Vibration dampening racket

A racket for playing tennis or similar ball games having a straight bar type stem part which continues to an annular ball hitting part. A hole is provided in the stem part in which a vibration absorbing member is stored. Said vibration absorbing member comprises a buffer layer made of a gel material and a mass member supported by this buffer layer. The buffer layer is fixed so that it can be deformed in said hole and said mass member is supported so that it does not contact the internal surface of the hole. Said vibration absorbing member can be put in an outer casing and inserted into the hole. In this case, the buffer layer is deformed in the outer casing and the mass member is held so that it does not contact the internal surface of the outer casing.

BACKGROUND OF THE INVENTION 
The present invention relates to the racket which absorbs a shock or impact 
produced on the ball hitting net surface by the vibration absorbing member 
such as, for example, tennis rackets, squash rackets or the like. 
This kind of conventional vibration absorbing type racket has the frame in 
which the buffer layer made of a gel material with the penetration value 
of approximately 50 to 200, such as silicone gel, is contained as a 
vibration absorbing means. 
This type of racket is disclosed in the U.S. Pat. Application Ser. No. 
161130 dated Feb. 26, 1988 and the U.S. Pat. Application Ser. No. 231211 
dated Aug. 11, 1988. 
In case of the racket as described above, a shock produced on the ball 
hitting net when a ball is hit is applied as a vibration wave to the 
buffer layer made of a gel material to deform said buffer layer and is 
thus damped. For this reason, this type of racket accompanies a problem 
that the shock absorbing effect will be deteriorated if the energy of 
shock is large. 
The other kind of vibration absorbing type racket is such that the frame is 
provided with the mass member which is transformed by a shock energy 
produced on the ball hitting net and the vibration wave is thus 
dissipated. This type of racket is disclosed in the U.S. Pat. No. 4182512. 
In case of this type of racket, a new vibration wave is often produced by a 
movement of the mass member and there is a problem in the vibration 
absorbing characteristics. 
In recent years, therefore, a racket using a composite vibration absorbing 
member which comprises a combination of a mass member and a tacky elastic 
member has been offered as disclosed in the Japanese Patent Gazettes Kokai 
SHO 62-192182 and Kokai SHO 62-192183. 
This type of racket is adapted to absorb the vibration wave by a movement 
of the mass member and a low repulsive deformation of a tacky elastic 
member and can therefore provide the satisfactory vibration absorbing 
characteristics. 
However, the conventional composite vibration absorbing member as described 
above is stored in the grip part of the racket frame and the assembling 
and replacing works will be troublesome. 
SUMMARY OF THE INVENTION 
An object of the present invention is to provide the racket in which the 
vibration absorbing member comprising the mass member and the buffer layer 
made of a gel material can be easily fitted. 
For this purpose, the racket in accordance with the present invention is 
provided with a hole in the straight bar part between the ball hitting 
part and the grip part to store therein the vibration absorbing member. 
Another object of the present invention is to provide the racket allowing 
easy replacement of said vibration absorbing member. 
For this purpose, in the racket in accordance with the present invention, 
said vibration absorbing member is encapsulated in the outer cylindrical 
case and this encapsulated vibration absorbing member is removably 
inserted and secured in the hole of the frame. 
Another further object of the present invention is to obtain a satisfactory 
design appearance by storing said vibration absorbing member in the hole 
of the frame. 
For this purpose, the opening end of said hole is closed with a 
decoratively designed cover and this cover is made of, for example, a 
convex lens and an end of the vibration absorbing member which can be seen 
through the convex lens is, for example, colored or engraved with the 
initials to ensure the design effect of the cover.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT 
Referring to FIGS. 1 to 4, there is shown the tennis racket as the first 
embodiment of the racket in accordance with the present invention. 
In this embodiment, the frame 10 formed by bending a single hard skeleton 
member has the ball hitting part 11 which is made in an annular form and 
the bar type stem part 12 which follows the ball hitting part, and the 
grip part 121 is formed on the free end side of the stem part 12. 
The netting 20 is formed on the ball hitting part 11 of said frame 10 and 
used as the ball hitting net 20. 
In the embodiment, said frame 10 is integrally formed with a shaft member 
made of a glass fiber reinforced plastic material having a core member of 
foamed synthetic resin. For this reason, the part continuing to said ball 
hitting part 11 of said stem part 12 is formed as a forked coupling part 
122 and this coupling part is provided so that the traverse frame member 
111 forms the lower part of said ball hitting part 11. 
For making said frame 10 as in the embodiment, there are available a method 
that the prepeg which is a molded glass fiber reinforced plastic material 
is wound around the core member which is bent and formed in advance into a 
frame and this prepeg-wound core member is heated under a pressure to be 
finally molded in the mold or a method that the prepeg is wound around the 
core member to make a bar type shaft member and this shaft member is 
fitted into the mold while bending it and heated under a pressure to be 
molded. 
For the stem part 12 of said frame, the straight bar part 123 between the 
coupling part 122 and the grip part 121 is provided with the hole 30 which 
is formed in the straight bar part 123 at right angles to the lengthwise 
direction of the stem part 12. 
Although said hole 30 can be a through hole which passes through the 
straight bar part 123, it can be made as a blind hole having a bottom. 
The vibration absorbing member 40 is sealed in said hole 30 and this 
vibration absorbing member 40 has the mass member 41 and the buffer layer 
42. 
Said mass member 41 can be optionally selected if it has the specified 
weight. However, it is desirable that the weight of the mass member 41 is 
heavy in spite of its small volume and therefore lead is generally used 
and this lead is coated with a synthetic resin. 
Said buffer layer 42 is made of a gel material and supports said mass 
member 41 while an area such as, for example, a space where said buffer 
layer is deformable is provided. Said buffer layer 42 supports the mass 
member 41 so that said mass member 41 does not come in contact with the 
internal surface of the hole 30 and accordingly the mass member 41 is 
displaced while deforming only the buffer layer 42 when a shock is 
applied. 
Said hole 30 can be formed by drilling a hole in the stem part 12 after the 
frame 10 has been formed. In the embodiment, since the hole is 
simultaneously formed when the shaft member is formed by heating under a 
pressure during bending of the shaft member, the hole wall 31 is made with 
a synthetic resin. 
Said hole 30 is provided with the cover 32 at its opening side by which the 
vibration absorbing member 40 is sealed in the hole. 
It is preferable that said cover 32 is attached to be refittable and, in 
the embodiment, therefore the cover 32 is screwed to the opening portion 
of the hole 30. Said hole 30 can be open at its both ends and, in this 
case, the cover 32 is fitted to both opening ends, respectively. 
Said vibration absorbing member 40 is made in a construction that the mass 
member 41 is sealed in a cylindrical buffer layer 42 and the buffer layer 
42 is partly cut away at both sides in the axial direction so that said 
buffer layer 42 can be deformed. Said buffer layer 42 is covered with the 
external covering layer 421 and this external covering layer 421 is fixed 
to the hole wall 31 with an adhesive agent or the like. 
In this case, said buffer layer 42 can be directly adhered to the hole wall 
31 without forming an external covering layer 421 and can be formed by 
pouring the original liquid for gel material into the hole 30 of the 
racket which is placed so that said hole 30 is faced up and gelling this 
original liquid. 
Also in this case, the space which allows deformation of the buffer layer 
42 can be formed by setting in advance a jig in the hole 30 or partly 
cutting off the gel material from the opening end of the hole 30 after 
said original liquid has been gelled. 
As the gel material for forming said buffer layer 42, it is preferable to 
use the silicone gel which has the penetration value of approximately 50 
to 200 measured according to JIS K2530-1976 (50g load). Such gel material 
includes Toray Silicone CF5027 (trade name) manufactured by Toray Silicone 
Kabushiki Kaisha and KE-1051(product name) manufactured by Shin Etsu 
Kagaku Kogyo Kabushiki Kaisha. It is most desirable to use, as said gel 
material, a composite silicone gel material as disclosed in the U.S. Pat. 
Application Ser. No. 87970 filed on Aug. 17, 1987 and this composite 
silicone gel material is made up by mixing fine hollow particles of 1 to 4 
weight % such as Fillite (registered trademark) manufactured by Nippon 
Fillite Kabushiki Kaisha or Expancel (registered trademark) sold by the 
same company in the gel material having the penetration value of 
approximately 50 to 200 and this gel material excels particularly in the 
buffer effect. 
In addition, said composite silicone gel material also includes a type of 
gel material made up by mixing fine silica powder in silicone gel having 
the penetration value of approximately 50 to 200. Since this silicone gel 
material has a characteristic of high tear strength, it can provide a 
larger effect in actual use if the weight of the mass member 41 is large 
and can ensure excellent adhesive effect of an adhesive agent to said 
buffer layer since the tackiness of the surface of the buffer layer 
employing this silicone gel material is small. 
In the above embodiment, an impact wave produced on the net 20 is conducted 
to the frame 10 and absorbed by the vibration absorbing member 40 in the 
stem part 12. 
In other words, the energy of said impact wave is dissipated and damped to 
displace the mass member 41 of the vibration absorbing member 40 and the 
kinetic energy of the mass member 41 is absorbed by a low elastic 
deformation, that is, a substantial non-elastic distortion of the buffer 
layer 42. 
Since the gel material has a conductive characteristic similar to a liquid, 
the impact wave which has displaced the mass member 41 is quickly 
dispersed throughout the buffer layer 42 and absorbed by the buffer layer 
42 only with slight vibration waves owing to small repulsive elasticity. 
If the gel material is mixed with fine hollw particles 401, the weight of 
the buffer layer 42 can be reduced and also the buffer effect can be 
improved. 
In the above embodiment, the vibration absorbing member 40 is directly 
sealed in the hole 30 and the mass member 41 of the vibration absorbing 
member 40 is supported by the buffer layer 42 so that said mass member 41 
does not come in contact with the internal surface of the hole which is 
formed by the hole wall 31 and the internal surface of the cover 32. 
However, in case of the construction as described above, it is difficult to 
replace the vibration absorbing member 40 and therefore to select, for 
example, the mass member 41. 
Referring to FIGS. 5 and 6, there is shown the vibration absorbing member 
40 sealed in the outer casing such as, for example, the outer cylindrical 
case 50. 
In the embodiments described in the following description, the same parts 
as in the above embodiment are given the same numbers as in the above 
embodiment to avoid duplication of the detailed description. 
In this embodiment, the outer cylindrical case 50 comprises the barrel part 
51 which accommodates the vibration absorbing member 40 and covers 52 and 
52' provided at the opening parts at both ends of this barrel part 51, and 
the buffer layer 42 of said vibration absorbing member 40 is fixed to be 
deformable inside the barrel part 51 and the mass member 41 is supported 
to be displaceable by this buffer layer 42. 
Said barrel part 51 can be open only at one end and, in this case, the 
cover 52 is attached to only one end of the barrel part 51. Said outer 
cylindrical case 50 is fixed in the hole 30. In this embodiment, the 
barrel part 51 of the outer cylindrical case 50 is adhered with an 
adhesive agent to the hole wall 31 of the hole 30 but, as described below, 
this outer cylindrical case 50 can be remountably set in the hole 30. 
Said mass member 41 is provided with the engaging projection 411 at its 
external surface and fixed by engaging this engaging projection 411 with 
the engaging recess 422 of the buffer layer 42. The external surface of 
this mass member 41 can further be adhered to the buffer layer 42 with the 
adhesive agent. 
Said covers 52 and 52' can be a plate cover but, in this embodiment, the 
covers are respectively made as a convex lens (or a concave lens). If the 
lens is thus used as the cover, it can provide an artistic design of 
appearance and permit a magnified observation of the end face of the mass 
member 41 contained. Accordingly, the factor of the artistic design of the 
racket can be further increased by, for example, entering the user's 
initials on the end face of the mass member 41 or coloring the end face of 
the vibration absorbing member 40 to give the appearance of more artistic 
design to the racket. 
Referring to FIG. 7, the mass member 41 of the vibration absorbing member 
40 as shown is supported at its both end faces by a pair of wall type 
buffer layers 43 and 43' and surrounded by a space formed on the external 
periphery of the mass member 41. 
Lustered surfaces 521 and 521' obtained by evaporating aluminum are formed 
on the internal surfaces of said covers 52 and 52' and these lustered 
surfaces can be observed through transparent covers 52 and 52' from 
outside. 
Referring to FIG. 8, the mass member 41 of the vibration absorbing member 
40 as shown has the through hole 412 in the axial direction and supported 
by the column type buffer layer 44 made of a gel material which passes 
through this through hole 412. 
Said column type buffer layer 44 is fixed by adhering both ends of this 
buffer layer to the internal surfaces of covers 52 and 52'. 
In this embodiment, accordingly, it is difficult to take out the vibration 
absorbing member after it has been built in the outer cylindrical case 50. 
Referring to FIGS. 9 and 10, in the embodiment as shown, the outer 
cylindrical case 50 containing the vibration absorbing member 40 is 
remountably inserted into the hole 30. 
In this embodiment, the internal threads 33 are provided respectively at 
the opening ends of the hole 30 and said covers 52 and 52' are 
thread-fitted to these internal threads 33. For the above purpose, covers 
52 and 52' are respectively provided with external threads 522 and 522' at 
their external peripheries and 0 rings 53 and 53' are respectively mounted 
between covers 52 and 52' and the barrel part 51 to hold the barrel part 
51 between covers 52 and 52'. 
In this embodiment, the barrel part 51 inserted into the hole can be taken 
out from the hole 30 by removing at least one of covers 52 and 52' and 
replacement of the vibration absorbing member 40 can therefore be easy. 
Referring to FIG. 11, there is shown another embodiment of said vibration 
absorbing member 40. 
This vibration absorbing member 40 is constructed by alternately stacking a 
plurality of mass members 45 and 45' and a plurality of buffer layers 46 
and 46' and the outermost layer of this stacking type vibration absorbing 
member 40 is made as the buffer layer 46. 
In this embodiment, since mass members 45 and 45' are coupled with the 
buffer layer 46', the resonance frequency band exists at a plural number 
of locations and a certain range of allowance can be given for variations 
of the natural frequency of a racket user. 
In the above description, though the hole 30 formed in the frame 10 is 
shown as a circular form, it can have another polygonal form such as, for 
example, triangle and hexagon and the vibration absorbing member 40 shown 
in the embodiment can comprise the mass members and the buffer layers in 
other types of shapes. Said hole 30 or said outer cylindrical case 50 need 
not always have a hollow space if the buffer layer 42 can be deformed 
inside the hole 30 and the outer cylindrical case 50. For example, the 
inside space can be filled with a soft foamed layer 34 as shown in FIG. 3. 
The racket in accordance with the present invention is not limited to said 
embodiments and can be modified or changed within the scope of claims of 
the present application.