Tennis racket

The tennis racket has the particularity that the cross-sectional area of the frame in the plane of the stringing of the head portion comprises locally widened zones opposite to each other in the region of greatest width of the head portion, measured perpendicular to the longitudinal axis in the plane of the stringing, and optionally one locally widened zone at the free end of the head portion.

The present invention relates to a tennis racket, and more particularly to 
a tennis racket of the kind having a longitudinal axis of symmetry, which 
comprises a handle extending substantially along the longitudinal axis, a 
head portion defined by a frame having an oval-shaped opening, stringing 
mounted on said frame and tensioned across said opening substantially 
along a plane, two connecting arms extending between the head and the 
handle, and a reinforcement member extending between the two connecting 
arms, as disclosed in co-pending U.S. patent application Ser. No. 618 294, 
filed on Nov. 27, 1990, commonly assigned to the Assignee of the present 
application, the contents of which are incorporated herein by reference. 
This prior application is concerned with the realization of a light-weight, 
high strength racket having a rigid frame for the stringing and, to that 
effect, provides that in a main portion of the head, the cross-sectional 
height of the frame is essentially constant and that the cross-sectional 
width of the frame is comprised between 50% and 75% of the height. 
The object of the present invention is to provide further means for 
increasing the strength of the frame to thereby improve the playing 
properties of the racket. 
In accordance with a first aspect of the present invention, this object is 
met in a tennis racket of the kind set forth at the beginning by the fact 
that the cross-section of the frame comprises locally widened zones 
opposite to each other in the region of greatest head width of the head 
portion, measured perpendicular to the longitudinal axis in the plane of 
the stringing. 
According to an other aspect of the invention, this object is met by the 
fact that the cross-section of the frame comprises a locally widened zone 
at the free end of the head portion and two locally widened zones opposite 
to each other in the region of greatest head width of the head portion, 
measured perpendicular to the longitudinal axis in the plane of the 
stringing. 
Owing to the local widenings of the cross-section of the frame in the head 
part, provided in accordance with the invention, an ideal and constant 
distribution of the stresses of the head part caused by the tensioning of 
the racket head, whereby improvements of the hitting properties are in 
turn achieved. 
Advantageous developments of the invention are described in the following 
description.

The tennis racket illustrated in plane view in FIG. 1 comprises in a usual 
manner three regions arranged successively along a longitudinal axis of 
symmetry LL: 
a handle part 1, 
a head part 2 which is formed by a frame 3 which surrounds an opening 4 and 
has a generally oval plane shape, 
two connecting arms 6, 6' which are integrally made with the frame 3 as 
extensions thereof and extend into the handle part 1. 
The racket further comprises a yoke part or reinforcing member 7, which 
connects integrally the connecting arms 6, 6' and delimits the opening 4 
towards the handle part 1. 
A stringing, not shown in order to simplify the figure, is tensioned over 
the opening 4 and lies generally in a plane, with the individual strings 
which constitute the stringing extending in directions parallel and 
perpendicular to the longitudinal axis of symmetry LL and are guided in a 
usual manner through passages or bores, not shown, provided in the frame 
of the head part 2 or in the reinforcing member 7. The frame 3 comprises a 
profile section having the typical cross-section shown in FIG. 4. This 
profile section is for example formed as a tube-shaped, thin-walled, 
closed profile, the inner cavity of which can be filled with a material 
which has practically no influence on the mechanical properties of the 
profile. 
Referring to the axes shown in FIG. 4, the axis XX extends in the plane and 
the axis YY extends perpendicular to the plane of the stringing. The outer 
edges of the cross-section can be inscribed in an isosceles triangle the 
basis of which lies on the stringing side. The profile comprises a 
reentrant concave portion or groove 8 on the XX axis and on the outer side 
remote from the opening 4, for accommodating the strings between two 
passages which lead to the opening 4 of the frame 3 (not shown). 
The cross-section of the frame increases at least in the upper half of the 
head remote from the handle towards the free end of the handle. The 
circumference of this cross-section is greater than or equal to 85 mm, and 
at the free end of the head, the cross-section has approximately a circular 
form and a circumference of about 90 mm. 
In order to resist without excessive inwardly directed deformations to the 
loads exerted by the stringing on the frame both under static and under 
dynamic conditions, the profile comprises substantially flat wall portions 
9 which connect the groove 8 to the upper and lower summit areas 10, 11, 
arranged on the YY axis and substantially planar, parallel to the plane of 
the stringing. The wall portions 9 are inclined relative to the plane of 
the stringing at an angle .alpha. comprised between 25.degree. and 
65.degree., and preferably 45.degree.. 
More precisely, the wall portions 9 extend between points A and B where the 
angle between a tangent to the profile and the plane of the stringing has 
the values 65.degree. and 25.degree. respectively. The width of the wall 
portions 9, measured between these points A and B in the plane of the 
stringing is denoted by Z, whereas the width of the profile, also measured 
in the same plane, is denoted by W. Preferably, within the scope of the 
present invention, the ratio between the width Z of the wall portions and 
the width W of the profile is comprised between 30 and 70%, and more 
preferably between 40 and 60%. 
The inner side 12 of the profile can be substantially straight at least in 
its middle region and is preferably slightly curved in the direction of 
the opening 4. 
The shapes and proportions of the above described typical cross-section 
vary in the handle part 1, in the connecting arms 6, 6' and in the various 
portions of the head part 2, as explained in the above-mentioned copending 
U.S. patent application Ser. No. 618 294, to which reference is made in 
this respect in order to avoid unnecessary repetitions. 
Owing to the special design of the cross-sections, the wall portions 9 
achieve an arch structure together with the inner side 12 of the profile, 
whereby one obtains a racket having a high stability, which simultaneously 
has a relatively low weight. The characteristic cross-sections achieve a 
high stiffness against flexions within and out of the plane of the racket, 
and the special geometry of the cross-sections for the head part allows a 
significant reduction of the wall thickness of the cross-section, which 
leads to the above mentioned weight reduction. It is important that the 
torsion moment of inertia can also be increased for a lower mass by means 
of these cross-sections. 
The profile can be advantageously realized as described in the already 
mentioned copending U.S. patent application Ser. No. 618 294, i.e. the 
profile is made out of a composite material and two plies of this 
composite material are overlapped in the region of the outer groove to 
achieve a reinforcement in this region. The various dimensions disclosed 
in this copending application can also be advantageously used in the 
present invention. 
In the first preferred embodiment of FIG. I the cross-sectional width W of 
the frame has widenings 30, 31 formed in the regions of the greatest width 
of the head part 2 and widen inwardly only in these regions of the frame in 
plane view. The maximum value of the cross-sectional width at section 
planes F--F continuously decreases in the direction of the cutting plane 
B--B, i.e. over a region having a length between 4/9 and 5/9, preferably 
4,5/9 (1/2) of the distance between the cutting planes FF and AA, measured 
from FF towards the free end 15 on the curved line in the plane of the 
stringing along the outer circumference of the head portion (FIG. 1). 
Thereafter the cross-sectional width W remains constant in the direction 
of the free end 15. 
Preferably, the height H of the cross-section of the frame, measured 
perpendicular to the plane of the stringing, remains substantially 
constant from the connecting arms 6 to at least beyond the region of 
greatest width of the head portion, for example up to about the last third 
of the head portion, measured along the longitudinal axis LL. 
In FIGS. 2 and 3 the cross-sectional views A--A, B--B and F--F are drawn up 
at a true scale in respect of the dimension relationships. 
In the second preferred embodiment of FIG. 5, local widenings 30, 31 of the 
width of the cross-section of the frame are provided in the region of the 
greatest width of the head part 2, and such a widening 32 of the 
cross-sectional width is also realized at the upper end 15 of the frame. 
The corresponding cross-sections AA & BB, CC, DD, EE, FF & GG shown in 
FIGS. 6, 7, 8, 9 and 10 are also drawn up at a true scale. 
The important point is that the local maximum value of the cross-sectional 
width W in section G--G decreases in the direction of the section B--B 
down to a minimum value which corresponds to the width at the section 
plane A--A, and increases again continuously, until reaching the maximum 
value of the cross-sectional width W at the upper end 15 at section F--F, 
with the width passing by the intermediate values of sections C--C, D--D, 
and E--E. 
The cross-sectional width decreases from the locally widened zone 32 at the 
free end 15 of the head portion over a zone having a length of about half 
the length between the position of the greatest head width of the frame 
and the free end of the head, measured on the curved line in the plane of 
the stringing along the outer circumference of the head portion, and 
increases thereafter towards the locally widened zones 30, 31 in the 
region of greatest width of the head portion. 
Preferably, the height H of the cross-section of the frame, measured 
perpendicular to the plane of the stringing, remains substantially 
constant from the connecting arms to at least beyond the region of 
greatest width of the head portion, for example up to about the last third 
of the head portion, measured along the longitudinal axis. 
Advantageously, in the two above-mentioned embodiments of the present 
invention, the circumference of the cross-section of the frame has the 
same characteristics as in U.S. patent application Ser. No. 618 294 
already mentioned.