Missle detection and location

A system is disclosed for detecting and locating missiles such as darts in a target having a plurality of discrete target areas in which each of the areas has a conductive surface which acts as an electromagnetic signal receiving antenna, and in which a plate is positioned on the back of the target which functions as an electromagnetic signal transmitting antenna. Each of the target areas are monitored for electromagnetic signals and the signals pass through a pin conductor to the monitoring equipment. When a dart is embedded in one of the areas, it also acts as an antenna and, thereby, increases the signal strength of that area to permit detection of the presence and location of the dart. The pin conductors and plate antenna at the back of the dart board substantially improve the discrimination and reliability of the system.

BACKGROUND AND SUMMARY OF INVENTION 
The present invention relates to the electronic detection of darts or other 
missiles which are embedded in discrete scoring segments or areas of a 
target, such as in a conventional fiber or bristle dart board. 
Various approaches have been taken in the past to automatically detect and 
electrically score games which employ a projectile which is to be 
propelled toward some form of target having areas denominated in different 
scores. One example of such game is the game of darts in which a dart is 
thrown at a dart board having plural segments or areas of differing 
scores. Depending upon which segment the dart becomes embedded in, the 
game player is credited with the score for that area. 
One prior system in which the location of the dart is automatically 
detected and electrically scored is shown for example in U.S. Pat. No. 
4,057,251 (JONES et al.). In that system the scoring segments are formed 
by a plurality of movable plates having holes therein. When the tip of a 
thrown dart enters one of the holes in a plate, the plate is mechanically 
displaced by the momentum of the dart so as to close and actuate an 
electrical switch to detect and locate the position of the dart on the 
dart board. However, these moveable mechanical plate and switch systems 
have a number of disadvantages including complexity, reliability and 
longevity. 
In another prior system the moveable mechanical plates have been eliminated 
and the dart board is formed of multiple, sandwiched layers of alternating 
conductive and insulative materials. When the metal tip of a dart is 
embedded in a scoring segment or area, it pierces and electrically 
connects two such conductive layers completing a circuit between them to 
indicate the location of the dart. Examples of such systems are shown in 
U.S. Pat. No. 4,244,583 (WOOD et al.) and published UK Patent Application 
No. 2,030,877. A principal disadvantage of the latter systems is their 
reduced longevity due to the deterioration of the scoring segments after 
repeated piercing. 
Various systems have also been proposed in which transmitting and receiving 
antennae are provided for the transmission of electromagnetic signals, and 
in which one of the antennae is formed by treating or otherwise coating 
the conventional sisal fibers of a conventional dart board so as to render 
the fibers electrically conductive to form one of these antennae. In these 
conductive fiber systems, when a metal tipped dart is embedded in the 
conductive fibers, the dart itself becomes a part of the antenna in which 
it is embedded and, thereby, increases the signal strength of either the 
received or transmitted signal depending upon the function of the 
conductive material in which the dart is embedded. Examples of these 
systems are shown in U.S. Pat. Nos. 4,678,198 (BOWYER et al.) and 
5,462,283 (ALLEN). Some of the disadvantages of these systems are their 
low scoring reliability and/or difficulty of placement or overall size of 
at least one of the antennae. 
Still other systems have relied upon the generation of electromagnetic 
fields utilizing individual coils fixed adjacent the respective scoring 
areas. When a dart having the ability to affect the electromagnetic 
activity is embedded in one of the areas, the field generated by the coil 
is altered and the alteration is detected to indicate the presence and 
location of the dart. Examples of these systems are described in German 
Utility Model G 88 06 580.4 and published UK Patent Application No. 
2,086,243. One of the disadvantages of these systems is that they are 
complex and cumbersome due to the need for placement and energization of 
the numerous and space consuming electromagnetic coils. 
More recently a system has also been proposed which like some of the prior 
systems can utilize a conventional sisal fiber dart board, but which 
avoids the need to coat or otherwise treat the fibers with an electrically 
conductive compound, and which relies on a principle of interference with 
electromagnetic radiation by an embedded dart, rather than the dart acting 
as part of a transmitting/receiving electromagnetic radiation antenna. An 
example of such system is shown in published PCT Application No. 
W095/04251. Although this system enjoys a number of advantages over the 
prior systems earlier described herein, there is still room for 
improvement in reliability, simplicity and reduction in manufacturing ease 
and expense. 
A system incorporating the principles of the present invention for 
automatically detecting and locating a missile embedded in a target, such 
as a dart in a dart board, enjoys one or more advantages over the 
aforementioned systems of the prior art. One such advantage is that the 
system of the present invention is simple, and is easier and less 
expensive to construct and assemble than many of the systems of the prior 
art. In the system of the present invention, an antenna is positioned on 
the back of the target so that it can be essentially equidistant to all of 
the scoring segments on the front of the target. This results in 
substantially improved reliability and simplicity, eliminates the need for 
an antenna external to the dart board, and in the case of the prior 
systems which required the spacing of an antenna peripherally of the dart 
board scoring area, reduces the size of the overall game assembly. 
Positioning of the antenna at the back of the dart board also 
substantially reduces the power needed from the signal generator. In 
addition, the system of the present invention enjoys an order of magnitude 
of improvement in reliability which will insure that even where darts are 
embedded in a scoring segment closely adjacent the next scoring segment, 
the location of the dart in the proper and correct segment will be easily 
discriminated and accurately read virtually all of the time. 
In one principal aspect of the present invention, a system is provided for 
detecting and locating a missile embedded in a target having a front face 
with a plurality of target areas formed of a first material into which 
first material one or more of the missiles may be selectively embedded 
from the front face of the target. A first electrically conductive area is 
located in the target areas and adjacent the front face, and a back is 
provided on the target opposite the front face. A second electrically 
conductive area is positioned adjacent the back, and the second 
electrically conductive area is spaced and electrically separated from the 
first electrically conductive area. A signal generator imparts a signal to 
one of the aforementioned conductive areas whereby that one of the 
conductive areas defines a transmitting antenna for an electromagnetic 
signal corresponding to the signal imparted to the one conductive area. 
The other of the conductive areas defines a receiving antenna for the 
electromagnetic signal which is transmitted from the transmitting antenna. 
A processor is electrically connected to the other of the conductive areas 
and distinguishes between a first electromagnetic signal which is received 
and sensed by the other of the conductive areas in the absence of a 
missile in a given target area, and a second electromagnetic signal which 
is an alteration of the first electromagnetic signal by the presence of a 
missile in the given target area to permit the detection of the presence 
and location of the missile. 
In another principal aspect of the present invention, the first material 
comprises dart board bristles and the first electrically conductive area 
comprises a conductive coating on the bristles. 
In still another principal aspect of the present invention, the 
aforementioned bristles have a given depth, and the first electrically 
conductive area is located within that bristle depth adjacent to the front 
face of the target and extends for a depth into the bristles which is less 
than the given depth. 
In still another principal aspect of the present invention, the system 
includes an electrically insulative barrier extending into the first 
material for a depth greater than the depth of the first electrically 
conductive area, and the insulative barrier defines the plurality of 
target areas and electrically divides and separates the first electrically 
conductive areas of adjacent target areas from each other. 
In still another principal aspect of the present invention, the second 
electrically conductive area adjacent the back of the target is an 
electrically conductive plate and, more preferably, one which is painted 
onto the target back. 
In still another principal aspect of the present invention, the system 
includes still another electrically conductive plate in addition to the 
last mentioned plate adjacent to the back, and an insulative material 
electrically separates the two conductive plates. 
In still another principal aspect of the present invention, an electrically 
conductive pin is coupled to the first conductive area so as to 
substantially increase the electromagnetic signal in the first conductive 
area. 
In still another principal aspect of the present invention, the first 
electrically conductive area is the receiving antenna and the second 
electrically conductive area is the transmitting antenna which transmits 
the electromagnetic signal from the back of the target to the receiving 
antenna at the front face of the target and to a missile when the missile 
is embedded in the first material. 
In still another principal aspect of the present invention, the missile is 
a dart and the target is a dart board. 
These and other objects, features and advantages of the present invention 
will be more clearly understood through a consideration of the following 
detailed description.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
As previously mentioned, the present invention relates to the automatic 
detection and location of a missile or projectile relative to a target, 
and the electrical scoring thereof. As shown in FIG. 1, the target may be 
a dart board T which has a plurality of discrete target scoring segments 
or areas A.sub.1, A.sub.2, etc., and which scoring areas have preselected 
but differing score values. Although a dart board T is described as an 
example of a target in which the missile detection and location of the 
present invention may be utilized, it will be appreciated that the 
invention may be employed in other uses and games which also employ some 
form of target and missile, such as archery. 
Referring more particularly to FIGS. 2 and 3, the dart board T is 
preferably of a relatively conventional construction, i.e. of a wood or 
chip board base 10 which is electrically insulative in nature, and having 
a plurality of organic sisal fibers 12 adhesively fixed to the front face 
of the base 10. The sisal fibers 12 extend frontally and outwardly from 
the base 10 and they are typically sheared to present a flat target front 
face 14 for receipt of darts D and D' which are to be embedded therein 
during game play, as seen in FIG. 3. 
In the system of the present invention the outer tips of the fibers 12 
adjacent the face 14 are processed or treated preferably by dipping or 
painting with an electrically conductive material, such as graphite or the 
like. This conductive material may be applied by coating it onto the 
exposed front face of the bristles or fibers after the fibers have been 
assembled and adhered to the base 10. In the alternative, individual 
bundles of the fibers or bristles may be dipped to a preselected depth of 
liquid coating material, dried, and then the other uncoated ends of the 
fibers are adhered to the front face of the base 10. In either event the 
fibers 12 are not coated to their full depth d.sub.1, but instead are only 
coated to a superficial depth d.sub.2, as shown in FIG. 3. The remainder 
of the depth d.sub.3 of the fibers which is not coated will be essentially 
non-electrically conductive in view of the typical organic nature of the 
fibers. The coated fiber tips thereby define a conductive area 16 covering 
the target front face 14. This conductive area 16 will define an antenna 
for an electromagnetic signal as will be described below. 
After the fibers 12 have been assembled and fixed to the base 10, have been 
coated to form the conductive area 16, and have been sheared as necessary 
to form the flat target front face 14, the several scoring areas A.sub.1, 
A.sub.2, etc. are formed by isolating and electrically separating the 
conductive area 16 into pieces and for each scoring area. This is 
preferably accomplished by pressing a preformed, preferably molded plastic 
electrically insulative spider 18 into the fibers from the target front 
face 14. This dart board spider 18 has a height h, as best seen in FIG. 3, 
which is sufficiently greater than the depth d.sub.2 of the conductive 
area 16 to insure that the conductive areas 16 of each of the respective 
scoring areas A.sub.1, A.sub.2, etc. are isolated and separated 
electrically from each other. By way of example, the total depth d.sub.1 
of the fibers or bristles 12 may be approximately 7/8 inch, the depth 
d.sub.2 of the conductive area 16 may be approximately 1/4 inch, and the 
height h of the spider 18 may be approximately 5/8 inch. However, it will 
be appreciated that these heights and depths may vary somewhat without 
departing from the principles of the invention. 
One important feature of the present invention is the positioning of 
another conductive area or layer 20 on the back 22 of the base 10 as shown 
in FIGS. 2 and 3. This conductive area or layer 20 may be a conductive 
metal plate or foil adhered or otherwise attached to the back face 22 of 
the base 10. However, the conductive area 20 is preferably applied to the 
back face 22 by painting or coating it on using for example a nickel based 
paint. As will be described below, this conductive area 20 will also 
function as an antenna for electromagnetic signals. It will be appreciated 
upon considering the construction and application of this conductive area 
20, that the assembly of the system will be simplified, and that the 
antennae provided by the conductive areas 16 and 20 respectively will be 
substantially equidistant from each other which will greatly improve the 
reliability of the system. 
A second electrically conductive plate 24 or the like is also preferably 
provided at the back of the target T as shown in FIGS. 2 and 3. This plate 
24 is electrically separated from the conductive area or layer 20, again 
as best seen in FIGS. 2 and 3, by an insulative plate 26 which may be 
formed of any suitable insulative material, such as a phenolic polymer. As 
shown in FIG. 3, the conductive plate 24 is grounded to minimize 
undesirable electrical interference and improve reliability. 
Another important feature of the present invention is the provision of a 
conductive nail or pin 28 which extends between the conductive area 16 in 
each of the target scoring areas A.sub.1, A.sub.2 etc. rearwardly through 
the back of the dart board. The pins 28 may be installed rearwardly 
through the fibers 12 from the target face 14. However, the pins 28 are 
preferably installed in the other direction, i.e. by being driven from the 
back 22 of the target T through the base 10, forwardly through the 
nonconductive depth d.sub.3 of the fibers 12 and into the depth d.sub.2 of 
the conductive area 16 of the fibers 12 as shown in FIG. 3. The tips 30 of 
the pins 28 are preferably pointed to facilitate such placement and 
installation, and to minimize the possibility of undesirable dart tip 
deflection when a dart tip strikes the dart board. The pin tips 30 are 
also preferably slightly beneath the target face 14, as viewed in FIG. 3, 
so that they are not actually visible at the target face 14. The pin tips 
30 have only been shown in FIGS. 1 and 2 on the target face 14 for the 
purpose of a full understanding of their placement relative to the scoring 
areas A.sub.1, A.sub.2, etc. However, it will be appreciated that in 
reality these tips 30 preferably would not be visible on the target face 
14. 
As shown in FIG. 3, the pins 28 are preferably inserted through openings 32 
in the base 10 which are slightly smaller in diameter than the diameter of 
the pins to ensure a firm press fit when the pins 28 are driven through 
the openings 32. On the other hand, the openings 34 and 36 through the 
conductive plates 20 and 24, respectively, are larger than the diameter of 
the pins 28 to ensure that the pins 28 are electrically separated and 
isolated from the plates 20 and 24. The end of each of the pins 28 at the 
rear of the target is connected by a suitable conductor 38, as seen in 
FIGS. 3 and 4, to a processor and score display 40 for receiving the 
signals present in the conductive area 16 of the respective scoring areas 
A.sub.1, A.sub.2 etc., and processing them to display a score as shown in 
FIG. 4. 
A signal generator 42, as shown in FIGS. 2-4, is also provided for the 
transmission of a suitable signal, for example of 125 khz, through a 
conductor 44 to the conductor plate 20. 
As shown in FIGS. 1 and 2, a non-scoring shoulder ring 46 typically 
encircles and surrounds the scoring region in a conventional dart board. 
Such ring provides an area to display the scoring indicia and the like and 
provides an adjacent area to catch darts which may just miss the scoring 
region. Although darts embedded in this ring 46 are not entitled to a 
score, it is preferable to be able to detect their presence and score them 
as a zero because each player only gets three darts in the usual scoring 
round. Thus, if the presence of darts embedded in this ring can be 
detected, the system will be more easily able to automatically determine 
when a player has completed his round. Accordingly, the construction of 
the board in the shoulder ring 46 area is preferably similar to the 
remainder of the scoring region and its target areas A, A.sub.2, etc. For 
this purpose, a plurality of pins 28', for example eight in number, are 
preferably located in spaced relation from each other about the board and 
in the non-scoring shoulder ring 46, as seen in FIGS. 1 and 2. 
To use the system of the invention as described above, it is first 
electrically energized. When energized, a signal will be imparted to the 
electrically conductive area 20 at the back 22 of the target T and its 
base 10 by the signal generator 42 and conductor 44 as seen in FIGS. 2-4. 
Because the conductive area 20 at the back of the target T forms an 
antenna, the signal which is imparted to it will be transmitted from the 
antenna area 20 as a discrete electromagnetic signal, and this transmitted 
signal will be picked up and received by the conductive area 16 on the 
front face 14 of the target T which acts as a receiving antenna. The 
signals received in the area 16 in each of the respective target scoring 
areas A.sub.1, A.sub.2, etc. will be relatively constant and uniform in 
the absence of any embedded darts due to the uniform and fixed distance 
between the conductive areas 16 and 20 because of the positioning of the 
latter on the front and back of the target, respectively. 
The signals received at the conductive areas 16 in each of scoring areas 
A.sub.1, A.sub.2, etc. will be communicated by the respective conductor 
pins 28 through the back of the target and via the respective conductors 
38 to the processor 40. In the absence of any embedded darts, these 
signals will remain constant and no score will be registered on the 
display part of the precessor 40. However, when the metal tip of a dart D 
becomes embedded for example in scoring area A.sub.1, as shown in FIG. 3, 
the dart D will add to the antenna effect of the conductive area 16 in 
area A.sub.1 and, thereby, will alter the signal which is received in area 
A.sub.1 to increase its voltage. Accordingly, this increased intensity 
voltage signal will be detected by the processor 40 which will determine 
that it came from scoring area A.sub.1 and the processor will process and 
display the score for that scoring area. Subsequently thrown darts will 
likewise be processed and their scores added to the scores of the earlier 
thrown darts. 
As previously mentioned, an important feature of the invention is the 
provision of pins 28 as conductors coupling the conductive area 16 of the 
respective scoring areas A.sub.1, A.sub.2, etc. to the back 22 of the 
target T. These pins 28 are selected to be of a suitable mass and the like 
so as to approximately simulate a dart D embedded in each of the scoring 
areas A.sub.1, A.sub.2 etc. In this manner the pins 28 will substantially 
improve the reliability and accuracy of the system by substantially 
increasing the level of discrimination between a dart D which embeds in 
the scoring area to be read, e.g. area A.sub.1 as shown in FIG. 3, and a 
dart D' which embeds in a next adjacent scoring area A.sub.2 but is quite 
close to and/or overlies the scoring area A.sub.1 being read, also as 
shown in FIG. 3. 
In this regard reference is made to FIGS. 5 and 6 which show exemplary 
graphical depictions of representative signal voltages in percentage of 
voltage range plotted against number of darts embedded. FIG. 5 shows the 
signal voltages without a conductor pin 28 and having just a simple light 
weight conductor from the conductive area 16. FIG. 6 depicts the signal 
voltages with the conductor pins 28 of the invention. 
If a dart D', as shown in FIG. 3, becomes embedded in scoring area A.sub.2 
which is next to and closely adjacent the scoring area A.sub.1 which is 
being read, and the dart D' assumes for example the position as shown in 
which it overlies the area A.sub.1, the dart D' will not only act to 
substantially raise the signal voltage as it should in the scoring area 
A.sub.2 in which it is embedded, but it will also tend to have some 
measurable effect on the signal voltage level in area A.sub.1 in which it 
is not embedded. This latter effect on the adjacent area Al is 
schematically shown in FIG. 5 by the dotted line. As shown in FIG. 5, the 
dart D' which has embedded in area A.sub.2 which is closely adjacent to 
area A.sub.1 may increase the ambient signal voltage from the 
approximately 10 percent level as shown with no darts in the target, to 
the approximately the 40 percent voltage level in the area A.sub.l --the 
area adjacent the area A.sub.2 in which the dart D' is actually embedded. 
The voltage level in the area A.sub.2 in which the dart D' is actually 
embedded also will rise as it should to a substantially higher level of 
approximately 92 percent of the voltage of range, also as shown in FIG. 5. 
If a second dart is also embedded in area A.sub.2 and closely adjacent to 
the area A.sub.1 as was the first dart D', there may be a still further 
increase in the signal voltage in area A.sub.1 of up to for example 60 
percent as shown by the dotted line in FIG. 5. As desired, there also will 
be a further slight increase in the signal voltage in area A.sub.2 in 
which the dart is actually embedded up to for example 94 percent from the 
92 percent voltage level, as shown in FIG. 5. If still a third dart is 
embedded in the same manner as the first two darts in area A.sub.2, the 
signal voltage in area A.sub.1 will further increase to for example 75 
percent, while the signal voltage in area A.sub.2 will also increase from 
94 as it should to approximately 96 percent as shown in FIG. 5. 
From this it will be seen that although a substantial difference exists 
between the signal voltage levels in the respective scoring areas A.sub.1 
and A.sub.2 in a no-pin system, and which substantial difference should 
permit relatively reliable discrimination between the two adjacent areas, 
the increases in voltage levels in the area A.sub.1 in which the dart is 
not embedded are more than simply nominal and may be sufficient to result 
in occasional false readings and a reduction in reliability. 
Referring now to FIG. 6 which depicts the signal voltage levels in the 
invention which includes the conductor pins 28, it will be seen that the 
pins 28 establish an increased ambient signal level condition with no 
darts which is greater than the levels which are produced in area A.sub.1 
in FIG. 3 by the dart D' which is embedded in the adjacent area A.sub.2. 
This increased ambient signal level is preferably similar but a bit less 
than starting a game with a dart embedded in each of the scoring areas 
A.sub.1, A.sub.2 etc. on the dart board T. In this condition, the ambient 
signal voltage at the beginning of a game with no darts embedded in the 
board will already present signal voltage levels which may be 
approximately 90 percent of the overall voltage level range as shown in 
FIG. 6, rather than the low ambient voltage levels of about 10 percent as 
shown in FIG. 5. Now when one or more darts do become embedded in a 
scoring area, for example when dart D' embeds in area A.sub.2 as shown in 
FIG. 3, the signal voltage in area A.sub.2 will only increase in small 
increments of about 2 percent for each dart as depicted in FIG. 6. 
However, due to the higher ambient signal voltage level already present in 
each of the areas A.sub.1, A.sub.2 etc. due to the pins 28, any 
undesirable effect on signal voltage in closely adjacent scoring areas, 
such as in area A.sub.1 as seen in FIG. 3, will be obscured by the already 
relatively large ambient signal voltage level in area A.sub.1, and will 
have little if any effect as will be seen by the dotted line in FIG. 6. 
Moreover, the signal voltage window which is actually scanned may be 
substantially electronically narrowed to for example between 80 and 100 
percent, as depicted by the dot and dash lines in FIG. 6, because all of 
the activity of any significance to be monitored, including the ambient no 
dart condition, is in that range. Thus, any dart-in-adjacent-area effect 
may be filtered out and the scale in the 80-100 percent range may be 
expanded to detect smaller variations in signal voltage as the result of 
sequential embedding of darts. 
Also and as previously discussed, a substantial increase in reliability is 
possible in the system of the present invention due to the placement of 
the conductive area 20 at the back of the dart board T. Such placement 
insures the substantial uniformity of electromagnetic signal at all of the 
target areas A.sub.1, A.sub.2, etc. and the conductive area 16 at the 
front face 14 of the target T. 
It will also be appreciated from the foregoing description of the preferred 
embodiment of the system of the invention, that the system is capable of 
rapid, accurate and inexpensive assembly, and a conventional readily 
available dart board may be easily and quickly adapted to the system of 
the invention with a minimum of modifications. Moreover, the spider 18 
which separates the target areas A.sub.1, A.sub.2, etc. may be 
manufactured by simple injection molding techniques from any one of a 
number of readily available suitable polymers, and the spider may be 
simply, easily and accurately installed in and held into the target face 
14 by pressing the spider into the bristles or fibers 12. Furthermore, the 
system of the invention is quite compact and does not require the 
provision of antennae and the like which are located outside of the 
confines of the perimeter of the dart board itself. 
It also will be appreciated that although in the foregoing description of 
the operation of the system of the invention the conductive area 20 has 
been described as a transmitting antenna and the conductive area 16 as a 
receiving antenna, these roles may be reversed. If reversed and a signal 
is imparted to the conductive area 16, the signal to each of the target 
areas A.sub.1, A.sub.2 etc. will likely be sequentially applied to each of 
the respective target areas and/or each signal will be unique in some 
characteristic to its particular area, such as frequency. This would 
permit recognition and identification of each of the respective target 
areas and the ability to distinguish them from each other. 
It also will be understood that the preferred embodiment of the present 
invention which has been described is merely illustrative of the 
principles of the invention. Numerous modifications may be made by those 
skilled in the art without departing from the true spirit and scope of the 
invention.