torsion and bending in the two principal axes. These values were rigorously calculated and are reported next. Foamed polyurethane integral stuffing used to fill the internal space of the frame strip for damping purposes is an option, but its affect on strength and weight is not included. Although the sections of FIGS. 2 and 3 have the desired strength-to-weight ratios, changes are possible; and the invention is not limited to the illustrated sections.
  • any variation in sectional shapes for frames according to the invention preferably keeps the string clearance depth distance 18 to a maximum.
  • This string clearance depth is measured along a perpendicular to the frame section in the plane of the string network from the inner perimeter 5 outward to the point where a string 3 or grommet clears the inside of the outer perimeter anchorage region 2.
  • the outermost point where a string 3 can vibrate free from interference with the anchorage region is preferably located as close to the outer perimeter 2 of the frame as possible, and vibrational clearance is preferably provided for the strings from that point inward toward the ball-hitting region. The importance and extent of vibrational clearance for strings 3 is explained more fully below.
  • a racket having a generally conventional shape and made with a frame strip having a cross-sectional shape such as shown in FIGS. 2 and 3 is illustrated in FIG 4.
  • the cross-sectional shape of the frame strip used in the racket of FIG 4 can be formed as an extrusion or draw in which string openings 8 are bored, or it can be formed as an open channel extrusion to which an inner perimeter wall with preformed openings 8 is secured. Wood and graphite frames can vary from this, and different construction possibilities are explained more fully.
  • Figure 4A illustrates a frame with circular apertures formedin the upper and lower side regions 9 and 10. Those at the centre are slightly larger than those near the nose or shaft.
  • Figure 4B shows triangular apertures in the regions 9 and 10, making a lattice pattern.
  • Torsion Rigidity Torsional rigidity of a one-cell box with variable wall thickness, as shown in FIGS. 2 and 3, is given by the following equation: where ⁇ is the angle of twist per unit length, T is the torque applied, G is the shear modulus of the material, J eff is the effective polar moment of inertia, A o is the area bounded by the center line of the box, Li is the length of a particular segment, and ti is its wall thickness with i as the subscript index of that particular segment. There are eight segments of different wall thickness in the sections of FIGS. 2 and 3.
  • FIG. 5 shows a prior art drawn aluminum frame strip section presently used in the HEAD EDGE medium-sized head racket.
  • This particular section as detailed in U.S. Patent No. 3,899,172, issued August 1975, was said to have a very high strength-to-weight ratio.
  • the strength ratio of I/A which is the moment of inertia to the cross-sectional area ratio,'was said to range from 0 . 33 cm 2 to 0.37 cm 2 .
  • the maximum shear stress at the web occurs at a point on the outer boundary of the web on the y-axis, as shown in FIG. 5.
  • the shear stress is:
  • Table 1 shows the section properties where d is the width 7 of the section in FIGS. 2 and 3, varied from . 1.2 cm to 2.5 cm.
  • Table 2 is the strength-to-area ratio calculated from Table 1
  • Table 3 is the ratio of comparison of strength-to-area ratio based on Table 2, with the strength ratio of the prior art section of FIG. 5 taken as the base for comparison.
  • Table 3 shows that the inventive frame strip is far superior to the prior art frame strip in all respects.
  • inventive section having a width of 1.5 cm and a sectional shape as shown in FIG. 3, for example. This section is relatively narrow and does not need air holes in the side regions 14 and 15. Its cross section is 14.5% lighter than the prior art section.
  • Alcoa 61S-T6 taken at 2.71 gms/cc for a frame strip length of 117 cm the saving in weight of a complete racket is about 33.2 grams, which is about 9.4% of the total weight.
  • the inventive racket is 84% more stiff than the prior art racket in resisting ball impact load. This makes the returning ball fly back faster.
  • the inventive section is also 657% more stiff in resisting inplane load. This not only makes the racket extremely strong against permanent deformation during stringing, but also helps to make the racket more rigid in resisting the ball load. When the string netwbrk tightens to resist the penetration of the ball, it not only bulges out to contain the ball, but each string has to pull inward toward the center of the net.
  • a racket having a stiffer inplane rigidity which is represented by its I z value, will make the net hard to be pulled inward toward its center, hence a stiffer frame allows the network to store more energy and impart its larger stored energy to the rebounding ball.
  • the inventive racket is also 530% more stiff in torsion. This ridigity reduces the "whippy" feeling of a racket, which affects player accuracy and reduces the strain energy loss to the frame.
  • the inventive racket also increases the free vibration area of the string-network by increasing the free vibration length of its strings. Since the strings are anchored at the outer perimeter region of the frame and the support region, which includes the inner perimeter of the frame, does not interfere with free vibration of the strings, the strings have a free vibration length that extends within the frame section to the region of the string anchorage at the outer perimeter.
  • the free vibrational length of the strings is shown by the longer dimension L f extending for the full length of each string between the points where the string clears its anchorage at the outer perimeter of the racket frame.
  • This dimension L f applied over all the strings of the network gives a larger free vibration area than the conventional "string area" based on the dimension L s for
  • a medium-sized head racket having an inventive frame strip with a width of 1.93 em has a string network with a free vibration area equal to a conventional over-sized head racket.
  • the resulting medium-sized racket head is half an inch narrower in its overall width than an over-sized racket head and does.not look as large, even though it performs at least as well.
  • FIGS. 7 and 8 respectively depict the bending moment at each nodal section about the local z-axis and the axial force.
  • the shear force can be obtained from the equilibrium of moments at the two ends of an element. The shear is quite small, however, and is neglected. From FIGS. 7 and 8, it is clear that the stringing load on the frame is maximum at node 1, with a magnitude of 2.76 10 5 cm.gms for the 36 kg string tension system.
  • the axial force is compressive and is almost uniform at about 318 kgs from node 1 to 20 at the throat bracket.
  • the bending stress is maximum at the outer perimeter of a section with c z as the distance from the neutral z-axis.
  • the maximum bending stress for the two sections are also in that ratio, which is a ratio of six to one in favor of the inventive section. Since the cross-sectional areas A of each section are almost equal, the axial compressive stress is almost the same.
  • the critical stress allowed is 3267 k g /cm 2 Compared with the actual stress of 835 kg/cm 2 from the 36 kg string force system, the local instability of the thin web is of no concern at all.
  • the combined compressive bending stress at node 1 for the prior art section is more than 3500 kg/cm 2 .
  • the loads on the sections are linearly proportional to the applied loads. For example, if the bending moment acting at node 1 from the 36 k g string load system is .277 cm - kg then the moment becomes 346 cm - kg when the string load system is increased to 45 kg each, with all the other things remaining the same.
  • the load from the ball impact similarly increases the bending moment. Therefore, the information revealed in FIGS. 7 to 10 affords a very useful.loading reference for a tennis racket of conventional size and shape.
  • FIGS. 9 and 10 show loads on the frame strip at different node points from the impact of the ball.
  • the ball impact produces no axial force along the longitudinal axis of a section, but it produces two bending moments.
  • One is a twisting or torque moment, M x , about the longitudinal axis of the section.
  • M x twisting or torque moment
  • the twist in the shank region beyond node 20 can be reduced by stiffening the throat piece.
  • the maximum twisting torque is at node 19, which is about 150 cm - kg in magnitude.
  • the maximum material stress of the inventive section is only 71% of the prior art section, regardless of the actual size of the moment.
  • the stresses are 2716 aud 1949 kg/cm 2 respectively, in favor of the inventive section.
  • FIG. 11 shows the lateral deflection at node 1, at the nose of an aluminum racket, for a ball impact load of q. 5 kg.
  • the prior art section deflects twice as much as the inventive section at different section widths d.
  • Stiffer material can reduce the deflection, but the ratios remain, and the deflection is proportional to different impact forces.
  • comparisons between strength-to-weight ratios and magnitudes of stress and displacement for the inventive section and the prior art section are more important than absolute magnitudes, per-se.
  • inventive frame section shapes shown in FIGS. 2 and 3 and subject to the foregoing analysis principally apply to medium and large size racket heads with frames made of metal, graphite, and other high strength to area ratio materials. These especially accommodate a hollow-walled chamber shape of frame strip that can be used to advantage for stiffness, strength, and'longer effective string lengths.
  • FIGS. 12-14 Several variations from the shapes shown in FIGS. 2 and 3 are also possible and practical for these materials as illustrated in FIGS. 12-14.
  • Frame section 40 of FIG. 12 is formed as an open channel with inturned edges 41 and no inner perimeter wall.
  • a string anchorage web 42 is arranged at the outer perimeter of section 40 and supports strings 3.
  • Support regions 43 extending inward from anchorage region 42 on opposite sides of the plane of the string network provide strength and rigidity as explained above.
  • Side regions 43 and inturned channel edges 41 also clear strings 3 and allow them to vibrate freely for effectively increasing the free vibrational length of strings 3 to the region of their anchorage at outer perimeter 42.
  • the outer surfaces of side support regions 43 have shallow recesses 44 extending along the length of the frame to guard against damage when the frame is scuffed against the court.
  • Frame section 50 of FIG. 13 is also formed in an open channel configuration and is rounded and curved, rather than angular. Its string anchorage region 52 is also at its outer perimeter, and its supporting side regions 53 extend inward on opposite sides of the plane of strings 3. Except for clearance around strings 3, the interior of frame strip 50 is filled with a foamed resin material 54 that helps stiffen and strengthen the frame. String 3 vibrates clear of resin 54 all the way to the region of its anchorage at outer perimeter web 52.
  • Frame 60 of FIG. 14 is similar in overall shape to frame section 1 of FIG. 2. Its anchorage web 62 is also at its outer perimeter and supports strings 3. Openings 64 formed in supporting side regions 63 have edges 65 that are formed to bend inward as illustrated. This helps strengthen side regions 63 around opening 64.
  • section 60 has an inner perimeter wall 66 formed as a separate strip perforated with openings 67 having inturned edges 68 as illustrated and securely attached to the inner edges 69 of side regions 63.
  • Wall 66 and side edges 69 can be secured together by welding, for example.
  • Such construction allows perforations 64 and 67 to be die shaped with inturned edges 65 and 68 for greater strength and smooth outer surfaces.
  • string 3 can vibrate clear of support regions 63 and inner perimeter wall 66.
  • the invention can also be applied to solid frame tennis rackets made of solid materials such as laminates of wood, resins, fiber-reinforced composite materials, and graphite.
  • An example of this is illustrated by the inventive section 70 of FIG. 15.
  • section 70 can be square or rectangular in cross section as is conventional for racket frames of solid materials, it is shown in FIGS. 15 and 16 as a regular trapezoidal shape that advantageously positions its strength supporting material toward its inner perimeter 71.
  • section 70 in addition to conventional laminates 74 formed of wood, can have an outer laminate 72 in the string anchorage region at the outer perimeter of the frame section and an inner laminate 73 formed of a higher strength material such as a resin.
  • laminates of different materials possible, but cross-sectional shapes for solid frame rackets can be varied to take advantage of the inventive discoveries.
  • Openings 75 preferably formed as tapered ovals to remove as little frame material as possible, provide clearance within frame section 70 for free vibration of strings 3. This achieves the important advantage of extending the-free vibrational length of strings 3 to the region of their anchorage at outer perimeter 72.
  • Solid frames -formed of wood and other laminates as shown in FIG. 15 are especially suitable for conventional small head rackets. Although these afford a playing area of only 451 cm 2 , use of string clearance opening 75 can provide a free vibrational area for the string network of up to . 555 cm 2 This can-allow the network to perform with a larger dynamically vibrating area equivalent to a medium-sized head racket.' The increase in the racket head's overall width and length is only 1 cm.
  • Small size head rackets have a substantial appeal because the small head allows the straight and narrow part of the handle to be very long for players who like to use two-handed grips.
  • Medium and large size rackets have a flaring shank that effectively shortens the potential length of two-handed grips.
  • the invention enables the small racket head to retain the two-handed handle advantage while enjoying the performance benefit of a free vibrational string network area equal to that of a medium size racket.
  • Racket frame sections are not necessarily uniform throughout the length of the frame and can vary in width and shape. Frame sections according to the invention can accommodate this and can be shaped to accommodate the loads encountered at different regions of a frame. For example, greater widths, thicknesses, and strengths are appropriate in the throat, shank, and lateral side regions and thinner widths, thicknesses, and strengths in the nose region of a racket.
  • transverse strings of the string network it is especially important for transverse strings of the string network to have maximum free. vibrational length so that the string clearance depth of the frame section should be at a maximum along lateral side regions of the frame where transverse strings are anchored. Maximum string clearance depth is not so necessary for longitudinal strings anchored in the nose region of the racket.
  • the elliptical shape of conventional rackets makes longitudinal -strings longer than transverse strings, anyway.
  • Racket bead 80 of FIG. 17 is formed of a frame strip 81 that is wider in lateral side regions 82 than in nose region 83 for accomplishing both objectives.
  • the greater width of frame strip 81 in lateral side regions 82 not only increases the moment of inertia. against a twisting moment, but also allows a greater string clearance depth.
  • the inner perimeter 84 of frame strip 81 preferably has the same elliptical shape as a conventional racket head, and the widening of frame strip 81 in lateral side regions 82 is formed to increase the distance between the outer perimeter regions 85 where the transverse strings are anchored. This increases the free vibrational length of the transverse strings and makes them more effective components of the vibrating string network.
  • Widening of frame strip 81 in lateral side regions 82 is preferably sufficient to exceed the width of frame strip 81 in nose region 83 by at least 0.3 cm and preferably by about 0.9 cm.. Such" widening also preferably increases the string clearance depth by the same amounts to increase the free vibrational length of the transverse strings while also increasing the moment of inertia of the racket about its longitudinal axis.
  • String clearance depth for the inventive racket is measured perpendicular to the frame strip and in the plane of the string network. This distance extends from the inner perimeter of the racket frame along the string plane in a direction perpendicular to the frame strip to the point where the strings clear and depart inwardly from their anchorage at the outer perimeter of the racket. Support regions of the racket frame section extending inward from the string anchorage at the outer perimeter clear. the strings by a sufficient margin to allow their free vibration under normal playing conditions. Then the strings, instead of vibrating only within the area enclosed by the inner perimeter of the racket frame, vibrate throughout their entire length including their string clearance depth within the frame to the region where they contact their anchorage at the frame's outer perimeter.
  • the clearance of the support region: from the strings is preferably sufficient to-allow the strings to vibrate freely within an angle of at least 5° on either side of the plane of the string network.
  • Such a 5° clearance angle is adequate to accommodate string deflection, in response to a normal ball impact load.
  • An 7° clearance angle on either side of the plane of the string network is preferred for accommodating the most severe ball impact forces that a racket can be expected to encounter.
  • the inventive cross-sectional shape for a racket frame preferably has an intertia to area ratio about its z-axis (I z/ A) of between 0.7 to 1.2 3 cm 2 and about its y-axis (Iy/A) of between 0.39 to 0.65 cm 2 for a section having a height from , 1.65 to 2.29 cm and a width of from 1.54 to 2.16 cm and a wall thickness of from 0.13 to 0.20 cm. Comparing this with the section of U.S. Patent No.
  • Racket frames made according to my invention enlarge and maximize the free vibrational area of the string network and thus clearly improve racket performance.
  • My frames are also stronger, stiffer, and better able to withstand string load without being heavier. They are less likely to be deformed under stringing or ball impact load, are less whippy, and provide a larger sweet spot playing. area.

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EP83305749A 1982-09-27 1983-09-27 Rahmen für Sportschläger Expired EP0104930B1 (de)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US42445982A 1982-09-27 1982-09-27
US424459 1982-09-27

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EP0104930A1 true EP0104930A1 (de) 1984-04-04
EP0104930B1 EP0104930B1 (de) 1989-04-26

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Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4903967A (en) * 1989-01-27 1990-02-27 Ferrari Importing Company, Inc. Racket frame having holes for tailoring frame stiffness
US4930778A (en) * 1986-07-25 1990-06-05 Yamaha Corporation Racket frame
US4989870A (en) * 1988-05-16 1991-02-05 Spalding & Evenflo Companies, Inc. Tennis racket
FR2682881A1 (fr) * 1991-07-09 1993-04-30 Sumitomo Rubber Ind Cadre de raquette de tennis.
US5211398A (en) * 1988-02-19 1993-05-18 Yamaha Corporation Hollow tennis racket frame with matched frequency of vibration
EP0556495A1 (de) * 1992-02-21 1993-08-25 Tsai Chen Soong Durchlochter Rahmen für Sportschläger
EP0671186A1 (de) * 1990-11-26 1995-09-13 S.A. Donnay International Tennisschläger
GB2316623A (en) * 1996-08-27 1998-03-04 Robert John Seymour A racket frame string hole system
EP0884074A3 (de) * 1997-06-13 1999-02-10 Wilson Sporting Goods Company Spielschläger mit Schlitzen für Saiten in der Innenwand
GB2351027A (en) * 1999-06-17 2000-12-20 Dunlop Slazenger Group Ltd Games racket
WO2007088070A2 (de) * 2006-02-02 2007-08-09 Head Technology Gmbh Ballspielschläger

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JP6776883B2 (ja) * 2016-12-26 2020-10-28 住友ゴム工業株式会社 テニスラケットフレーム

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1470878A (en) * 1923-10-16 Tennis racket
GB199387A (en) * 1922-06-15 1923-11-08 Roland Malone Glenn Improvements in tennis rackets or the like
US1937787A (en) * 1928-06-13 1933-12-05 Roy H Robinson Tennis or squash racket
US3568290A (en) * 1966-06-13 1971-03-09 Dunlop Co Ltd Method of making rackets having metal frames

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US1470878A (en) * 1923-10-16 Tennis racket
GB199387A (en) * 1922-06-15 1923-11-08 Roland Malone Glenn Improvements in tennis rackets or the like
US1937787A (en) * 1928-06-13 1933-12-05 Roy H Robinson Tennis or squash racket
US3568290A (en) * 1966-06-13 1971-03-09 Dunlop Co Ltd Method of making rackets having metal frames

Cited By (14)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4930778A (en) * 1986-07-25 1990-06-05 Yamaha Corporation Racket frame
US5211398A (en) * 1988-02-19 1993-05-18 Yamaha Corporation Hollow tennis racket frame with matched frequency of vibration
US4989870A (en) * 1988-05-16 1991-02-05 Spalding & Evenflo Companies, Inc. Tennis racket
WO1990009213A1 (en) * 1989-01-27 1990-08-23 Ferrari Importing Company, Inc. Racket frame having holes for frame stiffness
US4903967A (en) * 1989-01-27 1990-02-27 Ferrari Importing Company, Inc. Racket frame having holes for tailoring frame stiffness
EP0671186A1 (de) * 1990-11-26 1995-09-13 S.A. Donnay International Tennisschläger
FR2682881A1 (fr) * 1991-07-09 1993-04-30 Sumitomo Rubber Ind Cadre de raquette de tennis.
EP0556495A1 (de) * 1992-02-21 1993-08-25 Tsai Chen Soong Durchlochter Rahmen für Sportschläger
GB2316623A (en) * 1996-08-27 1998-03-04 Robert John Seymour A racket frame string hole system
EP0884074A3 (de) * 1997-06-13 1999-02-10 Wilson Sporting Goods Company Spielschläger mit Schlitzen für Saiten in der Innenwand
GB2351027A (en) * 1999-06-17 2000-12-20 Dunlop Slazenger Group Ltd Games racket
WO2007088070A2 (de) * 2006-02-02 2007-08-09 Head Technology Gmbh Ballspielschläger
WO2007088070A3 (de) * 2006-02-02 2008-02-28 Head Technology Gmbh Ballspielschläger
US7967706B2 (en) 2006-02-02 2011-06-28 Head Technology Gmbh Racket for ball games

Also Published As

Publication number Publication date
EP0104930B1 (de) 1989-04-26
DE3379712D1 (en) 1989-06-01

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