SURVEILLANCE TAGS

FIELD OF THE INVENTION

This invention relates to electronic article surveillance and, more particularly, to deactivating electronic article surveillance tags. BACKGROUND OF THE INVENTION

Electronic article surveillance (EAS) systems have employed either reusable EAS tags

or disposable EAS tags to monitor articles. The reusable EAS tags are normally removed from the articles before the customer exits the store. The disposable tags are generally

attached to the packaging by adhesive or are disposed inside the packaging. These tags

remain with the articles and must be deactivated before they are removed from the store by

the customer. Deactivation devices use coils which are energized to generate a magnetic field

of sufficient magnitude to render the EAS tag inactive. The deactivated tags are no longer

responsive to the incident energy of the EAS system so that an alarm is not triggered.

In one type of deactivation system the checkout clerk passes the articles one at a time

over a deactivation device to deactivate the tags and then places the articles into a shopping bag or other bulk container. This system employs one coil disposed horizontally within a

housing. The clerk moves the tagged articles across the horizontal top surface of the housing

such that the tag is disposed generally parallel to the coil.

Another deactivation system utilizes a housing having a cavity with three sets of two

coils each disposed around the cavity in respective x, y, and z axis planes, such that there is a

coil located in a plane parallel to each side of the cavity and two coils disposed around the

cavity with one being near the top and the other being near the bottom of the cavity. The

checkout clerk places a bag or bulk container into the cavity and then places the tagged

articles into the bag. After all of the articles have been placed into the bag or when the bag is

full, the clerk energizes the coils to deactivate all of the EAS tags in the bag. The clerk then

lifts the bag out of the cavity. This system provides deactivation of multiple tags at one time

and does not require specific orientation of the tags.

The widespread usage of EAS systems has created a demand for systems that provide improved reliability and reduced cost. This is especially true for the deactivation portion of

the EAS system including the deactivation coils and power supply for energizing the

deactivation coils. Each time the deactivation system is operated, the power supply must

reliably provide an accurate waveform of the appropriate power to energize the deactivation

coils. Accurately creating the desired field ensures that the EAS tag has been deactivated so

that it does not cause an alarm condition when the customer exits the store.

SUMMARY OF THE INVENTION

In accordance with the present invention there is provided an apparatus for

deactivating electronic article surveillance tags comprising a deactivation coil, a capacitor,

charging means for charging the capacitor to a predetermined level and an electronic switch.

The electronic switch is connected to the capacitor and the deactivation coil so that when the switch is open the capacitor can be charged by the charging means and when the switch is

closed the capacitor can discharge through the deactivation coil.

The present invention also provides a method of deactivating electronic article

surveillance tags comprising charging a capacitor to a predetermined level and connecting

the charged capacitor to a deactivation coil so that the capacitor discharges through the

deactivation coil.

Accordingly, the present invention provides an improved deactivator for deactivating

EAS tags utilizing the natural resonant decay of a precharged capacitor or capacitor bank in

series with the deactivation coil. The capacitor bank is charged to the required value which is

determined by the peak magnetic field desired, and the discharge is initiated by closing an electronic switch. The magnetic field created has an alternating polarity and a decaying

envelope at a particular decay rate. The EAS deactivator of the present invention operates at

a high voltage, i.e., approximately 2500 volts, compared to the low voltage operation, i.e.,

less than 400 volts, of prior art deactivators. In addition, the switching of the power supply of

the present invention is synchronized to the power line to reduce the noise generated by the

deactivator.

Other objectives, advantages, and applications of the present invention will be made

apparent by the following detailed description of the preferred embodiment of the invention. DESCRIPTION OF THE DRAWINGS

Fig. 1 is a perspective view of a bagging station utilizing the EAS tag deactivation

system of the present invention.

Fig. 2 is a perspective partially cut away view showing one embodiment of the

deactivation coils in the bagging station of Fig. 1.

Fig. 3 is a schematic block diagram of the EAS tag deactivation system of the present

invention. Fig. 4 is a diagram illustrating the waveform of the current through the deactivation

coil of the present invention.

Fig. 5 is a schematic block diagram of one embodiment of the gate drive circuit of the

present invention.

Fig. 6 is a schematic block diagram of one embodiment of the voltage regulation

circuit of the present invention.

Fig. 7 is a diagram illustrating the waveforms at several points in the voltage

regulation circuit of Fig. 6.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to Fig. 1, a bagging station 10 incorporating an EAS deactivation system

according to one embodiment of the present invention is shown. Bagging station 10 has three

sidewalls 12, 14, and 16 and a bottom 18 that define a volume 20 in which a shopping bag 22

or other bulk container can be placed. A quantity of plastic shopping bags can be placed on

bulk holder 24 with their handles on bag racks 26 and 28 and then pulled out for use one at a

time. Shopping bag 22 contains article 30 which has an associated EAS tag 32 for use with

an EAS system as is known in the art. Preferably EAS tag 32 is a magnetoacoustic EAS tag

sold by the assignee of this application under the brand name "ULTRA»MA_X®'\ such EAS

tags are used widely for theft deterrence.

Fig. 2 shows a deactivation coil arrangement of the present invention for use with

bagging station 10. Deactivation coil 34 is located inside sidewall 12, and deactivation coil

36 is located inside sidewall 14. Sidewalls 12 and 14 are parallel so that deactivation coils 34

and 36 are located in parallel planes. Deactivation coil 38 has four coil sections 40, 42, 44,

and 46. Coil section 40 is located in bottom 18, and coil section 42 is located in sidewall 16.

Coil sections 44 and 46 are located in sidewalls 12 and 14 respectively along the approximate

respective diagonals of deactivation coils 34 and 36. The power supply connected to

deactivation coils 34, 36, and 38 to provide them with the appropriate electrical energy to

create the magnetic fields to deactivate EAS tag 32 is discussed in detail below.

Referring to Fig. 3, a preferred embodiment of the deactivation system of the present invention is illustrated. A transformer 102 has a primary winding 104 and secondary winding

106. Primary winding 104 is connected to voltage regulator circuit 108 which in turn is

connected to power line 110 which provides an AC power source. The anode of diode 112 is

connected to leg 114 of secondary winding 106, and the cathode of diode 112 is connected to

node 1 16. Capacitor 1 18 is connected across node 1 16 and leg 120 of secondary winding

106. A voltage divider consisting of resistors 122 and 124 is also connected across node 1 16

and leg 120. Line 126 connected to node 128 between the series connection of resistors 122 and 124 provides a feedback signal to voltage regulator circuit 108 indicative of the voltage

across capacitor 118. Electronic switch 130 in series with deactivation coil 132 is also

connected across node 1 16 and leg 120. Electronic switch 130 comprises silicon controlled

rectifiers (SCR's) 134, 136, 138, and 140. SCR's 134 and 136 are connected in antiparallel,

SCR's 138 and 140 are connected in antiparallel, and these antiparallel sets are connected in

series. The gate drive signals for SCR's 134, 136, 138, and 140 are provided by gate drive

circuit 142 which is discussed in detail below with reference to Fig. 5. Gate drive circuit 142

provides simultaneous pulses across the gate and cathode of SCR's 134, 136, 138, and 140.

Deactivation coil 132 is exemplary of deactivation coils 34, 36, and 38 and can be one

of the deactivation coils or any number in series. In the embodiment shown, electronic

switch 130 has two sets of SCR's connected in antiparallel for illustration. However, depending on the breakdown voltage of the SCR's used and the voltage across capacitor 1 18,

either a single set of SCR's in antiparallel or more than two sets can be used. In addition,

electronic switch 130 can have multiple SCR's in each leg if the current required for

deactivation coil 132 exceeds the current carrying capacity of the single SCR's. In addition,

capacitor 1 18 is shown as a single capacitor; however, it can comprise a bank of capacitors

that are precharged to supply the energy level needed for deactivation coil 132.

Fig. 4 is a waveform illustrating the current through deactivation coil 132 when

electronic switch 130 is triggered by gate drive circuit 142. Since the current provided to

deactivation coil 132 from capacitor 118 is an alternating current of decreasing magnitude,

the resultant deactivation field created by deactivation coil 132 is an alternating decreasing

magnetic field.

Referring to Fig. 5, a schematic block diagram of one embodiment of gate drive

circuit 142 is disclosed. AND gate 144 has a first input which receives a deactivation

command signal 146 and a second input which is connected to pulse generator 148. Pulse

generator 148 provides high frequency pulses at, for example, 70 kilohertz. The output of

AND gate 144 is connected to the gate of power MOSFET 150 so that when and gate 144

receives both a deactivation command signal 146 and a pulse from pulse generator 148 power

MOSFET 150 is turned on. The drain of power MOSFET 150 is connected through resistor

152 to the base of transistor 154. When power MOSFET 150 is turned on, transistor 154 is

turned on. The collector of 154 transistor is connected through resistor 156 to the gate of

power MOSFET 158 so that when transistor 154 is on, power MOSFET 158 is also on. The

primary winding 160 of transformer 162 is in series with the drain to source of power

MOSFET 158 across circuit power supply V. Accordingly, primary winding 160 is energized

when power MOSFET 158 is turned on and is not energized when power MOSFET 158 is

turned off.

Transformer 162 has a plurality of identical secondary windings 164, 166, 168, and

170 with identical circuits connected to the respective secondary windings. Using the circuit

of secondary winding 164 as an example, leg 172 of secondary winding 164 is connected to

the anode of diode 174. The cathode of diode 174 is connected to node 176. Capacitor 178 is

connected across node 176 and leg 180 of secondary winding 164. Resistor 182 is also

connected to node 176 so that diode 174, capacitor 178, and resistor 182 provide a filtered

half wave rectified signal to terminals 184 and 186. Terminals 184 and 186 are connected to

the gate and cathode of one of the SCR's in Fig. 3 to provide the appropriate triggering

pulses. In like fashion each of secondary windings 166, 168, and 170 have identical circuit

configurations and are connected to a respective one of the SCR's in Fig. 3 so that each SCR

receives a simultaneous isolated triggering pulse.

One embodiment of a power line synchronized modulator of voltage regulator circuit

108 of Fig. 3 is illustrated in Fig. 6. Transformer 102 has secondary winding 106 connected

to the load as illustrated in Fig. 3. One leg of primary winding 104 is connected to one side

of power line 1 10, and the other is connected through the first and second anodes of triac 188

to the other side of power line 110. Cycle detection circuit 190 is connected to power line

110 to detect the beginning and ending of each half cycle of the power line signal. Cycle

detection circuit 190 provides a reset signal to ramp generator 192 so that ramp generator 192

provides a declining ramp signal that starts at the beginning of each half cycle of the power

line signal and terminates at the end of each half cycle of the power line signal. The output of

ramp generator 192 is provided to one input of comparator 194. The feedback voltage from

node 128 of Fig. 3 which is indicative of the voltage across capacitor 1 18 is provided to one input of operational amplifier 196. A predetermined reference voltage is provided to the

other input of operational amplifier 196 such that when the voltage at node 128 is less that the

predetermined reference voltage operational amplifier 196 provides a signal to the other input

of comparator 194. When the falling ramp voltage generated by ramp generator 192 is equal

to the signal provided by operational amplifier 196, comparator 194 switches and provides a

signal to inverter 200. The inverted signal is provided to one input of AND gate 202 and the

output of pulse generator 204 is provided to the other input of AND gate 202. The output of

AND gate 202 is provided to winding 206 of transformer 208 so that the pulse generator 204

is gated through winding 208 to triac 188 to turn on triac 188 to deliver AC power to primary

winding 104. The power cycle is terminated naturally as the AC line voltage crosses zero.

This cycle repeats at line frequency with the output of transformer 102 being provided to

capacitor 118 until capacitor 1 18 is charged to the predetermined amount.

Fig. 7 provides an illustration of the voltage waveforms at several points in voltage

regulator circuit 108. Fig. 7A is the AC line voltage provided by power line 1 10. Fig. 7B is the gate drive signal for triac 188. Fig. 7C is reference ramp signal provided by ramp

generator 192.

It is to be understood that variations and modifications of the present invention can be

made without departing from the scope of the invention. It is also to be understood that the

scope of the invention is not to be interpreted as limited to the specific embodiments

disclosed herein, but only in accordance with the appended claims when read in light of the

foregoing disclosure.