Note: Descriptions are shown in the official language in which they were submitted.
211~493
MET~OD FOR THE ID~NTIFIC~TION AND CORRECTION OF
LINE-C~L ERRORS IN TENNIS
The prssent invention relates to a method of
identifying and correcting line-call errors which occur in
the conventional line-call system used in the game of
tennis. The method, hereafter called the monitor system,
combines manual and elsctronic operations to give the chair
umpire a new overrule capability to correct line-call errors
made by line iudges on any line of the court~
The conventional line-call system used in tournament
tennis requires nine persons to act as line judges~ each of
1~ whom has the responsibility to watch a single line during
play, and to give the "in" hand signal if the ball bounce
was on the line or inside the line, and call "fault" or
"out" whenever the ball is seen clearly to have bounced
outside the line~ If the line judge gives an "unsighted"
signal the chair umpire is responsible for making that
particular line-call~
Some line-call errors by line judges result from
conditions where fatigue or distractions cause momentary
lack of attention, where lighting conditions change along
the line such as bright sun to shadow, or where the body of
a player may be blocking his line of sight. The chair
umpire has the authority to overrule the decision of a line
judge if a clear mistake has been made. However~ it is a
common observation that during a match several line-call
errors which are obvious to the players and spectators may
stand uncorrected simply because the chair umpire does not
have an adequate view of the line-call to overrule with
certainty~ Errors of this kind frustrate the players,
affect their play, and when they occur in crucial point
3~ situations may be instrumental in changing the outcome of a
match.
The mechanism provided in the monitor system
effectively expands the umpires visual input to that covered
by several additional people (line-call monitors) who are
widely dispersed in stands around the court and who
communicate their decisions to support the chair umpire in
making overrule decisions confidently and with
justification, no matter where a line-call has taken place
on the court.
4~ Several United States and Canadian patents have been
granted on schemes which are intended to help solve the
line-calling problem with the aid of sensing devices built
into the court surface or under the court surface~ These
devices include material that changes colour for a short
time after being compressed by the balli a plurality of
laminated, pressure sensitive contact type switches that
extend along the boundary of the court; coils under the
surface; and electrically conductive tennis balls and lines~
~n expensive electronic line-call system which detects the
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out-of-bound balls by means of electromagnetic sensing of
specially modified balls has been tested with considerable
success in terms of the measurement accuracy, however the
metal loops on some running shoes are said to cause false
signals.
None of the schemes mentioned above are presently
known to be used in maior tennis tournament competitions to
replace or support the conventional line-call system~ One
common disadvantage is that they require a permanent hard
court surface which excludes their use on all soft surfaces
such as clay or grass.
One line-call device that has found intermittent use
in major tennis tournaments for several years is a version
of the device illustrated and described in United States
Patent No. 4,004,805, dated January 25,1977 granted to Chen
et al for an "Electronic Line Monitoring System for a Tennis
Court" which uses a double beam laser to detect out-of-bound
balls along the two service lines of a tennis court~ Other
references to the use of a laser detector are found in
~-C United States Patent No~ 4,718,669, January 12,1988 and No.
4,867,449, September 19,1989 for an ~Electrically Operated
Line Monitor for Tennis", both by the same authors
W.C.Carlton et al~ The advantage of the laser line-call
system is its ability to accurately call the service lines
on any court surface. 8efore every serve the laser is
required to be enabled by an operator. The laser has a
limited detection range beyond the service line so that one
of the conventional line judges is still required to make
out-calls along with the laser system~ ~nother limitation
of the laser detector is that it can only be used in
singles, and only on the service lines, which make up only
two out of a total of 10 lines that have to be monitored.
The present invention is a monitor system intended
for use in tennis stadiums which have spectator stands that
preferably surround the tennis court.
~ number of persons (called monitors~ are each
equipped with a small call-box transmitter which will be
activated into transmitting a coded signal by the momentary
press of a push button. The monitors are seated above court
4 o level at positions disposed in a symmetrical fashion in the
stands surrounding the tennis court. Each monitor will
assess the on-court line judge's call and immediately press
the button on their own call-box if they have the opinion
that the line judge has clearly made a mistake. The call-
boxes that are activated will transmit their information on
different frequency channels to a multi-channel receiver
worn by the chair umpire. The electronic data processing in
the receiver will generate an appropriate alert signal if
certain preset requirements are met and the chair umpire is
S~ notified by means of an audible sound from a speaker or by
some visual indicator in the receiver or by an external
earphone or visual indicator connected to the receiver. The
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umpire can then correct the line-call error in response to
the alert signal~
The probability of correcting these errors is
considerably improved by the monitor system since it permits
every call to be independently observed and verified from
many different angles, both in elevation and direction~
As an example of how important the viewer's
perspective can be, it is a common observation among tennis
players that the server can often detect the exact point of
contact of a served ball. The server may notice that the
ball is slightly long by seeing a small space between the
service line and the ball at the point of bounce. This
often goes undetected by the player returning the ball, even
though he is positioned much closer to the contact point.
In the monitor system, the call-box monitors are
seated in the middle level of the stands and have a wider
field of view of the court than the on-court line judges.
This gives them a unique opportunity to determine the
correct call not only for normal line-calls but for those
~o instances where the ball may suddenly changes direction as
in a let-serve or a net-cord ball. The minimum number of
monitors required in the system was determined to be six to
obtain a useful consensus. This can be improved marginally
by the use of eight or ten monitors if the situation allows~
Electronic processing circuits are provided in the
receiver to perform the following functions:
a) Generate a timed interval or ~time-window" of
approximately 2 seconds duration which is started at the
beginning of the first call-box signal to be received;
b) record the number of call-boxes received during the
time-windowi
c) compare the data derived in b) with the alert signal
threshold numbers preset by the monitor configuration
switch;
d~ generate an appropriate audio tone or visual alert
signal which is sent at the end of the time-window to an
internal speaker or visual indicatorl or to an externally
connected earphone or visual indicator if one of the alert
signal thresholds has been exceeded.
4~ The following scheme of three audio alert signals is
proposed for the prefered embodiment:
A levsl 1 alert signal is a single tone sound or
"beep~ which is interpreted by the umpire to mean that a
significant number of monitors disagree with the current
line-call such that an overrule decision is justified. If
there is no "beep" sound at all for a given line-call, then
the umpire is advised not to make an overrule~
~ level 2 alert is a double soundJ Ubeep..beep", which
is interpreted to mean that there is a very high level of
So disagreement with the current line-calll and that an
overrule to correct the line-call is almost mandatory~ Final
authority for making a line-call overrule rests with the
211349~
chair umpire who must have good reason for ignoring the
group decision.
~ level 3 alert is a triple sound, "beep..beep..beep"
means that all monitors in the present configuration have
been received within the time-window. This is the signal
that is expected to be heard during the monitor system-check
prior to the match.
The magnitude of the time-window must be set close to
two seconds for the following reasons:
1~ a) When an umpire makes an overrule it must be made within
about two seconds after the offending call, otherwise it
will be criticized as a late call.
b~ Normally the monitor inputs will be completed well
within two seconds.
c) In cases of continuous play, line calls may occur as
quickly as two seconds apart. The counting circuit in the
receiver which records the number of call-box channels
received within a time-window period will be reset to zsro
at the end of each time-window, ready to count the next set
of monitor input signals.
Each call-box is an assembly of components comprising:
A light-weight box that can be held in the palm of one
hand, made from suitable material such as molded plastic,
an internal long-life battery;
a button switch for entering line-call data that also
applies battery power to the integrated circuits;
a single channel transmitter of suitable frequency and
power with built-in antenna; and
integrated circuits to modulate the transmitter with the
call-box identification code.
The receiver is an assembly of components comprising:
A light-weight box made of a suitable material such as
molded plastic with a clip for attaching to a pocket or
belt;
internal long-life battery;
a power switch and indicator disPlay;
a 1~ channel integrated circuit receiver ;
integrated circuits to scan the channels for call-box
signals and to demodulate the received signals and recover
4~ the call-box identification codes;
integrated logic circuits to perform the functions of
time-window generation, chec~ing identification codes,
counting, threshold comparison and audio tone or visual
display generation;
internal speaker or visual alert indicatori
connector for external earphone or external visual alert
indicator;
a monitor selector switch to configure the system to
accept 6,8 or 10 monitors; and
211349 3
a built-in or telescopic antenna.
The invention, as exemplified by the preferred
embodiment~ is described with reference to the drawings in
which:
Figure 1 shows the positions of line judges and
monitors in a plan view of a tennis court and the spectator
stands which surround the court.
Figure 2 is a block schematic of a typical call-box.
Figure 3 is a block schematic of the receiver.
l~ In Figure 1 the spectator stands (10) are shown in
four places surrounding the tennis court (12). Eight
conventional line judges (14) plus the service line judge
(16) are shown in their positions on the court with the
chair umpire (183. The service line judge (16) moves to an
alternate service line position after each even numbered
service game. The six monitors (20) are seated
approximately in the middle rows of the stands in a
symmetrical fashion.
Tennis players conduct a warm-up practice prior to
2~ the beginning of a match. During thls time the six monitors
and the umpire prepare for a monitor system check. Referring
to figure 2~ each monitor has a small call-box (22) in the
palm of one hand with a finger ready to press the call-
button (24). The chair umpire wears the receiver (26) shown
in Figure 3 and puts it into operation by pressing the power
switch (28) to the ON position, and checks that the liquid
crystal display (3~) gives a normal indication~ as a check
on the battery (32). At the end of the player's warm-up
period the chair umpire announces "linesmen ready". Within
two seconds each monitor should press their call-button
(24). If the monitor electronic system is operational~ the
chair umpire will then hear the level 3 alert signal
"beep~.beep..beep" in the earphone, and can give the
announcement for play to begin.
The monitors follow the tennis play while one finger
rests lightly on the call-button (24). When a line-call
mistake has clearly been detected by any monitor~ the
monitor presses the call-button~
A radio frequency signal will begin being transmitted
when the call-button (24) is pressed. The call-button is a
microswitch and when it is pressed the switch closure is
both felt and heard by an audible click. The battery (34)
sends power to the modulator/transmitter integrated circuits
(36). The radio frequency signal is produced in the
transmitter and modulated by integrated circuits in the
modulator which repeats the call-box code at 50 hertz
2113~93
minimum~ Every call-box has its own distinct modulation
code that is recogni~ed bY the receiver (26)~ The
transmission ends when the button is released with another
click~
Refer again to Figure 3~ The call-box signals,
having different frequencies or channels. are received by an
antenna (38) and are detected by an 10 channel receiver
(40)~ The input scanner and demodulator (42) cycling at
about 100 hertz, sequentially examines each channel for the
presence of a call-box input, and verifies that the call-box
signals have acceptable identification codes~ It sends data
to the logic circuits (44) which contain information about
the number of channels~
The logic circuits (44) gensrate a 2 second
time-window started by the channel which first detects a
transmission. Other channels are accepted if their
transmissions start during the time-window~ At the end of
the time-window, a threshold comparison test is performed to
determine if the channel count exceeds any of the alert
signal threshold levels 1, 2 or 3. These threshold levels
are preset by the position of the monitor configuration
switch (46~ and are diffsrent for the three choices of 6,8
or 10 monitors~
The tone generation circuit will produce an
appropriate one, two or three beep alert signal if one of
the threshold levels has been exceeded. This is sent to the
speaker (48~ through the earphone jack (50)~ If the
earphone is plugged into the jack, the speaker is
disconnected and the alert signal is sent to the earphone
(52).
Alth~ugh only a single embodiment of the present
invention has besn described and illustrated, the present
invention is not limited to the features of this embodiment7
but includes all variations and modifications within the
scope of the claims~
