DEACTIVATION DEVICE FOR RESONANCE LABELS
The present invention relates to a device for deactivating resonance labels provided with a printed on bar code for use in constructional combination with an optoelectronic, hand-held bar code reader, as part of an electronic product theft prevention system. As a result of the aforementioned combination electronic resonance labels applied to products and provided with a bar code can be deactivated at the checkout of shops and stores at the same time as the determination of the bar-coded data. A deactivator of the aforementioned type is known from WO 90/05968. In the known deactivator the transmitting antenna and the receiving antenna are constructionally integrated into the casing of a pistol-like hand-held bar code reader. They are constructed as air-cored coils and are positioned in directly succeeding manner in the front part of the hand-held reader. Their turns wind around the optical path of the bar code reader. In the same casing is integrated a so-called matching circuit connected to the antennas. Between said matching circuit and an external, fixed control unit radiofrequency signals are transmitted across a screened, multicore cable. Radiofrequency signals of the bar code reader are transmitted along the same cable. Between the high frequency signals of the deactivator and the bar code reader there is a problem of undesired interference. To avoid this, in the device according to WO 90/05968, there are special, but not described, constructional and circuitry measures, as well as screening measures. As a result of the limited size of the antennas due to the installation thereof in the hand-held bar code reader casing, the range of the known deactivator is very limited. Deactivation only functions if the hand-held reader is brought very close to the label. Therefore improvements are necessary with respect to the range. Its improvement by increasing the intensity of the electromagnetic field emitted by the transmitting antenna is not readily possible inter alia due to the aforementioned interference problems. An increase in the field intensity could also impair the operation of the electronics of other equipment located in the vicinity (e.g. cash register systems). The casing of the hand-held bar code reader known from WO 90/05968 is large compared with modern equipment. There is generally little or no further space available in modern hand-held bar code readers for the additional installation of components required for deactivating resonance labels. Therefore a subsequent fitting of such elements is either difficult or impossible. Therefore special hand-held readers with special casings must be designed. The deactivator according to WO 90/05968 operates continuously, i.e. the electromagnetic field emitted by means of the transmitting antenna has a specific frequency at all times. However, this frequency is not fixed and instead sweeps a given frequency range, which contains the resonant frequency of the resonance label. As a result of the sweep it is possible to detect the resonant frequency of the label to be deactivated in a first stage and then, in a following, second stage, it is deactivated with an electromagnetic field precisely at this frequency. EP-A1-287 905 discloses a deactivator, which also has a transmitting antenna and a receiving antenna. Unlike in the case of the device known from WO 90/05968, it operates in pulsed manner, i.e. a needle pulse is used for deactivating the resonance label. Therefore there is no possibility to detect the resonant frequency of the label to be deactivated. An embodiment of the invention is described hereinafter relative to the drawings, wherein show: FIG. 1 A hand-held bar code reader with a transmitting and receiving head of an inventive deactivator externally fixed thereto. FIG. 2 The transmitting and received head of FIG. 1, in partly cut away form. FIG. 3 A block diagram of the inventive deactivator. The same parts carry the same reference numerals in the drawings. In FIG. 1 1 is a hand-held bar code reader. The latter is e.g. connected by means of a cable 2 to a not shown electronic cash register. On its front end it is provided with a window 3 enabling bar code scanning, e.g. with a laser beam. The hand-held bar code reader can have a conventional construction and consequently need not be described in greater detail. A transmitting and receiving head 4 of a deactivator is fixed at the bottom and outside to the hand-held bar code reader. As shown in FIG. 1, the transmitting and receiving head can be fixed by means of a band 5 to the hand-held bar code reader, but any other fastening method is also suitable. By means of a multicore connecting cable 7 the transmitting and receiving head 4 is connected to a fixed base unit 16, which is only shown in FIG. 3. The transmitting and receiving head 4 has a transmitting antenna 8 and a receiving antenna 9, which are constructed as ferrite antennas. The coil windings of both antennas are wound orthogonal to one another on a single, flat ferrite core. The orthogonal arrangement of the two antenna windings serves to bring about a reciprocal decoupling thereof. The ferrite core 10 provided with the antenna windings is located in the front part of a flat casing 11, which is either, according to FIG. 1, open or is closed with a material which transmits radiofrequency electromagnetic waves. However, the remainder of the casing 11 and at least on its underside facing the hand-held bar code reader is made from a radiofrequency electromagnetic waveshielding material. In FIG. 2, the receiving antenna 9 lies in a plane normal to the plane of transmitting antenna 8 and is offset from the central axis of the transmitting antenna 8. In FIG. 2, in which the transmitting and receiving head 4 is shown with a partly cut away casing 11, it is possible to see that in the rear part of the casing 11 there are further components 13, which are separated by a shield 12 from the antennas 9 and 10. The electronic components 13 (e.g. three such components 13 are shown in FIG. 2, although no significance is attached to this number) on the one hand form a pulse generator for the transmitting antenna 8 generating needle pulses and on the other hand a recognition circuit connected downstream of the receiving antenna 9 for non-deactivated resonance labels excited to oscillate. In FIG. 3 the pulse generator is 14 and the recognition circuit 15. The pulse generator 14 and the recognition circuit 15 are connected by means of the multicore connecting cable 7 to the aforementioned, fixed base unit 16. By means of lines not shown in FIG. 3, the base unit supplies the supply voltages required for the operation of the pulse generator 14 and the recognition circuit 15. For the pulse generator they are typically approximately 400 V and for the recognition circuit approximately 5 V (d.c. voltage). By means of a line 17 in FIG. 3, the base unit 16 supplies a clock signal for the pulse generator. The typical frequency of this clock signal is approximately 20 Hz. Finally, the line 18 in FIG. 3 is used for transmitting a logic signal (or a binary signal) to the base unit, which is generated by the recognition circuit 15 on recognizing an oscillating resonance label (an oscillating resonance label is always detected if a sought deactivation has not been successful). In principle, the entire arrangement comprising the two antennas 8, 9, the pulse generator 14, the recognition circuit 15 and the base unit 16 can be constructed and operated in the manner described in detail in the aforementioned EP-A1-287 905. With regards to the pulse generator, it can be essentially formed by a capacitor in series with a thyristor, as well as the transmitting antenna 8 as the inductance. For generating the desired needle pulse, the thyristor should have a very marked snap-off effect. The clock signal generated by the base unit is then used for firing the thyristor. As no high frequency signals are transmitted by means of the connecting cable 7, it does not have to be shielded. Thus, no interference emanates from the cable 7. The problem of the present invention is to give a device of the aforementioned type, which can be constructionally combined with a plurality of very varied commercially available, hand-held bar code readers without special adaptation measures and without interference problems. The device must be small, inexpensive and have an improved range. According to the invention this problem is solved by a device having the features of claim 1. Therefore the inventive device is characterized in that the antennas are positioned in a casing which can be fixed to the outside of the front end of the hand-held bar code reader and are constructed as ferrite antennas. As a result of the housing of the antennas and preferably further components of the deactivator in a separate casing, the deactivator can be substantially used in combination with any random hand-held bar code reader, without it being necessary to make any changes or perform any adaptation measures. Screening to prevent interference is very simple. The placing of the antennas in a separate casing is more particularly made possible as a result of their construction as ferrite antennas. Therefore they can be made much smaller than air-cored coils and there is also a very effective directional action for the emitted electromagnetic field and consequently an improved deactivation range. Advantageous developments of the invention are characterized in the dependent claims. The described device is part of a product theft prevention system and is used for deactivating resonance labels. It is intended for use in combination with a hand-held optoelectronic bar code reader (1), so as to permit the deactivation at the checkout of shops and stores of electronic resonance labels provided with a bar code and attached to products in a single operation and simultaneously with the determination of the bar-coded data. The deactivator has antennas (8, 9), which are located in a casing (11) fixable externally to the front end of the hand-held bar code reader (1) and which are constructed as ferrite antennas. As a result of the housing of the antennas (8, 9) and preferably all the high frequency-carrying parts (14, 15) of the deactivator in a separate casing (11), the deactivator can be used in combination with any random hand-held bar code reader, without any changes having to be made to the latter. Device for deactivating resonance labels provided with a bar code, having a transmitting antenna (8) and a receiving antenna (9) for use in a structural combination with an optoelectronic hand-held bar code reader (8), which bar code reader has a first housing, characterized in that the antennas (8, 9) are arranged in a further housing (11) which can be fastened on the outside to the front end of the housing of the hand-held bar code reader (1) and are designed as ferrite antennas, the coil windings of the transmitting (8) and the receiving (9) antennas being wound at right angles to each other on a single flat ferrite core (10). Device according to Claim 1, characterized in that the receiving antenna (9) is wound onto the ferrite core (10) at right angles to the front end of the further housing (11), to be precise offset laterally with respect to its centre. Device according to either of Claims 1 or 2, characterized in that the housing (11) is provided on at least one side, facing the hand-held bar code reader (1), with screening against radio-frequency electromagnetic waves. Device according to one of Claims 1 to 3, characterized in that the transmitting antenna (8) is connected as an inductance into the circuit of a pulse generator (14) generating needle pulses. Device according to Claim 4, characterized in that the pulse generator (14) is also arranged in the housing (11). Device according to one of Claims 1 to 5, characterized in that the receiving antenna (9) has arranged downstream thereof a detection circuit (15) for non-deactivated resonance labels which have been stimulated into oscillation, the said circuit generating a logic signal upon detecting an oscillating resonance label. Device according to Claim 6, characterized in that the detection circuit (15) is likewise arranged in the housing (11). Device according to one of Claims 1 to 7, characterized in that the components which are arranged in the housing (11) are connected to a stationary base unit (16) via a separate, multiway connecting cable (7). Device according to Claim 8, characterized in that the connecting cable (7) contains no lines specifically designed for the transmission of radio-frequency signals and is also not provided with screening against radio-frequency electromagnetic waves. BRIEF DESCRIPTION OF THE DRAWINGS
MANNER OF REALIZING THE INVENTION
DESCRIPTION OF THE INVENTION