U.S. patent number 3,624,631 [Application Number 05/031,902] was granted by the patent office on 1971-11-30 for pilferage control system.
This patent grant is currently assigned to Sanders Associates, Inc.. Invention is credited to Marc Chomet, Donald E. Ellison, Robert F. Watterson.
United States Patent |
3,624,631 |
Chomet , et al. |
November 30, 1971 |
PILFERAGE CONTROL SYSTEM
Abstract
An antipilferage system comprising a cooperating radio frequency
transmitter and receiver pair. The transmitter directs swept radio
frequency energy to the cooperating receiver circuit wherein
balanced oscillating conditions are maintained in a normally steady
state. Passive tuned circuits, preferably in the form of printed
circuit elements are placed on the merchandise in a store and if an
attempt is made to remove unpurchased merchandise from the store
without first destroying a fusible link in the passive tuned
circuit an unbalance is caused in the receiver oscillator circuits
which operates to actuate a suitable alarm. A fully automatic
deactivation circuit is also included as part of the invention.
Inventors: |
Chomet; Marc (East Northport,
NY), Ellison; Donald E. (Sea Cliff, NY), Watterson;
Robert F. (Lake Ronkonkoma, NY) |
Assignee: |
Sanders Associates, Inc.
(Nashua, NH)
|
Family
ID: |
21862035 |
Appl.
No.: |
05/031,902 |
Filed: |
April 27, 1970 |
Current U.S.
Class: |
340/568.1;
340/572.3; 340/572.5; 334/39 |
Current CPC
Class: |
G08B
13/2431 (20130101); G08B 13/2414 (20130101) |
Current International
Class: |
G08B
13/24 (20060101); G08b 013/00 (); G08b
021/00 () |
Field of
Search: |
;340/258R,280
;343/6.5SS,6.8R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Yusko; Donald J.
Assistant Examiner: Slobasky; Michael
Claims
Having described what is new and novel and desired to secure by
Letters Patent, what is claimed is:
1. A pilferage control system for detecting the unauthorized
removal of goods from an area comprising
a passive tank circuit affixed to said goods, tuned such as to have
predetermined radiofrequency absorption characteristics in the
presence of a radiation field, and having fusible link disposed in
series therein,
means for transmitting a field of swept radiofrequency radiation of
a preselected first level into a volume of space including an exit
from said area,
means disposed remotely with respect to said transmitting means for
detecting said swept radiofrequency radiation and responsive to a
selected change in said radiation level to produce an electrical
output signal indicative thereof,
tuned circuit deactivation means for selectively applying swept
radiofrequency radiation of a preselected second level higher than
said first level to said passive tank circuit said second level
being sufficiently high to destroy said fusible link, and
indicating means coupled to said detecting means and responsive to
said electrical output signal therefrom to indicate the presence of
a passive tuned tank circuit having a complete fusible link therein
within said radiation field.
2. Apparatus as recited in claim 1 wherein said transmitting means
comprises
a variable radiofrequency oscillator,
means coupled to said oscillator for varying the frequency thereof
as a preselected function of time,
a planar radiofrequency transmitting antenna, and
means for driving said antenna coupled between said oscillator and
said antenna.
3. Apparatus as recited in claim 1 wherein said detecting means
comprises
a planar radiofrequency receiving antenna,
a radiofrequency passband receiver coupled to said receiving
antenna, and
means coupled to said receiver for rejecting detected changes in
said radiation level which correspond to other than absorption
produced by a passive tank circuit in said radiation field.
4. Apparatus as recited in claim 3 wherein said rejecting means
includes
a dual time constant detector means operative to produce an
electrical output signal only in response to detected changes in
said radiation level which correspond to the presence of a passive
tuned tank circuit having a complete fusible link in said radiation
field, and to reject detected changes both above and below a
preselected frequency bandwidth.
5. Apparatus as recited in claim 4 wherein said rejecting means
includes correlation means coupled to said dual time constant
detector means comprising
means for establishing a plurality of frequency bands within the
frequency range of said transmitting means,
means for determining in which one of said plurality of frequency
bands a change in said radiation level corresponding to the
presence of a passive tuned tank circuit is produced,
means for detecting only changes in said radiation level which
occur in said one frequency band for a predetermined number of
sequential sweeps through said frequency range of said transmitting
means, and
means for producing an electrical output signal only in response to
said predetermined number of sequential detections in said one
frequency band.
6. Apparatus as recited in claim 1 further including
means coupled between said detecting means and said indicating
means for sensing the presence of a person in said radiation field
and producing an electrical signal indicative thereof and wherein
said indicating means is responsive only to the combined electrical
signals from said detecting means and said sensing means.
7. Apparatus as recited in claim 1 wherein said passive tuned tank
circuit comprises in series
an inductance element,
first and second capacitive elements, and
a fusible link disposed in said circuit and susceptible to
destruction by the application of radiofrequency energy above a
preselected level.
8. Apparatus as recited in claim 1 wherein said tuned circuit
deactivation means comprises
means for transmitting swept radio frequency radiation at
selectable first and second levels into a preselected volume of
space,
means colocated with said transmitting means for detecting said
swept radiofrequency radiation and responsive to a selected change
in said radiation level to produce an electrical output signal
indicative of the presence of said tuned circuit, and
means coupled to said detecting means and to transmitting means for
selecting the higher of said first and second transmitting means
output radiation levels for a preselected period of time said
higher level being sufficiently high to burnout said fusible link
in said tuned circuit.
9. Apparatus as recited in claim 8 further including
means for indicating complete destruction of said fusible link.
10. A tuned passive tank circuit for use with a radiofrequency
pilferage control system comprising in series
an inductance element,
first and second capacitive elements, and
a fusible link disposed in said circuit and susceptible to
destruction by the application of radiofrequency radiation above a
preselected level.
11. Apparatus as recited in claim 10 wherein
said fusible link is formed of an electrically conductive material
wherein an electrical overload adequate to destroy said link is
induced by a radiofrequency radiation level of one hundred
milliwatts.
12. Apparatus as recited in claim 10 wherein:
said radio frequency pilferage control system employs swept radio
frequency radiation, and
said tuned passive tank circuit is tuned such as to absorb
radiation over a frequency range less than and within the range of
radiofrequencies over which said pilferage control system is swept.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to the field of
radiofrequency circuits and more specifically to a radiofrequency
antipilferage system.
DESCRIPTION OF THE PRIOR ART
Pilferage of merchandise from business establishments has become a
matter of great concern and many devices have been devised in an
attempt to minimize losses. One such device is a Detecting Means
for Stolen Goods described in U.S. Pat. No. 2,774,060 which issued
to T. F. Thompson on Dec. 11, 1956. In this system one or more
fixed frequency oscillators are employed to set up a radiation
field of predetermined shape and size and precision resonant
circuits are concealed in sales tags on the merchandise. When
merchandise with a resonant circuit is passed through the radiation
field the potential of the oscillator is changed and actuation of
an alarm results. In order to prevent false alarms by legitimately
purchased merchandise it is necessary that the sales tag containing
the circuit be physically destroyed.
Several practical problems attend the use of an antipilferage
system such as that described by Thompson. The use of a fixed
frequency oscillator requires that the resonant tuned circuit be
precision tuned to that frequency. In order to prevent actuation of
the alarm by an object of appropriate size carried by a legitimate
customer it is desirable to use three different fixed frequency
oscillators and three precision tuned circuits, one for each
frequency. In such an arrangement wherein frequency precision is
required a serious problem may arise in detuning of the tuned
circuit by body capacity, i.e. the electrical capacity of the human
body in close proximity to the tuned circuit is in many cases
sufficient to detune the circuit to the extent that detection by a
single frequency system is precluded. It will be noted that even in
the three oscillator embodiment of the Thompson apparatus detuning
of any of the precision circuits will preclude detection. The fact
that the Thompson apparatus necessitates a manual destruction of
the tuned circuit bearing tag increases the potential for
inadvertent and embarrassing triggering of the alarm should an
employee forget to remove the tag. An accomplished pilferer may
also become aware of the gross nature of the system from
observation of consistent removal of such tags and/or the
consequences of nonremoval. The apparatus described by Thompson
further involves the use of one antenna for both transmitting the
radiation pattern and detecting an absorption by the resonant
circuit. Such an arrangement has an inherently low-volumetric
efficiency and the tuned circuit must pass in close proximity to
the antenna for reliable detection. Many business establishments
are not physically laid out such as to assure such proximity.
OBJECTIVES AND SUMMARY OF THE INVENTION
From the foregoing it will be understood that among the objectives
of the present invention are the following:
To provide a new and novel radiofrequency antipilferage system.
To provide apparatus of the above-described character using a swept
radiofrequency.
To provide apparatus of the above-described character having a
cooperating transmitter and receiver remotely disposed with respect
to one another.
To provide apparatus of the above-described character wherein a
passive tuned circuit disposed on merchandise may be automatically
and surreptitiously deactivated.
To provide apparatus of the above-described character having
improved false alarm rejection.
The foregoing objectives are accomplished through the practice of
the present invention by providing a swept radiofrequency
oscillator and transmitting antenna and a remotely disposed
cooperating broad band radiofrequency receiver and antenna coupled
to a post detection signal processor. A passive tuned circuit
having a fusible link is affixed to articles of merchandise
preferably within a price tag or other item affixed by the store.
When pilfered merchandise bearing the tuned circuit is carried
between the transmitter and receiver there is absorption of energy
from the radiation field and an unbalance is produced in the
receiver which is used to actuate a suitable alarm. To preclude
actuation of the alarm by tags or legitimately purchased
merchandise each passive tuned circuit is provided with a fusible
link which is opened when the circuit is exposed to radiofrequency
energy above a preselected level. To accomplish the deactivation
swept radiofrequency energy above the preselected level is
transmitted for example through the surface of a check out counter
at which purchased merchandise is wrapped. This energy destroys the
fusible link in the passive tuned circuit and automatically checks
for the continued presence of an active circuit. Thereafter the
merchandise with the tag bearing the deactivated tuned circuit, and
in which there has been no change which is readily discernable to
the casual observer, may pass between the transmitter and receiver
without actuating the alarm. The deactivation portion of the
invention is fully automatic in operation and under normal
circumstances completely eliminates any requirement for manual
participation of sales employees in the deactivation of the tuned
circuit.
These and other objects, features and advantages of the present
invention will become more apparent from the detailed discussion
taken in conjunction with the appended drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a block diagram of a pilferage control system in
accordance with the present invention.
FIG. 2 is a schematic diagram of a fusible tuned circuit for use
with the present invention.
FIG. 3 is a schematic block diagram of a deactivation circuit for
use in the practice of the present invention.
DESCRIPTION OF PREFERRED EMBODIMENT
Turning now to FIG. 1 there is illustrated a block diagram of the
cooperating transmitter and receiver portions of the present
invention which would be placed across each exit of a store. The
transmitter generally designated 10 comprises a voltage controlled
oscillator 12 the output frequency of which is controlled by a
sweep control means 14. The swept radiofrequency output signal from
the oscillator 12 is coupled through a driver 16 to a transmitter
antenna 18. A radiation field 20 over a desired area defined by the
characteristics of the transmitter antenna 18 is thus established.
The transmitter 10 is preferably placed on one side of the
entrance/exit to the place of business.
The receiver designated generally at 22 is placed on the opposite
side of the store entrance/exit from the transmitter. A receiver
antenna 24 picks up the swept radiofrequency energy and is coupled
to a passband radio receiver 26. The output of the receiver 26 is
applied to a post detection processor 28 which comprises in
sequence a dual time constant detector 30, amplifier 32, passband
filter 34 and correlation circuit 36.
The receiver 26 output in the absence of a tuned circuit in the
radiation field will be substantially at a continuous level as the
transmitter oscillator 12 is swept in frequency. When a tuned
circuit enters the radiation field 20 there will result a
discernable dip in the receiver 26 output due to energy absorption
by the circuit at the frequency for which it is tuned. The dual
time constant detector 30 operates to reject false absorption
signals of two types; first, that caused by an individual merely
passing through the exit and which is manifested as an absorption
at all frequencies within the sweep range of the oscillator 12 and
second, the random noise within any electronic system which is
characterized by very sharp spikes. In that the frequency is swept
rather than fixed the dual time constant detector 30 may simply
reject any detected absorption which is of too long or short a
duration; i.e. corresponding to either too wide or too narrow
frequency bands to be produced by a tuned circuit in the radiation
field 20.
Thus receiver signals which have the proper frequency (and thus
time) characteristics are coupled to amplifier 32 and thence
through a passband filter 34 to a correlation circuit 36. The
correlation circuit 36 may, for example, comprise a plurality of
one shot multivibrators or any other of the recognized means for
dividing the frequency sweep of oscillator 12 into a given number
of bins or windows. Once the presence of a tuned circuit is
detected in the radiation field 20 by a proper absorption
characteristic the correlation circuit 36 establishes a frequency
window or bin; e.g. 10 percent of the total frequency sweep range,
within which the absorption was detected. Only after a
predetermined number of sequential detections have occurred in that
frequency window will the correlation circuit 36 produce an output
signal. A transient signal in the system is thus rejected since it
would not appear in the requisite number of successive sweeps and
random signals would not have the frequency stability to appear in
the same window for a long enough period to actuate the alarm. The
correlation circuit output signal could be coupled directly to a
suitable alarm 40, however, as an added false alarm rejection
feature this signal may be applied to an AND-gate 38 to which is
also coupled a signal from a foot switch (not shown) concealed for
example under a floor mat in an exit doorway. In this fashion the
alarm 40 would only be actuated by a person in the radiation field
20 who was carrying merchandise bearing an active tuned
circuit.
FIG. 2 is a schematic illustration of a passive tuned circuit which
is useful in the practice of the present invention. The circuit is
essentially a simple tank circuit comprising a coil 42 and
capacitors 44 and 46. A significant difference, however, which is
of great practical utility in the practice of this invention is the
incorporation of a fusible link 48 in the circuit. This link is
shown for the purpose of illustration as being disposed between
capacitors 44 and 46, however, it is to be understood that
disposition anywhere in the circuit is equally suitable in the
practice of the invention. The link 48, when placed in series in
the tuned circuit, has negligible current induced therein by the
radiation field across the entrance/exit of the store and thus has
substantially no effect upon the detection process discussed above.
The fusible link 48 is formed of a fine conductor such as steel
wire which may be "burned out" by a preselected level of
radiofrequency energy. The passive tuned circuit may be formed
using printed circuit techniques well known in the art and
incorporated into any of the variety of cards, tags or the like
which are normally found in or on merchandise displayed for sale.
Initially the circuit is complete and when placed in a radiation
field 20 operates to absorb energy in the field. On the application
of a relatively higher power RF field the induction field overloads
the fusible link, opening the circuit and thus rendering it
ineffective as an absorber.
FIG. 3 is a schematic block diagram of a fully automatic
deactivation circuit which is preferred in the practice of the
present invention. This circuit may be placed beneath the checkout
and wrapping counter usually found in business establishments and
operates to detect the tuned circuit carried by merchandise being
legitimately purchased, switch to an output power sufficient to
"burnout" or open the fusible link and check to assure that
deactivation has actually been accomplished. A voltage controlled
oscillator 50 having substantially the same frequency range as
oscillator 12 of FIG. 1 and which is controlled by a frequency
sweep control means 52 is coupled through a buffer amplifier 54 to
a power driver 56. The power driver 56 is coupled to a transmitter
antenna 58 which may be flush-mounted in or under the wrapping
counter. Mounted concentrically with the transmitter antenna 58 is
a receiver antenna 60. When a piece of merchandise bearing a tuned
circuit is placed on the wrapping counter an unbalance is produced
in the receiver 62 to which the receiver antenna 60 is coupled. The
receiver output is coupled through receiver logic circuitry 64 to a
deactivation control logic circuit 66. When the presence of a tuned
circuit is detected the receiver logic circuit 64 generates an
output signal which is applied to the deactivation control logic
circuit 66 which operates to switch the power driver 56 into a
relatively high-power mode (e.g., 100 mw.) for a predetermined
period of time. At the end of this time the power drive 56 is
returned to its normal lower level output. If the continued
presence of a tuned circuit is indicated the deactivation process
is automatically repeated. If, after a predetermined number of
deactivation cycles, as determined by feeding back the output of
the deactivation control logic circuit 66 to the receiver logic
circuit 64, a tuned circuit continues to be detected a manual
destruct indicator 68 such as a light, buzzer or the like, may be
activated to instruct the employee to manually remove and destroy
the circuit-bearing tag or label. To further discourage the
employee from simply ignoring the manual tag destruction indicator
a reset switch (not shown) may be provided which must be closed by
the employee before the indicator will be deactivated. The
deactivation circuit is thus both fully automatic and self-checking
in operation, and substantially precludes the actuation of the
entrance/exit alarm by legitimately purchased merchandise. It is
only in rare instances that the manual involvement of an employee
is required and even in this event the employee need have little if
any knowledge of what the under-counter unit is or how it
operates.
It will thus be seen that the objectives set forth hereinabove,
among those made apparent from the preceding description are
efficiently attained and since certain changes may be made in the
above construction without departing from the scope of the
invention, it is intended that all matter contained in the above
description or shown in the appended drawings shall be interpreted
as illustrative and not in a limiting sense.
* * * * *