EP0454021A1 - Method for deactivating a resonant tag and circuit for carrying out this method - Google Patents

Abstract

In order to deactivate a resonant tag, a pulse generator circuit (1-4) is provided which is designed to transmit a pulse group comprising a specific number of pulses. In addition or as an alternative, an attenuator (R1), which can be deactivated via a switching device (S1), is provided in the transmission antenna circuit to facilitate the subsequent identification of any post-oscillating, i.e. not yet deactivated tags. <IMAGE>

Description

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

A method of this type has already become known from EP-A-287 905 and has proven itself well in practice. However, it should be taken into account that there are conflicting requirements with regard to the power emitted by the deactivator. In order to be able to deactivate labels even over the greatest possible distance and not to have to set the manufacturing tolerances too closely for economic reasons, the highest possible energy to be transferred to the label is required. On the other hand, there are country-specific legal barriers that set upper limits for the power output. These limits are necessary because of the required compatibility with components of radio frequency security systems etc. The peak values and the duty cycle of the emitted power are particularly critical here.

The object of the invention is therefore to transmit a maximum of energy into the resonance label with the shortest possible transmission time and low peak power. This object is achieved by the deactivation method characterized in claim 1.

The invention is based on measurements and tests which show that in the case of a constant electromagnetic alternating field with a deactivation frequency corresponding to the label The balance between the radiated energy and the energy consumed in the label by heat loss and radiation can be achieved after only a few vibrations. Every further vibration train emitted by the deactivating antenna increases the probability of deactivating the resonance label only insignificantly.

Since one now works with successive pulses within a pulse group, instead of with a single pulse, as suggested by the EP-A mentioned, each pulse means a vibration excitation for the resonant circuit given by the label, whereby the energy - only gradually released by the label - is contained therein as it were saves and builds up. Each individual impulse can therefore be considerably weaker than before if one takes into account equally large ranges. This greatly reduces the possibility of interference with other components. Since the individual pulses are weaker, despite the use of a pulse group, i. ie of several pulses each, practically no increase in the radiated total energy.

According to a preferred embodiment, the procedure is carried out according to feature a) of claim 2, it being possible in itself to determine the burst pause duration, i.e. choose the duration between two pulse groups (bursts) in such a way that, with the label not yet deactivated, a certain amount of energy from the previously emitted pulse group remains therein and at most contributes to the oscillation build-up. However, features b) and / or c) of claim 2 are preferably provided.

A further advantageous embodiment resulting from the above-described knowledge is described in feature e) of claim 2.

Since several pulses are now delivered within a pulse group, it is possible to proceed according to feature d) of claim 2, whereby any manufacturing tolerances can be better taken into account.

A circuit arrangement according to the invention for carrying out the method according to the invention is characterized by the features of claim 3. This specifies two features in an alternative form, both of which work to solve the same problem. Because one must not forget that the pulse groups emitted according to the invention should have a verifiable deactivation effect. The damping switch provided according to the second feature of claim 3 enables problem-free post-detection as to whether the deactivation has been carried out or not. On the other hand, this switchover also makes it possible to make the range of the transmitter relatively large, since it is only conceivable with reasonable effort and high efficiency to feed a relatively high instantaneous power into the transmitting antenna with a low average power, by switching this resistor off or bypassing it during of the broadcasting operation is ensured that transmission power is not uselessly absorbed.

Fig.1

eine erste Ausführungsform einer erfindungsgemässen Schaltungsanordnung, insbesondere für Batteriebetrieb;

Fig.2

eine Alternative hierzu mit vereinfachter Schaltung; und

Fig.3

eine modifizierte Ausführungsform mit wenigstens zwei Sendeantennen.

Further details of the invention will become apparent from the following description of exemplary embodiments shown schematically in the drawing. Show it:

Fig. 1

a first embodiment of a circuit arrangement according to the invention, in particular for battery operation;

Fig. 2

an alternative to this with a simplified circuit; and

Fig. 3

a modified embodiment with at least two transmit antennas.

A central clock 1, for example with a clock frequency of 20 to 30 Hz, e.g. 25 Hz, is fed by a power supply unit 15, which - as symbolically indicated - can comprise one or more batteries; however, it can also be provided with mains connection terminals 16 and, if necessary, be switchable between the two current sources.

The clock generator 1 may have a synchronization clutch 17 in order to be able to be synchronized with other devices. The frequency of the clock generator determines the number of transmissions (number of emitted pulse groups or bursts per time unit) of the deactivator circuit. For this purpose, a sequence of short strobe pulses is generated from the edges of the rectangular output voltage of the clock generator 1 via a stage 2.

It should be mentioned here that it would also be possible per se to use the clock generator 1 with other signal shapes than square-wave pulses, but a downstream pulse shaping stage would then be expedient, since edges which are as clear as possible are advantageous for generating the blanking pulses in stage 2. This stage 2 represents a kind of timing element which determines the burst duration over the duration of the square-wave signals generated by it. For example, it can be designed as a monoflop responding to the rising edges of the square-wave signal generated by the clock generator 1.

Since, as explained at the beginning, the energy sent to the labels can really only be used for a limited period of time, the duration of the gating pulses must also be limited accordingly. The optimum number of pulses per pulse group will generally depend on the Q factor of the type of resonance label used. A label with a high Q factor will usually need more momentum to balance between absorbed and radiated power is achieved as a label with a low Q factor. It should be remembered that the Q factor, as already stated in EP-A-285 559, depends on the one hand on the quality of the dielectric of the label and on the other hand on the size of the space inside the inductor winding free of conductive coating. It is advantageous if the number of pulses per pulse group is calculated from Q / 2, ie corresponds to half the Q factor. Thus, for example, a label with the factor Q = 100 requires approximately 50 pulses, which corresponds to a duration of the blanking pulses of approximately 6 microseconds at a pulse frequency of 8 MHz, for example. Therefore, the time of the strobe should be a maximum of 100 microseconds, but for most applications it may be significantly less, for example 50 microseconds. In practice, it has been shown that time periods of 10 microseconds can also be sufficient. The conditions may vary depending on the label construction and the spatial conditions, but useful results have already been obtained with times of only about 5 microseconds (± 1 microsecond). Even times as short as 1 microsecond could be achieved.

The gating pulses emitted by the timing element 2 arrive at an input of a gate circuit (AND gate) 3, the other input of which is connected to a pulse train generator 4, which in turn generates a sequence of preferably square-wave pulses. The gate 3 is opened by the pulse pulses of the timing element 2 and allows a group of pulses emitted by the generator 4 to pass through for the corresponding duration (the burst duration). The gating time is chosen as explained above to pass the desired number of pulses.

It can thus be seen that stages 1 to 4 together represent the actual pulse generator circuit for delivering pulse groups or bursts. If need be, they can also be replaced by other circuits, for example by an RF start-stop generator which is repeatedly triggered by a timing element and which therefore switches itself off after each start and after a predetermined number of pulses have been emitted. However, since such a generator generally requires a certain settling time, the solution explained first is preferred.

It is known that the resonance labels are subject to a certain manufacturing tolerance, which should not be drawn too closely for manufacturing reasons. So the natural frequency or resonance frequency of such labels can be subject to certain deviations. It is therefore advantageous if the pulse train generator 4 either carries an pulse repetition frequency modulator itself or, as shown, is connected to an external modulator 14. This stage 14 can be designed differently and have different functions. On the one hand, an adjustment of the frequency spectrum is desirable for the very reason that an adaptation to the respective labels that are in use is advantageous. In this case, the stage 14 can be provided with a handle 18, which enables either continuous adjustment or a switchover.

On the other hand, two possibilities are conceivable for the purpose of modulating the pulse repetition frequency: The modulation can take place within a single pulse group or from burst to burst. Since the burst duration is relatively short, the former variant will only have limited success if it is not at least linked to the second variant. As The simplest structural solution is the modulator designed as a ramp generator, which impresses the generator 4 with a continuous shift in the pulse repetition frequency, which shift will then have an effect within each pulse group itself, but also from pulse group to pulse group. If, as shown, the modulator 14 is controlled by the output of an amplifier stage 5 and thus indirectly via the gating pulses of the time stage 2, the frequency is not adjusted during the burst pauses between the individual pulse groups, but always during a gating pulse, the length of the Ramp expediently corresponds to a multiple of the duration of a gating pulse and therefore only passed after several gating pulses.

The amplifier 5 plays the role of a driver circuit for an output stage (power stage) 6, which receives its operating voltage via a voltage converter 7. This, like the HF oscillator 4, is shown as connected to the supply stage 15, but it may have its own power supply when powered by batteries. The signal from the power stage 6 is then fed to the transmitting antenna C, L1.

Because of the relatively low total energy requirement, it is easily possible to design the deactivation circuit as a battery-operated device. In any case, it is advantageous to connect the circuit to a conventional bar code scanner 19 or to attach at least one of the two antennas C, L1 and / or L2 shown to the housing of this scanner 19. The scanner 19 can be designed differently, but is preferably a flat bed scanner or a vertical scanner as it is installed in cash register systems.

The advantage of such a measure is obvious: when the bar code - which is usually attached to a resonance label - is read by the scanner 19, the label is deactivated automatically at the same time. The deactivation circuit can be carried out much more simply because of the smaller dimension (= less deactivation power). With flatbed scanners, the antenna is e.g. simply mounted as an add-on on the scanner or set up in front of the scanner for vertical scanners. This may even ensure a particularly high deactivation rate if the scanner is held directly on the label. This can lead to the fact that the necessary deactivation energy can be further reduced.

The scanner 19 can be connected to the circuit arrangement shown by means of a jack plug 20 at a plug-in coupling 21, and if necessary it closes a changeover switch 22 by means of the jack plug 20 if the supply stage can optionally be switched from battery operation to mains operation. This switchover then results in the switchover to battery operation, if necessary.

As can be seen from FIG. 1, a further timing element 9, for example a monoflop, is connected to the output of timing element 2, which generates pulse pulses with a substantially longer pulse duration compared to the pulse duration of the gating pulses generated by timing element 2. This timing element 9 switches the receiving circuit on during the burst pauses. For this purpose, the timing element 9 is triggered by the falling edge of the blanking pulse from stage 2. With the receiving circle, a label that is still swinging (and thus obviously not yet deactivated) is determined. Such a signal comes in via the already mentioned receiving antenna L2, which has an upper limit stage 10 is connected downstream to prevent overdriving and destruction of the receiving part. As soon as an RF amplifier 11 is released by the timing element 9, the incoming signal can be fed via this, appropriately amplified, to an evaluation stage 12 which, as shown symbolically, actuates at most optical and / or acoustic signal devices 23, 24.

It may be desirable to activate the signaling devices 23, 24 on different occasions. In some places it is preferred if the respective signaling device 23 or 24 only alarms if it has not been deactivated. This will also be the normal case. At times, however, it is desirable if a deactivation that has taken place is acknowledged by the respective signaling device 23 and / or 24 by actuating the same. If this is the case, only one selector switch 25 needs to be closed in the circuit shown.

Different operating modes of the signaling devices 23, 24 are at most possible through different logic combinations, for example by linking the information "label recognized", "label generates decaying echo" (not deactivated), "label echo remains abruptly off" (deactivated). The changeover switch 25 can then, instead of a simple switch as shown, be formed by a switch which can be set to several positions.

Finally, it can be seen from FIG. 1 that the timer 9 not only opens and closes a time window while the receiving circuit L2, 10-12, 23-25 is activated, but also this time window signal via an amplifier 8 (for adapting the Impedance) to a switching stage S1.

A damping resistance circuit R1 is connected into the antenna circuit C, L1 by means of this switching stage S1, which is expediently formed by an electronic switch. The damping resistor circuit R1 can be formed in the manner shown by a single damping resistor or by several elements. The interfering influence of the resonant antenna circuit C, L1 on the receiving circuit is largely eliminated by the damping resistance circuit R1, thereby facilitating the subsequent detection of any label echo via the receiving antenna L2. During the duration of the strobe pulses, ie when the bursts are emitted and high powers are fed into the antenna C, L1, the switch S1 is closed and the damping resistor circuit R1 is bridged.

In order to avoid influencing a nearby label detection system by the label deactivation, the clock generator 1 can be synchronized with this detection system. On the one hand, this can be done simply by means of a cable via the connection 17; on the other hand, the required synchronization signal can also be obtained wirelessly via the existing receiving circuit. For this purpose, this is provided with means 26 (FIG. 1) which are able to discriminate the signals received by the label detection system and to use them to generate a synchronization signal suitable for the synchronization of the pulse train transmissions.

It should also be mentioned that it may not only be desirable to synchronize the clock generator 1 with other components via the connection 17, but also to derive a synchronization signal from the present circuit in order to determine when a burst pause occurs. This can be done via a synchronization output 17 '.

In the embodiment according to FIG. 2, parts of the same function have the same reference numerals as in FIG. 1. Parts of the illustration from FIG. 1 are missing because they either do not actually have to be present or they do exist but are not shown. In any case, it goes without saying that the individual features of the various exemplary embodiments are interchangeable or combined with one another.

Here too, the primary consideration is a battery-operated device, although network operation would also be conceivable. Therefore, the connection with a bar code scanner 19 can also be seen. To simplify the circuitry, and in order to be able to accommodate the antenna C, L more easily on the housing of the scanner 19, only a single antenna C, L is provided here, which is operated alternatively as a transmitting and receiving antenna.

For this purpose, the output of power stage 6 and the input of limiter stage 10 are connected to a controlled switchover stage S1 ', which alternatively connects antenna C, L to the output of power stage 6 or the input of limiter stage 10. This switching stage S1 'is controlled, similarly to the switching stage S1 in FIG. 1, via the time window signal of the timing element 9 and the amplifier 8. This allows the construction to be made more space-saving and, in contrast to known circuits, is where such a switching option is more likely reluctant to provide, is still a very advantageous embodiment. The damping resistor R1 can be switched as an input resistor of the limiter stage 10 and bridged by the switching stage S1. However, it could also be switched off in a different way than by bridging.

If a label on the goods is in an unfavorable position relative to a transmitting antenna, for example, is exactly perpendicular to it, it can absorb practically no energy from it. To remedy this, it is advantageous to provide a plurality of transmit antennas, i.e. at least two. In the case of the two transmitter antennas C ', L1' and C '', L1 '' shown in Figure 3, it is advantageous (precisely because of the phenomenon discussed at the beginning of this paragraph) if these antennas are perpendicular to each other. If more than two antennas are provided, which will generally not be necessary, they can be distributed in a correspondingly angular manner.

It is now important here that the output signals of power stage 6 are distributed to the transmission antennas C ', L1' and C '', L1 '', which in turn can be done by a switching stage S1 'assigned to the antennas, which in the case of several antennas Has the function of a multiplex stage. However, this multiplex stage S1 ″ is not controlled like the other switching stages S1 ′ and S1 assigned to the antennas via the timing element 9, but by a frequency divider 13, which divides the gating pulses from the timing element 2 again by the pulses in half the time a pulse group of the antenna C ', L1', in the other half of the antenna C '', L1 ''. Accordingly, the level 2 gating pulses will be longer than in the cases of Figs.

Since a separate receiving antenna is still used here, it is advisable to again provide attenuators R1 'and R1''in the antenna circuits C', L1 'and C'',L1'', which can be bridged for the transmission mode via switching stages S1a, S1b . Since the transmit antennas come into effect one after the other, it would be possible not only to control them from the timing element 9, but also to synchronize them with the frequency divider 13, but it is in most cases this effort is not necessary. It would also be conceivable to control the two antenna circuits C ', L1' and C '', L1 '' in parallel from the output of the power stage instead of one after the other; however, this also means a distribution of the energy, which can lead to problems, which is why the arrangement of a multiplex stage S1 ″ shown is preferred. It is also understood that such an arrangement of a plurality of transmit antennas, which is not predetermined in the prior art, can also be advantageously implemented regardless of whether the described burst signals are used or not and whether the described damping arrangement R1, R1 'or R1 can be switched off '' is present or not. On the other hand, such a multiple antenna arrangement can advantageously also be provided in the embodiments according to FIGS. 1 or 2.

With several antennas in particular, however, it may be advantageous if the entire arrangement is accommodated in a housing 26 on which only the signal devices 24 and 23 are guided to the outside. Such a housing 26 is RF-tight. and has at least one inlet opening (possibly also an outlet opening in the manner of baggage screening devices at airports), which can at most be closed by a cover, the goods being inserted into the housing or passed through it to deactivate the label. The design can be such that when the housing cover is closed, a deactivation switch can be closed, by means of which a deactivation pulse or, as in the case of the invention described above, a pulse group (burst) is triggered.

Numerous modifications are possible within the scope of the invention; so it goes without saying that stage 13 in FIG. 3 represents a synchronization element which, if desired, can also be replaced by any other synchronization circuit.

An additional timing element controlled by stage 2 and synchronized with this could also be provided to control the switching device S1 'in FIG. 2, but the use of the timing element 9, which is required anyway and determines the burst pauses, is evidently simpler.

Further modifications can result in relation to the housing 26 and its deactivation trigger switch actuated by the cover: in itself, the deactivation does not necessarily have to be triggered by such a switch; rather, it would be conceivable for the deactivation signal to run continuously within the housing 26, in particular if the housing is designed as a continuous housing. On the other hand, in most cases, even if no housing 26 is provided, such a trigger switch will be desirable. This can now (although not shown) be attached at various locations, for example on the power supply unit 15 itself, in order to be able to switch it on or off centrally and to switch off all circuit parts. However, it would also be conceivable to run at least part of the circuit, to a certain extent in standby mode (for example the clock generator 1 or the pulse train generator 4) and to switch off only the remaining parts, or just the trigger switch between the power supply unit 15 and to put the clock generator 1, in which case the gate circuit 3 cannot be opened at all. Another possibility can be to place the trigger switch between the oscillator 4 and the AND gate 3, the oscillator 4 per se being able to run freely and only being switched on when this is desired. Finally, it is also conceivable to place a trigger switch between voltage converter 7 and output stage 6. The antenna then delivers weak signals that only stimulate the resonance of a label if the trigger switch is not is pressed to determine theft. Otherwise it delivers deactivation pulses. In this case, however, a connection to a mode switch corresponding to the switch 25, but having a plurality of switch positions, is expedient for the evaluation circuit 12 in order to emit a "thief detection signal" when the transmitting antenna only emits weak label detection signals, otherwise only between "label deactivated" or label not deactivated "to distinguish.

As far as timing element 2 is concerned, it can be designed as a multivibrator, in particular as an astable multivibrator. However, it can, preferably, contain a counter that counts the incoming clock pulses and forms the respective strobe pulses from them.

Claims (11)

Method for deactivating a resonance label which has a resonant circuit which excites a transmitter emitting energy in the form of pulses, characterized in that the energy is emitted in the form of at least one pulse group (burst). Method according to Claim 1, characterized in that the procedure is based on at least one of the following features: a) at least two successive pulse groups are delivered, the burst duration of which is in each case less than the burst pause duration in between; b) the burst duration of a pulse group is calculated from the Q factor and the center frequency of the resonance tag to be deactivated and is a maximum of 100 microseconds, but preferably not more than 50 microseconds, in particular not more than 10 microseconds, for example about 5 microseconds; c) the burst pauses are at least ten times, preferably at least one hundred times, in particular approximately one thousand times, the burst duration of a pulse group; d) the pulse frequency is modulated within a pulse group and / or in successive pulse groups, the latter being preferred; e) each pulse group comprises a maximum of 100, preferably about 50 pulses. Circuit arrangement for performing the method according to claim 1 or 2, with a transmitting antenna, the pulses of a pulse generator circuit can be supplied, characterized in that the pulse generator circuit (1-4) is designed to emit at least one pulse group (burst) and / or that with the transmitting antenna (C, L1; C ', L1', C '', L1 '') an attenuator (R1; R1 ', R1'') is connected, which is switched from an attenuation state to a switching device (S1; S1a, S1b) the damping canceling state is switchable. Circuit arrangement according to claim 3, characterized in that it has a synchronization connection (17, 17 '), e.g. has a synchronization input (17). Circuit arrangement according to claim 3 or 4, characterized in that at least two, in particular mutually perpendicular, transmission antennas (C ', L1', C '', L1 '') are provided at an angle to each other, and that the pulse groups from the pulse generator circuit ( 1-4), preferably via a switchover or multiplexing device (s1 ''), these transmit antennas (C ', L1', C '', L1 '') can be fed in succession, which multiplexing device (s1 '') suitably via one to the Pulse generator circuit (1-4) connected synchronizing circuit (13) is controllable (Fig. 3). Circuit arrangement according to one of Claims 3 to 5, characterized in that at least one antenna (C, L) is provided both for transmitting and for receiving, and that this antenna (C, L) is connected to the pulse generator circuit (1- 4) synchronized timing element (9), in particular by means of the timing element determining the burst pauses, can be switched from transmission mode to reception mode. Circuit arrangement according to one of Claims 3 to 6, characterized in that a frequency modulation circuit (14), e.g. with a ramp generator to which the circuit part (4) of the pulse generator circuit (1-4) which emits pulse groups is connected for changing the frequency of the pulse groups, and that if necessary the frequency modulation circuit (14) with an adjustment handle (18) for adjustment, in particular for switching, its frequency spectra, e.g. from 8 to 11 MHz. Circuit arrangement according to one of claims 3 to 7, characterized in that it has at least one battery for power supply. Circuit arrangement according to one of Claims 3 to 8, characterized in that it is connected to a bar code scanner (19), in particular a flatbed scanner or a vertical scanner, preferably at least one antenna (C, L1, L2; C, L ) is housed on the scanner housing. Circuit arrangement according to one of claims 3 to 9, characterized in that at least one of the following features is provided: a) there is an evaluation circuit (12) provided with an operating mode switch (25), it being possible to switch over optionally on an acknowledgment display when a label has been deactivated successfully or to an alarm display when the deactivation is deficient; b) the circuit arrangement is accommodated in an HF-tight housing (26) with at least one opening for receiving the goods to be tested, this opening can expediently be closed with a lid and a trigger switch for deactivation can be closed over the lid. Circuit arrangement according to one of Claims 3 to 10, characterized in that the receiving device is provided with means which are able to discriminate the signals emitted by label detection devices which may be installed in the vicinity, and from this a suitable synchronization signal for synchronizing the pulse train transmissions to create.

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