This invention relates to vibration damped vibratile products, and to vibration damping units for use as components of vibratile products for damp¬ ing vibrations of those products, and the present application is a continuation-in-part of application Serial No. 534,065 filed September 20, 1983 (now abandoned) .

An object of this invention is to provide flexible vibration damping units for use as compon- ents of vibratile products and to have laminae and visco-elastic means in the unit interrelated in a worthwhile manner, for vibrations of the vibratile product to be damped through flexural relative move¬ ments of the laminae with reference to one another being retarded by the visco-elastic means in the unit.

Another object of this invention is the provision of a flexible vibration damping unit for use as a component of a vibratile product, with the unit being characterized by including a framework wherein flexible laminae are firmly secured together and the laminae relatively movably with reference to one another are adapted to co-act with visco-elastic means between the laminae when the unit is flexed. A further object of this invention is the provision of a flexible vibration damping unit for spot use as a component of a vibratile product and to combine, in this unit, firmly securely connected longitudinally relatively movable laminae with visco-elastic means interposed between the laminae,

and to afford compactly an appreciably large total surface area of the laminae which co-acts with the visco-elastic means in the unit.

Another object herein is that of provid- ing a vibratile product including at least one spot-located flexible laminar unit, of the character indicated, operatively interrelated therewith.

Other objects of the present invention in part will be obvious and in part pointed out more fully hereinafter.

As conducive to a clearer understanding of certain aspects of the present invention, it is noted at this point that a wide variety of vibratile products, during or after their production, are often needful of being equipped to suppress vibra¬ tions later to be developed within the body of the product. Among the many products within this gen¬ eral category are, by way of example, skis, whether for land or water use, hand-held impact implements such as tennis or badminton rackets, golf clubs, hammers, sledges and earth-digging implements, div¬ ing boards, helicopter blades, air foils, musical instruments having particular vibrations which desirably are to be suppressed, shipping cartons with vibratile walls or partitions, and structural panels, per se, tending to transmit sound or other vibrations, such as when installed in a building, a land vehicle or in an aircraft or marine craft. _

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The present invention accordingly provides vibration damping units as components for damping vibrations such as in the aforementioned and indeed numerous other vibratile products. It is observed by way of example that when land skis vibrate or flutter during travel at high speeds on icy slopes, or under other conditions of use, this hampers control, especially at turns along the course of travel, and, in the spirit of alleviat- ing difficulties encountered with vibrations or flutter, the prior art offers to add vibration or flutter damping means including a visco-elastic sub¬ stance to skis either by providing the vibration damping means substantially throughout the length of the ski inside the body of the ski, as in Patent 4,293,142 Davignon, or spot-located along the upper outside face of the ski, as proposed in Patent 3,537,717 Caldwell. Patent 3,844,576 Schultes offers a further example of ski damping means inte- riorily of the ski body and introduces in the damp¬ ing unit, which extends longitudinally throughout substantially the full length of the ski body, a strip enshrouded by or layered with a visco-elastic substance applied to the interior wall structure of the ski, having the strip anchored at one protruding longitudinal end portion directly to the wall struc¬ ture of the ski. In using vibration damping means added throughout substantially the length of the ski, there is a tendency to deaden the ski unduly. Further, when considering spot-located external

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damping means according to Patent 3,537,717 Caldwell, a flexible strip is used covered on one side with a visco-elastic substance and is applied to the ski having the visco-elastic substance next to the upper outside face of the ski body and, if desired, the remaining exposed face of the strip is covered with one or several superimposed strips, having a visco- elastic substance adjacent to the upper face of the strip next underneath, to contribute a vibration damping effect. Layering of strips as proposed in

Patent 3,537,717 Caldwell relies, without any unitary framework, only upon use of a lost motion thrust coupling afforded by the visco-elastic substance between any pair of strips and moreover would leave one of the strips in the pair prone to drift longi¬ tudinally relatively to the other of the strips in the pair and become dislocated as flexing continues.

By way of further example herein, stringed - rackets, such as tennis rackets or badminton rackets, after impact in normal use are prone to vibrate in the string frame and transmit vibrations from the string frame to the handle. In Patents 4,082,273 Ellzey, 4,105,205 Theodores and British 803,782, there is prior art for damping vibrations in stringed rackets; however, no vibration damping unit is pro¬ vided with any laminarly grouped portions being in a flexible framework wherein the strip portions are firmly secured together and associated with visco- elastic means to co-act while still being longi- tudinally relatively movable with reference to one another in the framework when the framework is flexed.

A further object of this invention accord¬ ingly is to provide a flexible laminar vibration damping unit to be spot-located along the length of. a vibratile product as a supplement to the body of the product, and in this to introduce a plurality of laterally opposed strips which in flexing are adapted to move relatively to one another while en¬ gaged with visco-elastic means between the strips and while the strips supplementally are firmly secured together in a skeletal framework in the unit to assure positive coupling under thrust and to resist strip dislocation.

In accordance with the present invention, laminar units for use as components of vibratile products to damp vibrations of the vibratile prod¬ ucts are provided. The units are characterized by including, in the unit, a flexible framework, com¬ prising at least one laminar group wherein flexible first strip means of the framework and longitudinally free-ended strip means of the framework are provided. The first strip means includes for the group a flex¬ ible first strip portion of the framework, and the longitudinally free-ended strip means comprises for the group at least one flexible longitudinally free- ended strip portion of the framework firmly secured to the framework first strip portion in the group, having the framework strip portions in the group in a longitudinally relatively movable interfacial relation to one another, for the framework strip portions in the group to be flexed and longitudinally

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relatively move with reference to one another. Visco- elastic means situated between the framework strip portions in the aforementioned group visco-elastically engages the framework strip portions in that group with one another, so that the framework strip por¬ tions, upon being flexed in the group, will longitud¬ inally relatively move with reference to one another and have those relative movements retarded by the visco-elastic means, such as when the vibration damp- ing unit is used as a component of a vibratile prod¬ uct and is responding to vibrations of the vibratile product.

In certain more particularly defined embod¬ iments in accordance with the. present invention vibration damping units are introduced for damping vibrations of vibratile products and are character¬ ized by including, in the unit, first and second laterally opposed strip means and intermediate strip means disposed between the laterally opposed first and second strip means. Longitudinally free-ended strip portions of the aforementioned intermediate and second strip means lap one another longitudinally in a sequence initiated from one of the two opposite longitudinal end portions of the aforementioned first strip afforded by the first strip means and are firmly secured progressively to one and the next of those two opposite longitudinal end portions of the first strip in a flexible framework having the longitudinal lead of one and the next of the longi- tudinally free-ended lapped strip portions progres¬ sively reversed. The longitudinally free-ended lapped strip portions have longitudinal reach in

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the unit and are engaged with the first strip and with one another by visco-elastic means in the unit so as longitudinally relatively to move laminarly with reference to one another and with reference to the first strip, in the unit, when the unit is flexed in response to vibrations of a vibratile product, and have those movements damped by the visco-elastic means.

According to certain other more particular embodiments of this invention, a first flexible strip afforded by the first of two laterally opposed strip means, and a plurality of longitudinally free-ended flexible strip portions afforded by intermediate strip means and the second of the two laterally opposed strip means, are interrelated in a vibra¬ tion damping unit having the longitudinally free- ended strip portions firmly secured to the first strip portion to be in a flexible framework with the first strip wherein the longitudinally free- ended strip portions lap one another in a plurality of sequences each initiated from the first strip with the longitudinal lead of one and the next of the longitudinally free-ended lapped strip portions in the sequence being progressively reversed. Among vibration damping units so characterized are those wherein one or more strips, each being inclusive of a pair of the longitudinally free-ended portions in the damping unit is or are interconnected by a con¬ nective portion of the strip firmly secured to an intermediate portion of the first strip, and other

of the longitudinally free-ended strip portions in the unit are members of strips which have connective portions thereof firmly secured either to one or the other of opposite longitudinal end portions of the first strip to dispose the several longitudinally free-ended strip portions longitudinally lapped with one another in two sequences each initiated from the first strip, having the longitudinal lead of one and the next of the longitudinally free-ended strip por- tions in the sequence progressively reversed. Vibra¬ tion damping units using plural sequences of the character described are further characterized by reach of the longitudinally free-ended strip portions in the sequence being adequate for the framework of the unit to be flexed in response to vibratile prod¬ uct vibrations and the longitudinally free-ended strip portions relatively to move one with reference to another in the sequences and relatively to the first strip, longitudinally laminarly, while visco- elastic means also used in the unit and disposed between the first strip and the longitudinally free- ended strip portions in the sequences damps those movements in response to the vibratile product vibrations. Vibration damping units in accordance with the present invention are operatively installed in certain instances either wholly inside or wholly out¬ side the bodies of vibratile products as vibration damping components of the products, and in certain other instances are installed operatively to be in

part inside and in part outside the bodies of the vibratile products as vibration damping components of the products, all as will be realized from illustrative embodiments which are hereinafter set forth.

In the ^* accompanying drawings, representing embodiments of this invention, and including embodi¬ ments thereof which are presently preferred:

Figure 1 is a longitudinal cross-sectional view of a vibration damping unit for use with a vibratile product;

Figure 2 is a schematic plan view of a vibratile product in the form of a ski having one of the vibration damping units of figure 1 installed inside the ski;

Figure 3 is a transverse cross-sectional view taken at 3-3 in figure 2;

Figures 4 and 5 are schematic plan views of skis wherein, in figure 4, vibration damping units according to figure 1 are located inside the ski, and in figure 5 are located outside the ski;

Figure 6 is a longitudinal cross-sectional view of a vibration damping unit generally in accord¬ ance with the unit of figure 1, but using a reduced number of strips in the framework;

Figures 7, 8 and 9 are longitudinal cross- sectional views representing other vibration damping units for vibratile products according to modified embodiments of this invention; Figure 10 is a plan view of a curved and thus modified vibration damping unit;

Figure 11 is a longitudinal sectional ele¬ vation of the vibration damping unit represented in figure 10, the section being along line A-A in figure 10; Figures 12 and 13 are opposite side eleva¬ tional views of a tennis racket including vibration damping units in situ as components thereof;

Figures 14 and 15 correspond to figures 12 and 13 and are outside and inside end views re- spectively of the outermost and innermost portions of the string frame of the racket in figures 12 and

13;

Figures 16 and 17 one and the other are longitudinal and transverse cross sections of the figure 12 racket handle structure, the sections re¬ spectively being along lines B-B and C-C in figure 12;

Figures 18 and 19 are details, comparable with figures 14 and 15, of modified structure of a tennis racket with vibration damping means;

Figure 20 is a view comparable with figure 19 and represents other modified tennis racket de¬ tails and related vibration damping means;

Figures 21 and 22 accompany the details of figure 20 and are comparable with figures 16 and 17;

Figure 23 is an isometric view represent¬ ing still another structurally modified vibration damping unit; Figure 24 is a side elevation of another tennis racket and related vibration damping units thereof;

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Figure 25 is a transverse cross-sectional elevation along line D-D in figure 24;

Figure 26 represents in side elevation still another modified vibration damping unit; Figures 27 and 28 are corresponding oppo¬ site side elevational views of outermost and inner¬ most portions of a tennis racket string frame having vibration damping units of the character of figure 26 as components thereof; Figures 29 and 30, respectively, are outer¬ most and innermost inside end views of the racket string frame represented in figures 27 and 28;

Figure 31 is a longitudinal cross-sectional view of another vibration damping unit and showing the unit installed; and

Figures 32 to 35 are longitudinal cross- sectional representations of still other vibration damping units which are also within the scope of this invention. Referring now more particularly to practices of the present invention and to the embodiment repre¬ sented in figure 1 of the accompanying drawings, a vibration damping unit 10 is provided comprising first and second laterally opposed cover strips 11 and 12 and a plurality of intermediate strips 13,

14 and 15, which notably are three in number in the present embodiment. All of the aforementioned strips are substantially equal in width to one another and are laminarly interrelated, the intermediate strips 13, 14 and 15 accordingly being covered by the first

and second strips 11 and 12. Connective longitudinal end portions 13a and 15a of the intermediate strips

13 and 15 are firmly secured to longitudinal end portion 11a of the first cover strip 11, and con- nective longitudinal end portions 12a and 14a of the second cover strip 12 and the intermediate strip

14 are firmly secured to the opposite longitudinal end portion lib of the first cover strip 11.

The firm securements referred to above as being in the unit 10 include lateral spacer means in the form of a plurality of shims 16 whereby the intermediate strips 13, 14 and 15 and the second cover strip 12 are laterally offset from one another and from the first cover strip 11 adjacent to the firm securements. Thus, in the present embodiment, the firm securements are achieved by securing to¬ gether the longitudinal end portion 11a of the first cover strip 11, the connective longitudinal end por¬ tions 13a and 15a of the intermediate strips 13 and 15, and those of the intermediate shims 16 related thereto, such as through use of a two-part epoxy cement or any other firmly setting adhesive, and by likewise securing together the opposite longitudinal end portion lib of strip 11, the longitudinal end portions 12a and 14a of the second cover strip 12 and the intermediate strip 14, and those of the intermediate shims 16 related thereto.

The laterally opposed cover strips 11 and 12 and the intermediate strips 13, 14 and 15 all are flexibly resilient in responding to vibrations,

and for example the several strips referred to are made of a hard flexible thermally set resin either with or without having a filler such as a layer of woven fabric, or other reinforcing material or mate- rials, embedded therein, or of resilient metallic material such as an aluminum base alloy or steel, of any suitable grade. If desired, the materials used in the strips may of course differ among the strips or within the strips themselves. A quite satisfactory strip material used for the purpose is a composite including an epoxy resin wherein woven graphite sheeting is embedded having the resin thermally set to lend flexibility and resilience, one such composite product being offered under the trade name "Magnamite" by Hercules Incorporated.

Notably, longitudinally free-ended strip portions 13b, 14b and 15b of the intermediate strips 13, 14 and 15 longitudinally are foreshortened to present longitudinal free ends 13c, 14c and 15c which are spaced an appreciable distance away from the adjacent shim means 16 thus relatively to move longitudinally laminarly with reference to one another and with reference to the first and second cover strips 11 and 12 when the unit 10 is flexed. The cover strip 12 meanwhile introduces a strip por¬ tion 12b having a longitudinal free end 12c movably outside the connective longitudinal end portion 15a of the intermediate strip 15 and, as preferred, is substantially of the same length as the first cover strip 11.

The outside cover strips 11 and 12 and the intermediate strips 13, 14 and 15 are members of a flexible framework wherein the longitudinally free- ended portions 13b, 14b and 15b of the intermediate strips 13, 14 and 15 and the longitudinally free- ended portion 12b of the second cover strip 12 in sequence, initiated from the firm securement of the connective longitudinal end portion 13a to the longi¬ tudinal end portion 11a of the first cover strip 11, progressively one to the next have a reversed longi¬ tudinal lead and are longitudinally lapped with one another to effect relative longitudinal movement with reference to one another and to the first cover strip 11 when the framework is flexed. It will be observed, too, that the opposite longitudinal end portions 11a and lib of the first cover strip 11, one and then the other progressively, have the con¬ nective longitudinal end portions 13a, 14a and 15a of the intermediate strips 13, 14 and 15 and the connective longitudinal end portion 12a of the second cover strip 12 one and the next sequentially firmly secured thereto adjacent to the shims 16 in the flexible framework so as to maintain the related longitudinally free-ended strip portions spaced- lat- erally apart from one another adjacent to the shims 16.

Visco-elastic means 17 in the unit 10 visco-elastically interengage_s the first cover strip 11 and the longitudinally free-ended portions 13b, 14b and 15b of the intermediate strips 13, 14 and 15

along with the longitudinally free-ended portion 12b of the second cover strip laminarly, for the unit 10 when secured to a vibratile product spot-located on the vibratile product to flex in response to vibra- tions of the vibratile product and damp those vibra¬ tions. In use of the unit 10, the first cover strip 11 is secured to the body of the vibratile product in any suitable manner, such as by cementing with a two-part epoxy adhesive or the like, having for ex- ample the first and second cover strips 11 and 12 and the intermediate strips 13, 14 and 15 longi¬ tudinally directed lengthwise of the vibratile prod¬ uct, so that the strips in the unit 10 will flex in response to the vibratile product vibrations and relatively move longitudinally with reference to one another while those movements are damped visco- elastically by the visco-elastic means 17. A tacky adhesive visco-elastic substance for the visco- elastic means 17 is beneficial, such as a silicone type material produced by C. E. Niehoff and Company and marketed as "Niehoff NL-3", for such adhesives serve to bond the strips in the vibration damping unit laminarly together while also producing a vibra¬ tion damping effect visco-elastically between the strips. To facilitate an understanding of the frame¬ work structure which is involved, the vibration damping unit 10, and most of the other vibration damping units disclosed in the accompanying drawings, are represented as having spacings between the grouped resiliently flexible strip portions in the

damping unit framework which are larger than those most often employed. When, as preferred, tacky visco-elastic adhesive means is included in the vibration damping units, this material usually takes the form of a thin layer reaching laterally from one to the next of the resiliently flexible strip portions of the framework, and thus the resiliently flexible strip portions of the framework are directly bonded laminarly together interfacially and visco- elastically by the adhesive thin layer means, such as with the latter in layer being even thinner than each of the adjacent resiliently flexible strip por¬ tions of the framework. Other visco-elastic mate¬ rials, which at times are substituted for a tacky visco-elastic adhesive still in accordance with the present invention, have a dough-like consistency enabling lamina of the visco-elastic material to be formed and interposed laminarly between the strips and be secured to the strips in the vibration damp- ing unit with a suitable adhesive. To accommodate this, the spacing between the flexible strip por¬ tions of the framework is altered as need may be.

Unit 10, though having the first and second cover strips 11 and 12 substantially fully interpose therebetween the intermediate strips 13, 14 and 15 along with the shim means 16 and the visco-elastic means 17, as preferred, is readily handled and in¬ stalled without appreciable contact with the visco- elastic means 17.

Toward providing examples of vibratile prod¬ ucts which are combined with vibration damping units in accordance with this invention, reference is had to the embodiment represented in figures 2 and 3, and to other embodiments represented in figures 4 and 5. In figures 2 and 3, a vibratile product in the form of a ski 50 has a top plastic layer 60, between which and a fiberglass load bearing full width layer 63 there are opposite protective side strips 61 of metal, such as aluminum base alloy, flanking a load bearing nar¬ row layer 62 of fiberglass. A core 69, wherein two wooden side layers 69a are interconnected by a strip 69b such as of steel, is flanked by a pair of phenolic type side walls 64 and is sandwiched, along with the side strips 64, between the load bearing fiberglass full width layer 63 and another load bearing fiber¬ glass full width layer, designated 68. There are spacer layers 65 such as of plastic on opposite sides of the ski 50 and these spacer layers are situated between the load bearing fiberglass full width layer 68 and a pair of steel runner members 66, the latter members being L-shaped in cross-section while having an intermediate bottom layer 67 of polyethylene against legs of those members. The above-described structure of ski 50 is sustained preferably through use of suitable connections such as adhesive bonds.

One of the vibration damping units 10 here¬ inbefore described is constructed to be about 2 milli¬ meters thick and in plan about 2 centimeters wide and approximately 45 centimeters long and has its

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rearward longitudinal end lOe (see figures 2 and 3) disposed at about the transverse centerline 51 of ski 50, which nominally is a ski 200 centimeters in length. The vibration damping unit 10 forwardly leads centered on the longitudinal centerline 52 of ski 50, having the first cover strip 11 secured at outside llg of strip 11 by epoxy cement to the inner face 67b of the polyethylene layer 67 (see figure 3) which forms an outer running face 67a of ski 50 and enables the unit 10 to flex with ski 50 in response to vibrations of ski 50. Meanwhile, the second cover strip 12 in the vibration damping unit 10 is disposed relatively to the load bearing fiberglass layer 68 so as longitudinally to move free-ended relatively to the layer 68 under constraint of the visco-elastic means 17 inside the unit 10 when unit

10 flexes in response to vibrations of the ski 50.

According to the embodiment in figure 4, three vibration damping units 10, each constructed also to be about 2 millimeters thick and about 2 centimeters wide, but in this about 30 centimeters long, are combined with a 200 centimeter ski 70 similar in structure to that of ski 50 in figures 2 and 3. A first of these three ski vibration damp- ing units 10 is situated having its forward longi¬ tudinal end lOf opposite the forward touchdown por¬ tion 73 of the ski 70 and longitudinally leads rear- wardly and centered on the longitudinal centerline 72. of the ski 70. The second of the units 10 has the rearward longitudinal end lOe thereof at

approximately the transverse centerline 71 of ski 70 and in leading longitudinally forwardly is centered on the longitudinal centerline 72 of ski 70. The last of the three units 10 is disposed with its rear- ward end lOe opposite the rear touchdown portion 74 of ski 70 and in leading longitudinally forwardly is centered on the longitudinal centerline 72 of ski 70. All three of the units 10 are situated inside the ski body in the position indicated and are secured to and interrelated with the ski body in a manner already described with reference to the figure 2 embodiment.

In figure 5, a ski 80, also 200 centimeters in length, is by way of example without a ski vibra- tion damping unit thereon at the rear and relies upon two forward vibration damping units 10 dimensioned about the same as the two forward damping units in figure 4. In this instance, the two vibration damp¬ ing units 10 are located in much the same general positions along the length of ski 80 as are the for¬ ward two vibration damping units for ski 70 in figure 4, but are disposed externally of the ski 80 having their first cover strips 11 secured at outer face to the top layer 60' of ski 80, for these units 10 to flex with ski 80 and damp vibrations of the ski.

In the embodiment of the present invention represented in figure 6, the first and second cover strips 11' and 12' in a vibration damping unit 10' for vibratile products are associated with only one intermediate strip therebetween, this being designated

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by the reference numeral 13*. In a progression of connections similar to that used in the figure 1 embodiment, a connective longitudinal end portion 13a ¹ of the intermediate strip 13* is firmly secured through shim means 16' to a longitudinal end portion 11a ¹ of the first cover strip ll ¹ and a connective longitudinal end portion 12a ¹ of the second cover strip 12' is firmly secured through further por¬ tions of the shim means 16' to the opposite longi- tudinal end portion lib ¹ of the first cover strip 11' , leaving a free longitudinal end 12c' of the second cover strip 12' laterally outside the con¬ nective longitudinal end portion 13a* of the inter¬ mediate strip 13' , with the intermediate strip 13' longitudinally being foreshortened, for the unit 10' to be flexurally used with visco-elastic means 17' also present, for purposes similar to those herein¬ before described with reference to the figure 1 embodiment. Turning now to an embodiment of this inven¬ tion according to figure 7, a vibration damping unit 20 is characterized by two sequences of longitudinally lapped free-ended resiliently flexible strip portions both initiated from a first resiliently flexible cover strip 21. In each of the sequences, the longi¬ tudinal lead of the free-ended strip portions re¬ verses from free-ended strip portion to free-ended strip portion progressively throughout the sequence. Thus, it will be seen that in the first of the two sequences longitudinally free-ended strip portions

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22a, 24a, 25a and 27a are involved and that in the other of the two sequences the longitudinally free- ended strip portions 23a, 24b, 26a and 27b are in¬ volved. The longitudinally free-ended strip portions 22a and 25a are members of resiliently flexible inter¬ mediate strips 22 and 25 in the unit 20 which include connective longitudinal end portions 22c and 25c firmly secured to a first longitudinal end portion 21a of the first cover strip 21, while the longitu- dinally free-ended portions 23a and 26a are members of resiliently flexible strips 23 and 26 which have connective longitudinal end portions 23c and 26c firmly secured to the opposite longitudinal end por¬ tion 21d of the first cover strip 21. Strip 24, also being an intermediate resiliently flexible strip in the unit 20, includes the two longitudinally free- ended strip portions 24a and 24b in common intercon¬ nected by a longitudinally generally central connec¬ tive portion 24c which is firmly secured to a longi- tudinally generally central portion 21e of the first cover strip 21. Strip 27, which is a second resil¬ iently flexible cover strip -and is laterally opposite the first cover strip 21, comprises the two longi¬ tudinally free-ended strip portions 27a and 27b, which in common are interconnected by a longitu¬ dinally generally central connective strip portion 27c firmly secured to portion 21e of the first cover strip 21.

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Visco-elastic means 28, preferably of tacky grade, is disposed between and visco-elastically en¬ gages the first cover strip portion 21b and the longi¬ tudinally free-ended intermediate and second cover strip portions 22a, 24a, 25a and 27a in the first sequence, and is between and visco-elastically en¬ gages the first cover strip portion 21c and the longi tudinally free-ended intermediate and second cover strip portions 23a, 24b, 26a and 27b in the second sequence and, as preferred, the connective portions 22c, 23c, 24c, 25c, 26c and 27c are laterally offset in the sequence progressively from the first cover strip 21 by lateral spacer means which in the present embodiment includes shims 29 through which the firm securements to the first cover strip 21 are made as with a firm-setting adhesive. The longitudinally free-ended intermediate strip portions 22a, 23a, 24a, 24b, 25a and 26a are longitudinally foreshortened to allow those portions to co-act longitudinally rela- tively movably laminarly with the first cover strip portions 21b and 21c and the laterally free-ended second cover strip portions 27a and 27b in the respective sequences and have the visco-elastic means 28 damp vibrations when the unit 20 is flexed. Cover strips 21 and 27 advantageously lengthwise and widthwise substantially fully interpose the intermediate strips 22, 23, 24, 25 and 26 there¬ between along with the visco-elastic means 28 and the shim means 29 and also in the present embodiment the first and second cover strips are substantially

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equal in length and width having the longitudinally free-ended portions 27d and 27e of the second cover strip 27 longitudinally movably substantially fully cover the connective longitudinal end portions 25c and 26c of the adjacent intermediate strips 25 and 26 while engaged therewith by the visco-elastic means 28. Unit 20 is adapted to have the outside face of the first cover strip 21 secured as by adhering with a firmly settable two part epoxy cement so as to be a vibration damping component of a vibratile product.

In a modified embodiment in accordance with this invention, and represented in figure 8, a vibration damping unit 30 depends upon having the second cover strip means include a pair of longi¬ tudinally free-ended cover strip portions 35a and 36a of a pair of second cover strips 35 and 36, and the unit 30 otherwise is similar to that in the figure 7 embodiment. Connective longitudinal end portions 35c and 36c of the pair of second cover strips 35 and 36 are firmly secured through shim means 38 to the longitudinal end portions 31c and 31d of the first cover strip 31. The pair of second cover strips 35 and 36 are longitudinally fore- shortened with reference to one another adjacent to the connective portion 34c of the intermediate strip 34 and are visco-elastically engaged with the latter strip by visco-elastic means 37 in the unit 30.

Vibration damping unit 40 according to a still further embodiment of this invention is repre¬ sented in figure 9, and is intended for use with a vibratile product such as in a manner hereinbefore described and provides also two sequences of lapping of resiliently flexible strips in conjunction with visco-elastic means interengaging the strips. Thus, a pair of strips 42 and 45 at longitudinally gen¬ erally central connective strip portions 42c and 45c thereof are firmly secured through portions of spacer means 48 to the longitudinally generally central portion 41e of a first cover strip 41, the strip 45. being a second cover strip and strip 42 being an intermediate strip. Intermediate strips 43 and 44 in the unit 40 have connective longi¬ tudinal end portions 43c and 44c firmly secured through other portions of the spacer means 48 to opposite longitudinal end portions 41c and 41d of the first cover strip 41 and include longitudinally free-ended strip portions 43a and 44a which are longitudinally lapped with longitudinally free-ended portions 42a and 42b of strip 42 and with longi¬ tudinally free-ended portions 45a and 45b of the second cover strip 45 in the presence of visco- elastic means 47 which interengages visco-elastically the several strips in unit 40 for the strips to move relatively to one another longitudinally when the unit 40 is flexed in response to vibratile product vibrations.

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A modified form of vibration damping unit 60, also within the scope of the present invention, is represented in figures 10 and 11 and has the laminarly superimposed flexible resilient strips 61, 62, 63 and 64 thereof curved in the plane of the strip and curving from longitudinal end to longi¬ tudinal end of the strip. Furthermore, the strips 62, 63 and 64 have widths similar to that of strip 61 and are firmly secured in a sequence to strip 61 through shims 65 and 66 in a manner similar to that in the sequence in figure 1. Visco-elastic means 60a is situated between the several strips 61, 62, 63 and 64 and visco-elastically engages those strips for the visco-elastic means 60a to damp vibrations which cause the strips 61, 62, 63 and 64 to flex, and relatively move longitudinally with reference to one another.

As illustrative of damping vibrations of tennis rackets in accordance with the present inven- tion, reference is had to a tennis racket 70 repre¬ sented in figures 12 to 17. One of the curved vibra¬ tion damping units 60 is operatively applied leading longitudinally along one side of outermost end por¬ tion 71a of the racket string frame 71. In the . present embodiment, a notch 72 is provided in the aforementioned side of the outermost string frame portion 71a and has a depth which is substantially equal to the over-all thickness of the damping unit 60, and a width which is slightly more than equal to the length of unit 60, so that the outer face

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afforded by strip 62 in unit 60 is substantially flush with the related side facial areas of the racket string frame 71 which lead away from notch 72. The width of unit 60 is substantially equal to the width of the curved string frame 71 along the notch 72, thus for the unit 60 substantially to fill the latter notch in view of the other dimensional interrelations hereinbefore described. Strip portion 61 of the unit 60 is secured to the base of notch 72 as by means of a two part epoxy adhesive. In a modified figure 18 embodiment, two of the vibration damping units 60 are installed laterally opposite one another on opposite sides of the outermost end portion 71a' of the string frame 71' of tennis racket 70', and are interrelated with notches 72' in the string frame 71' and connected with racket 70 ^τ as by cementing strips 61' thereof in place in a manner hereinbefore described with reference to figure 14, for co-operatively damp¬ ing vibrations in the outermost end portion 71a' of the string frame 71'.

Turning again to figure 12, and also having reference also to figures 16 and 17, it will be seen that the tennis racket 70 is further equipped with a vibration damping unit 80 which for example is of a type described hereinbefore with reference to figure 1. One end portion of damping unit 80 is situated inside a hollow handle 75 of racket 70 and projects outside an opening from the inner end 75a of the handle, thence bridging across the racket handle crotch space over to the innermost end portion 71b of the string frame 71. A notch 73 into one side of

the innermost end portion 71b of the string frame 71 is slightly more than equal in width to the width of vibration damping unit 80, and substantially equal in depth to the thickness of damping unit 80, thereby receiving one longitudinal end of the latter damping unit and having that one end firmly secured in place to the base of notch 73 at the outside face of the flexible strip of the unit which has the longitudinally free-ended strips of the unit firmly longitudinally relatively movably secure thereto. This same strip outside face in the damp¬ ing unit 80 is firmly secured to the racket handle 75 inside the hollow of handle 75 so as to have unit 80 effective for amplifying the stroking force of racket 70 by rigidifying the racket and for damping vibrations in racket 70 which otherwise would be intensified in the handle 75. Notably, too, the innermost portion 71b of the string frame 71 of racket 70, as represented in figures 13 and 15, has a notch 76 in the side face thereof which is opposite the notch 73. Notch 76 is wider than notch 73 so as to receive a curved vibration damping unit 85 which is similar to but somewhat longer than the curved damping unit 60 hereinbefore described. Vibration damping unit 85 is dimensioned and installed in the spring frame notch 76 so as operatively to be sub¬ stantially flush with the string frame faces outside the notch 76, for thereafter damping vibrations in the innermost end portion 71b of the string frame 71 while the racket 70 is in use.

In a modified embodiment represented in figure 19 and which is similar otherwise to that of figure 12, a wide notch 77 is added in the innermost end portion 71b of the string frame 71 and feeds at the center into a secondary narrower notch 73' . Notch 77 accommodates another one of the curved vibration damping units 85 having the latter firmly secured operatively to the string frame opposite the other damping unit 85 to damp vibrations in the innermost end portion 71b of the string frame.

Meanwhile, the position of the adjacent end of the substantially straight vibration damping unit 80 has been modified to be within notch 73' behind the covering vibration damping unit 85 in notch 77 for the damping unit 80 as thus installed to operate in a position and manner similar to that hereinbefore described with reference to figure 12.

In certain embodiments, such as that repre¬ sented in figures 20, 21 and 22, two of the sub- stantially straight vibration damping units 80 are used extending from opposite sides of the lowermost end portions 71b of the racket string frame 71 into the handle 75, co-operatively to damp vibrations in the racket while a pair of curved vibration damping units 85 are used on opposite sides of the innermost end portion of the string frame 71 for damping vibra¬ tions of the string frame 71.

In an embodiment of this invention accord¬ ing to figure 23, a laminar vibration damping unit 90, provided to be used as a component of a vibratile

product, includes a plurality of flexible resilient bi-furcated strips 91, 92, 93 and 94 which contribute as portions of a framework of unit 90 wherein the stem strip members 91a, 92a, 93a and 94a are laminarly superimposed, the furcations or branch strip members 91b, 92b, 93b and 94b are laminarly superimposed and the furcations or branch strip members 91c, 92c, 93c and 94c are laminarly superimposed. The bi-furcated strips 92, 93 and 94 in the flexible framework of unit 90 are firmly secured to the bi-furcated strip 91, the firm securements as by cementing for strips 92 and 94 being made adjacent to the ends of the stem strip members 92a and 94a through shims 95 to the corresponding end portion of the stem strip member 91a, leaving the stem strip member 93a longitudinally free-ended at 93d. Branch strip members 93b and 93c of strip 93 are firmly secured through shims 96 and 97 as by cementing to branch strip members 91b and 91c of strip 91, leaving the strip 92 longitudinally doubly free-ended as seen at 92d and 92e and the strip 94 longitudinally doubly free-ended as seen at 94d and 94e. The strips 91, 92, 93 and 94 accord¬ ingly in the framework are longitudinally relatively movable with reference to one another when the frame- work is flexed. The strips 91, 92, 93 and 94 are interengaged by a visco-elastic substance 98, which damps the relative longitudinal movements of the strips 91, 92, 93 and 94 when the vibration damping unit 90 is flexed. The branch strip members 91b, 92b, 93b and 94b and the branch strip members 91c,

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92c, 93c and 94c may be provided curved in the plane of the strip bi-furcation, if it is desired to have the vibration damping unit 90 conform to a given related curvature of a vibratile product with which the damping unit is to be used. For equpping a tennis racket 100 in accordance with figure ^' s 23, 24 and 25, curvature is introduced in the furcations of unit 90 to conform to curvature of tennis racket crotch-forming frame members 104 and 105 (see figure 24) which lead from an innermost end portion 102b of the string frame 102 in the tennis racket 100 and merge with the racket hollow handle structure 101. As will be understood from figures 23 and 25, the stem strip portions 91a, 92a, 93a and 94a of the damping unit 90 framework are substantially straight for the stem of unit 90 to extend from the furca¬ tions into the inner end of the hollow handle 101. Unit 90 has the outer face of the bi-furcated strip 91 firmly secured to racket 100 inside the handle 101 and to side surfaces of the racket on the crotch- forming members 104 and 105 outside the handle 101, thus for the unit 90 to damp vibrations initiated in the string frame 102 of the racket 100 and amplify stroking power of the racket by rigidifying the racket. If desired, another unit 90 (not shown) may be introduced upon the racket crotch-forming frame members 104 and 105 on the opposite side of the racket 100 from the first unit 90 and into handle 101, thus for two units 90 co-operatively to damp vibrations in the racket.

Vibration damping units in accordance with the present invention, when produced to be substan¬ tially flat initially in the plane of the flexible strip portions of the framework therein, are readily installed substantially flat against a corresponding substantially flat surface of a vibratile product which is to be vibration damped by the damping unit. Up to limits, the substantially flat vibration damp¬ ing units may be flexed, thereby arching or curving the laminar group or groups of the flexible strip portions of the framework out of the planes of those flexible strip portions in the laminar group or groups in the units, so as to provide a curvature of the damping unit substantially in conformity to a corre- sponding curvature of a face of the vibratile product to which the damping unit operatively is to be secured. Especially to avoid bending of a substan¬ tially flat vibration damping unit beyond permissible limits, curved vibration damping units also are pro- duced in accordance with this invention, having the laminar group or groups of flexible strip portions of the damping unit framework curved to retain sub¬ stantially sharp curvatures laminarly in the group or groups in a relaxed condition of the framework. One of the latter types of vibration damping units is represented in figure 26 and is designated in general by the reference numeral 10". Damping unit 10" is similar in construction to the hereinbefore described damping unit 10 in the figure 1 embodiment, except that with having the flexible framework in unit 10"

in a relaxed condition the flexible resilient lam¬ inarly related arched strip portions 11", 12", 13", 14" and 15", joined by the visco-elastic means 17", are sharply curved in the laminar group retentively out of the planes of those strip portions in the laminar group, the curvatures being substantially equivalent to curvatures having radii of less than say about six inches, so that the damping unit 10" more readily conforms, in being installed, to the supporting face of a tennis racket 110 represented in figures 27 to 30 herein. Notably, in figures 29 and 30, there are notches 112 and 113 entering from the opposite sides and inner rim of racket 110 in the outermost portion Ilia of the string frame 111 of the racket, and there are notches 114 and 115 entering from the opposite sides and inner rim of racket 110 in the innermost portion 111b of the string frame 111 of the racket, and each of these notches has one of the vibration damping units 10" ^' secured therein to the racket string frame 111 for damping vibrations in the racket. The longitudinal racket strings 116 pass between adjacent laminar sides of the units 10" into the string frame 111. If desired, of course, one of the units 10" may be omitted from each of the outermost and innermost por¬ tions 11a and lib of the racket frame 111, or only one of the units 10" may be used in the racket 110, selectively in one of the four positions represented in figures 27 to 30. Supplemental vibration damping means (not shown) may if desired be added to racket

110 in any event, such as by connecting a bi-furcated damping unit 90 (not shown) according to figure 24 to racket 110 in a manner akin to figures 24 and 25. Vibration damping unit 30' being a modifi- cation of the damping unit of figure 8 and repre¬ sented in figure 31 is for example generally rectan¬ gular in plan. Unit 30' is characterized by the addition of hollow rivets 119, 120 and 121 which pass through bores through the related flexible resilient strip portions and the shim means 38 ^τ of the unit 30' in the regions wherein the hollow rivets 119, 120 and 121 either supplement the firm securements had by cementing in a manner hereinbefore described with reference to figure 8 or act alone as clamps to effect the firm securements. Unit 30* lends itself to being installed as a component of a vibratile product 115 by cementing strip 31' to the body of the vibratile product and/or by screws 122, 123 and 124 or other suitable headed fasteners which lead through the hollow rivets 119, 120 and 121 and engage the unit 30' with the body of the vibratile product 115. As installed, the unit 30' avails upon visco-elastic means 37' therein to produce a vibration damping action when unit 30' is flexed in response to vibra- tions in the body of the vibratile product 115.

Each of the vibration damping units 130, 140, 150 and 160 represented as still further embodi¬ ments of this invention in figures 32, 33, 34 and 35 ^* respectively are by way of example generally rectan- gular in plan. Unit 130 in figure 32 comprises two

flexible resilient strip members 131 and 132 lami¬ narly superimposed and of substantially the same rectangular dimensions, and at one set of adjacent longitudinal ends the strip members 131 and 132 are firmly secured together through intermediate shim means 133 as by cementing to produce a flexible frame¬ work and have adjacent opposite longitudinal ends 131a and 132a whereby the strips 131 and 132 can relatively be longitudinally moved by flexure. Strips 131 and 132 are engaged at interface by visco- elastic means 134 which retards the relative longi¬ tudinal movement of the strips 131 and 132 when the unit flexes in response to vibrations while either having strip 131 or strip 132 secured to a vibratile product.

Vibration damping unit 140 in the figure 33 embodiment is similar to the unit 130 of figure 32, but has three flexible resilient strips 141, 142 and 143 laminarly superimposed and firmly secured together at first longitudinal ends through shims 144 to pro¬ vide adjacent longitudinally-free opposite ends 141a, 142a and 143a. Visco-elastic means 145 interfacially engaging the strips 141, 142 and 143 enables unit 140 to damp vibrations while secured at the outer face of either strip 141 or 143 to a vibratile product as a component thereof.

In the vibration damping unit according to figure 34, there are three flexible resilient laminarly superimposed generally rectangular strips 151, 152 and 153 dimensioned substantially alike rectangularly so

as to present a first set of adjacent longitudinally free ends 151a, 152a and 153a and an opposite set of adjacent longitudinally free ends 151b, 152b and 153b. Centrally of the aforementioned sets of longitudinally free ends, the flexible strips 151, 152 and 153 are firmly secured together through interposed shim means

154 as by cementing. A first group of flexible strip portions 151c, 152c and 153c and a second group of flexible strip portions 151d, 152d and 153d are in a resulting flexible framework. Visco-elastic means

155 between the strip portions in the groups engages the strip portions in the groups for visco-elastically retarding relative longitudinal movements of the strips in the groups in response to vibrations of a vibratile product with unit 150 secured at either strip 151 or 153 to the vibratile product.

Structurally, the flexible framework of vibration damping unit 160 in figure 35 includes a first elongated flexible resilient rectangular strip 161 and two additional flexible resilient rectangular strips 162 and 163 of substantially the same width as strip 161. First ends of the strips 162 and 163 are firmly secured to opposite longitudinal ends of strip 161 through shim means 164 as by cementing, having the flexible strips 162 and 163 laminarly dis¬ posed over flexible portions 161a and 161b respectively of the strip 161, and with the longitudinally free ends 162a and 163a of strips 162 and 163 forming an appreciable gap with one another substantially cen- trally between the longitudinal ends of strip 161.

The framework of unit 160 accordingly includes as flexible portions thereof the strip members 161a and 162 in a first group and the strip members 161b and 163 in a second group. The flexible framework strip portions are visco-elastically interengaged by visco-elastic means 165 between the strip por¬ tions in the groups. When the unit 160 is secured at the outer face of strip 161 to a vibratile prod¬ uct so as to flex and respond to vibrations trans- mitted from the vibratile product, the unit 160 will damp those vibrations.

In certain embodiments still in accordance with this invention the strip portions of the vibra¬ tion damping unit framework may be firmly united in the framework as by cementing in the group or groups thereof without use of shim means for spacing. It will be seen for example, in this respect, that in the vibration damping units 130, 140, 150 and 160, the shim means used serves to space the flexible strip portions within the group or groups apart from one another without there being a strip portion in the group to enter between shimmed-apart strip por¬ tions in the group. Therefore, the spacing produced by the shim means, between the strip portions of the flexible framework in units 130, 140, 150 and 160, primarily allows for the presence of the visco-elastic means, and where the visco-elastic means, such as a spread-thin tacky adhesive substance, calls for mini¬ mum space between the related strip portions, the shim means is sometimes omitted.

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As the invention lends itself to many possi¬ ble embodiments and as many possible changes may be made in the embodiments hereinbefore set forth, it will be distinctly understood that all matter described herein is to be interpreted as illustrative and not as a limitation.

I claim: