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Claims  |
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I claim:
1. An impact detection apparatus comprising:
a first primary multilayered sensor in the nature of a variable magnitude
signal generating device situated so as to abut an area enclosed by a
boundary of interest;
signal processing means having an input coupled to said multilayered
sensor, said signal processing means being responsive to a variable
magnitude input signal from said sensor and producing in response thereto
an output signal indicative of whether an impact of a given object of
interest has occurred to said sensor;
indicator means coupled to said signal processing means output signal for
producing in response thereto a sensible signal indicative of impact of
said given object of interest;
said multilayered sensor comprising a sandwiched multilayer device
including in respective order:
a first outer conductive layer;
a first insulative layer;
an inner conductive layer;
a second insulative layer;
a second outer conductive layer;
said outer conductive layers being electrically interconnected to form an
electrically shielded region therebetween within which said insulative
layers and said inner conductive layer are disposed; and,
at least one of said insulative layers is formed of a compressible
insulative medium.
2. The apparatus of claim 1 further comprising:
a secondary sensor located within the boundary of interest and abutting the
primary sensor, said secondary sensor being coupled to said signal
processing means to supply thereto a secondary input signal indicative of
impact on said secondary sensor to thereby detect the instance of the
object of interest landing within the boundary and then sliding across the
boundary where its impact will be detected by the primary sensor, said
signal processing means being adapted to cancel a signal from the primary
sensor upon receiving a signal from said secondary sensor.
3. The apparatus of claim 1 wherein said signal processing means comprises:
an analog-to-digital converter having an input coupled to said multilayered
sensor, having a plurality of input-threshold levels, and producing a
digital output signal representative of said input; and
digital pattern recognition means coupled to said analog-to-digital
converter output for comparison of said digital output signal to known
characteristics of a corresponding digital signal produced by impact of
said given object of interest, and producing in response to said
comparison an output signal indicative of whether said digital output
signal matches said corresponding digital signal, whereby said output
signal is indicative of impact of said given object.
4. The apparatus of claim 1 wherein:
said first insulating layer is compressible to permit varying separation
between said first outer conductive layer and said inner conductive layer,
and the second insulating layer may be either rigid, semi-rigid, or
compressible.
5. The apparatus of claim 1 wherein:
a fixed voltage is maintained between said inner conductive layer and each
of said outer conductive layers; and
a displacement current is generated when the distance between the inner
conductive layer and the outer conductive layers is changed due to an
impact.
6. The apparatus of claim 5 wherein:
the displacement current is converted to a digital pattern by signal
processing means.
7. The apparatus of claim 1 wherein said signal processing means comprises:
first signal-magnitude detecting means responsive to said input signal and
producing in response thereto a first step-function digital signal having
a time duration substantially identical to the time during which said
input signal exceeds a first threshold;
second signal-magnitude detecting means responsive to said input signal and
producing in response thereto a second step-function digital signal having
a time duration substantially identical to the time during which said
input signal exceeds a second threshold higher than said first threshold;
and
digital pattern recognition means, responsive to said first and second
step-function digital signals, for comparison of the characteristics of
said digital signals to known characteristics of corresponding digital
signals produced by impact of said given object of interest, and for
producing in response to said comparison an output signal indicative of
whether said first and second digital signals match said corresponding
digital signals, whereby said output signal is indicative of impact of
said given object.
8. The apparatus according to claim 7 further including:
hum cancellation means coupled to receive said input signal and to subtract
therefrom a hum signal, said hum cancellation means being coupled to each
of said signal magnitude detecting means to supply a substantially
hum-free input signal thereto.
9. The apparatus of claim 7 wherein said signal processing means further
comprises:
voltage source means coupled to said sensor for producing a constant
voltage difference between said inner conductive layer and said outer
conductive layers, whereby said input signal is a displacement-current
analog of the derivative of impact deflection of said sensor;
analog integrator means responsive to said input signal for producing in
response thereto an integrated output signal, whereby said integrated
output signal is an analog of impact deflection of said sensor;
third signal-magnitude detecting means responsive to said integrated output
signal and producing in response thereto a third step-function digital
signal having a time duration identical to the time during which said
integrated output signal exceeds a third threshold;
fourth signal-magnitude detecting means responsive to said integrated
output signal and producing in response thereto a fourth step-function
digital signal having a time duration identical to the time during which
said integrated output signal exceeds a fourth threshold higher than said
third threshold; and
said digital pattern recognition means effects comparison of the
characteristics of said first, second, third and fourth digital signals to
known characteristics of corresponding digital signals produced by impact
of said given object of interest, and produces in response to said
comparison an output signal indicative of whether said digital signals
match said corresponding digital signals, whereby said output signal is
indicative of impact of said given object.
10. The apparatus according to claim 1 further comprising:
a second primary multilayered sensor in the nature of a variable magnitude
signal generating device situated so as to abut an area enclosed by a
boundary of interest;
said signal processing means input being coupled to each of said first and
second multilayered sensors; and
said signal processing means also determines which of said sensors to
activate and which to deactivate, the determination being operator
selectable and dependent upon which boundary of an area with plural
boundaries is of interest at a given time.
11. An impact detection apparatus specifically adapted to determine whether
or not a ball lands in or out on a tennis court, comprising:
a plurality of primary multilayered sensors located on said tennis court in
a sensor array with each sensor being situated adjacent to the lines
defining the boundaries of the court;
each of said plurality of multilayered sensors comprising a sandwiched
multilayer device including in respective order;
a first outer conductive layer;
a first insulative layer;
an inner conductive layer;
a second insulative layer;
a second outer conductive layer;
in each of said devices, the outer conductive layers being electrically
interconnected to form an electrically shielded region there between
within which said insulative layers and said inner conductive layer are
disposed;
in each of said devices, at least one of said insulative layers is formed
of a compressible insulative medium;
signal processing means having an input coupled to each of said
multilayered sensors, said signal processing means being responsive to
variable magnitude input signals from said sensors and producing in
response thereto output signals indicative of whether an impact of a
tennis ball has occurred on said sensor array;
indicator means coupled to said signal processing means output signals for
producing in response thereto a sensible signal indicative of impact of
said tennis ball on said sensor array.
12. The apparatus of claim 11 wherein said signal processing means
comprises:
first signal-magnitude detecting means responsive to one of said input
signal and producing in response thereto a first step-function digital
signal having a time duration identical to the time during which said
input signal exceeds a first threshold;
second signal-magnitude detecting means responsive to said input signal and
producing in response thereto a second step-function digital signal having
a time duration identical to the time during which said one input signal
exceeds a second threshold; and
digital pattern recognition means responsive to said first and second
step-function digital signals for comparison of said digital signals to
corresponding digital signals characteristic of impact of said given
object of interest and producing in response to said comparison an output
signal indicative of whether said first and second digital signals match
said corresponding digital signals, whereby said output signal is
indicative of impact of said given object.
13. The apparatus according to claim 11 wherein:
said sensible signal is an audible and/or visual signal emitted when it is
determined that a ball landed out; and
said signal processing means also determined which of said sensors to
activate and which to deactivate, the determination being operator
selectable and dependent upon which boundaries of said tennis court are of
interest at a given time.
14. The apparatus of claim 11 wherein said senor array includes, at each
point along said boundary lines:
a primary sensor situated abutting the exterior edge of said line so as to
detect the impact of a ball landing in the out area; and
a secondary sensor situated abutting the interior edge of said line so as
to detect the impact of a ball in the in area, the secondary sensor then
providing a signal to override the corresponding primary sensor so that a
ball skidding into the out area will not be indicated as having landed
upon the primary sensor.
15. The apparatus of claim 11 wherein:
a fixed voltage is maintained between said inner conductive layer and said
outer conductive layer; and
a displacement current is generated by an impact of an object compressing
one or both of the insulating layers, thereby reducing the distance
between the inner conductive layer and one or both of the outer conductive
layers.
16. The apparatus of claim 11 wherein:
the outermost of said conductive layers are provided with a protective
coating layer to minimize deterioration, damage and interference with said
conductive layers.
17. An impact detection apparatus, comprising:
a source of constant electric potential;
an impact sensor means coupled to said source of electric potential, said
sensor means responding to impact thereon by producing an electrical
current signal having a magnitude dependent on the rate of change of
compression force;
said impact sensor means comprising a sandwiched multilayer device
including in respective order:
a first outer conductive layer;
a first insulative layer;
an inner conductive layer;
a second insulative layer;
a second outer conductive layer;
said outer conductive layers being electrically interconnected to form an
electrically shielded region therebetween within which said insulative
layers and said inner conductive layer are disposed; and,
at least one of said insulative layers if formed of a closed-cell elastomer
form.
18. The apparatus of claim 17 wherein said outer conductive layers are
electrically interconnected by being physically joined along at least one
common edge thereof.
19. The apparatus of claim 17 wherein said source of potential is connected
to said sensor means by a coaxial cable having an inner conductor, and an
outer conductor surrounding said inner conductor, said inner conductor
being connected to said inner conductive layer and said outer conductor
being connected to said outer conductive layers. |
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Claims |
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Description |
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TECHNICAL FIELD
The present invention relates generally to monitoring devices and more
specifically to an apparatus to determine whether a detected impact is on
one side or the other of a given boundary, e.g. whether a ball is in or
out on a tennis court.
BACKGROUND ART
The primary application of the present invention is envisioned to be in
conjunction with the game of tennis. Tennis is a game in which the outcome
of each point may be controlled by the determination of whether a ball
lands within or on a given boundary, and is therefore "in", or whether the
ball lands beyond the boundary, and is therefore "out". To the player of
ordinary skill, this determination is generally within reasonable limits.
The casual player's shots, and indeed the player himself, do not generally
travel with great velocity. This ordinarily keeps the in/out determination
within the bounds of human visual capabilities. Further, at the casual
level, the in/out determination is usually not critical to matters other
than personal pride. Generally, nothing more is at stake. However, as the
skill level of the players rises, the situation becomes more complex.
Tennis officials have long recognized that at top levels, the speed at
which the ball travels on shots, (in excess of 100 mph at times), combined
with the fact that the player who would ordinarily be required to make the
call will often also be moving at top speed and generally does not have
the best visual perspective, frequently makes it impossible for the player
to perceive accurately whether the ball was in or out. That the player
does not have the best perspective of where a ball lands has been proven
repeatedly. See, e.g., "In or Out", Robert H. Vincent, TENNIS, March,
1984, p.35; and "Vic Braden's Startling Revelations about Line Calls", Vic
Braden, TENNIS, May, 1983, p. 37. Recognition of this fact has led to the
use of linespeople at all major competitions. The linespeople are
positioned so that they have a fixed parallel viewpoint of the boundary
lines, which greatly reduces the number of erroneous calls. Unfortunately,
the use of linespeople is prohibitively expensive for most play. Only
those tournaments with large budgets can afford to use linespeople.
Further, even with linespeople there is still the possibility of erroneous
calls. Numerous studies, including those cited above, have consistently
shown that the in/out determination is often quite simply beyond the
bounds of human perception.
Improved accuracy in in/out determinations is desirable at all skill
levels. However, at the top levels of competitive tennis, the skill and
level of play differentials between the winner and loser of a given match
can be very minute. One or two key points can determine the outcome.
Considering that hundreds of thousands of dollars are at stake in the
major professional tournaments, it is not difficult to understand the
extreme desirability of eliminating human error in making line calls.
The prior art includes several examples of devices that have been built to
provide a method of determining, on a tennis court, whether or not balls
land in or out. The most common method involves a surface contact
detection system in conjunction with a specially adapted tennis ball. See
"Game Court Boundary Indicator System", Jokav and Grill. U.S. Pat. No.
3,774,194, issued Nov. 20, 1973; "Gaming face Contact Detecting Systems"
Van Auken, U.S. Pat. No.4,1O9,9ll, issued Aug. 29 1978; and
"Micro-Computer Network Systems for Making and Using Automatic Line-Call
Decisions in Tennis", Supran, U.S. Pat. No. 4,432,058 issued Feb. 14,
1984.
The inherent disadvantage of these systems is of course that the tennis
balls must be altered in one way or another. The Jokay device requires
that three conductive winding be installed in the interior cavity of the
tennis ball. The Van Auken system alters the exterior surface by requiring
that at least one portion of the surface be electrically conductive. The
Supran system also envisions the use of an electrically conductive ball.
These conductive balls are likely to be prohibitively expensive. A further
problem with altering the ball is that changing the ball may change the
game. Thus a line calling system that requires modified balls could be
expected to meet great resistance, as most players would be very hesitant
to accept anything other than the standard tennis ball. Furthermore, the
governing organizations and equipment manufacturers are highly resistant
to change of this nature. The number of years it took for the optic yellow
balls to be accepted is proof of the tendency.
A more useful sort of system is the "Tennis Court Line Monitoring
Apparatus" of Grant, U.S. Pat. No. 3,982,759,issued Sept. 28, 1976. This
system uses a series of small mechanical switches activated by the impact
of the ball. This means the system will operate when a standard ball is
used. However, since the switches are closed by physical contact, if a
player is standing on the switched area, that senor cannot detect the
impact of the ball. There is no way to detect the secondary impact.
(Defining secondary impact as an impact on a switch that is already
activated.)
In any system the detector area is broken into regions. In the switch type
sensor, a region consists of multiple normally open switches all wired in
parallel. With this arrangement any closed switch within a region closes
the circuit for that region. Thus, if someone is standing in a region
(activating it), the impact of a tennis ball anywhere within that region
will have no effect (it will not be sensed). To minimize the risk of this
occurring, a large number of smaller regions has to be used which requires
a prohibitively large number of channels,
A second disadvantage of the switch type senor is that the means of
discrimination between a footstep and a ball impact is limited to
measuring pulse width. (It is inherently a single threshold device, with
the threshold set by the mechanical parameters of the switch.) It can thus
be fooled by a tap dancer, and likewise a quick footed tennis player.
Another method in the prior art is the use of light beams. One such system,
known as "Cyclops", has been used at many professional tournaments. To
date, the system has been used only on the service lines, not all the
boundaries. One of the problems with this type of system is that anything
that breaks the beam triggers the device. There is no way to distinguish
between, for instance, a player's foot and the ball.
All the devices in the prior art suffer from at least one of the above
shortcomings. They either require the use of a modified ball, they have no
means to detect a secondary impact, or they have no means to differentiate
between contacts caused by various objects.
DISCLOSURE OF THE INVENTION
Accordingly, it is an object of the present invention to provide an
automated method of determining whether an object strikes an area within a
certain boundary, specifically, whether a ball lands "in" or "out" on a
tennis court.
Another object of the present invention is to provide an apparatus that
allows the use of standard tennis balls.
It is another object of the present invention to provide an apparatus that
can effectively discriminate among various impact events.
Yet another object of the present invention is to provide an apparatus that
can be effectively used with only a single official, or by the players
themselves.
A further object of the present invention is to provide an apparatus that
can detect a secondary impact.
Briefly, a preferred embodiment of the present invention is an impact
detection apparatus. The apparatus achieves a method of automated
determination of whether or not a ball lands in or out on a tennis court.
The apparatus includes a plurality of large surface area charge pump
transducers, strategically placed in the critical areas of the court. Any
impact upon the transducers generates an electrical impulse, which can
then be processed. Signal processing provides the means to determine
whether the impact was that of a tennis ball or a footstep. The apparatus
also includes monitoring means. The monitoring means provides a visual
and/or audible signal when a ball has landed out. It is envisioned that
the system will generally be used with a non-participant controlling its
operation. However, the system can be used in the absence of an operating
official.
An advantage of the present invention is that it allows for infinitely
variable levels of detection, thus making it possible to differentiate the
impact of a tennis ball from that of a footstep.
Another advantage of the present invention is that it makes use of a
standard tennis ball.
Yet another advantage of the present invention is that it helps eliminate
human error from the determination of whether a ball has landed in or out.
Still another advantage of the present invention is that it can detect a
secondary impact.
These and other objects and advantages will become clear to those skilled
in the art in view of the description of the best presently known mode of
carrying out the invention and the industrial applicability of the
preferred embodiment as described herein and as illustrated in the several
figures of the drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. l is a schematic view of a preferred embodiment the inventive
apparatus installed on a tennis court, the solid lines indicating the
boundaries of the court, and the broken lines indicating the placement of
the charge pump transducers;
FIG. 2 is a broken cross-sectional view of a sensor with no pressure
applied taken along line 2--2 of FIG. 1;
FIG. 3 is a broken cross-sectional view of the same sensor as FIG. 2, shown
with pressure applied;
FIG. 4 is an example of waveforms produced by the bounce of a tennis,
FIG. 5 is an alternate example of waveforms produced by the bounce of a
tennis ball;
FIG. 6 a flow chart type of block diagram illustrating the sensor and
associated signal processing elements;
FIG. 7 is a waveform diagram showing signals generated by a ball impact and
a light foot-tap analyzed with respect to three thresholds;
FIG. 8 is a waveform diagram showing the digital equivalents of the
waveforms of FIG. 7 analyzed with respect to a single selected detection
threshold; and
FIG. 9 is a waveform diagram showing the digital equivalents of the
waveforms of FIG. 7 analyzed with respect to a single selected detection
threshold, the selected threshold being lower than that selected in FIG.
8; and
FIG. 10 is a waveform diagram showing the digital equivalents of the
waveforms of FIG. 7 analyzed with respect to a single selected detection
threshold, the selected threshold being higher than that selected in FIG.
8.
BEST MODE OF CARRYING OUT THE INVENTION
The present invention is an impact detection apparatus that can be utilized
to detect localized impact events. The presently preferred embodiment is
specifically adapted to monitor the boundaries of a tennis court. The
preferred embodiment of the apparatus is shown in the drawing as a system
combining several individual components and is collectively referred to by
the general reference character 10 The sensing components of the apparatus
are a plurality of large area charge pump transducers, termed sensors,
which are differentiated by their positioning. For clarity of description,
each sensor 11 is identified, according to its specific position on a
conventional tennis court 12, by the reference characters 13 through 134.
The sensors 11 are situated outside the boundaries of the component areas
of the tennis court 12, in the arrangement depicted in FIG. 1. The sensors
11 are mounted underneath and/or made part of the playing surface.
The sensors 11 are situated so as to abut the exterior edge of each the
boundaries of the tennis court 12. The outermost boundaries of the court
12 are a first end line 138, a second end line 140, a first doubles side
line 142, and a second doubles side line 144. If the court 12 is being
used for singles, the lateral boundaries are a first singles side line 146
and a second singles side line 148. The interior of the court 136 is
further defined by a first service line 154, a second service line 156,
and a center line 158.
Each sensor 11 is in the form of an elongated rectangle having one long
edge linearly adjacent to the exterior edge of one of boundary lines. For
example, the sensor 98 is contiguous with the rear edge of the first
service line 154 and will be utilized to determine whether a serve has
landed out. The width of the sensors 11 is chosen bearing in mind that a
ball landing more than a given distance away from a boundary line will be
readily discernible to the unaided human eye. In one embodiment, the
sensors 11 are 48.3 cm (19.0 in) wide, that is, they extend 48.3 cm (19.0
in) beyond the outer edge of the boundary lines. The length is chosen only
as a matter of convenience, but is about 2.74 m (9.0 ft.) in the preferred
embodiment.
Each sensor 11 is a multilayered device, with the various layers serving
varying functions. The sensors 11 are laterally consistent such that a
cross section along any vertical plane will yield an identical pattern of
layers. As shown in FIG. 2, each sensor 11 includes an inner conductive
layer 160 situated between a first insulating layer 162 and a second
insulating layer 164. Above the first insulating layer 162 is a first
outer conductive layer 166, and beneath the second insulating layer 164 is
a second outer conductive layer 168. These layers are enclosed by an upper
coating 170 and a lower coating 172. The various layers 160, 162, 164,
166, and 168 are bound together by adhesive 173 (shown only with respect
to the boundary between layers 164 and 168 but understood as being present
at each boundary). It is envisioned that the conductive layers 160, 166,
and 168 will be aluminum metal foil, although any resilient conductive
material will suffice. The insulating layers 162 and 164 may be any
compressible, non-conductive material. The preferred embodiment utilizes
closed cell elastomer foam in layers 162 and 164. The coating layers 170
and 172 are simply durable plastic to protect the other layers.
The sensors 11 operate as transducers, known as "charge pump" transducers
in the preferred embodiment. In this application, a total displaced charge
("Q") is the integral of "i(dt)" over a given time interval with "i"
representing electrical current and "t" representing time. The symbol "i"
represents the displacement current that is generated during compression,
and is defined by V(dc/dt), where "V" is the fixed voltage maintained
between the inner conductive layer 160 and the outer conductive layers 166
and 168, and "dc/dt" is the time rate of change in capacitance due to
compression. Note that the displacement current i is independent of the
size of the sensor, but depends only on the voltage maintained and the
rate of change of compression (reflected as a rate of change in the
distance between conductive layers). Current is carried to and from the
sensors 11 by means of a standard coaxial cable 174. The coaxial cable 174
is shown in FIG. 2 with its component parts; an outer cover 176, a shield
wire 178, an insulation layer 180, and an interior wire 182. The outer
conductive layers 166 and 168 are in electrical contact via connecting
wiring 183 with the shield wire 178. The inner conductive layer 160 is in
electrical contact via connecting wiring 183 with the interior wire 182.
When pressure is applied to the sensor 11, i.e. when there is an impact,
the foam layers 162 and 164 are compressed. (See FIG. 3.) Therefore in the
impact area, the distance between the inner conductive layer 160 and outer
conductive layers 166 and 168 is reduced. This compression, through the
relationship defined above, yields a displacement current which is
analyzed to determine what caused the impact.
In an alternate embodiment, the second insulating layer 164 is not
compressible. Therefore, when an impact occurs, only the first insulating
layer 162 is compressed. This reduces the distance between the first outer
conductive layer 166 and the inner conductive layer 160, Which also yields
a displacement current which can be analyzed, through signal processing,
to determine what caused the impact. The processing of this signal is
equivalent to the processing of the signal output by the preferred
embodiment.
Once a raw signal has been generated in the sensor 11 by an impact of any
kind upon the upper coating layer 170 it is necessary to analyze the
signal to determine whether it is a relevant triggering impact (i.e. a
ball) or a spurious impact (i.e. a foot or a racket). Many available
methods of signal analysis may be utilized to make this determination but
one preferred method is illustrated in FIGS. 4, 5 and 6 of the drawing.
These figures are considered together in the following discussion. FIGS. 4
and 5 illustrate typical waveforms, both analog and digital, generated by
a tennis ball impact, while FIG. 6 is a flow chart block diagram
illustrating the method of analysis.
FIG. 4 illustrates a first analog waveform 184 corresponding to the current
generated Within the sensor 11 corresponding to a ball impact. The shape
of the waveform 184 is generally sinusoidal since the current generated
within a given sensor 11 is dependent upon the rate of change of
separation between the outer conductive layers 166 and 168 and the inner
conductive layer 160. The waveform 184 illustrated in FIG. 4 is inverted
from the actual signal generated since, by the time the current signal is
observed in the analysis apparatus of the preferred embodiment 10, it has
passed through an inverter element.
FIG. 5 illustrates a charge displacement analog waveform 186 which will be
generated as a result of the same impact generating the current analog
waveform 184 of FIG. 4. The charge displacement analog waveform 186
represents the net charge displaced in the charge pump transducer of the
sensor 11 upon an impact. Charge displacement is directly dependent upon
the separation between the conductive layers 160, 166 and 168 and is the
integral of the current. Thus, the charge displacement waveform 186 is
obtained by integrating the current waveform 184 (inverted). It is noted
that with an alternate detection apparatus it might be possible to
directly measure charge displacement and then take the derivative over
time to obtain the current waveform. However, since it is easier to
measure the current, the order of generation illustrated in FIGS. 4 and 5
is the more practical approach.
Since charge displacement directly (inversely) corresponds to the
separation distance between the conductive layers, with charge
displacement increasing as separation decreases, the charge displacement
waveform 186 directly mirrors the vertical motion of the surface impact
point on the sensor 11 over the time interval of the impact event.
The generation of the current and charge displacement waveforms 184 and 186
upon an impact event is as follows. Initially, the system is static and
separation is constant. This is represented by point A in FIGS. 4 and 5.
The rate of change of separation is zero and the charge displacement is
constant so both waveforms 184 and 186 are represented as corresponding to
baselines. As the tennis ball impacts the upper coating layer 170 of the
sensor 11 (Point B) the separation distance begins rapidly decreasing.
Thus the charge displacement increases and the current increases in a
derivative fashion. At a point shortly after impact (Point C) the rate of
depression of the impact point reaches a maximum. After Point C, the ball
continues to depress the sensor 11 further but its rate is slowed by the
compression resistance of the insulating layers 162 and 164 and that of
the ball itself. This results in the current waveform 184 returning toward
the baseline (zero). At maximum compression (Point D) the impact force and
resilient forces are balanced and the ball is actually instantaneously
stationary. The rate of separation change (current) is zero and the
separation distance is minimized (charge displacement maximized). From
Point D forward the resilience (bounce) of the ball and the conductive
layers 166 and 168 take over and the sensor 11 begins to return to normal
shape. At some point within this resilient interval (Point E), the rate of
expansion reaches its maximum and the current minimizes, although a
significant degree of compression still exists. When the ball leaves the
upper coating surface 170 (Point F) the sensor returns (assuming no
relevant oscillation) to the static condition (Point G) which corresponds
to the initial static condition (Point A). The impact event is then
completed.
In order to most effectively analyze the analog waveforms 184 and 186 the
preferred analysis circuitry utilizes various signal magnitude detectors
to generate step functions (digital signals) corresponding to aspects of
the waveform. As seen in FIG. 4 the preferred circuitry generates a first
digital current signal 188 based upon a first current threshold 189. The
first digital current signal 188 is switched from a low mode to a high
mode when the first analog current signal 184 has a negative magnitude
exceeding the selected first current threshold 189. Similarly the
circuitry generates a high mode in a second digital current signal 190
when the first analog waveform 184 has a positive magnitude exceeding that
of a second current threshold 191. The digital current signals 188 and 190
are more easily recognized by subsequent analysis circuitry than the raw
waveform 184 and also permit more detailed determinations.
In a similar manner, FIG. 5 illustrates how a first digital charge
displacement signal 192 is generated when the charge displacement analog
signal 186 has a magnitude exceeding a first charge displacement threshold
193 while a second digital charge displacement signal 194 is generated
when a second charge displacement threshold 195 is exceeded. It is noted
that while the first and second digital current signals 188 and 190 are
mutually exclusive, the first and second digital charge displacement
signals 192 and 194 are both in the high mode at the same time with the
second charge signal 194 having a longer duration than the first charge
signal 192.
The analysis circuitry utilized in the preferred embodiment of the present
invention is illustrated in a flow chart style of block diagram in FIG. 6.
In this illustration it may be seen that the sensor 11 generates current
signals carried by the coaxial cable 174 to the analysis elements. The
inner conductive layer 160 is provided with a +200 volt potential while
the first and second outer conductive layers 166 and 168 are grounded. The
compression of the sensor 11 causes a current to flow in the coaxial cable
174. This current is first delivered to a current mode op amp (operational
amplifier) 196. This element amplifies and inverts the signal and passes
it to a hum cancellation subcircuit 198. The hum cancellation subcircuit
198 acts to filter out system hum generated in the AC power line so that
the desired signals are more easily recognized.
The output of the hum Cancellation subcircuit 198 is in the form of the
first analog current waveform 184. It is then split with one branch being
delivered to an analog integrator 200 while the other branch is delivered
directly to an analog to digital converter circuit 202. The branch
delivered to the analog integrator is integrated therein to generate the
charge displacement analog waveform 186.
The analog to digital converter circuit 202 receives the analog waveforms
184 and 186 and outputs the digital signals 188, 190, 192 and 194. These
digital signals are then delivered to a digital pattern recognition module
204. The digital pattern recognition module 204 electronically sorts the
digital signals and, upon proper matches for a ball impact, sends an
activation signal to a control console 206. Depending on the nature of
control console 206 selected an indicator of some type (horn, bell, light,
etc.) will be triggered to alert the players and/or officials to the fact
that the ball has hit outside the boundary.
The necessity of being able to provide multiple detection thresholds can be
shown by reference to FIGS. 7-10. Each of these figures represents a plot
of selected signal amplitude versus elapsed time. FIG. 7 depicts a first
analog signal (ball analog signal) 208 of the same type as the charge
density analog signal 186 from a ball impact (shown as a dotted line) and
a second analog signal (toe tap analog signal) 210 of the same nature
generated by a light toe tap impact, such as when a player slightly steps
over the boundary (shown as a solid line). The horizontal lines above the
baseline represent the first charge displacement threshold 193, the second
threshold 195, and a third charge displacement threshold 212. It may be
seen that the ball analog signal 208 crosses all three thresholds 212, 195
and 193 while the toe tap analog signal 210 only exceeds the second and
third thresholds 195 and 212. It is also noted that the duration of the
toe tap signal 2lD is longer than that of the bouncing ball signal 208.
FIG. 8 depicts what could happen if a detection system utilized only a
single threshold, such as an on-off switching mechanism of the nature of
some prior art devices. For example, if only the second charge
displacement threshold 195 were utilized, the signals illustrated in FIG.
8 would be generated. In this instance a single ball impact digital signal
214 (dotted) is generated resulting from the ball analog signal 208
exceeding the second threshold 195. This ball digital signal 214 is of the
same nature as the second charge displacement digital signal 194 of FIG.
5. A similar type of signal is generated as a toe tap digital signal 216
(solid line). As may be seen in FIG. 8, the two digital signals 214 and
216 are congruent, having (by definition) the same magnitude and also the
same duration in this case. Thus for a ball impact and toe tap impact
occurring anywhere on the sensor (about nine feet in length in the
preferred embodiment) the signal threshold analysis mechanism would be
unable to distinguish the two impact events. False indications could
therefore result in an appreciable percentage of instances as the digital
pattern recognition subsystem 204 would be incapable of recognizing the
toe tap as an extraneous event. This is an undesirable result.
FIG. 9 illustrates the result of similar processing utilizing the third
charge displacement threshold 212 as the triggering magnitude. In this
case the ball impact digital signal 218 and the toe tap digital signal 220
again (by definition) have the same magnitude but have different
durations. In this case the pattern recognition subsystem 204 would be
able to distinguish the impacts by a duration comparison.
FIG. 10 illustrates the results based upon the first charge displacement
threshold 193. In this instance Only a ball impact digital signal 222 is
generated since the toe tap analog signal 210 never achieves the magnitude
of the first threshold 193. In this system only the ball impact would be
detected by the pattern recognition subsystem 204. However, a heavy foot
impact, rather than the light impact illustrated in FIG. 7, could result
in a spurious match.
As seen in FIGS. 7-10 it is possible to distinguish between ball impacts
and other types of impacts on the sensor 11 by the use of multiple
threshold analysis. It has been established that a ball bounce will
generate analog signals having patterns within a specified range of
parameters. Other types of impacts generate signals having different
ranges. By empirically determining the thresholds and durations
corresponding to ball impacts and excluding other impacts it is possible
to program the pattern recognition subsystem to be nearly foolproof in its
recognition of actual ball impacts. In this manner the accuracy of in
versus out determinations may be drastically improved over previously
utilized methods and the degree of certainty of line judgments may be
maximized.
Note also that the apparatus 10 of the present invention is not disabled by
two near-simultaneous impacts. Some of the prior art devices operate on an
on/off basis. That is, a signal is generated when a switch is physically
closed by an impact. Therefore, in the prior art systems, if a player
steps (or is standing) on the subject area and a ball then lands there,
the system would have no means to detect the impact of the ball. Since
there is no on/off aspe | | |
