EP0287905A1 - Method for deactivating a resonant target, and circuit for carrying out this method - Google Patents

Abstract

To deactivate a resonant target (E) only a single discharge pulse is sent out, which merely produces a crack signal instead of a vibration and destroys the target (E). As the energy source for providing the discharge pulse it is preferable to use a discharge capacitor (Cl) which is coupled in series with a transmitter aerial (Ll) and can be reversed in its charge via a circuit element (LDR, 1-5). <IMAGE>

Description

The invention relates to a method according to the preamble of claim 1 and to a circuit arrangement for performing the method.

In department stores, resonance labels are attached to the goods to protect them against theft, which must be deactivated when paying at the cash desk, but possibly also after showing the cash receipt confirmation when the goods are picked up at the packing table. If a label is not deactivated, this can be recognized by a monitoring system arranged in the exit area, which stimulates the labels to resonate and detects a label that has not been deactivated on the resonance.

The deactivation takes place conventionally by excitation of the label with about ten times the power, which leads to the burning of the resonant circuit or its capacitor. However, the high current surge can also trigger an alarm at the exit of the department store, especially if the cash register is located close enough. This risk can only be eliminated by expensive circuitry measures. Another difficulty is that such a high performance of a broadcaster (and this is what it is here for) requires the approval of the postal authority and it is difficult (or not at all) to obtain it. In order to switch off false alarms, it is of course possible to synchronize the monitoring device with the cash register in such a way that the monitoring is interrupted at the moment in which the cash register sends out a deactivation current surge. However, particularly in the case of several cash registers, this means that the monitoring device is ultimately switched off more than switched on, so that under certain circumstances a thief with stolen goods can still slip through.

The invention is based on the object of designing a method of the type mentioned at the outset and an associated circuit arrangement in such a way that the resonance labels can be checked or deactivated without interference.

A first step towards solving this task is the realization that the resonance frequency does not need to be released to deactivate the label, but that, with the appropriate strength, a single click pulse is sufficient to excite the resonant circuit of the label to self-destruct. In postal parlance, the term "cracking disorder" is common in a telephone line; a single pulse from such an interference signal is therefore a click pulse.

Based on this knowledge, the solution to the problem essentially consists in the features of the characterizing part of claim 1.

In order to be sure that the respective resonance label is deactivated, the procedure according to claim 3 can be followed, the label then being deactivated by a further pulse if this should not be the case with the first pulse. However, it can also be carried out according to claim 4, it being preferred to combine the two procedures by emitting at least one second discharge pulse, which may then also be used for checking.

A circuit arrangement for carrying out the method according to the invention is characterized by the features of claim 5.

Several advantages are obtained in each embodiment of the invention:
- Since only a single pulse is required, the energy requirement drops, so that it is possible to use a battery-operated handheld device for deactivation, which simplifies handling and increases the possible uses;
- Since the monitoring device is matched to a pulse series, a single pulse can no longer interfere;
- This eliminates the previously required synchronization between the deactivation device at the cash register or on the packing table on the one hand and the monitoring device, and the circuit arrangement is simplified;
- In addition, the postal authority restrictions no longer apply, meaning that a permit is no longer required;
- The environment or the receivers arranged in the vicinity are no longer exposed to interference;
the system becomes more secure, because variations in the quality of the oscillating circuit of the label influence the energy required to destroy it less than was previously the case when a vibration train was emitted;
- Finally, the circuit arrangement for deactivation is also simpler since it does not need to contain any adjustment elements;
in addition, deactivation is faster than before.

Further details of the invention will become apparent from the following description of an embodiment shown schematically in the drawing.

It is assumed that a goods provided with a resonance label E are either brought to the cash register or are collected from a packing table after payment at the cash register.

In any case, after the goods have been paid for, the resonance label E must be deactivated, which is initiated by actuating a switching element. This switching element can simply be manually, e.g. by the cashier to be operated, but is preferably formed by a sensor LDR, which automatically detects the passage of the goods and activates the deactivation circuit. In the exemplary embodiment shown, the sensor LDR is formed by a light barrier or a light reflector with a photoelectric converter LDR, but various configurations are possible, for example a piezosensor that detects the weight of the goods on a base or a circle that simulates the inspection circuit at the department store exit, the one Sends out resonance vibration and uses the "echo" of the label E to determine its presence.

An amplifier 1 is connected downstream of the sensor LDR, in particular one with a large gain, such as a threshold switch, which converts the voltage change at the output of the sensor LDR into a voltage step. From this step signal, a timing element 2, in particular a monoflop, is triggered, possibly via a coupling capacitor which supplies a needle pulse, which keeps a downstream OR gate 3 open for a predetermined time.

If a coupling capacitor delivering a needle pulse is mentioned here, it should be noted here that it could already be the one that delivers the discharge pulse instead of the capacitor C1 described later to a transmitting antenna L1, but below is a more favorable embodiment based on the illustration and the function of stages 3 and 4 shown.

A pulse generator 4 is switched on via the OR gate 3 switches, which emits at least two, preferably more, pulses with interposed pulse pauses. The pulse pause times are preferably a multiple of the pulse times. As will be described later, the pulse sequence delivered in this way serves a dual purpose, namely on the one hand to ensure the destruction of the resonance tag E (if this is not already possible with the first pulse) and on the other hand to check the success of the destruction. Since the lowest possible energy is used, the destruction can fail if the label E is placed on a very large piece of goods at a location distant from the transmitting antenna L1, for example on the underside. If in such a case it turns out through the test circuit described later that the oscillating circuit of the label E is still intact (and could therefore erroneously trigger a theft alarm at the exit of the department store by the inspection device attached there), the goods only need to be turned over and deactivated be repeated.

A voltage converter 6 charges a capacitor C1 via a resistor R1. If a resistor is referred to here, then it is understood to mean any circuit which results in a current resistor. For example, it is known that transistors can also be operated as variable resistors. The capacitor C1 is connected to ground via a controllable switch 5, the switch 5 being closed by the pulses from the pulse generator 5. It is therefore understood that the pulse pause times are to be dimensioned such that the capacitor C1 can be recharged by the voltage converter 6 during this time.

Another modification can be seen from the description so far: the timer 2 operates here to a certain extent as a gate circuit for determining the Number of pulses to be output by the pulse generator 4. It would therefore be readily possible to place a gate circuit at the output of a free-running pulse generator 4 and to pass pulses only during a predetermined time. It would also be conceivable to design the pulse generator 4 as a start-stop generator instead of the timing element 2, said generator generating a predetermined number of pulses after being triggered by the pulse from the amplifier 1. The ratio of pulse to pause time can advantageously be of the order of 1: 10000.

Here, the pulse pause times between the pulses of the pulse generator 4 will be discussed again. Normally, the pause times on such a generator are always the same, and the pulses occur periodically. However, this means that the pulses are emitted at a predetermined frequency. This can be a disadvantage for the present purposes if interference is to be expected from such a frequency. It is therefore expedient to make the pulse pause times uneven by switching the pulse generator 4 accordingly. This can either be done in such a way that they are determined by a connected or integrated random generator, or - as is preferred - that they are changed according to a predetermined law, i.e. either lengthened or shortened after each pulse, the extent of this change remaining constant or can be variable.

Whenever the switch 5 is closed via a pulse emitted by the pulse generator 4, the capacitor C1 discharges and this discharge pulse (= click pulse) is transmitted to the transmitter coil L1. The pulse emitted in this way is sufficient, as has been found, to destroy the resonance tag E, because this pulse stimulates it to produce natural oscillations which then decay exponentially, if not before the destruction follows. The destruction usually takes place, usually on the capacitor of the label resonant circuit.

If, on the other hand, there is no destruction and the vibration excitation of the label E decays after receiving a discharge pulse from the transmitter antenna L1, this can preferably be determined with the aid of a test circuit which has a receiving antenna L2 for recording the excitation vibration of the label E.

A comment regarding the formation of the capacitor C1 is inserted here. In any case, this must be dimensioned such that, on the one hand, the label E is almost certainly destroyed during the first discharge pulse, so that the pulses subsequently emitted serve only to carry out the test if possible. On the other hand, it should be small enough so that the discharge pulse does not have too much energy and could cause interference. It has now been found that a size of at most 60 nF, preferably at most 50 nF, is quite sufficient and that a practically expedient range comprises 5 to 50 nF. For example, a dimension of 10 nF ± 5 nF is quite realistic.

The receiving and test antenna L2 can be arranged together with the transmitting antenna L1. However, the transmitting antenna L1 at the cash register and the test antenna L2 at the packing table can also be provided. Theoretically, a procedure can also be adopted, as is known from radar and echo sounder technology, in that one and the same antenna is used by switching once as a transmitting antenna and then again as a receiving antenna. However, this is generally not preferred for the present purposes, as will be explained below.

The relatively strong discharge pulse of capacitor C1 will generally require limiting measures to protect the receiving circuit. As indicated in the drawing, it is advantageous to provide at least two groups of, in particular planar, partial coils L2ʹ, L2ʺ for the antenna L2. The number of turns times the area product should be of the same size, but connected in series with the opposite polarity, so that the voltage induced by the excitation coil L1 is compensated to a first approximation. For example, when assembling the antenna coils L1, L2, it would be possible to design the coil L1 as a rectangle, in which the receiving coil L2 (as shown) is installed as a symmetrical "8". This results in a signal of almost zero at the intersection of the two coil sections L2ʹ and L2ʺ, whereas the signal on the outside of these coil sections is greatest. There, according to the exemplary embodiment shown, the signal at the sub-coil L2ʺ is also taken.

The signal picked up at the sub-coil L2 wird is now expediently fed to a limiting circuit (circuit 7) before it is fed to the actual receiving circuit. On the input side, this limiting circuit contains a limiting transformer T, which is preferably designed as a symmetrical ferrite transformer, in particular a relatively small magnetic cross section. This measure alone leads to a first safe limitation and thus to protection of the downstream receiving circuit, because in addition to any down-transformation, the saturation of the ferrite core (which is relatively small in relation to the signal) constitutes a further limitation of the signal emitted.

A center tap is provided on the secondary side of the transformer T, which is connected to ground.

An alternative or additional measure can consist in the arrangement (provided on the output side of the ferrite transformer T) of a diode circuit D with diodes connected in parallel with the anit. Silicon diodes or a low junction capacitance are preferred. It would also be possible to use Schottky diodes, which are correspondingly fast, but they are more expensive than the silicon diodes mentioned.

In between, the circuit 7 has an amplifier A, which is expediently designed as a, in particular fully symmetrical, push-pull amplifier. This is also a protective measure by which common-mode interference signals, in particular capacitively transmitted to the receiving antenna L2, are effectively suppressed. At the same time, the cross-modulation products that occur in the event of overmodulation are reduced.

It not only makes no sense, but is also rather disadvantageous if the cracking signal of the discharge pulse from the capacitor C1 were also supplied to the receiving circuit. The receiving circuit would be heavily burdened on the one hand and would have to be made more expensive by additional security measures, on the other hand it should not be the discharge pulse itself that is to be checked, but a possible reverberation of the oscillating circuit of the label E if it remains undamaged.

A simple measure to circumvent this difficulty is that a timer 8 is in the receiving circuit, which switch 8 only closes the receiving circuit a predetermined time after the discharge pulse has been emitted via the antenna L1. Of course, this presupposes that the transmitting and receiving circuit are synchronized with one another, ie that the switch 8 is controlled by the transmitting circuit. For this purpose, the control input of the switch 8 connected to the switching element LDR, 1-5 discharging the capacitor C1. In principle, the control line 13 could be connected directly to the circuit of the capacitor C1 or to the switch 5, but this is generally not preferred for dimensional reasons. It is more favorable to connect the control line to the output of the pulse generator 4 (or one of the equivalent circuits mentioned above). The delay time after the discharge pulse is emitted until the switch 8 closes is determined by a timer integrated in the switch 8, for example a monoflop, but the timer or monoflop can also be provided separately in line 13. The delay time is at least 2 µs, but must not be too long. A range of 5 to 50 µs should be optimal. Subsequently, the switch 8 should not remain open too long in order to exclude interference signals as far as possible. An open time of 10 µs to a maximum of 60 µs, preferably a maximum of 50 µs, is entirely satisfactory.

As soon as the discharge pulse from the capacitor C1 has been delivered to the antenna L1 (instead of the capacitor C1, any energy source of appropriate strength could be provided), the above-mentioned predetermined, possibly adjustable by a jusiter device, not shown, passes until the closing of the switch 8 , Time. This time is chosen such that the interference vibrations generated in the system by the excitation pulse from the antenna L1 have decayed to such an extent that a signal originating from a label E which has remained undamaged at any rate can be recorded significantly.

If the switch 8 is closed and the receiving antenna L2 receives a ringing from an undamaged label E, these oscillations are expedient integrated in an integrator 9. This may also be protection against interference frequencies, because the integrator 9 is preferably followed by a threshold switch 10, so that a few interference vibrations are not sufficient to exceed the switching threshold of the threshold switch 10. In practice, the switch 10 serves as a comparator with a predetermined value, namely its threshold value, which can be set via an adjusting resistor (not shown).

In practice, integrator 9 and threshold switch 10 form the detection circuit for a resonance tag E that has remained capable of vibration. If desired, the detection circuit can be constructed in any way, as is known from radio and radar technology. At the output of this detection circuit there is a corresponding evaluation circuit, which is designed either as a pure display with an acoustic display device 11 and / or a visual display device 12, so that the cashier is made aware, for example, that the deactivation process must be repeated. However, the evaluation circuit can also have a signal line 14 in the manner also shown for automating the new deactivation process, which feeds a signal to the switching element LDR, 1-5, which discharges the capacitor C1, for a new start-up.

It has already been mentioned that the switching element LDR, 1-5 can be implemented in very different ways, and accordingly the output line 14 can also trigger a new switching operation at different points. For example, it would be conceivable to lay line 14 at the input of timing element 2, so that it is optionally switched on by sensor LDR or via line 14. However, it is simpler to provide the already mentioned OR gate 3 and to lay the line 14 at its second input, so that the pulse generator 4 for the Duration of a signal carried over line 14 emits pulses (ie at least one) in order to finally deactivate the still undestroyed label E. In this way, false alarms can be avoided better.

It has already been mentioned that, in principle, any other energy source of corresponding strength can be used instead of a capacitor C1. In the latter case, there will generally be no needle pulses, and it may even be that pulse shaping stages are then necessary. The described deactivation test with the receiving circuit L2, 7-12 could also be carried out in a conventional manner, in particular if the test is carried out at a different location, e.g. at the packing table, is made as the deactivation. However, the advantages achieved by the invention, such as speed, etc., are lost when working with frequencies that are matched as precisely as possible.

Numerous modifications are conceivable within the scope of the invention; For example, instead of one capacitor C1, there could also be several, which are either connected in parallel to one another, but are preferably switched on one after the other in order to emit one discharge pulse each. In order to ensure the deactivation of the label, it can be advantageous if the capacitors which are switched on one after the other and are thus discharged have increasing sizes. It is also understood that the voltage converter 6 is not absolutely necessary per se, but can increase the charging time considerably by increasing the charging voltage, as a result of which the processes can proceed even more quickly.

A further modification possibility is given at the receiving antenna L2, which is practically designed in the manner of a compensation variometer and can accordingly take all forms known for this design.

Claims (10)

1. A method for deactivating a resonance label , in which the same is excited via an energy-emitting transmitter, characterized in that a single discharge pulse is emitted as a click signal via the transmitter (L1). 2. The method according to claim 1, characterized in that the discharge pulse has the shape of a needle pulse. 3. The method according to claim 1 or 2, characterized in that at least two, preferably more, individual discharge pulses are emitted with pulse pauses in between,
and that preferably the pulse pauses between the discharge pulses are unevenly long, for example with a random distribution, but in particular with a regular change. 4. The method according to any one of the preceding claims, characterized in that after the discharge pulse is emitted at least one excitation signal for the resonance label (E) for checking that the deactivation has taken place, preferably in the form of at least one further discharge pulse, a possible resonance signal of the label (E ) is received via a receiving circuit,
and that the receiving circuit is preferably switched on only after a predetermined period of time after the deactivating discharge pulse has been emitted, the predetermined time being in particular at least 2 us, suitably 5 us to 30 us, and that against The open time, in which the receiving circuit is switched on, lasts 10 us to 60 us, preferably a maximum of 50 us. 5. Circuit arrangement for carrying out the method according to any one of the preceding claims, characterized in that at least one discharge capacitor (C1) is coupled in series with a transmitting antenna (L1) and can be recharged via a switching element (LDR, 1-5). 6. Circuit arrangement according to claim 5, characterized in that with the discharge capacitor (C1) a resistance branch (R1), preferably also a voltage converter (6) is provided for increasing the charging voltage. 7. Circuit arrangement according to claim 5 or 6, characterized in that the discharge capacitor (C1) has a size of at most 60 nF, preferably at most 50 nF, in particular 5 to 30 nF, e.g. of 10 nF ± 5. 8. Circuit arrangement according to one of claims 5 to 7, characterized in that a receiving circuit (L2, 7-11) is provided for checking the deactivation of the resonance tag (E) with a receiving antenna (L2), and that preferably at least one of the following features is realized: a) the receiving antenna (L2) is designed in the manner of a compensation varometer with at least two partial coils (L2ʹ, L2ʺ), for example in the form of a symmetrical figure eight; b) the receiving circuit (L2, 7-12) has at least one visual and / or acoustic indicator (11) on the output side; c) the receiving antenna (L2) is a transformer (T), preferably a, in particular symmetrical, Fer rittransfer relatively small magnetic cross section, downstream; d) the receiving antenna (L2) is followed by a balanced push-pull amplifier (A); e) a limiter circuit (D), preferably with diodes connected in anti-parallel, for example silicon diodes, in particular a relatively low junction capacitance, is provided to limit the received signal; f) the receiving antenna (L2) is followed by an integrator (9), preferably with a subsequent comparator, in particular a threshold switch (11). 9. Circuit arrangement according to one of claims 5 to 8, characterized in that the switching element (LDR, 1-5) has at least one of the following features: a) it has a sensor (LDR) for the goods carried past and / or the resonance label (E); b) it has a pulse generator (4) for the delivery of at least two, after a pulse pause, successive individual pulses, of which a switch (5) in the circuit of the discharge capacitor (C1) is controlled, the pulse generator (4) expediently via a timing element , for example a monoflop (2), can be switched; c) it can be switched via an OR gate (3), one input of which is connected to the receiving circuit (L2, 7-12) for checking the deactivation of the resonance tag (E). 10. Circuit arrangement according to one of claims 5 to 9, characterized in that the switching element (LDR, 1-5) with a timer (8) in the receiving circuit (L2, 7-12) for checking the deactivation of the resonance tag (E) for the purpose of delaying Activation of this receiving circuit is connected.

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