Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to a badminton racket.
The badminton game generally involves a nimble and
high-speed swing motion in batting a shuttlecock at a short
interval in a relatively small court as compared with tennis.
A badminton racket should be so constructed as to meet such
nimble and high-speed swing motions. To this end, it is requir-
ed that the badminton racket has a light weight, a satisfactory
resiliency, a sufficient mechanical strength and a minimum air
resistance. However, it is very difficult to fulfil these
requisites simultaneously since some of them are incompatible
with each other. For example, a light weight, desirable resil-
iency and minimum air resistance may all be provided simultan-
eously in the badminton racket, but all of these features are
responsible for a reduction of the mechanical strength thereof.
Unless a good balancing of the incompatible features can be
provided, any other improvement in the structure of the badmin- ~-
ton racket would be meaningless.
The present invention will be illustrated by way of
the accompanying drawings in which:
Fig. l(a) is a front elevation of a conventional bad-
minton racket,
Fig~ l(b) is a sectional view taken along line A - A
in Fig. l(a),
Fig. l(c) is a sectional view taken along line B - B
in Fig. l(a),
Fig. 2(a~ is an enlarged front elevation of a T-shaped
joint connecting a frame and a shaft of the badminton racket,
Fig. 2(b) is a sectional view taken along line A - A
in Fig. 2(a), and
Fig. 2(c) is a sectional view taken along line B - B
in Fig. 2(c).
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Fig. 3 shows a badminton racket according to a first
embodiment of the present invention wherein Fig. 3(a) is a
front elevation of the badminton racket, Fig. 3(b) is a section-
al view taken along line A - A in Fig. 3(a) and Fig. 3(c) is a
sectional view taken along line B - B in Fig. 3(a),
Fig. 4 mainly shows a T-shaped tubular joint of the
badminton racket, wherein Fig. 4(a) is a front elevation of the
badminton racket, Fig. 4(b) is a sectional view taken along
line B - B in Fig. 4(a), and Fig. 4(c) is a sectional view
taken along line B - B in Fig. 4(a), and
Fig. 5 shows, in a front elevational view, a badminton
racket according to a second embodiment of the present invention.
In an attempt to provide a badminton racket which
fulfils the above all requisites as much as possible, there
has been proposed to connect an oval-shaped frame to a shaft
by a T-shaped joint. Reference is now made first to a conven-
tional badminton racket shown in Figures 1 and 2.
.
71;~2
According to the conventinal badminton racket shown
in Fig. 1 and Fig. 2, a shaft 1 and a frame 2 are made of
light weight and rigid tubular material, such as stainless
steel tubing, and are connected with each other by means of a
tubular joint 3 as shown in Fig. l(a). The shaft 1 is construct-
ed of a tubing of circular cross section as shown in Fig. l(b),
while the frame 2 is of a tubing of irregularly rounded cross
section having a major axis thereof in the swing directlon
perpendicular to the racket's face as shown in Fig. l~c).
The tubular joint 3 is, as shown in Figs. 2(a) to
2(c), formed substantially in the shape of "T" and comprises
horizontal arm portions 3(b) and 3(c) in which terminal ends
2(b) and 2(c) of the frame 2 are fixedly inserted and vertical
portions 3(a) in which the upper end of the shaft 1 is fixedly
inserted.
This conventional badminton racket is thus constructed
with a view to achieving a high mechanical strength to meet
a high-speed swing motions in addition to light-weight, a
reduced air resistance and a satisfactory resiliency. However,
in this badminton
.:
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racket, various impact loads arising from the use
of the racket are structurely concentrated on the
small T-shaped tubular joint 3. This means that
the mechanical strength necessary for the badminton
racket depends heavily upon the part of the T-shaped
tubular joint 3. It becomes necessary, therefore,
to enhance the mechanical strength inherent in the
structure of the T-shaped tubular joint 3 in order
to obtain a satisfactory mechanical strength of the
racket frame as a whole as well as the other requi-
site elements.
Now referring to the important factor of en-
hancing the mechanical strength of the T-shaped
tubular joint 3, the present inventor has learned
that the mere pursuit of the mechanical strength of
the tubular joint may create another serious problem.
The enhanced mechanical strength of the tubular
joint 3 may involve the enlargement of dimensions
which causes higher air resistance. More seriously,
it has been learned that the shaft 1 and frame 2
will be more subjected to material fatigue in por-
tions l(a), 2(b) and 2(c) adjacent to free end por-
tions 3(a) 'o 3~c) of the T-shaped tubular joint 3.
That is, when the rigidity of the joint 3 is highly
increased by enhancing the mechanical strength there-
of, the joint cannot be bent or twisted in harmony -
with the bending and twisting of the shaft 1 and
frame 2. Accordingly, the bending and twisting
113~71;~2
stresses of the shaft and frame caused by high-speed
swinging motion of the racket will be concentrated
to the shaft and frame portions l(a), 2(b), 2(c~
adjacent to the free end portions 3(a~, 3(b), 3(c~
of the joint 3, respectively. This will result in
breakages of the shaft and frame at these portions
l(a~, 2(b~ and 2(c~.
From the reasons set forth above, although it is
essentially important that the joint 3 has a suffi-
cient mechanical strength, it cannot be too rigid.
Hitherto, it has been difficult to provide a T-shaped
tubular joint having a sufficient mechanical strength
as well as a desirable rigidity not to cause break-
ages of the joint itself and also the shaft and frame
portions adjacent to the free ends ofthe joint.
The present invention has been developed in
view of the above problems. Therefore, an object
of the present invention is to provide a badminton
racket having an oval frame connected to a shaft by
a T-shaped tubular joint, wherein the T-shaped tubu-
lar joint has a sufficient mechanical strength as
well as a desirable rigidity.
Another object of the present invention is to
provide a badminton racket of the type set forth
above, wherein a T-shaped tubular joint can be made
lighter compared with the conventional one without
decreasing the mechanical strength thereof.
A further object of the present invention is
113'713~
to provide a badminton racket of the type set forth above,
wherein a T-shaped tubular joint can reduce an air resistance
applied thereto when the badminton racket is swung at a high
speed.
A badminton racket according to the present invention
comprises a T-shaped tubular joint having fixedly inserted
therein an upper end portion of a shaft and lower free end por-
tions of an oval frame, wherein the tubular joint has a pair
of ribs integrally formed on opposite outer surfaces thereof,
each rib having a relatively wide area at the central part of
this outer surface and extending from this central part to
respective free end portions of the joint in such a manner that
the rib is formed substantially in the shape of "T" with the
thickness and width thereof gradually reducing toward the free
end portions of the joint.
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Referring once more to the accompanying drawings and
in particular to a first embodiment of the present invention
shown in Figs. 3 and 4, a shaft 4 and an oval frame 5 are joined
together by means of a tubular joint 6 formed substantially
in the shape of "T". the material of the shaft 4 may be, for
example, metal tubing of stainless steel, etc. or FRP. The
shaft 4 has a circular cross section as shown in Fig. 3(b). The
lower portion of the shaft 4 is connected to a grip portion 7.
The frame 5 may he made of a metal tubing or fiber reinforced
pipe. The frame 5 is of irregularly rounded cross section as
shown in Fig. 3(c), wherein a width (rl) thereof in the swing
direction perpendicular to the racket's face is larger than a
width ~r2) meeting at right angles with the width (rl), so that
the cross section of the frame 5 is substantially elliptical.
The T-shaped tubular joint 6 has a vertical extension 6(a) into
which inserted is an upper end portion of the
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shaft 4, and horizontal extensions 6(b) and 6(c)
thereof into which inserted are opposite lower end
portions of the frame 5. The upper end of the shaft
4 as well as the lower ends of the frame 5 terminate
at the central portion inside of the tubular joint
6. The tubular joint 6 is integrally constructed by
molding aluminum or a aluminum alloy in a conventional
die casting.
As is clarly shown in Fig. 4(a~ to Fig. 4(c),
the tubular joint 6 has a pair of ribs 8 - 8 inte-
grally formed or molded on opposite outer surfaces
thereof. Each rib 8 has a relatively wide area at
the central part of this outer surface and extends
from this central part to free ends 6(d) - 6(f) of
the joint along center lines of the vertical and
horizontal extension 6(al - 6(c) in su~h a manner
that the rib is formed substantially in the shape of
"Tt'. The width (w) and depth (d~ of the ribs 8 - 8
are gradually reduced toward the free ends of the
T-shaped joint and sharpened at these free ends of
the joint. Each rib 8 thus formed also fills up a
gap space 9(a~ between the vertical extension 6(a~
and horizontal extensions 6(b~ and 6(c~ of the joint
in such a manner that the outer surface of the rib
becomes flat.
It is demanded in the T-shaped tubular joint of
this type that the highest mechanical strength is
provided at the central part of the joint inside of
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which the upper end of the shaft as well as the lower
free ends of the frame terminate and also that the
rigidity of the T-shaped joint is not enhanced so
much at the free end portions 6(a~ - 6(c) thereof
so as to be able to absorb the bending stress applied
thereto by the bending of the shaft and frame.
According to the present invention, the ribs 8 - 8
integrally formed on the outer surfaces of the T-
shaped tubular joint 6 has a relatively wide area
at the central part of this outer surface of the
joint so that the central part of the joint is suf-
ficiently reinforced. The width and depth of the
ribs are gradually reduced toward the free ends 6(d)
- 6(f~ of the T-shaped joint, so that the rigidity
of the joint is reduced toward the free ends thereof.
Thus, the stresses applied to the shaft 4 and frame
S at the portions 4(a), 5(b) and 5(c) adjacent to
the free ends 6(d), 6(e) and 6(f) of-the joint can
be reduced, respectively, compared with the conven-
tional T-shaped joint having a uniform wall thickness
which is higher than that of the present joint at
the free end portions thereof. Further, it becomes
possible by forming the ribs on the T-shaped joint
to make the wall thickness of the joint thinner than
that of the conventional joint except the ribbed
portion and to make the weight of the present joint
itself lighter than that of the conventional one.
Accordingly, it becomes possible in the present
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113713~
invention to provide a lighter joint with sufficient
mechanical strength and not causing excessive stress
concentration on the shaft and frame adjacent to the
free ends of the joint. In addition, since the me-
chanical strength of the present joint is increased
due to the ribs integrally formed on the joint, the
external dimensions of the present joint can be re-
duced compared with the conventional joint. Also,
the rib on the T-shaped joint has a shape of smaller
"T", so that the air resistance to be developed on
the joint when the present badminton racket is swung
at a high speed can be reduced.
Tests carried out by using the present ribbed
joint has proved that the strength of the joint in
the swing direction of the frame could be enhanced
by about 60% in case the overall volume of the joint
is marginally increased by 5.9%.
Another preferred embodiment of the present
invention is shown in Fig. 5. In this second embodi-
ment, each extended end 6(a~ - 6(c) of the rib 8 is
not sharpened and does not reach the free ends of
the T-shaped joint, so that the rib 8 is formed in
the shape of "T" analogous to the outer surface of
the joint as clearly shown in Fig. 5. As it could
be undenstood easily from the description set forth
in connection with the first embodiment, the T-shaped
tubular joint of this second embodiment can provide
the same advantages as the first embodiment.
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113713Z
Thus, the badminton racket made by using the
T-shaped joint according to the present invention
can have such characteristics of sufficiently high
mechanical strength, satisfactory light weight an~
minimum air resistance all at once.
Although the present invention has been de-
scribed with reference to preferred embodiments
thereof, modifications and alterations may be made
within the spirit of the present invention.
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