U.S. patent number 3,801,099 [Application Number 05/155,902] was granted by the patent office on 1974-04-02 for tennis racquet.
Invention is credited to John C. Lair.
United States Patent |
3,801,099 |
Lair |
April 2, 1974 |
TENNIS RACQUET
Abstract
An improved tennis racquet constructed of magnesium, beryllium
or other metal with a low ratio of weight to stiffness and strength
wherein the elliptical head of the racquet is disposed so that the
long axis of the ellipse is transverse to the axis of the racquet
handle, thereby to increase the rotational moment of inertia about
the longitudinal axis of the racquet.
Inventors: |
Lair; John C. (Sierra Madre,
CA) |
Family
ID: |
22557237 |
Appl.
No.: |
05/155,902 |
Filed: |
June 23, 1971 |
Current U.S.
Class: |
473/537; 473/519;
473/541; 473/545 |
Current CPC
Class: |
A63B
60/02 (20151001); A63B 49/00 (20130101); A63B
49/12 (20130101); A63B 60/00 (20151001); A63B
2208/12 (20130101) |
Current International
Class: |
A63B
49/00 (20060101); A63B 49/04 (20060101); A63B
49/02 (20060101); A63B 49/12 (20060101); A63b
049/02 (); A63b 049/04 () |
Field of
Search: |
;273/67R,67B,73R,73A-L,76 ;34/5ST,5SP |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
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|
|
|
|
|
17,636 |
|
Jan 1929 |
|
AU |
|
1,643 |
|
Jan 1894 |
|
GB |
|
800,262 |
|
Apr 1936 |
|
FR |
|
1,442,020 |
|
Mar 1968 |
|
FR |
|
446,348 |
|
Apr 1936 |
|
GB |
|
755,257 |
|
Aug 1956 |
|
GB |
|
Primary Examiner: Pinkham; Richard C.
Assistant Examiner: Apley; Richard J.
Claims
I claim:
1. A tennis racquet comprising
a rigid frame structure forming a handle and a head frame in the
shape of an elliptically closed loop having a continuous concave
curvature presented towards the interior thereof, said head frame
having a long axis and a short axis,
the interior of said loop providing an elliptical string area which
is substantially symmetrical with respect to both said axes,
said head frame being provided with means for stringing the
encompassed elliptical area with resilient stringing, and
the long axis of said head frame being perpendicular to the
longitudinal axis of the handle and the short axis of said head
frame being coaxial with the longitudinal axis of the handle,
whereby greater inertial stability against roll about the handle
axis is provided than is the case with a conventional racquet
wherein the long axis of the elliptical head frame is coaxial with
the longitudinal axis of the handle.
Description
1. Field of the Invention
This invention relates to the design and construction of racquets,
and particularly of racquets intended for use in playing the
internationally popular game of tennis.
2. Description of the Prior Art
The game, once fully named "lawn tennis" but not known simply as
"tennis," has been played for almost one hundred years. Within the
past decade or so tennis has seen a great increase in its
popularity, particularly in areas of the world which are not
subjected to long cold winter periods. However, even in colder
areas, indoor facilities have been constructed to permit play at
any time. The game involves the stroking of a felt-covered ball by
players moving on opposite sides of a net bisecting a marked court
with each player employing a racquet, which, by custom and
convention but not by regulation, is approximately 27 inches long
with an elliptical head integrally secured on the end of a handle.
The racquet head is strung with nylon or cat-gut in a crossed
pattern, thereby providing a grid of approximately one-half inch
square openings to minimize the air resistance to the rapid
movement of the racquet head in a direction substantially normal to
the plane of racquet strings, and hopefully properly opposing the
trajectory of the ball.
For most of the years during which the game of tennis has been
played, the racquets were almost exclusively made of wood.
Initially, and for many years the racquet heads were in the shape
of an inverted isosocles triangle rounded at the base angles with
the apex integrated with the handle. Later the head assumed more
the shape of an ellipse, the long axis of which coincided with the
axis of the handle. Construction of these early racquets was
accomplished by steam or otherwise bending a wooden member into
such triangular or elliptical shapes with the extremities extending
beyond the apex of the triangle or the ellipse and laid one upon
the other to be secured together to constitute a handle.
Beginning in about the 1920's elliptical racquet heads were formed
separately as laminated wood ellipses and one end of the ellipse
was glued, cemented or otherwise joined to the bifurcated end of
the handle. This type of construction, in various improved
versions, is still employed for the standard still popular wooden
racquet. Sometime in the 1920's and 1930's certain racquets were
fabricated with metal elliptical heads and strung with wire instead
of gut, but these never acquired any real popularity and generally
disappeared entirely from the tennis scene by the early 1950's.
Although the laminated wood racquet continues to be popular, within
the last few years a number of new types of metal racquets strung
with gut or nylon have been made and sold and these are now in
widespread use. These metal racquets have generally assumed the
same shape as that of their wooden forebears, viz., an elliptical
head with the long axis of the ellipse being coaxial with the axis
of the handle. Such metal racquets now offered ar fabricated either
from formed tubular members, stampings or from extrusions with the
head frame being integral with the handle. The currently offered
metal racquets are generally designed to duplicate within 5 percent
both the weight and its distribution of their wooden predecessors
(and still competitors). Because the head frame of a metal racquet
may be thinner and thus appear to offer less air resistance than a
wood frame needed to provide sufficient rigidity to resist buckling
upon impact with a ball or warping under the tension imposed upon
the frame by the tight stringing, some players believe that a metal
head frame may be moved more rapidly through the air than a wooden
frame. However, complaints are often heard that metal frame
racquets lack the solid "feel" of wooden racquets to which many
tennis players have been accustomed through years of play.
In addition, since the efforts of manufacturers of metal racquets
have been directed toward duplicating the shape, weight and its
distribution and the stringing of the long accepted wooden
racquets, no consideration appears to have been given to the
possibility of utilizing certain advantages which metal frame
construction can offer to produce a novel racquet design with
features not possibly attainable with wood construction. In this
connection, it should be pointed out that the Rules of the American
Lawn Tennis Association make no provision for any particular size,
shape or construction of a racquet. Anything may be employed as a
racquet, but the conventional form in use today is based upon the
years of experience of the millions of tennis players and the
historical development of racquets as essentially wooden
constructed devices.
As previously mentioned, tennis racquets of both metal and wood,
have traditionally been approximately 27 inches in length with an
elliptical head providing a strung area of approximately 70 square
inches. The long dimension of the ellipse is approximately 11
inches, the short dimension, 9 inches. The handle, thus, extends
some 15 inches from one end of the ellipse.
Racquets traditionally weigh from about 12-1/2 oz. for children to
as much as 16 oz. for some men. The average racquet weight,
however, ranges between 13-1/2 oz. and 14 oz., normally distributed
so that the center of gravity lies at between 12-1/2 and 13-1/2
inches from the gripped end of the handle. This weight distribution
has not been arbitrarily selected but rather has resulted from the
weight of the average type of wood of the volume which has been
found necessary to provide sufficient strength in the usual racquet
configuration to enable the average player to impact the ball with
the greatest amount of force he normally can develop in his
stroking of the ball with the racquet. When racquet manufacturers
began substituting metal for wood in the racquet framing, they
generally sought to simulate the weight and its distribution of the
conventional wood racquet.
It has been found by many of the better players of tennis that the
best area of the strung head at which to impact the ball is not on
the geometric center (or centroid) of the strung elliptical area,
but may be as much as an inch toward the handle from that centroid.
This ideal impacting area is sometimes referred to as the "sweet
spot." In engineering terminology it may be called the "center of
percussion" (c.o.p.), and is defined as the square of the radius of
gyration about the instantaneous center of rotation, divided by the
coordinate of the center-of-gravity. I have determined that such
conventional off-centroid location of the sweet spot," or c.o.p.,
may be attributed to the fact that the center-of-gravity of the
racquet is conventionally located where it is, i.e., at about 13
inches from the end of the handle instead of further away from that
end toward the centroid of the strung ellipse. Because of its
location, a relatively large portion of the strung area of the
ellipse is not really effective in hitting, and the player's reach
for ideal stroking is decreased by the distance between the c.o.p.
and centroid of the ellipse.
In addition, since racquets have been designed originally for
wooden construction, they have been constructed to permit bending
in the direction of impact with the ball, but to minimize twisting
of the strung head. This is because although a wooden racquet head
can withstand bending, it cannot tolerate large twisting moments
without fracturing, owing to the intrinsic grain structure of wood
in which weakness is always sought out and exploited by a twisting
moment. Thus, there has resulted in the genesis of racquet design
based upon wood construction the conventional elliptical head
oriented with its long axis coaxial with the handle.
Moreover, the wooden racquet cannot stand too great a bending
moment at the throat (i.e., the portion of the racquet where the
handle is joined to the head), since in order to give the
appearance of reducing air resistance to the movement of the
racquet, racquet manufacturers narrow the throat to the minimum
width required to withstand maximum anticipated impacts of the ball
upon the head. To enable the width of the throat to be so
minimized, the center-of-gravity of the wooden racquet cannot be
disposed much farther toward the centroid of the racquet ellipse
than where it is conventionally located (i.e., about 13 inches from
the gripped end of the handle). To effect any material shift of the
center-of-gravity in such direction ain a wood racquet would
produce excessive bending, and possibly undesired twisting, moments
at the throat and shoulders, thereby resulting in their fracture
when the head is impacted with an overhead smash or hard forehand
shot.
Thus, racquets based upon the limitations in design imposed by the
use of wood in their construction, have heretofore assumed a fairly
standard shape and weight distribution even though, as pointed out
above, more recently, racquets have been constructed of metal. In
so constructing metal racquets, racquet designers and manufacturers
have apparently ignored certain structural capabilities of the
metals -- particularly of those exotic metals such as magnesium and
beryllium, or the high modulus carbon fiber composites developed
particularly for aerospace use, as well as certain principles of
physics and rigid body mechanics which have peculiar application to
the stroking of a tennis ball.
Among such principles of physics is the fact that a player's energy
is most efficiently transferred to the ball as he hits it if the
c.g. of his racquet is as far from his hand and as near the ball as
structural mechanics permit.
SUMMARY OF THE INVENTION
The present invention has resulted from considerable study of the
dynamics of the game of tennis and certain principles of rigid body
mechanics. Careful consideration of these principles has led to the
present redesign of a novel and improved tennis racquet. No longer
limited in designing a racquet by the physical properties and
characteristics of wood, I have evolved certain novel features
which, if incorporated in the construction of a tennis racquet,
will be found to result in a racquet of quite a radically different
appearance and rigid body mechanical effect. My approach to the
problems of racquet design and construction, which approach has
resulted in the present invention hereinafter to be described, is
as follows:
Should a racquet frame of present-day metal frame configuration be
constructed of a metal having a very low ratio of weight to
stiffness (and strength), such as magnesium or beryllium, it will
be considerably lighter in its over-all weight, than that of
present-day metal or wood racquet frames, and yet it may possess
all the stiffness and strength which may be required for impacting
the ball. One may then address himself to the optimum location of
the c.g. of the racquet and effect such location by design and/or
weight supplements so as to bring the c.g. nearer the ideal
impacting spot on the strung frame and further from the player's
hand. Such design and/or addition of such weight supplements may
still keep the over-all weight of the racquet at or below that of
present-day wood and metal racquets. The weight supplements may be
in the form of lead or silver or other metals having a high
specific gravity.
I have found that such weight supplements should be added at the
ends of a transverse diameter of the elliptical hitting face of the
racquet. In addition to more properly locating the c.g. of the
racquet for ball stroking in conformity with the principles of
physics hereinabove referred to, the addition of dead weight
supplements at the ends of such transverse diameter will be found
to contribute strongly to the racquet's moment of inertia about its
longitudinal axis, thereby minimizing for the player the
unfavorable consequences of his minor mis-hits about this axis.
It is a feature of the present invention to provide means on the
frame to receive such supplementary dead weights and to secure them
along the sides or even end of the frame. They may be added by the
player himself after he has purchased the strung frame or by the
vendor of the racquet at the time it is purchased. Conceivably, a
retailing professional may even engage in some type of "try-out"
session with the purchaser to arrive at the optimum disposition of
the weight supplements to the racquet head in order to give the
purchaser the best "feel" for ball stroking.
By this lightweight metal racquet construction and the addition of
such supplementary dead weights, there may be attained one object
of the invention, namely, to shift the center of gravity of the
racquet toward the head and away from the conventional location
about 13 inches from the handle end. This center of gravity shift
will be found to result in moving the c.o.p., or "sweet spot," of
the racquet from its off-center location in the string area nearer
to the centroid of the strung ellipse, thereby increasing the
strung area for the most effective response to ball impact.
However, this and other objectives may also be accomplished by
perhaps the most iconoclastic feature of the present invention
wherein the disposition of the elliptical head may be such that the
long axis of the strung ellipse is transverse to the axis of the
handle. This can readily be accomplished with metal framing and has
a number of unexpected and interesting results. Particularly
noticeable among end results are the following:
First, it inherently facilitates shifting the center of gravity
away from the handle.
Secondly, stability in roll about the longitudinal axis is
naturally increased to improve particularly volleys and overheads,
i.e., shots which, being hit in the air, are especially vulnerable
to small mis-hits about the long axis.
Third, since most players'errors occur through mishitting in the
cross dimension of the head, the greater string area in that cross
dimension tends naturally to attenuate the effects of such
mis-hitting.
Lastly, a chopped, undercut or "topped" ball, accomplished during
"ground stroking" or "serving," will receive a longer "dwell" on
the strings since each of those strokes is made by a movement which
subjects the ball to string action in the cross dimension.
A racquet frame of such head disposition is preferably also made of
lightweight metal such as magnesium or beryllium or the so-called
high modulus carbon fiber composites, and may be constructed to
receive dead-weight supplements.
BRIEF DESCRIPTION OF THE DRAWINGS
In the accompanying drawings:
FIG. 1 is a plan view of a metal racquet of conventional
shaping;
FIG. 2 is a plan view of a metal racquet constituted in accordance
with the present invention;
FIG. 3 is a section taken on the line 3--3 of FIG. 2.
FIG. 4 is a section similar to FIG. 3, but showing the addition of
a weight supplement on the cross-axis.
FIG. 5 is a partial view similar to FIG. 2, but showing the
addition of further outwardly disposed weight supplements.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 illustrates a metal racquet of generally conventional shape
and dimensions. It comprises an integral frame 10 which may be
constructed by bending a metal member 12 back upon itself in an
elliptical loop configuration to form a handle 13 and head 20. The
loop 14 may be completed by inserting and securing as by welding an
arcuate segment 15 inside the member 12. The long axis 22 of the
elliptical head coincides with the axis 24 of the handle 13 and the
short head axis 23 is perpendicular to handle axis 24.
To be compared with the conventional metal racquet illustrated in
FIG. 1 is the racquet constructed in accordance with the present
invention which is shown in FIG. 2. This racquet differs
substantially from the conventional tennis racquet configuration in
that the elliptical head 20a is turned 90 degrees so that the long
axis 22a of the ellipse is disposed perpendicularly to the handle
axis 24a and the short head axis 23a is coaxial with the handle. It
should be pointed out, however, that in order for the racquet of
this novel configuration to be accepted by tennis players who have
learned and long played the game with the racquets of the
conventional configuration, the centroid 26a of the ellipse of the
racquet of FIG. 2, should be located the same distance from the end
28a of the handle 13a as is the centroid 26 of the elliptical head
20 of the conventional racquet of FIG. 1, i.e., about 21-1/4 inches
from the end 28 of its handle 13. In order to effect such location
of the centroid of the ellipse in a racquet where the elliptical
head is disposed with its long axis 22a transverse to the axis 24a
of the handle 13a, the overall length of the racquet is necessarily
shortened from the standard 27 inches to about 26 inches.
Although a racquet in the configuration of FIG. 2 may be
constructed in any of the modes by which metal racquets now on the
market are constructed, I would prefer to construct it in the form
shown in FIGS. 2 and 3. Thus, the handle 13a is formed about a pair
of members 30, 32, secured together at their handle-forming
extremities 34, 36 and at several other points by struts 38. These
members 30,32, are curved arcuately away from each other and then
back to embrace a separately formed elliptical head 20a. Members
30, 32 are provided with channels 40 (FIG. 3) along their embracing
arcuate segments 42, 46 respectively. The head frame 20a is made of
a thickness and configuration to fit into said channels 40. The
arcuate segments 42, 46, may be welded or otherwise secured to the
inserted frame 20a. The latter preferably includes an inwardly
extending rib 48 with a plurality of orifices 50 to receive the gut
or nylong stringing 52.
One important advantage of constructing a racquet in the manner
illustrated in FIG. 2 is believed to be that because more of the
head frame mass is disposed further away from the handle, the
center of gravity is inherently disposed further away from the
handle and toward the centroid of the ellipse, thereby enabling the
c.o.p. to be located more nearly at such centroid. Other advantages
are:
a. Since the overall length of the racquet is slightly decreased,
the bending moment generated by a smash toward the racquet tip will
be somewhat less than that sustained by the conventional
racquet;
b. It has been found that most hitting errors of players occur as
lateral deviations in the head from the axis passing through the
handle. Where the short axis of the ellipse is transverse to such
handle axis, such deviations more naturally involve the ball
striking the frame or just inside the frame than they would where
the long axis is transverse to the handle axis. However, where the
long axis of the ellipse is transverse to the handle axis, there is
a greater string area in the head where such lateral deviations are
wont to occur. The effects of lateral mis-hits may, therefore, be
substantially decreased. In other words the stringing in the
radially greater lunes of the ellipse, which stringing is less
utilized for mis-hits when the ellipse is oriented with its longer
axis coaxial with the handle, is better utilized when the racquet
head is turned so that those lunes are disposed on an axis
transverse to the axis of the handle;
c. The disposition of the head ellipse with its long axis
transverse to the axis of the handle provides an increased inertial
stability against roll. The moment of inertia of the racquet about
the longitudinal axis is believed to be typically increased by more
than 200 percent without the addition of supplementary weights at
the ends of the long axis, and by more than 300 percent with the
addition of such weights;
d. Lastly, such disposition of the head permits greatly increased
"dwell" of the ball on the strings for undercut, chopped and topped
stroking of the ball, which may occur in the course of ground
strokes, serves and volleys.
With respect to item (c) above, it is known from elementary
mechanics that the torque required to produce a specified
rotational acceleration of a body about an axis is proportional to
the moment of inertia of the body about that axis. Hence any
increase in the moment of inertia of a tennis racquet about its
longitudinal axis increases the inertial stability of the racquet
against rotation about that axis. That is to say, a given applied
torque, such as results when a ball strikes the strings at a point
laterally offset from the longitudinal axis, causes a smaller
rotational disturbance of the racquet.
The moment of inertia of a body with respect to a specified axis
may be defined as the sum or integral, taken over all mass elements
of the body, of the product of each mass element by the square of
its distance from the axis. Since the distance term is squared, the
handle of a tennis racquet, being concentrated close to the
longitudinal axis, contributes relatively little to its moment of
inertia about that axis, and the value of that moment of inertia is
determined predominantly by the distribution of mass in the head. A
comparison of FIGS. 1 and 2 shows that the mass of the head is
distributed on the average appreciably farther from axis 24a in
FIG. 2 than from axis 24 in FIG. 1. Taking account of the squaring
of the distance, that redistribution of mass yields a significant
increase in stability against roll.
FIG. 4 illustrates a possible manner of attaching supplementary
weights 54 to each side of the elliptical frame 20a in the vicinity
of the cross axis 22a in order to provide such further increase in
inertial stability against roll. The weight 54 may comprise a
relatively thin arcuately-shaped strip of lead with an inner
contour 56 mating with the outer contour 58 of the arcuate segment
42 of the member 30. Such lead strip 54 may be held by a pair of
straps 60, the ends of which are held by a fastener 62 which passes
through a hole provided in the inwardly projecting rib 48 of the
frame 20a.
The present invention also contemplates that supplementary weights
64 could be applied to the racquet frame through strut-like
extensions 66 shown in FIG. 5, to provide lateral mass disposition
even further outwardly along the cross axis 22a' from the centroid
26a' of the ellipse. It should be appreciated, however, that
although FIG. 5 shows such strut-like extensions 66 supporting
supplementary weights 64 on the sides of a frame of the
configuration of FIG. 2, they could be similarly applied to a
conventional racquet of the type shown in FIG. 1, and a noticeable
improvement in the form of an increase of inertial stability
against roll of the FIG. 1 racquet would be obtained. The quantum
of such improvement would, of course, be a function of the square
of the distance of the two oppositely disposed masses from the
centroid of the ellipse. Obviously, with such a functional
relationship, a much greater roll stability effect is inherently
obtained with a racquet head of the configuration shown in FIG. 2,
since the sides of the racquet head to which the supplementary
weights are attached, are disposed at a substantially greater
distance from the ellipse centroid than are the sides of the FIG. 1
racquet from its centroid along the cross axis 22.
It will further be appreciated that many factors will affect the
particular design of the racquet which is considered optimum for
each player, but the present invention offers new parameters and
design factors which have not heretofore been considered or appear
to have been taken into account by manufacturers in design even for
metal racquets.
* * * * *