Note: Descriptions are shown in the official language in which they were submitted.
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1 Field of the Invention
.
The present invention relates to an improved method
and apparatus for pilferage control that detects the presence
of a telltale element in a precisely defined control zone.
More particularly, it is deirected both to a method and apparatus
that defines in a predetermined manner the precise dimensions
of a control zone, and which subjects said control zone to
electronic surveillance.
Background of the Invention
It is established in the art to secure specifically
constructed telltale elements or tags to merchandise which is
likely to be pilfered, and it is known to electronically monitor
:. .
the exits of stores and ware houses, etc., and even of zones within
them where such merchandise is dispensed to ascertain that the
tags are deactivated or detached in the manner provided for
authorized removal of the merchandise. In the past various `-i;
methods and apparatus along these lines have been employed, as
recited in patents No. 3,895,368; 3,711,848; and 3,707,711, but
many of these known methods and apparatus have limitations on ;
their reliability, tolerance and sensitivity. Some are suscep-
tible to false triggering by metallic structures conicidentally
manifesting similar properties to the special tags. In some, ;
proximity of the human body to the apparatus tends to mask the
effect of the equipment and to interfere with reliable operation.
The limitation on the method and apparatus disclosed
in the above patents are such that their respective systems have
proved incapable of discerning with a high level of reliability
whether a tab has been moved into a zone being monitored, i.e.,
a control zone, or is merely in proximity to it. This causes
3t too many false alarms when there is no telltale tag actually in
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l the control zone.
There is the further limitation on the method and
apparatus disclosed in Patent 3,895,368 because in that patent
the frequencies selected for use therein were limited by an attempt ;
to avoid frequencies that would be very susceptible to false
triggering.
Summary of the Invention
~lith the foregoing in mind, it is a primary object of
the present invention to provide a method and apparatus for pre- ~ .
cisely defining by predetermined limitations a control zone, within .:
which is electronically detected the presence of a telltale element
- and hence unauthorized movement of merchandise. . : .
It is further an object of the present invention to
minimize the inadvertent triggering of an electronically moni-
tored control zone alarm by the presence of a telltale element in
proximity to, but outside of, the control zone.
It is another object of the present invention to provide
a signal which will give a preliminary or warning signal when
a telltale element is moved close to the control zone but without
actually generating a false alarm that a telltale element is
actually in the control zone.
It is a resulting object of the present invention that
the warning signal provides advance notice that a telltale element
is about to enter the control zone, thereby allowing more time
to respond thereto. `
It is a further object of the present invention to
provide a device which allows greater flexibility in the choice
of frequencies and components capable of being used in the appara-
tus or in practicing the method of electronic surveillance of a
control zone by the use of a means for precisely defining the
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1 limits of the control zone.
Other objects and advantages will become apparent upon
reading the following descriptions of the invention and upon ;
reference to the drawings.
In accordance with the present invention there is pro-
vided an apparatus for detecting only within a quite precisely
defined control zone the presence of a telltale element, which ;-
is a transponder which has signal mixing capability. The appara- '
- tus includes a source of high frequency (HF) signals; means
coupled to the source of the HF signals for propagating in the
control zone an electronic wave corresponding to the HF signals
which means may include transducers or antennae; a first source
of center reference low frequency (LF) signals; a first modulation
oscillator coupled to the first source of LF signals to frequency --
.. : .
modulate (FM) said first source of LF signals; a first means,
, which may be transducers or antennae, coupled to the first source
of FM signals for establishing through the control zone an elec-
tronic field corresponding to the first source of FM signals; a
second source of center reference LF signals with the same center
frequency as the first source of LF signals, but coupled to a
second modulation oscillator having a different characteristic
than the first modulation oscillator; a second means, which may
also be transducers or antennae, coupled to the second source
of FM signals for establishing throughout the marginal area an ~-
electronic field corresponding to the second source of FM signals
and thereby precisely defining the limits of said control zone;
signal detecting means; means for coupling the detecting means
with the control zone for receiving the signals therefrom, with
the detecting means being constructed and arranged to detect the
FM signals only when received in combination with the HF signals;
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1 and a first means coupled to the detecting means for activating
an alarm circuit responsive to tne detection, when that occurs,
of the first source of the FM signals. Alternatively, there
may be provided a second means coupled to the detecting means
for activating a warning circuit responsive to the detection,
when that occurs, of the second source of the FM signals.
In accordance with another aspect of the present inven-
tion there is provided a method for detecting within a control
zone the presence of a transponder which has signal mixing capa-
bility, said method comprising the steps of generating HF signals;
propagating through a control zone an electronic wave corresponding
to the HF signals; generating LF signals using a first oscillator;
frequency modulating said first LF oscillator with a first modu-
lation oscillator; establishing through the control zone an
electronic field corresponding to the FM signals, modulated by
the first oscillator; generating further LF signals with a second
oscillator having the same center frequency as the first LF oscil- -
lator; modulating the further LF signals using a second modu-
lation oscillator; establishing throughout the marginal area an
electronic field corresponding to the FM signals modulated by the
second oscillator, to precisely define the limits of the control ~ ~
zone; detecting the signals in such manner as to detect the FM ~ -
signals only when received in combination withthe HF signals;
and translating the detection, when that occurs, of those FM sig-
nals, modulated by the first oscillator, into activation of an
alarm circuit. Alternatively, the method comprises the additional
step of translating the detection, when that occurs, of FM signals,
modulated by the second oscillator, into activation of a warning
circuit.
The invention will be better understood after reading
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1 the following detailed description of the embodiments thereof
~; with reference to the appended drawings, in which:
Description of the Drawings
Figure 1 is a block diagram of a surveillance system
constructed in accordance with the invention;
. ~ ,
; Figure 2 is a block diagram of an alternative embodi-
ment of the invention showing the utilization of both alarm and
warning functions;
Figure 3 is a block diagram of the invention showing
a preferred embodiment of the filter shown in Figure l;
Figure 4 is a block diagram of the invention showing
a preferred embodiment of the filters when both warning and alarm
functions are utilized as generally disclosed in Figure 2;
Figure 5 is a schematic diagram of a typical transponder
having signal mixing capability.
Detailed Description of the Preferred Embodiments .
Referring to Figure 1, a first oscillator 32 generates a
center reference frequency, which is frequency modulated (FM)
by oscillator 22 via conductor means 31. The FM output of the :~
first oscillator 32 is fed via conductor 33 to signal transmitting
means 34 and 35 and radiated into a control zone, 38. :~
There is also provided a second oscillator 132 which
generates the same center reference frequency as the first
oscillator 32. The center reference frequency from second oscil-
lator 132 is frequency modulated by oscillator 122 via conductor
131. The FM output of the second oscillator 132 has different
characteristics than the FM output of the first oscillator 32. The
FM output of the second oscillator 132 is fed via conductor 133
to signal transmitting means 134 and 135 and radiated into the
marginal area 138 outboard of the control zone 38. Signal trans-
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1 mitting means 34, 35, 134 and 135 may be located in housings
represented symbolically by the phantom lines 36 and 37.
:~ A HF oscillator 10 functions as a source of HF signals
and has its output connected over conductor 11, to a directional ~:
; 5 coupler 12. Outputs of the directional coupler are connectedvia conductors 13, 16 to their respective signal transmitting
and receiving means 14, and 15. The signal transmitting and
receiving means 14 and 15 may also be located in the housings
represented symbolically by the phantom lines 36 and 37. The
nature of the directional coupler 12 is such that most of the
signal from the source 10 is divided evenly to the conductors 13
and 16. However, a small amount of output from the coupler 12,
termed leakage, does flow through to conductor 17. This leakage
is utilized to bias a HF detector 18, providing a reference. ~
The area under surveillance, termed the control zone 38, :
is located between the enclosures 36 and 37. For this reason
elements 34 and 14 on one side of the space confront elements
: 35 and 15 on the opposite side. Signal transmitting means 134
and 135 are on the back of the enclosure radiating behind the
housings. This concentrates the energy from signal transmitting
means 34 and 35 between housings 36 and 37 and places the princi-
pal energy from the signal transmitting means 134 and 135 outboard
of the control zone between the housings 36 and 37.
In this configuration, when a transponder, such as shown
in Figure 5, is moved into the control zone, it will reradiate
a composite signal to signal transmitting and receiving means 14
and 15 which will be primarily the signal radiated from signal
transmitting means 34 and 35, combined with that from signal trans-
mitting and receiving means 14 and 15. However, some of the com-
posite signal reradiated from the transponder may be a signal com-
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1 ponent radiated from signal transmitting means 134 and 135
combined with a signal component from transmitting and receiving ; :~
means 14 and 15.
The signals received by signal transmitting and ~:
receiving means 14 and 15 pass through conductors 13 and 16 to
the directional coupler 12, where they are combined with very . ~:
.. :. .
little loss, isolated from signals on path 11, and sent out
conductor 17 to the HF detector 18. In a known and standard ` .
manner, the HF detector 18 will remove the HF component and -.
supply the detected FM signals via path 19 to the FM receiver 20.
The FM receiver 20 is tuned to the common center ref-
erence frequency of the FM oscillators 32 and 132. It is a well
known fact that an FM receiver will only "lock on" to the strongest -.
of a plurality of slightly different signals that are within
15 its pass band. Therefore, the FM receiver 20 will select the
FM signal radiated from signal transmitting means 34 and 35 while
the transponder is in the control zone, despite the fact that
some signal from transmitting means 134 and 135 may have also
been picked up. This is because signal radiated from transmitting
20 means 34 and 35 will be stronger when the transponder is in the
control zone than the signal from transmitting means 134 and 135. -
In like manner, if the transponder .is moved to the
outboard or marginal area 138, the composite signal reradiated
to signal transmitting and receiving means 14 and 15 will be -
25 primarily the signal radiated from signal transmitting means 134
and 135 combined with the HF signal later removed by HF detector
18. Secondarily, signals from transmitting means 34 and 35 may
be included in the composite signal, but the FM receiver 20 will
again "lock on" to the strongest signal, in this case the one
30 radiated from signal transmitting means 134 and 135 because the
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1 transponder is in the marginal area 138.
The output of FM receiver 20 is connected via conductor
21 to filter 60. Filter 60 is constructed such that signals
rom transmitting means 34 and 35, which originated in oscillator
32, will pass through it relatively unaffected. However, other
signals will be greatly attenuated. Thus, if the transponder is
located in the marginal area 138, and signals from transmitting ;~
means 134 and 135 accordingly predominate over signals from
transmitting means 34 and 35, the FM receiver 20 will lock on to
the signals from the transmitting means 134 and 135 which originate
in oscillator 132, and the output from FM receiver 20 will e~clude
any signals to which filter 60 is receptive. Therefore, when the
transponder is in the marginal area 138, the output from FM
receiver 20 will be greatly attenuated by filter 60, and will be
insufficient to trigger the alarm circuit 64.
Contrarywise, if the transponder is moved into the con-
; trol zone 38, signals from transmitting means 34 and 35, originating
in oscillator 32, will predominate and will pass through FM receiver
20 via conductor 21 to filter 50, which will pass those signals
through relatively unaffected. The output from filter 60 isconnected via conductor 62 to an alarm circuit 64.
Turning now to Figure 2, there is shown an alternative
embodiment, wherein the output of the FM receiver 20 is additionally
connected via a conductor 21' to a filter 68. This filter 68
is constructed such that signals from transmitting means 134
and 135, which originated in oscillator 132, will pass through
it relatively unaffected. However, other signals will be greatly
attenuated. The output from filter 68 is connected via conductor
70 to a warning circuit 72. The signals attenuated by filter 68
will be sufficient to trigger the warning circuit 72.
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,. . .
i Figure 5 shows a preferred embodiment of the trans-
ponder circuit, wherein each terminal of a diode 39 is connected
to parallel inductance and capacitance elements, 38 and 41 and
40 and 42 respectively which are embedded in a carrier and com-
prises a telltale tag 43.
Turning now to Figure 3, there is shown a preferred :~
embodiment of the filter 60 that is shown in Figure 1. In this
configuration, oscillator 22 has its output additionally connected
via conductor 23 to a frequency and phase comparator 24, which
~ ~ .
also receives the output of FM receiver 20 via conductor 21. The
output of the frequency and phase comparator 24 passes over path
25 to integrator 26, and thence over conductor 27 to a threshold ~ :~
level detector 28, such as a Shmitt trigger. If the comparator
24 determines that the frequency and phase of the signals received
from oscillator 22 and FM receiver 20 are identical for a given - ~ .
period of time, then the output from the integrator 26 on con-
ductor 27 will rise to the triggering point of the threshold level
detector 28, activating the alarm circuit 64 via conductor 62. ,
Finally, turning to Figure 4, there is shown an alter-
native embodiment analogous to that described above in regard to
Figure 2, wherein the filter 68 may comprise a freauency and
phase comparator 124, connected both to oscillator 122 (shown in
Figure 3) by conductor 123 and to FM receiver 20 by conductor 21',
an integrator 126 connected to the comparator 124 by conductor
125; a threshold level detector 128 connected via path 127 to the
integrator 126. If the comparator 124 determines that the fre- `
auency and phase of the signals received from the oscillator 122
and FM receiver 20 are identical for a given period of time,
then the output from the integrator 126 on conductor 127 will
rise to the triggering point of the threshold level detector 128, :
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i activating the warning circuit 72 via conductor 70.
Having described the presently preferred embodiments .
of the invention it should be understood that various changes in
construction and arrangement will be apparent to those skilled
in the art and are fully contemplated herein without departing
from the true spirit of the invention. Accordingly, there is
covered all alternatives, modifications and equivalents as
may be included within the spirit and scope of the invention as :
defined by the appended claims.
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