Note: Descriptions are shown in the official language in which they were submitted.
ELECTRICALLY CONDUCTIVE TENNIS BALL
AND L IN E CAI:.LING SYSTEM
FIELD OF THE INVENTICN
This invention relates to improvements in
electrically conductive tennis balls which are used with
auto~atic tennis court line calling systems to detect
whe~her the ball lands in or out of a tennis court
10 playing area or strikes the top of the net. Line
calling systems of this type have one or more sets of
exposed~ spaced apart conductors extending along
selected areas of the tennis court and the top of the
net to sense touchdown of the electrically conductive
15 ball.
When the ball lands across two or more of the
sensing conductor~, an electrical current-conducting
circuit is completed throu~h the ball to signal the
player~ that the ball touched down in an area occupied
20 by the oonductors.
Electrical conductivity of the tenni~ ball may
be established by incorporating electrically conductive
fibers into the cover of the ball.
25 SUMMARY AND C!E3JECTS OF I~IE INVENTION
In accordance with this invention, a blend of
electrically conductive and nonconductive fibers are
spun together to form yarn which is used to weave the
30 fabric for the tennis ball cover. The conductive and
nonconductive fibers are random lengths of filaments, as
opposed to staple fibers.
. .
--2--
The electrically conductive fibers may be made from
stainless steel. Alternatively, other types of electrically
conductive fibers may be used such as those described in U.S.
Patent No. ~,299,38~ which issued November 10, 1981, to John
5 A. Van Auken for ELECTRICALLY CONDUCTIVE GAME BALL.
One embodiment of this invention provides an
electrically conductive tennis ball for use with an electrical
detection circuit in which touchdown of the ball in a selected
area is detected by completion of a circuit between spaced apart
electrical conductors extending along that area. The electrically
conductive tennis ball comprises an elastically deformable sphere,
a cover of woven fabric covering the sphere with the fabric
being woven with a set of warp strands interlaced with a set
of woof strands, and with the strands of one of the sets
comprising a quantity of electrically conductive fibers and
a quantity of electrically nonconductive fibers, and the strands
of the other of the sets being composed entirely of electrically
nonconductive fibers.
In some oE the illustrated embodiments the tennis ball
advantageously includes an electrically conductive base which
lies between the woven cover and the elastically deformable
core of the ball to enhance electrical continuity amongst -the
conductive fibers in the cover. The electrically conductive
base preferably extends entirely around the core, thus bridging
the seams between the cover's panels to establish electrical
continuity between the panels.
The electrically conductive base may be an electrically
conductive adhesive which performs the additional function
of adhering the cover to the core of the ball. Other types
of electrically conductive bases may be employed.
For example, the electrically conductive base may be
an electrically conductive scrim of fibers of the type described
in U.S. Patent No. 4,299,384. Alternatively, the electrically
conductive base may be in the form of a thin, llexible, woven
or unwoven cloth or mat which may be bonded to the back side
of the cover. An electrically conductive adhesive may also
be used with the conductive scrim or ma-t to adhere the cover
in place on the core of the ball.
An electrically conductive coating may also be applied
S to the fabric which is used for the tennis ball cover -to
enhance continuity of the electrically concluctive paths in the
fabric~ The coating is applied to just the fabric's back side,
which becomes the cover's inner side in the final construction
of the ball. The coating may be applied before or after the
tennis ball cover panels are cut from the fabric.
The woven fabric for the tennis ball cover may
advantageously be needled to reorient a multitude of the
electrically conductive and nonconductive fibers in the woven
yarn preferably without fracturing the fibers in such a manner
that the reoriented fibers extend more transversely of the
plane of the fabric~ Because of this needling operation, free
ends of other portions of a multitude of the electrically
conductive fibers will project beyond the plane of the fabric
at least on the back side of the fabric and will be embedded
or otherwise engaged in the previously described electrically
conductive base (if usad) or the prevlously described
electrically conductive coating (if used) to enhance the
electrical continuity of the ball's electrically conductive
paths along the back side of the cover.
The fill yarn and the weaving pattern of the fill with
the warp, as well as the other features of this invention,
serve to reduce the number of electrically conductive fibers
which are required to make the ball sufficiently conductive
to operate the ball-sensiny circuits on the tennis court. By
reducing the required number of electrically conductive fibers,
objectionable discoloration of the ball is a~oided where the
color of the fabric's electrically conductive fibers is dis-
sirnilar to the color of the ball's cover. Furthermore, the
fill yarn, the weaving pattern of the cover, and the other
features of this invention do not impair the desirable playing
characteristics of the ball even where stainless steel fibers
are used.
%
In a further embodiment, the invention contemplates
an electrically conductive tennis ball for establishing a
current-conducting path across spaced apart: electrical conductors
extending along a selected area of a tennis court and/or the
top surface of a net. That electrically conductive tennis
ball comprises an elastically deforrnable sphere and a cover
of woven fabric covering the sphere with the fabric being
uniform over the entire surface of the ball. The fabric has
a set of strands of warp yarn interlaced with and extending
transversely of a set of strands of woof yarn with the yarn
for the strands in at least one of the sets being formed of
a plurality of electrically conductive fibers with metal
surfaces and electrically nonconductive fibers which are twisted
together and wherein the number of the electrically non-
conductive fibers exceeds the number of the electrically
conductive fibers in the yarn for the strands of the at least
one of the sets to the extent that excessive discoloration
of the cover by the electrically conductive fibers is avoided.
Al-ternatively, the fabric has a set of warp strands interlaced
with a set of woof strands with the strands of one of the last-
mentioned sets comprising a quantity of electrically conductive
filament fibers with metal surfaces and of random lengths and
a quantity of electrically nonconductive filament fibers mixed
with the conductive fibers, and with the conductive and non-
conductive filament fibers being twisted together to form the
yarn for the one of the sets of strands.
With the foregoing in mind, a major object of this
invention is to provide a novel electrically conductive
tennis ball which has a high degree of electrical conductivity,
which is economical to manufacture, and which does not degrade
the playing characteristics of the ball or objec~ionably
discolor the ball.
A more specific object of thi~; invention is to
provi.de a novel electrically conductive tennis ball in
which the fabric's electrically ~ondu~ive fibers are
electrically interconnected by treating the back side of
5 the fabric or the tennis cover with an electrically
conductive material such as a coating, an electrically
conductive ~&esive" an electrically conductive scrim,
or an electrically conductive cloth.
Another im~rtant object of this invention is
10 to provide a novel electrically conductive tennis ball
in which the electrical conductivi~y of the ball is
greater ~han the conductivity of water.
Yet another object of this invention is to
provide a novel line callinq system which senses
15 touc~hdown of an electrically conductive tennis ball, but
not the presence of water on the tenni~ court, to avoid
false signals due to water on the court.
Fur~her objects of this invention will appear
as the descripkion proceeds in connection ~ith the
20 below-described drawings and annexed claims.
BRIE~ DESCRIPTION ~F T~ D~AWINÇS
FIG. 1 is an elev~tion of an electrically
25 conductive tennis ball incorporating the principles of
this invention, and showing the ball touching down
against a tenni s court surf ace containing the
ball-sensing conductors of an electrical line calling
~y~tem.
FIG. ~ is a simplified schematic circuit
diagram of an electrical sensing circuit which is used
to ~ense or de~ect ~ouchdown of ~he ball in a line
calling ~yst~m;
~2~
FIG. 3 i6 a bott~ plan view of the ball as
viewed from lines 3-3 of FIG. l;
FIG. 4 is an enlarged fragmenltary plan view
showing the front face of the woven fabric from which
5 the balli6 cover is cut;
FIGo 5 is a section taken along lines 5~5 oiE
FIG. 4;
FIG. 6 is a view of a wocf strand used to
we~ve the fabric shown in FIGo 4;
FIG. 7 is an er;l~ged section similar t:o
FIG~, 5 and showing the reorientation of fiber~ after the
fabric is needled;
FIG. 8 is an enlarged f ragmentary section
taken alon~3 lines ~-8 of FIBJ l;
FIG. 9 is an enlarged section ~imi~ar to
FIG. 8 but shawing a modification of the ball;
FIG. 10 is an enlarged section similar to
FIG. 8 and shc~wing another modification of the ball;
~ IG. 11 is an enlarged section similar to
20 FIG. 8 and showing yet another modification of the ball;
FIS~ 12 is an enlarged section similar to
FIG. 8 and showing yet another modificatior~ in whi~h
s~me of the electrically conductive fibers have dangling
ends lying in the seam between the panels of the cover
25 to establish electrical continuity be~een the cover's
panels;
FIG,. 13 is a fragmentary plan view similar to
FIGo 4, but showing ano~her embodiment o~ this
invention; and
FI~. 14 is a section similar to FIG. 3 but
sho~7ing a tennis ball having a cover made fr~n the
fabric of FIG. 13.
DETAILED DEscRIpTIc~a OF ~HE INVENTI~N
~ eferring to FIG. 1, the elect:rically
conductive 'cennis ball incorporating the principles of
5 thi~ inventisn i~ îndicated at 20 and ccmprises an
innerV hollow, elastic~ly deformable sphere or core 22
and a ~w~piece cover 2D.. ~re 22 is ~ any sui}able
con~entional oonstrucgion and may be formed frcrQ rubber
or other sui~able elastically defo~mable material. ~he
io interior o~ core 22 may be filled with air or other gas
under pressure.
Cover 24 is a>nvenltionally divided into two
figure-eight- or dumbbell panels 26 and 28 which are s~ie
cut frcm a bolt or sheet o~ woven fabric or cloth 30
15 (see FIG. 4) and which are glued, adhered or otherwise
affixed to the outer suriEace of core ~;!2.
Ar~r suitable electrical sensing circuit may be
used with ball 20 for sensin9 touc:hdown of the ball in
selected areas on a tennis court. In FIG. 2, a
20 simplified foL~n of the electrical fien6ing circuit is
- inaicated at 32 and is shadn to cc~nprise a plurality of
expoæd, preferably parallel, spaced apart
conductors 34. me conductors of the sensing circuit
are preferably embedded in the tennis court to lie flu~h
25 or nearly ~lush witb ~urface 38~ In the illustrated
example, alternate conductors of sen~ing circuit 32 are
electrically connected to one tenminal of a suitable
d.c. voltage ~ource 3~, and the remaining conductors in
circuit 32 are electrically connected to the other
30 terminal of the vol~age source.
When ball 20 touches down on surface 38, it
defonms to onn a generally flat, circular touchdown
area or rebounding area 40 ~see FIG. 3) which i8 large
~2~ 2
enough to ~ridge at least two adjacent conductors in
sensing circuit 32. The conductors in sensing
circuit 32 are spaced apart by a ncminal distance which
is determined by the ball's flattened touchdown area 40.
5 For example, the spacing between adjacent conductors in
circuit 32 may be 3/16 inch fcr a touchdown area of as
little as 1 inch in dicameter. Being electrically
conductive, ball 20 will, upon touchdown in the area
occupied by circuit 3~ bridge two or more adjacent
10 conductors in circuit 32 to thus ccmplete a
current-conducting circuit between at least two adjacent
conductors in the sensing circuit.
me completion of the circuit across adjacent
conductors of circuit 32 results in the conduction of
15 current through ball 20 from source 37. This current is
- utilized to operate an indicating device 41 to signal
the players that the hall landed in the selected area
occupied by the conductors of circuit 32.
A ~uitable sensing circuit of the type
20 described above is disclosed in U.S. Patent
No. 4,109,911 which issued August 29, 1978.
Referring to FIGS. 4 and 5, the woven
fabric 30 is a unique satin weave having a multiplicity
of warp yarns 44 (or threads as they are sometimes
called~, or strands as they may also be called,
interlaced with and extending at right angles to, a
multiplicity of rows or parallel lengths of woof or
filling 46. It will be appreciated that multiple rows
of the woof or filling 46 customarily form a part of a
single yarn tor thread) by shuttling the filling yarn
back and forth in the loom. These rows of parallel
lengths of illing are therefore originally
inter~onnected through the fabric's selvedges, but are
separaked fran one another in the cover's panel~ 26
and 28 upon cutting the panels from fabric 30.
In this BpeCificatiOn~ the tenm "strandsn i~
8 u&ed to refer to the rows or parallel lengths of woof 46
i~ fabric 30 and in p~nels 26 and 28, which are cut frcm
~abric 30. q~he separate parallel lengths of warp yarn
are also referred to a~ ~;trands. In FIG. 1, lines
representing some of ~he paralleLlen~th~ or ~trand~ of
10 warp and woo~ are shawn to be spaced apart for purposes
of illu~tration. m e actual spacing of the parallel
lengths of woo~ 46 are more accurately represen~ed in
FIG. 4.
Referring ~o FIG. 6, ~he woof yarn 46 is
15 canposed of a large n~nber of electrically nonconductive
filament fibers 48 of random lengths and a sm~ller
number of electrically conductive filament fibers 50 of
randcm lengths, such as single untwisted synthetic
filament~ or monofilament type fibers~ m e electrically
20 conductive fibers 50 are blended with the nonconductive
fibers 48 so that the conductive fibers are distributed
throughout the gro~p of nonconductive fiber~;. After the
fibers are blended, they are twisted together as shown
in FIG. 6 to form the filling 46.
me nonconductive fibers 48 may be fonmed from
any suitable material used in manufacturing tennis ba:Ll
covers such as ~rlon~ cotton, and/or wc~ol.. ffle
electrically conductive fibers 50 are preferably thin,
finely drawn sta nless steel fibers. Alternatively~ the
30 electrically conductive fibera 50 may be Nylon fibers
coated with silver or other electrically conductive
material such as the plated or coated fibers disclo~ed
in U.S. Patent No. 4,299,384, which issued on November
--1~
10, 1981.
Preferablyf the number of nonconductive
fibers 48 is much greater than the number of
electrically conductive fibers 50 especially where the
electrically conductive fibers are stainless steel or
other material having a color dissimilar to the
nonconductive fibers 48. m e electrically conductive
fibers may be in sufficient number to represent 10 to 30
percent of ~he total number of conductive and
nonconducLive fibers in the yarn. In the illustrated
embodiment, the nonconductive fibers 48 make up as much
as 70 percent of the total number of fibers in the woof
or filli~g, and the electrically conductive fibers 50
make up the remaining 30 percent. After being wvven,
Pabric 30 may be dyed to provide the cover with a
suitable color such as yellow. The Lectra-ConK 3-7093
yarn, manufactured by the Schlegel Corporation of
Rochester, ~ew York, is made in accordance with the
foregoing teachings for the fill yarn and may be used
for the fill in weaving fabric 30; alternatively,
Lectra-Con~ 060-150 co~ductive material can be used in
manufacturing fill yarn such as the yarn typically used
for manufacturing tennis ball covers.
The parallel lengths or strands of warp 44 are
fonmed entirely of elec~rically nonconductive fibers
such as Nylon~ cotton and/or wool. The warp fibers may
also be filament fibers of randcm lengths~ such as
single untwisted synthetic filaments or monofilament
type fibers, and they are twisted together to fonm the
warp strands used in weaving fabric 30. Thus, only the
woof 46 of fabric 30 contains the electrically
conductive fibers ~or making the ball's cover 24
electrically conductive.
Preferably, the warp strands 44 are very thin,
and the yarn used for the woof ~6 is abou~ ten ~ne~ as
5 thick or coarse as ~he warp yarns or thread. ~he
woof 45 therefore has about ten time~ as many ibers as
the ~arp 44. Yarn having ~ Dtex o~ about 4400 to 5000
m~y be used for the woof.
me weave o~ fabric 30 i~ a co3lYentional type
10 used or tennis ball covers and is advantageollsly of the
type in which each len~th or r~ of the woof or
filling 46 passes or skips over more warp strands 4d~
than it passes under as view~d from the fabricls fro~t
face. The fron~c face of fabric 30 is shawn in FIG. 4
15 and is used as the ou~er side of the termis ball
co~rer 24 in the finished product.
For each warp strand that passes under,
filling 46 may pass over five to seven warp strands 44
(i.e. p under one and over five to seven~ O For each
20 group of eight sus::cessive warp strands 44 in the
embodiment sh~wn in FIG. 4, each r~w of ~he wovf 46
passes under one warp strand and over the other seven.
Because of this type of weave and because of the mu~h
grea'cer thickness of the woof 46, more fillings than
25 warp show on ~he ~ron~ ~ace of fabric 30 so that the
fillings 46 daninate the ~Eront face of the fabric and
occup~ most of the surf ace area on the f ront f ace of
fabric 30. Because of thi~ fabric construction, the
woof 46 will occuE~y a ~;ubstantially greater area of the
30 outer pe~iphery of the termis ball cover a~ canpared
with the aeea occupied by the warp 44.
Because of the large n~nber of electrically
nonconductive fibers and the relatively small number of
-12-
electrically conduc~ive fiber~ in each of the woof
strand~ 46, ~tainless s~eel fiber~ or ~he like may ke
~ed in the woof without causing any unacceptable
di~coloration of the tennis ball coverO
After the weaving operation, fabric 30 may be
felted by s~bjecting it in a conventional manner to
pre~sure and heat ~o as to pres~ ~he woven fabricO
After the felting operation, fabric 30 may
advantageously be ~ edled to reorient a substantial
10 majority o~ the electri~ally conductive fibers in the
filling 56 without fracturing ~he conductive or
nonconductive fiber~. The electrically nonconductive
fibers in the warp 44 and woof 46 will al~o b~
reoriented by the needling operation, but only the
15 reorientation o~ the elec~rically conductive fibers is
of significance.
Before needling, the fibers in warp 44 and
woof 46 lie generally in the plane of fabric 30 as ~hown
in FIG. 5. A~ter needling, a large n~mber of the
20 electrically conductive fibers 50 in the filling 46 will
have portions 51 (FIG. 7) reorien~ed to extend generally
transversely of the plane of fabric 30 as shown in
~IG. 7 so that the needled portion (which includes some
free ends) of the electrically conductive fibers 50
25 extends beyond the plane of fabric 30 on the fabric's
inner or reverse side, which will be used as the inner
or ba~k side of cover 24. me needling operation may be
such that portions of a multitude of the electrically
conductive fibers 50 extend beyond the plane of the
30 fabric on both sides or faces of the fabric.
Any suitable needling machine having fine or
t~in needles (not sh~wn) may be used to needle fabric 30
in the manner described above. ~ne suitable type of
~13--
needle i8 described and shown in Patent No, 4,299,3~40
~1 ~ernatively, needl es hav ing axi al ly opposi tely facing
notches may be utili2:ed to catch ~he fibers during both
the advancing and retracting strokes af the needles,
5 thu~ reorienting the caught fibers in ~3uch a way that
E~ortions of the caught fibers project transver~ely frarn
both sides or faces of fabric 30.
After fabric 30 is needled in 'che manner
de~cribed abovef it then is advantageously napped orl the
10 front face. and sheered so ~hat cover 24 will h~ve the
usual fuæziness on i~s outer periphery. ~ter these
operations, panels 26 and 28 are die cut fram fabric 30.
It will be appreciated that the process steps of
felting, needling and napping may be perf3rmed after
15 ~nels 26 and 28 are cut fr~m fabric 30, bu'c it
obviously i~ more con~enient and econanical to perform
these operation~ before the panels are cut fran the
fabric.
Upon being cut fr~n the fabric, panels 26
20 and 28 are cemented or adhered to ~e ball's COrQ 22.
~n electrically nonconductive adhesive or cement may be
used for this purpo6e, but an electrically conductive
adhesive is preferred~ ~rhe electrically conductive
adhesive fo~ns a thin layer 54 ~see FIG. 8~ perip~erally
25 around the entire outer surface of core 22 between
core 22 and panels 26 and 28. An example of a ~uitable
electrically conductive adhesive is the Vulcan
Corporation partic:ula~e carbon a~c-72 uniformly mixed
~?ith any ~uitable rubber cement for manufacturing tenni~
30 balls in an amount suf:Eicient to achieve the ~lred
conductivity of the ball. me conduc~ive and
nonconductive fiber portions 51 whicb are reoriented by
the previously described needling operation will be
enbedded in adhesive layers 54 and will be securely
fixed or held in place by the adhesiYe.
Because ibers 4B and 50 are relatively long
and are twisted together to form the yarn iEor wea~ring
5 fabric 30, ~ey will be retained in place and therefore
will no~ come loose and fall onlto the cour~ when
subjected to impact forces during play~,, FurthenDoret
retention of the fi~er~ which have been reoriented by
the previously described needling operation is enhanc:ed
10 by embedding the reoriented portions 51 in adhesive
layer 54. This construction 'chere~ore avoids the
objectionable condition where conducltive fibers come
loose and fall onto the sensing circuit 32 to produce a
false signal.
Frosn the foregoing description, it will be
appreciated that the electrically conductive fibers 50
create a maze of elect ically conductive networks 60
(FIG. 1) which are distributed throughout the entire
periphery of the ball. Networ1cs 60 deine a
20 multiplici~r of current-conducting paths passing through
cover 24 and extending along the outer si~le of cover 24
for completing a circuit between adjacent conductors in
sensing circuit 32 upon touchdown of the tennis ball on
circuit 32. Tlle portion~ of ne~orks 60 lying on the
25 outer periphery of cover 24 are distributed throughout
the entire outer surface of the cover so that a signal
is produced regardless of the orientation of the ball
up~n touchdown on the conduc~oræ of sensing circuit 32.
In addition to being in contact with ~he
30 needled portio~s of fibers 50, the electrically
cond~ctive adhesive layer 54 will also be in contact
with some of the unneedled electrically condllctive
fibers in the portions of fill 46 which loop under the
warp 44 to appear on the back side of c:over 24. Most of
the networks 60 are therefore interconnected through the
electrically conductive adhesive layer 54 which fonms an
electrically conductive base lying entirely along the
5 inner side of cover 24.
m e electrical conductivity of the tennis ball
for si~naling touchdown of the ball on sensing
circuit 32 i5 significantly enhanced because of the
large exterior surface area occupied by the woof in
10 cover 24, the presence of the electrically conductive
adhesive base 54 on the inner side of cover 24, and the
reorientation of a multitude of the electrically
sonductive fibers 50 by the previously described
needling operation.
In a modified embodiment of the ball
illustrated in FIG. 8, adhesive la~er 54 can be made of
a nonconductive material; and an electrically conductive
coating can be applied to the back of the cloth fonmed
by warp 44 and fill 46. This elec~rically conductive
20 coa~in~ would substantially fill the spaces between the
fibers of warp 44 and thus serve the same function as
the electrically conductive adhesive layer 54.
~ eferring to FIG. 9, a seam 56 is
conventionally formed between Fanels 26 and 28. m e
25 electrically conductive adhesive layer 54 bridges
seam 56 to ensure electrical continuity between
panels 26 and 28. Seam 56 is preferably filled with any
suitable, conventional nonconductive cement.
Alternatively, a conductive seam cement may be used, but
30 the conductive carbon particles in the cement produce an
undesirable discoloration of the ball. If panels 26
and 28 are closely matched, they will butt
-16
against each other at the apex of seam 56 to enhance
electrical continuity be~ween panel~ 26 and 28.
In the embodiment shown in FIG. 9, an
electrically conductive scrim 58 is ~an~wiched between
5 cover 24 and core 22 to establi~h the electrically
conductive ba~e on ~he back ~ide of cover 24. Scrim 58
is made up of an unwoven oFen mesh of fibers ~trung
together in an irregular array in a unitary unwo~en
body. Preferably~ all o~ the ~ibers in ~crim 58 are
10 electri~ally conducti.ve. Scrim 58 extends around and
cover~ ~he entire periphery of core 22. Scrim 58
therefore bridges seam 56 and lies entirely between
core 22 and cover 24.
Like the previously described electrically
15 conductive adhesive layer 54~ ~crim 58 also lies in
contact with needled portions of fibers 50 and alfio in
contact with same of the ~nneedled elec~rically
condu~tive fibers in the portions of fill 46 which loop
under the warp 44, thus enhancing the conductivity of
20 the ball and establishing electrical continuity betwee3n
panels 26 and 28. Scrim 58 may be adhered to core 22
and cover 24 with either an electrically nonconductive
~dhesive or an electrically ~onductive adhesive. It
will be appreciated that scrim 58 is tightly pressed
25 between coYer 24 and core 22.
Scrim 58 may be arranged in a stretched-out
~heet on the back or reverse sides of panels 26 and 28,
and the composite of each panel and the scrim may then
be adhered or cemented to core 22 with an electrically
30 conductive or nonconductive adhesive. The usual
nonconductive cement used for adhering 'che tennis ball
cover to the core of the ball i8 considered to be one
a~ailable type of adhesive. Scrim 58 may also be placed
on the back or reverse sides of fabric 30 before the
fabric is needled.
In the ~mbodiment shc;wn in FI~. 10~ scrim 5B
is replaced with a thin~ woven or urlwovlen doth or
S mat 62 which is sandwiched between and adhered to
cover 24 and core 22 with an electric~lly conductive or
norlconductive adhe~;ive, Mat 62 may be Eoraned fr~n ar~,
~uitable materia3 and m~y be adhered to core 22 before
application of cover 24. In the finished construction
of b~l 2a, mat S2 contac~:s the needled portions of the
electrically conduc~ive ~iber~ 50 and scme of ~he
unneedled electrically conductive fihers in the portions
of fill 46 which loop under 'che warp 44 to establish
electrical continuity be~een panel~ 26 and 28.
In~tead of a~plying mat 62 to core 22 before
placing cover 24 on the core, mat 62 may be adhered to
the back or reverse side of fabric 30 with an
electrically conductive or nonconductive adhesive before
the fabric is needled and before panels 26 and 28 are
20 cut frcm the fabric. After the panels are cut fr~m
fabric 30, the panel and ma~ composite may then be
adhered to core 22 wi~h an electrically conductive or
nonconductive adhesive.
Instead of e~ploying scrim 58 or mat 62, the
25 reverse or back side of fabric 30 (i.e., the side which
becomes the inner side of cover 24) may ~e coated
throughout with an electrically conductive coating 64
(~ee FIG. 111 after f~bric 30 is needled in the manner
de~cribed above and preferably after fabric 30 is n~pped
30 and before panels 26 and 28 are cut from the fabric.
Coating 64 is applied with sufficient thickness and in
su~h a manner that the reoriented portions of the
needled ibers, including fibers 50, become embeddecl and
~2~
-lB-
fixed in coating 64 to enhance the electrical
conduc~tivi~y o~ the ball. Pdditionally, coating 64 will
partially ~pregnate fabric 30 :Er~n the re~er~e side
thereof to electrically interconnect a large nunber of
S the unneedled electrically conductive woof fiber~ 50
still lying in the plane of fabric 3û.
Coating 64 may be co~ventional and ma~ be of
any ~ui~able type. For example, coating S4 m~y be
Schlegel Corporation's 12ltex base coating R3115-00-2.
After coati~g 64 is applied, panel~ 2b and 28
are die cut fram fabric: 3û. mus, coating 64 will fonn
a continuous unin~errupted electrically condactive ba~ie
along the entire inner surface area of each of the
panels 26 and 28 after the panels are cut frclm
15 ~abric 30,,
It will l~e appreciated that oating 64 m~y
alternatively be applied to panels 26 and 28 after they
are cut from ~abric 30.
~ pon being s::ut fr~n ~he c:oated fabric,
20 panels 26 and 28 are adhered to the ball's core 22 by an
electris::ally conductive or. nonconductive adhe~ive.
Flectrical continui~ bet~een panel~ 26 and 28
may be established bs~ separating the panels fran
fabric 30 in such a wa~ that a ~;ubstantial n~er of the
25 conductive fibers 50 are left with ends 66 (FIG. 12)
that dangle fr~xn the ed~e of each panel. This ma~ be
accomplished by only partially die cutting panels 26
and 28 from fabric 30 (that is cutting the fabric only
p~rtially around the periphery of each of lthe panels or
30 cutting only partially through the ~abric on spaced
apart regions) and by pulling the partially cut panels
loose frcsn Jche remainder o 'che fabric in ~uch a manner
that ends 66 dangle fram the edge oiE eacb of the p~nels
at the regions where the panels were not fully cut from
the fabric,
Upon adhering panels 26 and 23 in place on the
core of the ball, the dangling ends 6b frc~m the ~dO
S panel~ will in~erengage or bec~ne entanlgled to e tablish
electrically conductive E~ath8 ~his::h bridge the ~eaan
between the ~s: panel~;. EndE; 66 ~7ill be enbedded in the
~eam cement 67 ~FIG. 123 or o~her material used to fill
~eam 56 ~d ~chu~ will be fixed in place b~ the ~eam
10 cementr If desired, the seam material mz~ be
electric~lly conductive.
By utilizing.the fiber ends 66 to establish
electrical continuit~r be~een panels 2~ and 28 ~nd b~
usin~ electri~lly conductive warp strands, the
15 e:lectrically conductive base (namely, ~dhe~ive layer 54
scrim 58 or mat 62) ma~ be crnitted :fr~sn the ball, and
cover 24 may be adhered to core 22 with an electrically
nonconductive adhesive. Close matching of panels 26
and 28 which butt together at the apex of seam 56 may
20 even e~;tablish sufficient electrical continuity bebween
panels 26 and 28 to vbviate the need for panels with the
dangling ends 66 or an electrically conductive
seamrbridging baseO
In accordance with a further feature of this
25 invention, the electrically conductive networks 60 are
made significantly more conductive than water, and the
ball-sensing circuit 32 is designed so that it is
insensitiqe to wat r on the tennis court surface. This
may be accomplished by providing an adju6table
30 resistance 76 (see ~IG. 2~ in serie~ with the voltage
power source 37. Alternativelyt a comparator (not
shown) may be used to compare the ball-produced
electrical signal with a fixed reference signal in ~uch
--20--
a way that a false signal produced by water bet:w~en
adjacent conductors in circuit 32 is insufficient to
~;witch the output of the comparator. Hc~7ever, the
~tronger signal produced by the more conductive tenni~
5 ball will swi~ch the c:ompara or's ou~put, thus
~ignalling touchdown o~ the ball in the area occu~ied by
~e ~ensin~ circuit.
Preferably, the resitivity (which is the
reciprocal of c:onductivity~ of the electri¢ally
10 conductive l:ennis ball of this invention is equal to
between 10 and 500 ohns per square.
Referring to FIGS,, 13 and 14, an al'cerna~e
woven fabric 30a may be used for cover 24. It is the
same as fabric 30 except that the warp yarn or
15 strands 44a in fabric 30a also contain electrically
conductive fibers to further enhance the electrical
conductivity of the ball and to negate the need for
scri~s, conductive coatings or conductiYe adhesives.
The fill in fabric 30a is the s~me as the fill in
20 fabric 3n. Like reference n~merals have been therefore
applied to de~ignate like elements of the fill yarns for
~he two fabrics.
In the embodiment of FI~S. 13 and 14, a
quantity of electrically conductive fibers 50a are
25 blended with a much larger number of electrically
nonconductive fibers 48a, and the blended fibers are
twisted or spun together to form the yarn for the
warp 44a. ffl e ratio of conductive fibers to
nonconductive fibers in warp 44a preferably is less tban
30 but may be the same a6 or greater than ~he ratio of
conductive fibers to nonconductive fibers in the
fill 46. Fibers 50a are preferably the same as
fibers 50, ~nd fibers 48a may be the same as fibers 48.
-21-
l~e woven Fattern of fabric 30a is the ~ame as that of
f~bric 30.
In this specification (including the claim~
herein) the term ~yarn" is considered to include a
5 thread and any other type of yarn~ A thread is
considered to be a yarn having a noticeable ~wist~
The invention may ~e embodi~d,in other
specific fonms withou~ departing ~rom the spirit or
es~ential characteristics thereof. m e present
10 embodLments are therefore to be oonsidered in all
respect~ as illustrative and not restrictive, the ~cope
of the invention being indicated by the appended claims
rather than by the foregoiny description; and all
changes which came within the meaning and range of
15 ~quivalency are therefore intended to be ~mbraced
therein O
