R.f. System For Detecting Unauthorized Travel Of Articles Through A Selected Zone

Abstract

A theft detection system and method for detecting the passage of articles through a monitored zone including affixing a relay transponder to the articles, transmitting a preselected frequency signal to the zone for pickup by the transponder and retransmission to the ambient atmosphere, receiving and detecting the retransmitted signal, and providing simultaneous digital control to both the transmitting and the receiving means, whereby the latter may be alternately energized during monitoring operation to provide maximum sensitivity and minimum average power dissipation within the system. The relay transponder may advantageously be an LC parallel connected resonant tank circuit tuned to the preselected frequency of the transmitter and providing by ringing action the retransmitted signal detected in the receiver.

Description

FIELD OF INVENTION

This invention relates in general to detection systems and, more particularly, to a system for detecting movement of articles and the like through a predetermined zone, which system is clocked or programmed-controlled for maximum sensitivity with a minimum average power dissipation.

BACKGROUND

Heretofore extensive efforts have been expended for developing automatically operated theft detection systems primarily for usage in retail stores where in recent years pilferage has occasioned ever increasing financial loss. This development has been understandably abetted by the trend in such stores toward self-service. Various systems have been contrived for monitoring check points, that is, zones within a store which must be traversed by a customer immediately prior to, or in the course of, leaving the store premises. The prior art systems have not provided a requisite level of sensitivity so that detection of "protected articles" is not reliable; the same have extremely limited operational range; have required sophisticated electronics to process the detected signal; have required the utilization of substantial average power by requiring continuous operation. Examples of such inadequate prior developments are shown in U. S. Pat. Nos. 3,500,376; 3,534,358; 3,577,136; and 3,582,931.

Another example of a previous effort in this field is demonstrated by U. S. Pat. No. 3,500,373 which discloses a theft detection system comprehending a continuosly operating transmitter for generating electromagnetic waves at a check point which sweep repetitively through said check point at a given rate through a frequency range. A wafer having an LC resonant tank circuit provided thereon is attached to articles moving through the check point and being at a resonant frequency within the range being transmitted. The absorption of the wafer of power emitted by the transmitter causes a corresponding dip in the power level on the transmitter antenna and on the leads progressing therefrom. A suitable electric detection system is incorporated for detecting the power dip and thereby causes an alarm. Such system requires constant, costly operation and is effective in only a limited area, and with the power band being quite restricted. The wafer of this system can, understandably, absorb only so much energy consonant with its size so that a relative increase in the transmitted power may well prevent the detection of any power dip by reason of the relatively limited character thereof.

THE INVENTION

The general purpose of this invention is to provide a new and improved theft detection system having all of the advantages of similarly employed prior art theft detection systems and possessing none of the aforesaid described disadvantages. To attain this purpose, the theft detection system embodying the invention includes means for transmitting a signal to a zone selected for monitoring the passage therethrough of articles having suitably affixed thereto a transponder or energy relaying member adapted to receive a signal from the transmitting means and for retransmitting same, and means for receiving the retransmitted signal. Digital control means are connected to both the transmitting and receiving means and alternately energize the same at a preselected frequency. Means are coupled to the receiving means to detect a signal from said transponder for energizing an alarm, and with such detection means being uniquely contrived to avoid activation of said alarm by reason of receipt of an erroneous signal. The transponder is of electronic character and may be a resonant LC tank circuit or appropriate resonant device fabricated in a small, semiconductor wafer, or on a small printed circuit board which may be readily secured to any type or merchandise and be as easily utilized for personnel identification purposes.

Therefore, it is an object of the present invention to provide a new and improved theft detection system adapted to operate with maximum signal sensitivity and with a minimum average power dissipation.

It is another object of the present invention to provide a theft detection system of the character stated which is adapted for accommodating monitoring zones of any preselected extent without diminution in reliability.

It is a further object of the present invention to provide a theft detection system of the character stated which may be readily installed in stores and the like in a most economical fashion and without requiring any extensive alterations.

It is a still further object of the present invention to provide a detection system of the character stated which embodies means for preventing energization of the system from signals received from other than the bonafide source.

It is another object of the present invention to provide a theft detection system of the character stated which comprehends a simplicity of components, promoting substantial ecomony in production and assembly; which system is resistant to breakdown; which is durable and reliable in usage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram, being partially pictorial of a theft detection system constructed in accordance with and embodying the present invention.

FIG. 2 is a functional block diagram of the transmitter.

FIG. 3 is a wave form diagram of the clock and RF signals processed by the transmitter diagrammatically shown in FIG. 2.

FIG. 4 is a plan view of a transponder or energy relayer for engagement to articles to be monitored by the present system.

FIG. 5 is a functional block diagram of the receiver.

FIG. 6 is a functional block diagram of the signal selector.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now by reference characters to the drawings which illustrate the preferred embodiment of the present invention, Z broadly indicates a zone Z to be monitored by a detection system indicated generally A; said zone Z being a passageway, check point, or the like, having opposed, spaced-apart lateral support members 1,1' and an upper transverse member 2 extending therebetween; said members 1,1' and 2 being of any convenient character for properly supporting and maintaining antennas 3, 4 and 5, respectively, for purposes presently shown. It is apparent that zone Z may be located at any convenient point within a retail establishment, as within departments thereof, at check-out counters, exit ways, etc.

Antenna 3 is connected by an output conductor 6 to a transmitter 7, which latter is also interconnected to antenna 5 by another output conductor 8. Thus, lateral and overhead antennas 3,5 are disposed for effectively flooding, as it were, zone Z with radio waves radiated from transmitter 7 during energization thereof and at a predetermined frequency.

As indicated in FIG. 2, transmitter 7 may include, for example, a fixed frequency oscillator 9 having its output 10 connected to a gated power amplifier stage, indicated 11. The output of amplifier stage 11 is directly connected to transmitter antennas 3,5, as above described. Connected to amplifier stage 11 is a control input terminal 12 continuous with one output line 13 from a programmer or clock 14 which may, for example, be a free-running, or astable flip-flop, such as a cross-coupled, discrete transistor, or monolithic transistor flip-flop cross-coupled and/or any biased system used to generate simultaneously one or more distinct control output signals, indicated To and Ro, of any desired clock frequency. Also, it is apparent that programmer 14 may be a digital signal generating unit. Output signal To is provided for controlling transmitter 7 being conducted thereto along line 13 and terminal 12. As illustrated in FIG. 3, programmer output signal To is a fixed frequency square wave signal and drives amplifier stage 11 "on" and "off" at such frequency to gate the bursts of radio frequency (RF) output signal from oscillator 9 through said amplifier stage 11 for energizing antennas 3,5. Advantageously, oscillator 9 may be a 1.25 megacycle stable crystal oscillator. Programmer 14 is connected by a lead 15 to a control input 16 of a receiver 17 which latter is engaged to antenna 4 by a conductor 18. The output signal Ro provided by programmer 14, and which is out of phase with respect to output signal To, controls the operation of receiver 17. Accordingly, when signal Ro is delivered to receiver 17 the latter is energized and correspondingly transmitter 7 is activated upon receipt of signal To, as indicated above. However, since the said signals To and Ro are 180.degree. out of phase with each other, transmitter 7 and receiver 17 are, perforce, alternately energized or activated so that when transmitter 7 is transmitting, receiver 17 is in an off state, and, conversely, when receiver 17 is operative to receive signals, transmitter 7 is quiescent. The alternation of operation of transmitter 7 and receiver 17 is of any desired periodicity. However, for purposes of example, the same are turned on and off with extreme rapidity, preferably within a range of 2,000 to 10,000 times per second.

The output of receiver 17 is connected by a lead 19 to one input of digital signal detector 20 for control of the latter. Said signal detector 20 is also controlled by the output signal Ro of programmer 14, which signal is applied through a conductor 21 to another input of said detector 20. Digital detector 20 is provided with a pair of outputs connected by leads 22,23 to a theft alarm indicator 24, and a false alarm indicator 25, respectively. By reason of operation of programmer 14, detector 20 will only generate an output alarm signal along lead 22 upon the simultaneous application of digital signals on lead 19 and conductor 21 which, as shown, feed into detector 20.

From the foregoing it will be seen that zone Z is intermittently suffused with electromagnetic waves emanating from transmitter antennas 3,5 which, having a preselected frequency, cause energization of a transponder or energy relayer 26 disposed within zone Z. As will be developed more fully hereinbelow, transponder 26 will accept energy from the transmitter signals during the time period that control signal To from programmer 14 is activating transmitter 7. During the succeeding period in which transmitter 7 is turned off, and receiver 17 is energized by reason of acceptance of control signal Ro from programmer 14, transponder 26 acts as a transmitter and radiates the energy previously received from antennas 3,5 to receiving antenna 4, with the received signal being processed in receiver 17 and detector 20.

With reference being made to FIG. 4, it will be seen that transponder or relayer 26 comprises essentially an inductance, capacitance (LC) parallel, resonant tank circuit indicated generally 27, including an inductor 28 and a capacitor 29 connected in parallel by leads 30,30' and being suitably provided on one surface 31 of a small mounting member 32, which latter may, for example, be an extremely small printed circuit board with inductor 28 and capacitor 29 provided by the conventional printed circuit metallization or silk screen techniques. Also, if desired, mounting member 32 may be a monolithic semiconductor chip having capacitor 29 diffused therein and inductor 28 either provided on the chip surface or within the body thereof.

The LC resonant tank circuit 27 exhibits a well known "ringing" effect if the same is energized with electromagnetic radiation of, or close to, the frequency to which the said circuit is tuned. Such circuit will absorb such electromagnetic radiation and thereafter, because of the character of the current flowing in conductor 28 and capacitor 29, will demonstrate such ringing effect and radiate the received electromagnetic radiation into the ambient atmosphere. The energy stored in the transponder 26 is, by proper design, quickly radiated. The signal thus relayed or radiated by tank circuit 27 is recognizedly less strong than the received signal and, hence, must be accepted by a suitable receiving antenna, such as antenna 4, from which it may be considerably amplified. This so-called ringing action by tank circuit 27 is sufficiently strong within the period of the kilocycle clock frequency of programmer 14 for reception and amplification purposes.

It is apparent that transponder 26 may be of most limited size and weight so as to be readily affixed, as by a suitable pressure sensitive adhesive, to almost any type of article, particularly of the character found in retail stores, and with the dimensions thereof being such as to permit the application of such transponders to obscure places on the articles to avoid detection, except by authorized personnel. Thus, in the normal course of events, transponder 26 may be guardedly removed by a sales clerk at the time of recognizing the purchase. Articles from which the transponder 26 have not been removed will, upon passing through zone Z, effect the activation of an alarm, in the manner to be discussed hereinbelow, as an alert to the potential theft. Transponder 26 may also be appropriately utilized in conjunction with badges and the like for individuals moving into, and from, classified areas, as in military establishments and defense industries to assure security personnel of the clearance of such individuals. Therefore, the versatility of transponder 26 in conjunction with the system of the present invention is manifest.

By reason of the link of receiver 17 to programmer 14, the same is uninhibited when programmer 14 turns off transmitter 7. Thus, this synchronized action permits receiver 17 to receive energy only from transponder 26. As shown, the inhibit/uninhibit action of receiver 17 is controlled by the Ro signal of programmer 14. As shown in FIG. 5, receiver 17 may be of relatively conventional character but being modified to accept the aforesaid inhibit and uninhibit signals from programmer 14. Receiver 17 could be of the superheterodyne type comprising an RF amplifier 33 connected to antenna 4 for initially amplifying the received signal from transponder 26. The output of RF amplifier 33 is connected to a frequency converter or mixer 34, another input side of which is suitably connected to a local oscillator 35, the output of which is mixed with the RF carrier within mixer 34. The output of mixer 34, that is, the intermediate frequency (IF) is then directed sequentially to preferably a plurality of IF amplifiers 36,37. Although in actual practice a single IF amplifier is adequate, the provision of at least two is found to provide better peaking and the production of less erroneous signals. The output of said amplifiers 36,37 is applied to the input side of a detector or demodulator 38 for removing the intermediate frequency from the signal and thus provides a digital control signal for application to the digital signal detector 20 via lead 19.

The control signal Ro from programmer 14 being conducted along lead 15 and input 16 may be connected to either an input, as at 39 of RF amplifier 33 for gating the relayed signal therethrough in substantially the same manner as control signal To is used to control the burst of radio frequency through transmitter 7; or may be connected to an input 40 of local oscillator 35 for controlling the burst of intermediate frequency in the output of mixer 34; said alternative paths being selectively determined by positioning of switch 41.

It is understood that receiver 17 may be of any desired type, such as even a simple tuned amplifier with intermediate frequency filters.

Referring now to FIG. 6, a preferred embodiment of digital selector 20 is illustrated with the same including a main or alarm signal channel 42 and an auxilary or erroneous signal channel 43. The digital control signal from receiver 17 is conducted along lead 19 to one input of each of two AND gates 44,45 provided in signal channels 42,43, respectively. The output of AND gate 44 is suitably connected for driving a first shift register 46. After a predetermined number of sequential output pulses from AND gate 44 have been counted in register 46, the same will generate an output signal detected by a monitoring AND gate 47 and passed along a conductor 48 to theft alarm 24. Shift register 46 may be of conventional character utilizing a plurality of commercially available cascaded flip flops which can be clocked from a common clock line (not shown). Sequential decimal counting is preferred to a binary counter.

The output of AND gate 45 in channel 43 is connected to the input of a shift register 49, which is of the same character as register 46 and which, after having counted a predetermined number of sequential output pulses, generates an output signal for detection by a monitoring AND gate 50 for passage along a lead 51 to false alarm indicator 25 for energization of the latter.

The control signal Ro from programmer 14 passes along conductor 21 for delivery to the input 52 of a one-shot pulse shaper 53 which is within digital selector 20 and a part thereof. Said shaper 53 is operative to generate out-of-phase pulses .DELTA.Ro and .DELTA.Ro on output lines 54,55, respectively, which latter are connected to second inputs 56,57 on AND gates 44,45, respectively. A timing gate 58 is provided within pulse shaper 53 for modifying the time reference of signal .DELTA.Ro to avoid shift register 49 from "seeing" signals at other than .DELTA.Ro time. Thus, timing gate 58 permits shift register 49 to count during any interval when shift register 46 is not counting. Channels 42 and 43, by virtue of timing gate 58, are alternatively enabled during the presence of .DELTA.Ro and .DELTA.Ro signals, respectively, at the output of shaper 53. In this manner, main channel 42 may be utilized to detect the presence of an article bearing transponder 26 within zone Z and then be disabled during the subsequent .DELTA.Ro pulse which enables channel 43. The nature of the timing gate 58 is such that shift register 46 is enabled only for a short period of time immediately subsequent to the termination of the transmitter signal. It is within this short period that signals would be radiated from the transponder 26 if it is present in zone Z. During the balance of such period, between transmitter pulses, shift register 49 is enabled by .DELTA.Ro, thereby permitting spurious signals to be detected by channel 43. Shaper 53 may be of standard type, modified to produce timing signals for operation of channels 42,43.

Channel 43 serves to detect the presence of extraneous electromagnetic radiation which may be accepted by receiver antenna 4, but which does, obviously, not emanate from transponder 26. Such signals may originate with any of the myriad types of wave generating devices in current use, such as, transistor radios, heart pace makers, electrical appliances, static electricity, and the like.

The action of timing gate 58 is such as to render the circuit immune to external spurious signals which are of lower frequency than the pulsing rate of the transmitter and to signals of insufficient strength to be detected by shift registers 46,49. By suitable choice of transmitter pulsing frequency and transmitter power output level, the vast majority of spurious signals are thereby automatically excluded. If, however, a spurious signal is present of proper amplitude and frequency to be detected by registers 46,49, it will trigger the error channel. This will cause the error signal to be actuated, indicating that corrective action must be taken either to remove the source of the particular disturbance, or to adjust the power level and/or pulsing rate of the transmitter to cause the circuit to ignore the spurious signal.

It is apparent that theft alarm 24 and false alarm signal 25 may be of any suitable type, such as, providing an aural signal, or a visual signal, if desired; such being within the range of one skilled in the art.

In view of the foregoing, it is to be observed that the present system minimizes power dissipation by virtue of the alternative operation of transmitter 7 and receiver 17. Also by this arrangement a single tuned frequency may be utilized with full reliability since receiver 17 is controlled so as to be in a non-receiving state when transmitter 7 is operating.

Transponder 26 actually serves as a floating transmitter and may be energized by any given frequency and with a relatively low power level. Power may be increased or decreased as desired for commensurately increasing or decreasing the effective volume of zone Z.

Transponder 26, as indicated above, may be of any suitable type and being also adapted for encapsulation in plastic and attachment to any type of non-metallic card or the like, such as, fiber board, cardboard, plastic, etc. One shot pulse shaper 53 may be a monostable multi-vibrator and could be replaced by two such shapers, one for each signal period, but being appropriately tied together.

Claims

Having described our invention, what we claim and desire to obtain by Letters Patent is:

1. A theft detection system for detecting the passage of protected articles through a selected area, said system comprising:

a. a transmitter for transmitting, when activated, radio frequency signal bursts at a predetermined frequency to said selected area;

b. a parallel connected inductance capacitance tank circuit tuned to said predetermined frequency and adapted for affixation to articles passing through the selected area;

c. a superheterodyne receiver for detecting, when activated, radio frequency signal bursts retransmitted thereto from said tank circuit at said predetermined frequency;

d. control means connected to both said transmitter and said receiver and operative to alternately activate same at a chosen control frequency;

e. alarm means comprising a main alarm signal channel including a main alarm and an error alarm signal channel including an error alarm, said alarm means including pulse shaping means connected to said control means for reception of control signals therefrom and connected also to both said alarm signal channels, said pulse shaping means incorporating timing means for sorting the radio frequency bursts detected by said receiver into said main alarm channel if such bursts are detected during a predetermined time interval and into said error alarm signal channel if such bursts are detected at times other than said predetermined interval, and counting means for counting a predetermined number of radio frequency bursts for energizing at least one of said alarms.

2. A theft detection system as set forth in claim 1 wherein said pulse counting means comprises:

a. first counting means in said main alarm signal channel for counting a predetermined number of radio frequency bursts for energizing said main alarm means to signal passage of a protected article through said selected area; and b. second counting means in said error alarm signal channel for counting a predetermined number of radio frequency bursts for energizing said error alarm to signal detection of spurious radio frequency bursts.

3. A theft detection system as set forth in claim 2 wherein each of said alarm signal channels includes a respective AND gate, each of said AND gates having a first input for receiving detected radio frequency bursts and a second input interconnected with said pulse shaping means.

4. A theft detection system as set forth in claim 3 wherein said first and second counting means comprise respective shift registers.